A proteomics analysis of 5xFAD mouse brain regions reveals the lysosome-associated protein Arl8b as a candidate biomarker for Alzheimer’s disease

BACKGROUND: Alzheimer's disease (AD) is characterized by the intra- and extracellular accumulation of amyloid-ß (Aß) peptides. How Aß aggregates perturb the proteome in brains of patients and AD transgenic mouse models, remains largely unclear. State-of-the-art mass spectrometry (MS) methods can comprehensively detect proteomic alterations, providing relevant insights unobtainable with transcriptomics investigations. Analyses of the relationship between progressive Aß aggregation and protein abundance changes in brains of 5xFAD transgenic mice have not been reported previously. METHODS: We quantified progressive Aß aggregation in hippocampus and cortex of 5xFAD mice and controls with immunohistochemistry and membrane filter assays. Protein changes in different mouse tissues were analyzed by MS-based proteomics using label-free quantification; resulting MS data were processed using an established pipeline. Results were contrasted with existing proteomic data sets from postmortem AD patient brains. Finally, abundance changes in the candidate marker Arl8b were validated in cerebrospinal fluid (CSF) from AD patients and controls using ELISAs. RESULTS: Experiments revealed faster accumulation of Aß42 peptides in hippocampus than in cortex of 5xFAD mice, with more protein abundance changes in hippocampus, indicating that Aß42 aggregate deposition is associated with brain region-specific proteome perturbations. Generating time-resolved data sets, we defined Aß aggregate-correlated and anticorrelated proteome changes, a fraction of which was conserved in postmortem AD patient brain tissue, suggesting that proteome changes in 5xFAD mice mimic disease-relevant changes in human AD. We detected a positive correlation between Aß42 aggregate deposition in the hippocampus of 5xFAD mice and the abundance of the lysosome-associated small GTPase Arl8b, which accumulated together with axonal lysosomal membranes in close proximity of extracellular Aß plaques in 5xFAD brains. Abnormal aggregation of Arl8b was observed in human AD brain tissue. Arl8b protein levels were significantly increased in CSF of AD patients. CONCLUSIONS: We report a comprehensive biochemical and proteomic investigation of hippocampal and cortical brain tissue derived from 5xFAD transgenic mice, providing a valuable resource to the neuroscientific community. We identified Arl8b, with significant abundance changes in 5xFAD and AD patient brains. Arl8b might enable the measurement of progressive lysosome accumulation in AD patients and have clinical utility as a candidate biomarker

First person - Marcel Nowak and Benjamin Suenkel

First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Marcel Nowak and Benjamin Suenkel are co-first authors on 'DCAF8, a novel MuRF1 interaction partner, promotes muscle atrophy', published in JCS. Marcel subsequently worked as a Product Manager for a life science company. Benjamin is a postdoc in the lab of Thomas Sommer at Max-Delbrück-Center for Molecular Medicine (MDC), Berlin-Buch, Germany, investigating protein biochemistry and quality control

Gait analysis with wearables predicts conversion to Parkinson disease

Objective Quantification of gait with wearable technology is promising; recent cross-sectional studies showed that gait characteristics are potential prodromal markers for Parkinson disease (PD). The aim of this longitudinal prospective observational study was to establish gait impairments and trajectories in the prodromal phase of PD, identifying which gait characteristics are potentially early diagnostic markers of PD. Methods The 696 healthy controls (mean age = 63 ± 7 years) recruited in the Tubingen Evaluation of Risk Factors for Early Detection of Neurodegeneration study were included. Assessments were performed longitudinally 4 times at 2-year intervals, and people who converted to PD were identified. Participants were asked to walk at different speeds under single and dual tasking, with a wearable device placed on the lower back; 14 validated clinically relevant gait characteristics were quantified. Cox regression was used to examine whether gait at first visit could predict time to PD conversion after controlling for age and sex. Random effects linear mixed models (RELMs) were used to establish longitudinal trajectories of gait and model the latency between impaired gait and PD diagnosis. Results Sixteen participants were diagnosed with PD on average 4.5 years after first visit (converters; PDC). Higher step time variability and asymmetry of all gait characteristics were associated with a shorter time to PD diagnosis. RELMs indicated that gait (lower pace) deviates from that of non-PDC approximately 4 years prior to diagnosis. Interpretation Together with other prodromal markers, quantitative gait characteristics can play an important role in identifying prodromal PD and progression within this phase. ANN NEUROL 2019;86:357–36

Instrumented gait analysis identifies potential predictors for Parkinson’s disease converters [abstract]

