Prediction of Cognitive Heterogeneity in Parkinson's Disease: A 4-Year Longitudinal Study Using Clinical, Neuroimaging, Biological and Electrophysiological Biomarkers.

OBJECTIVE: Cognitive impairment in Parkinson's disease (PD) can show a very heterogeneous trajectory among patients. Here, we explored the mechanisms involved in the expression and prediction of different cognitive phenotypes over 4 years. METHODS: In 2 independent cohorts (total n = 475), we performed a cluster analysis to identify trajectories of cognitive progression. Baseline and longitudinal level II neuropsychological assessments were conducted, and baseline structural magnetic resonance imaging, resting electroencephalogram and neurofilament light chain plasma quantification were carried out. Linear mixed-effects models were used to study longitudinal changes. Risk of mild cognitive impairment and dementia were estimated using multivariable hazard regression. Spectral power density from the electroencephalogram at baseline and source localization were computed. RESULTS: Two cognitive trajectories were identified. Cluster 1 presented stability (PD-Stable) over time, whereas cluster 2 showed progressive cognitive decline (PD-Progressors). The PD-Progressors group showed an increased risk for evolving to PD mild cognitive impairment (HR 2.09; 95% CI 1.11-3.95) and a marked risk for dementia (HR 4.87; 95% CI 1.34-17.76), associated with progressive worsening in posterior-cortical-dependent cognitive processes. Both clusters showed equivalent clinical and sociodemographic characteristics, structural magnetic resonance imaging, and neurofilament light chain levels at baseline. Conversely, the PD-Progressors group showed a fronto-temporo-occipital and parietal slow-wave power density increase, that was in turn related to worsening at 2 and 4 years of follow-up in different cognitive measures. INTERPRETATION: In the absence of differences in baseline cognitive function and typical markers of neurodegeneration, the further development of an aggressive cognitive decline in PD is associated with increased slow-wave power density and with a different profile of worsening in several posterior-cortical-dependent tasks. ANN NEUROL 2024;96:981-993.

BACE2 beyond ß-processing of APP, its neuroprotective role in cerebrovascular endothelium.

Several proteases are involved in the proteolytic processing of the amyloid precursor protein (APP) generating the amyloidogenic Aß peptide, which can act as the triggering pathological effector of Alzheimer's disease (AD). Among these proteases, the ß-site amyloid precursor protein cleaving enzyme 2 (BACE2) is of particular interest because it was first proposed as an alternative ß-secretase to its homolog BACE1; however, accumulating evidence suggests that BACE2 acts as a non-amyloidogenic α-secretase and exerts neuroprotective effects. In this issue of J Neurochem, Katusic et al. present an interesting article reporting that BACE2 plays a role in preservation of cerebral vascular endothelial nitric oxide synthase (eNOS) function, thus exerting protective functions. Their data support that the process is mediated by the large soluble non-amyloidogenic APP fragment sAPPα through the γ-aminobutyric acid type B receptor 1, which enhances the expression of a major transcription factor for eNOS gene expression in endothelial cells, the Krüppel-like factor 2. These protective functions of BACE2 contrast with the pathogenic role of BACE1 as a key player in the AD amyloidogenic pathway. Indeed, many efforts have been invested in BACE1 inhibitors as potential disease modifiers for AD. Unfortunately, the results in clinical trials have been disappointing. In this scenario, a better understanding of the functions of BACE2, as well as the selectivity of BACE1 inhibitors with respect to other ß-secretases (mainly BACE2), is crucial for the development of new therapeutic agents. Furthermore, specific cellular targeting should also be considered to improve such therapies due to the diverse balance of secretases targeting APP and the complex cross-talk between them and the generated APP fragments.

Sex Differentially Alters Secretion of Brain Extracellular Vesicles During Aging: A Potential Mechanism for Maintaining Brain Homeostasis.

