Apolipoprotein A-1 expression is resistant to dimethyl sulfoxide inhibition of myogenic differentiation

Primary cultures of chick embryonic muscle (CEM) were analyzed for the differential expression of a 26-kDa protein during myogenesis. We have identified this 26-kDa protein as apolipoprotein A-1 (Apo A-1), the major protein of serum high density lipoprotein particles. Apo A-1 was expressed in a pattern temporally similar to those of muscle-specific proteins, by myoblasts at very low levels, and by myotubes at high levels. The half-life of Apo A-1 in CEM cell homogenates was 23 min. This fast turnover rate appeared to be due to the secretion of Apo A-1 into the culture medium. To further characterize the relationship of Apo A-1 expression and myogenic differentiation, CEM cultures were treated with dimethyl sulfoxide (DMSO). In the presence of 2% DMSO, myotubes exhibited an atrophied morphology and an inhibition of the synthesis and accumulation of muscle-specific sarcomeric proteins. During recovery from DMSO treatment, the expression and accumulation of muscle-specific proteins returned to high levels. In contrast, the rates of synthesis and secretion of Apo A-1 in control, DMSO-treated, and DMSO-recovered CEM cells were nearly equivalent. These results indicate that the expression of Apo A-1 is not strictly linked to the expression of muscle-specific sarcomeric proteins in skeletal muscle and suggest that independent, or additional regulatory mechanisms exist which modulate Apo A-1 expression during myogenesis.