Using Caenorhabditis elegans to fight human neurodegenerative diseases

Abstract

Debilitating age-associated neurodegenerative disorders (NDs) are a major public health challenge in increasingly ageing societies. Currently approved therapeutics are successful in slowing the progression of NDs but not in reversing or preventing the symptoms. A major goal of neurodegeneration research is therefore to identify potential new therapies for these devastating and eventually fatal disorders. In this study, multiple well-defined C. elegans neurodegeneration models were integrated to uncover effective therapeutic interventions that target shared pathogenic pathways. Using locomotion behaviour and lifespan as phenotypic readouts, the well-established anti-epileptic drug ethosuximide was identified as a promising compound with the potential to combat more than one ND. It not only rescued the short lifespan and chemosensory defects of a C. elegans null mutant model of the rare autosomal dominant human ND known as adult-onset neuronal ceroid lipofuscinosis (ANCL), but also ameliorated the mobility defect and short lifespan of worm tauopathy and polyglutamine models based on transgenic expression of mutant human disease proteins. The ability of ethosuximide to rescue these phenotypes did not correlate well with levels of aggregated Tau and polyglutamine protein, suggesting that ethosuximide suppresses proteotoxicity without preventing protein aggregation. Although the main proposed therapeutic target of ethosuximide in epilepsy is the T-type calcium channel, deletion of its worm homologue, cca-1, did not affect the increase in locomotion and lifespan in the tauopathy model. This suggests that ethosuximide counteracts proteotoxicity via a novel mechanism. To further investigate how ethosuximide might exert its neuroprotective properties, we conducted global gene expression analyses using the Affymetrix C. elegans whole genome microarray platform and compared the transcriptome of ethosuximide-treated ANCL models and wild-type worms to that of unexposed controls. Various downstream bioinformatic investigations including gene ontology analyses, regulatory motif discovery, publication enrichment analysis, comparative analyses with curated data sources and literature were performed and revealed a wide range of DAF-16-dependent transcriptional alterations. C. elegans DAF-16 is the sole orthologue of the mammalian FOXO family of transcription factors (TFs) that are implicated in the regulation of a wide range of physiological processes. Genes commonly regulated in ethosuximide-treated animals have varied roles in lipid metabolism, redox homeostasis, longevity/ageing, chromatin remodelling and ubiquitination. Many ethosuximide-responsive genes also contained DAF-16 regulatory elements within their promoter regions and were known to be among the top most responsive DAF-16 TF targets. The importance of DAF-16 in ethosuximide-mediated protection was further substantiated by RNA interference and cell culture experiments. Ethosuximide was shown to consistently induce the transcriptional activity of a subset of mammalian FOXO target genes and conferred protection against expanded polyglutamine peptides-induced aggregation in mammalian neuronal cells. These findings should encourage further screening and characterisation of other neuroprotective compounds, and ultimately may assist in expediting translational drug research and clinical testing for new therapeutic targets to combat protein conformational disorders in general.