Tissue Engineering of Vascularized Cardiac Muscle From Human Embryonic Stem Cells

Abstract:
Transplantation of a tissue-engineered heart muscle represents a novel experimental therapeutic paradigm for myocardial diseases. However, this strategy has been hampered by the lack of sources for human cardiomyocytes and by the scarce vasculature in the ischemic area limiting the engraftment and survival of the transplanted muscle. Beyond the necessity of endothelial capillaries for the delivery of oxygen and nutrients to the grafted muscle tissue, interactions between endothelial and cardiomyocyte cells may also play a key role in promoting cell survival and proliferation. In the present study, we describe the formation of synchronously contracting engineered human cardiac tissue derived from human embryonic stem cells containing endothelial vessel networks. The 3D muscle consisted of cardiomyocytes, endothelial cells (ECs), and embryonic fibroblasts (EmFs). The formed vessels were further stabilized by the presence of mural cells originating from the EmFs. The presence of EmFs decreased EC death and increased EC proliferation. Moreover, the presence of endothelial capillaries augmented cardiomyocyte proliferation and did not hamper cardiomyocyte orientation and alignment. Immunostaining, ultrastructural analysis (using transmission electron microscopy), RT-PCR, pharmacological, and confocal laser calcium imaging studies demonstrated the presence of
cardiac-specific molecular, ultrastructural, and functional properties of the generated tissue constructs with synchronous activity mediated by action potential propagation through gap junctions. In summary, this is the first report of the construction of 3D vascularized human cardiac tissue that may have unique applications for studies of cardiac development, function, and tissue replacement therapy.

Response:
It is without a doubt that there is need for artificial tissue and organs to battle against a myriad of human problems and complications with the body. It was amazing to me how this engineered heart tissue (EHT) was shown to beat and pulse synchronously and show similarities to that of real human hearts. This particular article interested me because they were able to create the first 3D, vascularized human cardiac tissue, which has multiple implications-- using it as a model for studying the human heart in vitro, as well as a huge advancement in tissue replacement therapy. This vascularization is important because all previous EHTs showed poor survival of seeded cells (myocytes) in the scaffold. Caspi then hypothesized that seeding endothelial cells, as well as embryonic fibroblasts, will improve vascularization in the EHT and improve cardiomyocyte growth and viability. Immunohistochemistry was used to show that the tri-cultured scaffolds had a higher density of vascularization, and immunoflourescent staining was used to show that the vascular networks in these scaffolds showed structural organization. RT-PCR was used to show that the cardiomyocytes in the tri-cultured scaffold were mature and differentiated-- more so than the controls. Other assays were used to analyze cell growth and viability, but you can read the paper for that. So, I thought this was a pretty thorough and well-done experiment with very promising potentials in the medical and research world. The only problem I had with it was that they don't go into how the addition of EC's and EmF's promote vascularization and survival--that is, the interactions, signalling pathways, etc. that allow for this to happen, but it is mentioned that this particular topic is currently being researched and offers potential answers.