The Smad ubiquitination regulatory factor 1 (Smurf1) is one of the E3 ubiquitin ligases and is related to multiple biological processes. Despite the various roles played by this protein, there is no report on the function of Smurf1 in neurodegeneration. Hirano bodies (HBs) are intracellular structures within neuronal processes and were first described in the hippocampus of individuals with amyotrophic lateral sclerosis and the parkinsonism-dementia complex of Guam. In addition, the number of HBs increases in the brains of patients with Alzheimer's disease (AD) compared with age-matched non-demented control individuals.
In this study, we immunohistochemically demonstrated that Smurf1 localized in HBs in the brains of patients with AD by using plural anti-Smurf1 antibodies, and Smurf1 co-localized with HBs marker proteins by using confocal microscopy. Moreover, we demonstrated that Smurf1 localized in HB-like F-actin aggregates in a cell culture system via treatment with the actin-stabilizing toxin jasplakinolide (jpk). Smurf1 represents a novel protein component of HBs, to be included in an expanding list of HB-associated proteins.