Abstract
Little is known about the molecular relationships among follicle stimulating hormone (FSH), lipid droplet (LD) degradation, and autophagy. In this study, we aimed to investigate the pathway by which FSH regulates autophagy and the potential role of autophagy in progesterone production. Our results revealed that FSH stimulated progesterone production in mammalian follicular granulosa cells (GCs) through a non-canonical pathway. In porcine secondary follicles cultured in vitro, FSH treatment increased the level of the autophagic marker, LC3-II, as well as increased the number of autophagic vacuoles in GCs. The underlying molecular mechanism and biological functions were then investigated in porcine GCs. Our results demonstrated that FSH could upregulate Beclin1 levels in porcine GCs; however, this effect was blocked by LY294002 (a PI3K/AKT inhibitor) and SP600125 (SAPK/JNK inhibitor). Further research confirmed that the transcriptional factor, c-Jun, was phosphorylated by FSH, then translocated into the nucleus from the cytoplasm and bound to the BECLIN1 promoter region, and that LY294002, SP600125, or c-Jun knockdown prevented the increase in Beclin1 levels induced by FSH. Interestingly, inhibition of autophagy using chloroquine or SP600125 decreased progesterone production in porcine GCs treated with FSH, although the expression of StAR and P450scc was not disturbed. Moreover, FSH treatment reduced the average number and size of LDs in porcine GCs, but these effects were eliminated by knocking down the key autophagy genes, ATG5 and BECLIN1; in addition, the effect of FSH on promoting progesterone secretion by the cells was also reduced significantly. Based on the above results, we concluded that FSH promoted progesterone production by enhancing autophagy through upregulation of Beclin1 via the PI3K/JNK/c-Jun pathway to accelerate LD degradation in porcine GCs, independent of the classical steroidogenic pathway.
Highlights
Ovarian follicle development is a dynamic process during which interactions between pituitary gonadotropins and numerous autocrine/paracrine growth factors from the ovary determine whether the follicles grow continuously or undergo atresia (Yuan et al, 2015)
With 0.01 IU/mL follicle stimulating hormone (FSH) already yielded a striking increase in light chain 3 (LC3)-II levels, this concentration was used for subsequent experiments
We found that FSH activated the PI3K/AKT and SAPK/JNK pathways to stimulate BECLIN1 expression, leading to upregulated autophagy and lipid droplet (LD) degradation, which promoted progesterone production independent of steroidogenesis enzymes in porcine granulosa cells (GCs)
Summary
Ovarian follicle development is a dynamic process during which interactions between pituitary gonadotropins and numerous autocrine/paracrine growth factors from the ovary determine whether the follicles grow continuously or undergo atresia (Yuan et al, 2015). New functions of FSH have been revealed in mammalian follicular development; for example, FSH can promote the survival of porcine granulosa cells (GCs) by decreasing the level of the proapoptotic protein, BimEL (Wang et al, 2012), and is involved in autophagy regulation in rat GCs (Choi et al, 2014). Autophagy is an evolutionarily conserved mechanism that plays an indispensable role in the recycling of intracellular proteins and organelles to maintain cellular homeostasis. It is tightly regulated by a series of autophagy-related gene (Atg) proteins. Beclin, the mammalian ortholog of Atg, plays a central role in autophagy and regulation of membrane trafficking (Kang et al, 2011). Studies have shown that intracellular LDs can store triglycerides and cholesterol esters, providing fatty acids or cholesterol for membrane biosynthesis and steroidogenesis (Beller et al, 2010; Brasaemle and Wolins, 2012)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