Extracellular vesicles (EVs) in the brain play a role in neuronal homeostasis by removing intracellular material and regulating cell-to-cell communication. Given that sex and aging differentially modulate brain networks, we investigated sex-dependent differences in EV levels and content in the brain during aging. EVs were isolated from the brains of 3, 6, 12, 18, and 24 month-old female and male C57BL/6 J mice, and the levels of different EV species determined. While the number of plasma membrane-derived microvesicles and a subset of late endosomes-derived exosomes increased with age in the brain of female mice, no significant changes were seen in males. Mitochondria-derived mitovesicles in the brain increased during aging in both sexes, a change that may reflect aging-dependent alterations in mitochondrial function. These findings reveal enhanced turnover during aging in female brains, suggesting a mechanism for advantageous successful female brain aging and sex-depending different susceptibility to age-related neurodegenerative diseases.

Extracellular vesicles: where the amyloid precursor protein carboxyl-terminal fragments accumulate and amyloid-ß oligomerizes.

Pleiotropic roles are proposed for brain extracellular vesicles (EVs) in the development of Alzheimer's disease (AD). Our previous studies have suggested a beneficial role for EVs in AD, where the endosomal system in vulnerable neurons is compromised, contributing to the removal of accumulated material from neurons. However, the involvement of EVs in propagating AD amyloidosis throughout the brain has been considered because the amyloid-ß precursor protein (APP), APP metabolites, and key APP cleaving enzymes were identified in association with EVs. Here, we undertook to determine whether the secretase machinery is actively processing APP in EVs isolated from the brains of wild-type and APP overexpressing Tg2576 mice. We found that full-length APP is cleaved in EVs incubated in the absence of cells. The resulting metabolites, both α- and ß-APP carboxyl-terminal fragments and APP intracellular domain accumulate in EVs over time and amyloid-ß dimerizes. Thus, EVs contribute to the removal from neurons and transport of APP-derived neurotoxic peptides. While this is potentially a venue for propagation of the pathology throughout the brain, it may contribute to efficient removal of neurotoxic peptides from the brain.

CLU rs11136000 promotes early cognitive decline in Parkinson's disease.

BACKGROUND: The C allele of the rs11136000 genetic variant of the clusterin gene has been associated with increased risk of Alzheimer's disease. However, a comprehensive characterization of the role of this genetic variant in early cognitive deterioration in PD is lacking. METHODS: Using the Parkinson's Progression Markers Initiative database, we compared baseline and 5-year cognitive performance between high-risk and low-risk clusterin genotypes. RESULTS: At baseline, recently diagnosed and drug-naive de novo PD patients with the high-risk clusterin genotype showed lower cognitive scores in memory and executive function tests. These differences were even higher at the 5-year follow-up, when they showed a higher prevalence of clinically diagnosed mild cognitive impairment or dementia. They also showed cortical thinning at baseline and increased annual thinning in frontal and posterior cortical regions. DISCUSSION: Our results provide evidence of this clusterin genotype promoting early cognitive deterioration in PD, but further research is needed to delineate the specific neurodegenerative pathways underlying this clinical association. © 2020 International Parkinson and Movement Disorder Society.

Intracellular metalloprotease activity controls intraneuronal Aß aggregation and limits secretion of Aß via exosomes.

Accumulating evidence suggests that the abnormal aggregation of amyloid-ß (Αß) peptide in Alzheimer's disease (AD) begins intraneuronally, within vesicles of the endosomal-lysosomal pathway where Aß is both generated and degraded. Metalloproteases, including endothelin-converting enzyme (ECE)-1 and -2, reside within these vesicles and normally limit the accumulation of intraneuronally produced Aß. In this study, we determined whether disruption of Aß catabolism could trigger Aß aggregation within neurons and increase the amount of Aß associated with exosomes, small extracellular vesicles derived from endosomal multivesicular bodies. Using cultured cell lines, primary neurons, and organotypic brain slices from an AD mouse model, we found that pharmacological inhibition of the ECE family of metalloproteases increased intracellular and extracellular Aß levels and promoted the intracellular formation of Aß oligomers, a process that did not require internalization of secreted Aß. In vivo, the accumulation of intraneuronal Aß aggregates was accompanied by increased levels of both extracellular and exosome-associated Aß, including oligomeric species. Neuronal exosomes were found to contain both ECE-1 and -2 activities, suggesting that multivesicular bodies are intracellular sites of Aß degradation by these enzymes. ECE dysfunction could lead to the accumulation of intraneuronal Aß aggregates and their subsequent release into the extracellular space via exosomes.-Pacheco-Quinto, J., Clausen, D., Pérez-González, R., Peng, H., Meszaros, A., Eckman, C. B., Levy, E., Eckman, E. A. Intracellular metalloprotease activity controls intraneuronal Aß aggregation and limits secretion of Aß via exosomes.

