Estradiol modulates myosin regulatory light chain phosphorylation and contractility in skeletal muscle of female mice

Impairment of skeletal muscle function has been associated with changes in ovarian hormones, especially estradiol. To elucidate mechanisms of estradiol on skeletal muscle strength, the hormone’s effects on phosphorylation of the myosin regulatory light chain (pRLC) and muscle contractility were investigated, hypothesizing an estradiol-specific beneficial impact. In a skeletal muscle cell line, C₂C₁₂, pRLC was increased by 17β- estradiol (E₂) in a concentration-dependent manner. In skeletal muscles of C57BL/6 mice that were E₂ deficient via ovariectomy (OVX), pRLC was lower than that from ovary-intact, sham-operated mice (Sham). The reduced pRLC in OVX muscle was reversed by in vivo E₂ treatment. Posttetanic potentiation (PTP) of muscle from OVX mice was low compared with that from Sham mice, and this decrement was reversed by acute E₂ treatment, demonstrating physiological consequence. Western blot of those muscles revealed that low PTP corresponded with low pRLC and higher PTP with greater pRLC. We aimed to elucidate signaling pathways affecting E₂-mediated pRLC using a kinase inhibitor library and C₂C₁₂ cells as well as a specific myosin light chain kinase inhibitor in muscles. PI3K/Akt, MAPK, and CamKII were identified as candidate kinases sensitive to E₂ in terms of phosphorylating RLC. Applying siRNA strategy in C₂C₁₂ cells, pRLC triggered by E₂ was found to be mediated by estrogen receptor- β and the G protein-coupled estrogen receptor. Together, these results provide evidence that E₂modulates myosin pRLC in skeletal muscle and is one mechanism by which this hormone can affect muscle contractility in females.