Overexpression of connexin 43 using a retroviral vector improves electrical coupling of skeletal myoblasts with cardiac myocytes in vitro
- Oleg Tolmachov†1Email author,
- Yu-Ling Ma†2,
- Michael Themis1,
- Pravina Patel2,
- Hilmar Spohr2,
- Kenneth T MacLeod3,
- Nina D Ullrich3,
- Yvonne Kienast1,
- Charles Coutelle1 and
- Nicholas S Peters2
© Tolmachov et al; licensee BioMed Central Ltd. 2006
Received: 20 October 2005
Accepted: 06 June 2006
Published: 06 June 2006
Organ transplantation is presently often the only available option to repair a damaged heart. As heart donors are scarce, engineering of cardiac grafts from autologous skeletal myoblasts is a promising novel therapeutic strategy. The functionality of skeletal muscle cells in the heart milieu is, however, limited because of their inability to integrate electrically and mechanically into the myocardium. Therefore, in pursuit of improved cardiac integration of skeletal muscle grafts we sought to modify primary skeletal myoblasts by overexpression of the main gap-junctional protein connexin 43 and to study electrical coupling of connexin 43 overexpressing myoblasts to cardiac myocytes in vitro.
To create an efficient means for overexpression of connexin 43 in skeletal myoblasts we constructed a bicistronic retroviral vector MLV-CX43-EGFP expressing the human connexin 43 cDNA and the marker EGFP gene. This vector was employed to transduce primary rat skeletal myoblasts in optimised conditions involving a concomitant use of the retrovirus immobilising protein RetroNectin® and the polycation transduction enhancer Transfectam®. The EGFP-positive transduced cells were then enriched by flow cytometry.
More than four-fold overexpression of connexin 43 in the transduced skeletal myoblasts, compared with non-transduced cells, was shown by Western blotting. Functionality of the overexpressed connexin 43 was demonstrated by microinjection of a fluorescent dye showing enhanced gap-junctional intercellular transfer in connexin 43 transduced myoblasts compared with transfer in non-transduced myoblasts. Rat cardiac myocytes were cultured in multielectrode array culture dishes together with connexin 43/EGFP transduced skeletal myoblasts, control non-transduced skeletal myoblasts or alone. Extracellular field action potential activation rates in the co-cultures of connexin 43 transduced skeletal myoblasts with cardiac myocytes were significantly higher than in the co-cultures of non-transduced skeletal myoblasts with cardiac myocytes and similar to the rates in pure cultures of cardiac myocytes.
The observed elevated field action potential activation rate in the co-cultures of cardiac myocytes with connexin 43 transduced skeletal myoblasts indicates enhanced cell-to-cell electrical coupling due to overexpression of connexin 43 in skeletal myoblasts. This study suggests that retroviral connexin 43 transduction can be employed to augment engineering of the electrocompetent cardiac grafts from patients' own skeletal myoblasts.
There is only minor potential for cell renewal in the adult myocardium . Loss of myocardial cells due to cardiac disease results in impairment of cardiac contractile and electrical function, and despite currently available medical therapies the mortality rate remains substantial and worsens with deteriorating myocardial function . Cardiac transplantation is currently the treatment offered to selected patients with end-stage left ventricular dysfunction, but due to limited donor supply and resources, this mode of therapy will remain confined to a minority of patients .
Cell transplantation is a promising means of repairing damaged myocardium. A number of different cell types and their combinations are under investigation for transplantation to the ventricular myocardium, including neonatal or fetal cardiomyocytes, autologous skeletal myoblasts, fibroblasts, hematopoetic stem cells, and embryonic stem cell-derived cells [4–6]. Transplanted cells have been widely reported to engraft into the host myocardium, but with variability in the degree of differentiation and integration with the host tissue [7–9].
Owing to immunological, ethical and practical advantages over some of the other cell types, transplantation of autologous skeletal myoblasts for myocardial repair was the first to undergo clinical trials [10, 11]. Although modest improvements of cardiac function have been reported, ventricular tachycardia was observed in a number of patients indicating absence of electrical incorporation of the grafted cells into the host myocardium. In general, the results obtained from cell, animal and human studies have indicated that the implanted myoblasts showed fusion and differentiated into multinucleated myotubes, did not transdifferentiate to cardiac myocytes and did not couple with the host cardiac myocytes. It is possible that lack of electrical coupling of the implanted cells with the host myocytes is the key factor blocking adequate functional incorporation of the grafted skeletal myoblasts into the beating cardiac muscle . Indeed, the major myocardial gap junctional protein connexin 43 is not expressed in mature skeletal myotubes . We therefore addressed the hypothesis that connexin 43 overexpression by retroviral transduction of the skeletal myoblasts can enhance their electrical integration with cardiac myocytes in co-culture.
