Type IV collagen degradation in the myocardial basement membrane after unloading of the failing heart by a left ventricular assist device

In vitro bioreactor for mechanical control and characterization of tissue constructs

Cardiac fibrosis is a key contributor to the onset and progression of heart failure and occurs from extracellular matrix accumulation via activated cardiac fibroblasts. Cardiac fibroblasts activate in response to mechanical stress and have been studied in the past by applying forces and deformations to three-dimensional, cell-seeded gels and tissue constructs in vitro. Unfortunately, previous stretching platforms have traditionally not enabled mechanical property assessment to be performed with an efficient throughput, thereby limiting the full potential of in vitro mechanobiology studies. We have developed a novel in vitro platform to study cell-populated tissue constructs under dynamic mechanical stimulation while also performing repeatable, non-destructive stress-strain tests in living constructs. Additionally, this platform can perform these tests across all constructs in a multi-well plate simultaneously, providing exciting potential for direct, functional readouts in future screening applications. In our pilot application, we showed that cyclically stretching cell-populated tissue constructs composed of murine cardiac fibroblasts within a 3D fibrin matrix leads to collagen accumulation and increased tissue stiffness over a three-day time course. Results of this study validate our platform's ability to apply mechanical loads to tissues while performing live mechanical analyses to observe cell-mediated tissue remodeling.

Possible Treatment of Myocardial Infarct Based on Tissue Engineering Using a Cellularized Solid Collagen Scaffold Functionalized with Arg-Glyc-Asp (RGD) Peptide

Currently, the clinical impact of cell therapy after a myocardial infarction (MI) is limited by low cell engraftment due to low cell retention, cell death in inflammatory and poor angiogenic infarcted areas, secondary migration. Cells interact with their microenvironment through integrin mechanoreceptors that control their survival/apoptosis/differentiation/migration and proliferation. The association of cells with a three-dimensional material may be a way to improve interactions with their integrins, and thus outcomes, especially if preparations are epicardially applied. In this review, we will focus on the rationale for using collagen as a polymer backbone for tissue engineering of a contractile tissue. Contractilities are reported for natural but not synthetic polymers and for naturals only for: collagen/gelatin/decellularized-tissue/fibrin/Matrigel™ and for different material states: hydrogels/gels/solids. To achieve a thick/long-term contractile tissue and for cell transfer, solid porous compliant scaffolds are superior to hydrogels or gels. Classical methods to produce solid scaffolds: electrospinning/freeze-drying/3D-printing/solvent-casting and methods to reinforce and/or maintain scaffold properties by reticulations are reported. We also highlight the possibility of improving integrin interaction between cells and their associated collagen by its functionalizing with the RGD-peptide. Using a contractile patch that can be applied epicardially may be a way of improving ventricular remodeling and limiting secondary cell migration.

Mitochondrial Morphology and Mitophagy in Heart Diseases: Qualitative and Quantitative Analyses Using Transmission Electron Microscopy

Transmission electron microscopy (TEM) has long been an important technique, capable of high degree resolution and visualization of subcellular structures and organization. Over the last 20 years, TEM has gained popularity in the cardiovascular field to visualize changes at the nanometer scale in cardiac ultrastructure during cardiovascular development, aging, and a broad range of pathologies. Recently, the cardiovascular TEM enabled the studying of several signaling processes impacting mitochondrial function, such as mitochondrial fission/fusion, autophagy, mitophagy, lysosomal degradation, and lipophagy. The goals of this review are to provide an overview of the current usage of TEM to study cardiac ultrastructural changes; to understand how TEM aided the visualization of mitochondria, autophagy, and mitophagy under normal and cardiovascular disease conditions; and to discuss the overall advantages and disadvantages of TEM and potential future capabilities and advancements in the field.

Galectin-3 and sST2 as Prognosticators for Heart Failure Requiring Extracorporeal Life Support: Jack n' Jill

Extracorporeal life support provides perfusion for patients with heart failure to allow time for recovery, function as a bridge for patients to heart transplantation, or serve as destination therapy for long term mechanical device support. Several biomarkers have been employed in attempt to predict these outcomes, but it remains to be determined which are suitable to guide clinical practice relevant to extracorporeal life support. Galectin-3 and soluble suppression of tumorigenicity-2 (sST2) are two of the more promising candidates with the greatest supporting evidence. In this review, we address the similarities and differences between galectin-3 and sST2 for prognostic prediction in adults and children with heart failure requiring extracorporeal life support and highlight the significant lack of progress in pediatric biomarker discovery and utilization.

microRNA-29b knocks down collagen type I production in cultured rainbow trout (Oncorhynchus mykiss) cardiac fibroblasts

