Exogenous CXCL4 infusion inhibits macrophage phagocytosis by limiting CD36 signalling to enhance post-myocardial infarction cardiac dilation and mortality

Glucocorticoids impair T lymphopoiesis after myocardial infarction

The thymus, where T lymphocytes develop and mature, is sensitive to insults such as tissue ischemia or injury. The insults can cause thymic atrophy and compromise T-cell development, potentially impairing adaptive immunity. The objective of this study was to investigate whether myocardial infarction (MI) induces thymic injury to impair T lymphopoiesis and to uncover the underlying mechanisms. When compared with sham controls, MI mice at day 7 post-MI exhibited smaller thymus, lower cellularity, as well as less thymocytes at different developmental stages, indicative of T-lymphopoiesis impairment following MI. Accordingly, the spleen of MI mice has less T cells and recent thymic emigrants (RTEs), implying that the thymus of MI mice releases fewer mature thymocytes than sham controls. Interestingly, the secretory function of splenic T cells was not affected by MI. Further experiments showed that the reduction of thymocytes in MI mice was due to increased thymocyte apoptosis. Removal of adrenal glands by adrenalectomy (ADX) prevented MI-induced thymic injury and dysfunction, whereas corticosterone supplementation in ADX + MI mice reinduced thymic injury and dysfunction, indicating that glucocorticoids mediate thymic damage triggered by MI. Eosinophils play essential roles in thymic regeneration postirradiation, and eosinophil-deficient mice exhibit impaired thymic recovery after sublethal irradiation. Interestingly, the thymus was fully regenerated in both wild-type and eosinophil-deficient mice at day 14 post-MI, suggesting that eosinophils are not critical for thymus regeneration post-MI. In conclusion, our study demonstrates that MI-induced glucocorticoids trigger thymocyte apoptosis and impair T lymphopoiesis, resulting in less mature thymocyte release to the spleen.NEW & NOTEWORTHY The thymus is essential for maintaining whole body T-cell output. Thymic injury can adversely affect T lymphopoiesis and T-cell immune response. This study demonstrates that MI induces thymocyte apoptosis and compromises T lymphopoiesis, resulting in fewer releases of mature thymocytes to the spleen. This process is mediated by glucocorticoids secreted by adrenal glands. Therefore, targeting glucocorticoids represents a novel approach to attenuate post-MI thymic injury.

Active Heme Metabolism Suppresses Macrophage Phagocytosis via the TLR4/Type I IFN Signaling/CD36 in Uterine Endometrial Cancer

BACKGROUND

Uterine endometrial cancer (UEC) is a common gynecological estrogen-dependent carcinoma, usually accompanied by intermenstrual bleeding. Active heme metabolism frequently plays an increasingly important role in many diseases, especially in cancers. Tumor-associated macrophages (TAMs) are the major population in the immune microenvironment of UEC. However, the roles of heme metabolisms in the crosstalk between UEC cells (UECCs) and macrophages are unclear.

MATERIALS AND METHODS

In our study, by using TCGA database analysis, integration analysis of the protein-protein interaction (PPI) network and sample RNA transcriptome sequencing were done. The expression level of both heme-associated molecules and iron metabolism-related molecules were measured by quantitative real-time polymerase chain reaction. Heme level detection was done through dehydrohorseradish peroxidase assay. In addition to immunohistochemistry, phagocytosis assay of macrophages, immunofluorescence staining, intracellular ferrous iron staining, as well as enzyme-linked immune sorbent assay were performed.

RESULTS

In the study, we verified that heme accumulation in UECCs is apparently higher than in endometrial epithelium cells. Low expression of succinate dehydrogenase B under the regulation of estrogen contributes to over-production of succinate and heme accumulation in UECC. More importantly, excessive heme in UECCs impaired macrophage phagocytosis by regulation of CD36. Mechanistically, this process is dependent on toll-like receptor (TLR4)/type I interferons alpha (IFN Iα) regulatory axis in macrophage.

CONCLUSION

Collectively, these findings elucidate that active heme metabolism of UECCs directly decreases phagocytosis by controlling the secretion of TLR4-mediated IFN Iα and the expression of CD36, and further contributing to the immune escape of UEC.

Macrophage-mediated heart repair and remodeling: A promising therapeutic target for post-myocardial infarction heart failure

Heart failure (HF) remains prevalent in patients who survived myocardial infarction (MI). Despite the accessibility of the primary percutaneous coronary intervention and medications that alleviate ventricular remodeling with functional improvement, there is an urgent need for clinicians and basic scientists to further reveal the mechanisms behind post-MI HF as well as investigate earlier and more efficient treatment after MI. Growing numbers of studies have highlighted the crucial role of macrophages in cardiac repair and remodeling following MI, and timely intervention targeting the immune response via macrophages may represent a promising therapeutic avenue. Recently, technology such as single-cell sequencing has provided us with an updated and in-depth understanding of the role of macrophages in MI. Meanwhile, the development of biomaterials has made it possible for macrophage-targeted therapy. Thus, an overall and thorough understanding of the role of macrophages in post-MI HF and the current development status of macrophage-based therapy will assist in the further study and development of macrophage-targeted treatment for post-infarction cardiac remodeling. This review synthesizes the spatiotemporal dynamics, function, mechanism and signaling of macrophages in the process of HF after MI, as well as discusses the emerging bio-materials and possible therapeutic agents targeting macrophages for post-MI HF.

Macrophages in cardiovascular diseases: molecular mechanisms and therapeutic targets

The immune response holds a pivotal role in cardiovascular disease development. As multifunctional cells of the innate immune system, macrophages play an essential role in initial inflammatory response that occurs following cardiovascular injury, thereby inducing subsequent damage while also facilitating recovery. Meanwhile, the diverse phenotypes and phenotypic alterations of macrophages strongly associate with distinct types and severity of cardiovascular diseases, including coronary heart disease, valvular disease, myocarditis, cardiomyopathy, heart failure, atherosclerosis and aneurysm, which underscores the importance of investigating macrophage regulatory mechanisms within the context of specific diseases. Besides, recent strides in single-cell sequencing technologies have revealed macrophage heterogeneity, cell-cell interactions, and downstream mechanisms of therapeutic targets at a higher resolution, which brings new perspectives into macrophage-mediated mechanisms and potential therapeutic targets in cardiovascular diseases. Remarkably, myocardial fibrosis, a prevalent characteristic in most cardiac diseases, remains a formidable clinical challenge, necessitating a profound investigation into the impact of macrophages on myocardial fibrosis within the context of cardiac diseases. In this review, we systematically summarize the diverse phenotypic and functional plasticity of macrophages in regulatory mechanisms of cardiovascular diseases and unprecedented insights introduced by single-cell sequencing technologies, with a focus on different causes and characteristics of diseases, especially the relationship between inflammation and fibrosis in cardiac diseases (myocardial infarction, pressure overload, myocarditis, dilated cardiomyopathy, diabetic cardiomyopathy and cardiac aging) and the relationship between inflammation and vascular injury in vascular diseases (atherosclerosis and aneurysm). Finally, we also highlight the preclinical/clinical macrophage targeting strategies and translational implications.

