CD1d deficiency inhibits the development of abdominal aortic aneurysms in LDL receptor deficient mice

A review of current status of cell-based therapies for aortic aneurysms

An aortic aneurysm (AA) is defined as focal aortic dilation that occurs mainly with older age and with chronic inflammation associated with atherosclerosis. The aneurysmal wall is a complex inflammatory environment characterized by endothelial dysfunction, macrophage activation, vascular smooth muscle cell (VSMC) apoptosis, and the production of proinflammatory molecules and matrix metalloproteases (MMPs) secreted by infiltrated inflammatory cells such as macrophages, T and B cells, dendritic cells, neutrophils, mast cells, and natural killer cells. To date, a considerable number of studies have been conducted on stem cell research, and growing evidence indicates that inflammation and tissue repair can be controlled through the functions of stem/progenitor cells. This review summarizes current cell-based therapies for AA, involving mesenchymal stem cells, VSMCs, multilineage-differentiating stress-enduring cells, and anti-inflammatory M2 macrophages. These cells produce beneficial outcomes in AA treatment by modulating the inflammatory environment, including decreasing the activity of proinflammatory molecules and MMPs, increasing anti-inflammatory molecules, modulating VSMC phenotypes, and preserving elastin. This article also describes detailed studies on pathophysiological mechanisms and the current progress of clinical trials.

Abdominal Aortic Aneurysm and PET/CT: From Molecular Mechanisms to Potential Molecular Imaging Targets

Abdominal aortic aneurysm (AAA) is the most common and critical aortic disease. Bleeding is the most serious complication from a ruptured AAA, which often results in death. Therefore, early diagnosis and treatment are the only effective means to reduce AAA associated mortality. Positron emission tomography/computed tomography (PET/CT) combines functional and anatomical imaging. The expanded application of PET/CT in the medical field could have benefits for the diagnosis and treatment of patients with AAA. This review explores the efficiency of PET/CT in the diagnosis of AAA based on our understanding of the underlying molecular mechanisms of AAA development.

A Novel Model of Tobacco Smoke-Mediated Aortic Injury

OBJECTIVE

Tobacco smoke exposure is a major risk factor for aortic aneurysm development. However, the initial aortic response to tobacco smoke, preceding aneurysm formation, is not well understood. We sought to create a model to determine the effect of solubilized tobacco smoke (STS) on the thoracic and abdominal aorta of mice as well as on cultured human aortic smooth muscle cells (HASMCs).

METHODS

Tobacco smoke was solubilized and delivered to mice via implanted osmotic minipumps. Twenty male C57BL/6 mice received STS or vehicle infusion. The descending thoracic, suprarenal abdominal, and infrarenal abdominal segments of the aorta were assessed for elastic lamellar damage, smooth muscle cell phenotype, and infiltration of inflammatory cells. Cultured HASMCs grown in media containing STS were compared to cells grown in standard media in order to verify our in vivo findings.

RESULTS

Tobacco smoke solution caused significantly more breaks in the elastic lamellae of the thoracic and abdominal aorta compared to control solution (P< .0001) without inciting an inflammatory infiltrate. Elastin breaks occurred more frequently in the abdominal aorta than the thoracic aorta (P < .01). Exposure to STS-induced aortic microdissections and downregulation of α-smooth muscle actin (α-SMA) by vascular smooth muscle cells (VSMCs). Treatment of cultured HASMCs with STS confirmed the decrease in α-SMA expression.

CONCLUSION

Delivery of STS via osmotic minipumps appears to be a promising model for investigating the early aortic response to tobacco smoke exposure. The initial effect of tobacco smoke exposure on the aorta is elastic lamellar damage and downregulation of (α-SMA) expression by VSMCs. Elastic lamellar damage occurs more frequently in the abdominal aorta than the thoracic aorta and does not seem to be mediated by the presence of macrophages or other inflammatory cells.

