Cardiac stem cells: at the heart of cell therapy

Micro- and nanoscale control of the cardiac stem cell niche for tissue fabrication

Advances in stem cell (SC) biology have greatly enhanced our understanding of SC self-renewal and differentiation. Both embryonic and adult SCs can be differentiated into a great variety of tissue cell types, including cardiac myocytes. In vivo studies and clinical trials, however, have demonstrated major limitations in reconstituting the myocardium in failing hearts. These limitations include precise control of SC proliferation, survival and phenotype both prior and subsequent to transplantation and avoidance of serious adverse effects such as tumorigenesis and arrhythmias. Micro- and nanoscale techniques to recreate SC niches, the natural environment for the maintenance and regulation of SCs, have enabled the elucidation of novel SC behaviors and offer great promise in the fabrication of cardiac tissue constructs. The ability to precisely manipulate the interface between biopolymeric scaffolds and SCs at in vivo scale resolutions is unique to micro- and nanoscale approaches and may help overcome limitations of conventional biological scaffolds and methods for cell delivery. We now know that micro- and nanoscale manipulation of scaffold composition, mechanical properties, and three-dimensional architecture have profound influences on SC fate and will likely prove important in developing the next generation of "transplantable SC niches" for regeneration of heart and other tissues. In this review, we examine two key aspects of micro- and nanofabricated SC-based cardiac tissue constructs: the role of scaffold composition and the role of scaffold architecture and detail how recent work in these areas brings us closer to clinical solutions for cardiovascular regeneration.

MUC1* mediates the growth of human pluripotent stem cells

The MUC1 protein is aberrantly expressed on an estimated 75% of all human solid tumor cancers. We recently reported that a transmembrane cleavage product, MUC1*, is the predominant form of the protein on cancer cells [1]. Further, our evidence indicated that MUC1* functions as a growth factor receptor on tumor cells, while the full-length protein appeared to have no growth promoting activity. Here, we report that MUC1* acts as a growth factor receptor on undifferentiated human embryonic stem cells (hESCs). Cleavage of the full-length ectodomain to form MUC1*, a membrane receptor, appears to make binding to its ligand, NM23, possible. Unexpectedly, we found that newly differentiated cells no longer express the cleaved form, MUC1*, or its ligand, NM23. Newly differentiated stem cells exclusively present full-length MUC1. Antibody-induced dimerization of the MUC1* receptor on hESCs stimulated cell growth to a far greater degree than currently used methods that require the addition of exogenous basic fibroblast growth factor (bFGF) as well as factors secreted by fibroblast “feeder cells”. Further, MUC1* mediated growth was shown to be independent of growth stimulated by bFGF or the milieu of factors secreted by feeder cells. Stimulating the MUC1* receptor with either the cognate antibody or its ligand NM23 enabled hESC growth in a feeder cell-free system and produced pluripotent colonies that resisted spontaneous differentiation. These findings suggest that this primal growth mechanism could be utilized to propagate large numbers of pluripotent stem cells for therapeutic interventions.