Neutrophil extracellular traps (NETs) and fibrotic diseases

Fibrosis, a common cause and serious outcome of organ failure that can affect any organ, is responsible for up to 45% of all deaths in various clinical settings. Both preclinical models and clinical trials investigating various organ systems have shown that fibrosis is a highly dynamic process. Although many studies have sought to gain understanding of the mechanism of fibrosis progression, their findings have been mixed. In recent years, increasing evidence indicates that neutrophil extracellular traps (NETs) are involved in many inflammatory and autoimmune disorders and participate in the regulation of fibrotic processes in various organs and systems. In this review, we summarize the current understanding of the role of NETs in fibrosis development and progression and their possibility as therapeutic targets.

2,5-Dimethyl-celecoxib induces early termination of inflammatory responses by transient macrophage accumulation and inhibits the progression of cardiac remodeling in a mouse model of cryoinjury-induced myocardial infarction

In our previous study, we reported that 2, 5-dimethyl-celecoxib (DM-C), a derivative of celecoxib, prevents cardiac remodeling in different mouse models of heart failure, including myocardial infarction (MI). The inflammatory response after MI affects the progression of cardiac remodeling, wherein the immune cells, mainly macrophages, play crucial roles. Therefore, we evaluated the effect of DM-C on macrophages in a cryoinjury-induced myocardial infarction (CMI) mouse model. We observed that DM-C attenuated the deterioration of left ventricular ejection fraction and cardiac fibrosis 14 d after CMI. Gene expression of pro-inflammatory cytokines at the infarct site was reduced by DM-C treatment. Analysis of macrophage surface antigens revealed that DM-C induced transient accumulation of macrophages at the infarct site without affecting their polarization. In vitro experiments using peritoneal monocytes/macrophages revealed that DM-C did not directly increase the phagocytic ability of the macrophages but increased their number, thereby upregulating the clearance capacity. Moreover, DM-C rapidly excluded the cells expressing necrotic cell marker from the infarct site. These results suggested that DM-C enhanced the clearance capacity of macrophages by transiently increasing their number at the infarct site, and terminated the escape from the inflammatory phase earlier, thereby suppressing excessive cardiac remodeling and ameliorating cardiac dysfunction.

Ruxolitinib attenuates acute rejection and can serve as an immune induction therapy in heart transplantation

The benefits of IL2RA antagonists in heart transplant patients are controversial. We aimed to elucidate the effects of IL2RA antagonists and identify targets that could be better than IL2RA antagonists. By using single-cell RNA sequencing of immune cells at different time points in patients receiving IL2RA antagonists, we identified nineteen types of cells. We revealed higher IL2RA expression in regulatory T cells (Tregs), suggesting that IL2RA antagonists attenuated IL-2-induced Treg activation. CD4_C04_IFNGR1 and CD8_C05_IFITM2 which had more cytotoxic effects, remained elevated at later time points. IFNGR1 was upregulated in these two subtypes, but was not expressed in Treg. Ruxolitinib targeted the pathways of IFNGR1 (JAK1/2) while not affecting the pathway of IL-2-induced Tregs activation (JAK3). Ruxolitinib showed prolonged survival compared to IL2RA mAb-treated mice. Our study provided dynamic changes of immune cells after IL2RA antagonists treatment at single-cell resolution. Ruxolitinib has potential as a new immunoinduction therapy without affecting Treg.

The role of candidate transport proteins in β-cell long-chain fatty acid uptake: Where are we now?

Type 2 diabetes (T2D) in humans is typically preceded by elevated levels of circulatory long-chain free fatty acids (LC-FFA). These excess LC-FFA are widely thought to be taken up by pancreatic β-cells, contributing to their dysfunction and death during the development of T2D; a process that has been termed lipotoxicity. Depending on their degree of saturation and carbon chain length, LC-FFA can exert different effects on pancreatic β-cells viability and function in vitro. Long-chain saturated fatty acids (LC-SFA) are thought to be toxic, whereas monounsaturated fatty acids are not and may even offer protection against the toxic effects of LC-SFAs. However, the mechanism of LC-FFA uptake into pancreatic β-cells is poorly understood, partly because it has been an understudied area of research. Determining how LC-FFA are taken up into β-cells is crucial for later formulation of therapies to prevent potential cellular overload of LC-FFA, thereby slowing the onset of T2D. In this work, we detail more than 40 years of literature investigating the role of membrane-associated transport proteins in LC-FFA uptake. By focussing on what is known in other cell types, we highlight where we can extrapolate our current understanding of protein-mediated transport to β-cells and uncover where further understanding is required.

Macrophage-driven cardiac inflammation and healing: insights from homeostasis and myocardial infarction

Early and prompt reperfusion therapy has markedly improved the survival rates among patients enduring myocardial infarction (MI). Nonetheless, the resulting adverse remodeling and the subsequent onset of heart failure remain formidable clinical management challenges and represent a primary cause of disability in MI patients worldwide. Macrophages play a crucial role in immune system regulation and wield a profound influence over the inflammatory repair process following MI, thereby dictating the degree of myocardial injury and the subsequent pathological remodeling. Despite numerous previous biological studies that established the classical polarization model for macrophages, classifying them as either M1 pro-inflammatory or M2 pro-reparative macrophages, this simplistic categorization falls short of meeting the precision medicine standards, hindering the translational advancement of clinical research. Recently, advances in single-cell sequencing technology have facilitated a more profound exploration of macrophage heterogeneity and plasticity, opening avenues for the development of targeted interventions to address macrophage-related factors in the aftermath of MI. In this review, we provide a summary of macrophage origins, tissue distribution, classification, and surface markers. Furthermore, we delve into the multifaceted roles of macrophages in maintaining cardiac homeostasis and regulating inflammation during the post-MI period.

Functions for platelet factor 4 (PF4/CXCL4) and its receptors in fibroblast-myofibroblast transition and fibrotic failure of arteriovenous fistulas (AVFs)

BACKGROUND

Over 60% of End Stage Renal Disease (ESRD) patients are relying on hemodialysis (HD) to survive, and the arteriovenous fistula (AVF) is the preferred vascular access method for HD. However approximately half of all newly created AVF fail to mature and cannot be used without a salvage procedure. We have recently demonstrated an association between AVF maturation failure and post-operative fibrosis, while our RNA-seq study also revealed that veins that ultimately failed during AVF maturation had elevated levels of platelet factor 4 (PF4/CXCL4). However, a link between these two findings was yet to be established.

