Real-world performance of plasma p-tau181 in a heterogeneous memory clinic cohort.

OBJECTIVE: In light of clinical trials and disease-modifying therapies, an early identification of patients at-risk of developing Alzheimer's disease (AD) is crucial. Blood-based biomarkers have shown promising results regarding the in vivo detection of the earliest neuropathological changes in AD. Herein, we investigated the ability of plasma p-tau181 to act as a prescreening marker for amyloid positivity in a heterogeneous memory clinic-based cohort. METHODS: In this retrospective cross-sectional study, we included a total of 115 patients along the clinical AD continuum (mild cognitive impairment [MCI] due to AD, n = 62, probable AD dementia, n = 53). Based on their biomarker status, they were stratified into an amyloid-positive (Aß+, n = 88) or amyloid-negative cohort (Aß-, n = 27). Plasma and CSF p-tau181 concentrations were quantified using an ultrasensitive single-molecule array (SIMOA©). Furthermore, age- and sex-adjusted receiver operating characteristic (ROC) curves were calculated and the area under the curve (AUC) of each model was compared using DeLong's test for correlated AUC curves. RESULTS: The median (interquartile range [IQR]) concentration of plasma p-tau181 was significantly higher in Aß+ patients (3.6 pg/mL [2.5-4.6]), compared with Aß- patients (1.7 pg/mL [1.2-1.9], p < 0.001). Regarding the distinction between Aß+ and Aß- patients and the prediction of amyloid positivity, a high diagnostic accuracy for plasma p-tau181 with an AUC of 0.89 (95% CI = 0.82-0.95) was calculated. Adding the risk factors, age and APOE4, to the model did not significantly improve its performance. INTERPRETATION: Our findings demonstrate that plasma p-tau181 could be a noninvasive and feasible prescreening marker for amyloid positivity in a heterogeneous clinical AD cohort and therefore help in identifying those who would benefit from more invasive assessment of amyloid pathology.

Clinical heterogeneity within the ALS-FTD spectrum in a family with a homozygous optineurin mutation.

OBJECTIVE: Mutations in the gene encoding for optineurin (OPTN) have been reported in the context of different neurodegenerative diseases including the amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) spectrum. Based on single case reports, neuropathological data in OPTN mutation carriers have revealed transactive response DNA-binding protein 43 kDa (TDP-43) pathology, in addition to accumulations of tau and alpha-synuclein. Herein, we present two siblings from a consanguineous family with a homozygous frameshift mutation in the OPTN gene and different clinical presentations. METHODS: Both affected siblings underwent (i) clinical, (ii) neurophysiological, (iii) neuropsychological, (iv) radiological, and (v) laboratory examinations, and (vi) whole-exome sequencing (WES). Postmortem histopathological examination was conducted in the index patient, who deceased at the age of 41. RESULTS: The index patient developed rapidly progressing clinical features of upper and lower motor neuron dysfunction as well as apathy and cognitive deterioration at the age of 41. Autopsy revealed an ALS-FTLD pattern associated with prominent neuronal and oligodendroglial TDP-43 pathology, and an atypical limbic 4-repeat tau pathology reminiscent of argyrophilic grain disease. The brother of the index patient exhibited behavioral changes and mnestic deficits at the age of 38 and was diagnosed with behavioral FTD 5 years later, without any evidence of motor neuron dysfunction. WES revealed a homozygous frameshift mutation in the OPTN gene in both siblings (NM_001008212.2: c.1078_1079del; p.Lys360ValfsTer18). INTERPRETATION: OPTN mutations can be associated with extensive TDP-43 pathology and limbic-predominant tauopathy and present with a heterogeneous clinical phenotype within the ALS-FTD spectrum within the same family.

The relation between BTK expression and iron accumulation of myeloid cells in multiple sclerosis.

