Wim Vandenberghe

High-frequency stimulation of the subthalamic nucleus suppresses oscillatory beta activity in patients with Parkinson's disease in parallel with improvement in motor performance.

High-frequency stimulation (HFS) of the subthalamic nucleus (STN) is a well-established therapy for patients with severe Parkinsons disease (PD), but its mechanism of action is unclear. Exaggerated oscillatory synchronization in the β (13–30 Hz) frequency band has been associated with bradykinesia in patients with PD. Accordingly, we tested the hypothesis that the clinical benefit exerted by STN HFS is accompanied by suppression of local β activity. To this end, we explored the after effects of STN HFS on the oscillatory local field potential (LFP) activity recorded from the STN immediately after the cessation of HFS in 11 PD patients. Only patients that demonstrated a temporary persistence of clinical benefit after cessation of HFS were analyzed. STN HFS led to a significant reduction in STN LFP β activity for 12 s after the end of stimulation and a decrease in motor cortical–STN coherence in the β band over the same time period. The reduction in LFP β activity correlated with the movement amplitude during a simple motor task, so that a smaller amount of β activity was associated with better task performance. These features were absent when power in the 5–12 Hz frequency band was considered. Our findings suggest that HFS may act by modulating pathological patterns of synchronized oscillations, specifically by reduction of pathological β activity in PD.

Paroxysmal exercise-induced dyskinesia and epilepsy is due to mutations in SLC2A1, encoding the glucose transporter GLUT1

Paroxysmal exercise-induced dyskinesia (PED) can occur in isolation or in association with epilepsy, but the genetic causes and pathophysiological mechanisms are still poorly understood. We performed a clinical evaluation and genetic analysis in a five-generation family with co-occurrence of PED and epilepsy (n = 39), suggesting that this combination represents a clinical entity. Based on a whole genome linkage analysis we screened SLC2A1, encoding the glucose transporter of the blood-brain-barrier, GLUT1 and identified heterozygous missense and frameshift mutations segregating in this and three other nuclear families with a similar phenotype. PED was characterized by choreoathetosis, dystonia or both, affecting mainly the legs. Predominant epileptic seizure types were primary generalized. A median CSF/blood glucose ratio of 0.52 (normal >0.60) in the patients and a reduced glucose uptake by mutated transporters compared with the wild-type as determined in Xenopus oocytes confirmed a pathogenic role of these mutations. Functional imaging studies implicated alterations in glucose metabolism in the corticostriate pathways in the pathophysiology of PED and in the frontal lobe cortex in the pathophysiology of epileptic seizures. Three patients were successfully treated with a ketogenic diet. In conclusion, co-occurring PED and epilepsy can be due to autosomal dominant heterozygous SLC2A1 mutations, expanding the phenotypic spectrum associated with GLUT1 deficiency and providing a potential new treatment option for this clinical syndrome.

Ca2+-permeable AMPA receptors and selective vulnerability of motor neurons

To evaluate the role of excitotoxicity in the pathogenesis of amyotrophic lateral sclerosis (ALS), we compared the sensitivity of motor neurons and that of dorsal horn neurons to kainic acid (KA). Short exposure to KA resulted in the death of motor neurons, while dorsal horn neurons were unaffected. This selective motor neuron death was completely dependent on extracellular Ca(2+) and insensitive to inhibitors of voltage-operated Ca(2+) or Na(+) channels. It was also completely inhibited by the specific AMPA antagonist LY300164 and by Joro spider toxin (JSTx), a selective blocker of AMPA receptors that lack the edited GluR2 subunit. KA selectively killed those motor neurons that stained positive for the Co(2+) histochemical staining, a measure for the presence of Ca(2+)-permeable AMPA receptors. These results suggest that Ca(2+) entry via Ca(2+)-permeable AMPA receptors is responsible for the selective motor neuron death. As the Ca(2+) permeability of the AMPA receptor is regulated by its GluR2 subunit, we stained motor neurons for GluR2. Immunoreactivity was present in all motor neurons, albeit to a variable degree. However, double-staining experiments demonstrated that motor neurons clearly expressing GluR2, also expressed Ca(2+)-permeable AMPA receptors. This indicates that despite the abundant expression of GluR2, this subunit is excluded from a subset of AMPA receptors and that the activation of these receptors is responsible for the selective motor neuron death.

