Endothelial cell-specific NF-kappaB inhibition protects mice from atherosclerosis

Sphingosine-1-phosphate receptor-2 deficiency leads to inhibition of macrophage proinflammatory activities and atherosclerosis in apoE-deficient mice

Sphingosine-1-phosphate (S1P) is a biologically active sphingolipid that has pleiotropic effects in a variety of cell types including ECs, SMCs, and macrophages, all of which are central to the development of atherosclerosis. It may therefore exert stimulatory and inhibitory effects on atherosclerosis. Here, we investigated the role of the S1P receptor S1PR2 in atherosclerosis by analyzing S1pr2-/- mice with an Apoe-/- background. S1PR2 was expressed in macrophages, ECs, and SMCs in atherosclerotic aortas. In S1pr2-/-Apoe-/- mice fed a high-cholesterol diet for 4 months, the area of the atherosclerotic plaque was markedly decreased, with reduced macrophage density, increased SMC density, increased eNOS phosphorylation, and downregulation of proinflammatory cytokines compared with S1pr2+/+Apoe-/- mice. Bone marrow chimera experiments indicated a major role for macrophage S1PR2 in atherogenesis. S1pr2-/-Apoe-/- macrophages showed diminished Rho/Rho kinase/NF-κB (ROCK/NF-κB) activity. Consequently, they also displayed reduced cytokine expression, reduced oxidized LDL uptake, and stimulated cholesterol efflux associated with decreased scavenger receptor expression and increased cholesterol efflux transporter expression. S1pr2-/-Apoe-/- ECs also showed reduced ROCK and NF-κB activities, with decreased MCP-1 expression and elevated eNOS phosphorylation. Pharmacologic S1PR2 blockade in S1pr2+/+Apoe-/- mice diminished the atherosclerotic plaque area in aortas and modified LDL accumulation in macrophages. We conclude therefore that S1PR2 plays a critical role in atherogenesis and may serve as a novel therapeutic target for atherosclerosis.

SIRT1 reduces endothelial activation without affecting vascular function in ApoE-/- mice

Excessive production of reactive oxygen species (ROS) contributes to progression of atherosclerosis, at least in part by causing endothelial dysfunction and inflammatory activation. The class III histone deacetylase SIRT1 has been implicated in extension of lifespan. In the vasculature,SIRT1 gain-of-function using SIRT1 overexpression or activation has been shown to improve endothelial function in mice and rats via stimulation of endothelial nitric oxide (NO) synthase (eNOS). However, the effects of SIRT1 loss-of-function on the endothelium in atherosclerosis remain to be characterized. Thus, we have investigated the endothelial effects of decreased endogenous SIRT1 in hypercholesterolemic ApoE^-/- mice. We observed no difference in endothelial relaxation and eNOS (Ser¹¹⁷⁷) phosphorylation between 20-week old male atherosclerotic ApoE^-/- SIRT1^+/- and ApoE^-/- SIRT1^+/+ mice. However, SIRT1 prevented endothelial superoxide production, inhibited NF-κB signaling, and diminished expression of adhesion molecules. Treatment of young hypercholesterolemic ApoE^-/- SIRT1^+/- mice with lipopolysaccharide to boost NF-κB signaling led to a more pronounced endothelial expression of ICAM-1 and VCAM-1 as compared to ApoE^-/- SIRT1^+/+ mice. In conclusion, endogenous SIRT1 diminishes endothelial activation in ApoE^-/- mice, but does not affect endothelium-dependent vasodilatation.

Tumor necrosis factor receptor-associated factor-6 and ribosomal S6 kinase intracellular pathways link the angiotensin II AT1 receptor to the phosphorylation and activation of the IkappaB kinase complex in vascular smooth muscle cells