Warm acclimation of rainbow trout can cause a decrease in the collagen content of the heart. This ability to remove cardiac collagen is particularly interesting considering that collagen deposition in the mammalian heart, following an injury, is permanent. We hypothesized that collagen removal can be facilitated by microRNA-29b (miR-29b), a highly conserved, small, non-coding RNA, as a reduction in this microRNA has been reported during the development of fibrosis in the mammalian heart. We also used a bioinformatics approach to investigate the binding potential of miR-29b to the seed sequences of vertebrate collagen isoforms. Cultured trout cardiac fibroblasts were transfected with zebrafish mature miR-29b mimic for 7 days with re-transfection occurring after 3 days. Transfection induced a 17.8-fold increase in miR-29b transcript abundance (P<0.05) as well as a 54% decrease in the transcript levels of the col1a3 collagen isoform, compared with non-transfected controls (P<0.05). Western blotting demonstrated that the level of collagen type I protein was 85% lower in cells transfected with miR-29b than in control cells (P<0.05). Finally, bioinformatic analysis suggested that the predicted 3'-UTR of rainbow trout col1a3 has a comparatively higher binding affinity for miR-29b than the 3'-UTR of col1a1 Together, these results suggest that miR-29b is a highly conserved regulator of collagen type I protein in vertebrates and that this microRNA decreases collagen in the trout heart by targeting col1a3.

Developmental and degenerative cardiac defects in the Taiwanese mouse model of severe spinal muscular atrophy

Spinal muscular atrophy (SMA), an autosomal recessive disease caused by a decrease in levels of the survival motor neuron (SMN) protein, is the most common genetic cause of infant mortality. Although neuromuscular pathology is the most severe feature of SMA, other organs and tissues, including the heart, are also known to be affected in both patients and animal models. Here, we provide new insights into changes occurring in the heart, predominantly at pre- and early symptomatic ages, in the Taiwanese mouse model of severe SMA. Thinning of the interventricular septum and dilation of the ventricles occurred at pre- and early symptomatic ages. However, the left ventricular wall was significantly thinner in SMA mice from birth, occurring prior to any overt neuromuscular symptoms. Alterations in collagen IV protein from birth indicated changes to the basement membrane and contributed to the abnormal arrangement of cardiomyocytes in SMA hearts. This raises the possibility that developmental defects, occurring prenatally, may contribute to cardiac pathology in SMA. In addition, cardiomyocytes in SMA hearts exhibited oxidative stress at pre-symptomatic ages and increased apoptosis during early symptomatic stages of disease. Heart microvasculature was similarly decreased at an early symptomatic age, likely contributing to the oxidative stress and apoptosis phenotypes observed. Finally, an increased incidence of blood retention in SMA hearts post-fixation suggests the likelihood of functional defects, resulting in blood pooling. These pathologies mirror dilated cardiomyopathy, with clear consequences for heart function that would likely contribute to potential heart failure. Our findings add significant additional experimental evidence in support of the requirement to develop systemic therapies for SMA capable of treating non-neuromuscular pathologies.

Canstatin modulates L-type calcium channel activity in rat ventricular cardiomyocytes

Excessive increase of cytosolic Ca²⁺ through the activation of L-type Ca²⁺ channels (LTCCs) via β adrenergic receptor induces apoptosis of cardiomyocytes. Canstatin, a cleaved fragment of collagen type IV α2 chain, is abundantly expressed in normal heart tissue. We previously reported that canstatin inhibits β adrenergic receptor-stimulated apoptosis in cardiomyoblasts. Here, we tested the hypothesis that canstatin regulates LTCCs activity in ventricular cardiomyocytes. Collagen type IV α2 chain (COL4A2) small interfering (si) RNA (for canstatin suppression) or control siRNA was injected via jugular vein in Wistar rats. Two days after the injection, electrocardiogram (ECG) was recorded and the left ventricular tissue was isolated using Langendorff apparatus. Immunofluorescence staining was performed to clarify the distribution of canstatin in cardiomyocytes. The knockdown efficiency was confirmed by Western blotting. The L-type Ca²⁺ channel current (I_CaL) of ventricular cardiomyocyte was measured by a whole-cell patch clamp technique. In immunofluorescence staining, colocalization of canstatin and α_v integrin was observed in the isolated ventricular cardiomyocytes. The I_CaL of ventricular cardiomyocyte isolated from COL4A2 siRNA-injected rats was significantly enhanced compared with control siRNA-injected rats. Recombinant canstatin (250 ng/ml) significantly reversed it. ECG analysis showed that QT interval tended to be shortened and amplitude of T wave was significantly increased in the COL4A2 siRNA-injected rats. In summary, we for the first time clarified that suppressing canstatin expression increases the basal I_CaL in ventricular cardiomyocytes. It is proposed that canstatin might play a role in the stabilization of cardiac function through the modulation of LTCC activity in cardiomyocytes.

