title: Vitreous-induced cytoskeletal rearrangements via the Rac1 GTPase-dependent signaling pathway in human retinal pigment epithelial cells.
abstract: Proliferative vitreoretinopathy (PVR) is mainly caused by retinal pigment epithelial (RPE) cell migration, invasion, proliferation and transformation into fibroblast-like cells that produce the extracellular matrix (ECM). The vitreous humor is known to play an important role in PVR. An epithelial-to-mesenchymal transdifferentiation (EMT) of human RPE cells induced by 25% vitreous treatment has been linked to stimulation of the mesenchymal phenotype, migration and invasion. Here, we characterized the effects of the vitreous on the cell morphology and cytoskeleton in human RPE cells. The signaling pathway that mediates these effects was investigated. Serum-starved RPE cells were incubated with 25% vitreous, and the morphological changes were examined by phase-contrast microscopy. Filamentous actin (F-actin) was examined by immunofluorescence and confocal microscopy. Protein phosphorylation of AKT, ERK1/2, Smad2/3, LIM kinase (LIMK) 1 and cofilin was analyzed by Western blot analysis. Vitreous treatment induced cytoskeletal rearrangements, activated Rac1 and enhanced the phosphorylation of AKT, ERK1/2 and Smad2/3. When the cells were treated with a Rac activation-specific inhibitor, the cytoskeletal rearrangements were prevented, and the phosphorylation of Smad2/3 was blocked. Vitreous treatment also enhanced the phosphorylation of LIMK1 and cofilin and the Rac inhibitor blocked this effect. We propose that vitreous-transformed human RPE cells undergo cytoskeletal rearrangements via Rac1 GTPase-dependent pathways that modulate LIMK1 and cofilin activity. The TGFβ-like activity of the vitreous may participate in this effect. Actin polymerization causes the cytoskeletal rearrangements that lead to the plasticity of vitreous-transformed RPE cells in PVR.
authors.affiliation: State Key Ophthalmic Laboratory, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China.
authors.forename: Xionggao
authors.initials: X
authors.lastname: Huang
authors.forename: Yantao
authors.initials: Y
authors.lastname: Wei
authors.forename: Haizhi
authors.initials: H
authors.lastname: Ma
authors.forename: Shaochong
authors.initials: S
authors.lastname: Zhang
mesh_terms: D002478:Cells, Cultured; D051338:Cofilin 1 / Q000378:metabolism; D003599:Cytoskeleton / Q000201:enzymology* / Q000473:pathology; D006801:Humans; D054461:Lim Kinases / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000201:enzymology* / Q000473:pathology; D015398:Signal Transduction; D051899:Smad2 Protein / Q000378:metabolism; D051900:Smad3 Protein / Q000378:metabolism; D018630:Vitreoretinopathy, Proliferative / Q000201:enzymology / Q000473:pathology*; D014822:Vitreous Body / Q000201:enzymology / Q000473:pathology*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D051338:Cofilin 1; C107953:RAC1 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; C515892:LIMK1 protein, human; D054461:Lim Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020830:rac1 GTP-Binding Protein