Abstract
Psychiatric and obstetric diseases are growing threats to public health and share high rates of co-morbidity. G protein-coupled receptor signaling (e.g., vasopressin, serotonin) may be a convergent psycho-obstetric risk mechanism. Regulator of G Protein Signaling 2 (RGS2) mutations increase risk for both the gestational disease preeclampsia and for depression. We previously found preeclampsia-like, anti-angiogenic obstetric phenotypes with reduced placental Rgs2 expression in mice. Here, we extend this to test whether conserved cerebrovascular and serotonergic mechanisms are also associated with risk for neurobiological phenotypes in the Rgs2 KO mouse. Rgs2 KO exhibited anxiety-, depression-, and hedonic-like behaviors. Cortical vascular density and vessel length decreased in Rgs2 KO; cortical and white matter thickness and cell densities were unchanged. In Rgs2 KO, serotonergic gene expression was sex-specifically changed (e.g., cortical Htr2a, Maoa increased in females but all serotonin targets unchanged or decreased in males); redox-related expression increased in paraventricular nucleus and aorta; and angiogenic gene expression was changed in male but not female cortex. Whole-cell recordings from dorsal raphe serotonin neurons revealed altered 5-HT1A receptor-dependent inhibitory postsynaptic currents (5-HT1A-IPSCs) in female but not male KO neurons. Additionally, serotonin transporter blockade by the SSRI sertraline increased the amplitude and time-to-peak of 5-HT1A-IPSCs in KO neurons to a greater extent than in WT neurons in females only. These results demonstrate behavioral, cerebrovascular, and sertraline hypersensitivity phenotypes in Rgs2 KOs, some of which are sex-specific. Disruptions may be driven by vascular and cell stress mechanisms linking the shared pathogenesis of psychiatric and obstetric disease to reveal future targets.
Subject terms: Neuroscience, Physiology
Introduction
Perinatal mood and psychiatric disorders are a significant and growing public health concern. Rates of new-onset major depressive disorder in pregnancy increased seven-fold in the last two decades to approximately 1:7 [1–3], and suicide is the leading cause of postpartum death in the United States [4, 5]. Risk factors influencing this precipitous rise include increased awareness/diagnosis, poor social supports, sociodemographic and maternal stress, and increased maternal morbidity; many of these were exacerbated during the COVID-19 pandemic [6–9]. Pregnancy-specific mechanisms of depression remain unclear, however, limiting clinical treatment and prevention.
Insights into psychiatric mechanisms may be gleaned from the pregnancy literature. For instance, epidemiologic reports find that gestational diseases such as preeclampsia and perinatal psychiatric disease share high rates of co-morbidity [10]. The pregnancy disease preeclampsia, a dangerous and common hypertensive disorder of pregnancy, is associated with increased risk for mood and anxiety disorders [11, 12]. Mood and anxiety disorders also increase preeclampsia risk up to three-fold [13]. This bi-directional risk suggests shared mechanisms that may reveal insights into novel treatment targets [14].
Many risk factors shared by both preeclampsia and psychiatric disease involve G-protein coupled receptor (GPCR) dysfunction. For example, preeclampsia is associated with serotonin signaling deficits across multiple receptor subtypes [15], impaired vascular reactivity to serotonin [16–18], and immunologic perturbation [19]. Many of these mechanisms are shared in psychiatric diseases such as major depressive disorder. Similarly, the GPCR signaling molecule arginine vasopressin (AVP) is increased as early as the first trimester in preeclamptic pregnancies [20, 21] and in postpartum depression [22], causing altered AVP receptor expression across tissues [23] and cardiovascular risk throughout the lifespan [24, 25]. Neuropeptides such as AVP interact with monoaminergic systems including serotonin in the brain and periphery, influencing the impacts of serotonin-selective reuptake inhibitors (SSRIs) on neurochemical and biobehavioral phenotypes [26].
One GPCR signaling factor that regulates serotonergic and vasopressin signaling is the Regulator of G protein Signaling 2 (RGS2). RGS2 is disrupted in preeclampsia and depression [27–29], and RGS2 polymorphisms are linked to preeclampsia [30–32]; RGS2 is down-regulated in preeclamptic placenta [33]. Our prior work reveals that decreased Rgs2 in placenta is sufficient to recapitulate preeclampsia-like phenotypes such as gestation-onset hypertension and placental anti-angiogenesis in mice [29, 33]. Rgs2 KO mice also exhibit uterine artery deficits and GPCR-mediated vasoconstriction [34, 35].
In addition to serving as a vascular risk gene for preeclampsia, neuropsychopharmacology studies reveal that RGS2 dysfunction contributes to animal behaviors relevant to anxiety and depression [28, 36–42], possibly via impacts on serotonergic systems. Rgs2 KO mice have decreased (mRNA) Htr1a and Htr1b expression in the dorsal raphe [43], and disrupted monoamine signaling in hippocampus which is related to sex-specific learning and memory phenotypes [44, 45].
RGS2 influences SSRI efficacy for the treatment of psychiatric disorders. For example, select RGS2 polymorphisms are predictive of substantial clinical benefit from sertraline in individuals with social anxiety disorder [36]. Here, we evaluate the impact of the most prescribed SSRI [46], sertraline, on mouse Rgs2 KO dorsal raphe serotonergic neurons using brain slice electrophysiology. Sertraline was selected given prior clinical data suggesting its significance in the mediation of preeclampsia features including hypertension and pro-inflammation [10, 47, 48], interaction with RGS2 [36], and its exceptionally high affinity for the serotonin transporter (SERT) relative to other neurotransmitter transporters [49].
Given prior work on RGS2 in obstetric disease reveals a critical role in anti-angiogenesis and vascular dysfunction [29, 33, 35], we had the goal here of extending these findings to the brain. We hypothesized that similar vascular mechanisms might also drive behavioral phenotypes in Rgs2 KO mice. We examined conserved regulators of cellular stress and angiogenesis to find that Rgs2-mediated mechanisms disrupt both cerebrovascular structure and brain function more broadly. These results implicate Rgs2-serotonin mechanisms in neurobiological risk and highlight the relevance of GPCR signaling for cerebrovascular health.
Materials and methods
Mice
Mice harboring a null Rgs2 allele (KOs) were recovered from cryopreservation (B6.129P2-RGS2tm1Dgen/Mmnc, MMRRC:011639-UNC), as described previously [33], and backcrossed (12 generations) against C57BL/6 J (Jax) animals. Adult homozygous Rgs2−/− (KO) and Rgs2+/+ wildtype (WT) littermate controls were used. Procedures were approved by the University of Iowa Office of the Institutional Animal Care and Use Committee. For additional details, see the Supplementary Materials and Methods.
Behavioral assessments
Adult offspring (12+ weeks of age) were assessed on one task daily during the light cycle, as previously [50–52]. For additional details, see the Supplementary Materials and Methods.
Elevated plus maze
Mice were placed in the center of an elevated plus maze (San Diego Instruments), facing one of the closed arms. The maze was lit to ~210 lux in open arms/center. They were allowed to freely explore the maze for five minutes. Time spent in the open and closed arms and center of the maze were measured and compared to assess anxiety-like behavior, as previously [53].
