Cardiac remodeling by fibrous tissue after infarction in rats

Simulated Effects of Acute Left Ventricular Myocardial Infarction on Mitral Regurgitation in an Ovine Model

Ischemic mitral regurgitation (IMR) occurs from incomplete coaptation of the mitral valve (MV) after myocardial infarction (MI), typically worsened by continued remodeling of the left ventricular (LV). The importance of LV remodeling is clear as IMR is induced by the post-MI dual mechanisms of mitral annular dilation and leaflet tethering from papillary muscle (PM) distension via the MV chordae tendineae (MVCT). However, the detailed etiology of IMR remains poorly understood, in large part due to the complex interactions of the MV and the post-MI LV remodeling processes. Given the patient-specific anatomical complexities of the IMR disease processes, simulation-based approaches represent an ideal approach to improve our understanding of this deadly disease. However, development of patient-specific models of left ventricle-mitral valve (LV-MV) interactions in IMR are complicated by the substantial variability and complexity of the MR etiology itself, making it difficult to extract underlying mechanisms from clinical data alone. To address these shortcomings, we developed a detailed ovine LV-MV finite element (FE) model based on extant comprehensive ovine experimental data. First, an extant ovine LV FE model (Sci. Rep. 2021 Jun 29;11(1):13466) was extended to incorporate the MV using a high fidelity ovine in vivo derived MV leaflet geometry. As it is not currently possible to image the MVCT in vivo, a functionally equivalent MVCT network was developed to create the final LV-MV model. Interestingly, in pilot studies, the MV leaflet strains did not agree well with known in vivo MV leaflet strain fields. We then incorporated previously reported MV leaflet prestrains (J. Biomech. Eng. 2023 Nov 1;145(11):111002) in the simulations. The resulting LV-MV model produced excellent agreement with the known in vivo ovine MV leaflet strains and deformed shapes in the normal state. We then simulated the effects of regional acute infarctions of varying sizes and anatomical locations by shutting down the local myocardial contractility. The remaining healthy (noninfarcted) myocardium mechanical behaviors were maintained, but allowed to adjust their active contractile patterns to maintain the prescribed pressure-volume loop behaviors in the acute post-MI state. For all cases studied, the LV-MV simulation demonstrated excellent agreement with known LV and MV in vivo strains and MV regurgitation orifice areas. Infarct location was shown to play a critical role in resultant MV leaflet strain fields. Specifically, extensional deformations of the posterior leaflets occurred in the posterobasal and laterobasal infarcts, while compressive deformations of the anterior leaflet were observed in the anterobasal infarct. Moreover, the simulated posterobasal infarct induced the largest MV regurgitation orifice area, consistent with experimental observations. The present study is the first detailed LV-MV simulation that reveals the important role of MV leaflet prestrain and functionally equivalent MVCT for accurate predictions of LV-MV interactions. Importantly, the current study further underscored simulation-based methods in understanding MV function as an integral part of the LV.

Phosphoproteomic and proteomic profiling in post-infarction chronic heart failure

Background: Post-infarction chronic heart failure is the most common type of heart failure. Patients with chronic heart failure show elevated morbidity and mortality with limited evidence-based therapies. Phosphoproteomic and proteomic analysis can provide insights regarding molecular mechanisms underlying post-infarction chronic heart failure and explore new therapeutic approaches. Methods and results: Global quantitative phosphoproteomic and proteomic analysis of left ventricular tissues from post-infarction chronic heart failure rats were performed. A total of 33 differentially expressed phosphorylated proteins (DPPs) and 129 differentially expressed proteins were identified. Bioinformatic analysis indicated that DPPs were enriched mostly in nucleocytoplasmic transport and mRNA surveillance pathway. Bclaf1 Ser658 was identified after construction of Protein-Protein Interaction Network and intersection with Thanatos Apoptosis Database. Predicted Upstream Kinases of DPPs based on kinase-substrate enrichment analysis (KSEA) app showed 13 kinases enhanced in heart failure. Proteomic analysis showed marked changes in protein expression related to cardiac contractility and metabolism. Conclusion: The present study marked phosphoproteomics and proteomics changes in post-infarction chronic heart failure. Bclaf1 Ser658 might play a critical role in apoptosis in heart failure. PRKAA1, PRKACA, and PAK1 might serve as potential therapeutic targets for post-infarction chronic heart failure.

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.

Photobiomodulation therapy's effects on cardiac fibrosis activation after experimental myocardial infarction

INTRODUCTION

Ischemic heart disease is the leading cause of death worldwide, and interventions to reduce myocardial infarction (MI) complications are widely researched. Photobiomodulation therapy (PBMT) has altered multiple biological processes in tissues and organs, including the heart.

OBJECTIVES

This study aimed to assess the temporal effects of PBMT on cardiac fibrosis activation after MI in rats. In this proof-of-concept study, we monitored the change in expression patterns over time of genes and microRNAs (miRNAs) involved in the formation of cardiac fibrosis post-MI submitted to PBMT.

MATERIALS AND METHODS

Experimental MI was induced, and PBMT was applied shortly after coronary artery ligation (laser light of wavelength 660 nm, 15 mW of power, energy density 22.5 J/cm² , 60 seconds of application, irradiated area 0.785 cm² , fluence 1.1 J/cm² ). Ventricular septal samples were collected at 30 minutes, 3, 6, 24 hours, and 3 days post-MI to determine temporal PBMT's effects on messenger RNA (mRNA) expression associated with cardiac fibrosis activation and miRNAs expression.

RESULTS

PBMT, when applied after ischemia, reversed the changes in mRNA expression of myocardial extracellular matrix genes induced by MI. Surprisingly, PBMT modified cardiac miRNAs expression related to fibrosis replacement in the myocardium. Expression correlations between myocardial mRNAs were assessed. The correlation coefficient between miRNAs and target mRNAs was also determined. A positive correlation was detected among miR-21 and transforming growth factor beta-1 mRNA. The miR-29a expression negatively correlated to Col1a1, Col3a1, and MMP-2 mRNA expressions. In addition, we observed that miR-133 and Col1a1 mRNA were negatively correlated.

CONCLUSION

The results suggest that PBMT, through the modulation of gene transcription and miRNA expressions, can interfere in cardiac fibrosis activation after MI, mainly reversing the signaling pathway of profibrotic genes.

MicroR-26b Targets High Mobility Group, AT-hook 2 to Ameliorate Myocardial Infarction-induced Fibrosis by Suppression of Cardiac Fibroblasts Activation

BACKGROUND

Myocardial Fibrosis (MF) is an important physiological change after myocardial infarction (MI). MicroRNA-26b (MiR-26b) has a certain inhibitory effect on pulmonary fibrosis. However, the role of miR-26b in MI-induced MF rats and underlying molecular mechanisms remain unknown.

METHODS

Forty male Sprague Dawley (SD) rats weighing 200-250 g were divided into four groups (n=10): Sham group, MF group, MF + negative control (NC) agomir group and MF + miR-26b agomir group. Cardiac fibroblasts were isolated from cardiac tissue. Fibrosis levels were detected by MASSON staining, while the expression of related genes was detected by RT-qPCR, Western blotting and Immunohistochemistry, respectively. TargetScan and dual-luciferase reporter assay were utilized to predict the relationship between miR-26b and high mobility group, AT-hook 2 (HMGA2).

