Hyperphosphorylated Tau as a Novel Biomarker for Traumatic Axonal Injury in the Spinal Cord.

Current biomarker research in spinal cord injury (SCI) and traumatic brain injury has focused on a number of structural protein candidates, including the microtubule-associated protein tau. Evidence from models of traumatic brain injury has demonstrated that hyperphosphorylation of tau (p-tau) occurs in injured axons and demonstrates its utility as a biomarker for brain injury; however, the potential of p-tau as a biomarker for SCI is not yet known. Therefore, the present study determined whether tau is hyperphosphorylated in injured spinal cord axons, and then examined cerebrospinal fluid (CSF) and serum concentrations of p-tau and total-tau protein after a clinically relevant severe impact-compression SCI in rats. We found that severe SCI at T8 showed the presence of p-tau in damaged axons with a similar time course and distribution pattern to β-APP, a biomarker of axonal injury. The presence of p-tau and β-APP positive axons extended no farther than 5000 μm rostral and caudal to the injury epicenter, and was at its maximum at one day post-SCI. CSF levels of p-tau and total-tau significantly increased at one day post-SCI; however, only serum p-tau levels were significantly elevated in rats with SCI compared with naïve rats. These results suggest that CSF and serum p-tau may be a useful biomarker for severe traumatic SCI.