Role of fatty acyl-CoA synthetases in the development of lipid induced insulin resistance in skeletal muscle cells

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Type 2 diabetes is characterised by the chronic elevation of glucose in the blood, and its worldwide prevalence is increasing. Obesity and the associated high levels of lipids and fatty acids in the circulation are key risk factors in the pathogenesis of type 2 diabetes. During the development of type 2 diabetes, lipids are not only stored in adipose tissue but also in other tissues like skeletal muscle. Insulin stimulates the uptake of glucose into skeletal muscle, but this function is impaired when the intracellular concentration of lipid metabolites is increased. This resistance towards the action of insulin has been shown to correlate with the concentration of activated fatty acids and downstream lipid derivatives. Activated fatty acids, i.e. acyl-CoA molecules are generated by the fatty acyl-CoA synthetase family of enzymes. Our lab demonstrated that these proteins also have an important role in fatty acid uptake, and that their enzyme activity is regulated by insulin signaling. However, little is known about the function of acyl-CoA synthetases in the development of insulin resistance and type 2 diabetes. The main hypothesis of this research proposal is that a reduction of acyl-CoA synthetases will prevent or diminish the development of insulin resistance, because less acyl-CoA molecules and other reactive lipid metabolites will be produced under these conditions. The model system for the detailed analysis of this processes are muscle cells differentiated into multinucleated myotubes. These myotubes are cultivated in vitro, which allows to control conditions precisely and to monitor the development of insulin resistance in time course experiments. The myotubes are genetically manipulated so that they have a reduced acyl-CoA synthetase enzyme activity. The progression of fatty acid-induced insulin resistance is then analysed by biochemical assays. There are thirteen different mammalian isoenzymes of the acyl-CoA synthetase family, and previous research has shown that they have overlapping but also unique functions. Therefore, analysis of the acyl-CoA synthetase family proteins on the level of mRNA, protein and enzyme activity will be used to identify the specific enzymes relevant for the development of insulin resistance. This approach is first used on the in vitro system, but will be complemented by the analysis of human muscle biopsies from obese and diabetic subjects. The results from these studies will define the correlation between the acyl-CoA synthetase family proteins and the development of insulin resistance in skeletal muscle, and identify the specific isoenzymes relevant for this process. It is envisaged that pharmacological inhibition of these enzymes could be a future therapeutic approach in the treatment or prevention of type 2 diabetes.