Collagen cross-linking: new dimension to cardiac remodeling

Extracellular stiffness induces contractile dysfunction in adult cardiomyocytes via cell-autonomous and microtubule-dependent mechanisms

The mechanical environment of the myocardium has a potent effect on cardiomyocyte form and function, yet an understanding of the cardiomyocyte responses to extracellular stiffening remains incomplete. We therefore employed a cell culture substrate with tunable stiffness to define the cardiomyocyte responses to clinically relevant stiffness increments in the absence of cell-cell interactions. When cultured on substrates magnetically actuated to mimic the stiffness of diseased myocardium, isolated rat adult cardiomyocytes exhibited a time-dependent reduction of sarcomere shortening, characterized by slowed contraction and relaxation velocity, and alterations of the calcium transient. Cardiomyocytes cultured on stiff substrates developed increases in viscoelasticity and microtubule detyrosination in association with early increases in the α-tubulin detyrosinating enzyme vasohibin-2 (Vash2). We found that knockdown of Vash2 was sufficient to preserve contractile performance as well as calcium transient properties in the presence of extracellular substrate stiffening. Orthogonal prevention of detyrosination by overexpression of tubulin tyrosine ligase (TTL) was also able to preserve contractility and calcium homeostasis. These data demonstrate that a pathologic increment of extracellular stiffness induces early, cell-autonomous remodeling of adult cardiomyocytes that is dependent on detyrosination of α-tubulin.

Biomarker of Collagen Turnover (C-Terminal Telopeptide) and Prognosis in Patients With Non- ST -Elevation Acute Coronary Syndromes

Background

Small studies have suggested an association between markers of collagen turnover and adverse outcomes in heart failure (HF). We examined C‐terminal telopeptide (beta‐CTx) and the risk of cardiovascular death or new or worsening HF in non–ST‐elevation acute coronary syndrome.

Methods and Results

We measured baseline serum beta‐CTx, NT‐proBNP (N‐terminal pro‐B‐type natriuretic peptide), hsTnT (high‐sensitivity cardiac troponin T) and hsCRP (high‐sensitivity C‐reactive protein) (Roche Diagnostics) in a nested biomarker analysis (n=4094) from a study of patients with non–ST‐elevation acute coronary syndrome. The relationship between quartiles of beta‐CTx and cardiovascular death or HF over a median follow‐up time of 12 months was analyzed using adjusted Cox models. Higher beta‐CTx levels identified a significantly higher risk of cardiovascular death/HF (Q4 10.9% versus Q1 3.8%, Logrank P<0.001). After multivariable adjustment, beta‐CTx in the top quartile (Q4) was associated with cardiovascular death/HF (Q4 versus Q1: adjusted hazard ratio 2.22 [1.50–3.27]) and its components (Q4 versus Q1: cardiovascular death: adjusted hazard ratio 2.48 [1.46–4.21]; HF: adjusted hazard ratio 2.04 [1.26–3.30]). In an adjusted multimarker model including NT‐proBNP, hsTnT, and hsCRP, beta‐CTx remained independently associated with cardiovascular death/HF (Q4 versus Q1: adjusted hazard ratio 1.98 [1.34–2.93]) and its components. Beta‐CTx correlated weakly with NT‐proBNP (r=0.17, P<0.001) and left ventricular ejection fraction (r=−0.05, P=0.008) and did not correlate with hsTnT (r=0.02, P=0.20), or hsCRP (r=−0.03, P=0.09).

Conclusions

Levels of beta‐CTx, a biomarker of collagen turnover, were associated with cardiovascular death and HF in patients with non–ST‐elevation acute coronary syndrome. This biomarker, which correlated only weakly or not significantly with traditional biomarkers of cardiovascular death and HF, may provide complementary pathobiological insight and risk stratification in these patients.

