Mitochondrial oxidative stress in aortic stiffening with age: the role of smooth muscle cell function.

OBJECTIVE: Age-related aortic stiffness is an independent risk factor for cardiovascular diseases. Although oxidative stress is implicated in aortic stiffness, the underlying molecular mechanisms remain unelucidated. Here, we examined the source of oxidative stress in aging and its effect on smooth muscle cell (SMC) function and aortic compliance using mutant mouse models. METHODS AND RESULTS: Pulse wave velocity, determined using Doppler, increased with age in superoxide dismutase 2 (SOD2)+/- but not in wild-type, p47phox-/- and SOD1+/- mice. Echocardiography showed impaired cardiac function in these mice. Increased collagen I expression, impaired elastic lamellae integrity, and increased medial SMC apoptosis were observed in the aortic wall of aged SOD2+/- versus wild-type (16-month-old) mice. Aortic SMCs from aged SOD2+/- mice showed increased collagen I and decreased elastin expression, increased matrix metalloproteinase-2 expression and activity, and increased sensitivity to staurosporine-induced apoptosis versus aged wild-type and young (4-month-old) SOD2+/- mice. Smooth muscle α-actin levels were increased with age in SOD2+/- versus wild-type SMCs. Aged SOD2+/- SMCs had attenuated insulin-like growth factor-1-induced Akt and Forkhead box O3a phosphorylation and prolonged tumor necrosis factor-α-induced Jun N-terminal kinase 1 activation. Aged SOD2+/- SMCs had increased mitochondrial superoxide but decreased hydrogen peroxide levels. Finally, dominant-negative Forkhead box O3a overexpression attenuated staurosporine-induced apoptosis in aged SOD2+/- SMCs. CONCLUSION: Mitochondrial oxidative stress over a lifetime causes aortic stiffening, in part by inducing vascular wall remodeling, intrinsic changes in SMC stiffness, and aortic SMC apoptosis.

Nox activator 1: a potential target for modulation of vascular reactive oxygen species in atherosclerotic arteries.

BACKGROUND: Despite a concerted effort by many laboratories, the critical subunits that participate in vascular smooth muscle cell (VSMC) NADPH oxidase function have yet to be elucidated. Given the potential therapeutic importance of cell-specific inhibition of NADPH oxidase, we investigated the role of Nox activator 1 (NoxA1), a homolog of p67phox, in VSMC NADPH oxidase function and atherosclerosis. METHODS AND RESULTS: The presence of NoxA1 in mouse aortic VSMCs was confirmed by reverse-transcription polymerase chain reaction and sequencing. NoxA1/p47phox interaction after thrombin treatment was observed by immunoprecipitation/Western analysis of lysates from p47phox(-/-) VSMCs transfected with adenoviral HA-NoxA1 and Myc-p47phox. Infection with adenoviral NoxA1 significantly enhanced thrombin-induced reactive oxygen species generation in wild-type but not in p47phox(-/-) and Nox1(-/-) VSMCs. Thrombin-induced reactive oxygen species production and VSMC proliferation were significantly reduced after downregulation of NoxA1 with shRNA. Infection with NoxA1 shRNA but not scrambled shRNA significantly decreased thrombin-induced activation of the redox-sensitive protein kinases (Janus kinase 2, Akt, and p38 mitogen-activated protein kinase) in VSMCs. Adenovirus-mediated overexpression of NoxA1 in guidewire-injured mouse carotid arteries significantly increased superoxide production in medial VSMCs and enhanced neointimal hyperplasia. NoxA1 expression was significantly increased in aortas and atherosclerotic lesions of ApoE(-/-) mice compared with age-matched wild-type mice. Furthermore, in contrast to p67phox, immunoreactive NoxA1 is present in intimal and medial SMCs of human early carotid atherosclerotic lesions. CONCLUSIONS: NoxA1 is the functional homolog of p67phox in VSMCs that regulates redox signaling and VSMC phenotype. These findings support the potential for modulation of NoxA1 expression as a viable approach for the treatment of vascular diseases.

Identification of a protective role for protein phosphatase 1cgamma1 against oxidative stress-induced vascular smooth muscle cell apoptosis.

