Liver proteomic analysis of cows exposed to heat stress or cooling conditions during the dry period

Abstract Text:

Heat stress negatively impacts cow performance, compromises immune function and increases susceptibility to metabolic disorders, particularly during the transition period. Metabolic adaptations of the liver are critical for successful transition from gestation to lactation, yet it is unclear how heat stress impacts metabolic pathways within the liver at the molecular level. The objective of this study was to investigate the liver proteome of cooled and heat stressed dry cows in order to gain insight into how molecular pathways are altered by heat stress and may contribute to poor performance and transition-related disorders. The experiment was conducted at the University of Florida Dairy Unit. During the dry period, cows were either housed in shaded barns with fans and soakers (cooled group [CL]; n=5) or in shaded barns lacking these cooling devices (heat stressed group [HT]; n=5). Liver biopsies were collected +2 days relative to calving. Proteins were analyzed by quantitative shotgun proteomics at the Weizmann Institute of Science (Rehovot, Israel). Proteins were extracted and subjected to in-solution tryptic digestion followed by nanoflow liquid chromatography coupled to high-resolution tandem mass spectrometry. Quantitative data was extracted using the Genedata Expressionist data analysis package and proteins identified using the Mascot search engine. Proteomics data, after logarithmic transformation, were analyzed by t-test to examine effect of treatment (CL vs. HT). Proteins were regarded as differential at P ≤ 0.05 and fold change ± 1.2. Differentially expressed proteins were analyzed by Ingenuity Pathway Analysis. A total of 3270 proteins were identified, 65 of which were differentially expressed between treatments. The most relevant pathways identified were hepatic oxidative phosphorylation and mitochondrial dysfunction. The abundance of several proteins related to these pathways was lower in the liver of HT cows relative to CL cows, including cytochrome c oxidase subunit 4 isoform 1(COX4I1, P < 0.04), NADH dehydrogenase 1 alpha subcomplex subunits 10, 11, and 12 (NDUFA10, P < 0.002; NDUFA11, P < 0.01; NDUFA12, P < 0.04), and thioredoxin-dependent peroxide reductase (PRDX3, P < 0.04). NADH dehydrogenase and cytochrome c oxidase are 2 of the 4 enzyme complexes in the inner mitochondrial membrane involved in the redox reactions that create the proton gradient necessary to power ATP synthesis. Thioredoxin-dependent peroxide reductase is an antioxidant and as such protects enzymes from oxidative damage. These results suggest that cooling late gestation cows improves liver function during early lactation. 

Keywords: oxidative phosphorylation, heat stress, mitochondrial dysfunction