Epithelial–mesenchymal transition of the retinal pigment epithelium causes choriocapillaris atrophy

Abstract

Epithelial-to-mesenchymal transition (EMT) of the retinal pigment epithelium (RPE) is commonly observed at sites of choroidal neovascularization in patients suffering from age-related macular degeneration. To learn in an experimental model how RPE EMT affects the biology of the choroidal vasculature, we studied transgenic mice (βB1-TGF-β1) with ocular overexpression of transforming growth factor-β1 (TGF-β1). RPE EMT was detectable at postnatal day (P)1 and included marked structural and functional alterations such as loss of the outer blood-retina barrier and reduced mRNA expression of the RPE-characteristic molecules Rlbp1, Rpe65, Rbp1 and Vegfa. Moreover, vascular endothelial growth factor (VEGF) was not detectable by immunohistochemistry at the RPE/choroid interface, while RPE cells stained intensely for α-smooth muscle actin. The choriocapillaris, the characteristic choroidal capillary network adjacent to the RPE, developed normally and was not obviously changed in embryonic transgenic eyes but was absent at P1 indicating its atrophy. At around the same time, photoreceptors stopped to differentiate and photoreceptor apoptosis was abundant in the second week of life. Structural changes were also seen in the retinal vasculature of transgenic animals, which did not form intraretinal vessels, and the hyaloid vasculature, which did not regress. In addition, the amounts of retinal HIF-1α and its mRNA were markedly reduced. We conclude that high amounts of active TGF-β1 in the mouse eye cause transdifferentiation of the RPE to a mesenchymal phenotype. The loss of epithelial differentiation leads to the diminished synthesis of RPE-characteristic molecules including that of VEGF. Lack of RPE-derived VEGF causes atrophy of the choriocapillaris, a scenario that disrupts photoreceptor differentiation and finally results in photoreceptor apoptosis. Lack of retinal vessel formation and of hyaloid vessel regression might be caused by the decrease in the metabolic requirements of the neuroretina leading to low amounts of retinal HIF-1α. In summary, our data indicate that failure of RPE differentiation may well precede and cause atrophy of the choriocapillaris. In contrast, RPE EMT is not sufficient to cause choroidal neovascularization.

TNFAIP3 inhibits migration and invasion in nasopharyngeal carcinoma by suppressing epithelial mesenchymal transition

“…EMT, a key promoting factor for cancer invasion and migration, results in the downregula-tion of epithelial marker and upregulation of mesenchymal markers toward mesenchymal phenotype [17][18][19]. Mounting evidence suggests that EMT is a vital prerequisite for invasion and migration in various cancer [18,[20][21][22]. In the present study, epithelial marker E-cadherin was found to be upregulated, whereas mesenchymal marker vimentin was downregulated in TNFAIP3-overexpressing cells.…”

Proteomic and phosphoproteomic analysis identifies novel liver-related signaling in retinal pigment epithelial cells during epithelial-mesenchymal transition

“…Our results complement previous findings that implicate HGF-Met in the cell wound response and migratory behavior of the RPE, phenomena that are linked to EMT (18)(19)(20). EMT has been well characterized in systems-based examinations of other tissues and cell types (21)(22)(23)(24)(25), and targetbased analyses of EMT have been conducted in RPE (26)(27)(28)(29), but to date EMT has not been thoroughly characterized in RPE. It is our hope that our findings provide a useful resource for future study of a variety of RPE diseases.…”

Cross-Inhibition of Norrin and TGF-β Signaling Modulates Development of Retinal and Choroidal Vasculature

“…In a recent study, we showed that transgenic bB1-TGF-b1 mice 35 with ocular overexpression of active TGF-b1 completely lack intraretinal capillaries and the layer of the choriocapillaris that is required for oxygen supply and nutrition of photoreceptors. 24 We now crossed transgenic bB1-TGF-b1 mice with bB1-Norrin animals that overexpress Norrin in the eye 8,35 to generate double transgenic bB1-TGF-b1/bB1-Norrin mice. After perfusion with FITC-coupled dextran, well-structured superficial and deep vascular plexuses were observed in retinae of wild type and transgenic bB1-Norrin mice at P16 (Figs.…”

“…22 In contrast, transgenic mice with TGF-b1 overexpression in the eye do not develop intraretinal vessels and lose their choriocapillaris, the capillary bed beneath the retinal pigment epithelium that is essential for photoreceptor nutrition. 23,24 The effects appear to be mediated via canonical TGF-b1 signaling, which involves the cytoplasmic phosphorylation of SMAD2 and 3, which in turn bind to SMAD4. 25,26 The complexes then translocate into the nucleus to activate specific target genes.…”