Rapid calpain I activation and cytoskeletal protein degradation following traumatic spinal cord injury: attenuation with riluzole pretreatment.
Immunocytochemical and immunoblotting techniques were used to investigate calpain I activation and the stability of the calpain-sensitive cytoskeletal proteins microtubule-associated protein 2 (MAP2) and spectrin at 1, 4, and 24 h after contusion injury to the spinal cord. Spinal cord injury resulted in the activation of calpain I at all time points examined, with the highest level of activation occurring at 1 h. At the same early time point, there was a loss of dendritic MAP2 staining in spinal cord sections, accompanied by pronounced perikaryal accumulation. The loss in MAP2 staining in the injured spinal cord progressed over the 24-h survival period to affect regions 3 mm distant to the site of injury. The presence of calpain I-specific spectrin degradation was apparent in neuronal cell bodies and fibers as early as 1 h after injury, with the most intense staining occurring within and juxtaposed to the injury site. Spectrin breakdown products in neuronal cell bodies declined rapidly at 4 h and were nearly undetectable at 24 h after injury. Immunoblot studies confirmed the immunocytochemical results by demonstrating a significant increase in calpain I activation, a significant decrease in MAP2 levels, and a significant increase in spectrin breakdown. Finally, treatment of animals with riluzole, an inhibitor of glutamate release, before surgery reduced significantly the loss of MAP2 levels observed at 24 h after injury. These results demonstrate that Ca2+-dependent protease activation and degradation of critical cytoskeletal proteins are early events after spinal cord injury and that treatments that minimize the actions of glutamate may limit their breakdown.
Springer
J E
JE
Department of Anatomy and Neurobiology, University of Kentucky Medical Center, Lexington 40536-0084, U.S.A.
Azbill
R D
RD
Kennedy
S E
SE
George
J
J
Geddes
J W
JW
D000818:Animals; D002154:Calpain / Q000378:metabolism*; D003288:Contusions / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D007150:Immunohistochemistry; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D051381:Rats; D019782:Riluzole / Q000494:pharmacology*; D013049:Spectrin / Q000378:metabolism; D013119:Spinal Cord Injuries / Q000378:metabolism*
D003598:Cytoskeletal Proteins; D018691:Excitatory Amino Acid Antagonists; D008869:Microtubule-Associated Proteins; D013049:Spectrin; D019782:Riluzole; D002154:Calpain