Filamentous tau pathologies are hallmark lesions of several neurodegenerative tauopathies including Alzheimer’s disease (AD) and corticobasal degeneration (CBD) which show cell type-specific and topographically distinct tau inclusions. Growing evidence supports templated transmission of tauopathies through functionally interconnected neuroanatomical pathways suggesting that different self-propagating strains of pathological tau could account for the diverse manifestations of neurodegenerative tauopathies. Here, we describe the rapid and distinct cell type-specific spread of pathological tau following intracerebral injections of CBD or AD brain extracts enriched in pathological tau (designated CBD-Tau and AD-Tau, respectively) in young human mutant P301S tau transgenic (Tg) mice (line PS19) ~6–9 months before they show onset of mutant tau transgene-induced tau pathology. At 1 month post-injection of CBD-Tau, tau inclusions developed predominantly in oligodendrocytes of the fimbria and white matter near the injection sites with infrequent intraneuronal tau aggregates. In contrast, injections of AD-Tau in young PS19 mice induced tau pathology predominantly in neuronal perikarya with little or no oligodendrocyte involvement 1 month post-injection. With longer post-injection survival intervals of up to 6 months, CBD-Tau- and AD-Tau-induced tau pathology spread to different brain regions distant from the injection sites while maintaining the cell type-specific pattern noted above. Finally, CA3 neuron loss was detected 3 months post-injection of AD-Tau but not CBD-Tau. Thus, AD-Tau and CBD-Tau represent specific pathological tau strains that spread differentially and may underlie distinct clinical and pathological features of these two tauopathies. Hence, these strains could become targets to develop disease-modifying therapies for CBD and AD.
Alzheimer’s disease; Corticobasal degeneration; Seeded transmission of pathological tau; Frontotemporal degeneration
The progression of many neurodegenerative diseases is thought to be driven by the template-directed misfolding, seeded aggregation and cell–cell transmission of characteristic disease-related proteins, leading to the sequential dissemination of pathological protein aggregates. Recent evidence strongly suggests that the anatomical connections made by neurons — in addition to the intrinsic characteristics of neurons, such as morphology and gene expression profile — determine whether they are vulnerable to degeneration in these disorders. Notably, this common pathogenic principle opens up opportunities for pursuing novel targets for therapeutic interventions for these neurodegenerative disorders. We review recent evidence that supports the notion of neuron–neuron protein propagation, with a focus on neuropathological and positron emission tomography imaging studies in humans.
Previous studies demonstrated that members of the aminothienopyridazine (ATPZ) class of tau aggregation inhibitors exhibit a promising combination of in vitro activity as well as favorable pharmacokinetic properties (i.e., brain-penetration and oral bioavailability). Here we report the synthesis and evaluation of several new analogues. These studies indicate that the thienopyridazine core is essential for inhibition of tau fibrillization in vitro, while the choice of the appropriate scaffold decoration is critical to impart desirable ADME-PK properties. Among the active, brain-penetrant ATPZ inhibitors evaluated, 5-amino-N-cyclopropyl-3-(4-fluorophenyl)-4-oxo-3,4-dihydrothieno[3,4-d]pyridazine-1-carboxamide (43) was selected to undergo maximum tolerated dose and one-month tolerability testing in mice. The latter studies revealed that this compound is well-tolerated with no notable side-effects at an oral dose of 50 mg/kg/day.
Alzheimer’s disease; Tauopathy; Aminothienopyridazine; Tau aggregation inhibitor; K18PL
Neuronal insulin signaling abnormalities have been associated with Alzheimer's disease (AD). However, the specificity of this association and its underlying mechanisms have been unclear. This study investigated the expression of abnormal serine phosphorylation of insulin receptor substrate 1 (IRS1) in 157 human brain autopsy cases that included AD, tauopathies, α-synucleinopathies, TDP-43 proteinopathies, and normal aging. IRS1-pS616, IRS1-pS312 and downstream target Akt-pS473 measures were most elevated in AD but were also significantly increased in the tauopathies: Pick's disease, corticobasal degeneration and progressive supranuclear palsy. Double immunofluorescence labeling showed frequent co-expression of IRS1-pS616 with pathologic tau in neurons and dystrophic neurites. To further investigate an association between tau and abnormal serine phosphorylation of IRS1, we examined the presence of abnormal IRS1-pS616 expression in pathological tau-expressing transgenic mice and demonstrated that abnormal IRS1-pS616 frequently co-localizes in tangle-bearing neurons. Conversely, we observed increased levels of hyperphosphorylated tau in the high-fat diet-fed mouse, a model of insulin resistance. These results provide confirmation and specificity that abnormal phosphorylation of IRS1 is a pathological feature of AD and other tauopathies, and provide support for an association between insulin resistance and abnormal tau as well as amyloid-β.
