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Objective To investigate the role and underlying mechanism of protein arginine methyltransferase 1 (PRMT1) and its inhibitor in alkali burn-induced corneal neovascularization (CNV).
Methods Seventy-two SPF-grade C57BL/6 mice were randomly divided into a normal group and 1 day post-modeling, 4 days post-modeling, and 7 days post-modeling groups to establish an alkali burn-induced CNV model and determine the optimal time point for analysis.Another 90 mice were randomly assigned to five groups: alkali burn group, dimethyl sulfoxide (DMSO) group, PRMT1 inhibitor group, fibroblast growth factor 2 (FGF2) inhibitor group, and PRMT1 inhibitor combined with FGF2 group to evaluate the role of PRMT1 in CNV.Human umbilical vein endothelial cells (HUVECs) and murine macrophage-like RAW264.7 cells were used to establish a hypoxia/reoxygenation (H/R)-induced in vitro model to mimic the ischemic microenvironment.Cells were assigned to the following groups: control group, H/R group, H/R+ DMSO group, H/R+ si-NC group, H/R+ si-PRMT1 group, H/R+ si-FGF2 group, H/R+ PRMT1 inhibitor group, and H/R+ PRMT1 inhibitor+ FGF2 group.Corneal opacity and CNV areas were assessed by slit-lamp microscopy.Corneal structural changes and inflammatory cell count were determined by hematoxylin and eosin staining.PRMT1-positive cell count was determined by immunohistochemistry and the expression of PRMT1, CD31, vascular endothelial growth factor (VEGF), F4/80, CD206, and inducible nitric oxide synthase (iNOS) was assessed by immunofluorescence staining.The expression levels of macrophage markers, including F4/80, iNOS, CD206, interleukin-10 (IL-10), and arginase-1 (Arg-1), were quantified by real-time quantitative PCR and Western blot.Cell proliferation, migration, and angiogenic capacity were evaluated by functional assays including the CCK-8 assay, wound healing assay, Transwell migration assay, and tube formation assay.The research process followed the relevant regulations of the Visual and Ophthalmology Association, and the research plan was approved by the Laboratory Animal Committee of Wuhan University (No.20220504A).
Results Compared with the normal group, the 7 days post-modeling group showed significantly increased corneal opacity scores and CNV area, upregulated VEGF expression, and increased inflammatory cells (all P<0.05).The number of PRMT1-positive cells in the alkali burn group was (39.67±3.51) cells/visual field, which was significantly higher than (3.33±0.58) cells/visual field in the normal group ( t=17.68, P<0.01).Both mRNA and protein expression levels of PRMT1 and FGF2 were significantly elevated in the alkali burn group compared with the normal group (all P<0.01).Compared with the alkali burn group, the PRMT1 inhibitor group showed reduced corneal opacity scores, decreased CNV area, fewer inflammatory cells, and lower expression levels of PRMT1, FGF2, VEGF, Arg-1, IL-10 proteins, as well as CD206 mRNA (all P<0.05).Cell viability, migration distance, migration number, and tubes formed were significantly increased in the H/R group compared with the control group, significantly reduced in the H/R+ si-PRMT1 and H/R+ PRMT1 inhibitor groups compared with the H/R group and significantly increased in H/R+ PRMT1 inhibitor+ FGF2 group than in H/R+ PRMT1 inhibitor group (all P<0.05).Compared with the H/R group, the H/R+ PRMT1 inhibitor group exhibited reduced expression of FGF2, VEGFA, p-PI3K, and p-Akt, while those were upregulated in the H/R+ PRMT1 inhibitor+ FGF2 group compared with the H/R+ PRMT1 inhibitor group (all P<0.05).The proportions of CD206-positive cells in the H/R, H/R+ DMSO, H/R+ PRMT1 inhibitor, and H/R+ PRMT1 inhibitor+ FGF2 groups were all significantly higher than those in the control group, and significantly higher in the H/R, H/R+ DMSO, and H/R+ PRMT1 inhibitor+ FGF2 groups compared with the H/R+ PRMT1 inhibitor group (all P<0.05).Compared with the alkali burn group, the FGF2 inhibitor group, PRMT1 inhibitor group, and PRMT1 inhibitor+ FGF2 group all showed reduced corneal opacity scores, CNV area, and decreased number of VEGFA-, CD206-, and F4/80-positive cells, with the above indicators being lower in the PRMT1 inhibitor group compared with the FGF2 inhibitor and PRMT1 inhibitor+ FGF2 groups and higher in PRMT1 inhibitor+ FGF2 group than in the FGF2 inhibitor group (all P<0.05).Compared with the alkali burn group, the PRMT1 inhibitor group had decreased protein expression levels of FGF2, p-PI3K, p-Akt, CD31, VEGFA and Arg-1, with higher protein expression levels in the PRMT1 inhibitor+ FGF2 group than in the PRMT1 inhibitor group (all P<0.05).
Conclusions PRMT1 may regulate macrophage activation and anti-inflammatory polarization via the FGF2/PI3K/Akt signaling pathway, thereby promoting the occurrence and development of CNV.Targeted inhibition of PRMT1 may serve as an effective therapeutic strategy for CNV.