Cellular and mitochondrial adaptation mechanisms in the colon of lactating dairy cows during hyperthermia

Abstract

Heat stress causes barrier dysfunction and inflammation of the small intestine of several species. However, less is known about the molecular and cellular mechanisms underlying the response of the bovine large intestine to hyperthermia. We aimed to identify changes in the colon of dairy cows in response to constant heat stress using a proteomic approach. Eighteen lactating Holstein dairy cows were kept under constant thermoneutral conditions (16°C and 68% relative humidity (RH); temperature-humidity-index (THI) = 60) for 6 d (period 1) with free access to feed and water. Thereafter, 6 cows were equally allocated to: 1) thermoneutral condition with ad libitum feeding (TNAL; 16°C, RH = 68%, THI = 60), 2) heat-stressed condition (HS; 28°C, RH = 50%, THI = 76) with ad libitum feeding, or 3) pair-feeding at thermoneutrality (TNPF; 16°C, RH = 68%, THI = 60) for another 7 d (period 2). Rectal temperature, milk yield, dry matter and water intake were monitored daily. Then, cows were sacrificed and colon mucosa samples were taken for proteomic analysis. Physiological data were analyzed by ANOVA and colon proteome data was processed using DESeq2 package in R. Rectal temperature was significantly higher in HS than in TNPF and TNAL cows in period 2. Proteomic analysis revealed an enrichment of activated pathways related to colonic barrier function and inflammation, heat shock proteins, amino acid metabolism, reduced overall protein synthesis rate, and post-transcriptional regulation induced by heat stress. Further regulations were found for enzymes of the tricarboxylic acid cycle and components of the mitochondrial electron transport chain, presumably to reduce the generation of reactive oxygen species, maintain cellular ATP levels, and prevent apoptosis in the colon of HS cows. These results highlight the cellular, extracellular, and mitochondrial adaptations of the colon during heat stress and suggest a dysfunction of the hindgut barrier integrity potentially resulting in a 'leaky' colon.