Alzheimer's disease; Tau; Synuclein; TDP-43; Insulin resistance; Insulin receptor substrate 1
Neurofibrillary tangles composed of hyperphosphorylated fibrillized tau are found in numerous tauopathies including Alzheimer's disease. Increasing evidence suggests that tau pathology can be transmitted from cell-to-cell; however the mechanisms involved in the initiation of tau fibrillization and spreading of disease linked to progression of tau pathology are poorly understood. We show here that intracerebral injections of preformed synthetic tau fibrils into the hippocampus or frontal cortex of young tau transgenic mice expressing mutant human P301L tau induces tau hyperphosphorylation and aggregation around the site of injection, as well as a time-dependent propagation of tau pathology to interconnected brain areas distant from the injection site. Furthermore, we show that the tau pathology as a consequence of injection of tau preformed fibrils into the hippocampus induces selective loss of CA1 neurons. Together, our data confirm previous studies on the seeded induction and the spreading of tau pathology in a different tau transgenic mouse model and reveals neuronal loss associated with seeded tau pathology in tau transgenic mouse brain. These results further validate the utility of the tau seeding model in studying disease transmission, and provide a more complete in vivo tauopathy model with associated neurodegeneration which can be used to investigate the mechanisms involved in tau aggregation and spreading, as well as aid in the search for disease modifying treatments for Alzheimer's disease and related tauopathies.
Seeding; Spreading; Tau pathology; Cell death
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.
Glycogen synthase kinase-3 (GSK-3) is linked to the pathogenesis of Alzheimer’s disease (AD) senile plaques (SPs) and neurofibrillary tangles (NFTs), but the specific contributions of each of the GSK-3 α and β isoforms to mechanisms of AD have not been clarified. In this study, we sought to elucidate the role of each GSK-3α and β using novel viral and genetic approaches. First, we developed recombinant adeno-associated virus 2/1 short hairpin RNA constructs which specifically reduced expression and activity of GSK-3α or -β. These constructs were injected intraventricularly in newborn AD transgenic (tg) mouse models of SPs (PDAPP+/−), both SPs and NFTs (PDAPP+/−;PS19+/−) or wild type controls. We found that knockdown (KD) of GSK-3α, but not -β reduced SP formation in PDAPP+/− and PS19+/−;PDAPP+/− tg mice. Moreover, both GSK-3α and GSK-3β KD reduced tau phosphorylation and tau misfolding in PS19+/−;PDAPP+/− mice. Next, we generated triple tg mice using the CaMKIIα-Cre (α-calcium/calmodulin-dependent protein kinase II-Cre) system to KD GSK-3α in PDAPP+/− mice for further study the effects of GSK-3α reduction on SP formation. GSK-3α KD showed a significant effect on reducing SPs and ameliorating memory deficits in PDAPP+/− mice. Together, the data from both approaches suggests that GSK-3α contributes to both SP and NFT pathogenesis while GSK-3β only modulates NFT formation, suggesting common but also different targets for both isoforms. These findings highlight the potential importance of GSK-3α as a possible therapeutic target for ameliorating behavioral impairments linked to AD SPs and NFTs.
Synthetic a-Synuclein fibrils injected into the brain spread far beyond the injection site and are sufficient to accelerate Parkinson’s disease–like pathology in mice.
