Dietary fat and reduced levels of TGFbeta1 act synergistically to promote activation of the vascular endothelium and formation of lipid lesions

Atherosclerosis: immunopathogenesis and strategies for immunotherapy

Atherosclerosis, a chronic inflammatory condition in which atheroma accumulates within the intima of the arterial wall, is a life-threatening manifestation of cardiovascular disease, due to atheroma rupture, chronic luminal narrowing and thrombosis. Current knowledge of the role of a protective immune response in atherosclerotic lesions has provided promising opportunities to develop new immunotherapeutic strategies. In particular, Tregs exert an atheroprotective role by releasing anti-inflammatory cytokines (IL-10/TGF-β) and suppressing autoreactive T lymphocytes. In vivo animal experiments have shown that this can be achieved by developing vaccines that stimulate immunological tolerance to atheroma antigens. Here, we present an overview of the current knowledge of the proatherogenic immune response, and we discuss the strategies currently used as immunoregulatory therapy.

Mechanics of ascending aortas from TGFβ-1, -2, -3 haploinsufficient mice and elastase-induced aortopathy

Transforming growth factor-beta (TGFβ-1, -2, -3) ligands act through a common receptor complex yet each is expressed in a unique and overlapping fashion throughout development. TGFβ plays a role in extra-cellular matrix composition with mutations to genes encoding TGFβ and TGFβ signaling molecules contributing to diverse and deadly thoracic aortopathies common in Loeys-Dietz syndrome (LDS). In this investigation, we studied the TGFβ ligand-specific mechanical phenotype of ascending thoracic aortas (ATA) taken from 4-to-6 months-old Tgfb1^+/-, Tgfb2^+/-, and Tgfb3^+/- mice, their wild-type (WT) controls, and an elastase infusion model representative of severe elastolysis. Heterozygous mice were studied at an age without dilation to elucidate potential pre-aortopathic mechanical cues. Our findings indicate that ATAs from Tgfb2^+/- mice demonstrated significant wall thickening, a corresponding decrease in biaxial stress, decreased biaxial stiffness, and a decrease in stored energy. These results were unlike the pathological elastase model where decreases in biaxial stretch were found along with increases in diameter, biaxial stress, and biaxial stiffness. ATAs from Tgfb1^+/- and Tgfb3^+/-, on the other hand, had few mechanical differences when compared to wild-type controls. Although aortopathy generally occurs later in development, our findings reveal that in 4-to-6 month-old animals, only Tgfb2^+/- mice demonstrate a significant phenotype that fails to model ubiquitous elastolysis.

TGFβ, smooth muscle cells and coronary artery disease: a review

Excessive vascular smooth muscle cell (SMC) proliferation, migration and extracellular matrix (ECM) synthesis are key events in the development of intimal hyperplasia, a pathophysiological response to acute or chronic sources of vascular damage that can lead to occlusive narrowing of the vessel lumen. Atherosclerosis, the primary cause of coronary artery disease, is characterised by chronic vascular inflammation and dyslipidemia, while revascularisation surgeries such as coronary stenting and bypass grafting represent acute forms of vascular injury. Gene knockouts of transforming growth factor-beta (TGFβ), its receptors and downstream signalling proteins have demonstrated the importance of this pleiotropic cytokine during vasculogenesis and in the maintenance of vascular homeostasis. Dysregulated TGFβ signalling is a hallmark of many vascular diseases, and has been associated with the induction of pathological vascular cell phenotypes, fibrosis and ECM remodelling. Here we present an overview of TGFβ signalling in SMCs, highlighting the ways in which this multifaceted cytokine regulates SMC behaviour and phenotype in cardiovascular diseases driven by intimal hyperplasia.

Elevated circulating TGF-β is not the cause of increased atherosclerosis development in biglycan deficient mice

BACKGROUND AND AIMS

Vascular biglycan contributes to atherosclerosis development and increased biglycan expression correlates with increased atherosclerosis. However, mice deficient in biglycan have either no reduction in atherosclerosis or an unexpected increase in atherosclerosis. Biglycan deficient mice have systemically elevated TGF-β, likely due to lack of sequestration of TGF-β in the extracellular matrix. The purpose of this study was to determine if prevention of TGF-β elevations in biglycan deficient mice affected atherosclerosis development.

METHODS

Biglycan deficient mice were crossed to Ldlr deficient mice. Diabetes was induced via streptozotocin and all mice were fed a high cholesterol diet. Diabetic biglycan wild type and biglycan deficient Ldlr deficient mice were injected with the TGF-β neutralizing antibody 1D11 or the irrelevant control antibody 13C4.

RESULTS

Biglycan deficient mice had significantly elevated plasma TGF-β levels, which was further increased by diabetes, and significantly increased atherosclerosis. There was a significant correlation between TGF-β concentrations and atherosclerosis. However, despite nearly complete suppression of plasma TGF-β levels in mice treated with the TGF-β neutralizing antibody 1D11, there was no significant difference in atherosclerosis between mice with elevated TGF-β levels and mice with suppressed TGF-β levels.

CONCLUSIONS

The increased atherosclerosis in biglycan deficient mice does not appear to be due to elevations in TGF-β.

Hypercholesterolemia Induces Differentiation of Regulatory T Cells in the Liver

RATIONALE

The liver is the central organ that responds to dietary cholesterol intake and facilitates the release and clearance of lipoprotein particles. Persistent hypercholesterolemia leads to immune responses against lipoprotein particles that drive atherosclerosis. However, the effect of hypercholesterolemia on hepatic T-cell differentiation remains unknown.

OBJECTIVE

To investigate hepatic T-cell subsets upon hypercholesterolemia.

METHODS AND RESULTS

We observed that hypercholesterolemia elevated the intrahepatic regulatory T (Treg) cell population and increased the expression of transforming growth factor-β1 in the liver. Adoptive transfer experiments revealed that intrahepatically differentiated Treg cells relocated to the inflamed aorta in atherosclerosis-prone low-density lipoprotein receptor deficient (Ldlr^-/-) mice. Moreover, hypercholesterolemia induced the differentiation of intrahepatic, but not intrasplenic, Th17 cells in wild-type mice, whereas the disrupted liver homeostasis in hypercholesterolemic Ldlr^-/- mice led to intrahepatic Th1 cell differentiation and CD11b⁺CD11c⁺ leukocyte accumulation.

CONCLUSIONS

Our results elucidate a new mechanism that controls intrahepatic T-cell differentiation during atherosclerosis development and indicates that intrahepatically differentiated T cells contribute to the CD4⁺ T-cell pool in the atherosclerotic aorta.

The Role of Cytokines in the Development of Atherosclerosis

Atherosclerosis contributes to the development of many cardiovascular diseases, which remain the leading cause of death in developed countries. Atherosclerosis is a chronic inflammatory disease of large and medium-sized arteries. It is caused by dyslipidemia and mediated by both innate and adaptive immune responses. Inflammation is a key factor at all stages of atherosclerosis progression. Cells involved in pathogenesis of atherosclerosis were shown to be activated by soluble factors, cytokines, that strongly influence the disease development. Pro-inflammatory cytokines accelerate atherosclerosis progression, while anti-inflammatory cytokines ameliorate the disease. In this review, we discuss the latest findings on the role of cytokines in the development and progression of atherosclerosis.

