P55 tumour necrosis factor receptor in bone marrow-derived cells promotes atherosclerosis development in low-density lipoprotein receptor knock-out mice

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Weak association of a TNFRSF1A polymorphism with Behcet's disease in Chinese Han

The purpose of this study was to investigate whether single nucleotide polymorphisms (SNPs) of the tumor necrosis factor receptor superfamily (TNFRSF) and their ligand (TNFSF) gene are associated with susceptibility to Behcet's Disease (BD) in Chinese Han. A two-phase case-control study was performed in 1055 BD patients and 1829 healthy controls. A total of 27 SNPs was tested using MassARRAY iPLEX® technology. Data were analyzed using a Chi-square (χ2) test and Fisher's exact calibration test. The Bonferroni correction was applied for multiple testing. A statistically significant higher frequency of the A allele and a lower frequency of the G allele of rs1800692 was found in BD (Pc = 0.013, OR = 1.233, 95% CI = 1.103-1.379: Pc = 0.013, OR = 0.811, 95% CI = 0.725-0.907, respectively). Our findings indicate that TNFRSF1A might confer genetic susceptibility to BD in a Chinese Han population.

Anti-inflammatory Therapies for Cardiovascular Disease: Signaling Pathways and Mechanisms

Cardiovascular diseases (CVD) are the clinical manifestation of atherosclerosis, a chronic inflammatory disease promoted by several risk factors such as dyslipidemia, type 2 diabetes mellitus, hypertension, and smoking. Acute CVD events are the result of an unresolved inflammatory chronic state that promotes the rupture of unstable plaque lesions. Of note, the existing intensive therapies modify risk factors but do not prevent life-threatening recurrent ischemic events in high-risk patients, who have a residual inflammatory risk displayed by increased C-reactive protein (CRP) levels. Better understanding of the role of innate and adaptive immunity in plaque development and rupture has led to intensive investigation of anti-inflammatory strategies for CVD. Some of them are being tested in specific clinical trials and use lower doses of existing medications originally developed for other inflammatory diseases such as rheumatoid arthritis and psoriasis, which have high CVD risk. Other investigations are retrospective and meta-analyses of existing clinical trials that evaluate the incidence of CVD in these inflammatory diseases. Others are based on preclinical testing such as vaccines. In this article, we summarize the main anti-inflammatory strategies and associated molecular mechanisms that are being evaluated in preclinical or clinical CVD studies.

Heterogeneity of atherosclerotic plaque macrophage origin, phenotype and functions: Implications for treatment

Macrophages are key players in atherosclerotic lesions, regulating the local inflammatory milieu and plaque stability by the secretion of many inflammatory molecules, growth factors and cytokines. Monocytes have long been considered to be the main source of plaque macrophages. However, recent findings provide evidence for proliferation of local macrophages or transdifferentiation from other vascular cells as alternative sources. Recent years of research focused on the further identification and characterisation of macrophage phenotypes and functions. In this review we describe the advances in our understanding of monocyte and macrophage heterogeneity and its implications for specific therapeutic interventions, aiming to reduce the ever growing significant risk of cardiovascular events without any detrimental side effects on the patient's immune response.

Genetic and Pharmacological Inhibition of TREM-1 Limits the Development of Experimental Atherosclerosis

BACKGROUND

Innate immune responses activated through myeloid cells contribute to the initiation, progression, and complications of atherosclerosis in experimental models. However, the critical upstream pathways that link innate immune activation to foam cell formation are still poorly identified.

OBJECTIVES

This study sought to investigate the hypothesis that activation of the triggering receptor expressed on myeloid cells (TREM-1) plays a determinant role in macrophage atherogenic responses.

METHODS

After genetically invalidating Trem-1 in chimeric Ldlr^-/-Trem-1^-/- mice and double knockout ApoE^-/-Trem-1^-/- mice, we pharmacologically inhibited Trem-1 using LR12 peptide.

