In vivo survival and function of transplanted rat cardiomyocytes

Engineered heart tissue for regeneration of diseased hearts

Cardiac tissue engineering aims at providing contractile heart muscle constructs for replacement therapy in vivo. At present, most cardiac tissue engineering attempts utilize heart cells from embryonic chicken and neonatal rats and scaffold materials. Over the past years our group has developed a novel technique to engineer collagen/matrigel-based cardiac muscle constructs, which we termed engineered heart tissue (EHT). EHT display functional and morphological properties of differentiated heart muscle and can be constructed in different shape and size from collagen type I, extracellular matrix proteins (Matrigel((R))), and heart cells from neonatal rats and embryonic chicken. First implantation studies in syngeneic Fischer 344 rats provided evidence of EHT survival and integration in vivo. This review will focus on our experience in tissue engineering of cardiac muscle. Mainly, EHT construction, matrix requirements, potential applications of different cell types including stem cells, and our first implantation experiences will be discussed. Despite many critical and unresolved questions, we believe that cardiac tissue engineering in general has an interesting perspective for the replacement of malfunctioning myocardium and reconstruction of congenital malformations.

Leptin increases cardiomyocyte hyperplasia via extracellular signal-regulated kinase- and phosphatidylinositol 3-kinase-dependent signaling pathways

Obesity is a major risk factor for the development of heart failure. Importantly, it is now appreciated that a change in the number of myocytes is one of multiple structural and functional alterations (remodeling) leading to heart failure. Here we investigate the effect of leptin, the product of the obese (ob) gene, on proliferation of human and murine cardiomyocytes. Leptin caused a time- and dose-dependent significant increase in proliferation of HL-1 cells that was inhibited by preincubation with PD98059 and LY294002, suggesting that leptin mediated proliferation via extracellular signal-regulated kinase-1/2- and phosphatidylinositol-3-kinase-dependent signaling pathways. We confirmed that leptin activates both extracellular signal-regulated kinase-1/2 phosphorylation and association of phosphatidylinositol-3-kinase (regulatory p85 subunit) with phosphotyrosine immunoprecipitates. We also examined bromodeoxyuridine incorporation as a measure of new DNA synthesis and demonstrated a stimulatory effect of leptin in both HL-1 cells and human cardiomyocytes. Bromodeoxyuridine incorporation in HL-1 cells was inhibited by PD98059 and LY294002. Our results establish a mitogenic effect of leptin in cardiomyocytes and provide additional evidence for a potential direct link between leptin and cardiac remodeling in obesity.

Engineering of muscle tissue

The loss or failure of an organ or tissue is one of the most frequent, devastating, and costly problems in health care. Tissue engineering and regenerative medicine is an emerging interdisciplinary field that applies the principles of biology and engineering to the development of viable substitutes that restore, maintain, or improve the function of human tissues and organs. Tissue engineering science has provided critical new knowledge that will deepen our understanding of the phenotype of an important category of cell types-the muscle cells-and this knowledge may enable meaningful advances in musculoskeletal tissue engineering. There are two principle strategies for the replacement of impaired muscle tissues. One approach uses the application of isolated and differentiated cells (in vivo tissue engineering), using a transport matrix for the cell delivery; the other uses in vitro-designed and pre-fabricated tissue equivalents (in vitro tissue engineering). Future developments and the decision regarding which approach is more promising depend on the elucidation of the relationships among cell growth and differentiation, the three-dimensional environment, the architecture of the cells, and gene expression of the developmental process and the survival of the cells and integration in the host in in vivo experiments. As the techniques of tissue engineering become more sophisticated and as issues such as vascularization and innervation are addressed, the usefulness of these methods for reconstructive surgery may grow significantly.

Myocardial tissue engineering and regeneration as a therapeutic alternative to transplantation

Ischemic cardiomyopathy leading to congestive heart failure remains the leading source of morbidity and mortality in Western society and medical management of this condition offers only palliative treatment. While allogeneic heart transplantation can both extend and improve the quality of life for patients with end-stage heart failure, this therapeutic option is limited by donor organ shortage. Even after successful transplantation, chronic cardiac rejection in the form of cardiac allograft vasculopathy can severely limit the lifespan of the transplanted organ. Current experimental efforts focus on cellular cardiomyoplasty, myocardial tissue engineering, and myocardial regeneration as alternative approaches to whole organ transplantation. Such strategies may offer novel forms of therapy to patients with end-stage heart failure within the near future.

Cardiomyocytes overexpressing TNF‐α attract migration of embryonic stem cells via activation of p38 and c‐Jun amino‐terminal kinase

Tumor necrosis factor-alpha (TNF-alpha) plays an important role in the pathogenesis of myocardial infarction. Stem cells are able to regenerate infarcted myocardium. This study investigated whether TNF-alpha was able to induce migration of embryonic stem cells (ESCs) in vitro. We used a Transwell assay in which neonatal rat cardiomyocytes, with or without transfection of TNF-alpha cDNA, were plated in the lower compartments and mouse ESCs tagged with green fluorescent protein were added to the upper compartments. TNF-alpha level was significantly increased in the medium of the lower compartments seeded with TNF-alpha-transfected cardiomyocytes. Compared with the controls, overexpression of TNF-alpha significantly enhanced migration of ESCs to the lower compartments. This enhancement was attenuated by preincubation of ESCs with the antibody against the type II TNF-alpha receptor (TNF-RII), but not by the antibody against the type I TNF-alpha receptor (TNF-RI). Western blot analysis showed that the phosphorylated protein levels of p38 and c-Jun amino-terminal kinase (JNK) were significantly increased in TNF-alpha-treated ESCs. Inhibition of the activity of p38 or JNK significantly attenuated TNF-alpha-induced ESC migration. Our data demonstrate that excessive TNF-alpha stimulates TNF-RII and enhances migration of ESCs in vitro. Activation of p38 and JNK is required for TNF-alpha-enhanced ESC migration.

