Jeanna M. Wheeler

Loss of murine TDP-43 disrupts motor function and plays an essential role in embryogenesis

Abnormal TDP-43 aggregation is a prominent feature in the neuropathology of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration. Mutations in TARDBP, the gene encoding TDP-43, cause some cases of ALS. The normal function of TDP-43 remains incompletely understood. To better understand TDP-43 biology, we generated mutant mice carrying a genetrap disruption of Tardbp. Mice homozygous for loss of TDP-43 are not viable. TDP-43 deficient embryos die about day 7.5 of embryonic development thereby demonstrating that TDP-43 protein is essential for normal prenatal development and survival. However, heterozygous Tardbp mutant mice exhibit signs of motor disturbance and muscle weakness. Compared with wild type control littermates, Tardbp+/− animals have significantly decreased forelimb grip strength and display deficits in a standard inverted grid test despite no evidence of pathologic changes in motor neurons. Thus, TDP-43 is essential for viability, and mild reduction in TDP-43 function is sufficient to cause motor deficits without degeneration of motor neurons.

Dopamine D2 Receptor Antagonism Suppresses Tau Aggregation and Neurotoxicity

BACKGROUND Tauopathies, including Alzheimers disease and frontotemporal dementia, are diseases characterized by the formation of pathological tau protein aggregates in the brain and progressive neurodegeneration. Presently no effective disease-modifying treatments exist for tauopathies. METHODS To identify drugs targeting tau neurotoxicity, we have used a Caenorhabditis elegans model of tauopathy to screen a drug library containing 1120 compounds approved for human use for the ability to suppress tau-induced behavioral effects. RESULTS One compound, the typical antipsychotic azaperone, improved the motility of tau transgenic worms, reduced levels of insoluble tau, and was protective against neurodegeneration. We found that azaperone reduces insoluble tau in a human cell culture model of tau aggregation and that other antipsychotic drugs (flupenthixol, perphenazine, and zotepine) also ameliorate the effects of tau expression in both models. CONCLUSIONS Reduction of dopamine signaling through the dopamine D2 receptor with the use of gene knockouts in Caenorhabditis elegans or RNA interference knockdown in human cell culture has similar protective effects against tau toxicity. These results suggest dopamine D2 receptor antagonism holds promise as a potential neuroprotective strategy for targeting tau aggregation and neurotoxicity.

The role of MSUT-2 in tau neurotoxicity: a target for neuroprotection in tauopathy?

We previously developed a transgenic Caenorhabditis elegans model of human tauopathy disorders by expressing human tau in nematode worm neurons to explore genetic pathways contributing to tau-induced neurodegeneration. This animal model recapitulates several hallmarks of human tauopathies, including altered behaviour, accumulation of detergent-insoluble phosphorylated tau protein and neurodegeneration. To identify genes required for tau neurotoxicity, we carried out a forward genetic screen for mutations that suppress tau neurotoxicity. We ultimately cloned the sut-2 (suppressor of tau pathology-2) gene, mutations in which alleviate tau neurotoxicity in C. elegans. SUT-2 encodes a novel subtype of CCCH zinc-finger protein conserved across animal phyla. SUT-2 shares significant identity with the mammalian SUT-2 (MSUT-2). We identified components of the aggresome as binding partners of MSUT-2. Thus we hypothesize that MSUT-2 plays a role in the formation and/or clearance of protein aggregates. We are currently exploring the role of MSUT-2 in tauopathy using mammalian systems. The identification of sut-2 as a gene required for tau neurotoxicity in C. elegans suggests new neuroprotective strategies targeting MSUT-2 that may be effective in modulating tau neurotoxicity in human tauopathy disorders.

High copy wildtype human 1N4R tau expression promotes early pathological tauopathy accompanied by cognitive deficits without progressive neurofibrillary degeneration