Single-Cell Transcriptome Profiles Reveal Fibrocytes as Potential Targets of Cell Therapies for Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is potentially life-threatening in aging population due to the risk of aortic rupture and a lack of optimal treatment. The roles of different vascular and immune cells in AAA formation and pathogenesis remain to be future characterized. Single-cell RNA sequencing was performed on an angiotensin (Ang) II-induced mouse model of AAA. Macrophages, B cells, T cells, fibroblasts, smooth muscle cells and endothelial cells were identified through bioinformatic analyses. The discovery of multiple subtypes of macrophages, such as the re-polarization of Trem2⁺Acp5⁺ osteoclast-like and M2-like macrophages toward the M1 type macrophages, indicates the heterogenous nature of macrophages during AAA development. More interestingly, we defined CD45⁺COL1⁺ fibrocytes, which was further validated by flow cytometry and immunostaining in mouse and human AAA tissues. We then reconstituted these fibrocytes into mice with Ang II-induced AAA and found the recruitment of these fibrocytes in mouse AAA. More importantly, the fibrocyte treatment exhibited a protective effect against AAA development, perhaps through modulating extracellular matrix production and thus enhancing aortic stability. Our study reveals the heterogeneity of macrophages and the involvement of a novel cell type, fibrocyte, in AAA. Fibrocyte may represent a potential cell therapy target for AAA.

Activated invariant natural killer T cells infiltrate aortic tissue as key participants in abdominal aortic aneurysm pathology

Adaptive immunity and innate immunity have been implicated in the pathogenesis of abdominal aortic aneurysm (AAA), and damage and remodelling in the tunica media are a focus of the aneurysm development. Thus, identification of key immune cells or molecules that might be targets for the treatment of AAA is critical. We characterized the innate immune cells in human AAA tissue specimens by flow cytometry and found that apart from other lymphocytes, many invariant natural killer T (iNKT) cells marked as CD3 and Va24Ja18 had invaded the aortic tissues and were numerous, especially in the tunica media. These infiltrating iNKT cells have a high expression of CD69, indicating a highly active function. We were interested in whether iNKT cells could be the drivers of media damage in AAA. To answer this question, we used an AAA mouse model induced by angiotensin II (Ang II) infusion, which can reproduce the inflammatory response of AAA in mouse, which was confirmed by RNAseq. The results showed that the incidence of AAA was significantly higher after administration of α-galactosylceramide (α-GalCer), a synthetic glycolipid that activates iNKT cells via CD1d, compared with the Ang II-induced AAA alone (61·54% vs 31·82%) in mice. Histopathological and immunofluorescent staining results showed significantly more severe inflammatory infiltration and pathological lesions in the Ang II+α-GalCer treatment group. These results are highly suggestive that activated iNKT cells greatly contribute to AAA development and that the control of the activation state in iNKT cells may represent an important therapeutic strategy for AAA.

A double-edged sword of immuno-microenvironment in cardiac homeostasis and injury repair

The response of immune cells in cardiac injury is divided into three continuous phases: inflammation, proliferation and maturation. The kinetics of the inflammatory and proliferation phases directly influence the tissue repair. In cardiac homeostasis, cardiac tissue resident macrophages (cTMs) phagocytose bacteria and apoptotic cells. Meanwhile, NK cells prevent the maturation and transport of inflammatory cells. After cardiac injury, cTMs phagocytose the dead cardiomyocytes (CMs), regulate the proliferation and angiogenesis of cardiac progenitor cells. NK cells prevent the cardiac fibrosis, and promote vascularization and angiogenesis. Type 1 macrophages trigger the cardioprotective responses and promote tissue fibrosis in the early stage. Reversely, type 2 macrophages promote cardiac remodeling and angiogenesis in the late stage. Circulating macrophages and neutrophils firstly lead to chronic inflammation by secreting proinflammatory cytokines, and then release anti-inflammatory cytokines and growth factors, which regulate cardiac remodeling. In this process, dendritic cells (DCs) mediate the regulation of monocyte and macrophage recruitment. Recruited eosinophils and Mast cells (MCs) release some mediators which contribute to coronary vasoconstriction, leukocyte recruitment, formation of new blood vessels, scar formation. In adaptive immunity, effector T cells, especially Th17 cells, lead to the pathogenesis of cardiac fibrosis, including the distal fibrosis and scar formation. CMs protectors, Treg cells, inhibit reduce the inflammatory response, then directly trigger the regeneration of local progenitor cell via IL-10. B cells reduce myocardial injury by preserving cardiac function during the resolution of inflammation.

