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Recent evidence supports a link between increased TDP-43 burden and the presence of an APOE4 gene allele in Alzheimer's disease (AD); however, it is difficult to conclude the direct effect of APOE on TDP-43 pathology due to the presence of mixed AD pathologies. The goal of this study is to address how APOE isoforms impact TDP-43 pathology and related neurodegeneration in the absence of typical AD pathologies.We overexpressed human TDP-43 via viral transduction in humanized APOE2, APOE3, APOE4 mice, and murine Apoe-knockout (Apoe-KO) mice. Behavior tests were performed across ages. Animals were harvested at 11 months of age and TDP-43 overexpression-related neurodegeneration and gliosis were assessed. To further address the human relevance, we analyzed the association of APOE with TDP-43 pathology in 160 postmortem brains from autopsy-confirmed amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with motor neuron disease (FTLD-MND) in the Mayo Clinic Brain Bank.We found that TDP-43 overexpression induced motor function deficits, neuronal loss, and gliosis in the motor cortex, especially in APOE2 mice, with much milder or absent effects in APOE3, APOE4, or Apoe-KO mice. In the motor cortex of the ALS and FTLD-MND postmortem human brains, we found that the APOE2 allele was associated with more severe TDP-43-positive dystrophic neurites.Our data suggest a genotype-specific effect of APOE on TDP-43 proteinopathy and neurodegeneration in the absence of AD pathology, with the strongest association seen with APOE2. This article is protected by copyright. All rights reserved.

Traumatic brain injury (TBI) is traditionally characterized by primary and secondary injury phases, both contributing to pathological and morphological changes. The mechanisms of damage and chronic consequences of TBI remain to be fully elucidated, but synaptic homeostasis disturbances and impaired energy metabolism are proposed to be a major contributor. It has been proposed that an increase of extracellular (eATP) adenosine triphosphate (ATP) in the area immediately surrounding impact may play a pivotal role in this sequence of events. After tissue injury, rupture of cell membranes allows release of intracellular ATP into the extracellular space, triggering a cascade of toxic events and inflammation. ATP is a ubiquitous messenger; however, simple and reliable techniques to measure its concentration have proven elusive. Here, we integrate a sensitive bioluminescent eATP sensor known as pmeLUC, with a controlled cortical impact mouse model to monitor eATP changes in a living animal after injury. Using the pmeLUC probe, a rapid increase of eATP is observed proximal to the point of impact within minutes of the injury. This event is significantly attenuated when animals are pretreated with an ATP hydrolyzing agent (apyrase) before surgery, confirming the contribution of eATP. This new eATP reporter could be useful for understanding the role of eATP in the pathogenesis in TBI and may identify a window of opportunity for therapeutic intervention.

Misfolding and aggregation of alpha-synuclein (α-synuclein) with concomitant cytotoxicity is a hallmark of Lewy body related disorders such as Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Although it plays a pivotal role in pathogenesis and disease progression, the function of α-synuclein and the molecular mechanisms underlying α-synuclein-induced neurotoxicity in these diseases are still elusive. Many in vitro and in vivo experimental models mimicking α-synuclein pathology such as oligomerization, toxicity and more recently neuronal propagation have been generated over the years. In particular, cellular models have been crucial for our comprehension of the pathogenic process of the disease and are beneficial for screening of molecules capable of modulating α-synuclein toxicity. Here, we review α-synuclein based cell culture models that reproduce some features of the neuronal populations affected in patients, from basic unicellular organisms to mammalian cell lines and primary neurons, to the cutting edge models of patient-specific cell lines. These reprogrammed cells known as induced pluripotent stem cells (iPSCs) have garnered attention because they closely reproduce the characteristics of neurons found in patients and provide a valuable tool for mechanistic studies. We also discuss how different cell models may constitute powerful tools for high-throughput screening of molecules capable of modulating α-synuclein toxicity and prevention of its propagation. This article is part of the Special Issue "Synuclein".

