A multiverse of α-synuclein: investigation of prion strain properties with carboxyl-terminal truncation specific antibodies in animal models.

Synucleinopathies are a group of neurodegenerative disorders characterized by the presence of misfolded α-Synuclein (αSyn) in the brain. These conditions manifest with diverse clinical and pathophysiological characteristics. This disease diversity is hypothesized to be driven by αSyn strains with differing biophysical properties, potentially influencing prion-type propagation and consequentially the progression of illness. Previously, we investigated this hypothesis by injecting brain lysate (seeds) from deceased individuals with various synucleinopathies or human recombinant αSyn preformed fibrils (PFFs) into transgenic mice overexpressing either wild type or A53T human αSyn. In the studies herein, we expanded on these experiments, utilizing a panel of antibodies specific for the major carboxyl-terminally truncated forms of αSyn (αSynΔC). These modified forms of αSyn are found enriched in human disease brains to inform on potential strain-specific proteolytic patterns. With monoclonal antibodies specific for human αSyn cleaved at residues 103, 114, 122, 125, and 129, we demonstrate that multiple system atrophy (MSA) seeds and PFFs induce differing neuroanatomical spread of αSyn pathology associated with host specific profiles. Overall, αSyn cleaved at residue 103 was most widely present in the induced pathological inclusions. Furthermore, αSynΔC-positive inclusions were present in astrocytes, but more frequently in activated microglia, with patterns dependent on host and inoculum. These findings support the hypothesis that synucleinopathy heterogeneity might stem from αSyn strains with unique biochemical properties that include proteolytic processing, which could result in dominant strain properties.

Interventional Treatment of Symptomatic Vasospasm in the Setting of Traumatic Brain Injury: A Systematic Review of Reported Cases.

Traumatic subarachnoid hemorrhage (tSAH) is frequently comorbid with traumatic brain injury (TBI) and may induce secondary injury through vascular changes such as vasospasm and subsequent delayed cerebral ischemia (DCI). While aneurysmal SAH is well studied regarding vasospasm and DCI, less is known regarding tSAH and the prevalence of vasospasm and DCI, the consequences of vasospasm in this setting, when treatment is indicated, and which management strategies should be implemented. In this article, a systematic review of the literature that was conducted for cases of symptomatic vasospasm in patients with TBI is reported, association with tSAH is reported, risk factors for vasospasm and DCI are summarized, and commonalities in diagnosis and management are discussed. Clinical characteristics and treatment outcomes of 38 cases across 20 studies were identified in which patients with TBI with vasospasm underwent medical or endovascular management. Of the patients with data available for each category, the average age was 48.7 ± 20.3 years (n = 31), the Glasgow Coma Scale score at presentation was 10.6 ± 4.5 (n = 35), and 100% had tSAH (n = 29). Symptomatic vasospasm indicative of DCI was diagnosed on average at postinjury day 8.4 ± 3.0 days (n = 30). Of the patients, 56.6% (n = 30) had a new ischemic change associated with vasospasm confirming DCI. Treatment strategies are discussed, with 11 of 12 endovascularly treated and 19 of 26 medically treated patients surviving to discharge. tSAH is associated with vasospasm and DCI in moderate and severe TBI, and patients with clinical and radiographic evidence of symptomatic vasospasm and subsequent DCI may benefit from endovascular or medical management strategies.

Evaluating analgesic medications utilized in the treatment of aneurysmal subarachnoid hemorrhage and association with delayed cerebral ischemia.

BACKGROUND: Spontaneous aneurysmal subarachnoid hemorrhage (aSAH) recovery may be hampered by delayed cerebral ischemia (DCI). Herein, we sought to identify whether frequently administered medications in the intensive care unit (ICU) are associated with DCI. METHODS: In this retrospective study, patients admitted to a tertiary care center neuro-ICU between 2012 and 2019 with aSAH who could verbalize pain intensity scores were included. Medication dosages and clinical characteristics were abstracted from the medical record. Both paired and unpaired analyses were utilized to measure individual DCI risk for a given patient in relation to drug dosages. RESULTS: 119 patients were included; average age was 61.7 ± 15.2 (SD) years, 89 (74.7%) were female, and 32 (26.9%) experienced DCI during admission. Patients with DCI had longer length of stay (19.3 ± 7.4 vs 12.7 ± 5.3 days, p < 0.0001). The combination medication of acetaminophen 325 mg/butalbital 50 mg/caffeine 40 mg (A/B/C) was associated with decreased DCI on paired (2.3 ± 2.0 vs 3.1 ± 1.9 tabs, p = 0.034) and unpaired analysis (1.84 ± 2.4 vs 2.6 ± 2.4 tabs, p < 0.001). No associations were found between DCI and opioids, dexamethasone, levetiracetam, or acetaminophen. Max and mean daily headache pain was not associated with DCI occurrence. CONCLUSION: We identified an association between a commonly administered analgesic and DCI. A/B/C is associated with decreased DCI in this study, while other medications are not associated with DCI risk.