Open field test
Mice were placed in the center of an open field arena (16 × 16.5 × 12 in, black acrylic, ~110 lux in center) and allowed to freely explore for 30 min. Distance traveled (cm/s) was assessed as a measure of locomotion in five-minute time bins. Anxiety-like behavior was assessed by measuring the time spent in the center versus the periphery of the field (each defined to include 50% of surface area), as previously [51–53].
Y maze
Mice freely explored the three-armed apparatus (San Diego Instruments; 150 lux) for five minutes, as previously [53]. Spontaneous alternations through the maze center were quantified using EthoVision XT software (Noldus). For additional details, see the Supplementary Materials and Methods.
Three-chamber social preference and social novelty preference
As previously [54–57], mice were first habituated (10 min) to the three-chamber social apparatus (10 × 20.5 × 9 in field) under dim lighting conditions (~5 lux) to promote social exploration. For social preference testing, an object (Lego Duplo) was placed into one cup and a sex-, size-, and age-matched “stranger” mouse was placed into the other. Experimental mice were allowed to freely explore for 10 min. Social preference was calculated as social cup exploration: non-social cup exploration time.
For social novelty preference testing, a new stranger mouse in a cup was placed into the chamber that previously contained the original stranger, and the original stranger was moved to the previously nonsocial cup. The experimental mouse was allowed to freely explore for 10 min. Social novelty preference was calculated as novel stranger cup exploration: total social interaction time. For additional details, see the Supplementary Materials and Methods.
Sucrose preference test
Sucrose preference testing followed standard protocols [58]. Mice were moved into static housing and single-housed 48 hours prior to sucrose preference testing. They were given water via a 25 mL serological pipette (gradations every 0.2 mL) modified with a sipper tube for these 48 h. After 48 h, an additional pipette containing 2% sucrose solution was added to the other side of the cage (counterbalanced across mice). Consumption of water and sucrose was measured twice daily for 48 h.
Tail suspension test
Following standard protocols [59], mice were suspended by the tail approximately 20 inches above a table for six minutes. Struggle or mobile time was defined as movement of any limbs or trunk for at least 0.5 s. For additional details, see the Supplementary Materials and Methods.
Tissue collection
Mice were euthanized via CO2 overdose and rapid decapitation. Brains were dissected and hemisectioned; one half was fixed (4% PFA) then cryopreserved (20% sucrose) for coronal cryosectioning at 20 μm (Leica) for immunohistochemistry and the other half was coronally sectioned at 100μm using a plexiglass mold for tissue punches. Punches were taken of isocortex (somatomotor areas), hypothalamic paraventricular nucleus (PVN), midbrain (at the dorsal raphe nucleus), and hindbrain (medulla) [49]. Aortas were dissected fresh, cleaned of adventitia, and flash frozen for molecular studies. For additional details, see the Supplementary Materials and Methods.
Quantitative polymerase chain reaction (qPCR)
Brain punches and aortas were processed for total mRNA (RNeasy Kit, Qiagen). RNA concentration was determined (Nanodrop Spectrophotometer, Thermofisher) and 1 μg reverse transcribed (Super Script IV Reverse transcriptase kit, Thermo Fisher). Reactions were run in triplicate (QuantStudio 5 Real-Time PCR System, Applied Biosystems) and gene expression was calculated from average Ct values normalized to 18 S rRNA as the housekeeping gene [formula: 2(−ΔCt)] (QuantStudio, Thermofisher). SYBR Green primers were used (Supplementary Table 1) for targets related to cell stress/redox (Tgfβ, HIF1α, Ho1, Nox4, Nox2, Nrf2, Nos2, Sod1, Gpx1), angiogenesis (Pdgfrb, Vegfr1, Angpt, Mmp9), and GPCR signaling and serotonin (Htr1a, Htr2a, Maoa, Avpr1a, Ido, Slc6a4, Tph1, Fgf2).
Immunohistochemistry
As previously described [51–53], sections were immunostained with NEUN monoclonal primary antibody (1:300; 24307S, catalog number NC1593317, Cell Signaling Technology) and secondary polyclonal antibody (1:500; DyLight 633, catalog number NBP1-75633, Novus Biologicals). Cerebrovasculature was labeled using Isolectin GS-IB4 (IB4) conjugated to Alexa Fluor 488 (1:1000; I21411, Invitrogen). Slides were coverslipped with DAPI mounting medium (H200010, Vector Laboratories). For additional details, see the Supplementary Materials and Methods.
Stereology
Neuronal, cellular, and cerebrovascular imaging was performed on an Olympus IX3 scanning fluorescent microscope with CellSens (Olympus Life Science) software. Assessments were performed by the same blinded experimenter utilizing CellSense imaging software and ImageJ. For additional details, see the Supplementary Materials and Methods.
Cerebrovascular assessments
As previously described [53], 20 μm coronal brain sections were side mounted, blocked, and vessels stained with IB4 lectin. For each animal, 2 neocortical images (1920 × 1200 pixels) per section were pseudo-randomly taken at 20x magnification across 3–6 coronal sections at intervals of 200 μm. Freehand draw in ImageJ was used to manually trace IB4 lectin+ vessels. Approximately 10 vessels were traced per image. Care was taken to exclude cellular structures (e.g., with DAPI+ nucleus), as IB4 lectin also labels microglia which often lie near microvessels in the brain [60, 61]. The length and diameter at the widest point of all vessel traces was calculated in ImageJ (measure command) per image then averaged across images (minimum 3) for each animal. To determine vessel branching, the number of branches or junctions on a given vessel trace was tabulated and averaged over length of the root vessel, as has been done in anti-angiogenic genetic modeling previously [62].
Enzyme-linked immunoassay (ELISA)
Trunk blood was collected upon animal sacrifice into a heparin-coated tube and frozen (−80 °C). Platelet-free plasma serotonin (5-HT) was measured by ELISA (ab133053, Abcam), per manufacturer protocols. Samples were assayed within two weeks of collection.
Tail-cuff plethysmography
Blood pressure was assessed in a separate cohort (n = 3–7/genotype/sex) by tail-cuff plethysmography on a high throughput non-invasive blood pressure monitoring system (CODA, Kent Scientific), as previously [63]. Briefly, mice were restrained in plexiglass tubes and acclimated to 30 min periods of restraint for 2 weeks prior to testing. Blood pressures were then averaged over 2 days of testing.
Evans blue blood-brain barrier permeability assay
Following established protocols [64], female brains were tested for presence of Evans blue (EB) dye 30 min after i.v. administration. For additional details, see the Supplementary Materials and Methods.
Brain slice preparation and electrophysiological recordings
Brain slices and electrophysiological recordings were made as previously described [65]. All recordings were made with the investigator blinded to genotype. In brief, WT and homozygous Rgs2 KO mice were deeply anesthetized with isoflurane and euthanized by decapitation. Brains were extracted and placed in warmed and bubbled (95/5% O2/CO2) modified Krebs’ buffer containing (in mM): 126 NaCl, 2.5 KCl, 1.2 MgCl2, 1.2 CaCl2, 1.2 NaH2PO4, 21.5 NaHCO3, and 11 D-glucose. To increase slice viability and limit excitotoxicity, 5 µM of MK-801 was added to the buffer solution. Coronal dorsal raphe slices (240 µm) were collected using a vibrating microtome (Leica VT 1000 S). Slices were then incubated in the same buffer solution at 28 °C for at least 30 min before recording.
