Glycogen Synthase Kinase-3β and Cathepsin B in Diabetic Endothelial Progenitor Cell Dysfunction: An Old Player Finds a New Partner

Abstract

Microvascular and macrovascular complications associated with type 2 diabetes are leading causes of morbidity and mortality. In fact, cardiovascular (CV) complications account for a major portion of health care costs in patients with diabetes. Although lifestyle changes and pharmacotherapy aimed at CV disease risk factor modification are the mainstay of medical treatment, revascularization (surgical and endovascular) is often necessary to restore tissue perfusion and function. Indeed, nearly 25% of coronary revascularization procedures performed in the U.S. occur in individuals with diabetes (1). Furthermore, diffuse atherosclerosis, impaired ability to form vascular collaterals, and restenosis contribute to higher rates of repeat revascularization in these patients (1). Consequently, cell-based therapy with bone marrow cells and endothelial progenitor cells (EPCs) aimed at inducing angiogenesis and reendothelialization is a promising strategy that is under active investigation in both preclinical and clinical studies (2,3). EPCs constitute a very small subset of circulating blood cells. They are progenitors of endothelial cells and have the ability to proliferate and differentiate to form perfused blood vessels in vivo and tube-like structures in vitro (4). EPC-induced neovascularization in response to tissue hypoxia and injury is a highly coordinated, temporally regulated, and complex set of events that involves mobilization, migration, and homing of EPCs to the target tissue (5,6). Endothelial injury and hypoxia activate the transcription factor hypoxia-induced factor (HIF) to initiate the expression and release of growth factors and chemokines. These include stromal cell–derived factor 1 (SDF-1), vascular endothelial growth factor (VEGF), c-Kit ligand (or SCF), angiopoietin, and interleukin-8 (IL-8), among others (5,6). Platelet aggregation leads to high levels of platelet-derived SDF-1 at the site of endothelial injury (7). EPCs are retained in the bone marrow in distinct niches by their interaction with stromal cells. …