Restoration and regeneration of failing myocardium with cell transplantation and tissue engineering

Injection of Sca-1+/CD45+/CD31+ mouse bone mesenchymal stromal-like cells improves cardiac function in a mouse myocardial infarct model

The objective of this study was to screen mouse bone marrow mesenchymal stromal cells (BMSCs) according to expression of cardiac stem cell (CSC) surface antigens and to assess the effects of resulting BMSC-like subsets on cardiac function after injection in a mouse myocardial infarct model. BMSCs were sorted by magnetic beads according to the expression of differentiation antigens on the surface of mouse CSCs, and four subsets were identified on the basis of CD45 and CD31 expression: stem cell antigen-1+ (Sca-1+)/CD45-/CD31-, Sca-1+/CD45-/CD31+, Sca-1+/CD45+/CD31-, and Sca-1+/CD45+/CD31+. When co-cultured with myocardial stem cells and 5-aza-2'-deoxycytidine for 14 days, each subset showed expression of cardiac markers α-actin, connexin 43, desmin, and cardiac troponin I; however, expression was greatest in Sca-1+/CD45+/CD31+ cells. To assess the ability of these cells to improve cardiac function, each subset was injected separately into mice with myocardial infarct induced by ligation of the left anterior descending coronary artery, and in vivo cardiac dual inversion recovery (DIR) imaging and Doppler echocardiography were performed 48 h, 96 h, and 7 days after injection. Results indicated that Sca-1+/CD45+/CD31+ cells were superior in improving cardiac function compared with the other subsets and with unsorted BMSCs. These results suggest that mouse BMSC cells are polyclonal and that the BMSC-like Sca-1+/CD45+/CD31+ subset was effective in directing cardiac differentiation and improving cardiac function in mice with myocardial infarcts.

Cell Therapy Limits Myofibroblast Differentiation and Structural Cardiac Remodeling

Background—

Experimental cell therapy attenuates maladaptive cardiac remodeling and improves heart function. Paracrine mechanisms have been proposed. The effect of cell therapy on post infarction cardiac fibroblast and extracellular matrix (ECM) regulation was examined.

Methods and Results—

Vascular smooth muscle cells (VSMC) were injected into the border zone of subacute infarcted syngeneic Fischer rat hearts and compared with medium-injected controls. Twelve weeks post injection, cell-treated hearts showed preserved ECM content and attenuated structural chamber remodeling. Myofibroblast activation (α-smooth muscle actin expression) was decreased significantly, while basic fibroblast growth factor (bFGF) expression, a known inhibitor of transforming growth factor β-1–induced fibroblast differentiation, was increased. Matrix metalloproteinase-2 expression and activation by gelatin zymography was unchanged between groups, while its endogenous inhibitor, tissue inhibitors of matrix metalloproteinase (TIMP)-2, showed both increased expression and enhanced inhibitory capacity in cell-treated hearts. To define paracrine mechanisms, in vitro effects of VSMC conditioned media on myofibroblast activation were assessed by 3-D collagen gel contraction assay. VSMC conditioned media significantly inhibited collagen contraction, while a specific bFGF inhibitor abolished this paracrine response. TIMP-2 induced collagen contraction, but the effect was suppressed in the presence of bFGF.

Conclusions—

Extracellular matrix dysregulation post myocardial infarction is improved by cell therapy. These data suggest that cell transplantation attenuates myofibroblast activation and subsequent maladaptive structural chamber remodeling through paracrine mechanisms involving bFGF and TIMP-2.

Design of a 3D aligned myocardial tissue construct from biodegradable polyesters

The heart does not regenerate new functional tissue when myocardium dies following coronary artery occlusion, or if it is defective. Ventricular restoration involves excising the infarct and replacing it with a cardiac patch to restore the heart to a more healthy condition. The goal of this study was to design and develop a clinically applicable myocardial patch to replace myocardial infarcts and improve long-term heart function. A basic design composed of 3D microfibrous mats that house mesenchymal stem cells (MSCs) was developed from human umbilical cord matrix (Wharton's Jelly) cells aligned in parallel to each other mimicking the native myocardium. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(L-D,L-lactic acid) (P(L-D,L)LA) and poly(glycerol sebacate) (PGS) were blended and electrospun into aligned fiber mats with fiber diameter ranging between 1.10 and 1.25 microm. The micron-sized parallel fibers of the polymer blend were effective in cell alignment and cells have penetrated deep within the mat through the fiber interstices, occupying the whole structure; 8-9 cell layers were obtained. Biodegradable macroporous tubings were introduced to serve as nutrient delivery route. It was possible to create a thick myocardial patch with structure similar to the native tissue and with a capability to grow.

