Background: Hypercholesterolemia is an atherosclerotic condition associated with endothelial dysfunction and impaired neovascularization in response to ischemia. This study sought to define the role of the anti-inflammatory microRNA-146b (miR-146b) in that pathophysiology.
Methods and results: qRT-PCR analyses showed that the expression of miR-146b is significantly reduced in the ischemic muscles of hypercholesterolemic ApoE-deficient (ApoE-/-) mice, and in HUVECs exposed to oxLDL. Inhibition of miR-146b (antimiR-146b) in native HUVECs impairs angiogenesis in vitro. On the other hand, forced expression of miR-146b using a miR mimic can rescue oxLDL-mediated impairment of endothelial cell migration and tubule formation. Using a mouse model of hindlimb ischemia, we found that intramuscular injection of miR-146b mimic restores blood flow recuperation, increases vascular densities in ischemic muscles, and reduces ischemic damages in hypercholesterolemic ApoE-/- mice. In addition, miR-146b treatment also increases the number and the functional activities of pro-angiogenic cells (PACs). Specific luciferase assays in HUVECs indicate that TNFa-associated-factor-6 (TRAF6) is a direct target of miR-146b, and that this pathway is involved in the anti-inflammatory and angiogenic effects of miR-146b. Moreover, in atherosclerotic conditions, miR-146b treatment of HUVECs in vitro and ischemic muscles in vivo can prevent the induction of TRAF6 and the downstream activation of inflammatory factors such as TNFa and VCAM1.
Conclusions: Hypercholesterolemia is associated with reduced expression of miR-146b, increased activation of pro-inflammatory factors and inefficient neovascularisation in response to ischemia. Forced expression of miR-146b using a miR mimic could constitute a novel therapeutic strategy to reduce inflammation and improve ischemia-induced neovascularization in atherosclerotic conditions.