Targeting Chondroitin Sulfate Glycosaminoglycans to Treat Cardiac Fibrosis in Pathological Remodeling

Differential expression profiles and bioinformatics analysis of tRNA-derived small RNAs in epicardial fat of patients with atrial fibrillation

The exact processes underlying atrial fibrillation (AF) are still unclear. It has been suggested that epicardial adipose tissue (EAT) may contribute to arrhythmias and can release various bioactive molecules, including exosomes containing tRNA-derived small RNAs (tsRNAs). Numerous studies have indicated that these tsRNAs can significantly affect key cellular functions. However, there is currently no research investigating the relationship between tsRNAs from EAT and AF. In order to explore the regulatory mechanisms of tsRNAs from EAT associated with AF, we conducted RNA-sequencing analysis on EAT samples collected from 6 AF patients and 6 control subjects with sinus rhythm. Our analysis revealed an upregulation of 146 tsRNAs and a downregulation of 126 tsRNAs in AF. Furthermore, we randomly selected four tsRNAs (tRF-SeC-TCA-001, tiRNA-Gly-CCC-003, tRF-Gly-GCC-002, and tRF-Tyr-GTA-007) for validation using quantitative reverse transcription-polymerase chain reaction. Following this, bioinformatic analyses revealed that the target genes of these tsRNAs were prominently involved in the regulation of cell adhesion and various cellular processes mediated by plasma membrane adhesion molecules. Additionally, based on KEGG analysis, it was suggested that the majority of these target genes might contribute to the pathogenesis of AF through processes such as glycosaminoglycan biosynthesis, AMP-activated protein kinase activity, and the insulin signaling pathway. Our results elucidate changes in the expression profiles of tsRNAs within EAT samples obtained from AF patients, and they forecast potential target genes and interactions between tsRNAs and mRNA within EAT that could contribute to the pathogenesis of AF.

Biomaterials targeting the microenvironment for spinal cord injury repair: progression and perspectives

Spinal cord injury (SCI) disrupts nerve pathways and affects sensory, motor, and autonomic function. There is currently no effective treatment for SCI. SCI occurs within three temporal periods: acute, subacute, and chronic. In each period there are different alterations in the cells, inflammatory factors, and signaling pathways within the spinal cord. Many biomaterials have been investigated in the treatment of SCI, including hydrogels and fiber scaffolds, and some progress has been made in the treatment of SCI using multiple materials. However, there are limitations when using individual biomaterials in SCI treatment, and these limitations can be significantly improved by combining treatments with stem cells. In order to better understand SCI and to investigate new strategies for its treatment, several combination therapies that include materials combined with cells, drugs, cytokines, etc. are summarized in the current review.

Chondroitin polymerizing factor promotes development and progression of colorectal cancer via facilitating transcription of VEGFB

Colorectal cancer (CRC) is a highly prevalent malignancy affecting the digestive system on a global scale. This study aimed to explore the previously unexplored role of CHPF in the progression of CRC. Our results revealed a significant upregulation of CHPF expression in CRC tumour tissues compared to normal tissues, with its levels correlating with tumour malignancy. In vitro experiments using CRC cell lines demonstrated that inhibiting CHPF expression suppressed cell proliferation, colony formation and cell migration, while promoting apoptosis. Conversely, overexpressing CHPF had the opposite effect. Additionally, our xenograft models in mice confirmed the inhibitory impact of CHPF knockdown on CRC progression using various cell models. Mechanistic investigations unveiled that CHPF may enhance VEGFB expression through E2F1-mediated transcription. Functionally, suppressing VEGFB expression successfully mitigated the oncogenic effects induced by CHPF overexpression. Collectively, these findings suggest that CHPF may act as a tumour promoter in CRC, operating in a VEGFB-dependent manner and could be a potential target for therapeutic interventions in CRC treatment.

SARS-CoV-2 spike protein-ACE2 interaction increases carbohydrate sulfotransferases and reduces N-acetylgalactosamine-4-sulfatase by p38 MAPK

Immunostaining in lungs of patients who died with COVID-19 infection showed increased intensity and distribution of chondroitin sulfate and decline in N-acetylgalactostamine-4-sulfatase (Arylsulfatase B; ARSB). To explain these findings, human small airway epithelial cells were exposed to the SARS-CoV-2 spike protein receptor binding domain (SPRBD) and transcriptional mechanisms were investigated. Phospho-p38 MAPK and phospho-SMAD3 increased following exposure to the SPRBD, and their inhibition suppressed the promoter activation of the carbohydrate sulfotransferases CHST15 and CHST11, which contributed to chondroitin sulfate biosynthesis. Decline in ARSB was mediated by phospho-38 MAPK-induced N-terminal Rb phosphorylation and an associated increase in Rb-E2F1 binding and decline in E2F1 binding to the ARSB promoter. The increases in chondroitin sulfotransferases were inhibited when treated with phospho-p38-MAPK inhibitors, SMAD3 (SIS3) inhibitors, as well as antihistamine desloratadine and antibiotic monensin. In the mouse model of carrageenan-induced systemic inflammation, increases in phospho-p38 MAPK and expression of CHST15 and CHST11 and declines in DNA-E2F binding and ARSB expression occurred in the lung, similar to the observed effects in this SPRBD model of COVID-19 infection. Since accumulation of chondroitin sulfates is associated with fibrotic lung conditions and diffuse alveolar damage, increased attention to p38-MAPK inhibition may be beneficial in ameliorating Covid-19 infections.

Cardiac Molecular Analysis Reveals Aging-Associated Metabolic Alterations Promoting Glycosaminoglycans Accumulation Via Hexosamine Biosynthetic Pathway

