Impact of chronic cyclic heat stress on breast muscle proteomics in broiler chicken.

1. Previous work has demonstrated that chronic cyclic heat stress (HS; 33°C for 8 h/day) resulted an 18.2% reduction in broiler breast muscle compared to a thermoneutral cohort (TN; 23°C). Given the deleterious impact of HS on broiler breast muscle mass, mass spectrometry (MS)-based proteomics was employed in the following trial to compare muscle protein expression in broiler chicken kept under HS or TN conditions. This investigated molecular mechanisms involved in HS-induced reduction of breast muscle mass.2. The experiment ran in broilers aged days 15-35. Acclimation occurred from day 15 to day 21, when birds in the HS group were exposed to a stepwise increase in temperature from 28°C to 33°C (8 h/day), achieving 33°C by day 21 which was maintained until day 35.3. On day 35, male birds were selected randomly (n = 10/treatment; total n = 20) and euthanised for breast muscle proteome profiling. Proteomic analyses were performed using pen-level biological replication (n = 4/treatment group) to identify proteins differentially abundant in response to chronic cyclic HS. The LC-MS/MS proteomics combined with bioinformatics was undertaken to identify proteins in breast muscle with significant changes in abundance in response to HS exposure.4. Bioinformatics confirmed that 116 proteins were differentially expressed, with the majority downregulated (88%) under HS, as determined at a significant fusion score ≤ 0.05. The KEGG pathways related to extracellular matrix organisation and structural integrity, including cytoskeleton in muscle cells, extra-cellular matrix (ECM)-receptor interaction and focal adhesion, were significantly enriched. The majority of associated proteins in these pathways were downregulated in breast muscle of HS-challenged broilers.5. Gene Ontology Cellular Component terms, including extracellular matrix and external encapsulating structure were enriched, likely indicating HS-induced impairment of muscle structural stability and cell-matrix interactions in broiler breast muscle.