Activation of NF-κB transcription factors by locally produced angiotensin II (Ang II) is proposed to be involved in chronic inflammatory reactions leading to atherosclerosis development. However, a clear understanding of the signaling cascades coupling the Ang II AT1 receptors to the activation of NF-κB transcription factors is still lacking. Using primary cultured aortic vascular smooth muscle cells, we show that activation of the IKK complex and NF-κB transcription factors by Ang II is regulated by phosphorylation of the catalytic subunit IKKβ on serine residues 177 and 181 in the activation T-loop. The use of pharmacological inhibitors against conventional protein kinases C (PKCs), mitogen-activated/extracellular signal-regulated kinase (MEK) 1/2, ribosomal S6 kinase (RSK), and silencing RNA technology targeting PKCα, IKKβ subunit, tumor growth factor β-activating kinase-1 (TAK1), the E3 ubiquitin ligase tumor necrosis factor receptor-associated factor-6 (TRAF6), and RSK isoforms, demonstrates the requirement of two distinct signaling pathway for the phosphorylation of IKKβ and the activation of the IKK complex by Ang II. Rapid phosphorylation of IKKβ requires a second messenger-dependent pathway composed of PKCα-TRAF6-TAK1, whereas sustained phosphorylation and activation of IKKβ requires the MEK1/2-ERK1/2-RSK pathway. Importantly, simultaneously targeting components of these two pathways completely blunts the phosphorylation of IKKβ and the proinflammatory effect of the octapeptide. This is the first report demonstrating activation of TAK1 by the AT1R. We propose a model whereby TRAF6-TAK1 and ERK-RSK intracellular pathways independently and sequentially converge to the T-loop phosphorylation for full activation of IKKβ, which is an essential step in the proinflammatory activity of Ang II.

MicroRNA-10a regulation of proinflammatory phenotype in athero-susceptible endothelium in vivo and in vitro

A chronic proinflammatory state precedes pathological change in arterial endothelial cells located within regions of susceptibility to atherosclerosis. The potential contributions of regulatory microRNAs to this disequilibrium were investigated by artery site-specific profiling in normal adult swine. Expression of endothelial microRNA10a (miR-10a) was lower in the athero-susceptible regions of the inner aortic arch and aorto-renal branches than elsewhere. Expression of Homeobox A1 (HOXA1), a known miR-10a target, was up-regulated in the same locations. Endothelial transcriptome microarray analysis of miR-10a knockdown in cultured human aortic endothelial cells (HAEC) identified IkappaB/NF-kappaB-mediated inflammation as the top category of up-regulated biological processes. Phosphorylation of IkappaBalpha, a prerequisite for IkappaBalpha proteolysis and NF-kappaB activation, was significantly up-regulated in miR-10a knockdown HAEC and was accompanied by increased nuclear expression of NF-kappaB p65. The inflammatory biomarkers monocyte chemotactic protein 1 (MCP-1), IL-6, IL-8, vascular cell adhesion molecule 1 (VCAM-1), and E-selectin were elevated following miR-10a knockdown. Conversely, knockin of miR-10a (a conservative 25-fold increase) inhibited the basal expression of VCAM-1 and E-selectin in HAEC. Two key regulators of IkappaBalpha degradation--mitogen-activated kinase kinase kinase 7 (MAP3K7; TAK1) and beta-transducin repeat-containing gene (betaTRC)--contain a highly conserved miR-10a binding site in the 3' UTR. Both molecules were up-regulated by miR-10a knockdown and suppressed by miR-10a knockin, and evidence of direct miR-10a binding to the 3' UTR was demonstrated by luciferase assay. Comparative expression studies of endothelium located in athero-susceptible aortic arch and athero-protected descending thoracic aorta identified significantly up-regulated MAP3K7, betaTRC, phopho-IkappaBalpha, and nuclear p65 expression suggesting that the differential expression of miR-10a contributes to the regulation of proinflammatory endothelial phenotypes in athero-susceptible regions in vivo.

Arterial aging: a journey into subclinical arterial disease

PURPOSE OF REVIEW

Age-associated arterial alterations in cells, matrix, and biomolecules are the foundation for the initiation and progression of cardiovascular diseases in older persons. This review focuses on the latest advances on the intertwining of aging and disease within the arterial wall at the cell and molecular levels.

