Angiotensin II-stimulated collagen production in cardiac fibroblasts is mediated by reactive oxygen species

Possible mechanisms of SARS-CoV-2-associated myocardial fibrosis: reflections in the post-pandemic era

Since December 2019, coronavirus disease 2019 (COVID-19) has been spreading worldwide with devastating immediate or long-term effects on people's health. Although the lungs are the primary organ affected by COVID-19, individuals infected with SARS-CoV-2 also develop systemic lesions involving multiple organs throughout the body, such as the cardiovascular system. Emerging evidence reveals that COVID-19 could generate myocardial fibrosis, termed "COVID-19-associated myocardial fibrosis." It can result from the activation of fibroblasts via the renin-angiotensin-aldosterone system (RAAS), transforming growth factor-β1 (TGF-β1), microRNAs, and other pathways, and can also occur in other cellular interactions with SARS-CoV-2, such as immunocytes, endothelial cells. Nonetheless, to gain a more profound insight into the natural progression of COVID-19-related myocardial fibrosis, additional investigations are necessary. This review delves into the underlying mechanisms contributing to COVID-19-associated myocardial fibrosis while also examining the antifibrotic potential of current COVID-19 treatments, thereby offering guidance for future clinical trials of these medications. Ultimately, we propose future research directions for COVID-19-associated myocardial fibrosis in the post-COVID-19 era, such as artificial intelligence (AI) telemedicine. We also recommend that relevant tests be added to the follow-up of COVID-19 patients to detect myocardial fibrosis promptly.

The impact of aging on cardiac repair and regeneration

In contrast to neonates and lower organisms, the adult mammalian heart lacks any capacity to regenerate following injury. The vast majority of our understanding of cardiac regeneration is based on research in young animals. Research in aged individuals is rare. This is unfortunate as aging induces many changes in the heart. The first part of this review covers the main technologies being pursued in the cardiac regeneration field and how they are impacted by the aging processes. The second part of the review covers the significant amount of aging-related research that could be used to aid cardiac regeneration. Finally, a perspective is provided to suggest how cardiac regenerative technologies can be improved by addressing aging-related effects.

Oxidative modification of miR-30c promotes cardiac fibroblast proliferation via CDKN2C mismatch

The response of cardiac fibroblast proliferation to detrimental stimuli is one of the main pathological factors causing heart remodeling. Reactive oxygen species (ROS) mediate the proliferation of cardiac fibroblasts. However, the exact molecular mechanism remains unclear. In vivo, we examined the oxidative modification of miRNAs with miRNA immunoprecipitation with O8G in animal models of cardiac fibrosis induced by Ang II injection or ischemia‒reperfusion injury. Furthermore, in vitro, we constructed oxidation-modified miR-30c and investigated its effects on the proliferation of cardiac fibroblasts. Additionally, luciferase reporter assays were used to identify the target of oxidized miR-30c. We found that miR-30c oxidation was modified by Ang II and PDGF treatment and mediated by excess ROS. We demonstrated that oxidative modification of G to O8G occurred at positions 4 and 5 of the 5' end of miR-30c (4,5-oxo-miR-30c), and this modification promoted cardiac fibroblast proliferation. Furthermore, CDKN2C is a negative regulator of cardiac fibroblast proliferation. 4,5-oxo-miR-30c misrecognizes CDKN2C mRNA, resulting in a reduction in protein expression. Oxidized miR-30c promotes cardiac fibroblast proliferation by mismatch mRNA of CDKN2C.

The Senescent Heart-"Age Doth Wither Its Infinite Variety"

Cardiovascular diseases are a leading cause of morbidity and mortality world-wide. While many factors like smoking, hypertension, diabetes, dyslipidaemia, a sedentary lifestyle, and genetic factors can predispose to cardiovascular diseases, the natural process of aging is by itself a major determinant of the risk. Cardiac aging is marked by a conglomerate of cellular and molecular changes, exacerbated by age-driven decline in cardiac regeneration capacity. Although the phenotypes of cardiac aging are well characterised, the underlying molecular mechanisms are far less explored. Recent advances unequivocally link cardiovascular aging to the dysregulation of critical signalling pathways in cardiac fibroblasts, which compromises the critical role of these cells in maintaining the structural and functional integrity of the myocardium. Clearly, the identification of cardiac fibroblast-specific factors and mechanisms that regulate cardiac fibroblast function in the senescent myocardium is of immense importance. In this regard, recent studies show that Discoidin domain receptor 2 (DDR2), a collagen-activated receptor tyrosine kinase predominantly located in cardiac fibroblasts, has an obligate role in cardiac fibroblast function and cardiovascular fibrosis. Incisive studies on the molecular basis of cardiovascular aging and dysregulated fibroblast function in the senescent heart would pave the way for effective strategies to mitigate cardiovascular diseases in a rapidly growing elderly population.

Potential molecular mechanism underlying cardiac fibrosis in diabetes mellitus: a narrative review

BACKGROUND

Diabetes mellitus (DM) is among the most common risk factors for cardiovascular disease in the world with prevalence of more than 500 million population in 2021. Cardiac fibrosis with its complex process has been hypothesized as one of the mechanisms explaining development of heart failure in diabetic patients. Recently, the biomolecular mechanism of cardiac fibrosis in the hyperglycemia setting has been focusing around transforming growth factor β-1 (TGFβ-1) as a major factor. However, there is interplay role of several factors including microRNAs (miRNAs) which acts as a potential regulator of cardiac fibrosis connected with TGFβ-1. In this review, we explored interplay role of several factors including microRNAs which acts as a potential regulator of cardiac fibrosis connected with TGFβ-1 in diabetes mellitus. This narrative review included articles from the PubMed and Science Direct databases published in the last 10 years (2012-2022).

MAIN TEXT

In diabetic patients, excessive activation of myofibroblasts occurs and triggers pro-collagen to convert into mature collagen to fill the cardiac interstitial space resulting in a pathological process of extracellular matrix remodeling. The balance between matrix metalloproteinase (MMP) and its inhibitor (tissue inhibitor of metalloproteinase, TIMP) is crucial in degradation of the extracellular matrix. Diabetes-related cardiac fibrosis is modulated by increasing level of TGF-β1 mediated by cellular components, including cardiomyocyte and non-cardiomyocyte cells involving fibroblasts, vascular pericytes smooth muscle cells, endothelial cells, mast cells, macrophages, and dendritic cells. Several miRNAs such as miR-21, miR-9, miR-29, miR-30d, miR-144, miR-34a, miR-150, miR-320, and miR-378 are upregulated in diabetic cardiomyopathy. TGF-β1, together with inflammatory cytokines, oxidative stress, combined sma and the mothers against decapentaplegic (smad) protein, mitogen-activated protein kinase (MAPK), and microRNAs, is interconnectedly involved in extracellular matrix production and fibrotic response. In this review, we explored interplay role of several factors including microRNAs which acts as a potential regulator of cardiac fibrosis connected with TGFβ-1 in diabetes mellitus.

CONCLUSIONS

Long-term hyperglycemia activates cardiac fibroblast via complex processes involving TGF-β1, miRNA, inflammatory chemokines, oxidative stress, smad, or MAPK pathways. There is increasing evidence of miRNA's roles lately in modulating cardiac fibrosis.

