Functional protection in J20/VLW mice: a model of non-demented with Alzheimer's disease neuropathology.

Alzheimer's disease comprises amyloid-ß and hyperphosphorylated Tau accumulation, imbalanced neuronal activity, aberrant oscillatory rhythms and cognitive deficits. Non-demented with Alzheimer's disease neuropathology defines a novel clinical entity with amyloid-ß and Tau pathologies but preserved cognition. The mechanisms underlying such neuroprotection remain undetermined and animal models of non-demented with Alzheimer's disease neuropathology are currently unavailable. We demonstrate that J20/VLW mice (accumulating amyloid-ß and hyperphosphorylated Tau) exhibit preserved hippocampal rhythmic activity and cognition, as opposed to J20 and VLW animals, which show significant alterations. Furthermore, we show that the overexpression of mutant human Tau in coexistence with amyloid-ß accumulation renders a particular hyperphosphorylated Tau signature in hippocampal interneurons. The GABAergic septohippocampal pathway, responsible for hippocampal rhythmic activity, is preserved in J20/VLW mice, in contrast to single mutants. Our data highlight J20/VLW mice as a suitable animal model in which to explore the mechanisms driving cognitive preservation in non-demented with Alzheimer's disease neuropathology. Moreover, they suggest that a differential Tau phosphorylation pattern in hippocampal interneurons prevents the loss of GABAergic septohippocampal innervation and alterations in local field potentials, thereby avoiding cognitive deficits.

Differential accumulation of Tau phosphorylated at residues Thr231, Ser262 and Thr205 in hippocampal interneurons and its modulation by Tau mutations (VLW) and amyloid-ß peptide.

Alzheimer's disease (AD) is characterized by the accumulation of amyloid-ß peptide (Aß) and hyperphosphorylated Tau protein (P-Tau). Our recent data showed a differential accumulation of Tau protein phosphorylated at residue Thr231 (pThr231) in distinct hippocampal neurons in VLW mice-a model that overexpresses mutated human Tau. Here we demonstrate that, in VLW mice, the accumulation of human P-Tau in pyramidal cells induces the phosphorylation of murine Tau at residue Thr231 in hippocampal interneurons. In addition, we show that pSer262 and pThr205 Tau are present specifically in the soma of some hippocampal interneurons in control mice. Analysis of J20 mice-a model that accumulates Aß-and of VLW animals showed that the density of hippocampal interneurons accumulating pThr205 Tau is lower in VLW mice than in controls. In contrast, the density of interneurons accumulating pThr205 Tau in J20 mice was increased compared to controls in hippocampal regions with a higher Aß plaque load, thereby suggesting that pThr205 Tau is induced by Aß. No significant differences were found between the density of hippocampal interneurons positive for pSer262 Tau in VLW or J20 mice compared to control animals. We also show that pSer262 and pThr205 Tau are present in the soma of some hippocampal interneurons containing Parvalbumin, Calbindin or Calretinin in control, VLW, and J20 mice. Moreover, our results reveal that some interneurons in human hippocampi of cases of AD and control cases accumulate pSer262 and pThr205 Tau. Taken together, these data point to a specific role of pSer262 and pThr205 Tau in the soma of hippocampal interneurons in control and pathological conditions.