Electrophysiological recordings were made at 35 °C from dorsal raphe serotonin neurons, identified based on location relative to the cerebral aqueduct and firing broad action potentials (>1 ms half-width) under 40 Hz to somatic current injection [65, 66] with Multiclamp 200B and 700B amplifiers (Molecular Devices), Digidata 1550B A/D converters (Molecular Devices), and Clampex software (Molecular Devices) with borosilicate glass electrodes (World Precision Instruments) wrapped with Parafilm to reduce pipette capacitance. Pipette resistances were 2.8 to 4.4 MΩ when filled with an internal solution containing: (in mM) 104.56 K-methylsulfate, 3.73 KCl, 5.3 NaCl, 4.06 MgCl2, 4.06 CaCl2, 7.07 HEPES (K), 3.25 BAPTA (K4), 0.26 GTP (sodium salt), 4.87 ATP (sodium salt), 4.59 creatine phosphate (sodium salt), pH 7.24 with KOH, mOsm ~274, for whole-cell patch-clamp recordings. Series resistance was monitored throughout the experiment. A liquid junction potential of −8 mV between the internal and external solution was used to correct all reported voltages. Brief pulses (0.5 ms, 60 Hz) of electrical stimulation were delivered to the brain slice in 60 s intervals via a borosilicate glass monopolar stimulating electrode (World Precision Instruments) inserted within 200 µm of the recorded neuron to evoke synaptic currents. To isolate the 5-HT1A-IPSC, synaptic currents were evoked in the presence of GluN (MK-801, Tocris), GluA/GluK (NBQX, 3 μM, Tocris), GABAA (picrotoxin, 100 μM, Sigma-Aldrich), and α1-adrenergic (prazosin, 100 nM, Tocris) receptor blockers. Drugs were applied to brain slices via bath application.
Statistical analyses
Based on our work in similar models [20, 51–53, 63, 67], sample sizes were selected to achieve 94–100% power to detect a respective change in sensitivity and specificity from 0.5 to 0.9. Normality (by Shapiro–Wilk test) and equal variance (by Brown-Forsythe test) were confirmed before performing two-way ANOVAs to test for sex, genotype, and interaction effects. As appropriate, post hoc pairwise multiple comparisons were performed via the Student-Newman-Keuls (SNK) Method. If either the assumption of normality or equal variance was violated, a nonparametric ANOVA on Ranks (Kruskal-Wallis) test was used, followed by Holm-Sidak corrected multiple comparisons. Normally distributed gene expression data were tested via one-sample t-test; non-normally distributed data were tested by the one sample Wilcoxon test. Associations were interrogated by linear regression on grouped male and female data to reveal underlying, associative mechanisms. Outliers (greater than two standard deviations from the mean) were excluded.
Dorsal raphe serotonin neuron recordings were analyzed using Clampfit 11.1. τ-decay were determined by fitting the 5-HT1A-IPSCs from the peak to the return to 0 current with a single exponential. Unless stated otherwise, n=number of cells. Significant differences were determined by Mann-Whitney U tests.
For all tests, P values < 0.05 were considered significant. All plotted averages depict means ± S.E.M. Statistical analyses were completed in SigmaPlot v12.3 (Systat Software, Inc.) or GraphPad Prism 9 and displayed using GraphPad Prism 9 (GraphPad Software, Inc.).
Results
Sex-specific behavioral alterations in the Rgs2 knockout mouse
To test sex-specific brain function changes relevant to psychiatry, we assessed male and female KO and WT behaviors (n = 8–12/sex/genotype). There was also no difference in distance traveled by epoch in males (two-way repeated measures ANOVA interaction: F[5,90] = 1.808, p = 0.12, main effect [ME] genotype: F[1,18] = 0.7327, p = 0.40) nor females (interaction: F[5,50] = 0.8042, p = 0.55, ME genotype: F[1,10] = 0.008, p = 0.93), though both animals habituated with diminished locomotion (p < 0.0001 ME time, males: F[2.978,53.60] = 38.34; females: F[3.432,34.32] = 28.09; Fig. 1A, B). Time spent in the center versus periphery of the open field test was unchanged by group (H[3] = 2.003, p = 0.57 by ANOVA on Ranks; Fig. 1C). Working memory, as measured by spontaneous alternation ratio on the Y-maze, was unchanged by genotype or sex (two-way ANOVA interaction: F[1,38] = 0.9654, p = 0.33; ME sex: F[1,38] = 1.560, p = 0.2193; ME genotype: F[1,38] = 0.09088, p = 0.76), and alternations were elevated beyond chance in all groups (males: WT: 0.57 ± 0.03, p = 0.02 by one sample t test, KO: 0.56 ± 0.02, p = 0.02; females: WT: 0.58 ± 0.03, p = 0.03, KO: 0.32 ± 0.03, p = 0.001; Fig. 1D). We found male-specific exploratory deficits on the Y-maze (latency to enter first arm, two-way ANOVA interaction: F[37] = 10.32, p = 0.003; ME sex: F[1,35] = 1.709, p = 0.20; ME genotype: F[1,35] = 0.8820, p = 0.35; post hoc genotype difference by Student-Newman-Keuls (SNK) method in males p = 0.008; Fig. 1E). Social preference was significantly increased above chance for males (WT: p = 0.0003, KO p = 0.0005) and females (WT p = 0.008, KO p = 0.0009) by single sample t-test, but unchanged by group (H[3] = 5.182, p = 0.16 by ANOVA on Ranks; Fig. 1F). Social novelty preference was increased above chance by single sample t-test only among WT males (p = 0.03; KO females: p = 0.09; KO males: p = 0.09; WT females: p = 0.88), but unchanged by group (two-way ANOVA interaction: F[1,38] = 0.3868, p = 0.54; ME sex: F[1,38] = 2.282, p = 0.14; ME genotype: F[1,38] = 0.7122, p = 0.40; Fig. 1G). Time spent on the open versus closed arms of the elevated plus maze was significantly decreased in KOs (two-way ANOVA, ME genotype: F[36] = 4.87, p = 0.03), driven by females (p = 0.02 by post hoc SNK; Fig. 1H). Sucrose consumption was significantly increased in KOs (two-way ANOVA, ME genotype: F[1,35] = 16.90, p = 0.0002; post hoc SNK males: p = 0.03, females: p = 0.001; Fig. 1I). We further found decreased struggle behavior on the tail suspension test in KOs (two-way ANOVA, ME genotype: F[1,37] = 5.752, p = 0.02; no significant post hoc SNK; Fig. 1J). Struggle time per bout was unchanged (two-way ANOVA interaction: F[1,37] = 0.062, p = 0.81; ME sex: F[1,37] = 0.9019, p = 0.35; ME genotype: F[1,37] = 0.7897, p = 0.38; Fig. 1K).
Fig. 1. Behavioral testing revealed Rgs2 KO sex-specific alterations.
