Mesenchymal Stromal Cells Modulate Monocytes Trafficking in Coxsackievirus B3-Induced Myocarditis

Mesenchymal stromal cells for improvement of cardiac function following acute myocardial infarction: a matter of timing

Acute myocardial infarction (AMI) is the leading cause of cardiovascular death and remains the most common cause of heart failure. Reopening of the occluded artery, i.e., reperfusion, is the only way to save the myocardium. However, the expected benefits of reducing infarct size are disappointing due to the reperfusion paradox, which also induces specific cell death. These ischemia-reperfusion (I/R) lesions can account for up to 50% of final infarct size, a major determinant for both mortality and the risk of heart failure (morbidity). In this review, we provide a detailed description of the cell death and inflammation mechanisms as features of I/R injury and cardioprotective strategies such as ischemic postconditioning as well as their underlying mechanisms. Due to their biological properties, the use of mesenchymal stromal/stem cells (MSCs) has been considered a potential therapeutic approach in AMI. Despite promising results and evidence of safety in preclinical studies using MSCs, the effects reported in clinical trials are not conclusive and even inconsistent. These discrepancies were attributed to many parameters such as donor age, in vitro culture, and storage time as well as injection time window after AMI, which alter MSC therapeutic properties. In the context of AMI, future directions will be to generate MSCs with enhanced properties to limit cell death in myocardial tissue and thereby reduce infarct size and improve the healing phase to increase postinfarct myocardial performance.

Regenerative loss in the animal kingdom as viewed from the mouse digit tip and heart

The myriad regenerative abilities across the animal kingdom have fascinated us for centuries. Recent advances in developmental, molecular, and cellular biology have allowed us to unearth a surprising diversity of mechanisms through which these processes occur. Developing an all-encompassing theory of animal regeneration has thus proved a complex endeavor. In this chapter, we frame the evolution and loss of animal regeneration within the broad developmental constraints that may physiologically inhibit regenerative ability across animal phylogeny. We then examine the mouse as a model of regeneration loss, specifically the experimental systems of the digit tip and heart. We discuss the digit tip and heart as a positionally-limited system of regeneration and a temporally-limited system of regeneration, respectively. We delve into the physiological processes involved in both forms of regeneration, and how each phase of the healing and regenerative process may be affected by various molecular signals, systemic changes, or microenvironmental cues. Lastly, we also discuss the various approaches and interventions used to induce or improve the regenerative response in both contexts, and the implications they have for our understanding regenerative ability more broadly.

The inflammatory spectrum of cardiomyopathies

Infiltration of the myocardium with various cell types, cytokines and chemokines plays a crucial role in the pathogenesis of cardiomyopathies including inflammatory cardiomyopathies and myocarditis. A more comprehensive understanding of the precise immune mechanisms involved in acute and chronic myocarditis is essential to develop novel therapeutic approaches. This review offers a comprehensive overview of the current knowledge of the immune landscape in cardiomyopathies based on etiology. It identifies gaps in our knowledge about cardiac inflammation and emphasizes the need for new translational approaches to improve our understanding thus enabling development of novel early detection methods and more effective treatments.

Lupeol alleviates autoimmune myocarditis by suppressing macrophage pyroptosis and polarization via PPARα/LACC1/NF-κB signaling pathway

BACKGROUND

Autoimmune myocarditis, with increasing incidence and limited therapeutic strategies, is in urgent need to explore its underlying mechanisms and effective drugs. Pyroptosis is a programmed cell death that may contribute to the pathogenesis of myocarditis. Nonetheless, no direct evidence validated the role of pyroptosis in autoimmune myocarditis. Lupeol (Lup), a pentacyclic triterpene, possesses various biological activities such as antidiabetic properties. However, the effects of Lup on autoimmune myocarditis and pyroptosis remain unelucidated.

PURPOSE

This study aimed to reveal the role of pyroptosis in autoimmune myocarditis and explore the protective effects of Lup, and its engaged mechanisms.

METHODS

The experimental autoimmune myocarditis (EAM) mouse model was established by immunization with a fragment of cardiac myosin in Balb/c mice. Lup and MCC950 were administered after EAM induction. The protective effects were assessed by inflammation score, cardiac injury, chronic fibrosis, and cardiac function. Mechanistically, the effects of Lup on the M1 polarization and pyroptosis of macrophages were evaluated. Transcriptome sequencing and molecular docking were subsequently employed, and the underlying mechanisms of Lup were further explored in vitro with small interfering RNA and adenovirus.

RESULTS

Administration of Lup and MCC950 alleviated EAM progression. Western blotting and immunofluorescence staining identified macrophages as the primary cells undergoing pyroptosis. Lup inhibited the expression of pyroptosis-associated proteins in macrophages during EAM in a dose-dependent manner. Furthermore, Lup suppressed pyroptosis in both bone marrow-derived macrophages (BMDMs) and THP-1-derived macrophages in vitro. In addition, Lup inhibited the M1 polarization of macrophages both in vivo and in vitro. Mechanistically, the protective effects of Lup were demonstrated via the suppression of the nuclear factor-κΒ (NF-κB) signaling pathway. Transcriptome sequencing and molecular docking revealed the potential involvement of peroxisome proliferator-associated receptor α (PPARα). Subsequently, we demonstrated that Lup activated PPARα to reduce the expression level of LACC1, thereby inhibiting the NF-κB pathway and pyroptosis.

CONCLUSION

Our findings indicated the crucial role of macrophage pyroptosis in the pathogenesis of EAM. Lup ameliorated EAM by inhibiting the M1 polarization and pyroptosis of macrophages through the PPARα/LACC1/NF-κB signaling pathway. Thus, our results provided a novel therapeutic target and agent for myocarditis.

Human Bone Marrow Mesenchymal Stem Cells Promote the M2 Phenotype in Macrophages Derived from STEMI Patients

Acute ST-elevation myocardial infarction (STEMI) leads to myocardial injury or necrosis, and M1 macrophages play an important role in the inflammatory response. Bone marrow mesenchymal stem/stromal cells (BM-MSCs) are capable of modulating macrophage plasticity, principally due to their immunoregulatory capacity. In the present study, we analyzed the capacity of MSCs to modulate macrophages derived from monocytes from patients with STEMI. We analyzed the circulating levels of cytokines associated with M1 and M2 macrophages in patients with STEMI, and the levels of cytokines associated with M1 macrophages were significantly higher in patients with STEMI than in controls. BM-MSCs facilitate the generation of M1 and M2 macrophages. M1 macrophages cocultured with MSCs did not have decreased M1 marker expression, but these macrophages had an increased expression of markers of the M2 macrophage phenotype (CD14, CD163 and CD206) and IL-10 and IL-1Ra signaling-induced regulatory T cells (Tregs). M2 macrophages from patients with STEMI had an increased expression of M2 phenotypic markers in coculture with BM-MSCs, as well as an increased secretion of anti-inflammatory cytokines and an increased generation of Tregs. The findings in this study indicate that BM-MSCs have the ability to modulate the M1 macrophage response, which could improve cardiac tissue damage in patients with STEMI.

The m6A methyltransferase METTL16 negatively regulates MCP1 expression in mesenchymal stem cells during monocyte recruitment

Mesenchymal stem cells (MSCs) possess strong immunoregulatory functions, one aspect of which is recruiting monocytes from peripheral vessels to local tissue by secreting monocyte chemoattractant protein 1 (MCP1). However, the regulatory mechanisms of MCP1 secretion in MSCs are still unclear. Recently, the N6-methyladenosine (m6A) modification was reported to be involved in the functional regulation of MSCs. In this study, we demonstrated that methyltransferase-like 16 (METTL16) negatively regulated MCP1 expression in MSCs through the m6A modification. Specifically, the expression of METTL16 in MSCs decreased gradually and was negatively correlated with the expression of MCP1 after coculture with monocytes. Knocking down METTL16 markedly enhanced MCP1 expression and the ability to recruit monocytes. Mechanistically, knocking down METTL16 decreased MCP1 mRNA degradation, which was mediated by the m6A reader YTH N6-methyladenosine RNA-binding protein 2 (YTHDF2). We further revealed that YTHDF2 specifically recognized m6A sites on MCP1 mRNA in the CDS region and thus negatively regulated MCP1 expression. Moreover, an in vivo assay showed that MSCs transfected with METTL16 siRNA showed greater ability to recruit monocytes. These findings reveal a potential mechanism by which the m6A methylase METTL16 regulates MCP1 expression through YTHDF2-mediated mRNA degradation and suggest a potential strategy to manipulate MCP1 expression in MSCs.

