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N. Miyamoto, Y. de Kozak, J.–C. Jeanny, A. Glotin, F. Mascarelli, P. Massin, D. BenEzra, F. Behar–Cohen; Plgf–1 in the Pathogenesis of Diabetic Retinopathy: Implication in Epithelial Hemato–Retinal Barrier Breakdown . Invest. Ophthalmol. Vis. Sci. 2006;47(13):960.
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© ARVO (1962-2015); The Authors (2016-present)
The tight–junction retinal pigment epithelial cells (RPE) ensure integrity of the external hemato–retinal barrier. Disruption of this barrier contributes to the pathogenesis of retinal edema and detachments as observed in diabetic retinopathy. High levels of placental growth factor (PlGF), which specifically interacts with VEGFR–1 have been found in the vitreous of diabetic patients. The purpose is to investigate the role of PlGF–1 in the RPE barrier.
Permeability was assessed by transepithelial electrical resistance (TER), and the passive permeation of tritiated inulin across confluent ARPE–19 monolayers, cultured on transwell filters for 4 weeks. Permeability changes were monitored after exposure to PlGF–1, VEGF165 and VEGF–E or after pretreatment with specific antisense oligonucleotides directed at either VEGFR–1 or 2. Hypoxia and insulin being two important factors in the pathogenesis of diabetic retinopathy, we evaluated the expression of PlGF and the paracellular permeability of RPE. To study the involvement of MEK/ERK signaling pathway, in PlGF–induced permeability, the effects of specific MEK1/2 inhibitor were evaluated. PlGF was injected in the vitreous of rats and its effect was evaluated on semi–thin histology and flat–mounted RPE after zonula occludens(ZO)–1 immunohistochemistry.
On tight–junction ARPE–19 cultures, both VEGF165 and PlGF–1 (but not VEGF–E) induce a TER decrease, and enhance tritiated inulin flux. Similarly, direct injection of PlGF–1 in the vitreous of rat induces an opening the RPE tight junctions with subsequent sub retinal fluid accumulation and edema. Immunohistochemistry shows that ZO–1 undergoes cytoplasmic translocation under PlGF–1 stimulation. Specific down–regulation of VEGF receptors expression using antisense oligonucleotides demonstrates that RPE permeability is under VEGFR–1 regulation. Exposure of ARPE–19 to hypoxia and insulin up–regulates PlGF–1 expression, together with an opening of the tight–junctions. The PlGF–1–induced RPE permeability is associated with increased ERK1/2 phosphorylation levels and is abolished by MEK1/2 inhibition, indicating involvement of MEK/ERK signaling pathway.
Our results indicate that PlGF–1, found at high levels in the vitreous of patients with diabetic retinopathy, may be an interesting regulation target to control edematous forms of diabetic retinopathy.
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