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IgE-mediated activation of Nhe1 (Na + -H + exchanger-1) induces aortic cell extracellular acidification and promotes cell apoptosis. A pH-sensitive probe pHrodo identified acidic regions at positions of macrophage accumulation, IgE expression, and cell apoptosis in human and mouse abdominal aortic aneurysm (AAA) lesions. Ang II (angiotensin II)-induced AAA in Nhe1-insufficient Apoe -/- Nhe1 +/- mice and Apoe -/- Nhe1 +/+ littermates tested Nhe1 activity in experimental AAA, because Nhe1 -/- mice develop ataxia and epileptic-like seizures and die early. Nhe1 insufficiency reduced AAA incidence and size, lesion macrophage and T-cell accumulation, collagen deposition, elastin fragmentation, cell apoptosis, smooth muscle cell loss, and MMP (matrix metalloproteinase) activity. Nhe1 insufficiency also reduced blood pressure and the plasma apoptosis marker TCTP (translationally controlled tumor protein) but did not affect plasma IgE. While pHrodo localized the acidic regions to macrophage clusters, IgE expression, and cell apoptosis in AAA lesions from Apoe -/- Nhe1 +/+ mice, such acidic areas were much smaller in lesions from Apoe -/- Nhe1 +/- mice. Nhe1-FcεR1 colocalization in macrophages from AAA lesions support a role of IgE-mediated Nhe1 activation. Gelatin zymography, immunoblot, and real-time polymerase chain reaction analyses demonstrated that Nhe1 insufficiency reduced the MMP activity, cysteinyl cathepsin expression, IgE-induced apoptosis, and NF-κB activation in macrophages and blocked IgE-induced adhesion molecule expression in endothelial cells. A near-infrared fluorescent probe (LS662) together with fluorescence reflectance imaging of intact aortas showed reduced acidity in AAA lesions from Nhe-1-insufficient mice. This study revealed extracellular acidity at regions rich in macrophages, IgE expression, and cell apoptosis in human and mouse AAA lesions and established a direct role of Nhe1 in AAA pathogenesis.

The present study tested the hypotheses that overexpression of an intracellular Ang II (angiotensin II) fusion protein, mito-ECFP/Ang II, selectively in the mitochondria of mouse proximal tubule cells induces mitochondrial oxidative and glycolytic responses and elevates blood pressure via the Ang II/AT 1a receptor/superoxide/NHE3 (the Na + /H + exchanger 3)-dependent mechanisms. A PT-selective, mitochondria-targeting adenoviral construct encoding Ad-sglt2-mito-ECFP/Ang II was used to test the hypotheses. The expression of mito-ECFP/Ang II was colocalized primarily with Mito-Tracker Red FM in mouse PT cells or with TMRM in kidney PTs. Mito-ECFP/Ang II markedly increased oxygen consumption rate as an index of mitochondrial oxidative response (69.5%; P <0.01) and extracellular acidification rate as an index of mitochondrial glycolytic response (34%; P <0.01). The mito-ECFP/Ang II-induced oxygen consumption rate and extracellular acidification rate responses were blocked by AT 1 blocker losartan ( P <0.01) and a mitochondria-targeting superoxide scavenger mito-TEMPO ( P <0.01). By contrast, the nonselective NO inhibitor L-NAME alone increased, whereas the mitochondria-targeting expression of AT 2 receptors (mito-AT 2 /GFP) attenuated the effects of mito-ECFP/Ang II ( P <0.01). In the kidney, overexpression of mito-ECFP/Ang II in the mitochondria of the PTs increased systolic blood pressure 12±3 mm Hg ( P <0.01), and the response was attenuated in PT-specific PT- Agtr1a -/- and PT- Nhe3 -/- mice ( P <0.01). Conversely, overexpression of AT 2 receptors selectively in the mitochondria of the PTs induced natriuretic responses in PT- Agtr1a -/- and PT- Nhe3 -/- mice ( P <0.01). Taken together, these results provide new evidence for a physiological role of PT mitochondrial Ang II/AT 1a /superoxide/NHE3 and Ang II/AT 2 /NO/NHE3 signaling pathways in maintaining blood pressure homeostasis.