Focal expression of mutated tau in entorhinal cortex neurons of rats impairs spatial working memory

Entorhinal cortex neuropathology begins very early in Alzheimer's disease (AD), a disorder characterized by severe memory disruption. Indeed, loss of entorhinal volume is predictive of AD and two of the hallmark neuroanatomical markers of AD, amyloid plaques and neurofibrillary tangles (NFTs), are particularly prevalent in the entorhinal area of AD-afflicted brains. Gene transfer techniques were used to create a model neurofibrillary tauopathy by injecting a recombinant adeno-associated viral vector with a mutated human tau gene (P301L) into the entorhinal cortex of adult rats. The objective of the present investigation was to determine whether adult onset, spatially restricted tauopathy could be sufficient to reproduce progressive deficits in mnemonic function. Spatial memory on a Y-maze was tested for approximately 3 months post-surgery. Upon completion of behavioral testing the brains were assessed for expression of human tau and evidence of tauopathy. Rats injected with the tau vector became persistently impaired on the task after about 6 weeks of postoperative testing, whereas the control rats injected with a green fluorescent protein vector performed at criterion levels during that period. Histological analysis confirmed the presence of hyperphosphorylated tau and NFTs in the entorhinal cortex and neighboring retrohippocampal areas as well as limited synaptic degeneration of the perforant path. Thus, highly restricted vector-induced tauopathy in retrohippocampal areas is sufficient for producing progressive impairment in mnemonic ability in rats, successfully mimicking a key aspect of tauopathies such as AD.

Research highlights▶ Entorhinal cortex injection of recombinant adeno-associated viral vector constructed to drive the expression of P301L mutated tau produces hyperphosphorylated tau and neurofibrillary tangles in the entorhinal area of rats. ▶ Rats with P301L viral-vector transduced neurons restricted to the entorhinal area exhibit memory deficits that gradually develop over about 2 months after injection. ▶ Once vector-induced deficits appear, the deficits persist for at least an additional 5 weeks of additional testing. ▶ Induction of asymptotic P301L expression and the subsequent development of tauopathy and mnemonic impairment indicates that this is a useful approach to study the relation between mutated tau expression in specific brain regions and mnemonic function.