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Reproductive Biology and Endocrinology : RB&E logoLink to Reproductive Biology and Endocrinology : RB&E
. 2016 Nov 9;14:78. doi: 10.1186/s12958-016-0207-4

Characterization of exosomal release in bovine endometrial intercaruncular stromal cells

Yong Qin Koh 1, Hassendrini N Peiris 1, Kanchan Vaswani 1, Sarah Reed 1, Gregory E Rice 1, Carlos Salomon 1, Murray D Mitchell 1,
PMCID: PMC5103490  PMID: 27829441

Abstract

Background

Cell-to-cell communication between the blastocyst and endometrium is critical for implantation. In recent years, evidence has emerged from studies in humans and several other animal species that exosomes are secreted from the endometrium and trophoblast cells and may play an important role in cell-to-cell communication maternal-fetal interface during early pregnancy. Exosomes are stable extracellular lipid bilayer vesicles that encapsulate proteins, miRNAs, and mRNAs, with the ability to deliver their cargo to near and distant sites, altering cellular function(s). Furthermore, the exosomal cargo can be altered in response to environmental cues (e.g. hypoxia). The current study aims to develop an in vitro system to evaluate maternal-embryo interactions via exosomes (and exosomal cargo) produced by bovine endometrial stromal cells (ICAR) using hypoxia as a known stimulus associated with the release of exosomes and alterations to biological responses (e.g. cell proliferation).

Methods

ICAR cells cultured under 8 % O2 or 1 % O2 for 48 h and changes in cell function (i.e. migration, proliferation and apoptosis) were evaluated. Exosome release was determined following the isolation (via differential centrifugation) and characterization of exosomes from ICAR cell-conditioned media. Exosomal proteomic content was evaluated by mass spectrometry.

Results

Under hypoxic conditions (i.e. 1 % O2), ICAR cell migration and proliferation was decreased (~20 and ~32 %, respectively) and apoptotic protein caspase-3 activation was increased (∼1.6 fold). Hypoxia increased exosome number by ~3.6 fold compared with culture at 8 % O2. Mass spectrometry analysis identified 128 proteins unique to exosomes of ICAR cultured at 1 % O2 compared with only 46 proteins unique to those of ICAR cultured at 8 % O2. Differential production of proteins associated with specific biological processes and molecular functions were identified, most notably ADAM10, pantetheinase and kininogen 2.

Conclusions

In summary, we have shown that a stimulus such as hypoxia can alter both the cellular function and exosome release of ICAR cells. Alterations to exosome release and exosomal content in response to stimuli may play a crucial role in maternal-fetal crosstalk and could also affect placental development.

Keywords: Bovine, Intercaruncular, Hypoxia, Exosomes

Background

In dairy cattle, the average gestation length is approximately 282 days. The placenta is epitheliochorial, cotyledonary and non-deciduate [1]. Placentation is restricted to the aglandular maternal caruncles, where the fetal cotyledons come into contact with each other [2, 3]. They then form the placentome for maternal-fetal exchange of oxygen, nutrients and waste products. The glandular intercaruncular regions are associated with preserving the uterus in a state of quiescence and allowing a progressive uterine hypertrophy to accommodate the increasing needs of the growing feto-placental unit [4]. The uterine glands present in the intercaruncular endometrial areas secrete and release histotroph that is crucial for conceptus survival and growth [5] and is transported into the fetal circulation via the placental areolae. The establishment of a successful pregnancy requires the interactions between the endometrial cells and the early conceptus during maternal recognition of pregnancy [6, 7].

Cells located within intercaruncular region and associated with maternal fetal crosstalk include cells of stromal (intercaruncular stromal cell; ICAR) and epithelial origin. Both cell types are known to produce prostaglandins (e.g. PGF) and have immunomodulatory functions [8, 9]. Interactions between these cells may also play a pivotal role in endometrial receptivity during early pregnancy as was reported in a co-culture study that human endometrial stromal cells can mediate epithelial cell function by promoting differentiation and inhibiting proliferation of endometrial epithelial cells [10]. In the bovine, endometrial stromal cells (as utilized in the current study) are known to differentially regulate the production of prostaglandins and enzymes related to the production of prostaglandins, in response to specific stimuli (e.g. inflammatory mediators and interferon tau) [8, 11]. ICAR cells were a kind gift from Professor Michel A. Fortier (Université Laval, Québec). ICAR cells are a transformed cell-line derived from the intercaruncular region of the bovine endometrium [12]. ICAR cells can be propagated while still maintaining the phenotypical characteristics of these cells which include the presence of SV40 TAG and the vimentin-positive and cytokeratin-negative features that support the stromal phenotype of these cells [8, 13]. This study aimed to evaluate the effect of a known stimulus of exosome release on the production of exosomes by ICAR cells.

In recent years, evidence has emerged from studies in humans [14] and several other animal species [1518] that exosomes are secreted from the endometrium and trophoblast cells and may play important roles at the conceptus-endometrial interface during early pregnancy. Exosomes are specific subsets of extracellular vesicles (smaller than 1000 nm) [19] that could provide insights into an alternative new explanation for the crosstalk between cells. Exosomes (30–120 nm) are stable extracellular lipid bilayer vesicles arising from the inward budding of multivesicular bodies and released via an exocytic pathway to the extracellular environment with the capacity to modify the biological function of target cells [20]. Exosomes provide a mechanism of cell-to-cell communication in physiological and pathological conditions and may be influenced by neighboring cells, distant tissues or local environmental factors. There is considerable evidence that hypoxia is a potent stimulant to the release of exosomes [2124]. It is also a useful investigatory agent since a lower-than-normal oxygen tension in utero can influence many developmental events with potentially lifelong consequences [25, 26].

Hypoxia is a well-known stimulus of exosome release as seen in breast cancer cells, endothelial cells and human trophoblasts [24, 27, 28]. Alterations have been documented in both the number of exosomes released as well as differences in the content (cargo) of the exosomes [24, 27, 29]. This study aimed to test the hypothesis that hypoxia as a known stimulus of exosome release (and altered biological response) will modify the phenotype of bovine endometrial stromal cells affecting their migration, proliferation, apoptosis as well as altering both the release and cargo of the exosomes generated.

Methods

Aim

This study investigated the effect(s) of a hypoxic environment on the function of bovine endometrial cells. In particular, alterations to migration, proliferation and apoptosis. Moreover, this study evaluated alterations to the release and cargo content of exosomes generated by bovine endometrial cells, when cultured under hypoxia.

Endometrial cell line

A well characterized bovine endometrial intercaruncular stromal cell line (ICAR cells) was utilized for the current study [8, 30]. ICAR cells were a kind gift from Professor Michel A. Fortier (Université Laval, Québec). ICAR cells were maintained in 175 cm2 (T175, Corning Costar) culture flasks supplemented with exosome-free media (1640 Roswell Park Memorial Institute (RPMI) medium (Invitrogen, Life Technologies) with 10 % heat-inactivated fetal bovine serum (Bovogen, Interpath services Pty Ltd) depleted of exosomes by ultracentrifugation (100,000 g for 20 h at 4 °C) and 1000 U/mL antibiotic-antimycotic solution (Gibco, Life Technologies) in a humidified cell culture incubator at 37 °C under an atmosphere of 5 % CO2-balanced N2 to obtain a hypoxic (1 % O2) environment or under physiologically relevant conditions (8 % O2). Lactate dehydrogenase (LDH) assay was also performed accordingly to the manufacturer’s protocol using the commercially available kit Pierce LDH cytotoxicity assay kit (Thermo scientific) to measure LDH in supernatants of ICAR cells cultured at 8 % O2 and 1 % O2 and ICAR cell viability was accessed. No significant difference in the LDH activity was observed (data not shown) between 8 % O2 and 1 % O2, indicating that the viability of ICAR cells was not affected by experimental condition.

Cell migration assay

The effect of oxygen tension on cell migration was assessed using methods as previously published [31]. Briefly, ICAR cells were plated (30,000 cells per well) and grown to confluence in a 96-well culture plate (Corning Costar) at 1 % O2 or 8 % O2 oxygen tension and a wound scratch was made on confluent monolayers using a 96-pin WoundMaker (Essen BioScience). Migration assays were performed in the presence of Mitomycin C (100 ng/mL, Sigma–Aldrich) to minimize any confounding effects of cell proliferation. The wound images were automatically acquired every 2 h for 48 h and registered by the IncuCyte software system (Essen BioScience). Data are presented as the Relative Wound Density (RWD, Eizen, v1.0 algorithm). RWD is a representation of the spatial cell density in the wound area relative to the spatial cell density outside of the wound area at every time point (time-curve).

