Effects of Fasting and Refeeding on Expression of Proteolytic-Related Genes in Skeletal Muscle of Chicks

This experiment was conducted to study the effects of fasting and refeeding on proteolytic-related gene expression in skeletal muscles of chicks. Chicks were fasted for 24h, and refed for 2h. Plasma N^T-methylhistidine concentration, as an index of myofibrillar protein degradation, was increased by fasting, and that increment was reduced by refeeding. We also examined the expression of the protease mRNAs (calpain, proteasome, cathepsin and caspase-3) by real-time PCR of cDNA in skeletal muscles of fasting and refeeding chicks. Calpain (m-, μ-, and p94/calpain-3) mRNA expressions were also increased by fasting, and their increment was reduced by refeeding. Ubiquitin and 20S proteasome α subunit (α6 and α7) mRNA expressions as well as cathepsin B, and caspase-3 mRNA expression were likewise increased by fasting, with their increment also reduced by refeeding. These results indicate that fasting stimulates proteolytic-related gene expression, resulting in an increase in myofibrillar protein degradation, and that refeeding suppresses proteolytic-related gene expression, resulting in a decrease in myofibrillar protein degradation in chicks.