CCL17 Protects Against Viral Myocarditis by Suppressing the Recruitment of Regulatory T Cells

Background Viral myocarditis is characterized by leukocyte infiltration of the heart and cardiomyocyte death. We recently identified C-C chemokine ligand (CCL) 17 as a proinflammatory effector of C-C chemokine receptor 2-positive macrophages and dendritic cells that are recruited to the heart and contribute to adverse left ventricular remodeling following myocardial infarction and pressure overload. Methods and Results Mouse encephalomyocarditis virus was used to investigate the function of CCL17 in a viral myocarditis model. Ccl17^Gfp reporter and knockout mice were used to identify the cell types that express CCL17 and delineate the functional importance of CCL17 in encephalomyocarditis virus clearance and myocardial inflammation. Cardiac CCL17 was expressed in C-C chemokine receptor 2-positive macrophages and dendritic cells following encephalomyocarditis virus infection. Colony-stimulating factor 2 (granulocyte-macrophage colony-stimulating factor) signaling was identified as a key regulator of CCL17 expression. Ccl17 deletion resulted in impaired encephalomyocarditis virus clearance, increased cardiomyocyte death, and higher mortality during infection early stage, and aggravated hypertrophy and fibrotic responses in infection long-term stage. An increased abundance of regulatory T cells was detected in the myocardium of injured Ccl17-deficient mice. Depletion of regulatory T cells in Ccl17-deficient mice abrogated the detrimental role of CCL17 deletion by restoring interferon signaling. Conclusions Collectively, these findings identify CCL17 as an important mediator of the host immune response during cardiac viral infection early stage and suggest that CCL17 targeted therapies should be avoided in acute viral myocarditis.

Regenerative medicine applications: An overview of clinical trials

Insights into the use of cellular therapeutics, extracellular vesicles (EVs), and tissue engineering strategies for regenerative medicine applications are continually emerging with a focus on personalized, patient-specific treatments. Multiple pre-clinical and clinical trials have demonstrated the strong potential of cellular therapies, such as stem cells, immune cells, and EVs, to modulate inflammatory immune responses and promote neoangiogenic regeneration in diseased organs, damaged grafts, and inflammatory diseases, including COVID-19. Over 5,000 registered clinical trials on ClinicalTrials.gov involve stem cell therapies across various organs such as lung, kidney, heart, and liver, among other applications. A vast majority of stem cell clinical trials have been focused on these therapies' safety and effectiveness. Advances in our understanding of stem cell heterogeneity, dosage specificity, and ex vivo manipulation of stem cell activity have shed light on the potential benefits of cellular therapies and supported expansion into clinical indications such as optimizing organ preservation before transplantation. Standardization of manufacturing protocols of tissue-engineered grafts is a critical first step towards the ultimate goal of whole organ engineering. Although various challenges and uncertainties are present in applying cellular and tissue engineering therapies, these fields' prospect remains promising for customized patient-specific treatments. Here we will review novel regenerative medicine applications involving cellular therapies, EVs, and tissue-engineered constructs currently investigated in the clinic to mitigate diseases and possible use of cellular therapeutics for solid organ transplantation. We will discuss how these strategies may help advance the therapeutic potential of regenerative and transplant medicine.

Spatiotemporal transcriptomics reveals pathogenesis of viral myocarditis

A significant fraction of sudden death in children and young adults is due to viral myocarditis, an inflammatory disease of the heart. In this study, by using integrated single-cell and spatial transcriptomics, we created a high-resolution, spatially resolved transcriptome map of reovirus-induced myocarditis in neonatal mouse hearts. We assayed hearts collected at three timepoints after infection and studied the temporal, spatial and cellular heterogeneity of host–virus interactions. We further assayed the intestine, the primary site of reovirus infection, to establish a full chronology of molecular events that ultimately lead to myocarditis. We found that inflamed endothelial cells recruit cytotoxic T cells and undergo pyroptosis in the myocarditic tissue. Analyses of spatially restricted gene expression in myocarditic regions and the border zone identified immune-mediated cell-type-specific injury and stress responses. Overall, we observed a complex network of cellular phenotypes and spatially restricted cell–cell interactions associated with reovirus-induced myocarditis in neonatal mice.

CCL7 as a novel inflammatory mediator in cardiovascular disease, diabetes mellitus, and kidney disease

Chemokines are key components in the pathology of chronic diseases. Chemokine CC motif ligand 7 (CCL7) is believed to be associated with cardiovascular disease, diabetes mellitus, and kidney disease. CCL7 may play a role in inflammatory events by attracting macrophages and monocytes to further amplify inflammatory processes and contribute to disease progression. However, CCL7-specific pathological signaling pathways need to be further confirmed in these chronic diseases. Given the multiple redundancy system among chemokines and their receptors, further experimental and clinical studies are needed to clarify whether direct CCL7 inhibition mechanisms could be a promising therapeutic approach to attenuating the development of cardiovascular disease, diabetes mellitus, and kidney disease.

Colchicine prevents disease progression in viral myocarditis via modulating the NLRP3 inflammasome in the cardiosplenic axis

Aim

The acute phase of a coxsackievirus 3 (CVB3)‐induced myocarditis involves direct toxic cardiac effects and the systemic activation of the immune system, including the cardiosplenic axis. Consequently, the nucleotide‐binding oligomerization domain‐like receptor pyrin domain‐containing‐3 (NLRP3) inflammasome pathway is activated, which plays a role in disease pathogenesis and progression. The anti‐inflammatory drug colchicine exerts its effects, in part, via reducing NLRP3 activity, and has been shown to improve several cardiac diseases, including acute coronary syndrome and pericarditis. The aim of the present study was to evaluate the potential of colchicine to improve experimental CVB3‐induced myocarditis.

Methods and results

C57BL6/j mice were intraperitoneally injected with 1 × 10⁵ plaque forming units of CVB3. After 24 h, mice were treated with colchicine (5 μmol/kg body weight) or phosphate‐buffered saline (PBS) via oral gavage (p.o.). Seven days post infection, cardiac function was haemodynamically characterized via conductance catheter measurements. Blood, the left ventricle (LV) and spleen were harvested for subsequent analyses. In vitro experiments on LV‐derived fibroblasts (FB) and HL‐1 cells were performed to further evaluate the anti‐(fibro)inflammatory and anti‐apoptotic effects of colchicine via gene expression analysis, Sirius Red assay, and flow cytometry. CVB3 + colchicine mice displayed improved LV function compared with CVB3 + PBS mice, paralleled by a 4.7‐fold (P < 0.01) and 1.7‐fold (P < 0.001) reduction in LV CVB3 gene expression and cardiac troponin‐I levels in the serum, respectively. Evaluation of components of the NLRP3 inflammasome revealed an increased percentage of apoptosis‐associated speck‐like protein containing a CARD domain (ASC)‐expressing, caspase‐1‐expressing, and interleukin‐1β‐expressing cells in the myocardium and in the spleen of CVB3 + PBS vs. control mice, which was reduced in CVB3 + colchicine compared with CVB3 + PBS mice. This was accompanied by 1.4‐fold (P < 0.0001), 1.7‐fold (P < 0.0001), and 1.7‐fold (P < 0.0001) lower numbers of cardiac dendritic cells, natural killer cells, and macrophages, respectively, in CVB3 + colchicine compared with CVB3 + PBS mice. A 1.9‐fold (P < 0.05) and 4.6‐fold (P < 0.001) reduced cardiac gene expression of the fibrotic markers, Col1a1 and lysyl oxidase, respectively, was detected in CVB3 + colchicine mice compared with CVB3 + PBS animals, and reflected by a 2.2‐fold (P < 0.05) decreased Collagen I/III protein ratio. Colchicine further reduced Col3a1 mRNA and collagen protein expression in CVB3‐infected FB and lowered apoptosis and viral progeny release in CVB3‐infected HL‐1 cells. In both CVB3 FB and HL‐1 cells, colchicine down‐regulated the NLRP3 inflammasome‐related components ASC, caspase‐1, and IL‐1β.

Conclusions

Colchicine improves LV function in CVB3‐induced myocarditis, involving a decrease in cardiac and splenic NLRP3 inflammasome activity, without exacerbation of CVB3 load.

