Cholesterol side-chain cleavage P450 messenger ribonucleic acid: evidence for hormonal regulation in rat ovarian follicles and constitutive expression in corpora lutea

Analysis on the desert adaptability of indigenous sheep in the southern edge of Taklimakan Desert

The southern margin of the Taklimakan Desert is characterized by low rainfall, heavy sandstorms, sparse vegetation and harsh ecological environment. The indigenous sheep in this area are rich in resources, with the advantages of perennial estrus and good resistance to stress in most sheep. Exploring the molecular markers of livestock adaptability in this environment will provide the molecular basis for breeding research to cope with extreme future changes in the desert environment. In this study, we analyzed the population genetic structure and linkage imbalance of five sheep breeds with three different agricultural geographic characteristics using four complementary genomic selection signals: fixation index (FST), cross-population extended haplotype homozygosity (xp-EHH), Rsb (extended haplotype homozygosity between-populations) and iHS (integrated haplotype homozygosity score). We used Illumina Ovine SNP 50K Genotyping BeadChip Array, and gene annotation and enrichment analysis were performed on selected regions of the obtained genome. The ovary of Qira Black sheep (Follicular phase, Luteal phase, 30th day of pregnancy, 45th day of pregnancy) was collected, and the differentially expressed genes were screened by transcriptomic sequencing. Genome-wide selective sweep results and transcriptome data were combined for association analysis to obtain candidate genes associated with perennial estrus and stable reproduction. In order to verify the significance of the results, 15 resulting genes were randomly selected for fluorescence quantitative analysis. The results showed that Dolang sheep and Qira Black sheep evolved from Kazak sheep. Linkage disequilibrium analysis showed that the decay rate of sheep breeds in the Taklimakan Desert was higher than that in Yili grassland. The signals of FST, xp-EHH, Rsb and iHS detected 526, 332, 308 and 408 genes, respectively, under the threshold of 1% and 17 overlapping genes under the threshold of 5%. A total of 29 genes were detected in association analysis of whole-genome and transcriptome data. This study reveals the genetic mechanism of perennial estrus and environmental adaptability of indigenous sheep breeds in the Taklimakan Desert. It provides a theoretical basis for the conservation and exploitation of genetic resources of indigenous sheep breeds in extreme desert environment. This provides a new perspective for the quick adaptation of sheep and other mammals to extreme environments and future climate changes.

Achieving full-term pregnancy in the vizcacha relies on a reboot of luteal steroidogenesis in mid-gestation (Lagostomus maximus, Rodentia)

Reactivation of the hypothalamic-pituitary-ovarian (HPO) axis triggered by the decline in serum progesterone in mid-gestation is an uncommon trait that distinguishes the vizcacha from most mammals. Accessory corpora lutea (aCL) developed upon this event have been proposed as guarantors of the restoration of the progesterone levels necessary to mantain gestation. Therefore, the steroidogenic input of primary CL (pCL) vs aCL was evaluated before and after HPO axis-reactivation (BP and AP respectively) and in term pregnancy (TP). Nonpregnant-ovulated females (NP) were considered as the pCL-starting point group. In BP, the ovaries mainly showed pCL, whose LH receptor (LHR), StAR, 3β-HSD, 20α-HSD, and VEGF immunoexpressions were similar or lower than those of NP. In AP, luteal reactivity increased significantly compared to the previous stages, and the pool of aCL developed in this stage represented 20% of the ovarian structures, equaling the percentage of pCL. Both pCL and aCL luteal cells shared similar histological features consistent with secretory activity. Although pCL and aCL showed equivalent labeling intensity for the luteotropic markers, pCL were significantly larger than aCL. Towards TP, both showed structural disorganization and loss of secretory characteristics. No significant DNA fragmentation was detected in luteal cells throughout gestation. Our findings indicate that the LH surge derived from HPO axis-reactivation targets the pCL and boost luteal steroidogenesis and thus progesterone production. Because there are many LHR-expressing antral follicles in BP, they also respond to the LH stimuli and luteinize without extruding the oocyte. These aCL certainly contribute but it is the steroidogenic restart of the pCL that is the main force that restores progesterone levels, ensuring that gestation is carried to term. Most importantly, the results of this work propose luteal steroidogenesis reboot as a key event in the modulation of vizcacha pregnancy and depict yet another distinctive aspect of its reproductive endocrinology.

Stanniocalcin-1 in the female reproductive system and pregnancy

BACKGROUND

Stanniocalcin-1 (STC-1) is a widely expressed glycoprotein hormone involved in a diverse spectrum of physiological and pathophysiological processes including angiogenesis, mineral homeostasis, cell proliferation, inflammation and apoptosis. Over the last 20 years, numerous studies have reported STC-1 expression within female reproductive tissues including the uterus, ovaries and placenta and implicated STC-1 in processes such as ovarian follicular development, blastocyst implantation, vascular remodelling in early pregnancy and placental development. Notably, dysregulation of STC-1 within reproductive tissues has been linked to the onset of severe reproductive disorders including endometriosis, polycystic ovary syndrome, poor trophoblast invasion and placental perfusion in early pregnancy. Furthermore, significant changes in tissue expression and in maternal systemic concentration take place throughout pregnancy and further substantiate the vital role of this protein in reproductive health and disease.

OBJECTIVE AND RATIONALE

Our aim is to provide a comprehensive overview of the existing literature, to summarise the expression profile and roles of STC-1 within the female reproductive system and its associated pathologies. We highlight the gaps in the current knowledge and suggest potential avenues for future research.

SEARCH METHODS

Relevant studies were identified through searching the PubMed database using the following search terms: ‘stanniocalcin-1’, ‘placenta’, ‘ovary’, ‘endometrium’, ‘pregnancy’, ‘reproduction’, ‘early gestation’. Only English language papers published between 1995 and 2020 were included.

OUTCOMES

This review provides compelling evidence of the vital function that STC-1 plays within the female reproductive system. The literature presented summarise the wide expression profile of STC-1 within female reproductive organs, as well as highlighting the putative roles of STC-1 in various functions in the reproductive system. Moreover, the observed link between altered STC-1 expression and the onset of various reproductive pathologies is presented, including those in pregnancy whose aetiology occurs in the first trimester. This summary emphasises the requirement for further studies on the mechanisms underlying the regulation of STC-1 expression and function.

WIDER IMPLICATIONS

STC-1 is a pleiotropic hormone involved in the regulation of a number of important biological functions needed to maintain female reproductive health. There is also growing evidence that dysregulation of STC-1 is implicated in common reproductive and obstetric disorders. Greater understanding of the physiology and biochemistry of STC-1 within the field may therefore identify possible targets for therapeutic intervention and/or diagnosis.

WOMEN IN REPRODUCTIVE SCIENCE: Discovering science and the ovary: a career of joy

My career has been about discovering science and learning the joys of the discovery process itself. It has been a challenging but rewarding process filled with many exciting moments and wonderful colleagues and students. Although I went to college to become a French major, I ultimately stumbled into research while pursuing a Masters Degree in teaching. Thus, my research career began in graduate school where I was studying NAD kinase in the ovary as a possible regulator of steroidogenesis, a big issue in the late 1960s. After a short excursion of teaching in North Dakota, I became a postdoctoral fellow at the University of Michigan, where radio-immuno assays and radio receptor assays had just come on the scene and were transforming endocrinology from laborious bioassays to quantitative science and of course these assays related to the ovary. From there I went to Baylor College of Medicine, a mecca of molecular biology, cloning genes and generating mouse models. It has been a fascinating and joyous journey.

Low glucose availability stimulates progesterone production by mouse ovaries in vitro

Steroid production by the ovary is primarily stimulated by gonadotropins but can also be affected by biological cues that provide information about energy status and environmental stress. To further understand which metabolic cues the ovary can respond to, we exposed gonadotropin-stimulated mouse ovaries in vitro to glucose metabolism inhibitors and measured steroid accumulation in media. Gonadotropin-stimulated ovaries exposed to 2-deoxy-d-glucose increased progesterone production and steroidogenic acute regulatory protein mRNA levels. However, oocytes and granulosa cells in antral follicles do not independently mediate this response because targeted treatment of these cell types with a different inhibitor of glucose metabolism (bromopyruvic acid) did not affect progesterone production. Elevated progesterone production is consistent with the homeostatic role of progesterone in glucose regulation in mammals. It also may regulate follicle growth and/or atresia within the ovary. These results suggest that ovaries can regulate glucose homeostasis in addition to their primary role in reproductive activity.

Androgen deficiency during mid- and late pregnancy alters progesterone production and metabolism in the porcine corpus luteum

We determined whether androgen deficiency induced by flutamide treatment during mid- and late pregnancy affects the functions of the porcine corpus luteum (CL). Pregnant gilts were injected with flutamide between days 43 and 49 (gestation day [GD] 50F), days 83 and 89 (GD90F), or days 101 and 107 (GD108F) of gestation. Antiandrogen treatment increased the luteal progesterone concentration in the GD50F group and decreased progesterone content in the GD90F and GD108F groups. Luteal levels of side-chain cleavage cytochrome P450 (CYP11A1) mRNA and protein were significantly downregulated in the GD90F and GD108F groups as compared with the respective controls. The 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (HSD3B) mRNA and protein expression were significantly reduced only in the GD108F group as compared with the control. Decreased luteal 20α-hydroxysteroid dehydrogenase (AKR1C1) mRNA and protein levels were observed in the GD50F group. Thus, androgen deficiency during pregnancy in pigs led to CL dysfunction that is marked by decreased progesterone production. Furthermore, exposure to flutamide during late pregnancy downregulated steroidogenic enzymes (CYP11A1 and HSD3B) in pigs. We conclude that androgens are important regulators of CL function during pregnancy.

