Biology subjects

Burtscher, J.

Publications and source records attributed to Burtscher, J..

7 recordsLinked to original sources

bioRxiv2023

Post-fibrillization nitration of alpha-synuclein abolishes its seeding activity and pathology formation in primary neurons and in vivo

Increasing evidence points to post-translational modifications (PTMs) as key regulators of alpha-synuclein (-Syn) function in health and disease. However, whether these PTMs occur before or after -Syn pathology formation and their role in regulating -Syn toxicity remain unclear. In this study, we demonstrate that post-fibrillization nitration of -Syn fibrils induced their fragmentation, modified their surface and dynamic properties but not their structure, and nearly abolished their seeding activity in primary neurons and in vivo. Furthermore, we show that the dynamic and surface properties of the fibrils, rather than simply their length, are important determinants of -Syn fibril seeding activity. Altogether, our work demonstrates that post-aggregation modifications of -Syn may provide novel approaches to target a central process that contributes to pathology formation and disease progression. Finally, our results suggest that the pattern of PTMs on pathological aggregates, rather than simply their presence, could be a key determinant of their toxicity and neurodegeneration. This calls for reconsidering current approaches relying solely on quantifying and correlating the level of pathology to assess the efficacy of novel therapies, as not all -Syn aggregates in the brain are pathogenic.

neuroscience↗

bioRxiv2022

Development and validation of an expanded antibody toolset that captures alpha-synuclein pathological diversity in Lewy body diseases

The abnormal aggregation and accumulation of alpha-synuclein (aSyn) in the brain is a defining hallmark of synucleinopathies. Different aSyn conformations and post-translationally modified forms accumulate in pathological inclusions and vary in abundance across synucleinopathies. Relying on antibodies that have not been assessed for their ability to capture the diversity of aSyn species may not provide an accurate estimation of aSyn pathology in human brains or disease models. To address this challenge, we developed and characterised an expanded antibody panel that targets different sequences and post-translational modifications along the length of aSyn and recognises all three aSyn conformations (monomeric, oligomeric, fibrillar). Next, we profiled aSyn pathology across sporadic and familial Lewy body diseases (LBDs) and reveal heterogeneously modified aSyn pathologies rich in Serine 129 phosphorylation but also in Tyrosine 39 nitration and N- and C-terminal tyrosine phosphorylations, scattered to neurons and glia. We also show that aSyn may become hyperphosphorylated during the aggregation and inclusion maturation processes in neuronal and animal models of aSyn aggregation and spreading. The antibody validation pipeline we describe here paves the way for more systematic investigations of aSyn pathological diversity in the human brain and peripheral tissues, and in cellular and animal models of synucleinopathies.

neuroscience↗

bioRxiv2020

Disentangling the sequence, cellular and ultrastructural determinants of Huntingtin nuclear and cytoplasmic inclusion formation

Despite the strong evidence linking the aggregation of the Huntingtin protein (Htt) to the pathogenesis of Huntingtons disease (HD), the mechanisms underlying Htt aggregation and neurodegeneration remain poorly understood. Herein, we investigated the ultrastructural properties and protein composition of Htt cytoplasmic and nuclear inclusions in mammalian cells and primary neurons overexpressing mutant exon1 of the Htt protein. Our findings provide novel insight into the ultrastructural properties of cytoplasmic and nuclear Htt inclusions and their mechanisms of formation. We show that Htt inclusion formation and maturation are complex processes that, although initially driven by polyQ-dependent Htt aggregation, also involve 1) polyQ and PRD domain-dependent sequestration of lipids and cytoplasmic and cytoskeletal proteins related to HD dysregulated pathways; 2) recruitment and accumulation of remodeled or dysfunctional membranous organelles, and 3) impairment of the protein quality control and degradation machinery. We also show that nuclear and cytoplasmic Htt inclusions exhibit distinct biochemical compositions and ultrastructural properties, suggesting different mechanisms of aggregation and toxicity. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=88 SRC="FIGDIR/small/226977v2_ufig1.gif" ALT="Figure 1"> View larger version (51K): org.highwire.dtl.DTLVardef@295056org.highwire.dtl.DTLVardef@594664org.highwire.dtl.DTLVardef@11c5384org.highwire.dtl.DTLVardef@af0e0a_HPS_FORMAT_FIGEXP M_FIG C_FIG Schematic depictions and original electron micrographs of cytoplasmic inclusions formed by native (tag-free) mutant Huntingtin exon1 proteins (Httex1 72Q, left) and the corresponding GFP fusion protein (Httex1 72Q-GFP, right).

neuroscience↗

bioRxiv2020

Pronounced α-synuclein pathology in a seeding-based mouse model is not sufficient to induce mitochondrial respiration deficits in the striatum and amygdala

