Regulation Of 4-PBA On Endoplasmic Reticulum And Fat Deposition Of Lateolabrax Maculatus

Studies have shown that the process of fat deposition can cause Endoplasmic Reticulum Stress(ERS),which alleviating ERS can reduce fat deposition in mammals.In this study,the effects of fat deposition and ERS of Lateolabrax maculatus fed high-fat diet,and the effects of dietary 4-Phenylbutyric acid(4-PBA),an ERS inhibitor,alleviating fat deposition and stress resistance of Lateolabrax maculatus,in order to provide a new direction for regulating the fat deposition of Lateolabrax maculatus.The main research contents are as follows:(1)Effects of high fat diet on fat deposition and ERS in Lateolabrax maculatusFish meal,soybean meal,chicken meal and gluten meal were used as the main protein sources,and fish oil and soybean oil were used as fat sources.The crude fat levels were 10% and16% respectively(LFD and HFD).The two experimental diets were fed to Lateolabrax maculatus,and the samples were collected at 2,4,6 and 8 weeks,respectively.The results showed that the body weight of LFD was significantly higher than that of HFD at the 8th week(P<0.05)The levels of serum TG and TC in HFD were significantly higher than those in LFD at the 4th and 8th week(P<0.05).Oil Red O staining showed that there were only a few lipid droplets in the liver of LFD in the first 4 weeks and increased gradually in the 6th and 8th weeks,while there were more lipid droplets in the HFD in the 4th week and the amount of lipid droplets increased obviously in the 8th week.The endoplasmic reticulum(ER)in LFD was found to be intact and closely arranged,while the ER in HFD became loose in the 4th week,and the ER in HFD was swollen and ruptured at the 8th week.In the first 4 weeks,there was no significant difference in the expression of ER stress-related genes between the two groups(P>0.05),and in the 6th and 8th weeks,the gene expressions of GRP78,CHOP,PERK,ATF-6 in HFD were significantly increased compared with LFD(P<0.05).The results showed that high-fat diet led to excessive fat deposition in liver of Lateolabrax maculatus,which became more serious with feeding time,and the process of fat deposition was accompanied by ERS.(2)Effects of dietary 4-PBA on growth performance,fat deposition and ERS of Lateolabrax maculatusFour diets were prepared: control group(LFD,10% fat),high fat group(HFD,16% fat),10 PBA(4-PBA with 10 mg/kg added in high fat diet)and 50 PBA group(4-PBA with 50 mg/kg added in high fat diet).The experiment period was 8 weeks.Samples were collected and analyzed after the culture experiment.The results showed that the weight gain rate,specific growth rate and food intake of LFD and 50 PBA were significantly higher than those of HFD(P<0.05),the Condition factor(CF)and crude fat content of whole-body were significantly lower than HFD(P<0.05),and the specific growth rate of 10 PBA was significantly higher(P<0.05),the CF decreased significantly(P<0.05).Compared with HFD,the protein expression of GRP78 and CHOP in LFD and 50 PBA were significantly down-regulated(P<0.05),while the gene expression of GRP78,CHOP,ATF-6,IRE1,PERK,ATF-4 and EIF-2α were significantly down-regulated(P<0.05),there was no significantly in the protein expression of CHOP,the gene expression of ATF-4 and EIF-2α in 10 PBA(P>0.05).The ER in LFD and 50 PBA was well arranged and the ultrastructure was normal,while the ER in HFD was swollen and fractured.The Oil Red O section showed that the number of lipid droplets in LFD and 50 PBA was less than HFD,and the number of lipid droplets in HFD was increased obviously.The levels of serum and liver triglyceride,total cholesterol and abdominal fat in 50 PBA were significantly lower than HFD(P<0.05).Compared with HFD,the gene expression of SREBP-1c,FAS and ACC were significantly down-regulated in 50 PBA(P<0.05).In conclusion,it was concluded that high-fat feeding resulted in fat deposition and ERS in Lateolabrax maculatus.Dietary4-PBA alleviated ERS and reduced fat deposition.(3)Effects of dietary 4-PBA on the anti-stress ability of liver of Lateolabrax maculatus under ammonia-nitrogen stressHigh fat(HFD)and 50 PBA(4-PBA with 50 mg/kg added in high fat diet)were fed fish for two weeks.After the stress test,samples were collected and analyzed.The results showed the mortality of 50 PBA was significantly reduced compared with HFD,the gene expression of GRP78,CHOP,ATF-6,EIF-2α and ATF-4 were significantly decreased(P<0.05),and the level of serum GPT was significantly reduced.In addition,MDA content in liver of 50 PBA was significantly lower than that of HFD(P<0.05).SOD activity of 50 PBA was significantly higher than HFD(P<0.05).The results showed that ammonia nitrogen stress could induce ERS and liver injury in Lateolabrax maculatus.Added 50mg/kg 4-PBA into the diet relieved the ERS caused by ammonia nitrogen stress and increased the survival rate of Lateolabrax maculatus under ammonia nitrogen stress,the tolerance to ammonia nitrogen stress was enhanced.