E. colistrain, transformation and bacterial culture conditions
E. coli strain DH10B F- mcrA Δ(mrr-hsdRMS-mcrBC) ϕ80lacZΔM15 ΔlacX74 recA1 endA1 araD139 Δ(ara, leu)7697 galU galK λ- rpsL(Str R ) nupG (Invitrogen) was used as a plasmid host. This strain was transformed by electroporation using the Gene Pulser® II apparatus (BioRad). Bacterial clones were cultured in the LB medium supplemented with appropriate antibiotics .
Plasmids, oligonucleotides, PCR and sequencing
Plasmid pGF1 containing human connexin 43 cDNA  and primers CX-NHE 5'-TACTGCAGAA GCTAGCAGCC GCCACCATGG GTGACTGGAG CGCCTTAGGC-3' and CX-BAM 5'-TGTTACTATA GGATCCCTAG ATCTCCAGGT CATCAGGCC-3' were employed to amplify the connexin 43 gene by PCR using high fidelity Pfx DNA polymerase (Invitrogen). The forward PCR primer CX-NHE included a recognition sequence for NheI followed by the consensus extended Kozak sequence 5'-GCCGCCACC-3'. The reverse PCR primer CX-BAM contained a BamHI recognition sequence at its 5' end. The obtained PCR product was cut by NheI and BamHI and inserted into the NheI and BamHI digested plasmid pIRES2EGFP (Clontech) to produce the new plasmid pCX43-IRES-EGFP. Then the entire connexin 43 cDNA insert was sequenced (Advanced Biotechnology Centre, Imperial College London) using primers CX-SEQ2 5'-TTGCTGCGAACCTACATCATCAGT-3', CX-SEQ3 5'-TTTCAATGGC TGCTCCTCACCAAC-3' and CX-SEQ4 5'-GAAGATGGTTTTCTCCGTGGGGCGAGA-3' to confirm its faithful reproduction by PCR.
Tissue culture techniques and construction of the producer cell line generating retroviral vector MLV-CX43-EGFP
Packaging cells, virus producer cells, and immortalised L6 rat myoblasts (ATCC CRL-1458) were grown in DMEM with glutamax-I supplemented with 10% FCS (Invitrogen) at 37°C with 5% CO2 in air.
To generate retroviral producer cell lines, the amphotropic MLV packaging cell line TEFLYA  was transfected with the obtained plasmid pMLV-CX43-EGFP. Transfection was performed using Lipofectamin® (Invitrogen) as recommended by the supplier. Transfected cells were selected in the medium supplemented with puromycin (10 μg/ml). Different dilutions of the trypsinised transfected cells were prepared and seeded onto 96 well plates. 267 individual clones were produced and expanded in 24 well plates. The clones were screened using an inverted fluorescence microscope (Leitz) for EGFP expression and also for viral vector production by transduction of L6 rat skeletal myoblasts. 39 clones (14.6%) were fluorescent of which 17 clones (6.4%) produced virus. Screening of supernatants from 267 potential producer cell lines revealed a broad variation in the titre of produced virus, determined by transduction of L6 rat skeletal myoblasts in the presence of 10 μg/ml of Polybrene™. Clones A113, A189 and A247 produced virus with the highest end-point titre (1 × 106 TU/ml in the freshly collected virus-containing medium). Clone A247 was used as a source of the MLV-CX43-EGFP virus vector for further experiments. Virus vector preparations were produced by centrifugation of culture supernatants from producer cells at 5000 rpm for 10 min and filtration of the obtained fluid through 0.8 μm filters (Sartorius). The virus vector preparations were stored frozen at -80°C.
Isolation and culture of skeletal myoblasts and cardiac myocytes
The manipulations of animals in this work conform to UK Home Office guidelines. Primary rat skeletal myoblasts were isolated from the hind leg muscles of adult male Wistar rats. The muscle slices were digested in 0.25% pancreatin, 1% trypsin for 1 hour with occasional agitation. The isolated cells were collected by filtering through 70 μm nylon cell strainers (Falcon). Counter-selection against fibroblasts was accomplished by 2 rounds of differential adhesion on collagen coated tissue culture flasks (40 min at 37°C for each adhesion step). Primary myoblasts were cultured in a CO2 incubator at 37°C in DMEM with glutamax-I (Invitrogen) supplemented with 20% FCS and further purified by sorting using paramagnetic beads (Dynal Biotech) coated with antibody H36 against myoblast specific α-7 integrin .