RESULTS

The study found the expression of miR-26b to be down-regulated in the myocardium of MF rats (P<0.01). miR-26b overexpression in vitro significantly reduced the survival rate of cardiac fibroblasts and inhibited the expression of the fibrillar-associated protein (α-SMA alphasmooth muscle actin (α-SMA) and collagen I) (P<0.01). TargetScan indicated that HMGA2 was one of the target genes of miR-26b; dual-luciferase reporter assay further confirmed the targeted regulatory relationship (P<0.01). Moreover, miR-26b overexpression significantly reduced the expression of HMGA2 (P<0.01). Notably, HMGA2 overexpression reversed the inhibitory effect of miR-26b overexpression on cardiac fibroblast viability and the expression of α-SMA and collagen I (P<0.01). Animal experiments further indicated that miR-26b overexpression inhibited MIinduced rat MF by inhibiting the expression of HMGA2 (P<0.05, P<0.01).

CONCLUSION

In short, these findings indicate that miR-26b targets HMGA2 to ameliorate MI-induced fibrosis by suppression of cardiac fibroblasts activation.

Photobiomodulation Therapy on Myocardial Infarction in Rats: Transcriptional and Posttranscriptional Implications to Cardiac Remodeling

BACKGROUND AND OBJECTIVES

Induction of myocardial infarction (MI) in rats by occlusion of the left anterior descending coronary artery is an experimental model used in research to elucidate functional, structural, and molecular modifications associated with ischemic heart disease. Photobiomodulation therapy (PBMT) has become a therapeutic alternative by modulating various biological processes eliciting several effects, including anti-inflammatory and pro-proliferative actions. The main objective of this work was to evaluate the effect of PBMT in the modulation of transcriptional and post-transcriptional changes that occurred in myocardium signal transduction pathways after MI.

STUDY DESIGN/MATERIALS AND METHODS

Continuous wave (CW) non-thermal laser parameters were: 660 nm wavelength, power 15 mW, with a total energy of 0.9 J, fluence of 1.15 J/cm² , spot size of 0.785 cm² , and time of 60 seconds. Using in silico analysis, we selected and then, quantified the expression of messenger RNA (mRNA) of 47 genes of 9 signaling pathways associated with MI (angiogenesis, cell survival, hypertrophy, oxidative stress, apoptosis, extracellular matrix, calcium kinetics, cell metabolism, and inflammation). Messenger RNA expression quantification was performed in myocardial samples by polymerase chain reaction real-time array using TaqMan customized plates.

RESULTS

Our results evidenced that MI modified mRNA expression of several well-known biomarkers related to detrimental cardiac activity in almost all signaling pathways analyzed. However, PBMT reverted most of these transcriptional changes. More expressively, PBMT provoked a robust decrease in mRNA expression of molecules that participate in post-MI inflammation and ECM composition, such as IL-6, TNF receptor, TGFb1, and collagen I and III. Global microRNA (miRNA) expression analysis revealed that PBMT decreased miR-221, miR-34c, and miR-93 expressions post-MI, which are related to deleterious effects in cardiac remodeling.

CONCLUSION

Thus, the identification of transcriptional and post-transcriptional changes induced by PBMT may be used to interfere in the molecular dynamics of cardiac remodeling post-MI.

Myocardial transcription of inflammatory and remodeling markers in cats with hypertrophic cardiomyopathy and systemic diseases associated with an inflammatory phenotype

Feline hypertrophic cardiomyopathy (HCM) is characterized by macrophage-driven myocardial remodeling processes in a pro-inflammatory environment. To further investigate the mechanisms behind these processes, the myocardial transcription of cytokines and remodeling enzymes was comparatively assessed in cats with HCM and cats without cardiac diseases. Sixty-seven cats were included, 17 cats with HCM (including 5 with atrial thrombus; AT), and 50 cats without cardiac diseases. The latter comprised 10 control cats (no cardiac or relevant systemic disease), 34 cats with diseases suspected to be associated with a systemic inflammatory state of which 18 suffered from feline infectious peritonitis (FIP), and 6 cats with multicentric lymphoma. Samples from atria, ventricular free walls and interventricular septum were examined using quantitative reverse transcriptase PCR. The overall highest myocardial marker transcriptions were observed in cats with multicentric lymphoma, FIP and HCM, followed by diseases likely associated with a systemic inflammatory state, and control cats. Inflammatory marker transcription predominated in the myocardium of cats with systemic inflammatory diseases, whereas in HCM the transcription of remodeling enzymes prevailed. Sex significantly influenced the myocardial transcription of several remodeling enzymes. These results suggest a versatile myocardial response depending on the disease and illustrates the relevance of sex for the cardiac response to cardiac and systemic disease in cats. A systemic inflammatory state appears to elicit an inflammatory phenotype in the myocardium, whereas in HCM, the myocardium mediates its own remodeling. In HCM, the identified markers might be involved in the ongoing remodeling processes causing structural and functional changes.

Epigenetic Control of circHNRNPH1 in Postischemic Myocardial Fibrosis through Targeting of TGF-β Receptor Type I

Postischemic myocardial fibrosis is a factor for the development of cardiac dysfunction and malignant cardiac arrhythmias, and no effective therapy is currently available. Circular RNAs are emerging as important epigenetic players in various biological functions; however, their roles in cardiac fibrosis are unknown. With the use of a rat model of postischemic myocardial fibrosis, we identified an increase in circHNRNPH1 in the ischemic myocardium after myocardial infarction, particularly in cardiac fibroblasts. In cardiac fibroblasts, circHNRNPH1 was responsive to transforming growth factor β1 (TGF-β1), the principal profibrotic factor. The downregulation of circHNRNPH1, in contrast to its overexpression, promoted myofibroblast migration and α-smooth muscle actin and collagen I expression and inhibited myofibroblast apoptosis. The recombinant adeno-associated virus 9 (rAAV9)-mediated, cardiac-specific knockdown of circHNNRPH1 accordingly facilitated cardiac fibrosis and aggravated cardiac dysfunction. Mechanistically, circHNRNPH1 colocalized with and sponged microRNA (miR)-216-5p in the cytoplasm of cardiac fibroblasts to induce SMAD7 (protein family of signal transduction component of the canonical transforming growth factor-β signaling pathway) expression, accelerating the degradation of TGF-β receptor I. Thus, our results indicated that circHNRNPH1 negatively regulates the fibrogenesis of cardiac fibroblasts and may provide a new therapeutic strategy for postischemic myocardial fibrosis.

Cholecystokinin octapeptide reduces myocardial fibrosis and improves cardiac remodeling in post myocardial infarction rats

BACKGROUND/AIMS

Myocardial infarction (MI) increases myocardial fibrosis (MF) and subsequent cardiac remodeling. Cholecystokinin octapeptide (CCK-8) is expressed in cardiomyocytes and plays an important role in cardiovascular regulation. In this study, we intend to use a rat model of myocardial infarction to evaluate the effects of CCK-8 on myocardial fibrosis and cardiac remodeling.

METHODS

Male Sprague-Dawley rats were separated into 3 groups: sham operation, MI + NaCl, and MI + CCK-8. All rats were subjected to left coronary artery ligation to induce MI or sham operation and then treated with CCK-8 or saline for 28 days. After 4 weeks, echocardiography was performed to assess cardiac function and myocardial fibrosis was evaluated using H&E and Masson's Trichrome-stained sections. The levels of BNP, CCK-8 in the plasma of all rats were detected by ELISA; RNA sequencing (RNA-seq) analysis was also adapted to detect differentially expressed genes in myocardial tissues of each group. Myocardial expression of fibrosis markers was analyzed by western blotting, immunohistochemistry and qRT-PCR.

RESULTS

CCK-8 was demonstrated to improve left ventricular function and results of H&E staining, Masson's trichrome staining, immunohistochemistry and western blotting showed that CCK-8 attenuated MF. Gene expression profiles of the left ventricles were analysed by RNA-seq and validated by qRT-PCR. Cardiac fibrosis genes were downregulated by CCK-8 in the left ventricle.

