Evidence for a role of macrophage migration inhibitory factor in vascular disease

MIF: a new cytokine link between rheumatoid arthritis and atherosclerosis

Macrophage migration inhibitory factor (MIF) is well established as a key cytokine in immuno-inflammatory diseases such as rheumatoid arthritis. Inflammation is now also recognized as having a crucial role in atherosclerosis, and recent evidence indicates that MIF could also be important in this disease. Here, we review the role of MIF in rheumatoid arthritis and atherosclerosis, discuss the ways in which MIF and its relationship with glucocorticoids could link these diseases, and consider the potential of MIF as a new therapeutic target for small-molecule and antibody-based anti-cytokine drugs.

Reduction of the aortic inflammatory response in spontaneous atherosclerosis by blockade of macrophage migration inhibitory factor (MIF)

Atherosclerosis is an inflammatory response of the arterial wall to "injury", which is prominently driven by cytokines. The inflammatory mediator macrophage migration inhibitory factor (MIF) is a unique cytokine that was recently associated with atherogenesis. Here, we have investigated whether MIF has a role in spontaneous atherosclerosis by studying apolipoprotein E-deficient (ApoE(-/-)) mice treated with neutralizing anti-MIF monoclonal antibody and comparison with isotype IgG-treated controls. After 14 weeks, the aortas and heart valves were analyzed for inflammatory status, macrophage content and plaque areas. MIF expression in the aortic wall was elevated upon spontaneous atherogenesis, with foam cells representing a major source. Of note, MIF blockade led to a marked reduction in intimal Mac-1-positive macrophages. Similarly, treatment with anti-MIF antibody led to a reduction of a variety of inflammatory mediators typically associated with atherosclerosis including the circulating levels of fibrinogen, MIF and IL-6. Importantly, the local aortic expression of ICAM-1, MMP-2, TNF, IL-12, and CD40L was reduced by MIF blockade, as were the levels of the phospho-c-Jun and C/EBPbeta transcription factors. The observed strong reduction of inflammatory parameters by anti-MIF treatment was associated with a small, yet non-significant, reduction in aortic plaque area. Thus, although MIF's role is not directly linked to plaque volume expansion, in this mouse model of spontaneous atherogenesis, MIF plays an important role in intimal inflammation.

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.

Association of systemic concentrations of macrophage migration inhibitory factor with impaired glucose tolerance and type 2 diabetes: results from the Cooperative Health Research in the Region of Augsburg, Survey 4 (KORA S4)

OBJECTIVE

Macrophage migration inhibitory factor (MIF) is a central cytokine in innate immunity. MIF expression can be regulated by glucose and insulin, but data on the association with type 2 diabetes are sparse. The aim of this study was to test whether MIF is associated with impaired glucose tolerance (IGT) and type 2 diabetes and whether these associations are independent of metabolic and immunological risk factors and to compare the associations of MIF and IGT/type 2 diabetes with those of C-reactive protein (CRP) and interleukin-6 (IL-6) with IGT/type 2 diabetes.

RESEARCH DESIGN AND METHODS

The Cooperative Health Research in the Region of Augsburg/Kooperative Gesundheitsforschung im Raum Augsburg, Survey 4 (KORA S4) is a population-based survey performed in Southern Germany (1999-2001). Of 1,653 participants aged 55-74 years, 236 patients with type 2 diabetes, 242 subjects with IGT, and 244 normoglycemic control subjects matched for age and sex were included in this cross-sectional study. Serum concentrations of MIF were measured by enzyme-linked immunosorbent assay.

RESULTS

Serum MIF concentrations are highly increased in individuals with IGT and type 2 diabetes. The associations of MIF with IGT and type 2 diabetes were independent of classical risk factors and of CRP and IL-6 and were much stronger before and after multivariate adjustment than the associations of CRP and IL-6 with IGT and type 2 diabetes.

CONCLUSIONS

Our data suggest that elevations of systemic MIF concentrations precede the onset of type 2 diabetes. This finding may be relevant because MIF has been reported to contribute to the development of type 2 diabetes-related diseases such as atherosclerosis and cancer.

