Endocrine Abstracts

11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) is an NADPH-dependant oxo-reductase located in the sarcoplasmic reticulum (SR) lumen of skeletal muscle. It generates active glucocorticoids to regulate permissive and adaptive metabolism. Hexose-6-phosphate dehydrogenase (H6PD) interacts with 11β-HSD1 to generate an appropriate NADPH/NADP+ ratio to support activity. H6PD depletion impairs SR NADPH generation triggering 11β-HSD1 to assume glucocorticoid inactivating dehydrogenase activity. We tested whether modulating cellular nicotinamide adenine dinucleotide (NAD+) availability (parent molecule of NAD(P)(H)) influenced 11β-HSD1 activity in muscle. We used FK866 to inhibit nicotinamide phospho-ribosyltransferase (NAMPT, rate-limiting enzyme in NAD+ biosynthesis) to deplete NAD(P)(H) in mouse and primary myotubes. 48 h FK866 treatment impaired cellular energetic status, reducing NAD+(>90%), NADP+(>50%) and ATP (>30%) without limiting cell viability. 11β-HSD1 reductase activity was decreased to 30% that of untreated cells (152±18 vs 512±44 pmol/mg protein/h respectively, P<0.005). Furthermore, NADP+-dependent 11β-HSD1 dehydrogenase (glucocorticoid inactivation), as seen in H6PDKO myotubes, is also impaired following NAMPT inhibition. The NAD+ precursor nicotinamide riboside (NR, 0.5 mM), which bypasses NAMPT inhibition, restored NAD+ levels and rescued 11β-HSD1 oxo-reductase activity in wild-type and dehydrogenase activity in H6PDKO myotubes. 11β-HSD1 activity normalised in as little as 30 min after NR treatment. To examine the in vivo relevance, FK866 (10 mg/kg) was administered intraperionteally to wild-type mice for 72 h which depleted NAD+ in skeletal muscle and liver, however, 11β-HSD1 activity only decreased in muscle compared to untreated mice (137±5.55 vs 83.78±3.014 pmol/mg/h, P<0.001), with the liver unaffected. These data suggest that a cross talk exists between the cytosol and the SR which can impact redox status and modulate 11β-HSD1 mediated glucocorticoid regeneration in skeletal muscle. Furthermore, NAMPT inhibition is being studied as a potential anti-cancer therapy and these data reveal hitherto unanticipated effects this therapy may have in a range of tissues.