Tissue Sodium Accumulation Induces Organ Inflammation and Injury in Chronic Kidney Disease

High salt intake is a primary cause of over-hydration in chronic kidney disease (CKD) patients. Inflammatory markers are predictors of CKD mortality; however, the pathogenesis of inflammation remains unclear. Sodium storage in tissues has recently emerged as an issue of concern. The binding of sodium to tissue glycosaminoglycans and its subsequent release regulates local tonicity. Many cell types express tonicity-responsive enhancer-binding protein (TonEBP), which is activated in a tonicity-dependent or tonicity-independent manner. Macrophage infiltration was observed in the heart, peritoneal wall, and para-aortic tissues in salt-loading subtotal nephrectomized mice, whereas macrophages were not prominent in tap water-loaded subtotal nephrectomized mice. TonEBP was increased in the heart and peritoneal wall, leading to the upregulation of inflammatory mediators associated with cardiac fibrosis and peritoneal membrane dysfunction, respectively. Reducing salt loading by a diuretic treatment or changing to tap water attenuated macrophage infiltration, TonEBP expression, and inflammatory marker expression. The role of TonEBP may be crucial during the cardiac fibrosis and peritoneal deterioration processes induced by sodium overload. Anti-interleukin-6 therapy improved cardiac inflammation and fibrosis and peritoneal membrane dysfunction. Further studies are necessary to establish a strategy to regulate organ dysfunction induced by TonEBP activation in CKD patients.

S-Doped carbonized polymer dots inhibit early myocardial fibrosis by regulating mitochondrial function

Myocardial fibrosis (MF) is a critical pathological lesion in the progression of various acute and chronic cardiovascular diseases. However, there is still a lack of clinically effective drugs and treatments for MF therapies. Herein, for the first time, we developed fluorescent sulfur-doped carbonized polymer dots (S-CPDs) as new nano-antioxidants to reduce the cardiomyocyte damage caused by reactive oxygen species (ROS) in the early stage of fibrotic lesions. In vitro results suggested that the pre-protection of S-CPDs significantly increased the survival rate of H9c2 cells under severe oxidative stress, inhibited the isoproterenol (ISO)-induced hypertrophy of myocardial cells through improving the content of mitochondria related proteins and adenosine triphosphate (ATP) in cells. Moreover, S-CPD administration could effectively decrease cardiac hypertrophy and promote heart function in MF rat models. The rapid internalization, high biocompatibility and fluorescence imaging potential of S-CPDs revealed their promising application prospects in the diagnoses and treatments of cardiovascular diseases.

Bioactivities and mechanisms of dietary proanthocyanidins on blood pressure lowering: A critical review of in vivo and clinical studies

Proanthocyanidins, widespread in natural plant sources, are bioactive substances that exhibit broad benefits to human health. Of note, proanthocyanidins have been reported to lower blood pressure and prevent hypertension, but a critical review of this is lacking. In this review, information on the basic structures and absorption of dietary proanthocyanidins as well as their bioactivities and related mechanisms on the lowering of blood pressure derived via in vivo and clinical studies are summarized. Clinical studies have shown that proanthocyanidins have a pronounced blood pressure-lowering effect, effectively preventing hypertension and reducing the occurrence of cardiovascular and cerebrovascular diseases. The potential mechanisms, which are herein reviewed in detail, involve the improvement of vascular function, reduction of oxidative stress and inflammation, and modulation of lipid metabolism. Taken together, this work provides information for a better understanding of the antihypertensive effects of proanthocyanidins, which may promote their use to reduce the risk of developing hypertension.

The emerging role of leptin in obesity-associated cardiac fibrosis: evidence and mechanism

Cardiac fibrosis is a hallmark of various cardiovascular diseases, which is quite commonly found in obesity, and may contribute to the increased incidence of heart failure arrhythmias, and sudden cardiac death in obese populations. As an endogenous regulator of adiposity metabolism, body mass, and energy balance, obesity, characterized by increased circulating levels of the adipocyte-derived hormone leptin, is a critical contributor to the pathogenesis of cardiac fibrosis. Although there are some gaps in our knowledge linking leptin and cardiac fibrosis, this review will focus on the interplay between leptin and major effectors involved in the pathogenesis underlying cardiac fibrosis at both cellular and molecular levels based on the current reports. The profibrotic effect of leptin is predominantly mediated by activated cardiac fibroblasts but may also involve cardiomyocytes, endothelial cells, and immune cells. Moreover, a series of molecular signals with a known profibrotic property is closely involved in leptin-induced fibrotic events. A more comprehensive understanding of the underlying mechanisms through which leptin contributes to the pathogenesis of cardiac fibrosis may open up a new avenue for the rapid emergence of a novel therapy for preventing or even reversing obesity-associated cardiac fibrosis.

Properties and Functions of Fibroblasts and Myofibroblasts in Myocardial Infarction

The adult mammalian heart contains abundant interstitial and perivascular fibroblasts that expand following injury and play a reparative role but also contribute to maladaptive fibrotic remodeling. Following myocardial infarction, cardiac fibroblasts undergo dynamic phenotypic transitions, contributing to the regulation of inflammatory, reparative, and angiogenic responses. This review manuscript discusses the mechanisms of regulation, roles and fate of fibroblasts in the infarcted heart. During the inflammatory phase of infarct healing, the release of alarmins by necrotic cells promotes a pro-inflammatory and matrix-degrading fibroblast phenotype that may contribute to leukocyte recruitment. The clearance of dead cells and matrix debris from the infarct stimulates anti-inflammatory pathways and activates transforming growth factor (TGF)-β cascades, resulting in the conversion of fibroblasts to α-smooth muscle actin (α-SMA)-expressing myofibroblasts. Activated myofibroblasts secrete large amounts of matrix proteins and form a collagen-based scar that protects the infarcted ventricle from catastrophic complications, such as cardiac rupture. Moreover, infarct fibroblasts may also contribute to cardiac repair by stimulating angiogenesis. During scar maturation, fibroblasts disassemble α-SMA+ stress fibers and convert to specialized cells that may serve in scar maintenance. The prolonged activation of fibroblasts and myofibroblasts in the infarct border zone and in the remote remodeling myocardium may contribute to adverse remodeling and to the pathogenesis of heart failure. In addition to their phenotypic plasticity, fibroblasts exhibit remarkable heterogeneity. Subsets with distinct phenotypic profiles may be responsible for the wide range of functions of fibroblast populations in infarcted and remodeling hearts.

PKM2 promotes angiotensin-II-induced cardiac remodelling by activating TGF-β/Smad2/3 and Jak2/Stat3 pathways through oxidative stress

Hypertensive cardiac remodelling is a common cause of heart failure. However, the molecular mechanisms regulating cardiac remodelling remain unclear. Pyruvate kinase isozyme type M2 (PKM2) is a key regulator of the processes of glycolysis and oxidative phosphorylation, but the roles in cardiac remodelling remain unknown. In the present study, we found that PKM2 was enhanced in angiotensin II (Ang II)-treated cardiac fibroblasts and hypertensive mouse hearts. Suppression of PKM2 by shikonin alleviated cardiomyocyte hypertrophy and fibrosis in Ang-II-induced cardiac remodelling in vivo. Furthermore, inhibition of PKM2 markedly attenuated the function of cardiac fibroblasts including proliferation, migration and collagen synthesis in vitro. Mechanistically, suppression of PKM2 inhibited cardiac remodelling by suppressing TGF-β/Smad2/3, Jak2/Stat3 signalling pathways and oxidative stress. Together, this study suggests that PKM2 is an aggravator in Ang-II-mediated cardiac remodelling. The negative modulation of PKM2 may provide a promising therapeutic approach for hypertensive cardiac remodelling.