H19 Overexpression Improved Efficacy of Mesenchymal Stem Cells in Ulcerative Colitis by Modulating the miR-141/ICAM-1 and miR-139/CXCR4 Axes

Overexpression of C-X-C motif chemokine receptor 4 (CXCR4) and intercellular cell adhesion molecule-1 (ICAM-1) may promote homing of mesenchymal stem cells (MSC). In this study, we treated ulcerative colitis animals with MSC preconditioned with or without H19 and compared the therapeutic effect of MSC and MSC-H19. We evaluated the regulatory relationship of H19 vs. miR-141/miR-139 and miR-141/miR-139 vs. ICAM-1/CXCR4. We established an ulcerative colitis mouse model to assess the effect of MSC and MSC-H19. H19 was found to bind to miR-141 and miR-139. The activity of H19 was strongly decreased in cells c-transfected with miR-141/miR-139 and WT H19. ICAM-1 was confirmed to be targeted by miR-141 and CXCR4 was targeted by miR-139. The H19 expression showed a negative regulatory relationship with the miR-141 and miR-139 expression but a positive regulatory relationship with the ICAM-1 and CXCR4 expression. In summary, the overexpression of H19 in MSC downregulated miR-139 and miR-141, thus increasing the activity of their targets ICAM-1 and CXCR4, respectively, to exhibit therapeutic effects in ulcerative colitis.

Effects of living and metabolically inactive mesenchymal stromal cells and their derivatives on monocytes and macrophages

Mesenchymal stromal cells (MSCs) are multipotent and self-renewing stem cells that have great potential as cell therapy for autoimmune and inflammatory disorders, as well as for other clinical conditions, due to their immunoregulatory and regenerative properties. MSCs modulate the inflammatory milieu by releasing soluble factors and acting through cell-to-cell mechanisms. MSCs switch the classical inflammatory status of monocytes and macrophages towards a non-classical and anti-inflammatory phenotype. This is characterized by an increased secretion of anti-inflammatory cytokines, a decreased release of pro-inflammatory cytokines, and changes in the expression of cell membrane molecules and in metabolic pathways. The MSC modulation of monocyte and macrophage phenotypes seems to be critical for therapy effectiveness in several disease models, since when these cells are depleted, no immunoregulatory effects are observed. Here, we review the effects of living MSCs (metabolically active cells) and metabolically inactive MSCs (dead cells that lost metabolic activity by induced inactivation) and their derivatives (extracellular vesicles, soluble factors, extracts, and microparticles) on the profile of macrophages and monocytes and the implications for immunoregulatory and reparative processes. This review includes mechanisms of action exhibited in these different therapeutic approaches, which induce the anti-inflammatory properties of monocytes and macrophages. Finally, we overview several possibilities of therapeutic applications of these cells and their derivatives, with results regarding monocytes and macrophages in animal model studies and some clinical trials.

Epicardial Fat Expansion in Diabetic and Obese Patients With Heart Failure and Preserved Ejection Fraction-A Specific HFpEF Phenotype

Heart failure with preserved ejection fraction (HFpEF) is a heterogeneous syndrome with diverse etiologies and pathophysiological factors. Obesity and type 2 diabetes mellitus (T2DM), conditions that coexist frequently, induce a cluster of metabolic and non-metabolic signaling derangements which are in favor to induce inflammation, fibrosis, myocyte stiffness, all hallmarks of HFpEF. In contrast to other HFpEF risk factors, obesity and T2DM are often associated with the generation of enlarged epicardial adipose tissue (EAT). EAT acts as an endocrine tissue that may exacerbate myocardial inflammation and fibrosis via various paracrine and vasocrine signals. In addition, an abnormally large EAT poses mechanical stress on the heart via pericardial restrain. HFpEF patients with enlarged EAT may belong to a unique phenotype that can benefit from specific EAT-targeted interventions, including life-style modifications and pharmacologically via statins and fat modifying anti-diabetics drugs; like metformin, sodium-glucose cotransporter 2 inhibitors, or glucagon-like peptide-1 receptor agonists, respectively.

Review of the potential of mesenchymal stem cells for the treatment of infectious diseases

The therapeutic value of mesenchymal stem cells (MSCs) for the treatment of infectious diseases and the repair of disease-induced tissue damage has been explored extensively. MSCs inhibit inflammation, reduce pathogen load and tissue damage encountered during infectious diseases through the secretion of antimicrobial factors for pathogen clearance and they phagocytose certain bacteria themselves. MSCs dampen tissue damage during infection by downregulating the levels of pro-inflammatory cytokines, and inhibiting the excessive recruitment of neutrophils and proliferation of T cells at the site of injury. MSCs aid in the regeneration of damaged tissue by differentiating into the damaged cell types or by releasing paracrine factors that direct tissue regeneration, differentiation, and wound healing. In this review, we discuss in detail the various mechanisms by which MSCs help combat pathogens, tissue damage associated with infectious diseases, and challenges in utilizing MSCs for therapy.

Fractalkine (CX3CL1) and Its Receptor CX3CR1: A Promising Therapeutic Target in Chronic Kidney Disease?

Innate immune cells are key contributors to kidney inflammation and fibrosis. Infiltration of the renal parenchyma by innate immune cells is governed by multiple signalling pathways. Since the discovery of the chemokine fractalkine (CX3CL1) and its receptor, CX3CR1 over twenty years ago, a wealth of evidence has emerged linking CX3CL1-CX3CR1 signalling to renal pathologies in both acute and chronic kidney diseases (CKD). However, despite the extent of data indicating a pathogenic role for this pathway in kidney disease and its complications, no human trials of targeted therapeutic agents have been reported. Although acute autoimmune kidney disease is often successfully treated with immunomodulatory medications, there is a notable lack of treatment options for patients with progressive fibrotic CKD. In this article we revisit the CX3CL1-CX3CR1 axis and its functional roles. Furthermore we review the accumulating evidence that CX3CL1-CX3CR1 interactions mediate important events in the intra-renal pathophysiology of CKD progression, particularly via recruitment of innate immune cells into the kidney. We also consider the role that systemic activation of the CX3CL1-CX3CR1 axis in renal disease contributes to CKD-associated cardiovascular disease. Based on this evidence, we highlight the potential for therapies targeting CX3CL1 or CX3CR1 to benefit people living with CKD.

The stromal vascular fraction mitigates radiation-induced gastrointestinal syndrome in mice

Background

The intestine is particularly sensitive to moderate-high radiation dose and the development of gastrointestinal syndrome (GIS) leads to the rapid loss of intestinal mucosal integrity, resulting in bacterial infiltration, sepsis that comprise patient survival. There is an urgent need for effective and rapid therapeutic countermeasures. The stromal vascular fraction (SVF) derived from adipose tissue is an easily accessible source of cells with angiogenic, anti-inflammatory and regenerative properties. We studied the therapeutic impact of SVF and its action on the intestinal stem cell compartment.

Methods

Mice exposed to the abdominal radiation (18 Gy) received a single intravenous injection of stromal vascular fraction (SVF) (2.5 × 10⁶ cells), obtained by enzymatic digestion of inguinal fat tissue, on the day of irradiation. Mortality was evaluated as well as intestinal regeneration by histological analyses and absorption function.

Results

The SVF treatment limited the weight loss of the mice and inhibited the intestinal permeability and mortality after abdominal irradiation. Histological analyses showed that SVF treatment stimulated the regeneration of the epithelium by promoting numerous enlarged hyperproliferative zones. SVF restored CD24⁺/lysozyme⁻ and Paneth cell populations in the ISC compartment with the presence of Paneth Ki67⁺ cells. SVF has an anti-inflammatory effect by repressing pro-inflammatory cytokines, increasing M2 macrophages in the ileum and anti-inflammatory monocyte subtypes CD11b⁺Ly6c^lowCX3CR1^high in the spleen.

Conclusions

Through the pleiotropic effects that contribute to limiting radiation-induced lethality, SVF opens up attractive prospects for the treatment of emergency GIS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02373-y.

Toll-Like Receptors: Are They Taking a Toll on the Heart in Viral Myocarditis?

Myocarditis is an inflammatory disease of the heart with viral infections being the most common aetiology. Its complex biology remains poorly understood and its clinical management is one of the most challenging in the field of cardiology. Toll-like receptors (TLRs), a family of evolutionarily conserved pattern recognition receptors, are increasingly known to be implicated in the pathophysiology of viral myocarditis. Their central role in innate and adaptive immune responses, and in the inflammatory reaction that ensues, indeed makes them prime candidates to profoundly affect every stage of the disease process. This review describes the pathogenesis and pathophysiology of viral myocarditis, and scrutinises the role of TLRs in every phase. We conclude with directions for future research in this field.

