Microglial tau undergoes phosphorylation-independent modification after ischemia

Area of Science:

• Neuroscience
• Immunohistochemistry
• Biochemistry

Background:

• Neurofibrillary tangles (NFTs) are hallmarks of Alzheimer's disease.
• Microglia activation is observed around ischemic foci in the brain.
• Tau protein is a key component of NFTs and can be modified in neurological conditions.

Purpose of the Study:

• To investigate the nature of tau2 immunoreactivity in microglia around ischemic foci.
• To determine if tau2 immunoreactivity in microglia is related to tau hyperphosphorylation.
• To compare the conformational state of tau in microglia and NFTs.

Main Methods:

• Immunohistochemistry using tau2 antibody on formalin-fixed, paraffin-embedded brain sections.
• Western blot analysis of brain homogenates to detect tau2-immunoreactive bands.
• Treatment with polyethyleneglycol-p-isooctylphenyl ether (Triton X-100; TX) to assess antibody binding and tau conformation.

Main Results:

• Tau2 antibody labeled NFTs and microglia around ischemic foci.
• Triton X-100 (TX) abolished tau2 immunoreactivity in microglia but not NFTs.
• Tau2-immunoreactive bands in microglia were found in the Tris-soluble fraction and were not due to hyperphosphorylation.
• TX disrupted tau2 binding in microglia, suggesting a reversible conformational change in tau after ischemia.
• NFT-associated tau showed relative resistance to TX, indicating conformational differences.

Conclusions:

• Tau modification after ischemia leads to a conformational change affecting tau2 binding in microglia.
• The tau2 epitope in microglia exhibits susceptibility to TX, differing from its state in NFTs.
• This conformational difference may be relevant for understanding tau pathology in ischemic conditions and neurodegenerative diseases.