Characterization of myofiber degeneration by assessment of ER-stress biomarkers

The sarco-endoplasmic reticulum (SR/ER) forms an extensive network within muscle fibers, playing a central role in calcium (Ca2 +) homeostasis, protein synthesis, folding, sorting and quality control. ER functional disturbance causes endoplasmic reticulum (ER) stress and leads to the accumulation of unfolded or misfolded proteins, thereby triggering the unfolded protein response (UPR) to alleviate cellular stress and re-establish homeostasis. ER stress can be triggered by defects in the balance between protein folding and degradation, altered calcium and lipid levels and changes in ER-mitochondria contacts. Accumulating evidence suggests that ER stress may play an important part in the pathogenesis of inflammatory myopathies and genetic muscle disorders characterized by myofiber degeneration and replacement with fibrotic tissue. In particular, myopathy could be due to chronic ER stress and a maladaptive response leading to defective muscle force and atrophy. Considering this evidence, the characterization of degenerated muscle fibers could be conducted through the analysis of proteins involved in endoplasmic reticulum stress. Here we propose a protocol, intended as a practical and reproducible workflow, for evaluating ER-stress associated proteins in muscle tissue.