Manganese superoxide dismutase deficiency exacerbates the mitochondrial ROS production and oxidative damage in Chagas disease

In this study, we have investigated the effects of manganese superoxide dismutase (SOD2 or MnSOD) deficiency on mitochondrial function and oxidative stress during Chagas disease. For this, C57BL/6 wild type (WT) and MnSOD^+/- mice were infected with Trypanosoma cruzi (Tc), and evaluated at 150 days’ post-infection that corresponded to chronic disease phase. Genetic deletion of SOD2 decreased the expression and activity of MnSOD, but it had no effect on the expression of other members of the SOD family. The myocardial expression and activity of MnSOD were significantly decreased in chronically infected WT mice, and it was further worsened in MnSOD^+/- mice. Chronic T. cruzi infection led to a decline in mitochondrial complex I and complex II driven, ADP-coupled respiration and ATP synthesis in the myocardium of WT mice. The baseline oxidative phosphorylation (OXPHOS) capacity in MnSOD^+/- mice was decreased, and it had an additive effect on mitochondrial dysregulation of ATP synthesis capacity in chagasic myocardium. Further, MnSOD deficiency exacerbated the mitochondrial rate of reactive oxygen species (ROS) production and myocardial oxidative stress (H₂O₂, protein carbonyls, malondialdehyde, and 4-hydroxynonenal) in Chagas disease. Peripheral and myocardial parasite burden and inflammatory response (myeloperoxidase, IL-6, lactate dehydrogenase, inflammatory infiltrate) were increased in all chagasic WT and MnSOD^+/- mice. We conclude that MnSOD deficiency exacerbates the loss in mitochondrial function and OXPHOS capacity and enhances the myocardial oxidative damage in chagasic cardiomyopathy. Mitochondria targeted, small molecule mitigators of MnSOD deficiency will offer potential benefits in averting the mitochondrial dysfunction and chronic oxidative stress in Chagas disease.

Infection by Trypanosoma cruzi parasitic protozoan remains endemic in Latin America. After acute parasitemia phase is controlled by host immune system, infected individuals remain clinically silent but manifest a number of micro and macro cardiac injuries for several years. Eventually many of the infected individuals develop chronic cardiomyopathy that leads to heart failure and sudden death. Cardiac muscle cells are rich in mitochondria and manganese superoxide dismutase (MnSOD) is the chief superoxide scavenging enzyme in the mitochondria. In this study, we show that a deficiency of MnSOD exacerbates the T. cruzi induced mitochondrial dysfunction of the electron transport chain and energy production in the heart. Further, MnSOD deficiency resulted in increased mitochondrial release of oxidants and caused excessive oxidative damage in the chagasic heart. Our results suggest that small molecule agonists of MnSOD will have potential utility as adjuvant therapy in preventing the development of chronic Chagas disease in infected individuals.

Inhibition of NFE2L2-Antioxidant Response Element Pathway by Mitochondrial Reactive Oxygen Species Contributes to Development of Cardiomyopathy and Left Ventricular Dysfunction in Chagas Disease

AIMS

We investigated the effects of mitochondrial reactive oxygen species (mtROS) on nuclear factor (erythroid 2)-like 2 (NFE2L2) transcription factor activity during Trypanosoma cruzi (Tc) infection and determined whether enhancing the mtROS scavenging capacity preserved the heart function in Chagas disease.

RESULTS

C57BL/6 wild type (WT, female) mice infected with Tc exhibited myocardial loss of mitochondrial membrane potential, complex II (CII)-driven coupled respiration, and ninefold increase in mtROS production. In vitro and in vivo studies showed that Tc infection resulted in an ROS-dependent decline in the expression, nuclear translocation, antioxidant response element (ARE) binding, and activity of NFE2L2, and 35-99% decline in antioxidants' (gamma-glutamyl cysteine synthase [γGCS], heme oxygenase-1 [HO1], glutamate-cysteine ligase modifier subunit [GCLM], thioredoxin (Trx), glutathione S transferase [GST], and NAD(P)H dehydrogenase, quinone 1 [NQO1]) expression. An increase in myocardial and mitochondrial oxidative adducts, myocardial interventricular septum thickness, and left ventricle (LV) mass, a decline in LV posterior wall thickness, and disproportionate synthesis of collagens (COLI/COLIII), αSMA, and SM22α were noted in WT.Tc mice. Overexpression of manganese superoxide dismutase (MnSOD) in cultured cells (HeLa or cardiomyocytes) and MnSOD^tg mice preserved the NFE2L2 transcriptional activity and antioxidant/oxidant balance, and cardiac oxidative and fibrotic pathology were significantly decreased in MnSOD^tg.Tc mice. Importantly, echocardiography finding of a decline in LV systolic (stroke volume, cardiac output, ejection fraction) and diastolic (early/late peak filling ratio, myocardial performance index) function in WT.Tc mice was abolished in MnSOD^tg.Tc mice. Innovation and Conclusion: The mtROS inhibition of NFE2L2/ARE pathway constitutes a key mechanism in signaling the fibrotic gene expression and evolution of chronic cardiomyopathy. Preserving the NFE2L2 activity arrested the mitochondrial and cardiac oxidative stress, cardiac fibrosis, and heart failure in Chagas disease. Antioxid. Redox Signal. 27, 550-566.