Age is a prominent risk factor for cardiometabolic disease, and often leads to heart structural and functional changes. However, precise molecular mechanisms underlying cardiac remodeling and dysfunction resulting from physiological aging per se remain elusive. Understanding these mechanisms requires biological models with optimal translation to humans. Previous research demonstrated that baboons undergo age-related reduction in ejection fraction and increased heart sphericity, mirroring changes observed in humans. The goal of this study was to identify early cardiac molecular alterations that precede functional adaptations, shedding light on the regulation of age-associated changes. We performed unbiased transcriptomics of left ventricle (LV) samples from female baboons aged 7.5-22.1 years (human equivalent ~30-88 years). Weighted-gene correlation network and pathway enrichment analyses were performed to identify potential age-associated mechanisms in LV, with histological validation. Myocardial modules of transcripts negatively associated with age were primarily enriched for cardiac metabolism, including oxidative phosphorylation, tricarboxylic acid cycle, glycolysis, and fatty-acid β-oxidation. Transcripts positively correlated with age suggest upregulation of glucose uptake, pentose phosphate pathway, and hexosamine biosynthetic pathway (HBP), indicating a metabolic shift towards glucose-dependent anabolic pathways. Upregulation of HBP commonly results in increased glycosaminoglycan precursor synthesis. Transcripts involved in glycosaminoglycan synthesis, modification, and intermediate metabolism were also upregulated in older animals, while glycosaminoglycan degradation transcripts were downregulated with age. These alterations would promote glycosaminoglycan accumulation, which was verified histologically. Upregulation of extracellular matrix (ECM)-induced signaling pathways temporally coincided with glycosaminoglycan accumulation. We found a subsequent upregulation of cardiac hypertrophy-related pathways and an increase in cardiomyocyte width. Overall, our findings revealed a transcriptional shift in metabolism from catabolic to anabolic pathways that leads to ECM glycosaminoglycan accumulation through HBP prior to upregulation of transcripts of cardiac hypertrophy-related pathways. This study illuminates cellular mechanisms that precede development of cardiac hypertrophy, providing novel potential targets to remediate age-related cardiac diseases.

Function and mechanism of MCM8 in the development and progression of colorectal cancer

Colorectal cancer (CRC) has become a global health problem which has almost highest morbidity and mortality in all types of cancers. This study aimed to uncover the biological functions and underlying mechanism of MCM8 in the development and progression of CRC. The expression level of MCM8 was found to be upregulated in CRC tissues and significantly associated with tumor grade and patients' survival. Knocking down MCM8 expression in CRC cells could restrain cell growth and cell motility while promoting cell apoptosis in vitro, as well as inhibit tumor growth in xenograft mice model. Based on the RNA screening performing on CRC cells with or without MCM8 knockdown and the following IPA analysis, CHSY1 was identified as a potential target of MCM8 in CRC, whose expression was also found to be higher in tumor tissues than in normal tissues. Moreover, it was demonstrated that MCM8 may regulate the expression of CHSY1 through affecting its NEDD4-mediated ubiquitination, both of which synergistically execute tumor promotion effects on CRC. In conclusion, the outcomes of our study showed the first evidence that MCM8 act as a tumor promotor in CRC, and may be a promising therapeutic target of CRC treatment.

Torpor-responsive microRNAs in the heart of the Monito del monte, Dromiciops gliroides

The marsupial Monito del monte (Dromiciops gliroides) utilizes both daily and seasonal bouts of torpor to preserve energy and prolong survival during periods of cold and unpredictable food availability. Torpor involves changes in cellular metabolism, including specific changes to gene expression that is coordinated in part, by the posttranscriptional gene silencing activity of microRNAs (miRNA). Previously, differential miRNA expression has been identified in D. gliroides liver and skeletal muscle; however, miRNAs in the heart of Monito del monte remained unstudied. In this study, the expression of 82 miRNAs was assessed in the hearts of active and torpid D. gliroides, finding that 14 were significantly differentially expressed during torpor. These 14 miRNAs were then used in bioinformatic analyses to identify Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways that were predicted to be most affected by these differentially expressed miRNAs. Overexpressed miRNAs were predicted to primarily regulate glycosaminoglycan biosynthesis, along with various signaling pathways such as Phosphoinositide-3-kinase/protein kinase B and transforming growth factor-β. Similarly, signaling pathways including phosphatidylinositol and Hippo were predicted to be regulated by the underexpression of miRNAs during torpor. Together, these results suggest potential molecular adaptations that protect against irreversible tissue damage and enable continued cardiac and vascular function despite hypothermia and limited organ perfusion during torpor.

Reproducing extracellular matrix adverse remodelling of non-ST myocardial infarction in a large animal model

The rising incidence of non-ST-segment elevation myocardial infarction (NSTEMI) and associated long-term high mortality constitutes an urgent clinical issue. Unfortunately, the study of possible interventions to treat this pathology lacks a reproducible pre-clinical model. Indeed, currently adopted small and large animal models of MI mimic only full-thickness, ST-segment-elevation (STEMI) infarcts, and hence cater only for an investigation into therapeutics and interventions directed at this subset of MI. Thus, we develop an ovine model of NSTEMI by ligating the myocardial muscle at precise intervals parallel to the left anterior descending coronary artery. Upon histological and functional investigation to validate the proposed model and comparison with STEMI full ligation model, RNA-seq and proteomics show the distinctive features of post-NSTEMI tissue remodelling. Transcriptome and proteome-derived pathway analyses at acute (7 days) and late (28 days) post-NSTEMI pinpoint specific alterations in cardiac post-ischaemic extracellular matrix. Together with the rise of well-known markers of inflammation and fibrosis, NSTEMI ischaemic regions show distinctive patterns of complex galactosylated and sialylated N-glycans in cellular membranes and extracellular matrix. Identifying such changes in molecular moieties accessible to infusible and intra-myocardial injectable drugs sheds light on developing targeted pharmacological solutions to contrast adverse fibrotic remodelling.

Current Perspectives on Nucleus Pulposus Fibrosis in Disc Degeneration and Repair

A growing body of evidence in humans and animal models indicates an association between intervertebral disc degeneration (IDD) and increased fibrotic elements in the nucleus pulposus (NP). These include enhanced matrix turnover along with the abnormal deposition of collagens and other fibrous matrices, the emergence of fibrosis effector cells, such as macrophages and active fibroblasts, and the upregulation of the fibroinflammatory factors TGF-β1 and IL-1/-13. Studies have suggested a role for NP cells in fibroblastic differentiation through the TGF-βR1-Smad2/3 pathway, inflammatory activation and mechanosensing machineries. Moreover, NP fibrosis is linked to abnormal MMP activity, consistent with the role of matrix proteases in regulating tissue fibrosis. MMP-2 and MMP-12 are the two main profibrogenic markers of myofibroblastic NP cells. This review revisits studies in the literature relevant to NP fibrosis in an attempt to stratify its biochemical features and the molecular identity of fibroblastic cells in the context of IDD. Given the role of fibrosis in tissue healing and diseases, the perspective may provide new insights into the pathomechanism of IDD and its management.