Activation of Bruton's tyrosine kinase (BTK) has been shown to play a crucial role in the proinflammatory response of B cells and myeloid cells upon engagement with B cell, Fc, Toll-like receptor, and distinct chemokine receptors. Previous reports suggest BTK actively contributes to the pathogenesis of multiple sclerosis (MS). The BTK inhibitor Evobrutinib has been shown to reduce the numbers of gadolinium-enhancing lesions and relapses in relapsing-remitting MS patients. In vitro, BTK inhibition resulted in reduced phagocytic activity and modulated BTK-dependent inflammatory signaling of microglia and macrophages. Here, we investigated the protein expression of BTK and CD68 as well as iron accumulation in postmortem control (n = 10) and MS (n = 23) brain tissue, focusing on microglia and macrophages. MS cases encompassed active, chronic active, and inactive lesions. BTK+ and iron+ cells positively correlated across all regions of interests and, along with CD68, revealed highest numbers in the center of active and at the rim of chronic active lesions. We then studied the effect of BTK inhibition in the human immortalized microglia-like HMC3 cell line in vitro. In particular, we loaded HMC3 cells with iron-dextran and subsequently administered the BTK inhibitor Evobrutinib. Iron treatment alone induced a proinflammatory phenotype and increased the expression of iron importers as well as the intracellular iron storage protein ferritin light chain (FTL). BTK inhibition of iron-laden cells dampened the expression of microglia-related inflammatory genes as well as iron-importers, whereas the iron-exporter ferroportin was upregulated. Our data suggest that BTK inhibition not only dampens the proinflammatory response but also reduces iron import and storage in activated microglia and macrophages with possible implications on microglial iron accumulation in chronic active lesions in MS.

No Association of Multiple Sclerosis with C9orf72 Hexanucleotide Repeat Size in an Austrian Cohort.

Multiple Sclerosis (MS) is a common immune-mediated disorder of the central nervous system that affects young adults and is characterized by demyelination and neurodegeneration. Recent studies have associated C9orf72 intermediate repeat expansions with MS. The objective of this study was to investigate whether C9orf72 repeat length is associated with MS or with a specific disease course in a monocentric Austrian MS cohort. Genotyping of 382 MS patients and 643 non-neurological controls for C9orf72 repeat expansions was performed. The study did not find a difference in the distribution of repeat numbers between controls and MS cases (median repeat units = 2; p = 0.39). Additionally, sub-analysis did not establish a link between intermediate repeats and MS (p = 0.23) and none of the patients with progressive disease course carried an intermediate allele (20-30 repeat units). Exploratory analysis for different cut-offs (of ≥7, ≥17, and ≥24) did not reveal any significant differences in allele frequencies between MS and controls. However, the study did identify a progressive MS patient with a pathogenic C9orf72 expansion and probable co-existing behavioral variant frontotemporal dementia (bvFTD) in a retrospective chart review. In conclusion, this study did not find evidence supporting an association between C9orf72 repeat length and MS or a specific disease course in the Austrian MS cohort. However, the identification of a progressive MS patient with a pathogenic C9orf72 expansion and probable co-existing with FTD highlights the complexity and challenges involved in recognizing distinct neurodegenerative diseases that may co-occur in MS patients.

Comprehensive genetic screening of early-onset dementia patients in an Austrian cohort-suggesting new disease-contributing genes.

Early-onset dementia (EOD), with symptom onset before age 65, has a strong genetic burden. Due to genetic and clinical overlaps between different types of dementia, whole-exome sequencing (WES) has emerged as an appropriate screening method for diagnostic testing and novel gene-finding approaches. We performed WES and C9orf72 repeat testing in 60 well-defined Austrian EOD patients. Seven patients (12%) carried likely disease-causing variants in monogenic genes, PSEN1, MAPT, APP, and GRN. Five patients (8%) were APOE4 homozygote carriers. Definite and possible risk variants were detected in the genes TREM2, SORL1, ABCA7 and TBK1. In an explorative approach, we cross-checked rare gene variants in our cohort with a curated neurodegeneration candidate gene list and identified DCTN1, MAPK8IP3, LRRK2, VPS13C and BACE1 as promising candidate genes. Conclusively, 12 cases (20%) carried variants relevant to patient counseling, comparable to previously reported studies, and can thus be considered genetically resolved. Reduced penetrance, oligogenic inheritance and not yet identified high-risk genes might explain the high number of unresolved cases. To address this issue, we provide complete genetic and phenotypic information (uploaded to the European Genome-phenome Archive), enabling other researchers to cross-check variants. Thereby, we hope to increase the chance of independently finding the same gene/variant-hit in other well-defined EOD patient cohorts, thus confirming new genetic risk variants or variant combinations.

