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A2106 - Na+-h+Exchanger 1 Determines Atherosclerotic Lesion Acidification Andpromotes Atherogenesis
Author Block: C. Liu, G. Sukhova, L. Peter, G. Shi; Brigham and Women's Hospital, Boston, MA, United States.
Rational: Na+-H+ exchanger (Nhe1) is a plasma membrane channel protein that regulates intracellular pH by extruding one proton in exchange for one extracellular Na+, thereby protecting cells from internal acidification. We previously testeda role of immunoglobulin E (IgE) in atherosclerosis by activating Nhe1, reducing extracellular pH, and promoting macrophage apoptosis. In this study, we hypothesize that human atherosclerotic lesions are acidic at regions rich in macrophage, IgE, and cell apoptosis. IgE-mediated Nhe1 activation and extracellular acidification may provide mechanistic explanation as why inactivation of IgE or Nhe1 reduced atherosclerosis in apolipoprotein E (ApoE)-deficient (Apoe-/-) mice. Methods: We used pH-sensitive pHrodo, a cell permeable fluorogenic probe thatturns into fluorescent under acidic pH, to examine intracellular acidic compartments. We further generated Nhe1 heterogeneous Apoe-/-Nhe1+/- mice and their littermate Apoe-/-Nhe1+/+ control mice, and fed them on an atherogenic diet for three months to test effects of Nhe1 on the progession of atherogenesis. Meanwhile intravenous administration of a near-infrared (NIR) fluorescent pH-sensitive probe LS662, followed by coregistrated fluorescent molecular tomography-computed tomography (FMT-CT) imaging allows detection of acidic atherosclerotic lesions from Apoe-/- mice and isolated thoracic-abdominal aortas. Results: We detected that human and murine atherosclerotic lesions are acidic in areas rich in macrophages, IgE, and cell apoptosis. In Apoe-/- mice, inactivation of Nhe1 reduces atherosclerotic lesion sizes, macrophage accumulation, necrotic core size, CD4+ T-cell accumulation, tissue remodeling, and apoptosis. Nhe1 inactivation also blocks lesion acidification in areas rich in macrophage accumulation, IgE expression and cell apoptosis from aortic root, aortic arch, to thoracic-abdominal aorta. Such pH-sensitive NIR fluorescent signals are dimmed in corresponding atherosclerotic lesions from Nhe1-inactivated mice. Ex vivo pHrodo detection and immunohistochemical analysis following FMT-CT imaging confirm the colocalization of acidic regions with macrophage accumulation, IgE expression, and apoptosis in atherosclerotic lesions. Conclusion: This study suggest that mouse and human atherosclerotic lesions are acidic in areas rich in macrophages. Such acidification is due to enhanced Nhe1 activation and proton extrusion to the extracellular milieu. LS662 or similar NIR pH-sensitive probes combined with FMT technique can be used as a non-invasive and non-radiation imaging system to monitor atherosclerotic lesion formation and progression.