Relationship between serum levels of macrophage migration inhibitory factor and the activity of antineutrophil cytoplasmic antibody-associated vasculitides

Macrophage migration inhibitory factor (MIF) is a central proinflammatory cytokine that regulates innate and adaptive immune responses. To evaluate its role in primary vasculitides, we determined MIF by enzyme-linked immunoassay in the sera of patients with Wegener's granulomatosis (WG; n=26), microscopic polyangiitis (MPA; n=10), polyarteritis nodosa (PAN; n=9) and giant cell arteritis (GCA; n=11). Healthy controls (n=26) and patients with sarcoidosis (n=14) were studied in parallel. Serum levels of MIF were significantly higher in patients with WG (median 41.1, range 3.2-120 ng/ml) than those in healthy controls (6.0, 0.015-36.5 ng/ml; P<0.001) and in patients with sarcoidosis (13.8, 0.015-67.1 ng/ml; P<0.05). MIF values were higher in MPA patients (29.5, 9.9-69.4 ng/ml; P<0.01) in comparison with those in healthy controls. In particular, increased levels of MIF were associated with active disease as assessed by the Birmingham Vasculitis Activity Score. Sequential studies showed decreased levels of MIF after initiation of immunosuppressive therapy, with clinical improvement in WG and MPA patients. In contrast, serum levels of MIF were not significantly elevated in patients with PAN and GCA. The results suggest that MIF contributes to the inflammatory process and correlates with disease activity in antineutrophil cytoplasmic antibody-associated vasculitides.

New therapeutic target in inflammatory disease: macrophage migration inhibitory factor

The cytokine macrophage migration inhibitory factor (MIF) participates in fundamental events in innate and adaptive immunity. The profile of activities of MIF in vivo and in vitro is strongly suggestive of a role for MIF in the pathogenesis of many inflammatory diseases, including rheumatoid arthritis (RA), and hence antagonism of MIF is suggested as a potential therapeutic strategy in inflammatory disease. The best developed case for therapeutic antagonism of MIF is in RA. In RA, MIF is abundantly expressed in serum and synovial tissue. MIF induces synovial expression of key pro-inflammatory genes, regulates the function of endothelial cells and leucocytes, and is implicated in the control of synoviocyte proliferation and apoptosis via direct effects on the expression of the tumour suppressor protein p53. In animal models of RA, anti-MIF antibodies or genetic MIF deficiency are associated with significant inhibition of disease. A similar case has been made, for example using MIF-deficient mice, in models of atheroma, colitis, multiple sclerosis and other inflammatory diseases. The relationship with p53 also means MIF may be important in the link between inflammatory disease and cancer, such as is seen in RA or colitis. MIF also has a unique relationship with glucocorticoids, in that despite antagonizing their effects, the expression of MIF is in fact induced by glucocorticoids. Thus, MIF functions as a physiological counter-regulator of the anti-inflammatory effects of glucocorticoids. This may be entrained by selective activation of mitogen-activated protein kinases rather than nuclear factor kappa B. Therapeutic MIF antagonism may therefore provide a specific means of 'steroid sparing'. Exploitation of antibody, soluble receptor or small molecule technologies may soon lead to the ability to test in the clinic the importance of MIF in human inflammatory diseases.

Mechanisms of monocyte recruitment in vascular repair after injury

The inflammatory response to acute vessel wall injury has been increasingly recognized to play a decisive role in neointima formation. In particular, the exuberant infiltration with monocytes aggravates neointimal growth and can thereby promote restenosis. The adhesion of circulating monocytes to the site of mechanical injury represents the key event in monocyte recruitment, and this review highlights recent insights into the molecular mechanisms of monocyte adhesion throughout the course of neointimal growth. An acute and a chronic phase of monocyte recruitment after vascular injury can be discerned. The adhesion of platelets to the denuded subendothelial matrix is the hallmark of the acute phase providing an adhesive substrate for monocytes, whereas chronic monocyte recruitment is regulated by the interaction with neointimal smooth muscle cells and recovering endothelial cells. Clearly, the mechanisms of monocyte rolling and adhesion differ considerably between these diverse substrates. This review is particularly focused on the contribution of chemokines and adhesion molecules to monocyte recruitment to injured vessels according to the different stages of neointimal growth, and on closely related functions of the chemokine-like molecule macrophage migration inhibitory factor. Understanding the complex molecular interactions of the injured vessel wall with circulating monocytes may enable therapeutic targeting to prevent the development of restenosis.