Multi-Parameter Analysis of Disseminated Tumor Cells (DTCs) in Early Breast Cancer Patients with Hormone-Receptor-Positive Tumors.

BACKGROUND: Patients with hormone-receptor-positive (HR+) breast cancer are at increased risk for late recurrence. One reason might be disseminated tumor cells (DTCs), which split off in the early stages of the disease and metastasize into the bone marrow (BM). METHODS: We developed a novel multi-parameter immunofluorescence staining protocol using releasable and bleachable antibody-fluorochrome-conjugates. This sequential procedure enabled us to analyze six distinct phenotypical and therapy-related markers on the same DTC. We characterized BM aspirates from 29 patients with a HR+ tumor and a known positive DTC status-based on the standardized detection of epithelial cells in BM. RESULTS: Using the immunofluorescence staining, a total of 153 DTCs were detected. Luminal A patients revealed a higher DTC count compared with luminal B. The majority of the detected DTCs were CK-positive (128/153). However, in 16 of 17 luminal A patients we found HER2-positive DTCs. We detected CK-negative DTCs (25/153) in 12 of 29 patients. Of those cells, 76% were Ki67-positive and 68% were HER2-positive. Moreover, we detected DTC clusters consisting of mixed characteristics in 6 of 29 patients. CONCLUSIONS: Using sequential multi-parameter imaging made it possible to identify distinct DTC profiles not solely based on epithelial features. Our findings indicate that characterization rather than quantification of DTCs might be relevant for treatment decisions.

Overlapping and Distinct Features of Cardiac Pathology in Inherited Human and Murine Ether Lipid Deficiency.

Inherited deficiency in ether lipids, a subgroup of glycerophospholipids with unique biochemical and biophysical properties, evokes severe symptoms in humans resulting in a multi-organ syndrome. Mouse models with defects in ether lipid biosynthesis have widely been used to understand the pathophysiology of human disease and to study the roles of ether lipids in various cell types and tissues. However, little is known about the function of these lipids in cardiac tissue. Previous studies included case reports of cardiac defects in ether-lipid-deficient patients, but a systematic analysis of the impact of ether lipid deficiency on the mammalian heart is still missing. Here, we utilize a mouse model of complete ether lipid deficiency (Gnpat KO) to accomplish this task. Similar to a subgroup of human patients with rhizomelic chondrodysplasia punctata (RCDP), a fraction of Gnpat KO fetuses present with defects in ventricular septation, presumably evoked by a developmental delay. We did not detect any signs of cardiomyopathy but identified increased left ventricular end-systolic and end-diastolic pressure in middle-aged ether-lipid-deficient mice. By comprehensive electrocardiographic characterization, we consistently found reduced ventricular conduction velocity, as indicated by a prolonged QRS complex, as well as increased QRS and QT dispersion in the Gnpat KO group. Furthermore, a shift of the Wenckebach point to longer cycle lengths indicated depressed atrioventricular nodal function. To complement our findings in mice, we analyzed medical records and performed electrocardiography in ether-lipid-deficient human patients, which, in contrast to the murine phenotype, indicated a trend towards shortened QT intervals. Taken together, our findings demonstrate that the cardiac phenotype upon ether lipid deficiency is highly heterogeneous, and although the manifestations in the mouse model only partially match the abnormalities in human patients, the results add to our understanding of the physiological role of ether lipids and emphasize their importance for proper cardiac development and function.

Usability testing of the first prototype of the Memento system: a technological device to promote an independent living in people with dementia.

