Embryonic and adult stem cell-derived cardiomyocytes: lessons from in vitro models

Small molecule cardiogenol C upregulates cardiac markers and induces cardiac functional properties in lineage-committed progenitor cells

BACKGROUND/AIMS

Cell transplantation into the heart is a new therapy after myocardial infarction. Its success, however, is impeded by poor donor cell survival and by limited transdifferentiation of the transplanted cells into functional cardiomyocytes. A promising strategy to overcome these problems is the induction of cardiomyogenic properties in donor cells by small molecules.

METHODS

Here we studied cardiomyogenic effects of the small molecule compound cardiogenol C (CgC), and structural derivatives thereof, on lineage-committed progenitor cells by various molecular biological, biochemical, and functional assays.

RESULTS

Treatment with CgC up-regulated cardiac marker expression in skeletal myoblasts. Importantly, the compound also induced cardiac functional properties: first, cardiac-like sodium currents in skeletal myoblasts, and secondly, spontaneous contractions in cardiovascular progenitor cell-derived cardiac bodies.

CONCLUSION

CgC induces cardiomyogenic function in lineage-committed progenitor cells, and can thus be considered a promising tool to improve cardiac repair by cell therapy.

2D and 3D self-assembling nanofiber hydrogels for cardiomyocyte culture

Collagen is a widely used biomaterial in cardiac tissue engineering studies. However, as a natural material, it suffers from variability between batches that can complicate the standardization of culture conditions. In contrast, synthetic materials are modifiable, have well-defined structures and more homogeneous batches can be produced. In this study, several collagen-like synthetic self-assembling nanofiber hydrogels were examined for their suitability for cardiomyocyte culture in 2D and 3D. Six different nanofiber coatings were used in the 2D format with neonatal rat cardiomyocytes (NRCs) and human embryonic stem-cell-derived cardiomyocytes (hESC-CMs). The viability, growth, and functionality of the 2D-cultured cardiomyocytes were evaluated. The best-performing nanofiber coatings were selected for 3D experiments. Hydrophilic pH-sensitive nanofiber hydrogel coassembled with hyaluronic acid performed best with both NRCs and hESC-CMs. Hydrophilic non-pH-sensitive nanofiber hydrogels supported the growth of NRCs; however, their ability to promote attachment and growth of hESC-CMs was limited. NRCs also grew on hydrophobic nanofiber hydrogels; however, the cell-supporting capacity of these hydrogels was inferior to that of the hydrophilic hydrogel materials. This is the first study demonstrating that hydrophilic self-assembling nanofiber hydrogels support the culture of both NRCs and hESC-CMs, which suggests that these biomaterials hold promise for cardiac tissue engineering.

Labeling human embryonic stem-cell-derived cardiomyocytes for tracking with MR imaging

BACKGROUND

Human embryonic stem cells (hESC) can generate cardiomyocytes (CM), which offer promising treatments for cardiomyopathies in children. However, challenges for clinical translation result from loss of transplanted cell from target sites and high cell death. An imaging technique that noninvasively and repetitively monitors transplanted hESC-CM could guide improvements in transplantation techniques and advance therapies.

OBJECTIVE

To develop a clinically applicable labeling technique for hESC-CM with FDA-approved superparamagnetic iron oxide nanoparticles (SPIO) by examining labeling before and after CM differentiation.

MATERIALS AND METHODS

Triplicates of hESC were labeled by simple incubation with 50 μg/ml of ferumoxides before or after differentiation into CM, then imaged on a 7T MR scanner using a T2-weighted multi-echo spin-echo sequence. Viability, iron uptake and T2-relaxation times were compared between groups using t-tests.

RESULTS

hESC-CM labeled before differentiation demonstrated significant MR effects, iron uptake and preserved function. hESC-CM labeled after differentiation showed no significant iron uptake or change in MR signal (P < 0.05). Morphology, differentiation and viability were consistent between experimental groups.

CONCLUSION

hESC-CM should be labeled prior to CM differentiation to achieve a significant MR signal. This technique permits monitoring delivery and engraftment of hESC-CM for potential advancements of stem cell-based therapies in the reconstitution of damaged myocardium.

Labeling human embryonic stem cell-derived cardiomyocytes with indocyanine green for noninvasive tracking with optical imaging: an FDA-compatible alternative to firefly luciferase

Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) have demonstrated the ability to improve myocardial function following transplantation into an ischemic heart; however, the functional benefits are transient possibly due to poor cell retention. A diagnostic technique that could visualize transplanted hESC-CMs could help to optimize stem cell delivery techniques. Thus, the purpose of this study was to develop a labeling technique for hESCs and hESC-CMs with the FDA-approved contrast agent indocyanine green (ICG) for optical imaging (OI). hESCs were labeled with 0.5, 1.0, 2.0, and 2.5 mg/ml of ICG for 30, 45, and 60 min at 37 degrees C. Longitudinal OI studies were performed with both hESCs and hESC-CMs. The expression of surface proteins was assessed with immunofluorescent staining. hESCs labeled with 2 mg ICG/ml for 60 min achieved maximum fluorescence. Longitudinal studies revealed that the fluorescent signal was equivalent to controls at 120 h postlabeling. The fluorescence signal of hESCs and hESC-CMs at 1, 24, and 48 h was significantly higher compared to precontrast data (p < 0.05). Immunocytochemistry revealed retention of cell-specific surface and nuclear markers postlabeling. These data demonstrate that hESCs and hESC-CMs labeled with ICG show a significant fluorescence up to 48 h and can be visualized with OI. The labeling procedure does not impair the viability or functional integrity of the cells. The technique may be useful for assessing different delivery routes in order to improve the engraftment of transplanted hESC-CMs or other stem cell progenitors.

