Abstract
Purpose :
Nrf2 acts as a master regulatory factor with cytoprotective antioxidant and anti-inflammatory properties. We have found that Nrf2 plays a protective role in retinal ischemia-reperfusion injury, diabetic retinopathy and oxygen-induced retinopathy (OIR). In a recent study, we demonstrated that Nrf2 promotes reparative angiogenesis via modulation of NADPH oxidase-2 (NOX2) in OIR. The objective of this study was to gain insights into the mechanism by which pharmacologic activation of Nrf2 promotes revascularization in OIR.
Methods :
Mice were subjected to 75% oxygen from postnatal day 7 (P7) to 12, followed by return to room air. Mice received intravitreal injection with 1 μL 24 nM CDDO-Im at P12 and P14. The human Müller cell line MIO-M1 was pretreated with CDDO-Im for 18h, followed by stimulation with Lipopolysaccharide (LPS). Quantitative RT-PCR was used to assess mRNA expression. Human retinal endothelial cells (HREC) were transfected with siRNA for 24 hours and then seeded on collagen for tube formation assay.
Results :
Pharmacologic Nrf2 activation by CDDO-Im increased revascularization and suppressed pathologic neovascularization at OIR P17. CDDO-Im treatment induced Nrf2 target gene expression while suppressing NOX2 and inflammatory cytokines. Pretreatment with CDDO-Im suppressed LPS-induced IL-1β, CCL2, and ICAM1 mRNA levels in a dose-dependent fashion in MIO-M1 cells. Retinas from mice treated with CDDO-Im exhibited decreased Sema6A mRNA levels. Plexin A2 (PlxnA2), a receptor for Sema6A, was detected in retinal blood vessels in OIR. Extracellular Sema6A treatment resulted in decreased HREC tube formation, and this effect was abrogated by siRNA-mediated knockdown of PlxnA2.
Conclusions :
These studies suggest that activation of Nrf2 suppresses inflammation and Sema6A/PlxnA2 signaling, which may play a key role in mediating enhanced revascularization by CDDO-Im treatment in OIR.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.