Effects of fasting and refeeding on expression of MAFbx and MuRF1 in chick skeletal muscle

The present study investigated the effects of fasting and refeeding on the expression of proteasome-related genes and their downstream targets in the skeletal muscles of chicks. Seven-day-old chicks were fasted for 24 or 48 h and then refed for 4 h. The expression levels of MAFbx and MuRF1, which function as E3 ligases in the ubiquitin-proteasome system, were investigated at the mRNA and protein levels. MAFbx and MuRF1 expression were increased by fasting and these increases were downregulated by refeeding. The expression of the target proteins of these E3 ligases, MyoD and M-CK, was also analyzed. The levels of these proteins were downregulated by fasting, and these decreases were rescued by refeeding. The results of this study indicate that fasting stimulates MAFbx and MuRF1 expression in chicks, possibly leading to increased degradation of their corresponding target proteins.