Traumatic axonal injury induces proteolytic cleavage of the voltage-gated sodium channels modulated by tetrodotoxin and protease inhibitors.
We demonstrated previously that dynamic stretch injury of cultured axons induces structural changes and Ca2+ influx modulated by tetrodotoxin (TTX)-sensitive voltage-gated sodium channels (NaChs). In the present study, we evaluated potential damage to the NaCh alpha-subunit, which can cause noninactivation of NaChs. In addition, we explored the effects of pre-injury and post-injury treatment with TTX and protease inhibition on proteolysis of the NaCh alpha-subunit and intra-axonal calcium levels ([Ca2+]i) over 60 min after trauma. After stretch injury, we found that [Ca2+]i continued to increase in untreated axons for at least 60 min. We also observed that the III-IV intra-axonal loop of the NaCh alpha-subunit was proteolyzed between 5 and 20 min after trauma. Pre-injury treatment of the axons with TTX completely abolished the posttraumatic increase in [Ca2+]i and proteolysis of the NaCh alpha-subunit. In addition, both pre-injury and post-injury inhibition of protease activity attenuated long-term increases in [Ca2+]i as well as mitigating degradation of the NaCh alpha-subunit. These results suggest a unique "feed-forward" deleterious process initiated by mechanical trauma of axons. Na+ influx through NaChs resulting from axonal deformation triggers initial increases in [Ca2+]i and subsequent proteolysis of the NaCh-subunit. In turn, degradation of the alpha-subunit promotes persistent elevations in [Ca2+]i, fueling additional pathologic changes. These observations may have important implications for developing therapeutic strategies for axonal trauma.
Iwata
Akira
A
Department of Neurosurgery, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6316, USA.
Stys
Peter K
PK
Wolf
John A
JA
Chen
Xiao-Han
XH
Taylor
Andrew G
AG
Meaney
David F
DF
Smith
Douglas H
DH
D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D005456:Fluorescent Dyes; D009474:Neurons / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D010447:Peptide Hydrolases / Q000187:drug effects / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D026941:Sodium Channel Blockers / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013314:Stress, Mechanical; D013779:Tetrodotoxin / Q000494:pharmacology*; D020196:Trauma, Nervous System / Q000503:physiopathology*
D005456:Fluorescent Dyes; D011480:Protease Inhibitors; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013779:Tetrodotoxin; D010447:Peptide Hydrolases; D002118:Calcium