PTEN inhibitor attenuates cardiac fibrosis by regulating the M2 macrophage phenotype via the PI3K/AKT/TGF-β/Smad 2/3 signaling pathway

Cardiac fibrosis is a key feature of hypertensive cardiac remodeling. In response to microenvironmental stimuli, phenotypic and functional changes in macrophages are considered important determinants of cardiac fibrosis attenuation. VO-OHpic, a phosphatase and tension homolog of chromosome 10 (PTEN) inhibitor, has been demonstrated to be cardioprotective in cardiac remodeling. However, whether VO-OHpic can improve cardiac fibrosis and macrophage polarization remains elusive. The interaction between VO-OHpic and the macrophage phenotype to attenuate cardiac fibrosis was studied in both spontaneously hypertensive rats in vivo and an Ang II-induced hypertension model in vitro. In vitro experiments showed that VO-OHpic promoted M2 macrophage polarization and markedly inhibited proinflammatory M1 macrophages, while VO-OHpic treatment of protein kinase B (AKT)-knockdown/LY294002 (a PI3K inhibitor) macrophages exerted a reduced effect. In a coculture system, culturing cardiac fibroblasts with VO-OHpic-treated macrophages led to significant suppression of proliferation, fibrotic marker expression, and transforming growth factor (TGF)-β and Smad 2/3 protein expression. Taken together, VO-OHpic mediated a fibro-protective effect and increased M2 macrophage polarization via the phosphatidylinositol 3-kinase (PI3K)/AKT/TGF-β/Smad2/3 pathway.

ChGn-2 Plays a Cardioprotective Role in Heart Failure Caused by Acute Pressure Overload

Background Cardiac extracellular matrix is critically involved in cardiac homeostasis, and accumulation of chondroitin sulfate glycosaminoglycans (CS-GAGs) was previously shown to exacerbate heart failure by augmenting inflammation and fibrosis at the chronic phase. However, the mechanism by which CS-GAGs affect cardiac functions remains unclear, especially at the acute phase. Methods and Results We explored a role of CS-GAG in heart failure using mice with target deletion of ChGn-2 (chondroitin sulfate N-acetylgalactosaminyltransferase-2) that elongates CS chains of glycosaminoglycans. Heart failure was induced by transverse aortic constriction in mice. The role of CS-GAG derived from cardiac fibroblasts in cardiomyocyte death was analyzed. Cardiac fibroblasts were subjected to cyclic mechanical stretch that mimics increased workload in the heart. Significant CS-GAGs accumulation was detected in the heart of wild-type mice after transverse aortic constriction, which was substantially reduced in ChGn-2^-/- mice. Loss of ChGn-2 deteriorated the cardiac dysfunction caused by pressure overload, accompanied by augmented cardiac hypertrophy and increased cardiomyocyte apoptosis. Cyclic mechanical stretch increased ChGn-2 expression and enhanced glycosaminoglycan production in cardiac fibroblasts. Conditioned medium derived from the stretched cardiac fibroblasts showed cardioprotective effects, which was abolished by CS-GAGs degradation. We found that CS-GAGs elicits cardioprotective effects via dual pathway; direct pathway through interaction with CD44, and indirect pathway through binding to and activating insulin-like growth factor-1. Conclusions Our data revealed the cardioprotective effects of CS-GAGs; therefore, CS-GAGs may play biphasic role in the development of heart failure; cardioprotective role at acute phase despite its possible unfavorable role in the advanced phase.

The heart under pressure: immune cells in fibrotic remodeling

The complex syndrome of heart failure (HF) is characterized by increased left ventricular pressures. Cardiomyocytes increase in size, cardiac fibroblasts transform and make extracellular matrix, and leukocytes infiltrate the cardiac tissue and alter cardiomyocyte and cardiac fibroblast function. Here we review recent advances in our understanding of the cellular composition of the heart during homeostasis and in response to cardiac pressure overload, with an emphasis on immune cell communication with cardiac fibroblasts and its consequences in cardiac remodeling.

Extracellular Matrix in Heart Failure: Role of ADAMTS5 in Proteoglycan Remodeling

BACKGROUND

Remodeling of the extracellular matrix (ECM) is a hallmark of heart failure (HF). Our previous analysis of the secretome of murine cardiac fibroblasts returned ADAMTS5 (a disintegrin and metalloproteinase with thrombospondin motifs 5) as one of the most abundant proteases. ADAMTS5 cleaves chondroitin sulfate proteoglycans such as versican. The contribution of ADAMTS5 and its substrate versican to HF is unknown.

METHODS

Versican remodeling was assessed in mice lacking the catalytic domain of ADAMTS5 (Adamts5ΔCat). Proteomics was applied to study ECM remodeling in left ventricular samples from patients with HF, with a particular focus on the effects of common medications used for the treatment of HF.

RESULTS

Versican and versikine, an ADAMTS-specific versican cleavage product, accumulated in patients with ischemic HF. Versikine was also elevated in a porcine model of cardiac ischemia/reperfusion injury and in murine hearts after angiotensin II infusion. In Adamts5ΔCat mice, angiotensin II infusion resulted in an aggravated versican build-up and hyaluronic acid disarrangement, accompanied by reduced levels of integrin β1, filamin A, and connexin 43. Echocardiographic assessment of Adamts5ΔCat mice revealed a reduced ejection fraction and an impaired global longitudinal strain on angiotensin II infusion. Cardiac hypertrophy and collagen deposition were similar to littermate controls. In a proteomics analysis of a larger cohort of cardiac explants from patients with ischemic HF (n=65), the use of β-blockers was associated with a reduction in ECM deposition, with versican being among the most pronounced changes. Subsequent experiments in cardiac fibroblasts confirmed that β1-adrenergic receptor stimulation increased versican expression. Despite similar clinical characteristics, patients with HF treated with β-blockers had a distinct cardiac ECM profile.

CONCLUSIONS

Our results in animal models and patients suggest that ADAMTS proteases are critical for versican degradation in the heart and that versican accumulation is associated with impaired cardiac function. A comprehensive characterization of the cardiac ECM in patients with ischemic HF revealed that β-blockers may have a previously unrecognized beneficial effect on cardiac chondroitin sulfate proteoglycan content.

Increase in Chondroitin Sulfate and Decline in Arylsulfatase B May Contribute to Pathophysiology of COVID-19 Respiratory Failure

INTRODUCTION

The potential role of accumulation of chondroitin sulfates (CSs) in the pathobiology of COVID-19 has not been examined. Accumulation may occur by increased synthesis or by decline in activity of the enzyme arylsulfatase B (ARSB; N-acetylgalactosamine-4-sulfatase) which requires oxygen for activity.

METHODS

Immunostaining of lung tissue from 28 patients who died due to COVID-19 infection was performed for CS, ARSB, and carbohydrate sulfotransferase (CHST)15. Measurements of mRNA expression of CHST15 and CHST11, sulfotransferase activity, and total sulfated glycosaminoglycans (GAGs) were determined in human vascular smooth muscle cells following angiotensin (Ang) II treatment.

