Background: Age-related macular degeneration (AMD) is the main cause of
irreversible blindness in the elderly. Oxidative stress in retinal pigment epithelium (RPE)
is deemed to play a pivotal role in the pathogenesis of AMD. miR-25 functions as an
essential modulator in response to oxidative-stress in several cell types, but its function
in RPE cells is poorly understood.
Objective: To explore the roles of miR-25 in RPE cells and in the development of AMD.
Methods: A rat model of retinal degeneration was induced by sodium iodate (SI).
Subretinal injection of antagomiR-25 was performed for the intervention while the
scramble as control. Visual responses were recorded with Electroretinogram (ERG).
TUNEL assay was performed to detect apoptosis. Phagosome quantification in vivo was
performed to evaluate RPE cell function. Oxygen-glucose deprivation treatment was
performed to mimic in vitro oxidative stress. Gene expression at mRNA level and protein
level were performed by quantitative polymerase chain reaction (qPCR) and Western
Blot, respectively. The pigment epithelium derived factor (PEDF) level in the cultured
medium was measured by Enzyme-linked immunosorbent assay (ELISA). The
interaction between miR-25 and integrin αV (IGTAV) / PEDF 3’UTR was examined by
dual luciferase assay. Chromatin immunoprecipitation (ChIP) assay was performed to
examine its transcriptional regulation of miR-25.
Results: Oxidative stress up-regulated miR-25 in RPE cells in very early stage,
accompanied by decreased phagocytosis and reduced growth factor secretion in those
cells. Such changes preceded RPE cell apoptosis and visual impairment in the SItreated
rats. Furthermore, antagomiR-25 intervention effectively rescued RPE cells from
degeneration in such model. The increased miR-25 was confirmed to mediate RPE
degeneration through direct targeting IGTAV and PEDF. On the other hand, upstream,
miR-25 was found to be up-regulated by STAT3 signaling under oxidative stress in both
in vivo and in vitro models.
Conclusion: Our findings demonstrate that, in SI-treated rats, oxidative stress activates
STAT3 signaling which up-regulates miR-25 expression, in a very early stage. The
increased miR-25 then inhibits ITGAV and PEDF expressions, resulting in RPE
phagocytosis dysfunction and then RPE apoptosis and visual impairment as observed in
patients with AMD. These findings lead us to a better understanding of AMD
pathogenesis, and suggest that miR-25 could be a potential therapeutic target for
oxidative stress related RPE diseases, like AMD.