Role of serum myostatin in the association between hyperinsulinemia and muscle atrophy in Japanese obese patients

The protein myostatin is a member of the transforming growth factor β superfamily. This is mainly expressed in skeletal muscle and negatively regulates skeletal muscle growth. The present study aimed to elucidate the associations among circulating myostatin level, skeletal muscle mass, and metabolic profiles in Japanese obese patients. Japanese obese outpatients (n = 74) were enrolled. We measured clinical parameters, quantified serum myostatin levels, and examined their associations in a cross-sectional manner. Both total skeletal muscle mass and serum myostatin level were higher in males than in females. Among 74 patients, serum myostatin level was positively correlated with skeletal muscle mass and serum immunoreactive insulin (IRI) level [correlation coefficient ( r ) = 0.294, P  = 0.011; r  = 0.262, P  = 0.024, respectively]. Furthermore, multivariate linear regression analysis revealed that serum myostatin level was positively correlated with IRI after adjusting for gender and skeletal muscle mass ( β -coefficient = 0.230, P  = 0.029, R 2  = 0.236). In obese patients, serum myostatin level was elevated in conjunction with an increase in IRI level independent of skeletal muscle mass. This may imply possible novel pathological implications of serum myostatin in muscle mass and metabolism in obese patients with hyperinsulinemia.