Heme oxidation of NO-receptor soluble guanylyl cyclase is an important contributor to cerebrovascular and cognitive dysfunctions
Authors: Awad Radwa , Beeghly Christopher , Barichello Tatiana , Giridharan Vijayasree V. , Martin Emil , Sharina Iraida 
Published: May 2024

Introduction: Decreased cerebral blood flow (CBF) is one of the major hemodynamic alterations leading to neurodegeneration and age-related cognitive decline. Nitric Oxide (NO)-dependent vasomotor reactivity is central in regulating cerebrovascular hemodynamics and adequate brain blood perfusion. NO receptor Soluble Guanylyl Cyclase (sGC) is the primary mediator of NO-dependent vasodilation. Oxidative stress, often persisting in diseased vasculature, renders sGC insensitive to NO and impairs the NO signaling. The objective of our study was to investigate the role of sGC oxidation in regulation CBF and brain function. Hypothesis: Oxidative stress disrupts NO/cGMP signaling in brain by decreasing sGC activity via oxidation of sGC heme. Approach: To assess causal effect of sGC oxidation on NO signaling function we administered ODQ, a sGC-specific heme oxidizing agent, to simulate long-term effect of sGC oxidation in cerebral vasculature. Two groups of young wild-type male and female mice (4 months old C57BL/6) were treated intraperitoneally (IP) twice a week for one month with ODQ (20 mg/kg) or a solvent as control. Changes in cerebrovascular reactivity and memory function were assessed and compared in treated and control groups. Using a non-invasive pulsed Doppler ultrasound-based system we assessed the changes in blood flow velocity (PVF, % of baseline) in the mouse middle cerebral artery (MCA) of male and female groups. MCA vasodilation was induced by bolus IP injection of NO-donor sodium nitroprusside (SNP) or BAY 58-2667, an allosteric NO-independent sGC activator. Memory function was assessed by the Novel Object Recognition Task (NORT, RI, recognition index) in all experimental groups. Western blotting and densitometry assessed the expression of major sGC subunits (α1, α2 and β1) in cleared brain lysates from ODQ-treated and control groups. Results: We observed a significantly blunted vasodilative response to SNP (1 mg/kg) in ODQ-treated mice vs controls of both genders (PVF, max response at 2 min post-injection, males 73.9 ± 10.4% (n=7/7) vs 58.5 ± 8.6 %, p=0.01; females (n=6/6) 77.4 ± 10.6 % vs 61.9 ± 5.4 %, p=0.01). Changes in response to NO-donor were more pronounced in males than females. The difference in BAY 58-2667 response between ODQ-treated and control groups was not statistically significant. ODQ significantly reduced the long-term memory in males but not female, according to NORT (RI, males (n=7/7) 0.58 ± 0.13 vs 0.69 ± 0.05; p=0.01; females (n=6/6) ODQ 0.59 ± 0.17 vs 0.73 ± 0.1, p=0.13). No statistically significant difference in expression of sGC subunits between control and ODQ-treated (n= 4/4) of male and female groups was determined. Conclusions: ODQ treatment significantly impairs vasodilation response to NO-donor but not to NO-independent sGC activator in mice MCA. ODQ treatment negatively affects long-term memory function in male, but not female mice. ODQ treatment does not significantly affect the expression of sGC subunits. Together our data suggest that the oxidation of sGC heme moiety impairs the regulation of cerebral blood flow of both genders and impairs long-term memory function gender-specifically in young mice. This research was supported by National Institute of Health grants RAG071999A (Iraida Sharina), HL139838, and American Heart Association 23TPA1070711 (Emil Martin). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.