RECENT FINDINGS

Endothelial dysfunction, vascular smooth muscle cell (VSMC) proliferation/invasion/secretion, matrix fragmentation, collagenization and glycation are characteristics of an age-associated arterial phenotype that creates a microenvironment enriched with reactive oxygen species (ROS) for the pathogenesis of arterial disease. This niche creates an age-associated arterial secretory phenotype (AAASP), which is orchestrated by the concerted effects of numerous age-modified angiotensin II signaling molecules. Most of these biomolecular, cell, and matrix modifications that constitute the AAASP can be elicited by experimental hypertension or atherosclerosis at a younger age. The arterial AAASP also shares features of a senescence-associated secretory phenotype (SASP) identified in other mesenchymocytes, that is, fibroblasts.

SUMMARY

A subclinical AAASP evolves during aging. Targeting this subclinical AAASP may reduce the incidence and progression of the quintessential age-associated arterial diseases, that is, hypertension and atherosclerosis.

Regulation of IkappaBalpha function and NF-kappaB signaling: AEBP1 is a novel proinflammatory mediator in macrophages

NF-κB comprises a family of transcription factors that are critically involved in various inflammatory processes. In this paper, the role of NF-κB in inflammation and atherosclerosis and the regulation of the NF-κB signaling pathway are summarized. The structure, function, and regulation of the NF-κB inhibitors, IκBα and IκBβ, are reviewed. The regulation of NF-κB activity by glucocorticoid receptor (GR) signaling and IκBα sumoylation is also discussed. This paper focuses on the recently reported regulatory function that adipocyte enhancer-binding protein 1 (AEBP1) exerts on NF-κB transcriptional activity in macrophages, in which AEBP1 manifests itself as a potent modulator of NF-κB via physical interaction with IκBα and a critical mediator of inflammation. Finally, we summarize the regulatory roles that recently identified IκBα-interacting proteins play in NF-κB signaling. Based on its proinflammatory roles in macrophages, AEBP1 is anticipated to serve as a therapeutic target towards the treatment of various inflammatory conditions and disorders.

Selective blockade of endothelial NF-kappaB pathway differentially affects systemic inflammation and multiple organ dysfunction and injury in septic mice

Endothelium has long been considered both a source and a target of systemic inflammation. However, to what extent endothelial activation contributes to systemic inflammation remains unclear. This study addresses the relative contribution of endothelial activation to systemic inflammation and multiple organ dysfunction and injury (MOD/I) in an E. coli peritonitis model of sepsis. We prevented endothelial activation using transgenic (TG) mice that conditionally overexpress a mutant I-kappaBalpha, a NF-kappaB inhibitor, selectively on endothelium. TG mice and their transgene negative littermates (WT) were injected with saline or E. coli (10(8) CFU per mouse). At 7 h after E. coli infection, markers of systemic inflammation, endothelial activation, and MOD/I were assessed. WT-E. coli mice showed significantly increased serum levels of TNF-alpha, IL-1beta, IFN-gamma, IL-6, KC, and MCP-1; tissue levels of TNF-alpha, IL-6, KC, MCP-1, ICAM-1, and VCAM-1; endothelial leakage index in heart, lungs, liver, and kidney; significantly increased serum levels of AST, ALT, BUN, and creatinine; and increased mortality. Blockade of NF-kappaB-mediated endothelial activation in TG mice had no effects on serum levels of TNF-alpha, IL-1beta, IFN-gamma, IL-6, KC, and MCP-1 (markers of systemic inflammation), and tissue levels of TNF-alpha, IL-6, KC, and MCP-1, but significantly reduced tissue levels of ICAM-1 and VCAM-1 (markers of endothelial inflammation and activation) in those four organs. TG-E. coli mice displayed reversed endothelial leakage index; reduced serum levels of AST, ALT, BUN, and creatinine; and improved survival. Our data demonstrate that endothelial NF-kappaB-driven inflammatory response contributes minimally to systemic inflammation, but plays a pivotal role in septic MOD/I, suggesting that endothelium is mainly a target rather than a source of systemic inflammation.

Mouse aorta smooth muscle cells differentiate into lymphoid tissue organizer-like cells on combined tumor necrosis factor receptor-1/lymphotoxin beta-receptor NF-kappaB signaling

OBJECTIVE

Mouse aorta smooth muscle cells (SMC) express tumor necrosis factor receptor superfamily member 1A (TNFR-1) and lymphotoxin beta-receptor (LTbetaR). Circumstantial evidence has linked the SMC LTbetaR to tertiary lymphoid organogenesis in hyperlipidemic mice. Here, we explored TNFR-1 and LTbetaR signaling in cultured SMC.