Cell transplantation to prevent heart failure: a comparison of cell types

BACKGROUND

Autologous cell transplantation may restore viable muscle after a myocardial infarction. We compared the effect of three cell types or an angiotensin-converting enzyme (ACE) inhibitor on preservation of ventricular function after cardiac injury.

METHODS

A uniform transmural myocardial scar was created in adult rats by cryoinjury. Three weeks later the rats were randomly assigned to one of four blinded treatments: transplantation with 5 x 10(6) aortic smooth muscle cells (SMC, n = 12), ventricular heart cells (VHC, n = 13), skeletal muscle cells (SKC, n = 13) or culture medium alone (control, n = 11). The ACE inhibitor group (n = 8) received enalapril (1.0 mg/kg per day), also beginning 3 weeks after cryoinjury. Five and 12 weeks after transplantation, left ventricle (LV) function was assessed in a Langendorff apparatus, and histologic and immunohistological evaluation of the LV scars was performed.

RESULTS

At 5 weeks, greater scar elastin content and better LV function was noted with cell transplantation or ACE inhibitor therapy compared with control rats (p < 0.05). Twelve weeks after transplantation, cell-transplanted rats still had greater elastin content and better LV function than control rats, although elastin content and LV function had declined in ACE inhibitor-treated animals to levels below those observed in control rats (p < 0.05).

CONCLUSIONS

Transplantation of SMC, VHC, and SKC preserved ventricular function equivalent to the effects of an ACE inhibitor. Muscle cell transplantation, but not ACE inhibitor therapy, continues to be effective later after cryoinjury. No differences were detected between the muscle cells.

Cardiomyocyte-mediated contact programs human mesenchymal stem cells to express cardiogenic phenotype

BACKGROUND

Intercellular crosstalk and cellular plasticity are key factors in embryogenesis and organogenesis. The microenvironment plays a critical role in directing the progression of stem cells into differentiated cells. We hypothesized that intercellular interaction between adult human mesenchymal stem cells and adult human cardiomyocytes would induce stem cells to acquire the phenotypical characteristics of cardiomyocytes, and we tested the role that direct cell-to-cell contact plays in directing this differentiation process. Human mesenchymal stem cells were cultured in the presence of human cardiomyocytes ("coculture") or in the presence of media conditioned by separate cultures of human cardiomyocytes ("conditioned media").

METHODS

Human cardiomyocytes were labeled with chloromethyl derivatives of fluorescein diacetate. In the coculture experiments, human mesenchymal stem cells and human cardiomyocytes were mixed at a 1:1 ratio in smooth muscle 2 media and seeded at a cell density of 10,000 cells/cm(2). Cells were cocultured in an incubator at 37 degrees C for 48 hours. Subsequently, fluorescence-activated cell sorting was used to extract the differentiating human mesenchymal stem cells. In the conditioned media experiments, human mesenchymal stem cells were incubated in media previously conditioned by cardiomyocytes, in the presence and absence of serum (+/-serum). The conditioned media was changed 3 times, at intervals of 48 hours. Total RNA was isolated and reverse transcriptase-polymerase chain reaction was performed for expression of contractile proteins and cardiac specific genes. Immunostaining against myosin heavy chain, beta-actin troponin-T, and troponin-I was performed.

RESULTS

Fluorescence-activated cell sorting analysis identified 66% of the human mesenchymal stem cells in the G1 phase. Differentiated hMSCs from the coculture experiments expressed myosin heavy chain, beta-actin, and troponin-T by reverse transcriptase-polymerase chain reaction. Immunostaining was also positive against myosin heavy chain and troponin-T. In contrast, only beta-actin expression was observed in the human mesenchymal stem cells incubated with conditioned media +/- serum.

CONCLUSION

In addition to soluble signaling molecules, direct cell-to-cell contact is obligatory in relaying the external cues of the microenvironment controlling the differentiation of adult stem cells to cardiomyocytes. These data indicate that human mesenchymal stem cells are plastic and can be reprogrammed into a cardiomyogenic lineage that may be used in cell-based therapy for treating heart failure.

Cardiomyocyte transplantation into the failing heart-new therapeutic approach for heart failure?

Heart failure, frequently the consequence of irreversible myocardial damage with subsequent formation of akinetic scar tissue, is a highly prevalent disease, and in its advanced stages associated with high mortality. The transplantation of exogenous cells with the inherent ability to contract has been put forward as one potential treatment strategy to increase contractility and cardiac performance. Besides skeletal myoblasts or stem cells from various sources, immature cardiomyocytes, such as fetal or neonatal cardiomyocytes, have been transplanted into normal, cryoinjured, infarcted myocardium, as well as into models of global heart failure. Survival of transplanted immature cardiomyocytes has been demonstrated up to 6-7 months, accompanied by vascularization of the grafted tissue. Transplants developed sarcomeric structures and other morphological features of differentiation. The principal possibility of cell-to-cell coupling between graft and host cells was demonstrated after cardiomyocyte transplantation into normal hearts and in some studies in damaged myocardium. But most long-term follow-up investigations in models of myocardial infarction reported that optimal integration of the engrafted cells appeared to be hindered by scar tissue, separating the transplant from the host. Nonetheless, in several studies, improved parameters of cardiac performance were demonstrated ex-vivo and in vivo. Potential mechanisms might involve beneficial effects on the remodeling process. In this review, we critically evaluate the potential value of cardiomyocyte transplantation as a new approach in the treatment of the syndrome of "heart failure".

