Phosphorylation and compactness of neurofilaments in multiple sclerosis: indicators of axonal pathology.
OBJECTIVE
Axonal pathology extends to the axonal cytoarchitecture leaving its signature on axoskeletal proteins. This study investigated whether neurofilament (NfH) phosphorylation would relate to the dynamics of axonal pathology in multiple sclerosis (MS).


METHODS
NfH phosphoforms (SMI32, SMI34, SMI35) were quantified by ELISA from microdissected samples of control and MS brain and spinal cord. Individual axons were analysed by electron microscopy, densitometrically and morphologically in adjacent tissue sections. Experiments were carried out pre- and post enzymatic dephosphorylation.


RESULTS
In control tissue a rostro-caudal gradient of NfH indicated an increase in axonal density from the brain gray matter towards the spinal cord. The highest levels of phosphorylated and hyperphosphorylated NfH were found in acute lesions of brain and spinal cord, in contrast to chronic lesions where levels were lower than in white matter, consistent with axonal loss. Dephosphorylated NfH was higher, but less densly packed in MS white matter axons compared to control tissue.


CONCLUSIONS
The findings suggest that a less organised/compact axoskeleton or impaired axonal transport may represent an early sign of axonal pathology within the normal appearing white matter in MS. Subsequently a proportional increase of dephosphorylated NfH, aberrant phosphorylation and/or aggregation may occur whilst the protein is transported through the white matter towards the MS plaque, where hyperphosphorylated NfH dominates.
Petzold
Axel
A
Department of Neuroinflammation, Institute of Neurology, Queen Square, London, UK. a.petzold@ion.ucl.ac.uk
Gveric
Djordje
D
Groves
Mike
M
Schmierer
Klaus
K
Grant
Donna
D
Chapman
Miles
M
Keir
Geoffrey
G
Cuzner
Louise
L
Thompson
Edward J
EJ
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001369:Axons / Q000737:chemistry / Q000378:metabolism* / Q000473:pathology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000378:metabolism* / Q000473:pathology*; D016900:Neurofilament Proteins / Q000032:analysis / Q000378:metabolism*; D010766:Phosphorylation; D020033:Protein Isoforms / Q000032:analysis / Q000378:metabolism
D016900:Neurofilament Proteins; D020033:Protein Isoforms