Sook Wern Chua

Site-specific phosphorylation of tau inhibits amyloid-β toxicity in Alzheimer’s mice

Tau phosphorylation—not all bad Alzheimers disease presents with amyloid-β (Aβ) plaques and tau tangles. The prevailing idea in the field is that Aβ induces phosphorylation of tau, which in turn mediates neuronal dysfunction. Working in Alzheimers disease mouse models, Ittner et al. found evidence for a protective role of tau in early Alzheimers disease. This protection involves specific tau phosphorylation at threonine 205 at the postsynapse. A protective role of phosphorylated tau in disease challenges the dogma that tau phosphorylation only mediates toxic processes. Science, this issue p. 904 Phosphorylation of tau at a specific site mitigates, rather than enhances, symptoms in a mouse model of Alzheimer’s disease. Amyloid-β (Aβ) toxicity in Alzheimer’s disease (AD) is considered to be mediated by phosphorylated tau protein. In contrast, we found that, at least in early disease, site-specific phosphorylation of tau inhibited Aβ toxicity. This specific tau phosphorylation was mediated by the neuronal p38 mitogen-activated protein kinase p38γ and interfered with postsynaptic excitotoxic signaling complexes engaged by Aβ. Accordingly, depletion of p38γ exacerbated neuronal circuit aberrations, cognitive deficits, and premature lethality in a mouse model of AD, whereas increasing the activity of p38γ abolished these deficits. Furthermore, mimicking site-specific tau phosphorylation alleviated Aβ-induced neuronal death and offered protection from excitotoxicity. Our work provides insights into postsynaptic processes in AD pathogenesis and challenges a purely pathogenic role of tau phosphorylation in neuronal toxicity.

The translocator protein as a drug target in Alzheimer's disease.

The translocator protein (TSPO) recently emerged as a potential drug target in Alzheimer’s disease (AD). This has been fuelled mainly by positron emission topography studies that show the upregulation of TSPO in AD, especially in relation to microgliosis and astrogliosis in amyloid-β and tau pathology. Although data as to the exact role of TSPO in AD is still inconclusive, TSPO appears to be involved in neuroinflammatory processes and AD has been shown to involve substantial inflammation. Therefore, further development and investigation of the pharmacological effect of TSPO ligands in AD pathology are warranted.

N-Arylalkyl-2-azaadamantanes as cage-expanded polycarbocyclic sigma (σ) receptor ligands

A series of racemic N-arylalkyl-2-azaadamantan-1-ols (9-15) and the corresponding deoxygenated, achiral N-arylalkyl-2-azaadamantanes (23-29) were synthesized and screened in competition binding assays against a panel of CNS targets. Adamantyl hemiaminals 9-15 displayed generally low affinity for both σ(1) (K(i) values= 294-1950 nM) and σ(2) receptors (K(i) values=201-1020 nM), and negligible affinity for 42 other CNS proteins. Deoxygenation of 9-15 to give the corresponding achiral azaadamantanes 23-29 greatly improved affinity for σ(1) (K(i) values=8.3-239 nM) and σ(2) receptors (K(i) values=34-312 nM).

Tau exacerbates excitotoxic brain damage in an animal model of stroke

Neuronal excitotoxicity induced by aberrant excitation of glutamatergic receptors contributes to brain damage in stroke. Here we show that tau-deficient (tau−/−) mice are profoundly protected from excitotoxic brain damage and neurological deficits following experimental stroke, using a middle cerebral artery occlusion with reperfusion model. Mechanistically, we show that this protection is due to site-specific inhibition of glutamate-induced and Ras/ERK-mediated toxicity by accumulation of Ras-inhibiting SynGAP1, which resides in a post-synaptic complex with tau. Accordingly, reducing SynGAP1 levels in tau−/− mice abolished the protection from pharmacologically induced excitotoxicity and middle cerebral artery occlusion-induced brain damage. Conversely, over-expression of SynGAP1 prevented excitotoxic ERK activation in wild-type neurons. Our findings suggest that tau mediates excitotoxic Ras/ERK signaling by controlling post-synaptic compartmentalization of SynGAP1.Excitotoxicity contributes to neuronal injury following stroke. Here the authors show that tau promotes excitotoxicity by a post-synaptic mechanism, involving site-specific control of ERK activation, in a mouse model of stroke.

