Extracellular vesicles from endothelial colony forming cells in the repair of ischemic retinal disease
Current treatments for ischemic retinopathies inhibit vascular leakage and proliferation in late-stage disease but do nothing to repair dysfunctional vasculature or alleviate the underlying causes of the ischemia/inflammation that drives pathological neovascularization. Stimulation of functional, physiologic vascular growth and stability is a promising alternative therapeutic approach that may be achieved by the use of endothelial progenitor cells called endothelial colony forming cells (ECFCs). Chapter 1 of this dissertation describes the characterization of ECFCs in an historical context and details the mechanisms mediating their neurovasculotrophic effects in the retina as well as other tissues. ECFCs differentiate into endothelial cells and can directly integrate into host vasculature, replacing lost or damage endothelial cells in vivo; ECFCs can also achieve their therapeutic effect by paracrine action. Extracellular vesicles (EVs) shed from ECFCs (EVsECFCs) have been newly identified as one such paracrine mechanism. Loaded with diverse cargo including proteins, RNA, and lipids, EVsECFCs facilitate intercellular communication and, through multiple mechanisms, may provide a novel approach for the treatment of complex retinal disorders. EVs’ role in retinal physiology and pathophysiology are discussed in Chapter 2, which outlines research using several animal disease models to investigate possible mechanisms of EVECFCs-based treatment for ischemic retinopathies.
Chapter 3 describes the laboratory research that forms the basis for my dissertation. This body of work exploits our lab’s recent publication demonstrating that ECFCs are not a homogeneous group of cells. ECFCs with high expression of CD44 hyaluronan receptor (CD44hi ECFCs) demonstrate superior rescue effects in mouse models of ischemic retinopathy and retinal degeneration when compared to ECFCs with low CD44 expression (CD44lo ECFCs). This dissertation research demonstrated that the superior effect of CD44hi ECFCs was attributable, at least in part, to bioactive microRNA (miR) cargo in EVs released from CD44hi ECFCs (EVshi). EVshi recapitulated rescue effects of CD44hi ECFCs; EVs from CD44lo ECFCs (EVslo) did not. Using small RNA sequencing to compare intravesicular miR within EVshi to EVslo and subsequent in vivo functional validation, candidate miRs mediating the augmented therapeutic effect of EVshi were identified.
Freestanding chapters 4 and 5 are reprints of publications I have co-authored during my PhD.
Overall, this dissertation describes the utility of ECFCs and their EVs in treating complex retinal diseases and provides novel insight into the neurovasculotrophic mechanisms of EVshi, bringing this therapy closer to clinical translation.