Cell proliferation assay

Proliferation of ICAR cells was assessed using methods as previously published [28, 31]. In brief, the effect of oxygen tension on ICAR cell proliferation was assessed using a non-labelled cell monolayer confluence approach with a high density phase contrast real-time cell imaging system (IncuCyte™). ICAR cells were seeded at 40,000 cells per well in a 12-well culture plate (Corning Costar) and exposed to oxygen tension at 1 % O2 or 8 % O2 and the cell confluence (as the proliferation parameter) was measured at 0, 24 and 48 h.

Cell apoptosis assay

To assess the effect of hypoxia on cell apoptosis, ICAR cells were seeded at 5000 cells per well in 96-well culture plate (Corning Costar) in the presence of CellPlayer Kinetic Caspase-3/7 Apoptosis Assay Reagent (1:5000; Essen Biosciences) and imaged at 48 h with IncuCyte™. Cell apoptosis is determined by the measurement of the number of activated caspase 3/7 fluorescent objects count per mm2 divided by the percentage of cell confluence at 48 h (percentage of the area of field of view covered by cells with the metric ‘phase object confluence’) with the IncuCyte Zoom software using an integrated object counting algorithm.

Exosome isolation from cell-conditioned media

To study the effect of oxygen tension on exosome release, ICAR cells were incubated at 1 % O2 or 8 % O2 for 48 h. Exosomes were isolated from ICAR cell culture-conditioned media by successive differential centrifugation steps at 300 × g for 10 min and 2000 × g for 30 min. The supernatant was filtered through a 0.22-μm filter (Corning Costar) and ultracentrifuged at 100,000 × g for 20 h at 4 °C (Sorvall, SureSpin 630/360, Swinging-bucket ultracentrifuge rotor). Another round of ultracentrifugation washing steps was performed at 100,000 × g for 2 h at 4 °C (Beckman, Type 70.1 Ti, Fixed angle ultracentrifuge rotor). Exosomes were further enriched by layering on top of a discontinuous iodixanol gradient (OptiPrep, Sigma–Aldrich), which was centrifuged at 100,000 × g for 20 h (Beckman, Sw41Ti, Swinging-bucket ultracentrifuge rotor). Twelve fractions were obtained and diluted in 10 mL PBS (Gibco, Life Technologies). The fractions were washed with PBS and centrifuge at 100,000 × g for 2 h (Beckman, Type 70.1 Ti, Fixed angle ultracentrifuge rotor) and the exosomal pellets were suspended in 50 μL PBS.

Nanoparticle Tracking Analysis (NTA)

NTA measurements were performed using a NanoSight NS500 instrument (NanoSight NTA 3.0 Nanoparticle Tracking and Analysis Release Version Build 0064) as previously described [32, 33].

Western blot analysis and transmission electron microscopy

Exosomes were solubilized in RIPA buffer (Sigma–Aldrich) and separated by polyacrylamide gel electrophoresis, transferred to a polyvinylidene fluoride (PVDF) membrane (Bio-Rad) and probed with primary rabbit polyclonal antibody anti-CD63 (1:1000; EXOAB-CD63A-1, System Biosciences) and TSG101 (1:500; sc-6037, Santa Cruz Biotechnology). 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, Oregon, USA).

Proteomic Analysis of Endometrial Exosomes by Mass Spectrometry (MS)

Exosomes (10 μg of protein) were solubilized in RIPA buffer (Sigma–Aldrich) and separated by polyacrylamide gel electrophoresis. The gel was fixed in fixing solution (10:1:9; ethanol, acetic acid, MilliQ water respectively) for 15 min, washed in (1:1, ethanol and MilliQ water) for 10 min and washed three times with MilliQ water. Proteins were stained with Coomassie Brilliant Blue R-250 staining solution (Bio-Rad) for 1 h and the gel was allowed to destain in MilliQ water until a clear background was obtained.

In-gel digestion methods for the mass spectrometric identification of exosomal proteins were performed by modification of previously published method [34]. In brief, each sample lane was cut into 24 gel slices and destained twice with 200 mM ammonium bicarbonate in 50 % acetonitrile solution for 45 min at 37 °C, desiccated using a vacuum centrifuge and then resuspended with 20 mM dithiothreitol (DTT) in 25 mM ammonium bicarbonate solution and reduced for 1 h at 65 °C. DTT was then removed, and the samples were alkylated in 50 mM iodoacetamide and 25 mM ammonium bicarbonate at 37 °C in darkness for 40 min. Gel slices were washed three times for 45 min in 25 mM ammonium bicarbonate and then desiccated. Individual dried slices were then allowed to swell in 20 μL of 40 mM ammonium bicarbonate, 10 % acetonitrile containing 20 μg/mL trypsin (Sigma) for 1 h at room temperature. An additional 50 μL of the same solution was added and the samples were incubated overnight at 37 °C.

The supernatants were removed from the gel slices, and residual peptides were washed from the slices by incubating them three times in 50 μL of 0.1 % formic acid for 45 min at 37 °C. The original supernatant and washes were combined and desalted according to a modified version of the stage tip protocol that we have published [35, 36] using a 3-mm piece of an Empore C18 (Octadecyl) SPE Extraction Disk and the eluted peptides were dried in a vacuum centrifuge prior to spectral acquisition.

The digested protein samples were analysed using the TripleTOF® 5600 mass spectrometer (ABSciex, Redwood City, CA) and Eksigent 1D+ NanoLC system with the cHiPLC system to obtain initial high mass accuracy survey MS/MS data, identifying the peptides present in the samples. The ChromXP C18-CL TRAP cHiPLC (200 μm × 6 mm, 3 μm, 120 Å) and analytical cHiPLC columns (200 μm × 15 cm; 3 μm, 120 Å) (Eksigent, Redwood City, CA) were used to separate the digested proteins. A 10 μL aliquot of digested material was injected onto the column and separated with a linear gradient of 5 to 10 % Buffer B for 2 min (Buffer A: 0.1 % Formic acid/water; Buffer B: acetonitrile/0.1 % formic acid), 10 to 40 % Buffer B (58 min), 40 to 50 % Buffer B (10 min), 50 to 95 % (10 min) with a flow rate of 500 nL/min. The column was flushed at 95 % buffer B for 15 min and re-equilibrated with 5 % Buffer B for 6 min. The in-depth proteomic analysis was performed using the Information Dependent Acquisition (IDA) experiments on the TripleTOF® 5600 System interfaced with a nanospray source. The source parameters were as follows: Cur gas at 25 psi, GS1 at 5 psi and IHT at 150 °C. A 250 msec accumulation time was set for the TOFMS survey scan and from this scan, the 10 most intense precursor ions were selected automatically for the MS/MS analysis (accumulation time of 150 msecs per MS/MS scan). Ions were isolated using unit resolution of the quadrupoles and rolling collision energy equation was used to calculate the collision energies of precursors. The precursor selection criteria included a minimum intensity of 50 counts per second (cps) and a charge state greater than 2 + .

Protein identification was determined using the ProteinPilot™ Software (v4.5 beta, AB Sciex, Redwood City, CA) with the Paragon algorithm. The search parameters were as follows: sample type, identification; cys alkylation, iodoacetamide; digestion, Trypsin; Instrument, TripleTOF 5600; special factors, none; and ID focus, biological modifications. The database was downloaded from the UniProt website in October 2015, which contained all proteins from Bos taurus. False discovery rate (FDR) was selected in the method and determined using a reversed sequence database. Data were subjected to ontology and pathway analysis using the protein analysis through evolutionary relationships tool (PANTHER) and gene ontology algorithms and classified based on biological process and molecular function categories [37].

