Human Adipocytes : Proteomic Approaches

Abstract: Type 2 diabetes is characterized by increased levels of glucose in the blood originating from insulin resistance in insulin sensitive tissues and from reduced pancreatic insulin production. Around 400 million people in the world are diagnosed with type 2 diabetes and the correlation with obesity is strong. In addition to life style induction of obesity and type 2 diabetes, there are indications of genetic and epigenetic influences. This thesis has focused on the characterization of primary human adipocytes, who play a crucial role in the development of type 2 diabetes.Histones are important proteins in chromatin dynamics and may be one of the factors behind epigenetic inheritance. In paper I, we characterized histone variants and posttranslational modifications in human adipocytes. Several of the specific posttranslational histone modifications we identified have been characterized in other cell types, but the majority was not previously known. Moreover, we identified a variant of histone H4 on protein level for the first time.In paper II, we studied specific histone H3 methylations in the adipocytes. We found that overweight is correlated with a reduction of H3K4me2 while type 2 diabetes is associated with an increase of H3K4me3. This shows a genome-wide difference in important chromatin modifications that could help explain the epidemiologically shown association between epigenetics and metabolic health.Caveolae is a plasma membrane structure involved in the initial and important steps of insulin signaling. In paper III we characterized the IQGAP1 interactome in human adipocytes and suggest that IQGAP1 is a link between caveolae and the cytoskeleton. Moreover, the amount of IQGAP1 is drastically lower in adipocytes from type 2 diabetic subjects compared with controls implying a potential role for IQGAP1 in insulin resistance.In conclusion, this thesis provides new insights into the insulin signaling frameworks and the histone variants and modifications of human adipocytes.