Research Models

TBA42

Synonyms: Truncated beta-amyloid 42

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Species: Mouse
Genes: APP
Modification: APP: Transgenic
Disease Relevance: Alzheimer's Disease
Strain Name: N/A

Summary

Phenotype Characterization

When visualized, these models will distributed over a 18 month timeline demarcated at the following intervals: 1mo, 3mo, 6mo, 9mo, 12mo, 15mo, 18mo+.

Absent

  • Tangles

No Data

  • Synaptic Loss
  • Changes in LTP/LTD

Plaques

Very rare extracellular Aβ deposits.

Tangles

Absent.

Synaptic Loss

Unknown.

Neuronal Loss

Age-dependent neuronal loss in the CA1 region of the hippocampus. No difference from wild-type mice at 3 and 6 months of age, but approximately 35% loss at 12 months of age.

Gliosis

Marked gliosis in the hippocampus as measured by GFAP staining at 12 months.

Changes in LTP/LTD

Unknown.

Cognitive Impairment

Age-dependent deficits in working and spatial reference memory at 12 months, but not at 3 and 6 months.

Last Updated: 06 Mar 2018

Further Reading

No Available Further Reading

Research Models

Tg4-42

Synonyms: Tg-Aβ(4-42)

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Species: Mouse
Genes: APP
Modification: APP: Transgenic
Disease Relevance: Alzheimer's Disease
Strain Name: N/A

Summary

Phenotype Characterization

When visualized, these models will distributed over a 18 month timeline demarcated at the following intervals: 1mo, 3mo, 6mo, 9mo, 12mo, 15mo, 18mo+.

Absent

  • Plaques
  • Tangles

No Data

  • Changes in LTP/LTD

Plaques

Absent.

Tangles

Absent.

Synaptic Loss

Altered synaptophysin staining in the CA3 region of the hippocampus. More pronounced in homozygous mice than hemizygous mice at 8 months.

Neuronal Loss

Age- and dose-dependent neuronal loss in the hippocampus CA1 region of hemizygous and homozygous mice. Compared with wild-type, hemizygous mice had 38% neuronal loss at 8 months, and 49% loss at 12 months. No difference at 3 months.

Gliosis

Reactive microglia and astrocytes in the hippocampus starting at 2 months.

Changes in LTP/LTD

Unknown.

Cognitive Impairment

Spatial reference memory is impaired as assessed by Morris water maze at 8 months in homozygous mice and 12 months in hemizygous mice. Deficit is age-dependent and is not detected at 3 months. Impaired contextual fear conditioning at 12 months.

Last Updated: 07 Apr 2022

Further Reading

No Available Further Reading

Research Models

APP NL-F Knock-in

Synonyms: APPNL-F/NL-F

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Species: Mouse
Genes: APP
Modification: APP: Knock-In
Disease Relevance: Alzheimer's Disease
Strain Name: Apptm2.1Tcs/Apptm2.1Tcs

Summary

Phenotype Characterization

When visualized, these models will distributed over a 18 month timeline demarcated at the following intervals: 1mo, 3mo, 6mo, 9mo, 12mo, 15mo, 18mo+.

Absent

  • Tangles
  • Neuronal Loss

No Data

  • Changes in LTP/LTD

Plaques

Homozygotes develop amyloid plaques starting at 6 months in the cortex and hippocampus. Heterozygotes develop amyloidosis after 24 months. Plaques contained Aβ1-42 and pyroglutamate Aβ (Aβ3(pE)-42); Aβx-40 was a minor species.

Tangles

Absent; although elevated levels of phosphorylated tau are observed in dystrophic neurites around plaques.

Synaptic Loss

Reduced synaptophysin and PSD95 immunoreactivities associated with Aβ plaques at 9-12 months.

Neuronal Loss

Absent.

Gliosis

Microglia and activated astrocytes accumulate with age, starting around 6 months of age, concurrent with plaque formation.

Changes in LTP/LTD

Unknown.

Cognitive Impairment

Memory impairment in homozygous mice at 18 months as measured by the Y maze test. APPNL/NL mice (with Swedish mutation only) were unimpaired at this age. No significant deficit was seen in the Morris water maze at 18 months.

