The effector cells and cellular mediators of immune system involved in cardiac inflammation and fibrosis after myocardial infarction

The cardiac repair after myocardial infarction (MI) involves two phases, namely, inflammatory response and proliferative response. The former is an inflammatory reaction, evoked by different kinds of pro-inflammatory leukocytes and molecules stimulated by myocardial necrosis, while the latter is a repair process, predominated by a magnitude of anti-inflammatory cells and cytokines, as well as fibroblasts. Cardiac remodeling post-MI is dependent on the balance of individualized intensity of the post-MI inflammation and subsequent cardiac fibrosis. During the past 30 years, enormous studies have focused on investigating immune cells and mediators involved in cardiac inflammation and fibrosis, which are two interacting processes of post-MI cardiac repair. These results contribute to revealing the mechanism of adverse cardiac remodeling after MI and alleviating the impairment of cardiac function. In this study, we will broadly discuss the role of immune cell subpopulation and the involved cytokines and chemokines during cardiac repair post-MI, particular in cardiac inflammation and fibrosis.     

Up‐regulated HMGB1 in EAM directly led to collagen deposition by a PKCβ/Erk1/2‐dependent pathway: cardiac fibroblast/myofibroblast might be another source of HMGB1

High mobility group box 1 (HMGB1), an important inflammatory mediator, is actively secreted by immune cells and some non‐immune cells or passively released by necrotic cells. HMGB1 has been implicated in many inflammatory diseases. Our previous published data demonstrated that HMGB1 was up‐regulated in heart tissue or serum in experimental autoimmune myocarditis (EAM); HMGB1 blockade could ameliorate cardiac fibrosis at the last stage of EAM. And yet, until now, no data directly showed that HMGB1 was associated with cardiac fibrosis. Therefore, the aims of the present work were to assess whether (1) up‐regulated HMGB1 could directly lead to cardiac fibrosis in EAM; (2) cardiac fibroblast/myofibroblasts could secrete HMGB1 as another source of high‐level HMGB1 in EAM; and (3) HMGB1 blockade could effectively prevent cardiac fibrosis at the last stage of EAM. Our results clearly demonstrated that HMGB1 could directly lead to cardiac collagen deposition, which was associated with PKCβ/Erk1/2 signalling pathway; furthermore, cardiac fibroblast/myofibroblasts could actively secrete HMGB1 under external stress; and HMGB1 secreted by cardiac fibroblasts/myofibroblasts led to cardiac fibrosis via PKCβ activation by autocrine means; HMGB1 blockade could efficiently ameliorate cardiac fibrosis in EAM mice.     

Retracted: Upregulated microRNA-132 rescues cardiac fibrosis and restores cardiocyte proliferation in dilated cardiomyopathy through the phosphatase and tensin homolog–mediated PI3K/Akt signal transduction pathway

Cardiac fibrosis is known to be present in dilated cardiomyopathy (DCM) and it predicts the occurrence of sudden death and congestive heart failure. The aim of our study is to investigate the expression of microRNA-132 (miR-132) and its effect on cardiocyte proliferation, apoptosis, and cardiac fibrosis by binding to phosphatase and tensin homolog (PTEN) through the phosphateidylinositol 3-kinase (PI3K)/protein kinase (Akt) signal transduction pathway in DCM rats. DCM rat models induced by doxorubicin were established and confirmed by an ultrasonic cardiogram. Epithelial cells were treated with inhibitors, activators, and small interfering RNAs to identify the mechanisms by which miR-132 controls cardiocyte activity and cardiac fibrosis. Angiotensin II (Ang II) and aldosterone (ALD) expressions were detected by an enzyme-linked immunosorbent assay. The relationship between PTEN and miR-132 was verified by a dual-luciferase reporter assay. Cell proliferation and apoptosis were tested by the MTT assay and flow cytometry. PTEN was determined to be the target gene of miR-132. Rat models of DCM exhibited a lower level of miR-132, PI3K, Akt, B-cell lymphoma 2, collagen I, and collagen III, but a higher level of PTEN, Bcl-2–associated X protein, and proliferating cell nuclear antigen as well as inflammatory response (Ang II and ALD), accompanied by declined cardiocyte proliferation and elevated apoptosis and cardiac fibrosis. Upregulated miR-132 or silenced PTEN activated the PI3K/Akt pathway, thus facilitating cardiocyte proliferation and repressing cardiocyte apoptosis and cardiac fibrosis, as well as inflammatory responses. Downregulated miR-132 reversed this tendency. These findings indicate that miR-132 activates the PI3K/Akt pathway by inhibiting PTEN expression, thus facilitating cardiocyte proliferation and inhibiting apoptosis and cardiac fibrosis in DCM rats.     