Cardiac myocytes were isolated from neonatal rats. Freshly excised ventricles were dissociated in trypsin-EDTA (Invitrogen) and the dispersed cells were suspended in the culture medium, a 4:1 mixture of DMEM and M199 media (Invitrogen) supplemented with 15% horse serum and 5% FCS. The cell suspension was pre-plated to separate fibroblasts from myocytes as described for skeletal myoblasts above. The myocytes remaining in the suspension were cultured in a CO2 incubator at 37°C.
Retroviral transduction of primary skeletal myoblasts and FACS analysis
The obtained population of connexin 43 transduced myoblasts was frozen in liquid nitrogen in the DMEM containing 20% FCS and 10% DMSO. Aliquots of the frozen transduced skeletal myoblasts were used to seed subcultures for Western blotting analysis, dye transfer and electrophysiological experiments.
Western blotting analysis of connexin 43 expression
Quantitative immunoblotting was performed to confirm overexpression of connexin 43 in the skeletal myoblasts containing the connexin 43 transgene. Seeded cells were allowed to expand until they reached complete confluence (7 days). Then the cells were scraped off, homogenised in the lysis buffer SB20 (20% SDS and 0.15 M Tris-HCl pH 6.8) and sonicated to shear the genomic DNA. The protein concentration was determined and adjusted to 0.5 mg/ml. Samples with 5.0 μg of total protein were resolved by SDS-PAGE on a 12.5% gel and transferred onto a polyvinylidene difluoride membrane. The mouse primary antibody against connexin 43 (Chemicon), the secondary alkaline phosphatase-conjugated anti-mouse antibody (Pierce) and the proprietary alkaline phosphatase substrate (Promega) were used to detect connexin 43. The protein bands were quantified by densitometry. Two independent cell cultivation experiments were performed and two independent gels were analysed by Western blotting for each cultivation experiment.
Microinjection and intercellular transfer of a fluorescent dye
Skeletal myoblasts transduced with the MLV-CX43-EGFP vector, control non-transduced skeletal myoblasts and co-cultures of these cells with cardiac myocytes were grown in culture dishes to ~80% confluence. The culture dishes were then placed onto the stage of an inverted fluorescence microscope. Microelectrodes with resistance 50–60 MΩ were loaded with a 5% solution of Cascade Blue derivative 8-methoxypyrene-trisulphonic acid (Molecular Probes, Oregon, USA) and were back-filled with 1 M LiCl. The dye was iontophoresed into each cell by 4–6 nA current for 2 min following impalement of a cell by the electrode. Dye transfer to the adjacent cells was recorded using a Nikon digital camera (Coolpix 990). Dye transfer images were captured 2 min after injection. The images were used to score the number of neighbouring cells to which the dye was transferred from each injected cell.
Electrophysiological measurements in cell co-cultures
Cell culture dishes incorporating a group of 60 embedded unipolar electrodes with diameter 30 μm with interelectrode distances of 100 μm (Multielectrode Array, MCS GmbH, Reutlingen, Germany) were used to study and compare the electrical integration of skeletal myoblasts (connexin 43/EGFP transduced and non-transduced) in co-cultures with cardiac myocytes. Five groups of cell cultures were under investigation: 1) cardiac myocytes alone; 2) skeletal myoblasts alone; 3) connexin 43 transduced skeletal myoblasts alone; 4) cardiac myocytes co-cultured in a ratio of 4:1 with connexin 43 transduced skeletal myoblasts; 5) cardiac myocytes co-cultured in the same ratio with non-transduced skeletal myoblasts. To establish co-cultures, cardiac myocytes were seeded in the multielectrode array dishes (1 million cells per dish) to allow the cells to settle. The cells were cultured in a medium composed of a 4:1 mixture of DMEM and M199 media (Invitrogen) supplemented with 15% horse serum and 5% FCS. At day 2 after the initial seeding, connexin 43 transduced skeletal myoblasts or non-transduced skeletal myoblasts (0.25 million cells per dish) were added to cardiac myocytes. At day 3, the cells reached confluence with both skeletal and cardiac cells distinguishable under the microscope. Then MEA dishes were placed onto the recording system and an extracellular stimulatory current was applied in 10 evenly spaced pulses (80 μA, 5 ms) during 10 s time interval. The stimulatory pulses were delivered to the cells by a pair of electrodes located outside the 60-electrode array. To register FAP, electrograms (potential against time) were recorded for 10 s. The FAP activation rate (that is, frequency of FAP firing) was determined from the discrete spikes on the electrograms with amplitude > 500 μV and duration > 5 ms using the spike sorter of the MC-Rack data analyser (Microcal Software, Northampton, MA, USA). The FAP activation rate data obtained from the 60 electrodes were then averaged.