On the open field, A KO males exhibited no locomotor differences by genotype across the full 30 min task (two-way repeated measures ANOVA interaction: F[5,90] = 1.808, p = 0.12, main effect [ME] genotype: F[1,18] = 0.7327, p = 0.40), though they did down-regulate locomotor behavior across the task (p < 0.0001 ME of time: F[2.978,53.60] = 38.34). B Females also exhibited no significant difference in distance traveled by genotype across the full open field task (two-way repeated measures ANOVA interaction: F[5,50] = 0.8042, p = 0.55, ME genotype: F[1,10] = 0.008, p = 0.93) while down-regulating locomotor behavior across the task (p < 0.0001 main effect of time: F[3.432,34.32] = 28.09). C Center time relative to peripheral zone time on the open field was unchanged by genotype (H[3] = 2.003, p = 0.57 by ANOVA on Ranks). D Working memory, as assessed by spontaneous alternations on the Y maze, was unchanged by genotype or sex (two-way ANOVA interaction: F[1,38] = 0.9654, p = 0.33; ME sex: F[1,38] = 1.560, p = 0.2193; ME genotype: F[1,38] = 0.09088, p = 0.76). Spontaneous alternation rates were elevated beyond chance (dashed line, 50%) in all groups by one-sample t-test (males: WT: 0.57 ± 0.03, p = 0.02, KO: 0.56 ± 0.02, p = 0.02; females: WT: 0.58 ± 0.03, p = 0.03, KO: 0.32 ± 0.03, p = 0.001). E Male-specific latency to explore any arm when first placed into the Y maze was significantly increased in KOs (two-way ANOVA interaction: F[37] = 10.32, p = 0.003; ME sex: F[1,35] = 1.709, p = 0.20; ME genotype: F[1,35] = 0.8820, p = 0.35; post hoc genotype difference by Student-Newman–Keuls (SNK) method in males p = 0.008). F Social preference for a novel stranger mouse versus a non-social stimulus (cylinder containing object) was significantly increased above chance (dashed line, 1) for males (WT: p = 0.0003, KO p = 0.0005) and females (WT p = 0.008, KO p = 0.0009) by single sample t-test, but unchanged by group (H[3] = 5.182, p = 0.16 by ANOVA on Ranks. G Social novelty preference was increased above chance (dashed line, 1) by single sample t-test only among WT males (p = 0.03; KO females: p = 0.09; KO males: p = 0.09; WT females: p = 0.88), but unchanged by group (two-way ANOVA interaction: F[1,38] = 0.3868, p = 0.54; ME sex: F[1,38] = 2.282, p = 0.14; ME genotype: F[1,38] = 0.7122, p = 0.40). H KO mice exhibited decreased time on the open relative to the closed arm and center of the elevated plus maze (two-way ANOVA, ME genotype: F[36] = 4.87, p = 0.03), which was driven by females (p = 0.02 by post hoc SNK) indicating an anxiety-like phenotype. I Hedonic behavior, as assessed by the sucrose preference test, was significantly increased in KOs (two-way ANOVA, ME genotype: F[1,35] = 16.90, p = 0.0002; post hoc SNK males: p = 0.03, females: p = 0.001). J The tail suspension test revealed decreased KO struggle behavior (two-way ANOVA, ME genotype: F[1,37] = 5.752, p = 0.02; no significant post hoc SNK) but K) unchanged struggle time per bout (two-way ANOVA interaction: F[1,37] = 0.062, p = 0.81; ME sex: F[1,37] = 0.9019, p = 0.35; ME genotype: F[1,37] = 0.7897, p = 0.38). All p values calculated by ANOVA (two-way or on Ranks, as noted) and by post hoc SNK. Data are displayed as mean ± SEM.
Cortical vessel density and length but not cell numbers are diminished in Rgs2 KO mice
We next conducted histological assessments of brain morphology, including of cerebrovasculature (n = 3–6/sex/genotype), which is changed in multiple models of obstetric and psychiatric disease and is associated with behavioral alternations including anxiety-like, hedonic, and depression-like behaviors [6, 68, 69]. These revealed significant reductions in cortical vascular density in KOs (two-way ANOVA, main effect genotype: F[1,19] = 30.75, p < 0.001; males and females p < 0.001 by SNK; Fig. 2A). Vessel length in KOs was also decreased (H[3] = 17.225, p < 0.001; post hoc Dunn’s Method WT vs KO males p = 0.005, WT vs KO females p = 0.10; Fig. 2B). Vessel elaboration (genotype: F[1,20] = 0.0009, p = 0.98; sex: F[1,20] = 0.9801, p = 0.33; Fig. 2C) and luminal diameter (genotype: F[1,21] = 0.0059, p = 0.94; sex: F[1,21] = 0.0087, p = 0.93; Fig. 2D) were unchanged. Vessels appeared more diffuse and fragmented in KO tissues (Fig. 2E). Cortical thickness (Fig. 2E) across regions of cerebral cortex was unchanged (ANOVA on ranks p < 0.001; no significant post hoc differences by region; Fig. 2F), nor was white matter thickness at the corpus callosum (interaction: F[1,8] = 0.05929, p = 0.81; ME genotype: F[1,8] = 0.1990, p = 0.67; ME sex: F[1,8] = 0.004360, p = 0.95; Fig. 2G).
Fig. 2. Cortical vascular density and length is decreased in Rgs2 KO animals, though brain morphology is otherwise intact.
IB4 lectin-stained cerebrovasculature in isocortex (somatomotor areas) in Rgs2 KO and wildtype (WT) mice revealed significant deficits in A density of vessels in cortex in KOs (two-way ANOVA, main effect genotype: F[1,19] = 30.75, p < 0.001; males and females p < 0.001 by SNK) and B average length in KOs (H[3] = 17.225, p < 0.001; post hoc Dunn’s Method WT vs KO males p = 0.005, WT vs KO females p = 0.10). C The elaboration of cerebral vessels, measured as branch points per length of vessel, was unchanged by genotype or sex (genotype: F[1,20] = 0.0009, p = 0.98; sex: F[1,20] = 0.9801, p = 0.33), nor was D average vessel diameter, taken at the widest point in the vessel (genotype: F[1,21] = 0.0059, p = 0.94; sex: F[1,21] = 0.0087, p = 0.93). E Example micrographs taken at 10x magnification in neocortex demonstrated deficiencies in cerebral vessel integrity throughout KO brain tissue. F Assessments of cortical thickness taken in rostra, middle, and caudal sections revealed no changes by genotype (ANOVA on ranks p < 0.001; no significant post hoc differences by region). G Corpus callosum thickness was also unchanged by sex or genotype (interaction: F[1,8] = 0.05929, p = 0.81; ME genotype: F[1,8] = 0.1990, p = 0.67; ME sex: F[1,8] = 0.004360, p = 0.95). H Cortical cell density of all cells (DAPI+; interaction: F[1,15] = 1.088, p = 0.31; ME genotype: F[1,15] = 0.4907, p = 0.49, ME sex: F[1,15] = 0.1454, p = 0.71), I) of neurons (NEUN + ; interaction: F[1,15] = 1.594, p = 0.23; ME genotype: F[1,15] = 0.1047, p = 0.75; ME sex: F[1,15] = 0.00043, p = 0.98), and of J) neurons:glia (interaction: F[1,15] = 1.174, p = 0.30; ME genotype: F[1,15] = 0.2252, p = 0.64; ME sex: F[1,15] = 0.01520, p = 0.90) revealed no changes by genotype or sex. All p values calculated by ANOVA (two-way or on Ranks, as noted) and by post hoc SNK or Dunn’s Method. Data are displayed as mean ± SEM.
