Pontus Dunér

Evidence for a role of regulatory T cells in mediating the atheroprotective effect of apolipoprotein B peptide vaccine

Abstract.  Wigren M, Kolbus D, Dunér P, Ljungcrantz I, Söderberg I, Björkbacka H, Fredrikson GN, Nilsson J. (Malmö University Hospital, Lund University; Malmö University, Malmo; Sweden) Evidence for a role of regulatory T cells in mediating the atheroprotective effect of apolipoprotein B peptide vaccine. J Intern Med 2011; 269: 546–556.

Pleiotropic Effects of GIP on Islet Function Involve Osteopontin

OBJECTIVE The incretin hormone GIP (glucose-dependent insulinotropic polypeptide) promotes pancreatic β-cell function by potentiating insulin secretion and β-cell proliferation. Recently, a combined analysis of several genome-wide association studies (Meta-analysis of Glucose and Insulin-Related Traits Consortium [MAGIC]) showed association to postprandial insulin at the GIP receptor (GIPR) locus. Here we explored mechanisms that could explain the protective effects of GIP on islet function. RESEARCH DESIGN AND METHODS Associations of GIPR rs10423928 with metabolic and anthropometric phenotypes in both nondiabetic (N = 53,730) and type 2 diabetic individuals (N = 2,731) were explored by combining data from 11 studies. Insulin secretion was measured both in vivo in nondiabetic subjects and in vitro in islets from cadaver donors. Insulin secretion was also measured in response to exogenous GIP. The in vitro measurements included protein and gene expression as well as measurements of β-cell viability and proliferation. RESULTS The A allele of GIPR rs10423928 was associated with impaired glucose- and GIP-stimulated insulin secretion and a decrease in BMI, lean body mass, and waist circumference. The decrease in BMI almost completely neutralized the effect of impaired insulin secretion on risk of type 2 diabetes. Expression of GIPR mRNA was decreased in human islets from carriers of the A allele or patients with type 2 diabetes. GIP stimulated osteopontin (OPN) mRNA and protein expression. OPN expression was lower in carriers of the A allele. Both GIP and OPN prevented cytokine-induced reduction in cell viability (apoptosis). In addition, OPN stimulated cell proliferation in insulin-secreting cells. CONCLUSIONS These findings support β-cell proliferative and antiapoptotic roles for GIP in addition to its action as an incretin hormone. Identification of a link between GIP and OPN may shed new light on the role of GIP in preservation of functional β-cell mass in humans.

Plasma fibronectin deficiency impedes atherosclerosis progression and fibrous cap formation

Atherosclerotic lesions are asymmetric focal thickenings of the intima of arteries that consist of lipids, various cell types and extracellular matrix (ECM). These lesions lead to vascular occlusion representing the most common cause of death in the Western world. The main cause of vascular occlusion is rupture of atheromatous lesions followed by thrombus formation. Fibronectin (FN) is one of the earliest ECM proteins deposited at atherosclerosis‐prone sites and was suggested to promote atherosclerotic lesion formation. Here, we report that atherosclerosis‐prone apolipoprotein E‐null mice lacking hepatocyte‐derived plasma FN (pFN) fed with a pro‐atherogenic diet display dramatically reduced FN depositions at atherosclerosis‐prone areas, which results in significantly smaller and fewer atherosclerotic plaques. However, the atherosclerotic lesions from pFN‐deficient mice lacked vascular smooth muscle cells and failed to develop a fibrous cap. Thus, our results demonstrate that while FN worsens the course of atherosclerosis by increasing the atherogenic plaque area, it promotes the formation of the protective fibrous cap, which in humans prevents plaques rupture and vascular occlusion.