The data are presented as the mean value and its standard error (mean ± standard error, M ± SE). The following formula was used to compute average standard error (ASE) of the ratio of two means (M1 ± SE1, M2 ± SE2): ASE = (M1/M2)*(SE1 2/M1 2+SE2 2/M2 2)1/2. The significance of the differences between experimental groups was estimated using unpaired t-test.
Construction of the retroviral connexin 43 vector MLV-CX43-EGFP and optimisation of myoblast transduction conditions
To be able to deliver the connexin 43 gene to skeletal myoblasts we constructed an amphotropic retroviral vector MLV-CX43-EGFP, co-expressing human connexin 43 cDNA and the EGFP marker gene (Figure 1).
The passaging time of primary skeletal myoblasts in tissue culture before transplantation is limited because of clinical considerations. Therefore, it is important to achieve maximum cell transduction efficiency with a minimal number of exposures of the myoblasts to the viral vector. Amphotropic MLV vector preparations commonly contain substances, which severely limit the efficiency of transduction. In an attempt to minimise the adverse effect of the transduction inhibitors, we used various dilutions of the MLV-CX43-EGFP viral vector preparation with end-point titre 2 × 105 TU/ml for infection of the primary rat skeletal myoblasts in the presence of 5 μg/ml of the commonly used transduction enhancer polycation Polybrene™ (hexadimethrine bromide). The highest efficiency of transduction (9.94 ± 0.50%) was achieved with 5-fold dilution of the viral vector and not with undiluted vector, confirming contamination of the vector preparation by transduction inhibitors (Figure 2A). To increase efficiency of transduction by the MLV-CX43-EGFP vector, we tested RetroNectin®-mediated virion capture  to immobilise the vector particles on a plastic surface and, thus, to get rid of the RetroNectin®-unbound portion of the transduction inhibitors. We compared the standard RetroNectin®-mediated transduction protocol, which is performed without polycation transduction enhancers, to RetroNectin®-mediated transduction in the presence of Polybrene™ or, alternatively, in the presence of lipopolyamine Transfectam® (dioctadecylamidoglycyl spermine, ). The obtained transduction efficiency data are summarised in Figure 2B. Employment of Transfectam® to enhance transduction of primary skeletal myoblasts by RetroNectin®-immobilized MLV-CX43-EGFP vector allowed transduction of 38.30 ± 0.89% cells. In contrast, the efficiency of transduction was 22.56 ± 0.75% in the RetroNectin®/Polybrene™ experiments and 14.34 ± 0.60% when RetroNectin®-immobilised virus was used without addition of a polycation substance.
To estimate the stability of connexin 43 expression, one part of the transduced population of skeletal myoblasts was stored frozen in liquid nitrogen and another part was used for continuous passaging. During 12-week cultivation, the cells were split and re-seeded in the ratio 1:10 each week with simultaneous FACS analysis of the EGFP transgene expression. The percentage of EGFP-positive cells stayed practically constant during passaging in vitro indicating absence of the EGFP transgene shut-down and suggesting the absence of shut-down of the linked connexin 43 transgene (Figure 2C).
The passaged and the stored populations of transduced myoblasts were then used for preparative FACS to enrich EGFP expressing cells to more than 70% (Figure 2D).
Western blotting analysis showed a 4.85 ± 0.25 times overexpression of connexin 43 in the population of sorted non-passaged MLV-CX43-EGFP transduced skeletal myoblasts compared with control non-transduced skeletal myoblasts. Confirming longevity of connexin 43 expression in tissue culture, Western blotting analysis showed a 4.71 ± 0.23 times overexpression of connexin 43 in the population of passaged sorted skeletal myoblasts compared with non-transduced skeletal myoblasts (Figure 2E).
Connexin 43 overexpression enhances intercellular dye transfer between skeletal myoblasts
Connexin 43 overexpression in skeletal myoblasts improves electrical coupling in co-cultures of cardiac myocytes and skeletal myoblasts
Thus, a comparison of all the experimental groups indicated that electrical coupling in the co-culture of skeletal myoblasts with cardiac myocytes is significantly enhanced in the presence of overexpressed connexin 43.