Differential impact of mechanical unloading on structural and nonstructural components of the extracellular matrix in advanced human heart failure

Adverse remodeling of the extracellular matrix (ECM) is a significant characteristic of heart failure. Reverse remodeling of the fibrillar ECM secondary to mechanical unloading of the left ventricle (LV) by left ventricular assist device (LVAD) has been subject of intense investigation; however, little is known about the impacts on nonfibrillar ECM and matricellular proteins that also contribute to disease progression. Explanted failing hearts were procured from patients with nonischemic dilated cardiomyopathy (DCM) with or without LVAD support, and compared to nonfailing control hearts. LV free wall specimens were formalin-fixed, flash-frozen or optimum cutting temperature-mount frozen. Histologic and biochemical assessment of fibrillar ECM showed that LVAD support was associated with lower levels of insoluble collagen, collagen type I mRNA, and collagen I/III ratio compared with no-LVAD hearts. A disintegrin and Metalloproteinase with Thrombospondin Motifs-2 (ADAM-TS2), a procollagen endopeptidase, was reduced in no-LVAD but not in LVAD hearts. The rise in ECM proteolytic activities was significantly lower in LVAD hearts. Matrix metalloproteinases (MMP1, MMP2, MMP8, MMP13, and MT1-MMP/MMP14) were comparable between DCM hearts. Tissue inhibitor of metalloproteinase (TIMP)3 and TIMP4 messenger RNA and protein showed the greatest reduction in no-LVAD hearts. Basement membrane proteins exhibited less severe disarray of laminin and fibronectin-1 in LVAD-supported hearts. The rise in matricellular protein, osteopontin, was suppressed in LVAD hearts, whereas secreted protein, acidic, cysteine-rich (SPARC) levels was unaffected by LVAD. Mechanical unloading of the failing DCM hearts can restore the fibrillar ECM and the basement membrane, contributing toward improved clinical outcomes. However, persistent elevation of matricellular proteins such as SPARC could contribute to the relapse of failing hearts on removal of LVAD support.

Differential protein expression and basal lamina remodeling in human heart failure

PURPOSE

A goal of this study was to identify and investigate previously unrecognized components of the remodeling process in the progression to heart failure by comparing protein expression in ischemic failing (F) and nonfailing (NF) human hearts.

EXPERIMENTAL DESIGN

Protein expression differences were investigated using multidimensional protein identification and validated by Western analysis. This approach detected basal lamina (BL) remodeling, and further studies analyzed samples for evidence of structural BL remodeling. A rat model of pressure overload (PO) was studied to determine whether nonischemic stressors also produce BL remodeling and impact cellular adhesion.

RESULTS

Differential protein expression of collagen IV, laminin α2, and nidogen-1 indicated BL remodeling develops in F versus NF hearts Periodic disruption of cardiac myocyte BL accompanied this process in F, but not NF heart. The rat PO myocardium also developed BL remodeling and compromised myocyte adhesion compared to sham controls.

CONCLUSIONS AND CLINICAL RELEVANCE

Differential protein expression and evidence of structural and functional BL alterations develop during heart failure. The compromised adhesion associated with this remodeling indicates a high potential for dysfunctional cellular integrity and tethering in failing myocytes. Therapeutically targeting BL remodeling could slow or prevent the progression of heart disease.

Building a bridge to recovery: the pathophysiology of LVAD-induced reverse modeling in heart failure

Heart failure mainly caused by ischemic or dilated cardiomyopathy is a life-threatening disorder worldwide. The previous work in cardiac surgery has led to many excellent surgical techniques for treating cardiac diseases, and these procedures are now able to prolong the human lifespan. However, surgical treatment for end-stage heart failure has been under-explored, although left ventricular assist device (LVAD) implantation and heart transplantation are options to treat the condition. LVAD can provide powerful circulatory support for end-stage heart failure patients and improve the survival and quality of life after implantation compared with the existing medical counterparts. Moreover, LVADs play a crucial role in the "bridge to transplantation", "bridge to recovery" and recently have served as "destination therapy". The structural and molecular changes that improve the cardiac function after LVAD implantation are called "reverse remodeling", which means that patients who have received a LVAD can be weaned from the LVAD with restoration of their cardiac function. This strategy is a desirable alternative to heart transplantation in terms of both the patient quality of life and due to the organ shortage. The mechanism of this bridge to recovery is interesting, and is different from other treatments for heart failure. Bridge to recovery therapy is one of the options in regenerative therapy which only a surgeon can provide. In this review, we pathophysiologically analyze the reverse remodeling phenomenon induced by LVAD and comment about the clinical evidence with regard to its impact on the bridge to recovery.

