Cell-specific effects of Nox2 on the acute and chronic response to myocardial infarction

BACKGROUND: Increased reactive oxygen species (ROS) production is involved in the process of adverse cardiac remodeling and development of heart failure after myocardial infarction (MI). NADPH oxidase-2 (Nox2) is a major ROS source within the heart and its activity increases after MI. Furthermore, genetic deletion of Nox2 is protective against post-MI cardiac remodeling. Nox2 levels may increase both in cardiomyocytes and endothelial cells and recent studies indicate cell-specific effects of Nox2, but it is not known which of these cell types is important in post-MI remodeling. METHODS AND RESULTS: We have generated transgenic mouse models in which Nox2 expression is targeted either to cardiomyocytes (cardio-Nox2TG) or endothelial cells (endo-Nox2TG). We here studied the response of cardio-Nox2TG mice, endo-Nox2TG mice and matched wild-type littermates (WT) to MI induced by permanent left coronary artery ligation up to 4weeks. Initial infarct size assessed by magnetic resonance imaging (MRI) and cardiac dysfunction were similar among groups. Cardiomyocyte hypertrophy and interstitial fibrosis were augmented in cardio-Nox2TG compared to WT after MI and post-MI survival tended to be worse whereas endo-Nox2TG mice showed no significant difference compared to WT. CONCLUSIONS: These results indicate that cardiomyocyte rather than endothelial cell Nox2 may have the more important role in post-MI remodeling

Cardioprotective effect of the mitochondrial unfolded protein response during chronic pressure overload

Background The mitochondrial unfolded protein response (UPRmt) is activated when misfolded proteins accumulate within mitochondria and leads to increased expression of mitochondrial chaperones and proteases to maintain protein quality and mitochondrial function. Cardiac mitochondria are essential for contractile function and regulation of cell viability, while mitochondrial dysfunction characterizes heart failure. The role of the UPRmt in the heart is unclear. Objectives The purpose of this study was to: 1) identify conditions that activate the UPRmt in the heart; and 2) study the relationship among the UPRmt, mitochondrial function, and cardiac contractile function. Methods Cultured cardiac myocytes were subjected to different stresses in vitro. Mice were subjected to chronic pressure overload. Tissues and blood biomarkers were studied in patients with aortic stenosis. Results Diverse neurohumoral or mitochondrial stresses transiently induced the UPRmt in cultured cardiomyocytes. The UPRmt was also induced in the hearts of mice subjected to chronic hemodynamic overload. Boosting the UPRmt with nicotinamide riboside (which augments NAD+ pools) in cardiomyocytes in vitro or hearts in vivo significantly mitigated the reductions in mitochondrial oxygen consumption induced by these stresses. In mice subjected to pressure overload, nicotinamide riboside reduced cardiomyocyte death and contractile dysfunction. Myocardial tissue from patients with aortic stenosis also showed evidence of UPRmt activation, which correlated with reduced tissue cardiomyocyte death and fibrosis and lower plasma levels of biomarkers of cardiac damage (high-sensitivity troponin T) and dysfunction (N-terminal pro–B-type natriuretic peptide). Conclusions These results identify the induction of the UPRmt in the mammalian (including human) heart exposed to pathological stresses. Enhancement of the UPRmt ameliorates mitochondrial and contractile dysfunction, suggesting that it may serve an important protective role in the stressed heart

Distinct regulatory effects of myeloid cell and endothelial cell Nox2 on blood pressure

