The Ovarian Antral Follicle: Living on the Edge of Hypoxia or Not? Thompson JG et al. (2015) Oocytes within antral follicles are thought to have restricted access to oxygen (O2) as the follicle vascularity is not adjacent and both granulosa and cumulus cells are metabolically active. Indeed, measured follicular antrum pO2 is regarded as low, but accurate and direct measurement represents a technical challenge that has yet to be overcome. The oocyte itself is highly dependent on oxidative phosphorylation for survival and competence for further development following fertilization, and it has been suggested that follicular pO2 levels are correlated with this capacity for further development. It is clear that gonadotrophins are involved in regulating antrum formation, follicle vascularization, cellular differentiation and the Hypoxia Inducible Factors (HIF), which are mainly regulated by dissolved O2 concentration. A newly discovered player in this story is the intracellular production of hemoglobin by both granulosa and cumulus cells, as well as the oocyte. Furthermore, cellular hemoglobin levels are dynamic, responding to the ovulatory luteinizing hormone (LH) surge. We hypothesize that this gas transport and antioxidant molecule is involved in: (a) the prevention of hypoxic-response signaling via HIFs within the pre-ovulatory antral follicle; (b) the transition of granulosa cells to luteal tissue, by facilitating the stabilization of HIFs, enabling the induction of luteinization signaling. Another possible role is via sequestering nitric oxide (NO) during the ovulatory period, which may facilitate the resumption of meiosis in the oocyte. Testing these hypotheses will be challenging, but important if the regulation of ovarian function is to be fully understood.//////////////////
Hypoxia-mediated carbohydrate metabolism and transport promotes early stage murine follicle growth and survival. Makanji Y 2014 et al.
Oxygen tension is critical for follicle growth and metabolism, especially for early-stage follicles where vascularity is limited. Its role and underlying mechanism in the in vitro activation and maturation of immature to ovulatory follicles, is largely unknown. In this study, early secondary (100 ?m) murine follicles were isolated and encapsulated in alginate hydrogels to replicate the in vivo environment of the growing/maturing follicle. Encapsulated follicles were cultured for 8 days at either 2.5% O2 or 20% O2. Survival (2.6-fold) and growth (1.2-fold) were significantly higher for follicles cultured at 2.5% O2 compared to 20% O2. Using a mouse hypoxia signaling pathway qRT-PCR array and GeneGo Metacore analysis, we found that direct target genes of hypoxia-activated HIF1-complex were significantly up-regulated in follicles cultured for 8 days at 2.5% O2 compared to 20% O2, including the carbohydrate transport and metabolism genes Slc2a3, Vegfa, Slc2a1, Edn1, Pgk1, Ldha, and Hmox1. Other up-regulated genes included carbohydrate transporters (Slc2a1, Slc2a3 and Slc16a3) and enzymes essential for glycolysis (Pgk1, Hmox1, Hk2, Gpi1, Pfkl, Pfkp, Aldoa, Gapdh, Pgam1, Eno1, Pkm2 and Ldha). For follicles cultured at 2.5% O2, a 7.2-fold up-regulation of Vegfa correlated to an 18-fold increase in VEGFA levels and a 3.2-fold up-regulation of Ldha correlated to a 4.8-fold increase in lactate levels. Both VEGFA and lactate levels were significantly higher in follicles cultured at 2.5% O2 compared to 20% O2. Therefore, enhanced hypoxia-mediated glycolysis is essential for growth and survival of early secondary follicles, and provides vital insights into improving in vitro culture conditions.
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NCBI Summary:
This gene encodes the alpha subunit of transcription factor hypoxia-inducible factor-1 (HIF-1), which is a heterodimer composed of an alpha and a beta subunit. HIF-1 functions as a master regulator of cellular and systemic homeostatic response to hypoxia by activating transcription of many genes, including those involved in energy metabolism, angiogenesis, apoptosis, and other genes whose protein products increase oxygen delivery or facilitate metabolic adaptation to hypoxia. HIF-1 thus plays an essential role in embryonic vascularization, tumor angiogenesis and pathophysiology of ischemic disease. Alternatively spliced transcript variants encoding different isoforms have been identified for this gene. [provided by RefSeq, Jul 2011]
General function
Intracellular signaling cascade, Nucleic acid binding, DNA binding, Transcription factor
Comment
Contribution of hypoxia-inducible factor-1a to transcriptional regulation of vascular endothelial growth factor in bovine developing luteal cells. Zhang Z et al. Vascular endothelial growth factor (VEGF)-dependent angiogenesis is crucial for corpus leteum formation and their functional maintenance in mammalian ovaries. The present study was designed to test the hypothesis that hypoxia-inducible factor (HIF)-1a-mediated transcriptional activation contributes to the increased expression of VEGF gene in response to hypoxia in the bovine developing luteal cells (LCs). By real-time RT-PCR analysis, VEGF messenger RNA (mRNA) expression was found to significantly increase under hypoxia or treatment with desferrioxamine (DFX), cobalt chloride (CoCl(2) ) or even N-carbobenzoxyl-L-leucinyl-L-leucinyl-L-norvalinal (MG-132), while these increased VEGF mRNA expressions could also be blocked by ferrous ammonium sulfate (FAS) or cis-element oligodeoxynucleotide (dsODN) transfection under hypoxia. Further analysis also found that these changes of VEGF mRNA were consistent with HIF-1a expression or HIF-1 activity. Taken together, our results indicate that VEGF is transcriptionally activated by hypoxia through HIF-1a-mediated mechanisms in LCs. This hypoxia-induced transcriptional activation may be one of the important mechanisms mediating the increase of VEGF expression in developing LCs during mammalian corpus leteum formation.
