Co-localization of glucocorticoid metabolizing and prostaglandin synthesizing enzymes in rat kidney and liver

Abstract

Aims The kidney metabolizes endogenous glucocorticoids using one of 2 isoforms of the enzyme 11ß-Hydroxysteroid Dehydrogenase (11ß-HSD). 11ß-HSD1 is located in the later portion of the proximal tubule and interstitial cells and 11ß–HSD2 is found in the mineralocorticoid sensitive collecting duct. Both renal isoforms appear to function as dehydrogenases, inactivating glucocorticoids. Since our laboratory has established that both renal cyclo-oxygenase-2 (COX-2) and 11ß-HSD1 co-localize in human kidney, we hypothesized that the two enzymes might functionally interact and influence each other's expression and/or activity. Methods and results Using immuno-histochemistry staining with specific antibodies, both enzymes co-localize in later segments of proximal tubules in rat kidney and in rat hepatocytes. There was no co-localization with 11ß-HSD2 in the kidney. The co-localization was confirmed by Western blot and by immuno-precipitation in cultured rat proximal tubular cells (IRPTC). IRPTC incubated with corticosterone 1 µM or with corticosterone 10 nM plus the 11ß-HSD inhibitor carbenoxolone 1 µM demonstrated a decrease in the expression of COX-2 by Western blot at 24 h. When IRPTC were exposed to the COX-2 inhibitor, celecoxib, 11ß-HSD1 dehydrogenase activity was inhibited in a dose dependent manner with an IC50 of 1.4 µM. Celecoxib 2 µM had minimal effect on reductase activity in liver slices. Conclusions Thus, COX-2 and 11ß-HSD1 co-localize in renal proximal tubules and in hepatocytes. In the kidney, each can influence the biological function of the other. The NSAID celecoxib may exert some of its anti-inflammatory effects on the kidney by locally prolonging the biologic half-life of endogenous glucocorticoids.