METHODS

In this study, we investigated potential mechanisms between PF4 levels and fibrotic remodeling in veins. We compared the local expression of PF4 and fibrosis marker integrin β6 (ITGB6) in veins that successfully underwent maturation with that in veins that ultimately failed to mature. We also measured the changes of expression level of α-smooth muscle actin (αSMA/ACTA2) and collagen (Col1/COL1A1) in venous fibroblasts upon various treatments, such as PF4 pharmacological treatment, alteration of PF4 expression, and blocking of PF4 receptors.

RESULTS

We found that PF4 is expressed in veins and co-localizes with αSMA. In venous fibroblasts, PF4 stimulates expression of αSMA and Col1 via different pathways. The former requires integrins αvβ5 and α5β1, while chemokine receptor CXCR3 is needed for the latter. Interestingly, we also discovered that the expression of PF4 is associated with that of ITGB6, the β subunit of integrin αvβ6. This integrin is critical for the activation of the major fibrosis factor TGFβ, and overexpression of PF4 promotes activation of the TGFβ pathway.

CONCLUSIONS

These results indicate that upregulation of PF4 may cause venous fibrosis both directly by stimulating fibroblast differentiation and expression of extracellular matrix (ECM) molecules and indirectly by facilitating the activation of the TGFβ pathway.

Skin wound healing as a mirror to cardiac wound healing

NEW FINDINGS

What is the topic of this review? Wound healing is a general response of the body to injury and can be divided into three phases: inflammation, inflammation resolution and repair. In this review, we compare the wound-healing response of the skin after an injury and the wound-healing response of the heart after a myocardial infarction. What advances does it highlight? We highlight differences and similarities between skin and cardiac wound healing and summarize how skin can be used to provide information about the heart.

ABSTRACT

Wound healing is a general response of the body to injury. All organs share in common three response elements to wound healing: inflammation to prevent infection and stimulate the removal of dead cells, active anti-inflammatory signalling to turn off the inflammatory response, and a repair phase characterized by extracellular matrix scar formation. The extent of scar formed depends on the ability of endogenous cells that populate each organ to regenerate. The skin has keratinocytes that have regenerative capacity, and in general, wounds are fully re-epithelialized. Heart, in contrast, has cardiac myocytes that have little to no regenerative capacity, and necrotic myocytes are entirely replaced by scars. Despite differences in tissue regeneration, the skin and heart share many wound-healing properties that can be exploited to predict the cardiac response to pathology. We summarize in this review article our current understanding of how the response of the skin to a wounding event can inform us about the ability of the myocardium to respond to a myocardial infarction.

The phagocytic role of macrophage following myocardial infarction

Myocardial infarction (MI) is one of the cardiovascular diseases with high morbidity and mortality. MI causes large amounts of apoptotic and necrotic cells that need to be efficiently and instantly engulfed by macrophage to avoid second necrosis. Phagocytic macrophages can dampen or resolve inflammation to protect infarcted heart. Phagocytosis of macrophages is modulated by various factors including proteins, receptors, lncRNA and cytokines. A better understanding of mechanisms in phagocytosis will be beneficial to regulate macrophage phagocytosis capability towards a desired direction in cardioprotection after MI. In this review, we describe the phagocytosis effect of macrophages and summarize the latest reported signals regulating phagocytosis after MI, which will provide a new thinking about phagocytosis-dependent cardiac protection after MI.

Prognostic Value of the Selected Polymorphisms in the CD36 Gene in the Domain-Encoding Lipid-Binding Region at a 10-Year Follow-Up for Early-Onset CAD Patients

The polymorphism of the CD36 gene may have a decisive impact on the formation and progression of atherosclerotic changes. The aim of the study was to confirm the prognostic values of the previously studied polymorphisms in the CD36 gene within a 10-year follow-up period. This is the first published report confirming the long-term observation of patients with CAD. The study group covered 100 early-onset CAD patients. It included 26 women not older than 55 years and 74 men not older than 50 years, tested in a ten-year study as a long-term follow-up after the first cardiovascular episode. There are no notable differences between the CD36 variants and the number of fatalities during observation, fatalities due to cardiological reasons, cases of myocardial infarction within a ten-year observation period, hospitalizations for cardiovascular issues, all cardiovascular occurrences, and the number of months lived. We have shown that the CD36 variants analyzed in this study do not appear to be related to the risk of early CAD occurrence in the Caucasian population in long-term observation.

Harnessing the Plasma Proteome to Mirror Current and Predict Future Cardiac Remodeling After Myocardial Infarction

To identify plasma proteins that mirror current and predict future remodeling after myocardial infarction (MI), we retrospectively interrogated plasma proteomes of day (D)0 control (n = 16) and D3 MI (n = 15) from C57BL/6 J mice (20 ± 1 months). A total of 165 unique proteins were correlated with cardiac physiology variables. We prospectively tested the hypothesis that candidates identified retrospectively would predict cardiac physiology at an extended timepoint (D7 MI) in a second cohort of mice (n = 4 ± 1 months). We also examined human plasma from healthy controls (n = 18) and patients 48 h after presentation for MI (n = 41). Retrospectively, we identified 5 strong reflectors of remodeling (all r ≥ 0.60 and p < 0.05). Prospectively, ApoA1, IgA, IL-17E, and TIMP-1 mirrored current and predicted future remodeling. In humans, cytokine-cytokine receptor signaling was the top enriched KEGG pathway for all candidates. In summary, we identified plasma proteins that serve as useful prognostic indicators of adverse remodeling and progression to heart failure.

Cellular mechanisms underlying the impairment of macrophage efferocytosis

The phagocytosis and clearance of dying cells by macrophages, a process termed efferocytosis, is essential for both maintaining homeostasis and promoting tissue repair after infection or sterile injury. If not removed in a timely manner, uncleared cells can undergo secondary necrosis, and necrotic cells lose membrane integrity, release toxic intracellular components, and potentially induce inflammation or autoimmune diseases. Efferocytosis also initiates the repair process by producing a wide range of pro-reparative factors. Accumulating evidence has revealed that macrophage efferocytosis defects are involved in the development and progression of a variety of inflammatory and autoimmune diseases. The underlying mechanisms of efferocytosis impairment are complex, disease-dependent, and incompletely understood. In this review, we will first summarize the current knowledge about the normal signaling and metabolic processes of macrophage efferocytosis and its importance in maintaining tissue homeostasis and repair. We then will focus on analyzing the molecular and cellular mechanisms underlying efferocytotic abnormality (impairment) in disease or injury conditions. Next, we will discuss the potential molecular targets for enhanced efferocytosis in animal models of disease. To provide a balanced view, we will also discuss some deleterious effects of efferocytosis.