Changes in CD4+CD25+ Tregs in the pathogenesis of atherosclerosis in ApoE-/- mice

The goal of this study was to observe the pathological characteristics of atherosclerotic plaques in the aortic walls of ApoE^-/- and C57BL/6J mice and the changes of CD4⁺CD25⁺ regulatory T cells (Tregs) in atherosclerotic mice. Twenty ApoE^-/- mice were split into high-fat diet (AH) and normal diet (AN) groups and 10 C57BL/6J male mice were designated as the control group (BN). The serum concentrations of IL-10 and TGF-β1 were detected by enzyme-linked immunosorbent assay; paraffin sections of the aorta were stained with hematoxylin & eosin, and morphometric parameters were measured using the Image Pro Plus 6.0 system. Verhoeff stain was used to observe the distribution of elastic fibers, and immunohistochemical staining was performed to verify the phenotype of the forkhead box protein 3 (Foxp3⁺) CD25⁺ cells in the atherosclerotic tissue. The proportion of CD4⁺CD25⁺ Tregs in the spleen was calculated by flow cytometry. The thickness of the intima, the intima/media ratio, the plaque area, and the plaque/lumen ratio of mice in AN group were significantly larger than those of mice in BN group. The thickness of the intima, the plaque area, and the plaque/lumen ratio of the mice in AH group were significantly increased compared with those of the AN group mice. The serum concentrations of IL-10 and TGF-β1 and the percentage of splenic CD4⁺CD25⁺ Tregs in AN group mice were significantly decreased compared with the control group. The serum concentrations of IL-10 and TGF-β1 and the percentage of splenic CD4⁺CD25⁺ Tregs in the mice in AH group were significantly decreased compared with those in AN group. The proportions of Foxp3⁺ and CD25⁺ cells within the total lymphocyte population were significantly decreased in AH group mice compared with those in AN group mice. Atherosclerosis in an experimental mouse model was correlated with Treg depletion in the lymphoid tissues and plaques, indicating the important antiatherosclerotic role of CD4⁺CD25⁺ Tregs. Impact statement In this article, we conclude that Tregs decreased with atherosclerosis (AS) as determined in ApoE knockout mice fed a high fat diet. It is an important matter for understanding the AS pathology.

Chemokine receptors CXCR2 and CX3CR1 differentially regulate functional responses of bone-marrow endothelial progenitors during atherosclerotic plaque regression

AIMS

Atherosclerosis manifests itself as arterial plaques, which lead to heart attacks or stroke. Treatments supporting plaque regression are therefore aggressively pursued. Studies conducted in models in which hypercholesterolaemia is reversible, such as the Reversa mouse model we have employed in the current studies, will be instrumental for the development of such interventions. Using this model, we have shown that advanced atherosclerosis regression occurs when lipid lowering is used in combination with bone-marrow endothelial progenitor cell (EPC) treatment. However, it remains unclear how EPCs home to regressing plaques and how they augment atherosclerosis reversal. Here we identify molecules that support functional responses of EPCs during plaque resolution.

METHODS AND RESULTS

Chemokines CXCL1 and CX3CL1 were detected in the vascular wall of atheroregressing Reversa mice, and their cognate receptors CXCR2 and CX3CR1 were observed on adoptively transferred EPCs in circulation. We tested whether CXCL1-CXCR2 and CX3CL1-CX3CR1 axes regulate functional responses of EPCs during plaque reversal. We show that pharmacological inhibition of CXCR2 or CX3CR1, or genetic inactivation of these two chemokine receptors interfered with EPC-mediated advanced atherosclerosis regression. We also demonstrate that CXCR2 directs EPCs to regressing plaques while CX3CR1 controls a paracrine function(s) of these cells.

CONCLUSION

CXCR2 and CX3CR1 differentially regulate EPC functional responses during atheroregression. Our study improves understanding of how chemokines and chemokine receptors regulate plaque resolution, which could determine the effectiveness of interventions reducing complications of atherosclerosis.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Prevention of TGFβ induction attenuates angII-stimulated vascular biglycan and atherosclerosis in Ldlr-/- mice

Angiotensin II (angII) accelerates atherosclerosis, but the mechanisms are not fully understood. The aim of this study was to determine whether TGFβ is required for angII-induced atherosclerosis. Ldlr-null mice fed a normal chow diet were infused with angII or saline for 28 days. A single injection of TGFβ neutralizing antibody 1D11 (2 mg/kg) prevented angII-induction of TGFβ1 levels, and strikingly attenuated angII-induced accumulation of aortic biglycan content. To study atherosclerosis, mice were infused with angII or saline for 4 weeks, and then fed Western diet for a further 6 weeks. 1D11 had no effect on systolic blood pressure or plasma cholesterol; however, angII-infused mice that received 1D11 had reduced atherosclerotic lesion area by 30% (P < 0.05). Immunohistochemical analyses demonstrated that angII induced both lipid retention and accumulation of biglycan and perlecan which colocalized with apoB. 1D11 strikingly reduced the effect of angII on biglycan but not perlecan. 1D11 decreased total collagen content (P < 0.05) in the lesion area without changing plaque inflammation markers (CD68 and CD45). Thus, this study demonstrates that neutralization of TGFβ attenuated angII stimulation of biglycan accumulation and atherogenesis in mice, suggesting that TGFβ-mediated biglycan induction is one of the mechanisms underlying angII-promoted atherosclerosis.

Pro- and Anti-Inflammatory Cytokine Networks in Atherosclerosis

Despite advances in prevention and treatment, atherosclerotic vascular disease continues to account for significant morbidity, mortality, and economic burden in the western world. Our current understanding of this disease presents atherosclerosis as a chronic inflammatory process involving multiple cell types in various stages of activation, apoptosis, and necrosis. These cells include monocyte/macrophage, dendritic cells, lymphocytes, endothelial cells, and vascular smooth muscle cells. Activation of these cells and their processes is initiated and sustained by a complex network of soluble factors termed cytokines. Cytokines are produced and recognized by both inflammatory and resident vascular cells, allowing crosstalk between these two systems. Cytokines also regulate the phenotype of many of these cell types. Recognizing functions of these cytokines and their effects on cells which populate atherosclerotic plaque is key to uncovering targets of therapeutic intervention. This paper will present recent studies which describe the cellular protagonists of atherosclerosis and the role they play in formation of atherosclerotic plaque. It will also describe the cytokines which have been identified as produced by and directly affecting dysfunction of these cells. Because atherosclerosis is considered an inflammatory condition, emphasis will be placed on inflammatory cytokines and their effects on atherogenesis. We will conclude with new directions in therapeutic strategies and points of emphasis for future research.

Accelerated atherosclerosis in SLE: mechanisms and prevention approaches

Systemic lupus erythematosus (SLE) is a multi-organ autoimmune disease characterized by increased serum autoantibody levels and tissue damage. With improved diagnosis and more effective treatment of the resultant kidney disease, accelerated atherosclerosis has become a major cause of morbidity in patients suffering from SLE. Although the exact mechanisms for SLE-accelerated atherosclerosis are unknown, multiple factors have been established as potential players in this process. Among these potential players are dysregulation of T and B cell populations and increased circulating levels of inflammatory cytokines. In addition, SLE patients exhibit a proatherogenic lipid profile characterized by low HDL and high LDL and triglycerides. Recent therapeutic approaches have focused on targeting B cells, the producers of autoantibodies, but most studies do not consider the effects of these treatments on atherosclerosis. Evidence suggests that T cells play a major role in SLE-accelerated atherosclerosis. Therefore, therapies targeted at T cells may also prove invaluable in treating SLE and atherosclerosis.

