GATA4 reduction enhances 3',5'-cyclic adenosine 5'-monophosphate-stimulated steroidogenic acute regulatory protein messenger ribonucleic acid and progesterone production in luteinized porcine granulosa cells

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

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

GATA Regulation and Function During the Ovarian Life Cycle

GATA4 and GATA6 are the sole GATA factors expressed in the ovary during embryonic development and adulthood. Up today, GATA4 and GATA6 are the only transcription factors that have been conditionally deleted during ovarian development and at each major stage of follicle maturation. The evidence from these transgenic mice revealed that GATA4 and GATA6 are crucial for follicles assembly, granulosa cell differentiation, postnatal follicle growth, and luteinization. Thus, conditional knockdown of both factors in the granulosa cells at any stage of development leads to female infertility. GATA targets impacting female reproduction include genes involved in steroidogenesis, hormone signaling, ovarian hormones, extracellular matrix organization, and apoptosis/cell division.

GATA4 and GATA6 Knockdown During Luteinization Inhibits Progesterone Production and Gonadotropin Responsiveness in the Corpus Luteum of Female Mice

The surge of luteinizing hormone triggers the genomic reprogramming, cell differentiation, and tissue remodeling of the ovulated follicle, leading to the formation of the corpus luteum. During this process, called luteinization, follicular granulosa cells begin expressing a new set of genes that allow the resulting luteal cells to survive in a vastly different hormonal environment and to produce the extremely high amounts of progesterone (P4) needed to sustain pregnancy. To better understand the molecular mechanisms involved in the regulation of luteal P4 production in vivo, the transcription factors GATA4 and GATA6 were knocked down in the corpus luteum by crossing mice carrying Gata4 and Gata6 floxed genes with mice carrying Cre recombinase fused to the progesterone receptor. This receptor is expressed exclusively in granulosa cells after the luteinizing hormone surge, leading to recombination of floxed genes during follicle luteinization. The findings demonstrated that GATA4 and GATA6 are essential for female fertility, whereas targeting either factor alone causes subfertility. When compared to control mice, serum P4 levels and luteal expression of key steroidogenic genes were significantly lower in conditional knockdown mice. The results also showed that GATA4 and GATA6 are required for the expression of the receptors for prolactin and luteinizing hormone, the main luteotropic hormones in mice. The findings demonstrate that GATA4 and GATA6 are crucial regulators of luteal steroidogenesis and are required for the normal response of luteal cells to luteotropins.

Effects of monobutyl phthalate on steroidogenesis through steroidogenic acute regulatory protein regulated by transcription factors in mouse Leydig tumor cells

OBJECTIVE

Dibutyl phthalate (DBP) is one of the most widely used phthalate esters, and it is ubiquitous in the environment. DBP and its major metabolite, monobutyl phthalate (MBP), change steroid biosynthesis and impair male reproductive function. However, the regulatory mechanism underlying the steroid biosynthesis disruption by MBP is still unclear.

METHODS

We analyzed the progesterone production, steroidogenic acute regulatory protein (StAR) mRNA, protein expression, and DNA-binding affinity of transcription factors (SF-1 and GATA-4).

RESULTS

Our results reveal that MBP inhibited progesterone production. At the same time, StAR mRNA and protein were decreased after MBP exposure. Furthermore, electrophoretic mobility shift assay showed that DNA-binding affinity of transcription factors (SF-1 and GATA-4) was decreased in a dose-dependent manner after MBP treatments. Western blot tests next confirmed that protein of SF-1 was decreased, but GATA-4 protein was unchanged. However, phosphorylated GATA-4 protein was decreased with 800 μM of MBP.

CONCLUSIONS

This study reveals an important and novel mechanism whereby SF-1 and GATA-4 may regulate StAR during MBP-induced steroidogenesis disruption.

Characterization of transforming growth factor beta superfamily, growth factors, transcriptional factors, and lipopolysaccharide in bovine cystic ovarian follicles

