Modern understanding of the role of calpains in muscles

Relevance. The study and understanding of the physiological processes that occur in muscles during physical activity is a crucial area in modern sports physiology. As our theoretical and practical knowledge expands, we realize that the classical ideas about these physiological processes under stress conditions do not provide complete information. To fully comprehend these processes, we need to conduct further analysis and systematize the existing data. This will help us identify key elements that we can influence to regulate the direction and extent of certain physiological processes. One such candidate for this regulation is the calpain protein family (CAPN). Initially, they were associated with regulating signal transmission, but now they are considered proteases involved in the turnover of myofibrillar protein and the proteolytic cleavage of sarcomeric and cytoskeletal proteins. CAPNs are often seen as «harmful» degrading proteases in pathological conditions, such as cardiovascular diseases. However, in reality, they are processing proteases rather than degrading ones. They differ from other major intracellular proteolytic components because they act through proteolytic processing, causing changes in protein activity, localization, or structure. For example, CAPNs can regulate the activity of NOS by suppressing the production of nitric oxide during muscle contractions. This helps prevent the negative consequences caused by excess nitric oxide production. They also reduce the contractile activity of muscles by acting on structures called «triads». Calpains play a significant role in the reparative processes of muscles after physical activity. They regulate the processes of cell membrane repair and the restructuring of protein components in muscle fibers. Another notable difference from classical proteolysis systems, such as ubiquitin - proteasome and autophagic systems that require ATP, is that calpains are ATP-independent. However, uncontrolled activity of calpains can trigger a cascade of proapoptotic systems leading to apoptosis and the death of myocytes. Conclusion . Calpains play an important role in the physiological processes that occur in muscles both in a healthy state and in various pathologies. Thus, the functions of calpains are not limited only to proteolysis (protein breakdown) - they are much broader. Therefore, the study of these enzymes is an important area of research. It will help us identify informative targets for developing treatment methods and monitoring muscle health after intense exercise.