Neocortical density of all cells (interaction: F[1,15] = 1.088, p = 0.31; ME genotype: F[1,15] = 0.4907, p = 0.49, ME sex: F[1,15] = 0.1454, p = 0.71; Fig. 2H), of neurons (interaction: F[1,15] = 1.594, p = 0.23; ME genotype: F[1,15] = 0.1047, p = 0.75; ME sex: F[1,15] = 0.00043, p = 0.98; Fig. 2I), and ratio of neurons to glia (interaction: F[1,15] = 1.174, p = 0.30; ME genotype: F[1,15] = 0.2252, p = 0.64; ME sex: F[1,15] = 0.01520, p = 0.90; Fig. 2J) were unchanged.
Sex-specific abnormalities in angiogenesis, G protein signaling, and redox related gene expression in Rgs2 KO mice
Given the known role of Rgs2 in cerebrovascular biology and mood and anxiety-related behaviors, we next assessed whether expression of angiogenic genes and those involved in regulation of signaling pathways dependent on Rgs2 (e.g., 5HT, AVP, etc.) were disrupted. Given large cerebrovascular deficits in this model, we also assessed angiogenic targets (Fig. 3). P values reference comparison of KO fold change (relative to WT) by one-sample Shapiro–Wilk t test (if normally distributed) or by one-sample Wilcoxon test (if non-normally distributed).
Fig. 3. qPCR studies of brain (cortex, paraventricular nucleus, midbrain/dorsal raphe, hindbrain) reveal changes in redox-, angiogenesis-, and GPCR-related genes in the Rgs2 KO mouse relative to wildtype (WT) comparators.
A In male KO isocortex (somatomotor areas), there is decreased redox (Hif1a, Ho1), angiogenic (Mmp9), and GPCR-related (Fgf2, Avpr1a) transcript expression, and in particular decreased serotonin signaling gene expression (Htr1a, Htr2a, Maoa, Ido, Slc6a4, Tph1), by comparison of fold change relative to wild type controls by one-sample t test. B In female KO cortex, there is also decreased Hif1a and Avpr1a, but increased Htr2a, Maoa, and Ido; Slc6a4 and Tph1 are decreased as in males. C In paraventricular nucleus (PVN), Rgs2 KO males have decreased Nos2, Ho1, Nox4, Avpr1a, Ido, Slc6a4, and Tph1 expression and increased Nos3 expression. D Large fold change increases were found in male PVN in Sod1, Hif1a, and Gpx1. E In female KO PVN, there was increased Nrf2 and Maoa, but decreased Nos2, Ho1, Nox4, Nox2, Htr1a, Avpr1a, Ido, Slc6a4, and Tph1. F As in males, there were large fold change increases in female PVN Sod1, Hif1a, and Gpx1 expression. G In male Rgs2 KO midbrain (inclusive of dorsal raphe nucleus), there was decreased serotonin signaling-related gene expression in Htr1a, Htr2a, Ido, Slc6a4, and Tph1, while expression of Avpr1a was also decreased. H In female KO midbrain, Htr1a, Avpr1a, Ido, Slc6a4, and Tph1 were also decreased, though Maoa was significantly increased. I, J In male and female KO Hindbrain, serotonin signaling differences were also found: Htr1a expression was decreased, while only in males Htr2a was also decreased. K Canonical biological functions of genes assessed. Dashed line indicates WT control expression (fold change=1). *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001, ****P ≤ 0.0001 by one-sample Shapiro-Wilk t test if normally distributed, or by one-sample Wilcoxon test if non-normally distributed (vs hypothetical fold change = 1.0). N = 6 WT, 6 KO for all comparisons. Data are displayed as mean ± SEM*.
In neocortex (Fig. 3A, B), redox-related targets Hif1a and Ho1 were decreased in males (Hif1a: 7.75% of controls, p = 0.03; Ho1: 45.30% of controls, p = 0.0002), while only Hif1a was decreased in females (62.25% of controls, p = 0.02). Tgfβ was decreased in males only (42.8% of controls, p < 0.0001) and Nox4 expression was unchanged by genotype across sexes. Expression of angiogenesis-related genes including Pdgtrb and Angpt was unchanged; Mmp9 was decreased (58.70% of controls, p = 0.03) and Vegfr1 was increased (613%, p = 0.008) in males only. In terms of cortical GPCR-related signaling, there were female-specific elevations in Htr2a (378.4% of controls, p = 0.02) and Maoa (237.6% of controls, p = 0.045) expression, while Slc6a4 (males: 13.86% of controls, p = 0.03; females: 51.01% of controls, p = 0.01) and Tph1 (males: 25.05% of controls, p = 0.03; females: 27.56% of controls, p = 0.0006) were decreased in both sexes. Fgf2 (14.16% of controls, p = 0.03), Ido (13.02%, p = 0.03), and Avpr1a (4.89% of controls, p = 0.03) were both down-regulated in male KOs, while only Avpr1a was down-regulated in female KOs (70.07% of controls, p = 0.04). Together, these data suggest female increases in serotonin systems gene expression, including receptors (Htr2a) and metabolic machinery (e.g., Maoa), possibly as compensation for a lack of Rgs2 mediation of GPCR signaling. Cell stress and hypoxia-related genes may be dysregulated as a result of aberrant signaling in Rgs2 KO cells.
Given redox-related changes in cortex, a slightly expanded subset of redox genes was next evaluated in paraventricular nucleus (PVN; Fig. 3C–F), a region critical to GPCR-related functions including vasopressin and oxytocin signaling. We hypothesized that redox-related genes may have been abnormal in KO animals given disinhibited intracellular signaling. Most patterns of gene expression in PVN remained consistent between male and female Rgs2 KO animals. In both sexes, redox-related Nos2 (males: 1.11% of controls, p < 0.0001; females: 1.36% of controls, p < 0.0001), Ho1 (males: 19.30% of controls, p < 0.0001; females: 42.06% of controls, p = 0.0008), Nox4 (males: 5.88% of controls, p < 0.0001; females: 8.86% of controls, p < 0.0001), and Nox2 (males: 2.83% of controls, p < 0.0001; females: 4.76% of controls, p < 0.0001) were down-regulated in KOs, while Sod1 (males: 7567% of controls, p < 0.0001; females: 12930% of controls, p = 0.0001) and Gpx1 (males: 3147% of controls, p = 0.0003; females: 6303% of controls, p < 0.0001) were strongly up-regulated. In KO females only, Nrf2 was significantly up-regulated (150% of controls, p = 0.04). In contrast to cortex, angiogenesis-related Hif1a was strongly up-regulated in both male (756.8% of controls, p = 0.004) and female KO PVN (1427% of controls, p = 0.0010). A subset of GPCR signaling genes were down-regulated in both male and female KO PVN: Avpr1a (males: 25.20% of controls, p = 0.002; females: 39.49% of controls, p = 0.002), Ido (males: 8.69% of controls, p < 0.0001; females: 0.67% of controls, p < 0.0001), Slc6a4 (males: 0.92% of controls, p < 0.0001; females: 9.68% of controls, p < 0.0001), and Tph1 (males: 3.65% of controls, p = 0.03; females: 1.46% of controls, p < 0.0001). Only in female KO PVN was serotonin-related target HTR1A down-regulated (35.30% of controls, p < 0.0001) and Maoa up-regulated (290.8% of controls, p = 0.03).
