Positive correlation between CD137 expression and complex stenosis morphology in patients with acute coronary syndromes

The levels of soluble CD137 are increased in tuberculosis patients and associated with disease severity and prognosis

Tuberculosis (TB) was the leading cause of death from a single infectious agent before the coronavirus pandemic. Therefore, it is important to search for severity biomarkers and devise appropriate therapies. A total of 139 pulmonary TB (PTB) patients and 80 healthy controls (HCs) were recruited for plasma soluble CD137 (sCD137) detection through ELISA. Moreover, pleural effusion sCD137 levels were measured in 85 TB patients and 36 untreated lung cancer patients. The plasma cytokine levels in 64 patients with PTB and blood immune cell subpopulations in 68 patients with PTB were analysed via flow cytometry. Blood sCD137 levels were higher in PTB patients (p = 0.012) and correlated with disease severity (p = 0.0056). The level of sCD137 in tuberculous pleurisy effusion (TPE) was markedly higher than that in malignant pleurisy effusion (p = 0.018). Several blood cytokines, such as IL-6 (p = 0.0147), IL-8 (p = 0.0477), IP-10 (p ≤ 0.0001) and MCP-1 (p = 0.0057), and some laboratory indices were significantly elevated in severe PTB (SE) patients, but the percentages of total lymphocytes (p = 0.002) and cytotoxic T cells (p = 0.036) were significantly lower in SE patients than in non-SE patients. In addition, the sCD137 level was negatively correlated with the percentage of total lymphocytes (p = 0.0008) and cytotoxic T cells (p = 0.0021), and PTB patients with higher plasma sCD137 levels had significantly shorter survival times (p = 0.0041). An increase in sCD137 is a potential biomarker for severe TB and indicates a poor prognosis.

CD137 Signaling Promotes Endothelial Apoptosis by Inhibiting Nrf2 Pathway, and Upregulating NF-κB Pathway

Background

Endothelial dysfunction and apoptosis resulting from oxidative stress can lead to the development of atherosclerosis. Our group has previously showed that CD137 signaling contributes to the progression of atherosclerosis and the vulnerability of plaques. The aim of this study is to investigate the effects of CD137 signaling in atherosclerosis on endothelial cells (ECs) apoptosis and to explore the underlying mechanisms.

Methods

Serum samples were collected from 11 patients with acute myocardial infarction and 4 controls. Peritoneal injection of agonist-CD137 recombinant protein in ApoE^−/− mice was used to determine whether CD137 signaling can promote apoptosis in vivo, and human umbilical vein endothelial cells treated with agonist-CD137 recombinant protein, M5580 (a Nrf2 pathway agonist) and CAPE (a NF-κB pathway inhibitor) were used to explore the effect of Nrf2 and NF-κB pathway in CD137 signaling-induced ECs apoptosis in vitro.

Results

ELISA showed that Bcl-2 in the serum of AMI patients was lower than that of the control group, while TNF-α and sCD137 were higher than that of the control group. Confocal microscopy and Western blot analysis showed that the nuclear translocation of Nrf2 in the agonist-CD137 group was significantly inhibited, and the expression of its downstream antioxidant enzymes was also decreased when compared with control. Immunofluorescence and Western blot results showed that the nuclear translocation of NF-κB in the agonist-CD137 group was enhanced, and ELISA results showed that the secretion of proinflammatory cytokines in the agonist-CD137 group was increased. Immunofluorescence results revealed that ROS production in the agonist-CD137 group was higher than that in control, M5580 (a Nrf2 pathway agonist) and CAPE (a NF-κB pathway inhibitor) groups. In vitro studies using HUVECs and in vivo studies using high-fat-fed ApoE^−/− mice showed that the number of apoptotic endothelial cells was the highest in the agonist-CD137 group. By contrast, both M5580 and CAPE treatments were able to reduce CD137 induced ECs apoptosis.

Conclusions

Our results showed that CD137 signaling promotes ECs apoptosis through prooxidative and proinflammatory mechanisms, mediated by Nrf2 and NF-κB pathways, respectively.

