MCP-1-activated monocytes induce apoptosis in human retinal pigment epithelium.

Purpose: The inflammatory response in age-related macular degeneration (AMD) is characterized by mononuclear leukocyte infiltration of the outer blood-retina barrier formed by the retinal pigment epithelium (RPE). A key mechanistic element in AMD progression is RPE dysfunction and apoptotic cell loss. The purpose of this study was to evaluate whether monocyte chemoattractant protein (MCP)-1-activated monocytes induce human RPE apoptosis and whether Ca(2+) and reactive oxygen species (ROS) are involved in this process.

Methods: A cell-based fluorometric assay was used to measure intracellular Ca(2+) concentrations ([Ca(2+)](i)) in RPE cells loaded with fluorescent Ca(2+) indicator. Intracellular RPE ROS levels were measured by using the 5- and 6-chloromethyl-2',7'-dichlorodihydrofluorescence diacetate acetyl ester (CM-H(2)DCFDA) assay. RPE apoptosis was evaluated by activated caspase-3, Hoechst staining, and apoptosis ELISA.

Results: MCP-1-activated human monocytes increased [Ca(2+)](i), ROS levels, and apoptosis in RPE cells, all of which were inhibited by 8-bromo-cyclic adenosine diphosphoribosyl ribose (8-Br-cADPR), an antagonist of cADPR. Although the ROS scavengers pyrrolidinedithiocarbamate (PDTC) and N-acetylcysteine (NAC) significantly inhibited ROS production and apoptosis induced by activated monocytes, they did not affect induced Ca(2+) levels. The induced Ca(2+) levels and apoptosis in RPE cells were inhibited by an antibody against cluster of differentiation antigen 14 (CD14), an adhesion molecule expressed by these cells.

Conclusions: These results indicate that CD14, Ca(2+), and ROS are involved in activated monocyte-induced RPE apoptosis and that cADPR contributes to these changes. Understanding the complex interactions among CD14, cADPR, Ca(2+), and ROS may provide new insights and treatments of retinal diseases, including AMD.