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Endocrinology logoLink to Endocrinology
. 2018 Oct 24;160(2):249–275. doi: 10.1210/en.2018-00836

Circulating Exosomal miRNA Profile During Term and Preterm Birth Pregnancies: A Longitudinal Study

Ramkumar Menon 1,✉,#, Chirantan Debnath 2,#, Andrew Lai 3, Dominic Guanzon 3, Shinjini Bhatnagar 2, Pallavi K Kshetrapal 2,, Samantha Sheller-Miller 1, Carlos Salomon 3,4,; The Garbhini Study Team
PMCID: PMC6394761  PMID: 30358826

Abstract

Despite decades of research in the field of human reproduction, the mechanisms responsible for human parturition still remain elusive. The objective of this study was to describe the changes in the exosomal miRNA concentrations circulating in the maternal plasma between mothers delivering term and preterm neonates, across gestation using a longitudinal study design. This descriptive study identifies the miRNA content in exosomes present in maternal plasma of term and preterm birth (PTB) (n = 20 and n = 10 per each gestational period, respectively) across gestation (i.e., first, second, and third trimesters and at the time of delivery). Changes in exosomal miRNA signature in maternal plasma during term and preterm gestation were determined using the NextSeq 500 high-output 75 cycles sequencing platform. A total of 167 and 153 miRNAs were found to significantly change (P < 0.05) as a function of the gestational age across term and PTB pregnancies, respectively. Interestingly, a comparison analysis between the exosomal miRNA profile between term and PTB reveals a total of 173 miRNAs that significantly change (P < 0.05) across gestation. Specific trends of changes (i.e., increase, decrease, and both) as a function of the gestational age were also identified. The bioinformatics analyses establish that the differences in the miRNA profile are targeting signaling pathways associated with TGF-β signaling, p53, and glucocorticoid receptor signaling, respectively. These data suggest that the miRNA content of circulating exosomes in maternal blood might represent a biomolecular “fingerprint” of the progression of pregnancy.


Normal term human parturition is initiated when fetal organ systems are matured at any time between 37 and 40 weeks of gestation. Conventional theories of parturition initiation signaling are primarily linked to fetomaternal endocrine and immune changes in the intrauterine cavity, correlating with fetal growth and development (1). Homeostatic imbalances produced by these changes, specifically biochemicals released by maturing fetal organs, can lead to an inflammatory overload that disrupts the maintenance of pregnancy, resulting in labor-related changes (2–4). More precise knowledge of these signals and their mechanisms in normal term pregnancies can provide insight into pathologic activation of these signals, which can cause spontaneous preterm parturitions. Besides the fetus, fetal components of the intrauterine tissues (fetal membranes and placenta) also contribute to parturition initiation signals. Recently, we and others have reported that senescence of the placenta/membranes generates “sterile inflammation” that can enhance inflammatory load in the maternal uterine tissues capable of triggering parturition (5).

Communication between the fetal tissues and maternal organs is fundamental for a healthy pregnancy, and recently the participation of extracellular vesicles, especially in a specific type of extracellular vesicles originated from endosomal compartments, called exosomes, in cell-to-cell communication has been identified (6, 7). We have recently identified the fetal-derived signaling through exosomes by senescent fetal membrane (amniochorion) cells at term (8). Exosomes transport materials from cells and function as intercellular communication channels. Exosomes are generated by the intraluminal invagination of early endosomes, giving rise to multivesicular bodies and released into the extracellular environment upon the fusion of multivesicular bodies with the plasma membranes (9–11). Exosome contents represent the character, that is, the physiologic and metabolic state, of the cell of origin. This makes the exosomes a good vector of paracrine signaling as well as biochemical indicators of function of the cell of origin (9). Therefore, the placenta and placental membrane cells provide functional contributions during pregnancy and signal their status through exosomes, contributing to the pregnancy and promotion of fetal delivery (as well as their own) when the fetus is mature (12).

Exosomes are involved in cell-to-cell signaling mainly due to their inherent property to carry bioactive molecules (consisting of proteins, bioactive lipids, and RNAs), which are delivered to the target cells to regulate the biological functions. Interestingly, exosomes are enriched in small noncoding RNA such as miRNAs (13). miRNAs are a class of small (∼22 nucleotides long) noncoding RNAs that negatively regulate gene expression by binding to the 3′ untranslated region of target mRNAs. Interestingly, several studies have demonstrated that changes in the maternal circulating miRNAs or in placental tissues might reflect the maternal metabolic state that may be used as biomarkers of pregnancy complications. Functional studies have also shown the roles of miRNAs in regulating myometrial contractility during parturition (14). However, most studies have been conducted on identifying the total circulating miRNAs (i.e., a mix of soluble, protein-associated, and vesicle-associated miRNAs) and at single time point during gestation, as a cross-sectional study design.

Multiple reports have identified the usefulness of placental-derived exosomes in predicting high-risk status for various adverse pregnancy outcomes. These include preeclampsia (15), gestational diabetes (16), and intrauterine growth restriction (17). Thus, the fetal tissue exosomes serve as proxy for underlying tissue level changes in normal and abnormal pregnancies (6). Therefore, the role of circulating exosomes in maternal blood merits further investigation. We designed a non–hypothesis-driven, descriptive study to discover exosome miRNA cargoes that are differentially expressed in total maternal plasma to generate a profile of their longitudinal changes during each stage of gestation and real-time insight into functional changes associated with gestational age in term and preterm birth (PTB) pregnancies. We also determined whether these miRNA signatures differ between preterm and term births and correlated their likely functions and reasons for their overabundance at a given state of pregnancy based on bioinformatics analysis.

Subjects and Methods

Study group and biospecimen collection

A hospital-based cohort of pregnant women was initiated in 2015 at a district hospital in Gurugram, Haryana (Gurugram Civil Hospital, GCH), India by the Pediatric Biology Center, Translational Health Science and Technology. Serial biospecimens are being collected across pregnancy (at the first, second, and third trimesters), at delivery, and after delivery. Ultrasound images are acquired serially during pregnancy, and the period of gestation is confirmed at enrolment by performing a dating ultrasound using standard fetal biometric parameters. Well-characterized clinical and environmental information is also maintained. The sample preparation at the study site is carried out in the research laboratory established at GCH on nationally accredited equipment from the National Accreditation Board for Testing and Calibration Laboratories. Plasma samples are stored at –80°C until analyses. All women provide written informed consent, and the study is approved by the Institute and Hospital Ethics Review Board.

Selection of samples for this study

The selection of biospecimens for this study has been carried using a nested case control design. The cases and controls have been selected from a defined universe comprised of participants who had a normal singleton vaginal delivery, with no congenital abnormalities or associated comorbidity (e.g., preeclampsia, gestational diabetes, pregnancy-induced hypertension, medical condition complicating complication) at any time in pregnancy. The cases were subjects delivered preterm defined as <37 completed weeks period of gestation. Participants who delivered at >37 completed weeks to 40 completed weeks were considered as controls. The cases and controls were matched to parity, sex of the baby, and month of delivery.

Enrichment of exosomes from maternal blood

Exosomes were isolated from plasma as previously described (18). In brief, plasma was diluted with an equal volume of PBS (pH 7.4) and centrifuged at 2000g for 30 minutes at 4°C (Sorvall® high-speed microcentrifuge, fixed rotor; Thermo Fisher Scientific, Asheville, NC). The 2000g supernatant fluid was then centrifuged at 12,000g for 45 minutes at 4°C (Sorvall® high-speed microcentrifuge, fixed rotor; Thermo Fisher Scientific). The resultant supernatant fluid (2 mL) was transferred to an ultracentrifuge tube (10 mL; Beckman, Brea, CA) and centrifuged at 100,000g for 2 hours (Sorvall® T-8100 fixed ultracentrifuge rotor). The 100,000g pellet was suspended in PBS (10 mL) and filtered through a 0.22-μm filter (Steritop™; Millipore, Billerica, MA) and then centrifuged at 100,000g for 2 hours. Finally, the pellet containing the enriched exosome population was resuspended in 250 μL of PBS for the characterization of exosomes and RNA extraction.

Transmission electron microscopy

For electron microscopy analysis, exosome pellets were fixed in 3% (w/v) glutaraldehyde and analyzed under an FEI Tecnai 12 transmission electron microscope (FEI, Hillsboro, OR) as we previously described (19).

Western blot

Western blot was performed to ascertain the identity of the exosomes using exosomal-specific markers (TSG101, CD9, and CD63) as well as Golgi marker Grp94, which is not enriched in exosomes. Standard Western blot protocols were used and the detailed protocols can be seen our prior reports (15, 20–22). An Odyssey® CLx imaging system (LI-COR Biosciences, Lincoln, NE) was used to visualize the fluorescent bands.

Nanoparticle tracking analysis

Nanoparticle tracking analyses were performed using a NanoSight NS500 instrument (NanoSight NTA 2.3 nanoparticle tracking and analysis release version build 0033; Malvern Instruments, Malvern, United Kingdom) following the manufacturer’s instructions. Samples were diluted 1:1000 with Dulbecco’s PBS to obtain 10:100 particles per image (optimal ∼50 particles per image). The NS500 instrument measured the rate of Brownian motion of nanoparticles in a light-scattering system that provides a reproducible platform for specific and general nanoparticle characterization (NanoSight, Amesbury, United Kingdom). Suspended nanoparticles were passed through the laser beam that traversed the sample chamber and scattered the light, discerning the nanoparticles through a microscope. The samples were mixed before introducing them into the chamber (temperature, 25°C), and the camera level was set to obtain an image that had sufficient contrast to clearly identify particles while minimizing background noise (camera level, 10; capture duration, 30 seconds). The captured videos (two videos per sample) were then processed and analyzed. Each video file was processed and analyzed to give the mean and mode of particle sizes, along with the concentration and the number of particles. An Excel spreadsheet was automatically generated and data were imported into GraphPad Prism 7 (La Jolla, CA).

Exosomal RNA isolation

Exosomal RNA was extracted using an RNeasy Mini Kit 50 (Qiagen, Hilden, Germany) and TRIzol LS reagent (Life Technologies, Carlsbad, CA). The manufacturers’ protocols were followed, with slight modifications in accordance with a protocol used previously (20, 23). A spectrophotometer (SPECTROstar Nano microplate reader; BMG Labtech, Cary, NC) was used to quantify RNA concentration. Following a cleanliness check and blank measurement using RNase-free water, 2 μL of sample was pipetted onto each microdrop well on an LVis plate. RNA concentration was measured using MARS data analysis microplate reader software.

Next-generation sequencing

Sequencing libraries were generated using the TruSeq Small RNA Library Prep Kit (Illumina, San Diego, CA), according to the manufacturer’s instructions, and as previously described (19, 20). Two hundred to 800 ng of exosomal RNA was used as input for library preparation. These RNA samples were barcoded by ligation with unique adaptor sequences to allow pooling of samples in groups of 24. Subsequently, these ligated samples were reverse transcribed, PCR amplified, and size selected using gel electrophoresis. Finally, the DNA libraries were eluted from the gel pieces overnight in 200 μL of nuclease-free H2O. The elution containing the pooled DNA library was further processed for cluster generation and sequencing using a NextSeq 500 high-output kit 75 cycles and Illumina NextSeq 500 sequencing platform, respectively.

Statistical analysis and bioinformatics analysis

The number of exosomes released from individuals are represented as mean ± SE (n = 20 for term and n = 10 for PTB, independent isolations from each patient from each trimester). For RNA sequencing, first the FASTQ file generated from next-generation sequencing was preprocessed to remove adaptor sequences using the TagCleaner program (http://edwards.sdsu.edu/tagcleaner). Subsequently, known and novel miRNAs were detected within the preprocessed FASTQ data using the miRDeep2 program (24). After detection, the miRNA counts and corresponding miRNAs were extracted from the output file. Differential expression and statistical analysis of sequencing data were performed by the DESeq2 package in R. This package uses a generalized linear model to perform differential expression. Statistical analysis and significance were calculated using various tests and adjusted for multiple testing. Adjusted statistical significance was assessed as P < 0.001–0.05. Sequencing data have been deposited in the Gene Expression Omnibus database under no. GSE115572. The effect of pregnancy condition (i.e., normal or PTB) on the size distribution (mean and mode) of the exosomes was assessed using a pairwise post hoc test (Tukey honest significant difference test). No significant differences (P > 0.05) were observed.

