A look between the cardiomyocytes: the extracellular matrix in heart failure

Selective Induction of Molecular Assembly to Tissue-Level Anisotropy on Peptide-Based Optoelectronic Cardiac Biointerfaces

The conduction efficiency of ions in excitable tissues and of charged species in organic conjugated materials both benefit from having ordered domains and anisotropic pathways. In this study, a photocurrent-generating cardiac biointerface is presented, particularly for investigating the sensitivity of cardiomyocytes to geometrically comply to biomacromolecular cues differentially assembled on a conductive nanogrooved substrate. Through a polymeric surface-templated approach, photoconductive substrates with symmetric peptide-quaterthiophene (4T)-peptide units assembled as 1D nanostructures on nanoimprinted polyalkylthiophene (P3HT) surface are developed. The 4T-based peptides studied here can form 1D nanostructures on prepatterned polyalkylthiophene substrates, as directed by hydrogen bonding, aromatic interactions between 4T and P3HT, and physical confinement on the nanogrooves. It is observed that smaller 4T-peptide units that can achieve a higher degree of assembly order within the polymeric templates serve as a more efficient driver of cardiac cytoskeletal anisotropy than merely presenting aligned -RGD bioadhesive epitopes on a nanotopographic surface. These results unravel some insights on how cardiomyocytes perceive submicrometer dimensionality, local molecular order, and characteristics of surface cues in their immediate environment. Overall, the work offers a cardiac patterning platform that presents the possibility of a gene modification-free cardiac photostimulation approach while controlling the conduction directionality of the biotic and abiotic components.

Framing Heartaches: The Cardiac ECM and the Effects of Age

The cardiac extracellular matrix (ECM) is involved in several pathological conditions, and age itself is also associated with certain changes in the heart: it gets larger and stiffer, and it develops an increased risk of abnormal intrinsic rhythm. This, therefore, makes conditions such as atrial arrythmia more common. Many of these changes are directly related to the ECM, yet the proteomic composition of the ECM and how it changes with age is not fully resolved. The limited research progress in this field is mainly due to the intrinsic challenges in unravelling tightly bound cardiac proteomic components and also the time-consuming and costly dependency on animal models. This review aims to give an overview of the composition of the cardiac ECM, how different components aid the function of the healthy heart, how the ECM is remodelled and how it is affected by ageing.

MicroRNA Let-7a, -7e and -133a Attenuate Hypoxia-Induced Atrial Fibrosis via Targeting Collagen Expression and the JNK Pathway in HL1 Cardiomyocytes

Fibrosis is a hallmark of atrial structural remodeling. The main aim of this study was to investigate the role of micro-ribonucleic acids (miRNAs) in the modulation of fibrotic molecular mechanisms in response to hypoxic conditions, which may mediate atrial fibrosis. Under a condition of hypoxia induced by a hypoxia chamber, miRNA arrays were used to identify the specific miRNAs associated with the modulation of fibrotic genes. Luciferase assay, real-time polymerase chain reaction, immunofluorescence and Western blotting were used to investigate the effects of miRNAs on the expressions of the fibrotic markers collagen I and III (COL1A, COL3A) and phosphorylation levels of the stress kinase c-Jun N-terminal kinase (JNK) pathway in a cultured HL-1 atrial cardiomyocytes cell line. COL1A and COL3A were found to be the direct regulatory targets of miR-let-7a, miR-let-7e and miR-133a in hypoxic atrial cardiac cells in vitro. The expressions of COL1A and COL3A were influenced by treatment with miRNA mimic and antagomir while hypoxia-induced collagen expression was inhibited by the delivery of miR-133a, miR-let-7a or miR-let-7e. The JNK pathway was critical in the pathogenesis of atrial fibrosis. The JNK inhibitor SP600125 increased miRNA expressions and repressed the fibrotic markers COL1A and COL3A. In conclusion, MiRNA let-7a, miR-let-7e and miR-133a play important roles in hypoxia-related atrial fibrosis by inhibiting collagen expression and post-transcriptional repression by the JNK pathway. These novel findings may lead to the development of new therapeutic strategies.

Identification of Adamts4 as a novel adult cardiac injury biomarker with therapeutic implications in patients with cardiac injuries

Pathological cardiac remodeling as an aftermath of a severe cardiac injury can lead to ventricular dysfunction and subsequent heart failure. Adamts4, a metalloproteinase, and disintegrin with thrombospondin-like motif, involved in the turnover of certain extracellular matrix molecules and pathogenesis of osteoarthritis, also plays a role in cardiac remodeling although little is presently known about its expression and function in the heart. Here, we have investigated the dynamic expression pattern of Adamts4 during cardiogenesis and also in the adult heart. To our surprise, adult cardiac injury reactivated Adamts4 expression concomitant with fibrosis induction. To better understand the mechanism, cultured H9c2 cardiomyocyte cells were subjected to ROS injury and Hypoxia. Moreover, through combinatorial treatment with SB431542 (an inhibitor of Tgf-β1), and Adamts4 siRNA mediated gene knockdown, we were able to decipher a regulatory hierarchy to the signal cascade being at the heart of Tgf-β regulation. Besides the hallmark expression of Adamts4 and Tgf-β1, expression of other fibrosis-related markers like Collagen-III, alpha-SMA and Periostin were also assessed. Finally, increased levels of Adamts4 and alpha-SMA proteins in cardiac patients also resonated well with our animal and cell culture studies. Overall, in this study, we highlight, Adamts4 as a novel biomarker of adult cardiac injury.

Inhibition of sphingolipid de novo synthesis counteracts muscular dystrophy

Duchenne muscular dystrophy (DMD), the most common muscular dystrophy, is a severe muscle disorder, causing muscle weakness, loss of independence, and premature death. Here, we establish the link between sphingolipids and muscular dystrophy. Transcripts of sphingolipid de novo biosynthesis pathway are up-regulated in skeletal muscle of patients with DMD and other muscular dystrophies, which is accompanied by accumulation of metabolites of the sphingolipid pathway in muscle and plasma. Pharmacological inhibition of sphingolipid synthesis by myriocin in the mdx mouse model of DMD ameliorated the loss in muscle function while reducing inflammation, improving Ca²⁺ homeostasis, preventing fibrosis of the skeletal muscle, heart, and diaphragm, and restoring the balance between M1 and M2 macrophages. Myriocin alleviated the DMD phenotype more than glucocorticoids. Our study identifies inhibition of sphingolipid synthesis, targeting multiple pathogenetic pathways simultaneously, as a strong candidate for treatment of muscular dystrophies.

Tanshinone IIA Improves Ventricular Remodeling following Cardiac Infarction by Regulating miR-205-3p

Objective

To illustrate the role of tanshinone IIA (TSN) in regulating cardiac structure and function following myocardial infarction (MI) and the involvement of miR-205-3p in TSN-induced antifibrosis effect on ventricular remodeling. Patients and Methods. One hundred MI patients were randomly assigned into two groups, and they were treated with TSN (TSN group, n = 50) or conventional therapy (control group, n = 50). Plasma levels of miR-205-3p and TGF-β1 were detected in each patient. Echocardiography was conducted in each patient at post-MI 1 day, 2 weeks, and 4 weeks, respectively, for recording LVIDd (left ventricular internal-diastolic diameter), LVIDs (left ventricular internal-systolic diameter), and LVEF (left ventricular ejection fraction). The interaction between miR-205-3p and TGF-β1 was examined by the RNA-Binding Protein Immunoprecipitation (RIP) assay. After induction of TGF-β1 and/or 10 μL of TSN in cardiac fibroblasts, relative levels of miR-205-3p, Col1a1, and Col3a1 were detected by quantitative real-time polymerase chain reaction (qRT-PCR).

Results

Compared with the control group, miR-205-3p and TGF-β1 were downregulated in plasma of MI patients in the TSN group. In the TSN group, LVIDd and LVIDs were reduced, and EF was enhanced at 2 weeks and 4 weeks compared with that at post-MI 1 day. miR-205-3p could negatively interact with TGF-β1. TSN induction abolished the regulatory effects of TGF-β1 on downregulating miR-205-3p and upregulating Col1a1 and Col3a1 in cardiac fibroblasts.

Conclusions

Through upregulating miR-205-3p and downregulating TGF-β1, TSN alleviates cardiac fibrosis and improves ventricular remodeling following MI.