RESULTS

CS immunostaining showed increase in intensity and distribution, and immunostaining of ARSB was diminished in COVID-19 compared to normal lung tissue. CHST15 immunostaining was prominent in vascular smooth muscle cells associated with diffuse alveolar damage due to COVID-19 or other causes. Expression of CHST15 and CHST11 which are required for synthesis of CSE and chondroitin 4-sulfate, total sulfated GAGs, and sulfotransferase activity was significantly increased following AngII exposure in vascular smooth muscle cells. Expression of Interleukin-6 (IL-6), a mediator of cytokine storm in COVID-19, was inversely associated with ARSB expression.

DISCUSSION/CONCLUSION

Decline in ARSB and resulting increases in CS may contribute to the pathobiology of COVID-19, as IL-6 does. Increased expression of CHSTs following activation of Ang-converting enzyme 2 may lead to buildup of CSs.

Epicardial and endothelial cell activation concurs with extracellular matrix remodeling in atrial fibrillation

BACKGROUND

Improved understanding of the interconnectedness of structural remodeling processes in atrial fibrillation (AF) in patients could identify targets for future therapies.

METHODS

We present transcriptome sequencing of atrial tissues of patients without AF, with paroxysmal AF, and persistent AF (total n = 64). RNA expression levels were validated in the same and an independent cohort with qPCR. Biological processes were assessed with histological and immunohistochemical analyses.

RESULTS

In AF patients, epicardial cell gene expression decreased, contrasting with an upregulation of epithelial-to-mesenchymal transition (EMT) and mesenchymal cell gene expression. Immunohistochemistry demonstrated thickening of the epicardium and an increased proportion of (myo)fibroblast-like cells in the myocardium, supporting enhanced EMT in AF. We furthermore report an upregulation of endothelial cell proliferation, angiogenesis, and endothelial signaling. EMT and endothelial cell proliferation concurred with increased interstitial (myo)fibroblast-like cells and extracellular matrix gene expression including enhanced tenascin-C, thrombospondins, biglycan, and versican. Morphological analyses discovered increased and redistributed glycosaminoglycans and collagens in the atria of AF patients. Signaling pathways, including cell-matrix interactions, PI3K-AKT, and Notch signaling that could regulate mesenchymal cell activation, were upregulated.

CONCLUSION

Our results suggest that EMT and endothelial cell proliferation work in concert and characterize the (myo)fibroblast recruitment and ECM remodeling of AF. These processes could guide future research toward the discovery of targets for AF therapy.

CHSY1 is upregulated and acts as tumor promotor in gastric cancer through regulating cell proliferation, apoptosis, and migration

Gastric cancer is one of the most frequently diagnosed malignant tumors, with rapid progression and poor prognosis. The role of chondroitin sulfate synthase 1 (CHSY1) in the development and progression of gastric cancer was explored and clarified in this study. The immunohistochemistry analysis of clinical tissue samples as well as data mining of public database showed that CHSY1 was significantly upregulated in gastric cancer and associated with more advanced tumor stage and poorer prognosis. In vitro loss-of-function experiments demonstrated the inhibited cell proliferation, colony formation, cell migration, as well as the promoted cell apoptosis by CHSY1 knockdown. Moreover, recovery of CHSY1 expression could attenuate the regulatory effects induced by CHSY1 knockdown. Correspondingly, gastric cancer cells with CHSY1 knockdown showed reduced tumorigenicity and slower tumor growth in vivo. In conclusion, this study identified CHSY1 as a tumor promotor in gastric cancer, which may be utilized as a novel indicator of patients' prognosis and therapeutic target for developing more effective drug for GC treatment.

Inhibition of HSP90 S-nitrosylation Alleviates Cardiac Fibrosis via TGFβ/SMAD3 Signaling Pathway

BACKGROUND AND PURPOSE

Effective anti-fibrotic therapeutic solutions are unavailable so far. The heat shock protein 90 (HSP90) exerts deleterious effects in some fibrotic diseases. S-nitrosylation (SNO) of HSP90 affects its own function, however, little is known about its role in pathological stress. Here, we investigated the effect of SNO-HSP90 on cardiac fibrosis.

EXPERIMENTAL APPROACH

SNO-HSP90 level was measured by biotin-switch. SNO sites were identified through mass spectrometry. S-nitrosylation site-mutated plasmids or adeno-associated virus, gene deletion and pharmacological antagonists were used to identify the contribution of SNO-HSP90 in myocardial fibrosis.

KEY RESULTS

SNO-HSP90 level was positively correlated with fibrosis marker expression in hearts from patients and significantly higher in fibrotic hearts from spontaneously hypertensive rats and mice subjected to transverse aortic constriction, as well as in angiotensin II- or isoproterenol-treated neonatal rat cardiac fibroblasts. S-nitrosylated site of HSP90 at cysteine 589 was identified. Inhibition of SNO-HSP90 by Cys589 mutation reduced fibrosis in angiotensin II- or isoproterenol-treated cardiac fibroblasts. Administration of recombinant adeno-associated virus of Cys589 mutation improved heart function and alleviated fibrosis in transverse aortic constriction mice. Mechanismly, SNO-HSP90 stimulated transforming growth factor-β type II receptor (TGFβ RII) binding to HSP90 in response to fibrotic stimuli, subsequently increased phosphorylation and nuclear translocation of SMAD3. Additionally, inducible nitric oxide synthase (iNOS) deficiency or iNOS inhibitor, 1400W, reduced SNO-HSP90 level and the activation of TGFβ/SMAD3 signaling pathway.

CONCLUSIONS AND IMPLICATIONS

We demonstrate that genetic or pharmacological inhibition of SNO-HSP90 mitigates fibrosis through blocking TGFβ/SMAD3 signaling pathway, providing a potential therapy for cardiac remodeling.

Blocking the death checkpoint protein TRAIL improves cardiac function after myocardial infarction in monkeys, pigs, and rats

Myocardial infarction (MI) is a leading cause of death worldwide for which there is no cure. Although cardiac cell death is a well-recognized pathological mechanism of MI, therapeutic blockade of cell death to treat MI is not straightforward. Death receptor 5 (DR5) and its ligand TRAIL [tumor necrosis factor (TNF)-related apoptosis-inducing ligand] are up-regulated in MI, but their roles in pathological remodeling are unknown. Here, we report that blocking TRAIL with a soluble DR5 immunoglobulin fusion protein diminished MI by preventing cardiac cell death and inflammation in rats, pigs, and monkeys. Mechanistically, TRAIL induced the death of cardiomyocytes and recruited and activated leukocytes, directly and indirectly causing cardiac injury. Transcriptome profiling revealed increased expression of inflammatory cytokines in infarcted heart tissue, which was markedly reduced by TRAIL blockade. Together, our findings indicate that TRAIL mediates MI directly by targeting cardiomyocytes and indirectly by affecting myeloid cells, supporting TRAIL blockade as a potential therapeutic strategy for treating MI.

