The integrity of the plasma membrane is maintained through an active repair process, especially in skeletal and cardiac muscle cells, in which contraction-induced mechanical damage frequently occurs in vivo. Muscular dystrophies (MDs) are a group of muscle diseases characterized by skeletal muscle wasting and weakness. An important cause of this group of diseases is defective repair of sarcolemmal injuries, which normally requires Ca2+ sensor proteins and Ca2+-dependent delivery of intracellular vesicles to the sites of injury. MCOLN1 (also known as TRPML1, ML1) is an endosomal and lysosomal Ca2+ channel whose human mutations cause mucolipidosis IV (ML4), a neurodegenerative disease with motor disabilities. This study reports that ML1-null mice develop a primary, early-onset MD independent of neural degeneration. Although the dystrophin-glycoprotein complex and the known membrane repair proteins are expressed normally, membrane resealing was defective in ML1-null muscle fibers and also upon acute and pharmacological inhibition of ML1 channel activity or vesicular Ca2+ release. Injury facilitated the trafficking and exocytosis of vesicles by upmodulating ML1 channel activity. In the dystrophic mdx mouse model, overexpression of ML1 decreased muscle pathology. Collectively, these data have identified an intracellular Ca2+ channel that regulates membrane repair in skeletal muscle via Ca2+-dependent vesicle exocytosis.
