Tubular and Interstitial Cell Apoptosis in the Streptozotocin-Diabetic Rat Kidney

摘要

Background/Aims: Angiotensin II (Ang II) mediates progressive nephron loss in diabetes and stimulates apop-totic cell death in several tissues. We studied the extent of apoptosis in streptozotocin (STZ) induced diabetic nephropathy in the rat and the effects of insulin and type 1 (AT-1) or type 2 (AT2) Ang II receptor blockade with losartan or PD123319, respectively. Methods:Three groups of rats were studied after 2 and 12 weeks: (1) controls ; (2) STZ-diabetic rats (STZ rats), and (3) STZ-diabet-ic rats with insulin implants. Additional rats were treated with losartan (25 mg/kg/day) and/or PD123319 (10 mg/ kg/day) for 2 weeks. Kidneys were examined for apoptosis, using the terminal deoxynucleotidyl transferase-me-diated dUTP nick-end labeling (TUNED assay, DNA laddering, and electron microscopy. Immunoblotting determined expression of the proapoptotic protein Bax and of the antiapoptotic protein Bcl-2 in proximal tubules. Results: Diabetes caused a significant increase in apoptosis, involving tubular and interstitial cells of cortex and medulla, but not glomerular cells (2 weeks: controls 264 +- 94 vs. STZ rats 1,501 +- 471 apoptotic nuclei/kidney section; p<0.02; n = 6-8), an effect reversed by insulin. In STZ rats, ultrastructural examination revealed chromatin condensation and nuclear fragmentation in tubular and interstitial cells. At 2 and 12 weeks, a significant decrease in the expression of the antiapoptotic protein Bcl-2 occurred in STZ rat proximal tubules, with restoration by insulin. In STZ rats, treatment for 2 weeks with losartan or PD123319 inhibited apoptosis in the kidneys, with no additive effect of the combination therapy. Conclusions: Apoptosis occurs in diabetic nephropathy, involving tubular and interstitial cells, an effect reversed by insulin therapy. Furthermore, the effects of AT-1 or AT_2 receptor blockade suggest that Ang II is involved in mediating apoptosis in the diabetic kidney.