Cardiac fibrosis and curcumin: a novel perspective on this natural medicine

BACKGROUND

According to WHO statistics, cardiovascular disease are the leading causes of death in the world. One of the main factors which is causing heart failure, systolic and diastolic dysfunction, and arrythmias is a condition named cardiac fibrosis. This condition is defined by the accumulation of fibroblast-produced ECM in myocardium layer of the heart.

OBJECTIVE

Accordingly, the current review aims to depict the role of curcumin in the regulation of different signaling pathways that are involved in cardiac fibrosis.

RESULTS

A great number of cellular and molecular mechanisms such as oxidative stress, inflammation, and mechanical stress are acknowledged to be involved in cardiac fibrosis. Despite the available therapeutic procedures which are designed to target these mechanisms in order to prevent cardiac fibrosis, still, effective therapeutic methods are needed. Curcumin is a natural Chinese medicine which currently has been declared to have therapeutic properties such as anti-oxidant and immunomodulatory activities. In this review, we have gathered several experimental studies in order to represent diverse impacts of this turmeric derivative on pathogenic factors of cardiac fibrosis.

CONCLUSION

Curcumin might open new avenues in the field of cardiovascular treatment.

Transient ACE (Angiotensin-Converting Enzyme) Inhibition Suppresses Future Fibrogenic Capacity and Heterogeneity of Cardiac Fibroblast Subpopulations

Transient ACE (angiotensin-converting enzyme) inhibition in spontaneously hypertensive rats is known to protect against future injury-induced cardiac inflammation, fibrosis, and dysfunction; however, the mechanisms of protection have not been delineated. Here, we used single-cell RNA sequencing to test the hypothesis that transient ACE inhibitor treatment would induce a persistent shift in cardiac fibroblast subpopulations. Adult male spontaneously hypertensive rats (11 weeks old, hypertensive with cardiac hypertrophy) were treated for 2 weeks with an ACE inhibitor, enalapril (30 mg/kg per day, PO), or water (untreated spontaneously hypertensive rats) followed by a 2-week washout period (n=7/group). Cardiac fibroblasts were isolated from the left ventricle and subjected to single-cell RNA sequencing. Nine clusters of fibroblasts were identified, with 98% of cells in clusters 0 to 6. The transient treatment produced significant changes both within and across clusters. Cluster 1 depicted a highly fibrogenic gene profile, with cluster 6 serving as a gateway to cluster 1. Transient ACE inhibition depleted the gateway and expanded cluster 0, which was the least fibrogenic profile. Moreover, within cluster 1 fibroblasts, ACE inhibition reduced expression of individual fibrosis genes (eg, COL1A1, COL3A1, and FN1; all P<1×10-35). Clusters 2 to 5 reflected proliferative, moderately fibrogenic, translationally active, and less inflammatory subsets of fibroblasts, all of which exhibited attenuated fibrogenic gene expression after transient ACE inhibition. In conclusion, transient ACE inhibition shifts cardiac fibroblast subpopulations and degree of activation resulting in an overall reduced fibrogenic phenotype.

Angiotensin II Induces Differentiation of Human Neuroblastoma Cells by Increasing MAP2 and ROS Levels

INTRODUCTION

The roles of angiotensin II (Ang II) in the brain are still under investigation. In this study, we investigated if Ang II influences differentiation of human neuroblastoma cells with simultaneous activation of NADPH oxidase and reactive oxygen species (ROS). Moreover, we investigated the Ang II receptor type involved during differentiation.

METHODS

Human neuroblastoma cells (SH-SY5Y; 5 × 10⁵ cells) were exposed to Ang II (600 nM) for 24 h. Differentiation was monitored by measuring MAP2 and NF-H levels. Cell size and ROS were analyzed by flow cytometry, and NADPH oxidase activation was assayed using apocynin (500 μM). Ang II receptors (ATR) activation was assayed using ATR blockers or Ang II metabolism inhibitors (10^-7 M).

RESULTS

(1) Cell size decreased significantly in Ang II-treated cells; (2) MAP2 and ROS increased significantly in Ang II-treated cells with no changes in viability; (3) MAP2 and ROS decreased significantly in cells incubated with Ang II plus apocynin. (4) A significant decrease in MAP2 was observed in cells exposed to Ang II plus PD123.319 (AT2R blocker).

CONCLUSION

Our findings suggest that Ang II influences differentiation of SH-SY5Y by increasing MAP2 through the AT2R. The increase in MAP2 and ROS were also mediated through NADPH oxidase with no cell death.

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.

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.

Targeting cardiac fibrosis in heart failure with preserved ejection fraction: mirage or miracle?

Cardiac fibrosis is central to the pathology of heart failure, particularly heart failure with preserved ejection fraction (HFpEF). Irrespective of the underlying profibrotic condition (e.g. ageing, diabetes, hypertension), maladaptive cardiac fibrosis is defined by the transformation of resident fibroblasts to matrix-secreting myofibroblasts. Numerous profibrotic factors have been identified at the molecular level (e.g. TGFβ, IL11, AngII), which activate gene expression programs for myofibroblast activation. A number of existing HF therapies indirectly target fibrotic pathways; however, despite multiple clinical trials in HFpEF, a specific clinically effective antifibrotic therapy remains elusive. Therapeutic inhibition of TGFβ, the master-regulator of fibrosis, has unfortunately proven toxic and ineffective in clinical trials to date, and new approaches are needed. In this review, we discuss the pathophysiology and clinical implications of interstitial fibrosis in HFpEF. We provide an overview of trials targeting fibrosis in HFpEF to date and discuss the promise of potential new therapeutic approaches and targets in the context of underlying molecular mechanisms.

Angiotensin Inhibition, TGF-β and EMT in Cancer

Angiotensin inhibitors are standard drugs in cardiovascular and renal diseases that have antihypertensive and antifibrotic properties. These drugs also exert their antifibrotic effects in cancer by reducing collagen and hyaluronan deposition in the tumor stroma, thus enhancing drug delivery. Angiotensin II signaling interferes with the secretion of the cytokine TGF-β-a known driver of malignancy. TGF-β stimulates matrix production in cancer-associated fibroblasts, and thus drives desmoplasia. The effect of TGF-β on cancer cells itself is stage-dependent and changes during malignant progression from inhibitory to stimulatory. The intracellular signaling for the TGF-β family can be divided into an SMAD-dependent canonical pathway and an SMAD-independent noncanonical pathway. These capabilities have made TGF-β an interesting target for numerous drug developments. TGF-β is also an inducer of epithelial-mesenchymal transition (EMT). EMT is a highly complex spatiotemporal-limited process controlled by a plethora of factors. EMT is a hallmark of metastatic cancer, and with its reversal, an important step in the metastatic cascade is characterized by a loss of epithelial characteristics and/or the gain of mesenchymal traits.

