Early transcriptome responses of the bovine midcycle corpus luteum to prostaglandin F2α includes cytokine signaling

Unraveling the role of lipid droplets and perilipin 2 in bovine luteal cells

Steroidogenic tissues contain cytosolic lipid droplets that are important for steroidogenesis. Perilipin 2 (PLIN2), a structural coat protein located on the surface of lipid droplets in mammalian cells, plays a crucial role in regulating lipid droplet formation and contributing to various cellular processes such as lipid storage and energy homeostasis. Herein, we examine the role that PLIN2 plays in regulating progesterone synthesis in the bovine corpus luteum. Utilizing gene array databases and Western blotting, we have delineated the expression pattern of PLIN2 throughout the follicular to luteal transition. Our findings reveal the presence of PLIN2 in both ovarian follicular and steroidogenic luteal cells, demonstrating an increase in its levels as follicular cells transition into the luteal phase. Moreover, the depletion of PLIN2 via siRNA enhanced progesterone production in small luteal cells, whereas adenovirus-mediated overexpression of both PLIN2 and Perilipin 3 (PLIN3) induced an increase in cytosolic lipid droplet accumulation and decreased hormone-induced progesterone synthesis in these cells. Lastly, in vivo administration of the luteolytic hormone prostaglandin F2α resulted in an upregulation of PLIN2 mRNA and protein expression, accompanied by a decline in serum progesterone. Our findings highlight the pivotal role of PLIN2 in regulating progesterone synthesis in the bovine corpus luteum, as supported by its dynamic expression pattern during the follicular to luteal transition and its responsiveness to luteotropic and luteolytic hormones. We suggest PLIN2 as a potential therapeutic target for modulating luteal function.

Mechanisms of angioregression of the corpus luteum

The corpus luteum is a transient ovarian endocrine gland that produces the progesterone necessary for the establishment and maintenance of pregnancy. The formation and function of this gland involves angiogenesis, establishing the tissue with a robust blood flow and vast microvasculature required to support production of progesterone. Every steroidogenic cell within the corpus luteum is in direct contact with a capillary, and disruption of angiogenesis impairs luteal development and function. At the end of a reproductive cycle, the corpus luteum ceases progesterone production and undergoes rapid structural regression into a nonfunctional corpus albicans in a process initiated and exacerbated by the luteolysin prostaglandin F2α (PGF2α). Structural regression is accompanied by complete regression of the luteal microvasculature in which endothelial cells die and are sloughed off into capillaries and lymphatic vessels. During luteal regression, changes in nitric oxide transiently increase blood flow, followed by a reduction in blood flow and progesterone secretion. Early luteal regression is marked by an increased production of cytokines and chemokines and influx of immune cells. Microvascular endothelial cells are sensitive to released factors during luteolysis, including thrombospondin, endothelin, and cytokines like tumor necrosis factor alpha (TNF) and transforming growth factor β 1 (TGFB1). Although PGF2α is known to be a vasoconstrictor, endothelial cells do not express receptors for PGF2α, therefore it is believed that the angioregression occurring during luteolysis is mediated by factors downstream of PGF2α signaling. Yet, the exact mechanisms responsible for angioregression in the corpus luteum remain unknown. This review describes the current knowledge on angioregression of the corpus luteum and the roles of vasoactive factors released during luteolysis on luteal vasculature and endothelial cells of the microvasculature.

Basic fibroblast growth factor induces proliferation and collagen production by fibroblasts derived from the bovine corpus luteum†

Cyclic regression of the ovarian corpus luteum, the endocrine gland responsible for progesterone production, involves rapid matrix remodeling. Despite fibroblasts in other systems being known for producing and maintaining extracellular matrix, little is known about fibroblasts in the functional or regressing corpus luteum. Vast transcriptomic changes occur in the regressing corpus luteum, among which are reduced levels of vascular endothelial growth factor A (VEGFA) and increased expression of fibroblast growth factor 2 (FGF2) after 4 and 12 h of induced regression, when progesterone is declining and the microvasculature is destabilizing. We hypothesized that FGF2 activates luteal fibroblasts. Analysis of transcriptomic changes during induced luteal regression revealed elevations in markers of fibroblast activation and fibrosis, including fibroblast activation protein (FAP), serpin family E member 1 (SERPINE1), and secreted phosphoprotein 1 (SPP1). To test our hypothesis, we treated bovine luteal fibroblasts with FGF2 to measure downstream signaling, type 1 collagen production, and proliferation. We observed rapid and robust phosphorylation of various signaling pathways involved in proliferation, such as ERK, AKT, and STAT1. From our longer-term treatments, we determined that FGF2 has a concentration-dependent collagen-inducing effect, and that FGF2 acts as a mitogen for luteal fibroblasts. FGF2-induced proliferation was greatly blunted by inhibition of AKT or STAT1 signaling. Our results suggest that luteal fibroblasts are responsive to factors that are released by the regressing bovine corpus luteum, an insight into the contribution of fibroblasts to the microenvironment in the regressing corpus luteum.

