Apoptosis occurs differentially according to glomerular size in diabetic kidney disease

Abstract

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, it was hypothesized that apoptosis may occur differentially and that Akt may be differentially activated according to glomerular size in diabetic kidney disease. Thirty male Sprague-Dawley rats were injected intraperitoneally with diluent (C, N=15) or streptozotocin (DM, N=15). After 3 months, glomeruli were isolated using sieves with pore sizes of 250 m, 150 m, 125 m, and 75 m and then classified into large glomeruli (on the 125 m sieve, LG) and small glomeruli (on the 75 m sieve, SG) groups. Western blot analyses for phospho-Akt, apoptosis-related molecules (Bax, Bcl-2, cleaved caspase-3, and phospho-p53), and cyclin-dependent kinase-inhibitors (CKIs) were performed. 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 cleaved caspase-3, phospho-Smad3 and phospho-p53 protein expression were significantly increased in DM-LG compared to DM-SG and C-SG (p<0.05 to p<0.001). In contrast, the expression of p27Kip1 and p21Cip1 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.