Chronic exposure to TNF[alpha] impairs RPE barrier and immunosuppressive functions

Purpose The retinal pigment epithelium (RPE) is a monolayer of pigmented cells with important roles in the outer blood-retinal barrier and subretinal immune suppression. Failure of RPE functions and inflammation have both been hypothesized to play a role in the pathophysiology of age related macular degeneration (AMD). We here investigated the long-term effects of TNF[alpha] on RPE morphology and function in vitro. Methods Primary porcine RPE cells were cultivated until confluence, then recombinant TNF[alpha] was added daily in the culture medium (at 0.8, 4, 20 or 100 ng/ml=C1,C2,C3 and C4) for 10 days. RPE cell morphology and gene expression, barrier, phagocytosis and immunosuppressive functions were assessed. Results Cell morphology and gene expression:TNF[alpha] (i) decreased cell number (3653.6,3428,3227,2791 and 2020 cells/mm2 respectively for control,C1,C2,C3 and C4, all p < 0.01); (ii) increased cell size (+5.3,+12.6,+13.9 and +9.5% of control for C1,C2,C3 and C4, all p < 0.05); (iii) increased the % of multinucleated cells (5.7,7.7,9.4,9.9 and 15.9% of multinucleated cells for control,C1,C2,C3 and C4, all p < 0.05); (iv) and decreased OTX2 (a major RPE gene) expression (-11.1, -19.7, -52 and -82.9% of control for C1,C2,C3 and C4, all p < 0.05). Barrier function: Stimulation by TNF[alpha] (i) disturbed Zonula Occludens 1 cellular distribution and actin F distribution and (ii) significantly decreased RPE transepithelial resistance in a dose-dependent manner (-70, -88.5 and -90.8% of control for C2,C3 and C4, p < 0.05). Immunossupressive function: 10 day pre-stimulation with -TNF[alpha] significantly decreased RPE capacity to induce monocyte death after 24 h of co-culture (p < 0.05). Conclusions Chronic exposure to TNF[alpha] deteriorates major RPE functions that are essential to visual function and might play a key role in the pathophysiology of AMD.