Cyclic cis-Locked Phospho-Dipeptides Reduce Entry of AβPP into Amyloidogenic Processing Pathway

Abstract

The cis/trans isomerization of X-Pro peptide bonds in proteins in some instances acts as a molecular switch in biological pathways. Our prior work suggests that the cis isomer of the phospho-Thr668-Pro669 motif, located in the cytoplasmic domain of the amyloid-β precursor protein (AβPP), is correlated with an increase in amyloidogenic processing of AβPP and production of amyloid beta (Aβ), the neurotoxic peptide fragment in Alzheimer’s disease (AD). We designed a 100% cis-locked cyclic dipeptide composed of cyclized phospho-Thr-Pro (pCDP) as a mimic for this putative pathological conformation, and three phosphate-blocked derivatives (pCDP-diBzl, pCDP-Bzl, and pCDP-diPOM). Two H4 neuroglioma cell lines were established as AD cell models for use in testing these compounds: H4-AβPP695 for stable overexpression of wild-type AβPP695, and H4-BACE1 for stable overexpression of β-site AβPP Cleaving Enzyme-1 (BACE1). The level of the secreted AβPP fragment resulting from BACE1 activity, sAβPPβ, served as a key proxy for amyloidogenic processing, since cleavage of AβPP by BACE1 is a requisite first step in Aβ production. Of the compounds tested, pCDP-diBzl decreased sAβPPβ levels in both cell lines, while pCDP-diPOM decreased sAβPPβ levels in only H4-BACE1 cells, all with similar dose-dependences and patterns of proteolytic AβPP fragments. Enzymatic assays showed that none of the pCDP derivatives directly inhibit BACE1 catalytic activity. These results suggest a model in which pCDP-diBzl and pCDP-diPOM act at a common point to inhibit entry of AβPP into the amyloidogenic AβPP processing pathway but through different targets, and provide important insights for the development of novel AD therapeutics. Keywords: Amyloid beta-Protein Precursor, Alzheimer’s Disease, cyclic dipeptides, diketopiperazine, phosphorylated Thr668.

Dietary Spray-Dried Porcine Plasma Reduces Neuropathological Alzheimer’s Disease Hallmarks in SAMP8 Mice

“…Activation of the amyloidogenic pathway of APP processing results in the production of sAPPβ and the generation of neurotoxic Aβ. Activation of this pathway involves the sequential cleavage of APP by β-secretase (BACE1) and γ-secretase, which results in the production of sAPPβ and the generation of neurotoxic Aβ peptides [ 38 ]. Furthermore, cleavage of APP by BACE1 is an essential first step in the production of Aβ that has been well recognized as an initial causal event of the disease [ 39 ].…”

Towards the design of anti-amyloid short peptide helices

“…The use of polyphenols is reported elsewhere [ 7 ] on the basis of hydrophobic arguments. Enzymes capable of breaking up amyloids [ 8 ], study the possible applications of nanoparticles in misfolding disease treatment [ 9 ] or investigate the properties of cyclic cis-locked phosphor-dipeptides are also known [ 10 ]. Physical methods include femtosecond laser-induced nanoexplosion of gold nanorods [ 11 ], while clearance and degradation of amyloid β peptides was observed with the use of anti-inflammatory Annexin A1 [ 12 ].…”