Objective: This longitudinal prospective observational study investigated if gait can predict Parkinson’s disease (PD) conversion from a cohort of community-dwelling older adults. Background: PD is a progressive disorder including a prodromal period when definitive motor/non-motor symptoms to permit a diagnosis have not yet appeared. Quantification of gait with wearable technology (WT) may serve as an accurate tool to identify surrogate markers of incipient disease manifestation. Recently arm swing and selective gait characteristics measured with WT have been shown to be potential prodromal markers for people at risk for PD [1]; however these data were obtained from a cross-sectional assessment; the potential of gait to predict PD conversion has not been investigated yet in a longitudinal cohort. Methods: 16 participants (69±5 years (yrs)) who were diagnosed with PD on average 4.5 yrs after baseline assessment (converters (PDC)) and 48 age-matched old healthy adults (HA) recruited in the TREND study were included. Assessments were performed longitudinally 4 times at 2-year intervals. Participants were asked to walk at their preferred speed, performing 2 straight-line trials over 20m with a WT device placed on the lower back; 14 validated clinically relevant gait characteristics were quantified [2]. ANCOVA was used to examine gait between-group differences; the value of baseline gait in predicting PDC was explored using AUC and stepwise, forward, logistic regression analyses. Random effects linear mixed-models (RELM) were used to predict latency gait deterioration and diagnosis of PD. Results: PDC walked with significantly lower pace, higher variability and asymmetry than HA (p≤0.027). Pace, variability and asymmetry characteristics were able to significantly predict PDC (AUC≥0.695). Step time variability was the best predictor for the stepwise, forward, logistic regression (sensitivity 25%, specificity 98%, accuracy of 80%). RELMs indicate gait impairment (step velocity and step length) is evident 4-6 yrs prior to diagnosis. Conclusions: Our preliminary results suggest that pace, variability and asymmetry of gait represent sensitive predictors of prodromal PD and that gait impairment starts 4-5 years prior to diagnosis. Therefore, gait assessment may play an important role in concert with other biomarkers to identify people at high risk of PD and aid early diagnosis

DCAF8, a novel MuRF1 interaction partner, promotes muscle atrophy

The muscle-specific RING-finger protein MuRF1 constitutes a bona fide ubiquitin ligase that routes proteins like Myosin heavy chain (MyHC) to proteasomal degradation during muscle atrophy. In two unbiased screens we identified DCAF8 as a new MuRF1 binding partner. MuRF1 physically interacts with DCAF8 and both proteins localize to overlapping structures in muscle cells. Noteworthy, similar to MuRF1, DCAF8 levels increase during atrophy and the down-regulation of either protein substantially impedes muscle wasting and MyHC degradation in C2C12 myotubes, a model system for muscle differentiation and atrophy. DCAF proteins typically serve as substrate receptors in Cullin 4-type (Cul4) ubiquitin ligases (CRL) and we demonstrate that DCAF8 and MuRF1 associate with the subunits of such a protein complex. Because genetic downregulation of DCAF8 and inhibition of Cullin activity also impair myotube atrophy in C2C12 cells, our data imply that the DCAF8 promotes muscle wasting by targeting proteins like MyHC as an integral substrate receptor of a CRL4A ubiquitin ligase

Age and Vascular Burden Determinants of Cortical Hemodynamics Underlying Verbal Fluency.

Aging processes and several vascular burden factors have been shown to increase the risk of dementia including Alzheimer's disease. While pathological alterations in dementia precede diagnosis by many years, reorganization of brain processing might temporarily delay cognitive decline. We hypothesized that in healthy elderly individuals both age-related neural and vascular factors known to be related to the development of dementia impact functional cortical hemodynamics during increased cognitive demands.Vascular burden factors and cortical functional hemodynamics during verbal fluency were assessed in 1052 non-demented elderly individuals (51 to 83 years; cross-sectional data of the longitudinal TREND study) using functional near-infrared spectroscopy (fNIRS). The prediction of functional hemodynamic responses by age in multiple regressions and the impact of single and cumulative vascular burden factors including hypertension, diabetes, obesity, smoking and atherosclerosis were investigated.Replicating and extending previous findings we could show that increasing age predicted functional hemodynamics to be increased in right prefrontal and bilateral parietal cortex, and decreased in bilateral inferior frontal junction during phonological fluency. Cumulative vascular burden factors, with hypertension in particular, decreased left inferior frontal junction hemodynamic responses during phonological fluency. However, age and vascular burden factors showed no statistical interaction on functional hemodynamics.Based on these findings, one might hypothesize that increased fronto-parietal processing may represent age-related compensatory reorganization during increased cognitive demands. Vascular burden factors, such as hypertension, may contribute to regional cerebral hypoperfusion. These neural and vascular hemodynamic determinants should be investigated longitudinally and combined with other markers to advance the prediction of future cognitive decline and dementia