Last Updated: 06 Apr 2022

COMMENTS / QUESTIONS

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Further Reading

No Available Further Reading

Research Models

APP NL-G-F Knock-in

Synonyms: APPNL-G-F/NL-G-F, AppNL-G-F

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Species: Mouse
Genes: APP
Modification: APP: Knock-In
Disease Relevance: Alzheimer's Disease
Strain Name: Apptm3.1Tcs/Apptm3.1Tcs

Summary

Phenotype Characterization

When visualized, these models will distributed over a 18 month timeline demarcated at the following intervals: 1mo, 3mo, 6mo, 9mo, 12mo, 15mo, 18mo+.

Absent

  • Tangles
  • Neuronal Loss

No Data

  • Changes in LTP/LTD

Plaques

Aggressive amyloidosis; plaques develop in homozygous mice starting at 2 months with near saturation by 7 months. Aβ deposition at 4 months in heterozygous mice. Cortical and subcortical amyloidosis present.

Tangles

Absent; although phosphorylated tau is elevated in dystrophic neurites around plaques.

Synaptic Loss

Reduction of synaptophysin and PSD95 immunoreactivities associated with Aβ plaques in both cortical and hippocampal areas.

Neuronal Loss

Absent.

Gliosis

Microglia and activated astrocytes accumulate with age starting around 2 months, especially around plaques in a manner concurrent with plaque formation.

Changes in LTP/LTD

Unknown.

Cognitive Impairment

Memory impairment in homozygous mice by 6 months of age as measured by the Y maze.

Last Updated: 25 Nov 2019

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Therapeutics

Sargramostim

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Overview

Name: Sargramostim
Synonyms: GM-CSF Leukine , Leukine®
Therapy Type: Other
Target Type: Inflammation (timeline), Other (timeline), Unknown
Condition(s): Alzheimer's Disease, Parkinson's Disease
U.S. FDA Status: Alzheimer's Disease (Phase 2), Parkinson's Disease (Phase 1)
Company: Genzyme, Partner Therapeutics, Inc., Sanofi
Approved for: Bone Marrow Stimulation

Background

GM-CSF leukine, aka sargramostim, is a synthetic form of the hematopoietic growth factor granulocyte-macrophage colony-stimulating factor. It is a 127-amino-acid glycoprotein produced by recombinant DNA technology in yeast. Sargramostim stimulates the innate immune system. It is FDA-approved for regenerating neutrophils, monocytes, and macrophages after bone marrow transplants, radiation therapy, and in conjunction with treatment for several types of leukemia. Sargramostim is also used for treating neutropenia, a condition of dangerously low white-blood-cell counts. Sargramostim is not to be confused with filgrastim, a recombinant form of the related granulocyte colony-stimulating factor (G-CSF). 

The rationale for evaluating this immune modulator in Alzheimer's disease is that it might increase phagocytosis of pathogenic protein deposits by bone-marrow-derived macrophages or brain-resident microglia, and that it might also stimulate other neuroprotective innate immunity processes (see review by Ahmed et al., 2021). GM-CSF was reported to activate microglia in response to amyloid pathology without also augmenting microglial release of pro-inflammatory cytokines, as is seen in response to other, closely related neurotrophic factors (Murphy et al., 1998). 

In transgenic mouse models of Alzheimer's disease, GM-CSF was reported to reduce amyloid pathology, improve cognition, and increase the number of microglia (Boyd et al., 2010Kiyota et al., 2018). However, contradictory findings exist, as well (Manczak et al, 2009). GM-CSF was also tested in Dp16 Down syndrome mice, a model that does not accumulate amyloid but does develop cognitive deficits due to neuroinflammation. Treatment reduced inflammation in the mice, and improved learning and memory in both DP16 and wild-type mice (Ahmed et al., 2022).

Both GM-CSF and its receptor appear to be expressed in aging human brains, both in controls and in people with Alzheimer's (Ridwan et al., 2012). Analysis of archived neuropsychology data from 19 patients who had received sargramostim as part of their supportive care for bone-marrow transplantation reported a cognitive benefit (Jim et al., 2012). 

Sargramostim is also of interest in Parkinson’s disease, where T cell immune responses have been linked to dopaminergic neuron loss and motor dysfunction (Reynolds et al., 2010; Saunders et al., 2012Benner et al., 2008). In mouse models, sargramostim increased the production of anti-inflammatory regulatory T cells, and was neuroprotective (Mangano et al., 2011; Kosloski et al., 2013).

Findings

In 2011, a Phase 2 randomized study at the University of Colorado, Denver, and the Byrd Alzheimer's Institute of the University of Southern Florida, Tampa, started enrolling 40 patients with mild to moderate Alzheimer's disease to evaluate a three-week course of GM-CSF Leukine (250 microg/m2 per day) or placebo injected under the skin for five days each week. Tolerability was the primary outcome, to be monitored for six months. Various cognitive tests were to be performed for up to six months after treatment as a secondary outcome. This study was set to complete in December 2017. 