Dioxin exposure reduces the steroidogenic capacity of mouse antral follicles mainly at the level of HSD17B1 without altering atresia

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent ovarian toxicant. Previously, we demonstrated that in vitro TCDD (1nM) exposure decreases production/secretion of the sex steroid hormones progesterone (P4), androstenedione (A4), testosterone (T), and 17β-estradiol (E2) in mouse antral follicles. The purpose of this study was to determine the mechanism by which TCDD inhibits steroidogenesis. Specifically, we examined the effects of TCDD on the steroidogenic enzymes, atresia, and the aryl hydrocarbon receptor (AHR) protein. TCDD exposure for 48h increased levels of A4, without changing HSD3B1 protein, HSD17B1 protein, estrone (E1), T or E2 levels. Further, TCDD did not alter atresia ratings compared to vehicle at 48h. TCDD, however, did down regulate the AHR protein at 48h. TCDD exposure for 96h decreased transcript levels for Cyp11a1, Cyp17a1, Hsd17b1, and Cyp19a1, but increased Hsd3b1 transcript. TCDD exposure particularly lowered both Hsd17b1 transcript and HSD17B1 protein. However, TCDD exposure did not affect levels of E1 in the media nor atresia ratings at 96h. TCDD, however, decreased levels of the proapoptotic factor Bax. Collectively, these data suggest that TCDD exposure causes a major block in the steroidogenic enzyme conversion of A4 to T and E1 to E2 and that it regulates apoptotic pathways, favoring survival over death in antral follicles. Finally, the down-regulation of the AHR protein in TCDD exposed follicles persisted at 96h, indicating that the activation and proteasomal degradation of this receptor likely plays a central role in the impaired steroidogenic capacity and altered apoptotic pathway of exposed antral follicles.

The ability of the aryl hydrocarbon receptor to regulate ovarian follicle growth and estradiol biosynthesis in mice depends on stage of sexual maturity

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the toxicity of environmental chemicals and regulates many physiological functions, including processes in female reproduction. Previous studies demonstrated that Ahr deletion leads to slow ovarian follicle growth because of impaired estradiol production and reduced gonadotropin responsiveness in prepubertal mice. These studies, however, did not determine how Ahr deletion impairs estradiol production or whether the effects of Ahr deletion on follicle growth and estradiol production persist in adulthood. Thus, the present study evaluated the effect of Ahr deletion on steroid precursors in the estradiol biosynthesis pathway. Furthermore, this study evaluated follicle growth and estradiol biosynthesis in wild-type (WT) and Ahr knockout (AhrKO) antral follicles at different stages of sexual maturity. AhrKO antral follicles from prepubertal mice had slower growth, produced lower estradiol levels, and had reduced cyclin D2 (Ccnd2) expression compared to WT follicles. AhrKO follicles from adult mice, however, produced higher androgen levels and expressed higher levels of Ccnd2 compared to WT follicles. Furthermore, AhrKO follicles from adult mice had growth to that of WT follicles. These findings suggest that the AHR regulates follicle growth by altering factors involved in the estradiol biosynthesis pathway as well as key regulators of follicle growth and that this role of AHR depends on stage of sexual maturity.

Luteinizing hormone receptor-stimulated progesterone production by preovulatory granulosa cells requires protein kinase A-dependent activation/dephosphorylation of the actin dynamizing protein cofilin

Activation of the LH receptor (LHR) on preovulatory granulosa cells stimulates the cAMP/protein kinase A (PKA) pathway to regulate expression of genes required for ovulation and luteinization. LHR signaling also initiates rearrangement of the actin cytoskeleton. Because disruption of the actin cytoskeleton has been causally linked to steroidogenesis in various cell models, we sought to identify the cellular mechanisms that may modulate reorganization of the actin cytoskeleton and to determine whether cytoskeletal reorganization is required for steroidogenesis. Herein we report that LHR signaling in preovulatory granulosa cells promotes rapid dephosphorylation of the actin-depolymerizing factor cofilin at Ser3 that is dependent on PKA. The LHR-stimulated dephosphorylation of cofilin(Ser3) switches on cofilin activity to bind actin filaments and enhance their dynamics. Basal phosphorylation of cofilin(Ser3) is mediated by active/GTP-bound Rho and downstream protein kinases; LHR signaling promotes a decrease in active/GTP-bound Rho by a PKA-dependent mechanism. LHR-dependent Rho inactivation and subsequent activation of cofilin does not involve ERK, epidermal growth factor receptor, or phosphatidylinositol 3-kinase pathways downstream of PKA. To understand the biological significance of cofilin activation, preovulatory granulosa cells were transduced with a mutant cofilin adenoviral vector in which Ser3 was mutated to Glu (S-E cofilin). Inactive S-E cofilin abolished LHR-mediated reorganization of the actin cytoskeleton and caused a 70% decrease in LHR-stimulated progesterone that is obligatory for ovulation. Taken together, these results show that LHR signaling via PKA activates a cofilin-regulated rearrangement of the actin cytoskeleton and that active cofilin is required to initiate progesterone secretion by preovulatory granulosa cells.

Expression of ectodermal neural cortex 1 and its association with actin during the ovulatory process in the rat

Ectodermal neural cortex (ENC) 1, a member of the kelch family of genes, is an actin-binding protein and plays a pivotal role in neuronal and adipocyte differentiation. The present study was designed to examine the gonadotropin regulation and action of ENC1 during the ovulatory process in immature rats. The levels of ENC1 mRNA and protein were stimulated by LH/human chorionic gonadotropin (hCG) within 3 h both in vivo and in vitro. In situ hybridization analysis revealed that ENC1 mRNA was localized not only in theca/interstitial cells but also in granulosa cells of preovulatory follicles but not of growing follicles in pregnant mare's serum gonadotropin/hCG-treated ovaries. LH-induced ENC1 expression was suppressed by a high dose of protein kinase C inhibitor RO 31-8220 (10 microM) but not by low doses of RO 31-8220 (0.1-1.0 microM), suggesting the involvement of atypical protein kinase C. ENC1 was detected in both nucleus and cytoplasm that was increased by LH/hCG treatment. Both biochemical and morphological analysis revealed that LH/hCG treatment increased actin polymerization within 3 h in granulosa cells. Interestingly, ENC1 physically associated with actin and treatment with cytochalasin D, an actin-depolymerizing agent, abolished this association. Confocal microscopy further demonstrated the colocalization of ENC1 with filamentous actin (F-actin). The present study demonstrates that LH/hCG stimulates ENC1 expression and increases F-actin formation in granulosa cells. The present study further shows the physical association of ENC1 and F-actin, implicating the role of ENC1 in cytoskeletal reorganization during the differentiation of granulosa cells.

Transcriptional regulation of steroidogenic genes: STARD1, CYP11A1 and HSD3B

Expression of the genes that mediate the first steps in steroidogenesis, the steroidogenic acute regulatory protein (STARD1), the cholesterol side-chain cleavage enzyme, cytochrome P450scc (CYP11A1) and 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (HSD3B), is tightly controlled by a battery of transcription factors in the adrenal cortex, the gonads and the placenta. These genes generally respond to the same hormones that stimulate steroid production through common pathways such as cAMP signaling and common actions on their promoters by proteins such as NR5A and GATA family members. However, there are distinct temporal, tissue and species-specific differences in expression between the genes that are defined by combinatorial regulation and unique promoter elements. This review will provide an overview of the hormonal and transcriptional regulation of the STARD1, CYP11A1 and specific steroidogenic HSD3B genes in the adrenal, testis, ovary and placenta and discuss the current knowledge regarding the key transcriptional factors involved.

FSH and FOXO1 regulate genes in the sterol/steroid and lipid biosynthetic pathways in granulosa cells

The forkhead box transcription factor FOXO1 is highly expressed in granulosa cells of growing follicles but is down-regulated by FSH in culture or by LH-induced luteinization in vivo. To analyze the function of FOXO1, we infected rat and mouse granulosa cells with adenoviral vectors expressing two FOXO1 mutants: a gain-of-function mutant FOXOA3 that has two serine residues and one threonine residue mutated to alanines rendering this protein constitutively active and nuclear and FOXOA3-mutant DNA-binding domain (mDBD) in which the DBD is mutated. The infected cells were then treated with vehicle or FSH for specific time intervals. Infection of the granulosa cells was highly efficient, caused only minimal apoptosis, and maintained FOXO1 protein at levels of the endogenous protein observed in cells before exposure to FSH. RNA was prepared from control and adenoviral infected cells exposed to vehicle or FSH for 12 and 24 h. Affymetrix microarray and database analyses identified, and real time RT-PCR verified, that genes within the lipid, sterol, and steroidogenic biosynthetic pathways (Hmgcs1, Hmgcr, Mvk, Sqle, Lss, Cyp51, Tm7sf2, Dhcr24 and Star, Cyp11a1, and Cyp19), including two key transcriptional regulators Srebf1 and Srebf2 of cholesterol biosynthesis and steroidogenesis (Nr5a1, Nr5a2), were major targets induced by FSH and suppressed by FOXOA3 and FOXOA3-mDBD in the cultured granulosa cells. By contrast, FOXOA3 and FOXOA3-mDBD induced expression of Cyp27a1 mRNA that encodes an enzyme involved in cholesterol catabolism to oxysterols. The genes up-regulated by FSH in cultured granulosa cells were also induced in granulosa cells of preovulatory follicles and corpora lutea collected from immature mice primed with FSH (equine choriogonadotropin) and LH (human choriogonadotropin), respectively. Conversely, Foxo1 and Cyp27a1 mRNAs were reduced by these same treatments. Collectively, these data provide novel evidence that FOXO1 may play a key role in granulosa cells to modulate lipid and sterol biosynthesis, thereby preventing elevated steroidogenesis during early stages of follicle development.

Transcription of steroidogenic acute regulatory protein in the rodent ovary and placenta: alternative modes of cyclic adenosine 3', 5'-monophosphate dependent and independent regulation

Steroid hormone synthesis is a vital function of the adrenal cortex, serves a critical role in gonadal function, and maintains pregnancy if normally executed in the placenta. The substrate for the synthesis of all steroid hormones is cholesterol, and its conversion to the first steroid, pregnenolone, by the cholesterol side-chain cleavage cytochrome P450 (CYP11A1) enzyme complex takes place in the inner mitochondrial membranes. Steroidogenic acute regulatory protein (STAR) facilitates the rate-limiting transfer of cholesterol from the outer mitochondrial membrane to CYP11A1 located in the inner organelle membranes. The current study explored the mechanisms controlling transcription of the Star gene in primary cell cultures of mouse placental trophoblast giant cells and rat ovarian granulosa cells examined throughout the course of their functional differentiation. Our findings show that the cis-elements required for Star transcription in the rodent placenta and the ovary are centered in a relatively small proximal region of the promoter. In placental trophoblast giant cells, cAMP is required for activation of the Star promoter, and the cis-elements mediating a maximal response were defined as cAMP response element 2 and GATA. EMSA studies show that placental cAMP-responsive element binding protein (CREB)-1 and activating transcription factor-2 (ATF2) bind to a -81/-78 sequence, whereas GATA-2 binds to a -66/-61 sequence. In comparison, patterns of Star regulation in the ovary suggested tissue-specific and developmental controlled modes of Star transcription. During the follicular phase, FSH/cAMP induced CREB-1 dependent activity, whereas upon luteinization STAR expression becomes cAMP and CREB independent, a functional shift conferred by FOS-related antigen-2 displacement of CREB-1 binding, and the appearance of a new requirement for CCAAT enhancer-binding protein beta and steroidogenic factor 1 that bind to upstream elements (-117/-95). These findings suggest that during evolution, the promoters of the Star gene acquired nonconsensus sequence elements enabling expression of a single gene in different organs, or allowing dynamic temporal changes corresponding to progressing phases of differentiation in a given cell type.

