Expression of JAM-A in the human corneal endothelium and retinal pigment epithelium: Localization and evidence for role in barrier function

PURPOSE. Junctional adhesion molecules (JAMs) are a family of adhesion proteins found in intercellular junctions. Evidence suggests that JAM-A is important for the regulation of tight junction assembly and epithelial barrier function. The authors recently reported that JAM- A is expressed in rabbit corneal endothelium and that antibody to JAM- A produces corneal swelling. In the present study, they investigate JAM-A expression in the human corneal endothelium and retinal pigment epithelium (RPE) and examine the effect of a function-blocking antibody to JAM- A on the permeability of cultured RPE cell monolayers. METHODS. Expression of JAM- A in human corneal endothelium, human RPE tissue, and cultured ARPE-19 monolayers was assessed by immunofluorescence confocal microscopy. Localization of JAM- A was compared with the tight junction-associated protein zonula occludens-1 (ZO-1). To investigate JAM- A function in ARPE-19 cells, ARPE-19 monolayers were subjected to a calcium switch protocol to disrupt cell junctions and treated with a function-blocking antibody to JAM- A or an isotype-matched control. Dextran flux assays were performed to assess the effect of JAM- A antibody on ARPE-19 monolayer permeability. RESULTS. Expression of JAM- A was observed in human corneal endothelium, and its distribution correlated with the tight junction-associated protein ZO-1. In addition, expression of JAM- A was observed in human RPE and in intercellular junctions of ARPE-19 monolayers. The localization pattern of JAM- A in the RPE and ARPE-19 monolayers was similar to that of ZO-1. ARPE-19 monolayers treated with antibody to JAM- A demonstrated a 33% increase in permeability to 10,000 MWt dextran compared with monolayers treated with control antibody. CONCLUSIONS. Results of this study provide new information about JAM- A expression in tight junctions of the human corneal endothelium and human RPE. The observation that antibodies to JAM- A increase ARPE-19 monolayer permeability is consistent with previous findings of JAM- A function in epithelial tight junctions and suggests JAM-A may have a role in the regulation of RPE barrier function.