Prostaglandin F2α regulates mitochondrial dynamics and mitophagy in the bovine corpus luteum

Prostaglandins are arachidonic acid-derived lipid mediators involved in numerous physiological and pathological processes. PGF2α analogues are therapeutically used for regulating mammalian reproductive cycles and blood pressure, inducing term labor, and treating ocular disorders. PGF2α exerts effects via activation of calcium and PKC signaling, however, little is known about the cellular events imposed by PGF2α signaling. Here, we explored the early effects of PGF2α on mitochondrial dynamics and mitophagy in the bovine corpus luteum employing relevant and well characterized in vivo and in vitro approaches. We identified PKC/ERK and AMPK as critical protein kinases essential for activation of mitochondrial fission proteins, DRP1 and MFF. Furthermore, we report that PGF2α elicits increased intracellular reactive oxygen species and promotes receptor-mediated activation of PINK-Parkin mitophagy. These findings place the mitochondrium as a novel target in response to luteolytic mediator, PGF2α. Understanding intracellular processes occurring during early luteolysis may serve as a target for improving fertility.

Dynamics of inflammatory cytokine expression in bovine endometrial cells exposed to cow blood plasma small extracellular vesicles (sEV) may reflect high fertility

Aberrant inflammation in the endometrium impairs reproduction and leads to poor fertility. Small extracellular vesicles (sEV) are nanoparticles 30-200 nm in-size and contain transferable bioactive molecules that reflect the parent cell. Holstein-Friesian dairy cows with divergent genetic merit, high- (n = 10) and low-fertile (n = 10), were identified based on fertility breeding value (FBV), cow ovulation synchronization and postpartum anovulatory intervals (PPAI). In this study, we evaluated the effects of sEVs enriched from plasma of high-fertile (HF-EXO) and low-fertile (LF-EXO) dairy cows on inflammatory mediator expression by bovine endometrial epithelial (bEEL) and stromal (bCSC) cells. Exposure to HF-EXO in bCSC and bEEL cells yielded lower expression of PTGS1 and PTGS2 compared to the control. In bCSC cells exposed to HF-EXO, pro-inflammatory cytokine IL1-α was downregulated compared to the untreated control, IL-12α and IL-8 were downregulated compared to the LF-EXO treatment. Our findings demonstrate that sEVs interact with both endometrial epithelial and stromal cells to initiate differential gene expression, specifically genes relate to inflammation. Therefore, even subtle changes on the inflammatory gene cascade in the endometrium via sEV may affect reproductive performance and/or outcomes. Further, sEV from high-fertile animals acts in a unique direction to deactivate prostaglandin synthases in both bCSC and bEEL cells and deactivate pro-inflammatory cytokines in the endometrial stroma. The results suggest that circulating sEV may serve as a potential biomarker of fertility.

Dual role of NR4A1 in porcine ovarian granulosa cell differentiation and granulosa-lutein cell regression in vitro

This study aimed to investigate the role of NR4A1 in forskolin (FSK)-induced granulosa cell (GC) differentiation and PGF_2α-induced granulosa-lutein cell (GLC) regression. For experiment 1, primary porcine GCs were pre-cultured for 6 d before induced-differentiation by FSK with or without siNR4A1, and changes in GC proliferation, lipid droplets (LDs), and P₄ level were detected. For experiment 2, the GLC model was established by FSK as in experiment 1, and then PGF_2α was utilized to induce GLC regression with or without siNR4A1, changes in P₄ secretion, apoptosis proteins, and associated signaling pathway members were detected. Results showed that in experiment 1, FSK up-regulated NR4A1 expression during GC differentiation and decreased GC proliferation activity, which was reversed by siNR4A1. siNR4A1 inhibited the FSK-induced decreases in Cyclin B1/D1 and CDK1/2 mRNA abundances, and increases in P21/P27 mRNA abundances, and FSK-induced LD accumulation. FSK up-regulated P₄ secretion and StAR, CYP11A1 and HSD3B expression, decreased CYP19A1 expression, which were reversed by siNR4A1 except for StAR expression. In experiment 2, PGF_2α induced NR4A1 expression and reduced GLC viability, which were reversed by siNR4A1. Compared with PGF_2α group, the levels of P₄ secretion and StAR expression were higher in PGF_2α+siNR4A1 group, while CYP11A1 and HSD3B expressions held at low levels. siNR4A1 inhibited PGF_2α-induced expression of apoptosis proteins (caspase3, Bax, Fas, TNFa), ATF3, and phosphorylated MAPKs (ERK1/2, P38, JNK). In summary, NR4A1 is involved in regulating porcine GC differentiation and GLC regression as well as the changes in cell proliferation, apoptosis, steroidogenesis, and MAPK pathways, which provide a theoretical basis for further understanding of the mechanism of porcine luteal formation and regression.

