Abstract 14083: Physiological and Pathological Functions of Nox2 and Nox4 in Myocardial Ischemia/Reperfusion Injury
INTRODUCTION: NAD(P)H oxidases (Noxes), including Nox2 and Nox4, are major sources of oxidative stress (OS) and critically affect growth/death of cardiomyocytes (CMs) in response to stress, such as pressure overload. The role of Nox2 and Nox4 in mediating OS and myocardial injury in response to ischemia/reperfusion (I/R) is poorly understood.
PURPOSE: To elucidate the isoform-specific functions of Nox2 and Nox4 during I/R in vivo.
METHODS AND RESULTS: Wild type (WT), systemic Nox2 KO (Nox2-/-), and cardiac specific Nox4 KO (cNox4-/-) mice were subjected to ischemia (30 min)/reperfusion (24 h). Myocardial infarct size/area at risk (MI/AAR), as evaluated with TTC staining, was significantly smaller in Nox2-/- and cNox4-/- than in WT mice (32 ± 3.1* and 28.0 ± 6.1* vs 40.3 ± 8.3%, *p < 0.05). O2- production, as evaluated with lucigenin-chemiluminescence assays, was significantly lower in Nox2-/- and cNox4-/- hearts than in WT hearts (433 ± 52*, 580 ± 106* vs 1250 ± 236 RLU, *p < 0.05). I/R experiments were also repeated with combined Nox2 and Nox4 KO (double KO: DKO) mice and DN-Nox transgenic (DN-Tg) mice. The MI/AAR was significantly greater in DKO and DN-Tg mice than in WT or single KO mice (58.0 ± 6.3* and 65.2±8.5*%, *p < 0.05 vs WT or either single KO) despite the fact that O2- production was significantly lower in the DKO and DN-Tg hearts (257 ± 42* and 232±12* RLU, *p < 0.05 vs either single KO) than in Nox2-/- or cNox4-/- hearts. These results suggest that marked suppression of OS by combined downregulation of Nox2 and Nox4 may exacerbate I/R injury. Since Noxes can act as oxygen sensors, we evaluated expression of hypoxia inducible factor-1alpha (HIF-1α). HIF-1α expression in the ischemic area was lower in DKO and DN-Tg mice than in WT, Nox2-/- or cNox4-/- mice. A genetic cross between DN-Tg and mice lacking prolyl hydroxylase 2, an enzyme mediating hydroxylation and downregulation of HIF-1α, partially rescued I/R injury in DN-Tg mice (35.8 ± 5.9 vs 65.2 ± 10.3%, p<0.05).
CONCLUSIONS: Both Nox2 and Nox4 mediate increases in OS and myocardial injury in response to I/R. However, combined downregulation of Nox2 and Nox4 induces marked downregulation of ROS, which in turn exacerbates I/R injury, possibly through downregulation of HIF-1α and impairment of hypoxic adaptation.
- © 2011 by American Heart Association, Inc.