Muscle actin isoforms are differentially expressed in human satellite cells isolated from donors of different ages

Myogenesis is mainly sustained by a subpopulation of myogenic cells known as satellite cells (SC). In this paper we studied α-smooth muscle (αSMA) and α-sarcomeric muscle (αSRA) actin isoform expression in cultures of human satellite cells (HSC) isolated from skeletal muscle biopsies from a 5-day-old newborn, a 34-year-old young adult and a 71-year-old donor. Myogenicity of cultures was assessed using immunocytochemical detection of desmin and myosin heavy chain. Time-course expression of αSRA and αSMA were studied with both immunocytochemistry and western blotting procedures. Although αSMA was never detected in whole skeletal muscle, both αSMA and αSRA were detected in proliferating and differentiating HSC derived from donors of all examined ages. The expression level experiments showed that αSRA was gradually up-regulated during HSC differentiation, but no significant differences were observed between newborn, young, and elderly HSC cultures. Our data demonstrated that HSC, isolated from subjects of different ages, re-expressed αSMA, but its levels and expression pattern varied considerably in the newborn with respect to the young adult and elderly donors. These results are discussed in relation to the myogenic differentiation capability of HSC during human muscle senescence.