Cardiac resident macrophages: key regulatory mediators in the aftermath of myocardial infarction

Tissue-Resident Macrophages in Cardiovascular Diseases: Heterogeneity and Therapeutic Potential

Tissue-resident macrophages (TRMs) play a crucial role in maintaining tissue homeostasis and regulating immune responses. In recent years, an increasing number of studies have highlighted their central role in cardiovascular diseases. This review provides a comprehensive overview of TRMs, with a particular emphasis on cardiac resident macrophages (CRMs), discussing their origin, heterogeneity, and functions in various cardiovascular diseases. We conduct an in-depth analysis of macrophage subpopulations based on C-C Chemokine Receptor Type 2 (CCR2) receptor expression, elucidating the role of CCR2+ macrophages in promoting fibrosis and cardiac remodeling, while highlighting the protective functions of CCR2- macrophages in suppressing inflammation and promoting tissue repair. In atherosclerosis, we focus on the role of metabolic reprogramming in regulating macrophage polarization, revealing how metabolic pathways influence the balance between pro-inflammatory M1 and anti-inflammatory M2 macrophages, thereby affecting plaque stability and disease progression. By summarizing the roles of these macrophage subpopulations in myocardial infarction, heart failure, and other diseases, we propose potential therapeutic strategies aimed at modulating different macrophage subtypes. These include targeting the CCR2 signaling pathway to mitigate inflammation and fibrosis, and metabolic reprogramming to restore the balance between M1 and M2 macrophages. Finally, we highlight the need for future research to focus on the functional diversity and molecular mechanisms of human TRMs to develop novel immunotherapeutic strategies and improve the prognosis of cardiovascular diseases.

Loss of macrophage fibroblast growth factor 12 attenuates cardiac fibrosis in pressure-overloaded myocardium

BACKGROUND

Cardiac fibrosis, a leading cause of death worldwide, plays a functional role in the development of heart failure. Unfortunately, there are currently no therapeutic strategies in clinical practice that can specifically attenuate the activation of cardiac fibroblasts, the effector cells of fibrosis in the heart. In this study, we aimed to identify a novel approach to target myocardial fibrosis through the crosstalk between macrophages and fibroblasts.

METHODS

We investigated the expression of fibroblast growth factor 12 (FGF12), a novel regulator of macrophage activation, in both human subjects and mouse models. We also generated myeloid cell-specific FGF12 knockout mice to determine the role of FGF12 in cardiac fibrosis. For in vitro studies, we isolated mouse primary bone marrow-derived macrophages (BMDMs) and cardiac fibroblasts to explore the mechanism by which FGF12 controls macrophage polarization and fibroblast activation.

RESULTS

We found that FGF12 expression was significantly upregulated in both human failing hearts and mouse pressure-overloaded myocardium. RNA sequencing revealed that FGF12 upregulation was associated with fibrosis progression, oxidative stress response, and macrophage activation in mouse heart tissues. Myeloid-specific knockout of FGF12 markedly attenuated pressure overload-induced myocardial fibrosis in our mouse models. We observed that FGF12 significantly affects interleukin-4-stimulated M2 polarization in BMDMs. Conditioned medium from FGF12 knockdown or overexpressed BMDMs also influenced cardiac fibroblast activation, primarily by affecting reactive oxygen species (ROS) accumulation in cardiac fibroblasts. Furthermore, we demonstrated that FGF12 controls BMDM M2 polarization through the SOCS/STAT pathway.

CONCLUSIONS

FGF12 is a novel regulator of myocardial fibrosis, acting through the modulation of crosstalk between macrophages and fibroblasts. Therapeutic approaches targeting FGF12 may represent a potential strategy to ameliorate cardiac fibrosis or other fibrosis-related diseases in the future.

Immunization induces inflammation in the mouse heart during spaceflight

Space travel is a growing area of interest and includes initiatives such as NASA's Moon-to-Mars Mission. Reports on the cardiovascular effects of space travel reveal changes in morphology, metabolism, and function of the cardiovascular system. In this study, the cardiovascular response to immunization in space was studied in mice which were housed and immunized while on the International Space Station (ISS). Mice were immunized with tetanus toxoid combined with the adjuvant CpG (TT + CpG) and the effects of vaccination in space were studied using transcriptomics. Analysis of the mouse heart transcriptome was performed on flight control and flight-immunized mice. The results show that immunization aboard the ISS stimulates heightened inflammation in the heart via induction of the nuclear factor kappa B (NF-κB) signaling pathway to promote the release of the pro-inflammatory cytokines IFNγ, IL-17 and IL-6. Additional transcriptomic changes included alterations in the cytoskeleton and in the expression of transcripts associated with protection from oxidative stress. In summary, inflammation in the heart can occur following immunization in space. This investigation explores the impact of immune challenges on the heart and lays the groundwork for future research into additional cardiac alterations which can occur during spaceflight.

IL-1 signaling pathway, an important target for inflammation surrounding in myocardial infarction

Acute myocardial infarction is an important cardiovascular disease worldwide. Although the mortality rate of myocardial infarction (MI) has improved dramatically in recent years due to timely treatment, adverse remodeling of the left ventricle continues to affect cardiac function. Various immune cells are involved in this process to induce inflammation and amplification. The infiltration of inflammatory cells in the infarcted myocardium is induced by various cytokines and chemokines, and the recruitment of leukocytes further amplifies the inflammatory response. As an increasing number of clinical anti-inflammatory therapies have achieved significant success in recent years, treating myocardial infarction by targeting inflammation may become a novel therapeutic option. In particular, successful clinical trials of canakinumab have demonstrated the important role of the inflammatory factor interleukin-1 (IL-1) in atherosclerosis. Targeted IL-1 therapy may decrease inflammation levels and improve cardiac function in patients after myocardial infarction. This article reviews the complex series of responses after myocardial infarction, including the involvement of inflammatory cells and the role of cytokines and chemokines, focusing on the progression of the IL-1 family in myocardial infarction as well as the performance of current targeted therapy drugs in experiments.