Inhibition of miR‐21 alleviated cardiac perivascular fibrosis via repressing EndMT in T1DM

In type 1 and type 2 diabetes mellitus, increased cardiac fibrosis, stiffness and associated diastolic dysfunction may be the earliest pathological phenomena in diabetic cardiomyopathy. Endothelial‐mesenchymal transition (EndMT) in endothelia cells (ECs) is a critical cellular phenomenon that increases cardiac fibroblasts (CFs) and cardiac fibrosis in diabetic hearts. The purpose of this paper is to explore the molecular mechanism of miR‐21 regulating EndMT and cardiac perivascular fibrosis in diabetic cardiomyopathy. In vivo, hyperglycaemia up‐regulated the mRNA level of miR‐21, aggravated cardiac dysfunction and collagen deposition. The condition was recovered by inhibition of miR‐21 following with improving cardiac function and decreasing collagen deposition. miR‐21 inhibition decreased cardiac perivascular fibrosis by suppressing EndMT and up‐regulating SMAD7 whereas activating p‐SMAD2 and p‐SMAD3. In vitro, high glucose (HG) up‐regulated miR‐21 and induced EndMT in ECs, which was decreased by inhibition of miR‐21. A highly conserved binding site of NF‐κB located in miR‐21 5′‐UTR was identified. In ECs, SMAD7 is directly regulated by miR‐21. In conclusion, the pathway of NF‐κB/miR‐21/SMAD7 regulated the process of EndMT in T1DM, in diabetic cardiomyopathy, which may be regarded as a potential clinical therapeutic target for cardiac perivascular fibrosis.     

The SGK1 inhibitor EMD638683, prevents Angiotensin II–induced cardiac inflammation and fibrosis by blocking NLRP3 inflammasome activation

Inflammation has emerged as a critical biological process contributing to hypertensive cardiac remodeling. Effective pharmacological treatments targeting the cardiac inflammatory response, however, are still lacking. Prior studies suggested that the serum- and glucocorticoid-inducible kinase (SGK1) plays a key role in inflammation and cardiac remodeling. Recently, a highly selective SGK1 inhibitor, EMD638683, was developed, though whether EMD638683 can prevent hypertension-induced cardiac fibrosis and the mechanisms by which this inhibitor may alter the disease process remain unknown. Using a murine Angiotension II (Ang II) infusion-induced hypertension model we found that EMD638683 treatment inhibited cardiac fibrosis and remodeling, with significant abatement of cardiac inflammation. EMD638683 was shown to suppress Ang II infusion-induced interleukin (IL)-1β release, and substantially reduce nucleotide-binding oligomerization domain-like receptor with pyrin domain 3 (NLRP3) expression and caspase-1 activation in cardiac tissues. In vitro experiments revealed that EMD638683 ameliorated Ang II-stimulated IL-1β secretion in macrophages by blocking NLRP3 inflammasome activation. By reducing IL-1β production in macrophages, the transformation of fibroblasts to myofibroblasts was inhibited. The effects of EMD638683 on cardiac fibrosis were abolished by supplementation with exogenous IL-1β. Administration of the NLRP3 inflammasome inhibitor MCC950 indicated that EMD638683 attenuated Ang II-induced cardiac inflammation and fibrosis by inhibiting the NLRP3 inflammasome/IL-1β secretion axis. These findings indicate that the SGK1 inhibitor EMD638683 can negatively regulate NLRP3 inflammasome activation, and may represent a promising approach to the treatment of hypertensive cardiac damage.     

