The role of placental growth factor (PlGF) in retinal pigment epithelial (RPE) barrier integrity and outer retinal integrity in geographic atrophy

Abstract

Purpose : PlGF has been widely investigated as a target for the mitigation of neovascular age-related macular degeneration (AMD). Previous investigations suggest PlGF inhibition may also be an effective target for the treatment of outer retinal degeneration seen in geographic atrophy (GA). However, this has only been reported in the light-induced retinal atrophy mouse model. This study tested the hypothesis that PlGF inhibition might protect RPE and the outer retina in the sodium iodate (NaIO₃) mouse model.

Methods : PlGF-2 (50ng/mL) was applied to human foetal RPE (hfRPE) for 24 hours in culture. Barrier integrity was assessed by transepithelial electrical resistance (TEER) and staining for ZO-1 and f-actin. Retinal degeneration was induced in mice by intraperitoneal delivery of 50mg/kg NaIO₃. PlGF and VEGFR1 expression were assessed by in situ hybridisation (ISH) and immunohistochemistry (IHC). Anti-PlGF antibody (5D11D4) was delivered via intravitreal injection. Control conditions were untreated; PBS vehicle control; and IgG antibody control. Retinal degeneration was assessed by optical coherence tomography and post-mortem analyses of retinal sections and RPE/ choroid flatmounts.

Results : PlGF reduced hfRPE barrier resistance by 66.96% ±7.78% compared to untreated RPE (mean ±SD, p- value ≤0.0005). There was fragmentation of the ZO-1 network and increased cells with stress fibres. In vivo, 50mg/kg NaIO₃ induced outer retina thinning and RPE and choroidal atrophy. Increased VEGFR1 mRNA was detected in the inner retina of NaIO₃-treated mice by ISH and in the RPE and choroid by IHC. PlGF was detected in the NaIO₃-treated choroid by IHC. 5D11D4 treatment significantly preserved portions of intact RPE after 24 hours NaIO₃ exposure compared to vehicle and IgG control groups (p-value ≤0.005 and ≤0.05 respectively). At the same time, 5D11D4 treatment improved choroidal vascular area after 72 hours NaIO₃ treatment compared to a vehicle control group, although this was not significant. However, 5D11D4 did not prevent RPE atrophy seen at 72 hours, nor retinal thinning.

Conclusions : These results suggest that while PlGF signalling suppresses RPE barrier activity in vitro, this growth factor does not play a significant role in RPE dysfunction observed during oxidative stress induced-retinal degeneration in vivo, in contrast to previous studies.

This is a 2021 ARVO Annual Meeting abstract.