RESULTS

Ldlr^-/- mice reconstituted with bone marrow deficient for Trem-1 (Trem-1^-/-) showed a strong reduction of atherosclerotic plaque size in both the aortic sinus and the thoracoabdominal aorta, and were less inflammatory compared to plaques of Trem-1^+/+ chimeric mice. Genetic invalidation of Trem-1 led to alteration of monocyte recruitment into atherosclerotic lesions and inhibited toll-like receptor 4 (TLR 4)-initiated proinflammatory macrophage responses. We identified a critical role for Trem-1 in the upregulation of cluster of differentiation 36 (CD36), thereby promoting the formation of inflammatory foam cells. Genetic invalidation of Trem-1 in ApoE^-/-/Trem-1^-/- mice or pharmacological blockade of Trem-1 in ApoE^-/- mice using LR-12 peptide also significantly reduced the development of atherosclerosis throughout the vascular tree, and lessened plaque inflammation. TREM-1 was expressed in human atherosclerotic lesions, mainly in lipid-rich areas with significantly higher levels of expression in atheromatous than in fibrous plaques.

CONCLUSIONS

We identified TREM-1 as a major upstream proatherogenic receptor. We propose that TREM-1 activation orchestrates monocyte/macrophage proinflammatory responses and foam cell formation through coordinated and combined activation of CD36 and TLR4. Blockade of TREM-1 signaling may constitute an attractive novel and double-hit approach for the treatment of atherosclerosis.

Targeting inflammation to reduce cardiovascular disease risk: a realistic clinical prospect?

Data from basic science experiments is overwhelmingly supportive of the causal role of immune-inflammatory response(s) at the core of atherosclerosis, and therefore, the theoretical potential to manipulate the inflammatory response to prevent cardiovascular events. However, extrapolation to humans requires care and we still lack definitive evidence to show that interfering in immune-inflammatory processes may safely lessen clinical atherosclerosis. In this review, we discuss key therapeutic targets in the treatment of vascular inflammation, placing basic research in a wider clinical perspective, as well as identifying outstanding questions.

LINKED ARTICLES

This article is part of a themed section on Targeting Inflammation to Reduce Cardiovascular Disease Risk. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.22/issuetoc and http://onlinelibrary.wiley.com/doi/10.1111/bcp.v82.4/issuetoc.

Macrophage Phenotype and Function in Different Stages of Atherosclerosis

The remarkable plasticity and plethora of biological functions performed by macrophages have enticed scientists to study these cells in relation to atherosclerosis for >50 years, and major discoveries continue to be made today. It is now understood that macrophages play important roles in all stages of atherosclerosis, from initiation of lesions and lesion expansion, to necrosis leading to rupture and the clinical manifestations of atherosclerosis, to resolution and regression of atherosclerotic lesions. Lesional macrophages are derived primarily from blood monocytes, although recent research has shown that lesional macrophage-like cells can also be derived from smooth muscle cells. Lesional macrophages take on different phenotypes depending on their environment and which intracellular signaling pathways are activated. Rather than a few distinct populations of macrophages, the phenotype of the lesional macrophage is more complex and likely changes during the different phases of atherosclerosis and with the extent of lipid and cholesterol loading, activation by a plethora of receptors, and metabolic state of the cells. These different phenotypes allow the macrophage to engulf lipids, dead cells, and other substances perceived as danger signals; efflux cholesterol to high-density lipoprotein; proliferate and migrate; undergo apoptosis and death; and secrete a large number of inflammatory and proresolving molecules. This review article, part of the Compendium on Atherosclerosis, discusses recent advances in our understanding of lesional macrophage phenotype and function in different stages of atherosclerosis. With the increasing understanding of the roles of lesional macrophages, new research areas and treatment strategies are beginning to emerge.