VEGF enhances functional improvement of postinfarcted hearts by transplantation of ESC-differentiated cells

Despite considerable advances in medicine, the incidence of heart failure remains high in patients after myocardial infarction (MI). This study investigated the effects of engrafted early-differentiated cells (EDCs) from mouse embryonic stem cells, with or without transfection of vascular endothelial growth factor (VEGF) cDNA (phVEGF(165)), on cardiac function in postinfarcted mice. EDCs were transfected with green fluorescent protein (GFP) cDNA and transplanted into infarcted myocardium. Compared with the MI mice receiving cell-free medium, cardiac function was significantly improved in the MI mice 6 wk after transplantation of EDCs. Moreover, improvement of heart function was significantly greater in the mice implanted with EDCs overexpressing VEGF (EDCs-VEGF) than with EDCs alone. Frozen sections of infarcted myocardium with EDCs or EDCs-VEGF transplantation showed GFP-positive tissue. The area with positive immunostaining for cardiac troponin I and alpha-myosin heavy chain was larger in injured myocardium with EDCs or EDCs-VEGF transplantation than with medium injection. Transplantation of EDCs or EDCs-VEGF significantly increased the number of blood vessels in the MI area. However, the density of capillaries was significantly higher in the EDCs-VEGF animals than in the EDC mice. Double staining for GFP and connexin-43 was positive in injured myocardium with EDC transplantation. Our data demonstrate that engrafted EDCs or EDCs-VEGF regenerated cardiac tissue and significantly improved cardiac function in postinfarcted hearts. The novel EDCs-VEGF synergistic approach may have an important impact on future cell therapy for patients experiencing MI or heart failure.

Cardiomyocyte transplantation does not reverse cardiac remodeling in rats with chronic myocardial infarction

BACKGROUND

Several reports have documented the potential benefits of cell transplantation as an alternative to cardiac transplantation. This study was designed to investigate whether cardiomyocyte transplantation is effective in rats with chronic myocardial infarction.

METHODS

Syngeneic Lewis rats were used in this study. Chronic myocardial infarction was induced in rats by ligating the left anterior descending artery. Four weeks later, after left ventricular (LV) dysfunction with akinetic regions was confirmed by echocardiography, the rats were randomized into two groups: a group that received fetal cardiomyocyte transplantation (TX group; n = 11); and a group that received an intramyocardial injection of culture medium only (control group; n = 12).

RESULTS

Four weeks after treatment, the TX group had smaller end-systolic dimension (LVDs) (7.5 +/- 0.9 vs 8.9 +/- 0.8 mm, p < 0.01) and better fractional shortening (FS) (26.2 +/- 5.9 vs 17.7% +/- 5.1%, p < 0.01) than the control group. However, there were no differences in LV end-diastolic dimension, LVDs, and FS between baseline and post-treatment values in the TX group. In addition, plasma levels of atrial natriuretic peptide were not significantly different between the two groups 4 weeks after treatment. In microscopic examination, small amounts of transplanted cardiomyocytes were found only in the periinfarct area, not in the center of scar area, and a thicker ventricular wall in the infarct area was detected in the TX group.

CONCLUSIONS

Fetal cardiomyocyte transplantation prevented, but did not reverse, cardiac remodeling that was accompanied with heart failure in myocardial infarction rats. Further investigation is warranted for optimal clinical application to the failing heart.

Prevascularization with gelatin microspheres containing basic fibroblast growth factor enhances the benefits of cardiomyocyte transplantation

OBJECTIVE

The effects of cell transplantation on the ischemic failing heart have already been documented. However, the area in and around infarct regions is not a good environment for cells to survive in because they are exposed to poor conditions in which certain requirements cannot be adequately supplied. We therefore designed a study to investigate the efficacy of prevascularization in ischemic regions before cell transplantation.

METHODS

Rats with myocardial infarction were randomized into 4 groups: 11 rats received a culture medium injection to the left ventricular wall (control group), 11 received fetal cardiomyocyte transplantation (TX group), 11 received gelatin hydrogel microspheres incorporating basic fibroblast growth factor (FGF group), and 11 received basic fibroblast growth factor pretreatment sequentially, followed by cardiomyocyte transplantation (FGF-TX group). Four weeks later, left ventricular function was assessed by means of echocardiography and cardiac catheterization.

RESULTS

In the FGF and FGF-TX groups neovascularization was found in the scar tissue 1 week later. The TX, FGF, and FGF-TX groups showed better fractional shortening than the control group (TX, FGF, FGF-TX, and control: 28% +/- 4.4%, 24% +/- 8.6%, 27% +/- 7.3%, and 17% +/- 4.6%, respectively; P <.01). Left ventricular maximum time-varying elastance was higher in the FGF-TX group than in the TX and FGF groups (FGF-TX, TX, and FGF: 0.52 +/- 0.23, 0.30 +/- 0.08, and 0.27 +/- 0.20 mm Hg/microL, respectively; P <.01). Histologically, more transplanted cells survived in the FGF-TX group than in the TX group.