Statistical analyses

The effects of oxygen tensions on ICAR cells are presented as mean ± SE for migration, proliferation and apoptosis assays (n = 6 independent experiments in duplicate). The number of exosomes is presented as number of particles per mL (mean ± SE, n = 3 independent isolations from 80 million cells each). The effects of oxygen tension on ICAR cells were identified by Student’s T tests (two-tailed) to compare the effect of hypoxia (i.e. 1 % O2) with the control group (i.e. 8 % O2) using a commercially-available software package (Prism 6, GraphPad Inc, La Jolla, CA 92037 USA).

Results

The Effect of Oxygen Tension on Bovine Endometrial (ICAR) cell migration and proliferation

The effect of normal oxygen tension (i.e. 8 % O2) and hypoxia (i.e. 1 % O2) on ICAR cell migration is presented in Fig. 1. ICAR cell migration was significantly lower under hypoxia compared with normal oxygen tension (Fig. 1a). Hypoxia decreased ICAR cell migration in a time-dependent manner (Fig. 1b). Area under the curve analysis indicated that hypoxia decreased ICAR cell migration by ~20 % compared with values observed at 8 % O2 (2173 ± 36 and 2620 ± 50 for 1 % O2 and 8 % O2, respectively) (Fig. 1c). Interestingly, hypoxia decreased ICAR cell proliferation in a time-dependent manner (Fig. 2a and b). Area under curve analysis showed that at 1 % O2, the proliferative capacity of ICAR cells was inhibited (p < 0.05) ~32 % compared with cell proliferation at 8 % O2 (2.32 ± 0.18 and 3.41 ± 0.2 for 1 % O2 and 8 % O2, respectively) (Fig. 2c).

Fig. 1.

Fig. 1

The effects of different oxygen tension on migration of bovine endometrial stromal cells (ICAR). a Graphical representation of the initial wound width (white) at 0 h and the area of the initial wound covered by advancing cells (grey) at 24 h and 48 h, Scale bar 300 μm. b Decreased ICAR cell migration under hypoxic conditions (1 % O2 (●) compared with a normoxic 8 % O2 (○)) over a period of 48 h. c Area under the curve analysis from (b); 8 % O2 (white bar) and 1 % O2 (black bar). Data are presented as mean ± SE, n = 6. In (b) and (c) P < 0.05

Fig. 2.

Fig. 2

The effects of different oxygen tension on proliferation of bovine endometrial stromal cells (ICAR). a Representative phase-contrast image of ICAR cells at 48 h when cultured under hypoxic conditions (1 % O2) compared with a normoxic 8 % O2, Scale bar 200 μm. b Decreased (p < 0.01) ICAR cell proliferation under hypoxic conditions (1 % O2 (●)) compared with a normoxic 8 % O2 (○) over a period of 48 h. c Area under the curve analysis from (b); 8 % O2 (white bar) and 1 % O2 (black bar). Data are presented as mean ± SE, n = 6. In (C) P < 0.05

The Effect of Oxygen Tension on Bovine Endometrial (ICAR) cell apoptosis

The effect of oxygen tension on cell apoptosis is presented in Fig. 3. A hypoxic (1 % O2) environment altered cell morphology compared with cells cultured under normal conditions (8 % O2), displaying morphological hallmarks of apoptotic death (Fig. 3A ,a and d). Fluorescent images acquired with IncuCyte™ (Fig. 3A, b and e) showed greater fluorescence in cells cultured under 1 % O2, indicating a higher activation of caspase-3/7 under hypoxic conditions compared with 8 % O2 (Fig. 3A, b and e). Apoptosis was quantified using the object counting algorithm in which the number of fluorescent objects was indicated with red x’s in Fig. 3A (c and f). Quantification analysis showed that hypoxia increased (~1.6 fold) the apoptosis ratio (presented as activated caspase 3/7 fluorescent objects count per mm2 divided by percentage of cell confluence at 48 h) compared with cells cultured under normal oxygen tension (Fig. 3B).

Fig. 3.

Fig. 3

The effects of different oxygen tension on activation of apoptotic protein caspase-3 of bovine endometrial stromal cells (ICAR). ICAR cells were cultured under normoxic (8 % O2) or hypoxic (1 % O2) conditions and the activated caspase-3/7 fluorescence was measured at 48 h. A Representative phase-contrast images (a and d), fluorescent signal images (b and e) and acquired fluorescent signal using integrated object counting algorithm with IncuCyte™ (Segmentation; c and f), Scale bar 400 μm. B Increased apoptosis of ICAR cells under hypoxic conditions as determined by acquired fluorescent signal using integrated object counting algorithm with IncuCyte™ were normalized against cell confluence, 8 % O2 (white bar) and 1 % O2 (black bar). Data are presented as mean ± SE, n = 6. In (B) P < 0.05

The Effect of Oxygen Tension on Exosome Release from Bovine Endometrial Cells (ICAR)

Exosomes were enriched by buoyant density gradient (see Material and Methods). We fractioned the 100,000 × g pellet into 12 fractions and the Western blot analysis for TSG101 and CD63 showed positive protein abundance in fractions 1.17 and 1.18 g/mL (Fig. 4a). Exosomes were pooled between densities 1.16 and 1.18 g/mL. Morphology of exosomes was determined by electron microscopy (Fig. 4b), exosomes displayed a cup-shaped morphology with an estimated diameter of 100 nm. Hypoxia did not alter the size distribution of exosomes compared with normal oxygen tension (123 ± 2.7 nm versus 127 ± 1.7 nm for 8 % O2 and 1 % O2, respectively) (Fig. 4c). Interestingly, hypoxia increased (~3.6 fold) the number of exosomes compared with values observed at normal oxygen tension (Fig. 4d).

Fig. 4.

Fig. 4

Characterization of exosomes release from 8 % O2 and 1 % O2 ICAR cell-conditioned media. Exosomes were characterized after enrichment from the 100,000 x g pellet by buoyant density centrifugation (see Methods). a Representative Western blot for exosome markers: TSG101 and CD63. b Representative electron micrograph exosome fractions, Scale bar 100 nm. c Representative Nanosight measurement of particle-size distribution exosomes from 8 % O2 and 1 % O2 cell-conditioned media after buoyant density gradient ultracentrifugation. (8 % normoxic condition mean size (127 ± 1.7 nm) (○), 1 % hypoxic condition mean size (123 ± 2.7 nm) (●) over a period of 48 h). d Exosomes concentration presented as vesicle per million cells per 48 h was higher (p < 0.05) at hypoxia (1 % O2) compared to normal oxygen tension (8 % O2); 8 % O2 (white bar) and 1 % O2 (black bar). Data are presented as mean ± SE, n = 3

Proteomic Analysis of Bovine Endometrial ICAR-Derived Exosomes

Mass spectrometric analysis identified over 250 exosomal proteins with 113 similar proteins identified as present in both exosomes of ICAR cultured at 1 % O2 and at 8 % O2 128 proteins identified as unique to exosomes of ICAR cultured at 1 % O2; 46 proteins were identified as unique to exosomes of ICAR cultured at 8 % O2 (Table 1 A-C; Fig. 5a). Data were subjected to ontology and pathway analysis using PANTHER and gene ontology algorithms and classified based on biological process (Fig. 5b) and molecular function (Fig. 5c). In biological process, the clusters identified from individual proteins that are unique to and present only in exosomes of ICAR cultured at 1 % O2 but not those at 8 % O2 were: growth (0.7 %), locomotion (0.7 %) and reproduction (1.4 %) (Fig. 5b). In molecular functions, the proteins related to binding and catalytic activity were the greatest recognized in both exosomes of ICAR cultured at 1 % O2 and to those of ICAR cultured at 8 % O2 (Fig. 5c).

Table 1.

