| Nowadays,obesity has become a worldwide problem either in developed countries or in some developing countries.The incidence of obesity shows a continuous increase and a younger age trend.In addition,obesity is also a significant risk factor of major diseases,including hypertension,type II diabetes,coronary heart disease,certain cancers,and obstructive sleep apnea syndrome threatening the physical health and reducing the life quality of those patients.What's more,the expense for the treatment of obesity and its complications has also carried out a considerable financial burden to the society.In spite of the high prevalence and significant negative impacts of the disease,the detailed molecular mechanism of obesity remains unclear.Therefore,the study of lipid metabolism has become one of the most important topics in the medical field.C/EBPs(CCAAT/enhancer-binding proteins)are a family of transcription factors which can bind to CCAAT area of the promoter.They are widely expressed in various species,such as humans,mice,C.elegans,and Mediterranean fruit flies.C/EBPs have been proved to mainly regulate cell proliferation and differentiation.Up to now,the following six members of the family have been found: C/EBP?(C/EBP alpha),C/EBP?(C/EBP beta),C/EBP?(C/EBP gamma),C/EBP?(C/EBP delta),C/EBP?(C/EBP epsilon),C/EBP?(C/EBP zeta),among which C/EBP?,C/EBP?,C/EBP?,and C/EBP? are involved in the regulation of the adipocyte differentiation and are expressed in a specific sequence.Recently,some members of this family,especially C/EBP? and C/EBP?,have been identified to control the expressions of certain lipogenesis.However,due to a lack of suitable model for study,more understanding of the role of C/EBPs in lipid and glucose metabolism still needs to be investigated.C.elegans(Caenorhabditis elegans)is a species of multicellular eukaryotes with no dedicated adipocytes.The fat in this species is stored in the form of lipid droplets in hypodermal cells and intestinal cells.Thus the research of homology of C/EBPs on lipid metabolism in C.elegans could avoid the interference of its effect on adipocytes differentiation and might show the direct function of the homology in governing the expressions and activities of metabolic enzymes.The lipid droplets could be easily stained and observed by employing a microscope because of the transparent bodies of the worms.Moreover,the major metabolic pathways and transcription factors are highly conserved in C.elegans.Many genes of C.elegans have homologous genes in other species.In addition,C.elegans is the first multicellular organism with its genome completely sequenced.Therefore,C.elegans has become one of the most important models in the study of metabolic diseases.In this work,we chose C.elegans as our study model to elucidate the effect of CEBP-2,the homolog of C/EBPs,on fat accumulation and the detailed mechanism in C.elegans.Employing RNAi(RNA-mediated interference),loss of activity of CEBP-2 resulted in low-fat phenotype in C.elegans,which was independent on the changes of intake and movement functions of the worms.This means the necessity of CEBP-2 in maintaining the normal lipid content of C.elegans.Because of the lack of adipocytes,we hypothesize that CEBP-2 could effect the metabolic pathways of the worms.To find a suitable model for further investigation of molecular mechanism of CEBP-2 on fat metabolim,we screened the fat accumulation of four types of cebp-2 mutants,among which cebp-2(gk509377)mutant has the lowest fat content.Using QRT-PCR(Quantitative Real-Time Polymerase Chain Reaction)and overexpression methods,cebp-2 was also proved to be lowly expressed at mRNA level in cebp-2(gk509377)mutant,and the fat content of the mutant was recovered after overexpression of cebp-2.To test the influence of cebp-2 on metabolic pathway,the expressions of 92 genes and isomers that encode the major enzymes in lipid and glucose metabolic pathways in cebp-2(gk509377)mutants were identified by employing QRT-PCR.The data showed that cebp-2 deficiency might lead to elevated expression of ech-1.1(enoyl-CoA hydratase-1.1)and reduced expression of fat-5(fatty acid desaturase-5).In order to clarify the role of these two genes in the effect of CEBP-2 on fat storage in C.elegans,we used either RNAi technique to lower the increased expression of ech-1.1 or overexpression skills to rescue the reduced expression of fat-5 in cebp-2(gk509377)mutants.As a result,both of them could relieve the low-fat phenotype of the mutants.In conclusion,CEBP-2 controls fat accumulation by negatively governing fatty acid mitochondria ?-oxidation(ECH-1.1)and positively regulating fatty acid desaturation(FAT-5)in C.elegans.Our work was the first study presenting a general screen of the effect of CEBP-2 on the expressions and activities of major enzymes in metabolic pathways in C.elegans.We also found the new function of CEBP-2 on the fatty acids anabolism and catabolism.It might be helpful to investigate the contribution of C/EBPs to the development of obesity in mammals and might provide some clues for the treatment of obesity and metabolic syndrome. |
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