Paracrine effects of cell transplantation: modifying ventricular remodeling in the failing heart

Structural ventricular remodeling determines the clinical progression of heart failure and has emerged as an important target for the development of novel medical and surgical therapeutic strategies. Cell transplantation is an innovative biologic therapy that may restore myocardial structure and function in failing hearts. With current forms of cell transplant therapy, true myocardial regeneration has been limited. However, cell transplantation can predictably limit maladaptive ventricular remodeling through multiple synergistic paracrine mechanisms. Some of the paracrine factors released by transplanted cells have been defined. These paracrine signals may provide beneficial effects by stimulating angiogenesis, limiting matrix disruption, and preventing apoptosis. In addition, cell transplantation may induce mobilization and homing of endogenous repair cells to injured myocardium through paracrine signals. Paracrine mediators released from transplanted cells work through multiple, diverse, and interrelated molecular pathways resulting in synergistic effects on the remodeling process. Although true myocardial regeneration remains the ultimate goal of cell therapy, the anti-remodeling abilities of cell transplantation can be harnessed to complement our contemporary surgical approaches for patients with myocardial injury at risk of congestive heart failure.

Effect of thyroid hormone on the contractility of self-organized heart muscle

Tissue-engineered heart muscle may provide an alternative treatment modality for end-stage congestive heart failure. We have previously described a method to engineer contractile heart muscle in vitro (termed cardioids). This study describes a method to improve the contractile properties of cardioids utilizing thyroid hormone (T3) stimulation. Cardioids were engineered by promoting the self-organization of primary neonatal cardiac cells into a contractile tissue construct. Cardioids were maintained in standard cell culture media supplemented with varying concentrations of T3 in the range 1-5ng/ml. The contractile properties of the cardioids were evaluated 48h after formation. Stimulation with T3 resulted in an increase in the specific force of cardioids from an average value of 0.52 +/- 0.16kPa (N = 6) for control cardioids to 2.42 +/- 0.29kPa (N = 6) for cardioids stimulated with 3ng/ml T3. In addition, there was also an increase in the rate of contraction and relaxation in response to T3 stimulation. Cardioids that were stimulation with T3 exhibited improved pacing characteristics in response to electrical pacing at 1-5Hz and an increase in the degree of spontaneous contractility. Changes in the gene expression of SERCA2, phospholamban, alpha-myosin heavy chain, and beta-myosin heavy chain correlated with the changes in contractile properties. This study demonstrates the modulation of the contractile properties of tissue-engineered heart muscle using T3 stimulation.

Cell therapy in congestive heart failure

Congestive heart failure (CHF) has emerged as a major worldwide epidemic and its main causes seem to be the aging of the population and the survival of patients with post-myocardial infarction. Cardiomyocyte dropout (necrosis and apoptosis) plays a critical role in the progress of CHF; thus treatment of CHF by exogenous cell implantation will be a promising medical approach. In the acute phase of cardiac damage cardiac stem cells (CSCs) within the heart divide symmetrically and/or asymmetrically in response to the change of heart homeostasis, and at the same time homing of bone marrow stem cells (BMCs) to injured area is thought to occur, which not only reconstitutes CSC population to normal levels but also repairs the heart by differentiation into cardiac tissue. So far, basic studies by using potential sources such as BMCs and CSCs to treat animal CHF have shown improved ventricular remodelling and heart function. Recently, however, a few of randomized, double-blind, placebo-controlled clinical trials demonstrated mixed results in heart failure with BMC therapy during acute myocardial infarction.

Engineering the heart piece by piece: state of the art in cardiac tissue engineering

According to the National Transplant Society, more than 7000 Americans in need of organs die every year owing to a lack of lifesaving organs. Bioengineering 3D organs in vitro for subsequent implantation may provide a solution to this problem. The field of tissue engineering in its most rudimentary form is focused on the developed of transplantable organ substitutes in the laboratory. The objective of this article is to introduce important technological hurdles in the field of cardiac tissue engineering. This review starts with an overview of tissue engineering, followed by an introduction to the field of cardiovascular tissue engineering and finally summarizes some of the key advances in cardiac tissue engineering; specific topics discussed in this article include cell sourcing and biomaterials, in vitro models of cardiac muscle and bioreactors. The article concludes with thoughts on the utility of tissue-engineering models in basic research as well as critical technological hurdles that need to be addressed in the future.

Heart cell implantation after myocardial infarction

In the last 15 years, heart cell implantation to regenerate infarcted myocardium has gone from the bench to clinical trial. Several phase I and II controlled randomized trials showed the feasibility, the side effects and the potential efficacy of cell implantation after myocardial infarction in humans. Preclinical experiments investigating the mechanisms of heart function improvement after cell implantation showed controversial results regarding implanted cell differentiation into cardiomyocytes and highlighted other effects including neovascularization and modifications of the extra cellular matrix remodelling. Ongoing clinical and experimental studies should pave the way for cell implantation to become a therapeutic option to prevent and treat post-myocardial infarction congestive heart failure in a near future.