Electric communication between cells is mediated by bursts of the action potential and gap junctions provide the low resistance pathway for its cell-to-cell propagation. In addition gap junctions mediate flux of small molecules that regulate normal tissue development and tissue patterning. It is, therefore, reasonable to hypothesise that gap junctions can play a central role in the electromechanical incorporation of cardiac grafts. Autologous skeletal myoblasts are an attractive source for cardiac transplants because of their immune privileges, availability and non-tumourogenicity (reviewed in ). However, when skeletal myoblasts differentiate into myotubes, they permanently lose expression of the major gap junctional protein, connexin 43, and, thus, do not have the apparatus for gap-junctional coupling. This is most likely to be the reason why, after transplantation of skeletal myoblasts, the newly developed graft has not been observed beating synchronously with the heart tissue . There was no intercellular transfer and electrical coupling between the cells developed from the transplanted myoblasts and the host cardiac myocytes . It was also reported that human patients with engrafted skeletal myoblasts suffered from ventricular tachycardia [24, 25]. Therefore, in pursuit of improved cardiac integration of skeletal muscle grafts we modified primary skeletal myoblasts by overexpression of the main gap-junctional protein connexin 43.
We have chosen a retroviral MLV vector for delivery and overexpression of the connexin 43 transgene into skeletal myoblasts because retroviral vectors are able to integrate stably into the genome of the transduced cells and thus to provide long-term expression of a transgene . Indeed, in our study, expression of connexin 43 and the EGFP marker in the transduced cells did not subside after 12 weeks of continuous passaging in tissue culture. However, long term gene expression in vitro can be only tentatively projected to long term gene expression in vivo, where transgene expression shutdown events are common . Therefore, one should consider the possible need of 'topping up' connexin 43 gene expression in the transplanted tissue in vivo. As the engrafted cells do not actively divide, the choice of the 'topping up' vector is limited to cell division independent vectors, for example lentiviral HIV-based vectors. In this context employment of an MLV vector at the ex vivo transduction step is beneficial because it allows subsequent use of efficient and MLV-compatible lentiviral vectors for additional transduction of the grafts in vivo. If lentiviral vectors were used for initial transduction ex vivo, there would be a possibility of a reduced efficiency of the 'topping up' transgene delivery in vivo because of a CD4-independent superinfection interference of the resident lentiviral vector with the incoming one (, reviewed in ).
Absence of connexin 43 in adult muscle can be due to shutdown of the native connexin 43 promoter during myoblast differentiation. We chose the MLV LTR and the CMV promoters to drive expression of human connexin 43 cDNA because these viral promoters are known to be able to direct transcription in adult muscle and therefore they are unlikely to shut down due to changes in the balance of transcription factors in the course of myoblast differentiation. A tandem arrangement of the two promoters in the MLV-CX43-EGFP vector could reduce the chances of transcription silencing after transplantation.
The EGFP marker of the generated viral vector MLV-CX43-EGFP was useful for the purification of the transduced cells by FACS and it can also be useful at the post-grafting stage to track the transplants in vivo.
Our observations show that confluent cultures of primary myoblasts can stay alive for at least a month in medium supplemented with FCS (and considerably longer in medium without serum). This property of primary myoblasts was in stark contrast to the transformed rat L6 myoblasts, which often died in a week after achieving confluency. Thus, fortuitously, the number of culture passages (and, therefore, cell divisions) required for our manipulation of primarily myoblasts (magnetic sorting, retroviral transduction, preparative FACS) was lower, than the number of passages needed for analogous manipulations with a permanent myoblast cell line L6.
To increase the yield of connexin 43 transduced skeletal myoblasts from a single muscle biopsy it is important to achieve a high efficiency of transduction by the MLV vector. However, preparations of amphotropic MLV commonly contain infection inhibiting substances, which reduce maximal transduction efficiencies without reduction of end-point virus titres . It is, therefore, important to optimise conditions for high efficiency of transduction. In our experiments we have shown for the first time that a combination of viral vector concentration on the plastic surface using the virus-binding protein RetroNectin®  and transduction in the presence of lipid polycation Transfectam®  is particularly effective for transduction of primary myoblasts by an amphotropic MLV vector. The achieved efficiency of transduction (38.30 ± 0.89%) can be further increased by: 1) improving the viral vector titre, for example by virion production at 32°C ; 2) additional concentration of the viral vector, e.g. by using magnetic nanoparticles  or low speed centrifugation ; 3) increasing transduction competence of the recipient cells, for example by phosphate starvation of the myoblasts  or boosting the myoblast division rate using growth factors .
We have demonstrated that connexin 43 transduction of skeletal myoblasts and ensuing connexin 43 overexpression significantly improves propagation of action potential (measured as FAP activation rate) in co-culture of cardiac myocytes and skeletal myoblasts in vitro. Enhanced gap junction formation between connexin 43 transduced skeletal myoblasts and cardiac myocytes is the most likely mechanism involved. This conjecture is supported by the results of Reinecke et al  who reported that transplantation of genetically engineered myoblasts, which were designed to express connexin 43 during differentiation, resulted in close apposition of the skeletal myotubes and the host cardiac myocytes.
