The microtubule associated protein tau promotes neuronal survival through binding and stabilization of MTs. Phosphorylation regulates tau–microtubule interactions and hyperphosphorylation contributes to the aberrant formation of insoluble tau aggregates in Alzheimer’s disease (AD) and related tauopathies1. However, other pathogenic post-translational tau modifications have not been well characterized. Here we demonstrate that tau acetylation inhibits tau function via impaired tau–microtubule interactions and promotes pathological tau aggregation. Mass spectrometry analysis identified specific lysine residues, including lysine 280 (K280) within the microtubule-binding motif as the major sites of tau acetylation. Immunohistochemical and biochemical studies of brains from tau transgenic mice and patients with AD and related tauopathies showed that acetylated tau pathology is specifically associated with insoluble, Thioflavin-positive tau aggregates. Thus, tau K280 acetylation in our studies was only detected in diseased tissue, suggesting it may have a role in pathological tau transformation. This study suggests that tau K280 acetylation is a potential target for drug discovery and biomarker development for AD and related tauopathies.

Senile plaques formed by ␤-amyloid peptides (A␤) and neurofibrillary tangles (NFTs) formed by hyperphosphorylated tau , a microtubule-associated protein , are the hallmark lesions of Alzheimer's disease (AD) in addition to loss of neurons. While several transgenic (Tg) mouse models have recapitulated aspects of AD-like A␤ and tau pathologies , a spatiotemporal mapping paradigm for progressive NFT accumulation is urgently needed to stage disease progression in AD mouse models. Braak and co-workers developed an effective and widely used NFT staging paradigm for human AD brains. The creation of a Braak-like spatiotemporal staging scheme for tau pathology in mouse models would facilitate mechanistic studies of AD-like tau pathology. Such a scheme would also enhance the reproducibility of preclinical AD therapeutic studies. Thus , we developed a novel murine model of A␤ and tau pathologies and devised a spatiotemporal scheme to stage the emergence and accumulation of NFTs with advancing age. Notably, the development of NFTs followed a spatiotemporal Braak-like pattern similar to that observed in authentic AD. More significantly , the presence of A␤ accelerated NFT formation and enhanced tau amyloidosis; however , tau pathology did not have the same effect on A␤ pathology. This novel NFT staging scheme provides new insights into the mechanisms of tau pathobiology , and we speculate that this scheme will prove useful for other basic and translational studies of AD mouse models. Alzheimer's disease (AD) is characterized by a triad of neuropathological hallmarks including senile plaques, neurofibrillary tangles (NFTs), and neuron loss. Senile plaques are extracellular lesions composed of ␤-amyloid (A␤) peptides, whereas NFTs are composed mainly of hyperphosphorylated tau, a microtubule-associated protein. Previous reports using the six-stage NFT progression scheme developed by Braak and co-workers defined a spatiotemporal pattern of tangle accumulation which correlates more closely with the severity of dementia in AD patients than the burden of A␤ plaques. [1][2][3] Despite the fact that the burden of A␤ plaques correlates less well with the degree of dementia, the amyloid cascade hypothesis posits that A␤ influences NFT evolution, although other evidence suggests tangles precede plaque formation. 4 -6 Thus, the influence of plaques and tangles on each other remains controversial, and methodological limitations of postmortem studies of AD brains precludes unequivocal resolution of this controversy.Thus, to probe the interplay between plaques and tangles, several transgenic (Tg) mouse models with both plaque and tangle pathology have been described as reviewed elsewhere.7 For example, bigenic mouse models harboring both human mutant tau and APP transgenes display enhanced tau tangle formation when compared to their monogenic counterparts.

Syntaxin-5 (Sed5) is the only syntaxin needed for transport into and across the yeast Golgi, raising the question of how a single syntaxin species could mediate vesicle transport in both the anterograde and the retrograde direction within the stack. Sed5 is known to combine with two light chains (Bos1 and Sec22) to form the t-SNARE needed to receive vesicles from the endoplasmic reticulum. However, the yeast Golgi contains several other potential light chains with which Sed5 could potentially combine to form other t-SNAREs. To explore the degree of specificity in the choice of light chains by a t-SNARE, we undertook a comprehensive examination of the capacity of all 21 Sed5-based t-SNAREs that theoretically could assemble in the yeast Golgi to fuse with each of the 7 potential v-SNAREs also present in this organelle. Only one additional of these 147 combinations was fusogenic. This functional proteomic strategy thereby revealed a previously uncharacterized t-SNARE in which Sed5 is the heavy chain and Gos1 and Ykt6 are the light chains, and whose unique cognate v-SNARE is Sft1. Immunoprecipitation experiments confirmed the existence of this complex in vivo. Fusion mediated by this second Golgi SNAREpin is topologically restricted, and existing genetic and morphologic evidence implies that it is used for transport across the Golgi stack. From this study, together with the previous functional proteomic analyses which have tested 275 distinct quaternary SNARE combinations, it follows that the fusion potential and transport pathways of the yeast cell can be read out from its genome sequence according to the SNARE hypothesis with a predictive accuracy of about 99.6%.organelle ͉ syntaxin vesicle