List of the common proteins identified in exosomes of ICAR cultured at 1 % O2 and at 8 % O2

A. List of 113 common proteins identified in exosomes of ICAR cultured at 1 % O2 and at 8 % O2
Protein ID Name Gene Name Biological Process (Total # Gene 69; Total #Function 146) Molecular function (Total # Gene 69; Total #Function 81)
 A1L523_BOVIN Copine II (Fragment) CPNE2
 A3KN51_BOVIN TSG101 protein TSG101 Metabolic process Catalytic activity
 A5D7L1_BOVIN CLEC11A protein CLEC11A Cellular process/Developmental process Binding/Structural molecule activity
 A5D9D2_BOVIN Complement component 4 binding protein, alpha chain C4BPA
 A5PJ69_BOVIN SERPINA10 protein SERPINA10 Biological regulation/Metabolic process Catalytic activity/Enzyme regulator activity
 A5PJE3_BOVIN Fibrinogen alpha chain FGA
 A5PK77_BOVIN SERPINA11 protein SERPINA11 Biological regulation/Metabolic process Catalytic activity/Enzyme regulator activity
 A6QLB7_BOVIN Adenylyl cyclase-associated protein CAP1
 A6QLL8_BOVIN Fructose-bisphosphate aldolase ALDOA
 A6QNZ7_BOVIN Keratin 10 (Epidermolytic hyperkeratosis; keratosis palmaris et plantaris) KRT10
 A6QPP2_BOVIN SERPIND1 protein SERPIND1 Biological regulation/Metabolic process Catalytic activity/Enzyme regulator activity
 A6QPR1_BOVIN PCYOX1 protein PCYOX1
 LG3BP_BOVIN Galectin-3-binding protein LGALS3BP Apoptotic process/Biological adhesion/Biological regulation/Cellular process/Developmental process/Immune system process/localization/Metabolic process Catalytic activity/Receptor activity
 A7MB82_BOVIN C1QTNF3 protein C1QTNF3
 A7YWB6_BOVIN LOC539596 protein LOC539596
 B0JYM4_BOVIN Tetraspanin CD63
 B0JYN6_BOVIN Alpha-2-HS-glycoprotein AHSG
 B0JYQ0_BOVIN ALB protein ALB
 B5B3R8_BOVIN Alpha S1 casein CSN1S1
 E1BDG5_BOVIN Protein Wnt WNT5A Biological regulation/Cellular process/Developmental process/Multicellular organismal process/Response to stimulus Binding
 CBG_BOVIN Corticosteroid-binding globulin SERPINA6 Biological regulation/Metabolic process Catalytic activity/Enzyme regulator activity
 F1MAV0_BOVIN Fibrinogen beta chain FGB
 F1MB08_BOVIN Alpha-enolase ENO1
 F1MC11_BOVIN Keratin, type I cytoskeletal 14 KRT14
 F1MM32_BOVIN Sulfhydryl oxidase QSOX1 Catalytic activity
 F1MMK9_BOVIN Protein AMBP AMBP
 F1MMP5_BOVIN Inter-alpha-trypsin inhibitor heavy chain H1 ITIH1
 ITA3_BOVIN Integrin alpha-3 ITGA3
 F1MNW4_BOVIN Inter-alpha-trypsin inhibitor heavy chain H2 ITIH2
 F1MSZ6_BOVIN Antithrombin-III SERPINC1
 F1MTV5_BOVIN Amino acid transporter SLC1A5
 F1MW44_BOVIN Coagulation factor XIII A chain F13A1
 F1MXJ5_BOVIN IST1 homolog IST1
 F1MXX6_BOVIN Lactadherin MFGE8
 F1MY85_BOVIN Complement C5a anaphylatoxin C5
 F1N045_BOVIN Complement component C7 C7
 HTRA1_BOVIN Serine protease HTRA1 HTRA1 Cellular process/Metabolic process Catalytic activity
 F1N1I6_BOVIN Gelsolin GSN
 F6QVC9_BOVIN Annexin ANXA5
 G3X6N3_BOVIN Serotransferrin TF
 G5E5A9_BOVIN Fibronectin FN1
 G5E5V0_BOVIN Carboxypeptidase N catalytic chain CPN1
 G8JKX6_BOVIN Tetraspanin (Fragment) CD9
 I7CT57_BOVIN Vitamin D binding protein
 M0QVZ6_BOVIN Keratin, type II cytoskeletal 5 KRT5
 THRB_BOVIN Prothrombin F2 Immune system process/Metabolic process/Response to stimulus Catalytic activity
 PROC_BOVIN Vitamin K-dependent protein C (Fragment) PROC Response to stimulus Binding
 KNG2_BOVIN Kininogen-2 KNG2
 THYG_BOVIN Thyroglobulin TG Metabolic process Catalytic activity
 HBA_BOVIN Hemoglobin subunit alpha HBA localization/Multicellular organismal process
 HBBF_BOVIN Hemoglobin fetal subunit beta localization/Multicellular organismal process
 ALBU_BOVIN Serum albumin ALB localization
 ANXA2_BOVIN Annexin A2 ANXA2 Developmental process/Metabolic process
 ASSY_BOVIN Argininosuccinate synthase ASS1 Cellular process/Metabolic process Catalytic activity
 APOH_BOVIN Beta-2-glycoprotein 1 APOH Cellular process/Immune system process/localization/Metabolic process/Response to stimulus Catalytic activity/Receptor activity/Transporter activity
 CLUS_BOVIN Clusterin CLU
 HSP7C_BOVIN Heat shock cognate 71 kDa protein HSPA8 Cellular component organization or biogenesis/Immune system process/Metabolic process/Response to stimulus
 ANXA7_BOVIN Annexin A7 ANXA7 Metabolic process
 ANX11_BOVIN Annexin A11 ANXA11 Metabolic process
 A2AP_BOVIN Alpha-2-antiplasmin SERPINF2 Biological regulation/Metabolic process Catalytic activity/Enzyme regulator activity
 A1AT_BOVIN Alpha-1-antiproteinase SERPINA1 Biological regulation/Metabolic process Catalytic activity/Enzyme regulator activity
 GDIB_BOVIN Rab GDP dissociation inhibitor beta GDI2 Biological regulation/Cellular process/localization/Metabolic process/Multicellular organismal process Binding/Catalytic activity/Enzyme regulator activity
 F12AI_BOVIN Factor XIIa inhibitor
 ITB1_BOVIN Integrin beta-1 ITGB1 Biological adhesion/Cellular process/Response to stimulus Receptor activity
 ITIH3_BOVIN Inter-alpha-trypsin inhibitor heavy chain H3 ITIH3 Biological regulation/Metabolic process Binding/Catalytic activity/Enzyme regulator activity
 ACTB_BOVIN Actin, cytoplasmic 1 ACTB Cellular component organization or biogenesis/Cellular process/Developmental process/localization Structural molecule activity
 ANXA6_BOVIN Annexin A6 ANXA6 Metabolic process
 CFAB_BOVIN Complement factor B CFB Biological adhesion/Cellular process/Immune system process/localization/Metabolic process/Response to stimulus Catalytic activity/Receptor activity/Transporter activity
 TBA1B_BOVIN Tubulin alpha-1B chain Cellular process/Developmental process/localization Structural molecule activity
 LUM_BOVIN Lumican LUM Biological adhesion/Biological regulation/Cellular process/Developmental process/Immune system process/Metabolic process/Multicellular organismal process Receptor activity
 UPAR_BOVIN Urokinase plasminogen activator surface receptor PLAUR
 5NTD_BOVIN 5’-nucleotidase NT5E Metabolic process Catalytic activity
 PGM1_BOVIN Phosphoglucomutase-1 PGM1 Cellular process/Metabolic process Catalytic activity
 Q09TE3_BOVIN Insulin-like growth factor binding protein acid labile subunit
 Q17R18_BOVIN Adenosine kinase ADK
 FA5_BOVIN Coagulation factor V F5 Biological adhesion/Biological regulation/Cellular process/Developmental process/Immune system process/localization/Metabolic process/Multicellular organismal process/Response to stimulus Binding/Catalytic activity/Enzyme regulator activity/Receptor activity/Transporter activity
 Q2KIF2_BOVIN Leucine-rich alpha-2-glycoprotein 1 LRG1 Cellular process/Multicellular organismal process Receptor activity
 CBPB2_BOVIN Carboxypeptidase B2 CPB2 Metabolic process Catalytic activity
 Q2KJ47_BOVIN EH-domain containing 2 EHD2 Biological regulation/Cellular process/localization/Metabolic process/Multicellular organismal process Binding/Catalytic activity/Enzyme regulator activity
 TBB5_BOVIN Tubulin beta-5 chain TUBB5 Cellular process/Developmental process/localization Structural molecule activity
 A1BG_BOVIN Alpha-1B-glycoprotein A1BG Cellular process/Immune system process/Response to stimulus Binding/Receptor activity
 HPT_BOVIN Haptoglobin HP Biological regulation/Immune system process/localization/Metabolic process/Multicellular organismal process/Reproduction/Response to stimulus Binding/Catalytic activity/Enzyme regulator activity/Receptor activity
 CO3_BOVIN Complement C3 C3 Biological regulation/Cellular process/Metabolic process/Response to stimulus Binding/Catalytic activity/Enzyme regulator activity
 Q3MHH8_BOVIN Alpha-amylase AMY2A
 SAHH_BOVIN Adenosylhomocysteinase AHCY Cellular process/Metabolic process Catalytic activity
 CO9_BOVIN Complement component C9 C9 Cellular process/localization/Metabolic process/Response to stimulus Catalytic activity/Receptor activity/Transporter activity
 Q3MHW2_BOVIN F10 protein (Fragment) F10
 Q3MHZ0_BOVIN FLOT1 protein (Fragment) FLOT1
 Q3SYR0_BOVIN Serpin peptidase inhibitor, clade A (Alpha-1 antiproteinase, antitrypsin), member 7 SERPINA7
 FETA_BOVIN Alpha-fetoprotein AFP Developmental process/localization
 Q3SZH5_BOVIN Angiotensinogen AGT
 HEMO_BOVIN Hemopexin HPX localization
 Q3SZZ9_BOVIN FGG protein FGG
 PGK1_BOVIN Phosphoglycerate kinase 1 PGK1 Metabolic process Catalytic activity
 Q3T101_BOVIN IGL@ protein IGL@