Carboxyl truncation of α-synuclein occurs early and is influenced by human APOE genotype in transgenic mouse models of α-synuclein pathogenesis.

Post-translational modifications to the carboxyl (C) terminus domain of α-synuclein can play an important role in promoting the pathologic aggregation of α-synuclein. Various cleavages that diminish this highly charged, proline-rich region can result in exposure of hydrophobic, aggregation-prone regions, thereby accelerating the aggregation kinetics of α-synuclein into misfolded, pathologic forms. C-terminally truncated forms of α-synuclein are abundant in human diseased brains compared to controls, suggesting a role in disease pathogenesis. Factors that alter the homeostatic proteolytic processing of α-synuclein may ultimately tip the balance towards a progressive disease state. Apolipoprotein E (APOE) has been implicated in the acceleration of cognitive impairment in patients with Lewy body diseases. The APOE4 isoform has been found to cause dysregulation in the endosomal-lysosomal pathway, which could result in altered α-synuclein degradation as a potential mechanism for promoting its pathologic misfolding. Herein, we investigate the spatiotemporal accumulation of C-terminally truncated α-synuclein in a seeded and progressive mouse model of synucleinopathy. Furthermore, we study how this process is influenced in the context of mice that are altered to express either the human APOE3 or APOE4 isoforms. We found that specific C-terminal truncation of α-synuclein occurs at early stages of pathogenesis. We also found that proteolytic processing of this domain differs across various brain regions and is influenced by the presence of different human APOE isoforms. Our data demonstrate an early pathogenic role for C-terminally truncated α-synuclein, and highlight the influence of APOE isoforms in modulating its impact.

Proteinopathies and Neurotrauma: Update on Degenerative Cascades.

Neurotrauma, especially repetitive neurotrauma, is associated with the development of progressive neurodegeneration leading to chronic traumatic encephalopathy (CTE). Exposure to neurotrauma regularly occurs during sports and military service, often not requiring medical care. However, exposure to severe and/or repeated sub-clinical neurotrauma has been shown cause physical and psychological disability, leading to reduce life expectancy. Misfolding of proteins, or proteinopathy, is a pathological hallmark of CTE, in which chronic injury leads to local and diffuse protein aggregates. These aggregates are an overlapping feature of many neurodegenerative diseases such as CTE, Alzheimer's Disease, Parkinsons disease. Neurotrauma is also a significant risk factor for the development of these diseases, however the mechanism's underlying this association are not well understood. While phosphorylated tau aggregates are the primary feature of CTE, amyloid-beta, Transactive response DNA-binding protein 43 (TDP-43), and alpha-synuclein (αSyn) are also well documented. Aberrant misfolding of these proteins has been shown to disrupt brain homeostasis leading to neurodegeneration in a disease dependent manor. In CTE, the interaction between proteinopathies and their associated neurodegeneration is a current area of study. Here we provide an update on current literature surrounding the prevalence, characteristics, and pathogenesis of proteinopathies in CTE.

Headache persisting after aneurysmal subarachnoid hemorrhage: A narrative review of pathophysiology and therapeutic strategies.

