Phosphorylation of the amyloid precursor protein (APP) at Ser-675 promotes APP processing involving meprin β

Abstract

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by abnormal deposition of β-amyloid (Aβ) peptides. Aβ is a cleavage product of the amyloid precursor protein (APP), and aberrant posttranslational modifications of APP can alter APP processing and increase Aβ generation. In the AD brain, seven different residues, including Ser-675 (APP695 numbering) in the APP cytoplasmic domain has been found to be phosphorylated. Here, we show that expression of a phosphomimetic variant of Ser-675 in APP (APP-S675E), in human neuroblastoma SK-N-AS cells, reduces secretion of the soluble APP ectodomain (sAPPα), even though the total plasma membrane level of APP was unchanged compared with APP levels in cells expressing APPwt or APP-S675A. Moreover, the level of an alternative larger C-terminal fragment (CTF) increased in the APP-S675E cells, whereas the CTF form that was most abundant in cells expressing APPwt or APP-S675A decreased in the APP-S675E cells. Upon siRNA-mediated knockdown of the astacin metalloprotease meprin β, the levels of the alternative CTF decreased and the CTF ratio was restored back to APPwt levels. Our findings suggest that APP–Ser-675 phosphorylation alters the balance of APP processing, increasing meprin β–mediated and decreasing α-secretase–mediated processing of APP at the plasma membrane. As meprin β cleavage of APP has been shown to result in formation of highly aggregation-prone, truncated Aβ2–40/42 peptides, enhanced APP processing by this enzyme could contribute to AD pathology. We propose that it would be of interest to clarify in future studies how APP–Ser-675 phosphorylation promotes meprin β–mediated APP cleavage.

The Potential Role of Cytokines and Growth Factors in the Pathogenesis of Alzheimer’s Disease

“…AD has been extensively characterized by the gradual decline of neuronal health. Neurotoxins, TAU protein neurofibrillary tangles, amyloid-beta (Aβ) plaque accumulation in mature neuron phenotypes [1][2][3][4][5], mitochondria dysfunction (fusion-fission imbalance) [6,7], and neuroinflammation collectively involves in neurodegeneration in AD [8][9][10][11]. Mitochondrial dysfunction results in the accumulation of harmful reactive oxygen species (ROS), which subsequently trigger CNS apoptotic decline [7].…”

A Bioengineering Strategy to Control ADAM10 Activity in Living Cells

“…We transiently transfected cells overexpressing APP695 with one of the following combinations of cDNA: (i) wt ADAM10 + EV; (ii) US-BS-TEVcs + TEV as negative control; (iii) BS-Cyt-TEVcs + EV; and (iv) BS-Cyt-TEVcs + TEV. The cell growth medium was analyzed to detect ADAM10-dependent release of soluble αAPP (sAPPα) fragment derived from α-secretase-mediated APP processing [ 45 , 46 ]. In Western blot analyses, we detected similar amounts of lysate loading control protein, allowing for a comparative analysis of its α-secretase activity on APP processing ( Figure 7 A).…”

Astrocyte-derived lactoferrin reduces Aβ burden by promoting the interaction of p38 and PP2A in APP/PS1 transgenic mice

“…Phosphorylation of APP at Tyr682 by Fyn tyrosine kinase promoted the APP translocated into acidic neuronal compartments where it is processed to generate Aβ (Iannuzzi et al, 2020). Phosphorylation of APP at Ser675 also altered the balance of APP-processing through increasing meprin β-mediated and decreasing α-secretase-mediated APP cleavage at the plasma membrane (Menon et al, 2019). Additionally, phosphorylation of APP at Thr668 promoted the APP transfer to the endosome where is cleaved by the BACE1 and subsequently promoted Aβ generation (Lee et al, 2003).…”

“…When phosphorylation of APP at Thr668, the APP is a tendency to translocate to the endosomes where is an enrichment of BACE1, thus promoting the Aβ production; in contrast, mutation of APP at Thr668 or inhibition of p-APP(Thr668) expression decreased the Aβ production (Lee et al, 2003). Furthermore, a recent study also revealed that the phosphorylation of APP at Ser675 enhanced the Aβ production by promoting the meprin β-mediated APP-processing at the plasma membrane (Menon et al, 2019). These data suggest that inhibition of APP phosphorylation at specific sites is a promising strategy to repress Aβ production.…”