7-Oxysterols Modulate Glucocorticoid Activity in Adipocytes through Competition for 11β-Hydroxysteroid Dehydrogenase Type

Abstract

Obesity is associated with an increased risk of diabetes type 2, dyslipidemia, and atherosclerosis. These cardiovascular and metabolic abnormalities are exacerbated by excessive dietary fat, particularly cholesterol and its metabolites. High adipose tissue glucocorticoid levels, generated by the intracellular enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), are also implicated in the pathogenesis of obesity, metabolic syndrome, and atherosclerosis. 11β-HSD1 also interconverts the atherogenic oxysterols 7-ketocholesterol (7KC) and 7β-hydroxycholesterol (7β-HC). Here, we report that 11β-HSD1 catalyzes the reduction of 7KC to 7β-HC in mature 3T3-L1 and 3T3-F442A adipocytes, leading to cellular accumulation of 7β-HC. Approximately 73% of added 7KC was reduced to 7β-HC within 24 h; this conversion was prevented by selective inhibition of 11β-HSD1. Oxysterol and glucocorticoid conversion by 11β-HSD1 was competitive and occurred with a physiologically relevant IC50 range of 450 nm for 7KC inhibition of glucocorticoid metabolism. Working as an inhibitor of 11β-reductase activity, 7KC decreased the regeneration of active glucocorticoid and limited the process of differentiation of 3T3-L1 preadipocytes. 7KC and 7β-HC did not activate liver X receptor in a transactivation assay, nor did they display intrinsic activation of the glucocorticoid receptor. However, when coincubated with glucocorticoid (10 nm), 7KC repressed, and 7β-HC enhanced, glucocorticoid receptor transcriptional activity. The effect of 7-oxysterols resulted from the modulation of 11β-HSD1 reaction direction, and could be ameliorated by overexpression of hexose 6-phosphate dehydrogenase, which supplies reduced nicotinamide adenine dinucleotide phosphate to 11β-HSD1. Thus, the activity and reaction direction of adipose 11β-HSD1 is altered under conditions of oxysterol excess, and could impact upon the pathophysiology of obesity and its complications.