The apolipoprotein E (APOE) ε4 allele is the strongest genetic risk factor for late-onset Alzheimer’s disease mainly by driving amyloid-β pathology. Recently, APOE4 has also been found to be a genetic risk factor for Lewy body dementia (LBD), which includes dementia with Lewy bodies (DLB) and Parkinson’s disease dementia (PDD). How APOE4 drives risk of LBD and whether it has a direct effect on α-synuclein pathology is not clear. Here we generated a mouse model of synucleinopathy using an adeno-associated virus (AAV) gene delivery of α-synuclein in human APOE-targeted replacement mice expressing APOE2, APOE3 or APOEE4. We found that APOE4, but not APOE2 or APOE3, increased α-synuclein pathology, impaired behavioral performances, worsened neuronal and synaptic loss, and increased astrogliosis at nine months of age. Transcriptomic profiling in APOE4-expressing α-synuclein mice highlighted altered lipid and energy metabolism, and synapse-related pathways. We also observed an effect of APOE4 on α-synuclein pathology in human postmortem brains with LBD and minimal amyloid pathology. Our data demonstrates a pathogenic role of APOE4 in exacerbating α-synuclein pathology independent of amyloid, providing mechanistic insights into how APOE4 increases the risk of LBD.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive motor disturbances and affects more than 1% of the worldwide population. Despite considerable progress in understanding PD pathophysiology, including genetic and biochemical causes, diagnostic approaches lack accuracy and interventions are restricted to symptomatic treatments. PD is a complex syndrome with different clinical subtypes and a wide variability in disorder course. In order to deliver better clinical management of PD patients and discovery of novel therapies, there is an urgent need to find sensitive, specific, and reliable biomarkers. The development of biomarkers will not only help the scientific community to identify populations at risk, but also facilitate clinical diagnosis. Furthermore, these tools could monitor progression, which could ultimately deliver personalized therapeutic strategies. The field of biomarker discovery in PD has attracted significant attention and there have been numerous contributions in recent years. Although none of the parameters have been validated for clinical practice, some candidates hold promise. This review summarizes recent advances in the development of PD biomarkers and discusses new strategies for their utilization.

The neurodegenerative synucleinopathies, which include Parkinson disease, multiple-system atrophy, and Lewy body disease, are characterized by the presence of abundant neuronal inclusions called Lewy bodies and Lewy neurites. These disorders remain incurable, and a greater understanding of the pathologic processes is needed for effective treatment strategies to be developed. Recent data suggest that pathogenic misfolding of the presynaptic protein, α-synuclein (α-syn), and subsequent aggregation and accumulation are fundamental to the disease process. It is hypothesized that the misfolded isoform is able to induce misfolding of normal endogenous α-syn, much like what occurs in the prion diseases. Recent work highlighting the seeding effect of pathogenic α-syn has largely focused on the detergent-insoluble species of the protein. In this study, we performed intracerebral inoculations of the sarkosyl-insoluble or sarkosyl-soluble fractions of human Lewy body disease brain homogenate and show that both fractions induce CNS pathology in mice at 4 months after injection. Disease-associated deposits accumulated both near and distal to the site of the injection, suggesting a cell-to-cell spread via recruitment of α-syn. These results provide further insight into the prion-like mechanisms of α-syn and suggest that disease-associated α-syn is not homogeneous within a single patient but might exist in both soluble and insoluble isoforms.

