Multiple system atrophy - a clinicopathological update

Multiple system atrophy (MSA) is a fatal, adult-onset neurodegenerative disorder of uncertain etiology, clinically characterized by various combinations of Levo-dopa-unresponsive parkinsonism, and cerebellar, motor, and autonomic dysfunctions. MSA is an α-synucleinopathy with specific glioneuronal degeneration involving striatonigral, olivopontocerebellar, autonomic and peripheral nervous systems. The pathologic hallmark of this unique proteinopathy is the deposition of aberrant α-synuclein (αSyn) in both glia (mainly oligodendroglia) and neurons forming pathological inclusions that cause cell dysfunction and demise. The major variants are striatonigral degeneration (MSA with predominant parkinsonism / MSA-P) and olivopontocerebellar atrophy (MSA with prominent cerebellar ataxia / MSA-C). However, the clinical and pathological features of MSA are broader than previously considered. Studies in various mouse models and human patients have helped to better understand the molecular mechanisms that underlie the progression of the disease. The pathogenesis of MSA is characterized by propagation of disease-specific strains of αSyn from neurons to oligodendroglia and cell-to-cell spreading in a "prion-like" manner, oxidative stress, proteasomal and mitochondrial dysfunctions, myelin dysregulation, neuroinflammation, decreased neurotrophic factors, and energy failure. The combination of these mechanisms results in neurodegeneration with widespread demyelination and a multisystem involvement that is specific for MSA. Clinical diagnostic accuracy and differential diagnosis of MSA have improved by using combined biomarkers. Cognitive impairment, which has been a non-supporting feature of MSA, is not uncommon, while severe dementia is rare. Despite several pharmacological approaches in MSA models, no effective disease-modifying therapeutic strategies are currently available, although many clinical trials targeting disease modification, including immunotherapy and combined approaches, are under way. Multidisciplinary research to elucidate the genetic and molecular background of the noxious processes as the basis for development of an effective treatment of the hitherto incurable disorder are urgently needed

Increased cortico-cortical functional connectivity in early-stage Parkinson's disease: a MEG study

We set out to determine whether changes in resting-state cortico-cortical functional connectivity are a feature of early-stage Parkinson's disease (PD), explore how functional coupling might evolve over the course of the disease and establish its relationship with clinical deficits. Whole-head magnetoencephalography was performed in an eyes-closed resting-state condition in 70 PD patients with varying disease duration (including 18 recently diagnosed, drug-naive patients) in an "OFF" medication state and 21 controls. Neuropsychological testing was performed in all subjects. Data analysis involved calculation of three synchronization likelihood (SL, a general measure of linear and non-linear temporal correlations between time series) measures which reflect functional connectivity within (local) and between (intrahemispheric and interhemispheric) ten major cortical regions in five frequency bands. Recently diagnosed, drug-naive patients showed an overall increase in alpha1 SL relative to controls. Cross-sectional analysis in all patients revealed that disease duration was positively associated with alpha2 and beta SL measures, while severity of parkinsonism was positively associated with theta and beta SL measures. Moderately advanced patients had increases in theta, alpha1, alpha2 and beta SL, particularly with regard to local SL. In recently diagnosed patients, cognitive perseveration was associated with increased interhemispheric alpha1 SL. Increased resting-state cortico-cortical functional connectivity in the 8-10 Hz alpha range is a feature of PD from the earliest clinical stages onward. With disease progression, neighboring frequency bands become increasingly involved. These findings suggest that changes in functional coupling over the course of PD may be linked to the topographical progression of pathology over the brain. © 2008 Elsevier Inc. All rights reserved

Aberrant brain network connectivity in pre-symptomatic and manifest Huntington's disease: a systematic review

Resting-state functional magnetic resonance imaging (rs-fMRI) has the potential to shed light on the pathophysiological mechanisms of Huntington's disease (HD), paving the way to new therapeutic interventions. A systematic review of the literature was conducted in three online databases according to PRISMA guidelines, using keywords for HD, functional connectivity, and rs-fMRI. We included studies investigating connectivity in pre-symptomatic (pre-HD) and manifest HD gene carriers compared to healthy controls, implementing seed-based connectivity, independent component analysis, regional property and graph analysis approaches. Visual network showed reduced connectivity in manifest HD, while network/areas underpinning motor functions were consistently altered in both manifest HD and pre-HD, showing disease stage-dependent changes. Cognitive networks underlying executive and attentional functions showed divergent anterior-posterior alterations, reflecting possible compensatory mechanisms. The involvement of these networks in pre-HD is still unclear. In conclusion, aberrant connectivity of the sensory-motor network is observed in the early stage of HD while, as pathology spreads, other networks might be affected, such as the visual and executive/attentional networks. Moreover, sensory-motor and executive networks exhibit hyper- and hypo-connectivity patterns following different spatiotemporal trajectories. These findings could help to implement future huntingtin-lowering interventions

Evaluation of neuropathology and neurodegeneration in experimental models of Parkinson’s disease based on alpha synuclein preformed fibrils or 6-hydroxydopamine

