NADH cytochrome b5 oxidoreductase (Ncb5or) is a ferric reductase widely expressed in animal cells. Ncb5or deficiency results in altered iron metabolism, mitochondrial dysfunction and proliferation, and increased oxidative and endoplasmic reticulum (ER) stress. Ncb5or null (KO) mice present early-onset lean diabetes, ataxia and hearing loss. Similar clinical manifestations are observed in patients with type 2 Wolfram Syndrome that is caused by mutations in CISD2 (CDGSH iron-sulfur domains 2). Its [2Fe-2S] iron-sulfur-cluster (ISC) is redox sensitive and becomes labile when oxidized. Because both proteins are associated with ER, Ncb5or may function as a CISD2 reductase for ISC redox regulation. This hypothesis appears to be supported by our recent data. When fed a chow admixture with 400 ppm pioglitazone, a FDA-approved drug capable of stabilizing FeII-ISC in vitro, Ncb5or KO mice exhibit a 4-week delay in developing overt diabetes, specifically, at age 11 weeks vs. 7 weeks under chow. Pioglitazone results in a significant increase in the content of FeII-ISC CISD2 among the total in the liver of prediabetic KO mice when compared to wild type (WT) counterparts, namely, a KO/WT ratio of 0.6 post pioglitazone vs. 0.3 under chow (by native gel electrophoresis and immuno-blot analyses with antibodies that preferentially recognize CISD2 containing FeII-ISC). Pioglitazone also reduces oxidative and ER stress response in the liver of KO mice (qRT-PCR of MT’s, ATF3, and XBP1-spliced transcripts) and attenuates mitochondrial dysfunction in KO mouse embryonic fibroblasts (extracellular flux analysis). However, iron dyshomeostasis, as indicated by transcript profiles of iron genes in KO cells and splenomegaly in KO mice, is not rescued by pioglitazone. Our findings suggest that Ncb5or maintains the redox status of ISC in CISD2 and that, through stabilizing ferrous ISC, pioglitazone can partially rescue defects in Ncb5or-null cells. Studies are underway to characterize the Ncb5or-CISD2 axis in beta-cells.
H. Zhu: None. A. Muto: None. T. Home: None. W. Wang: None. F. Urano: Board Member; Self; Healthbeat. Research Support; Self; Aetas, Amylyx, JDRF, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health. Stock/Shareholder; Self; CytRx. Other Relationship; Self; Novus Biologicals.
University of Kansas Medical Center Research Institute