 G6PI_BOVIN Glucose-6-phosphate isomerase GPI Metabolic process Catalytic activity
 Q3ZBX0_BOVIN Basigin BSG
 Q3ZC87_BOVIN Pyruvate kinase (Fragment) PKM2
 Q3ZCI4_BOVIN 6-phosphogluconate dehydrogenase, decarboxylating PGD Metabolic process Catalytic activity
 FETUB_BOVIN Fetuin-B FETUB
 EHD1_BOVIN EH domain-containing protein 1 EHD1 Biological regulation/Cellular process/localization/Metabolic process/Multicellular organismal process Binding/Catalytic activity/Enzyme regulator activity
 HPPD_BOVIN 4-hydroxyphenylpyruvate dioxygenase HPD Metabolic process Catalytic activity
 Q5EA67_BOVIN Inter-alpha (Globulin) inhibitor H4 (Plasma Kallikrein-sensitive glycoprotein) ITIH4
 Q5GN72_BOVIN Alpha-1-acid glycoprotein agp
 BHMT1_BOVIN Betaine--homocysteine S-methyltransferase 1 BHMT Cellular process/Metabolic process Catalytic activity
 Q5J801_BOVIN Endopin 2B
 Q6T182_BOVIN Sex hormone-binding globulin (Fragment) SHBG
 A2MG_BOVIN Alpha-2-macroglobulin A2M Biological regulation/Cellular process/Immune system process/Metabolic process/Response to stimulus Binding/Catalytic activity/Enzyme regulator activity
 PEDF_BOVIN Pigment epithelium-derived factor SERPINF1 Biological regulation/Metabolic process Catalytic activity/Enzyme regulator activity
 CHIA_BOVIN Acidic mammalian chitinase CHIA Immune system process/Metabolic process/Response to stimulus Binding/Catalytic activity
 IPSP_BOVIN Plasma serine protease inhibitor SERPINA5 Biological regulation/Metabolic process Catalytic activity/Enzyme regulator activity
 SPA31_BOVIN Serpin A3-1 SERPINA3-1 Biological regulation/Metabolic process Catalytic activity/Enzyme regulator activity
 V6F9A2_BOVIN Apolipoprotein A-I preproprotein APOA1
B. List of 128 unique proteins identified in exosomes of ICAR cultured at 1 % O2
Protein ID Name Gene Name Biological Process (Total # Gene 22; Total #Function 49) Molecular function (Total # Gene 22; Total #Function 28)
 G3X6T9_BOVIN Flotillin-2 (Fragment) FLOT2
 TSP1_BOVIN Thrombospondin-1 THBS1
 F1N2L9_BOVIN 4-trimethylaminobutyraldehyde dehydrogenase ALDH9A1
 E1B9F6_BOVIN Elongation factor 1-alpha EEF1A1
 APOE_BOVIN Apolipoprotein E APOE Apoptotic process/Biological regulation/Cellular component organization or biogenesis/Cellular process/Developmental process/Growth/localization/Metabolic process/Multicellular organismal process/Response to stimulus Binding/Catalytic activity/ Enzyme regulator activity/Transporter activity
 G1K1R6_BOVIN Galactokinase GALK1
 G3P_BOVIN Glyceraldehyde-3-phosphate dehydrogenase GAPDH Metabolic process Catalytic activity
 Q0P5B0_BOVIN Arrestin domain containing 1 ARRDC1
 RL40_BOVIN Ubiquitin-60S ribosomal protein L40 UBA52 Metabolic process Binding/Structural molecule activity
 A5D9B6_BOVIN Syntenin SDCBP
 Q8HZY1_BOVIN Serine protease inhibitor clade E member 2 SERPINE2
 Q5E962_BOVIN Aldo-keto reductase family 1, member B1 AKR1B1
 A7MBH9_BOVIN GNAI2 protein GNAI2 Biological regulation/Cellular process/Metabolic process/Response to stimulus Binding/Catalytic activity
 GBB2_BOVIN Guanine nucleotide-binding protein G(I)/G(S)/G(T) subunit beta-2 GNB2 Cellular process/Metabolic process/Multicellular organismal process Binding/Catalytic activity
 I6YIV1_BOVIN Annexin
 F16P1_BOVIN Fructose-1,6-bisphosphatase 1 FBP1 Metabolic process
 F1N3Q7_BOVIN Apolipoprotein A-IV APOA4
 AK1A1_BOVIN Alcohol dehydrogenase [NADP(+)] AKR1A1 localization/Metabolic process Catalytic activity/Transporter activity
 A5D784_BOVIN CPNE8 protein CPNE8 localization
 HS90A_BOVIN Heat shock protein HSP 90-alpha HSP90AA1 Immune system process/Metabolic process/Response to stimulus
 Q1JPA2_BOVIN Eukaryotic translation elongation factor 1 gamma (Fragment) EEF1G
 SERA_BOVIN D-3-phosphoglycerate dehydrogenase PHGDH Metabolic process Catalytic activity
 Q3T085_BOVIN OGN protein OGN
 A8DBT6_BOVIN Monocyte differentiation antigen CD14 CD14
 A5PK73_BOVIN Fructose-bisphosphate aldolase ALDOB
 G5E5U7_BOVIN S-adenosylmethionine synthase MAT1A
 F1N2W0_BOVIN Prostaglandin reductase 1 PTGR1
 IF4A1_BOVIN Eukaryotic initiation factor 4A-I EIF4A1 Biological regulation/Metabolic process Binding/Catalytic activity/Translation regulator activity
 Q05B55_BOVIN IGK protein IGK
 F1N1D4_BOVIN Protein tweety homolog TTYH3 localization Transporter activity
 A4FV94_BOVIN KRT6A protein KRT6A
 RGN_BOVIN Regucalcin RGN Cellular process/localization/Metabolic process Binding/Catalytic activity
 1433E_BOVIN 14-3-3 protein epsilon YWHAE Cellular process
 Q2HJB6_BOVIN Procollagen C-endopeptidase enhancer PCOLCE Biological adhesion/Biological regulation/Cellular process/Developmental process/Immune system process/localization/Metabolic process/Multicellular organismal process/Response to stimulus Binding/Catalytic activity/Enzyme regulator activity/Receptor activity/Transporter activity
 B8YB76_BOVIN Homogentisate 1,2-dioxygenase HGD
 DHSO_BOVIN Sorbitol dehydrogenase SORD Metabolic process Catalytic activity
 HS71A_BOVIN Heat shock 70 kDa protein 1A HSPA1A Cellular component organization or biogenesis/Immune system process/Metabolic process/Response to stimulus
 Q3ZBQ9_BOVIN APOM protein APOM
 PYGL_BOVIN Glycogen phosphorylase, liver form PYGL Metabolic process Catalytic activity
 A6QP30_BOVIN CPN2 protein CPN2 Cellular process/Multicellular organismal process Receptor activity
 ARF3_BOVIN ADP-ribosylation factor 3 ARF3 Cellular process/localization/Metabolic process Binding/Catalytic activity
 G3MYH4_BOVIN Tetraspanin (Fragment) CD81
 ACTC_BOVIN Actin, alpha cardiac muscle 1 ACTC1 Cellular component organization or biogenesis/Cellular process/Developmental process/localization Structural molecule activity
 GALM_BOVIN Aldose 1-epimerase GALM Metabolic process Catalytic activity
 TSN6_BOVIN Tetraspanin-6 TSPAN6 Biological adhesion/Cellular process/Immune system process/Multicellular organismal process/Reproduction/Response to stimulus Binding/Receptor activity
 Q3ZC83_BOVIN Solute carrier family 29 (Nucleoside transporters), member 1 SLC29A1 localization/Metabolic process Transporter activity
 B4GA1_BOVIN Beta-1,4-glucuronyltransferase 1 B4GAT1 Metabolic process Catalytic activity
 ADA10_BOVIN Disintegrin and metalloproteinase domain-containing protein 10 ADAM10 Apoptotic process/Developmental process/Reproduction
 A6QR28_BOVIN Phosphoserine aminotransferase PSAT1 Metabolic process Catalytic activity
 Q1JPB6_BOVIN Acetyl-Coenzyme A acetyltransferase 2 ACAT2
 DDBX_BOVIN Dihydrodiol dehydrogenase 3 localization/Metabolic process Catalytic activity/Transporter activity
 A2VE11_BOVIN IGSF8 protein IGSF8
 F1MS32_BOVIN Apolipoprotein D APOD
 A6QP64_BOVIN VPS37B protein (Fragment) VPS37B
 Q2KIW4_BOVIN Lecithin-cholesterol acyltransferase LCAT Metabolic process Catalytic activity
 GBB1_BOVIN Guanine nucleotide-binding protein G(I)/G(S)/G(T) subunit beta-1 GNB1 Cellular process/Metabolic process Binding/Catalytic activity
 GNA11_BOVIN Guanine nucleotide-binding protein subunit alpha-11 GNA11 Biological regulation/Cellular process/Metabolic process/Response to stimulus Catalytic activity
 Q17QK4_BOVIN Epoxide hydrolase 2, cytoplasmic EPHX2
 K2C7_BOVIN Keratin, type II cytoskeletal 7 KRT7 Cellular component organization or biogenesis/Cellular process/Developmental process Structural molecule activity
 CLIC1_BOVIN Chloride intracellular channel protein 1 CLIC1 Biological regulation/Cellular process/Metabolic process/Response to stimulus Binding/Catalytic activity/Structural molecule activity/Translation regulator activity
 Q08DW4_BOVIN Mannan-binding lectin serine peptidase 1 (C4/C2 activating component of Ra-reactive factor) MASP1
 B4GT1_BOVIN Beta-1,4-galactosyltransferase 1 B4GALT1
 A5D7E6_BOVIN Tetraspanin CD82 Cellular process/Response to stimulus Binding/Receptor activity
 A5D973_BOVIN Alpha isoform of regulatory subunit A, protein phosphatase 2 PPP2R1A
 E1B726_BOVIN Plasminogen PLG
 G5E6I9_BOVIN Histone H2B LOC101904777 Cellular component organization or biogenesis/Cellular process/Metabolic process Binding
 ADIPO_BOVIN Adiponectin ADIPOQ
 F1MBC5_BOVIN Coagulation factor IX F9
 A2VDL2_BOVIN Solute carrier family 2 (Facilitated glucose transporter), member 3 SLC2A3
 VPS4B_BOVIN Vacuolar protein sorting-associated protein 4B VPS4B
