Cerebral Vascular Redox Regulation in Stroke

Abstract: African Americans (AA) show disparities in ischemic stroke when compared to Euro-Americans, with 2x higher stroke prevalence and mortality, 4x higher incidence of ischemic stroke during middle age, as well as greater stroke disability, more post-stroke complications, and slower recovery. To reduce stroke morbidity and mortality and advance therapies to better treat AA with ischemic stroke, an improvement in our understanding of the basic pathways that regulate oxidative stress damage and cerebral blood flow is needed. Preclinical and clinical evidence suggest that redox imbalance occurs in ischemic stroke, with increased oxidant formation and suppressed nitric oxide (NO) signaling, which may be more compromised in the AA population. However, the mechanisms that contribute to redox imbalance in AA with ischemic stroke remain a major gap in our knowledge. We have identified that a high frequency variant in cytochrome b5 reductase 3 (CYB5R3) exists in the AA population (23% minor allele frequency), compared to less than 1% in whites. This CYB5R3 missense variant confers a threonine to serine amino acid change (T117S) leading to reduced CYB5R3 activity. To test the importance of this variant in cerebral vascular function following ischemic stroke, we generated a novel CYB5R3 T117S murine model. Preliminary studies show that CYB5R3 T117S mice develop significantly greater infarct volume, suggesting that CYB5R3 T117S mice are more vulnerable to oxidative stress. Mechanistically, our pilot studies suggest CYB5R3 T117S serves as a redox regulator of soluble guanylyl cyclase (sGC), the nitric oxide receptor. Based on these preliminary data, we hypothesize that CYB5R3 T117S causes a redox imbalance by impairing sGC heme redox regulation leading to exacerbated cerebral blood flow deficiency and ischemic stroke. Three aims are proposed to test this hypothesis: Aim 1) define whether impaired cerebrovascular function in Cyb5R3 T117S and SMC Cyb5R3 KO mice causes greater brain infarct and worsened stroke outcomes, Aim 2) determine whether NO-sGC-cGMP-mediated cerebral blood vessel damage causes dysregulation of cerebral arterial relaxation in Cyb5R3 T117S mice and SMC Cyb5R3 KO mice after ischemic stroke, and Aim 3) determine whether sGC activator and/or sGC stimulator therapy reduces stroke damage in Cyb5R3 T117S and SMC Cyb5R3 KO mice. Completion of these studies will fill a major gap in our understanding of the role of CYB5R3 T117S in the pathogenesis of ischemic stroke, potentially developing new precision strategies and therapies for a large proportion of AA who suffer from ischemic stroke.