Abstract P498: Redox Regulation of Vascular Smooth Muscle cGMP Signaling and Blood Pressure by Cytochrome B5 Reductase 3

Abstract

Oxidized soluble guanylate cyclase (sGC) heme iron (Fe 3+ ) is desensitized to nitric oxide (NO) and attenuates cGMP production needed for downstream activation of PKG-dependent signaling and vasodilation. While reactive oxygen species drive oxidation of sGC heme iron, the basic mechanism(s) governing sGC heme iron recycling to its NO-sensitive, reduced state (Fe 2+ ), are unknown. Here we report cytochrome b5 reductase 3 (Cyb5R3), also known as methemoglobin reductase, as a novel sGC heme iron reductase and regulator of cGMP production in vascular smooth muscle cells (VSMCs). Oxidant challenge studies demonstrate that VSMCs have an intrinsic ability to reduce oxidized sGC heme iron and form protein-protein complexes between Cyb5R3 and oxidized sGC. Genetic knockdown and pharmacological inhibition in VSMCs reveal Cyb5R3 expression and activity is critical for NO-stimulated cGMP production and vasodilation. Mechanistically, Cyb5R3 directly reduces oxidized sGC for NO sensitization assessed by biochemical, cellular, and ex vivo assays. Furthermore, generation of a smooth muscle specific Cyb5R3 knockout shows increased blood pressure and impaired endothelial dependent vasodilation. Together, these findings uncover new insights into NO-sGC-cGMP signaling and reveal Cyb5R3 as the first identified physiological sGC heme iron reductase in VSMC. The co-expression of Cyb5R3 and sGC in multiple cell types may unveil a fundamental mechanistic partnership that is critical in numerous physiological and pathophysiological processes.