Ischemic versus nonischemic dilated cardiomyopathy: the implications of heart failure etiology on left ventricular assist device outcomes

The effect of heart failure etiology on outcomes after left ventricular assist device (LVAD) implantation has not been fully investigated. The aim of this study was to compare postoperative survival, incidence of LVAD-related complications, left and right heart catheterizations, and echocardiographic findings in patients with ischemic cardiomyopathy (ICM) and nonischemic dilated cardiomyopathy (NIDCM) who underwent continuous-flow LVAD implantation. A total of 100 patients underwent implantation of a HeartMate II (Thoratec Corp., Pleasanton, CA) or HeartWare (HeartWare Inc., Framingham, MA) LVAD at our institution. Patients were stratified into two groups based on the etiology of heart failure, ICM and NIDCM. We identified 34 (34.0%) patients with ICM and 66 (66.0%) with NIDCM. Patients with ICM were significantly older (59.5 vs. 49.3; p < 0.001) and had higher rates of hypertension (91.2% vs. 84.8%; p = 0.021), chronic renal insufficiency (38.2% vs. 25.8%; p < 0.001), peripheral vascular disease (11.8% vs. 10.6%; p = 0.015), and previous cardiac surgery (58.8% vs. 13.6%; p < 0.001). Survival was similar for both groups with 30 day, 6 month, and 1 year survivals of 94.1%, 85.3%, and 82.4%, respectively, for ICM patients versus 95.5%, 92.4%, and 89.4%, respectively, for NIDCM patients (p = 0.743). Etiology of heart failure was not an independent predictor of survival in multivariate logistic regression analysis (p = 0.505). Post-LVAD complications and improvements in postoperative hemodynamic measurements were also similar for both groups. The etiology of heart failure did not appear to affect postoperative outcomes significantly.

Integrin expression during reverse remodeling in the myocardium of heart failure patients

BACKGROUND

The main anchoring proteins of myocardial cells with each other and with the extracellular matrix are integrins present in the membranes of myocardial cells. These integrins are important for maintaining the architecture of the myocardial tissue and the mechanotransduction in the heart. Heart failure leads to various alterations in the myocardium, such as changes in morphology, and in expression of mRNAs, miRNAs, and proteins. Left ventricular assist device (LVAD) support in heart failure patients has been described to induce reverse remodeling of the myocardium and thus to (some degree of) reversal of the aforementioned alterations. In this study, we evaluated whether changes in expression of integrins α-1, -3, -5, -6, -7, -10, -11 and β-1, -3, -5 and -6 play a role during reverse remodeling.

METHODS

Three-step immunoperoxidase staining procedures were applied on frozen heart tissue sections to locate the various integrins tested. Integrin mRNA expression was established by standard Q-PCR procedures.

RESULTS

It was shown that mRNA expression of several integrins changes significantly during LVAD support, however without subsequent changes in immunohistochemical detectable quantities. Various integrins showed different locations within the myocardium.

CONCLUSION

LVAD-induced reversed remodeling did not result in significant integrin protein expression, although changes in integrin mRNA expression suggested an adaptation to unloading.

Intimal fibrosis in human cardiac allograft vasculopathy

Human Cardiac Allograft Vasculopathy (CAV) is one of the major complications for patients after heart transplantation. It is characterized by a concentric luminal narrowing due to (neo) intimal expansion in the coronary arteries of donor hearts after heart transplantation. In this process fibrosis plays an important role. Aim of this study is to analyze the factors and cells involved in this fibrotic process. Coronary arteries from five heart transplantation patients and three controls were obtained at autopsy. Quantitative real-time PCR was performed on mRNA obtained from various arterial layers isolated by laser micro dissection. Positive gene expression was confirmed by immunohistochemistry and/or in situ hybridisation. The strongest mRNA expression of fibrotic factors (predominantly pro-fibrotic) was found in the neo-intima. Especially, connective tissue growth factor expression was higher in the CAV vessels than in the controls. The lymphocyte activity of interferon gamma was only detected in CAV vessels. Furthermore as shown by in situ hybridisation, the lymphocytes producing interferon gamma also expressed transforming growth factor beta. Anti-fibrotic factors, such as bone morphogenic protein 4, were only expressed in CD3(-)/CD68(-) stromal cells. Macrophages present in the CAV and control vessels showed to be of the M2 type and did not produce any fibrotic factor(s). In conclusion, T-cells producing both interferon gamma and transforming growth factor beta, may play an important role in the fibrotic process in CAV vessels by upregulation of connective tissue growth factor production.