PURPOSE: Assistive technologies have the potential for supporting people with memory complaints in their daily life. User-centered interaction design research helps developers to create systems that are suitable for users. The aim of this work is to describe the methodology and the results of the usability test for the first Memento prototype involving users. MATERIALS AND METHODS: In each country, 5 subjects with different levels of cognitive reserve and technical proficiency were enrolled in Italy, Austria and Spain, respectively (15 subjects; 6 M; 9 F, age 72.8 ± 10.8 years, MMSE score 25.6 ± 1.6). Observation methods, performance metrics and the System Usability Scale were used to collect data. RESULTS: The results are presented in terms of design, technical problems, target-group-related challenges and usability perception from the participant perspective. Suggestions for improvement were pointed out by the users. Considering the usability scores interpretation, the first prototype was classified as "OK" and "Good" by users. CONCLUSIONS: The results of the Lab Trials provide important information on usability and the users' needs in order to improve the Memento prototype and to create a final system to be evaluated during the Field Trials phase of the project.Implication for rehabilitationThe MEMENTO project mission is to improve the quality of life of people in the early and middle stages of dementia, by supporting the management of daily activities that are usually affected by the loss of memory and cognition. The Lab Trial phase is essential to have feedback on the usability of the Memento prototype to allow a better understanding of users' needs and expectations.

C9orf72 repeat length might influence clinical sub-phenotypes in dementia patients.

BACKGROUND: C9orf72 repeat expansions have been observed in a wide variety of neurodegenerative disorders. The cut-off between normal and pathogenic alleles is not well established as repeat sizing methods are often semi-quantitative. However, intermediate alleles might influence disease prevalence and phenotype, as seen for other repeat expansion disorders. We aimed to further delineate the prevalence of small, intermediate and expanded C9orf72 alleles and elucidate their potential influence on the disease phenotype. METHODS: DNA derived from patients (n = 1804) and healthy individuals (n = 643) was obtained from multiple collectives in Austria. Genotyping was performed using a two-step PCR assay followed by Southern blotting. RESULTS: 3.4% of clinically diagnosed frontotemporal dementia (FTD; n = 5/147) cases and 0.8% of clinically diagnosed Alzheimer's disease (AD; n = 5/602) cases were carriers of a pathological C9orf72 repeat expansion. A significantly earlier disease onset was detected in expansion carriers compared to non-carriers in the FTD and AD cohorts (median 50 years, range 39-64 vs. median 64 years, range 36-92, p = 0.018 and median 63 years, range 54-71 vs. median 74 years, range 45-92, p = 0.006, respectively). C9orf72 intermediate alleles were significantly associated with cerebellar symptoms (p = 0.0004) and sensory deficits in the dementia cohort (p = 0.01). CONCLUSIONS: C9orf72 repeat expansion carriers showed earlier disease onset compared to non-carriers with clinical diagnosis of FTD and AD. Furthermore, C9orf72 intermediate repeats might modify the phenotypic expression in dementia.

Real-world applicability of glial fibrillary acidic protein and neurofilament light chain in Alzheimer's disease.

Background: Blood-based biomarkers may add a great benefit in detecting the earliest neuropathological changes in patients with Alzheimer's disease (AD). We examined the utility of neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP) regarding clinical diagnosis and differentiation between amyloid positive and negative patients. To evaluate the practical application of these biomarkers in a routine clinical setting, we conducted this study in a heterogeneous memory-clinic population. Methods: We included 167 patients in this retrospective cross-sectional study, 123 patients with an objective cognitive decline [mild cognitive impairment (MCI) due to AD, n = 63, and AD-dementia, n = 60] and 44 age-matched healthy controls (HC). Cerebrospinal fluid (CSF) and plasma concentrations of NfL and GFAP were measured with single molecule array (SIMOA®) technology using the Neurology 2-Plex B kit from Quanterix. To assess the discriminatory potential of different biomarkers, age- and sex-adjusted receiver operating characteristic (ROC) curves were calculated and the area under the curve (AUC) of each model was compared. Results: We constructed a panel combining plasma NfL and GFAP with known AD risk factors (Combination panel: age+sex+APOE4+GFAP+NfL). With an AUC of 91.6% (95%CI = 0.85-0.98) for HC vs. AD and 81.7% (95%CI = 0.73-0.90) for HC vs. MCI as well as an AUC of 87.5% (95%CI = 0.73-0.96) in terms of predicting amyloid positivity, this panel showed a promising discriminatory power to differentiate these populations. Conclusion: The combination of plasma GFAP and NfL with well-established risk factors discerns amyloid positive from negative patients and could potentially be applied to identify patients who would benefit from a more invasive assessment of amyloid pathology. In the future, improved prediction of amyloid positivity with a noninvasive test may decrease the number and costs of a more invasive or expensive diagnostic approach.