Interleukin-27 receptor limits atherosclerosis in Ldlr-/- mice

RATIONALE

Atherosclerosis is a chronic inflammatory disease of the arterial wall. Several proinflammatory cytokines are known to promote atherosclerosis, but less is known about the physiological role of anti-inflammatory cytokines. Interleukin (IL)-27 is a recently discovered member of the IL-6/IL-12 family. The IL-27 receptor is composed of IL-27 receptor A (WSX-1) and gp130 and is required for all established IL-27 signaling pathways. The expression of the IL-27 subunit Ebi3 is elevated in human atheromas, yet its function in atherosclerosis remains unknown.

OBJECTIVE

The aim of this study was to test the role of IL-27 receptor signaling in immune cells in atherosclerosis development.

METHODS AND RESULTS

Atherosclerosis-prone Ldlr(-/-) mice transplanted with Il27ra(-/-) bone marrow and fed Western diet for 16 weeks developed significantly larger atherosclerotic lesions in aortic roots, aortic arches, and abdominal aortas. Augmented disease correlated with increased accumulation of CD45(+) leukocytes and CD4(+) T cells in the aorta, which produced increased amounts of IL-17A and tumor necrosis factor. Several chemokines, including CCL2, were upregulated in the aortas of Ldlr(-/-) mice receiving Il27ra(-/-) bone marrow, resulting in accumulation of CD11b(+) and CD11c(+) macrophages and dendritic cells in atherosclerotic aortas.

CONCLUSIONS

The absence of anti-inflammatory IL-27 signaling skews immune responses toward T-helper 17, resulting in increased production of IL-17A and tumor necrosis factor, which in turn enhances chemokine expression and drives the accumulation of proatherogenic myeloid cells in atherosclerotic aortas. These findings establish a novel antiatherogenic role for IL-27 receptor signaling, which acts to suppress the production of proinflammatory cytokines and chemokines and to curb the recruitment of inflammatory myeloid cells into atherosclerotic aortas.

TGF-β1 content in atherosclerotic plaques, TGF-β1 serum concentrations and incident coronary events

BACKGROUND

We tested the hypothesis that high TGF-β1 content in atherosclerotic plaques and high TGF-β1 serum levels are associated with lower risk of coronary events in two independent prospective studies.

MATERIALS AND METHODS

In the prospective Athero-Express biobank study, total TGF-β1 plaque levels were measured in 632 atherosclerotic lesions from patients who underwent carotid endarterectomy. In a population-based case-cohort study within the Monitoring of trends and determinants in cardiovascular disease (MONICA)/Cooperative Health Research in the Region of Augsburg (KORA) Augsburg studies, baseline total TGF-β1 serum levels were measured in 333 individuals with and 1728 without incident coronary events.

RESULTS

Patients with TGF-β1 content in their plaques above the study median did not have a lower risk of coronary events than patients with lower TGF-β1 levels [adjusted HR (95% CI) 1·46 (0·83-2·53); P = 0·16; mean follow-up 2·6 ± 0·7 years] in the Athero-Express biobank study. Cox proportional hazard models adjusting for age, sex, body mass index, metabolic factors, lifestyle factors and survey did not reveal a significant association between TGF-β1 serum levels and incident coronary events [HR (95% CI) for increasing TGF-β1 tertiles 1·0, 1·22 (0·88-1·68), 1·13 (0·82-1·57); P = 0·47; mean follow-up: 10·8 ± 4·6 years] in the MONICA/KORA Augsburg studies.

CONCLUSION

Our results indicate that high TGF-β1 content in human atherosclerotic plaques and high serum levels of TGF-β1 are not associated with reduced risk of coronary events.

Activation of human vascular cells decreases their expression of transforming growth factor-beta

OBJECTIVE

Despite pro-fibrotic effects, transforming growth factor (TGF)-β prevents arteriosclerosis by suppressing effector leukocytes and promoting smooth muscle differentiation. However, previous observations of increased TGF-β expression in arteriosclerotic plaques are not consistent with that of an effective protective factor. We investigated the expression, regulation, and responses of TGF-β in human arterial tissues and cells.

METHODS AND RESULTS

The expression of TGF-β by intrinsic vascular cells was lower in arteriosclerotic than non-diseased coronary arteries. Activation of resident and infiltrating leukocytes did not elicit TGF-β production from coronary artery segments in organ culture. Instead, the basal expression of TGF-β by coronary arteries decreased after vessel procurement and ex vivo culture. Activation of cultured smooth muscle cells and endothelial cells with phorbol ester and ionophore also decreased TGF-β expression. Isolated cell types representing those found in the artery wall were all capable of signaling in response to TGF-β, however production of the cytoprotective molecule, interleukin-11 was cell type-dependent and restricted to smooth muscle cells and fibroblasts. Interleukin-11 reduced smooth muscle cell apoptosis to T cell effectors.

CONCLUSIONS

Inflammation and cellular activation diminish the basal expression of TGF-β by quiescent human vascular cells. Induction of interleukin-11 may contribute to the anti-arteriosclerotic actions of TGF-β.

Recent advances on the role of cytokines in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall driven by innate and adaptive immune responses. Inflammation controls the development and the destabilization of arterial plaque. Cells involved in the atherosclerotic process secrete and are activated by soluble factors, known as cytokines. Important recent advances in the comprehension of the mechanisms of atherosclerosis have provided evidence for a dual role of cytokines: proinflammatory and T helper-1-related cytokines promote the development and progression of the disease, whereas antiinflammatory and regulatory T cell-related cytokines exert clear antiatherogenic activities. This review focuses on recent advances regarding the role of cytokines, with the exception of chemokines, in the development, progression, and complications of atherosclerosis.

Activation of the ROCK1 branch of the transforming growth factor-beta pathway contributes to RAGE-dependent acceleration of atherosclerosis in diabetic ApoE-null mice

RATIONALE

The multiligand RAGE (receptor for advanced glycation end products) contributes to atherosclerosis in apolipoprotein (Apo)E-null mice.

OBJECTIVE

To delineate the specific mechanisms by which RAGE accelerated atherosclerosis, we performed Affymetrix gene expression arrays on aortas of nondiabetic and diabetic ApoE-null mice expressing RAGE or devoid of RAGE at nine weeks of age, as this reflected a time point at which frank atherosclerotic lesions were not yet present, but that we would be able to identify the genes likely involved in diabetes- and RAGE-dependent atherogenesis.

METHODS AND RESULTS

We report that there is very little overlap of the genes that are differentially expressed both in the onset of diabetes in ApoE-null mice, and in the effect of RAGE deletion in diabetic ApoE-null mice. Pathway-Express analysis revealed that the transforming growth factor-beta pathway and focal adhesion pathways might be expected to play a significant role in both the mechanism by which diabetes facilitates the formation of atherosclerotic plaques in ApoE-null mice, and the mechanism by which deletion of RAGE ameliorates this effect. Quantitative polymerase chain reaction studies, Western blotting, and confocal microscopy in aortic tissue and in primary cultures of murine aortic smooth muscle cells supported these findings.