A single-cell atlas of the cycling murine ovary

The estrous cycle is regulated by rhythmic endocrine interactions of the nervous and reproductive systems, which coordinate the hormonal and ovulatory functions of the ovary. Folliculogenesis and follicle progression require the orchestrated response of a variety of cell types to allow the maturation of the follicle and its sequela, ovulation, corpus luteum formation, and ovulatory wound repair. Little is known about the cell state dynamics of the ovary during the estrous cycle and the paracrine factors that help coordinate this process. Herein, we used single-cell RNA sequencing to evaluate the transcriptome of >34,000 cells of the adult mouse ovary and describe the transcriptional changes that occur across the normal estrous cycle and other reproductive states to build a comprehensive dynamic atlas of murine ovarian cell types and states.

History, insights, and future perspectives on studies into luteal function in cattle

The corpus luteum (CL) forms following ovulation from the remnant of the Graafian follicle. This transient tissue produces critical hormones to maintain pregnancy, including the steroid progesterone. In cattle and other ruminants, the presence of an embryo determines if the lifespan of the CL will be prolonged to ensure successful implantation and gestation, or if the tissue will undergo destruction in the process known as luteolysis. Infertility and subfertility in dairy and beef cattle results in substantial economic loss to producers each year. In addition, this has the potential to exacerbate climate change because more animals are needed to produce high-quality protein to feed the growing world population. Successful pregnancies require coordinated regulation of uterine and ovarian function by the developing embryo. These processes are often collectively termed "maternal recognition of pregnancy." Research into the formation, function, and destruction of the bovine CL by the Northeast Multistate Project, one of the oldest continuously funded Hatch projects by the USDA, has produced a large body of evidence increasing our knowledge of the contribution of ovarian processes to fertility in ruminants. This review presents some of the seminal research into the regulation of the ruminant CL, as well as identifying mechanisms that remain to be completely validated in the bovine CL. This review also contains a broad discussion of the roles of prostaglandins, immune cells, as well as mechanisms contributing to steroidogenesis in the ruminant CL. A triadic model of luteolysis is discussed wherein the interactions among immune cells, endothelial cells, and luteal cells dictate the ability of the ruminant CL to respond to a luteolytic stimulus, along with other novel hypotheses for future research.

Insights from two independent transcriptomic studies of the bovine corpus luteum during pregnancy

Several recent studies have used transcriptomics to investigate luteal changes during the maternal recognition of the pregnancy period in ruminants. Although these studies have contributed to our understanding of luteal function during early pregnancy, few attempts have been made to integrate information across these studies and distinguish key luteal transcripts or functions that are repeatably identified across multiple studies. Therefore, in this study, two independent studies of the luteal transcriptome during early pregnancy were combined and compared. In the first study, corpora lutea (CL) from day 20 of pregnancy were compared with CL collected on day 14 of pregnancy, prior to embryonic signaling. The cattle were nonlactating. In the second study, CL from day 20 of pregnancy were compared with CL collected from day 20 cyclic cattle that had been confirmed as not yet undergoing luteal regression. These were lactating cattle. Three methods were used to compare these two datasets, to identify key luteal regulators. In the first method, all transcripts with Benjamini-Hochberg-adjusted P-value (Q value) < 0.05 in both datasets were considered. This yielded 22 transcripts, including several classical interferon-stimulated genes, as well as regulators of transforming growth factor-beta (TGFB) and latent TGFB-binding proteins (LTBP)1 and 2. In the second, less conservative method, all transcripts with P < 0.01 and changed in the same direction in both datasets were considered. This yielded an additional 20 transcripts that were not identified in the first analysis, for a total of 42 common transcripts. These transcripts were regulators of functions such as inflammatory balance and matrix remodeling. In the third method, transcripts with Q < 0.10 were subject to pathway analysis, and common pathways were identified. Retinoic acid signaling and classical interferon signaling pathways were identified with this method. Finally, regulation by interferon tau (IFNT) was investigated. Among the 42 transcripts identified, 32 were regulated by IFNT in cultured luteal cells (Q < 0.05). Among those not regulated by IFNT were LTBP1 and 2, which are TGFB-binding proteins. In summary, common transcripts from two studies of the luteal transcriptome during early pregnancy were combined and shared changes were identified. This not only generated a list of potential key luteal regulators, which were mostly IFNT regulated, but also included transcripts not regulated by IFNT, including LTBP1 and 2.