Freezing of gait in Parkinson's disease: The impact of dual‐tasking and turning

Background: Turning is the most important trigger for freezing of gait (FOG) in Parkinsons disease (PD), and dual‐tasking has been suggested to influence FOG as well. Objective: To understand the effects of dual tasking and turning on FOG. Methods: 14 Freezers and 14 non‐freezers matched for disease severity and 14 age‐matched controls were asked to turn 180° and 360° with and without a cognitive dual‐task during the off‐period of the medication cycle. Total number of steps, duration, cadence, freezing‐frequency, and secondary‐task performance were measured. Results: Seven freezers froze during the protocol. Freezing occurred in 37.5% of trials during 180° turning compared to 0% during straight‐line walking (X2 = 10.44, p < 0.01). The occurrence of FOG increased during 360° when also a dual‐task was added (X2 = 4.23, p = 0.04). Freezers took significantly more steps and were slower than controls in all conditions. The presence of a dual‐task increased these differences. Cadence increased significantly for freezers during 360° and 180° compared to straight‐line walking. In contrast, cadence was decreased during turning in controls and non‐freezers. During straight‐line walking, only freezers made errors in the secondary task. Controls increased their error‐rate during 180° turning, whereas freezers deteriorated their secondary task performance during 360°. Conclusions: 360° turning in combination with a dual‐task is the most important trigger for freezing. During turning, non‐freezers and controls decreased their cadence whereas freezers increased it, which may be related to FOG. Freezers adopted a posture second strategy in contrast to non‐freezers when confronted with a dual task.

Parkin Interacts with Ambra1 to Induce Mitophagy

Mutations in the gene encoding Parkin are a major cause of recessive Parkinsons disease. Recent work has shown that Parkin translocates from the cytosol to depolarized mitochondria and induces their autophagic removal (mitophagy). However, the molecular mechanisms underlying Parkin-mediated mitophagy are poorly understood. Here, we investigated whether Parkin interacts with autophagy-regulating proteins. We purified Parkin and associated proteins from HEK293 cells using tandem affinity purification and identified the Parkin interactors using mass spectrometry. We identified the autophagy-promoting protein Ambra1 (activating molecule in Beclin1-regulated autophagy) as a Parkin interactor. Ambra1 activates autophagy in the CNS by stimulating the activity of the class III phosphatidylinositol 3-kinase (PI3K) complex that is essential for the formation of new phagophores. We found Ambra1, like Parkin, to be widely expressed in adult mouse brain, including midbrain dopaminergic neurons. Endogenous Parkin and Ambra1 coimmunoprecipitated from HEK293 cells, SH-SY5Y cells, and adult mouse brain. We found no evidence for ubiquitination of Ambra1 by Parkin. The interaction of endogenous Parkin and Ambra1 strongly increased during prolonged mitochondrial depolarization. Ambra1 was not required for Parkin translocation to depolarized mitochondria but was critically important for subsequent mitochondrial clearance. In particular, Ambra1 was recruited to perinuclear clusters of depolarized mitochondria and activated class III PI3K in their immediate vicinity. These data identify interaction of Parkin with Ambra1 as a key mechanism for induction of the final clearance step of Parkin-mediated mitophagy.

Glycine receptor antibodies in PERM and related syndromes: characteristics, clinical features and outcomes.

See Martinez-Martinez et al. (doi:10.1093/brain/awu153) for a scientific commentary on this article. Carvajal-González et al. describe the first prospective cohort of patients with glycine receptor antibodies. The majority have progressive encephalomyelitis with rigidity and myoclonus. The antibodies bind to extracellular determinants on glycine receptor-α1 and to glycine receptors on spinal cord and brainstem neurons. The patients make a good recovery with immunotherapies.

The deubiquitinase USP15 antagonizes Parkin-mediated mitochondrial ubiquitination and mitophagy

Loss-of-function mutations in PARK2, the gene encoding the E3 ubiquitin ligase Parkin, are the most frequent cause of recessive Parkinsons disease (PD). Parkin translocates from the cytosol to depolarized mitochondria, ubiquitinates outer mitochondrial membrane proteins and induces selective autophagy of the damaged mitochondria (mitophagy). Here, we show that ubiquitin-specific protease 15 (USP15), a deubiquitinating enzyme (DUB) widely expressed in brain and other organs, opposes Parkin-mediated mitophagy, while a panel of other DUBs and a catalytically inactive version of USP15 do not. Moreover, knockdown of USP15 rescues the mitophagy defect of PD patient fibroblasts with PARK2 mutations and decreased Parkin levels. USP15 does not affect the ubiquitination status of Parkin or Parkin translocation to mitochondria, but counteracts Parkin-mediated mitochondrial ubiquitination. Knockdown of the DUB CG8334, the closest homolog of USP15 in Drosophila, largely rescues the mitochondrial and behavioral defects of parkin RNAi flies. These data identify USP15 as an antagonist of Parkin and suggest that USP15 inhibition could be a therapeutic strategy for PD cases caused by reduced Parkin levels.

