The two main pathological hallmarks of Parkinson's disease are loss of dopamine neurons in the substantia nigra pars compacta and proteinaceous amyloid fibrils composed mostly of α-synuclein, called ...Lewy pathology. Levodopa to enhance dopaminergic transmission remains one of the most effective treatment for alleviating the motor symptoms of Parkinson's disease (Olanow, Mov Disord 34:812-815, 2019). In addition, deep brain stimulation (Bronstein et al., Arch Neurol 68:165, 2011) to modulate basal ganglia circuit activity successfully alleviates some motor symptoms. MRI guided focused ultrasound in the subthalamic nucleus is a promising therapeutic strategy as well (Martinez-Fernandez et al., Lancet Neurol 17:54-63, 2018). However, to date, there exists no treatment that stops the progression of this disease. The findings that α-synuclein can be released from neurons and inherited through interconnected neural networks opened the door for discovering novel treatment strategies to prevent the formation and spread of Lewy pathology with the goal of halting PD in its tracks. This hypothesis is based on discoveries that pathologic aggregates of α-synuclein induce the endogenous α-synuclein protein to adopt a similar pathologic conformation, and is thus self-propagating. Phase I clinical trials are currently ongoing to test treatments such as immunotherapy to prevent the neuron to neuron spread of extracellular aggregates. Although tremendous progress has been made in understanding how Lewy pathology forms and spreads throughout the brain, cell intrinsic factors also play a critical role in the formation of pathologic α-synuclein, such as mechanisms that increase endogenous α-synuclein levels, selective expression profiles in distinct neuron subtypes, mutations and altered function of proteins involved in α-synuclein synthesis and degradation, and oxidative stress. Strategies that prevent the formation of pathologic α-synuclein should consider extracellular release and propagation, as well as neuron intrinsic mechanisms.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Abstract Lewy bodies and Lewy neurites composed primarily of α-synuclein characterize synucleinopathies including Parkinson
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s disease (PD) and Dementia with Lewy Bodies (DLB). Despite decades of ...research on the impact of α-synuclein, little is known how abnormal inclusion made of this protein compromise neuronal function. Emerging evidence suggests that defects in axonal transport caused by aggregated α
-synuclein contribute to neuronal dysfunction. These defects appear to occur well before the onset of neuronal death. Susceptible neurons in PD such as dopamine neurons with long elaborate axons may be particularly sensitive to abnormal axonal transport. Axonal transport is critical for delivery of signaling molecules to the soma responsible for neuronal differentiation and survival. In addition, axonal transport delivers degradative organelles such as endosomes and autophagosomes to lysosomes located in the soma to degrade damaged proteins and organelles. Identifying the molecular mechanisms by which axonal transport is impaired in PD and DLB may help identify novel therapeutic targets to enhance neuron survival and even possibly prevent disease progression. Here, we review the evidence that axonal transport is impaired in synucleinopathies, and describe potential mechanisms by which contribute to these defects.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Increasing evidence points to inflammation as a chief mediator of Parkinson's disease (PD), a progressive neurodegenerative disorder characterized by loss of dopamine neurons in the substantia nigra ...pars compacta (SNpc) and widespread aggregates of the protein α-synuclein (α-syn). Recently, microRNAs, small, noncoding RNAs involved in regulating gene expression at the posttranscriptional level, have been recognized as important regulators of the inflammatory environment. Using an array approach, we found significant upregulation of microRNA-155 (miR-155) in an in vivo model of PD produced by adeno-associated-virus-mediated expression of α-syn. Using a mouse with a complete deletion of miR-155, we found that loss of miR-155 reduced proinflammatory responses to α-syn and blocked α-syn-induced neurodegeneration. In primary microglia from miR-155(-/-) mice, we observed a markedly reduced inflammatory response to α-syn fibrils, with attenuation of major histocompatibility complex class II (MHCII) and proinflammatory inducible nitric oxide synthase expression. Treatment of these microglia with a synthetic mimic of miR-155 restored the inflammatory response to α-syn fibrils. Our results suggest that miR-155 has a central role in the inflammatory response to α-syn in the brain and in α-syn-related neurodegeneration. These effects are at least in part due to a direct role of miR-155 on the microglial response to α-syn. These data implicate miR-155 as a potential therapeutic target for regulating the inflammatory response in PD.