Expression patterns of chemokine (C-C motif) ligand 2, prostaglandin F2A receptor and immediate early genes at mRNA level in the bovine corpus luteum after intrauterine treatment with a low dose of prostaglandin F2A

The present study evaluated expression patterns of chemokine (C-C motif) ligand 2 gene/Monocyte chemoattractant protein-1 gene (CCL2/MCP-1), prostaglandin F2 alpha receptor gene (PTGFR) and immediate early genes including nuclear receptor subfamily 4, group A, member 1 (NR4A1), early growth response 1 (EGR1) and FBJ murine osteosarcoma viral oncogene homolog (FOS) in cells of the bovine corpus luteum after intrauterine infusion of a low dose of prostaglandin F2α (PGF2A) aimed at enhancing our understanding of the mechanisms of luteolysis. Holstein dairy cows were superovulated (>6 corpora lutea [CL]) and on day 9 of the estrous cycle were infused with a low dose of PGF2A (0.5 mg PGF2A in 0.25 ml phosphate buffered saline) into the greater curvature of the uterine horn ipsilateral to the CL. Ultrasound-guided biopsy samples of different CL were collected at 0 min, 15 min, 30 min, 1h, 2h and 6h after PGF2A infusion. Expression profiles and localization of mRNA for PTGFR, CCL2/MCP-1, and immediate early genes (NR4A1, EGR1 and FOS), were investigated by using qPCR and in situ hybridization. The concentrations of early response genes including FOS, NR4A1, and EGR1 exhibited the greatest increase at 30 min after PGF2A, compared to other time points. Expression profile of CCL2 mRNA increased gradually after intrauterine infusion of PGF2A with maximal up-regulation for CCL2 at 6h. Abundance of PTGFR mRNA only increased at 15 min and significantly decreased at 6h, compared to 0 min. Cellular localizations of all studied genes except CCL2 (primarily localized to apparent immune cells) were predominantly visualized in large luteal cells. Interestingly, early response genes demonstrated a changing profile in cellular localization with initial responses appearing to be in both large luteal cells and endothelial cells, although no staining for PTGFR mRNA was observed in endothelial cells. Later, sustained responses, were only observed in large luteal cells, although PTGFR mRNA was decreasing in large luteal cells over time after PGF2A. The involvement of the immune system was also highlighted by the immediate increases in CCL2 mRNA that became much greater over time as there was an apparent influx of CCL2-positive immune cells. Thus, the temporal and cell-specific localization patterns for the studied mRNA demonstrate the complex pathways that are responsible for initiation of luteolysis in the bovine CL.

Endometrial and luteal responses to a prostaglandin F2alpha pulse: A comparison between heifers and mares

In heifers and mares, multiple pulses of prostaglandin F2alpha (PGF) are generally associated with complete luteal regression. Although PGF pulses occur before and during luteolysis, little is known about the role of minor PGF pulses during preluteolysis on subsequent luteal and endometrial PGF production that may initiate luteolysis. Heifers (n = 7/group) and mares (n = 6/group) were treated with a single minor dose of PGF (3.0 and 0.5 mg, respectively) during mid-luteal phase (12 and 10 days postovulation in heifers and mares, respectively). After treatment, a transient decrease in progesterone (P4) concentrations occurred in heifers between Hours 0–2 but at Hour 4 P4 was not different from pre-treatment. In mares, P4 was unaltered between Hours 0 and 4. Concentrations of P4 decreased in both species by Hour 24 and complete luteolysis occurred in mares by Hour 48. Luteal and endometrial gene expression were evaluated 4 hours post-treatment. In heifers, luteal mRNA abundance of PGF receptor and PGF dehydrogenase were decreased while PTGS2, PGF transporter, and oxytocin receptor were increased. In the heifer endometrium, receptors for oxytocin, P4, and estradiol were upregulated. In mares, luteal expression of PGF receptor was decreased while PGF transporter and oxytocin receptor were increased. The decrease in P4 between Hours 4 and 24 and changes in gene expression were consistent with upregulation of endogenous synthesis of PGF. The hypotheses were supported that a single minor PGF treatment upregulates endogenous machinery for PGF synthesis in heifers and mares stimulating endogenous PGF synthesis through distinct regulatory mechanisms in heifers and mares.