SIGNIFICANCE

CCK-8 can alleviate fibrosis in the noninfarcted regions and delay the left ventricular remodeling and the progress of heart failure in a MI rat model.

Medium-term Electrophysiologic Effects of a Cellularized Scaffold Implanted in Rats After Myocardial Infarction

Background Cardiac repair strategies are being evaluated for myocardial infarctions, but the safety issues regarding their arrhythmogenic potential remain unresolved. By utilizing the in-vivo rat model, we have examined the medium-term electrophysiologic effects of a biomaterial scaffold that has been cellularized with spheroids of human adipose tissue, derived from mesenchymal stem cells and umbilical vein endothelial cells. Methods Mesenchymal stem cells, which exhibit adequate differentiation capacity, were co-cultured with umbilical vein endothelial cells and were seeded on an alginate based scaffold. After in-vitro characterization, the cellularized scaffold was implanted in (n=15) adult Wistar rats 15 min post ligation of the left coronary artery, with an equal number of animals serving as controls. Two weeks thereafter, monophasic action potentials were recorded and activation-mapping was performed with a multi-electrode array. An arrhythmia score for inducible ventricular tachyarrhythmias was calculated after programmed electrical stimulation. Results The arrhythmia score was comparable between the treated animals and controls. No differences were detected in the local conduction at the infarct border and in the voltage rise in monophasic action potential recordings. Treatment did not affect the duration of local repolarization, but tended to enhance its dispersion. Conclusions The fabricated bi-culture cellularized scaffold displayed favorable properties after in-vitro characterization. Medium-term electrophysiologic assessment after implantation in the infarcted rat myocardium revealed low arrhythmogenic potential, but the long-term effects on repolarization dispersion will require further investigation.

Immune cells in repair of the infarcted myocardium

The immune system plays a critical role in both repair and remodeling of the infarcted myocardium. Danger signals released by dying cardiomyocytes mobilize, recruit, and activate immune cells, triggering an inflammatory reaction. CXC chemokines containing the ELR motif attract neutrophils, while CC chemokines mediate recruitment of mononuclear cell subpopulations, contributing to clearance of the infarct from dead cells and matrix debris. Immune cell subsets also participate in suppression and containment of the postinfarction inflammatory response by secreting anti-inflammatory mediators, such as IL-10 and TGF-β. As proinflammatory signaling is suppressed, macrophage subpopulations, mast cells and lymphocytes, activate fibrogenic and angiogenic responses, contributing to scar formation. In the viable remodeling myocardium, chronic activation of immune cells may promote fibrosis and hypertrophy. This review discusses the role of immune cells in repair and remodeling of the infarcted myocardium. Understanding the role of immune cells in myocardial infarction is critical for the development of therapeutic strategies aimed at protecting the infarcted heart from adverse remodeling. Moreover, modulation of immune cell phenotype may be required in order to achieve the visionary goal of myocardial regeneration.

Cardiac telomere length in heart development, function, and disease

Telomeres are repetitive nucleoprotein structures at chromosome ends, and a decrease in the number of these repeats, known as a reduction in telomere length (TL), triggers cellular senescence and apoptosis. Heart disease, the worldwide leading cause of death, often results from the loss of cardiac cells, which could be explained by decreases in TL. Due to the cell-specific regulation of TL, this review focuses on studies that have measured telomeres in heart cells and critically assesses the relationship between cardiac TL and heart function. There are several lines of evidence that have identified rapid changes in cardiac TL during the onset and progression of heart disease as well as at critical stages of development. There are also many factors, such as the loss of telomeric proteins, oxidative stress, and hypoxia, that decrease cardiac TL and heart function. In contrast, antioxidants, calorie restriction, and exercise can prevent both cardiac telomere attrition and the progression of heart disease. TL in the heart is also indicative of proliferative potential and could facilitate the identification of cells suitable for cardiac rejuvenation. Although these findings highlight the involvement of TL in heart function, there are important questions regarding the validity of animal models, as well as several confounding factors, that need to be considered when interpreting results and planning future research. With these in mind, elucidating the telomeric mechanisms involved in heart development and the transition to disease holds promise to prevent cardiac dysfunction and potentiate regeneration after injury.

Magnetic susceptibility anisotropy outside the central nervous system

Magnetic-susceptibility-based MRI has made important contributions to the characterization of tissue microstructure, chemical composition, and organ function. This has motivated a number of studies to explore the link between microstructure and susceptibility in organs and tissues throughout the body, including the kidney, heart, and connective tissue. These organs and tissues have anisotropic magnetic susceptibility properties and cellular organizations that are distinct from the lipid organization of myelin in the brain. For instance, anisotropy is traced to the epithelial lipid orientation in the kidney, the myofilament proteins in the heart, and the collagen fibrils in the knee cartilage. The magnetic susceptibility properties of these and other tissues are quantified using specific MRI tools: susceptibility tensor imaging (STI), quantitative susceptibility mapping (QSM), and individual QSM measurements with respect to tubular and filament directions determined from diffusion tensor imaging. These techniques provide complementary and supplementary information to that produced by traditional MRI methods. In the kidney, STI can track tubules in all layers including the cortex, outer medulla, and inner medulla. In the heart, STI detected myofibers throughout the myocardium. QSM in the knee revealed three unique layers in articular cartilage by exploiting the anisotropic susceptibility features of collagen. While QSM and STI are promising tools to study tissue susceptibility, certain technical challenges must be overcome in order to realize routine clinical use. This paper reviews essential experimental findings of susceptibility anisotropy in the body, the underlying mechanisms, and the associated MRI methodologies. Copyright © 2016 John Wiley & Sons, Ltd.

Development of a human cardiac organoid injury model reveals innate regenerative potential

The adult human heart possesses a limited regenerative potential following an ischemic event, and undergoes a number of pathological changes in response to injury. Although cardiac regeneration has been documented in zebrafish and neonatal mouse hearts, it is currently unknown whether the immature human heart is capable of undergoing complete regeneration. Combined progress in pluripotent stem cell differentiation and tissue engineering has facilitated the development of human cardiac organoids (hCOs), which resemble fetal heart tissue and can be used to address this important knowledge gap. This study aimed to characterize the regenerative capacity of immature human heart tissue in response to injury. Following cryoinjury with a dry ice probe, hCOs exhibited an endogenous regenerative response with full functional recovery 2 weeks after acute injury. Cardiac functional recovery occurred in the absence of pathological fibrosis or cardiomyocyte hypertrophy. Consistent with regenerative organisms and neonatal human hearts, there was a high basal level of cardiomyocyte proliferation, which may be responsible for the regenerative capacity of the hCOs. This study suggests that immature human heart tissue has an intrinsic capacity to regenerate.

Prolonged intra-myocardial growth hormone administration ameliorates post-infarction electrophysiologic remodeling in rats

Experimental studies indicate improved ventricular function after treatment with growth hormone (GH) post-myocardial infarction, but its effect on arrhythmogenesis is unknown. Here, we assessed the medium-term electrophysiologic remodeling after intra-myocardial GH administration in (n = 33) rats. GH was released from an alginate scaffold, injected around the ischemic myocardium after coronary ligation. Two weeks thereafter, ventricular tachyarrhythmias were induced by programmed electrical stimulation. Monophasic action potentials were recorded from the infarct border, coupled with evaluation of electrical conduction and repolarization from a multi-electrode array. The arrhythmia score was lower in GH-treated rats than in alginate-treated rats or controls. The shape and the duration of the action potential at the infarct border were preserved, and repolarization-dispersion was attenuated after GH; moreover, voltage rise was higher and activation delay was shorter. GH normalized also right ventricular parameters. Intra-myocardial GH preserved electrical conduction and repolarization-dispersion at the infarct border and decreased the incidence of induced tachyarrhythmias in rats post-ligation. The long-term antiarrhythmic potential of GH merits further study.