Pregestational type 2 diabetes mellitus induces cardiac hypertrophy in the murine embryo through cardiac remodeling and fibrosis

BACKGROUND

Cardiac hypertrophy is highly prevalent in patients with type 2 diabetes mellitus. Experimental evidence has implied that pregnant women with type 2 diabetes mellitus and their children are at an increased risk of cardiovascular diseases. Our previous mouse model study revealed that maternal type 2 diabetes mellitus induces structural heart defects in their offspring.

OBJECTIVE

This study aims to determine whether maternal type 2 diabetes mellitus induces embryonic heart hypertrophy in a murine model of diabetic embryopathy.

STUDY DESIGN

The type 2 diabetes mellitus embryopathy model was established by feeding 4-week-old female C57BL/6J mice with a high-fat diet for 15 weeks. Cardiac hypertrophy in embryos at embryonic day 17.5 was characterized by measuring heart size and thickness of the right and left ventricle walls and the interventricular septum, as well as the expression of β-myosin heavy chain, atrial natriuretic peptide, insulin-like growth factor-1, desmin, and adrenomedullin. Cardiac remodeling was determined by collagen synthesis and fibronectin synthesis. Fibrosis was evaluated by Masson staining and determining the expression of connective tissue growth factor, osteopontin, and galectin-3 genes. Cell apoptosis also was measured in the developing heart.

RESULTS

The thicknesses of the left ventricle walls and the interventricular septum of embryonic hearts exposed to maternal diabetes were significantly thicker than those in the nondiabetic group. Maternal diabetes significantly increased β-myosin heavy chain, atrial natriuretic peptide, insulin-like growth factor-1, and desmin expression, but decreased expression of adrenomedullin. Moreover, collagen synthesis was significantly elevated, whereas fibronectin synthesis was suppressed, in embryonic hearts from diabetic dams, suggesting that cardiac remodeling is a contributing factor to cardiac hypertrophy. The cardiac fibrosis marker, galectin-3, was induced by maternal diabetes. Furthermore, maternal type 2 diabetes mellitus activated the proapoptotic c-Jun-N-terminal kinase 1/2 stress signaling and triggered cell apoptosis by increasing the number of terminal deoxynucleotidyl transferase 2'-deoxyuridine 5'-triphosphate nick end labeling-positive cells (10.4 ± 2.2% of the type 2 diabetes mellitus group vs 3.8 ± 0.7% of the nondiabetic group, P < .05).

CONCLUSION

Maternal type 2 diabetes mellitus induces cardiac hypertrophy in embryonic hearts. Adverse cardiac remodeling, including elevated collagen synthesis, suppressed fibronectin synthesis, profibrosis, and apoptosis, is implicated as the etiology of cardiac hypertrophy.