Interferon-Tau regulates a plethora of functions in the corpus luteum

The corpus luteum (CL) plays a vital role in regulating the reproductive cycle, fertility, and in maintaining pregnancy. Interferon-tau (IFNT) is the maternal recognition of a pregnancy signal in domestic ruminants; its uterine, paracrine actions, which extend the CL lifespan, are widely established. However, considerable evidence also suggests a direct, endocrine role for IFNT. The purpose of this review is to highlight the importance of IFNT in CL maintenance, acting directly and in a cell-specific manner. A transcriptomic study revealed a distinct molecular profile of IFNT-exposed day 18, pregnant bovine CL, compared to the non-pregnant gland. A substantial fraction of the differentially expressed genes was downregulated, many of which are known to be elevated by prostaglandin F2A (PGF2A). In vitro, IFNT was found to mimic changes observed in the luteal transcriptome of early pregnancy. Key luteolytic genes such as endothelin-1 (EDN1), transforming growth factor-B1 (TGFB1), thrombospondins (THBSs) 1&2 and serpine-1 (SERPINE1) were downregulated in luteal endothelial cells. Luteal steroidogenic large cells (LGCs) were also found to be a target for the antilutelotytic actions of IFNT. IFNT-treated LGCs showed a significant reduction in the expression of the proapoptotic, antiangiogenic THBS1&2, as well as TGFBR1 and 2. Furthermore, IFNT was shown to be a potent survival factor for luteal cells in vivo and in vitro, activating diverse pathways to promote cell survival while suppressing cell death signals. Pentraxin 3 (PTX3), robustly upregulated by IFNT in various luteal cell types, mediated many of the prosurvival effects of IFNT in LGCs. A novel reciprocal inhibitory crosstalk between PTX3 and THBS1 lends further support to their respective survival and apoptotic actions in the CL. Even though IFNT did not directly regulate progesterone synthesis, it could maintain its concentrations, by increasing luteal cell survival and by supporting vascular stabilization. The direct effects of IFNT in the CL, enhancing cell survival and vasculature stabilization while curbing luteolytic activities, may constitute an important complementary branch leading to the extension of the luteal lifespan during early pregnancy.

Protein Kinase A and 5' AMP-Activated Protein Kinase Signaling Pathways Exert Opposite Effects on Induction of Autophagy in Luteal Cells

In the absence of pregnancy the ovarian corpus luteum undergoes regression, a process characterized by decreased production of progesterone and structural luteolysis involving apoptosis. Autophagy has been observed in the corpus luteum during luteal regression. Autophagy is a self-degradative process important for balancing sources of cellular energy at critical times in development and in response to nutrient stress, but it can also lead to apoptosis. Mechanistic target of rapamycin (MTOR) and 5′ AMP-activated protein kinase (AMPK), key players in autophagy, are known to inhibit or activate autophagy, respectively. Here, we analyzed the signaling pathways regulating the initiation of autophagy in bovine luteal cells. In vivo studies showed increased activating phosphorylation of AMPKα (Thr172) and elevated content of LC3B, a known marker of autophagy, in luteal tissue during PGF2α-induced luteolysis. In vitro, AMPK activators 1) stimulated phosphorylation of regulatory associated protein of MTOR (RPTOR) leading to decreased activity of MTOR, 2) increased phosphorylation of Unc-51-Like Kinase 1 (ULK1) and Beclin 1 (BECN1), at sites specific for AMPK and required for autophagy initiation, 3) increased levels of LC3B, and 4) enhanced colocalization of autophagosomes with lysosomes indicating elevated autophagy. In contrast, LH/PKA signaling in luteal cells 1) reduced activation of AMPKα and phosphorylation of RPTOR, 2) elevated MTOR activity, 3) stimulated phosphorylation of ULK1 at site required for ULK1 inactivation, and 4) inhibited autophagosome formation as reflected by reduced content of LC3B-II. Pretreatment with AICAR, a pharmacological activator of AMPK, inhibited LH-mediated effects on RPTOR, ULK1 and BECN1. Our results indicate that luteotrophic signaling via LH/PKA/MTOR inhibits, while luteolytic signaling via PGF2α/Ca²⁺/AMPK activates key signaling pathways involved in luteal cell autophagy.

Effect of natural pre-luteolytic prostaglandin F2α pulses on the bovine luteal transcriptome during spontaneous luteal regression

The pulsatile pattern of prostaglandin F2alpha (PGF) secretion during spontaneous luteolysis is well-documented, with multiple pulses of exogenous PGF necessary to induce regression using physiologic concentrations of PGF. However, during spontaneous regression, the earliest pulses of PGF are small and not associated with detectable changes in circulating progesterone (P4), bringing into question what, if any, role these early, subluteolytic PGF pulses have during physiologic regression. To investigate the effect of small PGF pulses, luteal biopsies were collected throughout natural luteolysis in conjunction with bihourly blood samples to determine circulating P4 and PGF metabolite to retrospectively assign biopsies to early and later regression. Whole transcriptome analysis was conducted on CL biopsies. Early PGF pulses altered the luteal transcriptome, inducing differential expression of 210 genes (Q < 0.05) during early regression, compared to 4615 differentially expressed genes during later regression. In early regression, few of these differentially expressed genes were directly associated with luteolysis, rather there were changes in local steroid and glutathione metabolism. Most (94%) differentially expressed genes from early regression were also differentially expressed during later regression, with 98% of these continuing to be altered in the same direction compared to CL at a similar stage of the cycle that had not yet been exposed to PGF. Thus, early, subluteolytic PGF pulses impact the luteal transcriptome, though not by altering steroidogenesis or causing direct inhibition of cellular function. Rather, small pulses alter pathways resulting in removal of cellular support systems, which may sensitize the CL to later pulses of PGF.