Stimulation of vascular smooth muscle cell migration by macrophage migration inhibitory factor

Macrophage migration inhibitory factor (MIF) is a well known proinflammatory factor that influences the migration and proliferation of various cell types, predominantly monocytes and macrophages. Recent evidence suggests an important role for MIF in the progression of atherosclerosis and restenosis. For this reason, we studied the effect of MIF on platelet-derived growth factor-BB (PDGF-BB)-induced migration and PDGF receptor protein expression in vascular smooth muscle cells (VSMCs). Furthermore, the possibility of MIF influencing the migration of VSMCs was investigated. Our results show that short-term incubation of MIF is able to enhance PDGF-BB-induced migration. Long-term incubation decreases PDGF-BB-induced migration, but preserves a short-term stimulatory effect. These effects are not regulated at the level of PDGF receptor protein expression. MIF also acts as a chemoattractant for VSMCs, with a maximum response at 15 ng/ml. In contrast, the proliferation of VSMCs was unaffected by MIF. We conclude that MIF has a biphasic effect on VSMC migration. It remains unclear whether this effect is direct or involves the secretion of unidentified promigratory factors. Exogenous MIF does not stimulate VSMC proliferation; however, a role for MIF in proliferation cannot be fully ruled out. In view of the known key contributions of macrophage-derived MIF and VSMCs, the observed effects may well play a role in the progression of atherosclerosis and restenosis.

Colocalization of oxidized low-density lipoprotein, caspase-3, cyclooxygenase-2, and macrophage migration inhibitory factor in arteriosclerotic human carotid arteries

Apoptotic and inflammatory processes occur in human arteriosclerotic lesions. We examined the hypothesis whether both processes are possibly associated by studying the colocalization of corresponding markers. In 11 human arteriosclerotic carotid arteries, proapoptotic markers (CPP32 (caspase-3), poly(ADP-ribose) polymerase, apoptosis-inducing factor, c-Jun/AP-1, and p53) and proinflammatory markers (macrophage migration inhibitory factor (MIF) and cyclooxygenase-2) were found in macrophages (MPhi) evaluated by computer-assisted immunohistomorphometry. Double-labeling studies demonstrated a colocalization of, both, proapoptotic and proinflammatory markers in these MPhi. Moreover, these MPhi also contained oxidized low-density lipoproteins (oxLDL). Exposure of cultured human MPhi to oxLDL, C6-ceramide, and tumor necrosis factor-alpha or H2O2 resulted in a significant increase of the apoptosis rate as well as of the MIF protein expression. Our study of MPhi in arteriosclerotic carotid arteries and in vitro experiments provide evidence that markers of apoptosis and inflammation are not only significantly increased but are also coexpressed. We conclude there are reciprocal modulatory interactions between apoptotic and inflammatory pathways in human plaque MPhi, which might importantly modify plaque progression or stability.

Divergent mechanisms of cis 9, trans 11 ‐ and trans 10 , cis 12 ‐ conjugated linoleic acid affecting insulin resistance and inflammation in apolipoprotein E knockout mice: a proteomics approach

Conjugated linoleic acids (CLA) affect atherogenesis, but mechanisms are not well understood. We explored how two isomers of CLA, cis9, trans11-CLA and trans10, cis12-CLA, affected lipid and glucose metabolism, as well as hepatic protein expression, in apolipoprotein E knockout mice. After 12 wk of intervention, plasma triglyceride, NEFA, and glucose concentrations were significantly higher in the trans10, cis12-CLA group, whereas plasma triglyceride, NEFA, glucose, and insulin concentrations were significantly lower in the cis9, trans11-CLA group, compared with control mice consuming linoleic acid. Proteomics identified significant up- or down-regulation of 113 liver cytosolic proteins by either CLA isomer. Principal component analysis revealed that the treatment effect of cis9, trans11-CLA was mainly explained by the up-regulation of different posttranslational forms of heat shock protein 70 kD. In contrast, the treatment effect of trans10, cis12-CLA was mainly explained by up-regulation of key enzymes in the gluconeogenic, beta-oxidation, and ketogenesic pathways. Correlation analysis again emphasized the divergent effects of both CLA isomers on different pathways, but also revealed a linkage between insulin resistance and increased levels of hepatic serotransferrin. Thus, our systems biology approach provided novel insights into the mechanisms by which individual CLA isomers differentially affect pathways related to atherogenesis, such as insulin resistance and inflammation.

Macrophage migration inhibitory factor induces MMP-9 expression: implications for destabilization of human atherosclerotic plaques

Macrophage migration inhibitory factor (MIF) has been shown to participate in both experimental and human atherogenesis. Expression of MMP-9 has been shown to play a role in the instability of atherosclerotic plaque. Thus, we hypothesize that MIF may participate in the destabilization of atherosclerotic plaques by stimulating MMP-9 expression. This hypothesis was investigated by examining the expression of MIF and MMP-9 in human atherosclerotic plaques using two-color immunostaining and by determining the potential role of MIF in the induction of MMP-9 expression in vascular smooth muscle cells (VSMC) and macrophages in vitro. Two-color immunohistochemistry demonstrated that MIF was strongly upregulated by macrophages and VSMCs. This was associated with marked increase in MMP-9 expression in vulnerable atheromatous plaques, but not in the fibrous lesions. Upregulation of MIF and MMP-9 in vulnerable atheromatous plaques was associated with the weakening of fibrous caps. The role of MIF in MMP-9 expression was demonstrated by the ability of MIF to directly induce MMP-9 mRNA and protein expression in macrophages and in VSMCs in a dose and time-dependent manner, which was blocked by a neutralizing MIF antibody. In conclusion, MIF and MMP-9 are markedly upregulated in vulnerable atheromatous plaques. The ability of MIF to induce MMP-9 expression in VSMCs and macrophages suggests that MIF may play a role in the destabilization of human atherosclerotic plaques.

