Nitrite improves Zebrafish Cardiac Regeneration Potentially by Cytoglobin 1

Treatment with nitrite (NO 2 ‒ ) has been shown to have a beneficial effect on ischemia/reperfusion injury via the production of nitric oxide (NO) and modulation of reactive oxygen/nitrogen species (ROS/RNS). Nitrite can be converted to NO through the action of heme globins via a nitrite reductase reaction. The role of NO 2 ‒ and globins has not yet been investigated in the context of heart regeneration. Zebrafish can fully regenerate their hearts following ventricular amputation and were used a model to study the effects of hypoxia and NO 2 ‒ treatment on heart regeneration. We hypothesize that treatment with hypoxia/ NO 2 ‒ will improve cardiac regeneration through increased production of NO or signaling ROS/RNS. We have found that NO 2 ‒ /hypoxia treatment improves the rate of cardiomyocyte proliferation and improves neovascularization compared to hypoxia alone five days post amputation (dpa). Preceding these events, we observe an increase in thrombocytes (1 dpa) and neutrophils (3 dpa) migration to the injured area and a decrease in the blood clot size, suggesting that NO 2 ‒ treatment is able to modulate the immune response to improve healing following injury. Zebrafish Cytoglobin 1 (Cygb1) is a globin that may mediate the cardiac regenerative response to NO 2 ‒ . Our data show that Cygb1 is expressed in the epicardium (a tissue that is known to drive the regeneration process) and its expression is increased following cardiac injury. Cygb1 may be mediating this response via its fast nitrite reductase rate (28.6 ± 3.1 M (-1) s(-1)) in its deoxy state or oxy-Cygb1 may react with NO 2 - to produce RNS, modulating the immune response via ROS/RNS signaling. Given the extremely low Cygb1 oxygen P50 (0.277 torr), we hypothesize that it is the latter, even in the context of the hypoxic heart. Our current research aims to identify the mechanism by which nitrite treatment modulates the immune response in the healing heart and determine if Cygb1 expression is necessary and/or sufficient for cardiac regeneration.