Constitutively active protein kinase A qualitatively mimics the effects of follicle-stimulating hormone on granulosa cell differentiation

Activation of the protein kinase A (PKA) signaling system is necessary for FSH-induced granulosa cell differentiation, but it is not known whether activation of PKA is sufficient to account for the complex pattern of gene expression that occurs during this process. We addressed this question by infecting granulosa cells with a lentiviral vector that directs the expression of a constitutively active mutant of PKA (PKA-CQR) and compared the cellular responses to PKA-CQR with cells stimulated by FSH. Expression of PKA-CQR in undifferentiated granulosa cells resulted in the induction of both estrogen and progesterone production in the absence of cAMP. The stimulatory effects of both PKA-CQR and FSH on estrogen and progesterone production were suppressed by the PKA inhibitor H-89 and were mimicked by PKA-selective cAMP agonists. mRNA levels for P450scc and 3beta-HSD were induced to a similar extent by FSH and PKA-CQR, whereas mRNA levels for P450arom and the LHr were induced to a greater extent by FSH. Microarray analysis of gene expression profiles revealed that the majority of genes appeared to be comparably regulated by FSH and PKA-CQR but that some genes appear to be induced to a greater extent by FSH than by PKA-CQR. These results indicate that the PKA signaling pathway is sufficient to account for the induction of most genes (as identified by microarray analysis), including those of the progesterone biosynthetic pathway during granulosa cell differentiation. However, optimal induction of aromatase, the LHr, and other genes by FSH appears to require activation of additional signaling pathways.

Effect of estrogen on the expression of luteinizing hormone-human chorionic gonadotropin receptor messenger ribonucleic acid in cultured rat granulosa cells

Estrogen has been considered to enhance FSH actions in the ovary, including the induction of the LH receptor (LHR). In this study, we elucidated the mechanism underlying the effect of estrogen on the induction of LHR by FSH in rat granulosa cells. Estradiol clearly enhanced the FSH-induced LHR mRNA increase in a time- and dose-dependent manner, with a maximum increase of approximately 3.5-fold at 72 h, compared with the level of LHR mRNA solely induced by FSH. We then investigated whether the effect of estrogen on LHR mRNA was due to increased transcription and/or altered mRNA stability. A luciferase assay with the plasmid containing the LHR 5'-flanking region did not show that estradiol increased the promoter activity induced by FSH. In contrast, the decay curves for LHR mRNA showed a significant increase in half-life with FSH and estradiol, suggesting that the increased stability of LHR mRNA is at least responsible for the regulation of LHR mRNA by estrogen. Recently mevalonate kinase (Mvk) was identified as a trans-factor that binds to LHR mRNA and alters LHR mRNA stability in the ovary. We found that estradiol, with FSH, decreased Mvk mRNA levels in rat granulosa cell culture, resulting in up-regulation of LHR mRNA that was inversely correlated to Mvk mRNA expression. Furthermore, the augmentation of FSH-induced LHR expression in the presence of estrogen was erased with the overexpression of Mvk by transient transfection. Taken together, these data indicate that LHR mRNA is up-regulated due to increased stability when estrogen negatively controls Mvk.

AKR1B7 (mouse vas deferens protein) is dispensable for mouse development and reproductive success

AKR1B7 (aldo-keto reductase family 1, member 7; also known as mouse vas deferens protein) is a member of the AKR superfamily, and has been suggested to play a role in detoxifying processes on account of its preferred substrates, 4-hydroxynonenal and isocaproaldehyde. High levels of protein expression were found in the vas deferens and the adrenal gland, where sustained expression is dependent on androgen or ACTH respectively. Recently, a remarkable induction of AKR1B7 expression has been reported in the ovary following exogenous injections of LH. In the present study, we confirm this regulation physiologically during the estrous cycle, observing Akr1b7 expression to be restricted to the theca and stromal cells of the proestrus ovary. To further investigate the role of this detoxifying enzyme in both male and female reproduction, we generated knockout mice deficient in AKR1B7. Although AKR1B7 expression in the vas deferens is considerable and tightly regulated in the ovary of wild-type animals, homozygous mutant animals were found to be viable and no reproductive phenotype was observed. Ovarian follicle maturation and spermatozoa parameters remained normal in the absence of this protein. The determination of serum progesterone revealed an increase in hormone concentration in metestrus, while progesterone was found to be decreased in the estrus phase of the cycle in knockout females.

The molecular control of corpus luteum formation, function, and regression

The corpus luteum (CL) is one of the few endocrine glands that forms from the remains of another organ and whose function and survival are limited in scope and time. The CL is the site of rapid remodeling, growth, differentiation, and death of cells originating from granulosa, theca, capillaries, and fibroblasts. The apparent raison d'etre of the CL is the production of progesterone, and all the structural and functional features of this gland are geared toward this end. Because of its unique importance for successful pregnancies, the mammals have evolved a complex series of checks and balances that maintains progesterone at appropriate levels throughout gestation. The formation, maintenance, regression, and steroidogenesis of the CL are among the most significant and closely regulated events in mammalian reproduction. During pregnancy, the fate of the CL depends on the interplay of ovarian, pituitary, and placental regulators. At the end of its life span, the CL undergoes a process of regression leading to its disappearance from the ovary and allowing the initiation of a new cycle. The generation of transgenic, knockout and knockin mice and the development of innovative technologies have revealed a novel role of several molecules in the reprogramming of granulosa cells into luteal cells and in the hormonal and molecular control of the function and demise of the CL. The current review highlights our knowledge on these key molecular events in rodents.

Participation of mitogen-activated protein kinase in luteinizing hormone-induced differential regulation of steroidogenesis and steroidogenic gene expression in mural and cumulus granulosa cells of mouse preovulatory follicles

The LH surge induces the terminal differentiation and onset of luteinization in granulosa cells of preovulatory follicles, a process that involves the differential expression of genes essential for steroidogenesis and appears to be mediated by complex signaling pathways. The objective of this study was to investigate whether these processes that commonly occur in mural granulosa cells (MGCs) also occur in cumulus cells, and whether they are mediated by the mitogen-activated protein kinase (MAPK), specifically MAPK3/1 (also commonly known as extracellular signal-regulated kinase 1&2, ERK1/2). The standard superovulation model for premature female mice was used to obtain MGCs and cumulus-oocyte complexes (COCs), and sensitive real-time RT-PCR was used to simultaneously detect the expression levels of transcripts encoding key steroidogenic enzymes in the same sample. We observed significant downregulation of Cyp19a1 and upregulation of Star and Cyp11a1 mRNA expression in both COCs and MGCs after in vivo administration of hCG or in vitro treatment with gonadotropins or 8-Br-cAMP. This differential pattern of steroidogenic gene expression was correlated with the ultimate changes of circulating estradiol (E(2)) and progesterone (P(4)) levels after administration of hCG. In vitro, when MGCs and COCs were treated with U0126 - a specific inhibitor of MAPK3/1 activation - gonadotropin-induced P(4) production, 8-Br-cAMP-induced P(4) production, and expression of Star and Cyp11a1 mRNA were significantly downregulated, whereas the levels of E(2) and Cyp19a1 mRNA in the same samples were significantly upregulated. We conclude that the surge of preovulatory LH induces the differential expression of transcripts encoding key steroidogenic enzymes essential for E(2) and P(4) synthesis in both cumulus and MGCs, and this process is mediated by the MAPK3/1-dependent pathway.

Luteinizing hormone-induced RUNX1 regulates the expression of genes in granulosa cells of rat periovulatory follicles

The LH surge induces specific transcription factors that regulate the expression of a myriad of genes in periovulatory follicles to bring about ovulation and luteinization. The present study determined 1) the localization of RUNX1, a nuclear transcription factor, 2) regulation of Runx1 mRNA expression, and 3) its potential function in rat ovaries. Up-regulation of mRNA and protein for RUNX1 is detected in preovulatory follicles after human chorionic gonadotropin (hCG) injection in gonadotropin-treated immature rats as well as after the LH surge in cycling animals by in situ hybridization and immunohistochemical and Western blot analyses. The regulation of Runx1 mRNA expression was investigated in vitro using granulosa cells from rat preovulatory ovaries. Treatments with hCG, forskolin, or phorbol 12 myristate 13-acetate stimulated Runx1 mRNA expression. The effects of hCG were reduced by inhibitors of protein kinase A, MAPK kinase, or p38 kinase, indicating that Runx1 expression is regulated by the LH-initiated activation of these signaling mediators. In addition, hCG-induced Runx1 mRNA expression was inhibited by a progesterone receptor antagonist and an epidermal growth factor receptor tyrosine kinase inhibitor, whereas amphiregulin stimulated Runx1 mRNA expression, demonstrating that the expression is mediated by the activation of the progesterone receptor and epidermal growth factor receptor. Finally, knockdown of Runx1 mRNA by small interfering RNA decreased progesterone secretion and reduced levels of mRNA for Cyp11a1, Hapln1, Mt1a, and Rgc32. The hormonally regulated expression of Runx1 in periovulatory follicles, its involvement in progesterone production, and regulation of preovulatory gene expression suggest important roles of RUNX1 in the periovulatory process.

