Carol A. Eisenberg

Laser-patterned stem-cell bridges in a cardiac muscle model for on-chip electrical conductivity analyses

Following myocardial infarction there is an irreversible loss of cardiomyocytes that results in the alteration of electrical propagation in the heart. Restoration of functional electrical properties of the damaged heart muscle is essential to recover from the infarction. While there are a few reports that demonstrate that fibroblasts can form junctions that transmit electrical signals, a potential alternative using the injection of stem cells has emerged as a promising cellular therapy; however, stem-cell electrical conductivity within the cardiac muscle fiber is unknown. In this study, an in vitro cardiac muscle model was established on an MEA-based biochip with multiple cardiomyocytes that mimic cardiac tissue structure. Using a laser beam, stem cells were inserted adjacent to each muscle fiber (cell bridge model) and allowed to form cell-cell contact as determined by the formation of gap junctions. The electrical conductivity of stem cells was assessed and compared with the electrical conductivities of cardiomyocytes and fibroblasts. Results showed that stem cell-myocyte contacts exhibited higher and more stable conduction velocities than myocyte-fibroblast contacts, which indicated that stem cells have higher electrical compatibility with native cardiac muscle fibers than cardiac fibroblasts.

Mesenchymal Stem Cell-Cardiomyocyte Interactions under Defined Contact Modes on Laser-Patterned Biochips

Understanding how stem cells interact with cardiomyocytes is crucial for cell-based therapies to restore the cardiomyocyte loss that occurs during myocardial infarction and other cardiac diseases. It has been thought that functional myocardial repair and regeneration could be regulated by stem cell-cardiomyocyte contact. However, because various contact modes (junction formation, cell fusion, partial cell fusion, and tunneling nanotube formation) occur randomly in a conventional coculture system, the particular regulation corresponding to a specific contact mode could not be analyzed. In this study, we used laser-patterned biochips to define cell-cell contact modes for systematic study of contact-mediated cellular interactions at the single-cell level. The results showed that the biochip design allows defined stem cell-cardiomyocyte contact-mode formation, which can be used to determine specific cellular interactions, including electrical coupling, mechanical coupling, and mitochondria transfer. The biochips will help us gain knowledge of contact-mediated interactions between stem cells and cardiomyocytes, which are fundamental for formulating a strategy to achieve stem cell-based cardiac tissue regeneration.

Laser patterning for the study of MSC cardiogenic differentiation at the single-cell level

Mesenchymal stem cells (MSCs) have been cited as contributors to heart repair through cardiogenic differentiation and multiple cellular interactions, including the paracrine effect, cell fusion, and mechanical and electrical couplings. Due to heart–muscle complexity, progress in the development of knowledge concerning the role of MSCs in cardiac repair is heavily based on MSC–cardiomyocyte coculture. In conventional coculture systems, however, the in vivo cardiac muscle structure, in which rod-shaped cells are connected end-to-end, is not sustained; instead, irregularly shaped cells spread randomly, resulting in randomly distributed cell junctions. Consequently, contact-mediated cell–cell interactions (e.g., the electrical triggering signal and the mechanical contraction wave that propagate through MSC–cardiomyocyte junctions) occur randomly. Thus, the data generated on the beneficial effects of MSCs may be irrelevant to in vivo biological processes. In this study, we explored whether cardiomyocyte alignment, the most important phenotype, is relevant to stem cell cardiogenic differentiation. Here, we report (i) the construction of a laser-patterned, biochip-based, stem cell–cardiomyocyte coculture model with controlled cell alignment; and (ii) single-cell-level data on stem cell cardiogenic differentiation under in vivo-like cardiomyocyte alignment conditions.