Skeletal myoblasts are non-differentiated muscle cells and, unsurprisingly, we did not observe any FAP activation in pure cultures of skeletal myoblasts, whether overexpressing connexin 43 or not. Thus, although fluorescent dye transfer occurred to a significantly greater extent in connexin 43 transduced skeletal myoblasts, improved gap-junctional communication in these cells did not result in FAP generation. We registered only a limited FAP activation in co-cultures of non-transduced skeletal myoblasts with cardiac myocytes. However, with connexin 43 overexpression in the skeletal myoblasts, the FAP activation rate in the co-cultures of skeletal myoblasts and cardiac myocytes was significantly enhanced, and was close to the FAP activation rate in pure cultures of cardiac myocytes.
More than 4 times overexpression of connexin 43 in primary skeletal myoblasts was achieved after retroviral transduction in optimised conditions involving a concomitant use of the retrovirus immobilising protein RetroNectin® and the polycation transduction enhancer Transfectam®. Connexin 43 overexpression resulted in improvement of electrical coupling between transduced skeletal myoblasts and cardiac myocytes in vitro. Thus, retroviral connexin 43 transduction is a useful step for engineering of electrocompetent cardiac grafts.
- Ap – ampicillin:
ASE – average standard error, Cm – chloramphenicol, DMEM – Dulbecco's modified Eagle's medium, DMSO – dimethylsulphoxide, EDTA – ethylenediaminetetraacetic acid, EGFP – enhanced green fluorescence protein, FACS – fluorescence activated cell sorting, FAP – field action potential, FCS – fetal calf serum, CMV – cytomegalovirus, HIV – human immunodeficiency virus, IRES – internal ribosome entry site, KF – Klenow fragment of Escherichia coli DNA polymerase I, LTR – long terminal repeat, M – mean, MEA – multielectrode array, MLV – murine leukemia virus, PBS – phosphate buffered saline, PCR – polymerase chain reaction, rpm – revolutions per minute, SDS-PAGE – sodium dodecyl sulfate polyacrylamide gel electrophoresis, SE – standard error, TU – transduction unit.
The work was funded by the Wellcome Trust and the British Heart Foundation. We are grateful to Mark Poznansky (Harvard University, USA) for encouragement and Glenn Fishman (Mount Sinai School of Medicine, USA) for his kind gift of plasmid pGF1 containing human connexin 43 cDNA. Garry Nolan (Stanford University, USA) kindly provided retroviral vector plasmid pLZRS-LacZ(A). Yasuhiro Takeuchi (University College London, UK) generously provided the amphotropic MLV packaging cell line TEFLYA. We thank David Becker (University College London, UK) for his help in the microinjection experiments. Dominic Wells (Imperial College London, UK) shared with us his know-how on isolation of primary skeletal myoblasts and Yasmina Aguiar Martins (Imperial College London, UK) shared her desmin immunostaining expertise. We thank Stephen Fuller and Peter Sugden (Imperial College London, UK) for kind donations of cardiac myocytes and Stephen Kaufman (University of Illinois, USA) for the antibody H36 against α-7 integrin.
- Anversa P, Nadal-Ginard B: Myocyte renewal and ventricular remodelling. Nature. 2002, 415: 240-243. 10.1038/415240a.View ArticlePubMedGoogle Scholar
- Zannad F, Briancon S, Juilliere Y, Mertes PM, Villemot JP, Alla F, Virion JM: Incidence, clinical and etiologic features, and outcomes of advanced chronic heart failure: the EPICAL Study. Epidemiologie de l'Insuffisance Cardiaque Avancee en Lorraine. J Am Coll Cardiol. 1999, 33: 734-742. 10.1016/S0735-1097(98)00634-2.View ArticlePubMedGoogle Scholar
- Keon WJ: Heart transplantation in perspective. J Card Surg. 1999, 14: 147-151.View ArticlePubMedGoogle Scholar
- Muller-Ehmsen J, Kedes LH, Schwinger RH, Kloner RA: Cellular cardiomyoplasty – a novel approach to treat heart disease. Congest Heart Fail. 2002, 8: 220-227.View ArticlePubMedGoogle Scholar
