Elsevier

Experimental Neurology

Volume 232, Issue 2, December 2011, Pages 234-239
Experimental Neurology

Axonal damage in the making: Neurofilament phosphorylation, proton mobility and magnetisation transfer in multiple sclerosis normal appearing white matter

https://doi.org/10.1016/j.expneurol.2011.09.011Get rights and content
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Abstract

Aims

Multiple sclerosis (MS) leaves a signature on the phosphorylation and thus proton binding capacity of axonal neurofilament (Nf) proteins. The proton binding capacity in a tissue is the major determinant for exchange between bound and free protons and thus the magnetisation transfer ratio (MTR). This study investigated whether the MTR of non-lesional white matter (NLWM) was related to the brain tissue concentration of neurofilament phosphoforms.

Methods

Unfixed post-mortem brain slices of 12 MS patients were analysed using MTR, T1 at 1.5 T. Blocks containing NLWM were processed for embedding in paraffin and inspected microscopically. Adjacent tissue was microdissected, homogenised and specific protein levels were quantified by ELISA for the Nf heavy chain (NfH) phosphoforms, glial fibrillary acidic protein (GFAP), S100B and ferritin.

Results

Averaged hyperphosphorylated NfH (SMI34) but not phosphorylated NfH (SMI35) levels were different between individual patients NLWM. The concentration of hyperphosphorylated NfH-SMI34 correlated with T1 (R = 0.70, p = 0.0114) and — inversely — with MTR (R =−0.73, p = 0.0065). NfH-SMI35 was not correlated to any of the MR indices.

Conclusions

Post-translational modifications of axonal proteins such as phosphorylation of neurofilaments occur in NLWM and may precede demyelination. The resulting change of proton mobility influences MTR and T1. This permits the in vivo detection of these subtle tissue changes on a proteomic level in patients with MS.

Highlights

► Neurofilaments are phosphorylated ► Protein phosphorylation competes with the free proton binding capacity ► Magnetisation transfer depends on magnetisation exchange between macromolecular bound and free protons ► In multiple sclerosis the phosphorylation status of neurofilaments is changed in otherwise normal appearing axons ► In vivo assessment of early axonal pathology is possible using magnetisation transfer

Abbreviations

AL
acute lesion
BSP
brain-specific proteins
CDP
chronic disease progression
CNS
central nervous system
CTRL
control group
EDSS
Expanded Disability Status Scale
ELISA
enzyme linked immunoabsorbent assay
GM
grey matter
IQR
interquartile range
MS
multiple sclerosis
MRI
magnetic resonance imaging
MTR
magnetisation transfer ratio
NLWM
normal lesional white matter
Nf
neurofilament
NfH
neurofilament heavy chain
PP
primary progressive
RR
relapsing remitting
SAPK
stress-activated protein kinase
SP
secondary progressive
WM
white matter

Keywords

Neurofilament phosphoforms
Biomarker
MRI
MTR
Multiple sclerosis
Axonal injury

Cited by (0)

Financial support: KS has been supported by a Higher Education Funding Council for England (HEFCE) Clinical Senior Lectureship. Tissue for this study has been provided by the Multiple Sclerosis Tissue Bank (MSTB) based at Imperial College London. Part of this work was done at the NMR Research Unit of the UCL Institute of Neurology. The MSTB and the NMR Research Unit are supported by the MS Society of Great Britain and Northern Ireland. The NMR Research Unit is also supported by the UK Department of Health's NIHR Comprehensive Biomedical Research Centre at UCLH.