Senescent cardiac fibroblasts: A key role in cardiac fibrosis

Cardiac fibroblasts are a cell population that controls the homeostasis of the extracellular matrix and orchestrates a damage response to maintain cardiac architecture and performance. Due to these functions, fibroblasts play a central role in cardiac fibrosis development, and there are large differences in matrix protein secretion profiles between fibroblasts from aged versus young animals.Senescence is a multifactorial and complex process that has been associated with inflammatory and fibrotic responses. After damage, transient cellular senescence is usually beneficial, as these cells promote tissue repair. However, the persistent presence of senescent cells within a tissue is linked with fibrosis development and organ dysfunction, leading to aging-related diseases such as cardiovascular pathologies. In the heart, early cardiac fibroblast senescence after myocardial infarction seems to be protective to avoid excessive fibrosis; however, in non-infarcted models of cardiac fibrosis, cardiac fibroblast senescence has been shown to be deleterious. Today, two new classes of drugs, termed senolytics and senostatics, which eliminate senescent cells or modify senescence-associated secretory phenotype, respectively, arise as novel therapeutical strategies to treat aging-related pathologies. However, further studies will be needed to evaluate the extent of the utility of senotherapeutic drugs in cardiac diseases, in which pathological context and temporality of the intervention must be considered.     

微小RNAs在心力衰竭炎症机制中作用的研究进展

微小RNA是一组高度保守的长度约22个核苷酸非编码RNA,通过靶定相应的互补序列导致信使RNA的沉默,下调或者抑制翻译以调节基因和蛋白的表达。心力衰竭进程中存在慢性炎症激活和microRNA的异常表达,其中TLR4通路和NF-κB通路被广泛研究和认同,炎症因子如IL-1、IL-6、TNF-α参与心力衰竭的炎症激活过程,并且可以通过多种通路导致心肌细胞肥大,纤维化及凋亡,炎症因子激活、炎症通路中间因子及疾病进展形成复杂的病理网络,最终导致心肌功能紊乱和减退;microRNA可通过部分结合mRNA靶定部分在转录水平上抑制蛋白合成,参与心力衰竭炎症通路的整个过程,这一调节机制在心肌肥大、心力衰竭等多种心脏疾病中的作用逐渐被阐明。本文旨在总结微小RNAs在心力衰竭炎症机制中作用的研究进展,寻找微小RNA与心力衰竭中炎症激活过程的联系。     

Felodipine reduces cardiac expression of IL-18 and perivascular fibrosis in fructose-fed rats

Metabolic syndrome is associated with accelerated macrovascular and microvascular coronary disease, cardiomyopathy, and elevated inflammatory status. To determine whether metabolic syndrome-associated elevation of the inflammatory cytokine interleukin-18 (IL-18) in serum and cardiac tissue, and its potential sequelae could be attenuated pharmacologically, we studied fructose-fed rats. The fructose-fed rats exhibited increases in systolic blood pressure (SBP), body weight, heart weight, left ventricular weight, and blood insulin. Serum IL-18 levels in these rats were also elevated significantly. These changes were significantly different compared to those in control rats. Perivascular fibrosis around coronary arterioles was evident in the fructose-fed rats, accompanied by a paralleled increase in IL-18 by immunohistochemical analysis and real time polymerase chain reaction. Felodipine attenuated the increased levels in serum IL-18 and cardiac IL-18 mRNA as well as coronary perivascular fibrosis. Thus, augmented IL-18 in serum and cardiac tissue in metabolic syndrome may contribute to the coronary perivascular fibrosis; felodipine administration can attenuate the inflammatory and fibrosis process.     

The role of Hedgehog signaling in fibrogenic liver repair

Repair of adult liver, like many tissues, involves the coordinated response of a number of different cell types. In adult livers, fibroblastic cells, ductular cells, inflammatory cells, and progenitor cells contribute to this process. Our studies demonstrate that the fates of such cells are dictated, at least in part, by Hedgehog, a fetal morphogenic pathway that was once thought to be active mainly during embryogenesis. Studies of injured adult human and rodent livers demonstrate that injury-related activation of the Hedgehog pathway modulates several important aspects of repair, including the growth of hepatic progenitor populations, hepatic accumulation of myofibroblasts, repair-related inflammatory responses, vascular remodeling, liver fibrosis and hepatocarcinogenesis. These findings identify the Hedgehog pathway as a potentially important target for biomarker development and therapeutic manipulation, and emphasize the need for further research to advance knowledge about how this pathway is regulated by and interacts with other signals that regulate adult liver repair.     