CONCLUSIONS

Taken together, our work suggests that RAGE-dependent acceleration of atherosclerosis in ApoE-null mice is dependent, at least in part, on the action of the ROCK1 (rho-associated protein kinase 1) branch of the transforming growth factor-beta pathway.

Common pathogenic features of atherosclerosis and calcific aortic stenosis: role of transforming growth factor-beta

Calcific aortic stenosis and atherosclerosis have been investigated separately in experimental in vitro and in vivo studies and in clinical studies. The similarities identified in both diseases suggest that similar pathogenic pathways are involved in both conditions. Most current therapeutic studies are focused on statins. The evidence suggests that statin effects on valves may, in large part, be independent of the lipid lowering effects of the drug. There are several molecules that play significant regulatory roles on the development and progression of valve sclerosis and calcification and on growth and complications of atherosclerotic plaques. The purpose of this review is to discuss the pathogenic features of the two conditions, highlight the important similarities, and then review the data that suggest that transforming growth factor-beta may play a key regulatory role in both diseases and that this is worthy of study as a potential therapeutic target for both conditions.

Cytokine network and T cell immunity in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall where both innate and adaptive immune responses contribute to disease initiation and progression. Recent studies established that subtypes of T cells, regulatory T cells (Tregs), actively involved in the maintenance of immunological tolerance, inhibit the development and progression of atherosclerosis. Here, we review the current knowledge on the Treg response and the major cytokines involved in its modulation in the context of atherosclerosis.

TGF-[beta]1 limits plaque growth, stabilizes plaque structure, and prevents aortic dilation in apolipoprotein E-null mice

OBJECTIVE

Impairment of transforming growth factor (TGF)-beta1 signaling accelerates atherosclerosis in experimental mice. However, it is uncertain whether increased TGF-beta1 expression would retard atherosclerosis. The role of TGF-beta1 in aneurysm formation is also controversial. We tested whether overexpression of active TGF-beta1 in hyperlipidemic mice affects atherogenesis and aortic dilation.

METHODS AND RESULTS

We generated apolipoprotein E-null mice with transgenes that allow regulated overexpression of active TGF-beta1 in their hearts. Compared to littermate controls, these mice had elevated cardiac and plasma TGF-beta1, less aortic root atherosclerosis (P< or =0.002), fewer lesions in the thoracic and abdominal aortae (P< or =0.01), less aortic root dilation (P<0.001), and fewer pseudoaneurysms (P=0.02). Mechanistic studies revealed no effect of TGF-beta1 overexpression on plasma lipids or cytokines, or on peripheral lymphoid organ cells. However, aortae of TGF-beta1-overexpressing mice had fewer T-lymphocytes, more collagen, less lipid, lower expression of inflammatory cytokines and matrix metalloproteinase-13, and higher expression of tissue inhibitor of metalloproteinase-2.

CONCLUSIONS

When overexpressed in the heart and plasma, TGF-beta1 is an antiatherogenic, vasculoprotective cytokine that limits atherosclerosis and prevents aortic dilation. These actions are associated with significant changes in cellularity, collagen and lipid accumulation, and gene expression in the artery wall.

The role of adaptive T cell immunity in atherosclerosis

There is now solid evidence that T cell adaptive immunity is involved in atherogenesis. While initial studies have focused on the pathogenic arm of the immune response, more recent work clearly suggests an important role for several subsets of regulatory T cells in the protection against lesion development. Here, we review the current knowledge on the role of both pathogenic and regulatory adaptive T cell immunity in atherosclerosis, generated mainly from the study of mouse models of the disease.

Regulatory T-cell immunity and its relevance to atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall where both innate and adaptive immune responses contribute to disease initiation and progression. Recent studies from several groups suggest that subtypes of T cells, called regulatory T cells, previously shown to maintain immunological tolerance, inhibit the development and progression of atherosclerosis. Here, we review the current knowledge on the regulatory T-cell response and the major cytokines involved in its modulation in the context of atherosclerosis.

An overview of cytokine interactions in atherosclerosis and implications for peripheral arterial disease

Over the last three decades, a surge in research into the inflammatory pathophysiology of atherosclerosis has highlighted an array of cytokines and other inflammatory mediators associated with underlying inflammatory burden. The ability to identify and simultaneously measure multiple cytokines in peripheral blood highlights their potential as biomarkers of atherosclerosis. This has prompted much research in vascular medicine to identify the ;at-risk' groups for atherostenotic or atheroaneurysmal disease. This review is compiled with similar intentions and aims to discern the relevant evidence for cytokine profiling in peripheral arterial disease (PAD), where such information is lacking, while providing a holistic overview of cytokine interactions in atherosclerosis. This is pertinent given that cytokine profiles from coronary artery disease and aortic aneurysm studies cannot be directly extrapolated to PAD due to differences in inflammatory environments that exist in these conditions. Whilst plaque morphology and blood rheology play an important role in the cardiac manifestations of atherosclerosis, tissue thrombogenecity is very important in PAD. Further, cytokines act in concert rather than in isolation in a disease process, and no single cytokine in a cross-sectional model is able to serve as an absolute screening marker. Thus, it is essential to understand the regulation of cytokine production in atherosclerosis prior to evaluating the viability and merits of a multimarker approach for clinical risk stratification in PAD.

Cholesterol modulates cellular TGF-beta responsiveness by altering TGF-beta binding to TGF-beta receptors

Transforming growth factor-beta (TGF-beta) responsiveness in cultured cells can be modulated by TGF-beta partitioning between lipid raft/caveolae- and clathrin-mediated endocytosis pathways. The TbetaR-II/TbetaR-I binding ratio of TGF-beta on the cell surface has recently been found to be a signal that controls TGF-beta partitioning between these pathways. Since cholesterol is a structural component in lipid rafts/caveolae, we have studied the effects of cholesterol on TGF-beta binding to TGF-beta receptors and TGF-beta responsiveness in cultured cells and in animals. Here we demonstrate that treatment with cholesterol, alone or complexed in lipoproteins, decreases the TbetaR-II/TbetaR-I binding ratio of TGF-beta while treatment with cholesterol-lowering or cholesterol-depleting agents increases the TbetaR-II/TbetaR-I binding ratio of TGF-beta in all cell types studied. Among cholesterol derivatives and analogs examined, cholesterol is the most potent agent for decreasing the TbetaR-II/TbetaR-I binding ratio of TGF-beta. Cholesterol treatment increases accumulation of the TGF-beta receptors in lipid rafts/caveolae as determined by sucrose density gradient ultracentrifugation analysis of cell lysates. Cholesterol/LDL suppresses TGF-beta responsiveness and statins/beta-CD enhances it, as measured by the levels of P-Smad2 and PAI-1 expression in cells stimulated with TGF-beta. Furthermore, the cholesterol effects observed in cultured cells are also found in the aortic endothelium of atherosclerotic ApoE-null mice fed a high cholesterol diet. These results indicate that high plasma cholesterol levels may contribute to the pathogenesis of certain diseases (e.g., atherosclerosis) by suppressing TGF-beta responsiveness.

