Possible role for avPGC-1α in the control of expression of fiber type, along with avUCP and avANT mRNAs in the skeletal muscles of cold-exposed chickens

Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), a transcriptional coactivator, plays a role in mitochondrial biogenesis, muscle fiber specialization, and adaptive thermogenesis. Because of an absence of brown adipose tissue, the skeletal muscle tissue in chickens serves as an important source of thermogenesis to counter the cold. The present experiments were conducted (i) to clone the cDNA of PGC-1α homologs from chicken skeletal muscle and to examine alterations to PGC-1α mRNA expression in the skeletal muscles of cold-exposed chickens, (ii) to study the effect of cold-acclimation on the metabolic fiber phenotype of typically fast-glycolytic (type IIB) pectoralis muscles, and (iii) to compare avANT and avUCP mRNA expression in control and cold-exposed chickens. Results show that the cloned avPGC-1α cDNA encodes a 796 amino-acid protein (GenBank Accession No. AB170013) showing 84% identity with rodent PGC-1α cDNA. Exposure of chickens to a cold environment resulted in the prompt upregulation of avPGC-1α expression, which preceded increments in avUCP and avANT expression in skeletal muscle mitochondria. Consistent with the morphological appearance of muscles, an increase in the number of fast-oxidative-glycolytic (type IIA) fibers in the pectoralis muscle, which contains exclusively type IIB fibers in control chickens, was observed in cold-acclimated chickens. These findings provide novel information about possible regulatory pathways in avian skeletal muscle during thermogenesis.