OBJECTIVE: This narrative review of the literature concerns persistent headache attributed to past non-traumatic subarachnoid hemorrhage (SAH), based off demographic and clinical features, what are pathophysiologic mechanisms by which these headaches occur, which medical and interventional treatments have the most evidence for pain alleviation, and what pre-clinical evidence is there for emerging treatments for these patients. BACKGROUND: Following initial stabilization and treatment of spontaneous SAH, most commonly due to aneurysmal rupture, headache in the immediate inpatient setting and persisting after discharge are an important cause of morbidity. These headaches often receive heterogenous treatment of uncertain efficacy, and the risk factors and pathophysiology of their development has received little study. METHODS: A narrative review of current literature discussing post-SAH headache was conducted using a literature search in PubMed with search term combinations including "post subarachnoid hemorrhage pain", "subarachnoid hemorrhage headache", and "post subarachnoid hemorrhage headache". Clinical studies mentioning headache after SAH and/or treatment in the abstract/title were included through March, 2022. RESULTS AND CONCLUSION: Post-SAH headaches are shown to decrease quality of life, have a multi-modal pathophysiology in their occurrence, and only a select few medications (reviewed herein) have been demonstrated to have efficacy in alleviation of these headaches, while also harboring possible risks including vasospasm and re-bleeding. An effective treatment paradigm of these headaches will include trials of evidence-based therapeutics, rapid reduction of opioid medications if not effective, and consideration of multi-modal pain control strategies including nerve blocks.

Clinical risk factors associated with cerebrospinal fluid leak in facial trauma: A retrospective analysis.

OBJECTIVE: Cerebrospinal fluid (CSF) leak occurs most commonly following skull fracture, with a CSF leakage complicating up to 2% of all head traumas. This study aims to identify demographic and injury characteristics correlated with the highest risk of CSF leak in patients with known facial fractures. METHODS: Retrospective data was collected from a previously described trauma registry from 2010 to 2019. Patients over 18 years old with any type of facial fracture, known CSF leak status, available neuroimaging, and hospital admission were included. Chi-Square analysis for demographic and injury characteristic data were utilized. RESULTS: A total of 79 patients with CSF leak and 4907 patients without CSF leak were included in the database. Patients with CSF leak tended to be younger than those without CSF leak (38.45 +/- 0.28 vs 44.08 +/- 0.28, M +/- SE, p = 0.0197). CSF leak depended on the mechanism of injury (MOI; X2 =27.02, df=2, p = 0.0000013), with CSF leak rates highest in penetrating injuries (4.87%) and motor vehicle accidents (1.78%) compared to blunt injuries (0.95%); age did not significantly differ between the MOI groups (p = 0.11). CSF leak was also more common in patients with a lower Glasgow coma scale (GCS; 7.95 +/- 0.58 vs 12.21 +/- 0.10, p = 10-15), LeFort type 2&3 and pan-facial fractures compared to all other facial fracture types (8.9% vs 1.2%, p = 10-15), and radiographic midline shift (29.4% vs 9.1%, p = 10-15). There was a trend towards a higher proportion of males in those with CSF leak compared to those without (83.3% vs 73.7% males, p = 0.073), and in patients with prolonged loss of consciousness (LOC; 9.43% with LOC > 1 h vs 2.69% LOC < 1 h, p = 0.056). CONCLUSION: Facial fractures often present with CSF leak, and certain demographic and injury risk factors including younger age, worse GCS score, evidence of midline shift, and certain mechanisms of injury (penetrating and motor vehicle) are correlated with increased risk and warrant close screening and follow-up for CSF leak detection. LeFort type 2&3 and pan-facial fractures are at high risk of CSF leak.

Unique seeding profiles and prion-like propagation of synucleinopathies are highly dependent on the host in human α-synuclein transgenic mice.

α-synuclein (αSyn) is an intrinsically disordered protein which can undergo structural transformations, resulting in the formation of stable, insoluble fibrils. αSyn amyloid-type nucleation can be induced by misfolded 'seeds' serving as a conformational template, tantamount to the prion-like mechanism. Accumulation of αSyn inclusions is a key feature of dementia with Lewy bodies (DLB) and multiple system atrophy (MSA), and are found as additional pathology in Alzheimer's disease (AD) such as AD with amygdala predominant Lewy bodies (AD/ALB). While these disorders accumulate the same pathological protein, they exhibit heterogeneity in clinical and histological features; however, the mechanism(s) underlying this variability remains elusive. Accruing data from human autopsy studies, animal inoculation modeling, and in vitro characterization experiments, have lent credence to the hypothesis that conformational polymorphism of the αSyn amyloid-type fibril structure results in distinct "strains" with categorical infectivity traits. Herein, we directly compare the seeding abilities and outcome of human brain lysates from these diseases, as well as recombinant preformed human αSyn fibrils by the intracerebral inoculation of transgenic mice overexpressing either human wild-type αSyn or human αSyn with the familial A53T mutation. Our study has revealed that the initiating inoculum heavily dictates the phenotypic and pathological course of disease. Interestingly, we have also established relevant host-dependent distinctions between propagation profiles, including burden and spread of inclusion pathology throughout the neuroaxis, as well as severity of neurological symptoms. These findings provide compelling evidence supporting the hypothesis that diverse prion-type conformers may explain the variability seen in synucleinopathies.

