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Abstract γ‐Secretases are a family of intramembrane cleaving aspartyl proteases and important drug targets in Alzheimer's disease. Here, we generated mice deficient for all γ‐secretases in the pyramidal neurons of the postnatal forebrain by deleting the three anterior pharynx defective 1 (Aph1) subunits (Aph1abc cKO Cre+). The mice show progressive cortical atrophy, neuronal loss, and gliosis. Interestingly, this is associated with more than 10‐fold accumulation of membrane‐bound fragments of App, Aplp1, Nrg1, and Dcc, while other known substrates of γ‐secretase such as Aplp2, Lrp1, and Sdc3 accumulate to lesser extents. Despite numerous reports linking neurodegeneration to accumulation of membrane‐bound App fragments, deletion of App expression in the combined Aph1 knockout does not rescue this phenotype. Importantly, knockout of only Aph1a‐ or Aph1bc‐secretases causes limited and differential accumulation of substrates. This was not associated with neurodegeneration. Further development of selective Aph1‐γ‐secretase inhibitors should be considered for treatment of Alzheimer's disease.

Abstract Inherited familial Alzheimer's disease (AD) is characterized by small increases in the ratio of Aβ42 versus Aβ40 peptide which is thought to drive the amyloid plaque formation in the brain of these patients. Little is known however whether ageing, the major risk factor for sporadic AD, affects amyloid beta‐peptide (Aβ) generation as well. Here we demonstrate that the secretion of Aβ is enhanced in an in vitro model of neuronal ageing, correlating with an increase in γ‐secretase complex formation. Moreover we found that peroxynitrite (ONOO−), produced by the reaction of superoxide anion with nitric oxide, promoted the nitrotyrosination of presenilin 1 (PS1), the catalytic subunit of γ‐secretase. This was associated with an increased association of the two PS1 fragments, PS1‐CTF and PS1‐NTF, which constitute the active catalytic centre. Furthermore, we found that peroxynitrite shifted the production of Aβ towards Aβ42 and increased the Aβ42/Aβ40 ratio. Our work identifies nitrosative stress as a potential mechanistic link between ageing and AD.