Post-myocardial infarction fibrosis: Pathophysiology, examination, and intervention

Comprehensive macro and micro views on immune cells in ischemic heart disease

Ischemic heart disease (IHD) is a prevalent cardiovascular condition that remains the primary cause of death due to its adverse ventricular remodelling and pathological changes in end-stage heart failure. As a complex pathologic condition, it involves intricate regulatory processes at the cellular and molecular levels. The immune system and cardiovascular system are closely interconnected, with immune cells playing a crucial role in maintaining cardiac health and influencing disease progression. Consequently, alterations in the cardiac microenvironment are influenced and controlled by various immune cells, such as macrophages, neutrophils, dendritic cells, eosinophils, and T-lymphocytes, along with the cytokines they produce. Furthermore, studies have revealed that Gata6+ pericardial cavity macrophages play a key role in regulating immune cell migration and subsequent myocardial tissue repair post IHD onset. This review outlines the role of immune cells in orchestrating inflammatory responses and facilitating myocardial repair following IHD, considering both macro and micro views. It also discusses innovative immune cell-based therapeutic strategies, offering new insights for further research on the pathophysiology of ischemic heart disease and immune cell-targeted therapy for IHD.

m6A control programmed cell death in cardiac fibrosis

N6-methyladenosine (m6A) modification is closely related to cardiac fibrosis. As the most common and abundant form of mRNA modification in eukaryotes, m6A is deposited by methylases ("writers"), recognized and effected by RNA-binding proteins ("readers"), and removed by demethylases ("erasers"), achieving highly dynamic reversibility. m6A modification is involved in regulating the entire biological process of target RNA, including transcription, processing and splicing, export from the nucleus to the cytoplasm, and enhancement or reduction of stability and translation. Programmed cell death (PCD) comprises many forms and pathways, with apoptosis and autophagy being the most common. Other forms include pyroptosis, ferroptosis, necroptosis, mitochondrial permeability transition (MPT)-dependent necrosis, and parthanatos. In recent years, increasing evidence suggests that m6A modification can mediate PCD, affecting cardiac fibrosis. Since the correlation between some PCD types and m6A modification is not yet clear, this article mainly introduces the relationship between four common PCD types (apoptosis, autophagy, pyroptosis, and ferroptosis) and m6A modification, as well as their role and influence in cardiac fibrosis.

Antifibrotic effect of the P2X7 receptor antagonist A740003 against acute myocardial infarction-induced fibrotic remodelling

Post-acute myocardial infarction (AMI) fibrosis is a pathophysiologic process characterised by activation of the profibrotic mediator, transforming growth factor-β (TGF-β). AMI is associated with a substantial increase in the levels of extracellular adenosine triphosphate (eATP), which acts on the purinergic P2X7-receptor (P2X7-R) and triggers an inflammatory response that contributes to myocardial fibrotic remodelling. P2X7-R has been implicated in several cardiovascular diseases; however, its role in the regulation of cardiac fibrosis remains unclear. Therefore, the current study aimed to determine the effect of the P2X7-R antagonist, A740003, on post-AMI fibrosis, via the profibrotic TGF-β1/Smad signalling pathway, and elucidate whether its effect is mediated via the modulation of GSK-3β. AMI was induced by surgical ligation of the left anterior descending coronary artery, Thereafter, animals were divided into groups: sham control, MI-untreated, MI-vehicle, and MI-A740003 (50 mg/kg/day) and treated for seven days accordingly. The heart weight/body weight ratio of untreated-ligated rats significantly increased by 15.1 %, creatine kinase-MB (CK-MB) significantly increased by 40 %, troponin-I levels significantly increased by 25.4 %, and lactate dehydrogenase significantly increased by 47.2 %, indicating myocardial damage confirmed by morphological changes and massive cardiac fibrosis. The protein expression of cardiac fibronectin, TGF-β1, and p-Smad2 were also upregulated by 143 %, 40 %, and 8 %, respectively, indicating cardiac fibrosis. The treatment of ligated rats with A740003 led to improvement in all the above-mentioned parameters. Overall, A740003 exhibits potential cardio-protective effects on post-AMI fibrotic remodelling in the animal model of AMI through P2X7-R blockade, possibly by downregulating the profibrotic TGF-β1/Smad signalling pathway and restoring GSK-3β phosphorylation. Altogether, treatment with A740003 could serve as a new cardioprotective strategy to attenuate post-AMI fibrotic remodelling.

