BACKGROUND: Apoptosis; which is involved in the process of mesangial cell and podocyte loss in diabetic nephropathy; is known to be regulated by protein kinase B/Akt (Akt). A number of studies have therefore investigated the activity of Akt under diabetic conditions; but the results have not been consistent. In this study; we hypothesized that apoptosis may occur differentially and that Akt may be differentially activated according to glomerular size in diabetic kidney disease.
METHODS: Fifty male Sprague-Dawley rats were injected intraperitoneally with diluent (C; n = 25) or streptozotocin (DM; n = 25). After 3 months; glomeruli were isolated using sieves with pore sizes of 250; 150; 125 and 75 μm and then classified into large glomeruli (on the 125-μm sieve; LG) and small glomeruli (on the 75-μm sieve; SG) groups. Western blot analyses for phospho-Akt; apoptosis-related molecules (Bax; Bcl-2; active fragments of Caspase-3 and phospho-p53) and cyclin-dependent kinase inhibitors were performed.
CONCLUSIONS: The numbers of total cells and podocytes in isolated glomeruli were determined using transmission electron microscopy. Akt phosphorylation was significantly decreased in DM-LG; while it was significantly increased in DM-SG (P < 0.05). The ratio of Bax/Bcl-2 protein expression and active fragments of Caspase-3 and phospho-p53 protein expression were significantly increased in DM-LG compared to DM-SG and C-SG (P < 0.001 and P < 0.01; respectively). In contrast; the expression of p27(Kip1) and p21(Cip1) was significantly increased in DM-SG compared to DM-LG and C-SG (P < 0.05). The numbers of total glomerular cells and podocytes were significantly decreased in DM-LG (P < 0.05). In conclusion; these data show differential expression of Akt activity and apoptosis-related molecules according to glomerular size in diabetic nephropathy; suggesting that apoptosis may be more operative in more hypertrophic glomeruli; resulting in fewer glomerular cells and podocytes in diabetic nephropathy.