At the 2017 AAIC, investigators presented interim data on 32 participants, 13 on drug and 19 on placebo (Aug 2017 conference news). Patients were examined at baseline, at the end of the trial, and 45 and 90 days later, for safety and with cognitive and functional tests. Those in the treatment arm had an average MMSE score of 16.46 at baseline, versus 20.63 for those on placebo, a significant difference; ADL scores were also lower—54.61 for the treatment group and 63.16 for placebo. GM-CSF Leukine seemed well-tolerated, with no serious adverse events reported and no signs of ARIA. Patients on drug scored about 1.5 points higher in MMSE than at baseline; placebo scores stayed unchanged. ADL score rose about 1.5 points in the treatment group at three weeks, but then fell similarly in treatment and placebo arms, respectively. No differences were reported between the two groups at later time points. No significant difference emerged at any time between treatment and placebo arms on the ADAS-Cog, CDR-SB, or MOHS tests.

The trial ended in December 2019, with 40 patients completing treatment and both follow-up visits. According to results presented at the November 2020 CTAD conference, there were no serious adverse events attributed to drug, and no amyloid-related imaging abnormalities. At the end of treatment, the sargramostim group improved on the MMSE compared to baseline or placebo. The benefit over placebo was maintained at the 45-day follow-up, but disappeared by 90 days. The ADAS-Cog13 did not differ at end of treatment, but was worse in the treated group at day 45. Increases in blood immune cells and proinflammatory cytokines were confirmed, consistent with GM-CSF’s immune modulatory activity. Plasma Aβ, tau, and the neurodegeneration marker UCHL1 significantly moved toward normal during treatment, then returned to baseline in the follow-up. Trial results were published after peer review (Potter et al., 2021).

In May 2022, a trial comparing a six-month course of the same dose given five days/week to placebo began enrolling 42 participants whose mild to moderate Alzheimer's dementia is confirmed by brain amyloid pathology. The primary outcome is safety; secondary, the MMSE. The trial, at the University of Colorado, is set to run until July 2024.

In 2013, the National Institute on Aging awarded funding for a Phase 2 trial to be conducted by Sanofi Aventis to evaluate sargramostim for its ability to clear amyloid deposits and affect cognition in patients with mild cognitive impairment (Feb 2014 news). This study started in November 2016 and anticipated enrolling 30 people 40 or older who met NIA-AA criteria for MCI due to AD and had a positive amyloid PET scan. This study was to evaluate a six-month course of subcutaneous injection of sargramostim or placebo for reduction of brain amyloid as measured by change in florbetapir retention. Secondary outcome measures were to include safety, CSF analysis, MRI to look for ARIA, and measurement of antibodies against sargramostim. This study was to be conducted in Houston but was withdrawn prior to enrollment due to slow recruitment.

In September 2013, a Phase 1 study began in Parkinson’s disease. The single-center study at the University of Nebraska enrolled 20 Parkinson’s patients who were randomized to self-administer saline placebo or 6 micrograms/kg/day sargramostim for eight weeks. The primary outcome was adverse events; other outcomes included measures of motor function, immune profiling and magnetoencephalography (MEG). Adverse events were mild and included well-established responses to GM-CSF such as injection-site reactions, increased total white cell counts, and bone pain. Treatment led to an increase in numbers of functional regulatory T cells and other markers of immune modulation. There was a modest improvement on the Unified Parkinson’s Disease Rating Scale Part III scores by three points at six and eight weeks that reversed after treatment stopped. MEG markers of motor cortex activation also improved in people on sargramostim (Gendelman et al., 2017).

In January 2019, the same investigators began a two-year pilot study treating 10 people with PD with a reduced dose of 3 micrograms/kg/day sargramostim five days a week. The study assesses safety and tolerability, and includes motor assessment by the UPDRS Part III as a primary outcome. Secondary outcomes are changes in immune cell number, phenotype, and function. The study will run through September 2022. Results of one-year treatment in five male patients were published, showing a reduction in the number and severity of adverse events with 3 micrograms compared to the 6 microgram study (Olson et al., 2021). There was a transient increase in effector T cells in blood, and a sustained increase in regulatory T cells with immunosuppressive function. Participants’ motor function did not decline, and they improved UPDRS part III scores from baseline by about 5 points, although there was no placebo group for comparison.

