ANTIOXIDANT EXPRESSION IN EXPERIMENTAL HYDRONEPHROSIS - ROLE OF MECHANICAL STRETCH AND GROWTH-FACTORS

We assessed whether levels of renal reactive oxygen species (ROS) and antioxidant enzymes are perturbed in rats following unilateral uretera l obstruction (UUO). The mechanism of catalase perturbation was invest igated using proximal tubule suspensions following stimulation with tr ansforming growth factor (TGF)-beta and interleukin (IL)-1 and in a pr oximal tubular cell line (OKC) subjected to cyclic mechanical stretch, which mimics the early hydrodynamic derangement after UUO. Levels of catalase and copper-zinc superoxide dismutase (Cu,Zn-SOD) mRNA from 96 -h UUO rats showed a 5.5-fold (P < 0.001) and 5.0-fold (P < 0.001) dec rease, respectively, compared with the contralateral unobstructed kidn ey (CUK). Levels of superoxide anion and hydrogen peroxide showed a si gnificant 1.8-fold (P < 0.0001) and 14.0-fold (P < 0.0001) increase, r espectively, in 96-h UUO kidney slice cultures. In situ hybridization and immunohistochemistry showed Cu,Zn-SOD and catalase mRNA and protei n transcription expressed in proximal tubules of UUO and CUK specimens . Catalase mRNA levels were markedly downregulated following a 1-h exp osure of isolated proximal tubules to TGF-beta (0.1-10 ng) and IL-1 (1 -5 ng), in comparison to control proximal tubular suspensions. OKC sub jected to cyclic mechanical stretch for 1-24 h had marked decrements i n catalase mRNA levels, compared with unstretched cells at the same ti me point. These results indicate that a primary downregulation of prox imal tubular Cu,Zn-SOD and catalase expression develops in the proxima l tubules of UUO with consequent increments in cortical oxidant levels . These findings suggest that either an early mechanical disturbance p roduced by UUO or local tubular generation of cytokines can reduce tub ular catalase expression. The downregulation of catalase mRNA expressi on, together with increased oxidant stress in the rat renal cortex pos t-UUO, may amplify the proinflammatory state of experimental hydroneph rosis culminating in tubulointerstitial injury and fibrosis.