The Dynamic Interplay Between Cardiac Inflammation and Fibrosis

Heart failure is a leading cause of death worldwide. While there are multiple etiologies contributing to the development of heart failure, all cause result in impairments in cardiac function that is characterized by changes in cardiac remodeling and compliance. Fibrosis is associated with nearly all forms of heart failure and is an important contributor to disease pathogenesis. Inflammation also plays a critical role in the heart and there is a large degree of interconnectedness between the inflammatory and fibrotic response. This review discusses the cellular and molecular mechanisms contributing to inflammation and fibrosis and the interplay between the two.

NADPH Oxidase Inhibition in Fibrotic Pathologies

Significance: Fibrosis is a stereotypic, multicellular tissue response to diverse types of injuries that fundamentally result from a failure of cell/tissue regeneration. This complex tissue remodeling response disrupts cellular/matrix composition and homeostatic cell-cell interactions, leading to loss of normal tissue architecture and progressive loss of organ structure/function. Fibrosis is a common feature of chronic diseases that may affect the lung, kidney, liver, and heart. Recent Advances: There is emerging evidence to support a combination of genetic, environmental, and age-related risk factors contributing to susceptibility and/or progression of fibrosis in different organ systems. A core pathway in fibrogenesis involving these organs is the induction and activation of nicotinamide adenine dinucleotide phosphate oxidase (NOX) family enzymes. Critical Issues: We explore current pharmaceutical approaches to targeting NOX enzymes, including repurposing of currently U.S. Food and Drug Administration (FDA)-approved drugs. Specific inhibitors of various NOX homologs will aid establishing roles of NOXs in the various organ fibroses and potential efficacy to impede/halt disease progression. Future Directions: The discovery of novel and highly specific NOX inhibitors will provide opportunities to develop NOX inhibitors for treatment of fibrotic pathologies.

Superoxide-induced Type I collagen secretion depends on prolyl 4-hydroxylases

Reactive oxygen species (ROS) including superoxide (O₂^•-) play an important role in a variety of diseases, including Alzheimer's Disease, cancer, and atherosclerosis. Early reports showed that O₂^•- is a stimulant for collagen synthesis. However, the mechanism remains incompletely understood. Here we showed that LY83583 (6-anilinoquinoline-5,8-quinone), a substance known to induce O₂^•- production by smooth muscle cell (SMC), increases Type I collagen secretion. This effect could be blocked by treating the cells with Tiron, a scavenger for O₂^•-. LY83583-induced Type I collagen secretion required P4HA1 and P4HA2. Knockout of either P4ha1 or P4ha2 greatly reduced LY83583-stimulated Type I collagen maturation whereas silencing of both P4ha1 and P4ha2 completely blocked LY83583-induced Type I collagen maturation. Although significantly more hydroxyproline on purified Type I collagen was detected from LY83583 treated mouse embryonic fibroblast (MEF) cells by mass spectrometry, the level of prolyl 4-hydroxylases was not altered. Thus, LY83583 might increase the enzymatic activity of prolyl 4-hydroxylases to increase Type I collagen maturation. In addition, we found that LY83583 activated prolyl 4-hydrolases differed from ascorbate-activated prolyl 4-hydroxylase in two aspects: (1) LY83583 activated both P4HA1 and P4HA2 involved in collagen maturation whereas ascorbate mainly stimulated P4HA1 in collagen maturation; (2) LY83583 did not induce N259 glycosylation on P4HA1 as ascorbate did. The mechanisms remain to be investigated.

Kaempferol Prevents Against Ang II-induced Cardiac Remodeling Through Attenuating Ang II-induced Inflammation and Oxidative Stress

Heart failure characterized by cardiac remodeling is a global problem. Angiotensin II (Ang II) induces cardiac inflammation and oxidative stress, which also is implicated in the pathophysiology of adverse collagen accumulation-induced remodeling. Kaempferol (KPF), a kind of flavonoid compounds, is capable of anti-inflammatory and antioxidant activities. However, the target of KPF still remains blurred. In this study, we investigated the effect of KPF on Ang II-induced collagen accumulation and explored the underlying mechanisms. Our results suggested that KPF prevented Ang II-induced cardiac fibrosis and dysfunction, in mice challenged with subcutaneous injection of Ang II. In culture cells, KPF significantly reduced Ang II-induced collagen accumulation. Furthermore, KPF remarkably decreased inflammation and oxidative stress in Ang II-stimulated cardiac fibroblasts by modulating NF-κB/mitogen-activated protein kinase and AMPK/Nrf2 pathways.

BRD4 blockage alleviates pathological cardiac hypertrophy through the suppression of fibrosis and inflammation via reducing ROS generation

Hypertension is an essential regulator of cardiac injury and remodeling. However, the pathogenesis that contributes to cardiac hypertrophy remains to be fully explored. BRD4, as a bromodomain and extra-terminal (BET) family member, plays an important role in critical biological processes. In the study, our results showed that BRD4 expression was up-regulated in human and mouse hypertrophied hearts, and importantly these effects were modulated by reactive oxygen species (ROS) generation. In angiotensin II (Ang II)-treated cardiomyocytes, BRD4 decrease markedly blunted the prohypertrophic effect, which was further promoted by the combinational treatment of ROS scavenger (N-acetyl-cysteine, NAC). In addition, NAC pre-treatment markedly elevated the anti-fibrotic role of BRD4 suppression in Ang II-incubated cardiomyocytes by repressing transforming growth factor β1 (TGF-β1)/SMADs signaling pathway. NAC combined with BRD4 reduction further alleviated inflammation and oxidative stress in Ang II-exposed cardiomyocytes, which was partly through inhibiting nuclear factor-κB (NF-κB) signaling and improving nuclear erythroid factor 2-related factor 2 (Nrf-2)/heme oxygenase-1 (HO-1) pathway, respectively. Furthermore, the in vivo results confirmed the protective effects of BRD4 suppression on mice against aortic banding (AB)-induced cardiac hypertrophy, as evidenced by the reduced cross sectional area and fibrotic area using H&E and Masson trichrome staining. What's more, the degree of cardiac hypertrophy (ANP and BNP), the expression of pro-fibrotic genes (TGF-β1, Collagen I, Collagen III and CTGF), the levels of inflammation and oxidative stress were all significantly attenuated by the blockage of BRD4 in AB-operated mice. Taken together, repressing BRD4 expression was found to confer a protective effect against experimental cardiac hypertrophy in mice, demonstrating its potential as an effective therapeutic target for pathological cardiac hypertrophy.

Fibroblasts in the Infarcted, Remodeling, and Failing Heart

Expansion and activation of fibroblasts following cardiac injury is important for repair but may also contribute to fibrosis, remodeling, and dysfunction. The authors discuss the dynamic alterations of fibroblasts in failing and remodeling myocardium. Emerging concepts suggest that fibroblasts are not unidimensional cells that act exclusively by secreting extracellular matrix proteins, thus promoting fibrosis and diastolic dysfunction. In addition to their involvement in extracellular matrix expansion, activated fibroblasts may also exert protective actions, preserving the cardiac extracellular matrix, transducing survival signals to cardiomyocytes, and regulating inflammation and angiogenesis. The functional diversity of cardiac fibroblasts may reflect their phenotypic heterogeneity.

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.