Abdominal Aortic Aneurysm: Roles of Inflammatory Cells

Abdominal aortic aneurysms (AAAs) are local dilations of infrarenal segment of aortas. Molecular mechanisms underlying the pathogenesis of AAA remain not fully clear. However, inflammation has been considered as a central player in the development of AAA. In the past few decades, studies demonstrated a host of inflammatory cells, including T cells, macrophages, dendritic cells, neutrophils, B cells, and mast cells, etc. infiltrating into aortic walls, which implicated their crucial roles. In addition to direct cell contacts and cytokine or protease secretions, special structures like inflammasomes and neutrophil extracellular traps have been investigated to explore their functions in aneurysm formation. The above-mentioned inflammatory cells and associated structures may initiate and promote AAA expansion. Understanding their impacts and interaction networks formation is meaningful to develop new strategies of screening and pharmacological interventions for AAA. In this review, we aim to discuss the roles and mechanisms of these inflammatory cells in AAA pathogenesis.

IFI16 contributes to the pathogenesis of abdominal aortic aneurysm by regulating the caspase-1/IL-1β/MCPIP1 pathway

AIMS

Abdominal aortic aneurysm (AAA) is a multi-factorial progressive vascular disease characterized by chronic inflammatory cell infiltration. We investigated the roles played by IFI16 and ASC inflammasomes in AAA development and progression.

MATERIALS AND METHODS

Western blot and qRT-PCR studies were performed to analyze the expression of relative genes in AAA specimens and mouse vascular smooth muscle cells (VSMCs). The apoptosis rates and ROS levels of VSMCs were assessed by flow cytometry. Transwell assays were performed to analyze the migration ability of VSMCs. The levels of MCP-1, IL-1β, and IL-6 in the supernatants of cultured VSMCs were analyzed by ELISA.

KEY FINDINGS

Increased levels of IFI16 expression were found in AAA specimens and Ang-II-treated VSMCs. IFI16 and ASC silencing suppressed the apoptosis and migration ability of VSMCs undergoing Ang-II treatment, reduced elasticity damage to the aortic wall, and decreased the levels of MMP expression. The effect of IFI16 knockdown in Ang-II-induced VSMCs was reversed by MCPIP1 overexpression.

SIGNIFICANCE

Our data suggest that an up-regulation of IFI16 and ASC expression might promote the apoptosis of VSMCs, enhance the inflammatory response, and impairs vascular wall elasticity via a MCPIP1-related mechanism. The inflammasome components IFI16 and ASC might be involved in AAA progression and serve as target molecules for diagnosing and treating AAA.

Expression of Blood Cells Associated CD Markers and Cardiovascular Diseases: Clinical Applications in Prognosis

BACKGROUND

Cardiovascular diseases (CVDs) are a major cause of mortality worldwide. The results of various studies have shown that abnormality in the frequency and function of blood cells can be involved in CVD complications. In this review, we have focused on abnormalities in the expression of the CD (cluster of differentiation) markers of blood cells to assess the association of these abnormalities with CVD prognosis.

METHODS

We identified the relevant literature through a PubMed search (1990-2018) of English-language articles using the terms "Cardiovascular diseases", "CD markers", "leukocytes", "platelets", and "endothelial cells".

RESULTS

There is a variety of mechanisms for the effect of CD-marker expressions on CVDs prognosis, ranging from proinflammatory processes to dysfunctional effects in blood cells.

CONCLUSION

Considering the possible effects of CD-marker expression on CVDs prognosis, particularly prognosis of acute myocardial infarction and atherosclerosis, long-term studies in large cohorts are required to identify the prognostic value of CD markers and to target them with appropriate therapeutic agents.