CRISPR/Cas9 guided gene-editing is a potential therapeutic tool, however application to neurodegenerative disease models has been limited. Moreover, conventional mutation correction by gene-editing would only be relevant for the small fraction of neurodegenerative cases that are inherited. Here we introduce a CRISPR/Cas9-based strategy in cell and animal models to edit endogenous amyloid precursor protein (APP) at the extreme C-terminus and reciprocally manipulate the amyloid pathway, attenuating APP-β-cleavage and Aβ production, while up-regulating neuroprotective APP-α-cleavage. APP N-terminus and compensatory APP-homologues remain intact, with no apparent effects on neurophysiology in vitro. Robust APP-editing is seen in human iPSC-derived neurons and mouse brains with no detectable off-target effects. Our strategy likely works by limiting APP and BACE-1 approximation, and we also delineate mechanistic events that abrogates APP/BACE-1 convergence in this setting. Our work offers conceptual proof for a selective APP silencing strategy., Gene editing strategies are typically designed to correct mutant genes, but most neurodegenerative diseases are sporadic. Here the authors describe a strategy to selectively edit the C-terminus of APP and attenuate amyloid-β production, while upregulating neuroprotective α-cleavage.

The sirtuins are highly conserved nicotinamide adenine dinucleotide (NAD+)-dependent enzymes that play a broad role in cellular metabolism and aging. Mitochondrial sirtuin 3 (SIRT3) is downregulated in aging and age-associated diseases such as cancer and neuro-degeneration and plays a major role in maintaining mitochondrial function and preventing oxidative stress. Mitochondria dysfunction is central to the pathogenesis of Parkinson disease with mutations in mitochondrial-associated proteins such as PINK1 and parkin causing familial Parkinson disease. Here, we demonstrate that the presence of alpha-synuclein (αsyn) oligomers in mitochondria induce a corresponding decrease in mitochondrial SIRT3 activity and decreased mitochondrial biogenesis. We show that SIRT3 downregulation in the presence of αsyn accumulation is accompanied by increased phosphorylation of AMP-activated protein kinase (AMPK) and cAMP-response element binding protein (CREB), as well as increased phosphorylation of dynamin-related protein 1 (DRP1) and decreased levels of optic atrophy 1 (OPA1), which is indicative of impaired mitochondrial dynamics. Treatment with the AMPK agonist 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) restores SIRT3 expression and activity and improves mitochondrial function by decreasing αsyn oligomer formation. The accumulation of αsyn oligomers in mitochondria corresponds with SIRT3 down-regulation not only in an experimental cellular model, but also in vivo in a rodent model of Parkinson disease, and importantly, in human post mortem brains with neuropathologically confirmed Lewy body disease (LBD). Taken together our findings suggest that pharmacologically increasing SIRT3 levels will counteract αsyn-induced mitochondrial dysfunction by normalizing mitochondrial bioenergetics. These data support a protective role for SIRT3 in Parkinson disease-associated pathways and reveals significant mechanistic insight into the interplay of SIRT3 and αsyn.

The gradual accumulation of amyloid-β (Aβ) is a neuropathologic hallmark of Alzheimer’s disease (AD); playing a key role in disease progression. Aβ is generated by the sequential cleavage of amyloid precursor protein (APP) by β- and γ-secretases, with BACE-1 (β-site APP cleaving enzyme-1) cleavage as the rate limiting step 1–3. CRISPR/Cas9 guided gene-editing is emerging as a promising tool to edit pathogenic mutations and hinder disease progression 4,5,6 However, few studies have applied this technology to neurologic diseases 7–9. Besides technical caveats such as low editing efficiency in brains and limited in vivo validation 7, the canonical approach of ‘mutation-correction’ would only be applicable to the small fraction of neurodegenerative cases that are inherited (i.e. < 10% of AD, Parkinson’s, ALS); with a new strategy needed for every gene. Moreover, feasibility of CRISPR/Cas9 as a therapeutic possibility in sporadic AD has not been explored. Here we introduce a strategy to edit endogenous APP at the extreme C-terminus and reciprocally manipulate the amyloid pathway – attenuating β-cleavage and Aβ, while up-regulating neuroprotective a-cleavage. APP N-terminus, as well as compensatory APP homologues remain intact, and key physiologic parameters remain unaffected. Robust APP-editing is seen in cell lines, cultured neurons, human embryonic stem cells/iPSC-neurons, and mouse brains. Our strategy works by limiting the physical association of APP and BACE-1, and we also delineate the mechanism that abrogates APP/BACE-1 interaction in this setting. Our work offers an innovative ‘cut and silence’ gene-editing strategy that could be a new therapeutic paradigm for AD.

