Regulation of immune responses in atherosclerosis

Atherosclerose wordt veroorzaakt door een combinatie van verhoogde cholesterolniveaus en een chronische ontstekingsreactie. Deze ontstekingsreactie is het gevolg van een verstoorde balans tussen slechte, agressieve en goede, beschermende ontstekingscellen. In dit proefschrift wordt onderzocht hoe deze verstoorde balans in atherosclerose hersteld kan worden. Het onderzoek richt zich hierbij enerzijds op het remmen van de slechte ontstekingscellen en anderzijds op het stimuleren van de goede ontstekingscellen. Dit kan bereikt worden door de werking van costimulatoire en coinhibitoire eiwitten te be_nvloeden. Deze eiwitten zijn aanwezig op het celoppervlak van heel veel verschillende ontstekingscellen en bepalen of een ontstekingscel agressief of beschermend is. Costimulatoire eiwitten zorgen voor de activatie van een ontstekingscel, terwijl coinhibitoire eiwitten ontstekingscellen remmen. Blokkade van de costimulatoire eiwitten OX40L en CD30L remt atherosclerose, terwijl blokkade van het coinhibitoire eiwit Tim-3 atherosclerose verergert. Stimulatie van het coinhibitoire eiwit TIGIT vermindert de functie van T cellen. Een andere manier om de balans tussen goede en slechte ontstekingscellen te herstellen is door het aantal goede ontstekingscellen, zoals regulatoire T cellen en myeloid derived suppressor cellen, te laten toenemen. Eliminatie van regulatoire T cellen tot meer atherosclerose, terwijl een enorme expansie van regulatoire T cellen en myeloid derived suppressor cellen beschermend is.De Nederlandse Hartstichting, Universiteit Leiden, J.E.Jurriaanse Stichting, Special Diet Services (Tecnilab-BMI), Greiner Bio-One, BD BiosciencesUBL - phd migration 201

Adaptive immunity and atherosclerosis: aging at its crossroads

Adaptive immunity plays a profound role in atherosclerosis pathogenesis by regulating antigen-specific responses, inflammatory signaling and antibody production. However, as we age, our immune system undergoes a gradual functional decline, a phenomenon termed "immunosenescence". This decline is characterized by a reduction in proliferative naïve B- and T cells, decreased B- and T cell receptor repertoire and a pro-inflammatory senescence associated secretory profile. Furthermore, aging affects germinal center responses and deteriorates secondary lymphoid organ function and structure, leading to impaired T-B cell dynamics and increased autoantibody production. In this review, we will dissect the impact of aging on adaptive immunity and the role played by age-associated B- and T cells in atherosclerosis pathogenesis, emphasizing the need for interventions that target age-related immune dysfunction to reduce cardiovascular disease risk.Biopharmaceutic

The dynamics of B cell aging in health and disease

Aging is considered to be an important risk factor for several inflammatory diseases. B cells play a major role in chronic inflammatory diseases by antibody secretion, antigen presentation and T cell regulation. Different B cell subsets have been implicated in infections and multiple autoimmune diseases. Since aging decreases B cell numbers, affects B cell subsets and impairs antibody responses, the aged B cell is expected to have major impacts on the development and progression of these diseases. In this review, we summarize the role of B cells in health and disease settings, such as atherosclerotic disease. Furthermore, we provide an overview of age-related changes in B cell development and function with respect to their impact in chronic inflammatory diseases.Biopharmaceutic

Agonistic anti-TIGIT treatment inhibits T cell responses in LDLr deficient mice without affecting atherosclerotic lesion development

OBJECTIVE: Co-stimulatory and co-inhibitory molecules are mainly expressed on T cells and antigen presenting cells and strongly orchestrate adaptive immune responses. Whereas co-stimulatory molecules enhance immune responses, signaling via co-inhibitory molecules dampens the immune system, thereby showing great therapeutic potential to prevent cardiovascular diseases. Signaling via co-inhibitory T cell immunoglobulin and ITIM domain (TIGIT) directly inhibits T cell activation and proliferation, and therefore represents a novel therapeutic candidate to specifically dampen pro-atherogenic T cell reactivity. In the present study, we used an agonistic anti-TIGIT antibody to determine the effect of excessive TIGIT-signaling on atherosclerosis. METHODS AND RESULTS: TIGIT was upregulated on CD4(+) T cells isolated from mice fed a Western-type diet in comparison with mice fed a chow diet. Agonistic anti-TIGIT suppressed T cell activation and proliferation both in vitro and in vivo. However, agonistic anti-TIGIT treatment of LDLr(-/-) mice fed a Western-type diet for 4 or 8 weeks did not affect atherosclerotic lesion development in comparison with PBS and Armenian Hamster IgG treatment. Furthermore, elevated percentages of dendritic cells were observed in the blood and spleen of agonistic anti-TIGIT-treated mice. Additionally, these cells showed an increased activation status but decreased IL-10 production. CONCLUSIONS: Despite the inhibition of splenic T cell responses, agonistic anti-TIGIT treatment does not affect initial atherosclerosis development, possibly due to increased activity of dendritic cells

