Restoring the Final Frontier: Exosomal MicroRNA and Cutaneous Wound Repair

Abstract

Non-healing wounds present a major healthcare challenge associated with the ageing population, the rising incidence of diabetes and the obesity epidermic. Driven by the need to expand therapeutic options for the treatment of such wounds, a large body of evidence has emerged in recent years demonstrating that microRNAs (miRNAs) modulate various aspects of cutaneous wound healing through effects on diverse cell types, including keratinocytes, fibroblasts, endothelial cells and macrophages. However, clear translational pathways for non-invasive cutaneous delivery of miRNAs to facilitate wound repair have not yet been established. The recognition that miRNAs can be actively partitioned into extracellular vesicles (EVs)—exosomes, microvesicles and apoptotic bodies—has stimulated research into the regulation, function and translational exploitation of EV-derived miRNAs both as a novel mode of intercellular signalling and as a tool for miRNA transfer to cells for therapeutic purposes. In particular, because mesenchymal stem cells (MSCs) were found to support wound healing, there is much interest in the therapeutic potential of EVs, especially exosomes, derived from these cells. In this review, we survey some of the main mesenchymal stem cells (MSCs) for which exosomal miRNAs have been evaluated in the context of skin repair, including exosomes from adipose-derived MSCs, bone MSCs, amniotic MSCs and umbilical cord MSCs. Epithelial stem cell (EPSC)-derived exosomes are also considered, from keratinocytes and epidermal stem cells. The picture that emerges from studies on exosomes from various cell types reveal they share a limited set of exosomal miRNAs enhancing wound repair. We suggest a need for direct comparison of exosomal miRNA profiles from a range of MSCs and EPSCs. The ability of exogenous exosomal miRNAs to promote healing of chronic diabetic wounds also warrants further attention in order to more fully establish their therapeutic potential.