Severe headache trajectory following aneurysmal subarachnoid hemorrhage: the association with lower sodium levels.

BACKGROUND: A clinical hallmark of aneurysmal SAH (aSAH) is headache. Little is known about post-aSAH headache factors which may point to underlying mechanisms. In this study, we aimed to characterize the severity and trajectory of headaches in relation to clinical features of patients with aSAH. METHODS: This is a retrospective longitudinal study of adult patients admitted to an academic tertiary care center between 2012 and 2019 with aSAH who could verbalize pain scores. Factors recorded included demographics, aneurysm characteristics, analgesia, daily morning serum sodium concentration, and occurrence of vasospasm. Group-based trajectory modeling was used to identify headache pain trajectories, and clinical factors were compared between trajectories. RESULTS: Of 91 patients included in the analysis, mean age was 57 years and 20 (22%) were male. Headache score trajectories clustered into two groups: patients with mild-moderate and moderate-severe pain. Patients in the moderate-severe pain group were younger (P<0.05), received more opioid analgesia (P<0.001), and had lower sodium concentrations (P<0.001) than patients in the mild-moderate pain group. CONCLUSION: We identified two distinct post-aSAH headache pain trajectory cohorts and identified an association with age, analgesia, and sodium levels. Future prospective studies considering sodium homeostasis and volume status under standardized analgesic regimens are warranted.

α-Synuclein-induced dysregulation of neuronal activity contributes to murine dopamine neuron vulnerability.

Pathophysiological damages and loss of function of dopamine neurons precede their demise and contribute to the early phases of Parkinson's disease. The presence of aberrant intracellular pathological inclusions of the protein α-synuclein within ventral midbrain dopaminergic neurons is one of the cardinal features of Parkinson's disease. We employed molecular biology, electrophysiology, and live-cell imaging to investigate how excessive α-synuclein expression alters multiple characteristics of dopaminergic neuronal dynamics and dopamine transmission in cultured dopamine neurons conditionally expressing GCaMP6f. We found that overexpression of α-synuclein in mouse (male and female) dopaminergic neurons altered neuronal firing properties, calcium dynamics, dopamine release, protein expression, and morphology. Moreover, prolonged exposure to the D2 receptor agonist, quinpirole, rescues many of the alterations induced by α-synuclein overexpression. These studies demonstrate that α-synuclein dysregulation of neuronal activity contributes to the vulnerability of dopaminergic neurons and that modulation of D2 receptor activity can ameliorate the pathophysiology. These findings provide mechanistic insights into the insidious changes in dopaminergic neuronal activity and neuronal loss that characterize Parkinson's disease progression with significant therapeutic implications.

Disease-, region- and cell type specific diversity of α-synuclein carboxy terminal truncations in synucleinopathies.

