Hypoxia Conditioning as a Promising Therapeutic Target in Parkinson's Disease?

Several lines of research point to a key role of low oxygen supply (hypoxia) in Parkinson's disease pathogenesis. Although severe hypoxia is detrimental for the brain, physiological adaptations to mild hypoxia are neuroprotective. Herein we discuss, how neuroprotective effects can be induced by hypoxia conditioning and how related approaches have the potential to be harnessed as therapeutic strategies in Parkinson's disease. © 2021 International Parkinson and Movement Disorder Society.

A simple, versatile and robust centrifugation-based filtration protocol for the isolation and quantification of α-synuclein monomers, oligomers and fibrils: Towards improving experimental reproducibility in α-synuclein research.

Increasing evidence suggests that the process of alpha-synuclein (α-syn) aggregation from monomers into amyloid fibrils and Lewy bodies, via oligomeric intermediates plays an essential role in the pathogenesis of different synucleinopathies, including Parkinson's disease (PD), multiple system atrophy and dementia with Lewy bodies (DLB). However, the nature of the toxic species and the mechanisms by which they contribute to neurotoxicity and disease progression remain elusive. Over the past two decades, significant efforts and resources have been invested in studies aimed at identifying and targeting toxic species along the pathway of α-syn fibrillization. Although this approach has helped to advance the field and provide insights into the biological properties and toxicity of different α-syn species, many of the fundamental questions regarding the role of α-syn aggregation in PD remain unanswered, and no therapeutic compounds targeting α-syn aggregates have passed clinical trials. Several factors have contributed to this slow progress, including the complexity of the aggregation pathways and the heterogeneity and dynamic nature of α-syn aggregates. In the majority of experiment, the α-syn samples used contain mixtures of α-syn species that exist in equilibrium and their ratio changes upon modifying experimental conditions. The failure to quantitatively account for the distribution of different α-syn species in different studies has contributed not only to experimental irreproducibility but also to misinterpretation of results and misdirection of valuable resources. Towards addressing these challenges and improving experimental reproducibility in Parkinson's research, we describe here a simple centrifugation-based filtration protocol for the isolation, quantification and assessment of the distribution of α-syn monomers, oligomers and fibrils, in heterogeneous α-syn samples of increasing complexity. The protocol is simple, does not require any special instrumentation and can be performed rapidly on multiple samples using small volumes. Here, we present and discuss several examples that illustrate the applications of this protocol and how it could contribute to improving the reproducibility of experiments aimed at elucidating the structural basis of α-syn aggregation, seeding activity, toxicity and pathology spreading. This protocol is applicable, with slight modifications, to other amyloid-forming proteins.

Fatal attraction - The role of hypoxia when alpha-synuclein gets intimate with mitochondria.

Alpha-synuclein aggregation and mitochondrial dysfunction are main pathological hallmarks of Parkinson's disease (PD) and several other neurodegenerative diseases, collectively known as synucleinopathies. However, increasing evidence suggests that they may not be sufficient to cause PD. Here we propose the role of hypoxia as a missing link that connects the complex interplay between alpha-synuclein biochemistry and pathology, mitochondrial dysfunctions and neurodegeneration in PD. We review the partly conflicting literature on alpha-synuclein binding to membranes and mitochondria and its impact on mitochondrial functions. From there, we focus on adverse changes in cellular environments, revolving around hypoxic stress, that may trigger or facilitate PD progression. Inter-dependent structural re-arrangements of mitochondrial membranes, including increased cytoplasmic exposure of mitochondrial cardiolipins and changes in alpha-synuclein localization and conformation are discussed consequences of such conditions. Enhancing cellular resilience could be an integral part of future combination-based therapies of PD. This may be achieved by boosting the capacity of cellular and specifically mitochondrial processes to regulate and adapt to altered proteostasis, redox, and inflammatory conditions and by inducing protective molecular and tissue re-modelling.

Nanoparticle-Mediated Mitochondrial Damage Induces Apoptosis in Cancer.

Detouring of conventional DNA damaging anticancer drugs into mitochondria to damage mitochondrial DNA is evolving as a promising strategy in chemotherapy. Inhibiting single target in mitochondria would eventually lead to the emergence of drug resistance. Moreover, targeting mitochondria selectively in cancer cells, keeping them intact in healthy cells, remains a major challenge. Herein, triphenylphosphine (TPP)-coated positively charged 131.6 nm spherical nanoparticles (NPs) comprised of α-tocopheryl succinate (TOS, inhibitor of complex II in electron transport chain) and obatoclax (Obt, inhibitor of Bcl-2) were engineered. The TOS-TPP-Obt-NPs entered into acidic lysosomes via macropinocytosis, followed by lysosomal escape and finally homed into mitochondria over a period of 24 h. Subsequently, these TOS-TPP-Obt-NPs triggered mitochondrial outer membrane permeabilization (MOMP) by inhibiting antiapoptotic Bcl-2, leading to Cytochrome C release. These TOS-TPP-Obt-NPs mediated mitochondrial damage induced cellular apoptosis through caspase-9 and caspase-3 cleavage to show improved efficacy in HeLa cells. Moreover, TOS-TPP-Obt-NPs induced MOMP in drug-resistant triple negative breast cancer cells (MDA-MB-231), leading to remarkable efficacy, compared to the combination of free drugs in higher drug concentrations. Results presented here clearly stimulate the usage of multiple drugs to perturb simultaneously diverse targets, selectively in mitochondria, as next-generation cancer therapeutics.