Caspase-3 and apoptosis in experimental chronic renal scarring

Background. Caspase-3 is a member of the caspase enzyme family, having a ce ntral role in the execution of apoptosis. However, the significance of Casp ase-3 in the inappropriate and excessive apoptosis that contributes to the progression of non-immune-mediated renal scarring has not been established. Methods. Kidneys from sham-operated and subtotal nephrectomized (SNx) rats were harvested on days 7, 15, 30, 60, 90 and 120 post-surgery. These were a nalyzed for apoptosis (in situ end labeling of DNA, light and electron micr oscopy), Caspase-3 activity (fluorometric substrate cleavage assay), protei n and mRNA (Western and Northern blotting), as well as distribution (immuno histochemistry), inflammation (ED-1 immunohistochemistry) and fibrosis (Mas son's Trichrome staining). Results. Apoptosis, inflammation and fibrosis gradually increased in glomer uli, tubules and interstitium of SNx rats. Caspase-3 was mainly located in damaged tubules, but also was found in some glomerular and interstitial cel ls. Little or no staining was noted in sham-operated kidneys. In SNx kidney s, Caspase-3 activity was significantly increased from day 30 and peaked on day 120 (2.5-fold). This resulted from increases in the 17 and 24 kD activ e protein subunits. The 32 kD precursor was increased at all time points (1 861% on day 120, P<0.01). Caspase-3 changes were transcription-dependent wi th the 2.7 kb caspase-3 mRNA significantly increased at all time points (28 7% on day 120). Caspase-3 activity was a better predictor of apoptosis (Std <beta> coefficient = 0.347, P<0.05) than Caspase-3 proteins or mRNA; howev er, Caspase-3 at all levels correlated with apoptosis, inflammation and fib rosis (all P<0.01). Conclusions. Up-regulation of apoptosis in remnant kidneys is likely to be Caspase-3-dependent as it is associated with increases in Caspase-3 at the activity, protein and mRNA levels. Therefore, Caspase-3 is a potential ther apeutic target for the modification of renal cell apoptosis and subsequentl y renal fibrosis.