miR-21 is involved in norepinephrine-mediated rat granulosa cell apoptosis by targeting SMAD7

Substantive evidence has indicated that the sympathetic innervation contributes to the regulation and development of ovarian functions. Norepinephrine (NE) is one of the major neurotransmitters contained in the extrinsic ovarian sympathetic nerves and is thought to be a potent moderator of ovarian functions such as steroidogenesis and granulosa cell proliferation or apoptosis. However, the mechanisms of NE regulation of granulosa cell apoptosis in the rat ovary are rare. Real-time PCR and Western blot results show that NE regulates the expression of miR-21 in primary granulosa cells in a dose-dependent manner. Additionally, we found that miR-21 is involved in NE-mediated rat granulosa cells apoptosis and blocks granulosa cell apoptosis by targeting Smad7, a transforming growth factor-beta-inducible mediator of apoptosis in granulosa cells. In primary granulosa cells, a combined treatment of NE and TGF-β increased apoptosis and decreased miR-21 expression, but increased SMAD7 protein levels. We also demonstrated that NE regulates miR-21 by coupling to α_1A-adrenergic receptor (α_1A-AR). This is the first demonstration that NE controls the reproductive functions by modulating the expression of miR-21 and promoting TGF-β-induced granulosa cell apoptosis. Such NE-mediated effects could be potentially used for regulating the reproductive processes and for treating reproductive disorders.