Scavenger Receptors in Myocardial Infarction and Ischemia/Reperfusion Injury: The Potential for Disease Evaluation and Therapy

Scavenger receptors (SRs) are a structurally heterogeneous superfamily of evolutionarily conserved receptors that are divided into classes A to J. SRs can recognize multiple ligands, such as modified lipoproteins, damage-associated molecular patterns, and pathogen-associated molecular patterns, and regulate lipid metabolism, immunity, and homeostasis. According to the literature, SRs may play a critical role in myocardial infarction and ischemia/reperfusion injury, and the soluble types of SRs may be a series of promising biomarkers for the diagnosis and prognosis of patients with acute coronary syndrome or acute myocardial infarction. In this review, we briefly summarize the structure and function of SRs and discuss the association between each SR and ischemic cardiac injury in patients and animal models in detail. A better understanding of the effect of SRs on ischemic cardiac injury will inspire novel ideas for therapeutic drug discovery and disease evaluation in patients with myocardial infarction.

Exosomes from the Uterine Cavity Mediate Immune Dysregulation via Inhibiting the JNK Signal Pathway in Endometriosis

Endometriosis is a chronic inflammatory disease with an uncertain pathogenesis. Peritoneal immune dysregulation plays an important role in the pathogenesis of endometriosis. Exosomes are messengers of intercellular communication. This study mainly investigated the role of exosomes from the uterine cavity in endometriosis. Exosomes of the uterine aspirate fluid were isolated and cocultured with macrophages for 48 h. Flow cytometry was used to detect macrophage polarization. A Human MAPK Phosphorylation Antibody Array and Western blot were used to detect the phosphorylation of the MAPK pathway. A microRNA sequencing analysis was used to detect differentially expressed miRNAs. Our research found that exosomes of the uterine aspirate fluid from endometriosis could reduce the proportion of CD80⁺ macrophages. Additionally, it could inhibit the expression of P-JNK in macrophages. However, the JNK activator anisomycin could increase the proportion of CD80⁺ macrophages. In addition, exosomes of the uterine aspirate fluid from endometriosis could promote the migration and invasion of endometrial stromal cells by acting on macrophages. The expression of miR-210-3p was increased in both exosomes and the eutopic endometrium in patients with endometriosis through miRNA sequencing, which could also reduce the proportion of CD80⁺ macrophages. In summary, we propose that exosomes from the uterine cavity in patients with endometriosis may affect the phenotype of macrophages by inhibiting the JNK signaling pathway, thus mediating the formation of an immunological microenvironment conducive to the development of endometriosis.

Identification of Hub Genes in the Remodeling of Non-Infarcted Myocardium Following Acute Myocardial Infarction

(1) Background: There are few diagnostic and therapeutic targets for myocardial remodeling in the salvageable non-infarcted myocardium. (2) Methods: Hub genes were identified through comprehensive bioinformatics analysis (GSE775, GSE19322, and GSE110209 from the gene expression omnibus (GEO) database) and the biological functions of hub genes were examined by gene ontology (GO) functional enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment. Furthermore, the differential expression of hub genes in various cell populations between the acute myocardial infarction (AMI) and sham-operation groups was analyzed by processing scRNA data (E-MTAB-7376 from the ArrayExpress database) and RNA-seq data (GSE183168). (3) Results: Ten strongly interlinked hub genes (Timp1, Sparc, Spp1, Tgfb1, Decr1, Vim, Serpine1, Serpina3n, Thbs2, and Vcan) were identified by the construction of a protein-protein interaction network from 135 differentially expressed genes identified through comprehensive bioinformatics analysis and their reliability was verified using GSE119857. In addition, the 10 hub genes were found to influence the ventricular remodeling of non-infarcted tissue by modulating the extracellular matrix (ECM)-mediated myocardial fibrosis, macrophage-driven inflammation, and fatty acid metabolism. (4) Conclusions: Ten hub genes were identified, which may provide novel potential targets for the improvement and treatment of AMI and its complications.

The Role of CXC Chemokines in Cardiovascular Diseases

Cardiovascular disease (CVD) is a class of diseases with high disability and mortality rates. In the elderly population, the incidence of cardiovascular disease is increasing annually. Between 1990 and 2016, the age-standardised prevalence of CVD in China significantly increased by 14.7%, and the number of cardiovascular disease deaths increased from 2.51 million to 3.97 million. Much research has indicated that cardiovascular disease is closely related to inflammation, immunity, injury and repair. Chemokines, which induce directed chemotaxis of reactive cells, are divided into four subfamilies: CXC, CC, CX3C, and XC. As cytokines, CXC chemokines are similarly involved in inflammation, immunity, injury, and repair and play a role in many cardiovascular diseases, such as atherosclerosis, myocardial infarction, cardiac ischaemia-reperfusion injury, hypertension, aortic aneurysm, cardiac fibrosis, postcardiac rejection, and atrial fibrillation. Here, we explored the relationship between the chemokine CXC subset and cardiovascular disease and its mechanism of action with the goal of further understanding the onset of cardiovascular disease.

Faster skin wound healing predicts survival after myocardial infarction

Both skin wound healing and the cardiac response to myocardial infarction (MI) progress through similar pathways involving inflammation, resolution, tissue repair, and scar formation. Due to the similarities, we hypothesized that the healing response to skin wounding would predict future response to MI. Mice were given a 3-mm skin wound using a disposable biopsy punch and the skin wound was imaged daily until closure. The same set of animals was given MI by permanent coronary artery ligation 28 days later and followed for 7 days. Cardiac physiology was measured by echocardiography at baseline and MI days 3 and 7. Animals that survived until day 7 were grouped as survivors, and animals that died from MI were grouped as nonsurvivors. Survivors had faster skin wound healing than nonsurvivors. Faster skin wound healing predicted MI survival better than commonly used cardiac functional variables (e.g., infarct size, fractional shortening, and end diastolic dimension). N-glycoproteome profiling of MI day 3 plasma revealed α2-macroglobulin and ELL-associated factor 1 as strong predictors of future MI death and progression to heart failure. A second cohort of MI mice validated these findings. To investigate the clinical relevance of α2-macroglobulin, we mapped the plasma glycoproteome in patients with MI 48 h after admission and in healthy controls. In patients, α2-macroglobulin was increased 48 h after MI. Apolipoprotein D, another plasma glycoprotein, detrimentally regulated both skin and cardiac wound healing in male but not female mice by promoting inflammation. Our results reveal that the skin is a mirror to the heart and common pathways link wound healing across organs.NEW & NOTEWORTHY Faster skin wound healers had more efficient cardiac healing after myocardial infarction (MI). Two plasma proteins at D3 MI, EAF1 and A2M, predicted MI death in 66% of cases. ApoD regulated both skin and cardiac wound healing in male mice by promoting inflammation. The skin was a mirror to the heart and common pathways linked wound healing across organs.