Novel Fibrillar and Non-Fibrillar Collagens Involved in Fibrotic Scar Formation after Myocardial Infarction

Following myocardial infarction (MI), adverse remodeling depends on the proper formation of fibrotic scars, composed of type I and III collagen. Our objective was to pinpoint the participation of previously unreported collagens in post-infarction cardiac fibrosis. Gene (qRT-PCR) and protein (immunohistochemistry followed by morphometric analysis) expression of fibrillar (types II and XI) and non-fibrillar (types VIII and XII) collagens were determined in RNA-sequencing data from 92 mice undergoing myocardial ischemia; mice submitted to permanent (non-reperfused MI, n = 8) or transient (reperfused MI, n = 8) coronary occlusion; and eight autopsies from chronic MI patients. In the RNA-sequencing analysis of mice undergoing myocardial ischemia, increased transcriptomic expression of collagen types II, VIII, XI, and XII was reported within the first week, a tendency that persisted 21 days afterwards. In reperfused and non-reperfused experimental MI models, their gene expression was heightened 21 days post-MI induction and positively correlated with infarct size. In chronic MI patients, immunohistochemistry analysis demonstrated their presence in fibrotic scars. Functional analysis indicated that these subunits probably confer tensile strength and ensure the cohesion of interstitial components. Our data reveal that novel collagens are present in the infarcted myocardium. These data could lay the groundwork for unraveling post-MI fibrotic scar composition, which could ultimately influence patient survivorship.

Galanin Coordinates Macrophage-Associated Fibro-Inflammatory Response and Mitochondrial Integrity in Myocardial Infarction Reperfusion Injury

Myocardial infarction activates an intense fibro-inflammatory reaction that is essential for cardiac remodeling and heart failure (HF). Bioactive peptide galanin plays a critical role in regulating cardiovascular homeostasis; however, its specific functional relevance in post-infarction fibro-inflammatory reprogramming remains obscure. Here, we show that galanin coordinates the fibro-inflammatory trajectory and mitochondrial integrity in post-infarction reperfusion injury. Aberrant deposition of collagen was associated with a marked increase in CD68-positive macrophage infiltration in cardiac tissue in mice subjected to myocardial ischemia/reperfusion (I/R) for 14 days compared to sham controls. Furthermore, we found that the myocardial expression level of a specific marker of M2 macrophages, CD206, was significantly down-regulated in I/R-challenged mice. In contrast, galanin treatment started during the reperfusion phase blunted the fibro-inflammatory responses and promoted the expression of CD206 in I/R-remodeled hearts. In addition, we found that the anti-apoptotic and anti-hypertrophic effects of galanin were associated with the preservation of mitochondrial integrity and promotion of mitochondrial biogenesis. These findings depict galanin as a key arbitrator of fibro-inflammatory responses to cardiac I/R injury and offer a promising therapeutic trajectory for the treatment of post-infarct cardiovascular complications.

Cardiomyocyte-specific overexpression of GPR22 ameliorates cardiac injury in mice with acute myocardial infarction

BACKGROUND

The activation of G protein-coupled receptors (GPCR) signaling by external stimuli has been implicated in inducing cardiac stress and stress responses. GPR22 is an orphan GPCR expressed in brains and hearts, while its expression level is associated with cardiovascular damage in diabetes. Previous studies have suggested a protective role of GPR22 in mechanical cardiac stress, as loss of its expression increases susceptibility to heart failure post-ventricular pressure overload. However, the involvement and underlying signaling of GPR22 in cardiac stress response to ischemic stress remains unexplored.