Multiplexed imaging mass spectrometry of the extracellular matrix using serial enzyme digests from formalin-fixed paraffin-embedded tissue sections

We report a multiplexed imaging mass spectrometry method which spatially localizes and selectively accesses the extracellular matrix on formalin-fixed paraffin-embedded tissue sections. The extracellular matrix (ECM) consists of (1) fibrous proteins, post-translationally modified (PTM) via N- and O-linked glycosylation, as well as hydroxylation on prolines and lysines, and (2) glycosaminoglycan-decorated proteoglycans. Accessing all these components poses a unique analytical challenge. Conventional peptide analysis via trypsin inefficiently captures ECM peptides due to their low abundance, intra- and intermolecular cross-linking, and PTMs. In previous studies, we have developed matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS) techniques to capture collagen peptides via collagenase type III digestion, both alone and after N-glycan removal via PNGaseF digest. However, in fibrotic tissues, the buildup of ECM components other than collagen-type proteins, including elastin and glycosaminoglycans, limits efficacy of any single enzyme to access the complex ECM. Here, we have developed a novel serial enzyme strategy to define the extracellular matrix, including PTMs, from a single tissue section for MALDI-IMS applications. Graphical Abstract.

Identification of chondroitin polymerizing factor (CHPF) as tumor promotor in cholangiocarcinoma through regulating cell proliferation, cell apoptosis and cell migration

Cholangiocarcinoma (CCA) is a variety of biliary epithelial tumors involving intrahepatic, perihilar and distal bile duct. It is the most common malignant bile duct tumor in the liver and the second most common primary liver cancer, whose molecular mechanism not fully understood. Specifically, the relationship between CCA and chondroitin polymerizing factor (CHPF) is still not clear. In this study, detection of clinical specimens was performed to preliminarily study the role of CHPF in CCA. CCA cells with CHPF knockdown were constructed for in vitro study, which was also used in the construction of mice xenograft model for investigating the role of CHPF in the development of CCA. The results demonstrated that CHPF was significantly upregulated in CCA tissues compared with normal tissues. High expression of CHPF was correlated with more advanced tumor grade. Moreover, knockdown of CHPF significantly inhibited cell proliferation, cell migration, promoted cell apoptosis and arrest cell cycle in G2 phase in vitro, as well as suppressed tumor growth in vivo. In conclusion, CHPF was identified as a tumor promotor in the development and metastasis of CCA, which may provide a novel therapeutic target for the targeted therapy against CCA.

Topical Application of Peptide-Chondroitin Sulfate Nanoparticles Allows Efficient Photoprotection in Skin

In this article, we describe a method of delivery of chondroitin sulfate to skin as nanoparticles and demonstrate its anti-inflammatory and antioxidant role using UV irradiation as a model condition. These nanoparticles, formed through electrostatic interactions of chondroitin sulfate with a skin-penetrating peptide, were found to be homogenous with positive surface charges and stable at physiological and acidic pH under certain conditions. They were able to enter into the human keratinocyte cell line (HaCaT), artificial skin membrane (mimicking the human skin), and mouse skin tissue unlike free chondroitin sulfate. The preapplication of nanoparticles also exhibited reduced levels of oxidative stress, cyclobutane pyrimidine dimer formation, TNF-α, and so on in UV-B-irradiated HaCaT cells. In an acute UV-B irradiation mouse model, their topical application resulted in reduced epidermal thickness and sunburn cells, unlike in the case of free chondroitin sulfate. Thus, a completely noninvasive method was used to deliver a bio-macromolecule into the skin without using injections or abrasive procedures.

Higenamine Improves Cardiac and Renal Fibrosis in Rats With Cardiorenal Syndrome via ASK1 Signaling Pathway

The pathogenesis of cardiorenal syndrome (CRS) is very complex, and currently there is no effective treatment for CRS. Higenamine (HI) has been shown to improve cardiac function in rats with heart failure. However, the role of higenamine in CRS remains unknown. Here, in vitro, higenamine treatment markedly reduced neonatal rat cardiac fibroblast collagen synthesis and inhibited neonatal rat cardiac myocyte hypertrophy. In our study, a rat model of type 2 CRS was induced by left anterior descending coronary artery ligation combined with 5/6 subtotal nephrectomy (STNx). Higenamine treatment decreased serum creatinine (Scr), blood urea nitrogen, and brain natriuretic peptide levels and was capable of improving left ventricular remodeling and systolic function in CRS rats, accompanied with decreased expression of transforming growth factor-β1 (TGF-β1), α-smooth muscle actin (α-SMA) and collagen I (Col1A1). Moreover, higenamine significantly inhibited the protein expression of phosphorylated apoptosis signal-regulated kinase 1 (p-ASK1) and downstream mitogen-activated protein kinases (MAPK) (ERK, P38)/NF-κB in cardiorenal tissues of CRS rats and neonatal rat cardiac fibroblast/neonatal rat cardiac myocyte cells. Our study demonstrated that higenamine improved cardiorenal function in CRS rats and attenuated heart and kidney fibrosis possibly via targeting ASK1/MAPK (ERK, P38)/NF-κB signaling pathway. This finding extends our knowledge on the role of higenamine in cardiorenal fibrosis, providing a potential target to prevent the progression of CRS.