Role of transforming growth factor-beta superfamily signaling pathways in human disease

Transforming growth factor beta (TGF-beta) superfamily signaling pathways are ubiquitous and essential regulators of cellular processes including proliferation, differentiation, migration, and survival, as well as physiological processes, including embryonic development, angiogenesis, and wound healing. Alterations in these pathways, including either germ-line or somatic mutations or alterations in the expression of members of these signaling pathways often result in human disease. Appropriate regulation of these pathways is required at all levels, particularly at the ligand level, with either a deficiency or an excess of specific TGF-beta superfamily ligands resulting in human disease. TGF-beta superfamily ligands and members of these TGF-beta superfamily signaling pathways also have emerging roles as diagnostic, prognostic or predictive markers for human disease. Ongoing studies will enable targeting of TGF-beta superfamily signaling pathways for the chemoprevention and treatment of human disease.

Cholesterol suppresses cellular TGF-beta responsiveness: implications in atherogenesis

Hypercholesterolemia is a major causative factor for atherosclerotic cardiovascular disease. The molecular mechanisms by which cholesterol initiates and facilitates the process of atherosclerosis are not well understood. Here, we demonstrate that cholesterol treatment suppresses or attenuates TGF-beta responsiveness in all cell types studied as determined by measuring TGF-beta-induced Smad2 phosphorylation and nuclear translocation, TGF-beta-induced PAI-1 expression, TGF-beta-induced luciferase reporter gene expression and TGF-beta-induced growth inhibition. Cholesterol, alone or complexed in lipoproteins (LDL, VLDL), suppresses TGF-beta responsiveness by increasing lipid raft and/or caveolae accumulation of TGF-beta receptors and facilitating rapid degradation of TGF-beta and thus suppressing TGF-beta-induced signaling. Conversely, cholesterol-lowering agents (fluvastatin and lovastatin) and cholesterol-depleting agents (beta-cyclodextrin and nystatin) enhance TGF-beta responsiveness by increasing non-lipid raft microdomain accumulation of TGF-beta receptors and facilitating TGF-beta-induced signaling. Furthermore, the effects of cholesterol on the cultured cells are also found in the aortic endothelium of ApoE-null mice fed a high-cholesterol diet. These results suggest that high cholesterol contributes to atherogenesis, at least in part, by suppressing TGF-beta responsiveness in vascular cells.

Transforming growth factor activity is a key determinant for the effect of estradiol on fatty streak deposit in hypercholesterolemic mice

OBJECTIVE

Whereas estradiol prevents fatty streak deposit in immunocompetent apoE-/- or LDLr-/- mice, it is totally ineffective in immunodeficient mice, underlining the key role of immunoinflammation in this effect. In the present work, the role of several major pro- and antiinflammatory cytokines involved in the atheromatous process was evaluated in the effect of estradiol on fatty streak constitution.

METHODS AND RESULTS

The preventive effect of estradiol was fully maintained in LDLr-/- mice grafted with bone marrow from either IFN-gamma or interleukin (IL)-12-deficient mice, showing that this beneficial effect was not mediated through a specific decrease in the production of these 2 proinflammatory cytokines. Furthermore, IL-10-/- apoE-/- mice remained protected by estradiol, excluding a significant contribution of this antiinflammatory cytokine. In contrast, the protective effect of estradiol was (1) associated with enhanced aortic expression of TGF-beta1 in apoE-/- mice during early steps of atherogenesis; (2) abolished and even reversed in apoE-/- mice administered with a neutralizing anti-TGF-beta antibody; (3) abolished in LDLr-/- mice grafted with bone marrow from Smad3-deficient mice.

CONCLUSIONS

The status of the TGF-beta pathway crucially determines the antiatherogenic effect of estradiol in hypercholesterolemic mice, whereas neither IFN-gamma, IL-12, nor IL-10 are specifically involved in this protection.

Distinctive expression of chemokines and transforming growth factor-beta signaling in human arterial endothelium during atherosclerosis

Knowledge about the in vivo role of endothelium in chronic human atherosclerosis has mostly been derived by insights from mouse models. Therefore, we set out to establish by microarray analyses the gene expression profiles of endothelium from human large arteries, as isolated by laser microbeam microdissection, having focal atherosclerosis of the early or the advanced stage. Within individual arteries, the endothelial transcriptomes of the lesional and unaffected sides were compared pairwise, thus limiting genetic and environmental confounders. Specific endothelial signature gene sets were identified with changed expression levels in either early (n = 718) or advanced atherosclerosis (n = 403), relative to their paired plaque-free controls. Gene set enrichment analysis identified distinct sets of chemokines and differential enrichments of nuclear factor-kappaB-, p53-, and transforming growth factor-beta-related genes in advanced plaques. Immunohistochemistry validated the discriminative value of corresponding endothelial protein expression between early (fractalkine/CX3CL1, IP10/CCL10, TBX18) or advanced (BAX, NFKB2) stages of atherosclerosis and versus their plaque-free controls. The functional involvement of transforming growth factor-beta signaling in directing its downstream gene repertoire was substantiated by a consistent detection of activated SMAD2 in advanced lesions. Thus, we identified truly common, local molecular denominators of pathological changes to vascular endothelium, with a marked distinction of endothelial phenotype between early and advanced plaques.

The role of Smad3-dependent TGF-beta signal in vascular response to injury

Transforming growth factor (TGF)-beta is a multifunctional cytokine involved in the regulation of proliferation, differentiation, migration, and survival of many different cell types. The role of TGF-beta in atherosclerosis has been intensively studied, but the precise function of the downstream signals in this disease entity remains unclear. We recently discovered that mice lacking Smad3, a major downstream mediator of TGF-beta, show enhanced neointimal hyperplasia with decreased matrix deposition in response to vascular injury. This review summarizes the current view on involvement of TGF-beta in atherosclerotic vascular disease and discusses the role of Smad3-dependent TGF-beta signal in vascular response to injury.

Frequency of polymorphisms of signal peptide of TGF-beta1 and -1082G/A SNP at the promoter region of Il-10 gene in patients with carotid stenosis

The role of inflammation in atherosclerosis is well recognized. We have evaluated the allele frequencies of the +869T/C and +915G/C polymorphisms (SNPs) at the TGF-beta1 gene and -1082G/A SNP at IL-10 promoter sequence, two well-known immunosuppressive and anti-inflammatory cytokines, in patients with carotid stenosis. Our data suggest a lack of association between these SNPs and the susceptibility to atherosclerosis although other reports have demonstrated this association. These results may be due to the pleiotropic effects of the cytokines and/or differences in haplotype combination that should be investigated to elucidate the role of TGF-beta1 and IL-10 polymorphisms in atherosclerosis.

TGF-beta1 generates a specific multicomponent extracellular matrix in human coronary SMC

BACKGROUND

Transforming growth factor (TGF-beta(1)) is postulated to play an important role in maintaining the structure and function of arterial tissue and protection against development of arteriosclerosis. The TGF-beta(1)-induced production of a stable extra-cellular matrix-rich plaque phenotype is suggested to be part of the protection against a switch to an unstable rupture-prone arteriosclerotic plaque.

MATERIALS AND METHODS

This study addresses the question of whether the expression profile and the type of extra-cellular matrix (ECM) generated by TGF-beta(1) stimulation have the structural feature of a fibril-rich stable matrix. Seventeen genes codings for ECM components of human coronary smooth muscle cells (SMCs) after a 24-h stimulation by TGF-beta(1) have been analyzed.