Molecular hybridization of 4-azahexacyclo[5.4.1.02,6.03,10.05,9.08,11]dodecane-3-ol with sigma (σ) receptor ligands modulates off-target activity and subtype selectivity

A series of N-substituted 4-azahexacyclo[5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecan-3-ols incorporating the respective arylalkyl subunits from several known sigma (σ) receptor ligands were synthesized and evaluated for their affinity against σ receptors and dopamine receptors. The hybrid trishomocubane-derived ligands (4-6) showed good selectivity for σ(1) and σ(2) receptors over multiple dopamine receptors. The molecular hybrid obtained from haloperidol and 4-azahexacyclo[5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecan-3-ol (4, σ(1)K(i)=27 nM, σ(2)K(i)=55 nM) showed reduced affinity for D(1)-D(5) dopamine receptors when compared to haloperidol itself. The compound with the greatest σ(1) affinity in the series, benzamide 4 (σ(1)K(i)=7.6 nM, σ(2)K(i)=225 nM) showed a complete reversal of the subtype selectivity displayed by the highly σ(2) selective parent benzamide, RHM-2 (3, σ(1)K(i)=10412 nM, σ(2)K(i)=13.3 nM).

Amyotrophic lateral sclerosis-associated mutant profilin 1 increases dendritic arborisation and spine formation in primary hippocampal neurons

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease and familial ALS accounts for 10% of cases. The identification of familial ALS mutations in the actin-binding protein profilin 1 directly implicates actin dynamics and regulation in the pathogenesis of ALS. The mechanism by which these mutations cause ALS is unknown. In this study we show that expression of the ALS-associated actin-binding deficient mutant of PFN1 (PFN1(C71G)) results in increased dendritic arborisation and spine formation, and cytoplasmic inclusions in cultured mouse hippocampal neurons.

First Demonstration of Positive Allosteric-like Modulation at the Human Wild Type Translocator Protein (TSPO)

We show that changing the number and position of nitrogen atoms in the heteroatomic core of a pyrazolopyrimidine acetamide is sufficient to induce complex binding to wild type human TSPO. Only compounds with this complex binding profile lacked intrinsic effect on glioblastoma proliferation but positively modulated the antiproliferative effects of a synthetic TSPO ligand. To the best of our knowledge this is the first demonstration of allosteric-like interaction at the wild type human TSPO.

The Polyphenol Altenusin Inhibits in Vitro Fibrillization of Tau and Reduces Induced Tau Pathology in Primary Neurons

In Alzheimers disease, the microtubule-associated protein tau forms intracellular neurofibrillary tangles (NFTs). A critical step in the formation of NFTs is the conversion of soluble tau into insoluble filaments. Accordingly, a current therapeutic strategy in clinical trials is aimed at preventing tau aggregation. Here, we assessed altenusin, a bioactive polyphenolic compound, for its potential to inhibit tau aggregation. Altenusin inhibits aggregation of tau protein into paired helical filaments in vitro. This was associated with stabilization of tau dimers and other oligomers into globular structures as revealed by atomic force microscopy. Moreover, altenusin reduced tau phosphorylation in cells expressing pathogenic tau, and prevented neuritic tau pathology induced by incubation of primary neurons with tau fibrils. However, treatment of tau transgenic mice did not improve neuropathology and functional deficits. Taken together, altenusin prevents tau fibrillization in vitro and induced tau pathology in neurons.

Peptide nanofiber substrates for long-term culturing of primary neurons

The culturing of primary neurons represents a central pillar of neuroscience research. Primary neurons are derived directly from brain tissue and recapitulate key aspects of neuronal development in an in vitro setting. Unlike neural stem cells, primary neurons do not divide; thus, initial attachment of cells to a suitable substrate is critical. Commonly used polylysine substrates can suffer from batch variability owing to their polymeric nature. Herein, we report the use of chemically well-defined, self-assembling tetrapeptides as substrates for primary neuronal culture. These water-soluble peptides assemble into fibers which facilitate adhesion and development of primary neurons, their long-term survival (>40 days), synaptic maturation, and electrical activity. Furthermore, these substrates are permissive toward neuronal transfection and transduction which, coupled with their uniformity and reproducible nature, make them suitable for a wide variety of applications in neuroscience.