Atheroprotective Effects of Alum Are Associated With Capture of Oxidized LDL Antigens and Activation of Regulatory T Cells

The immune system represents a promising novel target for prevention of atherosclerosis. Several pilot vaccines that reduce atherosclerosis in experimental animals have been developed. The aluminum hydroxide adjuvant Alum has been shown to have antiatherogenic properties in itself, suggesting that it may be a suitable adjuvant in possible future atherosclerosis vaccines. To characterize the immune pathways mediating this protection, we treated wild-type C57BL/6 and Apoe−/− mice with Alum or PBS. Analyses of splenocytes isolated from 12-week-old mice demonstrated that Alum increased the presence of CD4+CD25+FoxP3+ regulatory T cells and downregulated the expression of T cell activation markers CD28 and ICOS in Apoe−/− mice but not in C57BL/6 wild-type mice. A similar immunosuppressive phenotype was found also in 25-week-old Apoe−/− mice and was associated with reduced atherosclerosis. Alum precipitates recovered from the injection site of Apoe−/− mice contained antigens derived from oxidized LDL. These findings demonstrate that treatment of Apoe−/− mice with Alum results in an increase of regulatory T cells and suggest that these are activated by tolerogenic antigen-presenting cells presenting oxidized LDL antigens. Our findings provide improved mechanistic understanding of the atheroprotective properties of aluminum hydroxide adjuvants but also point to the importance of determining if hypercholesterolemia may compromise the efficacy of Alum-containing vaccines used clinically today.

Plasma S100A8/A9 Correlates With Blood Neutrophil Counts, Traditional Risk Factors, and Cardiovascular Disease in Middle-Aged Healthy Individuals

Objective— The S100 alarmins A8, A9, and A8/A9, secreted by activated neutrophils and monocytes/macrophages, are involved in the pathogenesis of various inflammatory diseases. S100A8/A9 has previously been linked to atherogenesis and cardiovascular (CV) disease. We investigated whether S100A8, A9, and A8/A9 correlate with carotid artery disease and CV risk in apparently healthy individuals. Approach and Results— We measured baseline S100A8, A9, and A8/A9 in 664 individuals aged 63 to 68 years, with no previous history of CV disease, randomly selected from the Malmö Diet and Cancer population cohort. We examined the correlations between S100 proteins and circulating cell populations, plasma cytokines, carotid artery disease, and incidence of CV events during a median follow-up period of 16.2 years. We found that plasma S100A8/A9 concentration is positively influenced by circulating neutrophil numbers, smoking, body mass index, glycosylated hemoglobin A1c, and low-density lipoprotein. High-density lipoprotein was negatively associated with S100A8/A9. S100A8/A9 and the neutrophil counts were positively correlated with intima-media area in the common carotid artery, independently of age, sex, and CV risk factors. S100A8/A9 and circulating neutrophils presented similar associations with the incidence of coronary events (hazard ratio [95% confidence interval] per 1 SD: 1.28 [1.03–1.59] and 1.26 [1.04–1.53], respectively) and CV death (1.34 [1.06–1.71] and 1.59 [1.33–1.90], respectively). These relationships were mainly supported by strong associations in women, which were independent of traditional risk factors. There were no independent relationships between S100A8 and S100A9, and CV disease. Conclusions— Our study supports the value of S100A8/A9 as a potentially important link between neutrophils, traditional CV risk factors, and CV disease.

FcgammaRIIB inhibits the development of atherosclerosis in low-density lipoprotein receptor-deficient mice