Linking LOXL2 to Cardiac Interstitial Fibrosis

Cardiovascular diseases (CVDs) are the leading causes of death worldwide. CVD pathophysiology is often characterized by increased stiffening of the heart muscle due to fibrosis, thus resulting in diminished cardiac function. Fibrosis can be caused by increased oxidative stress and inflammation, which is strongly linked to lifestyle and environmental factors such as diet, smoking, hyperglycemia, and hypertension. These factors can affect gene expression through epigenetic modifications. Lysyl oxidase like 2 (LOXL2) is responsible for collagen and elastin cross-linking in the heart, and its dysregulation has been pathologically associated with increased fibrosis. Additionally, studies have shown that, LOXL2 expression can be regulated by DNA methylation and histone modification. However, there is a paucity of data on LOXL2 regulation and its role in CVD. As such, this review aims to gain insight into the mechanisms by which LOXL2 is regulated in physiological conditions, as well as determine the downstream effectors responsible for CVD development.

A three-tiered integrative analysis of transcriptional data reveals the shared pathways related to heart failure from different aetiologies

Heart failure (HF) is the end stage of most heart disease cases and can be initiated from multiple aetiologies. However, whether the molecular basis of HF has a commonality between different aetiologies has not been elucidated. To address this lack, we performed a three‐tiered analysis by integrating transcriptional data and pathway information to explore the commonalities of HF from different aetiologies. First, through differential expression analysis, we obtained 111 genes that were frequently differentially expressed in HF from 11 different aetiologies. Several genes, such as NPPA and NPPB, are early and accurate biomarkers for HF. We also provided candidates for further experimental verification, such as SERPINA3 and STAT4. Then, using gene set enrichment analysis, we successfully identified 19 frequently dysregulated pathways. In particular, we found that pathways related to immune system signalling, the extracellular matrix and metabolism were critical in the development of HF. Finally, we successfully acquired 241 regulatory relationships between 64 transcriptional factors (TFs) and 17 frequently dysregulated pathways by integrating a regulatory network, and some of the identified TFs have already been proven to play important roles in HF. Taken together, the three‐tiered analysis of HF provided a systems biology perspective on HF and emphasized the molecular commonality of HF from different aetiologies.

Micromechanobiology: Focusing on the Cardiac Cell-Substrate Interface

Engineered, in vitro cardiac cell and tissue systems provide test beds for the study of cardiac development, cellular disease processes, and drug responses in a dish. Much effort has focused on improving the structure and function of engineered cardiomyocytes and heart tissues. However, these parameters depend critically on signaling through the cellular microenvironment in terms of ligand composition, matrix stiffness, and substrate mechanical properties-that is, matrix micromechanobiology. To facilitate improvements to in vitro microenvironment design, we review how cardiomyocytes and their microenvironment change during development and disease in terms of integrin expression and extracellular matrix (ECM) composition. We also discuss strategies used to bind proteins to common mechanobiology platforms and describe important differences in binding strength to the substrate. Finally, we review example biomaterial approaches designed to support and probe cell-ECM interactions of cardiomyocytes in vitro, as well as open questions and challenges.

Functional and structural studies of tolloid-like 1 mutants associated with atrial-septal defect 6

Inactive mammalian tolloid-like 1 (tll1) and mutations detected in tolloid-like 1 (TLL1) have been linked to the lack of the heart septa formation in mice and to a similar human inborn condition called atrial-septal defect 6 (ASD6; OMIM 613087, formerly ASD II). Previously, we reported four point mutations in TLL1 found in approximately 20% of ASD6 patients. Three mutations in the coding sequence were M182L, V238A, and I629V. In this work, we present the effects of these mutations on TLL1 function. Three recombinant cDNA constructs carrying the mutations and one wild-type construct were prepared and then expressed in HT-1080 cells. Corresponding recombinant proteins were analyzed for their metalloendopeptidase activity using a native substrate, chordin. The results of these assays demonstrated that in comparison with the native TLL1, mutants cleaved chordin and procollagen I at significantly lower rates. CD analyses revealed significant structural differences between the higher order structure of wild-type and mutant variants. Moreover, biosensor-based assays of binding interactions between TLL1 variants and chordin demonstrated a significant decrease in the binding affinities of the mutated variants. The results from this work indicate that mutations detected in TLL1 of ASD6 patients altered its metalloendopeptidase activity, structure, and substrate-binding properties, thereby suggesting a possible pathomechanism of ASD6.

Knockdown of Sestrin2 Increases Lipopolysaccharide-Induced Oxidative Stress, Apoptosis, and Fibrotic Reactions in H9c2 Cells and Heart Tissues of Mice via an AMPK-Dependent Mechanism

Sestrin2 (sesn2) is an endogenous antioxidant protein that has recently gained attention for its potential to treat various inflammatory diseases. However, the relationship of sesn2 with cardiomyopathy is still unclear. In H9c2 cells, sesn2 knockdown reduced the level of 5′ adenosine monophosphate-activated protein kinase (AMPK) phosphorylation, downregulated antioxidant genes including catalase and superoxide dismutase (SOD2), and increased reactive oxygen species (ROS) production upon lipopolysaccharide (LPS) treatment. LPS-mediated cell death and the expression of matrix metalloproteinase (MMP) 2 and MMP9 were significantly increased by sesn2 knockdown. However, these increases were prevented by treatment with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an AMPK activator. Consistent with the in vitro results, AMPK phosphorylation was decreased in heart tissue from sesn2 knockdown mice compared to heart tissue from control C57BL/6 mice, which was associated with decreased expression of antioxidant genes and increased LPS-mediated cell death signaling. Furthermore, the decrease in AMPK phosphorylation caused by sesn2 knockdown increased LPS-mediated expression of cardiac fibrotic factors, including collagen type I and type III, in addition to MMP2 and MMP9, in heart tissue from C57BL/6 mice. These results suggest that sesn2 is a novel potential therapeutic target for cardiomyopathy under inflammatory conditions.

Targeting Chondroitin Sulfate Glycosaminoglycans to Treat Cardiac Fibrosis in Pathological Remodeling

Background:

Heart failure is a leading cause of mortality and morbidity, and the search for novel therapeutic approaches continues. In the monogenic disease mucopolysaccharidosis VI, loss-of-function mutations in arylsulfatase B lead to myocardial accumulation of chondroitin sulfate (CS) glycosaminoglycans, manifesting as myriad cardiac symptoms. Here, we studied changes in myocardial CS in nonmucopolysaccharidosis failing hearts and assessed its generic role in pathological cardiac remodeling.

Methods:

Healthy and diseased human and rat left ventricles were subjected to histological and immunostaining methods to analyze glycosaminoglycan distribution. Glycosaminoglycans were extracted and analyzed for quantitative and compositional changes with Alcian blue assay and liquid chromatography–mass spectrometry. Expression changes in 20 CS-related genes were studied in 3 primary human cardiac cell types and THP-1–derived macrophages under each of 9 in vitro stimulatory conditions. In 2 rat models of pathological remodeling induced by transverse aortic constriction or isoprenaline infusion, recombinant human arylsulfatase B (rhASB), clinically used as enzyme replacement therapy in mucopolysaccharidosis VI, was administered intravenously for 7 or 5 weeks, respectively. Cardiac function, myocardial fibrosis, and inflammation were assessed by echocardiography and histology. CS-interacting molecules were assessed with surface plasmon resonance, and a mechanism of action was verified in vitro.

Results:

Failing human hearts displayed significant perivascular and interstitial CS accumulation, particularly in regions of intense fibrosis. Relative composition of CS disaccharides remained unchanged. Transforming growth factor–β induced CS upregulation in cardiac fibroblasts. CS accumulation was also observed in both the pressure-overload and the isoprenaline models of pathological remodeling in rats. Early treatment with rhASB in the transverse aortic constriction model and delayed treatment in the isoprenaline model proved rhASB to be effective at preventing cardiac deterioration and augmenting functional recovery. Functional improvement was accompanied by reduced myocardial inflammation and overall fibrosis. Tumor necrosis factor–α was identified as a direct binding partner of CS glycosaminoglycan chains, and rhASB reduced tumor necrosis factor–α—induced inflammatory gene activation in vitro in endothelial cells and macrophages.

Conclusions:

CS glycosaminoglycans accumulate during cardiac pathological remodeling and mediate myocardial inflammation and fibrosis. rhASB targets CS effectively as a novel therapeutic approach for the treatment of heart failure.