Results

Description of the participants

Table 1 describes the comparison between the demographic and the clinical characteristics of the cases and controls. No significant differences between various sociodemographic parameters were seen between cases and controls, except for body mass index (which has been adjusted in our analysis).

Table 1.

Clinical and Demographic Characteristics of Cases and Controls

Controls (n = 20): N (%) or Median (IQR)
Cases (n = 10): N (%) or Median (IQR)
P Value
Maternal variables
 Age, y 22 (20, 24) 22 (20, 23) NS
 Weight, kg 49.3 (46.8, 55.0) 39.1 (37.0, 43.2)
 Height, cm 154.0 (150.0, 158.7) 151.8 (146.6, 157.2) NS
 BMI, kg/m2 20.8 (19.9, 23.9) 17.6 (16.0, 19.0) ≤0.001
 Period of gestationa at enrollment 12+1 (8+2, 13+1) 9+2 (7+1, 12+1) NS
 Period of gestationa at visit 2 (between 18 and 20 wk of gestation) 18+6 (18+4, 19+0) 18+6 (18+5, 19+2) NS
 Period of gestationa at visit 3 (between 26 and 28 wk of gestation) 26+2 (26+2, 26+4) 26+3 (26+2, 26+5) NS
 Period of gestationa at delivery 39+2 (38+6, 40+2) 36+0 (35+0, 36+3) ≤0.001
Newborn variables
 Placental weight, g 460.0 (405.0, 532.5) 377.5 (328.0, 433.0) ≤0.01
 Baby weight, g 3013.0 (2460.5, 3265.5) 2148.0 (1980.0, 2442.0) ≤0.001

Data are presented as N (%) or median (IQR). All pregnancies were normal singleton vaginal delivery with no congenital abnormalities and with no associated comorbidity at any time in pregnancy. The cases and controls were matched to parity, sex of the baby, and month of delivery. A standard two-tailed Student t test was used for comparisons between control and case samples. Statistical significance was assessed as P < 0.001–0.05. Statistical significance was found in maternal variables (BMI, period of gestation at delivery) and newborn variables (placental weight, baby weight).

Abbreviations: BMI, body mass index; IQR, interquartile range; NS, not significant.

a

Period of gestation is calculated by dating ultrasound performed at the time of enrollment.

Exosome isolation and characterization

Particles between 30 and 120 nm were identified on nanoparticle tracking analysis and analyzed per trimester (Fig. 1A–1C), and the cup-shaped morphology was identified using electron microscopy (Fig. 1D). Exosomes were found to be positive for CD63, CD9, and TSG101 (Fig. 1E) but negative for Golgi marker Grp94. No differences were observed in size distribution, protein abundance (CD9, CD63, and TSG101), and morphology between exosomes isolated from term and PTB.

Figure 1.

Figure 1.

Isolation of exosomes. Exosomes were isolated from maternal plasma obtained from normal and PTB pregnancies across gestation (see “Subjects and Methods”). (A–C) Graphical representation of the vesicle size distribution using a NanoSight NS500 instrument at different time points during pregnancy [(A) first trimester, (B) second trimester, and (C) third trimester]. (D) Representative image of electron micrograph of exosomes. Scale bar, 100 nm. (E) Representative Western blot for enriched exosome markers CD63, CD9, and TSG101, as well as negative control Grp94 for exosomes isolated from normal and PTB at different time points during pregnancy. In (A)–(C) and (E), none of the experiments performed was significantly different for normal vs PTB.

Exosomal miRNA signature across normal pregnancy

A total of 167 miRNAs across gestation in term pregnancies revealed significant changes (P < 0.05). Hierarchical clustering analysis of the average miRNA expression profiles across gestation revealed a variety of trends (Fig. 2). Specifically, trends that increased to a maximum peak expression in the third trimester are clusters A and C (A = 11, C = 15); trends that rapidly decreased in expression until the end of the first trimester and then increased to a peak at the end of the second trimester are clusters B, F, G, I, J, K, L, M, and N (B = 13, F = 2, G = 11, I = 13, J = 13, K = 21, L = 4, M = 13, N = 23); an increasing trend throughout gestation was identified in cluster E (E = 19); a trend that rapidly decreased in expression until the end of the first trimester and then increased in expression until the end of the third trimester was observed for cluster H (H = 2); and a trend that increased rapidly from the beginning of the third trimester is cluster D (D = 7). miRNAs with the largest maximum expression in each cluster are as follows (Fig. 3; Table 2): A, hsa-miR-3200-5p; B, hsa-miR-320a; C, hsa-miR-25-3p; D, hsa-miR-10b-3p; E, hsa-miR-143-3p; F, hsa-miR-4718; G, hsa-miR-203a-3p; H, hsa-miR-6862-1-5p; I, hsa-miR-3117-3p; J, hsa-miR-8060; K, hsa-miR-324-5p; L, hsa-miR-129-1-5p; M, hsa-miR-6769b-5p; and N, hsa-miR-6715a-3p.

Figure 2.

Figure 2.

Linear mixed modeling of 167 statistically significant miRNAs that change across gestation for normal pregnancies. miRNA counts were normalized using the DESeq2 package in R prior to statistical analysis using the likelihood ratio test. Subsequently, linear mixed modeling was performed on the 167 statistically significant miRNAs (P < 0.05) that change across gestation for normal pregnancies, using the lme4 package in R. The data were scaled between 0 and 1 before hierarchical clustering analysis using Euclidean distance, which is displayed as a circular cladogram (generated using the ggtree package in R). Each color of the circular cladogram represents a different cluster and its trend, as shown in (A)–(N).

Figure 3.

Figure 3.

Highest expressed miRNAs in each cluster identified using linear mixed modeling for normal pregnancies across gestation. Linear mixed modeling and circular cladogram analysis for normal pregnancies across gestation were divided into 14 clusters. The highest expressed miRNA from each cluster was extracted and color coded based on the cluster of origin. Clusters are in ascending order [corresponding to (A)–(N) in Fig. 2] starting from the top of the figure, reading from left to right and continuing onto the next line of graphs below.

Table 2.