HIF-1α Protects Granulosa Cells From Hypoxia-Induced Apoptosis During Follicular Development by Inducing Autophagy. Tang Z et al. (2021) Owing to the avascular structure of the ovarian follicle, proliferation of granulosa cells (GCs) and development of follicles occur under hypoxia, which is obviously different from the cell survival requirements of most mammalian cells. We hypothesized that autophagy may exert an inhibitory effect on GC apoptosis. To decipher the underlying mechanism, we constructed a rat follicular development model using pregnant mare serum gonadotropin and a cell culture experiment in hypoxic conditions (3% O2). The present results showed that the autophagy level was obviously increased and was accompanied by the concomitant elevation of hypoxia inducible factor (HIF)-1α and BNIP3 (Bcl-2/adenovirus E1B 19kDa-interacting protein 3) in GCs during follicular development. The levels of Bax (Bcl2-associated X) and Bcl-2 (B-cell lymphoma-2) were increased, while the activation of caspase-3 exhibited no obvious changes during follicular development. However, inhibition of HIF-1α attenuated the increase in Bcl-2 and promoted the increase in Bax and cleaved caspase-3. Furthermore, we observed the downregulation of BNIP3 and the decrease in autophagy after treatment with a specific HIF-1α activity inhibitor (echinomycin), indicating that HIF-1α/BNIP3 was involved in autophagy regulation in GCs in vivo. In an in vitro study, we also found that hypoxia did not obviously promote GC apoptosis, while it significantly enhanced the activation of HIF-1α/BNIP3 and the induction of autophagy. Expectedly, this effect could be reversed by 3-methyladenine (3-MA) treatment. Taken together, these findings demonstrated that hypoxia drives the activation of HIF-1α/BNIP3 signaling, which induces an increase in autophagy, protecting GC from apoptosis during follicular development.////////////////// HIF1 driven transcriptional activity regulates steroidogenesis and proliferation of bovine granulosa cells. Baddela VS et al. (2020) Hypoxia-inducible factor 1 (HIF1) is a heterodimeric transcription factor, consisting of a constitutively expressed β-subunit (HIF1B) and a regulated α-subunit (HIF1A). In the present study, we analyzed the HIF1 driven transcriptional activity in bovine granulosa cells (GC). Treatment of GC with FSH (follicle stimulating hormone) and IGF1 (insulin-like growth factor 1) resulted in the upregulation of HIF1A mRNA expression under normoxia. Immunohistochemistry of bovine ovarian sections showed distinct staining of HIF1A in the GC layer of different staged ovarian follicles. Suppression of HIF1 using echinomycin and gene knockdown procedures revealed that HIF1 transcriptionally regulates the genes associated with steroidogenesis (STAR, HSD3B and CYP19A1) and proliferation (CCND2 and PCNA) of GC. Further, our data suggest that CYP19A1, the key gene of estradiol production, is one of the plausible downstream targets of HIF1 in bovine GC as shown by gene expression, radioimmunoassay, and chromatin precipitation analysis. Based on these results, we propose that HIF1 driven transcriptional activity plays a crucial role in GC functionality, especially steroidogenesis and proliferation in developing bovine ovarian follicles.////////////////// Effects of mitochondrial dysfunction on energy metabolism switch by HIF-1α signaling in granulosa cells of polycystic ovary syndrome. Wang J et al. (2020) This study aims to determine the effects of mitochondrial dysfunction on energy metabolism of granulosa cells (GCs) and oocyte's competence in polycystic ovary syndrome (PCOS). A total of 158 patients who underwent controlled ovarian hyperstimulation (COH) were enrolled. The clinical outcomes of patients with and without PCOS under in vitro fertilization-embryo transfer (IVF-ET) were compared. Human primary GCs were exposed to mitochondrial and glycolysis inhibitors. Then, the related indicators of mitochondrial activity and glycometabolism were compared with controls. The viability of GCs after mitochondrial inhibitors was also determined. In PCOS patients, the number of retrieved oocytes significantly increased, but the high-quality embryos, available embryos and high quality blastocyst formation obviously decreased (P<0.05). Furthermore, the mitochondrial membrane potential, ATP content, mtDNA copy number, and HIF-1α mRNA and protein levels in GCs decreased, while the levels of reactive oxygen species increased (P<0.05). Mitochondrial inhibitors reduced the mitochondrial function, but increased the HIF-1α, GLUT1, LDHA and PFKP gene expression. Glucose consumption gradually increased at 24, 48 and 72 hours of GC culture after CCCP treatment, and the viability of cells tested by CCK-8 increased (P<0.05). GCs are dependent on mitochondrial respiration and glycolysis for energy provision. Mitochondrial dysfunction accompanied by abnormal glycolysis were observed in PCOS patients, which affect the switch of energy metabolic to glycolytic. The failure of transformation to glycolysis and low HIF-1α expression in GCs during the development of follicles might be correlated to the low oocyte competence of PCOS.