CONCLUSIONS

Prevascularization with basic fibroblast growth factor-incorporated microspheres enhances the benefits of cardiomyocyte transplantation. We expect that this system will contribute to regeneration medicine through its extensive application to other growth factors.

Biointerventional cardiology: the future interface of interventional cardiovascular medicine and bioengineering

Major advances in cardiovascular intervention for chronic disease are underway. These innovations lie at the interface of minimally invasive catheter-based technologies and biologic approaches for the management of complex cardiovascular diseases. This review highlights key areas where such 'biointerventional' cardiovascular therapies are envisioned to occur: cardiac cell transplantation, myocardial gene therapy, genetic and photodynamic endovascular interventions, and vascular tissue engineering.

Formation of the biopulsatile vascular pump by cardiomyocyte transplants circumvallating the abdominal aorta

In spite of the fact that patients with heart diseases requiring heart transplantation are increasing in the world, there are a lack of donors, which makes it hard to offer them these life-saving transplants. As a way to overcome this dilemma, we have researched the addition of the new biopump, which consists of the cultured embryonic cardiomyocytes grafted around the abdominal aorta and contracts spontaneously, which subsequently supports the function of the host heart. Ventricular tissues from ICR 14-day-old embryos were cultured and were injected to BALB/c nude mice (male, 8-week-old) subperitoneally around the abdominal aorta. At 3 and 7 days after implantation, action potential of the grafts was measured. Grafts were prepared for histological study. The grafts survived, showed vigorous angiogenesis, and contracted spontaneously. The cardiomyocytes in the grafts showed irregular arrangement, containing myofibrils with sarcomeres and intercalated disks. It was confirmed by immunohistochemistry that the cardiomyocytes in the grafts matured in accordance with normal development. The grafts were very quickly invaded by small vessels from the surrounding tissues showing the formation of new circulation. Embryonic cardiomyocytes have the ability to remodel the abdominal aorta into a spontaneous pulsating apparatus and to function as a vascular pump.

Transplantation of embryonic stem cells improves cardiac function in postinfarcted rats

Massive loss of cardiac myocytes after myocardial infarction (MI) is a common cause of heart failure. The present study was designed to investigate the improvement of cardiac function in MI rats after embryonic stem (ES) cell transplantation. MI in rats was induced by ligation of the left anterior descending coronary artery. Cultured ES cells used for cell transplantation were transfected with the marker green fluorescent protein (GFP). Animals in the treated group received intramyocardial injection of ES cells in injured myocardium. Compared with the MI control group injected with an equivalent volume of the cell-free medium, cardiac function in ES cell-implanted MI animals was significantly improved 6 wk after cell transplantation. The characteristic phenotype of engrafted ES cells was identified in implanted myocardium by strong positive staining to sarcomeric alpha-actin, cardiac alpha-myosin heavy chain, and troponin I. GFP-positive cells in myocardium sectioned from MI hearts confirmed the survival and differentiation of engrafted cells. In addition, single cells isolated from cell-transplanted MI hearts showed rod-shaped GFP-positive myocytes with typical striations. The present data demonstrate that ES cell transplantation is a feasible and novel approach to improve ventricular function in infarcted failing hearts.

Optimal time for cardiomyocyte transplantation to maximize myocardial function after left ventricular injury

BACKGROUND

This study was designed to determine the optimal time for cell transplantation after myocardial injury.

METHODS

The left ventricular free wall of adult rat hearts was cryoinjured and the animals were sacrificed at 0, 1, 2, 4, and 8 weeks for histologic studies. Fetal rat cardiomyocytes (transplant) or culture medium (control) were transplanted immediately (n = 8), 2 weeks (n = 8), and 4 weeks (n = 12) after cryoinjury. At 8 weeks, rat heart function, planimetry, and histologic studies were performed.

RESULTS

Cryoinjury produced a transmural injury. The inflammatory reaction was greatest during the first week but subsided during the second week after cryoinjury. Scar size expanded (p < 0.01) at 4 and 8 weeks. Cardiomyocytes transplanted immediately after cryoinjury were not found 8 weeks after cryoinjury. Scar size and myocardial function were similar to the control hearts. Cardiomyocytes transplanted at 2 and 4 weeks formed cardiac tissue within the scar, limited (p < 0.01) scar expansion, and had better (p < 0.001) heart function than the control groups. Developed pressure was greater (p < 0.01) in the hearts with transplanted cells at 2 weeks than at 4 weeks.

CONCLUSIONS

Cardiomyocyte transplantation was most successful after the inflammatory reaction resolved but before scar expansion.

Impact of low level laser irradiation on infarct size in the rat following myocardial infarction

Low energy level irradiation (LLLI) has been found to modulate biological processes. The effect of LLLI on the development of acute myocardial infarction (MI) was investigated following chronic ligation of the left anterior descending (LAD) coronary artery in laboratory rats. The hearts of 22 rats were laser irradiated (LI) using a diode laser (804 nm, 38 mW power output) through the intercostal muscles in the chest following MI and on day 3 post MI. In the control non laser irradiated (NLI) group (19 rats) MI was induced experimentally and laser irradiation was not applied. All rats were sacrificed 21 days post MI. Size, thickness and relative circumferential length of the infarct, as well as other parameters, were determined from histological sections stained with Masson's trichrome and hearts stained with triphenyl tetrazolium chloride (TTC) using histomorphometric methods. The infarct size (expressed as percent of total left ventricle area) of the LI rats was 10.1+/-5.8, which was significantly lower (65%; P<0.01) than the infarct size of NLI rats which was 28.7+/-9.6. Correlatively, the ratio of circumferential length of the infarcted area was significantly lower (2-fold; P<0.01) in the LI rats as compared to the NLI rats. LLLI of the infarcted area in the myocardium of experimentally induced MI rats, at the correct energy, duration and timing, markedly reduces the loss of myocardial tissue. This phenomenon may have an important beneficial effect on patients after acute MI or ischemic heart disease.

