Growing evidence indicates that chronic and acute overproduction of reactive oxygen species (ROS) under pathophysiologic conditions is integral in the development of cardiovascular diseases (CVD). These ROS can be released from nicotinamide adenine dinucleotide (phosphate) oxidase, xanthine oxidase, lipoxygenase, mitochondria, or the uncoupling of nitric oxide synthase in vascular cells. ROS mediate various signaling pathways that underlie vascular inflammation in atherogenesis: from the initiation of fatty streak development through lesion progress to ultimate plaque rupture. Various animal models of oxidative stress support the notion that ROS have a causal role in atherosclerosis and other cardiovascular diseases. Human investigations also support the oxidative stress hypothesis of atherosclerosis. Oxidative stress is the unifying mechanism for many CVD risk factors, which additionally supports its central role in CVD. Despite the demonstrated role of antioxidants in cellular and animal studies, the ineffectiveness of antioxidants in reducing cardiovascular death and morbidity in clinical trials has led many investigators to question the importance of oxidative stress in human atherosclerosis. Others have argued that the prime factor for the mixed outcomes from using antioxidants to prevent CVD may be the lack of specific and sensitive biomarkers by which to assess the oxidative stress phenotypes underlying CVD. A better understanding of the complexity of cellular redox reactions, development of a new class of antioxidants targeted to specific subcellular locales, and the phenotype-genotype linkage analysis for oxidative stress will likely be avenues for future research in this area as we move toward the broader use of pharmacological and regenerative therapies in the treatment and prevention of CVD.

Increased production of reactive oxygen species in mitochondria, accumulation of mitochondrial DNA damage, and progressive respiratory chain dysfunction are associated with atherosclerosis or cardiomyopathy in human investigations and animal models of oxidative stress. Moreover, major precursors of atherosclerosis—hypercholesterolemia, hyperglycemia, hypertriglyceridemia, and even the process of aging—all induce mitochondrial dysfunction. Chronic overproduction of mitochondrial reactive oxygen species leads to destruction of pancreatic β-cells, increased oxidation of low-density lipoprotein and dysfunction of endothelial cells—factors that promote atherosclerosis. An additional mechanism by which impaired mitochondrial integrity predisposes to clinical manifestations of vascular diseases relates to vascular cell growth. Mitochondrial function is required for normal vascular cell growth and function. Mitochondrial dysfunction can result in apoptosis, favoring plaque rupture. Subclinical episodes of plaque rupture accelerate the progression of hemodynamically significant atherosclerotic lesions. Flow-limiting plaque rupture can result in myocardial infarction, stroke, and ischemic/reperfusion damage. Much of what is known on reactive oxygen species generation and modulation comes from studies in cultured cells and animal models. In this review, we have focused on linking this large body of literature to the clinical syndromes that predispose humans to atherosclerosis and its complications.

Induction of molecular chaperones is the characteristic protective response to environmental stress, and is regulated by a transcriptional program that depends on heat shock factor 1 (HSF1), which is normally under negative regulatory control by molecular chaperones Hsp70 and Hsp90. In metazoan species, the chaperone system also provides protection against apoptosis. We demonstrate that the dual function co‐chaperone/ubiquitin ligase CHIP (C‐terminus of Hsp70‐interacting protein) regulates activation of the stress‐chaperone response through induced trimerization and transcriptional activation of HSF1, and is required for protection against stress‐induced apoptosis in murine fibroblasts. The consequences of this function are demonstrated by the phenotype of mice lacking CHIP, which develop normally but are temperature‐sensitive and develop apoptosis in multiple organs after environmental challenge. CHIP exerts a central and unique role in tuning the response to stress at multiple levels by regulation of protein quality control and transcriptional activation of stress response signaling.

Thrombin is a potent vascular smooth muscle cell (VSMC) mitogen. Because recent evidence implicates reactive oxygen intermediates (ROI) in VSMC proliferation in general and atherogenesis in particular, we investigated whether ROI generation is necessary for thrombin-induced mitogenesis. Treatment of human aortic smooth muscle cells with thrombin increased DNA synthesis, an effect that was antagonized by diphenyleneiodonium but not by other inhibitors of cellular oxidase systems. This effect of thrombin was accompanied by increased O-2 and H2O2 generation and NADH/NADPH consumption. ROI generation in response to thrombin pretreatment could also be blocked by diphenyleneiodonium, suggesting that the NAD(P)H oxidase was necessary for ROI generation and thrombin-induced mitogenesis. Because of observed differences between the VSMC and neutrophil oxidase, we examined whether the cytosolic components of the phagocytic NAD(P)H oxidase were present in VSMC. p47(phox) and Rac2 were present in VSMC. Furthermore, thrombin increased expression of p47(phox) and Rac2 and stimulated their translocation to the cell membrane. We examined whether p47(phox) might be similarly regulated in vivo in a rat aorta balloon injury model and found that p47(phox) protein was increased after injury. Immunocytochemistry localized expression of p47(phox) to the neointima and media of injured arteries. Our data demonstrate that generation of O-2 and H2O2 is required for thrombin-mediated mitogenesis in VSMC and that p47(phox) is regulated by thrombin in vitro and is associated with vascular lesion formation in vivo.

Objective— Reactive oxygen species (ROS) integrate cellular signaling pathways involved in aortic smooth muscle cell (SMC) proliferation and migration associated with atherosclerosis. However, the effect of subcellular localization of ROS on SMC mitogenic signaling is not yet fully understood. Methods and Results— We used superoxide dismutase (SOD)–deficient mouse aortic SMCs to address the role of subcellular ROS localization on SMC phenotype and mitogenic signaling. Compared with wild-type, a 54% decrease in total SOD activity (≈50% decrease in SOD1 protein levels) and a 42% reduction in SOD2 activity (≈50% decrease in SOD2 protein levels) were observed in SOD1 ^+/− and SOD2 ^+/− SMCs, respectively. Consistent with this, basal and thrombin-induced superoxide levels increased in these SMCs. SOD1 ^+/− and SOD2 ^+/− SMCs exhibit increased basal proliferation and enhanced [ ³ H]-thymidine and [ ³ H]-leucine incorporation in basal and thrombin-stimulated conditions. Our results indicate preferential activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinases in SOD1 ^+/− and janus kinase/signal transducer and activator of transcriptase (JAK/STAT) pathway in SOD2 ^+/− SMCs. Pharmacological inhibitors of ERK1/2 p38 and JAK2 confirm the SOD genotype-dependent SMC proliferation. Conclusions— Our results suggest that SOD1 and SOD2 regulate SMC quiescence by suppressing divergent mitogenic signaling pathways, and dysregulation of these enzymes under pathophysiological conditions may lead to SMC hyperplasia and hypertrophy.