Circulating regulatory T cells in patients with aortic valve stenosis: Association with disease progression and aortic valve intervention

Regulatory T Cells in Pathological Cardiac Hypertrophy: Mechanisms and Therapeutic Potential

BACKGROUND

Pathological cardiac hypertrophy is linked to immune-inflammatory injury, and regulatory T cells (Tregs) play a crucial role in suppressing immune-inflammatory responses. However, the precise role of Tregs in pathological cardiac hypertrophy remains unclear.

OBJECTIVE

To summarize the current knowledge on the role and mechanisms of Tregs in pathological cardiac hypertrophy and explore their perspectives and challenges as a new therapeutic approach.

RESULTS

Treg cells may play an important protective role in pressure overload (hypertension, aortic stenosis), myocardial infarction, metabolic disorders (diabetes, obesity), acute myocarditis, cardiomyopathy (hypertrophic cardiomyopathy, storage diseases), and chronic obstructive pulmonary disease-related pathological cardiac hypertrophy. Although some challenges remain, the safety and efficacy of Treg-based therapies have been confirmed in some clinical trials, and engineered antigen-specific Treg cells may have better clinical application prospects due to stronger immunosuppressive function and stability.

CONCLUSION

Targeting the immune-inflammatory response via Treg-based therapies might provide a promising and novel future approach to the prevention and treatment of pathological cardiac hypertrophy.

Innate and adaptive immunity: the understudied driving force of heart valve disease

Calcific aortic valve disease (CAVD), and its clinical manifestation that is calcific aortic valve stenosis, is the leading cause for valve disease within the developed world, with no current pharmacological treatment available to delay or halt its progression. Characterized by progressive fibrotic remodelling and subsequent pathogenic mineralization of the valve leaflets, valve disease affects 2.5% of the western population, thus highlighting the need for urgent intervention. Whilst the pathobiology of valve disease is complex, involving genetic factors, lipid infiltration, and oxidative damage, the immune system is now being accepted to play a crucial role in pathogenesis and disease continuation. No longer considered a passive degenerative disease, CAVD is understood to be an active inflammatory process, involving a multitude of pro-inflammatory mechanisms, with both the adaptive and the innate immune system underpinning these complex mechanisms. Within the valve, 15% of cells evolve from haemopoietic origin, and this number greatly expands following inflammation, as macrophages, T lymphocytes, B lymphocytes, and innate immune cells infiltrate the valve, promoting further inflammation. Whether chronic immune infiltration or pathogenic clonal expansion of immune cells within the valve or a combination of the two is responsible for disease progression, it is clear that greater understanding of the immune systems role in valve disease is required to inform future treatment strategies for control of CAVD development.

Inflammatory and immune checkpoint markers are associated with the severity of aortic stenosis

Objective

Aortic stenosis (AS) is a disease characterized by narrowing of the aortic valve (AV) orifice. In relation to this disease, the purpose of this study was to elucidate the relationships among factors such as expression of programmed cell death-1 ligand (PD-L1, which is the ligand of PD-1 protein; together, they play a central role in the inhibition of T lymphocyte function), clinicopathologic characteristics, infiltrating immune cells, and disease severity.

Methods

We performed immunohistochemical analysis on the surgically-resected AVs of 53 patients with AS. We used the resultant data to identify relationships among PD-L1 expression, disease severity, and the infiltration of immune cells including cluster of differentiation (CD8)-positive T lymphocytes, cluster of differentiation 163 (CD163)-positive macrophages, and forkhead box protein 3 (FOXP3)-positive regulatory T lymphocytes (Tregs).

Results

PD-L1 expression in resected AVs was significantly associated with being nonsmoker, valve calcification, and the infiltration of CD8-positive T cells and CD163-positive macrophages. Disease severity and valve calcification were significantly associated with low infiltration of FOXP3-positive Tregs and high infiltration of CD8-positive T cells and CD163-positive macrophages. Moreover, calcified AVs with high PD-L1 expression showed active inflammation without FOXP3-positive Tregs but with high levels of CD8-positive T lymphocytes and CD163-positive macrophages.

