The Mechanism Of Strontium Regulating The Lipid Metabolism Of Bovine Hepatocytes Via The SIRT1/SREBP Pathway

The energy requirement of dairy cows has increased dramatically period to meet the needs of fetal growth and lactation during the peripartum,while dairy cows experience an inevitable decrease in dry matter intake(DMI)and impaired liver gluconeogenesis.Thus,dairy cows are vulnerable to negative energy balance(NEB).In the NEB state,the body is highly inclined to promote the mobilization of long-chain fatty acids stored in adipose tissue,resulting in a general increase in the blood concentration of non-esterified fatty acids(NEFA),which supplements the energy requirements of peripheral tissues.However,when NEFA production is excessive,it can be incompletely oxidized to produce ketone bodies or reesterified to produce triglycerides(TG),leading to a high incidence of energy metabolism disorders such as ketosis and fatty liver in the perinatal period.Strontium(Sr)is an essential trace element.In recent years,several studies have shown that Sr has effects on improving lipid metabolism,such as interfering with the progression of atherosclerosis,reducing the serum levels of total cholesterol(TC)and TG in type Ⅱ diabetes rats,and improving metabolic disorders in rats with non-alcoholic fatty liver disease.At present,the clinical application of Sr in ruminants is limited to its being used as an indicator to evaluate the gastrointestinal Ca absorption capacity of cows and sheep.However,the effect of Sr on lipid metabolism in cow hepatocytes and its action mechanism are not clear.Sterol regulatory element binding proteins(SREBPs),a key transcription factors regulating lipid metabolism,are posttranslationally regulated by the deacetylated protein SIRT1 in the nucleus.However,the mechanism of Sr mediating the SIRT1/SREBP signaling pathway regulates NEFA induced lipid accumulation in dairy hepatocytes is unclear.To clarify the effect of Sr on lipid metabolism in bovine hepatocytes,this study was performed by isolating and culturing primary hepatocytes.NEFA was treated to establish a cellular model of bovine liver lipid deposition in vitro.After adding different concentrations of Sr,the changes in TC and TG contents in hepatocytes and the expression levels of factors related to fatty acid synthesis,cholesterol synthesis,lipid oxidation,and lipid transport were detected,to clarify the mechanism of Sr participating in the regulation of NEFA-induced lipid accumulation in dairy cow hepatocytes.The results show that:1.The cultured bovine primary hepatocytes were treated with Sr(0,5,10,20 μM)and NEFA(1.2 m M)for 12 h.The results of oil red O staining,Nile red staining,and flow cytometry showed that Sr reduced lipid accumulation in primary hepatocytes in a dosedependent manner.2.Sr reduced the contents of TG and TC in hepatocytes,reduce the expression and nucleation of SREBP-1c and SREBP2,and further down-regulated the expression of ACC1,ACLY,FASN,SCD1,and HMGCR,the key enzyme of TC synthesis,and inhibited the synthesis of fatty acids and TC in the liver.The expressions of lipid oxidation related factors(PPAR-α,PGC1 A,ACOX1,CPT-1A,and CPT-2)and lipid transport related factors(APOB,APOE,LDLR,CD36,and MTTP)were also significantly down-regulated.The level of lipid oxidation and the synthesis of VLDL in hepatocytes is decreased.3.The expression of SIRT1 was significantly upregulated by Sr,and the transcriptional activity of SREBPs was reduced by the deacetylation of SIRT1.Thus,the fatty acid and TC synthesis,lipid oxidation levels,and VLDL synthesis and secretion were reduced.The addition of SIRT1 inhibitors reverses the effect of Sr in alleviating hepatocyte lipid metabolism,suggesting that Sr mediates the SIRT1/SREBP pathway to alleviate hepatocyte lipid metabolism.In summary,Sr mediated the SIRT1/SREBP pathway to reduce hepatic fatty acid and sterol synthesis,while lipid oxidation levels and VLDL assembly were decreased,thereby,hepatocyte TG and TC contents were reduced,The NEFA-induced lipid accumulation in cow hepatocytes effectively alleviated by the action of Sr.The results of this study indicate that Sr can mediate the SIRT1/SREBP pathway to regulate hepatocyte lipid metabolism in cows,providing a theoretical basis and data support for the application of Sr in the prevention and treatment of energy metabolic diseases in cows.