For details of Alzheimer's disease trials, see clinicaltrials.gov

Clinical Trial Timeline

  • Phase 2
  • Study completed / Planned end date
  • Planned end date unavailable
  • Study aborted
Sponsor Clinical Trial 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035
NCT01409915
N=40
Sanofi NCT02667496
N=32

Last Updated: 13 May 2022

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Alzpedia

Leucine-rich repeat kinase 2 (LRRK2)

Synonyms: PARK8, dardarin

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Missense mutations in LRRK2 were first identified as a cause of Parkinson’s disease (PD) in 2004. Subsequent studies showed that these mutations account for up to 10 percent of familial cases, with even higher prevalence in Ashkenazi Jewish and North African Arab populations. In addition, polymorphic LRRK2 variants occur in about 2 percent of sporadic cases, making LRRK2 one of the most common PD genes. Candidate gene and genome-wide association studies have identified many LRRK2 variants in PD patients; of those, Gly2019Ser is the most common of six variants known thus far to be pathogenic. LRRK2 currently ranks fourth on PDGene.

LRRK2 missense mutations have an autosomal-dominant inheritance pattern. Unlike the APP or PS1 pathogenic Alzheimer’s mutations, whose penetrance is nearly complete, LRRK2 mutation penetrance is incomplete and highly variable. PD develops in 25 to 80 percent of LRRK2 mutation carriers, depending on the study sample. LRRK2-associated Parkinson’s first becomes symptomatic across a wide age range, but its clinical progression and pathology closely resemble that of idiopathic PD. Additionally, lrrk2 protein levels are elevated in sporadic PD.

LRRK2 is expressed throughout the brain in both neurons and microglia. Microglial expression rises in response to infection and inflammation. LRRK2 is also expressed in circulating immune cells, pointing to a role in innate immunity. Indeed, LRRK2 has also been linked to Crohn’s and other inflammatory bowel diseases.

Leucine-rich repeat kinase 2 encodes a large, complex protein containing a kinase, a GTPase, and multiple protein-protein interaction domains. The interplay of its enzymatic kinase and signaling GTPase domains remains unknown. The G2019S LRRK2 mutation increases lrrk2’s kinase activity, but other pathogenic variants have different effects, including dampening kinase or GTPase activity. Animal and cell culture studies have linked lrrk2’s kinase activity to toxicity, and kinase inhibitors are being pursued as a therapeutic strategy for PD. Even so, the role of the kinase remains controversial; other groups have found that toxicity depends instead on the cellular concentration of lrrk2 protein.

Lrrk2 has been implicated in numerous cellular processes, particularly protein trafficking, recycling of synaptic and Golgi vesicles, mitophagy, and autophagy, but the overall physiological function and regulation of LRRK2 is not clear. Lrrk2 promotes the accumulation of a-synuclein deposits by an unknown mechanism, and evidence shows that autophagy slows in cells expressing pathogenic LRRK2 variants. Exactly how mutations predispose to Parkinson’s disease remains poorly understood a decade after LRRK2’s discovery as a PD gene, in part because rodent models of LRRK2 recapitulate aspects of PD, but not the full disease.

LRRK2 has become a central focus of Parkinson’s research. At the molecular level, points of interaction with other PD genes are being studied to establish pathways of pathogenesis. At the human research level, a large longitudinal cohort study tracks mutation carriers in several populations worldwide to characterize the preclinical stages of pathology and to find biomarkers that predict disease progression.

Further Reading

No Available Further Reading

Alzpedia

GBA

Synonyms: Lysosomal glucocerebrosidase, acid β-glucosidase, GBA1, D-glucosyl-N-acylsphingosine glucohydrolase, GCase

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Homozygous mutations in the GBA gene cause Gaucher’s disease, the most common lysosomal storage disorder. GBA generated interest in the neurodegeneration field when clinicians observed parkinsonian symptoms in some patients with Gaucher’s—an autosomal recessive disease—and an increased incidence of Parkinson’s disease (PD) in their heterozygous older relatives. Subsequent studies in large samples of PD patients established GBA mutations as a genetic risk factor for PD, as well as for dementia with Lewy bodies (DLB) and Parkinson’s disease dementia (PDD). Initially found in the Ashkenazi Jewish population, this was subsequently confirmed in other populations and in meta-analyses of PD samples worldwide. GBA currently ranks third in PDGene, after tau and α-synuclein. GBA mutations increase a person’s risk of PD, PDD, and DLB about fourfold. Upward of 5 percent of all patients with PD are estimated to have a GBA mutation; that number is higher in familial PD.

