Biomedical subjects

Sumithra Urs

Publications and source records attributed to Sumithra Urs.

3 recordsLinked to original sources

PubMed2006

Selective expression of an aP2/Fatty Acid Binding Protein 4-Cre transgene in non-adipogenic tissues during embryonic development.

Mouse strains expressing the site-specific Cre recombinase facilitate conditional ablation or activation of genomic sequences when one or several exons of a gene of interest are flanked by loxP sites. Recently, several strains targeting Cre expression to adipocytes have been developed using promoter sequences from the aP2 (Fatty Acid Binding Protein 4, FABP4) gene for adipose tissue-specific gene expression studies. aP2/FABP4 is predominantly expressed in adipose tissue, and while this promoter provides adipocyte-restricted expression postnatally, its expression throughout embryonic development had not been previously characterized. In this report, we demonstrate that the aP2-Cre transgene is expressed and consistently localized within the embryo from mid-gestation stage 9.5 dpc. By 15.5 dpc, beta-gal activity was detected primarily in the brown adipose tissue, trigeminal ganglia, dorsal root ganglia, cartilage primordia and vertebrae. Immunofluorescence staining for Cre recombinase and FABP4 protein showed a corresponding staining pattern similar to that of beta-gal, confirming that Cre recombinase was produced in the transgenic line at late stages of development, and overlapped with endogenous aP2/FABP4 production. Further, fat-specific oil red O staining of tissue sections validated the presence of lipids in the stained tissues indicating that adipocytes and/or adipocyte-like cells were indeed present in these tissues. This is the first report to our knowledge to describe and confirm aP2/FABP4 promoter expression in this transgenic line during development in the mouse embryo and indicates that aP2/FABP4 expression occurs not only in mature adipocytes, but has a wider embryonic expression pattern than previously appreciated.

Adipose Tissue↗

PubMed2004

Gene expression profiling in human preadipocytes and adipocytes by microarray analysis.

Uncontrolled expansion of adipose tissue leads to obesity, a public health epidemic affecting >30% of adult Americans. Adipose mass increases in part through the recruitment and differentiation of an existing pool of preadipocytes (PA) into adipocytes (AD). Most studies investigating adipogenesis used primarily murine cell lines; much less is known about the relevant processes that occur in humans. Therefore, characterization of genes associated with adipocyte development is key to understanding the pathogenesis of obesity and developing treatments for this disorder. To address this issue, we performed large-scale analyses of human adipose gene expression using microarray technology. Differential gene expression between PA and AD was analyzed in 6 female patients using human cDNA microarray slides and data analyzed using the Stanford Microarray Database. Statistical analysis for the gene expression was performed using the SAS mixed models. Compared with PA, several genes involved in lipid metabolism were overexpressed in AD, including fatty acid binding protein, adipose differentiation-related protein, lipoprotein lipase, perilipin, and adipose most abundant transcript 1. Novel genes expressed in adipocytes included E2F5 transcriptional factor and SMARC (SWI/SNF-related, matrix associated, actin-dependent regulator of chromatin). PA predominantly expressed genes encoding extracellular matrix components such as fibronectin, matrix metalloprotein, and novel proteins such as lysyl oxidase. Despite the high differential expression of some of these genes, many did not differ significantly likely due to high variability and limited statistical power. A comprehensive list of differential gene expression is presented according to cellular function. In conclusion, these studies offer an overview of the gene expression profiles in PA and AD and identify new genes with potentially important functions in adipose tissue development and obesity that merit further investigation.

Adipocytes↗

PubMed2004

The human fatty acid synthase gene and de novo lipogenesis are coordinately regulated in human adipose tissue.

Despite its potential importance in obesity and related disorders, little is known about regulation of lipogenesis in human adipose tissue. To investigate this area at the molecular and mechanistic levels, we studied lipogenesis and the regulation of 1 of its core enzymes, fatty acid synthase (FAS), in human adipose tissue in response to hormonal and nutritional manipulation. As a paradigm for lipogenic genes, we cloned the upstream region of the human FAS gene, compared its sequence to that of FAS orthologs from other species, and identified important regulatory elements that lie upstream of the FAS coding region. Lipogenesis, as assessed by glucose incorporation into lipids, was increased by insulin and more so by the combination of insulin and dexamethasone (Dex, a potent glucocorticoid analogue). In parallel, FAS expression, activity, and gene transcription rate were also significantly increased by these treatments. We also showed that linoleic acid, a representative PUFA, attenuated the actions of insulin and Dex on fatty acid and lipid synthesis as well as FAS activity and expression. Using reporter assays, we determined that the regions responsible for hormonal regulation of the FAS gene lie in the proximal portion of the gene's 5'-flanking region, within which we identified an insulin response element similar to the E-box sequence we identified previously in the rat FAS gene. In summary, we demonstrated that lipogenesis occurs in human adipose tissue and can be induced by insulin, further enhanced by glucocorticoids, and suppressed by PUFA in a hormone-dependent manner.

Adipose Tissue↗