Changes in cardiac resident fibroblast physiology and phenotype in aging

The cardiac fibroblast plays a central role in tissue homeostasis and in repair after injury. With aging, dysregulated cardiac fibroblasts have a reduced capacity to activate a canonical transforming growth factor-β-Smad pathway and differentiate poorly into contractile myofibroblasts. That results in the formation of an insufficient scar after myocardial infarction. In contrast, in the uninjured aged heart, fibroblasts are activated and acquire a profibrotic phenotype that leads to interstitial fibrosis, ventricular stiffness, and diastolic dysfunction, all conditions that may lead to heart failure. There is an apparent paradox in aging, wherein reparative fibrosis is impaired but interstitial, adverse fibrosis is augmented. This could be explained by analyzing the effectiveness of signaling pathways in resident fibroblasts from young versus aged hearts. Whereas defective signaling by transforming growth factor-β leads to insufficient scar formation by myofibroblasts, enhanced activation of the ERK1/2 pathway may be responsible for interstitial fibrosis mediated by activated fibroblasts. Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/fibroblast-phenotypic-changes-in-the-aging-heart/ .

Reactive oxygen species: key regulators in vascular health and diseases

ROS are a group of small reactive molecules that play critical roles in the regulation of various cell functions and biological processes. In the vascular system, physiological levels of ROS are essential for normal vascular functions including endothelial homeostasis and smooth muscle cell contraction. In contrast, uncontrolled overproduction of ROS resulting from an imbalance of ROS generation and elimination leads to the development of vascular diseases. Excessive ROS cause vascular cell damage, the recruitment of inflammatory cells, lipid peroxidation, activation of metalloproteinases and deposition of extracellular matrix, collectively leading to vascular remodelling. Evidence from a large number of studies has revealed that ROS and oxidative stress are involved in the initiation and progression of numerous vascular diseases including hypertension, atherosclerosis, restenosis and abdominal aortic aneurysm. Furthermore, considerable research has been implemented to explore antioxidants that can reduce ROS production and oxidative stress in order to ameliorate vascular diseases. In this review, we will discuss the nature and sources of ROS, their roles in vascular homeostasis and specific vascular diseases and various antioxidants as well as some of the pharmacological agents that are capable of reducing ROS and oxidative stress. The aim of this review is to provide information for developing promising clinical strategies targeting ROS to decrease cardiovascular risks.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Cardiac Fibroblast Activation Post-Myocardial Infarction: Current Knowledge Gaps

In response to myocardial infarction (MI), the wound healing response of the left ventricle (LV) comprises overlapping inflammatory, proliferative, and maturation phases, and the cardiac fibroblast is a key cell type involved in each phase. It has recently been appreciated that, early post-MI, fibroblasts transform to a proinflammatory phenotype and secrete cytokines and chemokines as well as matrix metalloproteinases (MMPs). Later post-MI, fibroblasts are activated to anti-inflammatory and proreparative phenotypes and generate anti-inflammatory and proangiogenic factors and extracellular matrix (ECM) components that form the infarct scar. Additional studies are needed to systematically examine how fibroblast activation shifts over the timeframe of the MI response and how modulation at different activation stages could alter wound healing and LV remodeling in distinct ways. This review summarizes current fibroblast knowledge as the foundation for a discussion of existing knowledge gaps.

Alleviative effect of grape seed proanthocyanidin extract on small artery vascular remodeling in spontaneous hypertensive rats via inhibition of collagen hyperplasia

Vascular remodeling is a primary contributor to the initiation and development of hypertension, which has a pathological association with subsequent multi-organ damage. Grape seed proanthocyanidin extracts (GSPE) exhibit protective cardiovascular effects, resulting from their anti‑oxidant and anti‑inflammatory properties. However, the function and mechanism underlying the effect of GSPE on small artery remodeling remain to be elucidated. The present study investigated the effect of GSPE on vascular remodeling in the mesenteric small arteries of spontaneous hypertensive rats (SHR). Parameters associated with hypertension, including systolic blood pressure, oxidative stress, morphological and ultrastructural alteration of vessels, deposition of collagen and transforming growth factor (TGF)-β1, were analyzed. The results revealed that GSPE alleviated hypertension-induced hypertrophic vascular remodeling in the small arteries of SHR, which was independent of blood pressure. GSPE decreased oxidative stress associated with hypertension in SHR and suppressed the increased expression of TGF‑β1, which blocked the translocation and differentiation of adventitia fibroblasts and eventually inhibited collagen hyperplasia in the blood vessel. The inhibitory effect of GSPE on small artery remodeling was achieved via its suppressive effect on oxidant production and the subsequent intercellular and intracellular cascades. The findings of the present study supported the potential therapeutic value of GSPE for the treatment of hypertension.

Mitochondria in Structural and Functional Cardiac Remodeling

The heart must function continuously as it is responsible for both supplying oxygen and nutrients throughout the entire body, as well as for the transport of waste products to excretory organs. When facing either a physiological or pathological increase in cardiac demand, the heart undergoes structural and functional remodeling as a means of adapting to increased workload. These adaptive responses can include changes in gene expression, protein composition, and structure of sub-cellular organelles involved in energy production and metabolism. Mitochondria are essential for cardiac function, as they supply the ATP necessary to support continuous cycles of contraction and relaxation. In addition, mitochondria carry out other important processes, including synthesis of essential cellular components, calcium buffering, and initiation of cell death signals. Not surprisingly, mitochondrial dysfunction has been linked to several cardiovascular disorders, including hypertension, cardiac hypertrophy, ischemia/reperfusion and heart failure. The present chapter will discuss how changes in mitochondrial cristae structure, fusion/fission dynamics, fatty acid oxidation, ATP production, and the generation of reactive oxygen species might impact cardiac structure and function, particularly in the context of pathological hypertrophy and fibrotic response. In addition, the mechanistic role of mitochondria in autophagy and programmed cell death of cardiomyocytes will be addressed. Here we will also review strategies to improve mitochondrial function and discuss their cardioprotective potential.

Oxidative Stress and Hypertensive Diseases

It has become clear that reactive oxygen species (ROS) contribute to the development of hypertension via myriad effects. ROS are essential for normal cell function; however, they mediate pathologic changes in the brain, the kidney, and blood vessels that contribute to the genesis of chronic hypertension. There is also emerging evidence that ROS contribute to immune activation in hypertension. This article discusses these events and how they coordinate to contribute to hypertension and its consequent end-organ damage.

Phos-tag SDS-PAGE resolves agonist- and isoform-specific activation patterns for PKD2 and PKD3 in cardiomyocytes and cardiac fibroblasts

Protein kinase D (PKD) consists of a family of three structurally related enzymes that are co-expressed in the heart and have important roles in many biological responses. PKD1 is activated by pro-hypertrophic stimuli and has been implicated in adverse cardiac remodeling. Efforts to define the cardiac actions of PKD2 and PKD3 have been less successful at least in part because conventional methods provide a general screen for PKD activation but are poorly suited to resolve activation patterns for PKD2 or PKD3. This study uses Phos-tag SDS-PAGE, a method that exaggerates phosphorylation-dependent mobility shifts, to overcome this technical limitation. Phos-tag SDS-PAGE resolves PKD1 as distinct molecular species (indicative of pools of enzyme with distinct phosphorylation profiles) in unstimulated cardiac fibroblasts and cardiomyocytes; as a result, attempts to track PKD1 mobility shifts that result from agonist activation were only moderately successful. In contrast, PKD2 and PKD3 are recovered from resting cardiac fibroblasts and cardiomyocytes as single molecular species; both enzymes display robust mobility shifts in Phos-tag SDS-PAGE in response to treatment with sphingosine-1-phosphate, thrombin, PDGF, or H₂O₂. Studies with GF109203X implicate protein kinase C activity in the stimulus-dependent pathways that activate PKD2/PKD3 in both cardiac fibroblasts and cardiomyocytes. Studies with C3 toxin identify a novel role for Rho in the sphingosine-1-phosphate and thrombin receptor-dependent pathways that lead to the phosphorylation of PKD2/3 and the downstream substrate CREB in cardiomyocytes. In conclusion, Phos-tag SDS-PAGE provides a general screen for stimulus-specific changes in PKD2 and PKD3 phosphorylation and exposes a novel role for these enzymes in specific stress-dependent pathways that influence cardiac remodeling.