Apolipoprotein E4 genotype compromises brain exosome production.

In addition to being the greatest genetic risk factor for Alzheimer's disease, expression of the ɛ4 allele of apolipoprotein E can lead to cognitive decline during ageing that is independent of Alzheimer's amyloid-ß and tau pathology. In human post-mortem tissue and mouse models humanized for apolipoprotein E, we examined the impact of apolipoprotein E4 expression on brain exosomes, vesicles that are produced within and secreted from late-endocytic multivesicular bodies. Compared to humans or mice homozygous for the risk-neutral ɛ3 allele we show that the ɛ4 allele, whether homozygous or heterozygous with an ɛ3 allele, drives lower exosome levels in the brain extracellular space. In mice, we show that the apolipoprotein E4-driven change in brain exosome levels is age-dependent: while not present at age 6 months, it is detectable at 12 months of age. Expression levels of the exosome pathway regulators tumor susceptibility gene 101 (TSG101) and Ras-related protein Rab35 (RAB35) were found to be reduced in the brain at the protein and mRNA levels, arguing that apolipoprotein E4 genotype leads to a downregulation of exosome biosynthesis and release. Compromised exosome production is likely to have adverse effects, including diminishing a cell's ability to eliminate materials from the endosomal-lysosomal system. This reduction in brain exosome levels in 12-month-old apolipoprotein E4 mice occurs earlier than our previously reported brain endosomal pathway changes, arguing that an apolipoprotein E4-driven failure in exosome production plays a primary role in endosomal and lysosomal deficits that occur in apolipoprotein E4 mouse and human brains. Disruption of these interdependent endosomal-exosomal-lysosomal systems in apolipoprotein E4-expressing individuals may contribute to amyloidogenic amyloid-ß precursor protein processing, compromise trophic signalling and synaptic function, and interfere with a neuron's ability to degrade material, all of which are events that lead to neuronal vulnerability and higher risk of Alzheimer's disease development. Together, these data suggest that exosome pathway dysfunction is a previously unappreciated component of the brain pathologies that occur as a result of apolipoprotein E4 expression.

Cystatin C prevents neuronal loss and behavioral deficits via the endosomal pathway in a mouse model of down syndrome.

Cystatin C (CysC) plays diverse protective roles under conditions of neuronal challenge. We investigated whether CysC protects from trisomy-induced pathologies in a mouse model of Down syndrome (DS), the most common cause of developmental cognitive and behavioral impairments in humans. We have previously shown that the segmental trisomy mouse model, Ts[Rb(12.1716)]2Cje (Ts2) has DS-like neuronal and behavioral deficiencies. The current study reveals that transgene-mediated low levels of human CysC overexpression has a preventive effect on numerous neuropathologies in the brains of Ts2 mice, including reducing early and late endosome enlargement in cortical neurons and decreasing loss of basal forebrain cholinergic neurons (BFCNs). Consistent with these cellular benefits, behavioral dysfunctions were also prevented, including deficits in nesting behavior and spatial memory. We determined that the CysC-induced neuroprotective mechanism involves activation of the phosphotidylinositol kinase (PI3K)/AKT pathway. Activating this pathway leads to enhanced clearance of accumulated endosomal substrates, protecting cells from DS-mediated dysfunctions in the endosomal system and, for BFCNs, from neurodegeneration. Our findings suggest that modulation of the PI3/AKT pathway offers novel therapeutic interventions for patients with DS.

Small RNAs in plasma extracellular vesicles define biomarkers of premanifest changes in Huntington's disease.