Cytokines in atherosclerosis: Key players in all stages of disease and promising therapeutic targets

Atherosclerosis, a chronic inflammatory disorder of the arteries, is responsible for most deaths in westernized societies with numbers increasing at a marked rate in developing countries. The disease is initiated by the activation of the endothelium by various risk factors leading to chemokine-mediated recruitment of immune cells. The uptake of modified lipoproteins by macrophages along with defective cholesterol efflux gives rise to foam cells associated with the fatty streak in the early phase of the disease. As the disease progresses, complex fibrotic plaques are produced as a result of lysis of foam cells, migration and proliferation of vascular smooth muscle cells and continued inflammatory response. Such plaques are stabilized by the extracellular matrix produced by smooth muscle cells and destabilized by matrix metalloproteinase from macrophages. Rupture of unstable plaques and subsequent thrombosis leads to clinical complications such as myocardial infarction. Cytokines are involved in all stages of atherosclerosis and have a profound influence on the pathogenesis of this disease. This review will describe our current understanding of the roles of different cytokines in atherosclerosis together with therapeutic approaches aimed at manipulating their actions.

Cytokines and Immune Responses in Murine Atherosclerosis

Atherosclerosis is an inflammatory disease of the vessel wall characterized by activation of the innate immune system, with macrophages as the main players, as well as the adaptive immune system, characterized by a Th1-dominant immune response. Cytokines play a major role in the initiation and regulation of inflammation. In recent years, many studies have investigated the role of these molecules in experimental models of atherosclerosis. While some cytokines such as TNF or IFNγ clearly had atherogenic effects, others such as IL-10 were found to be atheroprotective. However, studies investigating the different cytokines in experimental atherosclerosis revealed that the cytokine system is complex with both disease stage-dependent and site-specific effects. In this review, we strive to provide an overview of the main cytokines involved in atherosclerosis and to shed light on their individual role during atherogenesis.

Soluble TNF and IL-6 receptors: indicators of vascular health in women without cardiovascular disease

Cytokine receptor subunits are released from cells in a regulated manner and circulate in soluble forms at concentrations that are orders of magnitude greater than the concentrations of the cytokines themselves. The purpose of this study was to determine if the circulating concentrations of soluble receptor subunits for interleukin-1 beta (IL-1β), tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6) might serve as early indicators of vascular dysfunction independent of the traditional cardiovascular disease (CVD) risk factors in women. Healthy women, aged 20-50 years (n = 36), were assessed for circulating concentrations of the cytokines IL-1β, IL-6 and TNFα and the soluble cytokine receptor subunits interleukin-1 receptor type I (sIL-1RI), sIL-1RII, sIL-6Rα, glycoprotein 130 (s-gp130), soluble TNF receptor type 1 (sTNFR1), and sTNFR2, along with traditional CVD risk factors. Cytokine receptor subunit expression on mononuclear cells and the release of these subunits in vitro were also determined. Brachial artery flow-mediated dilation (FMD), carotid intima-media thickness (cIMT) and carotid-femoral pulse wave velocity (cfPWV) were assessed by ultrasonography and Doppler probes. Circulating sIL-6Rα correlated negatively with FMD (r = -0.56, p = 0.007) independent of age and other CVD risk factors. Circulating sTNFR1 correlated positively with cfPWV (r = 0.60, p = 0.002). TNFR1 receptor expression on monocytes correlated positively with cIMT (r = 0.51, p = 0.004). Plasma concentrations of IL-1β, IL-6 and TNFα were not significantly associated with FMD, cIMT or cfPWV. These data suggest that the receptors for IL-6 and TNFα, rather than the cytokines themselves, may be better indicators of early vascular changes that are associated with CVD.

Aging mesenchymal stem cells fail to protect because of impaired migration and antiinflammatory response

RATIONALE

Aging is characterized by functional impairment and reduced capacity to respond appropriately to environmental stimuli and injury. With age, there is an increase in the incidence and severity of chronic and acute lung diseases. However, the relationship between age and the lung's reduced ability to repair is far from established and necessitates further research in the field.