Inhibitor of lysyl oxidase improves cardiac function and the collagen/MMP profile in response to volume overload

The cardiac extracellular matrix is a complex architectural network that serves many functions, including providing structural and biochemical support to surrounding cells and regulating intercellular signaling pathways. Cardiac function is directly affected by extracellular matrix (ECM) composition, and alterations of the ECM contribute to the progression of heart failure. Initially, collagen deposition is an adaptive response that aims to preserve tissue integrity and maintain normal ventricular function. However, the synergistic effects of proinflammatory and profibrotic responses induce a vicious cycle, which causes excess activation of myofibroblasts, significantly increasing collagen deposition and accumulation in the matrix. Furthermore, excess synthesis and activation of the enzyme lysyl oxidase (LOX) during disease increases collagen cross-linking, which significantly increases collagen resistance to degradation by matrix metalloproteinases (MMPs). In the present study, the aortocaval fistula model of volume overload (VO) was used to determine whether LOX inhibition could prevent adverse changes in the ECM and subsequent cardiac dysfunction. The major findings from this study were that LOX inhibition 1) prevented VO-induced increases in left ventricular wall stress; 2) partially attenuated VO-induced ventricular hypertrophy; 3) completely blocked the increases in fibrotic proteins, including collagens, MMPs, and their tissue inhibitors; and 4) prevented the VO-induced decline in cardiac function. It remains unclear whether a direct interaction between LOX and MMPs exists; however, our experiments suggest a potential link between the two because LOX inhibition completely attenuated VO-induced increases in MMPs. Overall, our study demonstrated key cardioprotective effects of LOX inhibition against adverse cardiac remodeling due to chronic VO. NEW & NOTEWORTHY Although the primary role of lysyl oxidase (LOX) is to cross-link collagens, we found that elevated LOX during cardiac disease plays a key role in the progression of heart failure. Here, we show that inhibition of LOX in volume-overloaded rats prevented the development of cardiac dysfunction and improved ventricular collagen and matrix metalloproteinase/tissue inhibitor of metalloproteinase profiles.

Sphingosine 1-Phosphate Receptor Modulator Fingolimod (FTY720) Attenuates Myocardial Fibrosis in Post-heterotopic Heart Transplantation

Background and Objective: Sphingosine 1-phosphate (S1P), and S1P receptor modulator fingolimod have been suggested to play important cardioprotective role in animal models of myocardial ischemia/reperfusion injuries. To understand the cardioprotective function of S1P and its mechanism in vivo, we analyzed apoptotic, inflammatory biomarkers, and myocardial fibrosis in an in vivo heterotopic rat heart transplantation model.

Methods: Heterotopic heart transplantation is performed in 60 Sprague–Dawley (SD) rats (350–400 g). The heart transplant recipients (n = 60) are categorized into Group A (control) and Group B (fingolimod treated 1 mg/kg intravenous). At baseline with 24 h after heart transplantation, blood and myocardial tissue are collected for analysis of myocardial biomarkers, apoptosis, inflammatory markers, oxidative stress, and phosphorylation of Akt/Erk/STAT-3 signaling pathways. Myocardial fibrosis was investigated using Masson’s trichrome staining and L-hydroxyline.

Results: Fingolimod treatment activates both Reperfusion Injury Salvage Kinase (RISK) and Survivor Activating Factor Enhancement (SAFE) pathways as evident from activation of anti-apoptotic and anti-inflammatory pathways. Fingolimod treatment caused a reduction in myocardial oxidative stress and hence cardiomyocyte apoptosis resulting in a decrease in myocardial reperfusion injury. Moreover, a significant (p < 0.001) reduction in collagen staining and hydroxyproline content was observed in fingolimod treated animals 30 days after transplantation demonstrating a reduction in cardiac fibrosis.

Conclusion: S1P receptor activation with fingolimod activates anti-apoptotic and anti-inflammatory pathways, leading to improved myocardial salvage causing a reduction in cardiac fibrosis.

Can Adiponectin Help us to Target Diastolic Dysfunction?

Adiponectin is the most abundant adipokine and exhibits anti-inflammatory, antiatherogenic and antidiabetic properties. Unlike other adipokines, it inversely correlates with body weight and obesity-linked cardiovascular complications. Diastolic dysfunction is the main mechanism responsible for approximately half of all heart failure cases, the so-called heart failure with preserved ejection fraction (HFpEF), but therapeutic strategies specifically directed towards these patients are still lacking. In the last years, a link between adiponectin and diastolic dysfunction has been suggested. There are several mechanisms through which adiponectin may prevent most of the pathophysiologic mechanisms underlying diastolic dysfunction and HFpEF, including the prevention of myocardial hypertrophy, cardiac fibrosis, nitrative and oxidative stress, atherosclerosis and inflammation, while promoting angiogenesis. Thus, understanding the mechanisms underlying adiponectin-mediated improvement of diastolic function has become an exciting field of research, making adiponectin a promising therapeutic target. In this review, we explore the relevance of adiponectin signaling for the prevention of diastolic dysfunction and identify prospective therapeutic targets aiming at the treatment of this clinical condition.

The lysyl oxidase inhibitor (β-aminopropionitrile) reduces leptin profibrotic effects and ameliorates cardiovascular remodeling in diet-induced obesity in rats

Lysyl oxidase (LOX) is an extracellular matrix (ECM)-modifying enzyme that has been involved in cardiovascular remodeling. We explore the impact of LOX inhibition in ECM alterations induced by obesity in the cardiovascular system. LOX is overexpressed in the heart and aorta from rats fed a high-fat diet (HFD). β-Aminopropionitrile (BAPN), an inhibitor of LOX activity, significantly attenuated the increase in body weight and cardiac hypertrophy observed in HFD rats. No significant differences were found in cardiac function or blood pressure among any group. However, HFD rats showed cardiac and vascular fibrosis and enhanced levels of superoxide anion (O2(-)), collagen I and transforming growth factor β (TGF-β) in heart and aorta and connective tissue growth factor (CTGF) in aorta, effects that were attenuated by LOX inhibition. Interestingly, BAPN also prevented the increase in circulating leptin levels detected in HFD fed animals. Leptin increased protein levels of collagen I, TGF-β and CTGF, Akt phosphorylation and O2(-) production in both cardiac myofibroblasts and vascular smooth muscle cells in culture, while LOX inhibition ameliorated these alterations. LOX knockdown also attenuated leptin-induced collagen I production in cardiovascular cells. Our findings indicate that LOX inhibition attenuates the fibrosis and the oxidative stress induced by a HFD on the cardiovascular system. The reduction of leptin levels by BAPN in vivo and the ability of this compound to inhibit leptin-induced profibrotic mediators and ROS production in cardiac and vascular cells suggest that interactions between leptin and LOX regulate downstream events responsible for myocardial and vascular fibrosis in obesity.

Integrins and integrin-related proteins in cardiac fibrosis

Cardiac fibrosis is one of the major components of the healing mechanism following any injury of the heart and as such may contribute to both systolic and diastolic dysfunction in a range of pathophysiologic conditions. Canonically, it can occur as part of the remodeling process that occurs following myocardial infarction or that follows as a response to pressure overload. Integrins are cell surface receptors which act in both cellular adhesion and signaling. Most importantly, in the context of the continuously contracting myocardium, they are recognized as mechanotransducers. They have been implicated in the development of fibrosis in several organs, including the heart. This review will focus on the involvement of integrins and integrin-related proteins, in cardiac fibrosis, outlining the roles of these proteins in the fibrotic responses in specific cardiac pathologies, discuss some of the common end effectors (angiotensin II, transforming growth factor beta 1 and mechanical stress) through which integrins function and finally discuss how manipulation of this set of proteins may lead to new treatments which could prove useful to alter the deleterious effects of cardiac fibrosis.