Exploring immune checkpoints as potential therapeutic targets in atherosclerosis

In the past decades, the inflammatory nature of atherosclerosis has been well-recognized and despite the development of therapeutic strategies targeted at its classical risk factors such as dyslipidemia and hypertension, atherosclerosis remains a major cause of morbidity and mortality. Additional strategies targeting the chronic inflammatory pathways underlying the development of atherosclerosis are therefore required. Interactions between different immune cells result in the secretion of inflammatory mediators, such as cytokines and chemokines, and fuel atherogenesis. Immune checkpoint proteins have a critical role in facilitating immune cell interactions and play an essential role in the development of atherosclerosis. Although the therapeutic potential of these molecules is well-recognized in clinical oncology, the use of immune checkpoint modulators in atherosclerosis is still limited to experimental models. Here, we review recent insights on the role of immune checkpoint proteins in atherosclerosis. Additionally, we explore the therapeutic potential and challenges of immune checkpoint modulating strategies in cardiovascular medicine and we discuss novel therapeutic approaches to target these proteins in atherosclerosis.

Direct CD137 costimulation of CD8 T cells promotes retention and innate-like function within nascent atherogenic foci

Effector CD8 T cells infiltrate atherosclerotic lesions and are correlated with cardiovascular events, but the mechanisms regulating their recruitment and retention are not well understood. CD137 (4-1BB) is a costimulatory receptor induced on immune cells and expressed at sites of human atherosclerotic plaque. Genetic variants associated with decreased CD137 expression correlate with carotid-intimal thickness and its deficiency in animal models attenuates atherosclerosis. These effects have been attributed in part to endothelial responses to low and disturbed flow (LDF), but CD137 also generates robust effector CD8 T cells as a costimulatory signal. Thus, we asked whether CD8 T cell-specific CD137 stimulation contributes to their infiltration, retention, and IFNγ production in early atherogenesis. We tested this through adoptive transfer of CD8 T cells into recipient C57BL/6J mice that were then antigen primed and CD137 costimulated. We analyzed atherogenic LDF vessels in normolipidemic and PCSK9-mediated hyperlipidemic models and utilized a digestion protocol that allowed for lesional T-cell characterization via flow cytometry and in vitro stimulation. We found that CD137 activation, specifically of effector CD8 T cells, triggers their intimal infiltration into LDF vessels and promotes a persistent innate-like proinflammatory program. Residence of CD137⁺ effector CD8 T cells further promoted infiltration of endogenous CD8 T cells with IFNγ-producing potential, whereas CD137-deficient CD8 T cells exhibited impaired vessel infiltration, minimal IFNγ production, and reduced infiltration of endogenous CD8 T cells. Our studies thus provide novel insight into how CD137 costimulation of effector T cells, independent of plaque-antigen recognition, instigates their retention and promotes innate-like responses from immune infiltrates within atherogenic foci. NEW & NOTEWORTHY Our studies identify CD137 costimulation as a stimulus for effector CD8 T-cell infiltration and persistence within atherogenic foci, regardless of atherosclerotic-antigen recognition. These costimulated effector cells, which are generated in pathological states such as viral infection and autoimmunity, have innate-like proinflammatory programs in circulation and within the atherosclerotic microenvironment, providing mechanistic context for clinical correlations of cardiovascular morbidity with increased CD8 T-cell infiltration and markers of activation in the absence of established antigen specificity.

Increased Peripheral CD137 Expression in a Mouse Model of Permanent Focal Cerebral Ischemia

Various studies demonstrate that CD137 (TNFRSF9, 4-1BB) promotes atherosclerosis and vascular inflammation in experimental models via interactions with the CD137 ligand (CD137L). However, the exact role of CD137 in ischemic stroke remains unclear. In this study, we analyzed dynamic changes of peripheral CD137 expression on T cells in a mouse model of cerebral ischemia-middle cerebral artery occlusion (MCAO), as well as alternation of neurological function, infarct size and cerebral inflammatory status after inhibition of the CD137/CD137L pathway using an anti-CD137L monoclonal antibody. MCAO mice showed elevated surface expression of CD137 on T cells in both peripheral blood and lymphoid tissues during early cerebral ischemia. Remarkably, blockade of the CD137/CD137L pathway reduced the post-ischemic brain damage. Our findings indicate that enhanced CD137 costimulation occurs in early cerebral ischemia and promotes T cell activation, which in turn upregulates inflammatory immune response and possibly exerting deleterious effects on cerebral ischemia.