Impact of Syndecan-2-Selected Mesenchymal Stromal Cells on the Early Onset of Diabetic Cardiomyopathy in Diabetic db/db Mice

Background: Mesenchymal stromal cells (MSCs) are an attractive cell type for cell therapy given their immunomodulatory, anti-fibrotic, and endothelial-protective features. The heparin sulfate proteoglycan, syndecan-2/CD362, has been identified as a functional marker for MSC isolation, allowing one to obtain a homogeneous cell product that meets regulatory requirements for clinical use. We previously assessed the impact of wild-type (WT), CD362^-, and CD362⁺ MSCs on local changes in protein distribution in left ventricular (LV) tissue and on LV function in an experimental model of early-onset diabetic cardiomyopathy. The present study aimed to further explore their impact on mechanisms underlying diastolic dysfunction in this model. Materials: For this purpose, 1 × 10⁶ WT, CD362^-, or CD362⁺ MSCs were intravenously (i.v.) injected into 20-week-old diabetic BKS.Cg-m+/+Lepr^db/BomTac, i.e., db/db mice. Control animals (db+/db) were injected with the equivalent volume of phosphate-buffered saline (PBS) alone. After 4 weeks, mice were sacrificed for further analysis. Results: Treatment with all three MSC populations had no impact on blood glucose levels in db/db mice. WT, CD362^-, and CD362⁺ MSC application restored LV nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) levels in db/db mice, which correlated with a reduction in cardiomyocyte stiffness. Furthermore, all stromal cells were able to increase arteriole density in db/db mice. The effect of CD362⁺ MSCs on NO and cGMP levels, cardiomyocyte stiffness, and arteriole density was less pronounced than in mice treated with WT or CD362^- MSCs. Analysis of collagen I and III protein expression revealed that fibrosis had not yet developed at this stage of experimental diabetic cardiomyopathy. All MSCs reduced the number of cardiac CD3⁺ and CD68⁺ cells in db/db mice, whereas only splenocytes from CD362^-- and CD362⁺-db/db mice exhibited a lower pro-fibrotic potential compared to splenocytes from db/db mice. Conclusion: CD362⁺ MSC application decreased cardiomyocyte stiffness, increased myocardial NO and cGMP levels, and increased arteriole density, although to a lesser extent than WT and CD362^- MSCs in an experimental model of early-onset diabetic cardiomyopathy without cardiac fibrosis. These findings suggest that the degree in improvement of cardiomyocyte stiffness following CD362⁺ MSC application was insufficient to improve diastolic function.

The innate immune response in myocarditis

Acute myocarditis is an inflammatory condition of the heart characterised by cellular injury and the influx of leucocytes, including neutrophils, monocytes, macrophages and lymphocytes. While this response is vital for tissue repair, excessive scar deposition and maladaptive ventricular remodelling can result in a legacy of heart failure. It is increasingly recognised as a clinical phenomenon due, in part, to increased availability of cardiac magnetic resonance imaging in patients presenting with chest pain in the absence of significant coronary artery disease. Emerging epidemiological evidence has associated myocarditis with poor outcomes in the context of left ventricular impairment, and even when the left ventricle is preserved outcomes are less benign than once thought. Despite this, our understanding of the contribution of the inflammatory response to the pathophysiology of acute myocarditis lags behind that of acute myocardial infarction, which is the vanguard cardiovascular condition for inflammation research. We recently reviewed monocyte and macrophage phenotype and function in acute myocardial infarction, concluding that their plasticity and heterogeneity might account for conflicting evidence from attempts to target specific leucocyte subpopulations. Here, we revise our understanding of myocardial inflammation, which is predominantly derived from myocardial infarction research, review experimental evidence for the immune response in acute myocarditis, focusing on innate immunity, and discuss potential future directions for immunotherapy research in acute myocarditis.

Apoptosis: A friend or foe in mesenchymal stem cell-based immunosuppression

Mesenchymal stem cells (MSC) are adult stem cells which reside in almost all postnatal tissue where, in juxtacrine and paracrine manner, regulate phenotype and function of immune cells, maintain tissue homeostasis, attenuate on-going inflammation and promote repair and regeneration of injured tissues. Due to their capacity to suppress detrimental immune response, MSC have been considered as potentially new therapeutic agents in the treatment of autoimmune and inflammatory diseases. It was recently revealed that apoptosis may increase anti-inflammatory properties of MSC by enhancing their capacity to induce generation of immunosuppressive phenotype in macrophages and dendritic cells. Upon phagocytosis, apoptotic MSC induce generation of immunosuppressive phenotype in monocytes/macrophages and promote production of anti-inflammatory cytokines and growth factors that attenuate inflammation and facilitate repair and regeneration of injured tissues. Importantly, immunomodulation mediated by apoptotic MSC was either similar or even better than immunomodulation accomplished by viable MSC. In contrast to viable MSC, which obtain either pro- or anti-inflammatory phenotype upon engraftment in different tissue microenvironments, apoptotic MSC were not subject to changes in their immunomodulatory characteristics upon diverse stimuli, indicating their potential for clinical use. In this chapter, we summarized current knowledge about beneficial effects of apoptotic MSC in the suppression of detrimental local and systemic immune response, and we emphasized their therapeutic potential in the treatment of inflammatory diseases.

Challenges and Limitations of Strategies to Promote Therapeutic Potential of Human Mesenchymal Stem Cells for Cell-Based Cardiac Repair

Mesenchymal stem cells (MSCs) represent a population of adult stem cells residing in many tissues, mainly bone marrow, adipose tissue, and umbilical cord. Due to the safety and availability of standard procedures and protocols for isolation, culturing, and characterization of these cells, MSCs have emerged as one of the most promising sources for cell-based cardiac regenerative therapy. Once transplanted into a damaged heart, MSCs release paracrine factors that nurture the injured area, prevent further adverse cardiac remodeling, and mediate tissue repair along with vasculature. Numerous preclinical studies applying MSCs have provided significant benefits following myocardial infarction. Despite promising results from preclinical studies using animal models, MSCs are not up to the mark for human clinical trials. As a result, various approaches have been considered to promote the therapeutic potency of MSCs, such as genetic engineering, physical treatments, growth factor, and pharmacological agents. Each strategy has targeted one or multi-potentials of MSCs. In this review, we will describe diverse approaches that have been developed to promote the therapeutic potential of MSCs for cardiac regenerative therapy. Particularly, we will discuss major characteristics of individual strategy to enhance therapeutic efficacy of MSCs including scientific principles, advantages, limitations, and improving factors. This article also will briefly introduce recent novel approaches that MSCs enhanced therapeutic potentials of other cells for cardiac repair.

Opioid-Induced Immunomodulation: Consequences for the Experimental Coxsackievirus B3-Induced Myocarditis Model

Simple Summary

Myocarditis is an inflammatory disorder of the heart mainly caused by viruses. To investigate viral myocarditis, the Coxsackievirus B3 (CVB3)-induced myocarditis model is the experimental model used since more than sixty years. In the pathogeneses of viral myocarditis, the subtle balance between pro-and anti-inflammatory immune responses is of great importance for disease manifestation. Parallel to the infection of the heart, experimental CVB3-induced myocarditis results in an infection of the pancreas, causing a severe burden for the challenged animals. In frame of animal welfare, application of analgesics is mandatory. So far, positive as well as negative effects of opioids on the immune system have been described. However, the impact of opioid application on the pathogenesis of experimental CVB3-induced myocarditis has not been investigated yet. Since examinations on disease pathways and new treatment options rely on established models to generate reproducible data, applicability of opioids in experimental CVB3-induced myocarditis needs to be carefully evaluated. For this purpose, we summarized published studies for 13 different opioids and discussed their potential impact on the CVB3-induced myocarditis model.