The accumulation of misfolded proteins is a fundamental pathogenic process in neurodegenerative diseases. However, the factors that trigger aggregation of α-Synuclein (α-Syn), the principal component of the intraneuronal inclusions known as Lewy bodies (LBs), and Lewy neurites (LNs), which characterize Parkinson’s disease (PD) and dementia with LBs (DLB), are poorly understood. We show here that in young asymptomatic α-Syn transgenic (Tg) mice, intracerebral injections of brain homogenates derived from older Tg mice exhibiting α-Syn pathology accelerate both the formation of intracellular LB/LN-like inclusions and the onset of neurological symptoms in recipient animals. Pathological α-Syn propagated along major central nervous system (CNS) pathways to regions far beyond injection sites and reduced survival with a highly reproducible interval from injection to death in inoculated animals. Importantly, inoculation with α-Syn amyloid fibrils assembled from recombinant human α-Syn induced identical consequences. Furthermore, we show for the first time that synthetic α-Syn fibrils are wholly sufficient to initiate PD-like LBs/LNs and to transmit disease in vivo. Thus, our data point to a prion-like cascade in synucleinopathies whereby cell–cell transmission and propagation of misfolded α-Syn underlie the CNS spread of LBs/LNs. These findings open up new avenues for understanding the progression of PD and for developing novel therapeutics.
Inclusions comprised of α-synuclein (α-syn), i.e. Lewy bodies (LBs) and Lewy neurites (LNs), define synucleinopathies including Parkinson’s Disease (PD) and dementia with Lewy Bodies (DLB). Here, we demonstrate that pre-formed fibrils generated from full length and truncated recombinant α-syn enter primary neurons, likely by adsorptive-mediated endocytosis and promote recruitment of soluble endogenous α-syn into insoluble PD-like LBs and LNs. Remarkably, endogenous α-syn was sufficient for formation of these aggregates, and overexpression of wild type or mutant α-syn was not required. LN-like pathology first developed in axons and propagated to form LB-like inclusions in perikarya. Accumulation of pathologic α-syn led to selective decreases in synaptic proteins, progressive impairments in neuronal excitability and connectivity, and eventually, neuron death. Thus, our data contribute important insights into the etiology and pathogenesis of PD-like α-syn inclusions, their impact on neuronal functions, and provide a model for discovering therapeutics targeting pathologic α-syn- mediated neurodegeneration.
An understanding of the anatomic distributions of major neurodegenerative disease lesions is important to appreciate the differential clinical profiles of these disorders and to serve as neuropathological standards for emerging molecular neuroimaging methods. To address these issues, here we present a comparative survey of the topographical distribution of the defining molecular neuropathological lesions among ten neurodegenerative diseases from a large and uniformly assessed brain collection. Ratings of pathological severity in sixteen brain regions from 671 cases with diverse neurodegenerative diseases were summarized and analyzed. These included: a) amyloid-β and tau lesions in Alzheimer’s disease, b) tau lesions in three other tauopathies including Pick’s disease, progressive supranuclear palsy and corticobasal degeneration, c) α-synuclein inclusion ratings in four synucleinopathies including Parkinson’s disease, Parkinson’s disease with dementia, dementia with Lewy bodies and multiple system atrophy, and d) TDP-43 lesions in two TDP-43 proteinopathies, including frontotemporal lobar degeneration associated with TDP-43 and amyotrophic lateral sclerosis. The data presented graphically and topographically confirm and extend previous pathological anatomic descriptions and statistical comparisons highlight the lesion distributions that either overlap or distinguish the diseases in each molecular disease category.