Despite the advances in the understanding of Huntington's disease (HD), there is a need for molecular biomarkers to categorize mutation carriers during the preclinical stage of the disease preceding functional decline. Small RNAs (sRNAs) are a promising source of biomarkers since their expression levels are highly sensitive to pathobiological processes. Here, using an optimized method for plasma extracellular vesicles (EVs) purification and an exhaustive analysis pipeline of sRNA sequencing data, we show that EV-sRNAs are downregulated early in mutation carriers and that this deregulation is associated with premanifest cognitive performance. Seven candidate sRNAs (tRF-Glu-CTC, tRF-Gly-GCC, miR-451a, miR-21-5p, miR-26a-5p, miR-27a-3p and let7a-5p) were validated in additional subjects, showing a significant diagnostic accuracy at premanifest stages. Of these, miR-21-5p was significantly decreased over time in a longitudinal study; and miR-21-5p and miR-26a-5p levels correlated with cognitive changes in the premanifest cohort. In summary, the present results suggest that deregulated plasma EV-sRNAs define an early biosignature in mutation carriers with specific species highlighting the progression and cognitive changes occurring at the premanifest stage.

Cognitive phenotype and neurodegeneration associated with Tau in Huntington's disease.

OBJECTIVE: The clinical phenotype of Huntington's disease (HD) can be very heterogeneous between patients, even when they share equivalent CAG repeat length, age, or disease burden. This heterogeneity is especially evident in terms of the cognitive profile and related brain changes. To shed light on the mechanisms participating in this heterogeneity, the present study delves into the association between Tau pathology and more severe cognitive phenotypes and brain damage in HD. METHODS: We used a comprehensive neuropsychological examination to characterize the cognitive phenotype of a sample of 30 participants with early-to-middle HD for which we also obtained 3 T structural magnetic resonance image (MRI) and cerebrospinal fluid (CSF). We quantified CSF levels of neurofilament light chain (NfL), total Tau (tTau), and phosphorylated Tau-231 (pTau-231). Thanks to the cognitive characterization carried out, we subsequently explored the relationship between different levels of biomarkers, the cognitive phenotype, and brain integrity. RESULTS: The results confirmed that more severe forms of cognitive deterioration in HD extend beyond executive dysfunction and affect processes with clear posterior-cortical dependence. This phenotype was in turn associated with higher CSF levels of tTau and pTau-231 and to a more pronounced pattern of posterior-cortical atrophy in specific brain regions closely linked to the cognitive processes affected by Tau. INTERPRETATION: Our findings reinforce the association between Tau pathology, cognition, and neurodegeneration in HD, emphasizing the need to explore the role of Tau in the cognitive heterogeneity of the disease.

The exosome secretory pathway transports amyloid precursor protein carboxyl-terminal fragments from the cell into the brain extracellular space.

In vitro studies have shown that neuronal cell cultures secrete exosomes containing amyloid-ß precursor protein (APP) and the APP-processing products, C-terminal fragments (CTFs) and amyloid-ß (Aß). We investigated the secretion of full-length APP (flAPP) and APP CTFs via the exosome secretory pathway in vivo. To this end, we developed a novel protocol designed to isolate exosomes secreted into mouse brain extracellular space. Exosomes with typical morphology were isolated from freshly removed mouse brains and from frozen mouse and human brain tissues, demonstrating that exosomes can be isolated from post-mortem tissue frozen for long periods of time. flAPP, APP CTFs, and enzymes that cleave both flAPP and APP CTFs were identified in brain exosomes. Although higher levels of both flAPP and APP CTFs were observed in exosomes isolated from the brains of transgenic mice overexpressing human APP (Tg2576) compared with wild-type control mice, there was no difference in the number of secreted brain exosomes. These data indicate that the levels of flAPP and APP CTFs associated with exosomes mirror the cellular levels of flAPP and APP CTFs. Interestingly, exosomes isolated from the brains of both Tg2576 and wild-type mice are enriched with APP CTFs relative to flAPP. Thus, we hypothesize that the exosome secretory pathway plays a pleiotropic role in the brain: exosome secretion is beneficial to the cell, acting as a specific releasing system of neurotoxic APP CTFs and Aß, but the secretion of exosomes enriched with APP CTFs, neurotoxic proteins that are also a source of secreted Aß, is harmful to the brain.