Activation of CD137 Signaling Enhances Vascular Calcification through c-Jun N-Terminal Kinase-Dependent Disruption of Autophagic Flux

Background

Vascular calcification is widespread and clinically significant, contributing to substantial morbidity and mortality. Calcifying vascular cells are partly derived from local vascular smooth muscle cells (VSMCs), which can undergo chondrogenic or osteogenic differentiation under inflammatory environment. Recently, we have found activation of CD137 signaling accelerated vascular calcification. However, the underlying mechanism remains unknown. This study aims to identify key mediators involved in CD137 signaling-induced vascular calcification in vivo and in vitro.

Methods

Autophagy flux was measured through mRFP-GFP-LC3 adenovirus and transmission electron microscopy. Von Kossa assay and alkaline phosphatase (ALP) activity were used to observe calcification in vivo and in vitro, respectively. Autophagosome-containing vesicles were collected and identified by flow cytometry and Western blot. Autophagy or calcification-associated targets were measured by Western blot, quantitative real-time PCR, and immunohistochemistry.

Results

Treatment with the agonist-CD137 displayed c-Jun N-terminal kinase- (JNK-) dependent increase in the expression of various markers of autophagy and the number of autophagosomes relative to the control group. Autophagy flux experiments suggested that agonist-CD137 blocked the fusion of autophagosomes with lysosomes in cultured VSMCs. Calcium deposition, ALP activity, and the expression of calcification-associated proteins also increased in agonist-CD137 group compared with anti-CD137 group, which could be recovered by autophagy stimulator rapamycin. Autophagosome-containing vesicles collected from agonist-CD137 VSMCs supernatant promoted VSMC calcification.

Conclusion

The present study identified a new pathway in which CD137 promotes VSMC calcification through the activation of JNK signaling, subsequently leading to the disruption of autophagic flux, which is responsible for CD137-induced acceleration of vascular calcification.

Increased Soluble CD137 Levels and CD4+ T-Cell-Associated Expression of CD137 in Acute Atherothrombotic Stroke

As a proinflammatory cytokine, CD137 (4‐1BB, TNFRSF9) is present in membrane‐bound and soluble forms. Increased expression of CD137 was recently found in T cells in human atherosclerotic plaques. However, the exact role of CD137 in ischemic stroke is not clear. In this study we analyzed the protein levels of soluble CD137 (sCD137) and the expression of CD137 on CD4+ T cells in the peripheral blood of patients with acute atherothrombotic stroke by using the cytometry beads array (CBA) and flow cytometry. Within 24 hours of onset, the stroke patients showed elevated levels of sCD137 (2.7 pg/ml) and CD137 expression on CD4+ T cells (4.9 ± 3.2%) compared with normal controls (1.1 pg/ml, P < 0.01; 1.3 ± 1.0%, P < 0.01). Alterations in CD137 expression may enhance ischemia‐induced inflammatory responses via bidirectional signaling and, consequently, aggravate brain injury in early stages of this disorder.

Activation of CD137 Signaling Promotes Angiogenesis in Atherosclerosis via Modulating Endothelial Smad1/5-NFATc1 Pathway

Background

Excessive angiogenesis is a key feature of vulnerable atherosclerotic plaques, and is considered an independent predictor of cardiovascular risk. CD137 signaling has previously been shown to be involved in atherosclerosis. However, the possible role of CD137 signaling in regulating angiogenesis has not been reported.

Methods and Results

Apolipoprotein E‐deficient (ApoE^−/−) mice were used as the in vivo model of atherosclerosis. Masson and immunohistochemical analysis of atherosclerotic plaques and Matrigel plug assay were used to evaluate the angiogenesis. Human umbilical vein endothelial cells and mouse brain microvascular endothelial cells were used as in vitro and ex vivo models to study how CD137 signaling affects angiogenesis. Matrigel tube formation assay, mouse aortic ring angiogenesis assay, and migration and proliferation assay were employed to assess angiogenesis. Western blot was used to detect protein expression. We found increased neovessel formation in atherosclerotic plaques of ApoE^−/− mice treated with agonist anti‐CD137 antibody. Activation of CD137 signaling induced angiogenesis, endothelial proliferation, and endothelial cell migration. CD137 signaling activates the pro‐angiogenic Smad1/5 pathway, induces the phosphorylation of Smad1/5 and nuclear translocation of p‐Smad1/5, which in turn promotes the expression and translocation of NFATc1. Blocking CD137 signaling with inhibitory anti‐CD137 antibody could inhibit this activation and attenuated agonist anti‐CD137 antibody‐induced angiogenesis.