Alzheimer’s disease; Pick’s disease; corticobasal degeneration; progressive supranuclear palsy; Parkinson’s disease; Parkinson’s disease dementia; dementia with Lewy bodies; multiple system atrophy; frontotemporal lobar degeneration - TDP; amyotrophic lateral sclerosis; amyloid-β; Tau α-synuclein; TDP-43
Alexander disease (AxD) is a rare neurodegenerative disorder characterized pathologically by the presence of eosinophilic inclusions known as Rosenthal fibers (RFs) within astrocytes, and is caused by dominant mutations in the coding region of the gene encoding glial fibrillary acidic protein (GFAP). GFAP is the major astrocytic intermediate filament, and in AxD patient brain tissue GFAP is a major component of RFs. TAR DNA binding protein of 43 kDa (TDP-43) is the major pathological protein in almost all cases of the neurodegenerative disease amyotrophic lateral sclerosis (ALS) and ∼50% of frontotemporal lobar degeneration (FTLD), designated as FTLD-TDP. In ALS and FTLD-TDP, TDP-43 becomes insoluble, ubiquitinated, and pathologically phosphorylated and accumulates in cytoplasmic inclusions in both neurons and glia of affected brain and spinal cord regions. Previously, TDP-43 was detected in RFs of human pilocytic astrocytomas; however, involvement of TDP-43 in AxD has not been determined. Here we show that TDP-43 is present in RFs in AxD patient brains, and that insoluble phosphorylated full-length and high molecular weight TDP-43 accumulates in white matter of such brains. Phosphorylated TDP-43 also accumulates in the detergent-insoluble fraction from affected brain regions of GfapR236H/+ knock-in mice, which harbor a GFAP mutation homologous to one that causes AxD in humans, and TDP-43 colocalizes with astrocytic RF pathology in GfapR236H/+ mice and transgenic mice overexpressing human wild-type GFAP. These findings suggest common pathogenic mechanisms in ALS, FTLD, and AxD, and this is the first report of TDP-43 involvement in a neurological disorder primarily affecting astrocytes.
Alexander disease; astrocyte; GFAP; mouse models; neurodegeneration; TDP-43
Apolipoprotein E (APOE) ε2 carriers may be protected from dementia because of reduced levels of cortical β-amyloid. In the oldest-old, however, APOE ε2 carriers have high β-amyloid plaque scores and preserved cognition. We compared different measures of β-amyloid pathology across APOE genotypes in the oldest-old, and their relationship with dementia.
The study included 96 participants from The 90+ Study. Using all information, dementia diagnoses were made. Neuropathological examination included staging for amyloid plaques and β-amyloid cortical percent area stained by NAB228 antibody.
Both APOE ε2 and APOE ε4 carriers had high Consortium to Establish a Registry for Alzheimer's Disease plaque scores. However, APOE ε2 carriers had low cortical β-amyloid percent areas. β-amyloid percent area was associated with dementia across APOE genotypes.
Lower levels of percent area in APOE ε2 carriers may reflect lower total β-amyloid and may contribute to APOE ε2 carriers' decreased risk of dementia, despite high β-amyloid plaque scores. The relationship between β-amyloid plaques and dementia in the oldest-old may vary by APOE genotype.
Alzheimer; Apolipoprotein E; Beta-amyloid; Dementia; Oldest-old
The assembly of tau proteins into paired helical filaments, the building blocks of neurofibrillary tangles, is linked to neurodegeneration in Alzheimer’s disease and related tauopathies. A greater understanding of this assembly process could identify targets for the discovery of drugs to treat Alzheimer’s disease and related disorders. Using recombinant human tau, we have delineated events leading to the conversion of normal soluble tau into tau fibrils
Atomic force microscopy and transmission electron microscopy methodologies were utilized to determine the structure of tau assemblies that formed when soluble tau was incubated with heparin for increasing lengths of time.
Tau initially oligomerizes into spherical nucleation units of 18–21 nm diameter that appear to assemble linearly into nascent fibrils. Among the earliest tau fibrils are species that resemble a string of beads formed by linearly aligned spheres that with time seem to coalesce to form straight and twisted ribbon-like filaments, as well as paired-helical filaments similar to those found in human tauopathies. An analysis of fibril cross-sections at later incubation times revealed three fundamental axial structural features.
By monitoring tau fibrillization, we show that different tau filament morphologies co-exist. Temporal changes in the predominant tau structural species suggest that tau fibrillization involves the generation of structural intermediates, resulting in the formation of tau fibrils with verisimilitude to their authentic human counterparts.