Conclusions

Immune cell infiltration in the AVs and expression of the immune checkpoint protein PD-L1 were associated with the calcification of AS and disease severity.

TLR7 Expression Is Associated with M2 Macrophage Subset in Calcific Aortic Valve Stenosis

Calcific aortic valve stenosis (CAVS) is a common age-related disease characterized by active calcification of the leaflets of the aortic valve. How innate immune cells are involved in disease pathogenesis is not clear. In this study we investigate the role of the pattern recognition receptor Toll-like receptor 7 (TLR7) in CAVS, especially in relation to macrophage subtype. Human aortic valves were used for mRNA expression analysis, immunofluorescence staining, or ex vivo tissue assays. Response to TLR7 agonist in primary macrophages and valvular interstitial cells (VICs) were investigated in vitro. In the aortic valve, TLR7 correlated with M2 macrophage markers on mRNA levels. Expression was higher in the calcified part compared with the intermediate and healthy parts. TLR7⁺ cells were co-stained with M2-type macrophage receptors CD163 and CD206. Ex vivo stimulation of valve tissue with the TLR7 ligand imiquimod significantly increased secretion of IL-10, TNF-α, and GM-CSF. Primary macrophages responded to imiquimod with increased secretion of IL-10 while isolated VICs did not respond. In summary, in human aortic valves TLR7 expression is associated with M2 macrophages markers. Ex vivo tissue challenge with TLR7 ligand led to secretion of immunomodulatory cytokine IL-10. These results connect TLR7 activation in CAVS to reduced inflammation and improved clearance.

Innate and adaptive immunity in cardiovascular calcification

Despite the focus placed on cardiovascular research, the prevalence of vascular and valvular calcification is increasing and remains a leading contributor of cardiovascular morbidity and mortality. Accumulating studies provide evidence that cardiovascular calcification is an inflammatory disease in which innate immune signaling becomes sustained and/or excessive, shaping a deleterious adaptive response. The triggering immune factors and subsequent inflammatory events surrounding cardiovascular calcification remain poorly understood, despite sustained significant research interest and support in the field. Most studies on cardiovascular calcification focus on innate cells, particularly macrophages' ability to release pro-osteogenic cytokines and calcification-prone extracellular vesicles and apoptotic bodies. Even though substantial evidence demonstrates that macrophages are key components in triggering cardiovascular calcification, the crosstalk between innate and adaptive immune cell components has not been adequately addressed. The only therapeutic options currently used are invasive procedures by surgery or transcatheter intervention. However, no approved drug has shown prophylactic or therapeutic effectiveness. Conventional diagnostic imaging is currently the best method for detecting, measuring, and assisting in the treatment of calcification. However, these common imaging modalities are unable to detect early subclinical stages of disease at the level of microcalcifications; therefore, the vast majority of patients are diagnosed when macrocalcifications are already established. In this review, we unravel the current knowledge of how innate and adaptive immunity regulate cardiovascular calcification; and put forward differences and similarities between vascular and valvular disease. Additionally, we highlight potential immunomodulatory drugs with the potential to target calcification and propose avenues in need of further translational inquiry.

Adaptive immune cells in calcific aortic valve disease

Calcific aortic valve disease (CAVD) is highly prevalent and has no pharmaceutical treatment. Surgical replacement of the aortic valve has proved effective in advanced disease but is costly, time limited, and in many cases not optimal for elderly patients. This has driven an increasing interest in noninvasive therapies for patients with CAVD. Adaptive immune cell signaling in the aortic valve has shown potential as a target for such a therapy. Up to 15% of cells in the healthy aortic valve are hematopoietic in origin, and these cells, which include macrophages, T lymphocytes, and B lymphocytes, are increased further in calcified specimens. Additionally, cytokine signaling has been shown to play a causative role in aortic valve calcification both in vitro and in vivo. This review summarizes the physiological presence of hematopoietic cells in the valve, innate and adaptive immune cell infiltration in disease states, and the cytokine signaling pathways that play a significant role in CAVD pathophysiology and may prove to be pharmaceutical targets for this disease in the near future.

