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

Cicognola, Claudia LU ; Satir, Tugce Munise ; Brinkmalm, Gunnar ; Matečko-Burmann, Irena ; Agholme, Lotta ; Bergström, Petra ; Becker, Bruno ; Zetterberg, Henrik LU ; Blennow, Kaj LU and Höglund, Kina (2020) In Journal of Alzheimer's disease : JAD
Abstract

BACKGROUND: 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.

OBJECTIVE: 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... (More)

BACKGROUND: 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.

OBJECTIVE: 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.

METHODS: 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).

RESULTS: 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.

CONCLUSIONS: Further investigation of the calpain-2 pathway in the pathogenesis of tauopathies is encouraged.

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Contribution to journal
publication status
epub
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in
Journal of Alzheimer's disease : JAD
publisher
IOS Press
external identifiers
  • scopus:85083895735
  • pmid:32144989
ISSN
1387-2877
DOI
10.3233/JAD-191130
language
English
LU publication?
no
id
73a98769-3aff-494e-bb44-9e0957f0810a
date added to LUP
2020-03-24 10:31:13
date last changed
2020-05-13 05:50:06
@article{73a98769-3aff-494e-bb44-9e0957f0810a,
  abstract     = {<p>BACKGROUND: 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.</p><p>OBJECTIVE: 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.</p><p>METHODS: 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).</p><p>RESULTS: 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.</p><p>CONCLUSIONS: Further investigation of the calpain-2 pathway in the pathogenesis of tauopathies is encouraged.</p>},
  author       = {Cicognola, Claudia and Satir, Tugce Munise and Brinkmalm, Gunnar and Matečko-Burmann, Irena and Agholme, Lotta and Bergström, Petra and Becker, Bruno and Zetterberg, Henrik and Blennow, Kaj and Höglund, Kina},
  issn         = {1387-2877},
  language     = {eng},
  month        = {03},
  publisher    = {IOS Press},
  series       = {Journal of Alzheimer's disease : JAD},
  title        = {Tauopathy-Associated Tau Fragment Ending at Amino Acid 224 Is Generated by Calpain-2 Cleavage},
  url          = {http://dx.doi.org/10.3233/JAD-191130},
  doi          = {10.3233/JAD-191130},
  year         = {2020},
}