Effects of chronic heat stress on Ca2+ homeostasis, apoptosis, and protein carbonylation profiles in the breast muscle of broilers

Heat stress (HS) largely impairs the quality of broiler breast meat through protein oxidative modification. This study aimed to investigate the carbonylation pattern of Ca²⁺ channels and apoptotic proteins in the breast muscle of heat-stressed broilers. A total of 144 twenty-eight-day-old male Arbor Acres broilers were randomly divided into three treatment groups. The normal control (NC) group was kept at 22°C and provided with unlimited feed. The HS group was exposed to 32°C and provided with unlimited feed. The pair-fed (PF) group was kept at 22°C and given an amount of feed equivalent to that consumed by the HS group on the previous day. Results showed that broilers under HS conditions had a higher respiratory rate than those in NC and PF groups (P < 0.05). HS disrupted the morphology and structure of breast muscle fibers by decreasing the average diameters and average density of myofibers compared to the NC group (P < 0.05). HS increased the mean fluorescence intensity of the positive carbonyl signal in breast muscle compared with the NC group (P < 0.05). Besides, the pectoral Ca²⁺ concentration in the sarcoplasmic reticulum, cytoplasm, and mitochondria was elevated by HS when compared with the NC group (P < 0.05). In comparison to the NC and PF groups, HS increased the apoptosis rate and caspase-3 activity in the breast muscle (P < 0.05). Furthermore, HS elevated the relative protein expressions of plasma membrane Ca²⁺-ATPase, Na⁺/Ca²⁺ exchanger 1, and sarco/endoplasmic reticulum calcium transport ATPase 1 compared to the NC group (P < 0.05). Higher relative protein expression of μ-calpain and lower relative protein expression of cytosolic cytochrome complex were found in the HS group than the NC group (P < 0.05). HS decreased the carbonylation levels of transient receptor potential canonical 1 and inositol 1,4,5-trisphosphate receptor compared to the NC group (P < 0.05). Additionally, the carbonylation levels of cleaved caspase-3 and precursor caspase-9 were increased and decreased, respectively, by HS treatment compared to the NC group (P < 0.05). In conclusion, HS damages the myofiber based on Ca²⁺ dyshomeostasis and apoptosis, which are potentially associated with protein carbonylation. These results shed new light on the possible mechanism behind the development of poor meat quality in broilers due to HS.