treating-sca1-mice-with-water-soluble-compounds-to-non-specifically

Treating SCA1 Mice with Water-Soluble Compounds to Non-Specifically Boost Mitochondrial Function

Mitochondrial dysfunction plays a significant role in the aging process and in neurodegenerative diseases including several hereditary spinocerebellar ...

Skidmore College

The principal pathological features of Alzheimer's disease (AD) are extracellular amyloid plaques and intracellular neurofibrillary tangles, the latter composed of the microtubule-binding protein tau assembled into paired helical and straight filaments. Recent studies suggest that these pathological entities may be functionally linked, although the mechanisms by which amyloid deposition promotes pathological tau filament assembly are poorly understood. Here, we report that tau is proteolyzed by multiple caspases at a highly conserved aspartate residue (Asp421) in its C terminus in vitro and in neurons treated with amyloid-beta (Abeta) (1-42) peptide. Tau is rapidly cleaved at Asp421 in Abeta-treated neurons (within 2 h), and its proteolysis appears to precede the nuclear events of apoptosis. We also demonstrate that caspase cleavage of tau generates a truncated protein that lacks its C-terminal 20 amino acids and assembles more rapidly and more extensively into tau filaments in vitro than wild-type tau. Using a monoclonal antibody that specifically recognizes tau truncated at Asp421, we show that tau is proteolytically cleaved at this site in the fibrillar pathologies of AD brain. Taken together, our results suggest a novel mechanism linking amyloid deposition and neurofibrillary tangles in AD: Abeta peptides promote pathological tau filament assembly in neurons by triggering caspase cleavage of tau and generating a proteolytic product with enhanced polymerization kinetics.

Caspase cleavage of tau: linking amyloid and neurofibrillary tangles in Alzheimer's disease.

Acido arachidonico (AA), rilasciato in risposta alla stimolazione (mAChR) recettori muscarinici dell&#39;acetilcolina, in precedenza &egrave; stato segnalato per funzionare come un inibitore reversibile feedback del mAChR. Per determinare se gli effetti di AA associazione per il mAChR sono sottotipo specifico e se AA inibisce il legame ligando con altre proteine recettori accoppiati G (GPCR), gli effetti di AA su Associazione ligando per i sottotipi di mAChR (M1, M2, M3, M4 e M5) e il micro-oppioidi recettore, recettori beta2-adrenergici (beta2-AR), sono stati esaminati, recettore 5-idrossitriptamina (5-HTR) e recettori nicotinici. AA &egrave; stato trovato per inibire il legame ligando per tutti i sottotipi di mAChR, beta2-AR, 5-HTR e il recettore di micro-oppioidi. Tuttavia, AA non inibisce legame del ligando al recettore nicotinico, anche a concentrazioni elevate di AA. Cos&igrave;, AA inibisce diversi tipi di GPCR, con inibizione del 50% che si verificano a mamma 3-25, mentre il recettore nicotinico, un non-GPCR, rimane inalterato. Sono necessarie ulteriori ricerche per determinare il meccanismo mediante il quale AA inibisce la funzione GPCR.

Inibizione del legame ligando di recettori accoppiati a proteine G di acido arachidonico.

Arachidonic acid (AA), released in response to muscarinic acetylcholine receptor (mAChR) stimulation, previously has been reported to function as a reversible feedback inhibitor of the mAChR. To determine if the effects of AA on binding to the mAChR are subtype specific and whether AA inhibits ligand binding to other G protein-coupled receptors (GPCRs), the effects of AA on ligand binding to the mAChR subtypes (M1, M2, M3, M4, and M5) and to the micro-opioid receptor, beta2-adrenergic receptor (beta2-AR), 5-hydroxytryptamine receptor (5-HTR), and nicotinic receptors were examined. AA was found to inhibit ligand binding to all mAChR subtypes, to the beta2-AR, the 5-HTR, and to the micro-opioid receptor. However, AA does not inhibit ligand binding to the nicotinic receptor, even at high concentrations of AA. Thus, AA inhibits several types of GPCRs, with 50% inhibition occurring at 3-25 MuM, whereas the nicotinic receptor, a non-GPCR, remains unaffected. Further research is needed to determine the mechanism by which AA inhibits GPCR function.

