Loss of calpains-1 and -2 prevents repair of plasma membrane scrape injuries, but not small pores, and induces a severe muscular dystrophy.

The ubiquitous calpains-1 and -2 play important roles in Ca(2+)-dependent membrane repair. Mechanically active tissues like skeletal muscle are particularly reliant on mechanisms to repair and remodel membrane injury, such as those caused by eccentric damage. We demonstrate that calpains-1 and -2 are master effectors of Ca(2+)-dependent repair of mechanical plasma membrane scrape injuries, though are dispensable for repair/removal of small wounds caused by pore-forming agents. Using CRISPR gene-edited HEK293 cell lines, we establish that loss of both calpains-1 and -2 (CAPNS1(-/-)) virtually ablates Ca(2+)-dependent repair of mechanical scrape injuries, though does not affect injury or recovery from perforation by streptolysin-O or saponin. In contrast, cells with targeted knockout of either calpain-1 (CAPN1(-/-)) or -2 (CAPN2(-/-)) show near-normal repair of mechanical injuries, inferring both calpain-1 and calpain-2 are capable equally of conducting the cascade of proteolytic cleavage events to reseal a membrane injury, including that of the known membrane repair agent dysferlin. A severe muscular dystrophy in a murine model with skeletal muscle knockout of Capns1 highlights vital roles for calpain-1 and/or -2 for health and viability of skeletal muscles, not compensated for by calpain-3 (CAPN3). We propose the dystrophic phenotype relates to loss of maintenance of plasma membrane/cytoskeletal networks by calpains-1 and -2 in response to directed and dysfunctional Ca(2+) signaling; pathways hyper-stimulated in the context of membrane injury. With CAPN1 variants associated with spastic paraplegia, a severe dystrophy observed with muscle-specific loss of calpain-1 and -2 activity identifies CAPN2 and CAPNS1 as plausible candidate neuromuscular disease genes.