F-Actin Binding Regions on the Androgen Receptor and Huntingtin Increase Aggregation and Alter Aggregate Characteristics

Protein aggregation is associated with neurodegeneration. Polyglutamine expansion diseases such as spinobulbar muscular atrophy and Huntington disease feature proteins that are destabilized by an expanded polyglutamine tract in their N-termini. It has previously been reported that intracellular aggregation of these target proteins, the androgen receptor (AR) and huntingtin (Htt), is modulated by actin-regulatory pathways. Sequences that flank the polyglutamine tract of AR and Htt might influence protein aggregation and toxicity through protein-protein interactions, but this has not been studied in detail. Here we have evaluated an N-terminal 127 amino acid fragment of AR and Htt exon 1. The first 50 amino acids of ARN127 and the first 14 amino acids of Htt exon 1 mediate binding to filamentous actin in vitro. Deletion of these actin-binding regions renders the polyglutamine-expanded forms of ARN127 and Htt exon 1 less aggregation-prone, and increases the SDS-solubility of aggregates that do form. These regions thus appear to alter the aggregation frequency and type of polyglutamine-induced aggregation. These findings highlight the importance of flanking sequences in determining the propensity of unstable proteins to misfold

Proliferating cell nuclear antigen is required for loading of the SMCX/KMD5C histone demethylase onto chromatin

UNLABELLED: ABSTRACT: BACKGROUND: Histone methylation is regulated by a large number of histone methyltransferases and demethylases. The recently discovered SMCX/KMD5C demethylase has been shown to remove methyl residues from lysine 4 of histone H3 (H3K4), and constitutes an important component of the regulatory element-1-silencing transcription factor (REST) protein complex. However, little is known about the cellular mechanisms that control SMCX activity and intracellular trafficking. RESULTS: In this study, we found that small interfering RNA-mediated knockdown of proliferating cell nuclear antigen (PCNA) resulted in the reduction of the chromatin-bound SMCX fraction. We identified a PCNA-interaction protein motif (PIP box) in the SMCX protein. Using site-directed mutagenesis, we found that the amino acids of the SMCX PIP box are involved in the association of SMCX with PCNA and its interaction with chromatin. CONCLUSIONS: Our data indicate that the intracellular trafficking of SMCX is controlled by its association with PCNA

In vivo microdialysis reveals age-dependent decrease of brain interstitial fluid tau levels in P301S human tau transgenic mice

Although tau is a cytoplasmic protein, it is also found in brain extracellular fluids, e.g., CSF. Recent findings suggest that aggregated tau can be transferred between cells and extracellular tau aggregates might mediate spread of tau pathology. Despite these data, details of whether tau is normally released into the brain interstitial fluid (ISF), its concentration in ISF in relation to CSF, and whether ISF tau is influenced by its aggregation are unknown. To address these issues, we developed a microdialysis technique to analyze monomeric ISF tau levels within the hippocampus of awake, freely moving mice. We detected tau in ISF of wild-type mice, suggesting that tau is released in the absence of neurodegeneration. ISF tau was significantly higher than CSF tau and their concentrations were not significantly correlated. Using P301S human tau transgenic mice (P301S tg mice), we found that ISF tau is fivefold higher than endogenous murine tau, consistent with its elevated levels of expression. However, following the onset of tau aggregation, monomeric ISF tau decreased markedly. Biochemical analysis demonstrated that soluble tau in brain homogenates decreased along with the deposition of insoluble tau. Tau fibrils injected into the hippocampus decreased ISF tau, suggesting that extracellular tau is in equilibrium with extracellular or intracellular tau aggregates. This technique should facilitate further studies of tau secretion, spread of tau pathology, the effects of different disease states on ISF tau, and the efficacy of experimental treatments

N17 Modifies mutant Huntingtin nuclear pathogenesis and severity of disease in HD BAC transgenic mice.

The nucleus is a critical subcellular compartment for the pathogenesis of polyglutamine disorders, including Huntington's disease (HD). Recent studies suggest the first 17-amino-acid domain (N17) of mutant huntingtin (mHTT) mediates its nuclear exclusion in cultured cells. Here, we test whether N17 could be a molecular determinant of nuclear mHTT pathogenesis in vivo. BAC transgenic mice expressing mHTT lacking the N17 domain (BACHD-ΔN17) show dramatically accelerated mHTT pathology exclusively in the nucleus, which is associated with HD-like transcriptionopathy. Interestingly, BACHD-ΔN17 mice manifest more overt disease-like phenotypes than the original BACHD mice, including body weight loss, movement deficits, robust striatal neuron loss, and neuroinflammation. Mechanistically, N17 is necessary for nuclear exclusion of small mHTT fragments that are part of nuclear pathology in HD. Together, our study suggests that N17 modifies nuclear pathogenesis and disease severity in HD mice by regulating subcellular localization of known nuclear pathogenic mHTT species

