Proteomic analysis to unravel the effect of heat stress on gene expression and milk synthesis in bovine mammary epithelial cells.

Heat stress can play a negative effect on milk yield and composition of dairy cattle, leading to immeasurable economic loss. The basic components of the mammary gland are the alveoli; these alveolar mammary epithelial cells reflect the milk producing ability of dairy cows. In this study, we exposed bovine mammary epithelial cells to heat stress and compared them to a control group using isobaric tags for relative and absolute quantitation combined with liquid chromatography coupled with tandem mass spectrometry. Compared with a control group, 104 differentially elevated proteins (>1.3-fold) and 167 decreased proteins (<0.77-fold) were identified in the heat treatment group. Gene Ontology analysis identified a majority of the differentially expressed proteins are associated in cell-substrate junction assembly, catabolic processes and metabolic processes. Some of these significantly regulated proteins were related to the synthesis and secretion of milk, such as milk protein and fat. This finding was further supported by the results obtained from the reduced β-casein expression through the system of plasminogen activator - plasminogen - plasmin and decreased fatty acid synthase could partly explain why milk fat synthesis ability of dairy cows decreased under heat stress. Our results highlight the effects of heat stress on synthesis of milk protein and fat, thus providing additional clues for further studies of heat stress on dairy milk production.