Increasing evidence suggests that crosstalk between -synuclein pathology formation and mitochondrial dysfunctions plays a central role in the pathogenesis of Parkinsons disease and related synucleinopathies. While mitochondrial dysfunction is a well-studied phenomenon in the substantia nigra, which is selectively vulnerable in Parkinsons disease and some models thereof, less information is available in other brain regions that are also affected by synuclein pathology. Therefore, we sought to test the hypothesis that early -synuclein pathology causes mitochondrial dysfunction, and that this effect might be exacerbated in conditions of increased vulnerability of affected brain regions, such as the amygdala. We combined a model of intracerebral -synuclein pathology seeding with chronic glucocorticoid treatment modelling non-motor symptoms of Parkinsons disease and affecting amygdala physiology. We measured mitochondrial respiration, ROS generation and protein abundance as well as -synuclein pathology in male mice. Chronic corticosterone administration induced mitochondrial hyperactivity in the amygdala. Although injection of -synuclein preformed fibrils into the striatum resulted in pronounced -synuclein pathology in both striatum and amygdala, mitochondrial respiration in these brain regions was altered in neither chronic corticosterone nor control conditions. Our results suggest that early stage -synuclein pathology does not influence mitochondrial respiration in the striatum and amygdala, even in corticosterone-induced respirational hyperactivity. We discuss our findings in light of relevant literature, warn of a potential publication bias and encourage scientist to report their negative results in the frame of this model. Significance statementWe provide evidence that early stage synucleinopathy by itself or in combination with exogenous corticosterone induced amygdala hyperactivity did not compromise mitochondrial respiration in the striatum and amygdala in one of the most commonly used models of synucleinopathies. These results may explain, why this model in the hands of many research groups does not elicit pronounced Parkinsons disease like symptoms in the absence of mitochondrial dysfunction in brain regions strongly affected by synuclein pathology and involved in non-motor (amygdala) and motor (striatum) symptoms. Our findings call for rigorous investigation of the short- and long-term effects of -synuclein pathology on mitochondrial function/dysfunction in this model, in particular in brain regions strongly affected by neurodegeneration such as the substantia nigra pars compacta.

neuroscience↗

bioRxiv2019

The process of Lewy body formation, rather than simply alpha-synuclein fibrillization, is the major driver of neurodegeneration in synucleinopathies

Parkinsons disease (PD) is characterized by the accumulation of misfolded alpha-synuclein (-syn) into intraneuronal inclusions named Lewy bodies (LB). Although it is widely believed that -syn plays a central role in the pathogenesis of PD and synucleinopathies, the processes that govern -syn fibrillization and LB formation in the brain remain poorly understood. In this work, we sought to reverse engineer LBs and dissect the spatiotemporal events involved in their biogenesis at the genetic, molecular, biochemical, structural, and cellular levels. Toward this goal, we took advantage of a seeding-based model of -syn fibril formation in primary neurons and further developed this model to generate the first neuronal model that reproduces the key events leading to LB formation; including seeding, fibrillization, and the formation of LB-like inclusions that recapitulate many of the biochemical, structural, and organizational features of LBs found in post-mortem human PD brain tissues. Next, we applied an integrative approach combining confocal and correlative light-electron microscopy (CLEM) imaging methods with biochemical profiling of -syn species and temporal proteomic and transcriptomic analyses to dissect the molecular events associated with LB formation and maturation and to elucidate their contributions to neuronal dysfunctions and neurodegeneration in PD and synucleinopathies. The results from these studies demonstrate that LB formation involves a complex interplay between -syn fibrillization, post-translational modifications, and interactions between -syn aggregates and membranous organelles, including mitochondria and the autophagosome and endolysosome. Furthermore, we demonstrate that the process of LB formation and maturation, rather than simply fibril formation, is the major driver of neurodegeneration through disruption of cellular functions and inducing mitochondria damage and deficits, as well as synaptic dysfunctions. Having a neuronal model that allows for unlinking of the key processes involved in LB formation is crucial for elucidating the molecular and cellular determinants of each process and their contributions to neuronal dysfunction and degeneration in PD and synucleinopathies. Such a model is essential to efforts to identify and investigate the mode of action and toxicity of drug candidates targeting -syn aggregation and LB formation.

neuroscience↗

bioRxiv2018

The making of a Lewy body: the role of alpha-synuclein post-fibrillization modifications in regulating the formation and the maturation of pathological inclusions.

Although converging evidence point to alpha-synuclein (a-syn) aggregation and Lewy body (LB) formation as central events in Parkinson's disease (PD), the molecular mechanisms that regulate these processes and their role in disease pathogenesis remain poorly understood. Herein, we applied an integrative biochemical, structural and imaging approach to elucidate the sequence, molecular and cellular mechanisms that regulate LB formation in primary neurons. Our results establish that post-fibrillization C-terminal truncation mediated by calpains 1 and 2 and potentially other enzymes, plays critical roles in regulating a-syn seeding, fibrillization and orchestrates many of the events associated with LB formation and maturation. These findings combined with the abundance of a-syn truncated species in LBs and pathological a-syn aggregates have significant implications for ongoing efforts to develop therapeutic strategies based on targeting the C-terminus of a-syn or proteolytic processing of this region.

neuroscience↗

bioRxiv2018

Chronic corticosterone enhancement aggravates alpha-synuclein brain spreading pathology and substantia nigra neurodegeneration in mice

Chronic stress and associated heightened glucocorticoid levels are risk factors for depression, a common non-motor symptom in Parkinsons disease (PD). However, how heightened glucocorticoids influence PD neuropathology [alpha-synuclein (-Syn) containing Lewy pathology and neurodegeneration] and disease progression is unclear. To address this knowledge gap, we investigated the impact of chronic corticosterone administration on -Syn pathology, neurodegeneration, behavior and mitochondrial function in a mouse model of -Syn pathology spreading after intracerebral injection of -Syn preformed fibrils (PFFs). Our results demonstrate that heightened corticosterone aggravates neurodegeneration and -Syn pathology spreading, intriguingly to specific brain regions, such as the entorhinal cortex. Corticosterone-treatment abolished distinct physiological adaptations after PFF-injection and induced differential physiological and behavioral consequences. Taken together, our work points to elevated glucocorticoids as a risk factor for the development of the neuropathological hallmarks of PD. Strategies aimed at reducing glucocorticoid levels might slow down pathology spreading and disease progression in synucleinopathy.

neuroscience↗