Mechanistic target of rapamycin is activated in bovine granulosa cells after LH surge but is not essential for ovulation.

Contents The LH surge induces functional and morphological changes in granulosa cells. Mechanistic target of rapamycin ( mTOR) is an integrator of signalling pathways in multiple cell types. We hypothesized that mTOR kinase activity integrates and modulates molecular pathways induced by LH in granulosa cells during the preovulatory period. Cows were ovariectomized and granulosa cells collected at 0, 3, 6, 12 and 24 hr after Gn RH injection. While RHEB mRNA levels increased at 3 and 6 hr, returning to basal levels by 12 hr after Gn RH treatment, RHOA mRNA levels increased at 6 hr and remained high thereafter. Western blot analyses revealed increased S6K phosphorylation at 3 and 6 hr after Gn RH injection. Similarly, mRNA levels of ERK1/2, STAR and EGR-1 were higher 3 hr after Gn RH treatment. Rapamycin treatment inhibited mTOR activity and increased AKT activity, but did not alter ERK1/2 phosphorylation and EGR1 protein levels in cultured bovine granulosa cells. Rapamycin also inhibited LH-induced increase in EREG mRNA abundance in granulosa cells in vitro. However, intrafollicular injection of rapamycin did not suppress ovulation. These findings suggest that mTOR is involved in the control of EREG expression in cattle, which may be triggered by LH surge stimulating RHEB and S6K activity. [ABSTRACT FROM AUTHOR]