Nature Clinical Practice. Cardiovascular Medicine最新文献

Since the feasibility of stem cell therapy has been recognized, enthusiasm for this therapy has grown exponentially. Nevertheless, as professionals we must realize that this enthusiasm should relate not only to our scientific interest but also to the care of our patients. Within the next decade, patients' demand for the latest therapies is likely to rise because of changes in health care systems that will broaden availability. Stem cell therapy is likely to be among these in-demand treatments, and we must be prepared for this change. In this Review we discuss the basic principles of how to launch a clinical program for stem cell therapy for cardiovascular repair. First, we look at the composition of the program team. Second, we describe the different types of stem cells available in clinical practice. Third, we present in depth the two most widely applicable delivery approaches. Finally, we discuss selection of patients and approaches and clinical and imaging methods by which to evaluate the safety and efficacy of this therapy.

Experimental studies and early-phase clinical trials suggest that mobilization of bone marrow stem cells by granulocyte-colony-stimulating factor (G-CSF) can be used to improve cardiac regeneration after acute myocardial infarction (AMI). In order to more fully evaluate this intervention in patients with AMI, we conducted the Regenerate Vital Myocardium by Vigorous Activation of Bone Marrow Stem Cells (REVIVAL-2) clinical trial. Following successful reperfusion by percutaneous coronary intervention for AMI, patients were randomly assigned to receive a subcutaneous daily dose of 10 microg/kg G-CSF or placebo for 5 days. Treatment with G-CSF produced a significant mobilization of stem cells. After 4-6 months the reduction in infarct size from baseline, as determined by technetium-99-labeled single-photon-emission CT, did not differ significantly between the G-CSF group and the placebo group. Furthermore, the improvement in left ventricular ejection fraction, as assessed by late-enhancement MRI, did not differ significantly between the two groups. G-CSF treatment did not increase the risk of adverse clinical events and did not promote restenosis. Our trial demonstrates that stem cell mobilization by G-CSF does not improve infarct size, left ventricular function, or coronary restenosis in patients with AMI who have had successful mechanical reperfusion.

Adequate cell-based repair of adult myocardium remains an elusive goal because most cells that are used cannot generate mature myocardium sufficient to promote large functional improvements. Embryonic stem cells can generate both mature cardiocytes and vasculature, but their use is hampered by associated teratoma formation and the need for an allogeneic source. The detection of sca-1(+), c-kit(+), or isl-1(+) cardiac precursors and the creation of cardiospheres from adult heart tissues suggest that a persistent population of immature progenitor cells is present in the mature myocardium. These cell populations probably represent stages along a continuum of cardiac stem cell development and differentiation. We report isolation from ventricle of uncommitted cardiac progenitor cells, which appear to resemble the more immature, common pool of embryonic lateral plate mesoderm progenitors that yield both myocardial and endocardial cells during normal cardiac development. Under controlled in vitro conditions and in vivo, these cells can differentiate into endothelial, smooth muscle, and cardiomyocyte lineages and can be isolated and expanded to clinically relevant numbers from adult rat myocardial tissue. In this article, we discuss the potential for autologous repair or even cardiac regeneration with cells that follow a developmental pathway similar to embryonic cardiac precursors but without the inherent limitations associated with undifferentiated embryonic stem cells.

The migration of myocardial precursor cells towards the embryonic midline underlies the formation of the heart tube and is a key process of heart organogenesis. The zebrafish mutation miles-apart (mil), which affects the gene encoding a sphingosine-1-phosphate receptor, is characterized by defective migration of myocardial precursor cells and results in the formation of two laterally positioned hearts, a condition known as cardia bifida. The mechanism that disrupts myocardial migration in mil mutants remains largely unclear. To investigate how mil regulates this process, here we analyze the interactions between mil and other mediators of myocardial migration. We show that mil function is associated with the other known cardia bifida locus, natter/fibronectin (nat/fn), which encodes fibronectin, a major component of the extracellular matrix, in the control of myocardial migration. By using a primary culture system of embryonic zebrafish cells, we also show that signaling from the sphingosine-1-phosphate receptor regulates cell-fibronectin interactions in zebrafish. In addition, localized inhibition and activation of cell-fibronectin interactions during the stages of myocardial migration reveal that the temporal regulation of cell-fibronectin interaction by mil is required for proper myocardial migration. Our study reveals novel functional links between sphingosine-1-phosphate receptor signaling and cell-fibronectin interaction in the control of myocardial migration during zebrafish heart organogenesis.

