MCLR induces dysregulation of calcium homeostasis and endoplasmic reticulum stress resulting in apoptosis in Sertoli cells

Microcystins-LR (MCLR) is a potent reproductive system toxin. We have previously shown that MCLR induced endoplasmic reticulum (ER) stress and apoptosis in testis. ER is the main calcium storage site in cells, and its calcium homeostasis plays an important role in the regulation of apoptosis. Hence, in the present study, we have investigated the role of calcium (Ca2+) in inducing apoptosis and how it affect the mitochondria and endoplasmic reticulum in TM4 cells. Our study found that MCLR induced an increase in Ca2+ concentration in TM4 cells. Compared to the controls, MCLR induced phosphorylation of calmodulin-dependent protein kinase II (CaMKII) which was involved in MAPKs activation, resulting in the induction of mitochondrial apoptosis pathways. Ca2+ chelator Bapta-AM partially reversed MCLR-induced apoptosis, confirming the possible involvement of calcium homeostasis disruption after MCLR exposure. Meanwhile, MCLR activated unfolded protein response and activated the ER apoptotic pathway by activating caspase-12. In addition, exposure to MCLR causes mitochondrial defects and increased apoptosis by up-regulating caspase 3 and cytosol cytochrome c expression. Collectively, these results demonstrated that MCLR disturbed calcium homeostasis, which caused ER-mitochondria dysfunction, ultimately promoted cell apoptosis in Sertoli cells.