Given GPCR-related changes in gene expression in cortex and hypothalamic PVN, we next sought to examine gene expression in the serotonergic dorsal raphe nucleus of the midbrain (Fig. 3G, H). In both male and female KO midbrain, there was pan-suppression of most serotonergic and GPCR-related targets: Htr1a (males: 32.54% of controls, p = 0.0069; females: 37.39% of controls, p = 0.010), Avpr1a (males: 8.69% of controls, p < 0.0001; females: 0.67% of controls, p < 0.0001), Ido (males: 2.73% of controls, p < 0.0001; females: 5.18% of controls, p = 0.03), Slc6a4 (males: 3.64% of controls, p < 0.0001; females: 0.88% of controls, p < 0.0001), and Tph1 (males: 1.01% of controls, p < 0.0001; females: 3.48% of controls, p < 0.0001). In male KOs only, there was decreased Htr2a (43.35% of controls, p = 0.02), while in female KOs there was increased Maoa (290.8% of controls, p = 0.008).
Finally, we measured expression of serotonin-related genes in hindbrain (Fig. 3I, J) to determine specificity of serotonin system changes. Of Htr1a, Htr2a, and Maoa, which were changed in the other brain regions in a sex-specific manner, only Htr1a was down-regulated in both male (23.51%, p < 0.0001) and female (23.44%, p = 0.0005) KO hindbrain. Htr2a was modestly down-regulated (48.89%, p = 0.03) in male KOs only.
Broadly, changes across brain regions in the Rgs2 KO mouse suggest sex-specific impacts on serotonin, redox, and angiogenic genes across the brain (Fig. 3K). Pan-suppression of serotonin systems in male cortex was contrasted by up-regulation of select targets (e.g., Htr2a, Maoa) in females, which may be compensatory. Angiogenic and redox-related gene expression was also disrupted, with particularly pronounced up-regulation in PVN, where GPCR-related signaling (e.g., AVP, OXT) is prominent.
Behavior and cerebrovasculature changes are associated with brain serotonin and angiogenesis-related gene expression in a sex- and genotype-specific manner in the Rgs2 KO mouse
To interrogate molecular pathways in Rgs2-dispruted endophenotypes, we tested correlations between gross somatomotor cortex output (locomotor behavior) and expression of key serotonin and angiogenesis-related genes in the brain: Ido, Tgfβ, Slc6a4, Angpt. These genes regulate immune/cell stress (Tgfβ), serotonin signaling (Slc6a4), and angiogenic mechanisms (Angpt). Tgfβr2 and Angpt are differentially expressed in placenta with reduced Rgs2, and Slc6a4 (encodes SERT) [33] is a critical regulator of serotonergic neurotransmission, which is altered with variation in RGS2 [36, 43, 70, 71]. Vascular density in the cortex was significantly and positively correlated with depressive behavior (tail suspension test) across all animals, regardless of genotype (linear regression: r(9) = 0.67, p = 0.03).
IDO is a rate-limiting antioxidant enzyme in the kynurenine pathway, which, when activated, depletes tryptophan to produce kynurenine and downstream metabolites. IDO is activated by immune and cellular stress mechanisms; activated IDO depletes tryptophan available for serotonin synthesis and leads to depression-like phenotypes [72–75]. Given this central role for IDO in tryptophan/serotonin metabolism and its response to cellular stress, we tested whether Ido expression was correlated with vascular deficits in Rgs2 KO versus WT control brain (Fig. 4A, B). Ido was positively correlated with vascular density in KO (linear regression: r[10] = 0.70, p = 0.02) but not WT brain (r[11] = 0.08, p = 0.80), suggesting a protective role for Ido expression in preventing angiogenic deficits.
Fig. 4. Vascular density and locomotor behavior are respectively related to expression of serotonin and angiogenesis-related genes in the brain in a sex- and genotype-specific manner.
A, B In Rgs2 knock outs (KOs) but not wild types (WTs), vascular density was significantly and positively correlated with cortex Ido expression by qPCR. C, D Total distance traveled on the open field was inversely correlated with cortical Tgfβ expression in WT but not KO animals. E, F Vascular density was significantly, positively correlated with cortical Slc6a4 (encodes the serotonin transporter, SERT) expression in females but not males, inclusive of both genotypes. G, H Locomotor behavior (total distance traveled on the open field) was inversely correlated with cortical Angpt expression in WT but not KO animals. Solid lines indicate line of best fit, dashed lines indicate 95% confidence interval. Goodness of fit reported by r2 value on each panel. All associations tested by simple linear regression; P values reported on each panel, with P ≤ 0.05 considered significant.
Next, we tested whether a cell stress/immune response in cortex might be related to cortically-mediated locomotor behavior in Rgs2 KO animals (Fig. 4C, D). Locomotor behavior is a gross output of the somatomotor cortex and therefore may reveal broad, cortical function deficits. Expression of Tgfβ, which encodes a pleiotropic cytokine with a wide variety of immune regulatory and cytostatic functions, was inversely correlated with locomotor behavior on the open field test in WT (r[11] = −0.74, p = 0.006) but not KO (r[10] = −0.18, p = 0.59) animals.
We next tested whether serotonin signaling might also be related to cerebrovascular density in a sex-specific manner (Fig. 4E, F). We found a positive, significant correlation between cerebrovascular density and cortical Slc6a4 in females (r[10] = 0.75, p = 0.008) but not in males (r[11] = −0.43, p = 0.17), suggestive of a female-specific protective role for SERT in cerebrovascular health.
Finally, we tested the role of angiogenic mechanisms in regulation of cortical function, as measured by locomotor output, in Rgs2 KO animals (Fig. 4G, H). In WT (r[11] = −0.73, p = 0.007) but not KO (r[10] = −0.30, p = 0.37) mice, cortical Angpt was inversely correlated with total distance traveled (Fig. 4G, H).
In separate cohorts, we found no disruptions in blood pressure by tail-cuff plethysmography (Fig. S1A–C), circulating 5-HT (Fig. S1D), or blood-brain barrier permeability in females only. We also measured cellular stress/redox-, fibrosis-, and angiogenesis-related gene expression in aortas of WT and KO animals (N = 3/sex/condition) (Fig. S1E, F): Angpt and Nox2 were down-regulated and Nox4 was up-regulated in female KOs. In male KOs, only fibrosis-related Mmp9 was down-regulated. For additional details, see Supplementary Results.
Serotonin synaptic transmission is altered and sensitivity to sertraline increased in female Rgs2 KO mice
Next, to determine whether deletion of Rgs2 alters serotonin synaptic transmission, we performed whole-cell electrophysiological recordings from dorsal raphe serotonin neurons in acute brain slices.
