ER stress disturbs SR/ER-mitochondria Ca2+ transfer: Implications in Duchenne muscular dystrophy.

Besides its role in calcium (Ca2+) homeostasis, the sarco-endoplamic reticulum (SR/ER) controls protein folding and is tethered to mitochondria. Under pathophysiological conditions the unfolded protein response (UPR) is associated with disturbance in SR/ER-mitochondria crosstalk. Here, we investigated whether ER stress altered SR/ER-mitochondria links, Ca2+ handling and muscle damage in WT (Wild Type) and mdx mice, the murine model of Duchenne Muscular Dystrophy (DMD). In WT mice, the SR/ER-mitochondria links were decreased in isolated FDB muscle fibers after injection of ER stress activator tunicamycin (TM). Ca2+ imaging revealed an increase of cytosolic Ca2+ transient and a decrease of mitochondrial Ca2+ uptake. The force generating capacity of muscle dropped after TM. This impaired contractile function was accompanied by an increase in autophagy markers and calpain-1 activation. Conversely, ER stress inhibitors restored SR/ER-mitochondria links, mitochondrial Ca2+ uptake and improved diaphragm contractility in mdx mice. Our findings demonstrated that ER stress-altered SR/ER-mitochondria links, disturbed Ca2+ handling and muscle function in WT and mdx mice. Thus, ER stress may open up a prospect of new therapeutic targets in DMD.