Aims/hypothesis: Peroxisome proliferator-activated receptor (PPAR) gamma agonists are used increasingly in the treatment of type 2 diabetes. In the context of renal disease, PPARgamma agonists reduce microalbuminuria in diabetic nephropathy; however, the mechanisms underlying this effect are unknown. Glomerular podocytes are newly characterised insulin-sensitive cells and there is good evidence that they are targeted in diabetic nephropathy. In this study we investigated the functional and molecular effects of the PPARgamma agonist rosiglitazone on human podocytes.
Methods: Conditionally immortalised human podocytes were cultured with rosiglitazone and functional effects were measured with glucose-uptake assays. The effect of rosiglitazone on glucose uptake was also measured in 3T3-L1 adipocytes, nephrin-deficient podocytes, human glomerular endothelial cells, proximal tubular cells and podocytes treated with the NEFA palmitate. The role of the glucose transporter GLUT1 was investigated with immunofluorescence and small interfering RNA knockdown and the plasma membrane expression of GLUT1 was determined with bis-mannose photolabelling.
Results: Rosiglitazone significantly increased glucose uptake in wild-type podocytes and this was associated with translocation of GLUT1 to the plasma membrane. This effect was blocked with GLUT1 small interfering RNA. Nephrin-deficient podocytes, glomerular endothelial cells and proximal tubular cells did not increase glucose uptake in response to either insulin or rosiglitazone. Furthermore, rosiglitazone significantly increased basal and insulin-stimulated glucose uptake when podocytes were treated with the NEFA palmitate.
Conclusions/interpretation: In conclusion, rosiglitazone has a direct and protective effect on glucose uptake in wild-type human podocytes. This represents a novel mechanism by which PPARgamma agonists may improve podocyte function in diabetic nephropathy.