Curcumin and extracellular matrix proteins synergistically act to inhibit the proliferation of breast cancer cells

Aim: Natural substances have been gaining attention as they are accessible, cheap and associated with milder adverse effects as compared with conventional treatment. Curcumin is polyphenol derived from turmeric plant and is known to possess anti-inflammatory, antioxidant and antimetastatic effects. In the present work, the effect of curcumin individually and in combination with extracellular matrix proteins has been systematically studied on the breast cancer cell line, MCF-7. Materials & methods: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was performed to screen the effect of various concentrations of curcumin on MCF-7 cells. Flow cytometry and caspase-3 assays were done to detect apoptosis. Nitric oxide and reactive oxygen species generation levels were also examined as both are known to play very important roles in cancer initiation and progression. Results: It was observed that at low concentrations curcumin exhibited significant antiproliferative activity which was supported with increased apoptosis and reduced levels of reactive oxygen species and nitric oxide. Moreover, the combined treatment of curcumin and proteins further boosted the antiproliferative effect of low concentrations of curcumin indicating that they act synergistically to inhibit the proliferation of breast cancer cells. Conclusion: This finding could be further investigated for development of novel anticancer therapies.

Collagen Production in Cardiac Fibroblasts During Inhibition of Aminopeptidase B

Objective. To determine whether the aminopeptidase B inhibitor, arphamenine A, could affect collagen production and expression in control and TGF-ß1-treated cardiac fibroblasts.

Design and Methods. Cardiac fibroblasts from passage 2 from normal male adult rats were cultured to confluency and incubated with and without 600 pmol/l TGF-ß1 for 2 days in serum-free Dulbecco's modified Eagle's medium and then incubated with 100 µmol/l arphamenine A for 1 day in this medium added ascorbic acid, ß-aminopropionitrile and titriated proline. Soluble collagen was measured in the conditioned medium and non-soluble collagen in the cell layer. Aminopeptidase activity was estimated by spectrophotometric determination of the liberation of p-nitroaniline from alanine- or arginine-p-nitroanilide. Matrix metalloproteinase (MMP) and lysyl oxidase activity were assayed in the conditioned medium. A semi-quantitative reverse transcriptase- polymerase chain reaction was used to examine the expression of lysyl oxidase and collagen type I and III. Results. Arphamenine A dose-dependently

inhibited basal and TGF-ß 1-stimulated aminopeptidase activity. Arphamenine A reduced soluble and non-soluble collagen production in control and TGF-ß1-treated cardiac fibroblasts, while it decreased collagen type I and III expression only in TGF-ß1-treated fibroblasts. Lysyl oxidase, MMP-1 and MMP-2 activity were inhibited by arphamenine A in the conditioned media of control and TGF-ß1treated cardiac fibroblasts.

Conclusions. Our data show that the specific aminopeptidase B inhibitor, arphamenine A, reduces collagen production in cardiac fibroblasts and that this reduction is accompanied by a pronounced inhibition of lysyl oxidase.

Current Perspectives of Electrical Remodeling and Its Therapeutic Implications

Electrical remodeling involves alterations in the electrophysiologic milieu of myocardium in various disease states, such as ventricular hypertrophy, heart failure, atrial tachyarrhythmias, myocardial ischemia, and infarction that are associated with cardiac arrhythmias. Although research in this area dates back to early part of the 19th century, we still lack the exact knowledge of ionic remodeling, the role of various genes and channel proteins, and their relevance for the newer antiarrhythmic therapies. Structural remodeling may also have an impact on the electrical remodeling process, although differences in both structural and electrical remodeling are associated with different disease states. Various electrophysiologic, cellular, and structural alterations, including anisotropic conduction, increased intracellular calcium levels, and gap junction remodeling predispose to increased dispersion of action potential duration and refractoriness. This constitutes a favorable substrate for early and late afterdepolarizations and reentrant arrhythmias. Studying the role of ionic remodeling in the initiation and propagation of cardiac arrhythmias has significant relevance for developing newer antiarrhythmic therapies, for identifying patients at risk of developing fatal arrhythmias, and for implementing effective preventive measures. Further research is required to understand the specific effects of individual ion channel remodeling, to understand the signal transduction mechanisms, and to address whether detrimental effects of electrical remodeling can be altered.