Alzheimer’s disease; tauopathy; amyloid; tangles; neurodegeneration
Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are characterized by cytoplasmic protein aggregates in the brain and spinal cord that include TAR-DNA binding protein 43 (TDP-43). TDP-43 is normally localized in the nucleus with roles in the regulation of gene expression, and pathological cytoplasmic aggregates are associated with depletion of nuclear protein. Here, we generated transgenic mice expressing human TDP-43 with a defective nuclear localization signal in the forebrain (hTDP-43-ΔNLS), and compared them with mice expressing WT hTDP-43 (hTDP-43-WT) to determine the effects of mislocalized cytoplasmic TDP-43 on neuronal viability. Expression of either hTDP-43-ΔNLS or hTDP-43-WT led to neuron loss in selectively vulnerable forebrain regions, corticospinal tract degeneration, and motor spasticity recapitulating key aspects of FTLD and primary lateral sclerosis. Only rare cytoplasmic phosphorylated and ubiquitinated TDP-43 inclusions were seen in hTDP-43-ΔNLS mice, suggesting that cytoplasmic inclusions were not required to induce neuronal death. Instead, neurodegeneration in hTDP-43 and hTDP-43-ΔNLS–expressing neurons was accompanied by a dramatic downregulation of the endogenous mouse TDP-43. Moreover, mice expressing hTDP-43-ΔNLS exhibited profound changes in gene expression in cortical neurons. Our data suggest that perturbation of endogenous nuclear TDP-43 results in loss of normal TDP-43 function(s) and gene regulatory pathways, culminating in degeneration of selectively vulnerable affected neurons.
Transgenic (Tg) mouse models of Parkinson’s disease (PD) generated to date have primarily been designed to overexpress human alpha-synuclein (α–syn) to recapitulate PD-like motor impairments as well as PD-like nigro-striatal degeneration and α–syn pathology. However, cognitive impairments and cortical α–syn pathology also are common in PD patients. To model these features of PD, we created forebrain-specific conditional Tg mice that overexpress human wild type (WT) or A53T mutant α–syn. Here we show that both WT and A53T mutant α–syn lead to massive degeneration of postmitotic neurons in the hippocampal dentate gyrus (DG) during postnatal development, with hippocampal synapse loss as evidenced by reduced levels of pre- and postsynaptic markers. However, when mutant and WT α–syn expression was repressed until the Tg mice were mature postnatally and then induced for several months, no hippocampal neuron loss was observed. These data imply that developing neurons are more vulnerable to degenerate than mature neurons as a consequence of forebrain WT and mutant α–syn overexpression.
α -synuclein; Parkinson’s disease; conditional transgenic mouse; hippocampus; dentate gyrus; postnatal development
C-reactive protein (CRP) participates in the systemic response to inflammation. Previous studies report inconsistent findings regarding the relationship between plasma CRP and Alzheimer’s disease (AD). We measured plasma CRP in 203 subjects with AD, 58 subjects with mild cognitive impairment (MCI) and 117 normal aging subjects and administered annual mini-mental state examinations (MMSE) during a three year follow-up period to investigate CRP’s relationship with diagnosis and progression of cognitive decline. Adjusted for age, sex, and education, subjects with AD had significantly lower levels of plasma CRP than subjects with MCI and normal aging. However, there was no significant association between plasma CRP at baseline and subsequent cognitive decline as assessed by longitudinal changes in MMSE score. Our results support previous reports of reduced levels of plasma CRP in AD and indicate its potential utility as a biomarker for the diagnosis of AD.
Alzheimer Disease; Mild Cognitive Impairment; C-Reactive Protein; Inflammation; Biological Markers
Tau is a microtubule-associated protein that promotes microtubule assembly and stability. In Alzheimer's disease and related tauopathies, tau fibrillizes and aggregates into neurofibrillary tangles. Recently, oleocanthal isolated from extra virgin olive oil was found to display non-steroidal anti-inflammatory activity similar to ibuprofen. Since our unpublished data indicates an inhibitory effect of oleocanthal on Aβ fibrillization, we reasoned that it might inhibit tau fibrillization as well. Herein we demonstrate that oleocanthal abrogates fibrillization of tau by locking tau into the naturally unfolded state. Using PHF6 consisting of the amino acid residues VQIVYK, a hexapeptide within the third repeat of tau that is essential for fibrillization, we show that oleocanthal forms an adduct with the lysine via initial Schiff base formation. Structure and function studies demonstrate that the two aldehyde groups of oleocanthal are required for the inhibitory activity. These two aldehyde groups show certain specificity when titrated with free lysine and oleocanthal does not significantly affect the normal function of tau. These findings provide a potential scheme for the development of novel therapies for neurodegenerative tauopathies.
