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Bassoon proteinopathy drives neurodegeneration in multiple sclerosis

ABSTRACT: During the course of multiple sclerosis (MS), inflammatory insults drive neuro-axonal loss and disability progression. However, pathways that guide neurons toward survival or death during central nervous system (CNS) inflammation are largely unexplored. Here we show that somatic deposition of the presynaptic protein bassoon (Bsn) in inflamed neurons directly contributes to neurodegeneration in MS. By comparing neuron-specific RNA-seq of healthy mice to mice undergoing experimental autoimmune encephalomyelitis (EAE), the animal model of MS, we identified key components of neurodegenerative pathways, including reduced mitochondrial ATP synthesis and increased protein catabolism. These changes were accompanied by neuronal induction and deposition of the intrinsically disordered protein Bsn in both EAE and in patients with MS. Somatic Bsn also accumulated in Bsn-overexpressing Neuro-2a (N2a) cells and single cell RNA-seq revealed dose-dependent repression of energy metabolism and induction of the unfolded protein response, reminiscent of our in vivo findings. Furthermore, Bsn overexpression in N2a cells or in Drosophila melanogaster neurons led to decreased survival and shortened lifespan, respectively. Conversely, genetic disruption of Bsn in mice was neuroprotective, with reduced neuro-axonal injury and clinical disability during EAE, establishing a toxic gain-of-function of Bsn during CNS inflammation. Our study provides systemic insights into neuronal responses to inflammation and identifies protein accumulation as a generic pathomechanism uniting primary and inflammatory neurodegeneration. Moreover, it offers a new explanation and possible treatment strategy to halt disability progression in MS, irrespective of immunotherapies.

ORGANISM(S): Mus musculus

PROVIDER: GSE104899 | GEO | 2019/04/03

REPOSITORIES: GEO

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Project description:Multiple Sclerosis (MS) is a leading cause of incurable progressive disability in young adults caused by inflammation in the central nervous system (CNS) that triggers demyelination, glial cell dysfunction and irreversible neuro-axonal damage1. While considerable progress has been made in treating early inflammatory relapsing-remitting MS, the mechanisms underpinning the progressive stage remain largely unknown. The capacity of microglia, the CNS-resident phagocytes, to clear tissue debris is essential for both maintaining and restoring CNS homeostasis2,3 and this capacity diminishes with age4-6. Age strongly associates with the risk of developing progressive MS7,8. Herein we demonstrate that the recovery from inflammation is dependent on the ability of microglia to clear tissue debris and that blocking this process leads to development of progressive disease in a murine model of MS. Microglia-specific deletion of the general autophagy regulator Atg7, but not the canonical macroautophagy protein Ulk1, led to increased intracellular accumulation of phagocytosed myelin. This further associated with the alteration of the microglial phenotype towards that previously described in other neurodegenerative diseases2,3,9. Moreover, Atg7 deficient microglia showed striking similarities with microglia from aged wild type mice, which also demonstrated accumulation of myelin debris and inability to recover from MS-like disease. In contrast, the induction of autophagy using the disaccharide Trehalose in aged mice led to functional myelin clearance and remission from MS-like disease. Our results demonstrate that a non-canonical form of autophagy in microglia is responsible for myelin clearance and that impairment of this pathway markedly changes microglial phenotype and prevents recovery from MS-like disease. Importantly, we show that using a disaccharide ubiquitously found in plant-derived foods to boost autophagy in cells in which this process is naturally diminished can be utilized for therapeutic purposes.Project was run on 4 lanes with a 10M sequencing depth

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Bassoon proteinopathy drives neurodegeneration in multiple sclerosis

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