Molecular mechanisms of extracellular vesicle-induced vessel destabilization in diabetic retinopathy

Diabetic retinopathy (DR) is characterized by early dropout of capillary pericytes, leading to loss of control on endothelial proliferation and, subsequently, angiogenesis. We have demonstrated that extracellular vesicles (EV) derived from mesenchymal stem cells (MSC) maintained in diabetic-like conditions may play a role in vessel destabilization, thus contributing to angiogenesis through paracrine signalling. In particular, a role for MMP-2 was described. This study was aimed at further investigating the molecular mechanisms of EV-induced vessel destabilization. We evaluated miR-126 expression, the subsequent HIF-1 alpha and VEGF modulation, Ang-2 and PDGF signalling pathways in human retinal pericytes (HRP) after exposure to MSC-derived EV obtained in diabetic-like conditions (high glucose and/or hypoxia). HRP express miR-126, and this expression is down-regulated in intermittent high glucose. MSC-derived EV obtained in hyperglycaemic/hypoxic conditions down-regulate miR-126 expression in pericytes, leading to increased expression of angiogenic molecules, such as VEGF and HIF-1 alpha. No modulation of Ang-2 and PDGF signalling pathways in pericytes was observed following EV exposure. HRP express miR-126, and this expression is down-regulated in diabetic-like conditions. Exposure of HRP to EV obtained in diabetic-like conditions is able to decrease miR-126 expression, consistently with previous observations of its involvement in DR and providing further insights into the role of EV in vessel destabilization. In contrast, PDGF and Ang-2 signalling pathways do not seem to be involved in these mechanisms.