Single-Cell RNA Sequencing Reveals the Temporal Diversity and Dynamics of Cardiac Immunity after Myocardial Infarction

Myocardial infarction (MI) is strongly associated with the temporal regulation of cardiac immunity. However, a variety of current clinical trials have failed because of the lack of post-MI immunomodulating/anti-inflammatory targets. Single-cell RNA sequencing analysis of the cardiac Cd45⁺ immune cell at 0, 3, 7, and 14 d after injury in a mouse left anterior descending coronary artery ligation model is performed. Major immune cell populations, distinct subsets, and dynamic changes are identified. Macrophages (Mø) are most abundant, peaking at 3 d after infarction. Mø-5 and Mø-6 are the predominant infiltrated subsets at this time point, with strong expression of inflammatory factors. Further analysis demonstrates that suppressing these sets attenuated pathological MI progression by preventing subsequent leukocyte extravasation and adverse remodeling. Abundant apoptotic neutrophils and a profibrotic macrophage subset on days 7 and 14, respectively, are also detected. These results provide a basis for developing cell type- and time-specific interventions in MI.

Circulating Lymphocyte Trafficking to the Bone Marrow Contributes to Lymphopenia in Myocardial Infarction

Some patients with myocardial infarction (MI) exhibit lymphopenia, a reduction in blood lymphocyte count. Moreover, lymphopenia inversely correlates with patient prognosis. The objective of this study was to elucidate the underlying mechanisms that cause lymphopenia after MI. Multiparameter flow cytometric analysis demonstrated that MI induced profound B and T lymphopenia in a mouse model, peaking at day 1 post-MI. The finding that non-MI control and MI mice exhibited similar apoptotic rate for blood B and T lymphocytes argues against apoptosis being essential for MI-induced lymphopenia. Interestingly, the bone marrow in day 1 post-MI mice contained more B and T cells but showed less B and T cell proliferation, compared to day 0 controls. This suggests that blood lymphocytes may travel to the bone marrow after MI. This was confirmed by adoptive transfer experiments demonstrating that MI caused the loss of transferred lymphocytes in the blood, but the accumulation of transferred lymphocytes in the bone marrow. To elucidate the underlying signaling pathways, β2 adrenergic receptor or sphingoshine-1-phosphate receptor type 1 (S1PR1) was pharmacologically blocked respectively. β2 receptor inhibition had no significant effect on blood lymphocyte count, whereas S1PR1 blockade aggravated lymphopenia in MI mice. Further, we discovered that MI-induced glucocorticoid release triggered lymphopenia. This was supported by the findings that adrenalectomy (ADX) completely prevented mice from MI-induced lymphopenia, and supplementation with corticosterone in adrenalectomized MI mice re-induced lymphopenia. In conclusion, our study demonstrates that MI-associated lymphopenia involves lymphocyte redistribution from peripheral blood to the bone marrow, which is mediated by glucocorticoids.

Transcriptomic and Lipidomic Mapping of Macrophages in the Hub of Chronic Beta-Adrenergic-Stimulation Unravels Hypertrophy-, Proliferation-, and Lipid Metabolism-Related Genes as Novel Potential Markers of Early Hypertrophy or Heart Failure

Sympathetic nervous system overdrive with chronic release of catecholamines is the most important neurohormonal mechanism activated to maintain cardiac output in response to heart stress. Beta-adrenergic signaling behaves first as a compensatory pathway improving cardiac contractility and maladaptive remodeling but becomes dysfunctional leading to pathological hypertrophy and heart failure (HF). Cardiac remodeling is a complex inflammatory syndrome where macrophages play a determinant role. This study aimed at characterizing the temporal transcriptomic evolution of cardiac macrophages in mice subjected to beta-adrenergic-stimulation using RNA sequencing. Owing to a comprehensive bibliographic analysis and complementary lipidomic experiments, this study deciphers typical gene profiles in early compensated hypertrophy (ECH) versus late dilated remodeling related to HF. We uncover cardiac hypertrophy- and proliferation-related transcription programs typical of ECH or HF macrophages and identify lipid metabolism-associated and Na⁺ or K⁺ channel-related genes as markers of ECH and HF macrophages, respectively. In addition, our results substantiate the key time-dependent role of inflammatory, metabolic, and functional gene regulation in macrophages during beta-adrenergic dependent remodeling. This study provides important and novel knowledge to better understand the prevalent key role of resident macrophages in response to chronically activated beta-adrenergic signaling, an effective diagnostic and therapeutic target in failing hearts.

CXCL4 drives fibrosis by promoting several key cellular and molecular processes

Fibrosis is a major cause of mortality worldwide, characterized by myofibroblast activation and excessive extracellular matrix deposition. Systemic sclerosis is a prototypic fibrotic disease in which CXCL4 is increased and strongly correlates with skin and lung fibrosis. Here we aim to elucidate the role of CXCL4 in fibrosis development. CXCL4 levels are increased in multiple inflammatory and fibrotic mouse models, and, using CXCL4-deficient mice, we demonstrate the essential role of CXCL4 in promoting fibrotic events in the skin, lungs, and heart. Overexpressing human CXCL4 in mice aggravates, whereas blocking CXCL4 reduces, bleomycin-induced fibrosis. Single-cell ligand-receptor analysis predicts CXCL4 to affect endothelial cells and fibroblasts. In vitro, we confirm that CXCL4 directly induces myofibroblast differentiation and collagen synthesis in different precursor cells, including endothelial cells, by stimulating endothelial-to-mesenchymal transition. Our findings identify a pivotal role of CXCL4 in fibrosis, further substantiating the potential role of neutralizing CXCL4 as a therapeutic strategy.