Cloning and characterization of a cDNA encoding cholesterol side-chain cleavage cytochrome P450 (CYP11A1): tissue-distribution and changes in the transcript abundance in ovarian tissue of Japanese eel, Anguilla japonica, during artificially induced sexual development

Cholesterol side-chain cleavage cytochrome P450 (CYP11A1: P450scc) is a crucial steroidogenic enzyme that catalyzes an initial step in the production of all classes of steroids. A cDNA encoding Japanese eel P450scc was cloned and characterized. The cDNA putatively encoded 521 amino acid residues with high homology to those of other vertebrate forms. The recombinant P450scc produced in COS-7 cells efficiently catalyzed the conversion of 25-hydroxycholesterol into pregnenolone. By northern blot, a single P450scc transcript of approximately 3.3 kb was detected in both ovary and head kidney. Transcript levels of this enzyme significantly increased throughout ovarian development artificially induced by salmon pituitary homogenate, which suggests that gonadotropic stimuli can induce ovarian expression of the P450scc gene in teleosts, as has been reported in mammals. Furthermore, RT-PCR analysis revealed that gene expression of three steroidogenic enzymes, P450scc, P450c17 and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) show distinctly different tissue-specific patterns of expression in the Japanese eel. The P450scc gene was expressed in ovary and head kidney while the sole source of the P450c17 transcript was ovary. In contrast, 3beta-HSD transcript was detected in all tissues examined, brain, liver, spleen and trunk kidney, etc. These suggest that some steroidogenic enzymes are also expressed in non-endocrine tissues and could potentially regulate the local and/or circulating steroid levels in teleosts, as they do in mammals.

FSH signaling pathways in immature granulosa cells that regulate target gene expression: branching out from protein kinase A

Follicle-stimulating hormone (FSH) is necessary and sufficient to induce maturation of ovarian follicles to a mature, preovulatory phenotype in the intact animal, resulting in the generation of mature eggs and production of estrogen. FSH accomplishes these actions by inducing a complex pattern of gene expression in target granulosa cells that is regulated by input from many different signaling cascades, including those for the extracellular regulated kinases (ERKs), p38 mitogen-activated protein kinases (MAPKs), and phosphatidylinositol-3 kinase (PI3K). The upstream kinase that appears to be responsible for initiating all of the signaling that regulates gene expression in these epithelial cells is protein kinase A (PKA). PKA not only signals to directly phosphorylate transcription factors like cAMP response element binding protein and to promote chromatin remodeling by phosphorylating histone H3, this versatile kinase also enhances the activity of the p38 MAPK, ERK, and PI3K pathways. Additionally, accumulating evidence suggests that activation of a single signaling cascade downstream of PKA is not sufficient to activate target gene expression. Rather, cross-talk between and among signaling cascades is required. We will review the signaling cascades activated by FSH in granulosa cells and how these cascades contribute to the regulation of select target gene expression.

Mice Null for Frizzled4 (Fzd4−/−) Are Infertile and Exhibit Impaired Corpora Lutea Formation and Function1

Previous studies showed that transcripts encoding specific Wnt ligands and Frizzled receptors including Wnt4, Frizzled1 (Fzd1), and Frizzled4 (Fzd4) were expressed in a cell-specific manner in the adult mouse ovary. Overlapping expression of Wnt4 and Fzd4 mRNA in small follicles and corpora lutea led us to hypothesize that the infertility of mice null for Fzd4 (Fzd4-/-) might involve impaired follicular growth or corpus luteum formation. Analyses at defined stages of reproductive function indicate that immature Fzd4-/- mouse ovaries contain follicles at many stages of development and respond to exogenous hormone treatments in a manner similar to their wild-type littermates, indicating that the processes controlling follicular development and follicular cell responses to gonadotropins are intact. Adult Fzd4-/- mice also exhibit normal mating behavior and ovulate, indicating that endocrine events controlling these processes occur. However, Fzd4-/- mice fail to become pregnant and do not produce offspring. Histological and functional analyses of ovaries from timed mating pairs at Days 1.5-7.5 postcoitus (p.c.) indicate that the corpora lutea of the Fzd4-/- mice do not develop normally. Expression of luteal cell-specific mRNAs (Lhcgr, Prlr, Cyp11a1 and Sfrp4) is reduced, luteal cell morphology is altered, and markers of angiogenesis and vascular formation (Efnb1, Efnb2, Ephb4, Vegfa, Vegfc) are low in the Fzd4-/- mice. Although a recently identified, high-affinity FZD4 ligand Norrin (Norrie disease pseudoglioma homolog) is expressed in the ovary, adult Ndph-/- mice contain functional corpora lutea and do not phenocopy Fzd4-/- mice. Thus, Fzd4 appears to impact the formation of the corpus luteum by mechanisms that more closely phenocopy Prlr null mice.

Mitochondrial 3 beta-hydroxysteroid dehydrogenase (HSD) is essential for the synthesis of progesterone by corpora lutea: an hypothesis

In mouse ovaries, the enzyme 3 beta-hydroxysteroid dehydrogenase (HSD) is distributed between microsomes and mitochondria. Throughout the follicular phase of the estrous cycle, the HSD activity in microsomes is predominant; whereas, after LH stimulation, HSD activity during the luteal phase is highest in the mitochondria. The current study examined whether or not LH stimulation always results in an increase in mitochondrial HSD activity. This was accomplished by measuring the HSD activity in microsomal and mitochondrial fractions from ovaries of pregnant mice. These animals have two peaks of LH during gestation, and one peak of LH after parturition. It was found that mitochondrial HSD activity was highest after each peak of LH. It is proposed that mitochondrial HSD is essential for the synthesis of high levels of progesterone. The increase in HSD activity in mitochondria after LH stimulation occurs because: 1) LH initiates the simultaneous synthesis of HSD and the cholesterol side-chain cleavage enzyme (P450scc); and, 2) HSD and P450scc bind together to form a complex, which becomes inserted into the inner membrane of the mitochondria. High levels of progesterone are synthesized by mitochondrial HSD because: 1) the requisite NAD+ cofactor for progesterone synthesis is provided directly by the mitochondria, rather than indirectly via the rate limiting malate-aspartate shuttle; and, 2) the end-product inhibition of P450scc by pregnenolone is eliminated because pregnenolone is converted to progesterone.

Identification of a stanniocalcin paralog, stanniocalcin-2, in fish and the paracrine actions of stanniocalcin-2 in the mammalian ovary

Stanniocalcin is a glycoprotein hormone important in the maintenance of calcium and phosphate homeostasis in fish. Two related mammalian stanniocalcin genes, STC1 and STC2, were found to be expressed in various tissues as paracrine regulators. We have demonstrated the existence of a second stanniocalcin gene in fish, designated fish STC2, with only 30% identity to fish STC1. However, phylogenetic analysis and comparison of the genomic structure of STC genes in vertebrates indicated that STC1 and STC2 genes were probably derived from a common ancestor gene. Based on the prominent expression of mammalian STC1 in the ovary, we tested STC2 expression in rat ovary and the regulation of STC2 expression by gonadotropins. Treatment of immature rats with pregnant mare serum gonadotropin increased STC2 transcripts, whereas subsequent treatment with human chorionic gonadotropin suppressed STC2 expression. Real-time PCR analyses also demonstrated that STC2 is expressed mainly in thecal layers. In situ hybridization studies also revealed that STC2 is expressed in thecal cell layers of antral and preovulatory follicles after gonadotropin stimulation. To elucidate the physiological functions of STC2, recombinant human and fish STC2 proteins were generated and found to be N-glycosylated homodimers. In cultured granulosa cells, treatment with human or fish STC2 suppressed FSH-induced progesterone, but not estradiol or cAMP, production. The STC2 suppression of progesterone production was associated with the inhibition of FSH-induced CYP11A and 3beta-hydroxysteroid dehydrogenase expression. Thus, STC2 is a functional homodimeric glycoprotein, and thecal cell-derived STC2 could play a paracrine role during follicular development.

Dexamethasone-induced Changes in Sympathetic Innervation of Porcine Ovaries and in Their Steroidogenic Activity

The aim of the present study was to determine changes in the density of sympathetic nerves in porcine ovaries with dexamethasone (DXM)-induced cysts and the alterations in steroidogenic activity and amounts of catecholamines in the affected gonads. Cystic ovaries were supplied by numerous sympathetic nerve fibers. The amount of noradrenaline in the cysts (fluid, wall) was significantly higher than in the large follicles of the control group. After DXM injections, the amounts of noradrenaline and adrenaline significantly increased in the walls of small and medium-sized follicles. In the cysts (fluid, wall) the levels of androgens and estrogens were significantly lower, whereas progesterone was higher in the cystic wall. DXM administration led to a significant increase in the estrone content in the fluid of small follicles. Moreover, a decrease in the amounts of progesterone and androgens was found in the follicular fluid and walls of medium-sized follicles. DXM injections resulted in a significant increase in the immunoexpression of P450(scc) and 3beta-HSD in the cysts, a significant increase of P450(scc) in the follicles, and a decrease of 3beta-HSD and P450(arom). The present study shows that the DXM treatment leads to an increase in the density of intraovarian sympathetic nerves, paralleled by the amount of catecholamines, and that it is capable of changing the steroidogenic activity of porcine ovary bearing cysts. Thus, it appears possible that these events may be, at least partly, involved in the pathogenesis of this disorder.

Expression of the GATA-4 and GATA-6 transcription factors in the fetal rat gonad and in the ovary during postnatal development and pregnancy

Immunohistochemical studies were undertaken to determine the distribution of GATA-4 and GATA-6 in rat fetal gonad and the postnatal ovary during development and pregnancy. In the undifferentiated gonad, GATA-4 was expressed in the somatic cells of both sexes. After differentiation of the ovary and testis, GATA-4 expression continued in both ovarian and testicular somatic cells; whereas, GATA-6 was expressed in both somatic and germ cells. In the ovary of postnatal rats, granulosa and thecal cells of healthy follicles expressed both GATA factors. In the adult rat, GATA-4 expression was lower in corpora lutea as compared to follicles; whereas, GATA-6 was strongly expressed in both structures. GATA-4 expression was greater in functional corpora lutea than regressing corpora lutea. GATA-6 was expressed in both functional and regressing corpora lutea. In all postnatal ovaries, the expression of P450scc localized with tissue expressing GATA-4 and/or GATA-6, but GATA expression also occurred in P450scc negative cells.