Conclusions

These findings suggest that CD137 signaling is a new regulator of angiogenesis by modulating the Smad1/5‐NFATc1 pathway.

The Roles of CD137 Signaling in Atherosclerosis

The tumor necrosis factor receptor superfamily (TNFRSF), which includes CD40, LIGHT, and OX40, plays important roles in the initiation and progression of cardiovascular diseases, involving atherosclerosis. CD137, a member of TNFRSF, is a well-known activation-induced T cell co-stimulatory molecule and has been reported to be expressed in human atherosclerotic plaque lesions, and plays pivotal roles in mediating disease processes. In this review, we focus on and summarize recent advances in mouse studies on the involvement of CD137 signaling in the pathogenesis and plaque stability of atherosclerosis, thereby highlighting a valuable therapeutic target in atherosclerosis.

CD137 Regulates NFATc1 Expression in Mouse VSMCs through TRAF6/NF-κB p65 Signaling Pathway

Our previous study proved that CD137-CD137L interaction can regulate the expression of NFATc1. Here, we investigated whether CD137 signaling regulates the expression of NFATc1 in mice VSMCs through TRAF6/NF-κB p65 pathway. Data shows that the CD137 expression can be stimulated by TNF-α in a time-dependent manner in mouse VSMCs. Knockdown of TRAF6 by siTRAF6 significantly attenuated agonist-CD137mAb induced increase of NF-κB p65 and NFATc1 in VSMCs. Pretreatment with a NF-κB inhibitor PDTC for 30 min inhibited the expression of p-p65 in both cytoplasm and nucleus in VSMCs. Thus, the protein level of NFATc1 can be suppressed through inhibition of p-p65. Finally, we also show that the levels of IL-2 and IL-6 can be increased by agonist-CD137 stimulation and decreased when NFATc1 was suppressed. Our data suggest that activated CD137 signaling regulates the expression of NFATc1 and its downstream factors through TRAF6/NF-κB p65 pathways in VSMCs. These findings provide a novel target for treatment of atherosclerosis.

CD137-CD137L interaction regulates atherosclerosis via cyclophilin A in apolipoprotein E-deficient mice

Background

Our previous studies showed that increased levels of cyclophilin A (CyPA) may be a valuable marker for predicting the severity of acute coronary syndromes and that interruption of CD137-CD137L interactions diminished the formation and progression of atherosclerosis in apolipoprotein E-deficient (ApoE−/−) mice. Here, we sought to determine whether the proinflammatory factor CyPA is involved in atherosclerosis regulated by CD137-CD137L interactions.

Methods and Results

A constrictive collar was placed around the right carotid arteries of ApoE−/− mice that were fed a high-fat diet to induce atherosclerotic plaque formation. After that, the mice were intraperitoneally injected with anti-CD137 or anti-CD137L in the presence or absence of the recombinant lentiviral vectors LVTHM-CyPA or pGC-FU-CyPA, respectively. Interestingly, activation of CD137-CD137L was negatively correlated with CyPA expression in vivo and in vitro. Stimulating CD137-CD137L interaction significantly increased CyPA, which was concurrent with the upregulation of proinflammatory cytokines, chemokines and matrix metalloproteinases and resulted in the promotion of atherosclerosis in ApoE-/- mice. Silencing CyPA could eliminate these effects, and restoration of CyPA effectively and consistently attenuated the atherosclerotic suppression phenotypes elicited by the blockade of CD137-CD137L.

Conclusion

These observations suggest that CD137-CD137L interactions mediated via regulation of CyPA contribute to the progression of atherosclerosis.