Renal ischemia/reperfusion-induced cardiac hypertrophy in mice: Cardiac morphological and morphometric characterization

Background

Tissue remodeling is usually dependent on the deposition of extracellular matrix that may result in tissue stiffness and impaired myocardium contraction.

Objectives

We had previously demonstrated that renal ischemia/reperfusion (I/R) is able to induce development of cardiac hypertrophy in mice. Therefore, we aimed to characterize renal I/R-induced cardiac hypertrophy.

Design

C57BL/6 J mice were subjected to 60 minutes’ unilateral renal pedicle occlusion, followed by reperfusion (I/R) for 5, 8, 12 or 15 days. Gene expression, protein abundance and morphometric analyses were performed in all time points.

Results

Left ventricle wall thickening was increased after eight days of reperfusion (p < 0.05). An increase in the number of heart ventricle capillaries and diameter after 12 days of reperfusion (p < 0.05) was observed; an increase in the density of capillaries starting at 5 days of reperfusion (p < 0.05) was also observed. Analyses of MMP2 protein levels showed an increase at 15 days compared to sham (p < 0.05). Moreover, TGF-β gene expression was downregulated at 12 days as well TIMP 1 and 2 (p < 0.05). The Fourier-transform infrared spectroscopy analysis showed that collagen content was altered only in the internal section of the heart (p < 0.05); such data were supported by collagen mRNA levels.

Conclusions

Renal I/R leads to impactful changes in heart morphology, accompanied by an increase in microvasculature. Although it is clear that I/R is able to induce cardiac remodeling, such morphological changes is present in only a section of the heart tissue.

VEGF-loaded microsphere patch for local protein delivery to the ischemic heart

BACKGROUND

Revascularization of the heart after myocardial infarction (MI) using growth factors delivered by hydrogel-based microspheres represents a promising therapeutic approach for cardiac regeneration. Microspheres have tuneable degradation properties and support the prolonged release of soluble factors. Cardiac patches provide mechanical restraint, preventing dilatation associated with ventricular remodelling.

METHODS

We combined these approaches and produced a compacted calcium-alginate microsphere patch, restrained by a chitosan sheet, to deliver vascular endothelial growth factor (VEGF) to the heart after myocardial injury in rats.

RESULTS

Microspheres had an average diameter of 3.2μm, were nonporous, and characterized by a smooth dimpled surface. Microsphere patches demonstrated prolonged in vitro release characteristics compared to non-compacted microspheres and VEGF supernatants obtained from patches maintained their bioactivity for the 5day duration of the study in vitro. In vivo, patches were assessed with magnetic resonance imaging following MI, and demonstrated 50% degradation 25.6days after implantation. Both VEGF^(-) and VEGF⁽⁺⁾ microsphere patch-treated hearts had better cardiac function than unpatched (chitosan sheet only) controls. However, VEGF⁽⁺⁾ microsphere-patched hearts had thicker scars characterized by higher capillary density in the border zone than did those treated with VEGF^(-) patches. VEGF was detected in the patches 4weeks post-implantation.

CONCLUSION

The condensed microsphere patch represents a new therapeutic platform for cytokine delivery and could be used as an adjuvant to current biomaterial and cell-based therapies to promote localized angiogenesis in the infarcted heart.

STATEMENT OF SIGNIFICANCE

Following a heart attack, a lack of blood flow to the heart results in loss of heart cells. Growth factors may facilitate growth of blood vessels and heart tissue repair and prevent the onset of heart failure. Determining a way to deliver these growth factors directly to the heart is vital. Here, we combined two biomaterial-based approaches to deliver vascular endothelial growth factor (VEGF) to rat hearts after heart attack: a microsphere for prolonged release of VEGF, and a cardiac patch for mechanical restraint to prevent heart dysfunction. The feasibility of this microsphere patch was demonstrated by surgically implanting it over the infarct region of the heart post-injury. VEGF-patched hearts had better blood vessel growth, tissue repair, and heart function.

Detection of small subendocardial infarction using speckle tracking echocardiography in a rat model

BACKGROUND

It is challenging to detect small nontransmural infarcts visually or automatically. As it is important to detect myocardial infarction (MI) at early stages, we tested the hypothesis that small nontransmural MI can be detected using speckle tracking echocardiography (STE) at the acute stage.

METHODS

Minimal nontransmural infarcts were induced in 18 rats by causing recurrent ischemia-reperfusion of the left anterior descending (LAD) coronary artery, followed by a 30-min ligation and by reperfusion. A week later, the scar size was measured by histological analysis. Each rat underwent three echocardiography measurements: at baseline, 1 day post-MI, and 1 week post-MI. To measure the peak circumferential strain (CS), peak systolic CS, radial strain (RS), and time-to-peak (TTP) of the CS, short-axis view of the apex was analyzed by a STE program. The TTP was normalized by the duration of the heart cycle to create percent change of heart cycle.

RESULTS

Histological analysis after 1 week showed scar size of 4±6% at the anterior wall. At 24 h post-MI, the peak CS, peak systolic CS, and RS were reduced compared to baseline at the anterior wall due to the MI, and at the adjacent segments-the anterior septum and lateral wall, due to stunning (P<.05). However, only the anterior wall, the genuine damaged segment, showed prolonged TTP vs baseline (baseline 36%, 24 h 48%, P<.05).

CONCLUSION

The TTP of the CS can distinguish between regions adjacent to MI (stunned or tethered) and MI, even in small nontransmural infarcts.

Differential activation of c‑Fos in the paraventricular nuclei of the hypothalamus and thalamus following myocardial infarction in rats

Proto-oncogene c-Fos (c-Fos) is frequently used to detect a pathogenesis in central nervous system disorders. The present study examined changes in the immunoreactivity of c-Fos in the paraventricular nucleus of the hypothalamus (PVNH) and paraventricular nucleus of the thalamus (PVNT) following myocardial infarction (MI) in rats. Infarction in the left ventricle was examined by Masson's trichrome staining. Neuronal degeneration was monitored for 56 days after MI using crystal violet and Fluoro-Jade B histofluorescence staining. Changes in the immunoreactivity of c-Fos were determined using immunohistochemistry for c-Fos. The average infarct size of the left ventricle circumference was ~44% subsequent to MI. Neuronal degeneration was not detected in PVNH and PVNT following MI. c-Fos immunoreactive (⁺) cells were infrequently observed in the nuclei of the sham-group. However, the number of c-Fos⁺ cells was increased in the nuclei following MI and peaked in the PVNH and PVNT at 3 and 14 days, respectively. The number of c-Fos⁺ cells were comparable with the sham group at 56 days after MI. Therefore, MI may induce c-Fos immunoreactivity in PVNH and PVNT, this increase of c-Fos expression levels may be associated with the stress that occurs in the brain following MI.

Stem cells and exosomes in cardiac repair

Cardiac diseases currently lead in the number of deaths per year, giving rise an interest in transplanting embryonic and adult stem cells as a means to improve damaged tissue from conditions such as myocardial infarction and coronary artery disease. After testing these cells as a treatment option in both animal and human models, it is believed that these cells improve the damaged tissue primarily through the release of autocrine and paracrine factors. Major concerns such as teratoma formation, immune response, difficulty harvesting cells, and limited cell proliferation and differentiation, hinder the routine use of these cells as a treatment option in the clinic. The advent of stem cell-derived exosomes circumvent those concerns, while still providing the growth factors, miRNA, and additional cell protective factors that aid in repairing and regenerating the damaged tissue. These exosomes have been found to be anti-apoptotic, anti-fibrotic, pro-angiogenic, as well as enhance cardiac differentiation, all of which are key to repairing damaged tissue. As such, stem cell derived exosomes are considered to be a potential new and novel approach in the treatment of various cardiac diseases.