Inhibition of ligand binding to G protein-coupled receptors by arachidonic acid.

Lib&eacute;r&eacute; en r&eacute;ponse &agrave; la stimulation des r&eacute;cepteurs (mAChR) muscariniques de l&#39;ac&eacute;tylcholine, l&#39;acide arachidonique (AA), pr&eacute;c&eacute;demment a &eacute;t&eacute; signal&eacute; pour fonctionner comme un inhibiteur r&eacute;versible de r&eacute;troaction de la mAChR. Afin de d&eacute;terminer si les effets de l&#39;AA sur la liaison &agrave; la mAChR sous-type sp&eacute;cifique et si AA inhibe la liaison du ligand d&#39;autres G protein-coupled receptors (RCPG), les effets de l&#39;AA sur la liaison du ligand pour les sous-types mAChR (M1, M2, M3, M4 et M5) et le r&eacute;cepteur opio&iuml;de micro, r&eacute;cepteurs b&ecirc;ta2-adr&eacute;nergiques (b&ecirc;ta2-AR), le r&eacute;cepteur 5-hydroxytryptamine (5-dB) et les r&eacute;cepteurs nicotiniques ont &eacute;t&eacute; examin&eacute;s. AA a &eacute;t&eacute; trouv&eacute; pour inhiber la liaison du ligand &agrave; tous les sous-types de mAChR, &agrave; la b&ecirc;ta2-AR, la 5-dB et pour le r&eacute;cepteur micro-opio&iuml;de. Cependant, AA n&#39;inhibe pas la liaison du ligand au r&eacute;cepteur nicotinique, m&ecirc;me &agrave; des concentrations &eacute;lev&eacute;es d&#39;AA. Ainsi, AA inhibe plusieurs types des RCPG, avec 50 % d&#39;inhibition se produisant &agrave; la maman de 3-25, tandis que le r&eacute;cepteur nicotinique, un non-RCPG, demeure inchang&eacute;e. Il faut poursuivre les recherches afin de d&eacute;terminer le m&eacute;canisme par lequel AA inhibe la fonction GPCR.

Inhibition de la liaison du ligand pour les r&eacute;cepteurs coupl&eacute;s aux prot&eacute;ines G par l&#39;acide arachidonique.

&Aacute;cido araquid&oacute;nico (AA), aparecido en respuesta a la estimulaci&oacute;n de receptores (mAChR) muscar&iacute;nico, previamente se ha divulgado para funcionar como un inhibidor reversible de la regeneraci&oacute;n de la mAChR. Para determinar si los efectos de AA en Uni&oacute;n a la mAChR subtipo espec&iacute;fico y si AA inhibe ligando a otros G prote&iacute;na-junt&oacute; los receptores (GPCRs), los efectos de AA en el ligando para los subtipos de mAChR (M1, M2, M3, M4 y M5) y el micro-opioid receptor, receptor beta2-adren&eacute;rgico (beta2-AR), el receptor 5-Hidroxitriptamina (5-HTR) y los receptores nicot&iacute;nicos fueron examinados. AA fue encontrado para inhibir ligando todos los subtipos de mAChR, beta2-AR, el reactor de 5 y el receptor del micro-opioide. No obstante, AA no inhibe ligando al receptor nicot&iacute;nico, incluso a altas concentraciones de AA. Por lo tanto, AA inhibe varios tipos de GPCRs, con 50% de inhibici&oacute;n que ocurren en la momia 3-25, mientras que los receptores nicot&iacute;nicos, un no-GPCR, permanece invariable. Se necesitan m&aacute;s investigaciones para determinar el mecanismo por el cual AA inhibe la funci&oacute;n GPCR.

Inhibici&oacute;n de ligando de receptores acoplados a prote&iacute;na de G de &aacute;cido araquid&oacute;nico.

