The cyclin kinase inhibitor p21(WAF1/CIP1) is required for glomerular hypertrophy in experimental diabetic nephropathy

Background. Diabetic nephropathy is characterized by glomerular hypertrophy . We have recently shown that experimental diabetes mellitus is associated with an increase in glomerular expression of the cyclin kinase inhibitor p2 1(WAF1/CIP1) (p21) Furthermore, in vitro glucose-induced mesangial cell hyp ertrophy is also associated with an up-regulated expression of p21. In this study. we tested the hypothesis that p21 mediates diabetic glomerular hype rtrophy in vivo. Methods. Experimental diabetes mellitus was induced by streptozotocin in mi ce in which p21 was genetically deleted (p21 -/-) and in wild-type mice (p2 1 +/+). Kidney biopsies were obtained from diabetic and control (citrate in jected) p21 +/+ and p21 -/- mice at day 60. The tissue was used for morphol ogic studies of glomerular size (measured by computer image-analysis system ), glomerular cellularity (cell count), glomerular matrix expansion (silver stain), apoptosis (TUNEL), and expression of transforming growth factor-Pi (TGF-PI) by in situ hybridization. Results. The glomerular tuft area increased 11.21% in diabetic p21 +/+ mice at day 60 compared with control (3329.98 +/- 244.05 mu m(2) vs. 2994.39 +/ - 176.22 mu m(2), P = 0.03), and the glomerular cell count did not change i n diabetic p21 +/+ mice at day 60 compared with the control. These findings are consistent with glomerular hypertrophy. In contrast, the glomerular tu ft area did not increase in diabetic p21 -/- mice at day 60 compared with t he control (3544.15 +/- 826.49 vs. 3449.15 +/- 109.65, P = 0.82), nor was t here an increase in glomerular cell count (41.41 +/- 13.18 vs. 46.95 +/- 3. 00, P = 0.43). Diabetic p21 +/+ mice, but not p21 -/- mice, developed an in crease in proteinuria at day 60 compared with the control. Tubular cell pro liferation, measured by proliferating cell nuclear antigen immunostaining, was increased in both diabetic p21 +/+ (2.1-fold) and p21 -/- (7.61-fold) m ice compared with controls. Glomerular cell apoptosis did not increase in d iabetic mice. Although glomerular TGF-beta(1), mRNA levels increased in bot h strains of diabetic mice at day 60, the glomerular matrix did not expand.