METHODS

In this study, we used cultured cells and a transgenic mouse model with cardiomyocyte-specific GPR22 overexpression to investigate the impact of ischemic stress on GPR22 expression and to elucidate its role in myocardial ischemic injury. Acute myocardial infarction (AMI) was induced by left coronary artery ligation in eight-week-old male GPR22 transgenic mice, followed by histopathological and biochemical examination four weeks post-AMI induction.

RESULTS

GPR22 expression in H9C2 and RL-14 cells, two cardiomyocyte cell lines, was decreased by cobalt chloride (CoCl2) treatment. Similarly, reduced expression of myocardial GPR22 was observed in mice with AMI. Histopathological examinations revealed a protective effect of GPR22 overexpression in attenuating myocardial infarction in mice with AMI. Furthermore, myocardial levels of Bcl-2 and activation of PI3K-Akt signaling were downregulated by ischemic stress and upregulated by GPR22 overexpression. Conversely, the expression levels of caspase-3 and phosphorylated ERK1/2 in the infarcted myocardium were downregulated with GPR22 overexpression.

CONCLUSION

Myocardial ischemic stress downregulates cardiac expression of GPR22, whereas overexpression of GPR22 in cardiomyocytes upregulates Akt signaling, downregulates ERK activation, and mitigates ischemia-induced myocardial injury.

Redox homeostasis in cardiac fibrosis: Focus on metal ion metabolism

Cardiac fibrosis is a major public health problem worldwide, with high morbidity and mortality, affecting almost all patients with heart disease worldwide. It is characterized by fibroblast activation, abnormal proliferation, excessive deposition, and abnormal distribution of extracellular matrix (ECM) proteins. The maladaptive process of cardiac fibrosis is complex and often involves multiple mechanisms. With the increasing research on cardiac fibrosis, redox has been recognized as an important part of cardiac remodeling, and an imbalance in redox homeostasis can adversely affect the function and structure of the heart. The metabolism of metal ions is essential for life, and abnormal metabolism of metal ions in cells can impair a variety of biochemical processes, especially redox. However, current research on metal ion metabolism is still very limited. This review comprehensively examines the effects of metal ion (iron, copper, calcium, and zinc) metabolism-mediated redox homeostasis on cardiac fibrosis, outlines possible therapeutic interventions, and addresses ongoing challenges in this rapidly evolving field.

Quercitrin improves cardiac remodeling following myocardial infarction by regulating macrophage polarization and metabolic reprogramming

The death and disability caused by myocardial infarction is a health problem that needs to be addressed worldwide, and poor cardiac repair and fibrosis after myocardial infarction seriously affect patient recovery. Postmyocardial infarction repair by M2 macrophages is of great significance for ventricular remodeling. Quercitrin (Que) is a common flavonoid in fruits and vegetables that has antioxidant, anti-inflammatory, antitumor and other effects, but whether it has a role in the treatment of myocardial infarction is unclear. In this study, we constructed a mouse myocardial infarction model and administered Que. We found through cardiac ultrasound that Que administration improved cardiac ejection fraction and reduced ventricular remodeling. Staining of heart sections and detection of fibrosis marker protein levels revealed that Que administration slowed fibrosis after myocardial infarction. Flow cytometry showed that the proportion of M2 macrophages in the mouse heart was increased and that the expression levels of M2 macrophage markers were increased in the Que-treated group. Finally, we identified by metabolomics that Que reduces glycolysis, increases aerobic phosphorylation, and alters arginine metabolic pathways, polarizing macrophages toward the M2 phenotype. Our research lays the foundation for the future application of Que in myocardial infarction and other cardiovascular diseases.

Neferine Pretreatment Attenuates Isoproterenol-Induced Cardiac Injury Through Modulation of Oxidative Stress, Inflammation, and Apoptosis in Rats