Tissue engineering: a 21st century solution to surgical reconstruction

Tissue engineering has emerged as a rapidly expanding approach to address the organ shortage problem. It is an "interdisciplinary field that applies the principles and methods of engineering and the life sciences toward the development of biological substitutes that can restore, maintain, or improve tissue function." Much progress has been made in the tissue engineering of structures relevant to cardiothoracic surgery, including heart valves, blood vessels, myocardium, esophagus, and trachea.

Influence of embryonic cardiomyocyte transplantation on the progression of heart failure in a rat model of extensive myocardial infarction

Cell transplantation has been proposed as a future therapy for various myocardial diseases. It is unknown, however, whether the encouraging results obtained in animal models of ischemia and reperfusion, cryoinjury or cardiomyopathy can be reproduced in the setting of permanent coronary artery occlusion and extensive myocardial infarction (MI). Embryonic cardiac cells were isolated and cultured for 3 days to confirm viability, morphology and to label cells with BrdU or the reporter gene LacZ. Seven days after extensive MI, rats were randomized to cell (1.5x10(6)) transplantation (n=11) or culture medium injection (n=16) into the myocardial scar. Echocardiography study was performed before and 53+/-3 days after implantation to assess left ventricular (LV) remodeling and function. During follow-up, there was no mortality among cell-treated rats v 4 of 16 control rats (P=0.12). X-gal staining, BrdU and alpha -SMA immunohistochemistry identified the engrafted cells 1 week, 4 weeks and 8 weeks after transplantation, respectively. Antibodies against alpha -SMA, connexin-43, fast and slow myosin heavy chain revealed grafts in various stages of differentiation in 10 of 11 cell-treated hearts. Many of them, however, kept their embryonic phenotype and were isolated from the host myocardium by scar tissue. Serial echocardiography studies revealed that cell transplantation prevented scar thinning, LV dilatation and dysfunction while control animals developed scar thinning, significant LV dilatation accompanied by progressive deterioration in LV contractility. Transplantation of embryonic cardiomyocytes after extensive MI in a rat model attenuate LV dilatation, infarct thinning, and myocardial dysfunction. Still, many grafts remain isolated and do not differentiate into an adult phenotype, even when studied 2 months after grafting.

Myocyte transplantation for myocardial repair: a few good cells can mend a broken heart

Cell transplantation is a potential therapeutic approach for patients with chronic myocardial failure. Experimental transplantation of neonatal and fetal cardiac myocytes showed that the grafted cells can functionally integrate with and augment the function of the recipient heart. Clinical application of this approach will be limited by shortage of donors, chronic rejection, and because it is ethically contentious. By contrast skeletal myoblasts (satellite cells) are abundant and can be grafted successfully into the animal's own heart even after genetic manipulation in vitro. Functional integration of myoblasts, however, is hampered by the lack of intercellular gap junction communication and the difference in excitation-contraction coupling between skeletal and cardiac myocytes. In experimental studies several other cell types have been used to augment cardiac function. In this review we discuss the published results of myocyte transplantation with emphasis on potential sources of cells, the ethics of using donor embryonic and fetal cardiomyocytes, genetic transformation of skeletal myoblasts for myocardial repair, and the functional benefits of cell transplantation to the failing heart.

Cardiomyocyte grafting for cardiac repair: graft cell death and anti-death strategies

M. Zhang, D. Methot, V. Poppa, Y. Fujio, K. Walsh and C. E. Murry. Cardiomyocyte Grafting for Cardiac Repair: Graft Cell Death and Anti-Death Strategies. Journal of Molecular and Cellular Cardiology (2001) 33, 907-921. Recent studies indicate that cardiomyocyte grafting forms new myocardium in injured hearts. It is unknown, however, whether physiologically significant amounts of new myocardium can be generated. Pilot experiments showed that death of grafted rat neonatal cardiomyocytes limited formation of new myocardium after acute cryoinjury. Time-course studies showed that, at 30 min after grafting, only 1.8(+/-0.4)% of graft cells were TUNEL-positive. At 1 day, however, TUNEL indices increased to 32.1(+/-3.5)% and remained high at 4 days, averaging 9.8(+/-3.8)%. By 7 days, TUNEL decreased to 1.0(+/-0.2)%. Electron microscopy revealed that dead cells had features of both irreversible ischemic injury and apoptosis. To test whether ischemia contributed to poor graft survival, grafts were placed into vascularized 2-week-old cardiac granulation tissue or normal myocardium. TUNEL indices were reduced by 53% and 86%, respectively. Adenoviral infection of graft cells with the cytoprotective kinase Akt, or constitutively active Akt, reduced TUNEL indices by 31% and 40%, respectively, compared to beta -gal-transfected controls. Neither treatment reached statistical significance compared to untreated controls, however. Heat shock reduced cardiomyocyte death in vitro in response to serum deprivation, glucose depletion, and viral activation of the Fas death pathway. When cardiomyocytes were heat shocked prior to grafting, graft cell death in vivo was reduced by 54% at day 1. Therefore, high levels of cardiomyocyte death occur for at least 4 days after grafting into injured hearts, in large part due to ischemia. Death can be limited by activating the Akt pathway and even more effectively by heat shock prior to transplantation.

