title: Endothelin-converting enzymes degrade intracellular β-amyloid produced within the endosomal/lysosomal pathway and autophagosomes.
abstract: Impairments in Aβ removal are increasingly being considered as a possible cause for the abnormal Aβ build-up typical of Alzheimer disease. Of particular interest is a pool of Aβ that accumulates intraneuronally and may contribute to neuronal toxicity. The mechanism for intraneuronal accumulation, however, is not well understood and is commonly attributed to impaired removal of extracellular Aβ by neurons. Based on the intracellular distribution of the well established Aβ degrading enzymes, ECE-1 and ECE-2, we tested whether impairments in their catalytic activity could lead to intracellular Aβ accumulation. Using SH-SY5Y cells overexpressing wild-type amyloid precursor protein and pharmacological inhibition of endogenous ECE activity, we found that ECEs participate in the degradation of at least two distinct pools of Aβ; one destined for secretion and the other being produced and degraded within the endosomal-autophagic-lysosomal pathways. Although ECE-1 regulates both pools of Aβ, ECE-2 regulates mainly the intracellular pool of the peptide. Consistent with this result, ECE-2 was found to co-localize with markers of the endosomal/lysosomal pathway but not with a trans-Golgi network marker. Furthermore, ECE-2 was detected in autophagic vesicles in cells treated with chloroquine. Under these conditions, ECE inhibition produced significantly higher elevations in intracellular Aβ than chloroquine treatment alone. This study highlights the existence of Aβ clearance mechanisms by ECEs at intracellular sites of production. Alterations in ECE activity may be considered as a cause for increased intraneuronal Aβ in Alzheimer disease.
authors.affiliation: Biomedical Research Institute of New Jersey, MidAtlantic Neonatology Associates and Atlantic Health System, Morristown, New Jersey 07960, USA.
authors.forename: Javier
authors.initials: J
authors.lastname: Pacheco-Quinto
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Eckman
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism*; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism*; D001343:Autophagy; D045744:Cell Line, Tumor; D018076:DNA, Complementary / Q000378:metabolism; D018450:Disease Progression; D011992:Endosomes / Q000378:metabolism*; D000072396:Endothelin-Converting Enzymes; D016232:Endothelins / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D006801:Humans; D008247:Lysosomes / Q000378:metabolism*; D008666:Metalloendopeptidases / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D021601:trans-Golgi Network / Q000378:metabolism
chemical_list: D016229:Amyloid beta-Peptides; D018076:DNA, Complementary; D016232:Endothelins; D016282:Aspartic Acid Endopeptidases; D008666:Metalloendopeptidases; C000606923:ECE1 protein, human; C000606924:ECE2 protein, human; D000072396:Endothelin-Converting Enzymes