Purinoceptor expression in regenerating skeletal muscle in the mdx mouse model of muscular dystrophy and in satellite cell cultures

ATP is an important extracellular signaling molecule mediating its effects by activation of P2X and P2Y receptors. P2 receptors are expressed during muscle development, and recent findings demonstrate that ATP can regulate myoblast proliferation and differentiation in vitro. However, the role of purinergic signaling during regeneration of injured skeletal muscle has not been investigated. To examine this process in a clinically relevant system, we used the mouse model of muscular dystrophy (mdx), in which muscle degeneration is rapidly followed by regeneration. The latter process, in vivo muscle regeneration, was the focus of this study, and to study the cellular mechanisms involved in it, a parallel study on normal rat skeletal myoblast cultures was conducted. Using immunohistochemistry, RT-PCR, and electrophysiology, we investigated the expression of the P2X(1-7) receptor subtypes and the P2Y(1,2,4,6) receptors. Experiments in vitro and in vivo demonstrated the sequential expression of the P2X(5), P2Y(1), and P2X(2) receptors during the process of muscle regeneration. The P2X(5) and P2Y(1) receptors were expressed first on activated satellite cells, and the P2Y(1) receptor was also expressed on infiltrating immune cells. Subsequent P2X(2) receptor expression on newly formed myotubes showed significant colocalization with AChRs, suggesting a role in regulation of muscle innervation. Thus, this study provides the first evidence for a role for purinergic signaling in muscle regeneration and raises the possibility of new therapeutic strategies in the treatment of muscle disease.