Myoblast Transfer in Ischemic Heart Failure: Effects on Rhythm Stability

Exogenous connexin43-expressing autologous skeletal myoblasts ameliorate mechanical function and electrical activity of the rabbit heart after experimental infarction

Acute myocardial infarction is one of the major causes of mortality worldwide. For regeneration of the rabbit heart after experimentally induced infarction we used autologous skeletal myoblasts (SMs) due to their high proliferative potential, resistance to ischaemia and absence of immunological and ethical concerns. The cells were characterized with muscle-specific and myogenic markers. Cell transplantation was performed by injection of cell suspension (0.5 ml) containing approximately 6 million myoblasts into the infarction zone. The animals were divided into four groups: (i) no injection; (ii) sham injected; (iii) injected with wild-type SMs; and (iv) injected with SMs expressing connexin43 fused with green fluorescent protein (Cx43EGFP). Left ventricular ejection fraction (LVEF) was evaluated by 2D echocardiography in vivo before infarction, when myocardium has stabilized after infarction, and 3 months after infarction. Electrical activity in the healthy and infarction zones of the heart was examined ex vivo in Langendorff-perfused hearts by optical mapping using di-4-ANEPPS, a potential sensitive fluorescent dye. We demonstrate that SMs in the coculture can couple electrically not only to abutted but also to remote acutely isolated allogenic cardiac myocytes through membranous tunnelling tubes. The beneficial effect of cellular therapy on LVEF and electrical activity was observed in the group of animals injected with Cx43EGFP-expressing SMs. L-type Ca(2+) current amplitude was approximately fivefold smaller in the isolated SMs compared to healthy myocytes suggesting that limited recovery of LVEF may be related to inadequate expression or function of L-type Ca(2+) channels in transplanted differentiating SMs.

Fate of modular cardiac tissue constructs in a syngeneic rat model

Modular cardiac tissues developed both vascular and cardiac structures in vivo, provided that the host response was attenuated by omitting xenoproteins from the modules. Collagen gel modules (with Matrigel(TM)) containing cardiomyocytes (CMs) alone or CMs with surface-seeded endothelial cells (ECs; CM/EC modules) were injected into the peri-infarct zone of the heart in syngeneic Lewis rats. After 3 weeks, donor ECs developed into blood vessel-like structures that also contained erythrocytes. However, no donor CMs were found within the implant sites, presumably because host cells including macrophages and T cells infiltrated extensively into the injection sites. To lessen the host response, Matrigel was omitted from the matrix and the modules were rinsed with serum-free medium prior to implantation. Host cell infiltration was attenuated, resulting in a higher degree of vascularization with CM/EC modules than with CM modules without ECs. Most importantly, donor CMs matured into striated muscle-like structures in Matrigel-free implants.

The proarrhythmic risk of cell therapy for cardiovascular diseases

Stem cell therapy is an emerging therapeutic approach for the treatment of cardiovascular diseases. Experimental studies have demonstrated that different types of stem cells, including bone marrow-derived cells, mesenchymal stem cells, skeletal myoblasts, and cardiac progenitor cells and embryonic stem cells, can improve cardiac function after myocardial injuries. Nevertheless, the potential proarrhythmic risk after stem cell transplantation remains a major concern. Several mechanisms, including the immaturity of electrical phenotypes of the transplanted cardiomyocytes, poor cell-cell coupling and cardiac nerve sprouting, may contribute to arrhythmogenic risk after stem cell transplantation. This review summarizes the potential theoretical arrhythmogenic mechanisms associated with different types of stem cells for the treatment of cardiovascular diseases. Nevertheless, current experimental and clinical data on the proarrhythmic risk for different types of stem cell transplantation are limited, and await further experimental and clinical investigation.