α‐Synuclein (α‐syn) is an abundant presynaptic protein that is the primary constituent of inclusions that define Lewy body diseases (LBDs). In these inclusions, α‐syn is phosphorylated at the ...serine‐129 residue. Antibodies directed to this phosphorylation site are used to measure inclusion abundance and stage disease progression in preclinical models as well as in postmortem tissues in LBDs. While it is critical to reliably identify inclusions, phospho‐specific antibodies often cross‐react with nonspecific antigens. Four commercially available monoclonal antibodies, two from rabbits (clones EP1536Y and MJF‐R13) and two from mice (81a and pSyn#64), have been the most widely used in detecting pS129‐α‐syn inclusions. Here, we systematically evaluated these antibodies in brain sections and protein lysates from rats and mice. All antibodies detected pS129‐α‐syn inclusions in the brain that were induced by preformed α‐syn fibrils in wild‐type rats and mice. Antibody titrations revealed that clones EP1536Y and 81a comparably labeled inclusions in both the perikarya and neuronal processes in contrast to clones MJF‐R13 and pSyn#64 that incompletely labeled inclusions at various antibody concentrations. Except for EP1536Y, the clones produced nonspecific diffuse neuropil labeling in α‐syn knockout mice as well as mice and rats injected with monomeric α‐syn, with some nonspecific staining titrating with pS129‐α‐syn inclusions. By immunoblot, all the clones cross‐reacted with proteins other than α‐syn, warranting caution in interpretations of specificity. Clone EP1536Y uniquely and robustly detected endogenous pS129‐α‐syn in highly soluble protein fractions from the mouse brain. In summary, EP1536Y had the highest sensitivity and specificity for detecting pS129‐α‐syn.
All antibodies detected pS129‐α‐syn inclusions in the brain induced by preformed α‐syn fibrils in wild‐type mice. Except for EP1536Y, the clones directed to phospho serine 129 residue of alpha synuclein (α‐syn) produced nonspecific diffuse neuropil labeling in α‐syn knockout mice as well as mice injected with monomeric α‐syn.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Animal models of Parkinson's disease (PD) are important for understanding the mechanisms of the disease and can contribute to developing and validating novel therapeutics. Ideally, these models ...should replicate the cardinal features of PD, such as progressive neurodegeneration of catecholaminergic neurons and motor defects. Many current PD models emphasize pathological forms of α‐synuclein, based on findings that autosomal dominant mutations in α‐synuclein and duplications/triplications of the SNCA gene cause PD. In addition, Lewy bodies and Lewy neurites, primarily composed of α‐synuclein, represent the predominant pathological characteristics of PD. These inclusions have defined features, such as insolubility in non‐ionic detergent, hyperphosphorylation, proteinase K sensitivity, a filamentous appearance by electron microscopy, and β‐sheet structure. Furthermore, it has become clear that Lewy bodies and Lewy neurites are found throughout the peripheral and central nervous system, and could account not only for motor symptoms, but also for non‐motor symptoms of the disease. The goal of this review is to describe two new α‐synuclein‐based models: the recombinant adeno‐associated viral vector‐α‐synuclein model and the α‐synuclein fibril model. An advantage of both models is that they do not require extensive crossbreeding of rodents transgenic for α‐synuclein with other rodents transgenic for genes of interest to study the impact of such genes on PD‐related pathology and phenotypes. In addition, abnormal α‐synuclein can be expressed in brain regions relevant for disease. Here, we discuss the features of each model, how each model has contributed thus far to our understanding of PD, and the advantages and potential caveats of each model.