Significant miRNAs That Change Across Gestation for Normal Pregnancies

Condition miRNA Gestational Age With Minimum Expression Minimum Expression (Normalized Counts) Gestational Age With Maximum Expression Maximum Expression (Normalized Counts) P Value Letter
Normal hsa-miR-3200-5p 41.857 −0.034 26.143 0.321 0.036 A
Normal hsa-miR-379-3p 41.857 −0.064 28.143 0.269 0.016 A
Normal hsa-miR-411-3p 41.857 −0.070 27.000 0.278 0.015 A
Normal hsa-miR-576-3p 41.857 −0.021 28.143 0.210 0.025 A
Normal hsa-miR-1197 13.571 −0.001 28.143 0.068 0.046 A
Normal hsa-miR-495-3p 12.143 −0.019 28.143 0.093 0.040 A
Normal hsa-miR-3130-2-5p 41.857 −0.030 27.000 0.090 0.016 A
Normal hsa-miR-944 41.857 −0.026 28.143 0.092 0.047 A
Normal hsa-miR-548j-3p 13.714 −0.009 27.000 0.062 0.017 A
Normal hsa-miR-3940-3p 41.857 −0.024 28.143 0.071 0.037 A
Normal hsa-miR-23b-5p 13.714 −0.003 27.000 0.012 0.016 A
Normal hsa-miR-320a 41.857 29.996 5.857 163.935 0.026 B
Normal hsa-miR-320b-2 41.857 21.416 5.857 145.869 0.030 B
Normal hsa-miR-320b-1 41.857 22.168 6.143 139.071 0.030 B
Normal hsa-miR-144-3p 40.857 −1.551 6.143 60.607 0.045 B
Normal hsa-miR-4732-3p 19.000 1.474 6.143 13.023 0.007 B
Normal hsa-miR-410-3p 19.000 0.419 28.143 11.632 0.007 B
Normal hsa-miR-28-5p 40.857 1.067 6.143 10.960 0.044 B
Normal hsa-miR-4446-3p 19.143 1.069 5.857 7.583 0.044 B
Normal hsa-miR-96-5p 41.857 −0.245 6.143 8.217 0.025 B
Normal hsa-miR-381-3p 19.000 0.222 6.143 7.765 0.021 B
Normal hsa-miR-17-3p 39.571 −0.028 12.000 1.535 0.035 B
Normal hsa-miR-18a-3p 18.714 0.116 5.857 1.629 0.023 B
Normal hsa-miR-433-3p 18.714 0.048 39.000 0.372 0.034 B
Normal hsa-miR-25-3p 39.571 39.144 38.857 342.593 0.039 C
Normal hsa-miR-151a-3p 40.857 53.696 27.000 293.888 0.044 C
Normal hsa-miR-148a-3p 13.857 72.308 27.000 321.138 0.005 C
Normal hsa-miR-146a-5p 41.857 33.933 27.429 206.489 0.016 C
Normal hsa-miR-423-3p 13.571 22.310 27.429 128.235 0.011 C
Normal hsa-miR-223-3p 13.857 8.677 27.000 89.880 0.011 C
Normal hsa-miR-584-5p 13.857 13.667 27.000 63.942 0.007 C
Normal hsa-miR-19b-2-3p 13.857 3.510 28.143 22.076 0.028 C
Normal hsa-miR-19b-1-3p 13.857 3.649 28.143 22.046 0.028 C
Normal hsa-miR-19a-3p 13.857 4.293 28.143 21.087 0.036 C
Normal hsa-miR-3615 13.571 2.770 37.000 9.088 0.038 C
Normal hsa-miR-328-3p 11.286 0.815 37.000 5.739 0.006 C
Normal hsa-miR-1304-3p 12.429 0.631 27.000 1.946 0.036 C
Normal hsa-miR-224-5p 19.000 0.412 27.000 2.165 0.027 C
Normal hsa-miR-199b-5p 6.143 −0.083 27.429 0.977 0.032 C
Normal hsa-miR-10b-3p 6.429 −0.002 41.857 0.513 0.041 D
Normal hsa-miR-500b-3p 20.571 0.001 41.857 0.066 0.012 D
Normal hsa-miR-4728-3p 19.000 −0.004 41.857 0.045 0.027 D
Normal hsa-miR-6876-5p 12.143 −0.004 41.857 0.043 0.038 D
Normal hsa-miR-8058 26.286 −0.005 41.857 0.028 0.021 D
Normal hsa-miR-4762-3p 26.571 −0.003 41.857 0.015 0.021 D
Normal hsa-miR-1295a 27.429 −0.005 41.857 0.029 0.021 D
Normal hsa-miR-143-3p 19.000 53.724 37.000 611.513 0.001 E
Normal hsa-miR-133a-1-3p 12.571 −0.252 40.429 7.449 0.000 E
Normal hsa-miR-133a-2-3p 10.286 −0.429 40.429 7.416 0.000 E
Normal hsa-miR-574-3p 19.000 0.551 40.429 3.305 0.043 E
Normal hsa-miR-145-3p 8.571 0.347 41.857 2.804 0.002 E
Normal hsa-miR-145-5p 6.143 0.107 41.857 3.038 0.000 E
Normal hsa-miR-518d-5p 6.286 −0.162 39.000 2.442 0.041 E
Normal hsa-miR-526a-1 5.857 −0.016 39.000 2.255 0.041 E
Normal hsa-miR-526a-2 6.286 −0.069 39.000 2.443 0.041 E
Normal hsa-miR-520c-5p 6.429 −0.144 39.000 2.291 0.040 E
Normal hsa-miR-185-3p 6.143 0.156 41.857 2.075 0.048 E
Normal hsa-miR-371b-5p 6.286 0.034 41.857 1.504 0.005 E
Normal hsa-miR-548k 6.286 0.009 39.000 1.300 0.047 E
Normal hsa-miR-518f-5p 6.429 −0.117 41.857 1.693 0.006 E
Normal hsa-miR-526b-5p 5.857 −0.026 41.857 1.468 0.022 E
Normal hsa-miR-518c-5p 6.286 −0.097 39.000 1.278 0.040 E
Normal hsa-miR-193b-3p 6.143 −0.004 40.429 0.860 0.017 E
Normal hsa-miR-873-3p 20.571 0.035 41.857 0.338 0.024 E
Normal hsa-miR-139-3p 10.286 0.001 41.857 0.273 0.047 E
Normal hsa-miR-4718 20.571 −0.025 5.857 0.470 0.045 F
Normal hsa-miR-3125 18.714 −0.016 5.857 0.250 0.008 F
Normal hsa-miR-203a-3p 20.286 −53.378 5.857 609.717 0.038 G
Normal hsa-miR-205-5p 18.571 −1.562 6.286 18.783 0.039 G
Normal hsa-miR-5689 19.143 −0.980 6.143 13.261 0.035 G
Normal hsa-miR-6767-5p 41.857 −0.933 6.143 7.801 0.033 G
Normal hsa-miR-889-3p 20.286 −0.202 6.143 6.763 0.009 G
Normal hsa-miR-4662a-5p 41.857 −0.301 5.857 2.447 0.028 G
Normal hsa-miR-376c-3p 20.286 0.000 5.857 0.309 0.017 G
Normal hsa-miR-3656 41.857 −0.025 5.857 0.188 0.014 G
Normal hsa-miR-6515-5p 41.857 −0.017 5.857 0.129 0.029 G
Normal hsa-miR-4688 18.714 −0.008 5.857 0.063 0.039 G
Normal hsa-miR-3202-2 41.857 −0.005 6.286 0.023 0.048 G
Normal hsa-miR-6862-1-5p 20.571 −0.003 5.857 0.054 0.031 H
Normal hsa-miR-6862-2-5p 20.571 −0.004 5.857 0.055 0.031 H
Normal hsa-miR-3117-3p 19.143 −1.534 6.143 9.596 0.018 I
Normal hsa-miR-6845-5p 20.286 −0.656 6.143 4.733 0.020 I
Normal hsa-miR-6889-5p 20.286 −0.226 6.143 1.603 0.021 I
Normal hsa-miR-548ap-5p 20.286 −0.245 6.143 1.582 0.025 I
Normal hsa-miR-6868-3p 19.000 −0.256 6.143 1.717 0.022 I
Normal hsa-miR-6729-5p 18.857 −0.215 6.143 1.716 0.014 I
Normal hsa-miR-622 20.286 −0.239 6.143 1.735 0.022 I
Normal hsa-miR-4538 20.571 −0.215 6.143 1.610 0.022 I
Normal hsa-miR-4652-5p 20.286 −0.224 6.143 1.632 0.022 I
Normal hsa-miR-3913-1-3p 20.286 −0.010 5.857 0.060 0.037 I
Normal hsa-miR-3913-2-3p 18.714 −0.008 5.857 0.059 0.037 I
Normal hsa-miR-4467 20.286 −0.011 5.857 0.096 0.004 I
Normal hsa-miR-3186-3p 19.143 −0.032 5.857 0.199 0.021 I
Normal hsa-miR-8060 18.571 −0.290 6.143 6.667 0.049 J
Normal hsa-miR-7977 41.857 −0.204 5.857 5.111 0.037 J
Normal hsa-miR-193a-3p 41.857 −0.092 6.286 1.340 0.026 J
Normal hsa-miR-6869-5p 41.857 −0.126 6.143 1.292 0.026 J
Normal hsa-miR-4798-5p 19.000 −0.125 5.857 1.247 0.027 J
Normal hsa-miR-4466 18.429 −0.105 6.429 1.140 0.032 J
Normal hsa-miR-4646-5p 20.286 −0.067 6.143 1.140 0.047 J
Normal hsa-miR-382-5p 19.000 −0.031 5.857 0.352 0.005 J
Normal hsa-miR-6867-5p 20.286 −0.003 6.143 0.018 0.030 J
Normal hsa-miR-4650-1-3p 41.857 −0.002 6.286 0.024 0.013 J
Normal hsa-miR-4650-2-3p 19.143 −0.003 6.143 0.024 0.013 J
Normal hsa-miR-1343-3p 18.857 −0.001 5.857 0.008 0.040 J
Normal hsa-miR-4717-3p 19.000 −0.002 5.857 0.013 0.019 J
Normal hsa-miR-324-5p 19.143 −0.289 5.857 3.734 0.022 K
Normal hsa-miR-5707 19.000 −0.487 5.857 3.490 0.020 K
Normal hsa-miR-3614-3p 19.000 −0.738 5.857 4.524 0.026 K
Normal hsa-miR-3196 18.714 −0.341 5.857 2.480 0.018 K
Normal hsa-miR-6509-5p 20.286 −0.306 5.857 2.429 0.026 K
Normal hsa-miR-4324 19.143 −0.595 5.857 3.828 0.015 K
Normal hsa-miR-455-5p 19.000 −0.437 6.143 3.332 0.032 K
Normal hsa-miR-4500 41.857 −0.122 6.286 1.190 0.029 K
Normal hsa-miR-6501-5p 18.714 −0.342 5.857 2.237 0.025 K
Normal hsa-miR-887-3p 20.571 −0.322 5.857 2.344 0.023 K
Normal hsa-miR-3143 18.429 −0.161 5.857 1.232 0.014 K
Normal hsa-miR-548j-5p 19.143 −0.135 5.857 1.107 0.049 K
Normal hsa-miR-490-3p 19.143 −0.132 5.857 1.145 0.033 K
Normal hsa-miR-6858-5p 41.857 −0.019 6.143 0.241 0.027 K
Normal hsa-miR-545-5p 20.286 −0.021 5.857 0.186 0.000 K
Normal hsa-miR-6809-5p 20.571 −0.004 6.143 0.058 0.019 K
Normal hsa-miR-541-3p 19.000 −0.010 5.857 0.095 0.010 K
Normal hsa-miR-6859-1-3p 20.286 −0.009 5.857 0.053 0.003 K
Normal hsa-miR-6859-2-3p 18.429 −0.006 5.857 0.052 0.003 K
Normal hsa-miR-6859-3-3p 18.857 −0.007 5.857 0.055 0.003 K
Normal hsa-miR-6859-4-3p 20.286 −0.009 5.857 0.055 0.003 K
Normal hsa-miR-129-1-5p 20.571 −0.013 5.857 0.097 0.021 L
Normal hsa-miR-129-2-5p 19.000 −0.014 5.857 0.103 0.021 L
Normal hsa-miR-202-5p 20.286 −0.016 5.857 0.125 0.003 L
Normal hsa-miR-592 40.857 −0.005 5.857 0.048 0.038 L
Normal hsa-miR-6769b-5p 18.571 −0.008 5.857 0.046 0.015 M
Normal hsa-miR-548t-5p 20.571 −0.007 5.857 0.045 0.025 M
Normal hsa-miR-4297 20.571 −0.017 5.857 0.090 0.015 M
Normal hsa-miR-6781-5p 20.571 −0.001 6.143 0.005 0.026 M
Normal hsa-miR-6888-5p 19.000 0.000 5.857 0.002 0.026 M
Normal hsa-miR-4684-3p 19.000 −0.005 6.143 0.036 0.031 M
Normal hsa-miR-8083 18.857 −0.003 5.857 0.018 0.031 M
Normal hsa-miR-3145-3p 18.571 0.000 5.857 0.002 0.026 M
Normal hsa-miR-4267 18.714 −0.002 6.143 0.017 0.031 M
Normal hsa-miR-6769a-3p 18.714 −0.003 5.857 0.018 0.031 M
Normal hsa-miR-4423-3p 19.000 0.000 6.143 0.002 0.026 M
Normal hsa-miR-6766-3p 18.857 −0.001 5.857 0.005 0.026 M
Normal hsa-miR-3157-5p 18.429 0.000 5.857 0.002 0.026 M
Normal hsa-miR-6715a-3p 19.000 −0.795 5.857 4.636 0.023 N
Normal hsa-miR-1915-3p 20.286 −0.594 5.857 3.537 0.024 N
Normal hsa-miR-4469 20.286 −0.016 6.143 0.085 0.013 N
Normal hsa-miR-4535 18.857 −0.008 5.857 0.052 0.020 N
Normal hsa-miR-7856-5p 19.143 −0.006 6.286 0.043 0.019 N
Normal hsa-miR-7845-5p 19.000 −0.017 5.857 0.087 0.015 N
Normal hsa-miR-4789-3p 19.000 −0.009 5.857 0.043 0.015 N
Normal hsa-miR-6772-5p 20.286 0.000 5.857 0.002 0.026 N
Normal hsa-miR-4716-3p 18.714 0.000 5.857 0.002 0.026 N
Normal hsa-miR-6783-3p 19.000 0.000 6.143 0.002 0.026 N
Normal hsa-miR-499a-3p 18.714 −0.012 6.143 0.067 0.031 N
Normal hsa-miR-718 19.000 −0.007 5.857 0.049 0.013 N
Normal hsa-miR-3177-5p 19.143 −0.001 6.429 0.002 0.026 N
Normal hsa-miR-5002-5p 19.143 −0.003 5.857 0.017 0.031 N
Normal hsa-miR-3166 18.857 −0.006 5.857 0.034 0.031 N
Normal hsa-miR-6499-3p 19.143 −0.003 5.857 0.017 0.031 N
Normal hsa-miR-4674 19.000 −0.003 5.857 0.016 0.031 N
Normal hsa-miR-4497 19.143 −0.003 5.857 0.017 0.031 N
Normal hsa-miR-5708 19.143 −0.002 5.857 0.017 0.031 N
Normal hsa-miR-6759-3p 18.714 −0.003 5.857 0.017 0.031 N
Normal hsa-miR-506-3p 20.286 −0.001 6.286 0.005 0.026 N
Normal hsa-miR-6741-5p 18.714 −0.001 5.857 0.005 0.026 N
Normal hsa-miR-1245b-5p 20.286 0.000 6.143 0.002 0.026 N

Exosomal miRNA signature across PTB pregnancy

A total of 153 miRNAs across gestation in PTB pregnancies demonstrated significant changes (P < 0.05). Hierarchical clustering analysis of the average miRNA expression profiles across gestation revealed a variety of trends (Fig. 4). Specifically, trends that had peak expression at the second trimester are clusters E, F, G, I, J, K, L, M, and N (E = 3, F = 4, G = 21, I = 5, J = 5, K = 8, L = 10, M = 9, N = 28); a trend that had peak expression at the beginning of the third trimester was identified in cluster A (A = 11); and decreasing trends in expression across gestation were observed for clusters B, C, D, and H (B = 12, C = 6, D = 20, H = 11). miRNAs with the largest maximum expression in each cluster are as follows (Fig. 5; Table 3): A, hsa-let-7a-2-5p; B, hsa-miR-520a-3p; C, hsa-miR-664a-3p; D, hsa-miR-4737; E, hsa-miR-3177-3p; F, hsa-miR-483-3p; G, hsa-miR-4433b-3p; H, hsa-miR-130b-3p; I, hsa-miR-142-5p; J, hsa-miR-941-1; K, hsa-miR-342-3p; L, hsa-miR-222-3p; M, hsa-miR-26a-2-5p; and N, hsa-miR-92a-1-3p.

Figure 4.

Figure 4.

