Extensive degradation of myelin basic protein isoforms by calpain following traumatic brain injury.
Axonal injury is one of the key features of traumatic brain injury (TBI), yet little is known about the integrity of the myelin sheath. We report that the 21.5 and 18.5-kDa myelin basic protein (MBP) isoforms degrade into N-terminal fragments (of 10 and 8 kDa) in the ipsilateral hippocampus and cortex between 2 h and 3 days after controlled cortical impact (in a rat model of TBI), but exhibit no degradation contralaterally. Using N-terminal microsequencing and mass spectrometry, we identified a novel in vivo MBP cleavage site between Phe114 and Lys115. A MBP C-terminal fragment-specific antibody was then raised and shown to specifically detect MBP fragments in affected brain regions following TBI. In vitro naive brain lysate and purified MBP digestion showed that MBP is sensitive to calpain, producing the characteristic MBP fragments observed in TBI. We hypothesize that TBI-mediated axonal injury causes secondary structural damage to the adjacent myelin membrane, instigating MBP degradation. This could initiate myelin sheath instability and demyelination, which might further promote axonal vulnerability.
Liu
Ming Cheng
MC
Department of Psychiatry, Center for Neuroproteomics and Biomarkers Research, University of Florida, Gainsville, Florida 32610, USA. liumc@mbi.ufl.edu
Akle
Veronica
V
Zheng
Wenrong
W
Kitlen
Jason
J
O'Steen
Barbara
B
Larner
Stephen F
SF
Dave
Jitendra R
JR
Tortella
Frank C
FC
Hayes
Ronald L
RL
Wang
Kevin K W
KK
D000595:Amino Acid Sequence; D000818:Animals; D001930:Brain Injuries / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002154:Calpain / Q000502:physiology*; D004195:Disease Models, Animal; D006868:Hydrolysis; D008297:Male; D008969:Molecular Sequence Data; D008970:Molecular Weight; D004676:Myelin Basic Protein / Q000235:genetics / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000494:pharmacology / Q000502:physiology; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D004676:Myelin Basic Protein; D020033:Protein Isoforms; D010447:Peptide Hydrolases; D002154:Calpain