The immune processes associated with atherogenesis have received considerable attention during recent years. IgG FcRs (FcγR) are involved in activating the immune system and in maintaining peripheral tolerance. However, the role of the inhibitory IgG receptor FcγRIIB in atherosclerosis has not been defined. Bone marrow cells from FcγRIIB-deficient mice and C57BL/6 control mice were transplanted to low-density lipoprotein receptor-deficient mice. Atherosclerosis was induced by feeding the recipient mice a high-fat diet for 8 wk and evaluated using Oil Red O staining of the descending aorta at sacrifice. The molecular mechanisms triggering atherosclerosis was studied by examining splenic B and T cells, as well as Th1 and Th2 immune responses using flow cytometry and ELISA. The atherosclerotic lesion area in the descending aorta was ~5-fold larger in mice lacking FcγRIIB than in control mice (2.75 ± 2.57 versus 0.44 ± 0.42%; p < 0.01). Moreover, the FcγRIIB deficiency resulted in an amplified splenocyte proliferative response to Con A stimulation (proliferation index 30.26 ± 8.81 versus 2.96 ± 0.81%, p < 0.0001) and an enhanced expression of MHC class II on the B cells (6.65 ± 0.64 versus 2.33 ± 0.25%; p < 0.001). In accordance, an enlarged amount of CD25-positive CD4 T cells was found in the spleen (42.74 ± 4.05 versus 2.45 ± 0.31%; p < 0.0001). The plasma Ab and cytokine pattern suggested increased Th1 and Th2 immune responses, respectively. These results show that FcγRIIB inhibits the development of atherosclerosis in mice. In addition, they indicate that absence of the inhibiting IgG receptor cause disease, depending on an imbalance of activating and inhibiting immune cells.

Elevated Plasma Levels of MMP-12 Are Associated With Atherosclerotic Burden and Symptomatic Cardiovascular Disease in Subjects With Type 2 Diabetes

Objective— Matrix metalloproteinases (MMPs) degrade extracellular matrix proteins and play important roles in development and tissue repair. They have also been shown to have both protective and pathogenic effects in atherosclerosis, and experimental studies have suggested that MMP-12 contributes to plaque growth and destabilization. The objective of this study was to investigate the associations between circulating MMPs, atherosclerosis burden, and incidence of cardiovascular disease with a particular focus on type 2 diabetes mellitus. Approach and Results— Plasma levels of MMP-1, -3, -7, -10, and -12 were analyzed by the Proximity Extension Assay technology in 1500 subjects participating in the SUMMIT (surrogate markers for micro- and macrovascular hard end points for innovative diabetes tools) study, 384 incident coronary cases, and 409 matched controls in the Malmö Diet and Cancer study and in 205 carotid endarterectomy patients. Plasma MMP-7 and -12 were higher in subjects with type 2 diabetes mellitus, increased with age and impaired renal function, and was independently associated with prevalent cardiovascular disease, atherosclerotic burden (as assessed by carotid intima-media thickness and ankle-brachial pressure index), arterial stiffness, and plaque inflammation. Baseline MMP-7 and -12 levels were increased in Malmö Diet and Cancer subjects who had a coronary event during follow-up. Conclusions— The plasma level of MMP-7 and -12 are elevated in type 2 diabetes mellitus, associated with more severe atherosclerosis and an increased incidence of coronary events. These observations provide clinical support to previous experimental studies, demonstrating a role for these MMPs in plaque development, and suggest that they are potential biomarkers of atherosclerosis burden and cardiovascular disease risk.

Immunization of apoE-/- mice with aldehyde-modified fibronectin inhibits the development of atherosclerosis

AIMS Oxidation of low-density lipoprotein in the extracellular matrix of the arterial wall results in the formation of malondialdehyde (MDA) that modifies surrounding matrix proteins. This is associated with the activation of an immune response against modified extracellular matrix proteins present in atherosclerotic plaques. Clinical studies have revealed an inverse association between antibodies to MDA-modified fibronectin and risk for development of cardiovascular events. To determine the functional role of these immune responses in atherosclerosis, we performed studies in which apoE-deficient mice were immunized with MDA-modified fibronectin. METHODS AND RESULTS Immunization of apoE-deficient mice with MDA-modified fibronectin resulted in a 70% decrease in plaque area and a less inflammatory phenotype of remaining plaques. Immunization shifted a weak naturally occurring Th1 antibody response against MDA-fibronectin into a Th2 antibody response. Cytokine expression and flow cytometry analyses of spleen cells from immunized mice showed an activation of regulatory T cells. Immunization with MDA-fibronectin was also found to reduce plasma fibronectin levels. CONCLUSION Immunization with MDA-fibronectin significantly reduces the development of atherosclerosis in apoE-deficient mice suggesting that the immune response observed in humans may have a protective effect. MDA-fibronectin represents a possible novel target for immunomodulatory therapy in atherosclerosis.

