Thymosins and muscle regeneration

Abstract

Thymosins are a family of highly conserved small peptides originally isolated from calf thymus. One representative member of the family is thymosin-β₄ (Tβ₄), a major G-actin-sequestering peptide present in many tissues. In the last decade, various studies have uncovered several important functions for Tβ₄ related to the regeneration of injured tissues including skin and heart. In particular, Tβ₄ promotes endothelial cell migration via the activation of Akt2 kinase at the leading edge of the cell. In the case of skeletal muscle injury, increased levels of Tβ₄ are produced by muscle fibers and surrounding immune cells. Satellite cell-derived myoblasts and myocytes are chemoattracted by Tβ₄, which facilitates skeletal muscle regeneration. Recently, it was reported that Tβ₄ interacts physically with F₁-F₀ ATP synthase on the plasma membrane to increase the local concentration of ATP, which stimulates the P2X₄ purinergic receptor to elicit a migratory response from endothelial cells. Thus, it is clear that Tβ₄ is an important chemotactic factor involved in stem/progenitor cell-mediated tissue regeneration.