Reduction of physical activity during the COVID-19 pandemic is related to increased neuropsychiatric symptoms in memory clinic patients.

The COVID-19 pandemic led to unprecedented restrictions on social contacts and mobility. Memory clinic patients were disproportionately affected when care was disrupted and routines were abruptly changed. This trial was designed as a pragmatic, prospective, observational study to evaluate the effects of lockdown on memory clinic patients. Outpatients were included when they returned in May to July 2020 for their first follow-up after the lockdown. Indicators of lockdown intensity and its effect on patients were recorded, patients and caregivers were interviewed, and neuropsychological tests were performed. We included 72 patients, most of them suffering from Alzheimer's dementia or mild cognitive impairment. The median time of isolation was 8 weeks and social contacts were significantly reduced from five to two per week (p<0.001). Light physical activity was significantly reduced (3.8 hours to 3 hours, p=0.016) during the lockdown, and this reduction was significantly correlated with higher scores on the Neuropsychiatric Inventory score (R -0.43, p>0.001). Fears regarding the pandemic were common and mostly related to the patients' health. Lockdown restrictions reduced physical activity in memory clinic patients which was associated with increased neuropsychiatric symptoms. Future restrictions should aim to mitigate the impacts on this vulnerable population.

User experience and acceptance of a device assisting persons with dementia in daily life: a multicenter field study.

BACKGROUND: Assistive technologies have the potential to facilitate everyday life of people with dementia and their families. Close collaboration with affected people and interdisciplinary research are essential to understand and address the needs of prospective users. In this study, we present the results of the evaluation of such an assistive system prototype. AIMS: Challenges from the patient and caregiver side, technical and design problems and acceptance and usability with regard to our special target group were evaluated. METHODS: MEMENTO, a system of two e-ink tablets and a smartwatch, was tested in the domestic environment of dementia patients. Thirty participants from Italy, Spain and Austria took part in a 3-month field trial and compared the MEMENTO system to traditional strategies in everyday life. Quantitative and qualitative data were collected and frequency of use of the system was monitored. RESULTS: There were no significant changes in quantitative measurements, such as activities of daily living and caregiver burden over the duration of the 3-month field trial. More frequent usage was significantly correlated with positive attitude towards technology (r = 0.723, p < 0.05), but not with age. The design of the system was positively emphasized, reducing fear of the technology on the one hand and stigmatization on the other. CONCLUSION: We show that a positive attitude towards technology is the essential variable for successful implementation of such systems, regardless of age. Participants showed great interest in digital solutions and agreed that technological systems will help in maintaining independency of persons with cognitive dysfunction in the future.

Genetics of Alzheimer's disease.

Alzheimer's disease (AD) is the leading cause of neurodegeneration in the elderly and is clinically characterized by slowly progressing cognitive decline, which most commonly affects episodic memory function. This eventually leads to difficulties in activities of daily living. Biomarker studies show that the underlying pathology of AD begins 20 years before clinical symptoms. This results in the need to define specific targets and preclinical stages in order to address the problems of this disease at an earlier point in time. Genetic studies are indispensable for gaining insight into the etiology of neurodegenerative diseases and can play a major role in the early definition of the individual disease risk. This review provides an overview of the currently known genetic features of AD.

Co-incidental C9orf72 expansion mutation-related frontotemporal lobar degeneration pathology and sporadic Creutzfeldt-Jakob disease.