Predictors of fitness to drive in people with Parkinson disease

Objective: To develop an efficient clinical screening battery to accurately predict the fitness to drive in people with Parkinson disease (PD). Methods: This prospective study included 80 participants: 40 patients with PD and 40 healthy age- and sex-matched control subjects. All participants were assessed using a driving simulator, a driving history survey, and the Clinical Dementia Rating. The patients with PD also underwent a clinical test battery and an evaluation of fitness to drive performed by an official center, which included visual, cognitive, and on-road tests. A two-class decision from this driving assessment center was the main outcome measure. Results: A screening battery assessing four clinical variables (disease duration, contrast sensitivity, Clinical Dementia Rating, and motor part of the Unified Parkinson’s Disease Rating Scale) provided the best model (R2 = 0.52) to predict the fitness to drive and correctly classified 36 (90%) of the patients with PD as pass or fail (sensitivity = 91%, specificity = 90%). The Test Ride for Investigating Practical fitness to drive (TRIP) driving simulator score discriminated significantly between drivers with PD and their healthy peers (p = 0.0008). When the TRIP driving simulator score was added to the clinical model, the total explained variance increased (R2 = 0.60) and correctly classified 39 (97.5%) of drivers with PD into the pass/fail category (sensitivity = 91%, specificity = 100%). Conclusions: A short clinical screening battery that measures disease duration, contrast sensitivity, cognitive and motor functions can predict fitness to drive in people with Parkinson disease with a high degree of accuracy. GLOSSARY: ADL = activities of daily living; CDR = Clinical Dementia Rating; CS = contrast sensitivity; DBS = deep brain stimulator; ESS = Epworth Sleepiness Scale; IQR = interquartile range (Q1–Q3); NA = not applicable; PD = Parkinson disease; rb = biserial correlation coefficient; rrb = rank biserial correlation coefficient; rs = Spearman rank correlation coefficient; TRIP = Test Ride for Investigating Practical fitness to drive; UFOV = useful field of view; UPDRS II = Unified Parkinson’s Disease Rating Scale, activities of daily living; UPDRS III = Unified Parkinson’s Disease Rating Scale, motor scale; w = Wilcoxon rank sum test.

Glial cells potentiate kainate-induced neuronal death in a motoneuron-enriched spinal coculture system

AMPA/kainate receptor-mediated excitotoxicity is believed to play a pathogenic role in amyotrophic lateral sclerosis. To further characterize the mechanisms involved in AMPA/kainate receptor-mediated motoneuron injury, we investigated the influence of spinal glial cells on kainate-induced motoneuron death in vitro. A motoneuron-enriched neuronal population was obtained from embryonic mouse spinal cord by metrizamide density centrifugation. This population was cultured either on a pre-established glial feeder layer of ventral spinal origin (coculture) or in glia-free conditions (monoculture). Glial feeder layers significantly enhanced basal survival of neurons, and supported neuronal differentiation as judged by neuronal morphology and expression of the motoneuron markers peripherin and SMI-32. Neuronal vulnerability to kainate was two- to three-fold higher in coculture than in monoculture, and increased significantly with time in coculture. The effects of glial feeder layers on neuronal basal survival, differentiation and kainate vulnerability were not mimicked by conditioned medium from glial cells. The increase in neuronal kainate vulnerability with time in coculture was associated with a marked rise in the proportion of cocultured neurons possessing Ca2+-permeable AMPA/kainate receptors, as determined by kainate-activated Co2+-uptake. Neurons in monoculture were unstained by kainate-activated Co2+-uptake. Neurons were immunoreactive to specific antibodies against the AMPA receptor subunits GluR1 and GluR2 both in monoculture and coculture. This study indicates that motoneuron differentiation in coculture is associated with increased vulnerability to kainate and increased expression of Ca2+-permeable AMPA/kainate receptors. In this paradigm glial cells support basal survival and differentiation of neurons, but potentiate kainate-induced neuronal death.

Regional changes in type 1 cannabinoid receptor availability in Parkinson's disease in vivo

The type 1 cannabinoid receptor (CB1) is a crucial modulator of synaptic transmission in brain and has been proposed as a potential therapeutic target in Parkinsons disease (PD), especially for treatment of levodopa-induced dyskinesias (LID). Our aim was to measure CB1 levels in brains of PD patients in vivo and to investigate the relation between CB1 availability and LID. We studied 12 healthy controls and 29 PD patients (9 drug-naïve patients with early PD, 10 patients with advanced PD and LID, and 10 patients with advanced PD without LID). PD patients were examined using the Unified Parkinsons Disease Rating Scale (UPDRS) and the modified Abnormal Involuntary Movement Scale (mAIMS). All subjects underwent positron emission tomography (PET) with the CB1-selective radioligand [(18)F] MK-9470 and magnetic resonance imaging (MRI). PD patients showed an absolute decrease in CB1 availability in the substantia nigra. By contrast, CB1 availability was relatively increased in nigrostriatal, mesolimbic, and mesocortical dopaminergic projection areas. CB1 availability did not differ significantly between advanced PD patients with and without LID. Within the group of PD patients with LID, there was no significant correlation between CB1 availability and LID severity. These data demonstrate regional changes in CB1 availability in PD in vivo, but do not support a role for dysregulation of CB1 levels in the pathogenesis of LID.