Activation of signal transducer and activator of transcription-3 in the spinal cord of sporadic amyotrophic lateral sclerosis patients

Background: Neuroinflammation has been implicated in the pathomechanism of amyotrophic lateral sclerosis (ALS). It is known that signal transducer and activator of transcription-3 (STAT3) is a proinflammatory transcription factor. However, it remains to be determined whether STAT3 is involved in ALS. Objective: To test the hypothesis that STAT3 may be upregulated, activated, or both in the spinal cord of ALS patients. Methods: We performed immunohistochemical, immunoblot and densitometric analyses of total STAT3 (t-STAT3) or phosphorylated active form of STAT3 (p-STAT3) in spinal cords obtained at autopsy from 10 sporadic ALS patients and 10 age-matched control subjects. Results: On sections, p-STAT3 immunoreactivity was localized in the nucleus as well as the cytoplasm of almost all activated microglia in the ALS cases, while it was detectable in a few resting microglia in the control cases. On blots, densitometric p-STAT3 levels in nuclear protein extracts significantly increased in the ALS group compared with the control group, although there was no significant difference in densitometric t-STAT3 levels in cytosolic protein extracts between the two groups. Additionally, there was no significant relationship between the nuclear p-STAT3 levels in the ALS cases and the clinical phenotypes, age at death, or disease duration. Conclusion: The present results suggest that persistent activation and nuclear translocation but not upregulation of STAT3 occurs in ALS spinal cord microglia, which may regulate inflammatory activity.