Neprilysin Is Suppressed by Dual-Specificity Tyrosine-Phosphorylation Regulated Kinase 1A (DYRK1A) in Down-Syndrome-Derived Fibroblasts

Abstract

Amyloid-β peptide (Aβ) accumulation is a triggering event leading to the Alzheimer's disease (AD) pathological cascade. Almost all familial AD-linked gene mutations increase Aβ production and accelerate the onset of AD. The Swedish mutation of amyloid precursor protein (APP) affects β-secretase activity and increases Aβ production up to ca. 6-fold in cultured cells; the onset age is around 50. Down syndrome (DS) patients with chromosome 21 trisomy present AD-like pathologies at earlier ages (40s) compared with sporadic AD patients, because APP gene expression is 1.5-fold higher than that in healthy people, thus causing a 1.5-fold increase in Aβ production. However, when comparing the causal relationship of Aβ accumulation with the onset age between the above two populations, early DS pathogenesis does not appear to be accounted for by the increased Aβ production alone. In this study, we found that neprilysin, a major Aβ-degrading enzyme, was downregulated in DS patient-derived fibroblasts, compared with healthy people-derived fibroblasts. Treatment with harmine, an inhibitor of dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A), which is located in the DS critical region of chromosome 21, and gene knockdown of DYRK1A, upregulated neprilysin in fibroblasts. These results suggest that a decrease in the Aβ catabolic rate may be, at least in part, one of the causes for accelerated AD-like pathogenesis in DS patients if a similar event occurs in the brains, and that neprilysin activity may be regulated directly or indirectly by DYRK1A-mediated phosphorylation. DYRK1A inhibition may be a promising disease-modifying therapy for AD via neprilysin upregulation.Key words Alzheimer's disease; chromosome 21; down syndrome; dual-specificity tyrosine phosphorylationregulated kinase 1A; neprilysin Alzheimer's disease (AD) brains are pathologically characterized by numerous senile plaques and neurofibrillary tangles, which consist of aggregation amyloid-β peptide (Aβ) and hyperphosphorylated tau, respectively, and prominent neuronal cell death. Aβ is generated from amyloid precursor protein (APP) by β-and γ-secretase-mediated sequential cleavages, followed by Aβ degradation by neprilysin (NEP). Aβ in healthy brains is maintained at a constant level by an equilibrium between the production and degradation rates. 1)An imbalance arising by a subtle change in either rate leads to Aβ accumulation.The Swedish double mutation (K670N/M671L) in APP, one of the most well-known mutations in familial AD, leads to a dramatic increase in total Aβ production.2,3) The average onset age of Swedish familial AD is around 55 years.4) On the other hand, Down syndrome (DS) is one of the most frequently occurring chromosomal abnormalities. 5,6) Approximately 95% of DS is caused by standard trisomy 21, which is an extra copy of chromosome 21. The remaining causes, chromosomal translocation and mosaicism, account for 1-5 and 1-2% of DS cases, respectively. DS patients have unique physical characteristics and suffer from various comp...

Correction of cognitive deficits in mouse models of Down syndrome by a pharmacological inhibitor of DYRK1A

“…There is strong support for the involvement of DYRK1A in cognitive deficits associated with Alzheimer's disease (AD): (1) DYRK1A mRNA ( Kimura et al, 2007 ) and DYRK1A protein ( Ferrer et al, 2005 ) levels are increased in postmortem human AD brains compared with healthy brains; (2) calpain 1-induced cleavage of DYRK1A is observed in AD brains and associated with increased activity ( Jin et al, 2015 ); (3) DYRK1A phosphorylates key AD players, such as amyloid precursor protein ( Ryoo et al, 2008 ), presenilin 1 ( Ryu et al, 2010 ), Tau (also known as MAPT) ( Woods et al, 2001 ; Ryoo et al, 2007 ; Azorsa et al, 2010 ; Coutadeur et al, 2015 ; Jin et al, 2015 ), septin ( Sitz et al, 2008 ) and neprylysin ( Kawakubo et al, 2017 ); (4) DYRK1A regulates splicing of Tau mRNA ( Shi et al, 2008 ; Wegiel et al, 2011 ; Yin et al, 2012 , 2017; Jin et al, 2015 ); (5) DYRK1A inhibition corrects cognitive defects in 3xTG-AD ( Branca et al, 2017 ), APP/PS1 (B. Souchet, unpublished) and Aβ25-35 peptide-injected wt mice ( Naert et al, 2015 ), three widely used mice models of AD. These facts provide additional incentive to investigate the regulation and substrates of brain DYRK1A and to develop potent and selective DYRK1A inhibitors to treat cognitive deficits observed in different indications.…”

A Curative Perspective on Down Syndrome

“…Normalizing DYRK1A dosage by breeding mice Ts65Dn with a triplication of this gene with mice trisomic for the same DNA segment but without the gene DYRK1A, has yielded TS65Dn mice with a normal dosage of this gene and a standard concentration of protein APP in the cerebral cortex, hippocampus, and cerebellum [32]. Kawakubo and associates [33] injected harmine, an inhibitor of protein DYRK1A, in fibroblasts obtained from DS persons with AD pathology. They measured an important increase in the concentration of enzyme neprilysin and correlatively a decrease in the concentration of the DYRK1A protein in the fibroblasts.…”

Down syndrome, beta-amyloid and neuroimaging

“…Neprilysin protein concentration is increased in DS and correlates with levels of insoluble Aβ [23]. Further, the overexpression of DRYK1a in DS [92] reduces neprilysin activity in DS fibroblasts [93]. Normalization of reduced neprilysin protein levels in the Ts65Dn mouse model of DS by environmental enrichment is associated with improved cognition [41].…”