3D collagen matrices modulate the transcriptional trajectory of bone marrow hematopoietic progenitors into macrophage lineage commitment

Physical signals provided by the extracellular matrix (ECM) are key microenvironmental parameters for the fate decision of hematopoietic stem and progenitor cells (HSPC) in bone marrow. Insights into cell-ECM interactions are critical for advancing HSC-based tissue engineering. Herein, we employed collagen hydrogels and collagen-alginate hydrogels of defined stiffness to study the behaviors of hematopoietic progenitor cells (HPCs). Three-dimensional (3D) collagen hydrogels with a stiffness of 45 Pa were found to promote HPC maintenance and colony formation of monocyte/macrophage progenitors. Using single-cell RNA sequencing (scRNA-seq), we also characterized the comprehensive transcriptional profiles of cells randomly selected from two-dimensional (2D) and 3D hydrogels. A distinct maturation trajectory from HPCs into macrophages within the 3D microenvironment was revealed by these results. 3D-derived macrophages expressed high levels of various cytokines and chemokines, such as Saa3, Cxcl2, Socs3 and Tnf. Furthermore, enhanced communication between 3D-macrophages and other hematopoietic clusters based on ligand-repair interactions was demonstrated through bioinformatic analyses. Our research underlines the regulatory role of matrix-dimensionality in HPC differentiation and therefore probably be applied to the generation of specialized macrophages.

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3D collagen hydrogels influenced the maintenance of hematopoietic progenitor cells.

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3D matrices modulated the lineage specification of hematopoietic progenitors and promoted the formation of CFU-M colonies.

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Single-cell RNA sequencing identified a cluster of specialized macrophages within a 3D microenvironment.

Potential of Point-of-Care and At-Home Assessment of Immune Status via Rapid Cytokine Detection and Questionnaire-Based Anamnesis

Monitoring the immune system's status has emerged as an urgent demand in critical health conditions. The circulating cytokine levels in the blood reflect a thorough insight into the immune system status. Indeed, measuring one cytokine may deliver more information equivalent to detecting multiple diseases at a time. However, if the reported cytokine levels are interpreted with considering lifestyle and any comorbid health conditions for the individual, this will promote a more precise assessment of the immune status. Therefore, this study addresses the most recent advanced assays that deliver rapid, accurate measuring of the cytokine levels in human blood, focusing on add-on potentials for point-of-care (PoC) or personal at-home usage, and investigates existing health questionnaires as supportive assessment tools that collect all necessary information for the concrete analysis of the measured cytokine levels. We introduced a ten-dimensional featuring of cytokine measurement assays. We found 15 rapid cytokine assays with assay time less than 1 h; some could operate on unprocessed blood samples, while others are mature commercial products available in the market. In addition, we retrieved several health questionnaires that addressed various health conditions such as chronic diseases and psychological issues. Then, we present a machine learning-based solution to determine what makes the immune system fit. To this end, we discuss how to employ topic modeling for deriving the definition of immune fitness automatically from literature. Finally, we propose a prototype model to assess the fitness of the immune system through leveraging the derived definition of the immune fitness, the cytokine measurements delivered by a rapid PoC immunoassay, and the complementary information collected by the health questionnaire about other health factors. In conclusion, we discovered various advanced rapid cytokine detection technologies that are promising candidates for point-of-care or at-home usage; if paired with a health status questionnaire, the assessment of the immune system status becomes solid and we demonstrated potentials for promoting the assessment tool with data mining techniques.

Role of Neutrophils in Cardiac Injury and Repair Following Myocardial Infarction

Neutrophils are first-line responders of the innate immune system. Following myocardial infarction (MI), neutrophils are quickly recruited to the ischemic region, where they initiate the inflammatory response, aiming at cleaning up dead cell debris. However, excessive accumulation and/or delayed removal of neutrophils are deleterious. Neutrophils can promote myocardial injury by releasing reactive oxygen species, granular components, and pro-inflammatory mediators. More recent studies have revealed that neutrophils are able to form extracellular traps (NETs) and produce extracellular vesicles (EVs) to aggravate inflammation and cardiac injury. On the contrary, there is growing evidence showing that neutrophils also exert anti-inflammatory, pro-angiogenic, and pro-reparative effects, thus facilitating inflammation resolution and cardiac repair. In this review, we summarize the current knowledge on neutrophils’ detrimental roles, highlighting the role of recently recognized NETs and EVs, followed by a discussion of their beneficial effects and molecular mechanisms in post-MI cardiac remodeling. In addition, emerging concepts about neutrophil diversity and their modulation of adaptive immunity are discussed.

Activin receptor-like kinase 4 haplodeficiency alleviates the cardiac inflammation and pacing-induced ventricular arrhythmias after myocardial infarction

BACKGROUND

Inflammation process is an important determinant for subsequent changes in cardiac function and remodeling after acute myocardial infarction (MI). Recent studies have implicated that ALK4 haplodeficiency improves cardiac function after MI. However, it remains unknown if the beneficial effects are partly attributed to ALK4 haplodeficiency-induced modulation on inflammatory response in the inflammatory phase of MI. In this research, we aimed to explore the mechanism of ALK4 haplodeficiency in the inflammatory stage of MI.

METHODS

ALK4, CD16, and CD14 were detected in peripheral blood mononuclear cells (PBMCs) isolated from MI patients and healthy volunteers. ALK4 haplodeficiency (ALK4^+/-) mice and wild-type (WT) littermates were randomly divided into the sham group and the MI group. Inflammation cytokines and chemokines were measured. Echocardiography and intracardiac electrophysiological recordings were performed on the 3^rd day and the 7^th day after MI operation. ALK4 expression and inflammation cytokines were also detected in LPS- or IL-4-stimulated bone marrow-derived macrophages (BMDM) from the ALK4^+/- mice and WT littermates.

RESULTS

ALK4 gene expression in circulating monocytes of MI patients was higher than that in those of healthy volunteers. Cardiac inflammation and vulnerability of ventricular arrhythmia after acute myocardial injury are significantly alleviated in ALK4^+/- mice as compared to WT littermates. On the 3^rd day post-MI, the level of M1 macrophages were decreased in ALK4^+/- mice as compared to WT littermates, while the level of M2 macrophages were increased on the 7^th day post-MI. BMDM isolated from ALK4^+/- mice displayed reduced secretion of pro-inflammation cytokines after stimulation by LPS in hypoxic condition and increased secretion of anti-inflammation cytokines after stimulation by IL-4. As a result, the haplodeficiency of ALK4 might be responsible for reduced inflammation response in the post-MI stage.

CONCLUSIONS

ALK4 haplodeficiency reduces cardiac inflammation, improves cardiac function, and finally reduces the vulnerability of ventricular arrhythmia in the inflammatory stage after MI.

