Abstract 17996: Broad Suppression of NADPH Oxidase Activity Exacerbates Ischemia/reperfusion Injury Via Disturbance of Cell Metabolism
NADPH oxidases (Noxs), including Nox2 and Nox4, are major sources of reactive oxidative species (ROS), which play a critical role in mediating myocardial injury in response to ischemia/reperfusion (I/R). The goal of this study was to elucidate the specific functions of Nox2 and Nox4 during I/R using loss of function mouse models. Systemic (s) Nox2 KO, sNox4 KO, and cardiac-specific (c) Nox4 KO mice were subjected to I/R (30min/24h). Both myocardial infarct size/area at risk (MI/AAR), evaluated with TTC staining (32 ± 3*,29 ± 4*, 28 ± 6*, 42 ± 4%, *p< 0.05 vs WT), and O2- production, evaluated with lucigenin assays (433 ± 52*,521 ± 88*, 580 ± 106*, 1250 ± 236 RLU), were significantly smaller in sNox2 KO, sNox4 KO, and cNox4 KO than in wild type (WT) mice, suggesting that both Nox2 and Nox4 play an essential role in mediating oxidative stress and myocardial injury in response to I/R. Unexpectedly, however, the MI/AAR was significantly greater in sNox2 KO+cNox4 KO (DKO) mice and transgenic mice (Tg-DN-Nox) with cardiac specific expression of dominant negative Nox, which suppresses both Nox2 and Nox4, than in WT or single KO mice (58±6*, 65±9*%), despite significantly lower O2- production in DKO and Tg-DN-Nox4 hearts (257 ± 42#, 232±12#, RLU, #p< 0.05 vs single KO) than in sNox2 KO, sNox4 KO and cNox4 KO hearts. Hypoxia inducible factor-1α (HIF-1α) was downregulated in the ischemic area (p<0.05) while peroxisome proliferator-activated receptor α (PPARα) was upregulated (p<0.05) in Tg-DN-Nox compared to in WT mice after I/R. A cross with mice deficient in prolyl hydroxylase 2, an enzyme that hydroxylates HIF-1α, reduced the I/R injury (36±6, 65±10%, p<0.05) and prevented upregulation of PPARα in Tg-DN-Nox mice. A cross with PPARα KO mice also attenuated the I/R injury in Tg-DN-Nox mice (42±4, 61± 9%, p<0.05), accompanied by a significant decrease in triglyceride deposits (19±2, 28± 2mmol /g wet tissue, p<0.05) in the heart. These results suggest that both Nox2 and Nox4 contribute to the increase in ROS and myocardial injury in response to I/R. However, a low level of ROS produced by either Nox2 or Nox4 regulates HIF-1α and PPARα, thereby protecting the heart against I/R and lipotoxicity, suggesting that Noxs also act as physiological sensors for metabolic adaptation in response to I/.
- © 2012 by American Heart Association, Inc.