Parkinson’s disease (PD) is a complex multisystem neurodegenerative disorder with no cure. Many PD patients will develop dementia, referred to as Parkinson’s disease dementia (PDD). The characteristic neuropathological hallmarks of PD are Lewy bodies (LBs) and Lewy neurites (LNs) that are composed primarily of misfolded a-synuclein. a-Synuclein pathology spreads to different regions of the brain as disease progresses and the presence of LBs and LNs correlate closely with the clinical features of PD. However, it is not yet understood which events are necessary to cause dementia in PD. With this in mind, it is important to understand events that facilitate the spread of phosphorylated a-synuclein to neuroanatomically connected regions, and the consequences of this spread on cellular events that lead to altered cognition. In rodents, injection into the brain of a-synuclein preformed fibrils (PFFs) has previously been shown to induce human-like Lewy body pathology, leading to neurodegeneration after prolonged periods of time, whereas injection of the free radical 6-hydroxydopamine (6-OHDA) induces rapid neurotoxicity of dopaminergic neurons and motor deficits in the apparent absence of a-synuclein modifications. To further investigate the brain changes underlying cognitive dysfunction in PD, the PD-related effects of PFFs and 6-OHDA were examined following their unilateral stereotactic injection into the medial forebrain bundle (MFB) of Sprague-Dawley (SD) rats. Behaviour tests to measure motor, executive and visuospatial related cognitive impairments were used. Tissues were collected at 60, 90 and 120 days post injection (d.p.i.) of PFFs or vehicle. Phosphorylated a-synuclein was examined in regions connected to the MFB, with a focus on the frontal cortex and hippocampal areas that control cognition. These areas were also examined for changes in tau, synaptic proteins, oxidative stress and astrocyte reactivity. Synaptic disruptions underlie cognitive decline. Synaptic fractions were therefore isolated from rat tissues and immunoblotting techniques were used to study changes in synaptic proteins. To investigate the impact of rapid neuronal loss in the substantia nigra (SN) on a-synuclein spreading and neurodegenerative events important for cognition, a similar experimental approach was taken following unilateral MFB lesions with 6-hydroxydopamine (6-OHDA). Validation tests were conducted at 3 weeks post injection (w.p.i.) to confirm dopaminergic loss within the SN. Results from this thesis established that injection of a-synuclein PFFs into rat MFB can lead to phosphorylation of endogenous a-synuclein and apparent “spreading” of phosphorylated a-synuclein to regions connected to the MFB. However, a-synuclein PFF injection did not cause alterations in tau, synapses or cause disruptions to rat behaviour or cognition up to 120 d.p.i., in partial agreement with previous findings. In contrast, 6-OHDA injection into rat MFB resulted in rapid mass neuronal loss in the SN, phosphorylation and “spreading” of phosphorylated a-synuclein to MFB connected regions that was associated with altered synaptic marker levels, and cognitive impairments. These results extend previously published reports and suggest that rapid neuronal loss in the SN may initiate a cascade of events that facilitates the phosphorylation and/or spread of a-synuclein, ultimately leading to cognitive deficits. The study elucidates events that facilitate a-synuclein modifications and neurodegenerative changes linked to cognitive dysfunction in PD. Oxidative stress-induced rapid neuronal loss may stimulate neuronal alterations that lead to the induction of oxidative stress and the appearance of phosphorylated a-synuclein in neuroanatomically connected regions, synaptic changes and cognitive abnormalities, whereas a-synuclein alone does not cause these neurodegenerative changes, at least not at the time points examined here. A future therapeutic intervention to reduce dementia related to a-synuclein in PD may therefore be an antioxidant or neuroprotective agent, rather than a-synuclein targeted therapy. Such a therapy could prevent the progression of a full-blown neurodegeneration cascade that results in PDD

Multimodal view on resting-state brain activity in Parkinson’s disease: examining the relation between functional resting-state networks and metabolic network activity

