Koo, S. Y. | Search bioRxiv

bioRxiv2019

THE C99 FRAGMENT OF APP REGULATES CHOLESTEROL TRAFFICKING

The link between cholesterol homeostasis and the cleavage of the amyloid precursor protein (APP), and their relationship to the pathogenesis of Alzheimers disease (AD) is still unknown. Cellular cholesterol levels are regulated by a crosstalk between the plasma membrane (PM), where most of the cholesterol resides, and the endoplasmic reticulum (ER), where the protein machinery that regulates cholesterol resides. This crosstalk between PM and ER is believed to be regulated by lipid-sensing peptide(s) that can modulate the internalization of extracellular cholesterol and/or its de novo synthesis in the ER. Our data here indicates that the 99-aa C-terminal fragment of APP (C99), a cholesterol-binding peptide, regulates cholesterol trafficking between the PM and the ER. In AD models, increases in C99 provoke the upregulation of cholesterol internalization and its delivery to the ER, which in turn result into the loss of lipid homeostasis and the appearance of AD signatures, such as higher production of longer forms of amyloid {beta}. Our data suggest a novel role of C99 as mediator of cholesterol disturbances in AD, and as a potential early hallmark of the disease.

molecular biology↗

bioRxiv2019

Aβ42 oligomers trigger synaptic loss through CAMKK2-AMPK-dependent effectors coordinating mitochondrial fission and mitophagy

During the early stages of Alzheimers disease (AD) in both mouse models and human patients, soluble forms of Amyloid-{beta}1-42 oligomers (A{beta}42o) trigger loss of excitatory synapses (synaptotoxicity) in cortical and hippocampal pyramidal neurons (PNs) prior to the formation of insoluble A{beta} plaques. We observed a spatially restricted structural remodeling of mitochondria in the apical tufts of CA1 PNs dendrites in the hAPPSWE,IND transgenic AD mouse model (J20), corresponding to the dendritic domain receiving presynaptic inputs from the entorhinal cortex and where the earliest synaptic loss is detected in vivo. We also observed significant loss of mitochondrial biomass in human neurons derived from a new model of human ES cells where CRISPR-Cas9-mediated genome engineering was used to introduce the Swedish mutation bi-allelically (APPSWE/SWE). Recent work uncovered that A{beta}42o mediates synaptic loss by over-activating the CAMKK2-AMPK kinase dyad, and that AMPK is a central regulator of mitochondria homeostasis in non-neuronal cells. Here, we demonstrate that A{beta}42o-dependent over-activation of CAMKK2-AMPK mediates synaptic loss through coordinated MFF-dependent mitochondrial fission and ULK2-dependent mitophagy in dendrites of PNs. We also found that the ability of A{beta}42o-dependent mitochondrial remodeling to trigger synaptic loss requires the ability of AMPK to phosphorylate Tau on Serine 262. Our results uncover a unifying stress-response pathway triggered by A{beta}o and causally linking structural remodeling of dendritic mitochondria to synaptic loss.

neuroscience↗