Mitigation of myocardial fibrosis by molecular cardiac surgery-mediated gene overexpression

OBJECTIVE

Heart failure is accompanied by up-regulation of transforming growth factor beta signaling, accumulation of collagen and dysregulation of sarcoplasmic reticulum calcium adenosine triphosphatase cardiac isoform 2a (SERCA2a). We examined the fibrotic response in small and large myocardial infarct, and the effect of overexpression of the SERCA2a gene.

METHODS

Ischemic cardiomyopathy was induced via creation of large or small infarct in 26 sheep. Animals were divided into 4 groups: small infarct; large infarct with heart failure; gene-treated (large infarct with heart failure followed by adeno-associated viral vector, serotype 1.SERCA2a gene construct transfer by molecular cardiac surgery with recirculating delivery); and control.

RESULTS

Heart failure was significantly less pronounced in the gene-treated and small-infarct groups than in the large-infarct group. Expression of transforming growth factor beta signaling components was significantly higher in the large-infarct group, compared with the small-infarct and gene-treated groups. Both the angiotensin II type 1 receptor and angiotensin II were significantly elevated in the small- and large-infarct groups, whereas gene treatment diminished this effect. Active fibrosis with de novo collagen synthesis was evident in the large-infarct group; the small-infarct and gene-treated groups showed less fibrosis, with a lower ratio of de novo to mature collagen.

CONCLUSIONS

The data presented provide evidence that progression of fibrosis is mediated through increased transforming growth factor beta and angiotensin II signaling, which is mitigated by increased SERCA2a gene expression.

Activation of immediate-early response gene c-Fos protein in the rat paralimbic cortices after myocardial infarction

c-Fos is a good biological marker for detecting the pathogenesis of central nervous system disorders. Few studies are reported on the change in myocardial infarction-induced c-Fos expression in the paralimbic regions. Thus, in this study, we investigated the changes in c-Fos expression in the rat cingulate and piriform cortices after myocardial infarction. Neuronal degeneration in cingulate and piriform cortices after myocardial infarction was detected using cresyl violet staining, NeuN immunohistochemistry and Fluoro-Jade B histofluorescence staining. c-Fos-immunoreactive cells were observed in cingulate and piriform cortices at 3 days after myocardial infarction and peaked at 7 and 14 days after myocardial infarction. But they were hardly observed at 56 days after myocardial infarction. The chronological change of c-Fos expression determined by western blot analysis was basically the same as that of c-Fos immunoreactivity. These results indicate that myocardial infarction can cause the chronological change of immediate-early response gene c-Fos protein expression, which might be associated with the neural activity induced by myocardial infarction.

RhoA Ambivalently Controls Prominent Myofibroblast Characteritics by Involving Distinct Signaling Routes

Introduction

RhoA has been shown to be beneficial in cardiac disease models when overexpressed in cardiomyocytes, whereas its role in cardiac fibroblasts (CF) is still poorly understood. During cardiac remodeling CF undergo a transition towards a myofibroblast phenotype thereby showing an increased proliferation and migration rate. Both processes involve the remodeling of the cytoskeleton. Since RhoA is known to be a major regulator of the cytoskeleton, we analyzed its role in CF and its effect on myofibroblast characteristics in 2 D and 3D models.

Results

Downregulation of RhoA was shown to strongly affect the actin cytoskeleton. It decreased the myofibroblast marker α-sm-actin, but increased certain fibrosis-associated factors like TGF-β and collagens. Also, the detailed analysis of CTGF expression demonstrated that the outcome of RhoA signaling strongly depends on the involved stimulus. Furthermore, we show that proliferation of myofibroblasts rely on RhoA and tubulin acetylation. In assays accessing three different types of migration, we demonstrate that RhoA/ROCK/Dia1 are important for 2D migration and the repression of RhoA and Dia1 signaling accelerates 3D migration. Finally, we show that a downregulation of RhoA in CF impacts the viscoelastic and contractile properties of engineered tissues.

Conclusion

RhoA positively and negatively influences myofibroblast characteristics by differential signaling cascades and depending on environmental conditions. These include gene expression, migration and proliferation. Reduction of RhoA leads to an increased viscoelasticity and a decrease in contractile force in engineered cardiac tissue.

Strain Analysis in the Detection of Myocardial Infarction at the Acute and Chronic Stages

BACKGROUND

Myocardial ischemia causes contractile dysfunction in ischemic, stunned, and tethered regions with larger infarcted zones having a negative prognostic impact on patients' outcomes. To distinguish the infarcted myocardium from the other regions, we investigated the diagnostic potential of circumferential strain (CS) and radial strain (RS) during the acute and chronic stages of myocardial infarction.

METHODS

Ten pigs underwent 90-minute occlusion of the left anterior descending artery, followed by reperfusion. Echocardiography was performed at baseline, after 90-minute occlusion, and at 2 hours, 30, and 60 days postreperfusion. CS and RS were measured using speckle tracking echocardiography. Subsequently, the pigs were sacrificed, and histological analysis for infarct size was performed.

RESULTS

After 90-minute occlusion, reduced strains were detected for all segments (infarcted anterior wall - baseline: CS: -17.6 ± 5.7%, RS: 54.4 ± 16.9%; 90 min: CS: -10.3 ± 3.0%, RS: 23.3 ± 7.0%; tethered posterior wall - baseline: CS: -18.4 ± 3.5%, RS: 68.7 ± 21.1%; 90 min: CS: -10.7 ± 6.4%, RS: 34.5 ± 14.7%, P < 0.001). However, postsystolic shortening was detected only in the infarcted segments, and the time-to-peak CS was 25% longer (P < 0.05). At 30 and 60 days postreperfusion, time-to-peak CS could only detect large scars in the anterior and anterior-septum walls (P < 0.05), while peak CS also detected smaller scars in the lateral wall (P < 0.05). RS failed to distinguish between normal, stunned/tethered, and infarcted myocardium.

CONCLUSIONS

During occlusion and 2 hours postreperfusion, time-to-peak CS could distinguish between infarcted and stunned/tethered myocardial segments, while at 30 and 60 days postreperfusion, peak CS was the best detector of infarction.

Physiological Implications of Myocardial Scar Structure

Once myocardium dies during a heart attack, it is replaced by scar tissue over the course of several weeks. The size, location, composition, structure, and mechanical properties of the healing scar are all critical determinants of the fate of patients who survive the initial infarction. While the central importance of scar structure in determining pump function and remodeling has long been recognized, it has proven remarkably difficult to design therapies that improve heart function or limit remodeling by modifying scar structure. Many exciting new therapies are under development, but predicting their long-term effects requires a detailed understanding of how infarct scar forms, how its properties impact left ventricular function and remodeling, and how changes in scar structure and properties feed back to affect not only heart mechanics but also electrical conduction, reflex hemodynamic compensations, and the ongoing process of scar formation itself. In this article, we outline the scar formation process following a myocardial infarction, discuss interpretation of standard measures of heart function in the setting of a healing infarct, then present implications of infarct scar geometry and structure for both mechanical and electrical function of the heart and summarize experiences to date with therapeutic interventions that aim to modify scar geometry and structure. One important conclusion that emerges from the studies reviewed here is that computational modeling is an essential tool for integrating the wealth of information required to understand this complex system and predict the impact of novel therapies on scar healing, heart function, and remodeling following myocardial infarction.

