Background: Imaging of human brain as well as cellular and animal models has highlighted a role for the actin cytoskeleton in the development of cell pathology in Alzheimer's disease (AD). Rods and aggregates of the actin-associated protein cofilin are abundant in grey matter of postmortem AD brain and rods are found inside neurites in animal and cell models of AD.
Objective: We sought further understanding of the significance of cofilin rods/aggregates to the disease process: Do rods/aggregates correlate with AD progression and the development of hallmark neurofibrillary tangles and neuropil threads? Are cofilin rods/aggregates found in the same neurites as hyperphosphorylated tau?
Methods: The specificity of rods/aggregates to AD compared with general aging and their spatial relationship to tau protein was examined in postmortem human hippocampus, inferior temporal cortex, and anterior cingulate cortex.
Results: The presence of cofilin rods/aggregates correlated with the extent of tau pathology independent of patient age. Densities of rods/aggregates were fourfold greater in AD compared with aged-matched control brains and rods/aggregates were significantly larger in AD brain. We did not find evidence for our hypothesis that intracellular cofilin rods are localized to tau-positive neuropil threads. Instead, data suggest the involvement of microglia in the clearance of cofilin rods/aggregates and/or in their synthesis in and around amyloid plaques and surrounding neuropil.
Conclusion: Cofilin rods and aggregates signify events initiated early in the pathological cascade. Further definition of the mechanisms leading to their formation in the human brain will provide insights into the cellular causes of AD.
Keywords: Actin; amyloid plaque; cofilin protein; cytoskeleton; microglia; neurofibrillary tangles; neuropil threads; tau protein.