OBJECTIVES

Little is currently known about age-related phenomena in mesenchymal stem cells (MSCs). On account of their ability to protect the endothelium and the alveolar epithelium through multiple paracrine mechanisms, we looked for adverse effects that aging might cause in MSC biology. Such age-related changes might partly account for the increased susceptibility of the aging lung to injury.

MEASUREMENTS AND MAIN RESULTS

We demonstrated that old mice have more inflammation in response to acute lung injury. To investigate the causes, we compared the global gene expression of aged and young bone marrow-derived MSCs (B-MSCs). Our results revealed that the expression levels of inflammatory response genes depended on the age of the B-MSCs. We demonstrated that the age-dependent decrease in expression of several cytokine and chemokine receptors is important for the migration and activation of B-MSCs. Finally, we showed by adoptive transfer of aged B-MSCs to young endotoxemic mice that aged cells lacked the antiinflammatory protective effect of their young counterparts.

CONCLUSIONS

Taken together, the decreased expression of cytokine and chemokine receptors in aged B-MSCs compromises their protective role by perturbing the potential of B-MSCs to become activated and mobilize to the site of injury.

Novel TNF-α receptor 1 antagonist treatment attenuates arterial inflammation and intimal hyperplasia in mice

AIM

Tumor necrosis factor receptor 1 (TNFR1) participates importantly in arterial inflammation in genetically altered mice; however it remains undetermined whether a selective TNFR1 antagonist inhibits arterial inflammation and intimal hyperplasia. This study aimed to determine the effect and mechanism of a novel TNFR1 antagonist in the suppression of arterial inflammation.

METHODS

We investigated intimal hyperplasia in IL-1 receptor antagonist-deficient mice two weeks after inducing femoral artery injury in an external vascular cuff model. All mice received intraperitoneal injections of TNFR1 antagonist (PEG-R1antTNF) or normal saline twice daily for 14 days.

RESULTS

PEG-R1antTNF treatment yielded no adverse systemic effects, and we observed no significant differences in serum cholesterol or blood pressure in either group; however, selective PEG-R1antTNF treatment significantly reduced intimal hyperplasia (19,671±4,274 vs. 11,440±3,292 µm(2); p=0.001) and the intima/media ratio (1.86±0.43 vs. 1.34±0.36; p=0.029), compared with saline injection. Immunostaining revealed that PEG-R1antTNF inhibits Nuclear factor-κB (NF-κB), suppressing smooth muscle cell (SMC) proliferation and decreasing chemokine and adhesion molecule expression, and thus decreasing intimal hyperplasia and inflammation.

CONCLUSIONS

Our data suggest that PEG-R1antTNF suppresses SMC proliferation and inflammation by inhibiting NF-κB. This study highlights the potential therapeutic benefit of selective TNFR1 antagonist therapy in preventing intimal hyperplasia and arterial inflammation.

Cytokines, macrophage lipid metabolism and foam cells: implications for cardiovascular disease therapy

Cardiovascular disease is the biggest killer globally and the principal contributing factor to the pathology is atherosclerosis; a chronic, inflammatory disorder characterized by lipid and cholesterol accumulation and the development of fibrotic plaques within the walls of large and medium arteries. Macrophages are fundamental to the immune response directed to the site of inflammation and their normal, protective function is harnessed, detrimentally, in atherosclerosis. Macrophages contribute to plaque development by internalizing native and modified lipoproteins to convert them into cholesterol-rich foam cells. Foam cells not only help to bridge the innate and adaptive immune response to atherosclerosis but also accumulate to create fatty streaks, which help shape the architecture of advanced plaques. Foam cell formation involves the disruption of normal macrophage cholesterol metabolism, which is governed by a homeostatic mechanism that controls the uptake, intracellular metabolism, and efflux of cholesterol. It has emerged over the last 20 years that an array of cytokines, including interferon-γ, transforming growth factor-β1, interleukin-1β, and interleukin-10, are able to manipulate these processes. Foam cell targeting, anti-inflammatory therapies, such as agonists of nuclear receptors and statins, are known to regulate the actions of pro- and anti-atherogenic cytokines indirectly of their primary pharmacological function. A clear understanding of macrophage foam cell biology will hopefully enable novel foam cell targeting therapies to be developed for use in the clinical intervention of atherosclerosis.

