Nrf2 activation has been shown to alleviate many pathological mechanisms associated with age-related diseases, particularly neurodegenerative diseases.
37,38 In angiogenesis-related diseases, Nrf2 acts as both a positive and a negative regulator.
39–41 In cancer, Nrf2 promotes cancer progression.
39,42,43 In contrast, Nrf2 in retinas decreases pathological angiogenesis.
44 Genetically, Nrf2 deletion disturbed vascular regrowth and increased pathological angiogenesis.
41 In the present study, we also clarified that Nrf2 activator decreased endothelial cell migration (
Fig. 1) and pathological angiogenesis in the OIR model (
Fig. 2). Tan et al.
45 indicated that increasing the expression of Nrf2-regulated antioxidant genes improved ischemic retinopathy by attenuating capillary vaso-obliteration and neovascularization in the OIR model. These results agree with previous reports on retinas. In Nrf2 knockout murine retina, proangiogenic factors and inflammatory factors are upregulated.
44 Specifically, proangiogenic factors such as hypoxia-inducible factor (HIF)-1α, VEGF, semaphorin (SEMA) 6A, and Notch signaling are increased.
41,44 As shown in
Figure 3, our data and these previous reports are not mutually exclusive. Moreover, another Nrf2 activator, dh404, decreased VEGF expression and improved glial cell expression in retinas.
46,47 It has been reported that retinal microglia cells contributed to vascular angiogenesis and vasculopathy induced by relative hypoxia.
48,49 Interestingly, RS9 has no influence on physiological neovascularization (
Figs. 2F–H). Nrf2 activation might inhibit pathophysiological neovascularization without side effects. Our research group
31 has previously reported that addition of RS9 significantly increased expression of Nrf2 in the nucleus of photoreceptors and showed no cytotoxicity. Although we did not examine the effect of RS9 on the normal retina in vivo, it can be estimated from previous in vitro data that RS9 increases the expression of Nrf2 and does not show toxicity in the normal retina. Furthermore, the overexpression of Nrf2 by RS9 in the normal retina might show hyperpermeability and/or an angiogenesis-preventing effect in the retina. In fact, we confirmed the cell toxicity of RS in HRMECs (
Supplementary Fig. S1). Based on our results, we speculated that Nrf2 activation normalized retinal angiogenic factors in pathological conditions, inhibited ocular neovascularization and hyperpermeability, and might also improve the expression and activation of retinal glial cells. These findings comprehensively indicate that Nrf2 activation could help improve symptoms.