Brutons tyrosine kinase inhibition to suppress mast cell activation in atherosclerosis

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Dutch Heart Foundation

Aim

Acute cardiovascular diseases, such as myocardial infarction or stroke, are still a major cause of death in Western Society. The main underlying pathology of cardiovascular diseases is atherosclerosis, which is caused by the accumulation of lipids and inflammatory cells in the vessel wall, in so-called atherosclerotic plaques. Mast cells accumulate within these atherosclerotic plaques and activation of mast cells leads to the progression and destabilization of advanced plaques via the secretion of pro-inflammatory mediators and cytokines. Mast cells can be activated by various stimuli, of which crosslinking of the Fcε receptor I (FcεRI) with IgE-antigen complexes is best known. Bruton’s tyrosine kinase (BTK), a cytoplasmic nonreceptor tyrosine kinase, is involved in the downstream signaling of FcεRI-mediated mast cell activation and degranulation. Therefore, BTK might be an attractive target to interfere in the FcεRI-mediated mast cell activation pathway. In this study, we thus aimed to assess the effects of the BTK inhibitor ACP-196 on FcεRI-mediated mast cell activation, plaque progression and destabilization in an atherosclerotic mouse model.

Methods and Results

Male LDLr knockout mice, 7-11 weeks old, were treated with ACP-196 (25 mg/kg p.o., n=15) or control solvent (n=14) three times per week for eight weeks. During treatment, mice were fed a Western-type diet (WTD) to induce atherosclerotic plaque formation. During the experiment, plasma total cholesterol levels and body weight did not differ between the control and treatment group. After eight weeks, mice were sacrificed and hearts were isolated to determine atherosclerotic plaque size and stability in the aortic root by histology. Other immunological relevant tissues, such as aorta, spleen and mediastinal lymph nodes were harvested to examine mast cell activation status and other immune cells by flow cytometry. After eight weeks of ACP-196 treatment in LDLr knockout mice, a significant 59% reduction in the frequency of CD117+ FcεRI+ mast cells was observed in aortic plaques of ACP-196 treated mice (0.24±0.06%) compared to control mice (0.57±0.08%, p<0.05), while relative mast cell activation status was not affected. Additionally, ACP-196 treatment inhibited B cell maturation in the circulation, spleen, mediastinal lymph nodes and peritoneal cavity of LDLr knockout mice compared to control mice. However, these effects on immune cells did not translate into effects on atherosclerosis, as ACP-196 treatment (size:12.3±2%; collagen:14.5±1.9%) did not significantly affect atherosclerotic plaque size and collagen content when compared to control mice (size:11.5±1.4%; collagen: 13.6±1.5%).

Conclusions

Conclusively, these findings suggest that ACP-196 treatment leads to reduced migration of mast cells to the atherosclerotic plaques of LDLr knockout mice, but does not directly affect mast cell activation and initial atherosclerotic lesion development.

B cell depletion skews cd4+ t cell towards a pro-inflammatory phenotype in aged atherosclerotic mice

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Dutch Heart Foundation

ERA CVD

Aims

Aging is associated with changes in the composition and function of the immune system, such as decreased B cell numbers and reduced antibody responses (1). In addition, aging is related to an increased incidence of inflammatory diseases, such as the lipid-driven chronic inflammatory disease atherosclerosis, the main underlying cause of cardiovascular disease (2). B cells play a major role in atherosclerosis progression by antibody secretion, antigen presentation and T cell regulation. Different B cell subsets, with either proatherogenic or antiatherogenic properties, have been identified in atherosclerosis, but the impact of aging on B cells during atherosclerosis remains to be elucidated. In contrast to young atherosclerotic mice where few B cells are found within the plaque, single cell RNA sequencing and flow cytometry data from our group revealed that B cells are one of the most dominant leukocytes present in atherosclerotic aortas from naturally aged LDLr-/- mice. In this study, we aimed to gain further insights into the role of these aged B cells on T cell immunity in atherosclerosis by depleting B cells in aged atherosclerotic mice.

Methods and Results

Aged (85-95 weeks) atherosclerotic male LDLr-/- mice were kept on a chow diet for six weeks, during which the mice received 250 µg B cell-depleting anti-CD20 antibody (Genentech) (n=12) or 250 µg rat IgG2a isotype control (n=12) once a week intraperitoneally. Mice that received the anti-CD20 antibody showed effective B cell depletion in the blood and lymphoid organs, such as the spleen and lymph nodes, but also locally in the atherosclerotic plaque. In addition, B cell depleted mice showed a significant increase in the percentage of T-bet expressing CD4+ T cells in aortic plaques compared to control mice (αCD20: 25.05±2.88% vs. ctrl: 15.94±2.14%, p<0.05). Furthermore, the percentage of RORyt+ and IL-17+ CD4+ T cells in the spleen and heart draining lymph nodes was increased after B cell depletion, indicating a shift towards Th17 differentiation.

Conclusions

Collectively, we show that CD20+ B cell depletion in aged LDLr-/- mice skews CD4+ T cells towards a Th1 phenotype in the atherosclerotic plaque and towards a Th17 phenotype in lymphoid organs, suggesting a protective role for aged B cells in atherosclerosis. However, B cells are a heterogeneous population and further research should elucidate whether aged B cells exert a pro- or anti-atherogenic role. In conclusion, our results indicate that aged B cells have an important function in CD4+ T cell differentiation and could be attractive targets to combat age-related cardiovascular disease.

Granzyme B+ CD4+ T cells associate with an unstable plaque phenotype in advanced human atherosclerosis

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): The Dutch Heart Foundation

Cytotoxic CD4+ T cells have previously been found in peripheral blood of patients with coronary artery disease (1), however their occurrence in atherosclerotic plaques and their association with the pathophysiology of atherosclerosis has not been established.