In the dorsal raphe, 5-HT release produces 5-HT1A receptor-mediated inhibitory postsynaptic currents (5-HT1A-IPSC) via activation of G protein-coupled inwardly rectifying potassium (GIRK) channels [76]. 5-HT release was evoked once every 60 s by a train of electrical stimuli (5 pulses, 0.5 ms, 60 Hz) delivered to the brain slice via a monopolar stimulating electrode. 5-HT1A-IPSCs were isolated by the presence of GluN, GluA/GluK, GABAA, and α1-adrenergic receptor blockers in the external solution (Fig. 5A). In control conditions using brain slices from female mice, there were no differences in the amplitude (WT: 89.0 ± 19.0 pA, n = 21; KO: 77.3 ± 13.1 pA, n = 14; p = 0.96) and time-to-peak (WT: 390.7 ± 23.3 ms, n = 20; KO: 375.5 ± 21.1 ms, n = 14; p = 0.82) of the 5-HT1A-IPSC between WT and Rgs2 KO neurons. However, there was a significant difference in the rate of decay (τ-decay) of the 5-HT1A-IPSC, such that the 5-HT1A-IPSC was faster in KO neurons (442.3 ± 36.9 ms, n = 14) when compared with WT neurons (533.7 ± 32.0 ms, n = 20, p = 0.047, Fig. 5B). Parallel studies done using brain slices from males revealed no differences in the 5-HT1A-IPSC between WT and Rgs2 KO (see Supplementary Results, Fig. S2).
Fig. 5. Sertraline augments serotonin synaptic transmission to a greater extent in female Rgs2 KO serotonin neurons.

A Representative traces of whole-cell voltage-clamp recordings of the 5-HT1A-IPSC in control conditions and after acute application of sertraline (sert., 300 nM, the presence of 5-HT1B receptor antagonist SB-216641) in WT and Rgs2 KO dorsal raphe serotonin neurons from female mice. B Plot of the rate of decay of the 5-HT1A-IPSC in control conditions in WT and Rgs2 KO serotonin neurons from female mice. C-E) Sertraline had a greater effect in Rgs2 KO neurons when compared with WT, increasing the C amplitude and D time-to-peak (ttp) of the 5-HT1A-IPSC. Sertraline substantially prolonged the E) rate of decay of the 5-HT1A-IPSC, but to a similar extent between WT and Rgs2 KO neurons from female mice. B–E statistical significance determined by two-tailed Mann-Whitney tests. Data are displayed as representative traces or in scatter plots and bar graphs (mean ± SEM), where individual cells are represented as points. F Overall model describing mechanism by which Rgs2 may interact with vascular dysfunction and cellular stress to increase psycho-obstetric risk. Environmental (e.g., stress [82], adverse childhood experiences and abuse [83]), genetic (e.g., Rgs2 [29, 33, 43], HTR mutations [15, 19]), and biologic (e.g., hypertension, obesity [84, 85]) risk factors interact to interrupt Rgs2-mediated serotonin signaling pathways. These disruptions in turn increase cellular stress [78] and downstream redox and inflammatory factor production [79, 80], thereby impairing angiogenic processes and vascular health, leading to increased risk for depression via cerebrovascular dysfunction [112] and increased risk for preeclampsia via placental and peripheral vascular dysfunction [84]. Made using BioRender.
The amplitude and time course of the 5-HT1A-IPSC in the dorsal raphe is limited by efficient clearance of extracellular serotonin by reuptake via SERT [77]. In WT and Rgs2 KO neurons from female mice, application of sertraline (300 nM) in the presence of 5-HT1B and α2-adrenergic receptor antagonists (SB-216641:1 μM, [77] and idazoxan: 1 µM), increased the amplitude and slowed the time-to-peak of the 5-HT1A-IPSC (Fig. 5A, C). However, the augmentation of the 5-HT1A-IPSC amplitude by sertraline was significantly greater in Rgs2 KO neurons (~160%) when compared with WT (~125%, p = 0.009, Fig. 5A, C). In addition, sertraline had a greater effect on the time-to-peak of the 5-HT1A-IPSC in KO neurons than WT (p = 0.03, Fig. 5A, D). Sertraline slowed the rate of decay dramatically, prolonging the 5-HT1A-IPSC by seconds in both WT and KO neurons (p = 0.46, Fig. 5A, E). In WT and Rgs2 KO neurons from male mice, sertraline had similar effects on the amplitude, time-to-peak, and rate of decay of the 5-HT1A-IPSC (see Supplementary Results and Fig. S2). The data revealed that increased sensitivity to sertraline was a female-specific consequence of the loss of Rgs2 (two-way ANOVA interaction: F[1,29] = 4.88, p = 0.035; Sidak’s multiple comparison test WT vs. KO: male: p = 0.09; female: p = 0.023; see Supplementary Results). These data suggest altered serotonin 5-HT1A receptor-dependent synaptic transmission between dorsal raphe nucleus serotonin neurons in female Rgs2 KO animals and increased sensitivity to sertraline. We propose that multiple risk factors converge on Rgs2-serotonin signaling mechanisms to alter neurobiology (Fig. 5F).
Discussion
In this study, we sought to determine whether vascular, function, and electrophysiologic features of brain health are disrupted with loss of Rgs2. Our prior work demonstrates that decreased placental Rgs2 is sufficient to drive obstetric risk phenotypes in a mouse model via vascular mechanisms [29, 33]. Here, we extended this obstetric modeling work to test whether RGS2-mediated vascular pathology in the brain is also implicated and associated with changes in GPCR signaling more broadly (e.g., serotonergic systems) and with cell stress and redox dysfunction. Overall, our findings demonstrate that altered serotonin signaling occurs in the Rgs2 KO [78–80], as does vascular and anti-angiogenic dysfunction in the brain and periphery. These results may suggest a central mechanism underlying both obstetric and psychiatric risk (Fig. 5F).
These studies were based on prior work linking Rgs2 to neurobiological and behavioral phenotypes in humans and in preclinical models [36, 81]. A variety of predisposing risk factors including environmental (e.g., stress [82], childhood abuse [83]), genetic (e.g., RGS2 [29, 33, 43], HTR mutations [15, 19]), and biologic (e.g., hypertension, obesity [84, 85]) factors interact to interrupt RGS2-mediated serotonin signaling pathways. Genetic mutations spanning RGS2 are associated with childhood behavioral inhibition, social anxiety, agoraphobia, PTSD, and limbic hyperactivation, as well as with anxiety-like phenotypes in mice [28, 36–40]. The RGS2 SNP rs4606 is associated with a doubling of risk for generalized anxiety disorder [86]. C alleles in the rs4606 RGS2 SNP are each associated with 5.59-fold increase in risk for suicidal ideation in a cohort of individuals exposed to natural disaster stress [42]. Postmortem work finds reduced RGS2 in the brains of female (but not male) individuals with depression [41].
In mice, we previously reported that diminished Rgs2 in placenta is sufficient to cause vascular, obstetric phenotypes [33]. RGS2 promotes vascular relaxation and adaptation by selectively inhibiting Gq signaling [87] and endothelial G(i/o) activity [88]. Despite significant interest in RGS2 function in the peripheral vasculature [34, 35, 89], no prior studies have evaluated its role in cerebrovasculature. Here, we found significant decreases in cortical vascular density and vessel length in Rgs2 KO mice despite no gross abnormalities in grey or white matter or in neuronal, glial, or total cell density. These gross neuroanatomical and cell density findings confirm one prior report in this model [45]. Redox mechanisms may also play a role in vascular vulnerability in the periphery, as our results in aorta suggest, though future studies will need to directly assess redox processes and reactive oxygen species production. Unlike RGS5, RGS2 effects on cerebrovasculature and behavior appeared independent of hypertension [90].