Effects of angiotensin-(1-7) on the proliferation and collagen synthesis of arginine vasopressin-stimulated rat cardiac fibroblasts: role of mas receptor-calcineurin-NF-κB signaling pathway

: Interstitial fibrosis is a common pathological change in various heart diseases, especially cardiac hypertrophy. Arginine vasopressin (AVP), one of the hallmarks of heart failure, exhibits a profibrotic effect by promoting the proliferation and differentiation of cardiac fibroblasts (CFs). In contrast, angiotensin-(1-7) [Ang-(1-7)] was reported to be beneficial for cardiac remodeling by its antifibrotic effect. To evaluate the effect of Ang-(1-7) on AVP-stimulated CFs and the subsequent signaling molecules involved, CFs isolated from neonatal rat hearts were incubated with AVP and treated with or without Ang-(1-7). Cell proliferation, cell cycle, collagen production, and related cellular signaling molecules were then assessed. The results showed that Ang-(1-7) dose-dependently inhibited cell proliferation and collagen production in AVP-stimulated CFs. In addition, Ang-(1-7) also significantly suppressed calcineurin activity in a dose-dependent manner in AVP-stimulated CFs, which was associated with reduced collagen production. Accordingly, the nuclear translocation and transcriptional activity of nuclear factor-kappa B (NF-κB), downstream signal of calcineurin, were also notably restrained by Ang-(1-7) in AVP-stimulated CFs. Furthermore, the inhibitory effect of Ang-(1-7) on AVP-activated calcineurin-NF-κB signaling was completely reversed by the Mas receptor antagonist A-799. These findings suggest that Ang-(1-7) exerts an antifibrotic effect by inhibiting AVP-stimulated CF proliferation and collagen synthesis by inactivating Mas receptor-calcineurin-NF-κB signaling pathway.

Fibrosis and heart failure

The extracellular matrix (ECM) is a living network of proteins that maintains the structural integrity of the myocardium and allows the transmission of electrical and mechanical forces between the myocytes for systole and diastole. During ventricular remodeling, as a result of iterations in the hemodynamic workload, collagen, the main component of the ECM, increases and occupies the areas between the myocytes and the vessels. The resultant fibrosis (reparative fibrosis) is initially a compensatory mechanism and may progress adversely influencing tissue stiffness and ventricular function. Replacement fibrosis appears at sites of previous cardiomyocyte necrosis to preserve the structural integrity of the myocardium, but with the subsequent formation of scar tissue and widespread distribution, it has adverse functional consequences. Continued accumulation of collagen impairs diastolic function and compromises systolic mechanics. Nevertheless, the development of fibrosis is a dynamic process wherein myofibroblasts, the principal cellular elements of fibrosis, are not only metabolically active and capable of the production and upregulation of cytokines but also have contractile properties. During the process of reverse remodeling with left ventricular assist device unloading, cellular, structural, and functional improvements are observed in terminal heart failure patients. With the advent of anti-fibrotic pharmacologic therapies, cellular therapy, and ventricular support devices, fibrosis has become an important therapeutic target in heart failure patients. Herein, we review the current concepts of fibrosis as a main component of ventricular remodeling in heart failure patients. Our aim is to integrate the histopathologic process of fibrosis with the neurohormonal, cytochemical, and molecular changes that lead to ventricular remodeling and its physiologic consequences in patients. The concept of fibrosis as living scar allows us to envision targeting this scar as a means of improving ventricular function in heart failure patients.

Adiponectin mediated APPL1-AMPK signaling induces cell migration, MMP activation, and collagen remodeling in cardiac fibroblasts

Defects in adiponectin action have been implicated in the development of cardiac dysfunction in obesity and diabetes. Cardiac fibroblasts play an important role in regulating extracellular matrix remodeling yet little is known regarding the direct effects of adiponectin on cardiac fibroblasts. In this study, we first demonstrated temporal relocalization of cellular APPL1 in response to adiponectin in primary cardiac fibroblasts and that siRNA-mediated knockdown of APPL1 attenuated stimulation of AMPK by adiponectin. The cell surface content of MT1-MMP and activation of MMP2 were induced by adiponectin and these responses were dependent on AMPK signaling. Enhanced MMP activity facilitated increased fibroblast migration in response to adiponectin which was also prevented by inhibition of AMPK, with no change in cell proliferation observed. Collagen and elastin immunofluorescence demonstrated reorganization of the extracellular matrix in accordance with increased MMP activity, whereas quantitative mRNA analysis, (3) H-proline incorporation and picrosirius red assays showed no change in intracellular or extracellular total collagen levels in response to adiponectin. In summary, these data are the first to report the adiponectin stimulated APPL1-AMPK signaling axis in cardiac fibroblasts and characterize MT1-MMP translocation, MMP2 activity and cell migration as functional outcomes. These effects may be of significance in heart failure associated with obesity and diabetes.

Engineering the extracellular matrix for clinical applications: endoderm, mesoderm, and ectoderm

Tissue engineering is rapidly progressing from a research-based discipline to clinical applications. Emerging technologies could be utilized to develop therapeutics for a wide range of diseases, but many are contingent on a cell scaffold that can produce proper tissue ultrastructure. The extracellular matrix, which a cell scaffold simulates, is not merely a foundation for tissue growth but a dynamic participant in cellular crosstalk and organ homeostasis. Cells change their growth rates, recruitment, and differentiation in response to the composition, modulus, and patterning of the substrate on which they reside. Cell scaffolds can regulate these factors through precision design, functionalization, and application. The ideal therapy would utilize highly specialized cell scaffolds to best mimic the tissue of interest. This paper discusses advantages and challenges of optimized cell scaffold design in the endoderm, mesoderm, and ectoderm for clinical applications in tracheal transplant, cardiac regeneration, and skin grafts, respectively.

NF-κB mediated miR-26a regulation in cardiac fibrosis

Micro-RNAs (miRNAs) are a class of small non-coding RNAs, recently emerged as a post-transcriptional regulator having a key role in various cardiac pathologies. Among them, cardiac fibrosis that occurs as a result from an imbalance of extracellular matrix proteins turnover and is a highly debilitating process that eventually lead to organ dysfunction. An emerging theme on is that miRNAs participate in feedback loop with transcription factors that regulate their transcription. NF-κB, a key transcription factor regulator controls a series of gene program in various cardiac diseases through positive and negative feedback mechanism. But, NF-κB mediated miRNA regulation in cardiac fibrosis remains obscure. Bioinformatics analysis revealed that miR-26a has targets collagen I and CTGF and possesses putative NF-κB binding element in its promoter region. Here, we show that inhibition of NF-κB in cardiac fibroblast restores miR-26a expression, attenuating collagen I, and CTGF gene expression in the presence of Ang II, conferring a feedback regulatory mechanism in cardiac fibrosis. The target genes for miR-26a were confirmed using 3'-UTR luciferase reporter assays for collagen I and CTGF genes. Using NF-κB reporter assays, we determine that miR-26a overexpression inhibits NF-κB activity. Finally, we show that miR-26a expression is restored along with the attenuation of collagen I and CTGF genes in cardiac specific IkBa triple mutant transgenic mice (preventing NF-κB activation) subjected to 4 weeks transverse aortic banding (TAC), compared to wild type (WT) mice. The data indicate a potential role of miR-26a in cardiac fibrosis and, offer novel therapeutic intervention.

Natural ECM as biomaterial for scaffold based cardiac regeneration using adult bone marrow derived stem cells

Cellular therapy using stem cells for cardiac diseases has recently gained much interest in the scientific community due to its potential in regenerating damaged and even dead tissue and thereby restoring the organ function. Stem cells from various sources and origin are being currently used for regeneration studies directly or along with differentiation inducing agents. Long term survival and minimal side effects can be attained by using autologous cells and reduced use of inducing agents. Cardiomyogenic differentiation of adult derived stem cells has been previously reported using various inducing agents but the use of a potentially harmful DNA demethylating agent 5-azacytidine (5-azaC) has been found to be critical in almost all studies. Alternate inducing factors and conditions/stimulant like physical condition including electrical stimulation, chemical inducers and biological agents have been attempted by numerous groups to induce cardiac differentiation. Biomaterials were initially used as artificial scaffold in in vitro studies and later as a delivery vehicle. Natural ECM is the ideal biological scaffold since it contains all the components of the tissue from which it was derived except for the living cells. Constructive remodeling can be performed using such natural ECM scaffolds and stem cells since, the cells can be delivered to the site of infraction and once delivered the cells adhere and are not "lost". Due to the niche like conditions of ECM, stem cells tend to differentiate into tissue specific cells and attain several characteristics similar to that of functional cells even in absence of any directed differentiation using external inducers. The development of niche mimicking biomaterials and hybrid biomaterial can further advance directed differentiation without specific induction. The mechanical and electrical integration of these materials to the functional tissue is a problem to be addressed. The search for the perfect extracellular matrix for therapeutic applications including engineering cardiac tissue structures for post ischemic cardiac tissue regeneration continues.

