Abstract P146: Cytochrome B5 Reductase (CYB5R3) Function in Smooth Muscle Cells and Blood Pressure Regulation

Abstract

Hypertension (HTN) is a major risk factor for cardiovascular-related morbidity and mortality. Dysregulation of nitric oxide (NO) signaling has been found in both human and mouse studies to impact the renin-angiotensin-aldosterone system (RAAS) and contribute to the vascular dysfunction leading to HTN. NO signals via soluble guanylyl cyclase (sGC) to generate cyclic guanosine monophosphate (cGMP) and downstream activation of protein kinase G (PKG) to induce vasodilation. However, the sGC heme iron needs to be in the reduced (Fe 2+ ) state for NO to bind as oxidized (Fe 3+ ) sGC is insensitive to NO signaling. We found that NADH cytochrome b5 reductase 3 (CYB5R3) is a sGC heme reductase that maintains sGC heme iron in its reduced state. Transient knockdown and pharmacological inhibition of CYB5R3 in smooth muscle cells (SMCs) blocks NO-mediated cGMP production and aortic relaxation. Taken together, we hypothesized that SMC CYB5R3 was important in blood pressure regulation. We created tamoxifen-inducible SMC-specific CYB5R3 knockout mice (SMC CYB5R3 KO) and found that they (n=8) had an ~5 mmHg increase in mean arterial blood pressure at baseline as compared to SMC CYB5R3 WT mice (n=9). In response to Angiotensin II (Ang II)-induced hypertension, SMC CYB5R3 KO mice (n=5) exhibited an ~14 mmHg increase in blood pressure and a significantly reduced heart rate as compared to SMC CYB5R3 WT mice (n=5). Lastly, ex vivo two-pin wire myography of Ang II-induced hypertensive SMC CYB5R3 KO (n= 6) mesenteric arteries treated with NO-independent sGC activator Bay 58-2667 showed increased vasodilation as compared to SMC CYB5R3 WT mice (n=10); Bay 58-2667 treatment at baseline showed no difference between groups. We predict that CYB5R3 regulation of SMC sGC heme iron redox state influences blood pressure in a NO-dependent manner. To test this, we will perform an intervention study where we will measure blood pressure in Ang II-induced hypertensive SMC CYB5R3 WT and SMC CYB5R3 KO mice treated with Bay 41-2272, a NO and heme dependent sGC stimulator, and Bay 58-2667. Also, we will assess the role of SMC CYB5R3 in protection against Ang II-induced vessel fibrosis and SMC dysfunction.