Inhibition of Nuclear Factor of Activated T-Cells (NFAT) Suppresses Accelerated Atherosclerosis in Diabetic Mice

Objective of the Study Diabetic patients have a much more widespread and aggressive form of atherosclerosis and therefore, higher risk for myocardial infarction, peripheral vascular disease and stroke, but the molecular mechanisms leading to accelerated damage are still unclear. Recently, we showed that hyperglycemia activates the transcription factor NFAT in the arterial wall, inducing the expression of the pro-atherosclerotic protein osteopontin. Here we investigate whether NFAT activation may be a link between diabetes and atherogenesis. Methodology and Principal Findings Streptozotocin (STZ)-induced diabetes in apolipoprotein E−/− mice resulted in 2.2 fold increased aortic atherosclerosis and enhanced pro-inflammatory burden, as evidenced by elevated blood monocytes, endothelial activation- and inflammatory markers in aorta, and pro-inflammatory cytokines in plasma. In vivo treatment with the NFAT blocker A-285222 for 4 weeks completely inhibited the diabetes-induced aggravation of atherosclerosis, having no effect in non-diabetic mice. STZ-treated mice exhibited hyperglycemia and higher plasma cholesterol and triglycerides, but these were unaffected by A-285222. NFAT-dependent transcriptional activity was examined in aorta, spleen, thymus, brain, heart, liver and kidney, but only augmented in the aorta of diabetic mice. A-285222 completely blocked this diabetes-driven NFAT activation, but had no impact on the other organs or on splenocyte proliferation or cytokine secretion, ruling out systemic immunosuppression as the mechanism behind reduced atherosclerosis. Instead, NFAT inhibition effectively reduced IL-6, osteopontin, monocyte chemotactic protein 1, intercellular adhesion molecule 1, CD68 and tissue factor expression in the arterial wall and lowered plasma IL-6 in diabetic mice. Conclusions Targeting NFAT signaling may be a novel and attractive approach for the treatment of diabetic macrovascular complications.

Immune responses against aldehyde-modified laminin accelerate atherosclerosis in Apoe(-/-) mice.

BACKGROUND LDL oxidation in the vascular wall is associated with aldehyde modification of surrounding extracellular matrix proteins that may target autoimmune responses against vascular tissues. Here we investigated the possible influence of immunity against a malondialdehyde (MDA)-modified form of the basement membrane protein laminin on atherosclerosis. METHODS AND RESULTS IgM and IgG autoantibodies were present in human plasma and a prospective clinical study demonstrated that individuals who later suffered from acute cardiovascular events had lower levels of MDA-laminin antibodies compared to those in the control group. Immunohistochemical analysis of atherosclerotic plaques from Apoe-/- mice demonstrated co-localization between laminin and MDA epitopes, however MDA-laminin IgG was absent in mouse plasma. To determine the effect of MDA-laminin immunity, Apoe-/- mice were immunized with MDA-laminin. Analysis of circulating leukocytes at 12 weeks demonstrated increased T-cell activation, expansion of Th17 cells and a lower fraction of regulatory T cells (Tregs) in mice immunized with MDA-laminin. At 25 weeks, aortic atherosclerosis was increased by more than 60% in mice immunized with MDA-laminin, together with increased levels of MDA-laminin IgG1 and MDA-laminin-specific T-cells expressing IL-2, IL-4 and IL-6 in the spleen. CONCLUSION The clinical observations suggest that immune responses against MDA-laminin may be involved in the development of cardiovascular disease in humans. Furthermore, observations in mice provide evidence for the presence of aldehyde-modified laminin in atherosclerotic lesions and demonstrate that induction of an immune response against these structures is associated with activation of Th17 cells, reduced fraction of Tregs and a more aggressive development of atherosclerosis.