Augmented endothelial l-arginine transport ameliorates pressure-overload-induced cardiac hypertrophy

NEW FINDINGS

What is the central question of this study? What is the potential role of endothelial NO production via overexpression of the l-arginine transporter, CAT1, as a mitigator of cardiac hypertrophy? What is the main finding and its importance? Augmentation of endothelium-specific l-arginine transport via CAT1 can attenuate pressure-overload-dependent cardiac hypertrophy and fibrosis. Our findings support the conclusion that interventions that improve endothelial l-arginine transport may provide therapeutic utility in the setting of myocardial hypertrophy. Such modifications may be introduced by exercise training or locally delivered gene therapy, but further experimental and clinical studies are required. Endothelial dysfunction has been postulated to play a central role in the development of cardiac hypertrophy, probably as a result of reduced NO bioavailability. We tested the hypothesis that increased endothelial NO production, mediated by increased l-arginine transport, could attenuate pressure-overload-induced cardiac hypertrophy. Echocardiography and blood pressure measurements were performed 15 weeks after transverse aortic constriction (TAC) in wild-type (WT) mice (n = 12) and in mice with endothelium-specific overexpression of the l-arginine transporter, CAT1 (CAT+; n = 12). Transverse aortic constriction induced greater increases in heart weight to body weight ratio in WT (by 47%) than CAT+ mice (by 25%) compared with the respective controls (P ≤ 0.05). Likewise, the increase in left ventricular wall thickness induced by TAC was significantly attenuated in CAT+ mice (P = 0.05). Cardiac collagen type I mRNA expression was greater in WT mice with TAC (by 22%; P = 0.03), but not in CAT+ mice with TAC, compared with the respective controls. Transverse aortic constriction also induced lesser increases in β-myosin heavy chain mRNA expression in CAT+ mice compared with WT (P ≤ 0.05). Left ventricular systolic pressure after TAC was 36 and 39% greater in WT and CAT+ mice, respectively, compared with the respective controls (P ≤ 0.001). Transverse aortic constriction had little effect on left ventricular end-diastolic pressure in both genotypes. Taken together, these data indicate that augmenting endothelial function by overexpression of l-arginine transport can attenuate pressure-overload-induced cardiac hypertrophy.

Adipose-derived stem cells increase angiogenesis through matrix metalloproteinase-dependent collagen remodeling

Adipose-derived stem cells (ASCs) are key regulators of new blood vessel formation and widely investigated for their role in tissue regeneration and tumorigenesis. However, the cellular and molecular mechanisms through which ASCs regulate angiogenesis are not well understood. Here, it was our goal to test the functional contribution of ASC-mediated extracellular matrix (ECM) remodeling on endothelial cell invasion. To isolate the effect of ECM-remodeling, ASCs were embedded within 3-D collagen type I hydrogels and pre-cultured for 7 days; controls were not pre-cultured. A confluent monolayer of human umbilical vein endothelial cells (HUVECs) was seeded on top and its invasion into the underlying hydrogel was analyzed. Without pre-culture, ASCs inhibited vascular sprouting by stabilizing the endothelium. In contrast, 7 day pre-culture of ASCs drastically increased invasion by HUVECs. This effect was largely mediated by proteolytic ECM degradation by ASC-derived matrix metalloproteinases (MMPs) rather than vascular endothelial growth factor (VEGF), as our results indicated that blockade of MMPs, but not VEGF, inhibited endothelial sprouting. Collectively, these data suggest that the angiogenic capability of ASCs is modulated by their proteolytic remodeling of the ECM, opening new avenues for pro- and anti-angiogenic therapies.

Circulating Procollagen Type III N-Terminal Peptide and Mortality Risk in African Americans With Heart Failure

BACKGROUND

Procollagen type III N-terminal peptide (PIIINP) is a biomarker of cardiac fibrosis that is associated with heart failure prognosis in whites. Its prognostic significance in African Americans is unknown. We sought to determine whether PIIINP is associated with outcomes in African Americans with heart failure.

