Expression, Localization, and Function of Junctional Adhesion Molecule-C (JAM-C) in Human Retinal Pigment Epithelium (original) (raw)

2008, Investigative Ophthalmology & Visual Science

Purpose-To determine the localization of JAM-C in human RPE and characterize its functions. Methods-Immunofluorescence, Western blot, and PCR was used to identify the localization and expression of JAM-C, ZO-1, N-cadherin, and ezrin in cultures of human fetal RPE (hfRPE) with or without si-RNA mediated JAM-C knockdown and in adult native RPE wholemounts. A transepithelial migration assay was used to study the migration of leukocytes through the hfRPE monolayer. Results-JAM-C localized at the tight junctions of cultured hfRPE cells and adult native RPE. During initial junction formation JAM-C was recruited to the primordial cell-cell contacts and after JAM-C knockdown, the organization of N-cadherin and ZO-1 at those contacts was disrupted. JAM-C knockdown caused a delay in the hfRPE cell polarization, as shown by reduced apical staining of ezrin. JAM-C inhibition significantly decreased the chemokine-induced transmigration of granulocytes but not monocytes through the hfRPE monolayer. Conclusions-JAM-C localizes specifically in the tight junctions of hfRPE and adult native RPE. It is important for tight junction formation in hfRPE, possibly by regulating the recruitment of Ncadherin and ZO-1 at the cell-cell contacts, and has a role in the polarization of hfRPE cells. Finally, JAM-C promotes the basal-to-apical transmigration of granulocytes but not monocytes through the hfRPE monolayer. The blood-retinal barrier (BRB) has two components. The inner BRB at the vitreous surface of the retina is formed by tightly opposed retinal endothelial cells and the pericytes surrounding them, whereas the outer BRB consists of a uniform monolayer of retinal pigment epithelial (RPE) cells. The outer component of the BRB is particularly important for maintaining the health and integrity of the retina-RPE complex. In the distal retina, the RPE helps maintain the volume and chemical composition of the extracellular spaces on both the retinal and choroidal sides of the tissue. The RPE apical processes are in close anatomic association with photoreceptor outer segments, and consequently this interface mediates a wide range of metabolic, electrical, and functional interactions. 1,2 In particular, the RPE avidly participates in the phagocytosis of the photoreceptor outer segments and the recycling of visual pigments during the light-dark cycle, 3 whereas pathophysiological processes in the RPE-photoreceptor complex can lead to widespread photoreceptor degeneration and vision loss. 4,5