The mitogen-activated protein (MAP) kinase SAPK/JNK phosphorylates tau protein at many of its proline-directed serine/threonine residues in vitro and is a likely candidate kinase to phosphorylate the pathologically relevant S422 site on tau. Since phosphorylation of tau, particularly at S422, is a relatively early marker of AD and seems to precede tangle formation, it appears likely that an early form of activated SAPK/JNK might be detected by immunohistochemical means around the time that tau begins to aggregate into tangles. We report here that an antibody to phospho-SAPK/JNK (p-SAPK/JNK) reacts with several types of lesions including granular bodies in limbic areas; NFTs in limbic cortex and temporal neocortex; occasional neuritic plaques in temporal neocortex; and select axons in the hippocampus, entorhinal cortex, and inferior temporal cortex. In order to characterize the appearance of granular p-SAPK/JNK and determine if it appears early in disease, we employed an immunohistochemical study of postmortem limbic tissue from 20 cases ranging from Braak stages I-VI. By co-staining with anti-tau antibodies specific to different molecular events that occur during tangle evolution, we were able to identify the appearance of p-SAPK/JNK in early Braak stages with an increased elevation during the limbic stages of AD and during the early stages of the formation of individual hippocampal tangles.

Formation of phospho-SAPK/JNK granules in the hippocampus is an early event in Alzheimer disease.

Protein misfolding is a distinguishing feature of a number of neurodegenerative diseases. Accumulation of misfolded protein often results in cellular lesions, the location of lesions correlating with the nature of symptoms. Alzheimer's disease (AD), Progressive Supranuclear Palsy (PSP), Corticobasal Degeneration (CBD) and Pick's Disease (PiD) all present with pathological lesions containing hyperphosphorylated filamentous tau protein; however, the location and type of lesion varies. In addition, granulovacuolar degeneration (GVD) bodies have been reported within hippocampal pyramidal neurons in AD, PSP, CBD and PiD tissue. GVDs are defined as electron-dense granules within double membrane-bound cytoplasmic vacuoles. We have previously reported that the phosphorylated form of stress-activated protein kinase/c-Jun N-terminal kinase (p-SAPK/JNK) accumulates in granules within hippocampal pyramidal cell bodies in AD tissue at the time that hyperphosphorylated tau begins to aggregate into early-stage NFTs. We now report that p-SAPK/JNK granules are found within the hippocampal CA1 region of PSP, CBD and PiD cases as well and that these granules are likely GVD bodies. Quantitatively, p-SAPK/JNK granules and GVDs are found in comparable numbers of CA1 cells. Within cells, p-SAPK/JNK granules are distributed throughout the cytoplasm in a manner similar to the distribution of GVDs and a subset of granules co-localize with GVD markers. Ultrastructurally, p-SAPK/JNK granules are located in large cytoplasmic vacuoles, thereby fitting the definition of a GVD body. With the implication of granular p-SAPK/JNK as a marker of GVDs, our study strongly suggests that a heterogeneous group of proteins form GVDs. The mechanism of GVD formation is therefore an interesting one, and is likely separate and distinct from the mechanism of tau inclusion formation.

Relation of hippocampal phospho-SAPK/JNK granules in Alzheimer's disease and tauopathies to granulovacuolar degeneration bodies.

Neurofibrillary tangles (NFTs), comprising human intracellular microtubule-associated protein tau, are one of the hallmarks of tauopathies, including Alzheimer's disease. Recently, a report that caspase-cleaved tau is present in NFTs has led to the hypothesis that the mechanisms underlying NFT formation may involve the apoptosis cascade. Here, we show that adenoviral infection of tau into COS-7 cells induces activation of c-jun N-terminal kinase (JNK), followed by excessive phosphorylation of tau and its cleavage by caspase. However, JNK activation alone was insufficient to induce sodium dodecyl sulfate (SDS)-insoluble tau aggregation and additional phosphorylation by GSK-3beta was required. In SH-SY5Y neuroblastoma cells, overexpression of active JNK and GSK-3beta increased caspase-3 activation and cytotoxicity more than overexpression of tau alone. Taken together, these results indicate that, although JNK activation may be a primary inducing factor, further phosphorylation of tau is required for neuronal death and NFT formation in neurodegenerative diseases, including those characterized by tauopathy.