Isolation of mitochondria-derived mitovesicles and subpopulations of microvesicles and exosomes from brain tissues.

Extracellular vesicles (EVs) are nanoscale vesicles secreted into the extracellular space by all cell types, including neurons and astrocytes in the brain. EVs play pivotal roles in physiological and pathophysiological processes such as waste removal, cell-to-cell communication and transport of either protective or pathogenic material into the extracellular space. Here we describe a detailed protocol for the reliable and consistent isolation of EVs from both murine and human brains, intended for anyone with basic laboratory experience and performed in a total time of 27 h. The method includes a mild extracellular matrix digestion of the brain tissue, a series of filtration and centrifugation steps to purify EVs and an iodixanol-based high-resolution density step gradient that fractionates different EV populations, including mitovesicles, a newly identified type of EV of mitochondrial origin. We also report detailed downstream protocols for the characterization and analysis of brain EV preparations using nanotrack analysis, electron microscopy and western blotting, as well as for measuring mitovesicular ATP kinetics. Furthermore, we compared this novel iodixanol-based high-resolution density step gradient to the previously described sucrose-based gradient. Although the yield of total EVs recovered was similar, the iodixanol-based gradient better separated distinct EV species as compared with the sucrose-based gradient, including subpopulations of microvesicles, exosomes and mitovesicles. This technique allows quantitative, highly reproducible analyses of brain EV subtypes under normal physiological processes and pathological brain conditions, including neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease.

Plasma TDP-43 Reflects Cortical Neurodegeneration and Correlates with Neuropsychiatric Symptoms in Huntington's Disease.

PURPOSE: Huntington's disease (HD) is a monogenic neurodegenerative disease with no effective treatment currently available. The pathological hallmark of HD is the aggregation of mutant huntingtin in the medium spiny neurons of the striatum, leading to severe subcortical atrophy. Cortical degeneration also occurs in HD from its very early stages, although its biological origin is poorly understood. Among the possible pathological mechanisms that could promote cortical damage in HD, the in vivo study of TDP-43 pathology remains to be explored, which was the main objective of this work. METHODS: We investigated the clinical and structural brain correlates of plasma TDP-43 levels in a sample of 36 HD patients. Neuroimaging alterations were assessed both at the macrostructural (cortical thickness) and microstructural (intracortical diffusivity) levels. Importantly, we controlled for mutant huntingtin and tau biomarkers in order to assess the independent role of TDP-43 in HD neurodegeneration. RESULTS: Plasma TDP-43 levels in HD specifically correlated with the presence and severity of apathy (p = 0.003). The TDP-43 levels also reflected cortical thinning and microstructural degeneration, especially in frontal and anterior-temporal regions (p < 0.05 corrected). These TDP-43-related brain alterations correlated, in turn, with the severity of cognitive, motor and behavioral symptoms. CONCLUSION: Our results suggest that the presence of TDP-43 pathology in HD has an independent contribution to the severity of neuropsychiatric symptoms and frontotemporal degeneration. These findings point out the importance of TDP-43 as an additional pathological process to be taken into consideration in this devastating disorder.

Dissociable contribution of plasma NfL and p-tau181 to cognitive impairment in Parkinson's disease.

