Effect Of ω3PUFA Diet On The Hepatic Lipid Metabolism Induced By Early Life Overnutrition And Its Mechanisms In Adult Rats

Growing evidence indicates that the incidence of obesity and metabolic syndrome among children and adulthood is increasing worldwide.Nonalcoholic fatty liver disease(NAFLD)is the manifestation of metabolic syndrome in liver.Nutrition in early life is not only associated with children’s growth but also related to adulthood obesity and metabolic syndrome.Therefore,it is necessary to explore early nutrition programming development mechanism and interference,which is benefit to reduce the development risk of NAFLD in future.It is confirmed that hepatic metabolism includes fatty acids uptake,synthesis,oxidation and export,which involving acetyl-coa carboxylase(ACC),stearyl coenzyme A saturated enzyme 1(SCD1),fatty acid synthase(FASN),lipoprotein lipase(LPL),hepatic type fatty acid binding protein(L-FABP),carnitine palmitoyl transferase(CPT1)and microsomal triglyceride transfer protein 1(MTP)and their nuclear receptors sterol regulating element binding protein 1 c(SREBP-1c)and peroxidase proliferation agent activated receptor(PPARa).Here we establish classic small litters rat model to mimic infant overfeeding,the results demostrate that lactation is the critical window period for developmental programming of ACC and SREBP-lc,and overnutrition in early life could enhance ACC activity and hepatic lipogenesis,thus increasing the risk of obesity and liver lipid depositon induced by high fat diets.It has been comfirmed that co3PUFA plays an important role in lipid metabolism and inflammation,which could affect the NAFLD development through improving insulin resistance and reducing hepatic steatosis and inflammation.However,it is not sure if dietary ω3PUFA could prevent the lipid metabolic disorders.due to early overnutrtion.If could,could it reverse ACC developmental programming?Researching the problems above will help us to understand the regulation of ω3PUFA in the prevention of hepatic lipid deposition and explore the exact molecular mechanism,furthermore provide a new idea on the prevention for NAFLD.PartⅠEffect of postweaning fish oil diet on hepatic lipid metabolism in ratsObjective To explore the effects of postnatal overfeeding and postweaning fish oil dietary on growth,glucolipids metabolism,and enzymes involved in hepatic lipid metabolism in rats model,and provide a scientific basis for reducing the risk of NAFLD in later life.Methods and material1.To establish an early life overnutrion model:Male Sprague-Dawley rat pup litters were adjusted to litter sizes of three(small litters,SL)or ten(normal litters,NL)on postnatal day 3.After weaning(P21),the two groups were given standard chow or fish oil diet enriched with polyunsaturated fatty acids to generate NL,SL,NL-FO and SL-FO until postnatal week 13(W13).2.Body weight,body length,tail length and food intake were monitored throughout life.Liver weight,glucose and lipid metabolism,liver TG content,histological analysis and NAS assess were detected at W13.3.The mRNA expression of ACC,SCD1,FASN,LPL,L-FABP,CPT1,MTP and SREBP-1c in liver were determined by read-time PCR.The enzyme activity of ACC was determined by isotopic assay;the protein expression of SREBP-lc was determined by western-blot.Results1.Compared to NL rats,body weight,serum TG and glucose increased in SL rats at W13.However,body weight,serum TG and glucose were reduced in SL-FO rats.The body weight in NL-FO rats was lower than that of NL rats but there was no difference in serum TG and glucose tolerance.2.Compared to NL rats,liver weight and TG content were elevated in SL rats from W3 to W13.However,liver weight and TG content were lower in SL-FO rats.NL-FO rats only exhibited lower liver weight than that of NL rats,but there was no significant difference in hepatosomatic index and liver content.3.SL rats exhibited hepatic steatosis at W13,whose livers were filled with droplets and were accompanied with ballooning and labular inflammation in hepatocytes.While SL-FO rats livers exhibited no obvious lipid droplets,ballooning and labular inflammation in hepatocytes.NL-FO rats livers exhibited as normal.4.Compared to NL rats,ACC mRNA expression and activity increased in SL rats,but decreased in SL-FO rats.However,there was no differece between NL and NL-FO rats.SCD1 and FASN expressions increased in SL rats and decreased in SL-FO rats,but there was no differece between NL-FO and NL rats.5.SREBP-1c mRNA and protein expression significantly increased in SL rats but decreased in SL-FO rats,which was similar to ACC expression pattern.However,there was no obvious differece between NL-FO and NL rats.ConclusionPostnatal overfeeding resultes in the increase of hepatic lipogenesis,and postweaning fish oil diets could reverse the ACC and SREBP-lc developmental programming and decrease hepatic lipogensis,which could reduce the risk of the devlopment of NAFLD in adulthood.PartⅡPathway of ACC regulated by EPA in HepG2 cellsObjectiveTo explore the effect of EPA on the regulation of ACC in HepG2 cells,and to elucidate the pathway of SREBP-c in this regulation.Methods and material1.Establish the lipid accumulation cell model:HepG2 cells was induced by Oleic acid(OA)and insulin for 24h,and then treated with EPA.In addition,SREBP-lc was knockdown using siRNA and further stimulated HepG2 cells by Oleic acid(OA)and insulin.2.The lipid accumulation observed:Using Oil red O staining to observe the hepatocellular lipid accumulation and detect the TG content with TG test kits.3.The mRNA expressions of ACC and SREBP-lc in HepG2 cells were determined by real-time PCR.The enzyme activity of ACC was determined by isotopic assay.The protein expression of SREBP-lc was determined by western-blot.Results1.Oil Red O staining showed that intracelluar lipid droplets obviously increased in cells induced by OA,which were decreased after EPA stimulation for 24h.If HepG2 cells treated with SREBP-lc siRNA first would lead to abolish the lipid accumulation induced by OA.TG contents were consistent with Oil red 0 staining.2.As expected,ACC mRNA expression and activity were strongly increased by OA treatment and decreased by EPA.If knocking-down SREBP-lc first could partially resisted the upregulation of ACC expression by OA,and there was no futher downregulation with EPA treatment.3.SREBP-lc mRNA and protein expression showed the same expression pattern with ACC,which were induced by OA and decreased by EPA.If inhibiting SERBP-1 mRNA fisrtly,OA and EPA could not further reduce its expression any more.ConclusionEPA could reduce lipid accumulation and ACC expression via SREBP-lc,which provide the molecular target for improving hepatic lipogenesis disorders.