Dissecting and Visualizing the Functional Diversity of Cardiac Macrophages

Cardiac macrophages represent a functionally diverse population of cells involved in cardiac homeostasis, repair, and remodeling. With recent advancements in single-cell technologies, it is possible to elucidate specific macrophage subsets based on transcriptional signatures and cell surface protein expression to gain a deep understanding of macrophage diversity in the heart. The use of fate-mapping technologies and parabiosis studies have provided insight into the ontogeny and dynamics of macrophages identifying subsets derived from embryonic and adult definitive hematopoietic progenitors that include tissue-resident and bone marrow monocyte-derived macrophages, respectively. Within the heart, these subsets have distinct tissue niches and functional roles in the setting of homeostasis and disease, with cardiac resident macrophages representing a protective cell population while bone marrow monocyte-derived cardiac macrophages have a context-dependent effect, triggering both proinflammatory tissue injury, but also promoting reparative functions. With the increased understanding of the clinical relevance of cardiac macrophage subsets, there has been an increasing need to detect and measure cardiac macrophage compositions in living animals and patients. New molecular tracers compatible with positron emission tomography/computerized tomography and positron emission tomography/ magnetic resonance imaging have enabled investigators to noninvasively and serially visualize cardiac macrophage subsets within the heart to define associations with disease and measure treatment responses. Today, advancements within this thriving field are poised to fuel an era of clinical translation.

The role and therapeutic potential of macrophages in the pathogenesis of diabetic cardiomyopathy

This review provides a comprehensive analysis of the critical role played by macrophages and their underlying mechanisms in the progression of diabetic cardiomyopathy (DCM). It begins by discussing the origins and diverse subtypes of macrophages, elucidating their spatial distribution and modes of intercellular communication, thereby emphasizing their significance in the pathogenesis of DCM. The review then delves into the intricate relationship between macrophages and the onset of DCM, particularly focusing on the epigenetic regulatory mechanisms employed by macrophages in the context of DCM condition. Additionally, the review discusses various therapeutic strategies aimed at targeting macrophages to manage DCM. It specifically highlights the potential of natural food components in alleviating diabetic microvascular complications and examines the modulatory effects of existing hypoglycemic drugs on macrophage activity. These findings, summarized in this review, not only provide fresh insights into the role of macrophages in diabetic microvascular complications but also offer valuable guidance for future therapeutic research and interventions in this field.

Cardiac fibrogenesis: an immuno-metabolic perspective

Cardiac fibrosis is a major and complex pathophysiological process that ultimately culminates in cardiac dysfunction and heart failure. This phenomenon includes not only the replacement of the damaged tissue by a fibrotic scar produced by activated fibroblasts/myofibroblasts but also a spatiotemporal alteration of the structural, biochemical, and biomechanical parameters in the ventricular wall, eliciting a reactive remodeling process. Though mechanical stress, post-infarct homeostatic imbalances, and neurohormonal activation are classically attributed to cardiac fibrosis, emerging evidence that supports the roles of immune system modulation, inflammation, and metabolic dysregulation in the initiation and progression of cardiac fibrogenesis has been reported. Adaptive changes, immune cell phenoconversions, and metabolic shifts in the cardiac nonmyocyte population provide initial protection, but persistent altered metabolic demand eventually contributes to adverse remodeling of the heart. Altered energy metabolism, mitochondrial dysfunction, various immune cells, immune mediators, and cross-talks between the immune cells and cardiomyocytes play crucial roles in orchestrating the transdifferentiation of fibroblasts and ensuing fibrotic remodeling of the heart. Manipulation of the metabolic plasticity, fibroblast-myofibroblast transition, and modulation of the immune response may hold promise for favorably modulating the fibrotic response following different cardiovascular pathological processes. Although the immunologic and metabolic perspectives of fibrosis in the heart are being reported in the literature, they lack a comprehensive sketch bridging these two arenas and illustrating the synchrony between them. This review aims to provide a comprehensive overview of the intricate relationship between different cardiac immune cells and metabolic pathways as well as summarizes the current understanding of the involvement of immune-metabolic pathways in cardiac fibrosis and attempts to identify some of the previously unaddressed questions that require further investigation. Moreover, the potential therapeutic strategies and emerging pharmacological interventions, including immune and metabolic modulators, that show promise in preventing or attenuating cardiac fibrosis and restoring cardiac function will be discussed.

Macrophage-based therapeutic approaches for cardiovascular diseases

Despite the advances in treatment options, cardiovascular disease (CVDs) remains the leading cause of death over the world. Chronic inflammatory response and irreversible fibrosis are the main underlying pathophysiological causes of progression of CVDs. In recent decades, cardiac macrophages have been recognized as main regulatory players in the development of these complex pathophysiological conditions. Numerous approaches aimed at macrophages have been devised, leading to novel prospects for therapeutic interventions. Our review covers the advancements in macrophage-centric treatment plans for various pathologic conditions and examines the potential consequences and obstacles of employing macrophage-targeted techniques in cardiac diseases.