BACKGROUND: Cognitive dysfunction is a disabling complication in Parkinson's disease (PD). Accuracy of diagnosis of mild cognitive impairment in PD (PD-MCI) depends on the tests performed, which limits results generalization. Blood-based biomarkers could provide additional objective information for PD-MCI diagnosis and progression. Blood neurofilament light chain (NfL), a marker of neuronal injury, has shown good performance for PD disease stratification and progression. While NfL is not disease-specific, phosphorylated-tau at threonine-181 (p-tau181) in blood is a highly specific marker of concomitant brain amyloid-ß and tau pathology. METHODS: We investigated the potential of plasma NfL and p-tau181 levels as markers of cognitive impairment in a prospective cohort of 109 PD patients with and without PD-MCI (age 68.1 ± 7 years, education 12.2± 5 years), and 40 comparable healthy controls. After a follow-up of 4 years, we evaluated their predictive value for progression to dementia. RESULTS: Although NfL and p-tau181 levels were significantly increased in PD compared with healthy controls, only NfL levels were significantly higher in PD-MCI compared with PD with normal cognition (PD-NC) at baseline. After a follow-up of 4 years, only NfL predicted progression to dementia (HR 1.23, 95% CI 1.02-1.53; p = 0.038). Significant correlations between fluid biomarkers and neuropsychological examination were only found with NfL levels. CONCLUSIONS: Plasma NfL levels objectively differentiates PD-MCI from PD-NC patients, and may serve as a plasma biomarker for predicting progression to dementia in PD. Plasma levels of p-tau181 does not seem to help in differentiating PD-MCI or to predict future cognitive deterioration.

Enrichment of Astrocyte-Derived Extracellular Vesicles from Human Plasma.

Extracellular vesicles (EVs) are biological nanoparticles secreted by all cells for cellular communication and waste elimination. They participate in a vast range of functions by acting on and transferring their cargos to other cells in physiological and pathological conditions. Given their presence in biofluids, EVs represent an excellent resource for studying disease processes and can be considered a liquid biopsy for biomarker discovery. An attractive aspect of EV analysis is that they can be selected based on markers of their cell of origin, thus reflecting the environment of a specific tissue in their cargo. However, one of the major handicaps related to EV isolation methods is the lack of methodological consensuses and standardized protocols. Astrocytes are glial cells with essential roles in the brain. In neurodegenerative diseases, astrocyte reactivity may lead to altered EV cargo and aberrant cellular communication, facilitating/enhancing disease progression. Thus, analysis of astrocyte EVs may lead to the discovery of biomarkers and potential disease targets. This protocol describes a 2-step method of enrichment of astrocyte-derived EVs (ADEVs) from human plasma. First, EVs are enriched from defibrinated plasma via polymer-based precipitation. This is followed by enrichment of ADEVs through ACSA-1-based immunocapture with magnetic micro-beads, where resuspended EVs are loaded onto a column placed in a magnetic field. Magnetically labeled ACSA-1+ EVs are retained within the column, while other EVs flow through. Once the column is removed from the magnet, ADEVs are eluted and are ready for storage and analysis. To validate the enrichment of astrocyte markers, glial fibrillary acidic protein (GFAP), or other specific astrocytic markers of intracellular origin, can be measured in the eluate and compared with the flow-through. This protocol proposes an easy, time-efficient method to enrich ADEVs from plasma that can be used as a platform to examine astrocyte-relevant markers.

Megalin interacts with APP and the intracellular adapter protein FE65 in neurons.

Increasing evidence has implicated megalin, a low-density lipoprotein receptor-related protein, in the pathogenesis of Alzheimer's disease (AD). In the brain, megalin is expressed in brain capillaries, ependymal cells and choroid plexus, where it participates in the clearance of brain amyloid ß-peptide (Aß) complex. Recently, megalin has also been detected in oligodendrocytes and astrocytes. In this study we demonstrate that megalin is widely distributed in neurons throughout the brain. Additionally, given that FE65 mediates the interaction between the low density lipoprotein receptor-related protein-1 and the amyloid precursor protein (APP) to modulate the rate of APP internalization from the cell surface, we hypothesize that megalin could also interact with APP in neurons. Our results confirm that megalin interacts with APP and FE65, suggesting that these three proteins form a tripartite complex. Moreover, our findings imply that megalin may participate in neurite branching. Taken together, these results indicate that megalin has an important role in Aß-mediated neurotoxicity, and therefore may be involved in the neurodegenerative processes that occur in AD.

Cortical microstructural correlates of plasma neurofilament light chain in Huntington's disease.

