CALCIUM HANDLING IN MYOGENIC PROGENITORS AND SKELETAL MYOBLASTS: THE ROLE OF CD20

The calcium ion plays an essential role in the physiology of all living cells. Accordingly, multiple mechanisms contribute to the precise control of its intracellular concentration ([Ca2+]i). Particularly in skeletal muscle, the efficient regulation of cytosolic Ca2+ is crucial for tissue functionality and impairment of Ca2+ homeostasis has been shown to contribute to the etiology of muscular disorders such as Duchenne muscular dystrophy (DMD). Although the impairment of Ca2+ homeostasis affecting dystrophic muscular cells has been extensively reported, the pathways involved in calcium-release and the role of store-operated Ca2+ channels in dystrophic myogenic progenitors were not investigated before. Among the heterogeneous population of circulating hematopoietic and endothelial progenitors, we identified a subpopulation of CD133+ cells displaying myogenic properties. Interestingly, expression of the B-cell marker CD20 was observed in blood-derived CD133+ stem cells. Among the scarce available data about the biological role of the membrane protein CD20, there are some evidences of its involvement in the regulation of intracellular calcium concentration ([Ca2+]i). Here, we show that a CD20-related pathway leading to an increase of cytosolic calcium is differently activated in normal and dystrophic blood-derived CD133+ stem cells, supporting the assumption of a CD20-related calcium impairment affecting dystrophic cells. Although CD20 can modulate cytosolic calcium through a specific signaling pathway, other studies demonstrated its association with lipid raft domains of the plasma membrane, where it probably functions directly as a store-operated Ca2+ channel. Recent works indicated that store-operated Ca2+ entry (SOCE) plays a central role in skeletal muscle physiology and development, but there remain a number of unresolved issues relating to SOCE modulation in this tissue. That being so, and considering that blood and muscle share common mesodermic origins, we were prompted to investigate whether CD20 contributes to calcium handling in committed muscular cells. Expression of CD20 was observed in skeletal muscle, displaying a membrane localization in myoblasts and adult muscle fibers. Additionally, we showed that inhibition of CD20 resulted in specific impairment of SOCE in C2C12 myoblasts. Together, reported findings contributed to identify deregulated pathways affecting dystrophic stem cells and potentially involved in DMD pathology. Moreover, our results suggested that functional CD20 is required for SOCE to consistently occur in C2C12 myoblasts, providing a novel insight to improve the understanding of store-operated Ca2+ entry regulation in skeletal muscle.