Enhanced cardiomyogenic lineage differentiation of adult bone-marrow-derived stem cells grown on cardiogel

The extracellular matrix (ECM) and its components are known to promote growth and cellular differentiation in vitro. Cardiogel, a three-dimensional extracellular matrix derived from cardiac fibroblasts, is evaluated for its cardiomyogenic-differentiation-inducing potential on bone-marrow-derived stem cells (BMSC). BMSC from adult mice were grown on cardiogel and induced to differentiate into specific lineages that were validated by morphological, phenotypic and molecular assays. The data revealed that the cardiogel enhanced cardiomyogenic and adipogenic differentiation and relegated osteogenic differentiation following specific induction. More importantly, increased cardiomyogenic differentiation was also observed following BMSC growth on cardiogel without specific chemical (5-azacytidine) induction. This is the first report of an attempt to use cardiogel as a biomaterial on which to achieve cardiomyogenic differentiation of BMSC without chemical induction. Our study suggests that cardiogel is an efficient extracellular matrix that enhances the cardiomyogenic differentiation of BMSC and that it can therefore be used as a scaffold for cardiac tissue regeneration.

Effects of early, late, and long-term nonselective β-blockade on left ventricular remodeling, function, and survival in chronic organic mitral regurgitation

BACKGROUND

Mitral regurgitation (MR) produces sympathetic nervous system activation which is detrimental in other causes of heart failure. However, whether β-blockade is beneficial in MR has not been determined.

METHODS AND RESULTS

Eighty-seven rats with significant organic MR were randomized to the β-blockade group (n=43) or the control group (n=44). Carvedilol was started in week 2 post MR induction and given for 23 to 35 weeks in the β-blockade group. Echocardiography was performed at baseline and at weeks 2, 6, 12, 24, 30, and 36 after MR induction. After 23 weeks of β-blockade, heart rates were significantly reduced by carvedilol (308 ± 25 versus 351 ± 31 beats per minute; P<0.001). Left ventricular end-diastolic (2.2 ± 0.7 versus 1.59 ± 0.6 mL; P<0.001), end-systolic volumes (0.72 ± 0.42 versus 0.40 ± 0.19 mL; P<0.001), and mass index (2.40 ± 0.55 versus 2.06 ± 0.62 g/kg; P<0.001) were significantly higher, and left ventricular fraction shortening (33 ± 7% versus 38 ± 7%; P<0.001) and ejection fraction (69 ± 11% versus 75 ± 7%; P<0.001) were significantly lower in the β-blockade group than in the control group. Systolic blood pressure was lower in the β-blockade group than in the control group (114 ± 10 versus 93 ± 12 mm Hg; P<0.005). Survival probability was significantly lower in the early β-blockade group than in the control group (88% versus 96%; P=0.03).

CONCLUSIONS

Early and long-term nonselective β-blockade was associated with adverse left ventricular remodeling, systolic dysfunction, and a reduction in survival in the experimental rat model of organic MR.

Physiologic and molecular characterization of a murine model of right ventricular volume overload

Pulmonary insufficiency (PI) is a common long-term sequel after repair of tetralogy of Fallot, causing progressive right ventricular (RV) dilation and failure. We describe the physiologic and molecular characteristics of the first murine model of RV volume overload. PI was created by entrapping the pulmonary valve leaflets with sutures. Imaging, catheterization, and exercise testing were performed at 1, 3, and 6 mo and compared with sham controls. RNA from the RV free wall was hybridized to Agilent whole genome oligonucleotide microarrays. Volume overload resulted in RV enlargement, decreased RV outflow tract shortening fraction at 1 mo followed by normalization at 3 and 6 mo (39 ± 2, 44 ± 2, and 41 ± 2 vs. 46 ± 3% in sham), early reversal of early and late diastolic filling velocities (E/A ratio) followed by pseudonormalization (0.87 ± 0.08, 0.82 ± 0.08, and 0.96 ± 0.08 vs. 1.04 ± 0.03; P < 0.05), elevated end-diastolic pressure (7.6 ± 0.7, 6.9 ± 0.8, and 7 ± 0.5 vs. 2.7 ± 0.2 mmHg; P < 0.05), and decreased exercise duration (26 ± 0.4, 26 ± 1, and 22 ± 1.3 vs. 30 ± 1.1 min; P < 0.05). Subendocardial RV fibrosis was evident by 1 mo. At 1 mo, 372 genes were significantly downregulated. Mitochondrial pathways and G protein-coupled receptor signaling were the most represented categories. At 3 mo, 434 genes were upregulated and 307 downregulated. While many of the same pathways continued to be downregulated, TNF-α, transforming growth factor-β(1) (TGF-β(1)), p53-signaling, and extracellular matrix (ECM) remodeling transitioned from down- to upregulated. We describe a novel murine model of chronic RV volume overload recapitulating aspects of the clinical disease with gene expression changes suggesting early mitochondrial bioenergetic dysfunction, enhanced TGF-β signaling, ECM remodeling, and apoptosis.

Cardiac primitive cells become committed to a cardiac fate in adult human heart with chronic ischemic disease but fail to acquire mature phenotype: genetic and phenotypic study

Adult human heart hosts a population of cardiac primitive CD117-positive cells (CPCs), which are responsible for physiological tissue homeostasis and regeneration. While the bona fide stem cells express telomerase, their progenies are no longer able to preserve telomeric DNA; hence the balance between their proliferation and differentiation has to be tightly controlled in order to prevent cellular senescence and apoptosis of CPCs before their maturation can be accomplished. We have examined at cellular and molecular level the proliferation, apoptosis and commitment of CPCs isolated from normal (CPC-N) and age-matched pathological adult human hearts (CPC-P) with ischemic heart disease. In the CPC-P, genes related to early stages of developmental processes, nervous system development and neurogenesis, skeletal development, bone and cartilage development were downregulated, while those involved in mesenchymal cell differentiation and heart development were upregulated, together with the transcriptional activation of TGFβ/BMP signaling pathway. In the pathological heart, asymmetric division was the prevalent type of cardiac stem cell division. The population of CPC-P consisted mainly of progenitors of cardiac cell lineages and less precursors; these cells proliferated more, but were also more susceptible to apoptosis with respect to CPC-N. These results indicate that CPCs fail to reach terminal differentiation and functional competence in pathological conditions. Adverse effects of underlying pathology, which disrupts cardiac tissue structure and composition, and cellular senescence, resulting from cardiac stem cell activation in telomere dysfunctional environment, can be responsible for such outcome.

Extracellular and intracellular proteases in cardiac dysfunction due to ischemia-reperfusion injury

Various procedures such as angioplasty, thrombolytic therapy, coronary bypass surgery, and cardiac transplantation are invariably associated with ischemia-reperfusion (I/R) injury. Impaired recovery of cardiac function due to I/R injury is considered to be a consequence of the occurrence of both oxidative stress and intracellular Ca(2+)-overload in the myocardium. These changes in the ischemic myocardium appear to activate both extracellular and intracellular proteases which are responsible for the cleavage of extracellular matrix and subcellular structures involved in the maintenance of cardiac function. It is thus intended to discuss the actions of I/R injury on several proteases, with a focus on calpain, matrix metalloproteinases, and cathepsins as well as their role in inducing alterations both inside and outside the cardiomyocytes. In addition, modifications of subcellular organelles such as myofibrils, sarcoplasmic reticulum and sarcolemma as well as extracellular matrix, and the potential regulatory effects of endogenous inhibitors on protease activities are identified. Both extracellular and intracellular proteolytic activities appear to be imperative in determining the true extent of I/R injury and their inhibition seems to be of critical importance for improving the recovery of cardiac function. Thus, both extracellular and intracellular proteases may serve as potential targets for the development of cardioprotective interventions for reducing damage to the heart and retarding the development of contractile dysfunction caused by I/R injury.