The adult mammalian myocardium has a robust intrinsic regenerative capacity because of the presence of cardiac stem cells (CSCs). Despite being mainly composed of terminally differentiated myocytes that cannot re-enter the cell cycle, the heart is not a postmitotic organ and maintains some capacity to form new parenchymal cells during the lifespan of the organism. Myocyte death and formation of new myocytes by the CSCs are the two processes that enable this organ to maintain a proper and uninterrupted cardiac output from birth to adulthood and into old age. CSCs are activated in response to pathological or physiological stimuli, whereby they enter the cell cycle and differentiate into new myocytes (and vessels) that significantly contribute to changes in myocardial mass. The future of regenerative cardiovascular medicine is arguably dependent on our success in dissecting the biology and mechanisms regulating the number, growth, differentiation, and aging of CSCs. This information will generate the means to manipulate CSC growth, survival, and differentiation and, therefore, will provide the tools for the design of more physiologically relevant clinical regeneration protocols. In this article, we review the developments in cardiac cell biology that might, in our opinion, have a broad impact on cardiovascular medicine.

Cardiogenesis within embryos or associated with heart repair requires stem cell differentiation into energetically competent, contracting cardiomyocytes. While it is widely accepted that the coordination of genetic circuits with developmental bioenergetics is critical to phenotype specification, the metabolic mechanisms that drive cardiac transformation are largely unknown. Here, we aim to define the energetic requirements for and the metabolic microenvironment needed to support the cardiac differentiation of embryonic stem cells. We demonstrate that anaerobic glycolytic metabolism, while sufficient for embryonic stem cell homeostasis, must be transformed into the more efficient mitochondrial oxidative metabolism to secure cardiac specification and excitation-contraction coupling. This energetic switch was programmed by rearrangement of the metabolic transcriptome that encodes components of glycolysis, fatty acid oxidation, the Krebs cycle, and the electron transport chain. Modifying the copy number of regulators of mitochondrial fusion and fission resulted in mitochondrial maturation and network expansion, which in turn provided an energetic continuum to supply nascent sarcomeres. Disrupting respiratory chain function prevented mitochondrial organization and compromised the energetic infrastructure, causing deficient sarcomerogenesis and contractile malfunction. Thus, establishment of the mitochondrial system and engagement of oxidative metabolism are prerequisites for the differentiation of stem cells into a functional cardiac phenotype. Mitochondria-dependent energetic circuits are thus critical regulators of de novo cardiogenesis and targets for heart regeneration.

Nuclear transport of transcription factors is a critical step in stem cell commitment to a tissue-specific lineage. While it is recognized that nuclear pores are gatekeepers of nucleocytoplasmic exchange, it is unknown how the nuclear transport machinery becomes competent to support genetic reprogramming and cell differentiation. Here, we report the dynamics of nuclear transport factor expression and nuclear pore microanatomy during cardiac differentiation of embryonic stem cells. Cardiac progeny derived from pluripotent stem cells displayed a distinct proteomic profile characterized by the emergence of cardiac-specific proteins. This profile correlated with the nuclear translocation of cardiac transcription factors. The nuclear transport genes, including nucleoporins, importins, exportins, transportins, and Ran-related factors, were globally downregulated at the genomic level, streamlining the differentiation program underlying stem cell-derived cardiogenesis. Establishment of the cardiac molecular phenotype was associated with an increased density of nuclear pores spanning the nuclear envelope. At nanoscale resolution, individual nuclear pores exhibited conformational changes resulting in the expansion of the pore diameter and an augmented probability of conduit occupancy. Thus, embryonic stem cells undergo adaptive remodeling of the nuclear transport infrastructure associated with nuclear translocation of cardiac transcription factors and execution of the cardiogenic program, underscoring the plasticity of the nucleocytoplasmic trafficking machinery in accommodating differentiation requirements.

Clinical trials looking at ways to promote myocardial regeneration have reported that the administered therapies have either neutral effects or modest benefits of questionable impact. These somewhat disappointing results should emphasize the need for translational research, with bidirectional feedback between the basic research laboratory and the clinical arena. Such a translational pathway is illustrated by the quest to find an effective therapy for restenosis, which culminated in the development of sirolimus. At this point a move away from the bedside and a return to the bench seems necessary to better understand the mechanisms of action of progenitor cells and stimulating factors. Without such basic knowledge research might be prematurely discouraged and the opportunity to fully understand the true potential of cardiovascular regenerative therapy might be missed.

Cardiac stem cell therapy with bone-marrow-derived stem cells is a promising approach to facilitate myocardial regeneration after acute myocardial infarction or in congestive heart failure. The clinical data currently available seem to indicate that this approach is safe and is not associated with an increase in the number of adverse clinical events; nevertheless, the level of safety confidence is limited because of the small number of patients who have been treated and the absence of long-term clinical follow-up data. In order to establish the clinical safety of cardiac stem cell therapy, it will be necessary to collect additional data from both previous and ongoing clinical trials in subsets of patients relative to their background risk. Several conceptual safety concerns should also be addressed. These concerns relate to a number of operational mechanisms and include biological effects on differentiation, remote homing of transplanted stem cells, progression of atherosclerosis, and arrhythmias. The proactive scrutiny of these phenomena could eventually facilitate the translation of the promise of cardiac regeneration into a safe and effective therapy.