Synucleinopathies, including Parkinson's disease (PD), Lewy body dementia (LBD), Alzheimer's disease with amygdala restricted Lewy bodies (AD/ALB), and multiple system atrophy (MSA) comprise a spectrum of neurodegenerative disorders characterized by the presence of distinct pathological α-synuclein (αSyn) inclusions. Experimental and pathological studies support the notion that αSyn aggregates contribute to cellular demise and dysfunction with disease progression associated with a prion-like spread of αSyn aggregates via conformational templating. The initiating event(s) and factors that contribute to diverse forms of synucleinopathies remain poorly understood. A major post-translational modification of αSyn associated with pathological inclusions is a diverse array of specific truncations within the carboxy terminal region. While these modifications have been shown experimentally to induce and promote αSyn aggregation, little is known about their disease-, region- and cell type specific distribution. To this end, we generated a series of monoclonal antibodies specific to neo-epitopes in αSyn truncated after residues 103, 115, 119, 122, 125, and 129. Immunocytochemical investigations using these new tools revealed striking differences in the αSyn truncation pattern between different synucleinopathies, brain regions and specific cellular populations. In LBD, neuronal inclusions in the substantia nigra and amygdala were positive for αSyn cleaved after residues 103, 119, 122, and 125, but not 115. In contrast, in the same patients' brain αSyn cleaved at residue 115, as well as 103, 119 and 122 were abundant in the dorsal motor nucleus of the vagus. In patients with AD/ALB, these modifications were only weakly or not detected in amygdala αSyn inclusions. αSyn truncated at residues 103, 115, 119, and 125 was readily present in MSA glial cytoplasmic inclusions, but 122 cleaved αSyn was only weakly or not present. Conversely, MSA neuronal pathology in the pontine nuclei was strongly reactive to the αSyn x-122 neo-epitope but did not display any reactivity for αSyn 103 cleavage. These studies demonstrate significant disease-, region- and cell type specific differences in carboxy terminal αSyn processing associated with pathological inclusions that likely contributes to their distinct strain-like prion properties and promotes the diversity displayed in the degrees of these insidious diseases.

Multiple system atrophy-associated oligodendroglial protein p25α stimulates formation of novel α-synuclein strain with enhanced neurodegenerative potential.

Pathology consisting of intracellular aggregates of alpha-Synuclein (α-Syn) spread through the nervous system in a variety of neurodegenerative disorders including Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. The discovery of structurally distinct α-Syn polymorphs, so-called strains, supports a hypothesis where strain-specific structures are templated into aggregates formed by native α-Syn. These distinct strains are hypothesised to dictate the spreading of pathology in the tissue and the cellular impact of the aggregates, thereby contributing to the variety of clinical phenotypes. Here, we present evidence of a novel α-Syn strain induced by the multiple system atrophy-associated oligodendroglial protein p25α. Using an array of biophysical, biochemical, cellular, and in vivo analyses, we demonstrate that compared to α-Syn alone, a substoichiometric concentration of p25α redirects α-Syn aggregation into a unique α-Syn/p25α strain with a different structure and enhanced in vivo prodegenerative properties. The α-Syn/p25α strain induced larger inclusions in human dopaminergic neurons. In vivo, intramuscular injection of preformed fibrils (PFF) of the α-Syn/p25α strain compared to α-Syn PFF resulted in a shortened life span and a distinct anatomical distribution of inclusion pathology in the brain of a human A53T transgenic (line M83) mouse. Investigation of α-Syn aggregates in brain stem extracts of end-stage mice demonstrated that the more aggressive phenotype of the α-Syn/p25α strain was associated with an increased load of α-Syn aggregates based on a Förster resonance energy transfer immunoassay and a reduced α-Syn aggregate seeding activity based on a protein misfolding cyclic amplification assay. When injected unilaterally into the striata of wild-type mice, the α-Syn/p25α strain resulted in a more-pronounced motoric phenotype than α-Syn PFF and exhibited a "tropism" for nigro-striatal neurons compared to α-Syn PFF. Overall, our data support a hypothesis whereby oligodendroglial p25α is responsible for generating a highly prodegenerative α-Syn strain in multiple system atrophy.

Robust α-synuclein pathology in select brainstem neuronal populations is a potential instigator of multiple system atrophy.

Multiple system atrophy (MSA) is an insidious middle age-onset neurodegenerative disease that clinically presents with variable degrees of parkinsonism and cerebellar ataxia. The pathological hallmark of MSA is the progressive accumulation of glial cytoplasmic inclusions (GCIs) in oligodendrocytes that are comprised of α-synuclein (αSyn) aberrantly polymerized into fibrils. Experimentally, MSA brain samples display a high level of seeding activity to induce further αSyn aggregation by a prion-like conformational mechanism. Paradoxically, αSyn is predominantly a neuronal brain protein, with only marginal levels expressed in normal or diseased oligodendrocytes, and αSyn inclusions in other neurodegenerative diseases, including Parkinson's disease and Dementia with Lewy bodies, are primarily found in neurons. Although GCIs are the hallmark of MSA, using a series of new monoclonal antibodies targeting the carboxy-terminal region of αSyn, we demonstrate that neuronal αSyn pathology in MSA patient brains is remarkably abundant in the pontine nuclei and medullary inferior olivary nucleus. This neuronal αSyn pathology has distinct histological properties compared to GCIs, which allows it to remain concealed to many routine detection methods associated with altered biochemical properties of the carboxy-terminal domain of αSyn. We propose that these previously underappreciated sources of aberrant αSyn could serve as a pool of αSyn prion seeds that can initiate and continue to drive the pathogenesis of MSA.