Linear mixed modeling of 153 statistically significant miRNAs that change across gestation for PTB pregnancies. miRNA counts were normalized using the DESeq2 package in R prior to statistical analysis using the likelihood ratio test. Subsequently, linear mixed modeling was performed on the 153 statistically significant miRNAs (P < 0.05) that change across gestation for PTB pregnancies, using the lme4 package in R. The data were scaled between 0 and 1 before hierarchical clustering analysis using Euclidean distance, which is displayed as a circular cladogram (generated using the ggtree package in R). Each color of the circular cladogram represents a different cluster and its trend, as shown in (A)–(N).

Figure 5.

Figure 5.

Highest expressed miRNAs in each cluster identified using linear mixed modeling for PTB pregnancies across gestation. Linear mixed modeling and circular cladogram analysis for normal pregnancies across gestation were divided into 14 clusters. The highest expressed miRNA from each cluster was extracted and color coded based on the cluster of origin. Clusters are in ascending order [corresponding to (A)–(N) in Fig. 4] starting from the top of the figure, reading from left to right and continuing onto the next line of graphs below.

Table 3.

Significant miRNAs That Change Across Gestation for PTB Pregnancies

Condition miRNA Gestational Age With Minimum Expression Minimum Expression (Normalized Counts) Gestational Age With Maximum Expression Maximum Expression (Normalized Counts) P Value Letter
PTB hsa-let-7a-2-5p 36.714 83.371 26.857 765.758 0.021 A
PTB hsa-let-7a-1-5p 36.000 112.699 26.857 783.444 0.020 A
PTB hsa-let-7a-3-5p 36.571 111.885 26.857 779.513 0.020 A
PTB hsa-let-7f-2-5p 36.714 87.346 26.857 756.329 0.020 A
PTB hsa-let-7f-1-5p 36.571 108.247 26.857 772.266 0.020 A
PTB hsa-miR-25-3p 36.714 −14.331 7.857 345.282 0.002 A
PTB hsa-let-7i-5p 36.000 −4.748 26.571 251.392 0.019 A
PTB hsa-miR-98-5p 36.571 0.600 26.857 18.092 0.031 A
PTB hsa-miR-548e-3p 36.714 −0.045 26.714 0.333 0.009 A
PTB hsa-miR-5010-3p 35.000 −0.079 19.429 0.423 0.028 A
PTB hsa-miR-495-3p 12.143 −0.008 26.714 0.041 0.044 A
PTB hsa-miR-520a-3p 26.857 −0.155 7.857 1.682 0.002 B
PTB hsa-let-7i-3p 26.714 −0.044 7.857 0.871 0.007 B
PTB hsa-miR-887-3p 32.571 −0.019 13.000 0.144 0.024 B
PTB hsa-miR-1287-5p 35.000 −0.039 9.714 0.317 0.005 B
PTB hsa-miR-548f-2-3p 26.714 −0.009 7.857 0.227 0.027 B
PTB hsa-miR-548f-3-3p 26.714 −0.010 7.857 0.240 0.027 B
PTB hsa-miR-760 32.571 0.010 7.143 0.434 0.005 B
PTB hsa-miR-548j-5p 26.857 −0.007 6.429 0.119 0.038 B
PTB hsa-miR-1908-3p 32.571 0.028 6.571 0.295 0.020 B
PTB hsa-miR-6770-1-3p 26.286 −0.005 6.429 0.054 0.031 B
PTB hsa-miR-6770-2-3p 26.857 −0.004 6.429 0.056 0.031 B
PTB hsa-miR-6770-3-3p 26.286 −0.005 6.571 0.055 0.031 B
PTB hsa-miR-664a-3p 36.714 −0.033 6.571 0.570 0.012 C
PTB hsa-miR-320d-1 36.714 −0.085 6.571 0.859 0.026 C
PTB hsa-miR-320d-2 36.714 −0.108 6.571 0.849 0.026 C
PTB hsa-miR-379-3p 36.714 −0.053 6.571 0.599 0.036 C
PTB hsa-miR-411-3p 36.571 −0.052 6.571 0.636 0.038 C
PTB hsa-miR-337-3p 36.714 −0.026 6.571 0.306 0.021 C
PTB hsa-miR-4737 19.429 −0.003 6.429 0.020 0.042 D
PTB hsa-miR-4778-5p 18.571 −0.019 6.571 0.240 0.020 D
PTB hsa-miR-6749-3p 19.143 −0.009 6.429 0.081 0.030 D
PTB hsa-miR-2277-3p 19.429 −0.035 6.571 0.246 0.017 D
PTB hsa-miR-4794 19.143 −0.004 6.429 0.020 0.042 D
PTB hsa-miR-3125 19.429 −0.005 6.429 0.077 0.008 D
PTB hsa-miR-8061 19.143 −0.010 6.429 0.055 0.042 D
PTB hsa-miR-152-5p 26.143 −0.002 6.429 0.068 0.032 D
PTB hsa-miR-451b 26.571 −0.004 6.429 0.044 0.032 D
PTB hsa-miR-371b-3p 35.000 −0.001 6.429 0.034 0.045 D
PTB hsa-miR-6783-3p 18.571 −0.010 6.429 0.082 0.042 D
PTB hsa-miR-1343-3p 32.571 −0.002 6.429 0.032 0.023 D
PTB hsa-miR-3908 19.429 −0.007 6.429 0.038 0.042 D
PTB hsa-miR-586 19.286 −0.008 6.571 0.038 0.042 D
PTB hsa-miR-645 19.429 −0.003 6.429 0.019 0.042 D
PTB hsa-miR-4769-5p 18.714 −0.004 6.429 0.019 0.042 D
PTB hsa-miR-572 19.429 −0.003 6.429 0.019 0.042 D
PTB hsa-miR-6759-5p 19.429 −0.004 6.571 0.019 0.042 D
PTB hsa-miR-6797-5p 19.286 −0.004 6.571 0.020 0.042 D
PTB hsa-miR-6798-5p 18.714 −0.004 6.429 0.019 0.042 D
PTB hsa-miR-3177-3p 26.857 −0.045 13.000 0.323 0.029 E
PTB hsa-miR-10a-3p 26.857 −0.046 7.857 0.390 0.046 E
PTB hsa-miR-3656 32.571 −0.037 13.000 0.284 0.031 E
PTB hsa-miR-483-3p 6.429 −0.037 18.571 0.668 0.014 F
PTB hsa-miR-183-3p 6.571 −0.049 18.571 0.134 0.017 F
PTB hsa-miR-615-3p 6.429 −0.019 18.571 0.138 0.016 F
PTB hsa-miR-5094 32.571 −0.011 18.571 0.055 0.028 F
PTB hsa-miR-4433b-3p 6.429 −0.038 19.429 0.334 0.032 G
PTB hsa-miR-132-3p 36.429 0.074 18.714 0.789 0.037 G
PTB hsa-miR-3158-1-3p 36.429 −0.103 19.429 1.200 0.000 G
PTB hsa-miR-3158-2-3p 36.429 −0.074 19.429 1.182 0.000 G
PTB hsa-miR-339-5p 36.714 0.062 18.571 0.715 0.040 G
PTB hsa-miR-517a-5p 36.286 −0.030 19.286 0.836 0.005 G
PTB hsa-miR-517b-5p 36.286 0.015 19.286 0.827 0.005 G
PTB hsa-miR-517c-5p 36.000 −0.017 19.286 0.816 0.005 G
PTB hsa-miR-517a-3p 36.000 −0.006 18.714 0.554 0.022 G
PTB hsa-miR-517b-3p 36.000 0.004 18.571 0.546 0.022 G
PTB hsa-miR-517c-3p 32.571 −0.006 19.286 0.538 0.023 G
PTB hsa-miR-532-3p 6.571 −0.002 18.571 0.397 0.046 G
PTB hsa-miR-33b-5p 34.429 0.059 18.714 0.496 0.040 G
PTB hsa-miR-550a-3-5p 36.000 −0.011 19.286 0.352 0.021 G
PTB hsa-miR-369-5p 36.000 0.030 12.857 0.472 0.018 G
PTB hsa-miR-22-5p 6.429 −0.009 18.714 0.361 0.035 G
PTB hsa-miR-149-5p 36.000 −0.003 18.714 0.091 0.028 G
PTB hsa-miR-4482-3p 6.429 −0.044 18.571 0.168 0.038 G
PTB hsa-miR-1185-1-3p 6.571 −0.023 19.429 0.115 0.038 G
PTB hsa-miR-1185-2-3p 6.571 −0.014 18.571 0.082 0.017 G
PTB hsa-miR-505-5p 32.571 −0.006 18.714 0.125 0.028 G
PTB hsa-miR-130b-3p 36.000 3.525 7.857 14.908 0.024 H
PTB hsa-miR-183-5p 36.571 2.118 6.429 10.095 0.001 H
PTB hsa-miR-652-3p 36.714 1.544 8.714 6.527 0.007 H
PTB hsa-miR-150-3p 36.429 0.086 12.143 2.111 0.002 H
PTB hsa-miR-1468-5p 36.000 0.105 18.571 0.900 0.027 H
PTB hsa-miR-1301-3p 36.714 0.077 6.571 0.485 0.028 H
PTB hsa-miR-550a-1-5p 36.571 0.017 13.000 0.489 0.027 H
PTB hsa-miR-550a-1-5p_var2 34.429 0.037 12.857 0.486 0.027 H
PTB hsa-miR-550a-2-5p 36.429 0.024 12.857 0.487 0.027 H
PTB hsa-miR-550a-2-5p_var2 36.000 0.046 13.000 0.471 0.027 H
PTB hsa-miR-589-3p 35.000 0.022 12.857 0.251 0.047 H
PTB hsa-miR-142-5p 36.000 57.040 7.857 480.207 0.002 I
PTB hsa-miR-502-3p 36.000 0.298 18.571 7.028 0.005 I
PTB hsa-miR-4677-3p 36.571 −0.054 13.000 0.463 0.003 I
PTB hsa-miR-140-5p 36.000 −0.047 13.000 0.477 0.032 I
PTB hsa-miR-6735-5p 36.714 −0.025 18.571 0.202 0.043 I
PTB hsa-miR-941-1 36.286 1.174 19.143 11.889 0.043 J
PTB hsa-miR-941-2 36.286 0.880 19.143 11.888 0.043 J
PTB hsa-miR-941-3 36.286 0.948 19.143 11.776 0.043 J
PTB hsa-miR-941-4 36.286 1.520 19.143 11.919 0.043 J
PTB hsa-miR-941-5 36.286 1.512 19.143 11.840 0.043 J
PTB hsa-miR-342-3p 36.000 0.844 18.571 13.061 0.000 K
PTB hsa-miR-155-5p 36.000 0.422 18.571 3.835 0.001 K
PTB hsa-miR-342-5p 36.714 0.249 18.571 1.759 0.015 K
PTB hsa-miR-374a-5p 36.714 0.078 18.571 1.270 0.004 K
PTB hsa-miR-1283-1 36.714 0.016 19.429 0.651 0.016 K
PTB hsa-miR-1283-2 36.714 −0.003 18.714 0.670 0.016 K
PTB hsa-miR-98-3p 36.714 0.096 18.714 1.058 0.009 K
PTB hsa-miR-2110 36.571 0.036 18.571 0.316 0.013 K
PTB hsa-miR-222-3p 36.714 2.400 19.429 18.711 0.020 L
PTB hsa-miR-1323 36.714 0.224 18.571 5.262 0.017 L
PTB hsa-miR-424-3p 36.714 0.633 18.714 3.845 0.003 L
PTB hsa-miR-1260b 36.571 0.114 18.571 4.723 0.003 L
PTB hsa-miR-1260a 36.000 −0.017 19.143 3.090 0.008 L
PTB hsa-miR-127-3p 36.714 −0.125 19.429 2.990 0.040 L
PTB hsa-miR-454-3p 36.000 0.125 19.143 1.584 0.035 L
PTB hsa-miR-130b-5p 36.714 0.003 26.143 1.323 0.028 L
PTB hsa-miR-93-3p 36.714 0.098 19.286 0.701 0.018 L
PTB hsa-miR-1249-3p 36.714 −0.003 26.857 0.378 0.013 L
PTB hsa-miR-26a-2-5p 36.714 87.226 19.429 443.127 0.002 M
PTB hsa-miR-26a-1-5p 36.571 106.815 19.429 448.290 0.002 M
PTB hsa-miR-182-5p 36.571 34.092 19.143 195.739 0.001 M
PTB hsa-miR-28-3p 36.571 28.378 19.429 127.465 0.010 M
PTB hsa-miR-26b-5p 36.571 17.921 26.857 80.645 0.011 M
PTB hsa-let-7g-5p 36.714 18.677 19.143 72.495 0.042 M
PTB hsa-let-7d-5p 36.571 4.335 19.429 17.103 0.041 M
PTB hsa-miR-532-5p 36.714 2.662 19.143 12.236 0.018 M
PTB hsa-miR-374b-5p 36.714 0.106 19.429 1.252 0.037 M
PTB hsa-miR-92a-1-3p 36.571 1463.034 19.143 3264.338 0.013 N
PTB hsa-miR-92a-2-3p 36.714 1452.078 19.429 3235.394 0.016 N
PTB hsa-miR-191-5p 36.000 313.059 18.571 1059.484 0.017 N
PTB hsa-miR-451a 36.000 370.301 9.714 878.724 0.033 N
PTB hsa-miR-30d-5p 36.714 129.580 12.857 285.232 0.040 N
PTB hsa-miR-181a-1-5p 36.714 63.476 19.143 294.151 0.004 N
PTB hsa-miR-181a-2-5p 36.571 75.583 19.429 294.918 0.004 N
PTB hsa-miR-151a-3p 36.000 54.679 26.857 321.801 0.004 N
PTB hsa-miR-146a-5p 36.571 59.045 7.143 195.970 0.033 N
PTB hsa-miR-92b-3p 36.429 42.148 19.143 137.752 0.024 N
PTB hsa-miR-146b-5p 36.000 2.335 9.714 62.211 0.017 N
PTB hsa-miR-144-3p 36.571 9.064 18.714 35.849 0.012 N
PTB hsa-miR-140-3p 36.286 14.249 19.143 40.063 0.048 N
PTB hsa-miR-425-5p 36.714 9.769 12.857 38.067 0.004 N
PTB hsa-miR-16-2-3p 36.571 5.511 13.000 18.210 0.012 N
PTB hsa-miR-106b-3p 36.429 3.341 19.143 18.945 0.003 N
PTB hsa-miR-128-1-3p 36.714 2.834 19.143 13.143 0.016 N
PTB hsa-miR-128-2-3p 36.571 2.517 18.571 11.922 0.021 N
PTB hsa-miR-181d-5p 36.429 1.657 18.571 10.690 0.009 N
PTB hsa-miR-181c-5p 36.571 1.259 10.571 5.873 0.005 N
PTB hsa-miR-197-3p 36.714 1.127 18.571 7.338 0.001 N
PTB hsa-miR-15b-5p 36.000 1.635 18.571 5.638 0.034 N
PTB hsa-miR-28-5p 34.429 2.210 18.714 5.857 0.048 N
PTB hsa-miR-199a-1-5p 36.714 0.553 19.429 4.492 0.041 N
PTB hsa-miR-199a-2-5p 36.571 0.864 19.143 4.406 0.041 N
PTB hsa-miR-361-5p 36.571 1.020 18.571 3.152 0.027 N
PTB hsa-miR-6852-5p 36.571 0.720 18.571 3.103 0.013 N
PTB hsa-miR-330-3p 36.714 0.223 18.714 1.357 0.038 N

