Amyloid Beta annular protofibrils in cell processes and synapses accumulate with aging and Alzheimer-associated genetic modification.

Amyloid beta (Abeta) annular protofibrils (APFs) have been described where the structure is related to that of beta barrel pore-forming bacterial toxins and exhibits cellular toxicity. To investigate the relationship of Abeta APFs to disease and their ultrastructural localization in brain tissue, we conducted a pre-embedding immunoelectron microscopic study using anti-annular protofibril antiserum. We examined brain tissues of young- and old-aged amyloid precursor protein transgenic mice (APP23), neprilysin knockout APP23 mice, and nontransgenic littermates.

Neprilysin-sensitive synapse-associated amyloid-beta peptide oligomers impair neuronal plasticity and cognitive function.

A subtle but chronic alteration in metabolic balance between amyloid-beta peptide (Abeta) anabolic and catabolic activities is thought to cause Abeta accumulation, leading to a decade-long pathological cascade of Alzheimer disease. However, it is still unclear whether a reduction of the catabolic activity of Abeta in the brain causes neuronal dysfunction in vivo. In the present study, to clarify a possible connection between a reduction in neprilysin activity and impairment of synaptic and cognitive functions, we cross-bred amyloid precursor protein (APP) transgenic mice (APP23) with neprilysin-deficient mice and biochemically and immunoelectron-microscopically analyzed Abeta accumulation in the brain.

Oligomeric proteins ultrastructurally localize to cell processes, especially to axon terminals with higher density, but not to lipid rafts in Tg2576 mouse brain.

We examined the ultrastructural localization of oligomeric proteins, Abeta42, and flotillin-1 in Tg2576 mouse brains by triple immunoelectron microscopy. Oligomer-specific immunoreactions localized to cell processes, especially to axon terminals with higher density in Tg than in nonTg mouse brains. The oligomer was less frequently colocalized to flotillin-1-immunoreactive rafts than Abeta42, suggesting that rafts are one of the sites of polymeric Abeta deposition, but not of oligomeric proteins including Abeta.

Part of membrane-bound Abeta exists in rafts within senile plaques in Tg2576 mouse brain.

To clarify whether rafts are the site of abnormal amyloid beta protein (Abeta) deposition, we examined the ultrastructural localization of both flotillin-1 (pre-embedding) and Abeta (post-embedding) in Tg2576 mouse brains. After observing the exact areas of senile plaques by reflection contrast microscopy, we observed these same plaques under an electron microscope. Membrane-bound Abeta was predominantly observed on plasma membranes of small processes in diffuse plaques.

Soluble Abeta oligomers ultrastructurally localize to cell processes and might be related to synaptic dysfunction in Alzheimer's disease brain.

Soluble Abeta oligomers have recently been considered to be responsible for cognitive dysfunction prior to senile plaque (SP) formation in Alzheimer's disease (AD) brain. To investigate the ultrastructural localization of soluble Abeta oligomers, we conducted the post-embedding immunoelectron microscopic (IEM) study using an antibody against a molecular mimic of oligomeric Abeta. We examined autopsied brains from AD patients and nondemented subjects.

Ultrastructural localization of flotillin-1 to cholesterol-rich membrane microdomains, rafts, in rat brain tissue.

There is much interest in research on cholesterol-rich membrane microdomains, rafts, in the field of neurobiology. However, no one has shown the ultrastructure of rafts in tissues. We examined the ultrastructure of rafts in rat brain tissue by pre-embedding immunoelectron microscopy using flotillin-1 antibody, which is a biochemical marker of lipid rafts, and BCtheta, which is nicked and biotinylated theta-toxin, and binds to membrane cholesterol of rafts.