Type 1 diabetes is associated with reduced vascular repair, as indicated by impaired wound healing and reduced collateral formation in ischemia. Recently, endothelial progenitor cells (EPCs) have been identified as important regulators of these processes. We therefore explored the concept that EPCs are dysfunctional in diabetes. The number of EPCs obtained from type 1 diabetic patients in culture was 44% lower compared with age-and sex-matched control subjects (P < 0.001). This reduction was inversely related to levels of HbA 1c (R ‫؍‬ ؊0.68, P ‫؍‬ 0.01). In addition, we demonstrated that patient EPCs were also impaired in function using an in vitro angiogenesis assay. Conditioned media from patient EPCs were significantly reduced in their capacity to support endothelial tube formation in comparison to control EPCs. Therefore, despite culturing the EPCs under normoglycemic conditions, functional differences between patient and control EPCs were maintained. Our findings demonstrate that adverse metabolic stress factors in type 1 diabetes are associated with reduced EPC numbers and angiogenicity. We hypothesize that EPC dysfunction contributes to the pathogenesis of vascular complications in type 1 diabetes. Diabetes 53: 195

BackgroundThe healthy vascular endothelium, which forms the barrier between blood and the surrounding tissues, is known to efficiently respond to stress signals like hypoxia and inflammation by adaptation of cellular physiology and the secretion of (soluble) growth factors and cytokines. Exosomes are potent mediators of intercellular communication. Their content consists of RNA and proteins from the cell of origin, and thus depends on the condition of these cells at the time of exosome biogenesis. It has been suggested that exosomes protect their target cells from cellular stress through the transfer of RNA and proteins. We hypothesized that endothelium-derived exosomes are involved in the endothelial response to cellular stress, and that exosome RNA and protein content reflect the effects of cellular stress induced by hypoxia, inflammation or hyperglycemia.MethodsWe exposed cultured endothelial cells to different types of cellular stress (hypoxia, TNF-α-induced activation, high glucose and mannose concentrations) and compared mRNA and protein content of exosomes produced by these cells by microarray analysis and a quantitative proteomics approach.ResultsWe identified 1,354 proteins and 1,992 mRNAs in endothelial cell-derived exosomes. Several proteins and mRNAs showed altered abundances after exposure of their producing cells to cellular stress, which were confirmed by immunoblot or qPCR analysis.ConclusionOur data show that hypoxia and endothelial activation are reflected in RNA and protein exosome composition, and that exposure to high sugar concentrations alters exosome protein composition only to a minor extend, and does not affect exosome RNA composition.

Key Points Endothelial cells secrete exosomes containing miR-214, which suppress senescence and stimulates an angiogenic program in target cells. Exosomal miR-214 regulates ataxia telangiectasia mutated expression in recipient endothelial cells.

Extracellular vesicles (EV) consist of exosomes, which are released upon fusion of the multivesicular body with the cell membrane, and microvesicles, which are released directly from the cell membrane. EV can mediate cell–cell communication and are involved in many processes, including immune signaling, angiogenesis, stress response, senescence, proliferation, and cell differentiation. The vast amount of processes that EV are involved in and the versatility of manner in which they can influence the behavior of recipient cells make EV an interesting source for both therapeutic and diagnostic applications. Successes in the fields of tumor biology and immunology sparked the exploration of the potential of EV in the field of regenerative medicine. Indeed, EV are involved in restoring tissue and organ damage, and may partially explain the paracrine effects observed in stem cell-based therapeutic approaches. The function and content of EV may also harbor information that can be used in tissue engineering, in which paracrine signaling is employed to modulate cell recruitment, differentiation, and proliferation. In this review, we discuss the function and role of EV in regenerative medicine and elaborate on potential applications in tissue engineering.

The adult mammalian heart has limited regenerative capacity and was generally considered to contain no dividing cells. Recently, however, a resident population of progenitor cells has been identified, which could represent a new source of cardiomyocytes. Here, we describe the efficient isolation and propagation of human cardiomyocyte progenitor cells (hCMPCs) from fetal heart and patient biopsies. Establishment of hCMPC cultures was remarkably reproducible, with over 70% of adult atrial biopsies resulting in robustly expanding cell populations. Following the addition of transforming growth factor beta, almost all cells differentiated into spontaneously beating myocytes with characteristic cross striations. hCMPC-derived cardiomyocytes showed gap-junctional communication and action potentials of maturing cardiomyocytes. These are the first cells isolated from human heart that proliferate and form functional cardiomyocytes without requiring coculture with neonatal myocytes. Their scalability and homogeneity are unique and provide an excellent basis for developing physiological, pharmacological, and toxicological assays on human heart cells in vitro.