Interaction between the guanylate kinase domain of PSD-95 and the proline-rich region and microtubule binding repeats 2 and 3 of tau.

The microtubule-associated protein tau is a key factor in neurodegenerative proteinopathies and is predominantly found in neuronal axons. However, somatodendritic localization of tau occurs in a subset of pathological and physiological tau. Dendritic tau can localize to post-synapses where it interacts with proteins of the post-synaptic density (PSD) protein PSD-95, a membrane-associated guanylate kinase (MAGUK) scaffold factor for organization of protein complexes within the PSD, to mediate downstream signals. However, the molecular details of this interaction remain unclear. Here, we used interaction mapping in cultured cells to demonstrate that tau interacts with the guanylate kinase (GUK) domain in the C-terminal region of PSD-95. The PSD-95 GUK domain is required for a complex with full-length human tau. Mapping the interaction of the MAGUK core with tau revealed that the microtubule binding repeats 2 and 3 and the proline-rich region contributes to this interaction, while the N- and C-terminal regions of tau inhibit interaction. These results reveal the intramolecular determinants of the protein complex of tau and PSD-95 and increase our understanding of tau interactions regulating neurotoxic signaling at the molecular level.

Reduction of advanced tau-mediated memory deficits by the MAP kinase p38γ.

Hyperphosphorylation of the neuronal tau protein contributes to Alzheimer's disease (AD) by promoting tau pathology and neuronal and cognitive deficits. In contrast, we have previously shown that site-specific tau phosphorylation can inhibit toxic signals induced by amyloid-ß (Aß) in mouse models. The post-synaptic mitogen-activated protein (MAP) kinase p38γ mediates this site-specific phosphorylation on tau at Threonine-205 (T205). Using a gene therapeutic approach, we draw on this neuroprotective mechanism to improve memory in two Aß-dependent mouse models of AD at stages when advanced memory deficits are present. Increasing activity of post-synaptic kinase p38γ that targets T205 in tau reduced memory deficits in symptomatic Aß-induced AD models. Reconstitution experiments with wildtype human tau or phosphorylation-deficient tauT205A showed that T205 modification is critical for downstream effects of p38γ that prevent memory impairment in APP-transgenic mice. Furthermore, genome editing of the T205 codon in the murine Mapt gene showed that this single side chain in endogenous tau critically modulates memory deficits in APP-transgenic Alzheimer's mice. Ablating the protective effect of p38γ activity by genetic p38γ deletion in a tau transgenic mouse model that expresses non-pathogenic tau rendered tau toxic and resulted in impaired memory function in the absence of human Aß. Thus, we propose that modulating neuronal p38γ activity serves as an intrinsic tau-dependent therapeutic approach to augment compromised cognition in advanced dementia.