Diminazene aceturate, an angiotensin-converting enzyme II activator, prevents gastric mucosal damage in mice: Role of the angiotensin-(1-7)/Mas receptor axis

The angiotensin (Ang) II converting enzyme (ACE II) pathway has recently been shown to be associated with several beneficial effects in various organisms, including gastroprotection. ACE II is responsible for converting Ang II into an active peptide, Ang-(1-7), which in turn binds the Mas receptor. Recent studies have shown that diminazene aceturate (Dize) a trypanocidal used in animals, activates ACE II. Thus, in this study, we aimed to evaluate the gastroprotective effects of Dize via the ACE II/Ang-(1-7)/Mas receptor pathway against gastric lesions induced by ethanol and acetic acid in mice. The results showed that Dize could promote gastric protection via several mechanisms, including increased levels of antioxidants and anti-inflammatory factors (e.g., decreasing tumor necrosis factor and interleukin-6 expression and reducing myeloperoxidase activity), maturation of collagen fibers, and promotion of re-epithelialization and regeneration of gastric tissue in different injury models. Thus, Dize represents a novel potential gastroprotective agent.

Electrical consequences of cardiac myocyte: fibroblast coupling

Gap junctions are channels which allow electrical signals to propagate through the heart from the sinoatrial node and through the atria, conduction system and onwards to the ventricles, and hence are essential for co-ordinated cardiac contraction. Twelve connexin (Cx) proteins make up one gap junction channel, of which there are three main subtypes in the heart; Cx40, Cx43 and Cx45. In the cardiac myocyte, gap junctions are present mainly at the intercalated discs between neighbouring myocytes, and assist in rapid electrical conduction throughout the ventricular myocardium. Fibroblasts provide the structural skeleton of the myocardium and fibroblast numbers significantly increase in heart disease. Fibroblasts also express connexins and this may facilitate heterocellular electrical coupling between myocytes and fibroblasts in the setting of cardiac disease. Interestingly, cardiac fibroblasts have been demonstrated to increase Cx43 expression in experimental models of myocardial infarction and functional gap junctions between myocytes and fibroblasts have been reported. Therefore, in the setting of heart disease enhanced cardiac myocyte: fibroblast coupling may influence the electrical activity of the myocyte and contribute to arrhythmias.

PEP-1-SOD1 fusion proteins block cardiac myofibroblast activation and angiotensin II-induced collagen production

Background

Oxidative stress is closely associated with cardiac fibrosis. However, the effect of copper, zinc-superoxide dismutase (SOD1) as a therapeutic agent is limited due to the insufficient transduction. This study was aimed to investigate the effect of PEP-1-SOD1 fusion protein on angiotensin II (ANG II)-induced collagen metabolism in rat cardiac myofibroblasts (MCFs).

Methods

MCFs were pretreated with SOD1 or PEP-1-SOD1 fusion protein for 2 h followed by incubation with ANG II for 24 h. Cell proliferation was measured by Cell Counting Kit-8. Superoxide anion productions were detected by both fluorescent microscopy and Flow Cytometry. MMP-1 and TIMP-1 were determined by ELISA. Intracellular MDA content and SOD activity were examined by commercial assay kits. Protein expression was analyzed by western blotting.

Results

PEP-1-SOD1 fusion protein efficiently transduced into MCF, scavenged intracellular O₂⁻, decreased intracellular MDA content, increased SOD activity, suppressed ANG II-induced proliferation, reduced expression of TGF-β1, α-SMA, collagen type I and III, restored MMP-1 secretion, and attenuated TIMP-1 secretion.

Conclusion

PEP-1-SOD1 suppressed MCF proliferation and differentiation and reduced production of collagen type I and III. Therefore, PEP-1-SOD1 fusion protein may be a potential novel therapeutic agent for cardiac fibrosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12872-015-0103-4) contains supplementary material, which is available to authorized users.

Cardiac melanocytes influence atrial reactive oxygen species involved with electrical and structural remodeling in mice

Cardiac melanocyte-like cells (CMLCs) contribute to atrial arrhythmias when missing the melanin synthesis enzyme dopachrome tautomerase (Dct). While scavenging reactive oxygen species (ROS) in Dct-null mice partially suppressed atrial arrhythmias, it remains unclear if CMLCs influence atrial ROS and structure or if the electrical response of CMLCs to ROS differs from that of atrial myocytes. This study is designed to determine if CMLCs contribute to overall atrial oxidative stress or structural remodeling, and if ROS affects the electrophysiology of CMLCs differently than atrial myocytes. Immunohistochemical analysis showed higher expression of the oxidative marker 8-hydroxy-2′-deoxyguanosine in Dct-null atria versus Dct-heterozygous (Dct-het) atria. Exposing isolated CMLCs from Dct-het and Dct-null mice to hydrogen peroxide increased superoxide anion more in Dct-null CMLCs. Trichrome staining showed increased fibrosis in Dct-null atria, and treating Dct-null mice with the ROS scavenger Tempol reduced atrial fibrosis. Action potential recordings from atrial myocytes and isolated Dct-het and Dct-null CMLCs in response to hydrogen peroxide showed that the EC₅₀ for action potential duration (APD) prolongation of Dct-null CMLCs was 8.2 ± 1.7 μmol/L versus 16.8 ± 2.0 μmol/L for Dct-het CMLCs, 19.9 ± 2.1 μmol/L for Dct-null atrial myocytes, and 20.5 ± 1.9 μmol/L for Dct-het atrial myocytes. However, APD₉₀ was longer in CMLCs versus atrial myocytes in response to hydrogen peroxide. Hydrogen peroxide also induced more afterdepolarizations in CMLCs compared to atrial myocytes. These studies suggest that Dct within CMLCs contributes to atrial ROS balance and remodeling. ROS prolongs APD to a greater extent and induces afterdepolarizations more frequently in CMLCs than in atrial myocytes.

Activation of common signaling pathways during remodeling of the heart and the bladder

The heart and the urinary bladder are hollow muscular organs, which can be afflicted by pressure overload injury due to pathological conditions such as hypertension and bladder outlet obstruction. This increased outflow resistance induces hypertrophy, marked by dramatic changes in the organs' phenotype and function. The end result in both the heart and the bladder can be acute organ failure due to advanced fibrosis and the subsequent loss of contractility. There is emerging evidence that microRNAs (miRNAs) play an important role in the pathogenesis of heart failure and bladder dysfunction. MiRNAs are endogenous non-coding single-stranded RNAs, which regulate gene expression and control adaptive and maladaptive organ remodeling processes. This Review summarizes the current knowledge of molecular alterations in the heart and the bladder and highlights common signaling pathways and regulatory events. The miRNA expression analysis and experimental target validation done in the heart provide a valuable source of information for investigators working on the bladder and other organs undergoing the process of fibrotic remodeling. Aberrantly expressed miRNA are amendable to pharmacological manipulation, offering an opportunity for development of new therapies for cardiac and bladder hypertrophy and failure.