Active c-jun N-terminal kinase induces caspase cleavage of tau and additional phosphorylation by GSK-3beta is required for tau aggregation.

The age-related pathological cascade underlying intraneuronal tau formation in 3xTg-AD mice, which harbor the human APP(Swe), PS1(M126V) , and Tau(P301L) gene mutations, remains unclear. At 3 weeks of age, AT180, Alz50, MC1, AT8, and PHF-1 intraneuronal immunoreactivity appeared in the amygdala and hippocampus and at later ages in the cortex of 3xTg-AD mice. AT8 and PHF-1 staining was fixation dependent in young mutant mice. 6E10 staining was seen at all ages. Fluorescent immunomicroscopy revealed CA1 neurons dual stained for 6E10 and Alz50 and single Alz50 immunoreactive neurons in the subiculum at 3 weeks and continuing to 20 months. Although electron microscopy confirmed intraneuronal cytoplasmic Alz50, AT8, and 6E10 reaction product in younger 3xTg-AD mice, straight filaments appeared at 23 months of age in female mice. The present data suggest that other age-related biochemical mechanisms in addition to early intraneuronal accumulation of 6E10 and tau underlie the formation of tau filaments in 3xTg-AD mice.

Staging of Alzheimer's pathology in triple transgenic mice: a light and electron microscopic analysis.

Many neurodegenerative disorders, such as Alzheimer's, Parkinson's and polyglutamine diseases, share a common pathogenic mechanism: the abnormal accumulation of disease-causing proteins, due to either the mutant protein's resistance to degradation or overexpression of the wild-type protein. We have developed a strategy to identify therapeutic entry points for such neurodegenerative disorders by screening for genetic networks that influence the levels of disease-driving proteins. We applied this approach, which integrates parallel cell-based and Drosophila genetic screens, to spinocerebellar ataxia type 1 (SCA1), a disease caused by expansion of a polyglutamine tract in ataxin 1 (ATXN1). Our approach revealed that downregulation of several components of the RAS-MAPK-MSK1 pathway decreases ATXN1 levels and suppresses neurodegeneration in Drosophila and mice. Importantly, pharmacological inhibitors of components of this pathway also decrease ATXN1 levels, suggesting that these components represent new therapeutic targets in mitigating SCA1. Collectively, these data reveal new therapeutic entry points for SCA1 and provide a proof-of-principle for tackling other classes of intractable neurodegenerative diseases.

RAS-MAPK-MSK1 pathway modulates ataxin 1 protein levels and toxicity in SCA1.

Ataxin-1 protein expression is found in the cytoplasm and nucleus of Purkinje cells, the primary site of spinocerebellar ataxia type 1 (SCA1). Phosphorylation at S776 occurs in the cytoplasm and stabilizes the protein through interaction with 14-3-3, allowing it to translocate into the nucleus where disease is initiated. Phosphorylation and stabilization are enhanced when the polyglutamine expansion is present. In this chapter, we present a model of neurodegeneration in SCA1 initiated through phosphorylation at S776 by cAMP-dependent protein kinase (PKA) and enhanced by the presence of the polyglutamine expansion. The biological methods used to uncover SCA1 pathogenesis and phosphorylation at S776 are described.

Regulation of ataxin-1 phosphorylation and its impact on biology.

Alzheimer's disease (AD) is a progressive neurodegenerative disease marked by deficits in episodic memory, working memory (WM), and executive function. Examples of executive dysfunction in AD include poor selective and divided attention, failed inhibition of interfering stimuli, and poor manipulation skills. Although episodic deficits during disease progression have been widely studied and are the benchmark of a probable AD diagnosis, more recent research has investigated WM and executive function decline during mild cognitive impairment (MCI), also referred to as the preclinical stage of AD. MCI is a critical period during which cognitive restructuring and neuroplasticity such as compensation still occur; therefore, cognitive therapies could have a beneficial effect on decreasing the likelihood of AD progression during MCI. Monitoring performance on working memory and executive function tasks to track cognitive function may signal progression from normal cognition to MCI to AD. The present review tracks WM decline through normal aging, MCI, and AD to highlight the behavioral and neurological differences that distinguish these three stages in an effort to guide future research on MCI diagnosis, cognitive therapy, and AD prevention.

