Glycosylphosphatidylinositol-specific phospholipase D is expressed by macrophages in human atherosclerosis and colocalizes with oxidation epitopes

Background-Glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) may play an important role in inflammation, because it can hydrolyze the GP I anchors of several inflammatory membrane proteins leg, CD106, CD55, and C D59) and its hydrolytic products upregulate macrophage cytokine expression (eg, interleukin-1 and tumor necrosis factor-alpha). Because of its potenti al regulatory role in inflammatory reactions, we hypothesized that GPI-PLD might be expressed in atherosclerosis. Methods and Results-Immunohistochemistry using human GPI-PLD-specific rabbi t polyclonal antiserum was performed on a total of 83 nonatherosclerotic an d atherosclerotic human coronary arteries from 23 patients. Macrophages, sm ooth muscle cells, apoA-I, and oxidation epitopes also were identified immu nohistochemically. Cell-associated GPI-PLD was detected in 95% of atheroscl erotic segments, primarily on a subset of macrophages. Extracellular GPI-PL D was present in only 30% of atherosclerotic segments and localized to regi ons with extracellular apoA-I. In contrast, GPI-PLD was not detected in non atherosclerotic segments. Expression of GPI-PLD mRNA by human macrophages w as confirmed in vitro by reverse transcription/polymerase chain reaction. F urther studies demonstrated that GPI-PLD-positive plaque macrophages contai ned oxidation epitopes, suggesting a link between oxidant stress and GPI-PL D expression. This possibility was supported by studies in which exposure o f a macrophage cell line to H2O2 led to a 50+/-3% increase in steady-state GPI-PLD mRNA levels. Conclusions-Collectively, these results suggest that oxidative processes ma y regulate GPI-PLD expression and suggest a role for GPI-PLD in inflammatio n and in the pathogenesis of atherosclerosis.