 G3X8B1_BOVIN Peptidyl-prolyl cis-trans isomerase LOC613401
 K4JB97_BOVIN Alpha-2-macroglobulin variant 4 A2M
 ACTG_BOVIN Actin, cytoplasmic 2 ACTG1 Cellular component organization or biogenesis/Cellular process/localization Structural molecule activity
 Q1JPG7_BOVIN Pyruvate kinase PKLR
 GTR1_BOVIN Solute carrier family 2, facilitated glucose transporter member 1 SLC2A1
 F1N342_BOVIN Protein tweety homolog TTYH2 localization Transporter activity
 ADHX_BOVIN Alcohol dehydrogenase class-3 ADH5 Metabolic process Catalytic activity
 URP2_BOVIN Fermitin family homolog 3 FERMT3
 E1B7N2_BOVIN Histone H4 HIST1H4I Cellular component organization or biogenesis/Cellular process/Metabolic process Binding
 EF2_BOVIN Elongation factor 2 EEF2 Biological regulation/Metabolic process Binding/Translation regulator activity
 KLKB1_BOVIN Plasma kallikrein KLKB1 Biological regulation/localization/Metabolic process/Response to stimulus Binding/Catalytic activity/Enzyme regulator activity/Receptor activity
 ESTD_BOVIN S-formylglutathione hydrolase ESD Metabolic process Catalytic activity
 SEPR_BOVIN Prolyl endopeptidase FAP FAP Cellular process/Immune system process/localization/Metabolic process/Multicellular organismal process / Response to stimulus Binding/Catalytic activity
 Q5EA54_BOVIN Solute carrier family 3 (Activators of dibasic and neutral amino acid transport), member 2 SLC3A2
 Q1JPD9_BOVIN G protein-coupled receptor, family C, group 5, member B GPRC5B Cellular process Receptor activity
 F1MS05_BOVIN Aconitate hydratase ACO1
 F1MJ12_BOVIN Complement C1s subcomponent C1S
 CNDP2_BOVIN Cytosolic non-specific dipeptidase CNDP2 Metabolic process Catalytic activity
 Q2TBQ1_BOVIN Coagulation factor XIII, B polypeptide F13B Biological adhesion/Cellular process/Immune system process/localization/Metabolic process/Response to stimulus Catalytic activity/Receptor activity/Transporter activity
 Q1JP72_BOVIN Colony stimulating factor 1 receptor CSF1R
 Q0VD03_BOVIN CD44 antigen CD44
 G3X6Y4_BOVIN Osteomodulin OMD
 GAMT_BOVIN Guanidinoacetate N-methyltransferase GAMT
 VWA1_BOVIN von Willebrand factor A domain-containing protein 1 VWA1
 SERC3_BOVIN Serine incorporator 3 SERINC3
 Q862H8_BOVIN Similar to 40S ribosomal protein SA (P40) (Fragment)
 A8E4P3_BOVIN STOM protein STOM
 F1MHP6_BOVIN Adenylosuccinate lyase ADSL
 E1BMG9_BOVIN 10-formyltetrahydrofolate dehydrogenase ALDH1L1 Metabolic process Catalytic activity
 Q705V4_BOVIN Kappa-casein (Fragment) csn3
 G3X6Q8_BOVIN Pentraxin-related protein PTX3 PTX3
 K7QEL2_BOVIN MHC class I antigen BoLA
 TCPQ_BOVIN T-complex protein 1 subunit theta CCT8 Cellular component organization or biogenesis / Metabolic process
 F1N6Z0_BOVIN 26S proteasome non-ATPase regulatory subunit 5 PSMD5
 ARLY_BOVIN Argininosuccinate lyase ASL Metabolic process Catalytic activity
 E1BNG2_BOVIN alpha-1,2-Mannosidase MAN1A1 Metabolic process
 F1MU79_BOVIN Peptidyl-prolyl cis-trans isomerase FKBP4 FKBP4
 DPYL2_BOVIN Dihydropyrimidinase-related protein 2 DPYSL2 Metabolic process Catalytic activity
 PRS23_BOVIN Serine protease 23 PRSS23
 B0JYN1_BOVIN Cathepsin L2 CTSL2
 A4FV99_BOVIN FCNB protein FCNB
 A7YW37_BOVIN CD58 protein (Fragment) CD58 Immune system process/Response to stimulus Binding
 F1MTP5_BOVIN WD repeat-containing protein 1 WDR1
 A7E3D0_BOVIN CCDC45 protein (Fragment) CCDC45
 Q0VCK1_BOVIN Myeloid-associated differentiation marker MYADM
 A1L570_BOVIN Ephrin-B1 EFNB1 Biological regulation/Cellular component organization or biogenesis/Cellular process/Developmental process/locomotion/Multicellular organismal process/Response to stimulus Binding
 F1N049_BOVIN Actin-related protein 3 (Fragment) ACTR3
 PAI1_BOVIN Plasminogen activator inhibitor 1 SERPINE1 Biological regulation/Metabolic process Catalytic activity/Enzyme regulator activity
 Q3ZC30_BOVIN Sulfotransferase SULT1E1
 COL11_BOVIN Collectin-11 COLEC11 Biological regulation/Immune system process/Multicellular organismal process
 MPZL1_BOVIN Myelin protein zero-like protein 1 MPZL1 Cellular process/localization Transporter activity
 G5E595_BOVIN Lys-63-specific deubiquitinase BRCC36 BRCC3
 O18977_BOVIN Tenascin-X TN-X
 A6H7D3_BOVIN KRT18 protein (Fragment) KRT18
 J9ZXG5_BOVIN Integrin alpha V subunit
 B0JYN3_BOVIN L-lactate dehydrogenase LDHB
 MB211_BOVIN Protein mab-21-like 1 MAB21L1
 E1B7R4_BOVIN Eukaryotic translation initiation factor 3 subunit A EIF3A Biological regulation/Metabolic process Binding/Translation regulator activity
C. List of 46 unique proteins identified in exosomes of ICAR cultured at 8 % O2
Protein ID Name Gene Name Biological Process (Total # Gene 22; Total #Function 49) Molecular function (Total # Gene 22; Total #Function 28)
 F1MMD7_BOVIN Inter-alpha-trypsin inhibitor heavy chain H4 ITIH4
 F1N3A1_BOVIN Thrombospondin-1 THBS1
 PLMN_BOVIN Plasminogen PLG Biological regulation/localization/Metabolic process/Response to stimulus Binding/Catalytic activity/Enzyme regulator activity/Receptor activity
 F1MYN5_BOVIN Fibulin-1 FBLN1 Cellular process/Developmental process Binding
 F1MNV5_BOVIN Kininogen-1 KNG1
 EF1A1_BOVIN Elongation factor 1-alpha 1 EEF1A1 Biological regulation/Metabolic process Binding/Catalytic activity/Translation regulator activity
 ITAV_BOVIN Integrin alpha-V ITGAV Biological adhesion
 F1MK44_BOVIN Integrin alpha-5 ITGA5
 TTHY_BOVIN Transthyretin TTR localization Transporter activity
 F1MC45_BOVIN Complement factor H (Fragment) CFH
 J9QD97_BOVIN Periostin variant 9
 ACTS_BOVIN Actin, alpha skeletal muscle ACTA1 Cellular component organization or biogenesis/Cellular process/Developmental process/localization Structural molecule activity
 E1B9K1_BOVIN Polyubiquitin-C UBC
 A7YWR0_BOVIN Apolipoprotein E APOE
 FA9_BOVIN Coagulation factor IX F9 Apoptotic process/Biological regulation/Developmental process/Immune system process/ localization/Metabolic process/Multicellular organismal process/Response to stimulus Binding/Catalytic activity/Enzyme regulator activity/Receptor activity
 COMP_BOVIN Cartilage oligomeric matrix protein COMP
 K2C80_BOVIN Keratin, type II cytoskeletal 80 KRT80 Cellular component organization or biogenesis/Cellular process/Developmental process Structural molecule activity
 TRFE_BOVIN Serotransferrin TF localization/Metabolic process Catalytic activity
 K4JDR8_BOVIN Alpha-2-macroglobulin variant 5 A2M
 Q32P72_BOVIN CP protein (Fragment) CP
 J9ZW47_BOVIN Integrin beta
 F1MM86_BOVIN Complement component C6 C6
 E1BI02_BOVIN Fibromodulin FMOD
 VNN1_BOVIN Pantetheinase VNN1 Biological adhesion/Cellular process/Metabolic process Catalytic activity
 G3X807_BOVIN Histone H4 (Fragment) Cellular component organization or biogenesis/Cellular process/Metabolic process Binding
 MOT1_BOVIN Monocarboxylate transporter 1 SLC16A1 Cellular process/localization Transporter activity
 TF_BOVIN Tissue factor F3 Biological regulation/Cellular process/Response to stimulus Binding/Receptor activity
 HS71L_BOVIN Heat shock 70 kDa protein 1-like HSPA1L Metabolic process/Response to stimulus
 Q3ZCA7_BOVIN Guanine nucleotide binding protein (G protein), alpha inhibiting activity polypeptide 3 GNAI3 Biological regulation/Cellular process/Metabolic process/Response to stimulus Binding/Catalytic activity
 IDHC_BOVIN Isocitrate dehydrogenase [NADP] cytoplasmic IDH1
 Q1PBC8_BOVIN CD14 (Fragment)
 F1MJJ8_BOVIN Radixin (Fragment) RDX
 IF4A2_BOVIN Eukaryotic initiation factor 4A-II EIF4A2 Biological regulation/Metabolic process Binding/Catalytic activity/Translation regulator activity
 C1QB_BOVIN Complement C1q subcomponent subunit B C1QB
 A6QPD4_BOVIN LOC790886 protein LOC790886
 CTL2_BOVIN Choline transporter-like protein 2 SLC44A2 localization Transporter activity
 HPCL1_BOVIN Hippocalcin-like protein 1 HPCAL1 Cellular process/Multicellularorganismal process
 Q24K07_BOVIN Vacuolar protein sorting 11 homolog (S. cerevisiae) VPS11
 Q5H9M6_BOVIN Dynein heavy chain (Fragment) Bv2
 Q864S1_BOVIN Cathepsin C (Fragment)
 Q4ZJS0_BOVIN MHC class I antigen (Fragment) BoLA-N
 Q58CZ4_BOVIN Flotillin 2 FLOT2
 MBL2_BOVIN Mannose-binding protein C MBL Binding
 TM214_BOVIN Transmembrane protein 214 TMEM214
 Q8MIR1_BOVIN Nicotinic acetylcholine receptor beta 2 subunit (Fragment) CHRNB2
 Q5E9W1_BOVIN CDC45-like CDC45L