Working memory and executive function decline across normal aging, mild cognitive impairment, and Alzheimer's disease.

Aggregation-prone proteins in neurodegenerative disease disrupt cellular protein stabilization and degradation pathways. The neurodegenerative disease spinocerebellar ataxia type 1 (SCA1) is caused by a coding polyglutamine expansion in the Ataxin-1 gene (ATXN1), which gives rise to the aggregation-prone mutant form of ATXN1 protein. Cerebellar Purkinje neurons, preferentially vulnerable in SCA1, produce ATXN1 protein in both cytoplasmic and nuclear compartments. Cytoplasmic stabilization of ATXN1 by phosphorylation and 14-3-3-mediated mechanisms ultimately drive translocation of the protein to the nucleus where aggregation may occur. However, experimental inhibition of phosphorylation and 14-3-3 binding results in rapid degradation of ATXN1, thus preventing nuclear translocation and cellular toxicity. The exact mechanism of cytoplasmic ATXN1 degradation is currently unknown; further investigation of degradation may provide future therapeutic targets. This review examines the present understanding of cytoplasmic ATXN1 stabilization and potential degradation mechanisms during normal and pathogenic states.

Stabilization and Degradation Mechanisms of Cytoplasmic Ataxin-1.

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Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disorder that primarily affects the cerebellum and brainstem. The genetic mutation is an expansion of CAG trinucleotide repeats within the coding region of the ataxin-1 gene, characterizing SCA1 as a polyglutamine expansion disease like Huntington's. As with most polyglutamine expansion diseases, SCA1 follows the rules of genetic anticipation: the larger the expansion, the earlier and more rapid the symptoms. Unlike the majority of polyglutamine expansion diseases, the presence of histidine interruptions within the polyglutamine tract of ataxin-1 protein can prevent or mitigate disease. The present review aims to synthesize three decades of research on the ataxin-1 polyglutamine expansion mutation that causes SCA1. Data from genetic population studies and case studies is gathered along with data from manipulation studies in animal models. Specifically, we examine the molecular mechanisms that cause tract expansions and contractions, the molecular pathways that confer instability of tract length in gametic and somatic cells resulting in gametic and somatic mosaicism, the influence of maternal or paternal factors in inheritance of the expanded allele, and the effects of CAT/histidine interruptions to the ataxin-1 allele and protein product. Our review of existing data supports the following conclusions. First, polyCAG expansion of gametic alleles occur due to the failure of gap repair mechanisms for single or double strand breaks during the transition from an immature haploid spermatid to a mature haploid sperm cell. Equivalent failures were not detected in female gametic cells. Second, polyCAG expansion of somatic alleles occur due to hairpins formed on Okazaki fragments and slipped strand structures due to failures in mismatch repair and transcription-coupled nucleotide excision repair mechanisms. Third, CAT trinucleotide interruptions, which code for histidines in the translated protein, attenuate the formation of slipped strand structures which may protect the allele from the occurrence of large expansions. Many of the mechanisms of expansion identified in this review differ from those noted in Huntington's disease indicating that gene -or sequence-specific factors may affect the behavior of the polyCAG/glutamine tract. Therefore, synthesis and review of research from the SCA1 field is valuable for future clinical and diagnostic work in the treatment and prevention of SCA1.

Sarita Lagalwar

Neuroscience Program

Skidmore College

Treating SCA1 Mice with Water-Soluble Compounds to Non-Specifically Boost Mitochondrial Function

Sarita Lagalwar

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Neuroscience Program

Skidmore College

Treating SCA1 Mice with Water-Soluble Compounds to Non-Specifically Boost Mitochondrial Function

Neuroscience Program