Common Pathways Linking Neurodegenerative Diseases The Role Of Inflammation

Alzheimer’s disease (AD) and Parkinson’s disease (PD) are the two most common neurodegenerative diseases with rates increasing along with the ageing global population. Despite best efforts, we still do not understand the etiopathogenesis of these diseases and there are no effective disease-modifying treatments. Cognitive deficiencies or motor complications that emerge during AD and PD are thought to be the result of the accumulation of misfolded, aggregate-prone proteins, such as amyloid-? (A?) and tau or ?-synuclein (?-syn), respectively. Growing evidence suggests that prefibrillar oligomers of A? and ?-syn (oA? and o?-syn) are key contributors to the progression of these diseases. The progressive accumulation of these proteins leads to a gradual spread of pathology throughout interconnected brain regions, but the mechanisms by which this spreading occurs are still largely unknown. Neuroinflammation has been recognised as an important contributor to neurodegenerative disease. It is hypothesised that a pro-inflammatory environment initiated by the innate immune system, either through activation from A? itself or indirectly through neuronal injury signals in AD. These phenomena are thought to either cause or accelerate AD, such that an anti-inflammatory approach may be neuroprotective. In paper I, we investigated whether different inflammatory environments affected the transfer of oA? between neuron-like cells, in addition to investigating inter- and intracellular protein changes. This study demonstrated that an anti-inflammatory environment reduces the transfer of oA? between cells. We also provide evidence that these cells begin to take on the “phenotype” of the inflammatory milieu, while also demonstrating that the expression profile of endosomal/lysosomal and protein trafficking proteins is altered during these conditions. Small extracellular vesicles called exosomes, which are key players in cell to cell communication, have been proposed to play an influential role in spreading neurodegenerative proteins between cells. Exosomes are small membranous vesicles that are formed by the inward budding of multivesicular bodies (MVBs). These MVBs can then merge with the plasma membrane to be released into the extracellular environment as vesicles, which serve as vehicles for transferring proteins, lipids, and mRNAs between cells. The ESCRT-dependent pathway is the most understood mechanism underlying exosome biogenesis. However, exosomes can also be formed through ESCRT-independent pathways, including through the hydrolysis of sphingomyelin by neutral sphingomyelinase 2 (nSMase2), which produces ceramide. Paper II investigated whether exosomes formed through an ESCRT-independent pathway plays a significant role in the transfer of o?-syn between neuron-like cells. As oxidative stress is a common feature in PD brains, which in turn dysregulates nSMase2 activity, we also tested our model under hypoxic conditions. Inhibition of nSMase2 significantly reduced the transfer of o?-syn between cells but also resulted in decreased ?-syn aggregation. Hypoxia did not influence o?-syn transfer, however, it significantly dysregulated the sphingolipid composition, which may be important for ?-syn binding to exosomes and exosome communication. During AD and PD, there is a noted reduction in the effectiveness of autophagy, a process critical to cellular proteostasis. Recent studies have uncovered shared regulatory mechanisms of exosome biogenesis and autophagy, suggesting that they are closely linked. Previous findings have shown that inhibition of autophagy in AD mice mediates A? trafficking through altering the secretion of A? in MVBs. To further study this effect, we investigated the interplay between autophagy and exosome secretion using ATG7 knock-out x APPNL-F knock-in AD mice in paper III. These autophagy-deficient AD mice had a reduced extracellular A? plaque load, but increased intracellular A?, which was found to be assembled into higher-ordered assemblies. While exosomal secretion was dysregulated in these mice, the amount of A? packaged into the exosomes was unchanged. Lastly, one of the biggest challenges in developing effective treatments for AD is the lack of early diagnosis of living patients. As the connection between exosomes and the spread of neurodegenerative proteins is still relatively new, there remains a diagnostic potential to be explored with exosomes. Paper IV aimed to develop a new diagnostic assay to detect oA? in exosomes isolated from human cerebrospinal fluid. Although exosomal oA? was readily detected in some of these samples, the assay’s sensitivity requires additional optimisation before it can be further validated for the clinic. In summary, the studies presented in this thesis have furthered our understanding of how inflammation, autophagy, and exosomes contribute to the intercellular transmission of AD and PD associated proteins. We have shown that an anti-inflammatory approach may slow down the progression of AD through reducing the transfer of oA? between cells. We also provide novel findings relating to the biogenesis of exosomes, which in turn affected the ability of exosomes to transmit neurodegenerative proteins between cells, and their association with autophagic processes. Finally, we have investigated the feasibility of exosomes as an early AD diagnostic marker. This work has helped to elucidate some of the mechanisms underlying the progression of neurodegenerative diseases, which may be useful targets for the investigation of new therapeutic avenues.

This comprehensive reference provides a detailed overview of current concepts regarding the cause of Parkinson's disease-emphasizing the issues involved in the design, implementation, and analysis of epidemiological studies of parkinsonism.

This book, written by members of the European network PROTEOSTASIS, provides an up-to-date review of the research regarding protein homeostasis in health and disease. With new discoveries contributing to the increasing complexity of this topic, the book offers a detailed overview of the pathways regulating protein homeostasis, including autophagy and the ubiquitin protein family. Following a basic introduction, it explains how defects in protein homeostasis contribute to numerous pathologies, including cancer, neurodegeneration, inflammation and a number of rare diseases. In addition, it discusses, the role of protein homeostasis in cellular development and physiology. Highlighting the latest research in the field of protein homeostasis and its implications for various clinically relevant diseases, the book appeals to researchers and clinicians, while also offering a reference guide for scholars who are new to the field.

Oxidative stress is the result of an imbalance in pro-oxidant/antioxidant homeostasis that leads to the generation of toxic reactive oxygen species. Brain cells are continuously exposed to reactive oxygen species generated by oxidative metabolism, and in certain pathological conditions defense mechanisms against oxygen radicals may be weakened and/or overwhelmed. DNA is a potential target for oxidative damage, and genomic damage can contribute to neuropathogenesis. It is important therefore to identify tools for the quantitative analysis of DNA damage in models on neurological disorders. This book presents detailed information on various neurodegenerative disorders and their connection with oxidative stress. This information will provide clinicians with directions to treat these disorders with appropriate therapy and is also of vital importance for the drug industries for the design of new drugs for treatment of degenerative disorders. * Contains the latest information on the subject of neurodegenerative disorders* Reflects on various factors involved in degeneration and gives suggestions for how to tackle these problems

This book provides medical professionals and researchers with a comprehensive overview of fundamental concepts and recent advances in neurochemistry, and offers new perspectives for all those involved with research in related disciplines. As drug discovery for neurodegenerative diseases is one of the largest subspecialties in the field of medicine, the book addresses topics that transcend the borders between disciplines, and presents a wealth of investigations into and discussions on critical questions relevant to the entire field of CNS drug research. It summarizes the available data on the fundamentals of neurotransmitters, treatment of and advanced care for neurodegenerative diseases; and outlines current and future research directions in this field. Combining both conventional and innovative approaches to the topic, the book offers a valuable guide for readers working in medicinal chemistry, the life sciences and allied fields.