The fate of a tissue-engineered cardiac graft in the right ventricular outflow tract of the rat

OBJECTIVE

The synthetic materials currently available for the repair of cardiac defects are nonviable, do not grow as the child develops, and do not contract synchronously with the heart. We developed a beating patch by seeding fetal cardiomyocytes in a biodegradable scaffold in vitro. The seeded patches survived in the right ventricular outflow tract of adult rats.

METHODS

Cultured fetal or adult rat heart cells (1 x 10(6) cells) were seeded into a gelatin sponge (15 x 15 x 1 mm), and the cell number was expanded in culture for 1 or 3 weeks, respectively. The free wall of the right ventricular outflow tract in syngeneic adult rats was resected and repaired with either unseeded patches or patches seeded with either fetal or adult cardiomyocytes (n = 10 for each group). The patches were examined histologically over a 12-week period.

RESULTS

A significant inflammatory reaction was noted in the patch at 4 weeks as the scaffold dissolved. At 12 weeks, the gelatin scaffold had completely dissolved. Both types of the seeded cells were detected in the patch with 5-bromo-2'-deoxyuridine staining, and they maintained their continuity. Unseeded patches had an ingrowth of fibrous tissue. The patches became thinner between the fourth and the twelfth weeks in unseeded (P =.003), fetal (P =.0001), and adult (P =.07) cardiomyocyte groups as the scaffold dissolved. The control patch, but not the cell-seeded patches, was thinner than the normal right ventricular outflow tract. The endocardial surface area of each patch was covered with endothelial cells identified by factor VIII staining.

CONCLUSIONS

A gelatin patch was used to replace the right ventricular outflow tract in syngeneic rats. The seeded cells survived in the right ventricular outflow tract after the scaffold dissolved 12 weeks after implantation. In addition, the unseeded patches encouraged the ingrowth of fibrous tissue as the scaffold dissolved and the patches remained completely endothelialized.

Myocardial regeneration: present and future trends

Cardiomyocytes are terminally differentiated and are unable to proliferate in response to injury. Genetic modulation, cell transplantation and tissue engineering promise a revolutionary approach for myocardial regeneration and tissue repair after myocardial injury. Current data derived from animal models suggest that it may be possible to treat heart failure by inserting genetic materials or myogenic cells into injured myocardium. Success with animal models has raised the hope for new treatment after heart attacks and could prove an alternative to transplantation, particularly in elderly patients for whom there is often a lack of donor hearts. This exciting research, however, still faces significant difficulties before it can develop into a clinical therapeutic tool and many challenges need to be overcome before cell transplantation, gene therapy and tissue engineering can be considered efficient, therapeutic strategies for myocardial regeneration.

Technical delivery of myogenic cells through an endocardial injection catheter for myocardial cell implantation

BACKGROUND: The next clinical frontier in the therapeutics of ischemic heart disease may involve the development and delivery of specific molecules and cells into the myocardium. The aim of the present study was to evaluate the efficiency and safety of the MyoStar injection catheter (Biosense-Webster Inc.) that has recently been developed to deliver molecules and cells to the myocardium. The 8 Fr (110 cm length) catheter comprises a navigation sensor with a 27 gauge needle at the distal tip. METHODS: Mouse myogenic cells (C2) were delivered to a tissue culture dish through different modalities: a standard laboratory pipette, a syringe needle (27 gauge) and the injection catheter. The cells were counted and monitored for growth and differentiation in the tissue culture immediately after delivery and two, three and six days later. Cells that were injected through a regular syringe needle or through the injection catheter demonstrated the same capacity to proliferate in tissue culture up to six days. RESULTS: The behavior of the cells in culture (fusion) was identical for the cells delivered to the tissue culture by a pipette or by the injection catheter. CONCLUSION: The results of the present study indicate that delivery of cells through the MyoStar injection catheter is a method with no significant loss or adverse effects to the cells along the path of the catheter. The catheter, which possesses both injection and navigation capabilities, can be used to deliver cell therapy to patients with ischemic heart disease.

Autologous porcine heart cell transplantation improved heart function after a myocardial infarction

OBJECTIVE

Fetal cardiomyocyte transplantation improved heart function after cardiac injury. However, cellular allografts were rejected despite cyclosporine (INN: ciclosporin) therapy. We therefore evaluated autologous heart cell transplantation in an adult swine model of a myocardial infarction.

METHODS

In 16 adult swine a myocardial infarction was created by occlusion of the distal left anterior descending coronary artery by an intraluminal coil. Four weeks after infarction, technetium 99m-sestamibi single photon emission tomography showed minimal perfusion and viability in the infarcted region. Porcine heart cells were isolated and cultured from the interventricular septum at the time of infarction and grown in vitro for 4 weeks. Through a left thoracotomy, either cells (N = 8) or culture medium (N = 8) was injected into the infarct zone.