Differential expression of exosomal miRNA across gestation in normal compared with PTB pregnancy

A total of 173 miRNAs were found to significantly change (P < 0.05) across gestation for normal compared with PTB pregnancies. Hierarchical clustering analysis of the average miRNA expression profiles across gestation revealed a variety of trends (Fig. 6). Specifically, trends that had the largest difference in expression within the first trimester comparing normal to PTB pregnancies are clusters I, M, and N (I = 8, M = 15, N = 43); trends that had the largest difference in expression within the second trimester comparing normal to PTB pregnancies are clusters A, D, F, G, J, and K (A = 14, D = 5, F = 5, G = 8, J = 17, K = 13); and trends that had the largest difference in expression within the third trimester comparing normal to PTB pregnancies are clusters B, C, E, H, and L (B = 5, C = 9, E = 12, H = 6, L = 13). miRNAs with the largest maximum expression in each cluster are as follows (Fig. 7; Table 4): A, hsa-let-7b-3p; B, hsa-miR-197-3p; C, hsa-miR-148a-3p; D, hsa-miR-1304-3p; E, hsa-miR-101-1-3p; F, hsa-miR-10a-3p; G, hsa-miR-1304-5p; H, hsa-miR-145-5p; I, hsa-let-7i-3p; J, hsa-miR-128-1-3p; K, hsa-miR-1275; L, hsa-miR-1249-5p; M, hsa-miR-202-5p; and N, hsa-miR-1255b-2-3p.

Figure 6.

Figure 6.

Linear mixed modeling of 173 statistically significant miRNAs that change across gestation when comparing normal to PTB pregnancies. miRNA counts were normalized using the DESeq2 package in R prior to statistical analysis using the likelihood ratio test. Subsequently, linear mixed modeling was performed on the 173 statistically significant miRNAs (P < 0.05) that change across gestation when comparing normal to PTB pregnancies, using the lme4 package in R. The data were scaled between 0 and 1 before hierarchical clustering analysis using Euclidean distance, which is displayed as a circular cladogram (generated using the ggtree package in R). Each color of the circular cladogram represents a different cluster and its trend, as shown in (A)–(N). Within the panels, red indicates normal pregnancies whereas blue indicates PTB pregnancies.

Figure 7.

Figure 7.

Highest expressed miRNAs in each cluster identified using linear mixed modeling when comparing normal pregnancies to PTB pregnancies across gestation. Linear mixed modeling and circular cladogram analysis when comparing normal pregnancies to PTB pregnancies across gestation were divided into 14 clusters. The highest expressed miRNA from each cluster was extracted and color coded based on the cluster of origin. Clusters are in ascending order [corresponding to (A)–(N) in Fig. 6] starting from the top of the figure, reading from left to right and continuing onto the next line of graphs below. Red indicates normal pregnancies whereas blue indicates PTB pregnancies.

Table 4.

Significant miRNAs That Change Across Gestation for Normal Versus PTB Pregnancies