BACKGROUND: The C9orf72 hexanucleotide expansion mutation is the most common cause of genetic frontotemporal dementia (FTD), amyotrophic lateral sclerosis (ALS) and combined FTD-ALS. Its underlying neuropathology combines TDP-43 pathology and dipeptide repeat protein (DPR) deposits and may also associate with other neurodegeneration-associated protein aggregates. Herein we present a unique combination of C9orf72 mutation with sporadic Creutzfeldt-Jakob disease (CJD) in a 74-year-old patient with rapidly progressive dementia. METHODS: Detailed neuropathological examination including immunohistochemistry for several proteinopathies. Genetic analysis was conducted by repeat primed polymerase chain reaction (PCR). Furthermore, we analyzed additional C9orf72 mutation carriers for prion-protein (PrP) deposits in brain tissue and screened the cerebellar cortex of other CJD cases for p62/DPR neuronal inclusions to assess the frequency of combined pathologies. RESULTS: Postmortem brain examination of a patient with a rapidly progressive neurological deterioration of 8 months' duration confirmed the diagnosis of CJD. She harbored valine homozygosity at PRNP codon 129. In addition, a frontotemporal lobar degeneration (FTLD)-pattern with TDP-43 protein aggregates and p62+/C9RANT+ positive inclusions along with a high degree of Alzheimer-related pathology (A3B3C3) were identified. The suspected C9orf72 expansion mutation was confirmed by repeat-primed PCR. Screening of 13 C9orf72 cases showed no pathological PrP aggregates and screening of 100 CJD cases revealed no other C9orf72 expansion mutation carriers. CONCLUSION: A combination of a C9orf72 expansion mutation-related FTLD with sporadic CJD in the same patient is rare. While the rarity of both diseases makes this concurrence most likely to be coincidental, questions regarding a potential link between these two neurodegenerative pathologies deserve further studies.

Prescription patterns of antidementives in a high income country: A pharmacoepidemiologic study.

INTRODUCTION: Dementia is a leading and growing cause of morbidity and mortality. The aim of this study was to investigate real-world prescription patterns of antidementive medication in one of the largest cohorts published thus far to optimize use in this growing population. METHODS: Prescription claims from 2005 to 2016 were provided by Austrian sickness funds, covering 98% of the population of Austria. Patients treated with at least one of the four approved antidementive drugs (ADDs) were included. Prescription prevalence was calculated for 2014 and 2015, and prescription patterns were traced on an individual level during the entire study period. RESULTS: A total of 127,896 patients were treated with an ADD between 2005 and 2016. The prevalence was 0.93% in 2014 and 1% in 2015. The median age at initiation of treatment was 82.3 years, and 65% were female. Initial therapy was a cholinesterase inhibitor (ChEI) in 80% and memantine in 20%. The median duration of therapy was 13.3 months. Eighteen percent of patients switched medication: two thirds to receive memantine, and one third to a different cholinesterase inhibitor. More than 26% discontinued treatment early. CONCLUSION: We find that discontinuation of ADDs is more frequent than switching; memantine is a common starting drug and age at the start of treatment is rather high in this population. Interpretation should be cautious, but the data may suggest that treatment guidelines are followed inconsistently. Appropriate provision of the available options should be emphasized to optimize cognitive survival, comorbidity, quality of life, and health care expenditures.

Radial somatic F-actin organization affects growth cone dynamics during early neuronal development.

The centrosome is thought to be the major neuronal microtubule-organizing center (MTOC) in early neuronal development, producing microtubules with a radial organization. In addition, albeit in vitro, recent work showed that isolated centrosomes could serve as an actin-organizing center, raising the possibility that neuronal development may, in addition, require a centrosome-based actin radial organization. Here, we report, using super-resolution microscopy and live-cell imaging of cultured rodent neurons, F-actin organization around the centrosome with dynamic F-actin aster-like structures with F-actin fibers extending and retracting actively. Photoactivation/photoconversion experiments and molecular manipulations of F-actin stability reveal a robust flux of somatic F-actin toward the cell periphery. Finally, we show that somatic F-actin intermingles with centrosomal PCM-1 (pericentriolar material 1 protein) satellites. Knockdown of PCM-1 and disruption of centrosomal activity not only affect F-actin dynamics near the centrosome but also in distal growth cones. Collectively, the data show a radial F-actin organization during early neuronal development, which might be a cellular mechanism for providing peripheral regions with a fast and continuous source of actin polymers, hence sustaining initial neuronal development.

Disturbed neurotransmitter homeostasis in ether lipid deficiency.