Downregulated luteolytic pathways in the transcriptome of early pregnancy bovine corpus luteum are mimicked by interferon-tau in vitro

Background

Maintenance of the corpus luteum (CL) beyond the time of luteolysis is essential for establishing pregnancy. Identifying the distinct features of early pregnancy CL remains unresolved, hence we analyzed here the transcriptome of CL on day 18 pregnant (P) and non-pregnant (NP) cows using RNA-Seq. CL of P cows expressed ISGs, verifying exposure to the pregnancy recognition signal, interferon-tau (IFNT), whereas the CL of NP cows had elevated luteal progesterone levels, implying that luteolysis had not yet commenced.

Results

The DEGs, IPA, and metascape canonical pathways, along with GSEA analysis, differed markedly in the CL of P cows from those of NP cows, at the same day of the cycle. Both metascape and IPA identified similar significantly enriched pathways such as interferon alpha/beta, sonic hedgehog pathway, TNFA, EDN1, TGFB1, and PDGF. However, type-1 interferon and sonic hedgehog pathways were positively enriched whereas most of the enriched pathways were downregulated in the P compared to NP samples. Thirty-four % of these pathways are known to be elevated by PGF2A during luteolysis. Notably, selective DEGs in luteinized granulosa cells were modulated by IFNT in vitro in a similar manner to their regulation in the CL of P cows.

Conclusion

This study unraveled the unique transcriptomic signature of the IFNT-exposed, early pregnancy CL, highlighting the abundance of downregulated pathways known to be otherwise induced during luteolysis. These and IFNT-regulated in vitro pregnancy-specific DEGs suggest that IFNT contributes to the characteristics and maintenance of early pregnancy CL.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07747-3.

Cloprostenol, a synthetic analog of prostaglandin F2α induces functional regression in cultured luteal cells of felids†

In the present study, we investigated the effect of the synthetic analog of prostaglandin F2α (PGF2α)-cloprostenol-on cultured steroidogenic luteal cells of selected felid species over a 2-day culture period. The changes induced by cloprostenol were measured based on progesterone concentration and mRNA expression analysis of selected genes. Cloprostenol significantly reduced concentration of progesterone in cell culture medium of small luteal cells isolated from domestic cat corpora lutea (CL) at the development/maintenance stage (P < 0.05), but did not influence progesterone production in cultured cells from the regression stage. A decrease or complete silencing of progesterone production was also measured in cultured luteal cells of African lion (formation stage) and Javan leopard (development/maintenance stage). Gene-expression analysis by real-time PCR revealed that treatment with cloprostenol did not have an influence on expression of selected genes coding for enzymes of steroidogenesis (StAR, HSD3B, CYP11A1) or prostaglandin synthesis (PTGS2, PGES), nor did it effect hormone receptors (AR, ESR1, PGR, PTGER2), an anti-oxidative enzyme (SOD1) or factors of cell apoptosis (FAS, CASP3, TNFRSF1B, BCL2) over the studied period. Significant changes were measured only for expressions of luteinizing hormone (P < 0.05), prolactin (P < 0.05) and PGF2α receptors (P < 0.005) (LHCGR, PRLR, and PTGFR). The obtained results confirm that PGF2α/cloprostenol is a luteolytic agent in CL of felids and its impact on progesterone production depends on the developmental stage of the CL. Cloprostenol short-term treatment on luteal cells was associated only with functional but not structural changes related to luteal regression.

Deciphering the functional role of EGR1 in Prostaglandin F2 alpha induced luteal regression applying CRISPR in corpus luteum of buffalo

Background

PGF2α is essential for the induction of the corpus luteum regression which in turn reduces progesterone production. Early growth response (EGR) proteins are Cys2-His2-type zinc-finger transcription factor that are strongly linked to cellular proliferation, survival and apoptosis. Rapid elevation of EGR1 was observed after luteolytic dose of PGF2α. EGR1 is involved in the transactivation of many genes, including TGFβ1, which plays an important role during luteal regression.

Methods

The current study was conducted in buffalo luteal cells with the aim to better understand the role of EGR1 in transactivation of TGFβ1 during PGF2α induced luteal regression. Luteal cells from mid stage corpus luteum of buffalo were cultured and treated with different doses of PGF2α for different time durations. Relative expression of mRNAs encoding for enzymes within the progesterone biosynthetic pathway (3βHSD, CYP11A1 and StAR); Caspase 3; AKT were analyzed to confirm the occurrence of luteolytic event. To determine if EGR1 is involved in the PGF2α induced luteal regression via induction of TGFβ1 expression, we knocked out the EGR1 gene by using CRISPR/Cas9.

Result

The present experiment determined whether EGR1 protein expression in luteal cells was responsive to PGF2α treatment. Quantification of EGR1 and TGFβ1 mRNA showed significant up regulation in luteal cells of buffalo at 12 h post PGF2α induction. In order to validate the role of PGF2α on stimulating the expression of TGFβ1 by an EGR1 dependent mechanism we knocked out EGR1. The EGR1 ablated luteal cells were stimulated with PGF2α and it was observed that EGR1 KO did not modulate the PGF2α induced expression of TGFβ1. In PGF2α treated EGR1 KO luteal cell, the mRNA expression of Caspase 3 was significantly increased compared to PGF2α treated wild type luteal cells maintained for 12 h. We also studied the influence of EGR1 on steroidogenesis. The EGR1 KO luteal cells with PGF2α treatment showed no substantial difference either in the progesterone concentration or in StAR mRNA expression with PGF2α-treated wild type luteal cells.