Novel biomarkers in human terminal heart failure and under mechanical circulatory support

This review summarizes recent findings on novel biochemical plasma biomarkers in terminal heart failure patients, which might predict an advanced mortality risk or even recovery. Moreover, we discussed the regulation of these heart failure-related biomarkers under mechanical circulatory support.

Osteopontin: a potential biomarker for heart failure and reverse remodeling after left ventricular assist device support

BACKGROUND

Left ventricular assist device (LVAD) support in end-stage heart failure (HF) leads to recovery of the patient's condition, size reduction of cardiomyocytes, and also volume reduction and change in the composition of the extracellular matrix (ECM). Myocardial expression of ECM osteopontin (OPN) protein increases with the severity of HF. We analyzed whether OPN messenger RNA expression in heart tissue and/or OPN protein in plasma are associated with reverse remodeling during LVAD support.

METHODS

Plasma and heart tissue specimens of 22 end-stage HF patients before and after LVAD implantation and subsequent heart transplantation (HTx) were used to determine the concentrations of OPN protein (EIA) and OPN messenger RNA (mRNA) by quantitative polymerase chain reaction. Immunohistochemistry (IHC) and in situ hybridization (ISH) were performed to locate OPN protein and mRNA.

RESULTS

The high OPN protein levels in plasma of HF patients did not differ significantly before and after LVAD support in ischemic heart disease (IHD) (pre-LVAD 167 ± 32 ng/ml; post-LVAD 165 ± 28 ng/ml) and in dilated cardiomyopathy (DCM) (pre-LVAD 99 ± 12 ng/ml; post-LVAD (142 ± 6 ng/ml). The OPN plasma levels after HTx decreased to control levels (IHD, 48 ± 6; DCM, 40 ± 5; control, 31 ± 3 ng/ml). In contrast, expression of OPN mRNA in heart biopsy specimens decreased significantly after LVAD support (the relative quantity decreased > 90% in IHD and 50% in DCM). ISH and IHC revealed that OPN was present in cardiomyocytes and in the ECM.

CONCLUSIONS

Levels of OPN mRNA in the myocardium of HF patients showed a significant decrease after LVAD support but OPN protein expression did not. LVAD support only induced a decrease of OPN plasma levels in individual patients, whereas OPN plasma levels reduced significantly in all patients after HTx.

Changes in regulatory microRNA expression in myocardium of heart failure patients on left ventricular assist device support

BACKGROUND

Left ventricular assist device support in heart failure patients leads to changes in mRNA and protein expression in the myocardium.

METHODS

MicroRNA's are important regulators of various cellular processes, so changes in their expression were tested by Q-PCR methods.

RESULTS

LVAD support (independently of the duration) leads to a decrease of the expression of miR-1, miR-133a and miR-133b in DCM patients but to an increase in expression in IHD patients. The expression of miR's pre- and post-LVAD in heart failure patients was low compared to the level of miR's in control myocardial tissue.

CONCLUSIONS

Alterations in miRs expression might also be important during repair processes in IHD patients.

Impact of left ventricular assist device (LVAD) support on the cardiac reverse remodeling process

With improved technology and expanding indications for use, left ventricular assist devices (LVADs) are assuming a greater role in the care of patients with end-stage heart failure. Following LVAD implantation with the intention of bridge to transplant, it became evident that some patients exhibit substantial recovery of ventricular function. This prompted explantation of some devices in lieu of transplantation, the so-called bridge-to-recovery (BTR) therapy. However, clinical outcomes following these experiences are not always successful. Patients treated in this fashion have often progressed rapidly back to heart failure. Special knowledge has emerged from studies of hearts supported by LVADs that provides insights into the basic mechanisms of ventricular remodeling and possible limits of ventricular recovery. In general, it was these studies that spawned the concept of reverse remodeling now recognized as an important goal of many heart failure treatments. Important examples of myocardial and/or ventricular properties that do not regress towards normal during LVAD support include abnormal extracellular matrix metabolism, increased tissue angiotensin levels, myocardial stiffening and partial recovery of gene expression involved with metabolism. Nevertheless, studies of LVAD-heart interactions have led to the understanding that although we once considered the end-stage failing heart of patients near death to be irreversibly diseased, an unprecedented degree of myocardial recovery is possible, when given sufficient mechanical unloading and restoration of more normal neurohormonal milieu. Evidence supporting and unsupporting the notion of reverse remodeling and clinical implications of this process will be reviewed.