Cardiac fibrosis

Myocardial fibrosis, the expansion of the cardiac interstitium through deposition of extracellular matrix proteins, is a common pathophysiologic companion of many different myocardial conditions. Fibrosis may reflect activation of reparative or maladaptive processes. Activated fibroblasts and myofibroblasts are the central cellular effectors in cardiac fibrosis, serving as the main source of matrix proteins. Immune cells, vascular cells and cardiomyocytes may also acquire a fibrogenic phenotype under conditions of stress, activating fibroblast populations. Fibrogenic growth factors (such as transforming growth factor-β and platelet-derived growth factors), cytokines [including tumour necrosis factor-α, interleukin (IL)-1, IL-6, IL-10, and IL-4], and neurohumoral pathways trigger fibrogenic signalling cascades through binding to surface receptors, and activation of downstream signalling cascades. In addition, matricellular macromolecules are deposited in the remodelling myocardium and regulate matrix assembly, while modulating signal transduction cascades and protease or growth factor activity. Cardiac fibroblasts can also sense mechanical stress through mechanosensitive receptors, ion channels and integrins, activating intracellular fibrogenic cascades that contribute to fibrosis in response to pressure overload. Although subpopulations of fibroblast-like cells may exert important protective actions in both reparative and interstitial/perivascular fibrosis, ultimately fibrotic changes perturb systolic and diastolic function, and may play an important role in the pathogenesis of arrhythmias. This review article discusses the molecular mechanisms involved in the pathogenesis of cardiac fibrosis in various myocardial diseases, including myocardial infarction, heart failure with reduced or preserved ejection fraction, genetic cardiomyopathies, and diabetic heart disease. Development of fibrosis-targeting therapies for patients with myocardial diseases will require not only understanding of the functional pluralism of cardiac fibroblasts and dissection of the molecular basis for fibrotic remodelling, but also appreciation of the pathophysiologic heterogeneity of fibrosis-associated myocardial disease.

Correlation of D-xylose with severity and morbidity-related factors of COVID-19 and possible therapeutic use of D-xylose and antibiotics for COVID-19

The SARS-Cov-2 pandemic that currently affects the entire world has been shown to be especially dangerous in the elderly (≥65 years) and in smokers, with notably strong comorbidity in patients already suffering from chronic diseases, such as Type 2 diabetes, cancers, chronic respiratory diseases, obesity, and hypertension. Inflammation of the lungs is the main factor leading to respiratory distress in patients with chronic respiratory disease and in patients with severe COVID-19. Several studies have shown that inflammation of the lungs in general and Type 2 diabetes are accompanied by the degradation of glycosaminoglycans (GAGs), especially heparan sulfate (HS). Several studies have also shown the importance of countering the degradation of HS in lung infections and Type 2 diabetes. D-xylose, which is the initiating element for different sulfate GAG chains (especially HS), has shown regeneration properties for GAGs. D-xylose and xylitol have demonstrated anti-inflammatory, antiglycemic, antiviral, and antibacterial properties in lung infections, alone or in combination with antibiotics. Considering the existing research on COVID-19 and related to D-xylose/xylitol, this review offers a perspective on why the association between D-xylose and antibiotics may contribute to significantly reducing the duration of treatment of COVID-19 patients and why some anti-inflammatory drugs may increase the severity of COVID-19. A strong correlation with scurvy, based on gender, age, ethnicity, smoking status, and obesity status, is also reviewed. Related to this, the effects of treatment with plants such as Artemisia are also addressed. CHEMICAL COMPOUNDS: D-xylose; xylitol; l-ascorbic Acid; D-glucuronic acid; N-acetylglucosamine; D-N-acetylglucosamine; N-acetylgalactosamine; galactose.

Critical roles of macrophages in pressure overload-induced cardiac remodeling

Macrophages are integral components of the mammalian heart that show extensive expansion in response to various internal or external stimuli. After the onset of sustained pressure overload (PO), the accumulation of cardiac macrophages through local macrophage proliferation and monocyte migration has profound effects on the transition to cardiac hypertrophy and remodeling. In this review, we describe the heterogeneity and diversity of cardiac macrophages and summarize the current understanding of the important roles of macrophages in PO-induced cardiac remodeling. In addition, the possible mechanisms involved in macrophage modulation are also described. Finally, considering the significant effects of cardiac macrophages, we highlight their emerging role as therapeutic targets for alleviating pathological cardiac remodeling after PO.

Chondroitin sulfate mediates liver responses to injury induced by dual endothelin receptor inhibition

Although dual endothelin receptor antagonists (ERAs) show great promise for treating various conditions, their propensity to induce liver injury limits their clinical usage. Inflammation and fibrosis are important processes in liver responses to injury and it has been suggested that they and dual ERA-induced liver injury are mediated by the proteoglycan component chondroitin sulfate (CS), which is synthesized by CHST3 and CHST13. In this study, we investigated whether dual ER inhibition in the liver could alter CHST3 and CHST13 expression and thus CS production and whether liver CS content could prevent inflammatory and fibrosis responses after liver injury. We observed increased CHST3 and CHST13 expression after liver injury in bile duct ligated mice and histologically confirmed abundant CS deposition in the injured liver. Moreover, treating Hep3B cells with a dual ERA mimic significantly increased CHST3 and CHST13 expression, inflammatory cytokine levels, and glycosaminoglycan deposition. Furthermore, pro-inflammatory and pro-fibrotic markers were observed after dual ERA treatment, while treatment with CS-degrading chondroitinase ABC was able to successfully reverse these phenotypes. These observations suggest that CHST3- and CHST13-induced CS production can mediate liver injury responses caused by dual ER inhibition and thus could be an alternative pathway for treating ERA-induced liver injury.

Cytosolic DNA sensor cGAS plays an essential pathogenetic role in pressure overload-induced heart failure

Growing evidence shows that activation of inflammation in the heart provokes left ventricular (LV) remodeling and dysfunction in humans and experimental animals with heart failure (HF). Moreover, recent studies found that cyclic GMP-AMP synthase (cGAS), serving as a cytosolic DNA sensor, was essential for activating innate immunity against infection and cellular damage by initiating the STING-IRFs-type I IFN signaling cascade, which played important roles in regulating the inflammatory response. However, the pathophysiological role of cGAS in pressure overload-induced HF is unclear. Wild-type C57BL/6J mice and cGAS inhibition mice were subjected to transverse aortic constriction (TAC) to induce HF or sham operation. Inhibition of cGAS in the murine heart was performed using adeno-associated virus 9 (AAV9). Alterations of the cGAS/STING pathway were examined by qPCR and Western blotting. Cardiac remodeling was assessed by echocardiography as well as histological and molecular phenotyping. Compared with sham-operated mice, the cGAS/STING pathway was activated in LV tissues in TAC mice. Whereas TAC mice exhibited significant pathological cardiac remodeling and LV dysfunction, inhibition of cGAS improved early survival rates after TAC, preserved LV contractile function, and blunted pathological remodeling, including cardiac hypertrophy, fibrosis, and apoptosis. Furthermore, downregulation of cGAS diminished early inflammatory cell infiltration and inflammatory cytokine expression in response to TAC. These results demonstrated that cGAS played an essential pathogenetic role in pressure overload-induced HF to promote pathological cardiac remodeling and dysfunction. Our results suggest that inhibition of cGAS may be a novel therapeutic approach for HF.NEW & NOTEWORTHY In this study, we first revealed a novel role of cGAS in the regulation of pathological cardiac remodeling and dysfunction upon pressure overload. We found that the cGAS/STING pathway was activated during pressure overload. Moreover, we also demonstrated that inhibition of the cGAS/STING pathway alleviated pathological cardiac remodeling and downregulated the early inflammatory response during pressure overload-induced HF. Together, these findings will provide a new therapeutic target for HF.