Luteal 3beta-hydroxysteroid dehydrogenase and 20alpha-hydroxysteroid dehydrogenase activities in the rat corpus luteum of pseudopregnancy: effect of the deciduoma reaction

BACKGROUND

In the rat, the maintenance of gestation is dependent on progesterone production from the corpora lutea (CL), which are under the control of pituitary, decidual and placental hormones. The luteal metabolism of progesterone during gestation has been amply studied. However, the regulation of progesterone synthesis and degradation during pseudopregnancy (PSP), in which the CL are mainly under the control of pituitary prolactin (PRL), is not well known. The objectives of this investigation were: i) to study the luteal metabolism of progesterone during PSP by measuring the activities of the enzymes 3beta-hydroxysteroid dehydrogenase (3betaHSD), involved in progesterone biosynthesis, and that of 20alpha-hydroxysteroid dehydrogenase (20alphaHSD), involved in progesterone catabolism; and ii) to determine the role of decidualization on progesterone metabolism in PSP.

METHODS

PSP was induced mechanically at 10:00 h on the estrus of 4-day cycling Wistar rats, and the stimulus for decidualization was provided by scratching the uterus on day 4 of PSP. 3betaHSD and 20alphaHSD activities were measured in the CL isolated from ovaries of PSP rats using a spectrophotometric method. Serum concentrations of progesterone, PRL, androstenedione, and estradiol were measured by radioimmunoassay (RIA).

RESULTS

The PSP stage induced mechanically in cycling rats lasted 11.3 +/- 0.09 days (n = 14). Serum progesterone concentration was high until day 10 of PSP, and declined thereafter. Serum PRL concentration was high on the first days of PSP but decreased significantly from days 6 to 9, having minimal values on days 10 and 11. Luteal 3betaHSD activities were elevated until day 6 of PSP, after which they progressively declined, reaching minimal values at the end of PSP. Luteal 20alphaHSD activities were very low until day 9, but abruptly increased at the end of PSP. When the deciduoma was induced by scratching the uterus of pseudopregnant animals on day 4 (PSP+D), PSP was extended to 18 +/- 2.2 days (n = 8). In PSP + D rats, serum progesterone and PRL levels, and luteal 3betaHSD activities were higher than in pseudopregnant rats on day 11. Decidualization also prevented the increase in luteal 20alphaHSD activities observed on day 11 of PSP. Administration of the dopaminergic agonist CB154 in PSP + D rats on day 10 of PSP induced a decline in both serum PRL and progesterone on day 11 of PSP, values that were not different from that of pseudopregnant controls.

CONCLUSIONS

We have established that during the final period of PSP a decline in progesterone biosynthesis occurs before the increase in progesterone catabolism. We have also shown that decidualization in pseudopregnant rats extends the life of the CL by prolonging the production of pituitary PRL, and by maintaining high 3betaHSD and low 20alphaHSD activities within the CL leading to sustained production of progesterone.

Inverse relationship between the expression of messenger ribonucleic acid for peroxisome proliferator-activated receptor gamma and P450 side chain cleavage in the rat ovary

Messenger RNA for peroxisome proliferator-activated receptor gamma (PPARgamma) has been found in granulosa cells, and its expression decreases after the LH surge. We determined which developmental stage of ovarian follicle expresses mRNA for PPARgamma and evaluated the impact of PPARgamma agonists on steroidogenesis. Ovaries were collected from immature eCG/hCG-treated rats at 0 (no eCG), 24, and 48 h post-eCG and 4 and 24 h post-hCG. Ovarian tissue was serially sectioned and processed for in situ hybridization to localize mRNA corresponding to PPARgamma, aromatase, and the LH receptor, and P450 side chain cleavage (P450SCC) and to determine whether apoptotic cells were present. During follicular development, there was no correlation between the expression of mRNAs for PPARgamma and aromatase or the presence of apoptotic cells, but a general inverse correlation was observed between the expression of PPARgamma mRNA and LH receptor mRNA. At 4 h post-hCG, follicles expressing P450SCC mRNA had lost expression of PPARgamma mRNA. This inverse pattern of expression between PPARgamma and P450SCC mRNAs was also observed 24 h post-hCG, with developing luteal tissue expressing high levels of P450SCC mRNA but little or no PPARgamma mRNA. To determine the impact of PPARgamma on steroidogenesis, granulosa cells were collected from ovaries 24 h post-eCG and cultured alone, with FSH alone, or with FSH in combination with the PPARgamma agonists ciglitazone or 15-deoxy-delta 12,14-prostaglandin J2 (PGJ2). Treatment of granulosa cells with PGJ2 stimulated basal progesterone secretion, whereas ciglitazone or PGJ2 had no significant effect on FSH-stimulated steroid production. These findings suggest that 1) PPARgamma may regulate genes involved with follicular differentiation and 2) the decline in PPARgamma in response to LH is important for ovulation and/or luteinization.

Phosphodiesterase regulation is critical for the differentiation and pattern of gene expression in granulosa cells of the ovarian follicle

Feedback regulations are integral components of the cAMP signaling required for most cellular processes, including gene expression and cell differentiation. Here, we provide evidence that one of these feedback regulations involving the cyclic nucleotide phosphodiesterase PDE4D plays a critical role in cAMP signaling during the differentiation of granulosa cells of the ovarian follicle. Gonadotropins induce PDE4D mRNA and increase the cAMP hydrolyzing activity in granulosa cells, demonstrating that a feedback regulation of cAMP is operating in granulosa cells in vivo. Inactivation of the PDE4D by homologous recombination is associated with an altered pattern of cAMP accumulation induced by the gonadotropin LH/human chorionic gonadotropin (hCG), impaired female fertility, and a markedly decreased ovulation rate. In spite of a disruption of the cAMP response, LH/hCG induced P450 side chain cleavage expression and steroidogenesis in a manner similar to wild-type controls. Morphological examination of the ovary of PDE4D-/- mice indicated luteinization of antral follicles with entrapped oocytes. Consistent with the morphological finding of unruptured follicles, LH/hCG induction of genes involved in ovulation, including cyclooxygenase-2, progesterone receptor, and the downstream genes, is markedly decreased in the PDE4D-/- ovaries. These data demonstrate that PDE4D regulation plays a critical role in gonadotropin mechanism of action and suggest that the intensity and duration of the cAMP signal defines the pattern of gene expression during the differentiation of granulosa cells.

Temporal effect of tamoxifen on cytochrome P450 side chain cleavage gene expression and steroid concentration in adult male rats

Adult male rats when treated with 0.4 mg tamoxifen (tam)/kg per day for 90 days show reduced circulating testosterone (T) and LH. The present study was designed to have an in depth understanding of tam induced androgen reduction in adult male rats. Adult male rats were orally administered 0.4 mg tam/kg per day for 30, 60 or 90 days and the temporal effects on intratesticular concentrations of pregnenolone (P(5)), progesterone (P(4)), T, 5 alpha-dihydrotestosterone (5 alpha-DHT) and estradiol (E(2)) were estimated. Control group rats were fed saline. Serum hormonal profile of LH, FSH, T and E(2) was also followed on these days. Testicular levels of cytochrome P450 scc mRNA transcripts on 30, 60 and 90 days of treatment with the same dose were quantitated by biplex RT-PCR using beta Actin as internal control followed by analysis using GelPro Analysis software.A significant reduction in intratesticular P(5), P(4), T, 5 alpha-DHT and E(2) was observed from day 30 of treatment. The P450 scc gene expression in the testis was reduced during treatment period from day 60 of treatment. This study demonstrates for the first time that tam reduces testicular pregnenolone biosynthesis through an effect on cholesterol transport and downregulation of P450 scc gene expression. In confirmation of the observed estrogenic effects of tam in this study, it is suggested that E(2) may have a role in cholesterol transport and testicular pregnenolone biosynthesis at the level of cytochrome P450 scc as shown by us.

Regulation of progesterone and prostaglandin F2alpha production in the CL

After the luteinizing hormone (LH) surge, the cells that remain from the ovulated follicle undergo a process of differentiation termed luteinization. Two key features of the cells after luteinization are the capacity for tremendous production of progesterone [10(16) molecules of progesterone per (min/(g of CL))] and the capacity to undergo regression or death of the cells at the appropriate time. There are two steroidogenic cell types, the small and large luteal cells that are regulated by different mechanisms. In small luteal cells, production of progesterone is stimulated by LH through the protein kinase A (PKA) pathway. The large luteal cells of ruminants produce large quantities of progesterone that is independent of LH stimulation. Although luteotrophins clearly regulate luteal function, much of luteal progesterone production in some species appears to be constitutive, consistent with the autonomous aspects of the large luteal cell. The key regulated step in luteal progesterone production appears to be regulation of transport of cholesterol to the inner mitochondrial membrane apparently mediated by the steroidogenic acute regulatory protein (StAR). In addition, our recent research indicates that PKA is tonically active in large luteal cells and this may be responsible for the high, relatively autonomous nature of luteal progesterone production. Regression of the corpus luteum (CL) in many species is initiated by prostaglandin (PG) F2alpha secreted from the uterus. Luteal cells also have the capacity for production of PGF2alpha. Luteal PGF2alpha production can be regulated by a variety of substances including inhibition by progesterone and stimulation by cytokines. We have also characterized a positive feedback pathway in ruminant and porcine CL in which small amounts of uterine PGF(2alpha) stimulate intraluteal production of PGF2alpha due to induction of the cycloxygenase-2 (Cox-2) enzyme in large luteal cells. This positive feedback pathway is only present in CL that has acquired the capacity for luteal regression ( approximately day 7 in cow, approximately day 13 in pig). Regulation by protein kinase C (PKC) of transcriptional factors interacting with an E-box in the 5' flanking region of the Cox-2 gene is the critical regulatory element involved in this positive feedback pathway. Thus, luteinization in some species appears to change specific gene transcription such that progesterone production becomes relatively independent of acute luteotrophic regulation and intraluteal PGF2alpha synthesis is induced by the second messenger pathways that are activated by PGF2alpha.

