There are several growth factors responsible for epithelial repair. Preliminary studies using recombinant growth factors seem promising in IBD preclinical and clinical trials.

Embryonic Stem Cells (ESCs) hold great potential for regeneration of damaged myocardium, however the molecular circuitry that guides ESC differentiation into cardiomyocytes remains poorly understood. This is exemplified by the elusive role of the transcription factor, Foxc1, during cardiac development. The only known Foxc1 target during heart development is Tbx1. Because Foxc1 null mice contain heart mutations that are far more severe than Tbx1 null mice, it is likely that Foxc1 has additional regulatory roles during heart development. The goal of our study was to test whether Foxc1 is critical for ESC differentiation into functional cardiomyocytes through proper regulation of specific downstream gene networks. Converging evidence from Foxc1 deficient and overexpression ESC models reveals a close relationship between Foxc1 levels and early cardiomyogenic factors Isl1, Mef2c, and Nkx2.5 and also the production of functional cardiomyocytes. We show Foxc1 regulates early cardiomyogenesis during a specific window of differentiation, D4-D6. Through whole transcriptome RNA-sequencing analysis, we report pathways regulated by Foxc1 involved in cardiac function including actin cytoskeleton, cell adhesion, tight and gap junctions, and calcium signaling. Our data indicate a novel Foxc1 direct gene target, Myh7, which encodes the predominant myosin heavy chain isoform, MHCb, expressed during cardiac development. These data lead us to conclude that Foxc1 regulates both early cardiomyogenesis and the functional properties of ESC-derived cardiomyocytes. Our findings shed light on the molecular circuitry governing cardiomyogenesis that may lead to the development of better translational strategies for the use of pluripotent stem cells in regenerative medicine towards repairing damaged myocardium. STEM CELLS 2016;34:1487-1500 SIGNIFICANCE STATEMENTHeart attacks and high blood pressure cause death of cardiomyocytes (CMs), the cells of the heart that are required to communicate together allowing the heart to contract and relax. CMs have a very low capacity to regenerate and therefore many studies have focused attention on embryonic stem cells (ESCs) as a source of CMs to regenerate the heart. However the mechanisms that guide ESCs to become CMs are not fully understood. Our study has identified a factor that enhances the production of CMs from ESCs. Additionally we demonstrate their ability to communicate with neighboring CMs allowing them to contract and relax in unison indicating their potential for future heart therapies.

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Exosomes transport biologically active cargo (e.g., proteins and microRNA) between cells, including many of the paracrine factors that mediate the beneficial effects associated with stem-cell therapy. Stem cell derived exosomes, in particular mesenchymal stem cells (MSCs), have been shown previously to largely replicate the therapeutic activity associated with the cells themselves, which suggests that exosomes may be a useful cell-free alternative for the treatment of cardiovascular disorders. However, the mechanisms that govern how exosomes home to damaged cells and tissues or the uptake and distribution of exosomal cargo are poorly characterized, because techniques for distinguishing between exosomal proteins and proteins in the targeted tissues are lacking. Here, we report the development of an in vivo model that enabled the visualization, tracking, and quantification of proteins from systemically administered MSC exosomes. The model uses bioorthogonal chemistry and cell-selective metabolic labeling to incorporate the non-canonical amino acid azidonorleucine (ANL) into the MSC proteome. ANL incorporation is facilitated via expression of a mutant (L274G) methionyl-tRNA-synthetase (MetRS∗) and subsequent incubation with ANL-supplemented media; after which ANL can be covalently linked to alkyne-conjugated reagents (e.g., dyes and resins) via click chemistry. Our results demonstrate that when the exosomes produced by ANL-treated, MetRS∗-expressing MSCs were systemically administered to mice, the ANL-labeled exosomal proteins could be accurately and reliably identified, isolated, and quantified from a variety of mouse organs, and that myocardial infarction (MI) both increased the abundance of exosomal proteins and redistributed a number of them from the membrane fraction of intact hearts to the cytosol of cells in infarcted hearts. Additionally, we found that Desmoglein-1c is enriched in MSC exosomes and taken up by ischemic myocardium. Collectively, our results indicate that this newly developed bioorthogonal system can provide crucial insights into exosome homing, as well as the uptake and biodistribution of exosomal proteins.