Background -Hypertension due to increased renin angiotensin system (RAS) activation is associated with elevated reactive oxygen species (ROS) production. Previous studies implicate NADPH oxidase (Nox) proteins as important ROS sources during RAS activation, with different Nox isoforms being potentially involved. Among these, Nox2 is expressed in multiple cell types including endothelial cells, fibroblasts, immune cells and microglia. Blood pressure (BP) is regulated at central nervous system, renal and vascular levels but the cell-specific role of Nox2 in BP regulation is unknown. Methods -We generated a novel mouse model with a Floxed Nox2 gene and used Tie2-Cre, LysM Cre or Cdh5-CreERT2 driver lines to develop cell-specific models of Nox2 perturbation to investigate its role in BP regulation. Results -Unexpectedly, Nox2 deletion in myeloid but not endothelial cells resulted in a significant reduction in basal BP. Tie2-CreNox2 knockout (KO) mice (in which Nox2 was deficient in both endothelial cells and myeloid cells) and LysM Cre Nox2KO mice (in which Nox2 was deficient in myeloid cells) both had significantly lower BP than littermate controls whereas basal BP was unaltered in Cdh5-CreERT2 Nox2 KO mice (in which Nox2 is deficient only in endothelial cells). The lower BP was attributable to an increased NO bioavailability which dynamically dilated resistance vessels in vivo under basal conditions, without change in renal function. Myeloid-specific Nox2 deletion had no effect on angiotensin II-induced hypertension which, however, was blunted in Tie2-CreNox2KO mice along with preservation of endothelium-dependent relaxation during angiotensin II stimulation. Conclusions -We identify a hitherto unrecognized modulation of basal BP by myeloid cell Nox2 whereas endothelial cell Nox2 regulates angiotensin II-induced hypertension. These results identify distinct cell-specific roles for Nox2 in BP regulation

Nox2 in regulatory T cells promotes angiotensin II–induced cardiovascular remodeling

The superoxide-generating enzyme Nox2 contributes to hypertension and cardiovascular remodeling triggered by activation of the renin-angiotensin system. Multiple Nox2-expressing cells are implicated in angiotensin II (AngII)-induced pathophysiology, but the importance of Nox2 in leukocyte subsets is poorly understood. Here, we investigated the role of Nox2 in T cells, particularly Tregs. Mice globally deficient in Nox2 displayed increased numbers of Tregs in the heart at baseline whereas AngII-induced T-effector cell (Teffs) infiltration was inhibited. To investigate the role of Treg Nox2, we generated a mouse line with CD4-targeted Nox2 deficiency (Nox2fl/flCD4Cre+). These animals showed inhibition of AngII-induced hypertension and cardiac remodeling related to increased tissue-resident Tregs and reduction in infiltrating Teffs, including Th17 cells. The protection in Nox2fl/flCD4Cre+ mice was reversed by anti-CD25 Ab-depletion of Tregs. Mechanistically, Nox2-/y Tregs showed higher in vitro suppression of Teffs proliferation than WT Tregs, increased nuclear levels of FoxP3 and NF-κB, and enhanced transcription of CD25, CD39, and CD73. Adoptive transfer of Tregs confirmed that Nox2-deficient cells had greater inhibitory effects on AngII-induced heart remodeling than WT cells. These results identify a previously unrecognized role of Nox2 in modulating suppression of Tregs, which acts to enhance hypertension and cardiac remodeling

Bone marrow transplantation modulates tissue macrophage phenotype and enhances cardiac recovery after subsequent acute myocardial infarction

AbstractBackgroundBone marrow transplantation (BMT) is commonly used in experimental studies to investigate the contribution of BM-derived circulating cells to different disease processes. During studies investigating the cardiac response to acute myocardial infarction (MI) induced by permanent coronary ligation in mice that had previously undergone BMT, we found that BMT itself affects the remodelling response.Methods and resultsCompared to matched naive mice, animals that had previously undergone BMT developed significantly less post-MI adverse remodelling, infarct thinning and contractile dysfunction as assessed by serial magnetic resonance imaging. Cardiac rupture in male mice was prevented. Histological analysis showed that the infarcts of mice that had undergone BMT had a significantly higher number of inflammatory cells, surviving cardiomyocytes and neovessels than control mice, as well as evidence of significant haemosiderin deposition. Flow cytometric and histological analyses demonstrated a higher number of alternatively activated (M2) macrophages in myocardium of the BMT group compared to control animals even before MI, and this increased further in the infarcts of the BMT mice after MI.ConclusionsThe process of BMT itself substantially alters tissue macrophage phenotype and the subsequent response to acute MI. An increase in alternatively activated macrophages in this setting appears to enhance cardiac recovery after MI