The effect of CD137-CD137 ligand interaction on phospholipase C signaling pathway in human endothelial cells

We previously reported the emerging role of CD137-CD137L interaction in inflammation and atherosclerosis. The mechanism of CD137-CD137L interaction may be related to a variety of signaling pathways. The most important signaling pathway involves the activation of phospholipase C(PLC) which induces the diacylglycerol-protein kinase C(DAG-PKC) and the inositol trisphosphate-intracellular free calcium (IP3-[Ca(2+)]i) pathway. In the current study, we investigated whether CD137-CD137L interaction can stimulate the PLC signaling pathway in human umbilical vein endothelial cells (HUVEC). The diacylglycerol (DAG) and inositol trisphosphate (IP3) levels in HUVEC were measured by radioenzymatic assay. The activity of protein kinase (PKC) was detected by its ability to transfer phosphate from [γ-(32)P]ATP to lysine-rich histone. The [Ca(2+)]i concentrations were measured by flow cytometric analysis. The DAG level and PKC activity were increased in a concentration-dependent, biphasic manner in HUVEC induced by anti-CD137. PKC activity was mainly in the cytosol at rest, and then translocated to the membrane when stimulated by anti-CD137. Similarly, rapid IP3 formation induced by anti-CD137 coincided with the peak of the DAG level. Moreover, anti-CD137 induced peak [Ca(2+)]i responses including the rapid transient phase and the sustained phase. However, anti-CD137L suppressed the activation of the DAG-PKC and IP3-[Ca(2+)]i signaling pathway, which was stimulated by anti-CD137 in HUVEC. In conclusion, the data suggested that CD137-CD137L interaction induces robust activation of the PLC signaling pathway in HUVEC.

Clinical implications of elevated serum soluble CD137 levels in patients with acute coronary syndrome

OBJECTIVES

Atherosclerosis is a chronic inflammatory disease. Research has focused on identifying specific serum biomarkers to detect vulnerable plaques. These markers serve as diagnostic tools for acute coronary syndrome and assist in identifying high-risk patients. However, the existing data are limited and conflicting. This study tested the hypothesis that CD137 levels identify patients with acute coronary syndrome who are at a heightened risk for recurrent cardiac events.

METHODS

The levels of soluble CD137 (sCD137) were measured using ELISA in 180 patients with acute coronary syndrome and 120 patients with acute chest pain. Platelet activation was assessed by flow cytometry. Receiver operating characteristic curve analysis was performed to evaluate the prognostic characteristics of sCD137.

RESULTS

The levels of sCD137 were elevated in 75 patients with acute coronary syndromes and 20 patients with acute chest pain (>35.0 ng/ml). In patients with acute coronary syndrome, elevated sCD137 levels (>35.0 ng/ml) indicated an increased risk for major adverse cardiovascular events (OR =1.93, 95% CI: 1.39-2.54). Elevated serum levels of sCD137 and cTnT were correlated with a significantly increased risk of major adverse cardiovascular events in both groups after 30 days, six months and nine months of follow-up. The increased sCD137 levels were significantly correlated with the levels of troponin I (r = 0.4799, p<0.001). Importantly, 26 patients with normal cTnI levels had acute coronary syndrome. However, elevated sCD137 levels identified these patients as a being high-risk subgroup (OR = 2.14, 95% CI: 1.25-4.13).

CONCLUSIONS

Elevated sCD137 levels indicate an increased risk of cardiovascular events in patients with acute coronary syndrome. Soluble CD137 may be a useful prognostic marker or indicator for adverse events in patients with acute coronary syndrome.

The role of costimulatory receptors of the tumour necrosis factor receptor family in atherosclerosis

Atherosclerosis is a chronic inflammatory disease that is mediated by both the innate and adaptive immune responses. T lymphocytes, that together with B cells are the cellular effectors of the adaptive immune system, are currently endowed with crucial roles in the development and progression of atherosclerosis. Costimulatory receptors are a class of molecules expressed by T lymphocytes that regulate the activation of T cells and the generation of effector T-cell responses. In this review we present the roles of costimulatory receptors of the tumour necrosis factor receptor (TNFR) superfamily in atherosclerosis and discuss the implications for future therapies that could be used to specifically modulate the immune response of pathogenic T cells in this disease.