Lysosomal dysfunction in the brain of a mouse model with intraneuronal accumulation of carboxyl terminal fragments of the amyloid precursor protein

Abstract

Recent data suggest that intraneuronal accumulation of metabolites of the amyloid β precursor protein (APP) is neurotoxic. We observed that transgenic mice overexpressing in neurons a human APP gene harboring the APPE693Q (Dutch) mutation have intraneuronal lysosomal accumulation of APP carboxyl-terminal fragments (APP-CTFs) and oligomeric amyloid β (oAβ) but no histological evidence of amyloid deposition. Morphometric quantification using the lysosomal marker protein 2 (LAMP-2) immunolabeling showed higher neuronal lysosomal counts in brain neurons of 12 months old APPE693Q as compared to age-matched non-transgenic littermates, and Western blots showed increased lysosomal proteins including LAMP-2, cathepsin D and LC3. At 24 months of age, these mice also exhibited an accumulation of α-synuclein in the brain, along with increased conversion of LC3-I to LC3-II, an autophagosomal/autolysosomal marker. In addition to lysosomal changes at 12 months of age, these mice developed cholinergic neuronal loss in the basal forebrain, GABAergic neuronal loss in the cortex, hippocampus and basal forebrain, and gliosis and microgliosis in the hippocampus. These findings suggest a role for the intraneuronal accumulation of oAβ and APP-CTFs and resultant lysosomal pathology at early stages of Alzheimer’s disease-related pathology.

Brain Transcriptomic Analysis of Hereditary Cerebral Hemorrhage With Amyloidosis-Dutch Type

“…Genes involved in cellular aerobic respiration were not affected in the transcriptome of 12-month APPE-693Q mice but phagosomal system genes were predominantly up-regulated, possibly indicating an early compensatory mechanism to remove the excess of toxic proteins. Consistently, an age-dependent lysosomal dysfunction was recently described in the APP-E693Q mice, with a higher lysosomal count in the entorhinal cortex of the 12-month mice and autophagosomal/autolysosomal protein level increases only in 24-month old mice, leading to an inflammatory reaction and neuronal loss ( Kaur et al, 2017 ). In HCHWA-D, the lysosomal pathway was significantly down-regulated probably representing an end-stage state of the disease.…”

Lysosomal Dysfunction in Down Syndrome Is APP-Dependent and Mediated by APP-βCTF (C99)

“…and R.A.N., manuscript in preparation). APP-␤CTF has also been previously linked to lysosomal dysfunction in AD models involving overexpressed forms of FAD-mutated APP with or without additional overexpression of other mutated human AD genes (Lauritzen et al, 2012(Lauritzen et al, , 2016Yang et al, 2014;Kaur et al, 2017;Bourgeois et al, 2018), and in iPSC generated Ts21 neurons (Hung and Livesey, 2018). We discovered that luminal acidification of lysosomes is significantly impaired in DS and primarily responsible for disrupting lysosomal hydrolase activities and CTSD protein buildup.…”

“…Early neuronal accumulation of APP-␤CTF in AD mouse models is linked to neuronal hyperactivity (Goutagny et al, 2013), A␤independent LTP deficits and cognitive impairment (Simó n et al, 2009;Tamayev et al, 2011;Lauritzen et al, 2012;Mondragó n-Rodríguez et al, 2014), and cholinergic neurodegeneration (Jiang et al, 2016). Intraneuronal accumulation of APP-␤CTF is reported to be both a cause and effect of autophagy-lysosomal pathology and APP-␤CTF aggregate accumulation in 3xTg AD mice (APPswe, PS1 M146V , and Tau P301L ) (Lauritzen et al, 2012(Lauritzen et al, , 2016 and in several FAD-mutated APP overexpression models in mice (Yang et al, 2014;Kaur et al, 2017;Bourgeois et al, 2018), and in the neurons generated from induced pluripotent stem cells derived from individuals with PSEN1 as well as APP mutations (Hung and Livesey, 2018).…”

The Transcription Factor EB Reduces the Intraneuronal Accumulation of the Beta-Secretase-Derived APP Fragment C99 in Cellular and Mouse Alzheimer’s Disease Models

“…The initial cleavage of APP by β-secretase results in the secretion of the soluble ectodomain sAPPβ and the generation of a membrane-tethered C-terminal fragment C99 (or βCTF) that 2 of 17 is cleaved by γ-secretase to form Aβ. Increasing evidence indicates that Aβ accumulation is preceded by intraneuronal accumulation of C99, which contributes to AD pathology by affecting the endolysosomal network [2][3][4][5][6][7][8][9][10][11]. Firstly, in brain fibroblasts derived from Down's syndrome (DS) patients, a disorder in which patients develop an early form of AD likely due to a third copy of APP present on chromosome 21 [12], C99 accumulation was found to cause enlargement of Rab5-positive early endosomes [2][3][4].…”