Gene Expression and Cellular Analyses of Genes in the Protein Biosynthesis Pathway in Meat-Type Chickens Under Heat Stress

Growth is significantly reduced in poultry under heat stress (HS), however, the molecular and cellular mechanisms that underlie protein accretion and degradation are largely unknown. We investigated the immediate and long term transcriptomics changes in chickens under heat stress. Forty-eight male chickens at 14 d old were divided into two groups and raised under either constant 25^oC or 35^oC from 14-26 days of age in individual cages. Five birds per treatment at 1 and 12 days post HS were euthanized and the Pectoralis (P.) major was sampled for gene expression analysis. mRNA expression of key genes in the avian target of rapamycin (avTOR) and the ubiquitin-proteosome pathways representing protein synthesis and breakdown, respectively were studied. The P. major mRNA indicated that, after a day of HS, avTOR and EIF4E expressions as well as UBE21, UBE3A, PSMC1, PSMD1 and FBXO32 were reduced in the heat stressed birds compared to controls suggesting that both protein synthesis and protein breakdown were significantly reduced. However, after 12 days of HS, there was an increased mRNA expression of UBE21, UBE3A, PSMC1, PSMD1 and FBXO32 compared to the controls suggesting a significant increase in protein ubiquitination and degradation. The results from this study suggest that the initial molecular response of birds to heat stress is to reduce both protein synthesis and degradation to maintain body weight. However, if the heat stress persists, protein breakdown is elevated relative to their control counterpart reflecting the differences in growth.