P1‐218: A NOVEL CELLULAR COMPLEX OF BACE1 AND γ‐SECRETASE SEQUENTIALLY GENERATES Aβ FROM APP
Year: 2019
Type: article
Abstract: Intramembrane proteolysis of transmembrane substrates by the presenilin–γ-secretase complex is preceded and regulated by shedding of the substrate's ectodomain by α- or β-secretase. We recently discovered that substrate processing by α- and γ-secretases can occur in a large, multi-protease fraction that mediates sequential cleavages of substrates within a high molecular weight (HMW) complex stabilized by members of the tetraspanin web. We now asked whether β- and γ-secretases also interact to mediate efficient sequential processing of APP, generating the amyloid β (Aβ) peptides that initiate Alzheimer's disease. We used coimmunoprecipitation (coIP), non-denaturing FPLC, and novel Aβ ELISAs to identify an endogenous high MW complex in HEK293 cells and normal mouse and human brains that contains β- and γ-secretases. We then designed a new experimental system in which incubation of FPLC fractions containing this native complex at 37°C generated a range of Aβ peptides from endogenous holo-APP, a paradigm we refer to as de novo Aβ generation. An endogenous HMW complex (∼5 MD) containing mature, proteolytically active β- and γ-secretases and holo-APP was catalytically active in vitro and generated a full array of Aβ peptides, with physiological Aβ42/40 ratios. The isolated complex responded properly to γ-secretase modulators in vitro. Alzheimer's-causing mutations in presenilin altered the Aβ42/40 peptide ratio generated by the HMW β/γ-secretase complex in vitro indistinguishably from that observed in the medium of the whole cells. We also discovered roburic acid, a natural compound which decreases Aβ production in HEK293 cells and iPS-derived neurons (iNs) by partially disrupting the HMW β/γ-secretase complex without inhibiting either β or γ-secretase activity per se. Aβ is generated from holo-APP by a BACE1/γ-secretase complex that provides sequential, efficient regulated intramembrane proteolysis (RIP) of full-length substrates to final products. We are currently exploring the subcellular localization of this HMW β/γ-secretase complex through super-resolution microscopy and searching for therapeutic compounds similar to roburic acid with better potency for dissociating the β/γ-secretase complex to reduce Aβ production without inhibiting either β or γ-secretase activity.
Source: Alzheimer s & Dementia
Authors: Lei Liu, Li Ding, Matteo Rovere, Michael S. Wolfe, Dennis J. Selkoe
Language: English
Subfield: Physiology (medical)
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W2980719117