Study of Intracellular Cargo Trafficking and Co-localization in the Phagosome and Autophagy-Lysosomal Pathways of Retinal Pigment Epithelium (RPE) Cells

Sigma-2 receptor modulator CT1812 alters key pathways and rescues retinal pigment epithelium (RPE) functional deficits associated with dry age-related macular degeneration (AMD)

Trafficking defects in retinal pigmented epithelial (RPE) cells contribute to RPE atrophy, a hallmark of geographic atrophy (GA) in dry age-related macular degeneration (AMD). Dry AMD pathogenesis is multifactorial, including amyloid-β (Aβ) accumulation and oxidative stress-common features of Alzheimer's disease (AD). The Sigma-2 receptor (S2R) regulates lipid and protein trafficking, and S2R modulators reverse trafficking deficits in neurodegeneration in vitro models. Given overlapping mechanisms contributing to AD and AMD, S2R modulator effects on RPE function were investigated. The S2R modulator CT1812 is in clinical trials for AD, dementia with Lewy bodies, and GA. Leveraging AD trials testing CT1812, unbiased analyses of patient biofluid proteomes revealed that proteins altered by CT1812 associated with GA and macular degeneration disease ontologies and overlapped with proteins altered in dry AMD. Differential expression analysis of RPE transcripts from APP-Swedish/London mutant transgenic mice, a model featuring Aβ accumulation, revealed reversal of autophagy/trafficking transcripts in S2R modulator-treated animals versus vehicle toward healthy control levels. Photoreceptor outer segment (POS) trafficking in human RPE cells showed deficits in response to Aβ1-42 or hydrogen peroxide compared to vehicle. S2R modulators normalized stressor-induced POS trafficking deficits, resembling healthy control. Taken together, S2R modulation may provide a novel therapeutic strategy for dry AMD.

An In-Vitro Cell Model of Intracellular Protein Aggregation Provides Insights into RPE Stress Associated with Retinopathy

Impaired cargo trafficking and the aggregation of intracellular macromolecules are key features of neurodegeneration, and a hallmark of aged as well as diseased retinal pigment epithelial (RPE) cells in the eye. Here, photoreceptor outer segments (POS), which are internalized daily by RPE cells, were modified by UV-irradiation to create oxidatively modified POS (OxPOS). Oxidative modification was quantified by a protein carbonyl content assay. Human ARPE-19 cells were synchronously pulsed with POS or OxPOS to study whether oxidatively modified cargos can recapitulate features of RPE pathology associated with blinding diseases. Confocal immunofluorescence microscopy analysis showed that OxPOS was trafficked to LAMP1, LAMP2 lysosomes and to LC3b autophagy vacuoles. Whilst POS were eventually degraded, OxPOS cargos were sequestered in late compartments. Co-localization of OxPOS was also associated with swollen autolysosomes. Ultrastructural analysis revealed the presence of electron-dense OxPOS aggregates in RPE cells, which appeared to be largely resistant to degradation. Measurement of cellular autofluorescence, using parameters used to assess fundus autofluorescence (FAF) in age-related macular disease (AMD) patients, revealed that OxPOS contributed significantly to a key feature of aged and diseased RPE. This in vitro cell model therefore represents a versatile tool to study disease pathways linked with RPE damage and sight-loss.