Initiation of the expression of peroxisome proliferator-activated receptor gamma (PPAR gamma) in the rat ovary and the role of FSH

The Role of Peroxisome Proliferator-Activated Receptors in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) constitutes the most common endocrine disorder in women of reproductive age. Patients usually suffer from severe menstrual irregularities, skin conditions, and insulin resistance-associated health conditions. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptor proteins that regulate gene expression. In order to investigate the role of PPARs in the pathophysiology of PCOS, we conducted a literature review using the MEDLINE and LIVIVO databases and were able to identify 74 relevant studies published between 2003 and 2023. Different study groups reached contradictory conclusions in terms of PPAR expression in PCOS. Interestingly, numerous natural agents were found to represent a novel, potent anti-PCOS treatment alternatives. In conclusion, PPARs seem to play a significant role in PCOS.

Oocytes suppress FOXL2 expression in cumulus cells in mice†

Cumulus cells and mural granulosa cells (MGCs) play distinct roles during follicular development, and normal development of these cell lineages is critical for the female fertility. Transcriptomic diversification between the two cell lineages is obviously a critical mechanism for their functional diversification; however, the transcriptional regulators responsible for this event have not been fully defined. In this study, we sought to identify key transcriptional regulators responsible for the differential gene expression between the two cell lineages. In silico analysis of transcriptomic comparison between cumulus cells and MGCs identified several candidate regulators responsible for the diversification of the two cell lineages. Among them, we herein focused on forkhead box L2 (FOXL2) and showed that expressions of FOXL2 as well as its target transcripts were differentially regulated between cumulus cells and MGCs. The lower expression of FOXL2 in cumulus cells seemed to be due to the suppression by oocyte-derived paracrine signals. These results suggest that FOXL2 is one of the critical transcription factors that determine cumulus cell and MGC lineages under the control of oocytes.

The myokine irisin: localization and effects in swine late medium and large antral ovarian follicle

Irisin is mainly synthesized by skeletal muscle tissue, where it is believed to be responsible for the benefits of exercise on metabolism and cardiovascular system. In adipose tissue, its best-known effect is the browning of white adipocytes, resulting in the increase of thermogenesis and energy expenditure. As it has been largely documented that metabolic dysfunctions can frequently be associated with reductions in fertility, the possible involvement of this molecule in the regulation of reproductive processes represents an issue to be addressed. On this basis, the first aim of this work was the evaluation of the presence of irisin in the swine ovary; then, we investigated the expression of the associated molecules FNDC5, PGC-1α, and PPAR-γ. To verify a potential modulatory role both on ovarian function and on redox status, cell growth, steroidogenesis, production of superoxide anion and nitric oxide, the nonenzymatic antioxidant scavengers, were assessed in vitro on granulosa cells treated with increasing concentrations of irisin (50, 100, and 150 ng/mL). The data collected demonstrate the presence of irisin in swine ovarian follicle. Moreover, the highest concentrations tested stimulated metabolic activity and inhibited cell proliferation (P < 0.05); the peptide exerted a biphasic effect on progesterone (P < 0.01) production and, at the highest concentrations, inhibited nitric oxide while stimulated the nonenzymatic antioxidant power (P < 0.05). Superoxide anion and estradiol 17β were unaffected. The demonstration of the local presence of irisin at the ovarian level and the highlighted effects allow us to qualify this molecule as a potential physiological regulator of follicular function.

Follicle-stimulating hormone administration affects amino acid metabolism in mammalian oocytes†

Culture media used in assisted reproduction are commonly supplemented with gonadotropin hormones to support the nuclear and cytoplasmic maturation of in vitro matured oocytes. However, the effect of gonadotropins on protein synthesis in oocytes is yet to be fully understood. As published data have previously documented a positive in vitro effect of follicle-stimulating hormone (FSH) on cytoplasmic maturation, we exposed mouse denuded oocytes to FSH in order to evaluate the changes in global protein synthesis. We found that dose-dependent administration of FSH resulted in a decrease of methionine incorporation into de novo synthesized proteins in denuded mouse oocytes and oocytes cultured in cumulus-oocyte complexes. Similarly, FSH influenced methionine incorporation in additional mammalian species including human. Furthermore, we showed the expression of FSH-receptor protein in oocytes. We found that major translational regulators were not affected by FSH treatment; however, the amino acid uptake became impaired. We propose that the effect of FSH treatment on amino acid uptake is influenced by FSH receptor with the effect on oocyte metabolism and physiology.