(Pro)renin Receptor Blockade Ameliorates Cardiac Injury and Remodeling and Improves Function After Myocardial Infarction

BACKGROUND

The (pro)renin receptor [(P)RR] is implicated in the pathogenesis of cardiovascular disease. We investigated the effects of (P)RR blockade after myocardial infarction (MI) in a mouse coronary-ligation model.

METHODS AND RESULTS

Mice underwent sham control surgeries (n = 8) or induction of MI followed by 28 days' treatment with a vehicle control (n = 8) or (P)RR antagonist (n = 8). Compared with sham control subjects, MI + vehicle mice demonstrated reduced left ventricular (LV) ejection fraction (LVEF: P < .001) and fractional shortening (P < .001), and increased LV end-systolic and -diastolic volumes (LVESV: P < .001; LVEDV: P < .001) 28 days after MI. In addition, MI decreased LV posterior wall and septal diameters (both P < .001), increased heart weight-body weight ratios (P < .05), LV collagen deposition, and cardiomyocyte diameter (both P < .001), and up-regulated collagen 1 (P < .01) and β-myosin heavy chain (β-MHC: P < .05) mRNA. Compared with MI + vehicle mice, (P)RR antagonism after MI reduced infarct size (P < .01), improved LVEF (P < .001), fractional shortening (P < .001), and stroke volume (P < .05), and decreased LVESV (P < .001) and LVEDV (P < .001). (P)RR antagonism also reversed MI-induced transmural thinning (P < .001) and reduced LV fibrosis (P < .01), cardiomyocyte size (P < .001), and ventricular collagen 1 (P < .01), β-MHC (P = .06), transforming growth factor β1 (P < .01), and angiotensin-converting enzyme (P < .05) expression.

CONCLUSIONS

The present study found that (P)RR blockade after MI in mice ameliorates infarct size, cardiac fibrosis/hypertrophy, and cardiac dysfunction and identifies the receptor as a potential therapeutic target in this setting.

Cardiac remodeling and physical training post myocardial infarction

After myocardial infarction (MI), the heart undergoes extensive myocardial remodeling through the accumulation of fibrous tissue in both the infarcted and noninfarcted myocardium, which distorts tissue structure, increases tissue stiffness, and accounts for ventricular dysfunction. There is growing clinical consensus that exercise training may beneficially alter the course of post-MI myocardial remodeling and improve cardiac function. This review summarizes the present state of knowledge regarding the effect of post-MI exercise training on infarcted hearts. Due to the degree of difficulty to study a viable human heart at both protein and molecular levels, most of the detailed studies have been performed by using animal models. Although there are some negative reports indicating that post-MI exercise may further cause deterioration of the wounded hearts, a growing body of research from both human and animal experiments demonstrates that post-MI exercise may beneficially alter the course of wound healing and improve cardiac function. Furthermore, the improved function is likely due to exercise training-induced mitigation of renin-angiotensin-aldosterone system, improved balance between matrix metalloproteinase-1 and tissue inhibitor of matrix metalloproteinase-1, favorable myosin heavy chain isoform switch, diminished oxidative stress, enhanced antioxidant capacity, improved mitochondrial calcium handling, and boosted myocardial angiogenesis. Additionally, meta-analyses revealed that exercise-based cardiac rehabilitation has proven to be effective, and remains one of the least expensive therapies for both the prevention and treatment of cardiovascular disease, and prevents re-infarction.

Discrete microstructural cues for the attenuation of fibrosis following myocardial infarction

Chronic fibrosis caused by acute myocardial infarction (MI) leads to increased morbidity and mortality due to cardiac dysfunction. We have developed a therapeutic materials strategy that aims to mitigate myocardial fibrosis by utilizing injectable polymeric microstructures to mechanically alter the microenvironment. Polymeric microstructures were fabricated using photolithographic techniques and studied in a three-dimensional culture model of the fibrotic environment and by direct injection into the infarct zone of adult rats. Here, we show dose-dependent down-regulation of expression of genes associated with the mechanical fibrotic response in the presence of microstructures. Injection of this microstructured material into the infarct zone decreased levels of collagen and TGF-β, increased elastin deposition and vascularization in the infarcted region, and improved functional outcomes after six weeks. Our results demonstrate the efficacy of these discrete anti-fibrotic microstructures and suggest a potential therapeutic materials approach for combatting pathologic fibrosis.

Role of protein kinase C β₂ in relaxin-mediated inhibition of cardiac fibrosis

INTRODUCTION

Relaxin is a pleiotropic hormone owing endogenous antifibrosis effect on numerous organs. We demonstrated relaxin's inhibitive effect on cardiac fibrosis previously.

OBJECTIVE

The aim of this study was to investigate the role of protein kinase C (PKC) β2 in relaxin's action under high glucose conditions.

METHODS AND RESULTS

Cardiac fibroblasts (CFs) were isolated, exposed to high glucose and incubated with recombinant human relaxin (rhRLX). Western blot analysis revealed a relaxin-mediated decrease in total expression and translocation of PKCβ2, showing downregulation of PKCβ2 is involved in relaxin's action. Blocking PKCβ2 pathway with ruboxistaurin accelerated rhRLX-mediated inhibition in both proliferation of CFs and deposition of collagen.

CONCLUSION

In conclusion, relaxin can inhibit high glucose-associated cardiac fibrosis partly through PKCβ2 pathway. Further work should be done to fully understand intracellular mechanisms of relaxin's action to accelerate its clinical use.

Pathological mechanism for delayed hyperenhancement of chronic scarred myocardium in contrast agent enhanced magnetic resonance imaging

Objectives

To evaluate possible mechanism for delayed hyperenhancement of scarred myocardium by investigating the relationship of contrast agent (CA) first pass and delayed enhancement patterns with histopathological changes.

Materials and Methods

Eighteen pigs underwent 4 weeks ligation of 1 or 2 diagonal coronary arteries to induce chronic infarction. The hearts were then removed and perfused in a Langendorff apparatus. The hearts firstly experienced phosphorus 31 MR spectroscopy. The hearts in group I (n = 9) and II (n = 9) then received the bolus injection of Gadolinium diethylenetriamine pentaacetic acid (0.05 mmol/kg) and gadolinium-based macromolecular agent (P792, 15 µmol/kg), respectively. First pass T₂^* MRI was acquired using a gradient echo sequence. Delayed enhanced T₁ MRI was acquired with an inversion recovery sequence. Masson's trichrome and anti- von Willebrand Factor (vWF) staining were performed for infarct characterization.

Results

Wash-in of both kinds of CA caused the sharp and dramatic T₂^* signal decrease of scarred myocardium similar to that of normal myocardium. Myocardial blood flow and microvessel density were significantly recovered in 4-week-old scar tissue. Steady state distribution volume (ΔR₁ relaxation rate) of Gd-DTPA was markedly higher in scarred myocardium than in normal myocardium, whereas ΔR₁ relaxation rate of P792 did not differ significantly between scarred and normal myocardium. The ratio of extracellular volume to the total water volume was significantly greater in scarred myocardium than in normal myocardium. Scarred myocardium contained massive residual capillaries and dilated vessels. Histological stains indicated the extensively discrete matrix deposition and lack of cellular structure in scarred myocardium.

Conclusions

Collateral circulation formation and residual vessel effectively delivered CA into scarred myocardium. However, residual vessel without abnormal hyperpermeability allowed Gd-DTPA rather than P792 to penetrate into extravascular compartment. Discrete collagen fiber meshwork and loss of cellularity enlarged extracellular space accessible to Gd-DTPA, resulting in the delayed hyper-enhanced scar.