CRISPR/Cas9 guided gene-editing is emerging as a promising therapeutic tool, however application to neurodegenerative diseases has been limited. Moreover, conventional ‘mutation correction’ by gene-editing would only be relevant for the small fraction of neurodegenerative cases that are inherited, and fresh ideas are needed. Here we introduce a CRISPR/Cas9-based strategy to edit endogenous APP (amyloid precursor protein) at the extreme C-terminus and reciprocally manipulate the amyloid pathway – attenuating β-cleavage and Aβ production, while upregulating neuroprotective α-cleavage. APP N-terminus and compensatory APP-homologues remain intact; with no apparent effects on neurophysiology. Robust APP-editing is seen in a variety of cells – including iPSC-neurons and mouse brains – with no detectable off-target effects. Our strategy works by limiting APP and BACE-1 approximation, and we also delineate the underlying mechanism that abrogates APP/BACE-1 convergence in this setting. Our work offers conceptual proof for a ‘cut and silence’ gene-editing strategy that could be a new therapeutic paradigm for AD.

Abnormal accumulation of alpha-synuclein (αsyn) is a pathological hallmark of Lewy body related disorders such as Parkinson’s disease and Dementia with Lewy body disease. During the past two decades, a myriad of animal models have been developed to mimic pathological features of synucleinopathies by over-expressing human αsyn. Although different strategies have been used, most models have little or no reliable and predictive phenotype. Novel animal models are a valuable tool for understanding neuronal pathology and to facilitate development of new therapeutics for these diseases. Here, we report the development and characterization of a novel model in which mice rapidly express wild-type αsyn via somatic brain transgenesis mediated by adeno-associated virus (AAV). At 1, 3, and 6 months of age following intracerebroventricular (ICV) injection, mice were subjected to a battery of behavioral tests followed by pathological analyses of the brains. Remarkably, significant levels of αsyn expression are detected throughout the brain as early as 1 month old, including olfactory bulb, hippocampus, thalamic regions and midbrain. Immunostaining with a phospho-αsyn (pS129) specific antibody reveals abundant pS129 expression in specific regions. Also, pathologic αsyn is detected using the disease specific antibody 5G4. However, this model did not recapitulate behavioral phenotypes characteristic of rodent models of synucleinopathies. In fact no deficits in motor function or cognition were observed at 3 or 6 months of age. Taken together, these findings show that transduction of neonatal mouse with AAV-αsyn can successfully lead to rapid, whole brain transduction of wild-type human αsyn, but increased levels of wildtype αsyn do not induce behavior changes at an early time point (6 months), despite pathological changes in several neurons populations as early as 1 month. Electronic supplementary material The online version of this article (doi:10.1186/s40478-017-0455-3) contains supplementary material, which is available to authorized users.

Misfolding and aggregation of alpha-synuclein (αsyn) resulting in cytotoxicity is a hallmark of Parkinson’s disease (PD) and related synucleinopathies. The recent body of evidence indicates that αsyn can be released from neuronal cells by nonconventional exocytosis involving extracellular vesicles (EVs) such as exosomes. The transfer of αsyn between cells has been proposed to be an important mechanism of disease propagation in PD. To date, exosome trafficking mechanisms, including release and cell-cell transmission, have not been fully described. To gain insight into the mechanisms involved, exosomes were purified from conditioned media of stable cells secreting αsyn oligomers. A novel bimolecular protein complementation assay was used to detect exosomes containing αsyn oligomers. Recipient cells were treated with exosomes containing αsyn oligomers or “free” non-exosome-associated αsyn oligomers and internalization was monitored. We demonstrate that cell-derived exosome-associated αsyn oligomers can be efficiently internalized by recipient cells. Interestingly exosome-free αsyn oligomers isolated from conditioned medium were not internalized but remained bound to the extracellular surface. To investigate the endocytic pathway(s) required for the exosome uptake different pharmacological inhibitors of caveolin-dependent, clathrin-dependent, and macropinocytosis pathways were utilized. Surprisingly, none of these pathways appear to play a significant role in the internalization of exosome-associated αsyn oligomers. Finally, the role of heparin sulfate proteoglycans (HSPGs) in exosome-associated αsyn internalization was investigated using genetic approach. Despite previous studies showing HSPGs can modulate internalization of fibrillar αsyn, genetic manipulations did not attenuate internalization of exosome-associated αsyn oligomers in our hands, suggesting that exosome-associated αsyn is internalized via an alternative endocytic pathway(s) that has yet to be elucidated.