Unconservative_15_2570409 suppresses progesterone receptor expression in the granulosa cells of Hu sheep

Female fertility potential depends on the number of mature follicles; however, the underlying molecular mechanisms remain unclear. Based on previously generated miRNA and mRNA sequencing data of healthy ovarian follicles (>5 mm in diameter) isolated from Hu sheep with different prolificacy, we investigated the roles of a novel miRNA (unconservative_15_2570409) and the progesterone receptor (PGR) gene in follicular development. During the periovulatory phase, the expression of unconservative_15_2570409 and PGR was lower and higher, respectively, in the >5 mm follicles of high prolificacy (HP) ewes than in those of low prolificacy (LP) ewes and in the >3 mm follicles than in the smaller follicles of the HP ewes. Subsequently, the granulosa cells (GCs) of Hu sheep were used as an in vitro model. PGR overexpression significantly increased the mRNA expression of steroidogenic acute regulatory protein (StAR), 3-beta-hydroxysteroid dehydrogenase/isomerase (3β-HSD), and cytochrome P450 family 19 subfamily A member 1 (CYP19A1), which promoted the secretion of progesterone (P₄) and estradiol (E₂). PGR knockdown significantly downregulated the levels of StAR and 3β-HSD mRNA and decreased the production of P₄, whereas no effects on CYP19A1 mRNA expression and E₂ levels were observed. We also found the negative regulatory effect of unconservative_15_2570409 on the mRNA and protein expression of PGR by targeting the 3'-untranslated region. The regulation of PGR levels resulted in a corresponding change in the ADAMTS1, PPAR-γ, and CTSL gene transcripts, which are important for follicular maturation and ovulation. Additionally, PGR, ADAMTS1, and PPAR-γ were predominantly localized in the GCs. Collectively, our results suggest that by regulating PGR expression and consequently affecting the expression of target genes and steroidogenesis, unconservative_15_2570409 plays a role in follicular development during the periovulatory stage, which provides novel insights into the molecular mechanisms affecting Hu sheep prolificacy.

Rosiglitazone increases expression of steroidogenic acute regulatory protein and progesterone production through PPARγ–EGFR–ERK1/2 in human cumulus granulosa cells

The mechanism by which rosiglitazone (ROSI: a thiazolidinedione (TZD)) affects steroid production in undifferentiated human granulosa cells is not known. In this study, cultured human cumulus granulosa cells were exposed to ROSI and pharmacological inhibitors of the extracellular signal-regulated kinase 1/2 (ERK1/2), epidermal growth factor receptor (EGFR) and peroxisome proliferator-activated receptor gamma (PPARγ) signalling pathways. Expression of progesterone biosynthetic enzymes, PPARγ and PPARα, progesterone production and ERK1/2 activation were analysed. After 48h, 30μM ROSI increased STAR, 3βHSD and PPARγ mRNA and elevated progesterone production in human cumulus granulosa cells. Addition of ERK1/2 (U0126), EGFR (AG1478) and PPARγ (GW9662) inhibitors prevented the ROSI-induced STAR mRNA expression and progesterone production after 48h. Inhibition of PPARγ, but not EGFR or ERK1/2, decreased the PPARγ mRNA levels induced by ROSI in human cumulus granulosa cells after 48h. On the other hand, U0126 and GW9662 prevented the ROSI-induced increase in PPARγ transcripts after 6h. Western blot analysis showed that ROSI induced a rapid ERK1/2 activation, which was prevented by inhibition of ERK1/2, EGFR and PPARγ in human cumulus granulosa cells. Overall, these data suggested that PPARγ, EGFR and ERK1/2 were involved in the stimulatory effect of ROSI on STAR expression and progesterone production in undifferentiated human cumulus granulosa cells.

In vitro interaction between resistin and peroxisome proliferator-activated receptor γ in porcine ovarian follicles