INTRODUCTION: Huntington's disease (HD) is a severe neurodegenerative disorder with no effective treatment. Minimally-invasive biomarkers such as blood neurofilament light chain (NfL) in HD are therefore needed to quantitatively characterize neuronal loss. NfL levels in HD are known to correlate with disease progression and striatal atrophy, but whether they also reflect cortical degeneration remains elusive. METHODS: In a sample of 35 HD patients, we characterized the cortical macro (cortical thickness) and microstructural (increased intracortical diffusivity) correlates of plasma NfL levels. We further investigated whether NfL-related cortical alterations correlated with clinical indicators of disease progression. RESULTS: Increased plasma NfL levels in HD reflected posterior-cortical microstructural degeneration, but not reduced cortical thickness (p < 0.05, corrected). Importantly, these imaging alterations correlated, in turn, with more severe motor, cognitive and behavioral symptoms. CONCLUSION: Plasma NfL levels may be useful for tracking clinically-meaningful cortical deterioration in HD. Additionally, our results further reinforce the role of intracortical diffusivity as a valuable imaging indicator in movement disorders.

Interaction between sex and neurofilament light chain on brain structure and clinical severity in Huntington's disease.

Female Huntington's disease (HD) patients have consistently shown a faster clinical worsening than male, but the underlying mechanisms responsible for this observation remain unknown. Here, we describe how sex modifies the impact of neurodegeneration on brain atrophy and clinical severity in HD. Cerebrospinal fluid neurofilament light chain (NfL) levels were used as a biological measure of neurodegeneration, and brain atrophy was assessed by structural magnetic resonance imaging. We found that larger NfL values in women reflect higher brain atrophy and clinical severity than in men (p < 0.05 for an interaction model). This differential vulnerability could have important implications in clinical trials.

Mitovesicles are a novel population of extracellular vesicles of mitochondrial origin altered in Down syndrome.

Mitochondrial dysfunction is an established hallmark of aging and neurodegenerative disorders such as Down syndrome (DS) and Alzheimer's disease (AD). Using a high-resolution density gradient separation of extracellular vesicles (EVs) isolated from murine and human DS and diploid control brains, we identify and characterize a previously unknown population of double-membraned EVs containing multiple mitochondrial proteins distinct from previously described EV subtypes, including microvesicles and exosomes. We term these newly identified mitochondria-derived EVs "mitovesicles." We demonstrate that brain-derived mitovesicles contain a specific subset of mitochondrial constituents and that their levels and cargo are altered during pathophysiological processes where mitochondrial dysfunction occurs, including in DS. The development of a method for the selective isolation of mitovesicles paves the way for the characterization in vivo of biological processes connecting EV biology and mitochondria dynamics and for innovative therapeutic and diagnostic strategies.

Serum neurofilament light chain levels reflect cortical neurodegeneration in de novo Parkinson's disease.

INTRODUCTION: Cognitive impairment and dementia are highly prevalent non-motor complications in Parkinson's disease (PD) with deleterious consequences for patients and caregivers. With no treatment currently available, finding and validating minimally-invasive biomarkers of neurodegeneration in this population represents an urgent need for clinical trials targeting its prevention or delay. Recently, serum neurofilament light chain (NfL) levels have been identified as a promising biomarker of neural loss, but whether they reflect cortical neurodegeneration in early PD stages has not been addressed. METHODS: From the Parkinson's Progression Markers Initiative (PPMI), we selected 133 de novo PD patients and 56 healthy controls (HC) with available structural neuroimaging and serum NfL data. We then studied whether NfL levels were abnormal in the PD group with respect to HC, and whether they correlated with cognitive indicators and cortical macro (cortical thinning) and microstructural (increased intracortical mean diffusivity) degeneration. RESULTS: Serum NfL levels were significantly increased in the PD group (p = 0.010), and were also related to worse cognitive performance and a cortical macro and microstructural compromise (p < 0.05 corrected). These associations were observed both cross-sectionally and longitudinally within a one-year follow-up period. Topographically, NfL levels reflected posterior-cortical deterioration rather than frontal damage. Importantly, NfL levels were not associated with striatal SPECT-DAT uptake or ß-amyloid burden. DISCUSSION: Our results show that serum NfL levels reflect cortical neurodegeneration from the very early stages of PD. Moreover, its brain structural correlates and its lack of relationship with dopaminergic depletion or amyloidosis suggests that NfL could track the underlying pathological process leading to PD dementia.