ABSTRACT
Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide and presents pathologically with Lewy pathology and dopaminergic neurodegeneration. Lewy pathology contains aggregated α-synuclein (αSyn), a protein encoded by the SNCA gene which is also mutated or duplicated in a subset of familial PD cases. Due to its predominant presynaptic localization, immunostaining for the protein results in a diffuse reactivity pattern, providing little insight into the types of cells expressing αSyn. As a result, insight into αSyn expression-driven cellular vulnerability has been difficult to ascertain. Using a combination of knock-in mice that target αSyn to the nucleus (SncaNLS) and in situ hybridization of Snca in wild-type mice, we systematically mapped the topography and cell types expressing αSyn in the mouse brain, spinal cord, retina, and gut. We find a high degree of correlation between αSyn protein and RNA levels and further identify cell types with low and high αSyn content. We also find high αSyn expression in neurons, particularly those involved in PD, and to a lower extent in non-neuronal cell types, notably those of oligodendrocyte lineage, which are relevant to multiple system atrophy pathogenesis. Surprisingly, we also found that αSyn is relatively absent from select neuron types, e.g., ChAT-positive motor neurons, whereas enteric neurons universally express some degree of αSyn. Together, this integrated atlas provides insight into the cellular topography of αSyn, and provides a quantitative map to test hypotheses about the role of αSyn in network vulnerability, and thus serves investigations into PD pathogenesis and other α-synucleinopathies.
ABSTRACT
BACKGROUND: Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson's disease (PD). These mutations elevate the LRRK2 kinase activity, making LRRK2 kinase inhibitors an attractive therapeutic. LRRK2 kinase activity has been consistently linked to specific cell signaling pathways, mostly related to organelle trafficking and homeostasis, but its relationship to PD pathogenesis has been more difficult to define. LRRK2-PD patients consistently present with loss of dopaminergic neurons in the substantia nigra but show variable development of Lewy body or tau tangle pathology. Animal models carrying LRRK2 mutations do not develop robust PD-related phenotypes spontaneously, hampering the assessment of the efficacy of LRRK2 inhibitors against disease processes. We hypothesized that mutations in LRRK2 may not be directly related to a single disease pathway, but instead may elevate the susceptibility to multiple disease processes, depending on the disease trigger. To test this hypothesis, we have previously evaluated progression of α-synuclein and tau pathologies following injection of proteopathic seeds. We demonstrated that transgenic mice overexpressing mutant LRRK2 show alterations in the brain-wide progression of pathology, especially at older ages. METHODS: Here, we assess tau pathology progression in relation to long-term LRRK2 kinase inhibition. Wild-type or LRRK2G2019S knock-in mice were injected with tau fibrils and treated with control diet or diet containing LRRK2 kinase inhibitor MLi-2 targeting the IC50 or IC90 of LRRK2 for 3-6 months. Mice were evaluated for tau pathology by brain-wide quantitative pathology in 844 brain regions and subsequent linear diffusion modeling of progression. RESULTS: Consistent with our previous work, we found systemic alterations in the progression of tau pathology in LRRK2G2019S mice, which were most pronounced at 6 months. Importantly, LRRK2 kinase inhibition reversed these effects in LRRK2G2019S mice, but had minimal effect in wild-type mice, suggesting that LRRK2 kinase inhibition is likely to reverse specific disease processes in G2019S mutation carriers. Additional work may be necessary to determine the potential effect in non-carriers. CONCLUSIONS: This work supports a protective role of LRRK2 kinase inhibition in G2019S carriers and provides a rational workflow for systematic evaluation of brain-wide phenotypes in therapeutic development.