Alteration of cardiac progenitor cell potency in GRMD dogs

Among the animal models of Duchenne muscular dystrophy (DMD), the Golden Retriever muscular dystrophy (GRMD) dog is considered the best model in terms of size and pathological onset of the disease. As in human patients presenting with DMD or Becker muscular dystrophies (BMD), the GRMD is related to a spontaneous X-linked mutation of dystrophin and is characterized by myocardial lesions. In this respect, GRMD is a useful model to explore cardiac pathogenesis and for the development of therapeutic protocols. To investigate whether cardiac progenitor cells (CPCs) isolated from healthy and GRMD dogs may differentiate into myocardial cell types and to test the feasibility of cell therapy for cardiomyopathies in a preclinical model of DMD, CPCs were isolated from cardiac biopsies of healthy and GRMD dogs. Gene profile analysis revealed an active cardiac transcription network in both healthy and GRMD CPCs. However, GRMD CPCs showed impaired self-renewal and cardiac differentiation. Population doubling and telomerase analyses highlighted earlier senescence and proliferation impairment in progenitors isolated from GRMD cardiac biopsies. Immunofluorescence analysis revealed that only wt CPCs showed efficient although not terminal cardiac differentiation, consistent with the upregulation of cardiac-specific proteins and microRNAs. Thus, the pathological condition adversely influences the cardiomyogenic differentiation potential of cardiac progenitors. Using PiggyBac transposon technology we marked CPCs for nuclear dsRed expression, providing a stable nonviral gene marking method for in vivo tracing of CPCs. Xenotransplantation experiments in neonatal immunodeficient mice revealed a valuable contribution of CPCs to cardiomyogenesis with homing differences between wt and dystrophic progenitors. These results suggest that cardiac degeneration in dystrophinopathies may account for the progressive exhaustion of local cardiac progenitors and shed light on cardiac stemness in physiological and pathological conditions. Furthermore, we provide essential information that canine CPCs may be used to alleviate cardiac involvement in a large preclinical model of DMD.

Direct intramyocardial mesenchymal stromal cell injections in patients with severe refractory angina: one-year follow-up

In patients with stable coronary artery disease (CAD) and refractory angina, we performed direct intramyocardial injections of autologous mesenchymal stromal cells (MSC) and followed the safety and efficacy of the treatment for 12 months. A total of 31 patients with stable CAD, moderate to severe angina, normal left ventricular ejection fraction, and no further revascularization options were included. Bone marrow MSCs were isolated and culture expanded for 6-8 weeks and then stimulated with vascular endothelial growth factor (VEGF) for 1 week. The 12-month follow-up demonstrated that it was safe to culture expand MSCs and use the cells for clinical treatment. The patients' maximal metabolic equivalent (MET) during exercise increased from 4.23 MET at baseline to 4.72 MET at 12-month follow-up (p < 0.001), Canadian Cardiovascular Society Class (CCS) was reduced from 3.0 to 0.8 (p < 0.001), angina attacks per week from 13.8 to 3.2 (p < 0.001), and nitroglycerin consumption from 10.7 to 3.4 per week (p < 0.001). In addition, Seattle Angina Questionnaire (SAQ) evaluations demonstrated highly significant improvements in physical limitation, angina stability, angina frequency, and quality of life (p < 0.001 for all). It is safe in the intermediate/long term to treat patients with stable CAD using autologous culture expanded MSCs. Previously reported, early and highly significant improvements in exercise capacity and clinical symptoms persist after 12 months. The results are encouraging, and a larger controlled study is warranted.

Isolation of myogenic stem cells from cultures of cryopreserved human skeletal muscle