In the present study, using real-time polymerase chain reaction and immunoblotting methods, we quantified the expression of peroxisome proliferator-activated receptor (PPAR) γ, PPARα and PPARβ in different sized ovarian follicles (small (SF), medium (MF) and large (LF) follicles) in prepubertal and adult pigs. In prepubertal pigs, PPARγ and PPARα expression was highest in LF; however, PPARβ expression did not differ among SF, MF and LF. In mature pigs, only protein expression of PPARγ and PPARα increased during ovarian follicle development. Following identification of very high levels of PPARγ expression in LF in prepubertal and adult pigs, using in vitro culture of ovarian follicles, we determined the effect of resistin at 0.1, 1 and 10 ng mL–1 on PPARγ mRNA and protein expression and the effect of rosiglitazone at 25 and 50 µM (a PPARγ agonist) on resistin mRNA and protein expression. Resistin increased PPARγ expression in ovarian follicles in both prepubertal and adult pigs, whereas rosiglitazone had an inhibitory effect on resistin expression. The role of PPARγ in regulating the effects of resistin on ovarian steroidogenesis was investigated using GW9662 (a PPARγ antagonist at dose of 1 μM). In these studies, GW9662 reversed the effect of resistin on steroid hormone secretion. The data suggest that there is local cooperation between resistin and PPARγ expression in the porcine ovary. Resistin significantly increased the expression of PPARγ, whereas PPARγ decreased resistin expression; thus, PPARγ is a new key regulator of resistin expression and function.

Expression Levels of PPARγ and CYP-19 in Polycystic Ovarian Syndrome Primary Granulosa Cells: Influence of ω-3 Fatty Acid

BACKGROUND

The omega-3 fatty acid (ω-3 fatty acid) such as eicosapentaenoic acid (EPA) is currently used in the clinic as a nutritional supplement in the treatment of poly- cystic ovarian syndrome (PCOS). The present study was designed to investigate the ef- fect of EPA on the expression levels of peroxisome proliferator-activated receptor gamma (PPARγ) and cytochrome P450 aromatase (encoded by the CYP-19) in primary cultured granulosa cells (GC) from patients undergoing in vitro fertilization (IVF), and also to compare these effects with those in GC of PCOS patients.

MATERIALS AND METHODS

In this experimental study, human GC were isolated, pri- mary cultured in vitro, exposed to a range of concentrations of the EPA and in- vestigated with respect to gene expression levels of PPARγ and CYP-19 using real time-polymerase chain reaction (PCR). The participants (n=30) were the patients admitted to the IVF Center in February-March 2013 at Alzahra Hospital, Tabriz, Iran, who were divided into two groups as PCOS (n=15) and non-PCOS (n=15) women (controls).

RESULTS

All doses of the EPA significantly induced PPARγ mRNA gene expression level as compared to the control recombinant follicle stimulating hormone (rFSH) alone condi- tion. High doses of EPA in the presence of rFSH produced a stimulatory effect on expres- sion level of PPARγ (2.15-fold, P=0.001) and a suppressive effect (0.56-fold, P=0.01) on the expression level of CYP-19, only in the PCOS GC.

CONCLUSION

EPA and FSH signaling pathway affect differentially on the gene ex- pression levels of PPARγ and CYP-19 in PCOS GC. Altered FSH-induced PPARγ activity in PCOS GC may modulate the CYP-19 gene expression in response to EPA, and possibly modulates the subsequent steroidogenesis of these cells.

Effect of hyperandrogenism on ovarian function

The objective of this work was to study the ovarian function when follicular development is induced during a hyperandrogenic condition. Female rats were injected with either equine chorionic gonadotropin (eCG group) to induce folliculogenesis or eCG together with DHEA to induce folliculogenesis in a hyperandrogenic condition (eCG+HA group). The control group was injected with vehicle. Ovarian mRNA levels of the peroxisome proliferator-activated receptor gamma (PPARγ) co-activator PGC1α, the PPARγ co-repressor NCoR, the main enzymes involved in the ovarian steroidogenesis (CYP17, 3β-hydroxysteroid dehydrogenase (3β-HSD), 17β-HSD, and CYP19A), and cyclooxygenase 2 (COX2) were evaluated only by real-time PCR. COX2 was evaluated by both real-time PCR and western blot. Serum steroid hormones and both the oxidative and inflammatory statuses were also quantified. We found that eCG-induced folliculogenesis induced increased mRNA levels of PGC1α and decreased those of NCoR when compared with controls. In addition, we found an increase in serum estradiol (E2) levels and enhanced mRNA expression of CYP19A. A pro-inflammatory status and a pro-oxidant status were also established. When folliculogenesis was induced in a hyperandrogenic condition, the mRNA levels of the PPARγ co-repressor NCoR remained higher than in controls and the pro-inflammatory and pro-oxidant statuses were enhanced. In addition, the enzymes involved in ovarian steroidogenesis were altered leading to the accumulation of testosterone and an unfavorable E2/testosterone ratio. These alterations led to abnormal follicular development.