Carnosine synthase deficiency in mice affects protein metabolism in skeletal muscle

Carnosine and anserine are abundant peptides found in the skeletal muscle and nervous system in many vertebrates. Several in vitro and in vivo studies have demonstrate that exogenously administered carnosine improves exercise performance. Furthermore, carnosine is an antioxidant and antifatigue supplement. However, the physiological functions of endogenous carnosine and its related histidine-containing dipeptides in a living organism remain unclear. We aimed to clarify the physiological roles of endogenous carnosine by investigating the characteristics of carnosine synthase gene-deficient mice and the effects of carnosine on skeletal muscle protein metabolism. We discovered that carnosine and anserine were undetectable in the skeletal muscle of carnosine synthase knockout mice. We also quantified protein gene expression and enzyme levels in muscle protein metabolism. Gene and protein levels of the muscle protein synthesizer insulin-like growth factor-1 (IGF-1) and the degrading enzyme cathepsin B were markedly lower in carnosine synthase gene-deficient mice than those in wild-type mice. The amount of 3-methylhistidine (a marker for muscle proteolysis) in forced exercise and the weight of the gastrocnemius muscle were considerably lower in carnosine synthase gene-deficient mice than in wild-type mice. Consequently, we showed that carnosine deficiency affects weight maintenance and protein metabolism in skeletal muscle, suggesting that carnosine regulates skeletal muscle protein metabolism.