////////////////// Hypoxia induces the dormant state in oocytes through expression of Foxo3. Shimamoto S et al. (2019) In mammals, most immature oocytes remain dormant in the primordial follicles to ensure the longevity of female reproductive life. A precise understanding of mechanisms underlying the dormancy is important for reproductive biology and medicine. In this study, by comparing mouse oogenesis in vivo and in vitro, the latter of which bypasses the primordial follicle stage, we defined the gene-expression profile representing the dormant state of oocytes. Overexpression of constitutively active FOXO3 partially reproduced the dormant state in vitro. Based on further gene-expression analysis, we found that a hypoxic condition efficiently induced the dormant state in vitro. The effect of hypoxia was severely diminished by disruption of the Foxo3 gene and inhibition of hypoxia-inducible factors. Our findings provide insights into the importance of environmental conditions and their effectors for establishing the dormant state.//////////////////
Hypoxia-inducible factor-1α-dependent autophagy plays a role in glycolysis switch in mouse granulosa cells. Zhou J et al. (2018) Autophagy is an essential cellular mechanism that degrades cytoplasmic proteins and organelles to recycle their components. Here we showed that autophagy was essential for the glycolysis switch and energy homeostasis in mouse granulosa cells (MGCs) under hypoxic condition. Our data indicated that hypoxia inducible factor-1α (HIF-1α) could be largely increased in developing follicles and this remarkable upregulation of HIF-1α triggered cell autophagy and glucose uptake. We found that blocking autophagy by Atg7 knockdown and 3-methyladenine (3-MA) treatment affected the glucose metabolism, with increased glycolytic enzyme activity and decreased ATP production. We also found enhanced lactate level, which was harmful to granulosa cells and could induce cell apoptosis. Thus, our findings highlight a protective role of HIF-1α-dependent autophagy for the granulosa cell glycolysis switch in both energy supply and cell survival.//////////////////
Expression pattern of HIF1alpha and vasohibins during follicle maturation and corpus luteum function in the bovine ovary. Berisha B et al. (2016) The aim of this study was to characterize expression patterns of hypoxia-inducible factor-1alpha (HIF1A) and vasohibin family members (VASH1 and VASH2) during different stages of ovarian function in cow. Experiment 1: Antral follicle classification occurred by follicle size and estradiol-17beta (E2) concentration in the follicular fluid into 5 groups (<0.5, 0.5-5, 5-40, 40-180 and >180 E2 ng/ml). Experiment 2: Corpora lutea (CL) were assigned to the following stages: days 1-2, 3-4, 5-7, 8-12, 13-16 and >18 (after regression) of oestrous cycle and of pregnancy (months 1-2, 3-4, 6-7, >8). Experiment 3: Cows on days 8-12 were injected with a prostaglandin F2alpha (PGF) analogue and CL were collected before and 0.5, 2, 4, 12, 24, 48 and 64 hr after PGF injection. Expression of mRNA was measured by qPCR, steroid hormone concentration by EIA and localization by immunohistochemistry. HIF1A mRNA expression in our study increases significantly in follicles during final maturation. The highest HIF1A mRNA expression was detected during the early luteal phase, followed by a significant decrease afterwards. In contrast, the mRNA of vasohibins in small follicle was high, followed by a continuous and significant downregulation in preovulatory follicles. The obtained results show a remarkable inverse expression and localization pattern of HIF1A and vasohibins during different stages of ovarian function in cow. These results lead to the assumption that the examined factors are involved in the local mechanisms regulating angiogenesis and that the interactions between proangiogenic (HIF1A) and antiangiogenic (vasohibins) factors impact all stages of bovine ovary function.//////////////////