Leukocyte ABCA1 remains atheroprotective in splenectomized LDL receptor knockout mice

Biopharmaceutic

Abca1 deficiency protects the heart against myocardial infarction-induced injury

Background and aims We explored the role of ATP-binding cassette transporter A1 (Abca1), in post-myocardial infarction (MI) cardiac injury. Methods In Abca1–/– mice, wild type (WT) mice, and WT mice transplanted with Abca1–/– or WT bone marrow, an MI was induced in vivo. Furthermore, an ex vivo MI was induced in isolated Abca1–/– and WT hearts. Results Twenty-four hours and two weeks after in vivo MI induction, MI size was reduced in Abca1–/– (−58%, p = 0.007; −59%, p = 0.03) compared to WT. Ex vivo MI induction showed no effect of Abca1–/– on infarct size. Interestingly, two weeks after MI, Abca1–/– mice showed higher circulating levels of B-cells (+3.0 fold, p = 0.02) and T-cells (+4.2 fold, p = 0.002) compared to WT. Bone marrow-specific Abca1–/– tended to reduce infarct size (−43%, p = 0.12), suggesting a detrimental role for hematopoietic Abca1 after MI. Conclusions Although Abca1 has a protective role in atherosclerosis, it exerts detrimental effects on cardiac function after MI. Keywords * Abca1 deficiency; * Myocardial infarction; * Immune cells; * Mic

Hepatic scavenger receptor class B type 1 knockdown reduces atherosclerosis and enhances the antiatherosclerotic effect of brown fat activation in APOE*3-Leiden.CETP mice

Objective:Brown fat activation attenuates atherosclerosis development by accelerating triglyceride-rich lipoprotein turnover and/or stimulation of reverse cholesterol transport via the SRB1 (scavenger receptor class B type 1). The aim of this study was to investigate the specific role of hepatic SRB1 in the atheroprotective properties of brown fat activation.Approach and Results:APOE*3-Leiden.CETP mice, a well-established model of human-like lipoprotein metabolism and atherosclerosis, were treated with vehicle or adenoassociated virus serotype 8-short hairpin RNA, which decreased hepatic SRB1 protein levels by 40% to 55%. After 2 weeks, mice without or with hepatic SRB1 knockdown were treated with vehicle or the beta 3-adrenergic receptor agonist CL316 243 to activate brown fat for 4 weeks to determine HDL (high-density lipoprotein) catabolism and for 9 weeks to evaluate atherosclerosis. Surprisingly, hepatic SRB1 knockdown additively improved the beneficial effects of beta 3-adrenergic receptor agonism on atherosclerosis development. In fact, hepatic SRB1 knockdown per se not only increased HDL-cholesterol levels but also reduced plasma triglyceride and non-HDL-cholesterol levels, thus explaining the reduction in atherosclerosis development. Mechanistic studies indicated that this is due to increased lipolytic processing and hepatic uptake of VLDL (very low density lipoprotein) by facilitating VLDL-surface transfer to HDL.Conclusions:Hepatic SRB1 knockdown in a mouse model with an intact ApoE (apolipoprotein E)-LDLR (low density lipoprotein receptor) clearance pathway, relevant to human lipoprotein metabolism, reduced atherosclerosis and improved the beneficial effect of brown fat activation on atherosclerosis development, explained by pleiotropic effects of hepatic SRB1 knockdown on lipolytic processing and hepatic uptake of VLDL. Brown fat activation could thus be an effective strategy to treat cardiovascular disease also in subjects with impaired SRB1 function.Functional Genomics of Systemic Disorder

Leukocyte TLR5 deficiency inhibits atherosclerosis by reduced macrophage recruitment and defective T-cell responsiveness

