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Tauopathy-Associated Tau Fragment Ending at Amino Acid 224 Is Generated by Calpain-2 Cleavage.

Journal article
Authors Claudia Cicognola
Tugce Munise Satir
Gunnar Brinkmalm
Irena Matečko-Burmann
Lotta Agholme
Petra Bergström
Bruno Becker
Henrik Zetterberg
Kaj Blennow
Kina Höglund
Published in Journal of Alzheimer's disease : JAD
ISSN 1875-8908
Publication year 2020
Published at Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry
Wallenberg Centre for Molecular and Translational Medicine
Centre for Ageing and Health (Agecap)
Language en
Links dx.doi.org/10.3233/JAD-191130
www.ncbi.nlm.nih.gov/entrez/query.f...
Subject categories Neurochemistry, Basic Medicine

Abstract

Tau aggregation in neurons and glial cells characterizes tauopathies as Alzheimer's disease (AD), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD). Tau proteolysis has been proposed as a trigger for tau aggregation and tau fragments have been observed in brain and cerebrospinal fluid (CSF). Our group identified a major tau cleavage at amino acid (aa) 224 in CSF; N-terminal tau fragments ending at aa 224 (N-224) were significantly increased in AD and lacked correlation to total tau (t-tau) and phosphorylated tau (p-tau) in PSP and CBD.Previous studies have shown cleavage from calpain proteases at sites adjacent to aa 224. Our aim was to investigate if calpain-1 or -2 could be responsible for cleavage at aa 224.Proteolytic activity of calpain-1, calpain-2, and brain protein extract was assessed on a custom tau peptide (aa 220-228), engineered with fluorescence resonance energy transfer (FRET) technology. Findings were confirmed with in-gel trypsination and mass spectrometry (MS) analysis of brain-derived bands with proteolytic activity on the FRET substrate. Finally, knock-down of the calpain-2 catalytic subunit gene (CAPN2) was performed in a neuroblastoma cell line (SH-SY5Y).Calpain-2 and brain protein extract, but not calpain-1, showed proteolytic activity on the FRET substrate. MS analysis of active gel bands revealed presence of calpain-2 subunits, but not calpain-1. Calpain-2 depletion and chemical inhibition suppressed proteolysis of the FRET substrate. CAPN2 knock-down caused a 76.4% reduction of N-224 tau in the cell-conditioned media.Further investigation of the calpain-2 pathway in the pathogenesis of tauopathies is encouraged.

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