GBA is one of a growing number of genes that can cause a severe, early onset disease in homozygous carriers of a pathogenic mutation and a later-onset neurodegenerative disease in heterozygous carriers of the same mutation. Another example of this is TREM2.

Clinically, Gaucher’s disease occurs in three subtypes, one that affects the liver and spleen, bone, and blood, and two that also affect the central nervous system (see OMIM links below).  Parkinson’s disease linked to heterozygous GBA mutations is indistinguishable from sporadic PD clinically, pharmacologically, and in terms of drug response, although it begins earlier in life and is likelier to affect cognition, as well.

GBA encodes glucocerebrosidase, a lysosomal hydrolase that digests glycolipids. When the enzyme’s activity is impaired, these lipids build up in lysosomes, leading to cellular damage and inflammation. As PD, PDD, and DLB are diseases of α-synuclein aggregation, the link between GBA and α-synuclein is under intense study. A bi-directional pathway connecting GBA and α-synuclein has been implicated in the pathogenesis of both idiopathic and genetic forms of PD, PDD, and DLB. Pathogenic GBA mutations tend to cause loss of function and accumulation of the enzyme’s substrate glucosylceramide; this has been proposed to lead to a buildup and oligomerization of α-synuclein. In turn, high levels of α-synuclein interfere with the lysosomal function of wild-type glucocerebrosidase.

In animal models, reduced glucocerebrosidase function increases the accumulation of α-synuclein, whereas ramping up glucocerebrosidase expression ameliorates disease symptoms. Broadly speaking, protein quality-control pathways such as autophagy, the unfolded protein response, and endoplasmic reticulum-associated degradation have been implicated in the pathogenesis of both Gaucher’s and Parkinson’s.

Enzyme-replacement therapy with recombinant glucocerebrosidase is available for people with Gaucher’s. It does not cross the blood-brain barrier, hence it cannot treat the disease’s neurological symptoms, or PD, PDD, or DLB. The role of GBA in these diseases has renewed interest in the development of CNS-targeted therapies that boost glucocerebrosidase activity in the brain.

Further Reading

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Research Models

htau

Synonyms: human tau

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Species: Mouse
Genes: MAPT, MAPT
Modification: MAPT: Knock-Out; MAPT: Transgenic
Disease Relevance: Alzheimer's Disease, Frontotemporal Dementia
Strain Name: B6.Cg-Mapttm1(EGFP)Klt Tg(MAPT)8cPdav/J

Summary

Phenotype Characterization

When visualized, these models will distributed over a 18 month timeline demarcated at the following intervals: 1mo, 3mo, 6mo, 9mo, 12mo, 15mo, 18mo+.

Absent

No Data

  • Gliosis
  • Synaptic Loss

Tangles

Aggregated tau and paired helical filaments detectable at nine months by immunoelectron microscopy, although paired helical filaments of aggregated insoluble tau can be isolated from brain tissue as early as two months. Tau first redistributes from axons to cell bodies. Hyperphosphorylated tau begins to accumulate by six months, and increases further by 13 and 15 months (Andorfer et al., 2003).

Synaptic Loss

Unknown.

Neuronal Loss

Decrease in cortical thickness and reduced cell number between 10 and 14 months of age. Increased ventricle size increased from age eight months to 18 months. Decrease in the thickness of the corpus callosum (Andorfer et al., 2005).

Gliosis

Unknown.

Changes in LTP/LTD

In hippocampal slices, LTP induced by high frequency stimulation (HFS) was normal at four months but abolished by 12 months. LTP induced by theta burst stimulation (TBS) was normal at both ages. Paired-pulse ratio (PPR) was unaffected at four months, but increased at 12 months compared with controls, suggesting a decrease in probability of transmitter release (Polydoro et al., 2009).

Cognitive Impairment

Abnormal spatial learning in six-month-old mice compared with control mice (Phillips et al., 2011). Normal object recognition and spatial learning and memory by MWM at four months, but deficits by 12 months (Polydoro et al., 2009). Impaired burrowing relative to control mice occurs by four months (Geiszler et al., 2016).

Last Updated: 13 Apr 2018

COMMENTS / QUESTIONS

  1. This could be the best model for studying AD like tauopathies, as these mice develop tangles without mutations. The finding that this only occurs when mouse tau is KO'ed is very interesting....

