Control of Chemokine Gradients by the Retinal Pigment Epithelium

¹ NEI, NIH, Bethesda, Maryland, United States
² National Eye Institute, National Institutes of Health, building 31, Rm 6A22, Bethesda, Maryland, 20892-2510, United States

^* To whom correspondence should be addressed. E-mail: millers{at}nei.nih.gov.

	Abstract

PURPOSE Pro-inflammatory cytokines in degenerative diseases can lead to the loss of normal physiology and destruction of surrounding tissues. In the present study, we sought to determine the physiological responses of human fetal retinal pigment epithelia (hfRPE) in vitro following polarized activation of pro-inflammatory cytokine receptors. METHODS Primary cultures of hfRPE were stimulated with an inflammatory cytokine mixture (ICM): interleukin-1 (IL-1), tumor necrosis factor- (TNF-), and interferon- (IFN-). Western blots and immunofluorescence were used to determine the expression/localization of the cytokine receptors on hfRPE. Polarized secretion of cytokines was measured using Searchlight Technology. A capacitance probe technique was used to measure transepithelial fluid flow (JV) and resistance (RT). RESULTS IL-1R1 is mainly localized to the apical membrane and TNFR1 to the basal membrane, while IFN-R1 is detected at both membranes. Activation by apical ICM induced a significant secretion of angiogenic and angiostatic chemokines mainly across the hfRPE apical membrane. Addition of the ICM to the basal, but not the apical bath significantly increased net fluid absorption (JV) across the hfRPE within 20 min. Similar increases in JV were produced by 24 hr exposure to ICM, which significantly decreased total tissue resistance (RT). CONCLUSIONS Chemokine gradients across the RPE can be altered: (1) through an ICM-induced change in polarized chemokine secretion; (2) through an increase in ICM-induced net fluid absorption. In vivo, both of these factors could contribute to the development of chemokine gradients that help mediate the progression of inflammation/angiogenesis at the retina/RPE/choroid complex.

Key Words: retinal pigment epithelium, age-related macular degeneration, chemotaxis, uveitis, tight junction, cytokine