CD36 as a target for metabolic modulation therapy in cardiac disease

Introduction: Disturbances in myocardial lipid metabolism are increasingly being recognized as drivers of the development and progression of heart disease. Therefore, there is a need for treatments that can directly target lipid metabolic defects in heart failure. The membrane-associated glycoprotein CD36 plays a pivotal role in governing myocardial lipid metabolism by mediating lipid signaling and facilitating the cellular uptake of long-chain fatty acids. Emerging evidence suggests that CD36 is a prominent target in the treatment of heart failure.Areas covered: This article provides an overview of the key role of CD36 for proper contractile functioning of a healthy heart, its implications in the development of cardiac disease (ischemia/reperfusion, cardiac hypertrophy, and diabetic cardiomyopathy), and its application as a target to normalize cardiac metabolism as part of so-called metabolic modulation therapy.Expert opinion: CD36 appears a promising and effective therapeutic target in the treatment of heart failure. Natural compounds and chemical agents known to alter the amount or subcellular distribution of CD36 or inhibit its functioning, should be evaluated for their potency to correct cardiac metabolism and cure heart disease.

Inhibition of Interleukin-21 prolongs the survival through the promotion of wound healing after myocardial infarction

Ly6C^low macrophages promote scar formation and prevent early infarct expansion after myocardial infarction (MI). Although CD4⁺ T cells influence the regulation of Ly6C^low macrophages after MI, the mechanism remains largely unknown. Based on the hypothesis that some molecule(s) secreted by CD4⁺ T cells act on Ly6C^low macrophages, we searched for candidate molecules by focusing on cytokine receptors expressed on Ly6C^low macrophages. Comparing the transcriptome between Ly6C^high macrophages and Ly6C^low macrophages harvested from the infarcted heart, we found that Ly6C^low macrophages highly expressed the receptor for interleukin (IL)-21, a pleiotropic cytokine which is produced by several types of CD4⁺ T cells, compared with Ly6C^high macrophages. Indeed, CD4⁺ T cells harvested from the infarcted heart produce IL-21 upon stimulation. Importantly, the survival rate and cardiac function after MI were significantly improved in IL-21-deficient (il21^-/-) mice compared with those in wild-type (WT) mice. Transcriptome analysis of infarcted heart tissue from WT mice and il21^-/- mice at 5 days after MI demonstrated that inflammation is persistent in WT mice compared with il21^-/- mice. Consistent with the transcriptome analysis, the number of neutrophils and matrix metalloproteinase (MMP)-9 expression were significantly decreased, whereas the number of Ly6C^low macrophages and MMP-12 expression were significantly increased in il21^-/- mice. In addition, collagen deposition and the number of myofibroblasts in the infarcted area were significantly increased in il21^-/- mice. Consistently, IL-21 enhanced the apoptosis of Ly6C^low macrophages. Finally, administration of neutralizing IL-21 receptor Fc protein increased the number of Ly6C^low macrophages in the infarcted heart and improved the survival and cardiac function after MI. Thus, IL-21 decreases the survival after MI, possibly through the delay of wound healing by inducing the apoptosis of Ly6C^low macrophages.

Network Analysis Reveals a Distinct Axis of Macrophage Activation in Response to Conflicting Inflammatory Cues

Macrophages are subject to a wide range of cytokine and pathogen signals in vivo, which contribute to differential activation and modulation of inflammation. Understanding the response to multiple, often-conflicting cues that macrophages experience requires a network perspective. In this study, we integrate data from literature curation and mRNA expression profiles obtained from wild type C57/BL6J mice macrophages to develop a large-scale computational model of the macrophage signaling network. In response to stimulation across all pairs of nine cytokine inputs, the model predicted activation along the classic M1-M2 polarization axis but also a second axis of macrophage activation that distinguishes unstimulated macrophages from a mixed phenotype induced by conflicting cues. Along this second axis, combinations of conflicting stimuli, IL-4 with LPS, IFN-γ, IFN-β, or TNF-α, produced mutual inhibition of several signaling pathways, e.g., NF-κB and STAT6, but also mutual activation of the PI3K signaling module. In response to combined IFN-γ and IL-4, the model predicted genes whose expression was mutually inhibited, e.g., iNOS or Nos2 and Arg1, or mutually enhanced, e.g., Il4rα and Socs1, validated by independent experimental data. Knockdown simulations further predicted network mechanisms underlying functional cross-talk, such as mutual STAT3/STAT6-mediated enhancement of Il4rα expression. In summary, the computational model predicts that network cross-talk mediates a broadened spectrum of macrophage activation in response to mixed pro- and anti-inflammatory cytokine cues, making it useful for modeling in vivo scenarios.

Neutrophil signaling during myocardial infarction wound repair

Neutrophils are key effector cells of the innate immune system, serving as a first line of defense in the response to injury and playing essential roles in the wound healing process. Following myocardial infarction (MI), neutrophils infiltrate into the infarct region to propagate inflammation and begin the initial phase of cardiac wound repair. Pro-inflammatory neutrophils release proteases to degrade extracellular matrix (ECM), a necessary step for the removal of necrotic myocytes as a prelude for scar formation. Neutrophils transition their phenotype over time to regulate MI inflammation resolution and stabilize scar formation. Neutrophils contribute to the evolution from inflammation to resolution and scar formation by serving anti-inflammatory and repair functions. As anti-inflammatory cells, neutrophils contribute ECM proteins during scar formation, in particular fibronectin, galectin-3, and vimentin. The diverse and polarizing functions that contribute to MI wound repair make this innate immune cell a viable target to improve MI outcomes. Thus, understanding the signaling involved in neutrophil physiology in the context of MI may help to identify novel therapeutic targets.

The role of CD36 in cardiovascular disease

CD36, also known as the scavenger receptor B2, is a multifunctional receptor widely expressed in various organs. CD36 plays a crucial role in the uptake of long-chain fatty acids, the main metabolic substrate in myocardial tissue. The maturation and transportation of CD36 is regulated by post-translational modifications, including phosphorylation, ubiquitination, glycosylation, and palmitoylation. CD36 is decreased in pathological cardiac hypertrophy caused by ischaemia-reperfusion and pressure overload, and increased in diabetic cardiomyopathy and atherosclerosis. Deficiency of CD36 alleviates diabetic cardiomyopathy and atherosclerosis, while overexpression of CD36 eliminates ischaemia-reperfusion damage, together suggesting that CD36 is closely associated with the progression of cardiovascular diseases and may be a new therapeutic target. This review summarizes the regulation and post-translational modifications of CD36 and evaluates its role in cardiovascular diseases and its potential as a therapeutic target.