tau; fibrillization; neurodegeneration; oleocanthal; aldehyde; lysine
The discovery that mutations within the tau gene lead to frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17) provided direct evidence that tau alterations can lead to neurodegenerative disease. While the presence of tau fibrils and tangles is a common feature of all tauopathies, including Alzheimer’s disease (AD), data are emerging from biochemical, cell-based and transgenic mouse studies which suggest that a pre-fibrillar form of pathological tau may play a key role in eliciting central nervous system (CNS) neurodegeneration and behavioral impairments. Herein we review recent findings that implicate diffusible tau pathology in the onset of neurodegeneration, and discuss the implications of these findings as they relate to tau tangles and possible therapeutic strategies for the treatment of AD and related tauopathies.
Fibrils; Neurodegeneration; Oligomers; Tangles; Tau; Transgenic
Molecular chaperones of the heat shock protein 70 (Hsp70) family counteract protein misfolding in a variety of neurodegenerative disease models. To determine whether human Hsp70 exerts similar effects on the aggregation of alpha-synuclein (α-Syn), the key component of insoluble fibrils present in Parkinson’s disease, we investigated α-Syn fibril assembly in the presence of Hsp70. We found in vitro assembly was efficiently inhibited by substoichiometric concentrations of purified Hsp70 in the absence of co-factors. Experiments using α-Syn deletion mutants indicated that interactions between the Hsp70 substrate binding domain and the α-Syn core hydrophobic region underlie assembly inhibition. This assembly process was inhibited prior to the elongation stage as we failed to detect any fibrils by electron microscopy. In addition, fluorescence polarization and binding assays suggest that Hsp70 recognizes soluble α-Syn species in a highly dynamic and reversible manner. Together, these results provide novel insights into how Hsp70 suppresses α-Syn aggregation. Furthermore, our findings suggest that this critical step in Parkinson’s disease pathogenesis may be subject to modulation by a common molecular chaperone.
Deposition of intracellular tau fibrils has been the focus of research on the mechanisms of neurodegeneration in Alzheimer’s disease (AD) and related tauopathies. Here, we developed a new class of tau ligands, phenyl/pyridinyl-butadienyl-benzothiazoles/benzothiazoliums (PBBs), for visualizing diverse tau inclusions in brains of living patients with AD or non-AD tauopathies and animal models of these disorders. In vivo optical and positron emission tomographic (PET) imaging of a transgenic mouse model demonstrated sensitive detection of tau inclusions by PBBs. A pyridinated PBB, [11C]PBB3 was next applied in a clinical PET study, and its robust signal in the AD hippocampus wherein tau pathology is enriched contrasted strikingly with that of a senile plaque radioligand, [11C]Pittsburgh Compound-B ([11C]PIB). [11C]PBB3-PET data were also consistent with the spreading of tau pathology with AD progression. Furthermore, increased [11C]PBB3 signals were found in a corticobasal syndrome patient negative for [11C]PIB-PET.
Inclusions comprising the microtubule
tau, are found within neurons in the brains of patients with Alzheimer’s
disease and related neurodegenerative disorders that are broadly referred
to as tauopathies. The sequestration of tau into inclusions is believed
to cause a loss of tau function, such that MT structure and function
are compromised, leading to neuronal damage. Recent data reveal that
the brain-penetrant MT-stabilizing agent, epothilone D (EpoD), improves
cognitive function and decreases both neuron loss and tau pathology
in transgenic mouse models of tauopathy. There is thus a need to identify
additional MT-stabilizing compounds with blood–brain barrier
(BBB) permeability and slow brain clearance, as observed with EpoD.
We report here that the MT-stabilizing natural product, dictyostatin,
crosses the BBB in mice and has extended brain retention. Moreover,
a single administration of dictyostatin to mice causes prolonged stabilization
of MTs in the brain. In contrast, the structurally related MT-stabilizer,
discodermolide, shows significantly less brain exposure. Thus, dictyostatin
merits further investigation as a potential tauopathy therapeutic.