Hypoxia-inducible factor 1 mediates hypoxia-enhanced synthesis of progesterone during luteinization of granulosa cells. Fadhillah S et al. (2016) Hypoxia has been suggested to enhance progesterone (P4) synthesis in luteinizing granulosa cells (GCs), but the mechanism is unclear. The present study was designed to test the hypothesis that the hypoxia-induced increase in P4 synthesis during luteinization in bovine GCs is mediated by hypoxia-inducible factor 1 (HIF-1). GCs obtained from small antral follicles were cultured with 2 µg/ml insulin in combination with 10 µM forskolin for 24 h as a model of luteinizing GCs. To examine the influence of HIF-1 on P4 synthesis, we determined the effect of changes in protein expression of the α-subunit of HIF-1 (HIF1A) on P4 production and on the expression levels of StAR, P450scc, and 3β-HSD. CoCl2 (100 µM), a hypoxia-mimicking chemical, increased HIF-1α protein expression in luteinizing GCs. After the upregulation of HIF-1α, we observed an increase in P4 production and in the gene and protein expression levels of StAR in CoCl2-treated luteinizing GCs. In contrast, CoCl2 did not affect the expression of either P450scc or 3β-HSD. Echinomycin, a small-molecule inhibitor of HIF-1's DNA-binding activity, attenuated the effects of CoCl2 and of low oxygen tension (10% O2) on P4 production and StAR expression in luteinizing GCs. Overall, these findings suggest that HIF-1 is one of the factors that upregulate P4 in GCs during luteinization.//////////////////
The role of hypoxia and HIF1α in the regulation of STAR-mediated steroidogenesis in granulosa cells. Kowalewski MP et al. (2015) The adaptive responses to hypoxia are mediated by hypoxia-inducible factor 1 alpha (HIF1α). Its role, however, in regulating steroidogenesis remains poorly understood. We examined the role of hypoxia and HIF1α in regulating steroid acute regulatory protein (STAR) expression and steroidogenesis in immortalized (KK1) mouse granulosa cells under progressively lowering O2 concentrations (20%, 15%, 10%, 5%, 1%). Basal and dbcAMP-stimulated progesterone synthesis was decreased under severe hypoxia (1% and 5% O2). The partial hypoxia revealed opposing effects, with a significant increase in steroidogenic response at 10% O2 in dbcAMP-treated cells: Star-promoter activity, mRNA and protein expression were increased. The hypoxia-stimulated STAR expression was PKA-dependent. Binding of HIF1α to the Star-promoter was potentiated under partial hypoxia. Inhibition of the transcriptional activity or expression of HIF1α suppressed STAR-expression. HIF1α appears to be a positive regulator of basal and stimulated STAR-expression, which under partial hypoxia is capable of increasing the steroidogenic capacity of granulosa cells.//////////////////
HIF1A-dependent increase in endothelin 2 levels in granulosa cells: role of hypoxia, LH/cAMP, and reactive oxygen species. Yalu R et al. (2014) Hypoxia-inducible factor 1 alpha (HIF1A) and endothelin 2 (EDN2) are transiently expressed during the same time window in the developing corpus luteum (CL). In this study, we sought to investigate the involvement of LH/cAMP, reactive oxygen species (ROS), and a hypoxia-mimetic compound (CoCl2) on HIF1A expression and how it affected EDN2 levels, using transformed human granulosa cells (thGCs) and primary bovine granulosa cells (GCs). CoCl2 elevated HIF1A protein levels in thGCs in a dose-dependent manner. Forskolin alone had no significant effect; however, forskolin and CoCl2 together further induced HIF1A protein and EDN2 mRNA expression in thGCs. Similarly, in primary GCs, LH with CoCl2 synergistically augmented HIF1A protein levels, which resulted in higher expression of EDN2 and another well-known hypoxia-inducible gene, VEGF (VEGFA). Importantly, LH alone elevated HIF1A mRNA but not its protein. The successful knockdown of HIF1A in thGCs using siRNA abolished hypoxia-induced EDN2 and also the additive effect of forskolin and CoCl2. We then examined the roles of ROS in thGCs: hydrogen peroxide (20 and 50 μM) elevated HIF1A protein as well as the expression of EDN2, implying that induction of HIF1A protein levels is sufficient to stimulate the expression of EDN2 (and VEGF) in normoxia. A broad-range ROS scavenger, butylated hydroxyanisole, inhibited CoCl2-induced HIF1A protein with a concomitant reduction in the mRNA expression of EDN2 and VEGF in thGCs. The results obtained in this study suggest that HIF1A, induced by various stimuli, is an essential mediator of EDN2 mRNA expression. The results may also explain the rise in the levels of HIF1A-dependent genes (EDN2 and VEGF) in the developing CL.//////////////////
HIF1 Activity in Granulosa Cells Is Required for FSH-Regulated Vegfa Expression and Follicle Survival in Mice. Rico C 2014 et al.