Expression of the bovine oestrogen receptor-beta (bERbeta) messenger ribonucleic acid (mRNA) during the first ovarian follicular wave and lack of change in the expression of bERbeta mRNA of second wave follicles after LH infusion into cows

In a previous study, the ERbeta cDNA protein-coding region was utilised to clone bovine ERbeta. The objectives in this study were to examine (1) ERbeta mRNA expression in ovarian follicles throughout the bovine first follicular wave, and (2) effect of LH infusion into cows on bERbeta mRNA expression during the second follicular wave. In experiment 1, heifers (4-5 per time point) were ovariectomized at 12, 24, 36, 48, 60, 72, 84, 96, 144, or 216 h after emergence of the first follicular wave after oestrus. In experiment 2, saline or LH was pulsed hourly (computer-controlled syringe pump) into cows (n = 31; 5-6 per treatment) at wave emergence for 2 or 4 days: wave 1-saline (W1S), wave 2-saline (W2S), or wave 2-LH (25 microg/h; W2LH). Ovaries were removed on day 2 or day 4 after wave emergence. Follicles, 2-19mm in size, were dissected, frozen, and stored at -80 degrees C for in situ hybridisation with two bERbeta cRNA probes. Expression of bERbeta mRNA was localised in granulosa cells of healthy follicles. In experiment 1, bERbeta mRNA expression did not change with time points of the wave showing no association of bERbeta mRNA expression with follicular selection and dominance. However, bERbeta mRNA expression decreased with increase in size of all follicles. Expression of bERbeta mRNA was greater in very small follicles (2-4 mm) than in large (> or = 9 mm) follicles. In experiment 2, expression of bERbeta mRNA in follicles did not differ either between W1S and W2S or between W2S and W2LH. In summary, bERbeta mRNA expression decreased with increasing follicular size. However, neither stage of the wave (selection or dominance), nor pulsatile infusion of LH influenced bERbeta mRNA expression.

Analysis of ovarian gene expression in follicle-stimulating hormone beta knockout mice

FSH is a heterodimeric glycoprotein hormone that is produced in the gonadotroph cells of the anterior pituitary. It acts on Sertoli cells of the testis and granulosa cells of the ovary. We previously demonstrated that FSHbeta knockout female mice are infertile due to a block in folliculogenesis preceding antral stage development. To investigate aberrations of ovarian gene regulation in the absence of FSH, we analyzed the expression of several important marker genes using Northern blot and in situ hybridization techniques. Key findings are as follows: 1) Follicles of FSHbeta knockout mice develop a well organized thecal layer, which is positive for P450 17alpha-hydroxylase and LH receptor messenger RNAs (mRNAs). This indicates that theca recruitment is completed autonomously with respect to FSH. 2) Granulosa cells in FSH-deficient mice demonstrate an increase in FSH receptor mRNA, and decreases in P450 aromatase, serum/glucocorticoid-induced kinase, and inhibin/activin subunit mRNAs. These data support studies that implicate FSH signaling cascades in the expression of these genes. 3) In contrast to the thecal layer, granulosa cell populations in FSHbeta knockout mice do not accumulate LH receptor mRNA. This suggests that although the granulosa cells have a block in proliferation at the antral follicle stage in the absence of FSH, they do not initiate programs of terminal differentiation as seen in luteinizing cells of wild-type ovaries. 4) Ovaries of FSH-deficient mice demonstrate a modest decrease in cyclin D2 mRNA, without up-regulation of cell cycle inhibitor mRNAs associated with luteinization (i.e. p15, p27, and p21). Although components of the FSH null phenotype may be caused by partial cyclin D2 loss of function, these findings indicate that the mechanisms of granulosa cell cycle arrest in FSHbeta knockout mice are distinct from those of cycle withdrawal at luteinization. Underscoring the usefulness of the FSH-deficient mouse model, this study clarifies aspects of gonadotropin-dependent folliculogenesis, thecal layer development, cycle control in granulosa cells, and luteinization.

Follicle-stimulating hormone regulates steroidogenic enzymes in cultured cells of the chick embryo ovary

This investigation addresses the potential regulation of enzymes involved in the biosynthesis of steroid hormones during early stages of gonadal development by follicle-stimulating hormone (FSH). Gonadal cells of 10-day-old chick embryo and cells of the left ovary of 18-day-old chick embryo were cultured for 60 h in a defined medium with or without the addition of FSH (2.0 IU/ml). At the end of the culture, cells were recovered and evaluated by biotransformation of tritiated steroid precursors and mRNA levels were evaluated by RT-PCR. The production of estrone from androstenedione was increased in the FSH-treated cells, both human FSH (hFSH) and recombinant human FSH (rhFSH), indicating a stimulatory effect on aromatase (P450arom). Similarly, the intensity of the band corresponding to P450arom mRNA was higher in hFSH and rhFSH than in control and chorionic gonadotropin (hCG) groups. The P450arom stimulation was observed in the ovary of 10- and 18-day-old chick embryo. The transformation of dehydroepiandrosterone to androstenedione was taken as evidence of 3beta-hydroxysteroid dehydrogenase function. This enzyme was stimulated in the cultured ovarian cells of 18-day-old chick embryos treated with hFSH and rhFSH compared with controls. The production of pregnenolone in the mitocondrial fraction of 18-day-old chick embryo ovary was increased when cultured with hFSH and rhFSH. This observation together with the increase in the band intensity corresponding to mRNA of P450 cholesterol side-chain cleavage indicates stimulation by FSH treatment; hCG produced a similar effect. Somatic cells of the medullary cords are proposed to be FSH target cells in the ovary of the chick embryo.

Equine P450 cholesterol side-chain cleavage and 3 beta-hydroxysteroid dehydrogenase/delta(5)-delta(4) isomerase: molecular cloning and regulation of their messenger ribonucleic acids in equine follicles during the ovulatory process

The preovulatory LH rise is the physiological trigger of follicular luteinization, a process during which the synthesis of progesterone is markedly increased. To study the control of follicular progesterone biosynthesis in mares, the objectives of this study were to clone and characterize the equine cholesterol side-chain cleavage cytochrome P450 (P450(scc)) and 3 beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4)-isomerase (3 beta-HSD), and describe the regulation and cellular localization of their transcripts in equine follicles during hCG-induced ovulation. Complementary DNA cloning and primer extension analyses revealed that the equine P450(scc) transcript is composed of a 5'-untranslated region (UTR) of 52 nucleotides, an open reading frame (ORF) of 1560 nucleotides, and a 3'-UTR of 225 nucleotides, whereas the equine 3 beta-HSD mRNA consists of a 5'-UTR of 61 nucleotides, an ORF of 1119 nucleotides, and a 3'-UTR of 432 nucleotides. The equine P450(scc) and 3 beta-HSD ORF encode 520 and 373 amino acid proteins, respectively, that are highly conserved (68-79% identity) when compared to homologs of other mammalian species. Northern blot analyses were performed with preovulatory follicles isolated 0, 12, 24, 30, 33, 36, and 39 h post-hCG, and corpora lutea obtained on day 8 of the cycle. Results showed that levels of P450(scc) mRNA in follicular wall (theca interna with attached granulosa cells) decreased after hCG treatment (30-39 h versus 0 h post-hCG, P: < 0.05), and increased again after ovulation to reach their highest levels in corpora lutea (P: < 0.05). Northern blots on isolated cellular preparations revealed that theca interna was the predominant site of P450(scc) expression in follicles prior to hCG (P: < 0.05). However, transcript levels decreased in theca interna between 30-39 h (P: < 0.05) and increased in granulosa cells at 39 h (P: < 0.05), making the granulosa cell layer the predominant site of P450(scc) expression at the end of the ovulatory process. A different pattern of regulation was observed for 3 beta-HSD, as transcript levels remained constant throughout the luteinization process (P: > 0.05). Also, in contrast to other species, expression of 3 beta-HSD mRNA in equine preovulatory follicles was localized only in granulosa cells and not in theca interna. Thus, this study characterizes for the first time the complete structure of equine P450(scc) and 3 beta-HSD mRNA and identifies novel patterns of expression and regulation of these transcripts in equine follicles prior to ovulation.

Ovarian steroidogenic responsiveness to exogenous gonadotropin stimulation in young and middle-aged female rats

Reproductive aging in the female rat is associated with gradual declines in LH secretion and ovarian progesterone (P) production. This study examined whether the influences of aging on P levels reflect decreased ovarian responsiveness to gonadotropin stimulation, as opposed to changes in gonadotropin release. Young and middle-aged regularly cyclic female rats received sodium pentobarbital to block endogenous proestrous luteinizing hormone (LH) surges, followed by administration of various doses of human chorionic gonadotropin (hCG). Similar treatments were performed in middle-aged acyclic persistent-estrous (PE) females. Injection of hCG resulted in equivalent plasma hCG levels in each treatment group. At the lowest hCG dose tested, a significant rise in plasma P levels was observed in middle-aged cyclic rats, but not in young cyclic or middle-aged PE females. This unexpected finding may reflect accelerated follicular development in middle-aged cyclic females, as suggested by a previous study. At the intermediate dose, young and middle-aged cyclic but not PE rats displayed significantly increased P in response to hCG. At the highest dose tested, all three groups of rats displayed increased P levels after hCG stimulation. However, P concentrations were significantly lower in middle-aged PE than regularly cyclic females. Northern and slot blot hybridization analyses revealed that ovarian mRNA levels for cytochrome P450 side-chain cleavage, the rate-limiting enzyme in P synthesis, were markedly reduced in PE rats following hCG stimulation. These findings indicate that ovarian responsiveness to gonadotropin stimulation is impaired in middle-aged PE, but not regularly cyclic rats, and suggest influences of cycle status on the biochemical and molecular mechanisms regulating ovarian steroid production. Furthermore, these findings reveal that attenuated P production in middle-aged proestrous rats is due to attenuated preovulatory LH surges, rather than decreased ovarian sensitivity to LH.

Demonstration of 2,3,7,8-tetrachlorodibenzo-p-dioxin attenuation of P450 steroidogenic enzyme mRNAs in rat granulosa cell in vitro by competitive reverse transcriptase-polymerase chain reaction assay

We investigated the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), in prepubertal (PP) and adult (A) rat granulosa cells (GC) in vitro by examining the changes in estrogen secretion, aromatase enzyme activity and mRNAs for steroidogenic enzymes P450scc, 3beta-HSDI, P450arom; and for components of the AHR signaling pathway-CYP1A1, aromatic hydrocarbon receptor (AHR), and the AHR nuclear translocator protein (ARNT). In PP and A rat GC, TCDD (3.1 nM) reduced estrogen secretion at 48 h without altering aromatase enzyme activity. Addition of FSH (50 ng/ml) increased aromatase activity in GC with or without TCDD. FSH-induced aromatase activity was significantly reduced by TCDD (3.1 nM) at 48 h. Semi-quantitative RT-PCR showed a significant increase in CYP1A1 mRNA both at 24 and 48 h with TCAP, while a significant reduction in P450scc and P450arom mRNA was observed with competitive RT-PCR. All steroidogenic enzyme mRNAs were significantly lower in adults than in PP GC. We conclude that in rat GC, TCDD modulates the level of cytochrome P450 enzymes involved in the steroid biosynthetic cascade. This effect may be attributable to AHR interaction with dioxin-responsive elements present in the genes encoding these enzymes.

