Research on the role of endoplasmic reticulum-mitochondria interactions in maintaining calcium homeostasis in skeletal muscle fibers of hibernating Daurian ground squirrels

The ability to maintain cytoplasmic Ca²⁺ homeostasis during the torpor-arousal cycle is a crucial strategy that enables hibernators to resist disuse-induced muscle atrophy during hibernation. However, whether ER-mitochondria interactions contribute to the regulation of cytoplasmic Ca²⁺ homeostasis in skeletal muscle fibers during hibernation remain unclear. Here, we systematically explored the expression of tethering proteins, Ca²⁺ axis-related proteins, and protein complexes involved in Ca²⁺ transport within the ER-mitochondria contact sites (ERMCS) of soleus (SOL) and extensor digitorum longus (EDL) muscles in Daurian ground squirrels (Spermophilus dauricus) during hibernation. Results demonstrated a significant increase in the expression of the tethering protein MFN2 and Ca²⁺ axis-related proteins GRP75 and VDAC1, as well as enhanced interactions within the Ca²⁺ axis complex in the SOL muscle in the inter-bout arousal (IBA) group, as compared to the late torpor (LT) group. In addition, these same indicators exhibited no significant alternation in the EDL muscle during the torpor-arousal cycle. These findings suggest that ER-mitochondria interactions may participate in maintaining Ca²⁺ homeostasis in the skeletal muscles during the torpor-arousal cycle, especially in slow-twitch muscle.