A metabolite of Danshen formulae attenuates cardiac fibrosis induced by isoprenaline, via a NOX2/ROS/p38 pathway

BACKGROUND AND PURPOSE

Cardiac fibrosis is a common feature of advanced coronary heart disease and is characteristic of heart disease. However, currently available drugs against cardiac fibrosis are still very limited. Here, we have assessed the role of isopropyl 3-(3,4-dihydroxyphenyl)-2-hydroxylpropanoate (IDHP), a new metabolite of Danshen Dripping Pills, in cardiac fibrosis mediated by the β-adrenoceptor agonist, isoprenaline, and its underlying mechanisms.

EXPERIMENTAL APPROACH

Identification of IDHP was identified by mass spectrometry, and proton and carbon nuclear magnetic resonance spectra. Myocardial collagen was quantitatively assessed with Picrosirius Red staining. Expression of mRNA for collagen was evaluated with real-time PCR. Phosphorylated and total p38 MAPK, NADPH oxidase (NOX) and superoxide dismutase (SOD) were analysed by Western blot. Generation of reactive oxygen species (ROS) generation was evaluated by dihydroethidium (DHE) fluorescent staining. NOX2 was knocked down using specific siRNA.

KEY RESULTS

IDHP attenuated β-adrenoceptor mediated cardiac fibrosis in vivo and inhibited isoprenaline-induced proliferation of neonatal rat cardiac fibroblasts (NRCFs) and collagen I synthesis in vitro. Phosphorylation of p38 MAPK, which is an important mediator in the pathogenesis of isoprenaline-induced cardiac fibrosis, was inhibited by IDHP. This inhibition of phospho-p38 by IDHP was dependent on decreased generation of ROS. These effects of IDHP were abolished in NRCFs treated with siRNA for NOX2.

CONCLUSIONS AND IMPLICATIONS

IDHP attenuated the cardiac fibrosis induced by isoprenaline through a NOX2/ROS/p38 pathway. These novel findings suggest that IDHP is a potential pharmacological candidate for the treatment of cardiac fibrosis, induced by β-adrenoceptor agonists.

Hyperglycemia and angiotensin II cooperate to enhance collagen I deposition by cardiac fibroblasts through a ROS-STAT3-dependent mechanism

Cardiac fibroblasts significantly contribute to diabetes-induced structural and functional changes in the myocardium. The objective of the present study was to determine the effects of high glucose (alone or supplemented with angiotensin II) in the activation of the JAK2/STAT3 pathway and its involvement in collagen I production by cardiac fibroblasts. We observed that the diabetic environment 1) enhanced tyrosine phosphorylation of JAK2 and STAT3; 2) induced nuclear localization of tyrosine phosphorylated STAT3 through a reactive oxygen species-mediated mechanism, with angiotensin II stimulation further enhancing STAT3 nuclear accumulation; and 3) stimulated collagen I production. The effects were inhibited by depletion of reactive oxygen species or silencing of STAT3 in high glucose alone or supplemented with exogenous angiotensin II. Combined, our data demonstrate that increased collagen I deposition in the setting of high glucose occurred through a reactive oxygen species- and STAT3-dependent mechanism. Our results reveal a novel role for STAT3 as a key signaling molecule of collagen I production in cardiac fibroblasts exposed to a diabetic environment.

The pathogenesis of cardiac fibrosis

Cardiac fibrosis is characterized by net accumulation of extracellular matrix proteins in the cardiac interstitium, and contributes to both systolic and diastolic dysfunction in many cardiac pathophysiologic conditions. This review discusses the cellular effectors and molecular pathways implicated in the pathogenesis of cardiac fibrosis. Although activated myofibroblasts are the main effector cells in the fibrotic heart, monocytes/macrophages, lymphocytes, mast cells, vascular cells and cardiomyocytes may also contribute to the fibrotic response by secreting key fibrogenic mediators. Inflammatory cytokines and chemokines, reactive oxygen species, mast cell-derived proteases, endothelin-1, the renin/angiotensin/aldosterone system, matricellular proteins, and growth factors (such as TGF-β and PDGF) are some of the best-studied mediators implicated in cardiac fibrosis. Both experimental and clinical evidence suggests that cardiac fibrotic alterations may be reversible. Understanding the mechanisms responsible for initiation, progression, and resolution of cardiac fibrosis is crucial to design anti-fibrotic treatment strategies for patients with heart disease.

Fibroblasts in myocardial infarction: a role in inflammation and repair

Fibroblasts do not only serve as matrix-producing reparative cells, but exhibit a wide range of functions in inflammatory and immune responses, angiogenesis and neoplasia. The adult mammalian myocardium contains abundant fibroblasts enmeshed within the interstitial and perivascular extracellular matrix. The current review manuscript discusses the dynamic phenotypic and functional alterations of cardiac fibroblasts following myocardial infarction. Extensive necrosis of cardiomyocytes in the infarcted heart triggers an intense inflammatory reaction. In the early stages of infarct healing, fibroblasts become pro-inflammatory cells, activating the inflammasome and producing cytokines, chemokines and proteases. Pro-inflammatory cytokines (such as Interleukin-1) delay myofibroblast transformation, until the wound is cleared from dead cells and matrix debris. Resolution of the inflammatory infiltrate is associated with fibroblast migration, proliferation, matrix protein synthesis and myofibroblast conversion. Growth factors and matricellular proteins play an important role in myofibroblast activation during the proliferative phase of healing. Formation of a mature cross-linked scar is associated with clearance of fibroblasts, as poorly-understood inhibitory signals restrain the fibrotic response. However, in the non-infarcted remodeling myocardium, local fibroblasts may remain activated in response to volume and pressure overload and may promote interstitial fibrosis. Considering their abundance, their crucial role in cardiac inflammation and repair, and their involvement in myocardial dysfunction and arrhythmogenesis, cardiac fibroblasts may be key therapeutic targets in cardiac remodeling. This article is part of a Special Issue entitled Myocyte-Fibroblast Signalling in Myocardium.

IL-1β suppresses TGF-β-mediated myofibroblast differentiation in cardiac fibroblasts

Cardiac fibrosis is a maladaptive response of the injured myocardium and is mediated through a complex interplay between molecular triggers and cellular responses. Interleukin (IL)-1β is a key inflammatory inducer in cardiac disease and promotes cell invasion and cardiomyocyte injury, but little is known of its impact on fibrosis. A major cornerstone of fibrosis is the differentiation of cardiac fibroblasts (CFs) into myofibroblasts (myoFbs), which is highly promoted by Transforming Growth Factor (TGF)-β. Therefore, we asked how IL-1β functionally modulated CF-to-myoFb differentiation. Using a differentiation model of ventricular fibroblasts, we found that IL-1β instigated substantial anti-fibrogenic effects. In specific, IL-1β reduced proliferation, matrix activity, cell motility and α-smooth muscle actin expression, which are all hallmarks of myoFb differentiation. These findings suggest that IL-1β, besides from its acknowledged adverse role in the inflammatory response, can also exert beneficial effects in cardiac fibrosis by actively suppressing differentiation of CFs into fibrogenic myoFbs.