Subject(s)
Brain , Dopaminergic Neurons , Animals , Humans , Mice , Leucine-Rich Repeat Serine-Threonine Protein Kinase-2/genetics , Lewy Bodies , Mice, Transgenic , Mutation/geneticsABSTRACT
A key hallmark of Parkinson's disease (PD) is Lewy pathology. Composed of α-synuclein, Lewy pathology is found both in dopaminergic neurons that modulate motor function, and cortical regions that control cognitive function. Recent work has established the molecular identity of dopaminergic neurons susceptible to death, but little is known about cortical neurons susceptible to Lewy pathology or molecular changes induced by aggregates. In the current study, we use spatial transcriptomics to capture whole transcriptome signatures from cortical neurons with α-synuclein pathology compared to neurons without pathology. We find, both in PD and related PD dementia, dementia with Lewy bodies and in the pre-formed fibril α-synucleinopathy mouse model, that specific classes of excitatory neurons are vulnerable to developing Lewy pathology. Further, we identify conserved gene expression changes in aggregate-bearing neurons that we designate the Lewy-associated molecular dysfunction from aggregates (LAMDA) signature. Neurons with aggregates downregulate synaptic, mitochondrial, ubiquitin-proteasome, endo-lysosomal, and cytoskeletal genes and upregulate DNA repair and complement/cytokine genes. Our results identify neurons vulnerable to Lewy pathology in the PD cortex and describe a conserved signature of molecular dysfunction in both mice and humans.
Subject(s)
Lewy Body Disease , Parkinson Disease , Synucleinopathies , Humans , Mice , Animals , alpha-Synuclein/metabolism , Lewy Body Disease/pathology , Parkinson Disease/metabolism , Dopaminergic Neurons/metabolism , Gene Expression ProfilingABSTRACT
Neuroscience studies are often carried out in animal models for the purpose of understanding specific aspects of the human condition. However, the translation of findings across species remains a substantial challenge. Network science approaches can enhance the translational impact of cross-species studies by providing a means of mapping small-scale cellular processes identified in animal model studies to larger-scale inter-regional circuits observed in humans. In this Review, we highlight the contributions of network science approaches to the development of cross-species translational research in neuroscience. We lay the foundation for our discussion by exploring the objectives of cross-species translational models. We then discuss how the development of new tools that enable the acquisition of whole-brain data in animal models with cellular resolution provides unprecedented opportunity for cross-species applications of network science approaches for understanding large-scale brain networks. We describe how these tools may support the translation of findings across species and imaging modalities and highlight future opportunities. Our overarching goal is to illustrate how the application of network science tools across human and animal model studies could deepen insight into the neurobiology that underlies phenomena observed with non-invasive neuroimaging methods and could simultaneously further our ability to translate findings across species.
Subject(s)
Brain , Neurosciences , Animals , Humans , Neuroimaging , Translational Research, Biomedical/methods , NeurobiologyABSTRACT
Lewy pathology composed of α-synuclein is the key pathological hallmark of Parkinson's disease (PD), found both in dopaminergic neurons that control motor function, and throughout cortical regions that control cognitive function. Recent work has investigated which dopaminergic neurons are most susceptible to death, but little is known about which neurons are vulnerable to developing Lewy pathology and what molecular changes an aggregate induces. In the current study, we use spatial transcriptomics to selectively capture whole transcriptome signatures from cortical neurons with Lewy pathology compared to those without pathology in the same brains. We find, both in PD and in a mouse model of PD, that there are specific classes of excitatory neurons that are vulnerable to developing Lewy pathology in the cortex. Further, we identify conserved gene expression changes in aggregate-bearing neurons that we designate the Lewy-associated molecular dysfunction from aggregates (LAMDA) signature. This gene signature indicates that neurons with aggregates downregulate synaptic, mitochondrial, ubiquitin-proteasome, endo-lysosomal, and cytoskeletal genes and upregulate DNA repair and complement/cytokine genes. However, beyond DNA repair gene upregulation, we find that neurons also activate apoptotic pathways, suggesting that if DNA repair fails, neurons undergo programmed cell death. Our results identify neurons vulnerable to Lewy pathology in the PD cortex and identify a conserved signature of molecular dysfunction in both mice and humans.