RESULTS

Real-time RT-PCR was used to quantify the mRNA of genes under investigation. It was found that after TGF-beta(1) stimulation (a) the up-regulation of COL1A1-specific mRNA was associated with increased [(3)H]proline incorporation into the alpha-1 and -2 chains of collagen type I, (b) the up-regulation of biglycan- and syndecan-1-specific mRNA corresponded to an increased [(35)S]sulphate and [4,5-(3)H]leucine incorporation into the biglycan molecule and to an increase of syndecan-1 protein, (c) the up-regulated FGF-2 gene accounted predominantly for the ECM-bound subfraction of FGF-2-protein and (d) fibronectin and thrombospondin exhibited a significantly higher mRNA level. In contrast collagen XIV, a minor collagen type, and the proteoglycan decorin were down-regulated. The down-regulated decorin changed its structure by elongation and reduced GlcA to IdoA epimerization of the dermatan sulphate side-chain as judged by [(35)S]sulphate metabolic labelling experiments. No significant changes in response to TGF-beta(1) were observed for the collagen types III, VI and XVI, for versican, perlecan and the syndecans-2 and -4.

CONCLUSIONS

It was concluded from the data that the TGF-beta(1)-induced formation of a highly specific multicomponent extra-cellular matrix on coronary arterial SMCs could provide in vivo mechanical strength to the neointima in arteriosclerotic lesions and to the fibrous cap overlying the lipid core.

Suppression of atherogenesis by delivery of TGFbeta1ACT using adeno-associated virus type 2 in LDLR knockout mice

TGFbeta(1) deficiency has been attributed to the development of atherosclerosis. There is, however, little direct evidence for this concept. To examine this hypothesis, low-density lipoprotein receptor knockout (LDLR(-/-)) mice were injected via tail vein with recombinant adeno-associated virus type 2 (rAAV) carrying a bioactive TGFbeta(1) mutant (AAV/TGFbeta1ACT, n=10) or granulocyte-macrophage-colony stimulating factor (AAV/GM-CSF, n=10, a negative control) or saline (n=9, control), and then put on a high cholesterol diet. At 18 weeks, blood lipids were found to be similarly elevated in all LDLR(-/-) mice. TGFbeta1ACT and GM-CSF (DNA, mRNA, and protein) were highly expressed in the tissues of mice given TGFbeta1ACT or AAV/GM-CSF, respectively, showing sustained transfection following gene delivery by the systemic route. Saline-treated and AAV/GM-CSF-treated LDLR(-/-) mice showed extensive areas of atherosclerotic lesion formation. There was evidence of intense oxidative stress (nitrotyrosine staining), inflammation (CD68 staining), and expression of adhesion molecules and the ox-LDL receptor LOX-1 (gene array analysis) in the atherosclerotic tissues. Importantly, atherosclerotic lesion formation was markedly inhibited in the LDLR(-/-) mice given AAV/TGFbeta1ACT. Expression of adhesion molecules and LOX-1, oxidative stress, and inflammatory response all were inhibited in the mice given AAV/TGFbeta1ACT (P<0.05 vs. saline-treated or GM-CSF-treated LDLR(-/-) mice). These data for the first time demonstrate that systemic delivery of TGFbeta1ACT gene via AAV can inhibit formation of atherosclerotic lesions, possibly via anti-inflammatory and anti-oxidant mechanisms. These findings suggest a novel view of TGFbeta(1) in atherogenesis and a potential new gene therapy for treatment of atherosclerosis.

Cytokines in Atherosclerosis: Pathogenic and Regulatory Pathways

Atherosclerosis is a chronic disease of the arterial wall where both innate and adaptive immunoinflammatory mechanisms are involved. Inflammation is central at all stages of atherosclerosis. It is implicated in the formation of early fatty streaks, when the endothelium is activated and expresses chemokines and adhesion molecules leading to monocyte/lymphocyte recruitment and infiltration into the subendothelium. It also acts at the onset of adverse clinical vascular events, when activated cells within the plaque secrete matrix proteases that degrade extracellular matrix proteins and weaken the fibrous cap, leading to rupture and thrombus formation. Cells involved in the atherosclerotic process secrete and are activated by soluble factors, known as cytokines. Important recent advances in the comprehension of the mechanisms of atherosclerosis provided evidence that the immunoinflammatory response in atherosclerosis is modulated by regulatory pathways, in which the two anti-inflammatory cytokines interleukin-10 and transforming growth factor-β play a critical role. The purpose of this review is to bring together the current information concerning the role of cytokines in the development, progression, and complications of atherosclerosis. Specific emphasis is placed on the contribution of pro- and anti-inflammatory cytokines to pathogenic (innate and adaptive) and regulatory immunity in the context of atherosclerosis. Based on our current knowledge of the role of cytokines in atherosclerosis, we propose some novel therapeutic strategies to combat this disease. In addition, we discuss the potential of circulating cytokine levels as biomarkers of coronary artery disease.

‘Not only…but also’: factors that contribute to accelerated atherosclerosis and premature coronary heart disease in systemic lupus erythematosus

Premature coronary heart disease (CHD) has emerged as a major cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). Overall SLE patients have a 5-6-fold increased risk of CHD and this excess risk is especially pronounced in younger women where the excess risk may be >50-fold. Studies from our group and others have also demonstrated that SLE patients have a higher prevalence of subclinical atherosclerosis compared with controls, with approximately 30% having evidence of subclinical involvement. It is important to consider what factors may underlie this excess risk. We have found that certain 'classic' risk factors, i.e. hypertension and diabetes mellitus, are more prevalent in SLE and that persistent hypercholesterolaemia independently predicts patients who will develop CHD. These risk factors alone do not completely explain the excess risk observed, and after adjusting for classic risk factors SLE remains independently associated with both clinical and subclinical outcomes. Certain other metabolic changes also occur more frequently in SLE, namely premature menopause, renal impairment, high triglycerides and higher plasma homocysteine. In addition, insulin resistance is more pronounced in patients with SLE, and approximately 18% have the metabolic syndrome. It is also increasingly accepted that atherosclerosis is a chronic inflammatory condition, and in SLE systemic complement activation as well as immune complex formation can result in changes that promote the development of atheroma. Similarly, autoantibody production, especially antibodies directed against lipoprotein subtypes and those in the antiphospholipid (APLA) family, are gaining increasing attention. The role of the latter are particularly controversial as different subtypes have been shown to both promote and protect against atherogenesis. In a study looking at carotid plaque in SLE, we found that APLA was independently associated with the presence of plaque; this study also found that patients with plaque had higher white cell counts, suggesting ongoing chronic inflammation. We have also noted a negative correlation between activation of transforming growth factor beta-1 and carotid intima-medial thickness. This cytokine, which is known to be a potent anti-inflammatory molecule, has also been shown to be protective against atherogenesis. With regard to therapy, steroids may be a true double-edged sword, with low doses exerting a beneficial anti-inflammatory role whereas higher doses may be detrimental through exacerbation of metabolic risk factors. In contrast, we have found that antimalarials have a beneficial effect on lipids especially when co-prescribed with steroids, and this, along with anti-inflammatory and proposed antiplatelet effects, may confer protection against CHD in lupus. The risk of premature CHD in SLE is therefore mediated by a number of factors that involve not only classic risk factors but also a range of factors associated with SLE itself. Preventative strategies will therefore need to address all potential risk factors of relevance. A more through understanding of the interplay between autoimmunity and atherogenesis should be possible by the study of SLE, and this may not only benefit lupus patients but also may have implications for our understanding of atherosclerosis in general.

