Caspase inhibition reduces tubular apoptosis and proliferation and slows disease progression in polycystic kidney disease

Abstract

We have previously demonstrated an increase in proapoptotic caspase-3 in the kidney of Han:SPRD rats with polycystic kidney disease (PKD). The aim of the present study was to determine the effect of caspase inhibition on tubular cell apoptosis and proliferation, cyst formation, and renal failure in the Han:SPRD rat model of PKD. Heterozygous (Cy/+) and littermate control (+/+) male rats were weaned at 3 weeks of age and then treated with the caspase inhibitor IDN-8050 (10 mg/kg per day) by means of an Alzet (Palo Alto, CA) minipump or vehicle [polyethylene glycol (PEG 300)] for 5 weeks. The two-kidney/total body weight ratio more than doubled in Cy/+ rats compared with +/+ rats. IDN-8050 significantly reduced the kidney enlargement by 44% and the cyst volume density by 29% in Cy/+ rats. Cy/+ rats with PKD have kidney failure as indicated by a significant increase in blood urea nitrogen. IDN-8050 significantly reduced the increase in blood urea nitrogen in the Cy/+ rats. The number of proliferating cell nuclear antigen-positive tubular cells and apoptotic tubular cells in non-cystic and cystic tubules was significantly reduced in IDN-8050-treated Cy/+ rats compared with vehicle-treated Cy/+ rats. On immunoblot, the active form of caspase-3 (20 kDa) was significantly decreased in IDN-8050-treated Cy/+ rats compared with vehicle-treated Cy/+ rats. In summary, in a rat model of PKD, caspase inhibition with IDN-8050 (i) decreases apoptosis and proliferation in cystic and noncystic tubules; (ii) inhibits renal enlargement and cystogenesis, and (iii) attenuates the loss of kidney function.

Fig. 1.

Effects of IDN-8050 (IDN) on caspase-3 protein in Han:SPRD rats. On immunoblot analysis, the processed form of caspase-3 (20 kDa) in the whole kidney was significantly reduced in the rats treated with IDN-8050. Pos, positive control (recombinant caspase-3). Representative immunoblot of six separate experiments.

Fig. 2.

Tubular cell proliferation. (A) The number of PCNA-positive cells (brown staining) per tubule in noncystic tubules in the cortex was increased in vehicle-treated Cy/+ rats compared with vehicle-treated and IDN-8050-treated +/+ rats. IDN-8050-treated Cy/+ rats had significantly less PCNA-positive cells per tubule compared with vehicle-treated Cy/+ rats. *, P < 0.01 vs. +/+; **, P < 0.05 vs. vehicle-treated Cy/+, not significant vs. +/+. P = 0.025 for the interaction between IDN-8050 and genotype on PCNA-positive cells per tubule. (B) Vehicle-treated +/+ rats had relatively few PCNA-positive cells per tubule compared with (C) vehicle-treated Cy/+ rats (arrows). (D) IDN-8050 decreased the number of PCNA-positive cells per tubule in Cy/+ rats (arrows). (E) The number PCNA-positive cells in tubular epithelial cells lining the cysts was significantly decreased by IDN-8050. *, P < 0.05 vs. vehicle-treated Cy/+.(F and G) Shown are representative pictures of the PCNA staining (arrows) in cysts of vehicle-treated Cy/+ (F) and IDN-8050-treated Cy/+ (G) rats.

Fig. 3.

Tubular cell apoptosis. (A) The number of TUNEL-positive cells (blue staining) per tubule in noncystic tubules in the cortex was increased in vehicle-treated Cy/+ rats compared with vehicle-treated +/+ rats. IDN-8050-treated Cy/+ rats had significantly fewer TUNEL-positive cells per tubule compared with vehicle-treated Cy/+ rats. *, P = 0.05 vs. +/+; **, P < 0.05 vs. vehicle-treated Cy/+, not significant vs. +/+.(B) Vehicle-treated +/+ rats had no TUNEL-positive cells per tubule compared with (C) vehicle-treated Cy/+ rats (arrows). (D) IDN-8050 decreased the number of TUNEL-positive cells per tubule in Cy/+ rats. (E) The number of TUNEL-positive cells in tubular epithelial cells lining the cysts was significantly decreased by IDN-8050. *, P = 0.02 vs. vehicle-treated Cy/+.(F and G) Representative picture of the TUNEL staining (arrows) in cysts of vehicle-treated Cy/+ (F) and IDN-8050-treated Cy/+ (G) rats.