Immunolocalization of ACE2 and AT2 receptors in rabbit atherosclerotic plaques

Evidence suggests that angiotensin type 2 receptor (AT(2)R) and angiotensin-converting enzyme 2 (ACE2) play a protective role in atherogenesis. These factors have not been identified in rabbit atherosclerotic plaques. Our goal was to localize ACE2 and AT(2)R in rabbit atherosclerotic tissues, and determine which cell types express these factors. New Zealand White rabbits were fed either a control diet or a 0.5% cholesterol diet (n=8/group) for 12 weeks. Paraffin-fixed thoracic aorta were serially sectioned and processed for immunohistochemistry using commercially available antibodies to ACE2, AT2R, RAM 11 (to identify macrophages), and alpha smooth muscle cell actin (alpha SMC) to identify smooth muscle cells and myofibroblasts. AT2R immunoreactivity, but not ACE2 immunoreactivity, was clearly present in endothelia overlying normal wall. However, both AT2R and ACE2 immunoreactivity were clearly present in endothelia overlying neo-intima formation and atherosclerotic plaques. Within plaques, both AT2R and ACE2 immunoreactivity were observed in macrophages and aSMC actin-positive cells. Examination of serial sections showed that the majority of cells were both ACE2- and AT(2)R-positive. Macrophages and alpha SMC actin-positive cells produce ACE2 and the AT(2)R in atherosclerotic plaques. Determining a role for these factors in the control of atherosclerosis will require additional studies.