ABSTRACT
Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are progressive neurodegenerative diseases characterized by the accumulation of misfolded α-synuclein in the form of Lewy pathology. While most cases are sporadic, there are rare genetic mutations that cause disease and more common variants that increase incidence of disease. The most prominent genetic mutations for PD and DLB are in the GBA1 and LRRK2 genes. GBA1 mutations are associated with decreased glucocerebrosidase activity and lysosomal accumulation of its lipid substrates, glucosylceramide and glucosylsphingosine. Previous studies have shown a link between this enzyme and lipids even in sporadic PD. However, it is unclear how the protein pathologies of disease are related to enzyme activity and glycosphingolipid levels. To address this gap in knowledge, we examined quantitative protein pathology, glucocerebrosidase activity and lipid substrates in parallel from 4 regions of 91 brains with no neurological disease, idiopathic, GBA1-linked, or LRRK2-linked PD and DLB. We find that several biomarkers are altered with respect to mutation and progression to dementia. We found mild association of glucocerebrosidase activity with disease, but a strong association of glucosylsphingosine with α-synuclein pathology, irrespective of genetic mutation. This association suggests that Lewy pathology precipitates changes in lipid levels related to progression to dementia.
ABSTRACT
Chronic high-fat feeding triggers widespread metabolic dysfunction including obesity, insulin resistance, and diabetes. While these ultimate pathological states are relatively well understood, we have a limited understanding of how high-fat intake first triggers physiological changes. Here, we identify an acute microglial metabolic response that rapidly translates intake of high-fat diet (HFD) to a surprisingly beneficial effect on spatial and learning memory. Acute high-fat intake increases palmitate levels in cerebrospinal fluid and triggers a wave of microglial metabolic activation characterized by mitochondrial membrane activation, fission and metabolic skewing towards aerobic glycolysis. These effects are generalized, detectable in the hypothalamus, hippocampus, and cortex all within 1-3 days of HFD exposure. In vivo microglial ablation and conditional DRP1 deletion experiments show that the microglial metabolic response is necessary for the acute effects of HFD. 13C-tracing experiments reveal that in addition to processing via ß-oxidation, microglia shunt a substantial fraction of palmitate towards anaplerosis and re-release of bioenergetic carbons into the extracellular milieu in the form of lactate, glutamate, succinate, and intriguingly, the neuro-protective metabolite itaconate. Together, these data identify microglial cells as a critical nutrient regulatory node in the brain, metabolizing away harmful fatty acids and liberating the same carbons instead as alternate bioenergetic and protective substrates. The data identify a surprisingly beneficial effect of short-term HFD on learning and memory.
ABSTRACT
Symptoms in the urogenital organs are common in multiple system atrophy (MSA), also in the years preceding the MSA diagnosis. It is unknown how MSA is triggered and these observations in prodromal MSA led us to hypothesize that synucleinopathy could be triggered by infection of the genitourinary tract causing É-synuclein (ÉSyn) to aggregate in peripheral nerves innervating these organs. As a first proof that peripheral infections could act as a trigger in MSA, this study focused on lower urinary tract infections (UTIs), given the relevance and high frequency of UTIs in prodromal MSA, although other types of infection might also be important triggers of MSA. We performed an epidemiological nested-case control study in the Danish population showing that UTIs are associated with future diagnosis of MSA several years after infection and that it impacts risk in both men and women. Bacterial infection of the urinary bladder triggers synucleinopathy in mice and we propose a novel role of ÉSyn in the innate immune system response to bacteria. Urinary tract infection with uropathogenic E. coli results in the de novo aggregation of ÉSyn during neutrophil infiltration. During the infection, ÉSyn is released extracellularly from neutrophils as part of their extracellular traps. Injection of MSA aggregates into the urinary bladder leads to motor deficits and propagation of ÉSyn pathology to the central nervous system in mice overexpressing oligodendroglial ÉSyn. Repeated UTIs lead to progressive development of synucleinopathy with oligodendroglial involvement in vivo. Our results link bacterial infections with synucleinopathy and show that a host response to environmental triggers can result in ÉSyn pathology that bears semblance to MSA.