Glycogen synthase kinase-3 (GSK-3) is linked to the pathogenesis of Alzheimer’s disease (AD) senile plaques (SPs) and neurofibrillary tangles (NFTs), but the specific contributions of each of the GSK-3 α and β isoforms to mechanisms of AD have not been clarified. In this study, we sought to elucidate the role of each GSK-3α and β using novel viral and genetic approaches. First, we developed recombinant adeno-associated virus 2/1 short hairpin RNA constructs which specifically reduced expression and activity of GSK-3α or -β. These constructs were injected intraventricularly in newborn AD transgenic (tg) mouse models of SPs (PDAPP+/−), both SPs and NFTs (PDAPP+/−;PS19+/−) or wild type controls. We found that knockdown (KD) of GSK-3α, but not -β reduced SP formation in PDAPP+/− and PS19+/−;PDAPP+/− tg mice. Moreover, both GSK-3α and GSK-3β KD reduced tau phosphorylation and tau misfolding in PS19+/−;PDAPP+/− mice. Next, we generated triple tg mice using the CaMKIIα-Cre (α-calcium/calmodulin-dependent protein kinase II-Cre) system to KD GSK-3α in PDAPP+/− mice for further study the effects of GSK-3α reduction on SP formation. GSK-3α KD showed a significant effect on reducing SPs and ameliorating memory deficits in PDAPP+/− mice. Together, the data from both approaches suggests that GSK-3α contributes to both SP and NFT pathogenesis while GSK-3β only modulates NFT formation, suggesting common but also different targets for both isoforms. These findings highlight the potential importance of GSK-3α as a possible therapeutic target for ameliorating behavioral impairments linked to AD SPs and NFTs.

Neuronal kainate receptors are typically heteromeric complexes composed of GluR5-7 and KA1-2 subunits. Although GluR5-7 can exist as functional homomeric channels, the KA subunits cannot. KA2 is widely expressed in the CNS, and KA2/GluR6 heteromers are the most prevalent subunit composition in brain. Previous work has identified endoplasmic reticulum (ER)-retention motifs in the C terminus of KA2, which prevent surface expression of KA2 homomers. However, we find that, when these motifs are mutated, only a small fraction of KA2 is surface expressed. We now identify an additional ER retention motif in the intracellular loop region of KA2, which, when mutated together with the C-terminal motifs, significantly increases the level of KA2 surface expression. However, electrophysiological analysis of surface-expressed KA2 homomers indicates that they do not form functional ion channels. In heterologous cells, a large fraction of KA2 remains intracellular even when the trafficking motifs are mutated or when GluR6 is coexpressed. Therefore, we analyzed the trafficking of endogenous KA2 in vivo. We find that native KA2 surface expression is dramatically reduced in GluR6 knock-out mice compared with wild-type mice. In contrast, KA2 trafficking was unaffected in the GluR5 knock-out. Thus, our study demonstrates that trafficking motifs in both the intracellular loop and C terminus regulate KA2 surface expression; however, in neurons, GluR6 oligomerization is required for egress of KA2 from the ER and transport to the cell surface. The combination of these mechanisms likely prevents surface expression of nonfunctional KA2 homomers and ensures a high level of GluR6/KA2 heteromeric kainate receptors.

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Kainate receptors are a class of ionotropic glutamate receptors that are widely expressed in the mammalian brain, yet little is known about their physiological role or the mechanisms by which they are regulated. Kainate receptors are composed of multiple subunits (GluR5-7; KA1-2), which can combine to form homomeric or heteromeric channels. While the kainate receptor subunit KA2 can combine with GluR5-7 to form heteromeric channels, it does not form functional homomeric channels when expressed alone. In an attempt to identify the molecular mechanisms for this, we have characterized the trafficking and surface expression of KA2. We find that KA2 alone does not traffic to the plasma membrane and is retained in the endoplasmic reticulum (ER). In contrast, co-expression with GluR6 disrupts ER-retention of KA2 and allows plasma membrane expression. Using a chimeric reporter protein we have identified an ER-retention motif within the KA2 cytosolic domain. Recent studies have identified a consensus ER-retention motif (RRR) that is contained within both the NMDA receptor NR1 subunit and K(+) channels. While KA2 contains a similar stretch of amino acids within its C-terminus (RRRRR), unlike the NR1 motif, disruption of this motif with alternating glutamic acid residues does not disrupt ER-retention of KA2, suggesting a unique mechanism regulating KA2 surface expression.

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