Osteopontin-stimulated expression of matrix metalloproteinase-9 causes cardiomyopathy in the mdx model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD), caused by mutations in the dystrophin gene, is a common and lethal form of muscular dystrophy. With progressive disease, most patients succumb to death from respiratory or heart failure, or both. However, the mechanisms, especially those governing cardiac inflammation and fibrosis in DMD, remain less understood. Matrix metalloproteinase (MMPs) are a group of extracellular matrix proteases involved in tissue remodeling in both physiologic and pathophysiologic conditions. Previous studies have shown that MMP-9 exacerbates myopathy in dystrophin-deficient mdx mice. However, the role and the mechanisms of action of MMP-9 in cardiac tissue and the biochemical mechanisms leading to increased levels of MMP-9 in mdx mice remain unknown. Our results demonstrate that the levels of MMP-9 are increased in the heart of mdx mice. Genetic ablation of MMP-9 attenuated cardiac injury, left ventricle dilation, and fibrosis in 1-y-old mdx mice. Echocardiography measurements showed improved heart function in Mmp9-deficient mdx mice. Deletion of the Mmp9 gene diminished the activation of ERK1/2 and Akt kinase in the heart of mdx mice. Ablation of MMP-9 also suppressed the expression of MMP-3 and MMP-12 in the heart of mdx mice. Finally, our experiments have revealed that osteopontin, an important immunomodulator, contributes to the increased amounts of MMP-9 in cardiac and skeletal muscle of mdx mice. This study provides a novel mechanism for development of cardiac dysfunction and suggests that MMP-9 and OPN are important therapeutic targets to mitigating cardiac abnormalities in patients with DMD.

Circulating levels of non-phosphorylated undercarboxylated matrix Gla protein are associated with disease severity in patients with chronic heart failure

We recently demonstrated that circulating MGP [matrix Gla (γ-carboxylated glutamate) protein] levels were associated with left ventricular dysfunction and increased mortality in patients with symptomatic aortic stenosis. We hypothesized that patients with chronic HF (heart failure) would have dysregulated MGP levels. We examined plasma dp-cMGP (non-phosphorylated carboxylated MGP) and dp-ucMGP (non-phosphorylated undercarboxylated MGP) in 179 patients with chronic HF and matched healthy controls as well as the relationship between MGP and cardiac dysfunction as assessed by echocardiographic measurements, inflammation [CRP (C-reactive protein)] and neurohormonal activation [NT-proBNP (N-terminal proB-type natriuretic peptide)] and the prognostic value of MGP levels in relation to mortality in these patients. We found markedly enhanced plasma dp-cMGP and, in particular, of dp-ucMGP in chronic HF with increasing levels with disease severity. Elevated MGP species were associated with ischaemic aetiology, increased CRP and NT-proBNP levels, as well as systolic and diastolic dysfunction. Finally, dp-ucMGP was associated with long-term heart transplant-free survival (n=48) in univariate, but not in multivariate, analysis. However, plasma dp-ucMGP was markedly higher in patients who died because of progression of HF (n=12) and gave prognostic information also in multivariate analysis. In conclusion, a dysregulated MGP system could be involved in left ventricular dysfunction in patients with chronic HF.

Physiological regulation of extracellular matrix collagen and elastin in the arterial wall of rats by noradrenergic tone and angiotensin II

The interactions between the effects of the sympathetic nervous system (SNS) and angiotensin II (ANG II) on vascular extracellular matrix (ECM) synthesis were determined in rats.

The mRNA and protein content of collagen I, collagen III and elastin in the abdominal aorta (AA) and femoral artery (FA) was investigated in Wistar–Kyoto rats treated for 5 weeks with guanethidine, a sympathoplegic, losartan, an ANG II AT1 receptor (AT1R) blocker, or both. The effects of noradrenaline (NE) and ANG II on collagen III and elastin mRNA, and the receptor involved, were tested in cultured vascular smooth muscle cells (VSMCs) in vitro.

Guanethidine increased collagen types I and III and decreased elastin, while losartan had an opposite effect, although without effect on collagen III. The combination of treatments abrogated changes induced by simple treatment with collagen I and elastin, but increased collagen III mRNA in AA and not in FA. NE stimulated collagen III mRNA via β receptors and elastin via α1 and α2 receptors. ANG II stimulated collagen III but inhibited elastin mRNA via AT1R.

Overall, SNS and ANG II exert opposite and antagonistic effects on major components of ECM in the vascular wall. This may be of relevance for the choice of a therapeutic strategy in vascular diseases.

The role of dietary fatty acids in predicting myocardial structure in fat-fed rats

Background

Obesity increases the risk for development of cardiomyopathy in the absence of hypertension, diabetes or myocardial ischemia. Not all obese individuals, however, progress to heart failure. Indeed, obesity may provide protection from cardiovascular mortality in some populations. The fatty acid milieu, modulated by diet, may modify obesity-induced myocardial structure and function, lending partial explanation for the array of cardiomyopathic phenotypy in obese individuals.

Methods

Adult male Sprague-Dawley rats were fed 1 of the following 4 diets for 32 weeks: control (CON); 50% saturated fat (SAT); 40% saturated fat + 10% linoleic acid (SAT+LA); 40% saturated fat + 10% α-linolenic acid (SAT+ALA). Serum leptin, insulin, glucose, free fatty acids and triglycerides were quantitated. In vivo cardiovascular outcomes included blood pressure, heart rate and echocardiographic measurements of structure and function. The rats were sacrificed and myocardium was processed for fatty acid analysis (TLC-GC), and evaluation of potential modifiers of myocardial structure including collagen (Masson's trichrome, hydroxyproline quantitation), lipid (Oil Red O, triglyceride quantitation) and myocyte cross sectional area.

Results

Rats fed SAT+LA and SAT+ALA diets had greater cranial LV wall thickness compared to rats fed CON and SAT diets, in the absence of hypertension or apparent insulin resistance. Treatment was not associated with changes in myocardial function. Myocardial collagen and triglycerides were similar among treatment groups; however, rats fed the high-fat diets, regardless of composition, demonstrated increased myocyte cross sectional area.

Conclusions

Under conditions of high-fat feeding, replacement of 10% saturated fat with either LA or ALA is associated with thickening of the cranial LV wall, but without concomitant functional changes. Increased myocyte size appears to be a more likely contributor to early LV thickening in response to high-fat feeding. These findings suggest that myocyte hypertrophy may be an early change leading to gross LV hypertrophy in the hearts of "healthy" obese rats, in the absence of hypertension, diabetes and myocardial ischemia.

Bosentan attenuates right ventricular hypertrophy and fibrosis in normobaric hypoxia model of pulmonary hypertension

BACKGROUND

Maladaptive right ventricular (RV) hypertrophic responses lead to RV dysfunction and failure in patients with pulmonary arterial hypertension, but the mechanisms responsible for these changes are not well understood. The objective of this study was to evaluate the effect of treatment with bosentan on RV hypertrophy (RVH), fibrosis and expression of protein kinase C (PKC) isoforms in the RV of rats exposed to chronic hypoxia.

METHODS

Adult Sprague-Dawley rats were housed in normoxia or hypoxia (FIO(2) = 10%) and administered vehicle or 100 mg/kg/day bosentan. After 3 weeks, echocardiographic and hemodynamic assessment was performed. PKC, procollagen-1 and collagen expression levels were assessed using immunoblot or colorimetric assay.

RESULTS

RV systolic pressure (RVSP) and RVH were higher in hypoxic compared with normoxic animals (RVSP: 72 ± 4 vs 25 ± 2 mm Hg, p < 0.05; RVH: 1.2 ± 0.06 vs 0.5 ± 0.03 mg/g body weight, p < 0.05). Bosentan had no effect on RVSP or mass in normoxic animals, but did attenuate RVH in hypoxic animals (hypoxic/vehicle: 1.2 ± 0.06; hypoxic/bosentan: 1.0 ± 0.05 mg/g body weight; p < 0.05). Hypoxia increased RV procollagen-1, and total collagen expression, effects that were attenuated by bosentan treatment. Hypoxia increased RV total and cytosolic PKC-δ protein expression, but had no effect on PKC-α or -ε isoforms. Administration with bosentan did not affect total PKC-δ protein expression. However, animals treated with bosentan had an increase in membranous PKC-δ when exposed to hypoxia.

CONCLUSIONS

Bosentan inhibits RVH and RV collagen expression in rats exposed to chronic hypoxia, possibly via alteration of PKC-δ activity.

Distinct effects of leukocyte and cardiac phosphoinositide 3-kinase γ activity in pressure overload-induced cardiac failure

BACKGROUND

Signaling from phosphoinositide 3-kinase γ (PI3Kγ) is crucial for leukocyte recruitment and inflammation but also contributes to cardiac maladaptive remodeling. To better understand the translational potential of these findings, this study investigates the role of PI3Kγ activity in pressure overload-induced heart failure, addressing the distinct contributions of bone marrow-derived and cardiac cells.