Condition miRNA Gestational Age With Minimum Expression Minimum Expression (Normalized Counts) Gestational Age With Maximum Expression Maximum Expression (Normalized Counts) P Value Letter
Normal hsa-let-7b-3p 19.000 0.405 40.429 2.590 0.044 A
PTB hsa-let-7b-3p 36.286 0.077 12.857 2.627 0.044 A
Normal hsa-miR-1249-3p 18.429 0.071 6.143 0.211 0.006 A
PTB hsa-miR-1249-3p 36.714 −0.011 26.143 0.375 0.006 A
Normal hsa-miR-1260a 19.000 1.028 6.143 3.592 0.012 A
PTB hsa-miR-1260a 36.714 0.118 19.143 2.901 0.012 A
Normal hsa-miR-1260b 41.857 1.489 5.857 4.403 0.001 A
PTB hsa-miR-1260b 36.714 0.078 18.714 4.841 0.001 A
Normal hsa-miR-130b-5p 18.571 0.251 6.286 1.578 0.013 A
PTB hsa-miR-130b-5p 36.714 −0.008 26.571 1.287 0.013 A
Normal hsa-miR-18a-3p 18.857 0.143 6.143 1.584 0.025 A
PTB hsa-miR-18a-3p 36.571 0.033 26.143 1.081 0.025 A
Normal hsa-miR-222-3p 41.857 6.562 5.857 18.303 0.039 A
PTB hsa-miR-222-3p 36.286 2.457 19.429 19.327 0.039 A
Normal hsa-miR-22-5p 18.714 0.067 5.857 0.227 0.010 A
PTB hsa-miR-22-5p 6.571 0.026 18.571 0.370 0.010 A
Normal hsa-miR-3677-3p 18.714 0.039 41.857 0.164 0.041 A
PTB hsa-miR-3677-3p 36.286 −0.008 12.143 0.144 0.041 A
Normal hsa-miR-4433b-5p 19.000 1.083 6.429 19.855 0.020 A
PTB hsa-miR-4433b-5p 36.000 0.569 6.571 18.526 0.020 A
Normal hsa-miR-4446-3p 19.143 1.216 5.857 7.518 0.033 A
PTB hsa-miR-4446-3p 36.714 1.288 26.286 5.254 0.033 A
Normal hsa-miR-483-3p 19.000 0.188 40.429 0.543 0.017 A
PTB hsa-miR-483-3p 6.571 −0.012 19.143 0.674 0.017 A
Normal hsa-miR-494-3p 41.857 0.019 5.857 0.177 0.009 A
PTB hsa-miR-494-3p 36.714 −0.025 19.286 0.248 0.009 A
Normal hsa-miR-5010-5p 19.000 0.520 6.143 2.483 0.011 A
PTB hsa-miR-5010-5p 36.000 0.349 19.143 2.647 0.011 A
Normal hsa-miR-197-3p 19.000 2.458 37.000 8.277 0.001 B
PTB hsa-miR-197-3p 36.000 0.812 18.571 7.698 0.001 B
Normal hsa-miR-24-1-3p 13.857 3.735 39.000 14.270 0.029 B
PTB hsa-miR-24-1-3p 36.571 2.000 12.857 11.039 0.029 B
Normal hsa-miR-24-2-3p 19.000 3.081 39.000 14.547 0.029 B
PTB hsa-miR-24-2-3p 36.571 2.855 12.857 10.512 0.029 B
Normal hsa-miR-339-5p 6.143 0.216 40.857 1.027 0.034 B
PTB hsa-miR-339-5p 32.571 0.087 18.571 0.716 0.034 B
Normal hsa-miR-424-3p 6.143 1.693 41.857 4.630 0.009 B
PTB hsa-miR-424-3p 36.571 0.644 18.714 3.890 0.009 B
Normal hsa-miR-148a-3p 10.286 79.632 27.429 312.515 0.028 C
PTB hsa-miR-148a-3p 7.143 85.944 18.571 165.603 0.028 C
Normal hsa-miR-152-3p 10.286 0.358 28.143 2.730 0.044 C
PTB hsa-miR-152-3p 36.000 0.390 13.000 1.897 0.044 C
Normal hsa-miR-223-3p 13.857 7.682 27.000 89.305 0.012 C
PTB hsa-miR-223-3p 36.000 16.825 18.571 44.779 0.012 C
Normal hsa-miR-3615 13.571 2.862 28.143 9.084 0.029 C
PTB hsa-miR-3615 34.429 2.152 19.429 5.248 0.029 C
Normal hsa-miR-550a-1-5p 13.000 0.142 28.143 0.585 0.004 C
PTB hsa-miR-550a-1-5p 34.429 0.036 12.857 0.512 0.004 C
Normal hsa-miR-550a-1-5p_var2 12.429 0.127 28.143 0.569 0.004 C
PTB hsa-miR-550a-1-5p_var2 35.000 0.026 12.143 0.476 0.004 C
Normal hsa-miR-550a-2-5p 13.000 0.133 27.000 0.580 0.004 C
PTB hsa-miR-550a-2-5p 35.857 0.042 13.000 0.488 0.004 C
Normal hsa-miR-550a-2-5p_var2 12.000 0.117 27.000 0.574 0.004 C
PTB hsa-miR-550a-2-5p_var2 36.714 0.036 12.143 0.500 0.004 C
Normal hsa-miR-550a-3-5p 13.571 0.112 28.143 0.462 0.005 C
PTB hsa-miR-550a-3-5p 36.429 0.005 19.143 0.349 0.005 C
Normal hsa-miR-1304-3p 41.857 0.675 28.143 2.003 0.018 D
PTB hsa-miR-1304-3p 36.000 0.850 18.714 1.882 0.018 D
Normal hsa-miR-361-5p 19.000 1.221 37.000 3.102 0.020 D
PTB hsa-miR-361-5p 36.429 1.080 19.143 3.191 0.020 D
Normal hsa-miR-423-3p 13.571 33.079 27.429 119.044 0.009 D
PTB hsa-miR-423-3p 36.286 30.309 18.571 88.296 0.009 D
Normal hsa-miR-92a-1-3p 19.000 1247.304 27.000 3712.668 0.002 D
PTB hsa-miR-92a-1-3p 36.714 1202.248 19.429 3587.438 0.002 D
Normal hsa-miR-92a-2-3p 19.000 1142.639 27.000 3732.389 0.002 D
PTB hsa-miR-92a-2-3p 36.714 1241.370 19.429 3553.979 0.002 D
Normal hsa-miR-101-1-3p 39.571 16.739 27.000 114.873 0.021 E
PTB hsa-miR-101-1-3p 36.000 21.077 19.429 94.615 0.021 E
Normal hsa-miR-101-2-3p 40.857 20.180 27.000 118.287 0.020 E
PTB hsa-miR-101-2-3p 36.000 17.958 18.571 93.111 0.020 E
Normal hsa-miR-103a-1-3p 40.857 38.378 27.000 247.984 0.046 E
PTB hsa-miR-103a-1-3p 36.000 62.859 9.714 220.993 0.046 E
Normal hsa-miR-103a-2-3p 40.857 45.190 27.000 243.098 0.046 E
PTB hsa-miR-103a-2-3p 34.429 67.586 9.714 219.811 0.046 E
Normal hsa-miR-106b-3p 40.857 5.819 27.000 24.471 0.041 E
PTB hsa-miR-106b-3p 36.000 2.176 19.429 19.745 0.041 E
Normal hsa-miR-107 40.857 44.043 27.000 236.691 0.047 E
PTB hsa-miR-107 36.000 50.350 9.714 224.599 0.047 E
Normal hsa-miR-140-3p 19.000 15.453 27.000 45.277 0.013 E
PTB hsa-miR-140-3p 36.000 7.497 18.571 41.822 0.013 E
Normal hsa-miR-16-2-3p 39.571 5.010 26.286 20.848 0.033 E
PTB hsa-miR-16-2-3p 36.714 4.330 7.857 19.259 0.033 E
Normal hsa-miR-29c-3p 13.571 3.852 27.000 14.952 0.040 E
PTB hsa-miR-29c-3p 26.857 3.551 18.571 11.390 0.040 E
Normal hsa-miR-342-3p 39.571 5.199 27.000 12.179 0.026 E
PTB hsa-miR-342-3p 36.000 0.799 18.571 13.442 0.026 E
Normal hsa-miR-425-5p 39.571 14.436 27.000 45.780 0.011 E
PTB hsa-miR-425-5p 36.000 5.925 18.571 38.338 0.011 E
Normal hsa-miR-502-3p 39.571 1.636 27.000 7.404 0.022 E
PTB hsa-miR-502-3p 36.000 0.962 18.571 6.580 0.022 E
Normal hsa-miR-10a-3p 11.286 −0.030 26.286 0.197 0.014 F
PTB hsa-miR-10a-3p 26.857 −0.033 13.000 0.335 0.014 F
Normal hsa-miR-379-5p 41.857 −0.003 26.429 0.007 0.026 F
PTB hsa-miR-379-5p 32.571 −0.007 13.000 0.027 0.026 F
Normal hsa-miR-524-3p 8.571 −0.006 28.143 0.059 0.029 F
PTB hsa-miR-524-3p 26.857 −0.010 12.857 0.118 0.029 F
Normal hsa-miR-525-3p 8.571 −0.004 28.143 0.029 0.020 F
PTB hsa-miR-525-3p 32.571 −0.001 13.000 0.076 0.020 F
Normal hsa-miR-548j-3p 13.714 −0.012 27.429 0.062 0.019 F
PTB hsa-miR-548j-3p 26.714 −0.015 12.857 0.067 0.019 F
Normal hsa-miR-1304-5p 41.857 −0.005 27.429 0.026 0.049 G
PTB hsa-miR-1304-5p 32.571 −0.012 18.571 0.064 0.049 G
Normal hsa-miR-138-1-3p 41.857 −0.006 28.143 0.019 0.025 G
PTB hsa-miR-138-1-3p 6.571 −0.028 18.571 0.066 0.025 G
Normal hsa-miR-3918 27.000 −0.002 8.571 0.005 0.048 G
PTB hsa-miR-3918 6.429 −0.010 19.143 0.038 0.048 G
Normal hsa-miR-4419a 39.000 −0.002 12.429 0.002 0.042 G
PTB hsa-miR-4419a 6.429 −0.011 18.714 0.021 0.042 G
Normal hsa-miR-4742-3p 41.857 0.024 5.857 0.130 0.032 G
PTB hsa-miR-4742-3p 6.429 −0.033 18.571 0.170 0.032 G
Normal hsa-miR-491-5p 41.857 −0.007 27.000 0.021 0.037 G
PTB hsa-miR-491-5p 6.429 −0.021 18.714 0.051 0.037 G
Normal hsa-miR-5189-3p 20.286 0.006 5.857 0.145 0.007 G
PTB hsa-miR-5189-3p 36.429 −0.005 18.714 0.172 0.007 G
Normal hsa-miR-6516-5p 41.857 −0.002 6.286 0.011 0.031 G
PTB hsa-miR-6516-5p 6.429 −0.014 18.714 0.032 0.031 G
Normal hsa-miR-145-5p 6.286 0.115 41.857 2.864 0.023 H
PTB hsa-miR-145-5p 6.429 0.468 26.857 1.474 0.023 H
Normal hsa-miR-371b-5p 8.571 0.070 41.857 1.473 0.041 H
PTB hsa-miR-371b-5p 6.571 0.161 19.143 0.623 0.041 H
Normal hsa-miR-377-5p 13.571 −0.005 41.857 0.154 0.047 H
PTB hsa-miR-377-5p 26.857 −0.008 19.429 0.159 0.047 H
Normal hsa-miR-3928-3p 13.571 −0.004 40.857 0.125 0.049 H
PTB hsa-miR-3928-3p 34.429 −0.006 13.000 0.090 0.049 H
Normal hsa-miR-6791-5p 6.429 −0.011 40.429 0.096 0.028 H
PTB hsa-miR-6791-5p 36.000 −0.014 9.714 0.091 0.028 H
Normal hsa-miR-6803-3p 27.000 0.014 40.857 0.130 0.024 H
PTB hsa-miR-6803-3p 36.714 −0.027 6.429 0.140 0.024 H
Normal hsa-let-7i-3p 39.571 0.055 12.857 0.343 0.050 I
PTB hsa-let-7i-3p 26.714 0.030 7.857 0.734 0.050 I
Normal hsa-miR-1908-3p 41.857 0.002 5.857 0.161 0.022 I
PTB hsa-miR-1908-3p 32.571 0.015 9.714 0.300 0.022 I
Normal hsa-miR-520a-3p 6.143 0.120 28.143 0.847 0.022 I
PTB hsa-miR-520a-3p 32.571 0.051 10.571 1.184 0.022 I
Normal hsa-miR-539-3p 12.429 0.011 28.143 0.218 0.010 I
PTB hsa-miR-539-3p 36.429 −0.025 12.857 0.357 0.010 I
Normal hsa-miR-589-3p 19.000 0.040 6.143 0.151 0.019 I
PTB hsa-miR-589-3p 35.286 0.018 12.143 0.258 0.019 I
Normal hsa-miR-6837-3p 11.286 0.001 26.429 0.141 0.021 I
PTB hsa-miR-6837-3p 36.571 −0.003 18.714 0.181 0.021 I
Normal hsa-miR-6852-5p 12.571 0.976 27.000 1.882 0.014 I
PTB hsa-miR-6852-5p 36.000 0.466 18.571 3.062 0.014 I
Normal hsa-miR-760 6.429 0.013 41.857 0.151 0.003 I
PTB hsa-miR-760 32.571 0.007 6.429 0.435 0.003 I
Normal hsa-miR-128-1-3p 13.857 3.453 26.286 15.183 0.013 J
PTB hsa-miR-128-1-3p 36.714 1.818 19.429 13.765 0.013 J
Normal hsa-miR-128-2-3p 13.286 2.890 26.286 14.693 0.013 J
PTB hsa-miR-128-2-3p 36.714 1.788 19.429 12.515 0.013 J
Normal hsa-miR-1285-1-3p 39.571 0.142 27.000 2.477 0.036 J
PTB hsa-miR-1285-1-3p 32.571 0.392 7.857 3.242 0.036 J
Normal hsa-miR-1285-2-3p 39.571 0.217 12.000 2.464 0.032 J
PTB hsa-miR-1285-2-3p 36.000 0.418 7.857 3.108 0.032 J
Normal hsa-miR-140-5p 13.286 0.028 27.429 0.328 0.024 J
PTB hsa-miR-140-5p 36.000 −0.017 13.000 0.412 0.024 J
Normal hsa-miR-199a-1-5p 40.857 0.619 27.000 4.821 0.039 J
PTB hsa-miR-199a-1-5p 36.000 −0.002 19.143 4.775 0.039 J
Normal hsa-miR-199a-2-5p 39.571 0.743 27.000 4.759 0.039 J
PTB hsa-miR-199a-2-5p 36.000 −0.010 19.143 5.143 0.039 J
Normal hsa-miR-224-5p 19.000 0.159 27.000 2.291 0.009 J
PTB hsa-miR-224-5p 36.714 0.002 18.714 2.244 0.009 J
Normal hsa-miR-25-3p 39.571 47.155 38.857 343.596 0.007 J
PTB hsa-miR-25-3p 36.714 −13.802 7.857 349.212 0.007 J
Normal hsa-miR-28-5p 40.857 1.226 6.143 9.605 0.038 J
PTB hsa-miR-28-5p 32.571 2.047 18.571 5.961 0.038 J
Normal hsa-miR-330-3p 40.857 0.170 6.429 1.881 0.046 J
PTB hsa-miR-330-3p 36.000 0.032 19.429 1.609 0.046 J
Normal hsa-miR-410-3p 19.000 0.577 28.143 11.516 0.015 J
PTB hsa-miR-410-3p 36.714 1.621 19.429 7.912 0.015 J
Normal hsa-miR-433-3p 13.571 0.029 40.857 0.404 0.014 J
PTB hsa-miR-433-3p 36.714 0.022 13.000 0.493 0.014 J