The process of transformation of growing bovine follicles into cysts is still a mystery. Local expression of proteins or factors, including transforming growth factor β, growth factors, and transcription factors, plays a central role in mammals. Therefore, in abattoir-derived cystic ovarian follicles and follicular fluid, the role of some transforming growth factor β superfamily proteins, insulinlike growth factor-1 (IGF-1) and GATA-4 and GATA-6, were investigated. The relationship between intrafollicular lipopolysaccharide (LPS) and etiopathogenesis of ovarian cysts was also assessed. Data on the preovulatory follicle and the largest follicle (F1) were compared. The number of intrafollicular LPS-positive samples and LPS concentrations were higher in cysts. Immunohistochemical staining was mildly positive for IGF-1, inhibin alpha, and GATA-4 in thecal cells. Staining for anti-Müllerian hormone (AMH), growth differentiation factor-9, bone morphogenetic protein-6 (BMP-6), and GATA-6 was insufficient for their quantitation, and oocytes could not be stained for any of the proteins tested in the cystic follicles. Expression of BMP-6, inhibin alpha, and IGF-1 was moderately higher in granulosa cells of F1 follicles, and all the proteins were moderately expressed in granulosa cells in preovulatory follicles. However, loss of GATA-6 staining was significant in F1 follicles. Intrafollicular progesterone, IGF-1, and AMH concentrations in cysts and F1 follicles were significantly higher than those in preovulatory follicles. Western blot analyses revealed that follicular fluid inhibin-α was strongly expressed, whereas expression of growth differentiation factor-9, BMP-6, GATA-4 and GATA-6 was lower in cysts than in preovulatory follicles. Also, high intrafollicular AMH concentration and low BMP-6 expression were closely associated with cystic degeneration and atresia. In conclusion, immunohistochemical loss of BMP-6 and GATA-6 in the granulosa cells together with high intrafollicular LPS levels may play important roles in disruption of the ovulatory mechanism and steroidogenic reactions in type 2 cyst. Also, high intrafollicular AMH concentration along with low BMP-6 expression may be used as indicators of the bovine degenarative ovarian follicles.

STARD6 is expressed in steroidogenic cells of the ovary and can enhance de novo steroidogenesis

STARD6 is a member of the StAR-related lipid transfer (START) domain family of proteins whose function thus far remains obscure. While it recently was shown to facilitate steroidogenesis in a cell-free setting, it has not been localized to steroidogenic cells of normal reproductive tissues. In a recent microarray study, we detected STARD6 mRNA in cultured porcine ovarian granulosa cells which are steroidogenic. In the present study, we examined regulation of STARD6 mRNA in porcine granulosa cultures, and found that it was not regulated by cyclic AMP, but it was reduced by combined knockdown of the transcription factors GATA4 and GATA6. We detected both STARD6 mRNA and protein in fresh granulosa cells and whole antral follicles and different stage corpora lutea of pig. The highest levels were discovered in the mid-luteal phase corpus luteum. Immunolocalization within ovarian tissues indicated robust STARD6 immunoreactivity in steroidogenic cells of the corpus luteum. Relatively lesser amounts of STARD6 signal were found in granulosa cells, theca cells, and oocytes. To test the ability of STARD6 to facilitate de novo steroidogenesis, non-steroidogenic COS-1 cells were co-transfected with components of the P450 cholesterol side-chain cleavage system, enabling them to make pregnenolone, and STARD6. STARD6 increased pregnenolone production by two- to three-fold over the empty vector control. In summary, STARD6 is found in the pig ovary, exhibits the strongest expression in highly steroidogenic luteal cells, and significantly enhances pregnenolone production in transfected COS cells independent of cyclic AMP treatment. Collectively, these findings indicate that STARD6 may contribute to steroidogenesis in ovarian cells, but also suggests other cellular functions that require cholesterol trafficking.

Involvement of transcription factor GATA-4 in regulation of CYP19 gene during folliculogenesis and luteinization in buffalo ovary

CYP19 gene encode aromatase, the key enzyme of estrogen biosynthesis, is regulated in species- and tissue-specific manner by alternate use of different promoters. Previously, we have reported the cloning and characterization of tissue-specific promoter and transcripts in buffalo ovary and placenta. In human and rat ovary, FSH induces the phosphorylation of transcription factor CREB (cAMP response element binding protein) through PKA pathway which binds to cAMP response element like sequence (CLS) in CYP19 gene ovarian promoter. However, in buffalo as well as in bovine, in silico analysis of ovary specific promoter sequence identified a single base pair deletion in CLS site and is designated as CLS-like sequence. To understand if CLS with a point mutation is still a functional cis-element and is involved in FSH stimulated transactivation of CYP19 gene in buffalo ovary, the present study was thus aimed to functionally characterize the role of buffalo CLS in CYP19 gene transactivation. We also studied the involvement of GATA-4, having consensus binding sites in CYP19 gene ovarian promoter in the vicinity of CLS during different stages of the buffalo estrus cycle. Reporter construct analyses and EMSA results showed that CLS is playing no significant role in CYP19 gene regulation in buffalo ovary. Real time absolute quantification of GATA-4 showed the differential expression of GATA-4 mRNA during folliculogenesis and luteinization with significantly higher transcript abundance in large follicle in comparison to other tissues. Western blot analysis of granulosa cells nuclear protein isolated from different stage of follicular development (small and large follicles) and differentiation (corpus luteum) showed that abundance of phosphorylated GATA-4 (Ser261) was significantly higher in granulosa cell nuclear protein of large follicles as compared to small follicles and corpora lutea. Interestingly, binding studies using ChIP showed significantly enhanced binding to the CYP19 gene promoter in large follicle which was seen to be declined in the luteal tissue. Similar results were obtained in the in vitro experiments as well. Finally, RNAi experiments were performed to validate the involvement of GATA-4 in CYP19 gene regulation. Results of RNAi showed that knockdown of GATA-4 mRNA significantly declined CYP19 gene mRNA as well as 17β-estradiol contents. In conclusion, result of the present study indicated that that in the absence of consensus CRE (cAMP response element); GATA-4 could be a downstream effector of cAMP/PKA pathway in regulation of CYP19 gene during folliculogenesis and luteinization.