Abstract

Myocarditis is an inflammatory disorder of the heart predominantly caused by infectious agents. Since more than sixty years, the Coxsackievirus B3 (CVB3)-induced myocarditis mouse model is the experimental model used to investigate viral myocarditis. The pathogenesis of viral myocarditis is conceptually a multiphase process, initiated by the infection of cardiomyocytes, followed by activation of the immune system, and resulting in myocardial fibrosis and left ventricular dysfunction. In parallel to the direct infection of the heart, CVB3 replicates in lymphatic organs such as the pancreas. Due to infection of the pancreas, the model of experimental CVB3-induced myocarditis is estimated as a severe burden for the challenged animals. Application of analgesics in frame of the animal welfare act (European directive 2010/63/EU) is more and more becoming a matter of debate. For this purpose, we summarized published studies for 13 different opioids and discussed their potential impact on CVB3-induced myocarditis. In addition, with this summary we also want to provide guidance for researchers beyond the myocarditis field to estimate the impact of opioids on the immune system for their specific model. In the literature, both immunosuppressive as well as immune-activating effects of opioids have been described, but examinations in experimental CVB3-induced myocarditis have still not been reported so far. Based on the existing publications, administration of opioids in experimental CVB3-induced myocarditis might result in more severe disease progression, including higher mortality, or a less pronounced myocarditis model, failing to be used for the establishment of new treatment options. Taken together, the applicability of opioids in experimental CVB3-induced myocarditis and in inflammatory models in general needs to be carefully evaluated and further investigated.

Myocarditis and inflammatory cardiomyopathy: current evidence and future directions

Inflammatory cardiomyopathy, characterized by inflammatory cell infiltration into the myocardium and a high risk of deteriorating cardiac function, has a heterogeneous aetiology. Inflammatory cardiomyopathy is predominantly mediated by viral infection, but can also be induced by bacterial, protozoal or fungal infections as well as a wide variety of toxic substances and drugs and systemic immune-mediated diseases. Despite extensive research, inflammatory cardiomyopathy complicated by left ventricular dysfunction, heart failure or arrhythmia is associated with a poor prognosis. At present, the reason why some patients recover without residual myocardial injury whereas others develop dilated cardiomyopathy is unclear. The relative roles of the pathogen, host genomics and environmental factors in disease progression and healing are still under discussion, including which viruses are active inducers and which are only bystanders. As a consequence, treatment strategies are not well established. In this Review, we summarize and evaluate the available evidence on the pathogenesis, diagnosis and treatment of myocarditis and inflammatory cardiomyopathy, with a special focus on virus-induced and virus-associated myocarditis. Furthermore, we identify knowledge gaps, appraise the available experimental models and propose future directions for the field. The current knowledge and open questions regarding the cardiovascular effects associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are also discussed. This Review is the result of scientific cooperation of members of the Heart Failure Association of the ESC, the Heart Failure Society of America and the Japanese Heart Failure Society.

Mesenchymal Stromal Cells for Graft Versus Host Disease: Mechanism-Based Biomarkers

The immunosuppressive activity of mesenchymal stromal cells (MSCs) in graft versus host disease (GvHD) is well-documented, but their therapeutic benefit is rather unpredictable. Prospective randomized clinical trials remain the only means to address MSC clinical efficacy. However, the imperfect understanding of MSC biological mechanisms has undermined patients' stratification and the successful design of clinical studies. Furthermore, although MSC efficacy seems to be dependent on patient-associated factors, the role of patients' signature to predict and/or monitor clinical outcomes remains poorly elucidated. The analysis of GvHD patient serum has identified a set of molecules that are associated with high mortality. However, despite their importance in defining GvHD severity, their role in predicting or monitoring response to MSCs has not been confirmed. A new perspective on the use of MSCs for GvHD has been prompted by the recent findings that MSCs are actively induced to undergo apoptosis by recipient cytotoxic cells and that this process is essential to initiate MSC-induced immunosuppression. This discovery has not only reconciled the conundrum between MSC efficacy and their lack of engraftment, but also highlighted the determinant role of the patient in promoting and delivering MSC immunosuppression. In this review we will revisit the extensive use of MSCs for the treatment of GvHD and will elaborate on the need that future clinical trials must depend on mechanistic approaches that facilitate the development of robust and consistent assays to stratify patients and monitor clinical outcomes.

A Toolbox of Potential Immune-Related Therapies for Inflammatory Cardiomyopathy

Myocarditis is a multifactorial disorder, characterized by an inflammatory reaction in the myocardium, predominantly triggered by infectious agents, but also by antigen mimicry or autoimmunity in susceptible individuals. Unless spontaneously resolved, a chronic inflammatory course concludes with cardiac muscle dysfunction portrayed by ventricular dilatation, clinically termed inflammatory cardiomyopathy (Infl-CM). Treatment strategies aim to resolve chronic inflammation and preserve cardiac function. Beside standard heart failure treatments, which only play a supportive role in this condition, systemic immunosuppressants are used to diminish inflammatory cell function at the cost of noxious side effects. To date, the treatment protocols are expert-based without large clinical evidence. This review describes concept and contemporary strategies to alleviate myocardial inflammation and sheds light on potential inflammatory targets in an evidence-based order.

Stimulating pro-reparative immune responses to prevent adverse cardiac remodelling: consensus document from the joint 2019 meeting of the ESC Working Groups of cellular biology of the heart and myocardial function

Cardiac injury may have multiple causes, including ischaemic, non-ischaemic, autoimmune, and infectious triggers. Independent of the underlying pathophysiology, cardiac tissue damage induces an inflammatory response to initiate repair processes. Immune cells are recruited to the heart to remove dead cardiomyocytes, which is essential for cardiac healing. Insufficient clearance of dying cardiomyocytes after myocardial infarction (MI) has been shown to promote unfavourable cardiac remodelling, which may result in heart failure (HF). Although immune cells are integral key players of cardiac healing, an unbalanced or unresolved immune reaction aggravates tissue damage that triggers maladaptive remodelling and HF. Neutrophils and macrophages are involved in both, inflammatory as well as reparative processes. Stimulating the resolution of cardiac inflammation seems to be an attractive therapeutic strategy to prevent adverse remodelling. Along with numerous experimental studies, the promising outcomes from recent clinical trials testing canakinumab or colchicine in patients with MI are boosting the interest in novel therapies targeting inflammation in cardiovascular disease patients. The aim of this review is to discuss recent experimental studies that provide new insights into the signalling pathways and local regulators within the cardiac microenvironment promoting the resolution of inflammation and tissue regeneration. We will cover ischaemia- and non-ischaemic-induced as well as infection-related cardiac remodelling and address potential targets to prevent adverse cardiac remodelling.

The therapeutic potential of mesenchymal stem cells for cardiovascular diseases

Mesenchymal stem cells (MSCs) are derived from a wide range of sources and easily isolated and cultured. MSCs have the capacity for in vitro amplification and self-renewal, low immunogenicity and immunomodulatory properties, and under certain conditions, MSCs can be differentiated into a variety of cells. In the cardiovascular system, MSCs can protect the myocardium by reducing the level of inflammation, promoting the differentiation of myocardial cells around infarct areas and angiogenesis, increasing apoptosis resistance, and inhibiting fibrosis, which are ideal qualities for cardiovascular repair. Preclinical studies have shown that MSCs can be transplanted and improve cardiac repair, but challenges, such as their low rate of migration to the ischemic myocardium, low tissue retention, and low survival rate after transplantation, remain. This article reviews the potential and methods of MSC transplantation in the treatment of cardiovascular diseases (CVDs) and the challenges of the clinical use of MSCs.

Management of Myocarditis-Related Cardiomyopathy in Adults

Myocarditis is generally a mild and self-limited consequence of systemic infection of cardiotropic viruses. However, patients can develop a temporary or permanent impairment of cardiac function including acute cardiomyopathy with hemodynamic compromise or severe arrhythmias. In this setting, specific causes of inflammation are associated with variable risks of death and transplantation. Recent translational studies suggest that treatments tailored to specific causes of myocarditis may impact clinical outcomes when added to guideline-directed medical care. This review summarizes recent advances in translational research that influence the utility of endomyocardial biopsy for the management of inflammatory cardiomyopathies. Emerging therapies for myocarditis based on these mechanistic hypotheses are entering clinical trials and may add to the benefits of established heart failure treatment.

Roles and Mechanisms of Interleukin-12 Family Members in Cardiovascular Diseases: Opportunities and Challenges

Cardiovascular diseases represent a complex group of clinical syndromes caused by a variety of interacting pathological factors. They include the most extensive disease population and rank first in all-cause mortality worldwide. Accumulating evidence demonstrates that cytokines play critical roles in the presence and development of cardiovascular diseases. Interleukin-12 family members, including IL-12, IL-23, IL-27 and IL-35, are a class of cytokines that regulate a variety of biological effects; they are closely related to the progression of various cardiovascular diseases, including atherosclerosis, hypertension, aortic dissection, cardiac hypertrophy, myocardial infarction, and acute cardiac injury. This paper mainly discusses the role of IL-12 family members in cardiovascular diseases, and the molecular and cellular mechanisms potentially involved in their action in order to identify possible intervention targets for the prevention and clinical treatment of cardiovascular diseases.

