Lysine-rich rice enhanced muscle growth and development in young rats.

Rice is the staple food for half of the world's population but is low in lysine content. We previously developed transgenic lysine-rich rice with enhanced free lysine content in rice seeds and demonstrated that it could improve skeletal growth and development in rats. However, the effects of lysine-rich rice on muscle remain to be studied. We hypothesized that lysine-rich rice was able to improve muscle growth in weaning rats via its anabolic effects on muscle metabolism. Male weaning Sprague-Dawley rats received lysine-rich rice (HFL) diet, wild-type rice (WT) diet, or wild-type rice with various doses of lysine supplementation (WT + Lys) diet (+ 0%, + 10%, + 20%, and + 40% lysine) for 70 days. Muscle strength and quality were analyzed by biomechanical test and muscle fiber typing of the extensor digitorum longus (EDL) muscles. Molecular mechanisms of lysine on muscle growth were also explored by rat serum biochemistry and cell culture systems. Results indicated that the HFL diet improved rats' muscle growth, strength, and physiological cross-sectional area (CSA) over the WT diet group. The CSAs of fast-twitch muscle fibers (Type IIb and IIx) were also increased. In addition, the HFL increased serum insulin-like growth factor 1 (IGF-1) and decreased serum myostatin (MSTN) concentrations. The cell culture model showed that lysine deficiency reduced IGF-1 expression and inhibited myoblast differentiation associated with muscle growth. Our findings showed that lysine-rich rice improved muscle growth and development in weaning rats. Higher dietary lysine possibly inhibited MSTN and activated of IGF-1 signaling pathway for muscle growth and development.