Research focusing on the pathophysiology of neurodegenerative disorders has undergone a fundamental shift towards a network perspective in the last decades. Besides regional aggregation of misfolded proteins and changes in cellular metabolism, accompanying changes of synaptic activity evolve and evoke dysregulation within neural circuits including remote brain regions. Modern theories of neurodegeneration propose a stereotypic pattern of these cerebral pathologies, which partly are in vivo accessible by multimodal neuroimaging techniques. The most often used indirect measurement of functional network integrity is resting-state functional magnetic resonance imaging, which depends on a complex interplay of hemodynamics, blood volume, and blood flow. Less is known about a potential metabolic component underlying resting-state networks in healthy brains and changes thereof in neurodegeneration and the influence of different transmitter systems. The current work therefore sought to investigate the association between functional resting-state networks and metabolic network activity and focused on metabolic consequences of nigrostriatal and striatocortical dysfunction in Parkinson’s disease. In the current work, a multimodal data set of the TP10 KFO219 cohort was analyzed regarding 1) the impact of nigrostriatal dopamine depletion on resting-state networks and 2) the relation between changes in functional connectivity and metabolic network activity. The first study addressed the subset of the KFO219 TP10 cohort who completed the trimodal imaging protocol (42 patients vs. 14 controls). Dopamine deficiency in Parkinson’s patients was examined by voxel-wise comparison of 6-[18F]fluoro-L-Dopa positron emission tomography scans. Resulting clusters served as seeds for restingstate functional connectivity maps that were compared between both groups by voxelwise t-tests. Metabolic activity was extracted from 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography scans for respective cortical clusters with striatocortical dysconnectivity and the relation to functional connectivity values was analyzed. In a separate study, functional and metabolic resting-state networks were obtained by performing spatial independent component analyses in a subset of the same cohort who underwent 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography and functional magnetic resonance imaging (56 vs 16) and completed neuropsychological testing. Multimodally obtained regions of interest in the default mode network were defined and metabolic activity as well as metabolic connectivity compared to functional connectivity differences between patients without or with mild cognitive impairment and healthy controls. Moreover, a third study was initiated in the context of the present work with the aim of establishing a dynamic 2-[18F]fluoro-2-deoxy-D-glucose positronemission tomography acquisition with a constant infusion protocol for examining interregional metabolic connectivity on single subject level and enable comparable analysis of hemodynamic and metabolic fluctuations in Parkinson’s disease. In the first study, a significant association between striatocortical functional connectivity changes of the data-driven defined dopamine depleted posterior putamen and metabolic activity of the cortical target area in the inferior parietal cortex was found in Parkinson’s disease. Interestingly, striatocortical connectivity of the inferior parietal cortex was associated with motor and cognitive impairment. In a second study, the multivariate approach revealed a moderate spatial convergence for the posterior default mode network in functional and metabolic data. For all multimodally obtained default mode network regions, a significant trend towards an increment of metabolic deficits from healthy controls via unimpaired patients to patients with mild cognitive impairment was identified. In addition, posterior default mode network regions with the strongest metabolic deficits and gradual decline in comparison to controls, also showed the strongest increases in both metabolic and functional connectivity compared to controls. The verification of the applicability of a constant infusion dynamic 2-[18F]fluoro-2-deoxy- D-glucose positron emission tomography protocol in Parkinson’s disease patients was started in a self-initiated study, which finished the acquisition phase with 10 participants per group by the time the current work was submitted. Together the first two studies highlight the added value of multimodal imaging in investigating human brain function and the pathophysiology of neurodegenerative disorders, in particular their great potential for identifying links between individual pathologies. The second study partly continued, and answered questions raised in response to the first study, which hinted at an involvement of default mode network regions in cognitive symptoms of Parkinson’s disease and a relation between functional network degeneration and metabolic activity. The current work shows exemplary the complementarity of both measures of brain network activity and their individual significance for cognitive symptoms in Parkinson’s disease. The presented work highlights how multimodal resting-state studies can provide new insights into the (patho-)physiological network organization of brain activity by confirming insights obtained by one modality and deepen our understanding of disease processes. The selfinitiated study further laid the ground for multimodal characterization of metabolic and hemodynamic network changes on single-subject level and the evaluation of dynamic positron emission tomography-based connectivity as metabolic network marker for Parkinson’s disease

Stem cell interactions with the injured brain

Neurodegenerative diseases such as Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis and acute neurological disorders such as brain ischemia and traumatic injury yearly affect millions of people. Neural stem cell (NSC) grafting is an emerging strategy to treat and potentially cure these conditions for which today no effective remedies exist. The restoration of function might occur both by replacement of lost neural cell populations and by rescue of host cells at risk. In this thesis we have investigated the early interactions between grafted NSCs and the injured brain and characterized potential mechanisms that underlie the functional improvements seen after NSCs grafting. For these aims, we employed an organotypic culture (OC) system to model injured neural host tissue and grafted both murine and human NSCs to this model. First, we recognized that the OC was a suitable model system to study the early interactions between NSCs and the host. After NSC grafting we observed a reduced host cell damage using metrics like astrogliosis, apoptosis and necrosis. The grafted NSCs also integrated functionally and participated in host calcium signaling networks. Employing a combination of immunohistochemistry, RNA interference, pharmaco- logical blockers, calcium imaging and dye coupling assays we identified gap-junctional graft-host couplings as the mechanism that conveyed both the beneficial impact on the host and the early functional interactions. We recognized that gap junction expression in the grafted NSCs and the injured host cells were highly dynamic processes. The investigations of the graft and host gap junction expression indicated a temporal window of opportunity for successful NSC engraftment. Finally, we noticed that graft- host gap-junctional couplings could be increased by treating the human embryonic stem cells with a Rho-associated kinase inhibitor. This was paralleled by an increased beneficial impact on the damaged host cells. The main conclusion in this thesis is that that gap-junctional coupling appears to be one of the first steps by which graft and host cells establish functional and beneficial interactions. This precedes the formation of more complex communication like chemical synapses. The direct cell-to-cell contact allows reciprocal exchange of a multitude of different health promoting substances and neutralization of pathological processes by diffusion of harmful substances. Increased knowledge of the exact molecular mechanisms involved in the interplay between the graft and host, and also how to direct them, can ultimately benefit the potential future use of NSCs grafts for the treatment of neurodegenerative disorders