Recent evidence has suggested that vascular endothelial growth factor A (VEGFA) is an important regulator of ovarian follicle development and survival. Both LH and FSH regulate Vegfa expression in granulosa cells, and signal via the transcription factor hypoxia inducible factor 1 (HIF1). To further study the mechanism of action of HIF1 in the regulation of Vegfa, we studied Vegfa(delta/delta) mice, which lack a hypoxia response element (HRE) in the Vegfa promoter. Granulosa cells from Vegfa(delta/delta) mice failed to respond to FSH or LH with an increase in Vegfa mRNA expression in vitro, and granulosa cells isolated from eCG-treated immature Vegfa(delta/delta) mice had significantly lower Vegfa mRNA levels compared to controls. However, normal Vegfa mRNA levels were detected in the granulosa cells from immature Vegfa(delta/delta) mice following hCG treatment. Vegfa(delta/delta) females produced infrequent litters and their pups died shortly after birth. Ovaries from Vegfa(delta/delta) mice were much smaller than controls and contained few antral follicles and corpora lutea. Antral follicles numbers were decreased by nearly 50% in ovaries from Vegfa(delta/delta) mice relative to controls, and 74% of antral follicles in Vegfa(delta/delta) ovaries were atretic. Serum progesterone levels in adult Vegfa(delta/delta) females were significantly lower, apparently reflecting reduced numbers of corpora lutea. This study demonstrates for the first time the requirement of HIF1 for FSH-regulated Vegfa expression in vivo, and that HIF1 acts via a single HRE in the Vegfa promoter to exert its regulatory functions. Our findings also further define the physiological role of VEGFA in follicle development.
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Effects of Echinomycin on Endothelin-2 Expression and Ovulation in Immature Rats Primed with Gonadotropins. Wang Z et al. Echinomycin is a small-molecule inhibitor of hypoxia-inducible factor-1 DNA-binding activity, which plays a crucial role in ovarian ovulation in mammalians. The present study was designed to test the hypothesis that hypoxia-inducible factor (HIF)-1alpha-mediated endothelin (ET)-2 expressions contributed to ovarian ovulation in response to hCG during gonadotropin-induced superuvulation. By real-time RT-PCR analysis, ET-2 mRNA level was found to significantly decrease in the ovaries after echinomycin treatment, while HIF-1alpha mRNA and protein expression was no obviously changes. Further analysis also found that these changes of ET-2 mRNA were consistent with HIF-1 activity in the ovaires, which is similar with HIF-1alpha and ET-2 expression in the granulosa cells with gonadotropin and echinomycin treatments. The results of HIF-1alpha and ET-2 expression in the granulosa cells transfected with cis-element oligodeoxynucleotide (dsODN) under gonadotropin treatment further indicated HIF-1alpha directly mediated the transcriptional activation of ET-2 during gonadotropin-induced superuvulation. Taken together, these results demonstrated this HIF-1alpha-mediated ET-2 transcriptional activation is one of the important mechanisms regulating gonadotropin-induced mammalian ovulatory precess in vivo.
Hormonally Regulated Follicle Differentiation And Luteinization In The Mouse Is Associated With Hypoxia Inducible Factor Activity. Tam KK et al. Hypoxia inducible factors (HIFs) are transcription factors that mediate physiological responses to hypoxia. Hypoxia is established as the major inducer of HIFs, but stimuli such as transition metals and hormones also induce HIF target genes. Whilst the ovarian granulosa cell layer is known to be avascular and the follicle is vascularised via the thecal cell layer, little is known about the role of hypoxia or HIFs in regulating ovarian function. In this study, we hypothesized that hypoxia as well as non hypoxic stimuli cooperate in promoting follicle differentiation and luteinization via HIF activity and resultant gene regulation. We quantitatively measured the HIF1alpha protein response to hCG in ovarian granulosa cell cultures and in vivo and developed a transgenic (HRE(4)-SV40-EGFP) HIF reporter mouse line. We observed a time-dependent increase of HIF1alpha protein levels in granulosa cells post hCG in vivo, maximal around time of ovulation. hCG alone was unable to promote HIF1alpha protein accumulation in cultured granulosa cells, but increased protein abundance was observed when combined with a hypoxic stimulus. HRE-EGFP ovaries showed no follicular EGFP in stages prior to antrum formation. However, HIF regulated EGFP was maximally induced in granulosa cells around the time of ovulation and readily observed in corpora lutea. There was also an increase in HIF regulated EGFP activity in the corpora lutea from functional to regressing stages. Taken together, these observations establish the notion that HIFs play a role during follicular differentiation and luteinization.