Onset of a Cardiac Phenotype in the Early Embryo

Soon after fertilization, vertebrate embryos grow very rapidly. Thus, very early in gestation a sizeable yet underdeveloped organism requires circulating blood. This need dictates the early appearance of a contractile heart, which is the first functional organ in both the bird and mammalian embryos. Incipient heart tissue makes its arrival within the mesoderm layer during the onset of gastrulation. The process whereby nondifferentiated cells of primary mesoderm give rise to contractile cardiomyocytes is a subject that has greatly intrigued developmental biologists throughout the twentieth century. Since the early 1990s, a number of regulatory molecules have been identified that are important players in these events. Yet, how these molecular parts fit into the total story is still far from understood. In this chapter, we will discuss what is known about the morphological events that underlie the formation of the primitive heart, relate that information to the identification of candidate regulators of cardiogenesis in the early embryo (and description of their presumptive roles), and finally bring this information on cardiac development in context with the overall diversification of the primary mesoderm. Like many topics in biology, the study of cardiac development has profited both from tissue culture and in vivo experimentation. Because the onset of cardiogenesis occurs so early during embryogenesis, avian embryos have proven to be the most practical model system for studying these events in higher vertebrates, especially with regard to examining the behavior of precardiac tissue in isolation from the embryo. Thus, much of the discussion will be dominated by avian development. It has only been during recent years with the advent of transgenic and gene-targeted mice that mammalian models have made major contributions to our understanding of the primary events in cardiogenesis. Additionally, studies using frog and zebrafish embryos have contributed to this field. Surprisingly, an animal model that has yielded much information on early cardiogenesis is the fruit fly, Drosophila melanogaster. Despite the significant morphological differences between vertebrate and invertebrate hearts, there appears to be at least some homology of the molecular events that mold their respective cardiac tissue. Among vertebrate species, the molecular biology of early cardiogenesis seems to be totally conserved. This has allowed a fuller picture of early cardiogenesis to be compiled with information gathered from these various animal models, a cross-reference necessitated by the various strengths and weaknesses of each of the experimental systems.

Conditioned serum-free medium from umbilical cord mesenchymal stem cells has anti-photoaging properties

Chronic exposure to solar radiation is the primary cause of photoaging and benign and malignant skin tumors. A conditioned serum-free medium (SFM) was prepared from umbilical cord mesenchymal stem cells (UC-MSCs) and its anti-photoaging effect, following chronic UV irradiation in vitro and in vivo, was evaluated. UC-MSC SFM had a stimulatory effect on human dermal fibroblast proliferation and reduced UVA-induced cell death. In addition, UC-MSC SFM blocked UVA inhibition of superoxide dismutase activity. Topical application of UC-MSC SFM to mouse skin prior to UV irradiation blocked the inhibition of superoxide dismutase and glutathione peroxidase activities, and prevented the upregulation of malonaldehyde. UC-MSC SFM thus protects against photoaging induced by UVA and UVB radiation and is a promising candidate for skin anti-photoaging treatments.

Inhibition of Heart Formation by Lithium is an Indirect Result of the Disruption of Tissue Organization within the Embryo

Lithium is a commonly used drug for the treatment of bipolar disorder. At high doses, lithium becomes teratogenic, which is a property that has allowed this agent to serve as a useful tool for dissecting molecular pathways that regulate embryogenesis. This study was designed to examine the impact of lithium on heart formation in the developing frog for insights into the molecular regulation of cardiac specification. Embryos were exposed to lithium at the beginning of gastrulation, which produced severe malformations of the anterior end of the embryo. Although previous reports characterized this deformity as a posteriorized phenotype, histological analysis revealed that the defects were more comprehensive, with disfigurement and disorganization of all interior tissues along the anterior‐posterior axis. Emerging tissues were poorly segregated and cavity formation was decreased within the embryo. Lithium exposure also completely ablated formation of the heart and prevented myocardial cell differentiation. Despite the complete absence of cardiac tissue in lithium treated embryos, exposure to lithium did not prevent myocardial differentiation of precardiac dorsal marginal zone explants. Moreover, precardiac tissue freed from the embryo subsequent to lithium treatment at gastrulation gave rise to cardiac tissue, as demonstrated by upregulation of cardiac gene expression, display of sarcomeric proteins, and formation of a contractile phenotype. Together these data indicate that lithium’s effect on the developing heart was not due to direct regulation of cardiac differentiation, but an indirect consequence of disrupted tissue organization within the embryo.

G9a histone methyltransferase inhibitor BIX01294 promotes expansion of adult cardiac progenitor cells without changing their phenotype or differentiation potential

As a follow‐up to our previous reports showing that the G9a histone methyltransferase‐specific inhibitor BIX01294 enhances bone marrow cell cardiac potential, this drug was examined for its effects on cardiomyocytes and mouse cardiac progenitor cells (CPCs).

PATIENTS THAT RESPOND TO ENHANCED EXTERNAL COUNTERPULSATION ARE AT DECREASED RISK FOR MAJOR ADVERSE CARDIAC EVENTS AND HAVE INCREASES IN ENDOTHELIAL PRECURSOR STEM CELLS

Does improved exercise capacity after treatment with enhanced external counterpulsation (EECP) decrease the risk for major adverse cardiac events (MACE) by mobilizing endothelial precursor cells (EPC) to enhance coronary collateral circulation?nnForty consecutive patients with angina refractory to