Heart attacks, also known as myocardial infarctions (MIs), are one of the main reasons people die from cardiovascular diseases (CVDs) worldwide. Neferine, an alkaloid derived from Nelumbo nucifera seeds, has garnered interest due to its purported medicinal effects. In the current research, we induced MI in rats using the β-adrenergic agonist isoproterenol to investigate whether neferine can improve cardiac dysfunction. The rats were separated into four groups: control, isoproterenol (ISO), and two treatment groups received neferine at doses of 10 or 20 mg/kg once daily for 28 days. On days 27 and 28, the groups undergoing treatment were administered with an ISO injection. Results showed that pretreatment with neferine strongly protected against changes in lipid profiles and cardiac functional markers in ISO-administered rats. Neferine attenuated histopathologic changes, collagen deposition, and myocardial fibrosis in rats administered ISO. Neferine pretreatment significantly inhibited the oxidative stress, inflammatory, and apoptotic markers in the heart of ISO-injected rats. This was achieved through Nrf2/Keap1/ARE signaling stimulation, TLR4/NF-κB/MAPK-mediated signaling inhibition, and activation of the intrinsic apoptotic pathway. Using CB-Dock-2, researchers determined that neferine has a high binding affinity with protein receptors that are pivotal in several biological processes. In conclusion, the study provides strong evidence that pretreatment with neferine protects rats from ISO-induced heart damage.

Abatacept: A Promising Repurposed Solution for Myocardial Infarction-Induced Inflammation in Rat Models

Myocardial infarction (MI) is irreversible damage to the myocardial tissue caused by prolonged ischemia/hypoxia, subsequently leading to loss of contractile function and myocardial damage. However, after a perilous period, ischemia-reperfusion (IR) itself causes the generation of oxygen free radicals, disturbance in cation homeostasis, depletion of cellular energy stores, and activation of innate and adaptive immune responses. The present study employed Abatacept (ABT), which is an anti-inflammatory drug, originally used as an antirheumatic response agent. To investigate the cardioprotective potential of ABT, primarily, the dose was optimized in a chemically induced model of myocardial necrosis. Thereafter, ABT optimized the dose of 5 mg/kg s.c. OD was investigated for its cardioprotective potential in a surgical model of myocardial IR injury, where animals (n = 30) were randomized into five groups: Sham, IR-C, Telmi10 + IR (Telmisartan, 10 mg/kg oral OD), ABT5 + IR, ABT perse. ABT and telmisartan were administered for 21 days. On the 21st day, animals were subjected to LAD coronary artery occlusion for 60 min, followed by reperfusion for 45 min. Further, the cardioprotective potential was assessed through hemodynamic parameters, oxidant-antioxidant biochemical enzymatic parameters, cardiac injury, inflammatory markers, histopathological analysis, TUNEL assay, and immunohistochemical evaluation, followed by immunoblotting to explore signaling pathways. The statistics were performed by one-way analysis of variance, followed by the Tukey comparison post hoc tests. Noteworthy, 21 days of ABT pretreatment amended the hemodynamic and ventricular functions in the rat models of MI. The cardioprotective potential of ABT is accompanied by inhibiting MAP kinase signaling and modulating Nrf-2/HO-1 proteins downstream signaling cascade. Overall, the present work bolsters the previously known anti-inflammatory role of ABT in MI and contributes a mechanistic insight and application of clinically approved drugs in averting the activation of inflammatory response.

To Repair a Broken Heart: Stem Cells in Ischemic Heart Disease

Despite improvements in contemporary medical and surgical therapies, cardiovascular disease (CVD) remains a significant cause of worldwide morbidity and mortality; more specifically, ischemic heart disease (IHD) may affect individuals as young as 20 years old. Typically managed with guideline-directed medical therapy, interventional or surgical methods, the incurred cardiomyocyte loss is not always completely reversible; however, recent research into various stem cell (SC) populations has highlighted their potential for the treatment and perhaps regeneration of injured cardiac tissue, either directly through cellular replacement or indirectly through local paracrine effects. Different stem cell (SC) types have been employed in studies of infarcted myocardium, both in animal models of myocardial infarction (MI) as well as in clinical studies of MI patients, including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), Muse cells, multipotent stem cells such as bone marrow-derived cells, mesenchymal stem cells (MSCs) and cardiac stem and progenitor cells (CSC/CPCs). These have been delivered as is, in the form of cell therapies, or have been used to generate tissue-engineered (TE) constructs with variable results. In this text, we sought to perform a narrative review of experimental and clinical studies employing various stem cells (SC) for the treatment of infarcted myocardium within the last two decades, with an emphasis on therapies administered through thoracic incision or through percutaneous coronary interventions (PCI), to elucidate possible mechanisms of action and therapeutic effects of such cell therapies when employed in a surgical or interventional manner.