Expression regulated by
FSH, LH, Steroids
Comment
In-vitro study of gonadotrophin signaling pathways in human granulosa cells in relation to progesterone receptor expression. Henríquez S et al. (2017) In humans, data on gonadotrophin-activated (LH, HCG and FSH) progesterone receptor expression and signalling pathways involved in matrix metalloproteinases (MMPs) expression presumably linked to the follicle rupture, are limited. Our hypothesis is LH, HCG and FSH increase progesterone receptor expression in granulosa cells through different signalling pathways, leading to an increased expression of ADAMTS-1 and MMP3/10, which may mediate follicular rupture through the transcription factor, HIF1A. Human granulosa cells were isolated from follicular aspirates obtained from 22 healthy women participating in our IVF programme for male-factor infertility. Progesterone receptor and HIF1A expression was assessed by immunofluorescence, and PKA-PKC-PI3K- ERK1/2, ADAMTS-1 and MMP3/10 expression by Western blot in pre-ovulatory and in cultured granulosa cells. Results show that HCG, LH and FSH regulate progesterone receptor expression and activate PKA, PKC, PI3K and ERK1/2 signalling pathways in granulosa cells but progesterone receptor expression is only mediated by PKA, PKC and ERK pathways. HCG, FSH and LH regulated MMPs expression through progesterone receptors. Moreover, HCG-progesterone-receptor-dependent HIF1A expression stimulated MMP3/10 expression but not that of ADAMTS-1. These results suggest differential downstream progesterone receptor signalling, as progesterone receptor regulates MMP3/10 expression via HIF1A, which is not involved in ADAMTS-1 expression.//////////////////
Signaling by Hypoxia-Inducible Factors is Critical for Ovulation In Mice. Kim J et al. The steroid hormone progesterone, acting via its nuclear receptor, is a major regulator of the process of ovulation. Female mice lacking progesterone receptor (PGR) exhibit an anovulatory phenotype due to failure in follicular rupture. To identify the PGR-regulated pathways that control ovulation, we analyzed global changes in gene expression in the ovaries of wild type (WT) and Pgr-null mice subjected to gonadotropin-induced superovulation. Our analysis uncovered several genes whose expression was reduced in the Pgr-null ovaries compared with the WT ovaries immediately preceding ovulation. Interestingly, these genes included three hypoxia-inducible factors (HIFs): HIF-1alpha, HIF-2alpha, and HIF-1beta. These transcription factors form alphabeta heterodimers, which regulate the transcription of specific cellular genes, thereby mediating adaptive response of the tissue to low oxygen levels. We observed that the expression of mRNAs and proteins corresponding to HIF-1alpha, HIF-2alpha, and HIF-1beta was induced in a PGR-dependent manner, specifically in the granulosa cells of the preovulatory follicles. Inhibition of the HIF transcriptional activity by echinomycin, a small-molecule inhibitor that suppresses the binding of HIF alphabeta heterodimers to target genes, blocked ovulation by preventing the rupture of the preovulatory follicles. Echinomycin specifically inhibited the expression of genes that are known regulators of ovulation, such as a disintegrin and metalloproteinase with thrombospondin-like motifs-1 (ADAMTS-1) and endothelin-2. Furthermore, echinomycin reduced the expression of vascular endothelial growth factor A, a key factor controlling vascularization/angiogenesis during ovulation. Collectively, these findings unveiled a novel ovarian role for the HIF transcription factors during the ovulatory period in mice.