Regulation of PKC delta expression by estrogen and rat placental lactogen-1 in luteinized rat ovarian granulosa cells

Protein kinase C (PKC) delta is dramatically upregulated in the corpus luteum in the second half of pregnancy in the rat. To gain insight into the hormonal regulation of PKC delta expression, studies were undertaken to analyze the regulation of PKC delta expression in a luteinized rat granulosa cell model. PKC delta protein expression was evaluated in luteinized granulosa cells, isolated from human (h)CG-treated immature female rats 7 h after the injection of an ovulatory dose of hCG and cultured up to 12 days. Cytochrome P450 cholesterol side chain cleavage enzyme expression was observed throughout the culture period, and a majority of the cells expressed steroidogenic acute regulatory protein and responded to rat placental lactogen (rPL)-1 by exhibiting hypertrophy, consistent with maintenance of the luteal phenotype. Both PKC delta protein and mRNA expression increased 3.5-4-fold with time of culture, and PKC delta mRNA expression could be eliminated by treatment of cells with the PKC inhibitor GF109203X. E(2) caused a specific dose- and time-dependent increase in expression of PKC delta protein of twofold, whereas PKC delta mRNA was unaffected by E(2) over a 12-day culture period. Treatment of cells with 500 ng/ml rPL-1 for the final 4 days of a 12-day culture in the absence of E(2) had no effect on PKC delta protein or mRNA expression, while treatment with 500 or 3000 ng/ml rPL-1 in the presence of E(2) significantly enhanced both PKC delta protein and mRNA expression (up to threefold). These results show that two of the major regulators of luteal function in the second half of pregnancy in the rat, E(2) and rPL-1, cooperate to regulate PKC delta expression in luteinized granulosa cells.

Expression and localization of serum/glucocorticoid-induced kinase in the rat ovary: relation to follicular growth and differentiation

Expression of serum/glucocorticoid-inducible kinase (Sgk), one member of an inducible serine/threonine kinase family, is induced by FSH/cAMP in rat granulosa cells cultured in defined medium. The FSH-stimulated pattern of sgk expression is biphasic, and transcriptional activation of the sgk gene depends on an intact Sp1/Sp3 binding site within the proximal promoter. To determine whether sgk was expressed in a hormone-dependent and physiologically relevant manner in vivo, the cellular levels of sgk messenger RNA (mRNA) and protein as well as the subcellular localization of this kinase were analyzed in ovaries containing follicles and corpora lutea at specific stages of differentiation. To stimulate follicular development and luteinization, hypophysectomized (H) rats were treated with estradiol (E; HE) and FSH (FSH; HEF) followed by hCG (hCG; HEF/hCG). To analyze Sgk in functional corpora lutea, PRL was administered to HEF/hCG rats, or ovaries of pregnant rats were obtained on day 7, 15, or 22 of gestation. In situ hybridization indicated that sgk mRNA was low/undetectable in granulosa cells of H and HE rats. An acute injection (i.v.) of FSH to HE rats rapidly increased sgk mRNA at 2 and 8 h. Sgk mRNA was also elevated in granulosa cells of preovulatory follicles of HEF rats and in luteal cells of HEF/hCG and pregnant rats. Northern blots and Western blots confirmed the in situ hybridization data, indicating that the amount and cellular localization Sgk protein were related to that of sgk mRNA. When the subcellular localization of this kinase was analyzed by immunohistochemistry, Sgk protein was nuclear in granulosa cells and some thecal cells of large preovulatory follicles. In contrast, Sgk protein was cytoplasmic in luteal cells as well as some cells within the stromal compartment. Intense immunostaining was also observed in oocytes present in primordial follicles, but not in growing follicles. Collectively, these results show that FSH and LH stimulate marked increases in the cellular content of Sgk, as well as dramatic changes in the subcellular distribution of this kinase. The specific nuclear vs. cytoplasmic compartmentalization of Sgk in granulosa cells and luteal cells, respectively, indicates that Sgk controls distinct functions in proliferative vs. terminally differentiated granulosa cells.

Effect of follicle-stimulating hormone on steroid secretion and messenger ribonucleic acids encoding cytochromes P450 aromatase and cholesterol side-chain cleavage in bovine granulosa cells in vitro

We determined 1) whether the previously observed induction of estradiol secretion in bovine granulosa cells cultured in serum-free conditions is associated with an increase in cytochrome P450 aromatase (P450(arom)) mRNA abundance and 2) whether P450(arom) mRNA levels are responsive to FSH in vitro. Granulosa cells from small (2-4-mm) follicles were cultured in serum-free medium. Estradiol secretion increased with time in culture and was correlated with increased P450(arom) mRNA abundance. Progesterone secretion also increased with time in culture, but P450 cholesterol side-chain cleavage (P450(scc)) mRNA abundance did not. FSH stimulated estradiol secretion and P450(arom) mRNA abundance; the effect was quadratic for both estradiol and P450(arom) mRNA. Estradiol secretion and P450(arom) mRNA levels were correlated. FSH stimulated progesterone secretion and P450(scc) mRNA abundance, although the minimum effective dose of FSH was lower for estradiol (0.1 ng/ml) than for progesterone (10 ng/ml) production. Insulin alone stimulated estradiol secretion and P450(arom) mRNA levels but not progesterone or P450(scc) mRNA abundance. We conclude that this cell culture system maintained both estradiol secretion and P450(arom) mRNA abundance responsiveness to FSH and insulin, whereas P450(scc) mRNA abundance and progesterone secretion were responsive to FSH but not insulin.

Expression and function of estrogen receptor subtypes in granulosa cells: regulation by estradiol and forskolin

The expression and function of estrogen receptor ERalpha/beta subtypes and ERbeta variants in granulosa cells have been determined using several integrated approaches:, Western blotting, indirect immunofluorescence, RT-PCR, and transient transfection assays. Each of these approaches has provided specific details concerning the dynamics of ER expression, ER functional activity, and estradiol (E) regulation of target genes in granulosa cells. Specifically, the studies presented herein document that messenger RNAs (mRNAs) encoding ERbeta and its splice variants, as well as mRNA encoding ERalpha, are expressed in granulosa cells of immature rats before and during culture in serum-free medium. The results also provide the first documentation that functional (DNA binding and transcriptionally active) ER is present in cultured granulosa cells and that its ability to bind consensus estrogen response element (ERE) oligonucleotide and to transactivate an ERE promoter-reporter construct is associated with the level (type?) of receptor protein as well as the stage of granulosa cell differentiation. Using a labeled ERE consensus oligonucleotide and antibodies specific for ERbeta and ERalpha, we show that ERbeta but not ERalpha was detected (supershifted in electrophoretic mobility shift assays) in extracts of granulosa cells cultured overnight (0 h) in defined medium alone. When the cells were cultured with FSH and testosterone (T) to stimulate their differentiation, ERbeta binding activity, as well as immunoreactive ERbeta as determined by Western blot analyses, decreased progressively from 24 to 48 h and was undetectable by 72 h. ERbeta mRNA was low, and ERbeta binding activity was not observed in luteinized granulosa cells. ERalpha DNA binding activity was not observed in any of the granulosa cell cultures, although low levels of immunoreactive ERalpha were detected by Western blot analyses. Immunofluorescent analyses documented that ERbeta, as well as ERalpha, were localized to granulosa cell nuclei and that the intensity of nuclear staining was related to agonist stimulation and differentiation: forskolin increased, whereas E decreased immunostaining for ERbeta and ERalpha at 48 h. When an ERE-E1b-luciferase vector was transfected into granulosa cells of unprimed rats, basal luciferase activity was low but increased by forskolin (3-4x) and by E (2x), responses to both agonists being blocked by the ER antagonist, ICI. When the same vector was transfected into differentiated granulosa cells (cultured for 48 h with FSH/T), forskolin alone increased activity. Collectively, these results show that ERbeta protein is preferentially expressed in immature granulosa cells, is functionally active (binds DNA), can transactivate (either as a homodimer or heterodimer with ERalpha) ERE-containing promoter constructs, and might be associated with increased expression of the endogenous gene encoding c-Jun.

Gonadotropin stimulation of pituitary adenylate cyclase-activating polypeptide (PACAP) messenger ribonucleic acid in the rat ovary and the role of PACAP as a follicle survival factor

Pituitary adenylate cyclase-activating polypeptide (PACAP), a novel neuropeptide with considerable homology to vasoactive intestinal peptide and GH-releasing hormone, exists in two biologically active forms, PACAP-38 and -27. The presence of PACAP in the ovary has been demonstrated, where it stimulates steroidogenesis and cAMP accumulation in cultured granulosa cells. In the present study, gonadotropin regulation of PACAP gene expression was examined in PMSG/human (h)CG-treated immature rat ovaries and cultured preovulatory follicles. Northern blot analysis of ovaries obtained from PMSG/hCG-treated immature animals revealed the transient induction of PACAP transcripts by hCG, reaching a maximum at 6 h. The major cell types expressing PACAP messenger RNA were granulosa cells of preovulatory follicles and some theca/interstitial cells. In preovulatory follicles cultured in serum-free medium, PACAP transcripts were transiently induced by LH and FSH, reaching a maximum 6-9 h after stimulation in granulosa cells but not in theca cells. Treatment with cycloheximide or alpha-amanitin abolished LH-induced PACAP transcripts, indicating that new protein synthesis and transcription are necessary. Treatment with MDL-12,330A, an inhibitor of adenylate cyclase, inhibited LH-induced PACAP messenger RNA, and forskolin mimicked the LH action, implying the role of adenylate cyclase activation. In contrast, treatment with chelerythrine, an inhibitor of protein kinase C, and 2-O-tetradecanol-phorbol-13-acetate had no effect. We further tested the role of PACAP in follicle apoptosis using apoptotic DNA fragmentation analysis. Treatment with PACAP-38 suppressed follicle apoptosis in a dose-dependent manner. Moreover, the LH suppression of follicle apoptosis was partially blocked by cotreatment with PACAP-38 antagonist, indicating mediation by endogenous PACAP-38. These results suggest that PACAP, transiently induced by the gonadotropin surge, could be a local regulator of a number of events and may act as a follicle survival factor during the periovulatory period.