In addition to cerebrovasculature, we also examined serotonin systems functioning in this risk model. Prior clinical and pre-clinical work implicates RGS2 in serotonin systems functioning [29, 36, 39, 70]. We found female-specific vulnerabilities in serotonin signaling and metabolism, as well as broad disruptions to expression of redox-related, inflammatory, and angiogenesis/vascular function genes in Rgs2 KOs. Finally, we confirmed that molecular disruptions in Rgs2 KO result in female-specific alterations to serotonin synaptic transmission between dorsal raphe serotonin neurons and increased sensitivity to the SSRI sertraline.
Prior work reveals behavioral abnormalities in the Rgs2 KO mouse similar to those we report here, including anxiety and depressive-like behaviors [27, 41, 43–45, 71, 91]. We find aspects of anxiety (e.g., increased latency to explore arms of the Y maze in males, decreased EMP open arm time in both males and females), depressive-like behavior (decreased struggle time on the TST), and increased hedonic behavior (sucrose preference) in KOs. Prior work finds that sociability may be particularly sensitive to stress in this model and may depend on RGS2 in the nucleus accumbens [41]. Our use of the three-chamber social task, which is limited in its ethological validity and ability to detect animal emotional cognition [68], may have limited our ability to detect social differences here. Future studies should utilize more reciprocal models (e.g., free-moving interaction) or refined approaches (e.g., social microstructure assessment).
Few studies have assessed sex-specificity of Rgs2 KO behavior, which we do not find is particularly pronounced here. However, those that have report learning [44], addiction and reward-seeking [81, 92, 93], but generally not mood-related phenotypes as we assess here. Further, we found that cortical Slc6a4 was correlated with vascular density in female but not male animals, suggesting a sex-specific role for serotonin dysregulation in this model. Future studies should evaluate the role of the serotonin transporter, either directly or by SSRI modulation, in the Rgs2 KO model to determine whether SERT underlies mood-related phenotypes with and without pregnancy.
Molecular profiling of the brain by qPCR in Rgs2 KOs revealed some increased serotonin-related gene expression in female cortex (e.g., Htr2a, Maoa) but decreases in males; increased redox- and angiogenesis-related gene expression in paraventricular nucleus of the hypothalamus (e.g., Sod1, Gpx1, Sod1, Hif1α); and sex-specific serotonin system dysregulation across midbrain and hindbrain. For example, Hif1α, Mmp9, and Fgf2 are known positive regulators of angiogenesis [94], and were all down-regulated in male cortex, while only Hif1α was down-regulated in females. Prior work finds that Mmp9 expression is influenced by estrogen, which is protective against matrix degradation and vascular disease in some settings [94]. Sod1 and Gpx1 were both strongly up-regulated in paraventricular nucleus of the hypothalamus (PVN), suggesting increased oxidative stress resistance [95, 96]. Sod1 expression is increased under oxidative conditions in the brain [97, 98].
The PVN was selected for additional molecular analyses given its functional dependence on RGS2 [99], regulation of affective and mood-related phenotypes [100, 101], reciprocal connections with dorsal raphe and other monoamine systems [102–104], and high expression of vasopressin GPCRs [99, 103], which are disrupted in both preeclampsia and depression [105–108]. In contrast to the cortex, angiogenesis-related Hif1α was strongly up-regulated in both male and female KO PVN. A subset of GPCR signaling genes were down-regulated in both male and female KO PVN: Avpr1a, Ido, Slc6a4, and Tph1. Only in female KO PVN were serotonin signaling targets Htr1a and Maoa up-regulated. This echoes prior reports that serotonin systems are particularly sensitive to perturbation in females [109, 110]. Interestingly, however, Rgs2 deletion in the PVN causes PVN neuronal death and hyper-consumptive behavior in males and females, echoing the increased sucrose preference we report across sexes here [99]. PVN Rgs2 should be assessed in future studies to determine the role of RGS2 in these neurons and in their broader networks, including serotonin networks (PVN has reciprocal connections to the dorsal raphe).
Future studies should extend our results by examining neurotransmission and brain function in pregnancy, with and without Rgs2. Given its known role in pregnancy-specific stress responses and anxiety phenotypes [27], future studies should evaluate the interaction between Rgs2 genotype and pregnancy in terms of the phenotypes described here. Complementary overexpression studies may also reveal whether Rgs2 is sufficient to drive phenotypes in the brain, placenta, and elsewhere, or may be protective.
Given high rates of co-occurrence of psychiatric and obstetric disorders, it is important to identify conserved molecular mechanisms [48, 111]. Together with prior work, we reveal a protective role for Rgs2-serotonin signaling in vascular dysfunction underlying shared psycho-obstetric risk mechanisms. Overall, our findings indicate that loss of Rgs2 leads to behavioral abnormalities, altered serotonergic gene expression and SSRI response in the brain, and central and peripheral vascular dysfunction. Some of these effects are sexually dimorphic. Neurobiological and behavioral disruptions in this model appear to be related to dysregulated cell stress and angiogenesis, which are dysregulated in both anxiety/depression and in preeclampsia. Future work should determine whether pregnancy sets the stage for differential psychiatric risk in the setting of Rgs2-serotonin dysfunction. As conserved mechanisms such as this are examined, it becomes increasingly possible to develop targets for personalized therapies and cures.
Supplementary information
Author contributions
SBG: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; Drafting the work or revising it critically for important intellectual content; final approval of the version to be published; and agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. MKS: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work. AG: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work. BS: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; Drafting the work or revising it critically for important intellectual content; final approval of the version to be published; KW: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work. ML: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; Drafting the work or revising it critically for important intellectual content. Hannah Sullivan: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work. KC: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work. BB: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work. MKS: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work. YZ: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work. ED: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; and final approval of the version to be published. DAS: Drafting the work or revising it critically for important intellectual content; final approval of the version to be published; and agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. SCG: Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; Drafting the work or revising it critically for important intellectual content; final approval of the version to be published; and agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. MKS: Drafting the work or revising it critically for important intellectual content; final approval of the version to be published; and agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Funding
This work was supported by the NIH (5T32HL007121-45 to SBG; HD089940, HD000849, RR024980, 3UL1TR002537, P50HD10355601A1 to MKS; T32 HL007344 to BMS), the American Heart Association (AHA) (18SCG34350001 and 19IPLOI34760288 to MKS; 22POST30908921 to SBG), a startup award from the University of Iowa Carver College of Medicine (SCG), and the Carver College of Medicine and Iowa Neuroscience Institute Carver Trust Early-Stage Investigator award (to SCG).
Competing interests
MKS is a member of the Medical Advisory Board for Comanche Pharmaceuticals and EndPreeclampsia, LLC. DAS is a member of the Medical Advisory Board for EndPreeclampsia, LLC. DAS and MKS hold patents related to the prediction and treatment of preeclampsia: US 293 #9,937,182 (April 10, 2018), EU #2,954,324, and PCT/US2018/027152. All other authors report no competing interests.
Footnotes
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Supplementary information
The online version contains supplementary material available at 10.1038/s41386-023-01749-3.
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