Role of the PI3-Kinase and ERK Pathways in the Induction of HIF-1 Activity and the HIF-1 Target VEGF in Ovarian Granulosa Cells in response to Follicle Stimulating Hormone. Alam H et al. FSH stimulation of granulosa cells (GCs) results in increased hypoxia-inducible factor (HIF)-1alpha protein levels and HIF-1 activity that is necessary for up-regulation of certain FSH target genes including vascular endothelial growth factor (VEGF). We report that the role of the phosphatidylinositol (PI)-3-kinase/AKT pathway in increasing HIF-1alpha protein in FSH-stimulated GCs extends beyond an increase in mammalian target of rapamycin (mTOR)-stimulated translation. FSH increases phosphorylation of the AKT target mouse double minute 2 (MDM2); a phosphomimetic mutation of MDM2 is sufficient to induce HIF-1 activity. The PI3-kinase/AKT target forkhead box-containing protein O subfamily 1 (FOXO1) also effects the accumulation of HIF-1alpha as evidenced by the ability of a constitutively active FOXO1 mutant to inhibit the induction by FSH of HIF-1alpha protein and HIF-1 activity. Activation of the PI3-kinase/AKT pathway in GCs by IGF-1 is sufficient to induce HIF-1alpha protein but surprisingly not HIF-1 activity. HIF-1 activity also appears to require a PD98059-sensitive protein (kinase) activity stimulated by FSH that is both distinct from mitogen-activated extracellular signal-regulated kinase (ERK) kinase1/2 or 5 and independent of the PI3-kinase/AKT pathway. These results indicate that FSH-stimulated HIF-1 activation leading to up-regulation of targets such as VEGF requires not only PI3-kinase/AKT-mediated activation of mTOR as well as phosphorylation of FOXO1 and possibly MDM2 but also a protein (kinase) activity that is inhibited by the classic ERK kinase inhibitor PD98059 but is not ERK1/2 or 5. Thus, regulation of HIF-1 activity in GCs by FSH under normoxic conditions is complex and requires input from multiple signaling pathways.
Human chorionic gonadotrophin up-regulates hypoxia inducible factor-1 alpha in luteinised granulosa cells: implications for the hormonal regulation of vascular endothelial growth factor A in the human corpus luteum. van den Driesche S et al. VEGF-dependent angiogenesis is essential for normal luteal development. Although it is believed that hypoxia is the primary inducer of VEGF, in the corpus luteum it is up-regulated by hCG. As HIF1A has been shown to regulate VEGFA under ligand-stimulated conditions, we hypothesised that the effect of hCG on luteal VEGFA was mediated through HIF1A. We studied the effect of hCG on VEGFA and HIF1A expression in human luteinised granulosa cells in vitro and in human corpora lutea in vivo. HCG up-regulated VEGFA (P<0.05) and HIF1A (P<0.001) in vitro and VEGFA (P<0.05) and HIF1A (P<0.05) in vivo. There was a correlation between HIF1A and VEGFA in vivo (P<0.005) and in vitro (P<0.05). Nuclear HIF1A in granulosa-lutein cells was highest during luteal formation and absent from the fully functional corpus luteum (P<0.05). Both VEGFA (P<0.001) and HIF1A (P<0.01) were up-regulated by dibutyryl-cAMP, through a PKA pathway. Hypoxia increased VEGFA (P<0.001) and HIF1A (P<0.05) expression and hCG further augmented VEGFA (P<0.001) and HIF1A (P<0.01) under hypoxic conditions. However progesterone increased hCG-stimulated VEGFA but had no effect on HIF1A expression. The expression of HIF1A is therefore hormonally regulated in luteal cells in vitro and in vivo and may regulate VEGFA expression under normoxic and hypoxic conditions. However the differential effects of progesterone suggest that not all regulation of VEGFA is associated with an up-regulation of HIF1A.
Ovarian localization
Granulosa, Luteal cells
Comment
Hypoxia-inducible factor-1alpha and nitric oxide synthases in bovine follicles close to ovulation and early luteal angiogenesis. Berisha B et al. (2020) The objective of the study was to characterize expression patterns of hypoxia-inducible factor-1alpha (HIF1A), inducible nitric oxide synthase (iNOS) and endothelial (eNOS) isoforms in time-defined follicle classes before and after GnRH application in the cow. Ovaries containing preovulatory follicles or corpora lutea were collected by transvaginal ovariectomy (n=5 cows/group) as follow: (I) before GnRH administration; (II) 4h after GnRH; (III) 10h after GnRH; (IV) 20h after GnRH; (V) 25h after GnRH, and (VI) 60h after GnRH (early corpus luteum). The mRNA abundance of HIF1A in the follicle group before GnRH was high, followed by a significant down regulation afterwards with a minimum level 25h after GnRH (close to ovulation) and significant increase only after ovulation. The mRNA abundance of iNOS before GnRH was high, decreased significantly during LH surge, with minimum levels afterwards. In contrast, the mRNA of eNOS decreased in the follicle group 20h after GnRH, followed by a rapid and significant upregulation just after ovulation. Immunohistochemically, the granulosa cells of antral follicles and the eosinophils of the theca tissue as well of the early corpus luteum showed a strong staining for HIF1A. The location of the eosinophils could be clearly demonstrated by immunostaining with an eosinophil-specific antibody (EMBP) and transmission electron microscopy. In conclusion, the parallel and acute regulated expression patterns of HIF1A and NOS isoforms, specifically during the interval between the LH surge and ovulation, indicates that these paracrine factors are involved in the local mechanisms, regulating final follicle maturation, ovulation and early luteal angiogenesis.