METHODS AND RESULTS

Blood was collected from 138 African Americans with heart failure for determining PIIINP and genetic ancestry, and patients were followed prospectively for death or hospitalization for heart failure. PIIINP was inversely correlated with West African ancestry (R(2) = 0.061; P = .010). PIIINP > 4.88 ng/mL was associated with all-cause mortality on univariate (hazard ratio [HR] 4.9, 95% confidence interval [CI] 2.2-11.0; P < .001) and multivariate (HR 5.8; 95% CI 1.9-17.3; P = .002) analyses over a median follow-up period of 3 years. We also observed an increased risk for the combined outcome of all-cause mortality or hospitalization for heart failure with PIIINP > 4.88 ng/mL on univariate (HR 2.6, 95% CI 1.6-5.0; P < .001) and multivariate (HR 2.4, 95% CI 1.2-4.7; P = .016) analyses.

CONCLUSIONS

High circulating PIIINP is associated with poor outcomes in African Americans with chronic heart failure, suggesting that PIIINP may be useful in identifying African Americans who may benefit from additional therapy to combat fibrosis as a means of improving prognosis.

Ectopic trypsin in the myocardium promotes dilated cardiomyopathy after influenza A virus infection

We have previously reported that ectopic trypsin in the myocardium triggers acute myocarditis after influenza A virus (IAV) infection. As myocarditis is a common precursor to dilated cardiomyopathy (DCM), the aim of the present study was to investigate the influence of trypsin on the progression of DCM after IAV infection. IAV-infected mice treated with saline or trypsin inhibitor were euthanized on days 0, 9, 20, 40 and 60 postinfection. Trypsin expression colocalized with myocardial inflammatory loci and IAV-induced myocarditis peaked on day 9 postinfection and alleviated by day 20 but persisted until day 60 postinfection, even though replication of IAV was not detected from day 20 postinfection. Similar time courses were observed for the activation of pro-matrix metalloproteinase (pro-MMP)-9 and expression of the proinflammatory cytokines IL-6, IL-1β, and TNF-α. Degradation of collagen type I, proliferation of ventricular interstitial collagen, and expression of collagen type I and III mRNA increased significantly during acute and chronic phases; collagen type III mRNA increased more significantly than collagen type I mRNA. Cardiac function progressively deteriorated with progressive left ventricular dilation. The trypsin inhibitor aprotinin suppressed pro-MMP-9 activation and cytokine release, alleviated myocardial inflammation, and restored collagen metabolism during acute and chronic phases of myocarditis. This effectively prevented ventricular dilation and improved cardiac function. These results suggest that ectopic trypsin in the myocardium promoted DCM through chronic activation of pro-MMP-9, persistent induction of cytokines, and mediation of collagen remodeling. Pharmacological inhibition of trypsin activity might be a promising approach for the prevention of viral cardiomyopathy.

Left and right ventricle late remodeling following myocardial infarction in rats

BACKGROUND

The mechanisms involved in cardiac remodeling in left (LV) and right ventricles (RV) after myocardial infarction (MI) are still unclear. We assayed factors involved in collagen turnover in both ventricles following MI in rats either presenting signs of heart failure (pulmonary congestion and increased LVEDP) or not (INF-HF or INF, respectively).

METHODS

MI was induced in male rats by ligation of the left coronary artery. Four weeks after MI gene expression of collagen I, connective tissue growth factor (CTGF), transforming growth factor β (TGF-β) and lysyl oxidase (LOX), metalloproteinase-2 (MMP2) and tissue inhibitor metalloproteinase-2 (TIMP2) as well as cardiac hemodynamic in both ventricles were evaluated.

RESULTS

Ventricular dilatation, hypertrophy and an increase in interstitial fibrosis and myocyte size were observed in the RV and LV from INF-HF animals, whereas only LV dilatation and fibrosis in RV was present in INF. The LV fibrosis in INF-HF was associated with higher mRNA of collagen I, CTGF, TGF-β and LOX expressions than in INF and SHAM animals, while MMP2/TIMP2 mRNA ratio did not change. RV fibrosis in INF and INF-HF groups was associated with an increase in LOX mRNA and a reduction in MMP2/TIMP2 ratio. CTGF mRNA was increased only in the INF-HF group.

