Physiological roles of 11β-hydroxysteroid dehydrogenase type 1 and hexose-6-phosphate dehydrogenase

Abstract

Inactive cortisone is converted to active cortisol by the reductase activity of 11 beta-hydroxysteroid dehydrogenase type 1, which can thus increase glucocorticoid effects in target tissues. This paper reviews the functional role(s) of 11 beta-hydroxysteroid dehydrogenase type 1 and examines factors influencing its activity. In obese humans, 11 beta-hydroxysteroid dehydrogenase type 1 is relatively highly expressed in adipose tissue. In mice, overexpression of 11 beta-hydroxysteroid dehydrogenase type 1 in adipose or liver causes obesity or insulin resistance, respectively, whereas mice lacking 11 beta-hydroxysteroid dehydrogenase type 1 resist diet-induced obesity and are insulin-sensitive. Thus, 11 beta-hydroxysteroid dehydrogenase type 1 is a promising drug target for treating the metabolic syndrome and type 2 diabetes. Studies in vitro and in mutant mice demonstrate that the reductase activity of 11 beta-hydroxysteroid dehydrogenase type 1 depends on reduced nicotinamide adenine dinucleotide phosphate synthesized within the endoplasmic reticulum by hexose-6-phosphate dehydrogenase. Apparent cortisone reductase deficiency is characterized by androgen excess in women or children and decreased urinary excretion of cortisol metabolites. Although polymorphisms in the genes encoding 11 beta-hydroxysteroid dehydrogenase type 1 and hexose-6-phosphate dehydrogenase were initially implicated in this condition, subsequent reports have not confirmed this. Hexose-6-phosphate dehydrogenase and 11 beta-hydroxysteroid dehydrogenase type 1 may play important roles in the pathogenesis of obesity and metabolic syndrome. Although the importance of polymorphisms in the corresponding genes remains uncertain, rare mutations have not been ruled out.