The Quest for Antiinflammatory and Immunomodulatory Strategies in Heart Failure

Intensive research over the last 3 decades has unequivocally demonstrated the relevance of inflammation in heart failure (HF). Despite our current and ever increasing knowledge about inflammation, the clinical success of antiinflammatory and immunomodulatory therapies in HF is still limited. This review outlines the complexity and diversity of inflammation, its reciprocal interaction with HF, and addresses future perspectives, calling for immunomodulatory therapies that are specific for factors that activate the immune system without the risk of nonspecific immune suppression.

Exosomes derived from cardiac progenitor cells attenuate CVB3-induced apoptosis via abrogating the proliferation of CVB3 and modulating the mTOR signaling pathways

Viral myocarditis is potentially fatal and lacking a specific treatment. Exosomes secreted by cardiac progenitor cells (CPCs) have emerged as a promising tool for cardioprotection and repair. In this study, we investigated whether CPCs-derived exosomes (CPCs-Ex) could utilize the mTOR signal pathway to reduce the apoptosis in viral myocarditis. In vitro, exosomes were, respectively, added to H9C2 cells after CVB3 infection to detect the anti-apoptosis effect of CPCs-Ex. Compared with the controls, the apoptosis rate was reduced, accompanied with the depressed expression of viral capsid protein 1 (VP1) and pro-apoptosis factors of Bim/caspase families. Meanwhile, the phosphorylation of Akt, mTOR, and p70S6K were promoted, but that of 4EBP1 was suppressed. In vivo, the results of apoptosis, expression of CVB3 and pro-apoptosis factors, and phosphorylation of Akt/mTOR factors of CVB3-infected cardiomyocytes were consistent with that of vitro. Following that, we use Rapamycin and MK-2206 to inhibit the Akt/mTOR signaling pathway, meanwhile, Rattus 4EBP1, p70S6K, Akt1 and Akt2 were transfected to H9C2 cells to establish the stably transfected cell lines. In the group with Rapamycin or MK-2206 pretreatment, CPCs-Ex also could decrease the apoptosis of H9C2 cells and expression of CVB3 mRNA, followed by decreased expression of apoptosis factors. In Akt2, p70S6K and 4EBP1 overexpression groups, CPCs-Ex promoted CVB3-induced apoptosis, VP1 expression and cleavage of caspase-3. Our results therefore identify CPCs-Ex exerts an anti-apoptosis effect in CVB3-infected cells by abrogating the proliferation of CVB3 and modulating the mTOR signaling pathways as well as the expression of Bcl-2 and caspase families. Viral myocarditis, mainly caused by CVB3 infection, is lacking a specific treatment. Our study identified an anti-apoptosis role of CPCs-Ex in CVB3-infected cells and rats, which shown that CPCs-Ex may be an effective tool to treat viral myocarditis. We believe that with more in-depth research on the functionality of CPCs-Ex, there will be a breakthrough in the treatment of viral myocarditis.

Immunomodulation by Mesenchymal Stem Cells (MSCs): Mechanisms of Action of Living, Apoptotic, and Dead MSCs

Expectations on mesenchymal stem cell (MSC) treatment are high, especially in the fields of sepsis, transplant medicine, and autoimmune diseases. Various pre-clinical studies have been conducted with encouraging results, although the mechanisms of action behind the observed immunomodulatory capacity of mesenchymal stem cells have not been fully understood. Previous studies have demonstrated that the immunomodulatory effect of MSCs is communicated via MSC-secreted cytokines and has been proven to rely on the local microenvironment as some of the observed effects depend on a pre-treatment of MSCs with inflammatory cytokines. Nonetheless, recent findings indicate that the cytokine-mediated effects are only one part of the equation as apoptotic, metabolically inactivated, or even fragmented MSCs have been shown to possess an immunomodulatory potential as well. Both cytokine-dependent and cytokine-independent mechanisms suggest a key role for regulatory T cells and monocytes in the overall pattern, but the principle as to why viable and non-viable MSCs have similar immunomodulatory capacities remains elusive. Here we review the current knowledge on cellular and molecular mechanisms involved in MSC-mediated immunomodulation and focus on the viability of MSCs, as there is still uncertainty concerning the tumorigenic potential of living MSCs.

Viral myocarditis: a prime example for endomyocardial biopsy-guided diagnosis and therapy

Purpose of review

Myocarditis is an inflammatory disease of the cardiac muscle mainly caused by viral infection. Due to the diverse clinical presentation of myocarditis, accurate diagnosis demands simultaneous histologic, immunohistochemical and molecular biological workup of endomyocardial biopsies (EMBs) as defined by the position statement of the Working Group on Myocardial and Pericardial Diseases of the European Society of Cardiology on myocarditis.

Recent findings

Endomyocardial biopsy-based analysis of viral transcriptional activity, mRNA expression, epigenetics and region-specific protein expression analysis via imaging mass spectrometry have led to the identification of novel potential diagnostic criteria, markers with prognostic value and therapeutic targets for the treatment of viral myocarditis, opening new avenues for novel therapies, including cell therapies, as well as the use of established treatment options, be it from other indications.

Summary

Under certain clinical scenarios EMB-based analysis is required to come to a tailored individualized therapy that improves symptoms and prognosis of patients with acute and chronic viral-driven cardiac inflammation.

Inflammation in myocardial injury: mesenchymal stem cells as potential immunomodulators

Ischemic heart disease is a growing worldwide epidemic. Improvements in medical and surgical therapies have reduced early mortality after acute myocardial infarction and increased the number of patients living with chronic heart failure. The irreversible loss of functional cardiomyocytes puts these patients at significant risk of ongoing morbidity and mortality after their index event. Recent evidence suggests that inflammation is a key mediator of postinfarction adverse remodeling in the heart. In this review, we discuss the cardioprotective and deleterious effects of inflammation and its mediators during acute myocardial infarction. We also explore the role of mesenchymal stem cell therapy to limit secondary injury and promote myocardial healing after myocardial infarction.

Myocarditis in Humans and in Experimental Animal Models

Myocarditis is defined as an inflammation of the cardiac muscle. In humans, various infectious and non-infectious triggers induce myocarditis with a broad spectrum of histological presentations and clinical symptoms of the disease. Myocarditis often resolves spontaneously, but some patients develop heart failure and require organ transplantation. The need to understand cellular and molecular mechanisms of inflammatory heart diseases led to the development of mouse models for experimental myocarditis. It has been shown that pathogenic agents inducing myocarditis in humans can often trigger the disease in mice. Due to multiple etiologies of inflammatory heart diseases in humans, a number of different experimental approaches have been developed to induce myocarditis in mice. Accordingly, experimental myocarditis in mice can be induced by infection with cardiotropic agents, such as coxsackievirus B3 and protozoan parasite Trypanosoma cruzi or by activating autoimmune responses against heart-specific antigens. In certain models, myocarditis is followed by the phenotype of dilated cardiomyopathy and the end stage of heart failure. This review describes the most commonly used mouse models of experimental myocarditis with a focus on the role of the innate and adaptive immune systems in induction and progression of the disease. The review discusses also advantages and limitations of individual mouse models in the context of the clinical manifestation and the course of the disease in humans. Finally, animal-free alternatives in myocarditis research are outlined.

Mechanical Unloading by Fulminant Myocarditis: LV-IMPELLA, ECMELLA, BI-PELLA, and PROPELLA Concepts

Mechanical circulatory support (MCS) is often required to stabilize patients with acute fulminant myocarditis with cardiogenic shock. This review gives an overview of the successful use of left-sided Impella in the setting of fulminant myocarditis and cardiogenic shock as the sole means of MCS as well as in combination with right ventricular (RV) support devices including extracorporeal life support (ECLS) (ECMELLA) or an Impella RP (BI-PELLA). It further provides evidence from endomyocardial biopsies that in addition to giving adequate support, LV unloading by Impella exhibits disease-modifying effects important for myocardial recovery (i.e., bridge-to-recovery) achieved by this newly termed “prolonged Impella” (PROPELLA) concept in which LV-IMPELLA 5.0, implanted via an axillary approach, provides support in awake, mobilized patients for several weeks. Finally, this review addresses the question of how to define the appropriate time point for weaning strategies and for changing or discontinuing unloading in fulminant myocarditis.