The development of therapeutic strategies to inhibit reactive oxygen species (ROS)-mediated damage in blood vessels has been limited by a lack of specific targets for intervention. Targeting ROS-mediated events in the vessel wall is of interest, because ROS play important roles throughout atherogenesis. In early atherosclerosis, ROS stimulate vascular smooth muscle cell (VSMC) growth, whereas in late stages of lesion development, ROS induce VSMC apoptosis, causing atherosclerotic plaque instability. To identify putative protective genes against oxidative stress, mouse aortic VSMC were infected with a retroviral human heart cDNA expression library, and apoptosis was induced in virus-infected cells by 2,3-dimethoxy-1,4-naphthoquinone (DMNQ) treatment. A total of 17 different, complete cDNAs were identified from the DMNQ-resistant VSMC clones by PCR amplification and sequencing. The cDNA encoding PP1cgamma1 (catalytic subunit of protein phosphatase 1) was present in several independent DMNQ-resistant VSMC clones. DMNQ increased mitochondrial ROS production, caspase-3/7 activity, DNA fragmentation, and decreased mitochondrial transmembrane potential in VSMC while decreasing PP1cgamma1 activity and expression. Depletion of PP1cgamma1 expression by short hairpin RNA significantly enhanced basal as well as DMNQ-induced VSMC apoptosis. PP1cgamma1 overexpression abrogated DMNQ-induced JNK1 activity, p53 Ser(15) phosphorylation, and Bax expression and protected VSMC against DMNQ-induced apoptosis. In addition, PP1cgamma1 overexpression attenuated DMNQ-induced caspase-3/7 activation and DNA fragmentation. Inhibition of p53 protein expression using small interfering RNA abrogated DMNQ-induced Bax expression and significantly attenuated VSMC apoptosis. Together, these data indicate that PP1cgamma1 overexpression promotes VSMC survival by interfering with JNK1 and p53 phosphorylation cascades involved in apoptosis.

Genetic markers of oxidative stress and coronary atherosclerosis.

Atherosclerosis, the primary cause of coronary artery disease (CAD), is a multifactorial disease, the molecular etiology of which involves interaction of many genes and environmental factors. Reactive oxygen species are integral to many cellular and biomolecular processes that are active in the transition of incipient fatty streaks into acute coronary syndromes. Animal models of atherosclerosis and correlative data from human studies support the oxidative stress hypothesis of atherosclerosis. However, the association of genetic polymorphisms that underlie enhanced oxidative stress with CAD is controversial. In this review, we discuss polymorphisms in genes that are main sources of reactive oxygen species generation (NADH oxidase, endothelial nitric oxide synthase, and myeloperoxidase) in mitochondria and the antioxidant enzymes paraoxonase, glutathione reductase, and heme oxygenase. The contribution of defined genetic variants involved in oxidative homeostasis to human atherosclerosis susceptibility is modest because regulation of oxidative stress is multifactorial. However, the contribution of genetic haplotypes in concert with environmental factors is likely significant. A more rigorous characterization of genetic and oxidative phenotypes together with characterization of novel gene polymorphisms may help in early therapeutic intervention for CAD.

Identification of novel mediators of NF-kappaB through genome-wide survey of monocyte adherence-induced genes.

The transcription factor nuclear factor (NF)-kappaB controls the expression of genes involved in inflammation, cell proliferation, apoptosis, and differentiation. Impaired regulation of NF-kappaB has been associated with many diseases; thus, there is significant interest in therapeutic approaches based on modulation of this transcription factor. NF-kappaB activity is controlled by numerous signaling molecules, many of which are potentially to be identified. Monocytes are principal effectors of the immune system, and monocyte adherence is the first step leading to their activation and differentiation. Adherence induces activation of NF-kappaB, resulting in the induction of proinflammatory genes as well as anti-inflammatory genes, which counterbalance and limit the intensity and duration of NF-kappaB activation. Here, to identify novel mediators of NF-kappaB signaling, we used the model of monocyte adherence to perform a systematic, genome-wide survey of adherence-induced genes. Having isolated mRNAs from nonadherent and adherent primary human monocytes, we constructed suppressive subtraction hybridization libraries containing cDNAs, which were differentially regulated by adherence. Of 366 identified differentially expressed genes, most were found to be up-regulated by adherence. Having analyzed a subset of these genes, we found that the library was enriched with inhibitors of NF-kappaB. Three of those (an orphan nuclear receptor NUR77, a guanosine 5'-diphosphate/guanosine 5'-triphosphate exchange factor RABEX5, and a PRK1-associated protein AWP1) were particularly potent inhibitors of NF-kappaB activation. Thus, the collection of monocyte adherence-regulated genes represents a rich source for the identification of novel components of the machinery that controls NF-kappaB activation.