Subject(s)
Multiple System Atrophy , Synucleinopathies , Urinary Tract Infections , Mice , Female , Animals , Synucleinopathies/pathology , Case-Control Studies , Escherichia coli , Mice, Transgenic , alpha-Synuclein , Multiple System Atrophy/complications , Multiple System Atrophy/pathology , Urinary Tract Infections/complications , Immunity, InnateABSTRACT
There is growing evidence for the key role of microglial functional state in brain pathophysiology. Consequently, there is a need for efficient automated methods to measure the morphological changes distinctive of microglia functional states in research settings. Currently, many commonly used automated methods can be subject to sample representation bias, time consuming imaging, specific hardware requirements and difficulty in maintaining an accurate comparison across research environments. To overcome these issues, we use commercially available deep learning tools Aiforia® Cloud (Aifoira Inc., Cambridge, MA, United States) to quantify microglial morphology and cell counts from histopathological slides of Iba1 stained tissue sections. We provide evidence for the effective application of this method across a range of independently collected datasets in mouse models of viral infection and Parkinson's disease. Additionally, we provide a comprehensive workflow with training details and annotation strategies by feature layer that can be used as a guide to generate new models. In addition, all models described in this work are available within the Aiforia® platform for study-specific adaptation and validation.
ABSTRACT
The presynaptic protein α-synuclein (αSyn) has been suggested to be involved in the pathogenesis of Parkinson's disease (PD). In PD, the amygdala is prone to develop insoluble αSyn aggregates, and it has been suggested that circuit dysfunction involving the amygdala contributes to the psychiatric symptoms. Yet, how αSyn aggregates affect amygdala function is unknown. In this study, we examined αSyn in glutamatergic axon terminals and the impact of its aggregation on glutamatergic transmission in the basolateral amygdala (BLA). We found that αSyn is primarily present in the vesicular glutamate transporter 1-expressing (vGluT1+) terminals in the mouse BLA, which is consistent with higher levels of αSyn expression in vGluT1+ glutamatergic neurons in the cerebral cortex relative to the vGluT2+ glutamatergic neurons in the thalamus. We found that αSyn aggregation selectively decreased the cortico-BLA, but not the thalamo-BLA, transmission; and that cortico-BLA synapses displayed enhanced short-term depression upon repetitive stimulation. In addition, using confocal microscopy, we found that vGluT1+ axon terminals exhibited decreased levels of soluble αSyn, which suggests that lower levels of soluble αSyn might underlie the enhanced short-term depression of cortico-BLA synapses. In agreement with this idea, we found that cortico-BLA synaptic depression was also enhanced in αSyn knockout mice. In conclusion, both basal and dynamic cortico-BLA transmission were disrupted by abnormal aggregation of αSyn and these changes might be relevant to the perturbed cortical control of the amygdala that has been suggested to play a role in psychiatric symptoms in PD.
Subject(s)
Basolateral Nuclear Complex , Parkinson Disease , Animals , Basolateral Nuclear Complex/metabolism , Mice , Neurons/metabolism , Parkinson Disease/metabolism , Presynaptic Terminals/metabolism , Synapses/metabolism , Synaptic Transmission , alpha-Synuclein/metabolismABSTRACT
Parkinson's disease (PD) is the most common neurodegenerative movement disorder, and motor dysfunction has been attributed to loss of dopaminergic neurons. However, motor dysfunction is only one of many symptoms experienced by patients. A neuropathological hallmark of PD is intraneuronal protein aggregates called Lewy pathology (LP). Neuropathological staging studies have shown that dopaminergic neurons are only one of the many cell types prone to manifest LP. Progressive appearance of LP in multiple brain regions, as well as peripheral nerves, has led to the popular hypothesis that LP and misfolded forms of one of its major components - α-synuclein (aSYN) - can spread through synaptically connected circuits. However, not all brain regions or neurons within connected circuits develop LP, suggesting that cell autonomous factors modulate the development of pathology. Here, we review studies about how LP develops and progressively engages additional brain regions. We focus on how connectivity constrains progression and discuss cell autonomous factors that drive pathology development. We propose a mixed model of cell autonomous factors and trans-synaptic spread as mediators of pathology progression and put forward this model as a framework for future experiments exploring PD pathophysiology.