CONCLUSIONS

INF and INF-HF animals presented different patterns of remodeling in both ventricles. In the INF-HF group, fibrosis seems to be consequence of collagen production in LV, and by reductions in collagen degradation in RV of both INF and INF-HF animals.

Emerging concepts in cardiac matrix biologyThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research

The cardiac extracellular matrix, far from being merely a static support structure for the heart, is now recognized to play central roles in cardiac development, morphology, and cell signaling. Recent studies have better shaped our understanding of the tremendous complexity of this active and dynamic network. By activating intracellular signal cascades, the matrix transduces myocardial physical forces into responses by myocytes and fibroblasts, affecting their function and behavior. In turn, cardiac fibroblasts and myocytes play active roles in remodeling the matrix. Coupled with the ability of the matrix to act as a dynamic reservoir for growth factors and cytokines, this interplay between the support structure and embedded cells has the potential to exert dramatic effects on cardiac structure and function. One of the clearest examples of this occurs when cell–matrix interactions are altered inappropriately, contributing to pathological fibrosis and heart failure. This review will examine some of the recent concepts that have emerged regarding exactly how the cardiac matrix mediates these effects, how our collective vision of the matrix has changed as a result, and the current state of attempts to pharmacologically treat fibrosis.

Adapter molecule DOC-2 is differentially expressed in pressure and volume overload hypertrophy and inhibits collagen synthesis in cardiac fibroblasts

DOC-2 (differentially expressed in ovarian carcinoma) is involved in Ras-, β-integrin-, PKC-, and transforming growth factor-β-mediated cell signaling. These pathways are implicated in the accumulation of extracellular matrix proteins during progression of hypertrophy to heart failure; however, the role of DOC-2 in cardiac pathophysiology has never been examined. This study was undertaken to 1) analyze DOC-2 expression in primary cultures of cardiac fibroblasts and cardiac myocytes and in the heart following different types of hemodynamic overloads and 2) examine its role in growth factor-mediated ERK activation and collagen production. Pressure overload and volume overload were induced for 10 wk in Sprague-Dawley rats by aortic constriction and by aortocaval shunt, respectively. ANG II (0.3 mg·kg−1·day−1) was infused for 2 wk. Results showed that, compared with myocytes, DOC-2 was found abundantly expressed in cardiac fibroblasts. Treatment of cardiac fibroblasts with ANG II and TPA resulted in increased expression of DOC-2. Overexpression of DOC-2 in cardiac fibroblasts led to inhibition of hypertrophy agonist-stimulated ERK activation and collagen expression. An inverse correlation between collagen and DOC-2 was observed in in vivo models of cardiac hypertrophy; in pressure overload and after ANG II infusion, increased collagen mRNA correlated with reduced DOC-2 levels, whereas in volume overload increased DOC-2 levels were accompanied by unchanged collagen mRNA. These data for the first time describe expression of DOC-2 in the heart and demonstrate its modulation by growth-promoting agents in cultured cardiac fibroblasts and in in vivo models of heart hypertrophy. Results suggest a role of DOC-2 in cardiac remodeling involving collagen expression during chronic hemodynamic overload.

The impact of angiotensin-converting enzyme inhibitor therapy on the extracellular collagen matrix during left ventricular assist device support in patients with end-stage heart failure

OBJECTIVES

We hypothesized that angiotensin-converting enzyme inhibition (ACE-I) during left ventricular assist device (LVAD) support in patients with end-stage heart failure prevents potentially deleterious effects on the extracellular matrix.

BACKGROUND

Left ventricular assist device-induced mechanical unloading increases myocardial collagen and stiffness and may contribute to the low rate of recovery.

METHODS

Heart samples obtained before and after LVAD implantation were divided into groups depending on whether the patients received (n = 7) or did not receive (control; n = 15) ACE-I. At transplant, ex vivo pressure-volume relationships were measured and chamber and myocardial stiffness constants determined. Myocardial tissue content of angiotensin (Ang) I and II, matrix metalloproteinase (MMP)-1, tissue inhibitor of MMPs (TIMP)-1, and total and cross-linked collagen was measured.