Lewy body dementia (LBD) is a term used to encompass both Parkinson’s disease dementia and dementia with Lewy body disorders. They are the second most common type of dementia after Alzheimer’s disease but are yet often misdiagnosed. Indeed, LBD appears to fall somewhere in the middle of a disease spectrum ranging from Alzheimer’s to Parkinson’s disease. LBD is characterized by manifestations of neuropsychiatric symptoms with motor impairment, and both disorders can be distinguished by the temporal manifestations of motor symptoms. The pathological hallmark of LBD is the presence of Lewy bodies with aggregated alpha-synuclein being a main component. To date, no cures are available for LBD. Consequently identifying and dissecting disease-modifying pathway for LBD is a priority for the discovery of neuroprotective therapeutics. Herein, we review promising targets and new innovative approaches. In this regard, strategies targeting the clearance of alpha-synuclein and prevention of its propagation will be discussed.

The accumulation of α-synuclein aggregates is the hallmark of Parkinson’s disease, and more generally of synucleinopathies. The accumulation of tau aggregates however is classically found in the brains of patients with dementia, and this type of neuropathological feature specifically defines the tauopathies. Nevertheless, in numerous cases α-synuclein positive inclusions are also described in tauopathies and vice versa, suggesting a co-existence or crosstalk of these proteinopathies. Interestingly, α-synuclein and tau share striking common characteristics suggesting that they may work in concord. Tau and α-synuclein are both partially unfolded proteins that can form toxic oligomers and abnormal intracellular aggregates under pathological conditions. Furthermore, mutations in either are responsible for severe dominant familial neurodegeneration. Moreover, tau and α-synuclein appear to promote the fibrillization and solubility of each other in vitro and in vivo. This suggests that interactions between tau and α-synuclein form a deleterious feed-forward loop essential for the development and spreading of neurodegeneration. Here, we review the recent literature with respect to elucidating the possible links between α-synuclein and tau.

Many neurodegenerative disorders including Alzheimer’s disease, Parkinson’s disease, Amyotrophic Lateral Sclerosis and Polyglutamine disorders are characterized by conformational change in proteins that result in misfolding, aggregation and accumulation of amyloid fibrils. These misfolded species result in toxicity in cells and ultimately lead to the death of specific neuronal populations. The cellular pathways involved in these neurological disorders are still unclear but a large body of evidence suggests that molecular chaperones, regulators of cellular protein quality control, may play a critical role in neurodegeneration. Indeed in patient post-mortem brain, chaperones are found in the hallmark neuronal inclusions. Molecular chaperones are able to inhibit the aggregation of denatured proteins and facilitate refolding of different disease-causing proteins. Experimental approaches in animal and cellular models have shown prevention of protein misfolding and facilitation of clearance mechanisms via up-regulation of molecular chaperones. Therefore manipulating the molecular chaperone system may be a successful strategy to counter the conformational changes occurring in protein misfolding diseases and may offer new therapeutic promise. Here we review the evidence for the involvement of various molecular chaperones in several neurodegenerative disorders and examine the current research investigating the role of the chaperones as novel targets for therapy of these devastating diseases.