Hormone and prostaglandin F2 alpha regulation of messenger ribonucleic acid encoding steroidogenic acute regulatory protein in human corpora lutea

Steroidogenic acute regulatory (StAR) protein mediates the rapid increase in steroid hormone biosynthesis in response to tropic hormones by facilitating transport of cholesterol into the inner mitochondrial membrane. Although our laboratory has recently reported on the hormonal regulation of StAR mRNA in the rat ovary, the same regulation in the human corpus luteum requires analysis. To this end, a human StAR complementary DNA (cDNA) probe of 858 bp was generated using reverse transcriptase-PCR and RNA from human corpora lutea. The StAR sequence was confirmed by dideoxy chain-termination sequence analysis. Northern blot analysis using the StAR cDNA probe on human corpora lutea mRNA showed that the probe hybridized to a major 1.6-kb transcript and a minor 4.4-kb transcript. Examination of corpora lutea of different luteal phases revealed that the basal expression of the 1.6-kb transcript was significantly more abundant in the early (days 15-19) luteal phase than in the middle (days 20-23) or late (days 24-28) phases. To examine the hormonal regulation of StAR mRNA, corpora lutea were treated in vitro with increasing concentrations of human chorionic gonadotropin (hCG) or prostaglandin F2 alpha (PGF2 alpha). Following hCG stimulation, both 1.6- and 4.4-kb StAR transcripts were increased. A statistically significant increase of 2.2- and 1.8-fold in the 1.6-kb transcript was seen with hCG concentrations of 50 and 100 mIU/mL, respectively. This increase was coupled with a significant elevation in media progesterone levels. In contrast, PGF2 alpha treatment significantly decreased both StAR messenger ribonucleic acid (mRNA) expression and media progesterone levels at concentrations of 500 and 5000 ng/mL. This investigation demonstrated that StAR mRNA is regulated by tropic hormones and prostaglandins in the human corpus luteum. The parallel change in StAR mRNA in conjunction with a change in progesterone levels further supports StAR's putative role in the regulation of steroidogenesis.

Follicle stimulating hormone-regulated expression of serum/glucocorticoid-inducible kinase in rat ovarian granulosa cells: a functional role for the Sp1 family in promoter activity

Recently, a family of novel, serine/threonine protein kinases has been identified. One of these transcriptionally inducible, immediate-early genes encodes serum/glucocorticoid inducible-protein kinase, sgk. By in situ hybridization, we show that sgk expression in the rat ovary is selectively localized to granulosa cells. In culture, FSH or forskolin, activators of the protein kinase A (PKA) pathway, rapidly (2 h) and transiently increased sgk mRNA levels in undifferentiated granulosa cells. Sgk mRNA exhibited a biphasic expression pattern, with maximal levels observed at 48 h of FSH/forskolin as granulosa cells differentiate to the preovulatory phenotype. Deletion analyses using sgk promoter-reporter constructs (-4.0 kb to -35 bp) identified a region between -63 and -43 bp that mediated FSH and forskolin-responsive transcription in undifferentiated and differentiated granulosa cells. This G/C-rich region 1) conferred both basal and inducible transcription to the minimal -35 sgk promoter chloramphenicol acetyltransferase reporter construct, 2) specifically bound Sp1 and Sp3 present in granulosa cell extracts, and 3) bound recombinant Sp1. Mutation of 2 bp in this region not only prevented Sp1 and Sp3 binding, but also abolished the PKA-mediated transactivation observed when using the wild type construct. Sp1 and Sp3 DNA-binding activity and protein levels did not change significantly during sgk induction. Collectively, these data indicate that Sp1/Sp3 transactivation of the sgk promoter likely involves regulated, phosphorylation-dependent interaction with other factors. Thus the novel, biphasic induction of sgk that correlates with granulosa cell progression from proliferation to differentiation appears to involve sequential, coordinated actions of FSH, PKA, and transcription factors, including Sp1 and Sp3.

Adrenocorticotropin induction of stress-activated protein kinase in the adrenal cortex in vivo

A broad array of stressors induce ACTH release from the anterior pituitary, with consequent stimulation of the adrenal cortex and release of glucocorticoids critical for survival of the animal. ACTH stimulates adrenocortical gene expression in vivo and inhibits adrenocortical cell proliferation. Binding of ACTH to its G-protein-coupled receptor stimulates the production of cAMP and activation of the protein kinase A pathway. The stress-activated protein kinases (SAPKs) (or c-Jun N-terminal kinases) and the extracellular signal-regulated kinases (ERKs) are members of the mitogen-activated protein kinase family of serine/threonine kinases, which have recently been implicated in G-protein-coupled receptor intracellular signaling. The SAPKs are preferentially induced by osmotic stress and UV light, whereas the ERKs are preferentially induced by growth factors and proliferative signals in cultured cells. In these studies, ACTH stimulated SAPK activity 3-4-fold both in the adrenal cortex in vivo and in the Y1 adrenocortical cell line. 12-O-Tetradecanoylphorbol-13-acetate but not cAMP induced SAPK activity in Y1 cells. The isoquinolinesulfonamide inhibitors H-8 and H-89 blocked ACTH induction of SAPK activity at protein kinase C inhibitory doses but not at protein kinase A inhibitory doses. The calcium chelating agent EGTA inhibited ACTH-induced SAPK activity and the calcium ionophore A23187 induced SAPK activity 3-fold. In contrast with the induction of SAPK by ACTH, ERK activity was inhibited in the adrenal cortex in vivo and in Y1 adrenal cells. Together these findings suggest that ACTH induces SAPK activity through a PKC and Ca+2-dependent pathway. The induction of SAPK and inhibition of ERK by ACTH in vivo may preferentially regulate target genes involved in the adrenocortical stress responses in the whole animal.

Expression of aromatase in the ovary: down-regulation of mRNA by the ovulatory luteinizing hormone surge

Aromatase (CYP19) mRNA is induced by follicle-stimulating hormone (FSH) in granulosa cells of preovulatory follicles and subsequently is rapidly diminished as a consequence of the luteinizing hormone (LH) surge. Primary cultures of rat granulosa cells were used to identify some of the cellular mechanisms by which FSH increases and LH decreases steady-state levels of aromatase mRNA. Induction of aromatase mRNA by FSH was increased by cycloheximide but was blocked by alpha-amanitin and the C-kinase activators gonadotropin-releasing hormone (GnRH) and phorbol 12-myristate 13-acetate (PMA). In contrast, the decrease in steady-state levels of aromatase mRNA by LH was mimicked by A-kinase (forskolin) and C-kinase (PMA or GnRH) activators. The decrease in aromatase mRNA was associated with decreased amounts of mRNA and protein for steroidogenic factor-1 (SF-1), a nuclear orphan receptor that binds and trans-activates the aromatase promoter, and with the A-kinase subunit type II (RII beta), which is required for mediating cAMP action in these cells. The down-regulation of aromatase, SF-1, and RII beta by each kinase activator and alpha-amanitin was prevented by cycloheximide when the drug was added in combination with the activator. If, however, cycloheximide was added 2 h after PMA (or LH), the drug did not prevent the rapid loss of mRNA. When granulosa cells were transfected with an aromatase CAT transgene, CAT activity was stimulated 10- to 20-fold by FSH and forskolin but not by PMA. Taken together, these results indicate that the A-kinase but not the C-kinase pathway can trans-activate the aromatase gene in immature granulosa cells, whereas the C-kinase, as well as A-kinase pathways, mimic the LH surge to decrease aromatase mRNA in preovulatory cells. By increasing degradation of aromatase mRNA and by inhibiting transcription, the LH surge rapidly terminates the granulosa cell pattern of gene expression while reprogramming the cells to express genes associated with ovulation and luteinization.

Prostaglandin F2α reduces steroidogenic acute regulatory (StAR) protein messenger ribonucleic acid expression in the rat ovary

Steroid biosynthesis begins with the enzymatic conversion of cholesterol to pregnenolone. This reaction is catalyzed by the cytochrome P450 side-chain cleavage enzyme (P450scc), which is located on the matrix side of the inner mitochondrial membrane. Although the rate-limiting enzymatic step in steroidogenesis is the conversion of cholesterol to pregnenolone by the side-chain cleavage enzyme, the true rate-limiting step in this process is the delivery of cholesterol to the inner mitochondrial membrane. Steroidogenic acute regulatory (StAR) protein is thought to mediate the rapid increase in steroid hormone biosynthesis in response to tropic hormones by facilitating cholesterol transport to the inner mitochondrial membrane. Cholesterol transport across the inner mitochondrial membrane has also been implicated as the target for prostaglandin F2α's (PGF2α) antisteroidogenic activity. Since cholesterol delivery to the P450scc is a rapidly regulated step in steroidogenesis, StAR mRNA levels were examined after the administration of a luteolytic injection of PGF2α. The results of this investigation revealed that both major StAR RNA transcripts were decreased in the ovary, 10 d after ovulation, following PGF2α administration. Serum progesterone levels were decreased following PGF2α administration in parallel with the decreased expression of StAR. Following PGF2α treatment, ovarian StAR transcripts at 3.4 and 1.6 kb were reduced 4-fold (p<0.01) and 2.5-fold (p<0.025), respectively, after 4 h. Ovarian P450scc mRNA levels were also reduced (70%) 4 h after PGF2α injection. Time course experiments following PGF2α administration showed a significant decrease in StAR expression as early as 30 min (p<0.02) following injection. In contrast to StAR's expression after PGF2α administration, StAR mRNA levels were elevated in response to human chorionic gonadotropin (hCG) 3 h postinjection. Administration of PGF2α followed by hCG injection effectively blocked induction of StAR expression. StAR mRNA levels were reduced 1.5-fold relative to control animals and 3.5-fold relative to the hCG-treated animals (p<0.05). The levels of serum progesterone paralleled the change in ovarian StAR mRNA in all experiments. This study provides the first evidence that StAR mRNA expression is mediated by prostaglandins in the rat ovary further supporting its important role in the regulation of steroid hormone biosynthesis.