NAD+ and the metabolism of cellular glucocorticoids in Endoplasmic Reticulum

Abstract

Nicotinamide Adenine Dinucleotide (NAD+) has a primary role in cellular metabolism and energy production as a cofactor for a set of enzymatic reactions. The endoplasmic reticulum (ER) lumen enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) obtains NADPH from hexose-6-phosphate dehydrogenase to reduce cortisone to the active glucocorticoid cortisol. Cells depleted in NAD+ (parent molecule of NADPH) have impaired 11β-HSD1 activity, which can be rapidly rescued with supplementation of the NAD+ precursor nicotinamide riboside (NR). This suggests the existence of an ER-specific pathway to NAD(P)(H). Here we depleted cellular NAD+ using FK866 (NAMPT inhibitor) and poly-ADP-ribose assisted protein localization assay to study ER-specific NAD+ metabolism using 11β-HSD1 as a readout. To assess the generalizability of our results, we examined the enzyme activity in multiple cell types such as liver, muscle, dermal fibroblast, and human kidney. Results show preliminary evidence that depleting ER NAD+ can impair NADPH-dependent 11β-HSD1 activity. Repleting NAD+ availability with NR treatment significantly rescued the enzyme activity. Further experiments are required to thoroughly evaluate the potential of a dynamic NAD(P)(H) pathway in the ER compartment.