METHODS AND RESULTS

After transverse aortic constriction, mice knock-in for a catalytically inactive PI3Kγ (PI3Kγ KD) showed reduced fibrosis and normalized cardiac function up to 16 weeks. Accordingly, treatment with a selective PI3Kγ inhibitor prevented transverse aortic constriction-induced fibrosis. To define the cell types involved in this protection, bone marrow chimeras, lacking kinase activity in the immune system or the heart, were studied after transverse aortic constriction. Bone marrow-derived cells from PI3Kγ KD mice were not recruited to wild-type hearts, thus preventing fibrosis and preserving diastolic function. After prolonged pressure overload, chimeras with PI3Kγ KD bone marrow-derived cells showed slower development of left ventricular dilation and higher fractional shortening than controls. Conversely, in the presence of a wild-type immune system, KD hearts displayed bone marrow-derived cell infiltration and fibrosis at early stages but reduced left ventricular dilation and preserved contractile function at later time points.

CONCLUSIONS

Together, these data demonstrate that, in response to transverse aortic constriction, PI3Kγ contributes to maladaptive remodeling at multiple levels by modulating both cardiac and immune cell functions.

Extracellular matrix of collagen modulates intracellular calcium handling and electrophysiological characteristics of HL-1 cardiomyocytes with activation of angiotensin II type 1 receptor

BACKGROUND

Myocardial fibrosis plays a critical role in heart failure, resulting in cardiac structural and electrical remodeling which can induce atrial arrhythmias. Collagen is the major element of fibrosis. However, it is not clear whether collagen can directly regulate the calcium homeostasis and the electrophysiologic characteristics of cardiomyocytes. The aim of this study was to determine the effects of collagen on calcium homeostasis and the electrical properties of atrial cardiomyocytes.

METHODS AND RESULTS

HL-1 cardiomyocytes were cultured with and without collagen type I (1 or 10 μg/mL) or losartan (10 μmol/L). Whole-cell clamp, indo-1 fluorescence, and Western blotting were used to evaluate the action potential (AP) and ionic currents, intracellular calcium homeostasis, and calcium regulatory proteins. Compared with the control samples, there was no significant difference in collagen (1 μg/mL)-treated HL-1 cardiomyocytes. However, collagen (10 μg/mL)-treated HL-1 cardiomyocytes exhibited larger intracellular calcium ([Ca(2+)](i)) transients by 113% and a larger sarcoplasmic reticulum calcium content by 86%. Collagen (10 μg/mL)-treated HL-1 cardiomyocytes had higher expression of sarcoplasmic reticulum ATPase (SERCA2a) and Thr17-phosphorylated phospholamban but similar protein expressions of the Na(+)/Ca(2+) exchanger and ryanodine receptor. Collagen (10 μg/mL)-treated HL-1 cardiomyocytes (n = 11) had larger AP amplitude (104 ± 5 vs 83 ± 7 mV; P < .05), and shorter 90% of AP duration (25 ± 2 vs 33 ± 2 ms, P < .05) than control cells (n = 11). Moreover, collagen (10 μg/mL)-treated HL-1 cells had larger I(to) and I(Ksus) values than control cells. The administration of losartan (10 μmol/L) attenuated collagen-induced changes in [Ca(2+)](i) transients, [Ca(2+)](i) stores, AP morphology, ionic currents, SERCA2a, and Thr17-phosphorylated phospholamban expressions.

CONCLUSIONS

This study demonstrates that collagen can directly modulate the calcium dynamics and electrical activities of atrial cardiomyocytes, which are associated with the renin-angiotensin system. These findings suggest a critical role of collagen in electrical remodeling during fibrosis.

Increased connective tissue growth factor associated with cardiac fibrosis in the mdx mouse model of dystrophic cardiomyopathy

Cardiomyopathy contributes to morbidity and mortality in Duchenne muscular dystrophy (DMD), a progressive muscle-wasting disorder. A major feature of the hearts of DMD patients and the mdx mouse model of the disease is cardiac fibrosis. Connective tissue growth factor (CTGF) is involved in the fibrotic process in many organs. This study utilized the mdx mouse model to assess the role of CTGF and other extracellular matrix components during the development of fibrosis in the dystrophic heart. Left ventricular function of mdx and control mice at 6, 29 and 43 weeks was measured by echocardiography. Young (6 weeks old) mdx hearts had normal function and histology. At 29 weeks of age, mdx mice developed cardiac fibrosis and increased collagen expression. The onset of fibrosis was associated with increased CTGF transcript and protein expression. Increased intensity of CTGF immunostaining was localized to fibrotic areas in mdx hearts. The upregulation of CTGF was also concurrent with increased expression of tissue inhibitor of matrix metalloproteinases (TIMP-1). These changes persisted in 43 week old mdx hearts and were combined with impaired cardiac function and increased gene expression of transforming growth factor (TGF)-β1 and matrix metalloproteinases (MMP-2, MMP-9). In summary, an association was observed between cardiac fibrosis and increased CTGF expression in the mdx mouse heart. CTGF may be a key mediator of early and persistent fibrosis in dystrophic cardiomyopathy.

Collagen XV Is Necessary for Modeling of the Extracellular Matrix and Its Deficiency Predisposes to Cardiomyopathy

Rationale:

The extracellular matrix (ECM) is a major determinant of the structural integrity and functional properties of the myocardium in common pathological conditions, and changes in vasculature contribute to cardiac dysfunction. Collagen (Col) XV is preferentially expressed in the ECM of cardiac muscle and microvessels.

Objective:

We aimed to characterize the ECM, cardiovascular function and responses to elevated cardiovascular load in mice lacking Col XV ( Col15a1 −/− ) to define its functional role in the vasculature and in age- and hypertension-associated myocardial remodeling.

Methods and Results:

Cardiac structure and vasculature were analyzed by light and electron microscopy. Cardiac function, intraarterial blood pressure, microhemodynamics, and gene expression profiles were studied using echocardiography, telemetry, intravital microscopy, and PCR, respectively. Experimental hypertension was induced with angiotensin II or with a nitric oxide synthesis inhibitor. Under basal conditions, lack of Col XV resulted in increased permeability and impaired microvascular hemodynamics, distinct early-onset and age-dependent defects in heart structure and function, a poorly organized fibrillar collagen matrix with marked interstitial deposition of nonfibrillar protein aggregates, increased tissue stiffness, and irregularly organized cardiomyocytes. In response to experimental hypertension, Col15a1 gene expression was increased in the left ventricle of wild-type mice, and mRNA expression of natriuretic peptides (ANP and BNP) and ECM modeling were abnormal in Col15a1 −/− mice.

Conclusions:

Col XV is necessary for ECM organization in the heart, and for the structure and functions of microvessels. Col XV deficiency leads to a complex cardiac phenotype and predisposes the subject to pathological responses under cardiac stress.

Micro- and nanoscale control of the cardiac stem cell niche for tissue fabrication

Advances in stem cell (SC) biology have greatly enhanced our understanding of SC self-renewal and differentiation. Both embryonic and adult SCs can be differentiated into a great variety of tissue cell types, including cardiac myocytes. In vivo studies and clinical trials, however, have demonstrated major limitations in reconstituting the myocardium in failing hearts. These limitations include precise control of SC proliferation, survival and phenotype both prior and subsequent to transplantation and avoidance of serious adverse effects such as tumorigenesis and arrhythmias. Micro- and nanoscale techniques to recreate SC niches, the natural environment for the maintenance and regulation of SCs, have enabled the elucidation of novel SC behaviors and offer great promise in the fabrication of cardiac tissue constructs. The ability to precisely manipulate the interface between biopolymeric scaffolds and SCs at in vivo scale resolutions is unique to micro- and nanoscale approaches and may help overcome limitations of conventional biological scaffolds and methods for cell delivery. We now know that micro- and nanoscale manipulation of scaffold composition, mechanical properties, and three-dimensional architecture have profound influences on SC fate and will likely prove important in developing the next generation of "transplantable SC niches" for regeneration of heart and other tissues. In this review, we examine two key aspects of micro- and nanofabricated SC-based cardiac tissue constructs: the role of scaffold composition and the role of scaffold architecture and detail how recent work in these areas brings us closer to clinical solutions for cardiovascular regeneration.

Obesity and preclinical changes of cardiac geometry and function

Overweight and obesity are rapidly increasing in prevalence due to adoption of the westernized life style in Korea. Obesity is strongly associated with the development of cardiovascular risk factors such as diabetes, hypertension, and dyslipidemia. In addition, accumulating evidence suggests that obesity per se has a direct effect on cardiac functional and structural changes that may not be the result of atherosclerosis. In this review, we focus on the view that obesity can influence on the structural and functional changes of the heart, drawing evidence from human and animal studies. We also review influencing factors such as physical, neurohormonal, and metabolic alterations that are associated with changes of the heart in obesity.