Toll-like receptors (TLR) provide a critical link between innate and adaptive immunity, both important players in atherosclerosis. Since evidence for the role of TLR5 is lacking, we aimed to establish this in the immune axis of atherosclerosis. We assessed the effect of the TLR5-specific ligand Flagellin on macrophage maturation and T-cell polarisation. Next, we generated TLR5-/-LDLr-/- chimeras to study the effect of hematopoietic TLR5 deficiency on atherosclerosis formation. Flagellin stimulation did not influence wildtype or TLR5-/- macrophage maturation. Only in wildtype macrophages, Flagellin exposure increased MCP-1 and IL6 expression. Flagellin alone reduced T-helper 1 proliferation, which was completely overruled in the presence of T-cell receptor activation. In vivo, hematopoietic TLR5 deficiency attenuated atherosclerotic lesion formation by ≈25% (1030*103 ± 63*103 vs. 792*103 ± 61*103 μm2; p = 0.013) and decreased macrophage area (81.3 ± 12.0 vs. 44.2 ± 6.6 μm2; p = 0.011). In TLR5-/- chimeric mice, we observed lower IL6 plasma levels (36.4 ± 5.6 vs. 15.1 ± 2.2 pg/mL; p = 0.003), lower (activated) splenic CD4+ T-cell content (32.3 ± 2.1 vs. 21.0 ± 1.2%; p = 0.0018), accompanied by impaired T-cell proliferative responses. In conclusion, hematopoietic TLR5 deficiency inhibits atherosclerotic lesion formation by attenuated macrophage accumulation and defective T-cell responsiveness

Blockade of the BLT1-LTB4 axis does not affect mast cell migration towards advanced atherosclerotic lesions in LDLr-/- mice

Mast cells have been associated with the progression and destabilization of advanced atherosclerotic plaques. Reducing intraplaque mast cell accumulation upon atherosclerosis progression could be a potent therapeutic strategy to limit plaque destabilization. Leukotriene B4 (LTB4) has been reported to induce mast cell chemotaxis in vitro. Here, we examined whether antagonism of the LTB4-receptor BLT1 could inhibit mast cell accumulation in advanced atherosclerosis. Expression of genes involved in LTB4 biosynthesis was determined by single-cell RNA sequencing of human atherosclerotic plaques. Subsequently, Western-type diet fed LDLr-/- mice with pre-existing atherosclerosis were treated with the BLT1-antagonist CP105,696 or vehicle control three times per week by oral gavage. In the spleen, a significant reduction in CD11b+ myeloid cells was observed, including Ly6Clo and Ly6Chi monocytes as well as dendritic cells. However, atherosclerotic plaque size, collagen and macrophage content in the aortic root remained unaltered upon treatment. Finally, BLT1 antagonism did not affect mast cell numbers in the aortic root. Here, we show that human intraplaque leukocytes may be a source of locally produced LTB4. However, BLT1-antagonism during atherosclerosis progression does not affect either local mast cell accumulation or plaque size, suggesting that other mechanisms participate in mast cell accumulation during atherosclerosis progression.Biopharmaceutic

Cardiovascular risk factors: the effects of ageing and smoking on the immune system, an observational clinical study

Currently immunomodulatory compounds are under investigation for use in patients with cardiovascular disease, caused by atherosclerosis. These trials, using recurrent cardiovascular events as endpoint, require enrollment of large patient groups. We investigated the effect of key risk factors for atherosclerosis development, ageing and smoking, on the immune system, with the objective to identify biomarkers differentiating between human populations, and potentially serving as endpoints for future phase 1B trials with immunomodulatory compounds. Blood was collected from young healthy volunteers (aged 18-25 years, n=30), young smokers (18-25 years, n=20), elderly healthy volunteers (>60 years, n=20), heavy smokers (>45 years, 15 packyears, n=11) and patients with stable coronary artery disease (CAD) (>60 years, n=27). Circulating immune cell subsets were characterized by flow cytometry, and collected plasma was evaluated by proteomics (Olink). Clear ageing effects were observed, mostly illustrated by a lower level in CD8+ and naïve CD4+ and CD8+ T cells, with an increase in CD4+ and CD8+ effector memory T cells in elderly healthy volunteers compared to young healthy volunteers. Heavy smokers showed a more inflammatory cellular phenotype, especially a shift in Th1/Th2 ratio: higher Th1 and lower Th2 percentages compared to young healthy volunteers. A significant decrease in circulating atheroprotective oxLDL-specific IgM was found in patients with CAD compared to young healthy volunteers. Elevated pro-inflammatory and chemotactic proteins TREM1 and CCL11 were observed in elderly volunteers compared to young volunteers. In addition, heavy smokers had an increase in pro-inflammatory cytokine IL-6 and lysosomal protein LAMP3. These data show that ageing and smoking are associated with an inflammatory immunophenotype, and that heavy smokers or aged individuals may serve as potential populations for future clinical trials investigating immunomodulatory drugs targeted for cardiovascular disease.Biopharmaceutic