Mass spectrometric (with a set FDR of 5 %) identification of proteins was present in exosomes generated by ICAR cultured at 1 % O2 and at 8 % O2. Data were subjected to ontology and pathway analysis using PANTHER and gene ontology algorithms and classified based on biological process and molecular function

Fig. 5.

Fig. 5

Proteomic analysis of bovine endometrial ICAR-derived exosomes. Mass spectrometric analyses of ICAR cell-derived exosome proteins. a Representative Venn diagram of common and unique proteins identified by 5600 Triple TOF MS (ABSciex) from exosomes released by ICAR cells at 48 h at both 8 % O2 and 1 % O2. b The gene ontology classification of ICAR cell-derived exosome proteins, on the basis of their involvement in biological process, identified clusters that are unique to and present only in exosomes of ICAR cultured at 1 % O2 but not those at 8 % O2. These biological processes were: growth (0.7 %), locomotion (0.7 %) and reproduction (1.4 %). c Molecular function (using PANTHER and Gene Ontology algoritnms) of exosome proteins were mostly related to binding and catalytic activity in both ICAR cultured at 1 % O2 and at 8 % O2

Discussion

A successful pregnancy is dependent of having a quality embryo and a receptive uterus synergizing with a synchronized crosstalk between the endometrium and embryo. Any insults or disturbances to its normal course can compromise implantation and the ability for the growing fetus to develop properly in the uterus [26]. The endometrium clearly has important functions in dairy cow pregnancy and we have now shown that exosomal release (30–120 nm) is part of its armamentarium which has analogous properties to similar tissues of other mammalian species.

In the present case, we have shown for the first time the effects of hypoxia on the biological activities of endometrial ICAR cells, including actions on the release and protein content of exosomes. Although it remains to be determined whether exosomes released from ICAR cells at different oxygen tensions also serve different functional goals, our data underscore that the content of exosomes may reflect the physiological state of the cells.