Scleraxis is required for cell lineage differentiation and extracellular matrix remodeling during murine heart valve formation in vivo

Heart valve structures, derived from mesenchyme precursor cells, are composed of differentiated cell types and extracellular matrix arranged to facilitate valve function. Scleraxis (scx) is a transcription factor required for tendon cell differentiation and matrix organization. This study identified high levels of scx expression in remodeling heart valve structures at embryonic day 15.5 through postnatal stages using scx-GFP reporter mice and determined the in vivo function using mice null for scx. Scx(-/-) mice display significantly thickened heart valve structures from embryonic day 17.5, and valves from mutant mice show alterations in valve precursor cell differentiation and matrix organization. This is indicated by decreased expression of the tendon-related collagen type XIV, increased expression of cartilage-associated genes including sox9, as well as persistent expression of mesenchyme cell markers including msx1 and snai1. In addition, ultrastructure analysis reveals disarray of extracellular matrix and collagen fiber organization within the valve leaflet. Thickened valve structures and increased expression of matrix remodeling genes characteristic of human heart valve disease are observed in juvenile scx(-/-) mice. In addition, excessive collagen deposition in annular structures within the atrioventricular junction is observed. Collectively, our studies have identified an in vivo requirement for scx during valvulogenesis and demonstrate its role in cell lineage differentiation and matrix distribution in remodeling valve structures.

Mesenchymal stem cell transplantation attenuates cardiac fibrosis associated with isoproterenol-induced global heart failure

We aimed to examine the ability of transplanted mesenchymal stem cells (MSCs) to attenuate cardiac fibrosis caused by global heart failure, and investigate the mechanisms that are possibly mediating this effect. Global heart failure was induced in Wistar rats by isoproterenol injection. Four weeks later, MSCs were transplanted by intramyocardial injection, while control groups were treated by injection of cell culture medium alone. Four weeks after transplantation, heart function was assessed, and histologic and molecular analyses conducted. Compared with the medium-treated group, MSC transplantation significantly decreased the expression of collagens I and III, and matrix metalloproteinase 2 and 9, but heart function was improved in MSC-treated animals. In addition, expression of antifibrotic factor, hepatocyte growth factor (HGF), was detected in cultured MSCs, suggesting a possible mechanism underlying antifibrotic effects. Importantly, HGF expression levels were higher in MSC-treated hearts, compared with medium-treated hearts. Therefore, we could conclude that MSC transplantation can attenuate myocardial fibrosis in a rat model of global heart failure, and this may be at least partially mediated by paracrine signaling from MSCs via antifibrotic factors such as HGF.

Cardiac remodeling in obesity

The dramatic increase in the prevalence of obesity and its strong association with cardiovascular disease have resulted in unprecedented interest in understanding the effects of obesity on the cardiovascular system. A consistent, but puzzling clinical observation is that obesity confers an increased susceptibility to the development of cardiac disease, while at the same time affording protection against subsequent mortality (termed the obesity paradox). In this review we focus on evidence available from human and animal model studies and summarize the ways in which obesity can influence structure and function of the heart. We also review current hypotheses regarding mechanisms linking obesity and various aspects of cardiac remodeling. There is currently great interest in the role of adipokines, factors secreted from adipose tissue, and their role in the numerous cardiovascular complications of obesity. Here we focus on the role of leptin and the emerging promise of adiponectin as a cardioprotective agent. The challenge of understanding the association between obesity and heart failure is complicated by the multifaceted interplay between various hemodynamic, metabolic, and other physiological factors that ultimately impact the myocardium. Furthermore, the end result of obesity-associated changes in the myocardial structure and function may vary at distinct stages in the progression of remodeling, may depend on the individual pathophysiology of heart failure, and may even remain undetected for decades before clinical manifestation. Here we summarize our current knowledge of this complex yet intriguing topic.

Myocardial Matrix Remodeling and the Matrix Metalloproteinases: Influence on Cardiac Form and Function

It is now becoming apparent that dynamic changes occur within the interstitium that directly contribute to adverse myocardial remodeling following myocardial infarction (MI), with hypertensive heart disease and with intrinsic myocardial disease such as cardiomyopathy. Furthermore, a family of matrix proteases, the matrix metalloproteinases (MMPs) and the tissue inhibitors of MMPs (TIMPs), has been recognized to play an important role in matrix remodeling in these cardiac disease states. The purpose of this review is fivefold: 1) to examine and redefine the myocardial matrix as a critical and dynamic entity with respect to the remodeling process encountered with MI, hypertension, or cardiomyopathic disease; 2) present the remarkable progress that has been made with respect to MMP/TIMP biology and how it relates to myocardial matrix remodeling; 3) to evaluate critical translational/clinical studies that have provided a cause-effect relationship between alterations in MMP/TIMP regulation and myocardial matrix remodeling; 4) to provide a critical review and analysis of current diagnostic, prognostic, and pharmacological approaches that utilized our basic understanding of MMP/TIMPs in the context of cardiac disease; and 5) most importantly, to dispel the historical belief that the myocardial matrix is a passive structure and supplant this belief that the regulation of matrix protease pathways such as the MMPs and TIMPs will likely yield a new avenue of diagnostic and therapeutic strategies for myocardial remodeling and the progression to heart failure.

ColVa1 and ColXIa1 are required for myocardial morphogenesis and heart valve development

Genetic mutations in minor fibrillar collagen types Va1 (ColVa1) and XIa1 (ColXI) have been identified in connective tissue disorders including Ehlers-Danlos syndrome and chondrodysplasias. ColVa1+/- and ColXIa1-/- mutant mice recapitulate these human disorders and show aberrations in collagen fiber organization in connective tissue of the skin, cornea, cartilage, and tendon. In the heart, fibrous networks of collagen fibers form throughout the ventricular myocardium and heart valves, and alterations in collagen fiber homeostasis are apparent in many forms of cardiac disease associated with myocardial dysfunction and valvular insufficiency. There is increasing evidence for cardiac dysfunction in connective tissue disorders, but the mechanisms have not been addressed. ColVa1+/- and ColXIa1-/- mutant mice were used to identify roles for ColVa1 and ColXIa1 in ventricular myocardial morphogenesis and heart valve development. These affected cardiac structures show a compensatory increase in type I collagen deposition, similar to that previously described in valvular and cardiomyopathic disease. Morphological cardiac defects associated with changes in collagen fiber homeostasis identified in ColVa1+/- and ColXIa1-/- mice provide an insight into previously unappreciated forms of cardiac dysfunction associated with connective tissue disorders.

Diastolic ventricular-vascular stiffness and relaxation relation: elucidation of coupling via pressure phase plane-derived indexes

Because systole and diastole are coupled and systolic ventricular-vascular coupling has been characterized, we hypothesize that diastolic ventricular-vascular coupling (DVVC) exists and can be characterized in terms of relaxation and stiffness. To characterize and elucidate DVVC mechanisms, we introduce time derivative of pressure (dP/d t) vs. time-varying pressure [P( t)] (pressure phase plane, PPP)-derived analogs of ventricular and vascular “stiffness” and relaxation parameters. Although volume change (dV) = 0 during isovolumic periods, and time-varying left ventricular (LV) stiffness, typically expressed as change in pressure per unit change in volume (dP/dV), is undefined, our formulation allows determination of a PPP-derived stiffness analog during isovolumic contraction and relaxation. Similarly, an aortic stiffness analog is also derivable from the PPP. LV relaxation was characterized via τ, the time constant of isovolumic relaxation, and vascular (aortic pressure decay) relaxation was characterized in terms of its equivalent (windkessel) exponential decay time constant κ. The results show that PPP-derived systolic and diastolic ventricular and vascular stiffness are strongly coupled [Formula: see text]. In support of the DVVC hypothesis, a strong linear correlation between relaxation (rate of pressure decay) indexes κ and τ (κ = 9.89τ − 90.3, r = 0.81) was also observed. The correlations observed underscore the role of long-term, steady-state DVVC as a diastolic function determinant. Awareness of the PPP-derived DVVC parameters provides insight into mechanisms and facilitates quantification of arterial stiffening and associated increase in diastolic chamber stiffness. The PPP method provides a tool for quantitative assessment and determination of the functional coupling of the vasculature to diastolic function.