Arterial endothelial dysfunction in baboons fed a high-cholesterol, high-fat diet

BACKGROUND

Endothelial dysfunction signals the initiation and progression of atherosclerosis. Elevated LDL-cholesterol concentrations have been suggested to induce endothelial dysfunction, but direct in vivo evidence for the relation is still lacking.

OBJECTIVE

We examined the hypothesis that a high-cholesterol, high-fat (HCHF) diet can directly cause endothelial dysfunction in vivo.

DESIGN

We measured inflammatory and endothelial dysfunctional markers in circulating blood and directly in endothelial cells, which were collected by femoral artery biopsies, in 10 baboons before and after a 7-wk HCHF dietary challenge.

RESULTS

We found that the HCHF diet induced a high inflammatory status, as indicated by increased concentrations of interleukin 6, tumor necrosis factor alpha (TNF-alpha), and monocyte chemoattractant protein 1. Although the concentrations of endothelial dysfunctional markers, such as soluble vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1, were not increased by the HCHF diet, membrane-bound VCAM-1 and membrane-bound E-selectin on endothelial cells were highly increased after 7 wk of the HCHF diet (P < 0.01). In contrast, the concentrations of endothelial nitric oxide synthase in endothelial cells were significantly reduced by the 7-wk HCHF diet (P < 0.01). Furthermore, the dietary challenge attenuated endothelial cell responses to TNF-alpha, lipopolysaccharide, native LDL cholesterol, and oxidized LDL-cholesterol stimulation.

CONCLUSIONS

Our results show that an HCHF diet can directly induce inflammation and endothelial dysfunction. Prior in vivo exposure to an HCHF diet attenuates the in vitro responses of endothelial cells to atherogenic risk factors. This preconditioning phenomenon may have significant clinical relevance.

Nicotine modulates cytokine production by Chlamydia pneumoniae infected human peripheral blood cells

Nicotine, the addictive component of cigarette smoke, has been shown to have immunomodulatory effects. This drug alters proinflammatory cytokine production by immune cells, including lymphocytes, monocytes, and macrophages. The present study focuses on the effects of nicotine on infection by Chlamydia pneumoniae (Cpn), a ubiquitous intracellular pathogen which causes acute and chronic inflammatory diseases such as pulmonary infections, and may be associated with arthritis and atherosclerosis. Previous studies in our laboratory showed that lymphocytes and macrophages are susceptible to Cpn infection. The present study aimed at investigating the effect of nicotine on TGF-beta1, IL-10, IL-12, and TNF-alpha production in Cpn-infected human peripheral blood mononuclear cells (PBMCs). Cytokine levels in the supernatant were assessed by ELISA. The results showed that Cpn infection alters the expression levels of IL-10, IL-12, and TNF-alpha in a time-dependent fashion. Nicotine treatment of the Cpn-infected cells up-regulated IL-10, but not TNF-alpha and IL-12, and also resulted in significant down-regulation of TGF-beta1 production which was marked in the Cpn-infected control cells. The combined action of nicotine and Cpn on cytokine production may have an impact in chronic inflammatory diseases.

Inhibitory control of TGF-beta1 on the activation of Rap1, CD11b, and transendothelial migration of leukocytes

Beta2-integrins are a family of dimeric adhesion molecules expressed on leukocytes. Their capacity to bind ligand is regulated by their state of activation. CD11b, an alphaMbeta2 integrin, is implicated in a number of physiological and pathological events such as inflammation, thrombosis, or atherosclerosis. The GTPase Rap1 is essential for its activation and could therefore play a strategic role in the regulation of leukocyte functioning. Because low levels of circulating TGF-beta have been linked with severe atherosclerosis, we have assessed the role of this cytokine in the regulation of Rap1 and CD11b activation in differentiated U937 cells and in human peripheral blood monocytes. TGF-beta1 caused a significant reduction in the expression of CD11b but not in the expression of other integrins tested. More importantly, TGF-beta1 greatly reduced the capacity of PMA or chemokines to activate CD11b and Rap1, a phenomenon paralleled by a loss of the Epac transcript and a reduction in 8-pCPT-2'-O-Me-cAMP-mediated activation of Rap1. This inhibition diminished the capacity of monocytes to migrate across a monolayer of endothelial cells. The inhibitory effect of TGF-beta1 on Rap1 activity may exert a general protective influence against aberrant transendothelial migration, thereby holding inflammatory responses in check.

Matrix GLA protein stimulates VEGF expression through increased transforming growth factor-beta1 activity in endothelial cells

Matrix GLA protein (MGP) is expressed in endothelial cells (EC), and MGP deficiency results in developmental defects suggesting involvement in EC function. To determine the role of MGP in EC, we cultured bovine aortic EC with increasing concentrations of human MGP (hMGP) for 24 h. The results showed increased proliferation, migration, tube formation, and increased release of vascular endothelial growth factor-A (VEGF-A) and basic fibroblast growth factor (bFGF). HMGP, added endogenously or transiently expressed, increased VEGF gene expression dose-dependently as determined by real-time PCR. To determine the mechanism by which hMGP increased VEGF expression, we studied the effect of MGP on the activity of transforming growth factor (TGF)-beta1 compared with that of bone morphogenetic protein (BMP)-2 using transfection assays with TGF-beta- and BMP-response element reporter genes. Our results showed a strong enhancement of TGF-beta1 activity by hMGP, which was paralleled by increased VEGF expression. BMP-2 activity, on the other hand, was inhibited by hMGP. Neutralizing antibodies to TGF-beta blocked the effect of MGP on VEGF expression. The enhanced TGF-beta1 activity specifically activated the Smad1/5 pathway indicating that the TGF-beta receptor activin-like kinase 1 (ALK1) had been stimulated. It occurred without changes in expression of TGF-beta1 or ALK1 and was mimicked by transfection of constitutively active ALK1, which increased VEGF expression. Expression of VEGF and MGP was induced by TGF-beta1, but the induction of MGP preceded that of VEGF, consistent with a promoting effect on VEGF expression. Together, the results suggest that MGP plays a role in EC function, altering the response to TGF-beta superfamily growth factors.

Transforming growth factor-beta1 inhibits thrombin activation of endothelial cells

Transforming growth factor-beta1 (TGF-beta1) is reported to exert both pro- and anti-inflammatory effects on the chronic activation of endothelial cells (ECs) in vitro by cytokines such as tumour necrosis factor-alpha (TNF-alpha). However, the effects of TGF-beta1 on acute inflammatory responses of ECs in vitro (e.g. to thrombin) have not been characterised. Pretreatment with TGF-beta1 (10 ng/mL) effectively inhibited all the thrombin-stimulated responses in rat aortic endothelial cells (RAECs) examined: adhesion and migration of polymorphonuclear leukocytes, adhesion of platelets and lymphocytes. Substantial inhibition of thrombin stimulation occurred after 30 min of pretreatment with TGF-beta1 and maximal inhibition was obtained after 1-20 h of pretreatment. Inhibition by TGF-beta1 pretreatment for 30 min was not affected by cycloheximide and was therefore independent of protein synthesis. Treatment with TGF-beta1 for 20 h did not affect the total levels of P-selectin and von Willebrand factor (vWF) in RAECs, but reduced thrombin-stimulated recruitment of P-selectin and vWF to the cell surface. The data demonstrate that TGF-beta1 exerts a potent anti-thrombin effect on ECs, effective after long and short pretreatment times.