Immune regulation of cardiac fibrosis post myocardial infarction

Pathological changes resulting from myocardial infarction (MI) include extracellular matrix alterations of the left ventricle, which can lead to cardiac stiffness and impair systolic and diastolic function. The signals released from necrotic tissue initiate the immune cascade, triggering an extensive inflammatory response followed by reparative fibrosis of the infarct area. Immune cells such as neutrophils, monocytes, macrophages, mast cells, T-cells, and dendritic cells play distinct roles in orchestrating this complex pathological condition, and regulate the balance between pro-fibrotic and anti-fibrotic responses. This review discusses how molecular signals between fibroblasts and immune cells mutually regulate fibrosis post-MI, and outlines the emerging pharmacological targets and therapies for modulating inflammation and cardiac fibrosis associated with MI.     

Calhex231 ameliorates myocardial fibrosis post myocardial infarction in rats through the autophagy‐NLRP3 inflammasome pathway in macrophages

The calcium‐sensing receptor (CaSR) is involved in the pathophysiology of many cardiovascular diseases, including myocardial infarction (MI) and hypertension. The role of Calhex231, a specific inhibitor of CaSR, in myocardial fibrosis following MI is still unclear. Using Wistar rats, we investigated whether Calhex231 ameliorates myocardial fibrosis through the autophagy‐NLRP3 inflammasome pathway in macrophages post myocardial infarction (MI). The rats were randomly divided into sham, MI and MI + Calhex231 groups. Compared with the sham rats, the MI rats consistently developed severe cardiac function, myocardial fibrosis and infiltration of inflammatory cells including macrophages. Moreover, inflammatory pathway including activation of NLRP3 inflammasome, IL‐1β and autophagy was significantly up‐regulated in myocardial tissue, infiltrated cardiac macrophages and peritoneal macrophages of the MI rats. These impacts were reversed by Calhex231. In vitro, studies revealed that calindol and rapamycin exacerbated MI‐induced autophagy and NLRP3 inflammasome activation in peritoneal macrophages. Calhex231 and 3‐Methyladenine (a specific inhibitor of autophagy) attenuated both autophagy and NLRP3 inflammasome activation; however, the caspase‐1 inhibitor Z‐YVAD‐FMK did not. Our study indicated that Calhex231 improved cardiac function and ameliorated myocardial fibrosis post MI, likely via the inhibition of autophagy‐mediated NLRP3 inflammasome activation; this provides a new therapeutic target for ventricular remodelling‐related cardiovascular diseases.     

Attenuation of bleomycin-induced pneumopathy in mice by a caspase inhibitor

Caspases have been implicated in the effector process of apoptosis in several systems including the Fas-Fas ligand pathway. We previously demonstrated that excessive apoptosis of lung epithelial cells and the Fas-Fas ligand pathway were essential in the pathogenesis of bleomycin-induced pneumopathy in mice. Therefore, the purpose of this study was to investigate whether a caspase inhibitor could prevent the development of this model. The expression of caspase-1 and caspase-3 was upregulated on lung epithelial cells, alveolar macrophages, and infiltrating inflammatory cells in this model. We demonstrated that a broad-spectrum caspase inhibitor, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone, decreased the caspase-1- and caspase-3-like activity, the number of apoptotic cells, the pathological grade of lung inflammation and fibrosis, and the hydroxyproline content in lung tissues in this model. We conclude that caspase inhibitors could be a new therapeutic approach against lung injury and pulmonary fibrosis.     