Bone marrow-derived CXCR4-overexpressing MSCs display increased homing to intestine and ameliorate colitis-associated tumorigenesis in mice

Background and Objective

Increasing interest has developed in the therapeutic potential of bone marrow-derived mesenchymal stem cells (MSCs) for the treatment of inflammatory bowel disease (IBD) and IBD-induced cancer. However, whether MSCs have the ability to suppress or promote tumor development remains controversial. The stromal cell-derived factor 1 (SDF-1)/C-X-C chemokine receptor type 4 (CXCR4) axis is well known to play a critical role in the homing of MSCs. In this study, we aimed to evaluate the role of CXCR4-overexpressing MSCs on the tumorigenesis of IBD.

Methods

MSCs were transduced with lentiviral vector carrying either CXCR4 or green fluorescent protein (GFP). Chemotaxis and invasion assays were used to detect CXCR4 expression. A mouse model of colitis-associated tumorigenesis was established using azoxymethane and dextran sulfate sodium (DSS). The mice were divided into three groups and then injected with phosphate buffer saline (PBS), MSC-GFP or MSC-CXCR4.

Results

Compared with the mice injected with MSC-GFP, the mice injected with MSC-CXCR4 showed relieved weight loss, longer colons, lower tumor numbers and decreased tumor load; expression of pro-inflammatory cytokines decreased, and signal transducer and activator of transcription 3 (STAT3) phosphorylation level in colon tissue was down-regulated.

Conclusion

CXCR4-overexpressing MSCs exhibited effective anti-tumor function, which may be associated with enhanced homing to inflamed intestinal tissues.

Immunomodulation by adoptive regulatory T-cell transfer improves Coxsackievirus B3-induced myocarditis

Regulatory T (Treg) cells offer new therapeutic options for controlling undesired systemic and local immune responses. The aim of the current study was to determine the impact of therapeutic Treg administration on systemic and cardiac inflammation and remodeling in coxsackievirus B3 (CVB3) -induced myocarditis. Therefore, syngeneic Treg cells were applied intravenously in CVB3-infected mice 3 d after infection. Compared with CVB3 + PBS mice, CVB3 + Treg mice exhibited lower left ventricular (LV) chemokine expression, accompanied by reduced cardiac presence of proinflammatory Ly6ChighCCR2highCx3Cr1low monocytes and higher retention of proinflammatory Ly6CmidCCR2highCx3Cr1low monocytes in the spleen. In addition, splenic myelopoiesis was reduced in CVB3 + Treg compared with CVB3 + PBS mice. Coculture of Treg cells with splenocytes isolated from mice 3 d post-CVB3 infection further demonstrated the ability of Treg cells to modulate monocyte differentiation in favor of the anti-inflammatory Ly6ClowCCR2lowCx3Cr1high subset. Treg-mediated immunomodulation was paralleled by lower collagen 1 protein expression and decreased levels of soluble and insoluble collagen in LV of CVB3 + Treg compared with CVB3 + PBS mice. In agreement with these findings, LV systolic and diastolic function was improved in CVB3 + Treg mice compared with CVB3 + PBS mice. In summary, adoptive Treg transfer in the inflammatory phase of viral-induced myocarditis protects the heart against inflammatory damage and fibrosis via modulation of monocyte subsets.-Pappritz, K., Savvatis, K., Miteva, K., Kerim, B., Dong, F., Fechner, H., Müller, I., Brandt, C., Lopez, B., González, A., Ravassa, S., Klingel, K., Diez, J., Reinke, P., Volk, H.-D., Van Linthout, S., Tschöpe, C. Immunomodulation by adoptive regulatory T-cell transfer improves Coxsackievirus B3-induced myocarditis.

Innate and adaptive immunity in atherosclerosis

Atherosclerosis is a chronic inflammatory disorder of the large and medium-size arteries characterized by the subendothelial accumulation of cholesterol, immune cells, and extracellular matrix. At the early onset of atherogenesis, endothelial dysfunction takes place. Atherogenesis is further triggered by the accumulation of cholesterol-carrying low-density lipoproteins, which acquire properties of damage-associated molecular patterns and thereby trigger an inflammatory response. Following activation of the innate immune response, mainly governed by monocytes and macrophages, the adaptive immune response is started which further promotes atherosclerotic plaque formation. In this review, an overview is given describing the role of damage-associated molecular patterns, NLRP3 inflammasome activation, and innate and adaptive immune cells in the atherogenesis process.

Cardiac (myo)fibroblasts modulate the migration of monocyte subsets

Cardiac fibroblasts play an important role in the regulation of the extracellular matrix and are newly recognized as inflammatory supporter cells. Interferon (IFN)-γ is known to counteract transforming growth factor (TGF)-ß1-induced myofibroblast differentiation. This study aims at investigating in vitro how IFN-γ affects TGF-ß1-induced monocyte attraction. Therefore, C4 fibroblasts and fibroblasts obtained by outgrowth culture from the left ventricle (LV) of male C57BL6/j mice were stimulated with TGF-β1, IFN-γ and TGF-β1 + IFN-γ. Confirming previous studies, IFN-γ decreased the TGF-ß1-induced myofibroblast differentiation, as obviated by lower collagen I, III, α-smooth muscle actin (α-SMA), lysyl oxidase (Lox)-1 and lysyl oxidase-like (LoxL)-2 levels in TGF-β1 + IFN-γ- versus TGF-ß1-stimulated cardiac fibroblasts. TGF-β1 + IFN-γ-stimulated C4 and cardiac fibroblasts displayed a higher CC-chemokine ligand (CCL) 2, CCL7 and chemokine C-X3-C motif ligand (Cx3CL1) release versus sole TGF-ß1-stimulated fibroblasts. Analysis of migrated monocyte subsets towards the different conditioned media further revealed that sole TGF-β1- and IFN-γ-conditioned media particularly attracted Ly6C^low and Ly6C^high monocytes, respectively, as compared to control media. In line with theses findings, TGF-β1 + IFN-γ-conditioned media led to a lower Ly6C^low/Ly6C^high monocyte migration ratio compared to sole TGF-ß1 treatment. These differences in monocyte migration reflect the complex interplay of pro-inflammatory cytokines and pro-fibrotic factors in cardiac remodelling and inflammation.

Mesenchymal stromal cells inhibit NLRP3 inflammasome activation in a model of Coxsackievirus B3-induced inflammatory cardiomyopathy

Inflammation in myocarditis induces cardiac injury and triggers disease progression to heart failure. NLRP3 inflammasome activation is a newly identified amplifying step in the pathogenesis of myocarditis. We previously have demonstrated that mesenchymal stromal cells (MSC) are cardioprotective in Coxsackievirus B3 (CVB3)-induced myocarditis. In this study, MSC markedly inhibited left ventricular (LV) NOD2, NLRP3, ASC, caspase-1, IL-1β, and IL-18 mRNA expression in CVB3-infected mice. ASC protein expression, essential for NLRP3 inflammasome assembly, increased upon CVB3 infection and was abrogated in MSC-treated mice. Concomitantly, CVB3 infection in vitro induced NOD2 expression, NLRP3 inflammasome activation and IL-1β secretion in HL-1 cells, which was abolished after MSC supplementation. The inhibitory effect of MSC on NLRP3 inflammasome activity in HL-1 cells was partly mediated via secretion of the anti-oxidative protein stanniocalcin-1. Furthermore, MSC application in CVB3-infected mice reduced the percentage of NOD2-, ASC-, p10- and/or IL-1β-positive splenic macrophages, natural killer cells, and dendritic cells. The suppressive effect of MSC on inflammasome activation was associated with normalized expression of prominent regulators of myocardial contractility and fibrosis to levels comparable to control mice. In conclusion, MSC treatment in myocarditis could be a promising strategy limiting the adverse consequences of cardiac and systemic NLRP3 inflammasome activation.

Mesenchymal-myeloid interaction in the regulation of immunity

Several studies have demonstrated how different cell types of mesenchymal and myeloid origin can independently exhibit immunoregulatory activities. In response to inflammatory cues, they transcribe a molecular repertoire that restores the tissue microenvironment to what it was before the injury. There is accumulating evidence that stromal and myeloid-derived cells do not act independently but that the establishment of a cross-talk between them is a fundamental requirement. Stromal cells, prompted by inflammatory molecules, orchestrate and initiate myeloid cell recruitment and their functional reprogramming. Once instructed, myeloid cells effect the anti-inflammatory activity or, if alternatively required, enhance immune responses. The cross-talk plays a fundamental role in tissue homeostasis, not only to regulate inflammation, but also to promote tissue regeneration and cancer progression.