//////////////////. Expression of hypoxia-inducible factor-1α during ovarian follicular growth and development in Sprague-Dawley rats. Zhang ZH et al. (2015) Hypoxia-inducible factor-1α (HIF-1α) has been identified as a transcription factor that is involved in diverse physiological and pathological processes in the ovary. In this study, we examined whether HIF-1α is expressed in a cell- and stage-specific manner during follicular growth and development in the mammalian ovaries. Using immunohistochemistry and Western blot analysis, HIF-1α expression was observed in granulosa cells specifically and was significantly increased during the follicular growth and development of postnatal rats. Furthermore, pregnant mare serum gonadotropin also induced HIF-1α expression in granulosa cells and ovaries during the follicular development of immature rats primed with gonadotropin. Moreover, we also examined proliferation cell nuclear antigen, a cell proliferation marker, during follicular growth and development and found that its expression pattern was similar to that of HIF-1α protein. Granulosa cell culture experiments revealed that proliferation cell nuclear antigen expression may be regulated by HIF-1α. These results indicated that HIF-1α plays an important role in the follicular growth and development of these 2 rat models. The HIF-1α-mediated signaling pathway may be an important mechanism regulating follicular growth and development in mammalian ovaries in vivo.//////////////////
FSH activation of HIF-1 by the PI3-kinase/AKT/Rheb/mTOR pathway is necessary for induction of select protein markers of follicular differentiation.
Alam H, et al sought to elucidate the role of AKT in follicle-stimulating hormone (FSH)-mediated granulosa cell (GC) differentiation. Their results define a signaling pathway in GCs whereby the inactivating phosphorylation of tuberin downstream of phosphatidylinositol-3 (PI3)-kinase/AKT activity leads to ras homolog enriched in brain (Rheb) and subsequent mammalian target of rapamycin (mTOR) activation. mTOR then stimulates translation by phosphorylating p70 S6 kinase and, consequently, the 40S ribosomal protein S6. Activation of this pathway is required for FSH-mediated induction of several follicular differentiation markers including luteinizing-hormone receptor (LHR), inhibin-alpha, microtubule-associated protein 2D, and the PKA type IIbeta regulatory subunit. FSH also promotes activation of the transcription factor hypoxia-inducible factor-1 (HIF-1). FSH-stimulated HIF-1 activity is inhibited by the PI3-kinase inhibitor LY294002, the Rheb inhibitor FTI-277, and the mTOR inhibitor rapamycin. Finally, the authors find that the FSH-mediated up-regulation of reporter activities for LHR, inhibin-alpha, and vascular endothelial growth factor is dependent upon HIF-1 activity as a dominant negative form of HIF-1alphainterferes with the up-regulation of these genes. These results show that FSH enhances HIF-1 activity downstream of the PI3-kinase/AKT/Rheb/mTOR pathway in GCs and that HIF-1 activity is necessary for FSH to induce multiple follicular differentiation markers.
Follicle stages
Antral, Preovulatory, Corpus luteum
Comment
Expression and localization of hypoxia inducible factor-1alpha mRNA in the porcine ovary Boonyaprakob U, et al .
Angiogenesis is an essential process during follicular development and corpora lutea (CL) formation. Recent studies have shown that vascular endothelial growth factor (VEGF) is an essential regulator of ovarian angiogenesis. Several lines of evidence have indicated that the production of VEGF is regulated by hypoxia inducible factor-1alpha (HIF-1alpha), especially under hypoxic conditions, but the expression of HIF-1alpha has not been well characterized in the porcine ovary. The present study examined the expression of HIF-1alpha mRNA and its localization in porcine ovaries at different stages of the estrous cycle. Northern blot analyses of total CL RNA indicated hybridization of the porcine HIF-1alpha probe to transcripts of approximately 3.8 kb. The mRNA expression of HIF-1alpha was highest in CL during the early luteal phase, followed by a decrease during the mid- and late-luteal phases. Using in situ hybridization, abundant HIF-1alpha mRNA was evident in follicles and CL. Within non-atretic follicles, HIF-1alpha mRNA was highly expressed in the granulosa cell layer, while weaker labeling was evident in the theca interna. These results suggest that HIF-1alpha may play a role in the regulation of cellular metabolism and blood supply during follicular growth and CL formation.