This review describes two α‐synuclein‐based rodent models of Parkinson's disease: the rAAV‐α‐synuclein model and the α‐synuclein fibril model. The key features of these models are described, and the extent to which they recapitulate features of PD, such as α‐synuclein inclusion formation, loss of dopaminergic synapses in the striatum, motor defects, inflammation, and dopamine neuron death.
This article is part of a special issue on Parkinson disease.
This review describes two α‐synuclein‐based rodent models of Parkinson's disease: the rAAV‐α‐synuclein model and the α‐synuclein fibril model. The key features of these models are described, and the extent to which they recapitulate features of PD, such as α‐synuclein inclusion formation, loss of dopaminergic synapses in the striatum, motor defects, inflammation, and dopamine neuron death.
This article is part of a special issue on Parkinson disease.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract Proteinaceous inclusions in neurons, composed primarily of α-synuclein, define the pathology in several neurodegenerative disorders. Neurons can internalize α-synuclein fibrils that can seed ...new inclusions from endogenously expressed α-synuclein. The factors contributing to the spread of pathology and subsequent neurodegeneration are not fully understood, and different compositions and concentrations of fibrils have been used in different hosts. Here, we systematically vary the concentration and length of well-characterized α-synuclein fibrils and determine their relative ability to induce inclusions and neurodegeneration in different hosts (primary neurons, C57BL/6 J and C3H/HeJ mice, and Sprague Dawley rats). Using dynamic-light scattering profiles and other measurements to determine fibril length and concentration, we find that femptomolar concentrations of fibrils are sufficient to induce robust inclusions in primary neurons. However, a narrow and non-linear dynamic range characterizes fibril-mediated inclusion induction in axons and the soma. In mice, the C3H/HeJ strain is more sensitive to fibril exposures than C57BL/6 J counterparts, with more inclusions and dopaminergic neurodegeneration. In rats, injection of fibrils into the substantia nigra pars compacta (SNpc) results in similar inclusion spread and dopaminergic neurodegeneration as injection of the fibrils into the dorsal striatum, with prominent inclusion spread to the amygdala and several other brain areas. Inclusion spread, particularly from the SNpc to the striatum, positively correlates with dopaminergic neurodegeneration. These results define biophysical characteristics of α-synuclein fibrils that induce inclusions and neurodegeneration both in vitro and in vivo, and suggest that inclusion spread in the brain may be promoted by a loss of neurons.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Missense mutations in the leucine-rich repeat kinase 2 (LRRK2) gene can cause late-onset Parkinson disease. Past studies have provided conflicting evidence for the protective effects of LRRK2 ...knockdown in models of Parkinson disease as well as other disorders. These discrepancies may be caused by uncertainty in the pathobiological mechanisms of LRRK2 action. Previously, we found that LRRK2 knockdown inhibited proinflammatory responses from cultured microglia cells. Here, we report LRRK2 knockout rats as resistant to dopaminergic neurodegeneration elicited by intracranial administration of LPS. Such resistance to dopaminergic neurodegeneration correlated with reduced proinflammatory myeloid cells recruited in the brain. Additionally, adeno-associated virus-mediated transduction of human α-synuclein also resulted in dopaminergic neurodegeneration in wild-type rats. In contrast, LRRK2 knockout animals had no significant loss of neurons and had reduced numbers of activated myeloid cells in the substantia nigra. Although LRRK2 expression in the wild-type rat midbrain remained undetected under nonpathological conditions, LRRK2 became highly expressed in inducible nitric oxide synthase (iNOS)-positive myeloid cells in the substantia nigra in response to α-synuclein overexpression or LPS exposures. Our data suggest that knocking down LRRK2 may protect from overt cell loss by inhibiting the recruitment of chronically activated proinflammatory myeloid cells. These results may provide value in the translation of LRRK2-targeting therapeutics to conditions where neuroinflammation may underlie aspects of neuronal dysfunction and degeneration.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
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