Endothelial S1pr1 regulates pressure overload‐induced cardiac remodelling through AKT‐eNOS pathway

Cardiac vascular microenvironment is crucial for cardiac remodelling during the process of heart failure. Sphingosine 1‐phosphate (S1P) tightly regulates vascular homeostasis via its receptor, S1pr1. We therefore hypothesize that endothelial S1pr1 might be involved in pathological cardiac remodelling. In this study, heart failure was induced by transverse aortic constriction (TAC) operation. S1pr1 expression is significantly increased in microvascular endothelial cells (ECs) of post‐TAC hearts. Endothelial‐specific deletion of S1pr1 significantly aggravated cardiac dysfunction and deteriorated cardiac hypertrophy and fibrosis in myocardium. In vitro experiments demonstrated that S1P/S1pr1 praxis activated AKT/eNOS signalling pathway, leading to more production of nitric oxide (NO), which is an essential cardiac protective factor. Inhibition of AKT/eNOS pathway reversed the inhibitory effect of EC‐S1pr1‐overexpression on angiotensin II (AngII)‐induced cardiomyocyte (CM) hypertrophy, as well as on TGF‐β‐mediated cardiac fibroblast proliferation and transformation towards myofibroblasts. Finally, pharmacological activation of S1pr1 ameliorated TAC‐induced cardiac hypertrophy and fibrosis, leading to an improvement in cardiac function. Together, our results suggest that EC‐S1pr1 might prevent the development of pressure overload‐induced heart failure via AKT/eNOS pathway, and thus pharmacological activation of S1pr1 or EC‐targeting S1pr1‐AKT‐eNOS pathway could provide a future novel therapy to improve cardiac function during heart failure development.     

3,3-Dimethyl-1-butanol attenuates cardiac remodeling in pressure-overload-induced heart failure mice

Trimethylamine N-oxide (TMAO) is closely related to cardiovascular diseases, particularly heart failure (HF). Recent studies shows that 3,3-dimethyl-1-butanol (DMB) can reduce plasma TMAO levels. However, the role of DMB in overload-induced HF is not well understood. In this research study, we explored the effects and the underlying mechanisms of DMB in overload-induced HF. Aortic banding (AB) surgery was performed in C57BL6/J mice to induce HF, and a subset group of mice underwent a sham operation. After surgery, the mice were fed with a normal diet and given water supplemented with or without 1% DMB for 6 weeks. Cardiac function, plasma TMAO level, cardiac hypertrophy and fibrosis, expression of inflammatory, electrophysiological studies and signaling pathway were analyzed at the sixth week after AB surgery. DMB reduced TMAO levels in overload-induced HF mice. Adverse cardiac structural remodeling, such as cardiac hypertrophy, fibrosis and inflammation, was elevated in overload-induced HF mice. Susceptibility to ventricular arrhythmia also significantly increased in overload-induced HF mice. However, these changes were prevented by DMB treatment. DMB attenuated all of these changes by reducing plasma TMAO levels, hence negatively inhibiting the p65 NF-κB signaling pathway and TGF-β1/Smad3 signaling pathway. DMB plays an important role in attenuating the development of cardiac structural remodeling and electrical remodeling in overload-induced HF mice. This may be attributed to the p65 NF-κB signaling pathway and TGF-β1/Smad3 signaling pathway inhibition.     

AMPK and cardiac remodelling

Cardiac remodelling is generally accepted as a critical process in the progression of heart failure. Myocyte hypertrophy,inflammatory responses and cardiac fibrosis are the main pathological changes associated with cardiac remodelling.AMP-activated protein kinase(AMPK) is known as an energy sensor and a regulator of cardiac metabolism under normal and ischaemic conditions. Additionally, AMPK has been shown to play roles in cardiac remodelling extending well beyond metabolic regulation. In this review, we discuss the currently defined roles of AMPK in cardiac remodelling and summarize the effects of AMPK on cardiac hypertrophy, inflammatory responses and fibrosis and the molecular mechanisms underlying these effects. In addition, we discuss some pharmacological activators of AMPK that are promising treatments for cardiac remodelling.     