Involvement of inflammatory responses in the early development of calcific aortic valve disease: lessons from statin therapy

Calcific aortic valve disease (CAVD) is the most common degenerative heart valve disease. Among the many risk factors for this disease are age, hypercholesterolemia, hypertension, smoking, type-2 diabetes, rheumatic fever, and chronic kidney disease. Since many of these overlap with risk factors for atherosclerosis, the molecular and cellular mechanisms of CAVD development have been presumed to be similar to those for atherogenesis. Thus, attempts have been made to evaluate the therapeutic efficacy of statins, representative anti-atherosclerosis drugs with lipid-lowering and anti-inflammatory effects, against CAVD. Unfortunately, statins have shown little or no effect on CAVD development. But some reports suggest that statins may prevent or reduce the development of early stage CAVD in which having calcification is absent or minimal. These results suggest that therapeutic approaches should differ according to the stage of disease, and that a precise understanding of the mechanism of aortic valve calcification is required to identify novel therapeutic targets for advanced CAVD. Given the involvement of inflammatory processes in the development and progression of CAVD, current therapeutic approaches for chronic inflammatory cardiovascular disease like atherosclerosis may help to prevent or minimize the early development of CAVD. In this review, we focus on several inflammatory cellular and molecular components involved in CAVD that might be considered drug targets for preventing CAVD.

Lymphocyte and monocyte subpopulations in severe aortic stenosis at the time of surgical intervention

INTRODUCTION

Aortic stenosis (AS) is the most common acquired valvular heart disease in adults. Immune system involvement becomes evident during AS development. We sought to investigate the role of different circulating lymphocyte and monocyte subpopulations, with focus on CD4⁺CD8⁺ and natural killer T (NKT) cells, in AS.

MATERIAL AND METHODS

Blood samples and aortic valves were obtained from patients undergoing elective aortic valve surgery. Valves were dissected and underwent genetic analyses and calcium content assessment. Lymphocytes and monocytes subsets were assessed by flow cytometry.

RESULTS

Thirty-eight AS patients were studied. Maximal transvalvular pressure gradient (PG_max) as well as mean transvalvular pressure gradient (PG_mean) correlated with the CD4⁺CD8⁺ lymphocyte count (r=0.35, P=.03 and r=0.43, P=.006, respectively) and fraction (r=0.43, P=.007 and r=0.48, P=.002, respectively). PG_max and PG_mean correlated with CD16⁺CD56⁺CD3⁺ NKT cell count (r=0.39, P=.01 and r=0.43, P=.007, respectively) and fraction (r=0.49, P=.002 and r=0.47, P=.003, respectively). The classical monocyte subpopulation increased after the surgery by 68% (P<.0001). Patients after mini-sternotomy surgery had 47% lower nonclassical monocyte counts than those with full-sternotomy (P=.03). Patients treated with statins had significantly lower postoperative levels of both classical (-25%, P=.04) and nonclassical monocytes (-37%, P=.004) than nontreated individuals.

CONCLUSIONS

In patients with severe isolated AS, CD4⁺CD8⁺ T cells and CD16⁺CD56⁺CD3⁺ NKT cells are associated with AV pressure gradients. Postoperative monocyte levels are affected by procedure invasiveness and use of statins.

Advances in Pathophysiology of Calcific Aortic Valve Disease Propose Novel Molecular Therapeutic Targets

Calcific Aortic Valve Disease (CAVD) is the most common heart valve disease and its incidence is expected to rise with aging population. No medical treatment so far has shown slowing progression of CAVD progression. Surgery remains to this day the only way to treat it. Effective drug therapy can only be achieved through a better insight into the pathogenic mechanisms underlying CAVD. The cellular and molecular events leading to leaflets calcification are complex. Upon endothelium cell damage, oxidized LDLs trigger a proinflammatory response disrupting healthy cross-talk between valve endothelial and interstitial cells. Therefore, valve interstitial cells transform into osteoblasts and mineralize the leaflets. Studies have investigated signaling pathways driving and connecting lipid metabolism, inflammation and osteogenesis. This review draws a summary of the recent advances and discusses their exploitation as promising therapeutic targets to treat CAVD and reduce valve replacement.