Blood−brain barrier; discodermolide; dictyostatin; microtubule; pharmacokinetics; tauopathy
α-Synuclein (SYN) is the major component of Lewy bodies, the neuropathological hallmarks of Parkinson's disease (PD). Missense mutations and multiplications of the SYN gene cause autosomal dominant inherited PD. Thus, SYN is implicated in the pathogenesis of PD. However, the mechanism where by SYN promotes neurodegeneration remains unclear. Familial PD with SYN gene mutations are rare because the majority of PD is sporadic and emerging evidence indicates that sporadic PD may result from genetic and environmental risk factors including neuroinflammation. Hence, we examined the relationship between SYN dysfunction and neuroinflammation in mediating dopaminergic neurodegeneration in mice and dopaminergic neuronal cultures derived from wild-type SYN and mutant A53T SYN transgenic mice in a murine SYN-null (SYNKO) background (M7KO and M83KO, respectively). Stereotaxic injection of an inflammagen, lipopolysaccharide, into substantia nigra of these SYN genetically engineered mice induced similar inflammatory reactions. In M7KO and M83KO, but not in SYNKO mice, the neuroinflammation was associated with dopaminergic neuronal death and the accumulation of insoluble aggregated SYN as cytoplasmic inclusions in nigral neurons. Nitrated/oxidized SYN was detected in these inclusions and abatement of microglia-derived nitric oxide and superoxide provided significant neuroprotection in neuron-glia cultures from M7KO mice. These data suggest that nitric oxide and superoxide released by activated microglia may be mediators that link inflammation and abnormal SYN in mechanisms of PD neurodegeneration. This study advances understanding of the role of neuroinflammation and abnormal SYN in the pathogenesis of PD and opens new avenues for the discovery of more effective therapies for PD.
α-synuclein; dopamine; neuroinflammation; microglia; Parkinson's disease; neurodegeneration
Over the past decade it has become clear that there is significant overlap in the clinical spectrum of frontotemporal lobar degeneration and amyotrophic lateral sclerosis. The identification of TDP-43 as the major disease protein in the pathology of both frontotemporal lobar degeneration with ubiquitin inclusions and amyotrophic lateral sclerosis provides the first molecular link for these diseases. Pathological TDP-43 is abnormally phosphorylated, ubiquitinated, and cleaved to generate carboxy-terminal fragments in affected brain regions. The normal nuclear expression of TDP-43 is also reduced leading to the hypothesis that sequestration of TDP-43 in pathological inclusions contributes to disease pathogenesis. Thus, TDP-43 is the newest member of the growing list of neurodegenerative proteinopathies, but unique in that it lacks features of brain amyloidosis.
Slow Component-b (SCb) translocates ∼200 diverse proteins from the cell body to the axon and axon tip at average rates of ∼2-8 mm/day. Several studies suggest that SCb proteins are co-transported as one or more macromolecular complexes, but the basis for this co-transport is unknown. The identification of actin and myosin in SCb led to the proposal that actin filaments function as a scaffold for the binding of other SCb proteins and that transport of these complexes is powered by myosin- the “microfilament complex” model. Later, several SCb proteins were also found to bind f-actin, supporting the idea, but despite this, the model has never been directly tested. Here, we test this model by disrupting the cytoskeleton in a live-cell model-system wherein we directly visualize transport of SCb cargoes. We focused on three SCb proteins we previously showed were co-transported in our system- α-synuclein, synapsin-1 and glyceraldelyde-3-phosphate dehydrogenase (GAPDH). Disruption of actin filaments with latrunculin had no effect on the velocity or frequency of transport of these three proteins. Furthermore, co-transport of these three SCb proteins continued in actin-depleted axons. We conclude that actin filaments do not function as a scaffold to organize and transport these and possibly other SCb proteins. In contrast, depletion of microtubules led to a dramatic inhibition of vectorial transport of SCb cargoes. These findings do not support the “microfilament complex” model, but instead indicate that the transport of protein complexes in SCb is powered by microtubule motors.
Axonal transport; slow transport; slow component-b; α-synuclein; synapsin-I; protein complexes