Many neurodegenerative diseases are characterized by the accumulation of insoluble protein aggregates, including neurofibrillary tangles comprised of tau in Alzheimer’s disease and Lewy bodies ...composed of α-synuclein in Parkinson’s disease. Moreover, different pathological proteins frequently codeposit in disease brains. To test whether aggregated α-synuclein can directly cross-seed tau fibrillization, we administered preformed α-synuclein fibrils assembled from recombinant protein to primary neurons and transgenic mice. Remarkably, we discovered two distinct strains of synthetic α-synuclein fibrils that demonstrated striking differences in the efficiency of cross-seeding tau aggregation, both in neuron cultures and in vivo. Proteinase K digestion revealed conformational differences between the two synthetic α-synuclein strains and also between sarkosyl-insoluble α-synuclein extracted from two subgroups of Parkinson’s disease brains. We speculate that distinct strains of pathological α-synuclein likely exist in neurodegenerative disease brains and may underlie the tremendous heterogeneity of synucleinopathies.
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•In vitro fibrillization can generate conformationally distinct α-synuclein fibrils•These distinct fibril strains differ in their ability to cross-seed tau aggregation•N and C termini of α-synuclein contribute to dynamics of strain conformations•Conformationally different α-synuclein can be detected in Parkinson’s disease brains
Two distinct conformers of alpha-synuclein fibrils differ in their ability to seed native alpha-synuclein and to cross-seed another protein, tau. The findings suggest that conformational variations of seed aggregates may underlie diversity in the pathology of synucleinopathies.
Inclusions composed 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 preformed fibrils generated from full-length and truncated recombinant α-syn enter primary neurons, probably 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 and their impact on neuronal functions, and they provide a model for discovering therapeutics targeting pathologic α-syn-mediated neurodegeneration.
► Internalized preformed fibrils cause α-syn to form inclusions in primary neurons ► Higher concentrations of endogenous presynaptic α-syn enhance inclusion formation ► Aggregates form first in axons and propagate throughout the entire neuron ► Parkinson-like inclusion formation impairs neuronal function and viability
Tauopathies are characterized by abnormal accumulation of tau protein in neurons and glia. In Alzheimer's disease (AD), tau aggregates in neurons, while in corticobasal degeneration (CBD) and ...progressive supranuclear palsy (PSP), tau also aggregates in astrocytes and oligodendrocytes. We previously demonstrated that human CBD and PSP tauopathy lysates (CBD-tau and PSP-tau) contain distinct tau strains that propagate neuronal and glial tau aggregates in nontransgenic (nonTg) mouse brain. Yet the mechanism of glial tau transmission is unknown. Here, we developed a novel mouse model to knock down tau in neurons to test for glial tau transmission. While oligodendroglial tau pathology propagated across the mouse brain in the absence of neuronal tau pathology, astrocytic tau pathology did not. Oligodendroglial tau aggregates propagated along white matter tracts independently of neuronal axons, and resulted in oligodendrocyte cell loss. Thus, glial tau pathology has significant functional consequences independent of neuronal tau pathology.
Studies have shown an overlap of Aβ plaques, tau tangles, and α-synuclein (α-syn) pathologies in the brains of Alzheimer’s disease (AD) and Parkinson’s disease (PD) with dementia (PDD) patients, with ...increased pathological burden correlating with severity of cognitive and motor symptoms. Despite the observed co-pathology and concomitance of motor and cognitive phenotypes, the consequences of the primary amyloidogenic protein on the secondary pathologies remain poorly understood. To better define the relationship between α-syn and Aβ plaques, we injected α-syn preformed fibrils (α-syn mpffs) into mice with abundant Aβ plaques. Aβ deposits dramatically accelerated α-syn pathogenesis and spread throughout the brain. Remarkably, hyperphosphorylated tau (p-tau) was induced in α-syn mpff-injected 5xFAD mice. Finally, α-syn mpff-injected 5xFAD mice showed neuron loss that correlated with the progressive decline of cognitive and motor performance. Our findings suggest a “feed-forward” mechanism whereby Aβ plaques enhance endogenous α-syn seeding and spreading over time post-injection with mpffs.
•α-syn burden is associated with Aβ plaque load in the cortex of LBD patients•Aβ plaques potentiate α-syn spreading in 5xFAD mice•Aβ plaques establish a dynamic pre-misfolded pool of α-syn in dystrophic neurites•Aβ/α-syn co-pathology induces neurodegeneration and behavioral deficits
Bassil et al. describe a new model that shows how Aβ plaques in the brain can potentiate α-synuclein pathogenesis. The authors provide evidence that the interaction of both proteins in the brain lead to neurodegeneration.