Pravastatin up-regulates transforming growth factor-β1 in THP-1 human macrophages: effect on scavenger receptor class A expression

Statins have been shown to interact with several monocyte/macrophage functions. We tested the effect of pravastatin on transforming growth factor-beta1 (TGF-beta1) production and its possible involvement in scavenger receptors class A (SRA) expression in human THP-1 cells. TGF-beta1s biological activity in THP-1 cell conditioned medium, evaluated by luciferase activity of transfected cell with a TGF-beta responsive promoter, was increased in a dose-dependent manner after incubation with pravastatin (1-20 microM). Pravastatin (1-20 microM) induced a dose-dependent increase in TGF-beta1 mRNA expression and protein production in THP-1 cells. PMA-induced SRA gene and protein expression was suppressed by pravastatin with a mean 3-fold decrease at 10 microM. This last effect was reversed by a mouse monoclonal anti-TGF-beta1 neutralizing antibody. PD98059, a specific inhibitor of MAP kinase cascade, completely reversed pravastatin-induced SRA down-regulation. p44 and p42 isoforms showed a dose-dependent phosphorylation after treatment with pravastatin (1-20 microM) which was inhibited by a mouse monoclonal anti-TGF-beta1 antibody. Our results demonstrate that pravastatin significantly up-regulates TGF-beta1 expression which may be in involved in down-regulation of SRA expression in THP-1 cell cultures. A new pathway for pravastatin effects in atherogenesis can be suggested.

Transforming growth factor beta and atherosclerosis: so far, so good for the protective cytokine hypothesis

The role of the anti-inflammatory cytokine transforming growth factor beta (TGF-beta) in atherosclerosis has been the subject of considerable debate for a decade. In the early 1990s, we postulated that TGF-beta played an important role in maintaining normal vessel wall structure and that loss of this protective effect contributed to the development of atherosclerosis. We termed this the protective cytokine hypothesis. This proposal was slow to gain broad acceptance, however, because at that time there were little data available on the role of TGF-beta during the development of atherosclerosis but much information about its role during trauma-induced neointima formation. Because TGF-beta apparently aggravates neointima formation, both by inhibiting endothelial regeneration and by promoting fibrosis, it was difficult to accept that its presence might ameliorate the superficially similar atherogenesis process. But several recent studies revealed beyond doubt the fact that TGF-beta protects against lipid lesion formation, at least in mouse models of atherosclerosis. Therefore, two important questions remain. First, is the role of TGF-beta in vascular biology similar in humans and in mice? Secondly, how important, compared with defects in thrombosis or lipoprotein metabolism, is the protective role of TGF-beta during atherogenesis?

Disruption of TGF-beta signaling in T cells accelerates atherosclerosis

Increasing evidence suggests that atherosclerosis is an inflammatory disease promoted by hypercholesterolemia. The role of adaptive immunity has been controversial, however. We hypothesized that proatherogenic T cells are controlled by immunoregulatory cytokines. Among them, TGF-beta has been implied in atherosclerosis, but its mechanism of action remains unclear. We crossed atherosclerosis-prone ApoE-knockout mice with transgenic mice carrying a dominant negative TGF-beta receptor II in T cells. The ApoE-knockout mice with disrupted TGF-beta signaling in T cells exhibited a sixfold increase in aortic lesion surface area, a threefold increase in aortic root lesion size, and a 125-fold increase in aortic IFN-gamma mRNA when compared with age-matched ApoE-knockout littermates. When comparing size-matched lesions, those of mice with T cell-specific blockade of TGF-beta signaling displayed increased T cells, activated macrophages, and reduced collagen, consistent with a more vulnerable phenotype. Ab's to oxidized LDL, circulating T cell cytokines, and spleen T cell activity were all increased in ApoE-knockout mice with dominant negative TGF-beta receptors in T cells. Taken together, these results show that abrogation of TGF-beta signaling in T cells increases atherosclerosis and suggest that TGF-beta reduces atherosclerosis by dampening T cell activation. Inhibition of T cell activation may therefore represent a strategy for antiatherosclerotic therapy.

Protective effect of the immunosuppressant sirolimus against aortic atherosclerosis in apo E-deficient mice

Atherosclerosis is a chronic inflammatory disease that develops in response to injury to the vessel wall, and is augmented by hypercholesterolemia. To further delineate the role of the immune system and local factors in this process, we assessed the effects of the immunosuppressant sirolimus (Rapamycin, RAPAMUNE, Wyeth, Collegeville, PA) on atherosclerosis in the apoE-deficient (apoE KO) mouse, a well-accepted model of cardiovascular disease. ApoE KO mice were fed a high fat diet and sirolimus was administered. After 12 weeks, atherosclerotic lesions and plasma lipoproteins were measured. The expression of cytokines associated with atherosclerosis was also examined. All groups demonstrated plasma total cholesterol (TC) >1100 mg/dL. Sirolimus treatment was associated with a 30% increase in LDL-cholesterol (LDLc) and a dose-dependent elevation in HDL-cholesterol (HDLc). Despite increased LDLc, aortic atherosclerosis was markedly reduced in all sirolimus-treated groups. Sirolimus treatment resulted in decreased expression of IL-12p40, IFN-gamma and IL-10 mRNA. In contrast, TGF-beta1 was elevated. Sirolimus significantly reduced atherosclerosis in apo E-KO mice; this effect is independent of, and obviates, elevated plasma TC and LDLc. Sirolimus might therefore be of benefit on atherosclerosis in patients undergoing therapy, independent of any impact on circulating lipids.

The role of transforming growth factor beta in atherosclerosis: novel insights and future perspectives

PURPOSE OF REVIEW

Atherosclerosis is a disease of the arterial wall that seems to be tightly modulated by the local inflammatory balance. Transforming growth factors beta 1, 2 and 3 are cytokines/growth factors with broad activities on cells and tissues in the cardiovascular system, and have been suggested to play a role in the pathogenesis of atherosclerosis.

RECENT FINDINGS

In the present review, we discuss recent developments in the role of transforming growth factor beta in the regulation of the immuno-inflammatory balance that modulates atherosclerosis. Such studies strongly suggest that the inhibition of endogenous transforming growth factor beta signalling favours the development of atherosclerotic lesions with an increased inflammatory component (T cells and macrophages) and decreased collagen content, features that are characteristic of unstable atherosclerotic plaques.

SUMMARY

Transforming growth factor beta is identified as a critical modulator of the immuno-inflammatory balance in atherosclerosis, and a crucial plaque-stabilizing factor. Future studies should aim at defining the precise molecular mechanisms responsible for this protective effect, and developing immunomodulatory strategies based on the promotion of transforming growth factor beta activity (T regulatory T helper type 3 cells) to limit disease complications.