Transcriptome profiling of white adipose tissue in a mouse model for 15q duplication syndrome.

Obesity is not only associated with unhealthy lifestyles, but also linked to genetic predisposition. Previously, we generated an autism mouse model (patDp/+) that carries a 6.3 Mb paternal duplication homologous to the human 15q11-q13 locus. Chromosomal abnormalities in this region are known to cause autism spectrum disorder, Prader-Willi syndrome, and Angelman syndrome in humans. We found that, in addition to autistic-like behaviors, patDp/+ mice display late-onset obesity and hypersensitivity to a high-fat diet. These phenotypes are likely to be the results of genetic perturbations since the energy expenditures and food intakes of patDp/+ mice do not significantly differ from those of wild-type mice. Intriguingly, we found that an enlargement of adipose cells precedes the onset of obesity in patDp/+ mice. To understand the underlying molecular networks responsible for this pre-obese phenotype, we performed transcriptome profiling of white adipose tissue from patDp/+ and wild-type mice using microarray. We identified 230 genes as differentially expressed genes. Sfrp5 - a gene whose expression is positively correlated with adipocyte size, was found to be up-regulated, and Fndc5, a potent inducer of brown adipogenesis was identified to be the top down-regulated gene. Subsequent pathway analysis highlighted a set of 35 molecules involved in energy production, lipid metabolism, and small molecule biochemistry as the top candidate biological network responsible for the pre-obese phenotype of patDp/+. The microarray data were deposited in NCBI Gene Expression Omnibus database with accession number GSE58191. Ultimately, our dataset provides novel insights into the molecular mechanism of obesity and demonstrated that patDp/+ is a valuable mouse model for obesity research.

Model mice for 15q11-13 duplication syndrome exhibit late-onset obesity and altered lipid metabolism.

Copy number variations on human chromosome 15q11-q13 have been implicated in several neurodevelopmental disorders. A paternal loss or duplication of the Prader-Willi syndrome/Angelman syndrome (PWS/AS) region confers a risk of obesity, although the mechanism remains a mystery due to a lack of an animal model that accurately recreates the obesity phenotype. We performed detailed analyses of mice with duplication of PWS/AS locus (6 Mb) generated by chromosome engineering and found that animals with a paternal duplication of this region (patDp/+) show late-onset obesity, high sensitivity for high-fat diet, high levels of blood leptin and insulin without an increase in food intake. We show that prior to becoming obese, young patDp/+ mice already had enlarged white adipocytes. Transcriptome analysis of adipose tissue revealed an up-regulation of Secreted frizzled-related protein 5 (Sfrp5), known to promote adipogenesis. We additionally generated a new mouse model of paternal duplication focusing on a 3 Mb region (3 Mb patDp/+) within the PWS/AS locus. These mice recapitulate the obese phenotypes including expansion of visceral adipose tissue. Our results suggest paternally expressed genes in PWS/AS locus play a significant role for the obesity and identify new potential targets for future research and treatment of obesity.

GAREM, a novel adaptor protein for growth factor receptor-bound protein 2, contributes to cellular transformation through the activation of extracellular signal-regulated kinase signaling.

Adaptor proteins for the various growth factor receptors play a crucial role in signal transduction through tyrosine phosphorylation. Several candidates for adaptor proteins with potential effects on the epidermal growth factor (EGF) receptor-mediated signaling pathway have been identified by recent phosphoproteomic studies. Here, we focus on a novel protein, GAREM (Grb2-associated and regulator of Erk/MAPK) as a downstream molecule of the EGF receptor. GAREM is phosphorylated at tyrosine 105 and 453 after EGF stimulation. Grb2 was identified as its binding partner, and the proline-rich motifs of GAREM are recognized by the N- and C-terminal SH3 domains of Grb2. In addition, the tyrosine phosphorylations of GAREM are necessary for its binding to Grb2. Because the amino acid sequence surrounding tyrosine 453 is similar to the immunoreceptor tyrosine-based inhibitory motif, Shp2, a positive regulator of Erk, binds to GAREM in this phosphorylation-dependent manner. Consequently, Erk activation in response to EGF stimulation is regulated by the expression of GAREM in COS-7 and HeLa cells, which occurs independent of the presence of other binding proteins, such as Gab1 and SOS, to the activated EGF receptor. Furthermore, the expression of GAREM has an effect on the transformation activity of cultured cells. Together, these findings suggest that GAREM plays a key role in the ligand-mediated signaling pathway of the EGF receptor and the tumorigenesis of cells.