FRI376 Regulation Of Theca Cell Function By Salt-Inducible Kinases

Disclosure: M. Rodriguez Esquivel: None. E. Hayes: None. O. Lakomy: None. M. Hassan: None. R. Filzen: None. C.O. Stocco: Grant Recipient; Self; NIH R01HD097202. The most common identifiable factors of female infertility are ovulatory disorders. Ovulation is the pinnacle of folliculogenesis, a process that requires an interplay between the oocyte, the granulosa cells, and the theca cells (TCs). TCs are the only source of ovarian androgens. Androgens play vital roles in female fertility acting as substrates for estrogen production in granulosa cells and directly regulating ovarian function via the activation of the androgen receptor. However, abnormally elevated androgen levels reduce fertility in humans and animals, suggesting that a delicate equilibrium exists between the beneficial and harmful effects of androgens in the ovary. Therefore, uncovering novel mechanisms regulating androgen synthesis in TCs is of great significance. The capacity of TCs to synthesize androgens relies on the expression of the rate-limiting enzyme CYP17A1, which converts progestogens into androgens, and its stimulation by the luteinizing hormone (LH). Previously, our group showed that salt-inducible kinases (SIKs) regulate granulosa cell steroidogenesis. Here, we investigated whether SIKs play any role in the regulation of androgen production in TCs. SIK2 and SIK3 were detected by IHC in the TCs of rat ovaries. Western blot confirmed this finding using isolated rat TCs. Next, rat TCs in culture were treated with LH in the presence or absence of HG, a highly specific SIK inhibitor. SIK inhibition enhanced the stimulatory effect of LH on Cyp17a1 mRNA expression. HG alone also increased Cyp17a1 expression to levels higher than those found in the presence of LH. Similarly, HG alone increased testosterone and potentiated LH stimulation of testosterone production. SIK inhibition also enhanced the stimulatory effect of LH on the expression of StAR and Cyp11a1. Concentration-response experiments for the SIK inhibitor in the presence or absence of LH show that SIK inhibition stimulates Cyp17a1 in a concentration-dependent manner from 0.1 to 1 µM. Of note, at 3 µM, HG was less effective in inducing Cyp17a1 than at 1 µM, suggesting that higher concentrations of HG may have alternative unknown effects. Activation of adenyl cyclase with forskolin or emulation of increased intracellular cAMP with dbcAMP stimulated Cyp17a1 an effect that was also enhanced by the inhibition of SIK. Since the main target of cAMP is PKA, we used lentivirus to express constitutively active PKA (caPKA). Overexpression of caPKA was sufficient to stimulate testosterone production, an effect that was significantly augmented by SIK inhibition, suggesting that SIKs regulate factors downstream of PKA. This evidence shows that TCs express SIKs and reveal novel roles for SIKs in the regulation of TC function and androgen production. This information could contribute to uncovering therapeutic targets to treat hyperandrogenic diseases such as PCOS. Presentation: Friday, June 16, 2023