Drug delivery to macrophages: A review of targeting drugs and drug carriers to macrophages for inflammatory diseases

Macrophages play a key role in defending against foreign pathogens, healing wounds, and regulating tissue homeostasis. Driving this versatility is their phenotypic plasticity, which enables macrophages to respond to subtle cues in tightly coordinated ways. However, when this coordination is disrupted, macrophages can aid the progression of numerous diseases, including cancer, cardiovascular disease, and autoimmune disease. The central link between these disorders is aberrant macrophage polarization, which misguides their functional programs, secretory products, and regulation of the surrounding tissue microenvironment. As a result of their important and deterministic roles in both health and disease, macrophages have gained considerable attention as targets for drug delivery. Here, we discuss the role of macrophages in the initiation and progression of various inflammatory diseases, summarize the leading drugs used to regulate macrophages, and review drug delivery systems designed to target macrophages. We emphasize strategies that are approved for clinical use or are poised for clinical investigation. Finally, we provide a prospectus of the future of macrophage-targeted drug delivery systems.

Disparate Remodeling of the Extracellular Matrix and Proteoglycans in Failing Pediatric Versus Adult Hearts

Background

Dilated cardiomyopathy (DCM) is a common cause of heart failure in adult and pediatric patients, but the underlying mechanism may vary in adults and children, with few studies conducted to date. The objective of the present study was to determine whether differential remodeling of the extracellular matrix contributes to the differences between pediatric and adult DCM hearts.

Methods and Results

Explanted hearts were procured from adult (age, 46–61 years) and pediatric (age, 2–8) patients with DCM‐related heart failure and nonfailing control hearts. Fibrillar and nonfibrillar extracellular matrix (proteoglycans, glycosaminoglycans, glycoprotein), their regulatory enzymes (matrix metalloproteinases, disintegrin and metalloproteinases, and disintegrin and metalloproteinases with a thrombospondin domain), and their inhibitors (tissue inhibitor of metalloproteinases) were assessed. Pediatric DCM hearts exhibited less fibrosis compared with adult DCMs. Total glycosaminoglycans increased similarly in both DCM groups but exhibited a significantly lower affinity for transforming growth factor‐β in adult DCMs versus pediatric DCMs, resulting in increased bioavailability of transforming growth factor‐β1 and a significantly higher activity of the Smad2/3 pathway in adult DCMs. Glycosylated biglycan and versican, and cleaved thrombospondin‐1 increased in both DCMs. Protein expression of disintegrin and metalloproteinases with thrombospondin domains (‐1, ‐2, ‐4, ‐7) and disintegrin and metalloproteinases (‐12, ‐15, ‐17, ‐19) were altered differently in pediatric and adult control and failing hearts. Total matrix metalloproteinase activity increased in both DCMs. Tissue inhibitor of metalloproteinase levels were altered similarly with heart failure in both age groups, and only tissue inhibitor of metalloproteinase 3 decreased in both DCM groups.

Conclusions

Differential remodeling of glycosaminoglycans in pediatric DCMs versus adult DCMs could underlie the enhanced activation of the transforming growth factor‐β pathway, leading to more fibrosis in adult DCM hearts. The distinct remodeling of the fibrillar and nonfibrillar extracellular matrix between pediatric and adult DCM hearts highlights a distinct pathophysiological basis for these cohorts.

GDF11 Decreases Pressure Overload-Induced Hypertrophy, but Can Cause Severe Cachexia and Premature Death

RATIONALE

Possible beneficial effects of GDF11 (growth differentiation factor 11) on the normal, diseased, and aging heart have been reported, including reversing aging-induced hypertrophy. These effects have not been well validated. High levels of GDF11 have also been shown to cause cardiac and skeletal muscle wasting. These controversies could be resolved if dose-dependent effects of GDF11 were defined in normal and aged animals as well as in pressure overload-induced pathological hypertrophy.

OBJECTIVE

To determine dose-dependent effects of GDF11 on normal hearts and those with pressure overload-induced cardiac hypertrophy.

METHODS AND RESULTS

Twelve- to 13-week-old C57BL/6 mice underwent transverse aortic constriction (TAC) surgery. One-week post-TAC, these mice received rGDF11 (recombinant GDF11) at 1 of 3 doses: 0.5, 1.0, or 5.0 mg/kg for up to 14 days. Treatment with GDF11 increased plasma concentrations of GDF11 and p-SMAD2 in the heart. There were no significant differences in the peak pressure gradients across the aortic constriction between treatment groups at 1 week post-TAC. Two weeks of GDF11 treatment caused dose-dependent decreases in cardiac hypertrophy as measured by heart weight/tibia length ratio, myocyte cross-sectional area, and left ventricular mass. GDF11 improved cardiac pump function while preventing TAC-induced ventricular dilation and caused a dose-dependent decrease in interstitial fibrosis (in vivo), despite increasing markers of fibroblast activation and myofibroblast transdifferentiation (in vitro). Treatment with the highest dose (5.0 mg/kg) of GDF11 caused severe body weight loss, with significant decreases in both muscle and organ weights and death in both sham and TAC mice.

CONCLUSIONS

Although GDF11 treatment can reduce pathological cardiac hypertrophy and associated fibrosis while improving cardiac pump function in pressure overload, high doses of GDF11 cause severe cachexia and death. Use of GDF11 as a therapy could have potentially devastating actions on the heart and other tissues.