Subject(s)
Parkinson Disease , Synucleinopathies , Dopaminergic Neurons/metabolism , Humans , Parkinson Disease/metabolism , Phenotype , alpha-Synuclein/metabolismABSTRACT
Neuropathological staging studies have suggested that tau pathology spreads through the brain in Alzheimer's disease (AD) and other tauopathies, but it is unclear how neuroanatomical connections, spatial proximity, and regional vulnerability contribute. In this study, we seed tau pathology in the brains of nontransgenic mice with AD tau and quantify pathology development over 9 months in 134 brain regions. Network modeling of pathology progression shows that diffusion through the connectome is the best predictor of tau pathology patterns. Further, deviations from pure neuroanatomical spread are used to estimate regional vulnerability to tau pathology and identify related gene expression patterns. Last, we show that pathology spread is altered in mice harboring a mutation in leucine-rich repeat kinase 2. While tau pathology spread is still constrained by anatomical connectivity in these mice, it spreads preferentially in a retrograde direction. This study provides a framework for understanding neuropathological progression in tauopathies.
ABSTRACT
BACKGROUND: Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson's disease (PD) and are also associated with genetic risk in idiopathic PD. Mutations in LRRK2, including the most common p.G2019S lead to elevated kinase activity, making LRRK2 kinase inhibitors prime targets for therapeutic development. However, the role of LRRK2 kinase activity in PD pathogenesis has remained unclear. While essentially all LRRK2-PD patients exhibit dopaminergic neuron loss, many of these patients do not have α-synuclein Lewy bodies in their brains. So, what is the neuropathological substrate of LRRK2-PD? Tau has emerged as a possible candidate due to the presence of tau pathology in the majority of LRRK2 mutation carriers and reports of hyperphosphorylated tau in LRRK2 animal models. OBJECTIVE: In the current study, we aim to address whether a mutation in LRRK2 changes the cell-autonomous seeding of tau pathology in primary neurons. We also aim to assess whether LRRK2 kinase inhibitors are able to modulate tau pathology. METHODS/RESULTS: Treatment of primary neurons with LRRK2 kinase inhibitors leads to prolonged kinase inhibition but does not alter tau pathology induction. The lack of an effect of LRRK2 kinase activity was further confirmed in primary neurons expressing LRRK2G2019S and with two different forms of pathogenic tau. In no case was there more than a minor change in tau pathology induction. CONCLUSION: Together, our results indicate that LRRK2 kinase activity is not playing a major role in the induction of tau pathology in individual neurons. Understanding the impact of LRRK2 kinase inhibitors on pathology generation is important as kinase inhibitors move forward in clinical trials.
Subject(s)
Parkinson Disease , Animals , Brain/metabolism , Humans , Leucine-Rich Repeat Serine-Threonine Protein Kinase-2/genetics , Lewy Bodies/metabolism , Mutation/genetics , Neurons/metabolism , Parkinson Disease/geneticsABSTRACT
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.