CD1d-dependent natural killer T cells attenuate angiotensin II-induced cardiac remodelling via IL-10 signalling in mice

Aims

CD1d is a member of the cluster of differentiation 1 (CD1) family of glycoproteins expressed on the surface of various antigen-presenting cells, which is recognized by natural killer T (NKT) cells. CD1d-dependent NKT cells play an important role in immune-mediated diseases; but the role of these cells in regulating cardiac remodelling remains unknown.

Methods and results

Cardiac remodelling was induced by angiotensin (Ang) II infusion for 2 weeks. Ang II-induced increase in hypertension, cardiac performance, hypertrophy and fibrosis, inflammatory response, and activation of the NF-kB and TGF-β1/Smad2/3 pathways was significantly aggravated in CD1d knockout (CD1dko) mice compared with wild-type (WT) mice, but these effects were markedly abrogated in WT mice treated with α-galactosylceramide (αGC), a specific activator of NKT cells. Adoptive transfer of CD1dko bone marrow cells to WT mice further confirmed the deleterious effect of CD1dko. Moreover, IL-10 expression was significantly decreased in CD1dko hearts but increased in αGC-treated mice. Co-culture experiments revealed that CD1dko dendritic cells significantly reduced IL-10 mRNA expression from NKT cells. Administration of recombinant murine IL-10 to CD1dko mice improved hypertension, cardiac performance, and adverse cardiac remodelling induced by Ang II, and its cardioprotective effect was possibly associated with activation of STAT3, and inhibition of the TGF-β1 and NF-kB pathways.

Conclusion

These findings revealed a previously undefined role for CD1d-dependent NKT cells in Ang II-induced cardiac remodelling, hence activation of NKT cells may be a novel therapeutic target for hypertensive cardiac disease.

Defective Autophagy in T Cells Impairs the Development of Diet-Induced Hepatic Steatosis and Atherosclerosis

Macroautophagy (or autophagy) is a conserved cellular process in which cytoplasmic cargo is targeted for lysosomal degradation. Autophagy is crucial for the functional integrity of different subsets of T cells in various developmental stages. Since atherosclerosis is an inflammatory disease of the vessel wall which is partly characterized by T cell mediated autoimmunity, we investigated how advanced atherosclerotic lesions develop in mice with T cells that lack autophagy-related protein 7 (Atg7), a protein required for functional autophagy. Mice with a T cell-specific knock-out of Atg7 (Lck-Cre Atg7^f/f) had a diminished naïve CD4⁺ and CD8⁺ T cell compartment in the spleen and mediastinal lymph node as compared to littermate controls (Atg7^f/f). Lck-Cre Atg7^f/f and Atg7^f/f mice were injected intravenously with rAAV2/8-D377Y-mPCSK9 and fed a Western-type diet to induce atherosclerosis. While Lck-Cre Atg7^f/f mice had equal serum Proprotein Convertase Subtilisin/Kexin type 9 levels as compared to Atg7^f/f mice, serum cholesterol levels were significantly diminished in Lck-Cre Atg7^f/f mice. Histological analysis of the liver revealed less steatosis, and liver gene expression profiling showed decreased expression of genes associated with hepatic steatosis in Lck-Cre Atg7^f/f mice as compared to Atg7^f/f mice. The level of hepatic CD4⁺ and CD8⁺ T cells was greatly diminished but both CD4⁺ and CD8⁺ T cells showed a relative increase in their IFNγ and IL-17 production upon Atg7 deficiency. Atg7 deficiency furthermore reduced the hepatic NKT cell population which was decreased to < 0.1% of the lymphocyte population. Interestingly, T cell-specific knock-out of Atg7 decreased the mean atherosclerotic lesion size in the tri-valve area by over 50%. Taken together, T cell-specific deficiency of Atg7 resulted in a decrease in hepatic steatosis and limited inflammatory potency in the (naïve) T cell compartment in peripheral lymphoid tissues, which was associated with a strong reduction in experimental atherosclerosis.