The Extracellular Matrix in Ischemic and Nonischemic Heart Failure

The ECM (extracellular matrix) network plays a crucial role in cardiac homeostasis, not only by providing structural support, but also by facilitating force transmission, and by transducing key signals to cardiomyocytes, vascular cells, and interstitial cells. Changes in the profile and biochemistry of the ECM may be critically implicated in the pathogenesis of both heart failure with reduced ejection fraction and heart failure with preserved ejection fraction. The patterns of molecular and biochemical ECM alterations in failing hearts are dependent on the type of underlying injury. Pressure overload triggers early activation of a matrix-synthetic program in cardiac fibroblasts, inducing myofibroblast conversion, and stimulating synthesis of both structural and matricellular ECM proteins. Expansion of the cardiac ECM may increase myocardial stiffness promoting diastolic dysfunction. Cardiomyocytes, vascular cells and immune cells, activated through mechanosensitive pathways or neurohumoral mediators may play a critical role in fibroblast activation through secretion of cytokines and growth factors. Sustained pressure overload leads to dilative remodeling and systolic dysfunction that may be mediated by changes in the interstitial protease/antiprotease balance. On the other hand, ischemic injury causes dynamic changes in the cardiac ECM that contribute to regulation of inflammation and repair and may mediate adverse cardiac remodeling. In other pathophysiologic conditions, such as volume overload, diabetes mellitus, and obesity, the cell biological effectors mediating ECM remodeling are poorly understood and the molecular links between the primary insult and the changes in the matrix environment are unknown. This review article discusses the role of ECM macromolecules in heart failure, focusing on both structural ECM proteins (such as fibrillar and nonfibrillar collagens), and specialized injury-associated matrix macromolecules (such as fibronectin and matricellular proteins). Understanding the role of the ECM in heart failure may identify therapeutic targets to reduce geometric remodeling, to attenuate cardiomyocyte dysfunction, and even to promote myocardial regeneration.

Dihydrotestosterone inhibits arylsulfatase B and Dickkopf Wnt signaling pathway inhibitor (DKK)-3 leading to enhanced Wnt signaling in prostate epithelium in response to stromal Wnt3A

BACKGROUND

In tissue microarrays, immunostaining of the enzyme arylsulfatase B (ARSB; N-acetylgalactosamine-4-sulfatase) was less in recurrent prostate cancers and in cancers with higher Gleason scores. In cultured prostate stem cells, decline in ARSB increased Wnt signaling through effects on Dickkopf Wnt Signaling Pathway Inhibitor (DKK)3. The effects of androgen exposure on ARSB and the impact of decline in ARSB on Wnt signaling in prostate tissue were unknown.

METHODS

Epithelial and stromal tissues from malignant and normal human prostate were obtained by laser capture microdissection. mRNA expression of ARSB, galactose-6-sulfate-sulfatase (GALNS) and Wnt-signaling targets was determined by QPCR. Non-malignant human epithelial and stromal prostate cells were grown in tissue culture, including two-cell layer cultures. ARSB was silenced by specific siRNA, and epithelial cells were treated with stromal spent media following treatment with IWP-2, an inhibitor of Wnt secretion, and by exogenous recombinant human Wnt3A. Promoter methylation was detected using specific DKK3 and ARSB promoter primers. The effects of DHT and of ARSB overexpression on DKK expression were determined. Cell proliferation was assessed by BrdU incorporation.

RESULTS

Normal stroma showed higher expression of vimentin, ARSB, and Wnt3A than epithelium. Normal epithelium had higher expression of E-cadherin, galactose 6-sulfate-sulfatase (GALNS), and DKK3 than stroma. In malignant epithelium, expression of ARSB and DKK3 declined, and expression of GALNS and Wnt signaling targets increased. In cultured prostate epithelial cells, Wnt-mediated signaling was greatest when ARSB was silenced and cells were exposed to exogenous Wnt3A. Exposure to 5α-dihydrotestosterone (DHT) increased ARSB and DKK3 promoter rmethylation, and effects of DHT on DKK3 expression were reversed when ARSB was overexpressed.

CONCLUSIONS

Androgen-induced declines in ARSB and DKK3 may contribute to prostate carcinogenesis by sustained activation of Wnt signaling in prostate epithelium in response to stromal Wnt3A.

Emerging roles of proteoglycans in cardiac remodeling

Cardiac remodeling is the response of the heart to a range of pathological stimuli. Cardiac remodeling is initially adaptive; however, if sustained, it ultimately causes adverse clinical outcomes. Cardiomyocyte loss or hypertrophy, inflammation and fibrosis are hallmarks of cardiac remodeling. Proteoglycans, which are composed of glycosaminoglycans and a core protein, are a non-structural component of the extracellular matrix. The lack of proteoglycans results in cardiovascular defects during development. Moreover, emerging evidence has indicated that proteoglycans act as significant modifiers in ischemia and pressure overload-related cardiac remodeling. Proteoglycans may also provide novel therapeutic strategies for further improvement in the prognosis of cardiovascular diseases.

Cardiac fibrosis: Cell biological mechanisms, molecular pathways and therapeutic opportunities

Cardiac fibrosis is a common pathophysiologic companion of most myocardial diseases, and is associated with systolic and diastolic dysfunction, arrhythmogenesis, and adverse outcome. Because the adult mammalian heart has negligible regenerative capacity, death of a large number of cardiomyocytes results in reparative fibrosis, a process that is critical for preservation of the structural integrity of the infarcted ventricle. On the other hand, pathophysiologic stimuli, such as pressure overload, volume overload, metabolic dysfunction, and aging may cause interstitial and perivascular fibrosis in the absence of infarction. Activated myofibroblasts are the main effector cells in cardiac fibrosis; their expansion following myocardial injury is primarily driven through activation of resident interstitial cell populations. Several other cell types, including cardiomyocytes, endothelial cells, pericytes, macrophages, lymphocytes and mast cells may contribute to the fibrotic process, by producing proteases that participate in matrix metabolism, by secreting fibrogenic mediators and matricellular proteins, or by exerting contact-dependent actions on fibroblast phenotype. The mechanisms of induction of fibrogenic signals are dependent on the type of primary myocardial injury. Activation of neurohumoral pathways stimulates fibroblasts both directly, and through effects on immune cell populations. Cytokines and growth factors, such as Tumor Necrosis Factor-α, Interleukin (IL)-1, IL-10, chemokines, members of the Transforming Growth Factor-β family, IL-11, and Platelet-Derived Growth Factors are secreted in the cardiac interstitium and play distinct roles in activating specific aspects of the fibrotic response. Secreted fibrogenic mediators and matricellular proteins bind to cell surface receptors in fibroblasts, such as cytokine receptors, integrins, syndecans and CD44, and transduce intracellular signaling cascades that regulate genes involved in synthesis, processing and metabolism of the extracellular matrix. Endogenous pathways involved in negative regulation of fibrosis are critical for cardiac repair and may protect the myocardium from excessive fibrogenic responses. Due to the reparative nature of many forms of cardiac fibrosis, targeting fibrotic remodeling following myocardial injury poses major challenges. Development of effective therapies will require careful dissection of the cell biological mechanisms, study of the functional consequences of fibrotic changes on the myocardium, and identification of heart failure patient subsets with overactive fibrotic responses.