Changes in ApoE and TIMP-1 expression correlate with outer blood-retinal barrier disruption in an in vitro model of retinal aging

Age-related macular degeneration (AMD) is a leading cause of blindness worldwide. Unfortunately, the early stages of this disease are poorly understood, which has led to limited treatment options. Investigating normal changes in tissues eventually affected by AMD can further elucidate the mechanisms of disease progression and lead to novel therapeutic targets. The primary cell layer affected in AMD is the retinal pigment epithelium (RPE), which forms the outer blood-retinal barrier (oBRB). Beneath the RPE lies Bruch's membrane, a proteinaceous layer that naturally thickens and stiffens with age. These changes to Bruch's membrane are also implicated in RPE dysfunction and AMD progression. To investigate the relationship between normal, age-related changes in Bruch's membrane and AMD development, we engineered a tunable in vitro model of Bruch's membrane to support primary porcine RPE cells. We performed transepithelial electrical resistance (TEER) measurements, viability assays, morphological analysis, immunocytochemistry, and enzyme-linked immunosorbent assays (ELISA) to evaluate monolayer integrity and angiogenic factor expression. Cells cultured on our aged model exhibited changes similar to those seen in AMD, including reduced monolayer integrity, the formation of sub-RPE deposits, and eventual cell death. Notably, apolipoprotein E (ApoE), a known drusen component and Alzheimer's disease marker, was overexpressed prior to deposit accumulation and cell death. Regions of ApoE overexpression corresponded with disrupted expression of zonula occludens-1, a junctional protein. While most angiogenic factors remained unchanged, tissue inhibitor of metalloproteinases-1 (TIMP-1) was transiently overexpressed before cell death. These findings suggest that ApoE and TIMP-1 may play key roles in early AMD pathogenesis and represent potential targets for future therapeutic intervention.