We demonstrate that subpopulations of adult human skeletal muscle-derived stem cells, myogenic endothelial cells (MECs), and perivascular stem cells (PSCs) can be simultaneously purified by fluorescence-activated cell sorting (FACS) from cryopreserved human primary skeletal muscle cell cultures (cryo-hPSMCs). For FACS isolation, we utilized a combination of cell lineage markers: the myogenic cell marker CD56, the endothelial cell marker UEA-1 receptor (UEA-1R), and the perivascular cell marker CD146. MECs expressing all three cell lineage markers (CD56(+)UEA-1R(+)CD146(+)/CD45(-)) and PSCs expressing only CD146 (CD146(+)/CD45(-)CD56(-)UEA-1R(-)) were isolated by FACS. To evaluate their myogenic capacities, the sorted cells, with and without expansion in culture, were transplanted into the cardiotoxin-injured skeletal muscles of immunodeficient mice. The purified MECs exhibited the highest regenerative capacity in the injured mouse muscles among all cell fractions tested, while PSCs remained superior to myoblasts and the unpurified primary skeletal muscle cells. Our findings show that both MECs and PSCs retain their high myogenic potentials after in vitro expansion, cryopreservation, and FACS sorting. The current study demonstrates that myogenic stem cells are prospectively isolatable from long-term cryopreserved primary skeletal muscle cell cultures. We emphasize the potential application of this new approach to extract therapeutic stem cells from human muscle cells cryogenically banked for clinical purposes.

Skeletal myoblasts for cardiac repair

Stem cells provide an alternative curative intervention for the infarcted heart by compensating for the cardiomyocyte loss subsequent to myocardial injury. The presence of resident stem and progenitor cell populations in the heart, and nuclear reprogramming of somatic cells with genetic induction of pluripotency markers are the emerging new developments in stem cell-based regenerative medicine. However, until safety and feasibility of these cells are established by extensive experimentation in in vitro and in vivo experimental models, skeletal muscle-derived myoblasts, and bone marrow cells remain the most well-studied donor cell types for myocardial regeneration and repair. This article provides a critical review of skeletal myoblasts as donor cells for transplantation in the light of published experimental and clinical data, and indepth discussion of the advantages and disadvantages of skeletal myoblast-based therapeutic intervention for augmentation of myocardial function in the infarcted heart. Furthermore, strategies to overcome the problems of arrhythmogenicity and failure of the transplanted skeletal myoblasts to integrate with the host cardiomyocytes are discussed.

Stem/Progenitor Cells, Atherosclerosis and Cardiovascular Regeneration

Regenerative cell based therapy has potential to become effective adjuvant treatment for patients with atherosclerotic disease. Although data from animal studies support this notion, clinical studies undertaken in patients with acute and chronic coronary artery disease do not conclusively demonstrate benefits of such therapy. There are many questions on the stem cell translational roadmap. The basic mechanisms of stem cell-dependent tissue regeneration are not well understood. There is a debate regarding characterization of specific cell types conferring therapeutic effects. In particular, the role of endothelial progenitor cells as a specific reparative cell subtype is questioned, and the role of myeloid cell linage in fostering of vasculo- and angiogenesis is being increasingly appreciated. Intense discussions surround the place of stem/progenitor cells in atherosclerosis progression, plaque destabilization and vessel remodeling. This paper summarizes the current knowledge on the regenerative stem/progenitor cell definitions, mechanisms of stem cell trafficking, homing and their involvement in atherosclerosis progression.

Stem/Progenitor cells, atherosclerosis and cardiovascular regeneration

Regenerative cell based therapy has potential to become effective adjuvant treatment for patients with atherosclerotic disease. Although data from animal studies support this notion, clinical studies undertaken in patients with acute and chronic coronary artery disease do not conclusively demonstrate benefits of such therapy. There are many questions on the stem cell translational roadmap. The basic mechanisms of stem cell-dependent tissue regeneration are not well understood. There is a debate regarding characterization of specific cell types conferring therapeutic effects. In particular, the role of endothelial progenitor cells as a specific reparative cell subtype is questioned, and the role of myeloid cell linage in fostering of vasculo- and angiogenesis is being increasingly appreciated. Intense discussions surround the place of stem/progenitor cells in atherosclerosis progression, plaque destabilization and vessel remodeling. This paper summarizes the current knowledge on the regenerative stem/progenitor cell definitions, mechanisms of stem cell trafficking, homing and their involvement in atherosclerosis progression.