Inflammation and endothelial dysfunction during aging: role of NF-kappaB

Abstract

One of the major conceptual advances in our understanding of the pathogenesis of age-associated cardiovascular diseases has been the insight that age-related oxidative stress may promote vascular inflammation even in the absence of traditional risk factors associated with atherogenesis (e.g., hypertension or metabolic diseases). In the present review we summarize recent experimental data suggesting that mitochondrial production of reactive oxygen species, innate immunity, the local TNF-alpha-converting enzyme (TACE)-TNF-alpha, and the renin-angiotensin system may underlie NF-kappaB induction and endothelial activation in aged arteries. The theme that emerges from this review is that multiple proinflammatory pathways converge on NF-kappaB in the aged arterial wall, and that the transcriptional activity of NF-kappaB is regulated by multiple nuclear factors during aging, including nuclear enzymes poly(ADP-ribose) polymerase (PARP-1) and SIRT-1. We also discuss the possibility that nucleophosmin (NPM or nuclear phosphoprotein B23), a known modulator of the cellular oxidative stress response, may also regulate NF-kappaB activity in endothelial cells.

Fig. 1.

Proposed scheme for pathways contributing to cellular oxidative stress and NF-κB activation in aged endothelial cells. In aged endothelial cells, increased levels of O₂^•− generated by the electron transport chain and NAD(P)H oxidases [stimulated by elevated TNF-α levels and/or by the activated local renin-angiotensin system (RAS) in the vascular wall] are dismutated to H₂O₂. Increased cytoplasmic H₂O₂ levels and activation of toll-like receptors (TLRs) each contribute to the activation and nuclear translocation of NF-κB, which results in a proinflammatory shift in the endothelial gene expression profile, endothelial activation, and increased monocyte adhesiveness to the endothelium. The transcriptional activity of NF-κB is regulated by nucleophosmin (NPM) and SIRT-1 (hatched arrows represent inhibition), and both pathways exhibit age-related alterations. In addition, poly(ADP-ribose) polymerase (PARP-1) activation also modulates transcriptional activity of NF-κB. Increased O₂^•− production and/or downregulation of endothelial nitric oxide synthase (eNOS) are mutually responsible for impaired bioavailability of NO and endothelial vasodilator dysfunction in aged arteries. The model predicts that upregulation of TNF-α and/or impaired NO bioavailability may also contribute to development of mitochondrial oxidative stress during aging. Increased TNF-α levels also promote endothelial apoptotic cell death, which, along with increased oxidative stress and vascular inflammation, increases the risk for coronary artery disease. iNOS, inducible nitric oxide synthase; SOD2, superoxide dismutase 2.

Fig. 2.

A: reporter gene assay demonstrates the knockdown effects of NPM [by small interfering RNA (siRNA)] on TNF-α (10 ng/ml)-induced NF-κB reporter activity in cultured primary human coronary arterial endothelial cells (HCAECs). The resulting overexpression of NPM with respect to endothelial NF-κB activation is also shown, as well as effects of resveratrol (10 μmol/l) on TNF-α (10 ng/ml)-induced NF-κB reporter activity. Cells were transiently cotransfected with NF-κB-driven firefly luciferase and CMV-driven Renilla luciferase constructs, followed by NPM knockdown, NPM overexpression, or TNF-α stimulation. Cells were then lysed and subjected to luciferase activity assay. Following normalization, relative luciferase activity was obtained from 6 independent transfections. Data are means ± SE. *P < 0.05 vs. control; #P < 0.05 vs. TNF-α only; &P < 0.05 vs. NPM overexpression. B: effect of knockdown of SIRT-1 (siRNA) and/or resveratrol (10 μmol/l) treatment on mRNA expression of NPM in cultured HCAECs. Analysis of mRNA expression was performed by real-time QRT-PCR. β-Actin was used for normalization. Data are means ± SE (n = 5 for each group). C: NPM mRNA expression in carotid arteries of ad libitum-fed young (3 mo old), ad libitum fed aged (28 mo old), and caloric-restricted aged (28 mo old) F344 rats. Analysis of mRNA expression was performed by real-time QRT-PCR. β-Actin was used for normalization. Data are means ± SE (n = 5 for each group). *P < 0.05. vs. young; #P < 0.05 vs. ad libitum-fed aged. All animal use protocols were approved by the Institutional Animal Care and Use Committee of the New York Medical College, Valhalla, NY.