Conclusion

These results suggest that EGR1 signaling is not the only factor which plays a role in the regulation of PGF2α induced TGFβ1 signaling for luteolysis.

Pregnancy-induced changes in the transcriptome of the bovine corpus luteum during and after embryonic interferon-tau secretion†

Understanding luteal maintenance during early pregnancy is of substantial biological and practical importance. Characterizing effects of early pregnancy, however, has historically been confounded by use of controls with potential exposure to early Prostaglandin F2-alpha (PGF) pulses or differences in Corpus Luteum (CL) age. To avoid this, the present study utilized bihourly blood sampling to ensure control CL (n = 6) were of a similar age to CL from pregnant animals (n = 5), yet without exposure to PGF pulses. Additionally, CL from second month of pregnancy (n = 4) were analyzed to track fate of altered genes after cessation of embryonic interferon tau (IFNT) secretion. The major alteration in gene expression in first month of pregnancy occurred in interferon-stimulated genes (ISGs), with immune/interferon signaling pathways enriched in three independent over-representation analyses. Most ISGs decreased during second month of pregnancy, though, surprisingly, some ISGs remained elevated in the second month even after cessation of IFNT secretion. Investigation of luteolytic genes found few altered transcripts, in contrast to previous reports, likely due to removal of controls exposed to PGF pulses. An exception to this trend was decreased expression of transcription factor NR4A1. Beyond luteolytic genes and ISGs, over representation analyses highlighted the prevalence of altered genes within the extracellular matrix and regulation of Insulin-like growth factor (IGF) availability, confirming results of other studies independent of luteolytic genes. These results support the idea that CL maintenance in early pregnancy is related to lack of PGF exposure, although potential roles for CL expression of diverse ISGs and other pathways activated during early pregnancy remain undefined.

Transcriptome profiling of different developmental stages of corpus luteum during the estrous cycle in pigs

To better understand the molecular basis of corpus luteum (CL) development and function RNA-Seq was utilized to identify differentially expressed genes (DEGs) in porcine CL during different physiological stages of the estrous cycle viz. early (EL), mid (ML), late (LL) and regressed (R) luteal. Stage wise comparisons obtained 717 (EL vs. ML), 568 (EL vs. LL), 527 (EL vs. R), 786 (ML vs. LL), 474 (ML vs. R) and 534 (LL vs. R) DEGs with log₂(FC) ≥1 and p < 0.05. The process of angiogenesis, steroidogenesis, signal transduction, translation, cell proliferation and tissue remodelling were significantly (p < 0.05) enriched in EL, ML and LL stages, where as apoptosis was most active in regressed stage. Pathway analysis revealed that most annotated genes were associated with lipid metabolism, translation, immune and endocrine system pathways depicting intra-luteal control of diverse CL function. The network analysis identified genes AR, FOS, CDKN1A, which were likely the novel hub genes regulating CL physiology.

Molecular profiling demonstrates modulation of immune cell function and matrix remodeling during luteal rescue†

The corpus luteum (CL) is essential for maintenance of pregnancy in all mammals and luteal rescue, which occurs around day 16-19 in the cow, is necessary to maintain luteal progesterone production. Transcriptomic and proteomic profiling were performed to compare the day 17 bovine CL of the estrous cycle and pregnancy. Among mRNA and proteins measured, 140 differentially abundant mRNA and 24 differentially abundant proteins were identified. Pathway analysis was performed using four programs. Modulated pathways included T cell receptor signaling, vascular stability, cytokine signaling, and extracellular matrix remodeling. Two mRNA that were less in pregnancy were regulated by prostaglandin F2A in culture, while two mRNA that were greater in pregnancy were regulated by interferon tau. To identify mRNA that could be critical regulators of luteal fate, the mRNA that were differentially abundant during early pregnancy were compared to mRNA that were differentially abundant during luteal regression. Eight mRNA were common to both datasets, including mRNA related to regulation of steroidogenesis and gene transcription. A subset of differentially abundant mRNA and proteins, including those associated with extracellular matrix functions, were predicted targets of differentially abundant microRNA (miRNA). Integration of miRNA and protein data, using miRPath, revealed pathways such as extracellular matrix-receptor interactions, abundance of glutathione, and cellular metabolism and energy balance. Overall, this study has provided a comprehensive profile of molecular changes in the corpus luteum during maternal recognition of pregnancy and has indicated that some of these functions may be miRNA-regulated.