Synucleinopathies are characterized by the accumulation of insoluble α-synuclein (αSyn). To test whether αSyn aggregates modulate synaptic activity, we used a recently developed model in primary ...neurons for inducing αSyn pathology. We demonstrated that preformed fibrils (PFFs) generated with recombinant human αSyn compromised synaptic activity in a time- and dose-dependent manner and that the magnitude of these deficits correlated with the formation of αSyn pathology in cultured excitatory hippocampal neurons from both sexes of mice. Remarkably, acute passive infusion of αSyn PFFs from whole-cell patch-clamp pipette decreased mEPSC frequency within 10 min followed by induction of αSyn pathology within 1 d. Moreover, by direct addition of αSyn PFFs into culture medium, the formation of misfolded αSyn inclusions dramatically compromised the colocalization of synaptic markers and altered dynamic changes of dendritic spines, but the viability of neurons was not affected up to 7 d post-treatment with αSyn PFFs. Our data indicate that intraneuronal αSyn fibrils impaired the initiation of synaptogenesis and their physiological functions, thereby suggesting that targeting synaptic dysfunction in synucleinopathies may provide a promising therapeutic direction.
Under pathological conditions, the presynaptic protein α-synuclein (αSyn) aggregates to form intraneuronal inclusions. To understand how and to what extent αSyn aggregates modulate synaptic activity before neuron loss, we demonstrate that αSyn preformed fibrils (PFFs) reduced synaptic activity in a dose- and time-dependent manner. The magnitude of these deficits correlated with the deposition of αSyn pathology, which dramatically compromised the colocalization of synaptic markers and altered the dendritic spine dynamics. The present work further highlights the impact of αSyn PFFs on synaptogenesis and physiological function, which may be applicable to other types of synucleinopathies.
Mutations in the GBA1 gene are the most common genetic risk factor for Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). GBA1 encodes the lysosomal lipid hydrolase glucocerebrosidase ...(GCase), and its activity has been linked to accumulation of α-synuclein. The current study systematically examines the relationship between GCase activity and both pathogenic and non-pathogenic forms of α-synuclein in primary hippocampal, cortical, and midbrain neuron and astrocyte cultures, as well as in transgenic mice and a non-transgenic mouse model of PD. We find that reduced GCase activity does not result in aggregation of α-synuclein. However, in the context of extant misfolded α-synuclein, GCase activity modulates neuronal susceptibility to pathology. Furthermore, this modulation does not depend on neuron type but rather is driven by the level of pathological α-synuclein seeds. This study has implications for understanding how GBA1 mutations influence PD pathogenesis and provides a platform for testing novel therapeutics.
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•GCase inhibition does not lead to α-synuclein aggregation in cell or animal models•Reducing GCase activity enhances pre-existing α-synuclein aggregation•GCase modulation of α-synuclein aggregation does not depend on neuron type•GCase activity enhances α-synuclein pathology when pathological seeds are low
Henderson et al. use cell and animal models of Parkinson’s disease to show that reducing glucocerebrosidase activity leads to an enhancement of pre-existing α-synuclein pathology that does not depend on neuron type, reconciling experimental biology with human epidemiology.
Aggregates of α-synuclein (α-syn) accumulate in neurons in Parkinson's disease and other synucleinopathies. These inclusions predominantly localize to axons even in the early stages of the disease, ...but their affect on axon function has remained unknown. Previously we established a model in which the addition of preformed α-syn fibrils to primary neurons seeds formation of insoluble α-syn inclusions built from endogenously expressed α-syn that closely recapitulate the neuropathological phenotypes of Lewy neurites found in human diseased brains. Here we show, using live-cell imaging, that immobile α-syn inclusions accumulate in axons from the recruitment of α-syn located on mobile α-syn-positive vesicles. Ultrastructural analyses and live imaging demonstrate that α-syn accumulations do not cause a generalized defect in axonal transport; the inclusions do not fill the axonal cytoplasm, disrupt the microtubule cytoskeleton, or affect the transport of synaptophysin or mitochondria. However, the α-syn aggregates impair the transport of Rab7 and TrkB receptor-containing endosomes, as well as autophagosomes. In addition, the TrkB receptor-associated signaling molecule pERK5 accumulates in α-syn aggregate-bearing neurons. Thus α-syn pathology impairs axonal transport of signaling and degradative organelles. These early effects of α-syn accumulations may predict points of intervention in the neurodegenerative process.
Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are progressive neurodegenerative diseases for which there is no disease-modifying treatment. PD and DLB are characterized by aggregation ...of the synaptic protein α-synuclein, and there is compelling evidence to suggest that progression of these diseases is associated with the trans-cellular spread of pathogenic α-synuclein through the brains of afflicted individuals. Therapies targeting extracellular, pathogenic α-synuclein may therefore hold promise for slowing or halting disease progression. In this regard, it has been suggested that highly-selective antibodies can be administered as therapeutic agents targeting pathogenic proteins. In the current study, we screened a series of antibodies using multiple selection criterion to identify those that selectively bind pathogenic α-synuclein and show potent inhibition of pathology seeding in a neuronal model of α-synucleinopathy. A lead antibody was tested in a mouse model of PD, and it was able to reduce the spread of α-synuclein pathology in the brain and attenuate dopamine reductions in the striatum. This study highlights the therapeutic potential of α-synuclein immunotherapy for the treatment of PD and DLB, and provides a framework for screening of α-synuclein antibodies to identify those with preferred properties.
•Conformation selective antibodies have less potential for off-target effects.•Inoculation of mice with misfolded α-synuclein generated a new class of antibodies.•Multi-assay screening identified highly selective and potent antibodies.•Lead antibody reduces α-synuclein pathology and improves dopamine in vivo.
The accumulation of misfolded α-synuclein (aSyn) and neuron loss define several neurodegenerative disorders including Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). However, the ...precise relationship between pathology and neurotoxicity and why these processes disproportionately affect certain neuron subpopulations are poorly understood. We show here that Math2-expressing neurons in the hippocampal
Cornu ammonis
(CA), a region significantly affected by aSyn pathology in advanced PD and DLB, are highly susceptible to pathological seeding with pre-formed fibrils (PFFs), in contrast to dentate gyrus neurons, which are relatively spared. Math2
+
neurons also exhibited more rapid and severe cell loss in both in vitro and in vivo models of synucleinopathy. Toxicity resulting from PFF exposure was dependent on endogenous aSyn and could be attenuated by
N
-acetyl-cysteine through a glutathione-dependent process. Moreover, aSyn expression levels strongly correlate with relative vulnerability among hippocampal neuron subtypes of which Math2
+
neurons contained the highest amount. Consistent with this, antisense oligonucleotide (ASO)-mediated knockdown of aSyn reduced the neuronal pathology in a time-dependent manner. However, significant neuroprotection was observed only with early ASO intervention and a substantial reduction of aSyn pathology, indicating toxicity occurs after a critical threshold of pathological burden is exceeded in vulnerable neurons. Together, our findings reveal considerable heterogeneity in endogenous aSyn levels among hippocampal neurons and suggest that this may contribute to the selective vulnerability observed in the context of synucleinopathies.
Abstract
Aggregation of tau into fibrillar structures within the CNS is a pathological hallmark of a clinically heterogeneous set of neurodegenerative diseases termed tauopathies. Unique misfolded ...conformations of tau, referred to as strains, are hypothesized to underlie the distinct neuroanatomical and cellular distribution of pathological tau aggregates. Here, we report the identification of novel tau monoclonal antibodies (mAbs) that selectively bind to an Alzheimer disease (AD)-specific conformation of pathological tau. Immunohistochemical analysis of tissue from various AD and nonAD tauopathies demonstrate selective binding of mAbs GT-7 and GT-38 to AD tau pathologies and absence of immunoreactivity for tau aggregates that are diagnostic of corticobasal degenerations (CBD), progressive supranuclear palsy (PSP), and Pick's disease (PiD). In cases with co-occurring AD tauopathy, GT-7 and GT-38 distinguish comorbid AD tau from pathological tau in frontotemporal lobar degeneration characterized by tau inclusions (FTLD-Tau), as confirmed by the presence of both 3 versus 4 microtubule-binding repeat isoforms (3R and 4R tau isoforms, respectively), in AD neurofibrillary tangles but not in the tau aggregates of CBD, PSP, or PiD. These findings support the concept of an AD-specific tau strain. The mAbs described here enable the selective detection of AD tau pathology in nonAD tauopathies.
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