METHODS AND RESULTS

TNFR-1 signaling activated the classical RelA NF-kappaB pathway, whereas LTbetaR signaling activated the classical RelA and alternative RelB NF-kappaB pathways, and both signaling pathways synergized to enhance p100 inhibitor processing to the p52 subunit of NF-kappaB. Microarrays showed that simultaneous TNFR-1/LTbetaR activation resulted in elevated mRNA encoding leukocyte homeostatic chemokines CCL2, CCL5, CXCL1, and CX3CL1. Importantly, SMC acquired features of lymphoid tissue organizers, which control tertiary lymphoid organogenesis in autoimmune diseases through hyperinduction of CCL7, CCL9, CXCL13, CCL19, CXCL16, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1. TNFR-1/LTbetaR cross-talk resulted in augmented secretion of lymphorganogenic chemokine proteins. Supernatants of TNFR-1/LTbetaR-activated SMC markedly supported migration of splenic T cells, B cells, and macrophages/dendritic cells. Experiments with ltbr(-/-) SMC indicated that LTbetaR-RelB activation was obligatory to generate the lymphoid tissue organizer phenotype.

CONCLUSIONS

SMC may participate in the formation of tertiary lymphoid tissue in atherosclerosis by upregulation of lymphorganogenic chemokines involved in T-lymphocyte, B-lymphocyte, and macrophage/dendritic cell attraction.

Role of nuclear factor kappaB in cardiovascular health and disease

Cardiovascular pathologies are still the primary cause of death worldwide. The molecular mechanisms behind these pathologies have not been fully elucidated. Unravelling them will bring us closer to therapeutic strategies to prevent or treat cardiovascular disease. One of the major transcription factors that has been linked to both cardiovascular health and disease is NF-kappaB (nuclear factor kappaB). The NF-kappaB family controls multiple processes, including immunity, inflammation, cell survival, differentiation and proliferation, and regulates cellular responses to stress, hypoxia, stretch and ischaemia. It is therefore not surprising that NF-kappaB has been shown to influence numerous cardiovascular diseases including atherosclerosis, myocardial ischaemia/reperfusion injury, ischaemic preconditioning, vein graft disease, cardiac hypertrophy and heart failure. The function of NF-kappaB is largely dictated by the genes that it targets for transcription and varies according to stimulus and cell type. Thus NF-kappaB has divergent functions and can protect cardiovascular tissues from injury or contribute to pathogenesis depending on the cellular and physiological context. The present review will focus on recent studies on the function of NF-kappaB in the cardiovascular system.

Salsalate may have broad utility in the prevention and treatment of vascular disorders and the metabolic syndrome

In the high proportion of vascular disorders associated with excessive oxidative stress and production of pro-inflammatory cytokines, activation of NF-kappaB plays a key pathogenic role. Thus, there is considerable evidence that NF-kappaB is a mediator of atherogenesis, plaque destabilization, ischemia-reperfusion damage, cardiac remodeling, atrial fibrillation, and aneurysm formation and rupture; some studies suggest that it may also play a role in the microvascular complications of diabetes. I kappaB kinase-beta (IKK beta) is the upstream kinase that appears to be primarily responsible for NF-kappaB activation in these disorders; moreover, chronic IKK beta activation plays a prominent role in induction of insulin resistance in the metabolic syndrome. Salicylate inhibits IKK beta in concentrations that are achievable with dose schedules traditionally used in treating rheumatoid arthritis (3-4.5 g daily); indeed, this is likely to be the mechanism responsible for salicylate's utility in this disorder. Salicylate, unlike aspirin, is only a very weak, reversible inhibitor of cyclooxygenase in clinical doses, and thus is not associated with the potentially dangerous side effects seen with NSAIDs; fully reversible ototoxicity, the dose-limiting side effect in salicylate therapy, can be avoided in most patients by dosage adjustment. Hence, it is proposed that salicylate may have practical utility in the prevention or management of a wide range of vascular disorders as well as of metabolic syndrome and diabetes; its efficacy in these regards would likely be complemented by effective antioxidant measures, which would lessen the stimulus to NF-kappaB activation while providing benefits independent of NF-kappaB activity. Salsalate, consisting of two salicylate molecules united by an ester bond, is a venerable drug that may be the best tolerated delivery vehicle for salicylate. Appropriate rodent studies should pave the way for clinical trials with salsalate in patients at vascular risk.