- Scorsin M, Hagege A, Vilquin JT, Fiszman M, Marotte F, Samuel JL, Rappaport L, Schwartz K, Menasche P: Comparison of the effects of fetal cardiomyocyte and skeletal myoblast transplantation on postinfarction left ventricular function. 2. J Thorac Cardiovasc Surg. 2000, 119: 1169-1175. 10.1067/mtc.2000.104865.View ArticlePubMedGoogle Scholar
- Ott HC, Bonaros N, Marksteiner R, Wolf D, Margreiter E, Schachner T, Laufer G, Hering S: Combined transplantation of skeletal myoblasts and bone marrow stem cells for myocardial repair in rats. Eur J Cardiothorac Surg. 2004, 25: 627-634. 10.1016/j.ejcts.2003.12.031.View ArticlePubMedGoogle Scholar
- Hutcheson KA, Atkins BZ, Hueman MT, Hopkins MB, Glower DD, Taylor DA: Comparison of benefits on myocardial performance of cellular cardiomyoplasty with skeletal myoblasts and fibroblasts. Cell Transplant. 2000, 9: 359-368.PubMedGoogle Scholar
- Jain M, DerSimonian H, Brenner DA, Ngoy S, Teller P, Edge AS, Zawadzka A, Wetzel K, Sawyer DB, Colucci WS, Apstein CS, Liao R: Cell therapy attenuates deleterious ventricular remodelling and improves cardiac performance after myocardial infarction. Circulation. 2001, 103: 1920-1927.View ArticlePubMedGoogle Scholar
- Reinecke H, MacDonald GH, Hauschka SD, Murry CE: Electromechanical coupling between skeletal and cardiac muscle. Implications for infarct repair. J Cell Biol. 2000, 149: 731-740. 10.1083/jcb.149.3.731.View ArticlePubMedPubMed CentralGoogle Scholar
- Assmus B, Schachinger V, Teupe C, Britten M, Lehmann R, Dobert N, Grunwald F, Aicher A, Urbich C, Martin H, Hoelzer D, Dimmeler S, Zeiher AM: Transplantation of progenitor cells and regeneration enhancement in acute myocardial infarction (TOPCARE-AMI). Circulation. 2002, 106: 3009-3017. 10.1161/01.CIR.0000043246.74879.CD.View ArticlePubMedGoogle Scholar
- Menasche P, Hagege AA, Scorsin M, Pouzet B, Desnos M, Duboc D, Schwartz K, Vilquin JT, Marolleau JP: Myoblast transplantation for heart failure. Lancet. 2001, 357: 279-280. 10.1016/S0140-6736(00)03617-5.View ArticlePubMedGoogle Scholar
- Abraham MR, Henrikson CA, Tung L, Chang MG, Aon M, Xue T, Li RA, O'Rourke B, Marban E: Antiarrhythmic engineering of skeletal myoblasts for cardiac transplantation. Circulation Research. 2005, 97: 159-167. 10.1161/01.RES.0000174794.22491.a0.View ArticlePubMedGoogle Scholar
- Schmalbruch H: Skeletal muscle fibers of newborn rats are coupled by gap junctions. Dev Biol. 1982, 91: 485-490. 10.1016/0012-1606(82)90056-2.View ArticlePubMedGoogle Scholar
- Sambrook J, Fritsch EF, Maniatis T: Molecular Cloning: A Laboratory Manual. 1989, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NYGoogle Scholar
- Fishman GI, Spray DC, Leinwand LA: Molecular characterization and functional expression of the human cardiac gap junction channel. J Cell Biol. 1990, 111: 589-598. 10.1083/jcb.111.2.589.View ArticlePubMedGoogle Scholar
- Kinsella TM, Nolan GP: Episomal vectors rapidly and stably produce high-titer recombinant retrovirus. Hum Gene Ther. 1996, 7: 1405-1413.View ArticlePubMedGoogle Scholar
- Slingsby JH, Baban D, Sutton J, Esapa M, Price T, Kingsman SM, Kingsman AJ, Slade A: Analysis of 4070A envelope levels in retroviral preparations and effect on target cell transduction efficiency. Hum Gene Ther. 2000, 11: 1439-1451. 10.1089/10430340050057512.View ArticlePubMedGoogle Scholar
- Blanco-Bose WE, Yao CC, Kramer RH, Blau HM: Purification of mouse primary myoblasts based on alpha 7 integrin expression. Exp Cell Res. 2001, 265: 212-220. 10.1006/excr.2001.5191.View ArticlePubMedGoogle Scholar
- Tonks A, Tonks AJ, Pearn L, Mohamad Z, Burnett AK, Darley RL: Optimized retroviral transduction protocol which preserves the primitive subpopulation of human hematopoietic cells. Biotechnol Prog. 2005, 21: 953-958. 10.1021/bp0500314.View ArticlePubMedGoogle Scholar
