The Biological Characteristic And Functional Research Of Lyrm1, A Novel Gene Related With Human Obesity

Obesity, results from interactions between genetic, environmental, and psychosocial factors, is an important public health problem in the developed world and a growing problem in the developing world. Obesity is considered a major risk factor for type 2 diabetes and has also been linked to cancer and immune dysfunction. Understanding the genes involved in the development of obesity is important for the development of new therapies that directly target molecular mechanisms underlying obesity. Currently, over 600 genes, markers and chromosomal regions have been identified as associated with or linked to human obesity phenotypes. However, in >95 % of severe obesity cases the responsible genes remain unknown. Thus, identification and characterization of novel genes and proteins associated with obesity remain an important issue.In a previous report, we analyzed the gene expression profiles of omental adipose tissue of obese individuals （age 45.2±14.5 years; body mass index 31.6±0.4; insulin sensitivity index 0.016±0.004） and normal control individuals （age 47.8±16.7 years; body mass index 20.7±1.2; insulin sensitivity index 0.017±0.007） to identify novel genes that may be implicated in the genetic susceptibility or the pathological consequences of obesity. We identified 216 genes up-regulated in obese subjects and 210 genes up-regulated in normal subjects. Notably, a novel gene termed homo sapiens LYR motif containing 1 （LYRM1） in Genbank （Genbank accession number NM₀20424）, encoding a wholly novel protein （Genbank accession number NP₀65157） was identified by 8 clones, suggesting an important role in human obesity. Therefore, this gene was selected for further analysis in this study.The LYRM1 derives from an mRNA of 1589 basepairs （bps） with a 369 bp open reading frame （ORF） which encodes a 122 amino acids （aas） protein with a molecular mass of 13.27 kDa. NCBI Map Viewer analysis revealed that the LYRM1 gene is located on chromosome 16 and is composed of 4 exons. Amino acid sequence analysis revealed that LYRM1 was not a membrane-spanning protein and was an unsecreted protein. LYRM1 localizes in the nucleus and has a LYR domain related with mitochondrial function and energy metabolism. A sequence comparison of mouse and rat LYRM1 orthologous genes suggests that LYRM1 represents a novel gene highly conserved across primates and rodents.In this study, differential expression of LYRM1 was confirmed by RT-PCR and Western-Blot analysis. LYRM1 was expressed at a higher level in samples from obese versus normal weight subjects at both the mRNA and protein levels. To examine the tissue distribution of LYRM1 mRNA, we performed RT-PCR analysis of various human tissues. The expression of LYRM1 was found in all 9 tissues tested, with the highest levels of expression in adipose tissue. These results support a role for LYRM1 in human obesity.We used subcellular localization studies to determine the localization of LYRM1 in various cell lines and human adipose tissue. Expression of GFP-tagged LYRM1 and Western-Blot analysis showed that LYRM1 localized primarily to the nucleus.RT-PCR and Western-Blot analysis were used to observe the changes of LYRM1 gene expression during human preadipocyte differentiation. The level of LYRM1 gene expression was dramatically up-regulated on day 2.Furthermore, we examined the effect of LYRM1 on cell differentiation, proliferation, and apoptosis in vitro by establishing a stable preadipocyte cell line overexpressing LYRM1, and found that: （i） LYRM1 does not affect the differentiation of 3T3-L1 cells, as shown by Oil Red staining and the expression of adipocyte-specific molecular markers; （ii） the result of the MTT assay indicated that LYRM1 causes the promotion of cell population growth of 3T3-L1 preadipocytes and cell cycle analysis showed a dramatic increase in the percentage of cells in S-phase; and （iii） LYRM1 can prevent apoptosis induced by serum deprivation and addition of TNF- in preadipocytes with the analysis of annexin V-FITC and caspase-3 activity. In summary, our data demonstrate that by increasing cell proliferation and lowering apoptotic rate, LYRM1 has the potential to affect the size of the preadipocyte pool and influence adipose tissue homeostasis.In addition, 2-Deoxy-glucose labeled by isotope 3H was used to assay glucose uptake of mature adipocytes. The data showed that ectopic expression of LYRM1 dramatically decreases insulin-stimulated glucose uptake in adipocytes.In conclusion, we characterized several original features of the novel gene LYRM1 although the precise functional properties of this gene remain to be clarified and await further investigation.