Effects Of PRL And GC On Lipid Metabolism In Adipocytes And Hepatocytes Of Dairy Cows

Milk fat is an important nutrient composition in milk. The synthesis of milk fat isregulated by nutrition metabolic signals and neuroendocrine hormone. Adipose andliver are important lipid metabolism organs in body, which play a significant role inenergy and lipid metabolism balance. Prolactin is a hormone which promotesmammary gland development and initiates milk production. PRL has an “energytransfer” function which makes nutrition to breast during lactation period.Glucocorticoid is a hormone of hypothalamic–pituitary–adrenal axis. It play aimportant role in the carbonhydrate, lipid and protein metabolism. Therefore, studyson effects of PRL and GC on lipid metabolism in adipose and liver are very helpfulfor understanding milk fat production mechanism.In this study, pre-adipocytes were isolated from visceral adipose of dairy cows,induced to differentiation and identified fundamentally. The results showed that lipiddroplets and triglyceride increased during cell differentiation and reached a peakabout13days after differentiation. With differentiation of pre-adipocytes, lipidmetabolism related nuclear factors PPARγ2and SREBP-1c gradually increased andtheir mRNA expression levels reached maxium on4days after differentiation anddecreased thereafter. The protein expression levels and nuclear location levels ofPPARγ2and SREBP-1c on13day were significantly higher than those of0day. ThenPRL was added to mature adipocyte medium to study its effects on lipid metabolism.Results showed that PRL activated JAK2/STAT5signal pathway through prolactinreceptors and thereby inhibited SREBP-1c expression. Expression levels oflipogenesis related genes decreased, expression levels of lipolysis related genesincreased, and concentration of glycerol in culture medium increased. These resultsindicated that PRL promotes lipid mobilization by direct effect. In order to study the effects of dexamethasone on lipid metabolism in adipocytesand hepatocytes, DXM was added, and then a variety of molecular biology techniquessuch as qRT-PCR，Western blotting and IF were used to detect the expression levels ofmRNA and protein of related genes. Results showed that DXM promoted lipogenesisboth in adipocytes and hepatocytes. In adipocytes, DXM activated SREBP-1c throughGR, and then promoted lipogenesis related genes expression and inhibited lipolysisrelated genes expression. Concentrate of glycerol in culture medium decreased at last.In hepatocytes, DXM activated SREBP-1c, chRBP and PPARα through GR. Therebyexpression levels of lipogenesis related genes increased, of lipid oxidation relatedgenens decreased and concentration of TG increased. Expression levels ofapolipoprotein also increased resulting from DXM, and thereby increased theconcentration of VLDL. These results indicated that DXM promoted lipogenesis,increased concentraction of TG and promoted production and secretion of VLDL inhepatocytes.