Glucose transporters of the glomerulus and the implications for diabetic nephropathy

Several glucose transporters have recently been identified in glomeruli, and in cultured glomerular cells. These include the facilitative glucose transporter isoforms GLUTs 1, 3 and 4, and sodium-glucose cotransport activity with characteristics of SGLT1. GLUTs 1, 3 and 4 are all high affinity, low capacity, facilitative glucose transporters which typically would be saturated at or near physiologic glucose concentrations. The SGLT transporter of mesangial cells is also a high affinity transporter which similarly could be saturated under normal glucose conditions. This suggests that in order for mesangial cells to take up excessive quantities of glucose in diabetes, changes in glucose transporter expression, translocation or activity may be required. Accordingly, recent investigations discovered positive-feedback regulation of the mesangial cell GLUT1 transporter by glucose, and a regulatory role for GLUT1 in glucose metabolism and extracellular matrix synthesis. Future investigations of glucose transporters in the pathogenesis of diabetic renal disease will now likely proceed in multiple directions, including but not limited to: (1) examination of their regulation by growth factors implicated in diabetic nephropathy, and the resultant effects on ECM synthesis; (2) determination of the mechanisms by which GLUT1 regulates the expression of aldose reductase, PKC, GLUT1, and other genes in the mesangial cell; and (3) Suppression of glucose transporters in attempts to prevent high glucose-induced diabetic glomerulosclerosis.