One of the important metabolic functions of glycerol-3-phosphate dehydrogenase (GPDH; sn-glycerol-3-phosphate: NAD+ 2-oxidoreductase, EC 1.1.1.8) is to provide the glycerol backbone for glyceride lipid synthesis. For this reason, induction of GPDH activity is a primary event in adipocyte development. Early onset obesity in humans is characterized by adipocyte hyperplasia with or without hypertrophy while late onset obesity is characterized by adipocyte hypertrophy alone. Mutations that cause obesity in mice also cause adipocyte hyperplasia and hypertrophy. A cDNA clone for mouse GPDH has been obtained. In this project the human and mouse genes coding for the adult forms of GPDH will be molecularly cloned and their structures determined. Comparison of the human and mouse genes at the structural and sequence levels will identify elements such as enhancers, promoters, repetitive sequences, and untranslated mRNA regions that are conserved in evolution. These elements may have an important role in regulating GPDH expression which is ubiquitous in mouse tissues. The long term goal is to understand how expression of this enzyme is regulated in each specific cell type since levels of expression vary over 100-fold. Methylation of specific regulatory sequences within or flanking the mouse adult GPDH gene, Gdc-1, will be analyzed to determine if methylation has a role in regulating lipid accumulation and adipocyte differentiation. The methylation status of the Gdc-1 gene will be measured during adipocyte differentiation both in vivo and in vitro. The long term goal is to control lipogenesis by modulating GPDH expression. To test this possibility, an oncogenic retrovirus, murine sarcoma virus, will be used to block lipogenesis in cultures of murine preadipocytes. A second method will use the adipocyte storage deficiency mutation, asd, to block development of white adipose tissue in asd/asd mice. This study will compare GPDH expression and gene methylation in normal, viral infected, and asd/asd predipocytes. If mechanisms tht increase GPDH expression during adipocyte formation can be determined and regulated, it may be possible to develop modes of therapy to prevent adipocyte hyperplasia in early onset human obesity or decrease lipid formation in late onset hypertrophic obesity.