The role of low endothelial shear stress in the conversion of atherosclerotic lesions from stable to unstable plaque

PURPOSE OF REVIEW

Local hemodynamic factors are major determinants of the natural history of individual atherosclerotic plaque progression in coronary arteries. The purpose of this review is to summarize the role of low endothelial shear stress (ESS) in the transition of early, stable plaques to high-risk atherosclerotic lesions.

RECENT FINDINGS

Low ESS regulates multiple pathways within the atherosclerotic lesion, resulting in intense vascular inflammation, progressive lipid accumulation, and formation and expansion of a necrotic core. Upregulation of matrix-degrading proteases promotes thinning of the fibrous cap, severe internal elastic lamina fragmentation, and extracellular matrix remodeling. In the setting of plaque-induced changes of the local ESS, coronary regions persistently exposed to very low ESS develop excessive expansive remodeling, which further exacerbates the proinflammatory low ESS stimulus. Recent studies suggest that the effect of recognized cardioprotective medications may be mediated by attenuation of the proinflammatory effect of the low ESS environment in which a plaque develops.

SUMMARY

Low ESS determines the severity of vascular inflammation, the status of the extracellular matrix, and the nature of wall remodeling, all of which synergistically promote the transition of stable lesions to thin cap fibroatheromata that may rupture with subsequent formation of an occlusive thrombus and result in an acute coronary syndrome.

Inflammatory cytokines in vascular dysfunction and vascular disease

The vascular inflammatory response involves complex interaction between inflammatory cells (neutrophils, lymphocytes, monocytes, macrophages), endothelial cells (ECs), vascular smooth muscle cells (VSMCs), and extracellular matrix (ECM). Vascular injury is associated with increased expression of adhesion molecules by ECs and recruitment of inflammatory cells, growth factors, and cytokines, with consequent effects on ECs, VSMCs and ECM. Cytokines include tumor necrosis factors, interleukins, lymphokines, monokines, interferons, colony stimulating factors, and transforming growth factors. Cytokines are produced by macrophages, T-cells and monocytes, as well as platelets, ECs and VSMCs. Circulating cytokines interact with specific receptors on various cell types and activate JAK-STAT, NF-kappaB, and Smad signaling pathways leading to an inflammatory response involving cell adhesion, permeability and apoptosis. Cytokines also interact with mitochondria to increase the production of reactive oxygen species. Cytokine-induced activation of these pathways in ECs modifies the production/activity of vasodilatory mediators such as nitric oxide, prostacyclin, endothelium-derived hyperpolarizing factor, and bradykinin, as well as vasoconstrictive mediators such as endothelin and angiotensin II. Cytokines interact with VSMCs to activate Ca(2+), protein kinase C, Rho-kinase, and MAPK pathways, which promote cell growth and migration, and VSM reactivity. Cytokines also interact with integrins and matrix metalloproteinases (MMPs) and modify ECM composition. Persistent increases in cytokines are associated with vascular dysfunction and vascular disease such as atherosclerosis, abdominal aortic aneurysm, varicose veins and hypertension. Genetic and pharmacological tools to decrease the production of cytokines or to diminish their effects using cytokine antagonists could provide new approaches in the management of inflammatory vascular disease.

Innate immune signals in atherosclerosis

Atherosclerosis is a chronic disease characterised by lipid retention and inflammation in the arterial intima. Innate immune mechanisms are central to atherogenesis, involving activation of pattern-recognition receptors (PRRs) and induction of inflammatory processes. In a complex tissue, such as the atherosclerotic lesion, innate signals can originate from several sources and promote atherogenesis through ligation of PRRs. The receptors recognise conserved molecular patterns on pathogens and endogenous products of tissue injury and inflammation. Activation of PRRs might affect several aspects of atherosclerosis by acting on lesion resident cells. Scavenger receptors mediate antigen uptake and clearance of lipoproteins, thereby promoting foam cell formation. Signalling receptors, such as Toll-like receptors (TLRs), lead to induction of pro-inflammatory cytokines and antigen-specific immune responses. In this review we describe the innate mechanisms present in the plaque. We focus on TLRs, their cross-talk with other PRRs, and how their signalling cascades influence inflammation within the atherosclerotic lesion.