Thematic review series: The immune system and atherogenesis. Cytokines affecting endothelial and smooth muscle cells in vascular disease

The cellular and extracellular matrix accumulations that comprise the lesions of atherosclerosis are driven by local release of cytokines at sites of predilection for lesion formation, and by the specific attraction and activation of cells expressing receptors for these cytokines. Although cytokines were originally characterized for their potent effects on immune and inflammatory cells, they also promote endothelial cell dysfunction and alter smooth muscle cell (SMC) phenotype and function, which can contribute to or retard vascular pathologies. This review summarizes in vivo studies that have characterized endothelial- and smooth muscle-specific effects of altering cytokine signaling in vascular disease. Although multiple reports have identified cytokines as pivotal players in endothelial and SMC responses in vascular disease, they also have highlighted the need to delineate the critical genes and specific cellular functions regulated by individual cytokine signaling pathways.

Obesity, macrophage migration inhibitory factor, and weight loss

OBJECTIVE

Elevated macrophage migration inhibitory factor (MIF) has been implicated as a causal mechanism in a number of disease conditions including cardiovascular disease (CVD), diabetes, and cancer. Excess body fat is associated with an increased risk of numerous health conditions including CVD, diabetes, and cancer. To our knowledge, the association between MIF and obesity status and the effect of weight loss on serum MIF concentrations have not been reported. In this study, we examined the effects of participation in a behavior-based weight loss program on MIF concentrations in obese individuals.

SUBJECTS

Study participants were 71 men and women enrolled in The Cooper Institute Weight Management Program. Participants were predominantly female (68%, n=48), middle-aged (46.5+/-9.8 y), and severely obese (BMI=43.0+/-8.6).

METHOD

Plasma MIF concentrations and other standard risk factors were measured before and after participation in a diet and physical activity based weight management program.

RESULTS

The mean follow-up was 8.5+/-3.0 months with an average weight loss of 14.4 kg (P<0.001). The majority of clinical risk factors significantly improved at follow-up. Median levels of plasma MIF concentration were significantly lower at follow-up (median [IQR]; 5.1[3.6-10.3]) compared to baseline (8.4 [4.3-48.8]; P=0.0005). The percentage of participants with plasma MIF concentration > or =19.5 mg/nl (highest tertile at baseline) decreased from 33.8 to 5.6% (P<0.001). Further, elevated baseline plasma MIF concentration was associated with markers of beta-cell dysfunction and reductions in MIF were associated with improvements in beta-cell function.

CONCLUSIONS

Circulating MIF concentrations are elevated in obese but otherwise healthy individuals; however, this elevation in MIF is not uniform across individuals. In obese individuals with elevated circulating MIF concentrations, participation in physical activity and a dietary-focused weight management program resulted in substantial reduction in MIF.

Inflammatory mediators in atherosclerotic vascular disease

An impressive body of work has established the current paradigm of atherosclerosis as an inflammatory process that promotes lesion development and progression. Early atheroma formation is characterized by leukocyte recruitment and expression of inflammatory mediators which is confounded in the context of hyperlipidemia. Evidence for an involvement of both innate and adaptive immunity in lesion formation has emerged, supporting a causal relation between the balance of pro- and anti-inflammatory cytokines and atherogenesis. The function of chemokines in distinct steps during mononuclear cell recruitment to vascular lesions has been studied in genetically deficient mice and other suitable models, and displays a high degree of specialization and cooperation. The contribution of platelet chemokines deposited on endothelium to monocyte arrest, differences in the presentation and involvement of chemokines between native and neointimal lesion formation, and related functions of macrophage migration inhibitory factor, a cytokine with striking structural homology to chemokines are of note. A novel role of chemokines in the recruitment of vascular progenitors during neointimal hyperplasia and in the recovery of endothelial denudation underscores their relevance for atherosclerotic vascular disease. The functional diversity of chemokines in vascular inflammation may potentially allow the selective therapeutic targeting of different atherosclerotic conditions.