Normal hsa-miR-484 19.000 16.538 27.000 41.184 0.050 J
PTB hsa-miR-484 36.714 −2.373 26.571 70.214 0.050 J
Normal hsa-miR-485-5p 12.143 0.172 5.857 0.796 0.017 J
PTB hsa-miR-485-5p 34.429 0.121 19.429 1.094 0.017 J
Normal hsa-miR-6735-5p 40.429 −0.009 20.571 0.225 0.024 J
PTB hsa-miR-6735-5p 36.571 −0.045 18.571 0.217 0.024 J
Normal hsa-miR-98-3p 13.857 0.167 27.000 0.835 0.003 J
PTB hsa-miR-98-3p 36.714 0.060 19.429 1.090 0.003 J
Normal hsa-miR-1275 12.143 −0.004 40.857 0.006 0.048 K
PTB hsa-miR-1275 36.714 −0.010 26.857 0.061 0.048 K
Normal hsa-miR-1298-5p 40.857 −0.002 5.857 0.005 0.027 K
PTB hsa-miR-1298-5p 13.000 −0.007 26.571 0.032 0.027 K
Normal hsa-miR-3138 6.429 −0.028 20.286 0.103 0.012 K
PTB hsa-miR-3138 36.571 −0.137 26.571 0.641 0.012 K
Normal hsa-miR-32-3p 6.429 −0.006 26.143 0.014 0.013 K
PTB hsa-miR-32-3p 36.714 −0.029 26.571 0.142 0.013 K
Normal hsa-miR-3689a-3p 28.143 −0.009 12.429 0.022 0.002 K
PTB hsa-miR-3689a-3p 36.714 −0.053 26.857 0.241 0.002 K
Normal hsa-miR-3689a-5p 19.000 −0.001 20.571 0.070 0.026 K
PTB hsa-miR-3689a-5p 36.571 −0.069 26.857 0.218 0.026 K
Normal hsa-miR-3689b-5p 12.857 −0.005 20.571 0.075 0.026 K
PTB hsa-miR-3689b-5p 7.857 −0.061 26.857 0.212 0.026 K
Normal hsa-miR-3689e 12.857 −0.006 12.429 0.062 0.026 K
PTB hsa-miR-3689e 36.571 −0.056 26.857 0.225 0.026 K
Normal hsa-miR-409-3p 13.571 5.563 27.000 17.099 0.008 K
PTB hsa-miR-409-3p 36.714 −9.655 26.571 71.852 0.008 K
Normal hsa-miR-4467 19.000 −0.006 5.857 0.059 0.001 K
PTB hsa-miR-4467 6.429 −0.010 26.714 0.075 0.001 K
Normal hsa-miR-597-5p 13.857 −0.002 27.000 0.005 0.014 K
PTB hsa-miR-597-5p 36.714 −0.008 6.429 0.032 0.014 K
Normal hsa-miR-6750-3p 28.143 −0.002 19.143 0.004 0.014 K
PTB hsa-miR-6750-3p 36.714 −0.006 26.857 0.029 0.014 K
Normal hsa-miR-889-5p 28.143 −0.001 12.857 0.005 0.019 K
PTB hsa-miR-889-5p 36.429 −0.006 26.714 0.027 0.019 K
Normal hsa-miR-1249-5p 28.143 −0.009 41.857 0.013 0.020 L
PTB hsa-miR-1249-5p 26.286 −0.027 36.714 0.176 0.020 L
Normal hsa-miR-141-3p 41.857 −3.057 27.000 8.385 0.039 L
PTB hsa-miR-141-3p 26.857 −4.227 36.714 53.676 0.039 L
Normal hsa-miR-146b-3p 19.143 −1.544 26.429 3.242 0.041 L
PTB hsa-miR-146b-3p 26.571 −3.755 36.571 50.654 0.041 L
Normal hsa-miR-193a-5p 41.857 −0.010 28.143 0.061 0.032 L
PTB hsa-miR-193a-5p 26.143 −0.033 36.714 0.189 0.032 L
Normal hsa-miR-200a-3p 6.429 −1.486 28.143 7.882 0.040 L
PTB hsa-miR-200a-3p 26.286 −3.358 36.571 50.665 0.040 L
Normal hsa-miR-376a-1-5p 41.857 −0.013 6.143 0.089 0.035 L
PTB hsa-miR-376a-1-5p 26.857 −0.024 36.571 0.178 0.035 L
Normal hsa-miR-382-5p 20.571 −0.047 6.429 0.347 0.037 L
PTB hsa-miR-382-5p 26.143 −0.023 36.571 0.600 0.037 L
Normal hsa-miR-3936 12.571 −8.814 12.000 9.239 0.015 L
PTB hsa-miR-3936 26.857 −28.825 36.714 171.652 0.015 L
Normal hsa-miR-4447 38.857 −11.147 27.000 6.753 0.015 L
PTB hsa-miR-4447 26.857 −24.998 36.714 166.559 0.015 L
Normal hsa-miR-4516 28.143 −3.132 6.286 2.609 0.045 L
PTB hsa-miR-4516 26.286 −3.764 36.571 50.392 0.045 L
Normal hsa-miR-4695-5p 11.286 −0.011 26.571 0.013 0.045 L
PTB hsa-miR-4695-5p 6.429 −0.024 36.714 0.174 0.045 L
Normal hsa-miR-6769b-5p 19.143 −0.014 6.143 0.050 0.018 L
PTB hsa-miR-6769b-5p 26.714 −0.026 36.714 0.168 0.018 L
Normal hsa-miR-7976 37.714 −0.013 26.429 0.060 0.030 L
PTB hsa-miR-7976 6.571 −0.034 36.571 0.397 0.030 L
Normal hsa-miR-202-5p 20.286 −0.020 5.857 0.151 0.030 M
PTB hsa-miR-202-5p 36.714 −0.004 36.286 0.004 0.030 M
Normal hsa-miR-3656 41.857 −0.034 5.857 0.309 0.006 M
PTB hsa-miR-3656 35.000 −0.030 13.000 0.244 0.006 M
Normal hsa-miR-4535 19.000 −0.008 6.429 0.052 0.027 M
PTB hsa-miR-4535 6.571 −0.008 18.714 0.027 0.027 M
Normal hsa-miR-4650-1-3p 20.286 −0.002 6.286 0.024 0.046 M
PTB hsa-miR-4650-1-3p 6.571 −0.002 18.714 0.010 0.046 M
Normal hsa-miR-4650-2-3p 20.571 −0.001 6.143 0.024 0.046 M
PTB hsa-miR-4650-2-3p 6.571 −0.003 18.571 0.011 0.046 M
Normal hsa-miR-4688 19.143 −0.004 5.857 0.054 0.046 M
PTB hsa-miR-4688 6.429 −0.003 26.143 0.032 0.046 M
Normal hsa-miR-4717-3p 20.286 −0.002 6.429 0.013 0.047 M
PTB hsa-miR-4717-3p 6.571 −0.002 19.286 0.003 0.047 M
Normal hsa-miR-4789-3p 19.143 −0.010 5.857 0.049 0.032 M
PTB hsa-miR-4789-3p 6.429 −0.010 19.143 0.024 0.032 M
Normal hsa-miR-4798-5p 39.000 −0.080 5.857 1.121 0.048 M
PTB hsa-miR-4798-5p 36.571 −0.117 26.143 0.506 0.048 M
Normal hsa-miR-545-5p 19.000 −0.021 5.857 0.190 0.040 M
PTB hsa-miR-545-5p 36.429 −0.011 6.429 0.062 0.040 M
Normal hsa-miR-6859-1-3p 18.857 −0.007 5.857 0.053 0.017 M
PTB hsa-miR-6859-1-3p 6.429 −0.003 36.714 0.010 0.017 M
Normal hsa-miR-6859-2-3p 18.714 −0.007 5.857 0.054 0.017 M
PTB hsa-miR-6859-2-3p 6.571 −0.001 36.286 0.008 0.017 M
Normal hsa-miR-6859-3-3p 19.000 −0.007 5.857 0.054 0.017 M
PTB hsa-miR-6859-3-3p 6.571 −0.002 36.571 0.010 0.017 M
Normal hsa-miR-6859-4-3p 18.857 −0.007 5.857 0.054 0.017 M
PTB hsa-miR-6859-4-3p 6.429 −0.002 36.714 0.009 0.017 M
Normal hsa-miR-7856-5p 19.143 −0.008 6.286 0.043 0.028 M
PTB hsa-miR-7856-5p 6.429 −0.005 18.571 0.027 0.028 M
Normal hsa-miR-1255b-2-3p 20.571 −0.001 6.429 0.001 0.014 N
PTB hsa-miR-1255b-2-3p 19.143 −0.002 6.429 0.012 0.014 N
Normal hsa-miR-129-1-3p 12.571 −0.001 19.143 0.000 0.014 N
PTB hsa-miR-129-1-3p 19.429 −0.002 6.429 0.012 0.014 N
Normal hsa-miR-129-2-3p 6.286 0.000 6.429 0.000 0.014 N
PTB hsa-miR-129-2-3p 19.143 −0.002 6.429 0.012 0.014 N
Normal hsa-miR-1343-3p 41.857 −0.002 5.857 0.007 0.029 N
PTB hsa-miR-1343-3p 36.571 −0.001 6.429 0.033 0.029 N
Normal hsa-miR-147b 12.429 −0.004 39.000 0.003 0.042 N
PTB hsa-miR-147b 32.571 −0.015 7.857 0.109 0.042 N
Normal hsa-miR-15a-3p 41.857 −0.001 13.571 0.002 0.031 N
PTB hsa-miR-15a-3p 19.429 −0.003 6.571 0.023 0.031 N
Normal hsa-miR-2277-3p 6.286 −0.014 19.143 0.028 0.001 N
PTB hsa-miR-2277-3p 18.714 −0.037 6.429 0.254 0.001 N
Normal hsa-miR-301b-5p 41.857 −0.002 28.143 0.004 0.043 N
PTB hsa-miR-301b-5p 18.714 −0.001 6.429 0.021 0.043 N
Normal hsa-miR-3116-1 38.857 −0.001 37.000 0.001 0.014 N
PTB hsa-miR-3116-1 19.429 −0.002 6.429 0.011 0.014 N
Normal hsa-miR-3116-2 39.571 0.000 10.286 0.000 0.014 N
PTB hsa-miR-3116-2 19.429 −0.002 6.429 0.011 0.014 N
Normal hsa-miR-3184-3p 27.429 −0.001 13.000 0.002 0.046 N
PTB hsa-miR-3184-3p 19.429 −0.003 6.571 0.044 0.046 N
Normal hsa-miR-337-3p 19.000 −0.003 5.857 0.094 0.017 N
PTB hsa-miR-337-3p 36.714 −0.024 6.571 0.323 0.017 N
Normal hsa-miR-3665 6.429 −0.011 13.714 0.010 0.004 N
PTB hsa-miR-3665 19.286 −0.034 6.571 0.212 0.004 N
Normal hsa-miR-379-3p 41.857 −0.046 27.429 0.286 0.004 N
PTB hsa-miR-379-3p 36.714 −0.044 6.571 0.606 0.004 N
Normal hsa-miR-3908 26.429 −0.001 6.286 0.004 0.007 N
PTB hsa-miR-3908 19.286 −0.007 6.429 0.038 0.007 N
Normal hsa-miR-3942-3p 10.286 −0.003 27.429 0.003 0.006 N
PTB hsa-miR-3942-3p 18.571 −0.009 6.571 0.059 0.006 N
Normal hsa-miR-411-3p 41.857 −0.046 27.429 0.274 0.004 N
PTB hsa-miR-411-3p 36.714 −0.050 6.571 0.616 0.004 N
Normal hsa-miR-4301 41.857 −0.001 5.857 0.002 0.013 N
PTB hsa-miR-4301 35.286 −0.002 6.429 0.032 0.013 N
Normal hsa-miR-4318 27.000 −0.001 10.286 0.003 0.031 N
PTB hsa-miR-4318 19.286 −0.003 6.429 0.023 0.031 N
Normal hsa-miR-433-5p 41.857 −0.001 6.143 0.001 0.046 N
PTB hsa-miR-433-5p 19.429 −0.002 6.571 0.021 0.046 N
Normal hsa-miR-4502 19.143 −0.002 13.571 0.001 0.040 N
PTB hsa-miR-4502 19.286 −0.002 6.429 0.022 0.040 N
Normal hsa-miR-4522 20.286 0.000 37.714 0.001 0.014 N
PTB hsa-miR-4522 19.286 −0.002 6.429 0.011 0.014 N
Normal hsa-miR-4529-3p 26.429 −0.001 6.286 0.001 0.039 N
PTB hsa-miR-4529-3p 19.429 −0.002 6.429 0.012 0.039 N
Normal hsa-miR-4530 13.286 −0.021 41.857 0.015 0.004 N
PTB hsa-miR-4530 18.714 −0.068 6.429 0.407 0.004 N
Normal hsa-miR-4640-3p 12.143 0.000 38.857 0.001 0.014 N
PTB hsa-miR-4640-3p 19.143 −0.002 6.571 0.011 0.014 N
Normal hsa-miR-4709-5p 6.143 −0.003 18.714 0.004 0.008 N
PTB hsa-miR-4709-5p 18.714 −0.007 6.429 0.038 0.008 N
Normal hsa-miR-4769-5p 12.429 −0.001 39.000 0.001 0.003 N
PTB hsa-miR-4769-5p 19.429 −0.003 6.429 0.019 0.003 N
Normal hsa-miR-500a-5p 26.429 −0.010 11.286 0.019 0.007 N
PTB hsa-miR-500a-5p 19.286 −0.067 6.429 0.421 0.007 N
Normal hsa-miR-500b-5p 41.857 −0.015 11.286 0.026 0.006 N
PTB hsa-miR-500b-5p 19.143 −0.069 6.429 0.430 0.006 N
Normal hsa-miR-5698 6.286 −0.010 39.000 0.007 0.009 N
PTB hsa-miR-5698 19.286 −0.014 6.429 0.208 0.009 N
Normal hsa-miR-572 37.714 −0.001 12.857 0.001 0.003 N
PTB hsa-miR-572 19.143 −0.003 6.429 0.019 0.003 N
Normal hsa-miR-579-3p 5.857 −0.001 19.143 0.002 0.015 N
PTB hsa-miR-579-3p 19.429 −0.003 6.571 0.023 0.015 N
Normal hsa-miR-586 19.000 −0.002 12.571 0.001 0.003 N
PTB hsa-miR-586 18.571 −0.007 6.429 0.038 0.003 N
Normal hsa-miR-655-3p 20.571 −0.001 19.143 0.001 0.014 N
PTB hsa-miR-655-3p 19.429 −0.003 6.429 0.024 0.014 N
Normal hsa-miR-6759-5p 6.286 −0.001 12.857 0.001 0.003 N
PTB hsa-miR-6759-5p 19.286 −0.003 6.429 0.020 0.003 N
Normal hsa-miR-6783-3p 39.571 −0.003 5.857 0.003 0.005 N
PTB hsa-miR-6783-3p 19.143 −0.008 6.429 0.082 0.005 N
Normal hsa-miR-6797-5p 8.286 −0.001 19.143 0.001 0.003 N
PTB hsa-miR-6797-5p 19.429 −0.004 6.429 0.019 0.003 N
Normal hsa-miR-6798-5p 12.143 −0.001 20.571 0.001 0.003 N
PTB hsa-miR-6798-5p 19.429 −0.004 6.571 0.019 0.003 N
Normal hsa-miR-6802-5p 41.857 −0.015 28.143 0.040 0.032 N
PTB hsa-miR-6802-5p 19.429 −0.009 6.429 0.105 0.032 N
Normal hsa-miR-6838-3p 12.571 0.000 10.286 0.001 0.014 N
PTB hsa-miR-6838-3p 18.571 −0.002 6.429 0.011 0.014 N
Normal hsa-miR-6856-5p 40.857 −0.001 28.143 0.002 0.024 N
PTB hsa-miR-6856-5p 19.429 −0.002 6.429 0.012 0.024 N
Normal hsa-miR-8079 5.857 −0.001 12.429 0.000 0.046 N
PTB hsa-miR-8079 19.429 −0.002 6.429 0.022 0.046 N
Normal hsa-miR-933 26.571 −0.001 13.714 0.003 0.028 N
PTB hsa-miR-933 19.429 −0.004 6.429 0.023 0.028 N

