The Effect Of Instillation Intranasal E.coli On Lipid Metabolism In High-fat Diet-induced Obese Mice

In order to evaluate the effects and mechanisms of acute infection on lipid metabolism in obesity,and to provide a theoretical basis for the further study of obesity related metabolic syndrome,we detected lipid related indexes of serum and liver during intranasal instillation of Escherichia coli(E.coli)in high-fat diet-induced obese mice.(1)320 24-to 25-days healthy Kunming male mice were randomly divided into group HF(176)fed with high fat diet and group NF(144)fed with normal diet.After 8 weeks,144 mice were selected from group HF of which 150 mice were diagnosed as obesity,and were randomly divided into group ?(72)and group ?(72),mice from NF group were randomly divided into group ?(72)and group IV(72).Mice in group ?,? were intranasally infected with 40 ?L of a bacterial suspension containing approximately 4×109 CFUs of E.coli diluted in PBS via a sterile 24-gauge needle.And mice in group ?,?were inoculatedintranasally with 40 ?L PBS as control groups.Before infection(0 h)and 2 h,6 h,12 h,24 h,48 h,72 h,96h post-infection,9 mice in each group were selected to collect blood,epididymal adipose tissue and liver;Weighing the mass of body,epididymal fat and livers with electronic balance to calculate organ index;The sizes of epididymalfat cells and the pathologicalchanges of livers were examined with hematoxylin and eosin(H&E);The key indexes of glucolipid metabolism in blood were detected with reagent kit.As a result.? after being fed high-fat diet for 8 weeks,the obese mice showed higher body weight(P<0.05),higher mass and index of epididymal fat and liver,as well as the serum RETN,GLU,INS and HOMA-IR(P<0.05).Besides,the levels of serum FFA,TG,VLDL-C,TC,LDL-C were significantly increased,with the levels of HDL-C were markedly decreased(P<0.05).? Following inoculation with E.coli,the body weight,fat mass and index in mice of group ? were significantly lower than group ?(P<0.05),which in group ? were significantly lower than group ?(P<0.05).Consistently,the adipocytes diameter markedly reduced at 48 h post-infectious(P<0.05).Although the liver mass showed no obvious changes,the liver index significantly increased from 12-96 h in group ? and from 48 h to 96 h in group ?(P<0.05),with the hepatic tissue disorder and steatosis.?After treatment with E.coli,the level of serum RETN significantly increased both in group I and group ?(P<0.05),and that in group I was higher than group ? from 24 h to 48h(P<0.05).The FGB,FINS and HOMA-IR in group I were lower than group II from 2 h to 24h(P<0.05),however,from 48 h to 96 h,they were significantly raised(P<0.05).In group III,they were obviously increased from 6 h to 72 h;Inner 24 h infectious,the levels of FGB,FINS and HOMA-IRwe detected in group? were lower than in group ?,but higher from 48 h to 96 h(P<0.05).? The levels of serum FFA,TG and VLDL-C in group ? and ? significantly increased from 6 h to 96 h(P<0.05),and group I were higher than group ?(P<0.05).Contrarily,the levels of serum TC,LDL-C,HDL-C in group ? markedly decreased from 6h to 96 h and were lowest at 48 h(P<0.05).However,the TC,LDL-C and HDL-C in group ? showed a transient elevation inner 12 h post-infectious and then decreased significantly(P<0.05).(2)Selecting livers of mice in group ? and group ? from 0 h,24 h,48 h,72 h,96 h post-infection for analysis of hepatic TG contents and measurement of the mRNA levels of RETN,SREBP-lc,PPARa and their downstream target genes with RT-PCR.Besides,livers from 0 h,48 h and 96 h post-infection were selected for observing hepatic lipid by oil red O staining and detecting the protein levels of AMPKa,p-AMPKa,SREBP-lc,PPARa with Western blot.As a result,? the liver TG contents significantly increased from 48 h to 96 h in group ? and from 24 h to 96 h in group ? in response to E.coli instillation(P<0.05),group ? were higher than group ? during the whole experiment(P<0.05).An obvious hepatic lipid accumulation was observed both in the mice of group ? and group ? at 48 h,which was decreased at 96 h.?Then we found the mRNA levels of RETN,SREBP-1c and its downstream genes ACC1?FAS?SCD-1 were obviously up-regulated(P<0.05),however,the PPARa and CPT-1? mRNA were significantly decreased(P<0.05).Compared with group ?,increases in the mRNA levels of RETN,SREBP-1c,ACC1,FAS and decreases in PPARa mRNA levels were more pronounced in group ?(P<0.05).In protein levels,we failed to detected obvious changes in SREBP-lc,however,the PPARa were significantly decreased(P<0.05).Consistently,the phosphorylation levels of AMPKa were declined both in group ? and ?,and greater decrease in blunted AMPKa activity were observed in group ?(P<0.05).Conclusion:1.Feeding Kunming mice with high-fat diet for 8 weeks is able to establish the model of obesity,the obese mice displayed glucose and lipid metabolism disorders.2.Intranasal instillation of 40 ?L 4×109 CFU/?L E.coli aggravates the degree of insulin resistance and dyslipidemia in obese mice.3.Intranasal instillation of E.coli induces hepatic lipid accumulation in obese mice by activating SREBP-1c related lipid synthesis pathway and inhibiting PPARa related fatty acid oxidation pathway,which was related to the increased expression of RETN and the decreased phosphorylation of AMPKa.However,E.coli-induced increased or decreased range of lipid metabolism-associated factors or genes could be lower in obese mice.It suggested that obesity improved the host tolerance to infection induced lipid metabolic disorders,which may concern with the inhibition of RETN to AMPKa related lipid metabolism.