Fasting Induces Gene Expression of Insulin-like Growth Factor-binding Proteins in Skeletal Muscles of Chicks

In mammals, evidence suggests that insulin-like growth factor-binding proteins (IGFBPs) affect skeletal muscle growth in an autocrine and paracrine manner. In the present study, fasting induced significant transcriptional changes in IGFBP genes in the skeletal muscles of layer and broiler chickens. Twelve hours of fasting significantly increased mRNA levels of IGFBP-1 in the biceps femoris (BF; largest skeletal muscle in the thigh) of both chicken types. mRNA levels of IGFBP-2 in both the pectoralis major (PM; breast muscle) and the BF significantly increased in layer chicks and tended to increase in broiler chicks. Fasting significantly decreased mRNA levels of IGFBP-3 in the BF and PM of both chicken type. mRNA levels of IGFBP-4 and -5 differed responses in the PM and BF of layer and broiler chicks. mRNA levels of most IGFBP genes were not affected by insulin-like growth factor-1 (IGF-1) in chicken embryonic myotubes, suggesting that skeletal muscle IGFBPs were transcriptionally regulated in an IGF-1-independent manner. Overall, these findings suggested that IGFBP-1, -2, and -3, which were expressed in skeletal muscles, played conserved roles in layer and broiler chicks.