Immunomodulation By Therapeutic Mesenchymal Stromal Cells (MSC) Is Triggered Through Phagocytosis of MSC By Monocytic Cells

Mesenchymal stem or stromal cells (MSC) are under investigation as a potential immunotherapy. MSC are usually administered via intravenous infusion, after which they are trapped in the lungs and die and disappear within a day. The fate of MSC after their disappearance from the lungs is unknown and it is unclear how MSC realize their immunomodulatory effects in their short lifespan. We examined immunological mechanisms determining the fate of infused MSC and the immunomodulatory response associated with it. Tracking viable and dead human umbilical cord MSC (ucMSC) in mice using Qtracker beads (contained in viable cells) and Hoechst33342 (staining all cells) revealed that viable ucMSC were present in the lungs immediately after infusion. Twenty-four hours later, the majority of ucMSC were dead and found in the lungs and liver where they were contained in monocytic cells of predominantly non-classical Ly6C^low phenotype. Monocytes containing ucMSC were also detected systemically. In vitro experiments confirmed that human CD14⁺⁺ /CD16^- classical monocytes polarized toward a non-classical CD14⁺⁺ CD16⁺ CD206⁺ phenotype after phagocytosis of ucMSC and expressed programmed death ligand-1 and IL-10, while TNF-α was reduced. ucMSC-primed monocytes induced Foxp3⁺ regulatory T cell formation in mixed lymphocyte reactions. These results demonstrate that infused MSC are rapidly phagocytosed by monocytes, which subsequently migrate from the lungs to other body sites. Phagocytosis of ucMSC induces phenotypical and functional changes in monocytes, which subsequently modulate cells of the adaptive immune system. It can be concluded that monocytes play a crucial role in mediating, distributing, and transferring the immunomodulatory effect of MSC. Stem Cells 2018;36:602-615.

Heart Failure with Preserved Ejection Fraction and Future Pharmacological Strategies: a Glance in the Crystal Ball

PURPOSE OF REVIEW

The current definition of heart failure is mainly based on an inappropriate measure of cardiac function, i.e., left ventricular ejection fraction (LVEF). The initial sole entity, heart failure with reduced ejection fraction (HFrEF, LVEF <40%), was complemented by the addition of heart failure with preserved ejection fraction (HFpEF, LVEF ≥50%) and most recently, heart failure with mid-range ejection fraction (HFmrEF, LVEF 40-49%). Initially, HFpEF was believed to be a purely left ventricular diastolic dysfunction. Pathophysiological concepts of HFpEF have changed considerably during the last years. In addition to intrinsic cardiac mechanisms, the heart failure pathogenesis is increasingly considered as driven by non-cardiac systemic processes including metabolic disorders, ischemic conditions, and pro-inflammatory/pro-fibrotic or immunological alterations. Presentation and pathophysiology of HFpEF is heterogeneous, and its management remains a challenge since evidence of therapeutic benefits is scarce. Up to now, there are no therapies improving survival in patients with HFpEF.

RECENT FINDINGS

Several results from clinical and preclinical interventions targeting non-cardiac mechanisms or non-pharmacological interventions including new anti-diabetic or anti-inflammatory drugs, mitochondrial-targeted anti-oxidants, anti-fibrotic strategies, microRNases incl. antagomirs, cell therapeutic options, and high-density lipoprotein-raising strategies are promising and under further investigation. This review addresses mechanisms and available data of current best clinical practice and novel approaches towards HFpEF.

Placenta-Derived Adherent Stromal Cells Improve Diabetes Mellitus-Associated Left Ventricular Diastolic Performance

Left ventricular (LV) diastolic dysfunction is among others attributed to cardiomyocyte stiffness. Mesenchymal stromal cells (MSC) have cardiac-protective properties. We explored whether intravenous (i.v.) application of PLacenta-eXpanded (PLX) MSC-like cells (PLX) improves LV diastolic relaxation in streptozotocin (STZ)-induced diabetic mice and investigated underlying mechanisms. Diabetes mellitus was induced by STZ application (50 mg/kg body weight) during five subsequent days. One week after the first STZ injection, PLX or saline were i.v. applied. Two weeks later, mice were hemodynamically characterized and sacrificed. At this early stage of diabetic cardiomyopathy with low-grade inflammation and no cardiac fibrosis, PLX reduced LV vascular cell adhesion molecule-1, transforming growth factor-β1, and interferon-γ mRNA expression, induced the percentage of circulating regulatory T cells, and decreased the splenic pro-fibrotic potential in STZ mice. STZ + PLX mice exhibited higher LV vascular endothelial growth factor mRNA expression and arteriole density versus STZ mice. In vitro, hyperglycemic PLX conditioned medium restored the hyperglycemia-impaired tube formation and adhesion capacity of human umbelical vein endothelial cells (HUVEC) via increasing nitric oxide (NO) bioavailability. PLX further induced the diabetes-downregulated activity of the NO downstream protein kinase G, as well as of protein kinase A, in STZ mice, which was associated with a raise in phosphorylation of the titin isoforms N2BA and N2B. Concomitantly, the passive force was lower in single isolated cardiomyocytes from STZ + PLX versus from STZ mice, which led to an improvement of LV diastolic relaxation. We conclude that i.v. PLX injection improves diabetes mellitus-associated diastolic performance via decreasing cardiomyocyte stiffness. Stem Cells Translational Medicine 2017;6:2135-2145.

CX3CR1 knockout aggravates Coxsackievirus B3-induced myocarditis

Studies on inflammatory disorders elucidated the pivotal role of the CX3CL1/CX3CR1 axis with respect to the pathophysiology and diseases progression. Coxsackievirus B3 (CVB3)-induced myocarditis is associated with severe cardiac inflammation, which may progress to heart failure. We therefore investigated the influence of CX3CR1 ablation in the model of acute myocarditis, which was induced by inoculation with 5x105 plaque forming units of CVB3 (Nancy strain) in either CX3CR1-/- or C57BL6/j (WT) mice. Seven days after infection, myocardial inflammation, remodeling, and titin expression and phosphorylation were examined by immunohistochemistry, real-time PCR and Pro-Q diamond stain. Cardiac function was assessed by tip catheter. Compared to WT CVB3 mice, CX3CR1-/- CVB3 mice exhibited enhanced left ventricular expression of inflammatory cytokines and chemokines, which was associated with an increase of immune cell infiltration/presence. This shift towards a pro-inflammatory immune response further resulted in increased cardiac fibrosis and cardiomyocyte apoptosis, which was reflected by an impaired cardiac function in CX3CR1-/- CVB3 compared to WT CVB3 mice. These findings demonstrate a cardioprotective role of CX3CR1 in CVB3-infected mice and indicate the relevance of the CX3CL1/CX3CR1 system in CVB3-induced myocarditis.

Inflammation - Cause or Consequence of Heart Failure or Both?

PURPOSE OF REVIEW

With the intention to summarize the currently available evidence on the pathophysiological relevance of inflammation in heart failure, this review addresses the question whether inflammation is a cause or consequence of heart failure, or both.

RECENT FINDINGS

This review discusses the diversity (sterile, para-inflammation, chronic inflammation) and sources of inflammation and gives an overview of how inflammation (local versus systemic) can trigger heart failure. On the other hand, the review is outlined how heart failure-associated wall stress and signals released by stressed, malfunctioning, or dead cells (DAMPs: e.g., mitochondrial DNA, ATP, S100A8, matricellular proteins) induce cardiac sterile inflammation and how heart failure provokes inflammation in various peripheral tissues in a direct (inflammatory) and indirect (hemodynamic) manner. The crosstalk between the heart and peripheral organs (bone marrow, spleen, gut, adipose tissue) is outlined and the importance of neurohormonal mechanisms including the renin angiotensin aldosteron system and the ß-adrenergic nervous system in inflammation and heart failure is discussed. Inflammation and heart failure are strongly interconnected and mutually reinforce each other. This indicates the difficulty to counteract inflammation and heart failure once this chronic vicious circle has started and points out the need to control the inflammatory process at an early stage avoiding chronic inflammation and heart failure. The diversity of inflammation further addresses the need for a tailored characterization of inflammation enabling differentiation of inflammation and subsequent target-specific strategies. It is expected that the characterization of the systemic and/or cardiac immune profile will be part of precision medicine in the future of cardiology.