GATA4 deficiency impairs ovarian function in adult mice

Transcription factor GATA4 is expressed in granulosa cells and, to a lesser extent, in other ovarian cell types. Studies of mutant mice have shown that interactions between GATA4 and its cofactor, ZFPM2 (also termed FOG2), are required for proper development of the fetal ovary. The role of GATA4 in postnatal ovarian function, however, has remained unclear, in part because of prenatal lethality of homozygous mutations in the Gata4 gene in mice. To circumvent this limitation, we studied ovarian function in two genetically engineered mouse lines: C57BL/6 (B6) female mice heterozygous for a Gata4-null allele, and 129;B6 female mice in which Gata4 is deleted specifically in proliferating granulosa cells using the Cre-loxP recombination system and Amhr2-cre. Female B6 Gata4(+/-) mice had delayed puberty but normal estrous cycle lengths and litter size. Compared to wild-type mice, the ovaries of gonadotropin-stimulated B6 Gata4(+/-) mice were significantly smaller, released fewer oocytes, produced less estrogen, and expressed less mRNA for the putative GATA4 target genes Star, Cyp11a1, and Cyp19. Gata4 conditional knockout (cKO) mice had a more severe phenotype, including impaired fertility and cystic ovarian changes. Like Gata4(+/-) mice, the ovaries of gonadotropin-stimulated cKO mice released fewer oocytes and expressed less Cyp19 than those of control mice. Our findings, coupled with those of other investigators, support the premise that GATA4 is a key transcriptional regulator of ovarian somatic cell function in both fetal and adult mice.

RNA interference and ovarian functions

RNA interference, a recently discovered new mechanism controlling gene expression via small RNAs, was shown to be involved in characterization and control of basic ovarian cell functions. The main classes of small RNAs, as well as their expression in ovaries have been described. Furthermore, the successful application of RNA interference for study and control of basic ovarian functions (proliferation, apoptosis, secretory activity, luteogenesis, oocyte maturation, and related ovarian cell malignant transformation) and production of recombinant proteins have been demonstrated. Application of RNA interference in reproductive biology and medicine can be successful in two main areas: (1) characterization and prediction of physiological and pathological state (association between particular small RNA and physiological or pathological processes), (2) application of small RNAs for regulation of reproductive processes and treatment of reproductive disorders or their particular indexes. Problems of improvement of small RNA delivery to target ovarian cells and potent RNA interference-related approaches for treatment of ovarian disorders (especially of ovarian cancer) have been discussed.

GATA depletion impacts insulin-like growth factor 1 mRNA and protein levels in luteinizing porcine granulosa cells

GATA4 and GATA6 are zinc-finger transcription factors that regulate specific genes involved in steroidogenesis. Using RNA interference (RNAi)-mediated reduction of GATA4 and/or GATA6 with microarray analysis, we aimed to identify novel GATA target genes in luteinizing porcine granulosa cells under vehicle- and cAMP-treated conditions. Microarray analysis identified IGF1 mRNA to be cAMP- and GATA-responsive, and real-time PCR demonstrated that the cAMP-induced increase in IGF1 mRNA was reduced under conditions of GATA6 depletion and GATA4 plus GATA6 depletion, but not GATA4 depletion. Insulin-like growth factor 1 protein levels in media were also decreased by GATA6 or GATA4 plus GATA6 reduction. IGFBP2 and IGFBP4 mRNAs were increased and IGFBP5 mRNA decreased with vehicle and cAMP treatment under GATA4 plus GATA6 RNAi conditions. GATA6 reduction alone increased basal IGFBP4 and decreased IGFBP5 with both vehicle and cAMP, and GATA4 reduction alone lowered cAMP IGFBP5 levels with cAMP. No changes in IGFBP3 mRNA were observed with GATA reduction relative to the control RNAi condition. Levels of insulin-like growth factor binding proteins 2-5 in media as assessed by Western ligand blotting were not altered by GATA reduction. Electromobility gel shift assays with two GATA-containing oligonucleotides of the IGF1 5'-regulatory region showed GATA4 and GATA6 could bind the more proximal GATA-B site. These studies indicate that although GATA4 and GATA6 can bind the porcine IGF1 5'-region, GATA6 is functionally most important for cAMP-stimulated mRNA levels. Using microarray analysis, we identified other mRNAs that were altered by GATA-reduced conditions, including ALDH1, DIO2, and EDNRB. Our findings further support GATA as a coordinator of endocrine/paracrine/autocrine signals in the ovary.

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.