RESULTS

Four weeks after cell transplantation, technetium 99m-sestamibi single photon emission tomography demonstrated greater wall motion scores in the pigs receiving transplantation than in control animals (P =.01). Pigs receiving transplantation were more likely to have an improvement in perfusion scores (P =.03). Preload recruitable stroke work (P =.009) and end-systolic elastance (P =. 02) were greater in the pigs receiving transplantation than in control animals. Scar areas were not different, but scar thickness was greater (P =.02) in pigs receiving transplantation. Cells labeled with bromodeoxyuridine in vitro could be identified in the infarct zone 4 weeks after transplantation. Swine receiving transplantation gained more weight than control animals (P =.02).

CONCLUSION

Autologous porcine heart cell transplantation improved regional perfusion and global ventricular function after a myocardial infarction.

Fetal cell transplantation: a comparison of three cell types

OBJECTIVE

We have previously reported that fetal cardiomyocyte transplantation into myocardial scar improves heart function. The mechanism by which this occurs, however, has not been elucidated. To investigate possible mechanisms by which cell transplantation may improve heart function, we compared cardiac function after transplantation of 3 different fetal cell types: cardiomyocytes, smooth muscle cells (nonstriated muscle cells), and fibroblasts (noncontractile cells).

METHODS

A left ventricular scar was created by cryoinjury in adult rats. Four weeks after injury, cultured fetal ventricular cardiomyocytes (n = 13), enteric smooth muscle cells (n = 10), skin fibroblasts (n = 10), or culture medium (control, n = 15 total) were injected into the myocardial scar. All rats received cyclosporine A (INN: ciclosporin). Four weeks after transplantation, left ventricular function was evaluated in a Langendorff preparation.

RESULTS

The implanted cells were identified histologically. All transplanted cell types formed tissue within the myocardial scar. At an end-diastolic volume of 0.2 mL, developed pressures in cardiomyocytes group were significantly greater than smooth muscle cells and skin fibroblasts groups (cardiomyocytes, 134% +/- 22% of control; smooth muscle cells, 108% +/- 14% of control; skin fibroblasts, 106% +/- 17% of control; P =.0001), as were +dP/dt(max) (cardiomyocytes, 119% +/- 37% of control; smooth muscle cells, 98% +/- 18% of control; skin fibroblasts, 92% +/- 11% of control; P =. 0001) and -dP/dt(max) (cardiomyocytes, 126% +/- 29% of control; smooth muscle cells, 108% +/- 19% of control; skin fibroblasts, 99% +/- 16% control; P =.0001).

CONCLUSIONS

Fetal cardiomyocytes transplanted into myocardial scar provided greater contractility and relaxation than fetal smooth muscle cells or fetal fibroblasts. The contractile and elastic properties of transplanted cells determine the degree of improvement in ventricular function achievable with cell transplantation.

Cardiac organogenesis in vitro: reestablishment of three-dimensional tissue architecture by dissociated neonatal rat ventricular cells

The mammalian heart does not regenerate in vivo. The heart is, therefore, an excellent candidate for tissue engineering approaches and for the use of biosynthetic devices in the replacement or augmentation of defective tissue. Unfortunately, little is known about the capacity of isolated heart cells to re-establish tissue architectures in vitro. In this study, we examined the possibility that cardiac cells possess a latent organizational potential that is unrealized within the mechanically active tissue but that can be accessed in quiescent environments in culture. In the series of experiments presented here, total cell populations were isolated from neonatal rat ventricles and recombined in rotating bioreactors containing a serum-free medium and surfaces for cell attachment. The extent to which tissue-like structure and contractile function were established was assessed using a combination of morphological, physiological, and biochemical techniques. We found that mixed populations of ventricular cells formed extensive three-dimensional aggregates that were spontaneously and rhythmically contractile and that large aggregates of structurally-organized cells contracted in unison. The cells were differentially distributed in these aggregates and formed architectures that were indistinguishable from those of intact tissue. These architectures arose in the absence of three-dimensional cues from the matrix, and the formation of organotypic structures was apparently driven by the cells themselves. Our observations suggest that cardiac cells possess an innate capacity to re-establish complex, three-dimensional, cardiac organization in vitro. Understanding the basis of this capacity, and harnessing the organizational potential of heart cells, will be critical in the development of tissue homologues for use in basic research and in the engineering of biosynthetic implants for the treatment of cardiac disease.

Bio-stretch, a computerized cell strain apparatus for three-dimensional organotypic cultures

In the present study, a unique mechanical strain apparatus for three-dimensional organotypic cultures was developed into a computerized system. It consists of a personal computer running Windows-based software, the Bio-Stretch Manager, a Bio-Stretch Controller, and three sets of magnet boards. Cells are cultured on a Gelfoam sponge that is placed in a 35 mm petri dish with one end glued to the dish, and the other end attached to a coated steel bar. The petri dish is placed in front of a magnet, and the movement of the steel bar is controlled by dynamically changing the magnetic field. Up to five stretch patterns of variable frequency, duty cycle, and magnitude can be designed for each stretch regimen. Three different stretch regimens can be tested simultaneously. The operational characteristics of sponges were examined. Attachment of cells to the sponges was observed on several cell types. These features provide wide options for using this system to study the effects of mechanical stretch on cells.