Characterization of the inflammatory and fibrotic response in a mouse model of cardiac pressure overload

Myocardial fibrosis is an integral component of most cardiac pathologic conditions and contributes to the development of both systolic and diastolic dysfunction. Because of the availability of genetically manipulated animals, mouse models are essential for understanding the mechanisms involved in the pathogenesis of cardiac fibrosis. Accordingly, we characterized the inflammatory and fibrotic response in a mouse model of cardiac pressure overload due to transverse aortic constriction (TAC). Following TAC, mouse hearts exhibited induction of chemokines and proinflammatory cytokines, associated with macrophage, but not neutrophil, infiltration. Induction of inflammatory cytokines was followed by a late upregulation of transforming growth factor (TGF)-β isoforms, activation of the Smad2/3 and Smad1/5 pathways, induction of matricellular proteins, and deposition of collagen. Inflammatory activity decreased after 28 days of TAC; at this timepoint established fibrosis was noted, accompanied by ventricular dilation and systolic dysfunction. Late induction of inhibitory mediators, such as TGF-β, may play an essential role in the transition from inflammation to fibrosis by suppressing inflammatory gene synthesis while inducing matrix deposition. Our findings identify molecular mediators and pathways with a potential role in cardiac fibrosis laying the foundations for studies exploring the pathogenesis of fibrotic cardiac remodeling using genetically targeted mice.     

Ageing related periostin expression increase from cardiac fibroblasts promotes cardiomyocytes senescent

Periostin, as an extracellular matrix (ECM) protein, plays a critical role in myocardial fibrosis and also might be involved in the heart inflammatory process since it is a downstream molecule of IL4 and IL13. Considering the possible important role of periostin in heart aging, this study explored periostin expression pattern in both rat and human, the effect of periostin expression on cardiomyocyte senescent and expression of three cytokines (IL13, IL4 and IL6) in different age groups of human. This study found heart aging is associated with increased expression of periostin from cardiac fibroblasts and serum inflammatory cytokines (IL13 and IL6). Excessive periostin expression contributed to cardiomyocyte senescent, which could be alleviated through blocking the Ang-II-TGF β1-MAPK/ERK pathway. Thus, periostin might play an important role in a vicious circle (aging-fibrosis-inflammation-aging) of heart through promoting myocardial fibrosis and cardiomyocyte senescent simultaneously. It is a potential aging marker that could be directly measured in serum.     

miR-222 inhibits cardiac fibrosis in diabetic mice heart via regulating Wnt/β-catenin-mediated endothelium to mesenchymal transition

miR-222 participates in many cardiovascular diseases, but its effect on cardiac remodeling induced by diabetes is unclear. This study evaluated the functional role of miR-222 in cardiac fibrosis in diabetic mice. Streptozotocin (STZ) was used to establish a type 1 diabetic mouse model. After 10 weeks of STZ injection, mice were intravenously injected with Ad-miR-222 to induce the overexpression of miR-222. miR-222 overexpression reduced cardiac fibrosis and improved cardiac function in diabetic mice. Mechanistically, miR-222 inhibited the endothelium to mesenchymal transition (EndMT) in diabetic mouse hearts. Mouse heart fibroblasts and endothelial cells were isolated and cultured with high glucose (HG). An miR-222 mimic did not affect HG-induced fibroblast activation and function but did suppress the HG-induced EndMT process. The antagonism of miR-222 by antagomir inhibited HG-induced EndMT. miR-222 regulated the promoter region of β-catenin, thus negatively regulating the Wnt/β-catenin pathway, which was confirmed by β-catenin siRNA. Taken together, our results indicated that miR-222 inhibited cardiac fibrosis in diabetic mice via negatively regulating Wnt/β-catenin-mediated EndMT.     

A fatty-acid synthesis mechanism specialized for parasitism

Most cells use either a type I or type II synthase to make fatty acids. Trypanosoma brucei, the sleeping sickness parasite, provides the first example of a third mechanism for this process. Trypanosomes use microsomal elongases to synthesize fatty acids de novo, whereas other cells use elongases to make long-chain fatty acids even longer. The modular nature of the pathway allows synthesis of different fatty-acid end products, which have important roles in trypanosome biology. Indeed, this newly discovered mechanism seems ideally suited for the parasitic lifestyle.