    View all comments by Todd E. Golde

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Alzpedia

SNCA (α-synuclein)

Synonyms: PD1, NACP, PARK1, PARK

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Point mutations in the α-synuclein gene (SNCA), as well as duplication or triplication of wild-type SNCA, cause autosomal-dominant Parkinson’s disease. α-synuclein is abundantly expressed in the nervous system. In neurons, the protein is primarily localized to presynaptic terminals.

Under normal conditions, α-synuclein exists as a natively unfolded monomer or is bound to membranes with an a-helical secondary structure. Though the protein’s primary physiological function remains ambiguous, it has been implicated in synaptic vesicle trafficking, neurotransmitter release, and fatty acid uptake.

α-synuclein is a major component of Lewy bodies and Lewy neurites, intracellular aggregates that represent a neuropathologic hallmark of synucleinopathies such as Parkinson’s disease (PD), Dementia with Lewy bodies (DLB), and Multiple system atrophy (MSA). Lewy bodies are also found in many patients with Alzheimer’s disease.

Early in the path to forming these fibrillar, insoluble aggregates, the α-synuclein protein accumulates, misfolds, and aggregates into soluble oligomeric species. α-synuclein can be secreted and taken up by other cells; it is thought that misfolded α-synuclein propagates from one cell to anatomically connected cells, triggering aggregation in the recipient cell. In this way, a slow spread from the brainstem to limbic and neocortical areas would give rise to the stereotypical pattern of Lewy body pathology in PD.

These smaller aggregates may be the main pathogenic species that cause degeneration of dopaminergic neurons. α-synuclein-induced neurotoxicity may involve remodeling of membranes, impairment of mitochondria, and dysfunction of the autophagy-lysosomal pathway.

High levels are associated with impaired cognition in humans and in transgenic mouse models, and soluble α-synuclein is elevated in AD brain. The concentration of α-synuclein in the CSF is reduced in PD and DLB, and it is being explored as a potential biomarker for the differential diagnosis of these diseases against AD. Co-occurring α-synuclein and Aβ or tau pathology is a sign of worse prognosis and frequently marks mixed disease such as DLB or Parkinson’s disease dementia (PDD.) PET tracers for α-synuclein are at the animal research stage. α-synuclein is a drug target, and therapeutic antibodies are beginning to enter early stage clinical trials.

Further Reading

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Alzpedia

FUS

Synonyms: Fused in Sarcoma, Translated in Liposarcoma (TLS), FUS/TLS, HNRNPP2, ALS6

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Originally identified as a pro-oncogene, FUS came to the attention of neurodegenerative disease research in 2009, when mutations in this gene were linked to amyotrophic lateral sclerosis (ALS). FUS mutations account for about 4 percent of inherited ALS, including some juvenile-onset cases. FUS mutations in sporadic ALS are rare. FUS protein forms part of disease-related aggregates in most kinds of ALS, regardless of whether a FUS mutation is present. An exception to this is ALS caused by mutations in superoxide dismutase 1, SOD1. In FTD, mutations in FUS are rare; however, the FUS protein has become the characteristic pathological marker for neuronal inclusions in the subset of sporadic FTD cases that lack the more established aggregate markers TDP-43 and tau.

FUS is a member of a protein family called FET, which includes FUS, Ewing’s sarcoma or EWS, and TATA-binding protein-associated factor 15 or TAF15. These are RNA-binding proteins that participate in transcription, processing and nucleus-to-cytoplasm transport of mRNAs. One emerging difference between ALS-FUS and FTD-FUS is that only the latter typically involves co-aggregation of the FET proteins EWS and TAF15 along with FUS itself. 

More than 40 FUS mutations have been identified in ALS. Many occur in a terminal nuclear localization sequence or in a glycine-rich region that forms part of a prion-like domain involved in protein-protein interactions. Like TDP-43, another ALS gene and RNA-binding protein, FUS is normally a nuclear protein but in disease states it redistributes to the cytoplasm and forms RNA-protein granules.

Researchers have used yeast, Drosophila, nematodes, zebrafish, rats and mice to model FUS biology. FUS knockouts in rodents indicate that the gene is required for normal development. Mice expressing FUS mutatations develop a progressive motor neuron degeneration and paralysis somewhat like ALS, whereas those overexpressing wild-type FUS showing a milder phenotype. Currently, researchers are investigating whether mutant FUS toxicity results from a loss of normal nuclear function, a toxic gain of function in the cell body, or both. Scientists are also studying the more than 5,000 known mRNAs that are targets of FUS for clues about the protein’s normal function and role in disease.

Further Reading

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