OR18-4 Increased expression of NRK2 links an NAD+ salvage pathway to the metabolic and redox status of the sarcoplasmic reticulum in skeletal muscle of H6PDKO mice

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: OR18-Diabetes-Associated Genes & Pathways
Sunday, June 16, 2013: 11:15 AM-12:45 PM
Presentation Start Time: 12:00 PM
Room 304 (Moscone Center)
Agnieszka Ewa Zielinska*1, Craig Doig2 and Gareth Geoffrey Lavery2
1University of Birmingham, Birmingham, United Kingdom, 2University of Birmingham, United Kingdom
Hexose-6-phosphate dehydrogenase (H6PDH) is critical in setting the metabolic and redox status of the endo/sarco-plasmic reticulum (ER/SR) lumen, establishing an NADPH/NADP+ ratio sufficient to drive 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1)-mediated glucocorticoid (GC) activation. H6PDH knockout (H6PDKO) mice develop a severe myopathy, low insulin with increased basal and insulin stimulated glucose uptake, a 10-fold elevation in muscle glycogen content and fasting hypoglycaemia. Microarray analysis identified a large set of differentially expressed genes enriched for networks of the ER stress and the unfolded protein response pathways, most severely in type IIb fibers, but with time affecting type I fibers as well. H6PDH/11β-HSD1 double KO mice recapitulate H6PDKO mice highlighting an 11β-HSD1 and GC independent role for H6PDH in skeletal muscle homeostasis. To identify factors interacting with H6PDH and initiating myopathy, we screened the mRNA expression of ER stress and an additional panel of the most differentially regulated genes previously identified in H6PDKO muscle by real-time PCR in 3 and 8 week old mice. Unlike at 8 weeks, at 3 weeks we did not detect increased expression of ER stress genes (BIP, calreticulin, HSP70B1 or DDIT3) however, of a panel of additional genes examined only 4 (SMOX1, PYCR1, EEF2, MHY2) were marginally but significantly differentially expressed, though not to the same degree as at 8 weeks. The most striking and highly significant difference observed was for the increased expression of nicotinamide riboside kinase (NRK2 also known as MIBP or  ITGB1BP3), which at 3 weeks was elevated 85-fold and at 8 weeks elevated 12-fold compared to control. NRK2 expression is restricted to skeletal and cardiac muscle and is 5-fold enriched in type IIb rich tibialis anterior compared to type I fibre rich soleus, correlating with the fiber type most severely affected and suggesting it as an early and initiating factor. NRK2 is involved in NAD+ salvage and biosynthesis and when over-expressed in C2C12 muscle cells leads to suppression of terminal differentiation. NAD+ is a factor central to metabolism and activation of the sirtuins. We suggest a mechanism where the NAD+ salvage pathway in muscle is responding to changes in the SR NADPH/NADP+ ratio due to H6PDH deficiency, affecting differentiation and influencing changes in metabolism, showing that this link may have important relevance to metabolic control of skeletal muscle.

Nothing to Disclose: AEZ, CD, GGL

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: BBSRC