Our non-exosomal characterization of the ICAR cells indicated that the migration and proliferative capacity of ICAR cells decreased, while activation of apoptotic caspase-3 was enhanced at 1 % O2 (hypoxia), compared with an oxygen tension that was close to the bovine endometrial physiological oxygen levels (8 % O2; [38]). Moreover, the effect on migration was greater when exposed at 1 % O2 [39]. Interestingly, no relationship between oxygen tension and cell proliferation and apoptosis was observed in this previous study. Differences in cell types may explain this observation. Ito et al. described the rate of proliferation of human mesenchymal stem cell (MSCs) was observed to be highest in 5 % O2 and the lowest in < 0.1 % O2 conditions [40]. The MSCs at severely induced hypoxic conditions (<0.1 % O2), showed a decrease in proliferative ability, but were able to maintain viability for at least 48 h through increased glucose availability, to facilitate the generation of energy. Similar results were obtained from an airway smooth muscle study [41]. Hence, our cells have relatively normal proliferation responses to decreased oxygen tension.

Our study suggests that exosomes can serve as a vector for signaling molecules that harbor a variety of bioactive molecules including proteins at the conceptus-endometrial interface and that has the potential to modulate the functions of targeted cells during early pregnancy. Endometrial exosome release may also be modulated during an insult such as infection [42, 43]. In the current study we utilized hypoxia (i.e. 1 % O2) as a known modulator of exosome release as documented by alteration to both the number of exosomes released as well as differences in the exosomal content (cargo) [24, 27, 29].

In our study, endometrial cells exposed to 1 % O2released ~3.6 more exosomes relative to the 8 % O2 culture treatment, suggesting that hypoxia modulates cell function, including the release of exosomes. Hypoxia has already been reported to be a stimulus to increase secretion of exosomes by several groups [4446]. It is also suggested that the protein and RNA content of exosomes can reflect the physiological state of the cell as well as when the cells are in stress condition [47, 48]. However, the initial stress insult that contributed to an alteration of the exosomal content in relation to the functional effects of the subsequent cargo transfer and their role in cell-to-cell communication remains unclear. It is possible that exposure to other stressors such as adverse environmental hazards [4951] will also increase secretion of exosomes and alter composition of the cargo.

The protein content of exosomes from ICAR cells cultured under the 1 % O2 contained unique proteins compared to the contents of the ICAR exosomes cultured at 8 % O2. Our proteomic analyses detected the presence of tetraspanin-6 (TSPAN6), disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) that are only unique to exosomes of ICAR cultured at 1 % O2. These proteins are involved in the biological processes for reproduction. Interestingly, to evaluate TSPAN6, belonging to the transmembrane 4 superfamily that mediate the regulation of signal transduction events, as well as the disintegrin-like metalloproteinase ADAM10 which participates in ectodomain shedding activity could provide great insights into their functional role and regulation that is important for reproduction.

Studies using immunohistochemistry of human placental explants [52] have demonstrated that ADAM10 expression is significantly increased in preeclamptic placentas compared with normal placentas. Up-regulation of ADAM10 could induce placental release of soluble vascular endothelial growth factor receptor-1 (sFlt-1) and this cascade is associated with endothelial dysfunction, suggesting the significant role of oxidative change in preeclamptic placentas. ADAM10 is also a sheddase [53] that could induce CD46 shedding attributed to cell apoptotic processes [54], as well as mediate E-cadherin shedding affecting cellular adhesion and cell migration [55].

Mass spectrometry detection of pantetheinase (VNN1) in exosomes was unique to ICAR cultured at 8 % O2. VNN1 is an enzyme that hydrolyses pantetheine to form pantothenic acid (a precursor of coenzyme A) and the antioxidant cysteamine [56]. VNN1 could promote tissue inflammation through peroxisome proliferator-activated receptor gamma as well as modulate levels of glutathione [57]. It is proposed that VNN1 have innate immune functions and might contribute to tissue injury in endometritis [58, 59]. VNN1 was also reported being involved in proteolysis and can denature proteins by reducing disulfides [60], suggesting that it may have a role in regulating uterine receptivity for implantation and trophoblast invasion [61].

Mass spectrometry detected kininogen-2 (KNG2) in exosomes generated by ICAR cells cultured at either 1 or 8 % O2. KNG2 is a precursor protein to high molecular weight kininogen, low molecular weight kininogen and bradykinin and the concentration were reported to fluctuate during ovulation, pregnancy, and parturition [62]. Studies also showed that the release of vasoactive bradykinins from high molecular weight kininogen and low molecular weight kininogen are responsible for micro-vascular permeability and vascular growth, which plays an essential role in utero-placental vasculature and angiogenesis, necessary for embryonic and fetal survival [63].

Conclusion

Our present findings show that ICAR cell function, release of exosomes and exosomal content can be altered when subjected to adverse stimuli. These findings should be expanded to include cells of endometrial epithelial origin, interactions between these cells (i.e. stromal—epithelial crosstalk) and in the presence of common pathophysiological factors associated with reduced fertility (e.g. infectious or inflammatory agents). The identification of unique proteins (by mass spectrometry) in exosomes of ICAR cultured at 1 % O2 compared to 8 % O2 suggests that the cells respond and release proteins encapsulated within the exosomes to signal the environment in which they live. It is hoped that identification of unique proteins in exosomes following stimulation by factors affecting the physiological condition of cows may lead to novel targets for manipulation to aid fertility. Moreover, investigations into the release, uptake and content of exosomes may offer the opportunity to evaluate maternal-fetal crosstalk.

Acknowledgments

The authors acknowledge the assistance of Dr. Jamie Riches and Dr. Rachel Hancock of the Central Analytical Research Facility, Institute for Future Environments, Queensland University of Technology (QUT) for the electron microscope analyses.

We also thank our colleagues at DairyNZ for their helpful insights. YQ Koh is supported by a student scholarship from a partnership fund (DRCX1302) between the New Zealand Ministry of Business, Innovation and Employment and New Zealand dairy farmers through DairyNZ Inc. CS holds a research fellowship at The University of Queensland Centre for Clinical Research, Brisbane, Australia. GER was in receipt of an NMHRC Principal Research Fellowship. These studies were funded in part by the Australian Research Council, Therapeutic Innovation Australian and National Collaborative Research Infrastructure Strategy.

Funding

Australian Research Council and a partnership fund (DRCX1302) between the New Zealand Ministry of Business, Innovation and Employment and New Zealand dairy farmers through DairyNZ Inc.

Availability of data and materials

The datasets during and/or analyzed during the current study available from the corresponding author on reasonable request.

Authors’ contributions

YQK performed the study, collected and interpreted data performing statistical analysis and wrote the manuscript. YQK, SR, HNP and KV performed mass spectrometry analyses and reviewed the data generated. YQK, CS, HNP, GER and MDM were responsible for the study concept and participated in designing the study and interpreted data. CS, GER, HNP, MDM revised and approved the final version of manuscript.

Competing interests

The authors declare that they have no competing interests.

Consent for publication

Not applicable.

Ethics approval and consent to participate

Not applicable.

Abbreviations

ADAM 10

Metalloproteinase domain-containing protein 10

DTT

Dithiothreitol

FDR

False discovery rate

ICAR

Intercaruncular stromal cell

KNG2

Kininogen-2

LDH

Lactate dehydrogenase

MS/MS

Mass spectrometry/mass spectrometry

PANTHER

Protein analysis through evolutionary relationships

PBS

Phosphate buffered saline

PGF

Prostaglandin F

PVDF

Polyvinylidene fluoride

RIPA

Radioimmunoprecipitation assay buffer

RWD

Relative wound density

sFLT-1

Soluble vascular endothelial growth factor receptor-1

TSPAN6

Tetraspanin-6

VNN1

Pantetheinase

Contributor Information

Yong Qin Koh, Email: y.qinkoh@uq.edu.au.

Hassendrini N. Peiris, Email: h.peiris@uq.edu.au

Kanchan Vaswani, Email: k.vaswani@uq.edu.au.

Sarah Reed, Email: sj.reed@uq.edu.au.

Gregory E. Rice, Email: g.rice@uq.edu.au

Carlos Salomon, Email: c.salomongallo@uq.edu.au.

Murray D. Mitchell, Phone: +61 7 33465016, Email: murray.mitchell@uq.edu.au

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The datasets during and/or analyzed during the current study available from the corresponding author on reasonable request.


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