Clustered microRNAs: The molecular mechanism supporting the maintenance of luteal function during early pregnancy

MicroRNAs (miRNAs) are recognized as the important regulators of ovarian function. However, little is known about the hormonal regulation of miRNA expression and the role of the specific miRNA-mRNA interactions in corpus luteum. Therefore, the present study was undertaken to determine: (a) the expression of miRNAs in the corpus luteum in early pregnancy vs regression; (b) the effect of conceptus and uterine signals in the expression of selected miRNAs; and (c) the role of specific miRNA-mRNA interactions in the molecular changes and secretory function of the corpus luteum in the pig. The results showed that the majority of miRNAs differentially expressed in the corpus luteum in early pregnancy vs regression belong to independent clusters (eg, miR-99b, miR-532), which are highly conserved among different animal species. The main conceptus signal in the pig (17β-estradiol) elevated the luteal expression of the miR-99b cluster and lowered the expression of NR4A1 and AKR1C1, the genes involved in corpus luteum regression. Furthermore, the delivery of miR-99b cluster mimics to luteal tissue concomitantly decreased NR4A1 and AKR1C1 expression and enhanced progesterone secretion. The present study demonstrated that conceptus signals can support the maintenance of luteal function during pregnancy by clustered miRNA-stimulated pathways, governing the expression of genes involved in luteal regression.

Perturbations in Lineage Specification of Granulosa and Theca Cells May Alter Corpus Luteum Formation and Function

Anovulation is a major cause of infertility, and it is the major leading reproductive disorder in mammalian females. Without ovulation, an oocyte is not released from the ovarian follicle to be fertilized and a corpus luteum is not formed. The corpus luteum formed from the luteinized somatic follicular cells following ovulation, vasculature cells, and immune cells is critical for progesterone production and maintenance of pregnancy. Follicular theca cells differentiate into small luteal cells (SLCs) that produce progesterone in response to luteinizing hormone (LH), and granulosa cells luteinize to become large luteal cells (LLCs) that have a high rate of basal production of progesterone. The formation and function of the corpus luteum rely on the appropriate proliferation and differentiation of both granulosa and theca cells. If any aspect of granulosa or theca cell luteinization is perturbed, then the resulting luteal cell populations (SLC, LLC, vascular, and immune cells) may be reduced and compromise progesterone production. Thus, many factors that affect the differentiation/lineage of the somatic cells and their gene expression profiles can alter the ability of a corpus luteum to produce the progesterone critical for pregnancy. Our laboratory has identified genes that are enriched in somatic follicular cells and luteal cells through gene expression microarray. This work was the first to compare the gene expression profiles of the four somatic cell types involved in the follicle-to-luteal transition and to support previous immunofluorescence data indicating theca cells differentiate into SLCs while granulosa cells become LLCs. Using these data and incorporating knowledge about the ways in which luteinization can go awry, we can extrapolate the impact that alterations in the theca and granulosa cell gene expression profiles and lineages could have on the formation and function of the corpus luteum. While interactions with other cell types such as vascular and immune cells are critical for appropriate corpus luteum function, we are restricting this review to focus on granulosa, theca, and luteal cells and how perturbations such as androgen excess and inflammation may affect their function and fertility.

The Ovarian Cycle

The "ovarian cycle" is an exquisite and dynamic endocrine system that includes ovarian events, hypothalamic-pituitary interactions, uterine endometrial and myometrial changes during implantation and pregnancy, cervical alterations in structure, and breast development. The ovarian cycle and the steroid hormones produced by the ovary also impact epithelial cancer development in the ovary, uterus, cervix, and breast. This chapter provides a personal view of recent developments that occur in this complex endocrine environment.

Transcriptomic and bioinformatics analysis of the early time-course of the response to prostaglandin F2 alpha in the bovine corpus luteum

RNA expression analysis was performed on the corpus luteum tissue at five time points after prostaglandin F2 alpha treatment of midcycle cows using an Affymetrix Bovine Gene v1 Array. The normalized linear microarray data was uploaded to the NCBI GEO repository (GSE94069). Subsequent statistical analysis determined differentially expressed transcripts ± 1.5-fold change from saline control with P ≤ 0.05. Gene ontology of differentially expressed transcripts was annotated by DAVID and Panther. Physiological characteristics of the study animals are presented in a figure. Bioinformatic analysis by Ingenuity Pathway Analysis was curated, compiled, and presented in tables. A dataset comparison with similar microarray analyses was performed and bioinformatics analysis by Ingenuity Pathway Analysis, DAVID, Panther, and String of differentially expressed genes from each dataset as well as the differentially expressed genes common to all three datasets were curated, compiled, and presented in tables. Finally, a table comparing four bioinformatics tools’ predictions of functions associated with genes common to all three datasets is presented. These data have been further analyzed and interpreted in the companion article “Early transcriptome responses of the bovine mid-cycle corpus luteum to prostaglandin F2 alpha includes cytokine signaling” [1].