- Themis M, Forbes SJ, Chan L, Cooper RG, Etheridge CJ, Miller AD, Hodgson HJ, Coutelle C: Enhanced in vitro and in vivo gene delivery using cationic agent complexed retrovirus vectors. Gene Ther. 1998, 5: 1180-1186. 10.1038/sj.gt.3300715.View ArticlePubMedGoogle Scholar
- Menasche P: Skeletal myoblast for cell therapy. Coron Artery Dis. 2005, 16: 105-110. 10.1097/00019501-200503000-00005.View ArticlePubMedGoogle Scholar
- Reinecke H, Poppa V, Murry CE: Skeletal muscle stem cells do not transdifferentiate into cardiomyocytes after cardiac grafting. J Mol Cell Cardiol. 2002, 34: 241-249. 10.1006/jmcc.2001.1507.View ArticlePubMedGoogle Scholar
- Leobon B, Garcin I, Menasche P, Vilquin JT, Audinat E, Charpak S: Myoblasts transplanted into rat infarcted myocardium are functionally isolated from their host. Proc Natl Acad Sci U S A. 2003, 100: 7808-7811. 10.1073/pnas.1232447100.View ArticlePubMedPubMed CentralGoogle Scholar
- Menasche P, Hagege AA, Vilquin JT, Desnos M, Abergel E, Pouzet B, Bel A, Sarateanu S, Scorsin M, Schwartz K, Bruneval P, Benbunan M, Marolleau JP, Duboc D: Autologous skeletal myoblast transplantation for severe postinfarction left vetricular dysfunction. J Am Coll Cardiol. 2003, 41: 1078-1083. 10.1016/S0735-1097(03)00092-5.View ArticlePubMedGoogle Scholar
- Smits PC, van Geuns RJ, Poldermans D, Bountioukos M, Onderwater EE, Lee CH, Maat AP, Serruys PW: Catheter-based intramyocardial injection of autologous skeletal myoblasts as a primary treatment of ischemic heart failure: clinical experience with six-month follow-up. J Am Coll Cardiol. 2003, 42: 2063-2069. 10.1016/j.jacc.2003.06.017.View ArticlePubMedGoogle Scholar
- el Oakley RM, Brand NJ, Burton PB, McMullen MC, Adams GB, Poznansky MC, Barton PJ, Yacoub MH: Efficiency of a high-titer retroviral vector for gene transfer into skeletal myoblasts. J Thorac Cardiovasc Surg. 1998, 115: 1-8. 10.1016/S0022-5223(98)70436-2.View ArticlePubMedGoogle Scholar
- Loser P, Jennings GS, Strauss M, Sandig V: Reactivation of the previously silenced cytomegalovirus major immediate-early promoter in the mouse liver: involvement of NFkappaB. J Virol. 1998, 72: 180-190.PubMedPubMed CentralGoogle Scholar
- Federico M, Bona R, D'Aloja P, Baiocchi M, Pugliese K, Nappi F, Chelucci C, Mavilio F, Verani P: Anti-HIV viral interference induced by retroviral vectors expressing a nonproducer HIV-1 variant. Acta Haematol. 1996, 95: 199-203.View ArticlePubMedGoogle Scholar
- Nethe M, Berkhout B, van der Kuyl AC: Retroviral superinfection resistance. Retrovirology. 2005, 2: 52-10.1186/1742-4690-2-52.View ArticlePubMedPubMed CentralGoogle Scholar
- Beer C, Buhr P, Hahn H, Laubner D, Wirth M: Gene expression analysis of murine cells producing amphotropic mouse leukaemia virus at a cultivation temperature of 32 and 37 degrees C. J Gen Virol. 2003, 84: 1677-1686. 10.1099/vir.0.18871-0.View ArticlePubMedGoogle Scholar
- Hughes C, Galea-Lauri J, Farzaneh F, Darling D: Streptavidin paramagnetic particles provide a choice of three affinity-based capture and magnetic concentration strategies for retroviral vectors. Mol Ther. 2001, 3: 623-630. 10.1006/mthe.2001.0268.View ArticlePubMedGoogle Scholar
- Fresnay S, Chalmers DE, Ferrand C, Colombain C, Newton I, Yerly-Motta V, Lienard A, Darodes de Tailly P, Herve P, Tiberghien P, Saas P: Polybrene and interleukin-4: two opposing factors for retroviral transduction of bone-marrow-derived dendritic cells. J Gene Med. 2002, 4: 601-612. 10.1002/jgm.311.View ArticlePubMedGoogle Scholar
- Reinecke H, Minami E, Virag JI, Murry CE: Gene transfer of connexin43 into skeletal muscle. Hum Gene Ther. 2004, 15: 627-636. 10.1089/1043034041361253.View ArticlePubMedGoogle Scholar
- The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2261/6/25/prepub
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