Ablation of TNF-alpha receptors influences mesenchymal stem cell-mediated cardiac protection against ischemia

Mesenchymal stem cell (MSC) infusion may reduce myocardial ischemic injury. TNF-alpha is a proinflammatory cytokine produced in large quantities during myocardial ischemia that can exert beneficial or detrimental effects on MSC function by binding to a 55-kd receptor (TNFR1) or a 75-kd receptor (TNFR2) on MSCs. We investigated whether genetic modification with ablation of TNFR1 and/or TNFR2 affects MSC-mediated protection against myocardial ischemic injury. The MSCs were harvested from wild-type mice (WT-MSCs) and knockout mice with ablation of TNFR1 and/or TNFR2 (TNFR1KO, TNFR2KO, and TNFR1/R2KO MSCs). After anesthesia was initiated via inhalation of isoflurane, myocardial ischemia was induced in rats via coronary artery ligation. Hearts were then injected with vehicle or MSCs (1 x 10 cells/mL). Myocardial function was assessed 28 days postsurgery with 2-dimensional echocardiograms and isolated heart perfusion. Myocardial tissue was collected for cytokine analysis and infarct measurements. We found that MSC treatment offered significant protection against myocardial ischemia, namely by decreasing infarct size, improving heart function, and decreasing ventricular remodeling compared with vehicle. Compared with WT-MSCs, TNFR1KO MSCs conferred increased cardiac protection, although TNFR2KO and TNFR1/R2KO MSCs conferred less cardiac protection. In addition, treatment with TNFR1KO MSCs was associated with decreased levels of proinflammatory cytokines and an increased level of vascular endothelial growth factor in the myocardium, whereas treatment with TNFR2KO or TNFR1/R2KO MSCs was associated with increased levels of proinflammatory cytokines and a decreased level of vascular endothelial growth factor compared with treatment with WT-MSCs. We conclude that MSC TNFR1 and TNFR2 play important roles in MSC-mediated cardiac protection after myocardial ischemia.

The TNF-like protein 1A-death receptor 3 pathway promotes macrophage foam cell formation in vitro

TNF-like protein 1A (TL1A), a TNF superfamily cytokine that binds to death receptor 3 (DR3), is highly expressed in macrophage foam cell-rich regions of atherosclerotic plaques, although its role in foam cell formation has yet to be elucidated. We investigated whether TL1A can directly stimulate macrophage foam cell formation in both THP-1 and primary human monocyte-derived macrophages with the underlying mechanisms involved. We demonstrated that TL1A promotes foam cell formation in human macrophages in vitro by increasing both acetylated and oxidized low-density lipoprotein uptake, by enhancing intracellular total and esterified cholesterol levels and reducing cholesterol efflux. This imbalance in cholesterol homeostasis is orchestrated by TL1A-mediated changes in the mRNA and protein expression of several genes implicated in the uptake and efflux of cholesterol, such as scavenger receptor A and ATP-binding cassette transporter A1. Furthermore, through the use of virally delivered DR3 short-hairpin RNA and bone marrow-derived macrophages from DR3 knockout mice, we demonstrate that DR3 can regulate foam cell formation and contributes significantly to the action of TL1A in this process in vitro. We show, for the first time, a novel proatherogenic role for both TL1A and DR3 that implicates this pathway as a target for the therapeutic intervention of atherosclerosis.

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.