Epithelial cell localization of type 2 11 beta-hydroxysteroid dehydrogenase in rat and human colon.

11 beta-Hydroxysteroid dehydrogenase (11 beta HSD), by catalyzing the interconversion of active corticosterone (B) to inactive 11-dehydrocorticosterone (A) in the rat and cortisol (F) to cortisone in man, maintains normal in vivo specificity of the mineralocorticoid receptor (MR) in both kidney and distal colon. Two isoforms of 11 beta HSD have been reported: the cloned type I, NADP(H)-dependent 11 beta-dehydrogenase/oxo-reductase, and a high affinity NAD+-dependent 11 beta-dehydrogenase (type 2 isoform). Previous studies indicate that the MR in the distal colon is localized to ion-transporting surface epithelial cells and non-epithelial neuroendocrine cells within the lamina propria. We have now analyzed the expression and activity of 11 beta HSD in specific cells isolated from both rat and human colonic mucosa by a chemical shear and microdissection method. Both isoforms of 11 beta HSD were detected in rat and human colonic mucosa. Type 2 11 beta HSD activity, with an apparent Km (mean +/- SE) of 56.3 +/- 2.2 nM for B in the rat and 35.3 +/- 1.2 nM for F in man, was exclusively localized to surface and crypt epithelial cells. In contrast, the type I isoform in the rat, with an apparent Km of 0.95 +/- 0.14 microM for B, was localized exclusively to specific nonepithelial cells in the lamina propria. Human colon type I 11 beta HSD, however, which has an apparent Km for F of 0.51 +/- 0.04 microM, was present in both the lamina propria and the surface epithelium. Northern blot analysis of rat colonic RNA using a 32P-labeled complementary DNA probe for rat type I 11 beta HSD confirmed the presence of type I 11 beta HSD messenger RNA in intact distal colon mucosa, but failed to detect 11 beta HSD messenger RNA in surface epithelial cells. In conclusion, abundant levels of a high affinity NAD(+)-dependent type 2 11 beta HSD isoform are expressed in both rat and human colon. Colonic type 2 11 beta HSD is kinetically distinct from the low affinity NADP-dependent type I isoform, behaves predominantly as a dehydrogenase, is localized exclusively to the ion-transporting epithelia, and is likely to be the product of a second 11 beta HSD gene. Furthermore, the spatially distinct patterns of expression of these isoforms suggest that in vivo there are two physiologically distinct populations of MR in the colon: the aldosterone selective MR in the epithelium and the nonselective MR in the nonepithelial cells within the lamina propria.