Beneficial effects of muscone on cardiac remodeling in a mouse model of myocardial infarction

Musk has been traditionally used in East Asia to alleviate the symptoms of angina pectoris. However, it remains unclear as to whether muscone, the main active ingredient of musk, has any beneficial effects on persistent myocardial ischemia in vivo. The aim of the present study was to investigate whether muscone can improve cardiac function and attenuate myocardial remodeling following myocardial infarction (MI) in mice. Mice were subjected to permanent ligation of the left anterior descending coronary artery to induce MI, and then randomly treated with muscone (2 mg/kg/day) or the vehicle (normal saline) for 3 weeks. Sham-operated mice were used as controls and were also administered the vehicle (normal saline). Treatment with muscone significantly improved cardiac function and exercise tolerance, as evidenced by the decrease in the left ventricular end-systolic diameter, left ventricular end-diastolic diameter, as well as an increase in the left ventricular ejection fraction, left ventricular fractional shortening and time to exhaustion during swimming. Pathological and morphological assessments indicated that treatment with muscone alleviated myocardial fibrosis, collagen deposition and improved the heart weight/body weight ratio. Muscone inhibited the inflammatory response by reducing the expression of transforming growth factor (TGF)‑β1, tumor necrosis factor (TNF)-α, interleukin (IL)-1β and nuclear factor (NF)-κB. Treatment with muscone also reduced myocardial apoptosis by enhancing Bcl-2 and suppressing Bax expression. Muscone also induced the phosphorylation of protein kinase B (Akt) and endothelial nitric oxide synthase (eNOS). Our results demonstrate that muscone ameliorates cardiac remodeling and dysfunction induced by MI by exerting anti-fibrotic, anti-inflammatory and anti-apoptotic effects in the ischemic myocardium.

Expression of the tissue inhibitor of metalloproteinase-3 by transplanted VSMCs modifies heart structure and function after myocardial infarction

OBJECTIVES

Extracellular matrix (ECM) remodelling is a critical aspect of cardiac remodelling following myocardial infarction. Tissue inhibitors of metalloproteinases (TIMPs) are physiological inhibitors of matrix metalloproteinases (MMPs) that degrade the ECM proteins. TIMP-3 is highly expressed in the heart and is markedly downregulated in patients with ischaemic cardiomyopathy. Cell-based gene therapy can enhance the effects of cell transplantation by temporally and spatially regulating the release of the gene product. The purpose of this study was to investigate the role of TIMP-3 gene-transfected vascular smooth muscle cells (VSMCs) in modifying heart structure and function in rats when transplanted 3days after myocardial infarction (MI).

METHODS

Anesthetised rats were subjected to coronary artery ligation followed 3days later by thoracotomy and transplantation of TIMP-3 gene-transfected VSMCs, untransfected VSMCs or medium injected directly into the ischaemic myocardium. We assessed left ventricular structure and function by echocardiography and morphometry, and measured the levels of myocardial matrix metalloproteinase-2 and -9 (MMP-2, MMP-9), TIMP-3 and tumour necrosis factor-α (TNF-α) at 4weeks post-myocardial infarction.

RESULTS

Transplantation of TIMP-3 gene-transfected VSMCs and untransfected VSMCs significantly decreased scar expansion and ventricular dilatation 25days post-transplantation (4weeks after MI). MMPs and TNF-α levels were reduced in the transplantation groups when compared to the group that was given an injection of medium only. Transplantation of TIMP-3 gene-transfected VSMCs was more effective in preventing progressive cardiac dysfunction, ventricular dilatation and in reducing MMP-2, MMP-9 and TNF-α levels when compared to the transplantation of untransfected VSMCs.

CONCLUSIONS

TIMP-3 gene transfection was associated with attenuated left ventricular dilation and recovery of systolic function after MI compared with the control. TIMP-3 transfection enhanced the effects of transplanted VSMCs in rats by inhibiting matrix degradation and inflammatory cytokine expression, leading to improved myocardial remodelling.

TRPM7 is involved in angiotensin II induced cardiac fibrosis development by mediating calcium and magnesium influx

Cardiac fibrosis is involved in a lot of cardiovascular pathological processes. Cardiac fibrosis can block conduction, cause hypoxia, strengthen myocardial stiffness, create electrical heterogeneity, and hamper systolic ejection, which is associated with the development of arrhythmia, heart failure and sudden cardiac death. Besides the initial stimulating factors, the cardiac fibroblasts (CFs) are the principal responsible cells in the fibrogenesis cascade of events. TRPM7, a member of the TRPM (Melastatin) subfamily, is a non-selective cation channel, which permeates both Ca(2+) and Mg(2+). Here we demonstrated TRPM7 expression in CFs, and 2-APB (TRPM7 inhibitor), inhibited Ang II-induced CTGF, α-SMA expression and CFs proliferation. Besides, knocking down TRPM7 by shRNA, we proved that TRPM7 mediated both calcium and magnesium changes in cardiac fibroblasts which contribute to fibrosis progress. This study suggested that TRPM7 should play a pivotal role in cardiac fibroblast functions associated to cardiac fibrosis development.

Vascular endothelial growth factor-C: its unrevealed role in fibrogenesis

Vascular endothelial growth factor (VEGF)-C is a key mediator of lymphangiogenesis. Our recent study shows that VEGF-C/VEGF receptors (VEGFR)-3 are significantly increased in the infarcted rat myocardium, where VEGFR-3 is expressed not only in lymph ducts but also in myofibroblasts, indicating that VEGF-C has an unrevealed role in fibrogenesis during cardiac repair. The current study is to explore the regulation and molecular mechanisms of VEGF-C in fibrogenesis. The potential regulation of VEGF-C on myofibroblast differentiation/growth/migration, collagen degradation/synthesis, and transforming growth factor (TGF)-β and ERK pathways was detected in cultured cardiac myofibroblasts. Our results showed that VEGF-C significantly increased myofibroblast proliferation, migration, and type I/III collagen production. Matrix metalloproteinase (MMP)-2 and -9 were significantly elevated in the medium of VEGF-C-treated cells, coincident with increased tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2. Furthermore, VEGF-C activated the TGF-β1 pathway and ERK phosphorylation, which was significantly suppressed by TGF-β or ERK blockade. This is the first study indicating that in addition to lymphangiogenesis, VEGF-C is also involved in fibrogenesis through stimulation of myofibroblast proliferation, migration, and collagen synthesis, via activation of the TGF-β1 and ERK pathways.

Coronary vessels and cardiac myocytes of middle-aged rats demonstrate regional sex-specific adaptation in response to postmyocardial infarction remodeling

Background

An increasing body of evidence indicates that left ventricular (LV) remodeling, especially the degree of reactive myocardial hypertrophy after myocardial infarction (MI), differs in males and females. Surprisingly, to date, the sex-specific post-MI alterations of the coronary vasculature remain undetermined. Therefore, we tested the hypothesis that adaptive coronary arteriolar and capillary modifications occurring in response to reactive myocyte hypertrophy differ between middle-aged male and female post-MI rats.

Methods

A large MI was induced in 12-month-old male (M-MI) and female (F-MI) Sprague–Dawley rats by ligation of the left coronary artery. Four weeks after surgery, rats with transmural infarctions, greater than 50% of the LV free wall (FW), were evaluated. Sham-operated male (M-Sham) and female (F-Sham) rats served as an age-matched controls.

