Mitoguardin 1 and 2 promote granulosa cell proliferation by activating AKT and regulating the Hippo-YAP1 signaling pathway.

Mitochondria have been identified to be involved in oxidative phosphorylation, lipid metabolism, cell death, and cell proliferation. Previous studies have demonstrated that mitoguardin (Miga), a mitochondrial protein that governs mitochondrial fusion, mitochondria-endoplasmic reticulum (ER) contacts, lipid formation, and autophagy, is crucial for ovarian endocrine and follicular development. Nevertheless, whether mammalian MIGA1 or MIGA2 (MIGA1,-2) regulates ovarian granulosa cell proliferation remains unclear. This study revealed that mammalian MIGA1,-2 promotes cell proliferation and regulates the phosphorylation and localization of Yes-associated protein 1 (YAP1) in ovarian granulosa cells. MIGA2 upregulation resulted in reduced YAP1 activity, while MIGA2 removal led to increased YAP1 activity. Further analysis indicated that MIGA1,-2 regulated YAP1 via the Hippo signaling pathway and regulated protein kinase B (AKT) activity in collaboration with YAP1. In addition, lysophosphatidic acid (LPA) regulated MIGA2 expression and AKT activity by activating YAP1. Briefly, we demonstrated that the mitochondrial MIGA1 and MIGA2, especially MIGA2, promoted cellular proliferation by activating AKT and regulating the Hippo/YAP1 signaling pathway in ovarian granulosa cells, which may contribute to the molecular pathogenesis of reproductive endocrine diseases, such as polycystic ovary syndrome (PCOS).

Mitoguardin2 Is Associated With Hyperandrogenism and Regulates Steroidogenesis in Human Ovarian Granulosa Cells.

Polycystic ovary syndrome (PCOS) is an endocrinopathy characterized by hyperandrogenism, anovulation, and polycystic ovaries, in which hyperandrogenism manifests by excess androgen and other steroid hormone abnormalities. Mitochondrial fusion is essential in steroidogenesis, while the role of mitochondrial fusion in granulosa cells of hyperandrogenic PCOS patients remains unclear. In this study, mRNA expression of mitochondrial fusion genes mitoguardin1, -2 (MIGA 1, -2) was significantly increased in granulosa cells of hyperandrogenic PCOS but not PCOS with normal androgen levels, their mRNA expression positively correlated with testosterone levels. Dihydrotestosterone (DHT) treatment in mice led to high expression of MIGA2 in granulosa cells of ovulating follicles. Testosterone or forskolin/ phorbol 12-myristate 13-acetate treatments increased expression of MIGA2 and the steroidogenic acute regulatory protein (StAR) in KGN cells. MIGA2 interacted with StAR and induced StAR localization on mitochondria. Furthermore, MIGA2 overexpression significantly increased cAMP-activated protein kinase A (PKA) and phosphorylation of AMP-activated protein kinase (pAMPK) at T172 but inhibited StAR protein expression. However, MIGA2 overexpression increased CYP11A1, HSD3B2, and CYP19A1 mRNA expression. As a result, MIGA2 overexpression decreased progesterone but increased estradiol synthesis. Besides the androgen receptor, testosterone or DHT might also regulate MIGA2 and pAMPK (T172) through LH/choriogonadotropin receptor-mediated PKA signaling. Taken together, these findings indicate that testosterone regulates MIGA2 via PKA/AMP-activated protein kinase signaling in ovarian granulosa cells. It is suggested mitochondrial fusion in ovarian granulosa cells is associated with hyperandrogenism and potentially leads to abnormal steroidogenesis in PCOS.

Loss of oocyte Rps26 in mice arrests oocyte growth and causes premature ovarian failure.

Global transcriptional activity increases as oocytes grow and is silenced in fully grown oocytes. Thus, the chromatin configuration varies during oocyte growth, but the molecular mechanisms regulating these changes remain to be clarified. Here, we studied a susceptibility gene of polycystic ovary syndrome (PCOS), RPS26, which is a ribosomal protein-encoding gene that is highly expressed in the ovary, but the functions of which remain unknown. Specific knockout of Rps26 in mouse oocytes resulted in retarded follicle development from pre-antral follicles to antral follicles, while the chromatin configurations of the oocytes were arrested at the transition from the non-surrounded nucleolus (NSN) to surrounded nucleolus (SN)-type. As a consequence, all oocytes died by postnatal day 84 resulting in premature ovarian failure (POF). Loss of Rps26 in oocytes led to decreased mRNA transcription and low levels of histone trimethylation on H3K4/H3K9 and DNA methylation at 5-cytosine, high levels of which are required for oocytes to transform from NSN to SN-type. Low protein levels of oocyte-derived growth differentiation factor 9, bone morphogenetic protein 15, and the oocyte-granulosa cell gap junction protein connexin 37 inhibited oocyte growth and retarded follicle development. The disruption of the phosphoinositide 3-kinase/protein kinase B/Forkhead box O-3a pathway contributed to oocyte death and follicle atresia. These results provide genetic clues for the clinical diagnosis of POF, especially in PCOS patients without treatment.