A pivotal role of endothelial-specific NF-kappaB signaling in the pathogenesis of septic shock and septic vascular dysfunction

Although the role of NF-kappaB in the pathogenesis of sepsis and septic shock has been extensively studied, little is known about the causative contribution of endothelial-intrinsic NF-kappaB to these pathological processes. In this study, we used transgenic (TG) mice (on FVB genetic background) that conditionally overexpress the NF-kappaB inhibitor, mutant I-kappaBalpha, selectively on endothelium and their transgene-negative littermates (wild type (WT)) to define the causative role of endothelial-specific NF-kappaB signaling in septic shock and septic vascular dysfunction. In WT mice, LPS challenge caused systemic hypotension, a significantly blunted vasoconstrictor response to norepinephrine, and an impaired endothelium-dependent vasodilator response to acetylcholine, concomitant with a markedly increased aortic inducible NO synthase expression, significantly elevated plasma and aortic levels of nitrite/nitrate, increased aortic TNF-alpha expression, and decreased aortic endothelial NO synthase (eNOS) expression. In TG mice whose endothelial NF-kappaB was selectively blocked, LPS caused significantly less hypotension and no impairments in vasoconstrictor and endothelium-dependent vasodilator responses, associated with significantly reduced aortic inducible NO synthase expression, decreased plasma and aortic levels of nitrite/nitrate, reduced aortic TNF-alpha expression, and increased aortic eNOS expression. TNF-alpha knockout mice prevented LPS-induced eNOS down-regulation. WT mice subjected to cecal ligation and puncture showed significant systemic hypotension, which was prevented in TG mice. Our data show that selective blockade of endothelial-intrinsic NF-kappaB pathway is sufficient to abrogate the cascades of molecular events that lead to septic shock and septic vascular dysfunction, demonstrating a pivotal role of endothelial-specific NF-kappaB signaling in the pathogenesis of septic shock and septic vascular dysfunction.

Absence of p55 TNF receptor reduces atherosclerosis, but has no major effect on angiotensin II induced aneurysms in LDL receptor deficient mice

Background

The aim of the current study was to investigate the role of p55 TNF Receptor (p55 TNFR), the main signaling receptor for the pro-inflammatory cytokine tumor necrosis factor (TNF), in the development of two vascular disorders: atherosclerosis and angiotensin (Ang) II-induced abdominal aortic aneurysms (AAA).

Methodology/Principal Findings

p55 TNFR deficient mice were crossed to an LDL receptor deficient background and were induced for the development of either atherosclerosis or AngII-induced AAA, and compared to littermate controls, wild-type for p55 TNFR expression. p55 TNFR deficient mice developed 43% smaller atherosclerotic lesions in the aortic sinuses compared to controls. Moreover, expression of CD68, a macrophage specific marker, exhibited a 50% reduction in the aortic arches. Decreased atherosclerosis correlated with a strong down-regulation in the expression of adhesion molecules, such as VCAM-1 and ICAM-1, by p55 TNFR deficient endothelium. In addition, expression levels of the pro-inflammatory cytokines and chemokines TNF, IL-6, MCP-1 and RANTES were significantly reduced in aortas of p55 TNFR deficient mice. In contrast, in the AngII-induced model of AAA, p55 TNFR deficiency correlated with a slight trend towards increased aneurismal lethality, but the incidence of aortic rupture due to a dissecting aneurysm, and the expansion of the suprarenal aorta were not significantly different compared to controls.

Conclusion/Significance

We found that p55 TNFR expression promotes atherosclerosis, among other mechanisms, by enhancing expression of endothelial adhesion molecules, while it seems to have no major role in the development of AngII-induced AAA.