Plasmalogens, the most prominent ether (phospho)lipids in mammals, are structural components of most cellular membranes. Due to their physicochemical properties and abundance in the central nervous system, a role of plasmalogens in neurotransmission has been proposed, but conclusive data are lacking. Here, we targeted this issue in the glyceronephosphate O-acyltransferase (Gnpat) KO mouse, a model of complete deficiency in ether lipid biosynthesis. Throughout the study, focusing on adult male animals, we found reduced brain levels of various neurotransmitters. In the dopaminergic nigrostriatal tract, synaptic endings but not neuronal cell bodies were affected. Neurotransmitter turnover was altered in ether lipid-deficient murine as well as human post-mortem brain tissue. A generalized loss of synapses did not account for the neurotransmitter deficits, since the levels of several presynaptic proteins appeared unchanged. However, reduced amounts of vesicular monoamine transporter indicate a compromised vesicular uptake of neurotransmitters. As exemplified by norepinephrine, the release of neurotransmitters from Gnpat KO brain slices was diminished in response to strong electrical and chemical stimuli. Finally, addressing potential phenotypic correlates of the disturbed neurotransmitter homeostasis, we show that ether lipid deficiency manifests as hyperactivity and impaired social interaction. We propose that the lack of ether lipids alters the properties of synaptic vesicles leading to reduced amounts and release of neurotransmitters. These features likely contribute to the behavioral phenotype of Gnpat KO mice, potentially modeling some human neurodevelopmental disorders like autism or attention deficit hyperactivity disorder.

The Parkinson's disease VPS35[D620N] mutation enhances LRRK2-mediated Rab protein phosphorylation in mouse and human.

Missense mutations in the LRRK2 (Leucine-rich repeat protein kinase-2) and VPS35 genes result in autosomal dominant Parkinson's disease. The VPS35 gene encodes for the cargo-binding component of the retromer complex, while LRRK2 modulates vesicular trafficking by phosphorylating a subgroup of Rab proteins. Pathogenic mutations in LRRK2 increase its kinase activity. It is not known how the only thus far described pathogenic VPS35 mutation, [p.D620N] exerts its effects. We reveal that the VPS35[D620N] knock-in mutation strikingly elevates LRRK2-mediated phosphorylation of Rab8A, Rab10, and Rab12 in mouse embryonic fibroblasts. The VPS35[D620N] mutation also increases Rab10 phosphorylation in mouse tissues (the lung, kidney, spleen, and brain). Furthermore, LRRK2-mediated Rab10 phosphorylation is increased in neutrophils as well as monocytes isolated from three Parkinson's patients with a heterozygous VPS35[D620N] mutation compared with healthy donors and idiopathic Parkinson's patients. LRRK2-mediated Rab10 phosphorylation is significantly suppressed by knock-out or knock-down of VPS35 in wild-type, LRRK2[R1441C], or VPS35[D620N] cells. Finally, VPS35[D620N] mutation promotes Rab10 phosphorylation more potently than LRRK2 pathogenic mutations. Available data suggest that Parkinson's patients with VPS35[D620N] develop the disease at a younger age than those with LRRK2 mutations. Our observations indicate that VPS35 controls LRRK2 activity and that the VPS35[D620N] mutation results in a gain of function, potentially causing PD through hyperactivation of the LRRK2 kinase. Our findings suggest that it may be possible to elaborate compounds that target the retromer complex to suppress LRRK2 activity. Moreover, patients with VPS35[D620N] associated Parkinson's might benefit from LRRK2 inhibitor treatment that have entered clinical trials in humans.

Microtubules Modulate F-actin Dynamics during Neuronal Polarization.

Neuronal polarization is reflected by different dynamics of microtubule and filamentous actin (F-actin). Axonal microtubules are more stable than those in the remaining neurites, while dynamics of F-actin in axonal growth cones clearly exceed those in their dendritic counterparts. However, whether a functional interplay exists between the microtubule network and F-actin dynamics in growing axons and whether this interplay is instrumental for breaking cellular symmetry is currently unknown. Here, we show that an increment on microtubule stability or number of microtubules is associated with increased F-actin dynamics. Moreover, we show that Drebrin E, an F-actin and microtubule plus-end binding protein, mediates this cross talk. Drebrin E segregates preferentially to growth cones with a higher F-actin treadmilling rate, where more microtubule plus-ends are found. Interruption of the interaction of Drebrin E with microtubules decreases F-actin dynamics and arrests neuronal polarization. Collectively the data show that microtubules modulate F-actin dynamics for initial axon extension during neuronal development.