Selenoprotein K knockdown induces apoptosis in skeletal muscle satellite cells via calcium dyshomeostasis-mediated endoplasmic reticulum stress

Skeletal muscle satellite cells (SMSCs), known as muscle stem cells, play an important role in muscle embryonic development, post-birth growth, and regeneration after injury. Selenoprotein K (SELENOK), an endoplasmic reticulum (ER) resident selenoprotein, is known to regulate calcium ion (Ca(2+)) flux and ER stress (ERS). SELENOK deficiency is involved in dietary selenium deficiency-induced muscle injury, but the regulatory mechanisms of SELENOK in SMSCs development remain poorly explored in chicken. Here, we established a SELENOK deficient model to explore the role of SELENOK in SMSCs. SELENOK knockdown inhibited SMSCs proliferation and differentiation by regulating the protein levels of paired box 7 (Pax7), myogenic factor 5 (Myf5), CyclinD1, myogenic differentiation (MyoD), and Myf6. Further analysis exhibited that SELENOK knockdown markedly activated the ERS signaling pathways, which ultimately induced apoptosis in SMSCs. SELENOK knockdown-induced ERS is related with ER Ca(2+) ([Ca(2+)](ER)) overload via decreasing the protein levels of STIM2, Orai1, palmitoylation of inositol 1,4,5-trisphosphate receptor 1 (IP3R1), phospholamban (PLN), and plasma membrane Ca(2+)-ATPase (PMCA) while increasing the protein levels of sarco/endoplasmic Ca(2+)-ATPase 1 (SERCA1) and Na(+)/Ca(2+) exchanger 1 (NCX1). Moreover, thimerosal, an activator of IP3R1, reversed the overload of [Ca(2+)](ER), ERS, and subsequent apoptosis caused by SELENOK knockdown. These findings indicated that SELENOK knockdown triggered ERS driven by intracellular Ca(2+) dyshomeostasis and further induced apoptosis, which ultimately inhibited SMSCs proliferation and differentiation.