Heat-shock protein 25 ameliorates calcium oxalate crystal-mediated oxidative stress in renal epithelial cells

OBJECTIVE To investigate whether the antioxidant protection attributed to small heat-shock proteins (sHSPs) affects calcium oxalate stone formation, a pro-oxidant disease. MATERIALS AND METHODS Canine distal tubular epithelial cells (Madin-Darby canine kidney, MDCK cells) were grown as confluent monolayers. Treatment regimens included control and HS-treated cells (37 degrees C and 42 degrees C for 1 h) with or without calcium oxalate monohydrate (COM) or free oxalate treatment (28 mu g/cm(2)) 16 h later. In digitonin-permeabilized cells, O(2)(-) was measured by lucigenin-enhanced chemiluminescence over a 5-min period, to measure mitochondrial O(2)(-) production. Protein expression was assessed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis Western blot analysis using specific antibodies. RESULTS COM significantly increased O(2)(-) production in MDCK cells. HS treatment, which up-regulated HSP25 expression, significantly decreased this O(2)(-) production (P < 0.05) but had no effect in control cells. In COM-treated cells (20 h) there was a marked and significant down-regulation of both HSP 25, HSP 70 and heme oxygenase-1 expression compared to cells treated with HS alone (P < 0.05). Free oxalate had no effect on HSP 25 expression. CONCLUSION The results suggest that the COM-induced increase in mitochondrial O(2)(-) production in MDCK cells is ameliorated by HSP 25 up-regulation via HS. Specific COM inhibition of HSP 25, HSP 70 and heme oxygenase-1 up-regulation suggests that COM-induced reactive oxygen species damage is unable to benefit from HSP-associated physiological resistance.