Clinical and neuropathological studies have shown that tau pathology better correlates with the severity of
dementia than
amyloid plaque burden, making tau an attractive target for the cure of
Alzheimer's disease. We have explored whether passive immunization with the 12A12
monoclonal antibody (26-36aa of
tau protein) could improve the
Alzheimer's disease phenotype of two well-established mouse models, Tg2576 and 3xTg mice. 12A12 is a cleavage-specific
monoclonal antibody which selectively binds the pathologically relevant neurotoxic NH226-230 fragment (i.e. NH2htau) of
tau protein without cross-reacting with its full-length physiological form(s). We found out that
intravenous administration of 12A12
monoclonal antibody into symptomatic (6 months old) animals: (i) reaches the hippocampus in its biologically active (
antigen-binding competent) form and successfully neutralizes its target; (ii) reduces both pathological tau and
amyloid precursor
protein/amyloidβ metabolisms involved in early disease-associated synaptic deterioration; (iii) improves episodic-like type of learning/memory skills in hippocampal-based novel object recognition and object place recognition behavioural tasks; (iv) restores the specific up-regulation of the activity-regulated cytoskeleton-associated
protein involved in consolidation of experience-dependent synaptic plasticity; (v) relieves the loss of dendritic spine connectivity in pyramidal hippocampal CA1 neurons; (vi) rescues the
Alzheimer's disease-related electrophysiological deficits in hippocampal long-term potentiation at the CA3-CA1 synapses; and (vii) mitigates the neuroinflammatory response (reactive
gliosis). These findings indicate that the 20-22 kDa NH2-terminal tau fragment is crucial target for
Alzheimer's disease therapy and prospect
immunotherapy with 12A12
monoclonal antibody as safe (normal tau-preserving), beneficial approach in contrasting the early Amyloidβ-dependent and independent neuropathological and cognitive alterations in affected subjects.