Angiotensin II-induced mitochondrial reactive oxygen species and peroxiredoxin-3 expression in cardiac fibroblasts

OBJECTIVE

The aim of this study was to determine whether angiotensin II (ANG II) affects the protein and mRNA expression of the mitochondrial antioxidant peroxiredoxin-3 (Prx-3) in cardiac fibroblasts, thereby contributing to the oxidative stress in the myocardium.

METHOD

Cardiac fibroblasts (passage 2) from normal male adult rats were cultured to confluency and incubated in Dulbecco's modified Eagle's medium for 24  h. The cells were then preincubated with(out) the tested inhibitors for 1  h and further incubated with/without ANG II (1 μmol/l) for 24  h.

RESULTS

ANG II increased (P < 0.001) the mitochondrial production of reactive oxygen species in cardiac fibroblasts from 187.8 ± 38.6 to 313.8 ± 30.6 a.u./mg mitochondrial protein (n = 15). ANG II decreased (P < 0.01) the mRNA and protein expression of Prx-3 by 36.9 ± 3.0% and 29.7 ± 2.7% (n = 4), respectively. The ANG II-induced decrease in mRNA expression of Prx-3 was prevented by the angiotensin type 1 receptor blocker, losartan but not by the angiotensin type 2 receptor blocker, PD 123 319.

CONCLUSION

Our data indicate that ANG II-stimulated mitochondrial reactive oxygen species production in rat cardiac fibroblasts is accompanied by a reduction in the expression of the mitochondrial antioxidant Prx-3, and thereby potentially contributing to oxidative stress in the myocard.

Hydrogen peroxide-mediated oxidative stress and collagen synthesis in cardiac fibroblasts: blockade by tanshinone IIA

ETHNOPHARMACOLOGICAL RELEVANCE

We have recently reported that tanshinone IIA attenuated cardiac fibrosis in two-kidney, two-clip renovascular hypertensive rats via inhibiting NAD(P)H oxidase. However, little is known about the cellular and molecular mechanisms of tanshinone IIA mediated anti-fibrotic effects in cardiac fibroblasts after H(2)O(2) stimulation. The present study was performed to investigate whether H(2)O(2) may increase collagen synthesis in cardiac fibroblasts by affecting the expression and activity of NAD(P)H oxidase and whether the effects of H(2)O(2) on cardiac fibroblasts can be blocked by treatment of tanshinone IIA.

MATERIALS AND METHODS

Cardiac fibroblasts were treated with H(2)O(2) (100 μmol/L) in the presence or absence of tanshinone IIA (1 μmol/L), NAD(P)H oxidase inhibitors diphenyleneiodonium (10 μmol/L), siRNA-p47phox, siRNA-Nox2 and siRNA-Nox4. Collagen synthesis was measured by [(3)H]proline incorporation, O(2)(-) production were determined by flow cytometry and DHE fluorescence microscopy. NAD(P)H oxidase activity was measured by lucigenin-enhanced chemiluminescence.

RESULTS

H(2)O(2) induced the activity of NAD(P)H oxidase, O(2)(-) production, collagen synthesis and fibronectin expression in cardiac fibroblasts, and DPI abolished this induction. Exposure of adult rat cardiac fibroblasts to H(2)O(2) had time-dependent increase in the expression of p47phox, Nox2 and Nox4 oxidases. In addition, tanshinone IIA significantly inhibited H(2)O(2)-induced collagen synthesis via attenuation of O(2)(-) generation and NAD(P)H oxidase activity. Moreover, siRNA-mediated knockdown of p47phox, Nox2 and Nox4 inhibited H(2)O(2)-induced NADPH oxidase activity. H(2)O(2)-induced collagen synthesis and fibronectin expression were also inhibited by p47phox, Nox2 and Nox4 knock down.

CONCLUSIONS

Our data show that NAD(P)H oxidase plays a significant role in regulating collagen synthesis in H(2)O(2)-stimulated cardiac fibroblasts. Inhibition of NAD(P)H oxidase with tanshinone IIA completely blocked the H(2)O(2)-stimulated collagen production, which will raise the experimental basis for using tanshinone IIA to cardiac fibrosis in clinic.

Fibroblasts in post-infarction inflammation and cardiac repair

Fibroblasts are the predominant cell type in the cardiac interstitium. As the main matrix-producing cells in the adult mammalian heart, fibroblasts maintain the integrity of the extracellular matrix network, thus preserving geometry and function. Following myocardial infarction fibroblasts undergo dynamic phenotypic alterations and direct the reparative response. Due to their strategic location, cardiac fibroblasts serve as sentinel cells that sense injury and activate the inflammasome secreting cytokines and chemokines. During the proliferative phase of healing, infarct fibroblasts undergo myofibroblast transdifferentiation forming stress fibers and expressing contractile proteins (such as α-smooth muscle actin). Mechanical stress, transforming growth factor (TGF)-β/Smad3 signaling and alterations in the composition of the extracellular matrix induce acquisition of the myofibroblast phenotype. In the highly cellular and growth factor-rich environment of the infarct, activated myofibroblasts produce matrix proteins, proteases and their inhibitors regulating matrix metabolism. As the infarct matures, "stress-shielding" of myofibroblasts by the cross-linked matrix and growth factor withdrawal may induce quiescence and ultimately cause apoptotic death. Because of their critical role in post-infarction cardiac remodeling, fibroblasts are promising therapeutic targets following myocardial infarction. However, the complexity of fibroblast functions and the pathophysiologic heterogeneity of post-infarction remodeling in the clinical context discourage oversimplified approaches in clinical translation. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.

Total Flavonoids of Fructus Chorspondiatis inhibits collagen synthesis of cultured rat cardiac fibroblasts induced by angiotensin II: correlated with NO/cGMP signaling pathway

AIM

To investigate the molecular mechanism of Total Flavonoids of Fructus Chorspondiatis (TFFC) on preventing cardiac fibroblasts collagen synthesis induced by angiotensin II.

METHODS

Collagen synthesis was determined by measuring (3)H-proline incorporation cardiac fibroblasts and hydroxyproline content in the culture mediums. The expression of collagen types I and III mRNA and protein was measured by RT-PCR and western blot, respectively. NO level in the culture medium was measured by the Griess reagent. NOS level in the culture medium was measured by chemical colorimetric method. The cellular concentration of cyclic GMP (cGMP) was measured by radioimmunoassay.

RESULTS

TFFC (25, 50, and 100mg/L) inhibited collagen synthesis in cardiac fibroblasts in a dose-dependent manner compared with angiotensin II group (P<0.01), and the inhibitory effects were blocked by pretreatment with NG-nitro-L-arginine methyl ester (L-NAME) and 1H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one (ODQ). TFFC increased nitric oxide (NO) and nitric oxide synthase (NOS) levels in the culture medium, increased intracellular cGMP level in cardiac fibroblasts, decreased collagen types I and III protein level in cardiac fibroblasts. The mRNA expression of collagen type I and III was suppressed by TFFC.

CONCLUSIONS

These results suggested that TFFC inhibited collagen synthesis induced by angiotensin II in cardiac fibroblasts, and the inhibitory effect might associate with the activation of the NO/cGMP signaling pathway.