Quantitating myocardial fibrosis using extracellular extravascular volume determined from computed tomography myocardial perfusion imaging

PURPOSE

Both of extracellular extravascular volume (EEV) and extracellular volume fraction (ECV) were proposed to quantify enlargement of myocardial interstitial space due to myocardium loss or fibrosis. The study aimed to investigate the feasibility of using EEV derived from myocardial computed tomography (CT) perfusion imaging (VPCT) and extracellular volume quantification with single-energy subtraction CT (ECV- SECT) for quantifying myocardial fibrosis.

METHODS

In this study, 17 patients with suspected and known coronary artery disease underwent examination using a dual-source CT scanner. The EEV- VPCT was derived from dynamic whole-heart myocardial perfusion imaging, and the ECV_SECT was calculated from late-enhanced images 5 min after bolus contrast injection by subtracting the noncontrast baseline. The late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR) imaging was used as a reference.

RESULTS

In total, 11 patients and 73 segments exhibited positivity for LGE on CMR imaging. These were classified into three groups according to the segments: fibrotic segments (group I, n = 73), nonfibrotic segments in LGE-positive patients (group II, n = 103), and segments in LGE-negative patients (group III, n = 80). ECV- SECT, EEV- VPCT, myocardial blood flow (MBF), and myocardial blood volume (MBV) significantly differed among these groups (all P < 0.05). ECV- SECT was significantly higher and EEV- VPCT, MBF, and MBV were significantly lower in fibrotic myocardial segments than in nonfibrotic ones (all P < 0.01). ECV- SECT and EEV- VPCT independently affected myocardial fibrosis. There was no significant correlation between ECV- SECT and EEV- VPCT. The capability of EEV- VPCT to diagnose myocardial fibrosis was equivalent to that of ECV- SECT (area under the curve: 0.798 vs. 0.806, P = 0.844). ECV- SECT of > 41.2% and EEV- VPCT of < 10.3% indicated myocardial fibrosis.

CONCLUSIONS

EEV- VPCT is actually first-pass distribution volume that can feasibly be used to quantify myocardial fibrosis. Furthermore, the diagnostic efficacy of EEV- VPCT is comparable to that of ECV- SECT.

Marein Ameliorates Myocardial Fibrosis by Inhibiting HIF-1α and TGF-β1/Smad2/3 Signaling Pathway in Isoproterenol-stimulated Mice and TGF-β1-stimulated Cardiac Fibroblasts

BACKGROUND

Myocardial fibrosis significantly contributes to the pathogenesis and progression of heart failure.

OBJECTIVE

We probe into the impact of marein, a key bioactive compound in functional food Coreopsis tinctoria, on isoproterenol-stimulated myocardial fibrotic mice and transforming growth factor β1 (TGF-β1)-stimulated cardiac fibroblasts (CFs).

METHODS

Isoproterenol was administered to the experimental mice via subcutaneous injection, and simultaneous administration of marein (25-100 mg/kg) was performed via oral gavage. CFs were stimulated with TGF- β1 to trigger differentiation and collagen synthesis, followed by treatment with marein at concentrations of 5-20 μM.

RESULTS

Treatment with marein in mice and CFs resulted in a significant reduction in the protein expression levels of α-smooth muscle actin, collagen type I, and collagen type III. Additionally, marein treatment decreased the protein expression levels of TGF-β1, hypoxia-inducible factor-1α (HIF-1α), p-Smad2/3, and Smad2/3. Notably, molecular docking analysis revealed that marein directly targets HIF-1α.

CONCLUSION

Marein might exert a protective function in isoproterenol-stimulated myocardial fibrotic mice and TGF-β1-stimulated CFs, which might result from the reduction of TGF-β1 induced HIF-1α expression, then inhibiting p-Smad2/3 and Smad2/3 expressions.