Chemokines in cardiac fibrosis

Several members of the chemokine family are involved in regulation of fibrosis. This review manuscript discusses the role of the chemokines in the pathogenesis of myocardial fibrosis. The CC chemokine CCL2 exerts fibrogenic actions through recruitment and activation of monocytes and macrophages expressing its receptor, CCR2. Other CC chemokines may also contribute to fibrotic remodeling by recruiting subsets of fibrogenic macrophages. CXC chemokines containing the ELR motif may exert pro-fibrotic actions, through recruitment of activated neutrophils and subsequent formation of neutrophil extracellular traps (NETs), or via activation of fibrogenic monocytes. CXCL12 has also been suggested to exert fibrogenic actions through effects on fibroblasts and immune cells. In contrast, the CXCR3 ligand CXCL10 was found to reduce cardiac fibrosis, inhibiting fibroblast migration. Chemokines are critical links between inflammation and fibrosis in myocardial disease and may be promising therapeutic targets for patients with heart failure accompanied by prominent inflammation and fibrosis.

Exogenous IL-4 shuts off pro-inflammation in neutrophils while stimulating anti-inflammation in macrophages to induce neutrophil phagocytosis following myocardial infarction

INTRODUCTION

Macrophages and neutrophils are primary leukocytes involved in the inflammatory response to myocardial infarction (MI). While interleukin (IL)-4 is an in vitro anti-inflammatory stimulus, the MI myocardium does not express a considerable amount of IL-4 but does express IL4 receptors. We hypothesized that continuous exogenous IL-4 infusion starting 24 h after MI would promote a polarization switch in inflammatory cells towards a reparative phenotype.

METHODS

C57BL/6J male mice (3-6 months of age) were subcutaneously infused with either saline (n = 17) or IL-4 (20 ng/g/day; n = 17) beginning 24 h after MI and evaluated at MI day 3.

RESULTS

Macrophages and neutrophils were isolated ex vivo from the infarct region and examined. Exogenous IL-4 decreased pro-inflammatory Ccl3, Il12a, Tnfa, and Tgfb1 in neutrophils and increased anti-inflammatory Arg1 and Ym1 in macrophages (all p < .05). Tissue clearance by IL-4 treated neutrophils was not different, while selective phagocytosis of neutrophils doubled in IL-4 treated macrophages (p < .05). Of 24,339 genes examined by RNA-sequencing, 2042 genes were differentially expressed in macrophages from IL-4 stimulated infarct (all FDR p < .05). Pdgfc gene expression was ranked first, increasing 3-fold in macrophages stimulated with IL-4 (p = 1 × 10-9). Importantly, changes in macrophage physiology and transcriptome occurred in the absence of global LV effects. Bone marrow derived monocytes stimulated with mouse recombinant PDGF-CC protein (10 μg/ml) or PDGF-CC blocking antibody (200 ng/ml) did not change Arg1 or Ym1 expression, indicating the in vivo effect of IL-4 to stimulate macrophage anti-inflammatory gene expression was independent of PDGF-CC.

CONCLUSIONS

Our results indicate that exogenous IL-4 promotes inflammation resolution by turning off pro-inflammation in neutrophils while stimulating anti-inflammation in macrophages to mediate removal of apoptotic neutrophils.

Loss of CD36 protects against diet-induced obesity but results in impaired muscle stem cell function, delayed muscle regeneration and hepatic steatosis

AIM

The prevalence of obesity is a major risk factor for cardiovascular and metabolic diseases including impaired skeletal muscle regeneration. Since skeletal muscle regenerative capacity is regulated by satellite cells, we aimed to investigate whether a high-fat diet impairs satellite cell function and whether this is linked to fatty acid uptake via CD36. We also aimed to determine whether loss of CD36 impacts on muscle redox homeostasis and skeletal muscle regenerative capacity.

METHODS

We studied the impact of a high-fat diet and CD36 deficiency on murine skeletal muscle morphology, redox homeostasis, satellite cell function, bioenergetics and lipid accumulation in the liver. We also determined the effect of CD36 deficiency on skeletal muscle regeneration.

RESULTS

High-fat diet increased body weight, intramuscular lipid accumulation and oxidative stress in wild-type mice that were significantly mitigated in CD36-deficient mice. High-fat diet and CD36 deficiency independently attenuated satellite cell function on single fibres and myogenic capacity on primary satellite cells. CD36 deficiency resulted in delayed skeletal muscle regeneration following acute injury with cardiotoxin. CD36-deficient and wild-type primary satellite cells had distinct bioenergetic profiles in response to palmitate. High-fat diet induced hepatic steatosis in both genotypes that was more pronounced in the CD36-deficient mice.

CONCLUSION

This study demonstrates that CD36 deficiency protects against diet-induced obesity, intramuscular lipid deposition and oxidative stress but results in impaired muscle satellite cell function, delayed muscle regeneration and hepatic steatosis. CD36 is a key mediator of fatty acid uptake in skeletal muscle, linking obesity with satellite cell function and muscle regeneration.

Understanding the mechanisms that determine extracellular matrix remodeling in the infarcted myocardium

Myocardial Infarction (MI) initiates a series of wound healing events that begins with up-regulation of an inflammatory response and culminates in scar formation. The extracellular matrix (ECM) is intricately involved in all stages from initial break down of existing ECM to synthesis of new ECM to form the scar. This review will summarize our current knowledge on the processes involved in ECM remodeling after MI and identify the gaps that still need to be filled.

Inflammation and fibrosis in murine models of heart failure

Heart failure is a consequence of various cardiovascular diseases and associated with poor prognosis. Despite progress in the treatment of heart failure in the past decades, prevalence and hospitalisation rates are still increasing. Heart failure is typically associated with cardiac remodelling. Here, inflammation and fibrosis are thought to play crucial roles. During cardiac inflammation, immune cells invade the cardiac tissue and modulate tissue-damaging responses. Cardiac fibrosis, however, is characterised by an increased amount and a disrupted composition of extracellular matrix proteins. As evidence exists that cardiac inflammation and fibrosis are potentially reversible in experimental and clinical set ups, they are interesting targets for innovative heart failure treatments. In this context, animal models are important as they mimic clinical conditions of heart failure patients. The advantages of mice in this respect are short generation times and genetic modifications. As numerous murine models of heart failure exist, the selection of a proper disease model for a distinct research question is demanding. To facilitate this selection, this review aims to provide an overview about the current understanding of the pathogenesis of cardiac inflammation and fibrosis in six frequently used murine models of heart failure. Hence, it compares the models of myocardial infarction with or without reperfusion, transverse aortic constriction, chronic subjection to angiotensin II or deoxycorticosterone acetate, and coxsackievirus B3-induced viral myocarditis in this context. It furthermore provides information about the clinical relevance and the limitations of each model, and, if applicable, about the recent advancements in their methodological proceedings.