Results

F-MI and M-MI rats had similar sized infarcts (61.3% ± 3.9% vs. 61.5% ± 1.2%) and scale of LV remodeling, as indicated analogous remodeling indices (1.41 ± 0.11 vs. 1.39 ± 0.09). The degree of reactive post-MI myocardial hypertrophy was adequate to normalize LV weight-to-body weight ratio in both sexes; however, the F-MI rats, in contrast to males, showed no myocyte enlargement in the LVFW epimyocardium. At the same time, a greater than 50% expansion of myocyte area in the male epimyocardium and in the female endomyocardium was accompanied by a 23% (P < 0.05) increase in capillary-to-myocyte ratio, indicative of adaptive angiogenesis. Based on arteriolar length density in post-MI hearts, the resistance vessels grew in the male LVFW as well as the septum by 24% and 29%, respectively. In contrast, in females, a significant (30%) expansion of arteriolar bed was limited only to the LVFW. Moreover, in F-MI rats, the enlargement of the arteriolar bed occurred predominantly in the vessels with diameters <30 μm, whereas in M-MI rats, a substantial (two- to threefold) increase in the density of larger arterioles (30 to 50 μm in diameter) was also documented.

Conclusion

Our data reveal that while both sexes have a relatively similar pattern of global LV remodeling and adaptive angiogenesis in response to a large MI, male and female middle-aged rats differ markedly in the regional scale of reactive cardiac myocyte hypertrophy and adaptive arteriogenesis.

Intramyocardial injection of a synthetic hydrogel with delivery of bFGF and IGF1 in a rat model of ischemic cardiomyopathy

It is increasingly appreciated that the properties of a biomaterial used in intramyocardial injection therapy influence the outcomes of infarcted hearts that are treated. In this report the extended in vivo efficacy of a thermally responsive material that can deliver dual growth factors while providing a slow degradation time and high mechanical stiffness is examined. Copolymers consisting of N-isopropylacrylamide, 2-hydroxyethyl methacrylate, and degradable methacrylate polylactide were synthesized. The release of bioactive basic fibroblast growth factor (bFGF) and insulin-like growth factor 1 (IGF1) from the gel and loaded poly(lactide-co-glycolide) microparticles was assessed. Hydrogel with or without loaded growth factors was injected into 2 week-old infarcts in Lewis rats and animals were followed for 16 weeks. The hydrogel released bioactive bFGF and IGF1 as shown by mitogenic effects on rat smooth muscle cells in vitro. Cardiac function and geometry were improved for 16 weeks after hydrogel injection compared to saline injection. Despite demonstrating that left ventricular levels of bFGF and IGF1 were elevated for two weeks after injection of growth factor loaded gels, both functional and histological assessment showed no added benefit to inclusion of these proteins. This result points to the complexity of designing appropriate materials for this application and suggests that the nature of the material alone, without exogenous growth factors, has a direct ability to influence cardiac remodeling.

Cardiac sympathetic innervation and PGP9.5 expression by cardiomyocytes after myocardial infarction: effects of central MR blockade

Central mechanisms involving mineralocorticoid receptor (MR) activation contribute to an increase in sympathetic tone after myocardial infarction (MI). We hypothesized that this central mechanism also contributes to cardiac sympathetic axonal sprouting and that central MR blockade reduces cardiac sympathetic hyperinnervation post-MI. Post-MI, tyrosine hydroxylase (TH) and norepinephrine transporter protein content in the noninfarcted base of the heart remained unaltered. In contrast, protein gene product (PGP)9.5 protein was increased twofold in the base of the heart and sixfold in the peri-infarct area at 1 wk post-MI and was associated with increased ubiquitin expression. These changes persisted to a lesser extent at 4 wk post-MI and were no longer present at 12 wk. Cardiac myocytes rather than sympathetic axons were the main source of this elevated PGP9.5 expression. At 7–10 days post-MI, in the peri-infarct area, sympathetic hyperinnervation was observed with a fourfold increase in growth-associated protein 43, a twofold increase in TH, and a 50% increase in PGP9.5-positive fibers compared with the epicardial side of the left ventricle in sham rats. Central infusion of the MR blocker eplerenone markedly attenuated these increases in nerve densities but did not affect overall cardiac PGP9.5 and ubiquitin protein overexpression. We conclude that central MR activation contributes to sympathetic hyperinnervation, possibly by decreasing cardiac sympathetic activity post-MI, or by affecting other mechanisms, such as the expression of nerve growth factor. Marked PGP9.5 expression occurs in cardiomyocytes early post-MI, which may contribute to the increase in ubiquitin.

Structural composition of myocardial infarction scar in middle-aged male and female rats: does sex matter?

The present study was designed to determine whether the structural composition of the scar in middle-aged post-myocardial infraction (MI) rats is affected by the biological sex of the animals. A large MI was induced in 12-month-old male (M-MI) and female (F-MI) Sprague-Dawley rats by ligation of the left coronary artery. Four weeks after the MI, rats with transmural infarctions, greater than 50% of the left ventricular (LV) free wall, were evaluated. The extent of LV remodeling and fractional volumes of fibrillar collagen (FC), myofibroblasts, vascular smooth muscle (SM) cells, and surviving cardiac myocytes (CM) in the scars were compared between the two sexes. The left ventricle of post-MI male and female rats underwent a similar degree of remodeling as evidenced by the analogous scar thinning ratio (0.46 ± 0.02 vs. 0.42 ± 0.05) and infarct expansion index (1.06 ± 0.07 vs. 1.12 ± 0.08), respectively. Most important, the contents of major structural components of the scar revealed no evident difference between M-MI and F-MI rats (interstitial FC, 80.74 ± 2.08 vs. 82.57 ± 4.53; myofibroblasts, 9.59 ± 1.68 vs.9.56 ± 1.15; vascular SM cells, 2.27 ± 0.51 vs. 3.38 ± 0.47; and surviving CM, 3.26 ± 0.39 vs. 3.05 ± 0.38, respectively). Our data are the first to demonstrate that biological sex does not influence the structural composition of a mature scar in middle-aged post-MI rats.

Protease-activated receptor 1 inhibition by SCH79797 attenuates left ventricular remodeling and profibrotic activities of cardiac fibroblasts

PURPOSE

Fibroblast activity promotes adverse left ventricular (LV) remodeling that underlies the development of ischemic cardiomyopathy. Transforming growth factor-β (TGF-β) is a potent stimulus for fibrosis, and the extracellular signal-regulated kinases(ERK) 1/2 pathway also contributes to the fibrotic response. The thrombin receptor, protease-activated receptor 1 (PAR1), has been shown to play an important role in the excessive fibrosis in different tissues. The aim of this study was to investigate the influence of a PAR1 inhibitor, SCH79797, on cardiac fibrosis, tissue stiffness and postinfarction remodeling, and effects of PAR1 inhibition on thrombin-induced TGF-β and (ERK) 1/2 activities in cardiac fibroblasts.

METHODS

We used a rat model of myocardial ischemia-reperfusion injury, isolated cardiac fibroblasts, and 3-dimensional (3D) cardiac tissue models fabricated to ascertain the contribution of PAR1 activation on cardiac fibrosis and LV remodeling.

RESULTS

The PAR1 inhibitor attenuated LV dilation and improved LV systolic function of the reperfused myocardium at 28 days. This improvement was associated with a nonsignificant decrease in scar size (%LV) from 23 ± % in the control group (n = 10) to 16% ± 5.5% in the treated group (n = 9; P = .052). In the short term, the PAR1 inhibitor did not rescue infarct size or LV systolic function after 3 days. The PAR1 inhibition abolished thrombin-mediated ERK1/2 phosphorylation, TGF-β and type I procollagen production, matrix metalloproteinase-2/9 activation, myofibroblasts transformation in vitro, and abrogated the remodeling of 3D tissues induced by chronic thrombin treatment.

CONCLUSION

These studies suggest PAR1 inhibition initiated after ischemic injury attenuates adverse LV remodeling through late-stage antifibrotic events.