Widespread Tau Seeding Activity at Early Braak Stages

Transcellular propagation of tau aggregates may underlie the progression of pathology in Alzheimer\u27s disease (AD) and other tauopathies. Braak staging (B1, B2, B3) is based on phospho-tau accumulation within connected brain regions: entorhinal cortex (B1); hippocampus/limbic system (B2); and frontal and parietal lobes (B3). We previously developed a specific and sensitive assay that uses flow cytometry to quantify tissue seeding activity based on fluorescence resonance energy transfer (FRET) in cells that stably express tau reporter proteins. In a tauopathy mouse model, we have detected seeding activity far in advance of histopathological changes. It remains unknown whether individuals with AD also develop seeding activity prior to accumulation of phospho-tau. We measured tau seeding activity across four brain regions (hippocampus, frontal lobe, parietal lobe, and cerebellum) in 104 fresh-frozen human AD brain samples from all Braak stages. We observed widespread seeding activity, notably in regions predicted to be free of phospho-tau deposition, and in detergent-insoluble fractions that lacked tau detectable by ELISA. Seeding activity correlated positively with Braak stage and negatively with MMSE. Our results are consistent with early transcellular propagation of tau seeds that triggers subsequent development of neuropathology. The FRET-based seeding assay may also complement standard neuropathological classification of tauopathies

Anti-tau antibody reduces insoluble tau and decreases brain atrophy

OBJECTIVE: We previously found a strong reduction in tau pathology and insoluble tau in P301S tau transgenic mice following intracerebroventricular infusion of the anti-tau antibody HJ8.5. We sought to determine the effects of HJ8.5 in the same model following peripheral administration. METHODS: The primary objective was to determine if HJ8.5 administered at a dose of 50 mg kg(−1) week(−1) by intraperitoneal (IP) injection to 6-month-old P301S mice for 3 months would influence phospho-tau (p-tau) accumulation, tau insolubility, and neurodegeneration. RESULTS: Treatment with HJ8.5 at 50 mg/kg showed a very strong decrease in detergent-insoluble tau. Importantly, HJ8.5 significantly reduced the loss of cortical and hippocampal tissue volumes compared to control treated mice. HJ8.5 treatment reduced hippocampal CA1 cellular layer staining with the p-tau antibody AT8 and thio-S-positive tau aggregates in piriform cortex and amygdala. Moreover, mice treated with HJ8.5 at 50 mg/kg showed a decrease in motor/sensorimotor deficits compared to vehicle-treated mice. Some effects of HJ8.5, including reduction in brain atrophy, and p-tau immunostaining were also seen with a dose of 10 mg kg(−1) week(−1). In BV2-microglial cells, we observed significantly higher uptake of P301S tau aggregates in the presence of HJ8.5. HJ8.5 treatment also resulted in a large dose-dependent increase of tau in the plasma. INTERPRETATION: Our results indicate that systemically administered anti-tau antibody HJ8.5 significantly decreases insoluble tau, decreases brain atrophy, and improves motor/sensorimotor function in a mouse model of tauopathy. These data further support the idea that anti-tau antibodies should be further assessed as a potential treatment for tauopathies

A Rapid Cellular FRET Assay of Polyglutamine Aggregation Identifies a Novel Inhibitor

AbstractMany neurodegenerative diseases, including tauopathies, Parkinson's disease, amyotrophic lateral sclerosis, and the polyglutamine diseases, are characterized by intracellular aggregation of pathogenic proteins. It is difficult to study modifiers of this process in intact cells in a high-throughput and quantitative manner, although this could facilitate molecular insights into disease pathogenesis. Here we introduce a high-throughput assay to measure intracellular polyglutamine protein aggregation using fluorescence resonance energy transfer (FRET). We screened over 2800 biologically active small molecules for inhibitory activity and have characterized one lead compound in detail. Y-27632, an inhibitor of the Rho-associated kinase p160ROCK, diminished polyglutamine protein aggregation (EC50 ≅ 5 μM) and reduced neurodegeneration in a Drosophila model of polyglutamine disease. This establishes a novel high-throughput approach to study protein misfolding and aggregation associated with neurodegenerative diseases and implicates a signaling pathway of previously unrecognized importance in polyglutamine protein processing