Pathway analysis and gene target and gene ontology prediction

Gene target and pathway analyses of the largest maximum expression exosomal miRNAs that were revealed to be differentially expressed in term, PTB, and term vs PTB across gestation were analyzed using in silico tools, including the CyTargetLinker application in Cytoscape, as well as Ingenuity pathway analysis (IPA). In term, PTB, and term vs PTB pregnancies, the largest maximum expression miRNAs were linked to 645, 1677, and 686 target genes, respectively, and these gene targets were represented in at least two miRNA databases. The target genes of the differentially expressed miRNAs were subjected to gene ontology analysis using the BiNGO application in Cytoscape that identified a total of 1000, 1172, and 995 gene ontology terms, respectively, being regulated by these miRNAs. Within this gene ontology network, pathways regulating the immune system process were enriched (P < 0.05) in term and PTB pregnancies (Fig. 8A and 8B). Then, we performed a bioinformatics analysis on the largest maximum expression miRNA profile in term, PTB, and term vs PTB analysis, and our data establish that the differences in the miRNA profile between these groups target the signaling pathways associated with TGF-β signaling, p53, and glucocorticoid receptor signaling, respectively (Fig. 8C–8E).

Figure 8.

Figure 8.

miRNA gene target and gene ontology analysis for the highest abundant miRNAs per cluster in each condition. Gene target analysis for significant and highest abundant miRNAs in each cluster for normal, PTB, and normal vs PTB pregnancies across gestation are shown. Gene ontology analysis for these gene targets showed enrichment for immune systems process in (A) normal and (B) PTB pregnancies. The yellow circles indicate statistically significant gene ontologies (P value <0.05), while the change of color from yellow to orange indicates increasing statistical significance. Bioinformatics analysis on the largest maximum expression miRNA profile in (C) term, (D) PTB, and (E) term vs PTB show differences in the miRNA profile between these groups target signaling pathways (circled in green) associated with (C) TGF-β signalling, (D) p53, and (E) glucocorticoid receptor signalling.

Discussion

The aim of this study was to characterize serial changes in the exosomal miRNA concentration present in maternal circulation across gestation in term and PTB pregnancies. We implemented an innovative approach using linear mixed modeling to determine exosomal miRNA expression as a function of gestational age in term and PTB pregnancies. The data obtained identified exosomal miRNA changes specific to term and PTB as a function of the gestational age during pregnancy.

Exosomal miRNA changes in normal pregnancies

miRNA clusters that are differentially regulated are functionally linked to various physiologic and pathologic conditions during pregnancy. These functions include regulation of cell growth (miR-3200) (25), control of cell transition factors in female reproductive tract by IGF receptor 1 and TGF-β receptor 2 functions (miR-3200-5p) (26), anomalous placentation (miR-320a) (27), epithelial mesenchymal transition involved in tissue remodeling (miR-25-3p) (28), gestational hypertension, preeclampsia, and intrauterine growth restriction (miR-143-3p) (29), cell proliferation and migration (miR129-1 cluster) (30), oocyte aging and embryogenesis (miR-203a-3p) (29, 31), cell proliferation and migration (miR-324-5p) (32), MAPK function and induction of cell cycle arrest as seen in senescent uterine cells (miR129-1 cluster) (30), and immune responses and inflammatory reactions (miR-6769b-5p) (33).

miRNAs collectively represent TGF-β signaling during various stages of gestation ending in term deliveries (34, 35). TGF-β is an anti-inflammatory cytokine, and ongoing work in the Menon laboratory suggests that they can contribute to epithelial mesenchymal transitions of amnion epithelial cells to maintain fetal membrane homeostasis. In placenta, TGF-β1 and IGFBP-3 have been shown to signal through TGF-β receptors to influence human cytotrophoblast proliferation (36). Similarly, TGF-β1 upregulates connexin43-mediated gap junctional intercellular communication required for human trophoblast differentiation (37). Therefore, miRNA profiling in exosomes during normal gestation and parturition indicates that TGF-β–mediated tissue homeostasis (regulates cellular proliferation and transitions) is required for pregnancy maintenance.

Exosomal miRNA changes in PTB

Examination of differentially expressed exosomal miRNA in PTB samples provided more distinct clusters than for normal birth. A summary of functional roles already reported for many of the miRNAs identified in exosomes from PTB suggests that miRNAs are functionally linked to cell cycle regulation (let-7a-2-5p) (38, 39), MAPK kinase kinases and inhibition of cell growth (miR-520a-3p) (40), cellular transitions and inflammation (miR-520a-3p and miR-483-3p) (41, 42), placental oxidative stress response and impairment of mitochondrial function (miR-130b-3p and miR-4433b-3p) (43, 44), macrophage programming contributing to inflammatory and oxidative stress damages (miR-142-5p) (45), preeclampsia (miR-342-3p) (46, 47), as well as placental dysfunction and impaired fetal growth due to folate deficiency (miR-222-3p) (48).

PTB

One of the key pathways affected in PTB (as determined in our IPA analysis) is a p53-mediated mechanism (49). The function of p53 is overtly represented in exosomes during gestation ending in PTB compared with normal term birth. p53 is a well-reported tumor suppressor protein that is implicated in placental and decidual cell senescence and fetal membrane apoptosis (50). Overrepresentation of the p53 pathway in exosomes during pregnancies ending in PTB suggests disturbances in normal cell cycle indicative of cellular senescence and/or programmed cell death.

IPA analysis of differentially expressed miRNAs represented glucocorticoid signaling as one of the key pathways implicated in PTB. Several reports by Zakar et al. (51, 52) and Zakar and Olson (53) have shown the effect of glucocorticoids on prostaglandin production (uterotonin) as well as their role in organ maturation and fetal growth. In most mammalian species, increased concentrations of glucocorticoids are evident in the maternal and fetal circulations and amniotic fluid prior to the onset of labor. Glucocorticoids directly increase fetal placental prostaglandin production, and they indirectly increase prostaglandin production by maternal uterine tissues through the stimulation of placental estradiol synthesis (54, 55). Thus, exosomal miRNA representation of glucocorticoid signaling implicates untimely activation of this signaling in PTB during early gestation compared with those ending in normal term deliveries (56, 57).

The strengths of this study are longitudinal sampling at four separate time points from a well-defined cohort of subjects and technological approaches to isolate and characterize exosomal miRNAs. This study precisely is a hypothesis-generation work, and the pathways and networks identified in this study still need further testing using in vitro cell culture models or animal models. We have correlated the networks and pathways to pregnancy whenever data were available in the literature and or suggested potential functions based on the reported functions in other systems. Another important point about this study is that we profiled the miRNAs associated with the total circulating exosomes present in maternal plasma across gestation, and the origin of these exosomes (i.e., placenta) was not identified. Owing to technical difficulties, miRNA quantity that can be obtained from the fetal portion of maternal plasma (∼15% to 20%) is not sufficient to yield a fetal-only miRNA signature. Thus, the miRNA profile is an indication of an overall change in fetal as well as maternal tissues and is not restricted to either fetal or uterine tissues. Regardless, the exosome miRNA profile is unique at different trimesters, at term and preterm, and it differs substantially between pregnancies ending up with preterm and term births. Irrespective of origin of exosomes, these are indicative of overall physiologic changes in fetomaternal tissues.

In summary, the exosomal miRNAs showing maximum expression for each trend of change were associated with inflammation and cellular movement for term pregnancy. Alternatively, the top molecular and cellular functions targeted by the top exosomal miRNAs in PTB were cell-to-cell signaling and interaction, cellular growth and proliferation, and cellular development. Comparative analysis between the exosomal miRNA in term and PTB reveals that main differences are in cell morphology and cellular development. The data presented in this study establish that circulating exosomes carry a specific set of miRNAs as a function of the gestational age in term pregnancy, and that the circulating exosomal miRNA profile changes in PTB pregnancies compared with normal term deliveries. We posit that exosomes may contribute to the inflammatory state and metabolic changes associated with pregnancy by the specific incorporation of miRNAs, which might be delivered to maternal cells to support the normal maternal physiological changes during gestation, a phenomenon dysregulated in PTB pregnancies.

Acknowledgments

The Garbhini Study Team consists of a group of scientific investigators from academic and medical research centers that are involved in the study of preterm birth.

Financial Support: This work was supported by the Bill and Melinda Gates Foundation awarded to R.M. Samples were collected under The Garbhini Study funded by the Department of Biotechnology (DBT), Government of India, augmented by Biotechnology Industry Research Assistance Council–All Children Thriving (BIRAC-ACT), India. C.S. is supported by the Lions Medical Research Foundation, National Health and Medical Research Council Grant 1114013, and by Fondo Nacional de Desarrollo Científico y Tecnológico Grant 1170809.

Disclosure Summary: The authors have nothing to disclose.

Glossary

Abbreviations:

IPA

Ingenuity pathway analysis

PTB

preterm birth

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