RESULTS

Duration of support was comparable between ACE-I and control subjects (96 +/- 65 days vs. 109 +/- 22 days). Pre-LVAD Ang I and II and total and cross-linked collagen were similar between groups. Post-LVAD, Ang II was reduced in the ACE-I group but increased in control subjects (181 +/- 7 fmol/g vs. 262 +/- 41 fmol/g; p < 0.05). Similarly, cross-linked collagen decreased during LVAD support in the ACE-I group. Left ventricular (LV) mass and myocardial stiffness were lower in the ACE-I group. ACE-I normalized the LV and right ventricular (RV) MMP-1/TIMP-1 ratio. Collagen content and characteristics of the RV were not affected by ACE-I.

CONCLUSIONS

ACE-I therapy was associated with decreased Ang II, myocardial collagen content, and myocardial stiffness during LVAD support. This is the first demonstration of a pharmacologic therapy that can impact myocardial properties during mechanical unloading, and it could foster new lines of investigation in strategies of enhancing myocardial recovery during LVAD support.

Type VI collagen induces cardiac myofibroblast differentiation: implications for postinfarction remodeling

Cardiac fibroblast (CF) proliferation and differentiation into hypersecretory myofibroblasts can lead to excessive extracellular matrix (ECM) production and cardiac fibrosis. In turn, the ECM produced can potentially activate CFs via distinct feedback mechanisms. To assess how specific ECM components influence CF activation, isolated CFs were plated on specific collagen substrates (type I, III, and VI collagens) before functional assays were carried out. The type VI collagen substrate potently induced myofibroblast differentiation but had little effect on CF proliferation. Conversely, the type I and III collagen substrates did not affect differentiation but caused significant induction of proliferation (type I, 240.7 +/- 10.3%, and type III, 271.7 +/- 21.8% of basal). Type I collagen activated ERK1/2, whereas type III collagen did not. Treatment of CFs with angiotensin II, a potent mitogen of CFs, enhanced the growth observed on types I and III collagen but not on the type VI collagen substrate. Using an in vivo model of myocardial infarction (MI), we measured changes in type VI collagen expression and myofibroblast differentiation after post-MI remodeling. Concurrent elevations in type VI collagen and myofibroblast content were evident in the infarcted myocardium 20-wk post-MI. Overall, types I and III collagen stimulate CF proliferation, whereas type VI collagen plays a potentially novel role in cardiac remodeling through facilitation of myofibroblast differentiation.

Crosslink breakers: a new approach to cardiovascular therapy

PURPOSE OF REVIEW

Advanced glycation end-products accumulate on body proteins with aging, and their formation is greatly enhanced with rising plasma glucose level. Advanced glycation end-products bond together and, consequently, increase protein crosslinking. In the circulatory system, increased collagen crosslinking caused by advanced glycation end-products increases cardiovascular stiffness as well as the risk for cardiovascular morbidity and mortality. A breaker of advanced glycation end-products-related crosslinks, ALT-711, has been recently discovered. This review summarizes the latest evidence that breaking collagen crosslinks may be an efficient new therapeutic approach to the adverse cardiovascular and renal consequences of aging and diabetes.

RECENT FINDINGS

The results of recent studies clearly demonstrated that ALT-711, a breaker of advanced glycation end-products-related protein crosslinks, ameliorated the adverse cardiovascular and renal changes associated with aging, diabetes, and hypertension. In diabetic animals, ALT-711 improved left ventricular function, decreased ventricular collagen content and improved its solubility, reduced aortic stiffness, ameliorated diabetic nephrosclerosis, and improved renal function. In older spontaneously hypertensive rats, it reduced left ventricular mass and collagen content, reduced proteinuria, and extended survival. The results of recent studies also indicated that the effects of crosslinks breakers may be mediated in part via reduction in oxidative stress and profibrotic cytokines.

SUMMARY

The results of experimental studies and one clinical trial have clearly established the usefulness of ALT-711 in the therapy of the cardiovascular and renal disorders associated with aging, diabetes, and hypertension. Thus, breaking advanced glycation end-products-related collagen crosslinks has emerged as a new approach to cardiovascular therapy.