ChBE Seminar Series: Sheldon Miller
Tuesday, December 4, 2007
11:00 a.m.-12:00 p.m.
Room 2110, Chemical & Nuclear Engineering Bldg.
Professor Nam Sun Wang
Breaking into the Subretinal Space: Cytokine secretion, leukocyte traffic and fluid transport across human retinal pigment epithelium
Presented by Dr. Sheldon Miller
National Eye Institute
National Institutes of Health
In the eye, diseases such as uveitis or age-related macular degeneration lead to tissue inflammation in and around the subretinal space. The retinal pigment epithelium (RPE) can respond to this insult by the polarized secretion of angiogenic and antiangiogenic cytokines. These cytokines and chemokines as well as the RPE itself form complicated feedback pathways that could alter RPE physiology and stimulate or suppress components of both the innate and adaptive immune systems in the distal retina and choroid. In vitro experiments using a recently developed model of human fetal RPE primary cultures have shown the polarized constitutive secretion of MCP-1, IL-8 and IL-6 primarily to the apical bath. A cocktail of pro-inflammatory cytokines (Il-1β, TNF-β, and IFN-γ) significantly increases the apical secretion of MCP-1 and many other pro and anti-inflammatory cytokines. This cocktail also decreases RPE transepithelial resistance (TER) and increases fluid absorption from retina to choroid. The signaling pathway for the fluid transport increase involves the phosphorylation of cell membrane receptors, the activation of transcription factors, and the cystic fibrosis transmembrane conductance regulator (CFTR). In vivo, this decrease in TER and increase in epithelial fluid transport may serve to concentrate the chemokine activity in the subretinal space and thereby increase the chemotactic gradient for the entry of neutrophils, monocytes and other immune system cells into the subretinal space. In separate experiments, we show the expression and localization of tight junction proteins that preserve epithelial polarity and paracellular permeability. In particular, a specific tight junction protein, JAM-C, affects monocyte and neutrophil traffic into the subretinal space. In vivo, a relatively small constitutive MCP-1 gradient may provide chemotactic signaling for monocytes that provide protective immune system surveillance on both sides of the RPE. This protection may be lost either by pro-inflammatory cytokine alteration of RPE physiology or by an age-related decrease in RPE paracellular permeability.