Subject(s)
Astrocytes/metabolism , Glucosylceramidase/genetics , Neurons/metabolism , Parkinsonian Disorders/genetics , Protein Aggregation, Pathological/genetics , alpha-Synuclein/metabolism , Animals , Astrocytes/cytology , Astrocytes/pathology , Cerebral Cortex/cytology , Cerebral Cortex/metabolism , Cerebral Cortex/pathology , Disease Susceptibility , Genetic Predisposition to Disease , Glucosylceramidase/metabolism , HEK293 Cells , Hippocampus/cytology , Hippocampus/metabolism , Hippocampus/pathology , Humans , Lewy Body Disease/genetics , Lewy Body Disease/metabolism , Lewy Body Disease/pathology , Mesencephalon/cytology , Mesencephalon/metabolism , Mesencephalon/pathology , Mice , Mice, Transgenic , Neurons/cytology , Neurons/pathology , Parkinson Disease/genetics , Parkinson Disease/metabolism , Parkinson Disease/pathology , Parkinsonian Disorders/metabolism , Parkinsonian Disorders/pathology , Primary Cell Culture , Protein Aggregation, Pathological/metabolism , Protein Aggregation, Pathological/pathology , Synucleinopathies/genetics , Synucleinopathies/metabolism , Synucleinopathies/pathologyABSTRACT
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.
Subject(s)
Antibodies, Monoclonal/administration & dosage , Immunotherapy/methods , Lewy Body Disease/immunology , Lewy Body Disease/therapy , Parkinson Disease/immunology , Parkinson Disease/therapy , alpha-Synuclein/administration & dosage , Animals , Antibodies, Monoclonal/chemistry , Antibodies, Monoclonal/genetics , Cells, Cultured , Dose-Response Relationship, Immunologic , Female , Humans , Lewy Body Disease/genetics , Male , Mice , Mice, Inbred BALB C , Parkinson Disease/genetics , alpha-Synuclein/chemistry , alpha-Synuclein/geneticsABSTRACT
Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson's disease (PD). While the clinical presentation of LRRK2 mutation carriers is similar to that of idiopathic PD (iPD) patients, the neuropathology of LRRK2 PD is less clearly defined. Lewy bodies (LBs) composed of α-synuclein are a major feature of iPD, but are not present in all LRRK2 PD cases. There is some evidence that tau may act as a neuropathological substrate in LB-negative LRRK2 PD, but this has not been examined systematically. In the current study, we examined α-synuclein, tau, and amyloid ß (Aß) pathologies in 12 LRRK2 mutation carriers. We find that α-synuclein pathology is present in 63.6% of LRRK2 mutation carriers, but tau pathology can be found in 100% of carriers and is abundant in 91% of carriers. We further use an antibody which selectively binds Alzheimer's disease (AD)-type tau and use quantitative analysis of tau pathology to demonstrate that AD tau is the prominent type of tau present in LRRK2 mutation carriers. Abundant Aß pathology can also be found in LRRK2 mutation carriers and is consistent with comorbid AD pathology. Finally, we assessed the association of neuropathology with clinical features in LRRK2 mutation carriers and idiopathic individuals and find that LRRK2 PD shares clinical and pathological features of idiopathic PD. The prevalence of AD-type tau pathology in LRRK2 PD is an important consideration for understanding PD pathogenesis and refining clinical trial inclusion and progression criterion.
Subject(s)
Alzheimer Disease/genetics , Leucine-Rich Repeat Serine-Threonine Protein Kinase-2/genetics , Mutation/genetics , Parkinson Disease/genetics , tau Proteins/genetics , Alzheimer Disease/pathology , Brain/pathology , Heterozygote , Humans , Parkinson Disease/pathologyABSTRACT
Studies of patients afflicted by neurodegenerative diseases suggest that misfolded proteins spread through the brain along anatomically connected networks, prompting progressive decline. Recently, mouse models have recapitulated the cell-to-cell transmission of pathogenic proteins and neuron death observed in patients. However, the factors regulating the spread of pathogenic proteins remain a matter of debate due to an incomplete understanding of how vulnerability functions in the context of spread. Here we use quantitative pathology mapping in the mouse brain, combined with network modeling to understand the spatiotemporal pattern of spread. Patterns of α-synuclein pathology are well described by a network model that is based on two factors: anatomical connectivity and endogenous α-synuclein expression. The map and model allow the assessment of selective vulnerability to α-synuclein pathology development and neuron death. Finally, we use quantitative pathology to understand how the G2019S LRRK2 genetic risk factor affects the spread and toxicity of α-synuclein pathology.