Single-cell RNA sequencing was performed on human carotid atherosclerotic plaques of 18 patients to identify specific T cell populations (2). Next, human femoral and carotid atherosclerotic plaques (n=95) and matched blood samples (n=49) were analyzed by flow cytometry for the presence of CD4+GZMB+ T cells. Plaque morphology was assessed by Movat’s Pentachrome staining.

A distinct cytotoxic GZMB+ PRF1+ CD28- CD4+ T cell cluster was identified using single-cell RNA sequencing. Furthermore, flow cytometry analysis showed that the percentage of GZMB+CD4+ T cells was significantly elevated in plaque compared to blood (Blood: 12.17±2.0 vs. Plaque: 17.40±1.0; P=0.0002). Moreover, a significant positive correlation was observed between the percentage of GZMB+CD4+ T cells in blood versus plaque (P=0.031). In line with the proinflammatory character of these cells, we found a positive association of GZMB+CD4+ T cells (P=0.036) with necrotic core size, whereas no correlation was found with this subtype in the circulation.

In this study we have shown an enrichment of cytotoxic CD4+ T cells in atherosclerotic lesions, which positively correlate with necrotic core size. Future studies are aimed at elucidating the role of these cells in advanced atherosclerosis.

Immune checkpoint proteins: exploring their therapeutic potential to regulate atherosclerosis

The immune system provides a large variety of immune checkpoint proteins, which involve both costimulatory and inhibitory proteins. Costimulatory proteins can promote cell survival, cell cycle progression and differentiation to effector and memory cells, whereas inhibitory proteins terminate these processes to halt ongoing inflammation. Immune checkpoint proteins play a pivotal role in atherosclerosis by regulating the activation and proliferation of various immune and non-immune cells, such as T-cells, macrophages and platelets. Upon activation within the atherosclerotic lesions or in secondary lymphoid organs, these cells produce large amounts of pro-atherogenic cytokines that contribute to the growth and destabilization of lesions, which can result in rupture of the lesion causing acute coronary syndromes, such as a myocardial infarction. Given the presence and regulatory capacity of immune checkpoint proteins in the circulation and atherosclerotic lesions of cardiovascular patients, modulation of these proteins by, for example, the use of monoclonal antibodies, offers unique opportunities to regulate pro-inflammatory immune responses in atherosclerosis. In this review, we highlight the latest advances on the role of immune checkpoint proteins, such as OX40-OX40L, CTLA-4 and TIM proteins, in atherosclerosis and discuss their therapeutic potential as promising immunotherapies to treat or prevent cardiovascular disease.

LINKED ARTICLES

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

Heat-killed Staphylococcus aureus reduces atherosclerosis by inducing anti-inflammatory macrophages

BACKGROUND

Staphylococcus aureus cell wall components can induce IL-10 responses by immune cells, which may be atheroprotective. Therefore, in this study, we investigated whether heat-killed S. aureus (HK-SA) could inhibit the development of atherosclerosis.

METHODS

Atherosclerosis-susceptible LDL receptor-deficient mice were administered intraperitoneal HK-SA twice weekly and fed a Western-type diet for 6 weeks.

RESULTS

HK-SA administration resulted in a 1.6-fold increase in IL-10 production by peritoneal macrophages and splenocytes, and a 12-fold increase in serum IL-10 levels. Moreover, aortic plaque ICAM-1, VCAM-1 and CCL2 expression levels were significantly downregulated by on average 40%. HK-SA-treated mice had reduced numbers of inflammatory Ly-6C(hi) monocytes as well as Th1 and Th17 cells in the circulation and spleen, respectively. Attenuated leucocyte recruitment resulted in a significant inhibition of macrophage and T cell infiltration in atherosclerotic plaques, culminating in a significant 34% reduction in the development of atherosclerosis. To determine the effects of intraperitoneal HK-SA treatment, we stimulated macrophages with HK-SA in vitro. This resulted in a significant toll-like receptor 2 (TLR2)-dependent increase in IL-10, arginase-1, iNOS, TNF-α, PD-L1, CCL22 and indoleamine 2,3-dioxygenase expression. It was found that phosphoinositide 3-kinase crucially determined the balance of pro- and anti-inflammatory gene expression. The HK-SA-induced macrophage phenotype resembled M2b-like immunoregulatory macrophages.

CONCLUSIONS

We have shown that HK-SA treatment induces strong anti-inflammatory IL-10 responses by macrophages, which are largely dependent on TLR2 and PI3K, and protects against the development of atherosclerosis. Commensalism with S. aureus could thus reduce cardiovascular events.

Vaccination against Foxp3(+) regulatory T cells aggravates atherosclerosis

OBJECTIVE

Regulatory T cells are crucial for immune homeostasis and an impaired regulatory T cell function results in many pathological conditions. Regulatory T cells have already been described to be protective in atherosclerosis. However the exact contribution of Foxp3-expressing natural regulatory T cells in atherosclerosis has not been elucidated yet.

METHODS AND RESULTS

In this study we vaccinated LDL receptor deficient mice with dendritic cells which are transfected with Foxp3 encoding mRNA and studied the effect on initial atherosclerosis. Vaccination against Foxp3 resulted in a reduction of Foxp3(+) regulatory T cells in several organs and in an increase in initial atherosclerotic lesion formation. Furthermore we observed an increase in plaque cellularity and increased T cell proliferation in the Foxp3 vaccinated mice.

CONCLUSION

We further establish the protective role of Tregs in atherosclerosis. The results illustrate the important role for Foxp3-expressing regulatory T cells in atherosclerosis, thereby providing a potential opportunity for therapeutic intervention against this disease.