A photopolymerizable hydrogel for 3-D culture of human embryonic stem cell-derived cardiomyocytes and rat neonatal cardiac cells

The purpose of this study was to assess the in vitro ability of two types of cardiomyocytes (cardiomyocytes derived from human embryonic stem cells (hESC-CM) and rat neonatal cardiomyocytes (rN-CM)) to survive and generate a functional cardiac syncytium in a three-dimensional in situ polymerizable hydrogel environment. Each cell type was cultured in a PEGylated fibrinogen (PF) hydrogel for up to two weeks while maturation and cardiac function were documented in terms of spontaneous contractile behavior and biomolecular organization. Quantitative contractile parameters including contraction amplitude and synchronization were measured by non-invasive image analysis. The rN-CM demonstrated the fastest maturation and the most significant spontaneous contraction. The hESC-CM maturation occurred between 10-14 days in culture, and exhibited less contraction amplitude and synchronization in comparison to the rN-CMs. The maturation of both cell types within the hydrogels was confirmed by cardiac-specific biomolecular markers, including alpha-sarcomeric actin, actinin, and connexin-43. Cellular responsiveness to isoproterenol, carbamylcholine and heptanol provided further evidence of the cardiac maturation in the 3-D PF hydrogel as well as identified a potential to use this system for in vitro drug screening. These findings indicate that the PF hydrogel biomaterial can be used as an in situ polymerizable biomaterial for stem cells and their cardiomyocyte derivatives.

Time-lapse analysis and microdissection of living 3D melanoma cell cultures for genomics and proteomics

A novel technique is presented for the monitoring and morphological characterization of 3D cell cultures targeted for laser capture microdissection (LCM). A custom-made chamber enables time-lapse topography and pre-selection of cell targets in order to minimize microdissection time, optimizing the quality of biomolecules for downstream analyses. The method complements the recently presented novel application of LCM in living 3D cultures, whose compatibility with standard genomics and proteomics assays such as microarrays, real-time PCR, and 2D gel electrophoresis is further corroborated here. Specifically, the above techniques are employed in tandem to study, as a proof of principle, the dynamics of in vitro vasculogenic mimicry. It was shown previously that aggressive melanoma cells spontaneously differentiate on collagen gels into vascular-like networks with strong endogenous angiogenic potential. Here the evolution of vasculogenic mimicry was quantified by three time-dependent variables: the distribution of the vascular-like network lengths, widths, and area coverage. Based on these morphological descriptors the networks were locally classified over time as "early" or "mature" stage. LCM of networks and randomly oriented cells followed by real-time PCR for select genes revealed that differential expression was time-dependent and increased with network maturity. The method is widely applicable for microgenomics and microproteomics analyses in phenotypically evolving 3D cultures (i.e., of stem cells), under spontaneous or directed differentiation. Therefore beyond enabling future rigorous analyses on the mechanistics of vasculogenic mimicry, it provides a practical discovery engine for a range of developmental studies and tissue regenerative engineering applications.

Involvement of NF-kappaB and AP-1 activation in icariin promoted cardiac differentiation of mouse embryonic stem cells

Icariin has been reported to facilitate the differentiation of mouse embryonic stem (ES) cells into cardiomyocytes; however, the mechanism on cardiomyogenic cell lineage differentiation has not been fully elucidated yet. In the present studies, an underlying signaling network including p38, extracellular signal-regulated kinase 1, 2 (ERK1, 2), nuclear factor-kappaB (NF-kappaB), activator protein-1 (AP-1) transcription factors c-jun and c-fos was assumed in icariin induced cardiomyogenesis. Icariin rapidly activated p38 and ERK1, 2 in embryoid bodies, treatment with p38 antagonist 4-(4-Fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole (SB203580) or ERK1, 2 inhibitor 1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio] butadiene (U0126) significantly abolished icariin induced cardiac commitment, MEF2C gene expression and nuclear translocation, as well as cardiac-specific protein alpha-actinin expression, indicating that p38 and ERK1, 2 are specifically involved in icariin stimulated cardiomyogenic cell lineage differentiation of ES cells. Further, IkappaBalpha phosphorylation and NF-kappaB p65 translocation to the nucleus appeared rapidly when embryoid bodies exposed to icariin, and the expression of IkappaBalpha or NF-kappaB p65 in cytoplasm was decreased concomitantly. Moreover, icariin increased c-jun and c-fos mRNA and protein expression. Either SB203580 or U0126 displayed inhibitory effect on icariin induced NF-kappaB and AP-1 activation. It could be concluded that p38 and ERK1, 2 are activated in a coordinated manner, which in turn contribute to NF-kappaB and AP-1 activation in icariin induced cardiomyogenic cell lineage differentiation of mouse ES cells.