Effect Of La + Ce Mediated By ABCG1 On Fat Deposition In Heat-stressed Broilers And Its Mechanism

Heat stress is one of the main factors affecting broiler growth.Heat stress not only reduces broiler feed intake,feed conversion rate and carcass quality,but also causes oxidative stress in broiler fat tissue,leading to fat deposition and increased mortality.The rare earth elements lanthanum?La?and cerium?Ce?have a high biological value,and can increase the activity of lecithin cholesterol acyltransferase,reduce fat deposition,and regulate the lipid balance in the blood.Activation of ATP-binding cassette transporters G1?ABCG1?can promote cholesterol efflux in cells and play an important role in the regulation of cholesterol efflux in macrophages and atherosclerosis.Therefore,it is of great significance to study the effects of La+Ce and ABCG1 on heat-stressed fat deposition and the mechanism of regulation.The research content of this paper mainly includes three parts:1.Effects of La+Ce on histological changes of fat and intramuscular fat content in broilers caused by heat-stress.Broilers were divided into control group,heat stress group and La+Ce group.Heat stress treatment lasted for 14 days,then broilers were slaughtered and sampled after 1 week and 2 weeks of heat stress treatment,respectively.The results showed that heat stress increased the diameter of intermuscular adipocytes and increased the intramuscular fat content of pectoral and leg muscles.After adding La+Ce,the diameter of adipocytes and intramuscular fat content tended to the control group.This indicates that La+Ce can inhibit fat deposition caused by heat stress.2.Effects of La+Ce on the expression of ABCG1 and localization of ABCG1 on adipocytes of broiler caused by heat-stress.The expression of ABCG1 was tested by fluorescent quantitative PCR technology,and the location of ABCG1 was tested by immunohistochemistry.Fluorescence quantitative results showed that,compared with the control group and the heat stress group,the expression level of ABCG1 m RNA in the adipose tissue of the La+Ce group was significantly higher than that of the control group and the heat stress group?P<0.05?.Compared with the heat stress group,the expression level of ABCG1 m RNA in the visceral and subcutaneous adipose tissue of the La+Ce group was significantly reduced?P<0.01?.Through immunohistochemical analysis,it was found that after 1 and 2 weeks of heat stress,ABCG1 was mainly located on the adipocyte membrane,and ABCG1 in the heat stress group and the La+Ce group showed a brownish yellow area higher than that in the control group,which was consistent with the PCR.3.La+Ce regulates adipocyte metabolic changes induced by heat-stress mediated by ABCG1.The chicken adipocytes were isolated and cultured in vitro,and then the isolated and cultured cells were divided into a control group?37±1°C?,a La+Ce group?37±1°C,1.0 mmol/L La+Ce?,and a heat stress group.?42±1??and heat stress plus La+Ce group?42±1?,1.0mmol/L La+Ce?.The adipocytes were collected after cultured in the same humidity and 5%CO₂ incubator for 3 h.fluorescent quantitative PCR analysis showed that,compared with the control group,the m RNA expression levels of ABCG1 and malicenzyme 1?ME1?in the heat stress group were significantly increased?P<0.05?,and acetyl Co A carboxylase?ACC?and fatty acid synthase?FAS?m RNA expression was significantly increased?P<0.01?in the heat stress group,and the expression of ABCG1 in the heat stress plus rare earth treatment group was extremely significant up-regulated?P<0.01?,carnitine palmitoyl transterase-1?CPT-1?and peroxisome proliferator-activated receptor?alfa,PPAR?)m RNA expression was significantly reduced?P<0.01?.Compared with the heat stress group,the m RNA expression levels of ACC and FAS in the heat stress plus rare earth treatment group were significantly reduced?P<0.05?.CPT-1 m RNA expression was significantly increased in the rare earth treatment group?P<0.01?and PPAR?m RNA expression was significantly increased?P<0.05?.cholesterol regulatory element binding protein-1c?sterol regulatory element binding protein-1c,SREBP-1c?m RNA expression had no significant differences in each group.The results confirmed that La+Ce participated in the regulation of fat deposition by increasing the expression of ABCG1 and lipolysis-related genes and reducing the expression of fat synthesis-related genes.In summary,this experiment found that adding to the diet will relieve the fat deposition caused by heat stress,make the subcutaneous,visceral and intermuscular fat cells smaller,and reduce the intramuscular fat content.It was found by immunohistochemistry and fluorescent quantitative PCR that the ABCG1 gene was localized on the cell membrane with heat stress treatment and the ABCG1 expression level was up-regulated with addition of La+Ce.The results show that both ABCG1and lipid metabolism-related genes changed after heat stress treatment,La+Ce may affect fat synthesis and catabolism mediated by ABCG1,thereby alleviating fat deposition caused by heat stress.