IntroductionAccumulation of insoluble conformationally altered hyperphosphorylated tau occurs as part of the pathogenic process in Alzheimer’s disease (AD) and other tauopathies. In most AD subjects, wild-type (WT) tau aggregates and accumulates in neurofibrillary tangles and dystrophic neurites in the brain; however, in some familial tauopathy disorders, mutations in the gene encoding tau cause disease.ResultsWe generated a mouse model, Tau4RTg2652, that expresses high levels of normal human tau in neurons resulting in the early stages of tau pathology. In this model, over expression of WT human tau drives pre-tangle pathology in young mice resulting in behavioral deficits. These changes occur at a relatively young age and recapitulate early pre-tangle stages of tau pathology associated with AD and mild cognitive impairment. Several features distinguish the Tau4RTg2652 model of tauopathy from previously described tau transgenic mice. Unlike other mouse models where behavioral and neuropathologic changes are induced by transgenic tau harboring MAPT mutations pathogenic for frontotemporal lobar degeneration (FTLD), the mice described here express the normal tau sequence.ConclusionsFeatures of Tau4RTg2652 mice distinguishing them from other established wild type tau overexpressing mice include very early phenotypic manifestations, non-progressive tau pathology, abundant pre-tangle and phosphorylated tau, sparse oligomeric tau species, undetectable fibrillar tau pathology, stability of tau transgene copy number/expression, and normal lifespan. These results suggest that Tau4RTg2652 animals may facilitate studies of tauopathy target engagement where WT tau is driving tauopathy phenotypes.

Potential neuroprotective strategies against tauopathy

Tauopathies are neurodegenerative diseases, including AD (Alzheimers disease) and FTLD-T (tau-positive frontotemporal lobar degeneration), with shared pathology presenting as accumulation of detergent-insoluble hyperphosphorylated tau deposits in the central nervous system. The currently available treatments for AD address only some of the symptoms, and do not significantly alter the progression of the disease, namely the development of protein aggregates and loss of functional neurons. The development of effective treatments for various tauopathies will require the identification of common mechanisms of tau neurotoxicity, and pathways that can be modulated to protect against neurodegeneration. Model organisms, such as Caenorhabditis elegans, provide methods for identifying novel genes and pathways that are involved in tau pathology and may be exploited for treatment of various tauopathies. In the present paper, we summarize data regarding characterization of MSUT2 (mammalian suppressor of tau pathology 2), a protein identified in a C. elegans tauopathy model and subsequently shown to modify tau toxicity in mammalian cell culture via the effects on autophagy pathways. MSUT2 represents a potential drug target for prevention of tau-related neurodegeneration.

THE POLY(A) BINDING PROTEIN MSUT2 MODULATES GLIOSIS IN TAUOPATHY

also examined in other tauopathies (FTLD-Tau and corticobasal degeneration), other rare amyloidoses (familial Danish dementia, HCHWA-D, Hungarian amyloidosis), and in Down syndrome. Interaction of secernin-1 with phosphorylated tau or Ab in human cortical tissue was examined using co-immunoprecipitation. Results: Immunohistochemistry showed that secernin-1 is a neuronal protein that abundantly accumulates in NFTs and plaque-associated dystrophic neurites in AD. Quantification of secernin-1 immunohistochemistry confirmed that there was significantly more secernin-1 inside NFTs in comparison to surrounding neurons (p<0.0001). Secernin-1 colocalization in NFTs appeared early in NFT development; secernin-1 was present in NFTs in MCI and secernin-1 colocalized with the antibodyMC1, a marker of early NFT development. Additionally, there was increased secernin-1 expression in Down syndrome. Unexpectedly, secernin-1 did not colocalize with phosphorylated tau positive lesions in other types of tauopathies, suggesting that its presence is specific to NFTs in AD. Co-immunoprecipitation studies showed that secernin-1 directly bound to phosphorylated tau in human AD brains. Further co-immunoprecipitation studies are ongoing to determine whether secernin-1 also binds to Ab. Conclusions:Here we present evidence that secernin-1 is a novel early marker of NFTs in AD. Protein binding studies suggest that its presence in NFTs is a result of direct binding to phosphorylated tau. As such, secernin-1 has potential as a novel therapeutic target for AD and could serve as a useful biomarker for AD.

Identifying protective strategies against tau neurotoxicity

but not GSK3̂I6, reduced BACE1-mediated cleavage of APP and Ab production by decreasing BACE1 gene transcription and expression. The regulation of BACE1 gene expression by GSK3b is dependent on NF̂IB signaling. Specific inhibition of GSK3 signaling markedly reduced Ab deposition and neuritic plaque formation, and rescued memory deficits in the double transgenic AD model mice. Taken together, our data provide evidence for regulation of BACE1 expression and AD pathogenesis by GSK3b and that inhibition of GSK3 signaling can reduce Ab neuropathology and alleviate memory deficits in AD model mice. Conclusions: Our study suggests that interventions that target the b-isoform of GSK3 specifically may be a safe and effective approach for treating AD.