Ectopic skeletal muscles derived from myoblasts implanted under the skin

We investigated the potential of cultured myoblasts to generate skeletal muscle in an ectopic site. Myoblasts from a clonal cell line or from expanded primary cultures were injected under the skin of the lumbar region of adult syngenic Balb/c mice. One to 7 weeks after injection, distinct muscles, of greater mass in mice injected with clonal myoblasts (6–78 mg, n=37) than in mice injected with primary myoblasts (1–7 mg, n=26), had formed between the subcutaneous panniculus carnosus muscle and the trunk muscles of host animals. These ectopic muscles exhibited spontaneous and/or electrically-evoked contractions after the second week and, when stimulated directly in vitro, isometric contractile properties similar to those of normal muscles. Histological, electron microscopical and tissue culture examination of these muscles revealed their largely mature morphology and phenotype. The fibres, most of which were branched, were contiguous, aligned and capillarised, exhibited normal sarcormeric protein banding patterns, and expressed muscle-specific proteins, including desmin, dystrophin, and isoforms of developmental and adult myosin heavy chain. Enveloping each fibre was a basal lamina, beneath which lay quiescent satellite cells, which could be stimulated to produce new muscle in culture. Presence of endplates (revealed by alpha-bungarotoxin and neurofilament staining), and the eventual loss of expression of neural cell adhesion molecule and extrasynaptic acetylcholine receptors, indicated that some fibres were innervated. That these muscle fibres were of implanted-cell origin was supported by the finding of Y-chromosome and a lack of dystrophin in ectopic muscles formed after subcutaneous injection of, respectively, male myoblasts into female mice and dystrophin-deficient (mdx) myoblasts into normal C57Bl/10 muscle. Our results demonstrate that an organised, functional muscle can be generated de novo from a disorganised mass of myoblasts implanted in an extramuscular subcutaneous site, whereby the host contributes significantly in providing support tissues and innervation. Our observations are also consistent with the idea that myogenic cells behave like tissue-specific stem cells, generating new muscle precursor (satellite) cells as well as mature muscle. Subcutaneous implantation of myoblasts may have a range of useful applications, from the study of myogenesis to the delivery of gene products.

Ultrastructure and cell-cell coupling of cardiac myocytes differentiating in embryonic stem cell cultures

Differentiation cultures of embryonic stem (ES) cells can be a useful in vitro system for understanding cardiac myocyte development. However, cell morphometry, sarcomere development, and functional cell-cell junction formation have not been examined in detail to determine whether ES cell-derived cardiac myocytes exhibit structural and functional characteristics similar to cardiac myocytes within the developing heart. Therefore, we examined cellular dimensions, sarcomere formation, and cell-cell contacts in differentiating cardiac myocytes derived from mouse D3-ES cell cultures. Cells exhibited rod-shaped morphology and had single centrally located nuclei, typical of maturing cardiac myocytes. The cellular dimensions of 59 individual cardiac myocytes within contracting foci of ES cell cultures were analyzed (length = 42.2 +/- 2.1 microns, area = 197 +/- 19 microns2, and diameter = 5.5 +/- 0.3 microns) and found to be similar to myocytes in vivo. Transmission electron micrographs of ES cell-derived cardiac myocytes indicated myofibrillar architecture ranged from sparse and disorganized to densely packed, parallel arrays of myofibrils organized into mature sarcomeres. This pattern of myofibrillar assembly in maturing sarcomeres was similar to that observed during in vivo myocyte differentiation. Another hallmark of cardiac development is the formation of intercalated discs, which functionally couple adjacent cardiac myocytes. Electron micrographs indicated nascent intercalated discs were forming in foci of ES cell-derived cardiac myocytes. In addition, indirect immunostaining with anti-connexin 43 antibody (Ab), a monoclonal Ab to the gap junction component of the intercalated disc, indicated that gap junctions were present in contracting ES cell foci. Furthermore, microinjection of single cardiac myocytes with Lucifer yellow (2.5 microM) resulted in the spread of fluorescence to adjacent cells within a contracting focus, an indication of functional cell-cell coupling across these gap junctions. Together, these results indicate ES cell-derived cardiac myocytes exhibit cell morphology, sarcomere formation, and cell-cell junctions similar to those observed in cardiac myocytes developing in vivo.

Cardiomyocyte transplantation improves heart function

BACKGROUND

Transplantation of cultured cardiomyocytes into myocardial scar tissue may prevent heart failure.

METHODS

Scar tissue was produced in the left ventricular free wall of 15 rats (weight, 450 g) by cryoinjury. Seven animals had operation only and survived for 8 weeks (sham group). Four weeks after cryoinjury, cultured fetal rat cardiomyocytes or culture medium was injected into the scar tissue of transplantation (n = 5) and control (n = 5) animals, respectively. Five other rats were sacrificed for scar assessment. Eight weeks after cryoinjury heart function in the transplantation, control, and sham groups was measured using a Langendorff preparation. Histologic studies were performed to quantify the extent of the scar and the transplanted cells.

RESULTS

Four weeks after cryoinjury, 36% +/- 4% (mean +/- 1 standard error) of the left ventricular free wall surface area was scar tissue. At 8 weeks, the scar size had increased (p < 0.01) to 55% +/- 3% in the control group. Although the scar size (43% +/- 2%) in the transplantation group at 8 weeks was not significantly different from that at 4 weeks, it was less (p < 0.05) than that in the control group. Hearts in the sham group had no scar tissue. The transplanted cardiomyocytes had formed cardiac tissue within the myocardial scar. Systolic and developed pressures in the transplantation group hearts were greater (p = 0.0001) than in the control group hearts but less (p < 0.01) than those in the sham group hearts.

CONCLUSIONS

The transplanted cardiomyocytes formed cardiac tissue in the myocardial scar, limited scar expansion, and improved heart function compared with findings in the control hearts.