title: The Na+/H+ exchanger NHE6 modulates endosomal pH to control processing of amyloid precursor protein in a cell culture model of Alzheimer disease.
abstract: Early intervention may be key to safe and effective therapies in patients with Alzheimer disease. Endosomal dysfunction is an early step in neurodegeneration. Endosomes are a major site of production of Aβ peptide from the processing of amyloid precursor protein (APP) by clipping enzymes (β- and γ-secretases). The β-secretase enzyme BACE1 requires acidic lumen pH for optimum function, and acid pH promotes Aβ aggregation. The Na(+)/H(+) exchanger NHE6 provides a leak pathway for protons, limiting luminal acidification by proton pumps. Like APP, NHE6 expression was induced upon differentiation of SH-SY5Y neuroblastoma cells and localized to an endosomal compartment. Therefore, we investigated whether NHE6 expression altered APP localization and processing in a stably transfected cell culture model of human APP expression. We show that co-expression with NHE6 or treatment with the Na(+)/H(+) ionophore monensin shifted APP away from the trans-Golgi network into early and recycling endosomes in HEK293 cells. NHE6 alkalinized the endosomal lumen, similar to monensin, and significantly attenuated APP processing and Aβ secretion. In contrast, Aβ production was elevated upon NHE6 knockdown. We show that NHE6 transcript and protein levels are lowered in Alzheimer brains relative to control. These findings, taken together with emerging genetic evidence linking endosomal Na(+)/H(+) exchangers with Alzheimer disease, suggest that proton leak pathways may regulate Aβ generation and contribute to disease etiology.
authors.affiliation: From the Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
authors.forename: Hari
authors.initials: H
authors.lastname: Prasad
authors.affiliation: From the Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 rrao@jhmi.edu.
authors.forename: Rajini
authors.initials: R
authors.lastname: Rao
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000235:genetics / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D011992:Endosomes / Q000737:chemistry / Q000378:metabolism*; D015870:Gene Expression; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D018613:Microscopy, Confocal; D008954:Models, Biological; D008985:Monensin / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects; D061209:Proton Ionophores / Q000494:pharmacology; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D021601:trans-Golgi Network / Q000378:metabolism
chemical_list: D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D061209:Proton Ionophores; C445316:SLC9A6 protein, human; D017923:Sodium-Hydrogen Exchangers; D049452:Green Fluorescent Proteins; D008985:Monensin
keywords: Alzheimer Disease; Amyloid Precursor Protein (APP); Amyloid-β (AB); Endosomal pH; Gene Expression; Proton Pump; Proton Transport; Sodium-Proton Exchange; Vesicle Trafficking; beta-Secretase 1 (BACE1)