The Mechanism Of SREBP-1c/Cidea Pathway In The Hepatic Lipidosis Of Dairy Cows With Negative Energy Balance

Fatty liver of dairy cows is characterized by excessive accumulation triacylglycerol(TAG) in liver and it is one of the nutritional metabolic diseases usually occurring in transition period. The pathologic basis of fatty liver in dairy cows is negative energy balance. Almost more than 50% of the perinatal cows will appear to varying degrees of lipids deposition in liver. Sterol regulatory element binding-1c(SREBP-1c) plays vital roles in hepatic lipids metabolism. Cell death-inducing DNA fragmentation factor 45-like effector-α(Cidea) is a new target gene of SREBP-1c and is closely linked to fatty liver in human and mouse. However, it has not been reported that whether SREBP-1c/Cidea is involved in the regulation of hepatic lipids metabolism in transition dairy cows. Therefore, in this study, we detect the expression of key molecules of SREBP-1c/Cidea in vivo. In vitro, bovine hepatocytes were transfected with overexpression SREBP-1c and Cidea adenovirus, respectively. Furthermore, cells were treated with different concentrations of non-esterified fatty acid(NEFA), SREBP-1c and Cidea silencing adenovirus to clarify the regulatory mechanism of SREBP-1c/Cidea pathway in hepatic lipids metabolism and the effects of NEFA on the SREBP-1c/Cidea pathway in dairy cows.In vivo experiments, blood NEFA, β-hydroxybutyrate(BHBA), glucose(Glu), TAG and very low density lipoprotein(VLDL) were detected in healthy and fatty liver cows. In addition, we also detected the expression of key molecules of SREBP-1c/Cidea through western blotting. The results showed that fatty liver cows displayed with severe negative energy balance and SREBP-1c and Cidea were high expressed fatty liver cows.The key enzymes of de novo fatty acid synthesis: fatty acid synthase(FAS) and acetyl coenzyme A carboxylase enzyme 1(ACC1) were significantlyincreased in fatty liver cows; the related proteins involved in the assembling of VLDL: microsomal triglyceride transfer protein(MTP), apolipoprotein B100(Apo B100) and apolipoprotein E(Apo E) were significantly decreased.In vitro experiments, bovine hepatocytes were transferred with overexpression SREBP-1c and Cidea adenovirus, respectively. The results showed that SREBP-1c could directly regulate the expression of Cidea. Overexpression of Cidea significantly increased the expression of FAS and ACC1 and inhibitedthe expression of MTP, Apo B100 and Apo E, resulting in TAG accumulation and larger lipid droplets. Over expression of Cidea can promote SREBP-1c expression, transcriptional activity and maturation in cultured bovine hepatocytes. Mixed transfection of overexpression SREBP-1c and silencing Cidea adenovirus, we found that Cidea silencing inhibited the de novo synthesis of fatty acids in hepatocytes, thereby, alleviating the accumulation of TAG induced by SREBP-1c. Bovine hepatocytes were transfected with silencing SREBP-1c adenovirus, then, the cells were treated with different concentrations of NEFA(0, 0.6, 1.2 and 2.4 m M). The results showed that, compared with the control group, NEFA up-regulated the expression of SREBP-1c and Cidea, reaching the peak at 1.2 m M. 1.2 m M NEFA enhanced the transcriptional activity of SREBP-1c. When SREBP-1c was silenced, this activation was blocked. Later, the cells were transfected with silencing Cidea adenovirus, then, the cells were treated with 1.2 m M NEFA. The results showed that Cidea silencing alleviated the accumulation of TAG induced by NEFA.These results showed that SREBP-1c/Cidea pathway was activated in fatty liver cows. The vitro experiments showed that Cidea promoted the accumulation of TAG and larger lipid drops in bovine hepatocytes. NEFA could activate SREBP-1c/Cidea pathway to promote the accumulation of TAG in bovine hepatocytes.