’Mechanistic studies on the regulation of glucose transport by insulin: how common polymorphisms lead to diabetes and obesity’

The prevalence of obesity and type 2 diabetes (T2DM) has reach epidemic proportions with over a quarter of adults in England classified as obese and 6% of the English population have T2DM (1). T2DM manifests from insulin resistance, a state which is characterised by the inability of cells, primarily muscle and fat (adipose), to promote the translocation of the glucose transporter GLUT4 to the cell surface to response to insulin. Our objective is to define the molecular events underpinning this regulated GLUT4 translocation and hence glucose uptake. Using cultured adipocytes and myotubes as cell culture model, we are focusing on identifying novel proteins involved in this process, in addition to furthering our understanding of the role of proteins involved in both the signalling and trafficking steps of insulin action.

Of particular interest is the Rab-GTPase Activating Protein, TBC1D1, which integrates the signalling with the trafficking steps to mediate the ability of insulin and contraction to stimulate glucose uptake into muscle cells (2-4). Interestingly a protein coding variant, R125W, in TBC1D1 has previously been reported to be associated with familial obesity in women (5, 6). We have recently used SILAC proteomics to identify a number of novel interacting proteins with TBC1D1. This project will validate these candidate interacting proteins, establishing whether the R125W mutation affects their interaction and elucidating their role in facilitating glucose uptake in myotubes. Using time-lapse confocal microscopy we have found that the R125W mutation alters the subcellular distribution of TBC1D1; this phenotype will be further explored, with particular reference to the role of the interacting proteins. This project will employ a range of biochemical and molecular cell biology techniques in addition to high-resolution imaging to further characterise and define the role of these novel regulators on GLUT4 biology and skeletal muscle energy homeostasis.