An Erythritol-Sweetened Beverage Induces Satiety and Suppresses Ghrelin Compared to Aspartame in Healthy Non-Obese Subjects: A Pilot Study.

Despite the reduced caloric content of artificially sweetened beverages (ASBs) relative to those sweetened with sucrose, consumption of ASBs fail to consistently decrease the risk of obesity and associated diseases. This failure may be due to the inability of ASBs to effectively reduce appetite and hence overall caloric intake. A variety of non-nutritive sweeteners (NNS), however, remain to be screened for effectiveness in promoting satiety and reducing calorie consumption. Erythritol is well-tolerated, low-calorie sugar alcohol widely used as a sugar substitute. It is unique among NNS due to its low sweetness index relative to glucose, meaning that it is typically served at much higher concentrations than other common NNS. Animal and human studies have noted correlations between osmolarity, satiety, and levels of satiety hormones, independent of the effects of sweetness or nutritive value. We hypothesized that consumption of a beverage sweetened with erythritol to the sweetness and osmolarity of a common soft drink will improve self-reported satiety and more strongly affect the magnitude of changes in the hormone ghrelin than would an iso sweet beverage sweetened only with aspartame, a sweetener with a high sweetness index relative to glucose. Using a randomized double-blind crossover trial, we found that serum ghrelin was significantly decreased after consumption of an erythritol-sweetened beverage compared to aspartame. Likewise, consumption of the erythritol-sweetened beverage increased various measures of satiety in volunteers. Knowledge gained from this project demonstrates that high-osmolarity NNS may be useful in formulating ASBs that are satiating and low in calories.

Novel monoclonal antibodies targeting the RRM2 domain of human TDP-43 protein.

Transactive response DNA-binding protein of 43 kilodaltons (TDP-43) is a 414 amino acid protein that under physiologic conditions localizes to the nucleus and participates in the regulation of RNA metabolism through two RNA recognition motifs (RRM1 and RRM2). In neurodegenerative diseases, TDP-43 may become hyperphosphorylated, ubiquitinated, and aggregate into cytoplasmic inclusions. TDP-43 is now well-characterized as a pathologic protein of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with TDP-43 proteinopathy (FTLD-TDP). Additionally, a common TDP-43 proteinopathy arising outside of the context of ALS and FTLD-TDP has been recently described, termed "limbic predominant age-related TDP-43 encephalopathy (LATE)." In the current study, two novel mouse-derived monoclonal antibodies, 2G11 and 2H1, raised against an epitope within the RRM2 domain of TDP-43 (residues 198-216), were characterized for specificity and immunohistochemical application in human brain from cases of Alzheimer's disease (AD), Lewy Body Disease (LBD), amyotrophic lateral sclerosis (ALS), and frontotemporal lobe degeneration with TDP-43 inclusions (FTLD-TDP). Immunoblot analysis of these antibodies in HEK293T cells revealed efficient detection of intact human TDP-43 protein, and in N2A cells showed no reactivity for mouse TDP-43. Immunohistochemically applied to formalin-fixed paraffin-embedded tissues, 2G11 and 2H1 robustly identified the classic inclusions of ALS and FTLD-TDP, and efficaciously provided a diagnosis of LATE in cases of AD and LBD. These novel antibodies label aberrant intracytoplasmic protein inclusions without relying on hyperphosphorylated epitopes, and provide elegant discrimination between TDP-43 and tau neurofibrillary tangles within neurodegenerative comorbidity.

Tau Ser208 phosphorylation promotes aggregation and reveals neuropathologic diversity in Alzheimer's disease and other tauopathies.

