Human Obesity-related Novel Gene Nyggf4, Tnfaip9 Functional Studies

Obesity is an increasing prevalent, costly and important healthproblem throughout the world. The prevalence of obesity in children hasbeen rising quickly. Obesity is a multifactorial disease resulting from theinteractions between susceptibility genes and environmental factors. Nowstudies have shown consistently that～40 to 70% of the variation inobesity-relate phenotypes is heritable. Thus searching for new humanobesity genes is very necessary.During the development of obesity, adipose tissue plays a key role inenergy homeostasis by regulating the balance between energy storage andrelease according to nutritional status. Adipocytes synthesize and storetriglyceride in periods of nutritional abundance and mobilize the lipids inresponse to fasting. Fat tissue is also involved in regulating blood glucoselevels through the expression of the insulin responsive glucose transporter,Glut4. Now it is recognized that adipose tissue is a major secretory organthat secretes numerous kinds cytokines including tumor necrosisfactor-alpha, leptin, adiponectin and resistin. These factors are known toinfluence insulin sensitivity, food intake, arteriosclerosis, and severalcommon diseases. Thus, identify some of the genes differentiallyexpressed in adipose tissue between obese and normal individuals couldpotentially be related to the regulation of body mass and to the pathogenesis of obesity. The identification of such genes may providenew candidates for ongoing and future studies.To help clarify the mechanism for obesity development, mRNAsexpressed in abdominal subcutaneous fat from obese subjects (BMI＞30kg/m~2) were subtracted with those from normal-weight subjects (BMI=18-25 kg/m~2) using suppression subtractive hybridization (SSH). Afterthe work, 426 genes were screened as the potential obesity-related genes.In this study, we chose two of the differential expressed genes for furtherresearch.In the 1st part of this study, we report the cDNA and deduced aminoacid sequence of the new gene, NYGGF4. The 1527-bp cDNA contains753 nucleotides of an ORF predicting 250 amino acids with a molecularmass of 28.27 kDa. Using a domain predicting program, the predictedNYGGF4 protein was shown to contain a phosphotyrosine-binding (PTB)domain. The PTB domain was originally identified as a 186-residuesegment of the signaling protein Shc and binds specifically to thetyrosine-phosphorylated form of an unidentified 145-kDa protein inresponse to many growth factors. We also identified that NYGGF4 geneexpression is up-regulated in omental adipose tissues of obese subjectsusing RT-PCR. Northern blot analysis revealed NYGGF4 is expressedprimarily in adipose tissue, heart, and skeletal muscle but not in any othertissue examined. Confocal imagery analyses with green fluorescent protein -tagged protein transiently expressed in 3T3-L1 preadipocytes,293-T and COS-7 cells show that NYGGF4 localizes in the cytoplasm.Furthermore, ectopic expression of NYGGF4 dramatically increases theproliferation of 3T3-L1 peadipocytes without affecting adipocyticdifferentiation. And the NYGGF4 expression 3T3-L1 cells had a greaternumber of cells in S-phase. Our data suggest that NYGGF4 might be asignaling molecule and could play a role in cell growth and adipogenesisprocess.In the 2nd part of this study, we chose the gene TNFAIP9 for furtherresearch. Protein sequence analysis shows that TNFAIP9 contains sixtransmembrane domains, which indicates TNFAIP9 may be iontransporter or channels. Using BlastP analysis, we found that TNFAIP9has high similarity to TIARP gene which demonstated that TNFAIP9might have similar biological function to TIARP and maybe play a role inthe cell singnaling transduction process of TNF-alpha. TIARP is a newgene which is up-regulated during 3T3-L1 cells differentiation.withTNF-alpha induction. TNFAIP9 gene expression is down-regulated inomental adipose tissues of obese subjects using RT-PCR. Using RT-PCRto study its tissue expression patterns, we found that TNFAIP9 is highestexpressed in human adipose tissue, followed by placenta. Immuno-histological chemistry demonstrated that TNFAIP9 localizes at theplasma membrane. Treatment of cultured adipose tissue in vitro with TNF-alpha, we found that TNFAIP9 mRNA and protein expression areenhanced. These indicate that TNFAIP9 may represent an importantmediator of the physiological or pathological effects of TNF-alpha.In summary, we have described the identification andcharacterization of two new genes NYGGF4 and TNFAIP9, which aredifferentially expressed in omental adipose tissue between obese andnormal-weight subjects. To help clarify the mechanism for obesitydevelopment, we need to do further research on these genes.