Mechanisms Of Methionine Regulating Fat Deposition In Pekin Ducks

Methionine(Met)is one of important nutrients in diet of meat ducks,which regulate growth and fat deposition.Firstly,the effects of Met levels in different energy diets on the growth performance and fat deposition of Pekin ducks were studied,and the optimal Met/energy ratio was estimated.The effects of Met on fat deposition and its molecular mechanism in Pekin ducks were investigated at the molecular level by experiments in vivo and in vitro.In experiment 1,two experiments were conducted to investigate the effects of Met levels in different energy diets on growth performance and fat deposition of Pekin ducks.The both experiments were designed with two-factor(ME and Met)for 1 to 21 and 15 to 42 days of age,respectively.The results showed that ducks those fed the basal diets without Met supplementation have growth depression,which were counteracted via the dietary Met supplementation.Based on the linear broken-line model,it exists significant differences(P < 0.05)for Met requirements(0.36% and 0.47%)at both energy diets for Pekin ducks of 1 to 21 days of age(0.36% and 0.47%)and 15 to 42 days of age(0.41% and 0.50%),while no difference(P > 0.05)was observed when expressed as g/MJ ME diet in both dietary ME levels(0.376 and0.388 g/MJ)of Pekin ducks of 15 to 42 days of age.Met deficiency in different energy diets significantly decreased breast muscle percentage and leg muscle percentage(P < 0.05),and significantly increased abdominal fat percentage and sebum percentage(P < 0.05)of Pekin ducks at 42 days of age.Increasing dietary Met significantly decreased plasma TCHO and HDLC contents(P < 0.05)of Pekin ducks at 21 days of age,and TG content of Pekin ducks at 42 days of age had a decreasing trend(P = 0.08).These results showed that Met deficiency in different energy diets results in poor growth performance,and affected the fat metabolism of Pekin ducks.Moreover,dietary Met deficiency causing the increase of fat deposition in body are mainly at growing stage of Pekin ducks.Experiment 2 was conducted to investigate the effects of dietary Met level on fat deposition of Pekin ducks and its regulatory mechanism.The growing Pekin ducks were selected to design a single-factor experiment.Ducks were fed one of 5 diets with different Met levels(0.28%,0.35%,0.43%,0.50%,0.58%),and lasted from 15 to 42 days of age.The results showed that Pekin ducks fed basal diet without Met supplementation showed growth depression and excess fat deposition,which were gradually ameliorated after feeding the diets with Met supplementation.According to the results of growth performance and fat deposition,the Met deficiency group(0.28%)and Met sufficiency group(0.43%)were selected for subsequent studies on the regulation mechanism of fat deposition.Dietary Met deficiency(0.28% Met)resulted in significantly increased serum TG and NEFA contents of Pekin ducks(P < 0.05),and decreased TCHO,LDLC,TP and ALB contents(P < 0.05),but had no difference on lipid content in liver(P > 0.05).Proteomics analysis indicates that dietary Met deficiency resulted in 56 upregulated proteins and 117 down-regulated in liver of Pekin ducks,which were mainly related in fatty acid transport,fatty acid oxidation,tricarboxylic acid cycle,glycolysis/gluconeogenesis,ketogenesis,and electron transport chain.The mainly verified gene and protein expression by RT-PCR and Western blot were consistent with the results of proteomics.In addition,dietary Met deficiency resulted in enlarged adipocyte diameter and area,and down-regulated(P < 0.05)of lipogenic genes and proteins(LPL,ATGL,HSL)in abdominal fat.Experiment 3 was conducted to investigate the effects of Met levels on the growth and lipid deposition of Hep G2 and duck primary hepatocytes,including two tests in vitro.Hepatocytes were cultured in different Met medium for 24 h,and the results showed that cell viability of Hep G2 cells and duck primary hepatocytes was significantly decreased(P < 0.05)when no Met(0 ?M)was added in medium.Compared with the control group(200 ?M),the lipid deposition in Hep G2 cells in Met deficiency groups(0,25 ?M)was significantly increased.Compared with the control group,Met deficiency in medium resulted in down-regulation(P < 0.05)of genes and proteins related to fatty acid transport(ALB),fatty acid ?-oxidation(ACADM),tricarboxylic acid cycle(MDH1,MDH2,DLD)and respiratory chain electron transport(ETFA,ETFED,NDUFS1)processes in Hep G2 cells.The results in present study were in consistent with the proteomics in liver of Pekin ducks,and provided verification in vitro used hepatocyte models for proteomics in liver.In conclusion,Met deficiency in different diets resulted in growth depression of Pekin ducks,and excess fat deposition in growing Pekin ducks.Both experiments in vivo and in vitro showed that dietary Met deficiency resulted in inhibition of fatty acid oxidation,tricarboxylic acid cycle,electron transport in respiratory chain,and ketoplasia in liver of Pekin ducks,which led to insufficient ATP production in body and growth depression of Pekin ducks.The reduced secretion amounts of albumin in liver to serum,and the deceleration of fatty acids transportation and lipolysis caused by dietary Met deficiency reduced the free fatty acids to other tissues from abdominal fat,which led to excessive fat deposition.