Tau protein abnormally aggregates in tauopathies, a diverse group of neurologic diseases that includes Alzheimer's disease (AD). In early stages of disease, tau becomes hyperphosphorylated and mislocalized, which can contribute to its aggregation and toxicity. We demonstrate that tau phosphorylation at Ser208 (pSer208) promotes microtubule dysfunction and tau aggregation in cultured cells. Comparative assessment of the epitopes recognized by antibodies AT8, CP13, and 7F2 demonstrates that CP13 and 7F2 are specific for tau phosphorylation at Ser202 and Thr205, respectively, independently of the phosphorylation state of adjacent phosphorylation sites. Supporting the involvement of pSer208 in tau pathology, a novel monoclonal antibody 3G12 specific for tau phosphorylation at Ser208 revealed strong reactivity of tau inclusions in the brains of PS19 and rTg4510 transgenic mouse models of tauopathy. 3G12 also labelled neurofibrillary tangles in brains of patients with AD but revealed differential staining compared to CP13 and 7F2 for other types of tau pathologies such as in neuropil threads and neuritic plaques in AD, tufted astrocytes in progressive supranuclear palsy and astrocytic plaques in corticobasal degeneration. These results support the hypothesis that tau phosphorylation at Ser208 strongly contributes to unique types of tau aggregation and may be a reliable marker for the presence of mature neurofibrillary tangles.

The emerging role of α-synuclein truncation in aggregation and disease.

α-Synuclein (αsyn) is an abundant brain neuronal protein that can misfold and polymerize to form toxic fibrils coalescing into pathologic inclusions in neurodegenerative diseases, including Parkinson's disease, Lewy body dementia, and multiple system atrophy. These fibrils may induce further αsyn misfolding and propagation of pathologic fibrils in a prion-like process. It is unclear why αsyn initially misfolds, but a growing body of literature suggests a critical role of partial proteolytic processing resulting in various truncations of the highly charged and flexible carboxyl-terminal region. This review aims to 1) summarize recent evidence that disease-specific proteolytic truncations of αsyn occur in Parkinson's disease, Lewy body dementia, and multiple system atrophy and animal disease models; 2) provide mechanistic insights on how truncation of the amino and carboxyl regions of αsyn may modulate the propensity of αsyn to pathologically misfold; 3) compare experiments evaluating the prion-like properties of truncated forms of αsyn in various models with implications for disease progression; 4) assess uniquely toxic properties imparted to αsyn upon truncation; and 5) discuss pathways through which truncated αsyn forms and therapies targeted to interrupt them. Cumulatively, it is evident that truncation of αsyn, particularly carboxyl truncation that can be augmented by dysfunctional proteostasis, dramatically potentiates the propensity of αsyn to pathologically misfold into uniquely toxic fibrils with modulated prion-like seeding activity. Therapeutic strategies and experimental paradigms should operate under the assumption that truncation of αsyn is likely occurring in both initial and progressive disease stages, and preventing truncation may be an effective preventative strategy against pathologic inclusion formation.

Carboxy-terminal truncation and phosphorylation of α-synuclein elongates survival in a prion-like seeding mouse model of synucleinopathy.

Pathologic intracellular inclusions formed from polymers of misfolded α-synuclein (αsyn) protein define a group of neurodegenerative diseases termed synucleinopathies which includes Parkinson's disease (PD). Prion-like recruitment of endogenous cellular αsyn has been demonstrated to occur in animal models of synucleinopathy, whereby misfolded αsyn can induce further pathologic αsyn inclusions to form through a prion-like mechanism. It has been suggested that misfolded αsyn may assume differing conformations which lead to varied clinical and pathological manifestations of disease; this phenomenon bears similarities to that of prion strains whereby the same misfolded protein can produce unique diseases. It is unclear what factors influence the development of unique αsyn strains, however post-translational modifications (PTMs) such as phosphorylation and truncation that are present in misfolded αsyn in disease may play a role due to their modulation of biochemical and structural αsyn properties. Herein, we investigate the prion-like properties of misfolded αsyn polymers containing either phosphomimetic (S129E) αsyn, 5 different major carboxy (C)-truncated forms of αsyn (1-115, 1-119, 1-122, 1-125, and 1-129 αsyn), or a mixture of these PTM containing αsyn forms compared to full-length (FL) αsyn in HEK293T cells and M83 transgenic mice overexpressing A53T αsyn. It is demonstrated that upon peripheral intramuscular injection of these C-truncated or S129E αsyn polymers into M83 mice, prion-like progression and time to disease onset in this mouse model is elongated when any of these PTMs are present, demonstrating that common modifications to the C-terminus of αsyn present in disease modulates the prion-like seeding properties of αsyn.