Regulatory feedback cycle of the insulin-degrading enzyme and the amyloid precursor protein intracellular domain: Implications for Alzheimer's disease.

Anna A Lauer,Marcus O W Grimm,Matthias Riemenschneider,Ulrike C Müller,Christoph P Stahlmann,Tobias Hartmann,Cornel M Bachmann,Felix Ritzmann,Bianca Schrul,Reuven Stein,Andrea Thiel,Daniel Janitschke,Janine Mett,Heike S Grimm

doi:10.1111/acel.13264

Abstract

One of the major pathological hallmarks of Alzheimer´s disease (AD) is an accumulation of amyloid‐β (Aβ) in brain tissue leading to formation of toxic oligomers and senile plaques. Under physiological conditions, a tightly balanced equilibrium between Aβ‐production and ‐degradation is necessary to prevent pathological Aβ‐accumulation. Here, we investigate the molecular mechanism how insulin‐degrading enzyme (IDE), one of the major Aβ‐degrading enzymes, is regulated and how amyloid precursor protein (APP) processing and Aβ‐degradation is linked in a regulatory cycle to achieve this balance. In absence of Aβ‐production caused by APP or Presenilin deficiency, IDE‐mediated Aβ‐degradation was decreased, accompanied by a decreased IDE activity, protein level, and expression. Similar results were obtained in cells only expressing a truncated APP, lacking the APP intracellular domain (AICD) suggesting that AICD promotes IDE expression. In return, APP overexpression mediated an increased IDE expression, comparable results were obtained with cells overexpressing C50, a truncated APP representing AICD. Beside these genetic approaches, also AICD peptide incubation and pharmacological inhibition of the γ‐secretase preventing AICD production regulated IDE expression and promoter activity. By utilizing CRISPR/Cas9 APP and Presenilin knockout SH‐SY5Y cells results were confirmed in a second cell line in addition to mouse embryonic fibroblasts. In vivo, IDE expression was decreased in mouse brains devoid of APP or AICD, which was in line with a significant correlation of APP expression level and IDE expression in human postmortem AD brains. Our results show a tight link between Aβ‐production and Aβ‐degradation forming a regulatory cycle in which AICD promotes Aβ‐degradation via IDE and IDE itself limits its own production by degrading AICD.

Highlights

More than 50 million people globally are estimated to suffer from dementia
No significant differences in β-actin signals exist between the two compared cell lines (MEF WT: 109.4%, p = 0.640; MEF PS1/2−/−: 104.3%, p = 0.877; MEF PS1/2−/− + insulin-degrading enzyme (IDE)-KD: 103.5%, p = 0.441; MEF amyloid precursor protein (APP)/APLP2−/−: 90.4%, p = 0.357; MEF APPΔCT15: 95.2%, p = 0.111)
Extracellular senile plaques composed of aggregated Aβ peptides are one of the main pathological hallmarks of Alzheimer’s disease (AD), oligomeric forms of Aβ seem to be the primary toxic species causing synaptic damage and neurodegeneration (Lambert et al, 1998; Umeda et al, 2011) and levels of soluble Aβ strongly correlate with markers of AD severity (McLean et al, 1999)

Summary

| INTRODUCTION

More than 50 million people globally are estimated to suffer from dementia. Total cerebral Aβ level is determined by Aβ-production, and by Aβ-clearance and degradation mechanisms, which have been reported to be impaired in the predominant late onset form of AD (Mawuenyega et al, 2010). These Aβ-clearance mechanisms include among others the enzymatic elimination of Aβ peptides by proteases like insulin-degrading enzyme (IDE) and neprilysin (NEP) (Nalivaeva & Turner, 2019). The two major Aβdegrading enzymes IDE and NEP are transcriptionally upregulated by AICD This indicates the existence of a regulatory cycle in which proteolytic APP processing generates Aβ peptides and concurrently ensures their enzymatic degradation

| RESULTS

B IDE gene expression

| DISCUSSION

Findings

| EXPERIMENTAL PROCEDURES