Subject(s)
Brain/pathology , Connectome/psychology , Neural Networks, Computer , alpha-Synuclein/genetics , Animals , Brain Mapping , Cell Death , Female , Leucine-Rich Repeat Serine-Threonine Protein Kinase-2/genetics , Linear Models , Male , Mice , Mice, Inbred C57BL , Models, Neurological , Neurons/pathologyABSTRACT
Over 20 years ago, the synaptic protein α-synuclein was identified as the primary component of the Lewy bodies (LBs) that are a sine qua non of Parkinson's disease (PD). Since that time, extensive research has demonstrated that α-synuclein pathology is not only a hallmark of PD, but can also cause neuronal dysfunction and death. Detailed staging of α-synuclein pathology in the brains of patients has revealed a progressive pattern of pathology that correlates with the symptoms of disease. Early in the disease course, PD patients exhibit motor dysfunction, and α-synuclein pathology at this stage is primarily found in regions controlling motor function. At later stages of disease as patients' cognitive function deteriorates, α-synuclein pathology can be found in cortical structures responsible for higher cognitive processing. The stereotypical progression of α-synuclein pathology through the brain over time suggests that there may be a physical transmission of pathological α-synuclein from one area of the brain to another. The transmission hypothesis posits that an initial seed of pathological α-synuclein in one neuron may be released and taken up by another vulnerable neuron and thereby initiate pathological misfolding of α-synuclein in the recipient neuron. In recent years, convergent evidence from various studies has indicated that pathological protein transmission can occur in the human brain. Cell and animal models based on the transmission hypothesis have shown not only that pathological α-synuclein can be transmitted from cell-to-cell, but that this pathology can lead to neuronal dysfunction and degeneration. The α-synuclein transmission hypothesis has profound implications for treatment of what is currently an intractable neurodegenerative disease. In this review, we explore the evidence for cell-to-cell transmission of pathological α-synuclein, the current understanding of how pathological α-synuclein can move to a new cell and template misfolding, and the therapeutic implications of α-synuclein transmission.
Subject(s)
Brain/metabolism , Parkinson Disease/metabolism , Synucleinopathies/metabolism , alpha-Synuclein/metabolism , Animals , Brain/pathology , Glymphatic System/metabolism , Glymphatic System/pathology , Humans , Lewy Bodies/metabolism , Lewy Bodies/pathology , Parkinson Disease/genetics , Parkinson Disease/pathology , Synucleinopathies/genetics , Synucleinopathies/pathology , alpha-Synuclein/geneticsABSTRACT
Mutations in leucine-rich repeat kinase 2 (LRRK2) are one of the most common causes of familial Parkinson's disease (PD). The most common mutations in the LRRK2 gene induce elevated kinase activity of the LRRK2 protein. Recent studies have also suggested that LRRK2 kinase activity may be elevated in idiopathic PD patients, even in the absence of LRRK2 mutations. LRRK2 is therefore a prime candidate for small molecule kinase inhibitor development. However, it is currently unknown how LRRK2 influences the underlying pathogenesis of PD and how LRRK2 might influence extant pathogenesis. To understand whether LRRK2 inhibition would show some benefit in the absence of LRRK2 mutations, we treated a preclinical mouse model of PD with the potent LRRK2 inhibitor MLi-2. The inhibitor was well-tolerated by mice and dramatically reduced LRRK2 kinase activity. However, LRRK2 inhibition did not reverse motor phenotypes, pathological α-synuclein accumulation or neuron loss. The current study suggests that LRRK2 is not necessary for α-synuclein pathogenesis in this mouse model of PD and that further studies are needed to assess the likely clinical benefit of LRRK2 inhibition in idiopathic PD.