Large-scale functional RNAi screen in C. elegans identifies genes that regulate the dysfunction of mutant polyglutamine neurons

Abstract

BackgroundA central goal in Huntington's disease (HD) research is to identify and prioritize candidate targets for neuroprotective intervention, which requires genome-scale information on the modifiers of early-stage neuron injury in HD.ResultsHere, we performed a large-scale RNA interference screen in C. elegans strains that express N-terminal huntingtin (htt) in touch receptor neurons. These neurons control the response to light touch. Their function is strongly impaired by expanded polyglutamines (128Q) as shown by the nearly complete loss of touch response in adult animals, providing an in vivo model in which to manipulate the early phases of expanded-polyQ neurotoxicity. In total, 6034 genes were examined, revealing 662 gene inactivations that either reduce or aggravate defective touch response in 128Q animals. Several genes were previously implicated in HD or neurodegenerative disease, suggesting that this screen has effectively identified candidate targets for HD. Network-based analysis emphasized a subset of high-confidence modifier genes in pathways of interest in HD including metabolic, neurodevelopmental and pro-survival pathways. Finally, 49 modifiers of 128Q-neuron dysfunction that are dysregulated in the striatum of either R/2 or CHL2 HD mice, or both, were identified.ConclusionsCollectively, these results highlight the relevance to HD pathogenesis, providing novel information on the potential therapeutic targets for neuroprotection in HD.

Experimental Models for Identifying Modifiers of Polyglutamine-Induced Aggregation and Neurodegeneration

“…An interesting observation from these C. elegans genetic screens was the minimal overlap between the hits derived from aggregation screens [102,105] and those from the toxicity screen described previously [101]: only 15 modifiers were identified in common. This emphasizes the critical roles of assay readouts (e.g., aggregation vs toxicity), and of molecular and cellular context in such genetic screens.…”

“…This system was used to investigate the effect of increased sir2.1 deacetylase activity in rescuing nematode neurons from polyQ-mediated toxicity [100]. The Q128 nematode model was also used in a large-scale RNAi screen to identify genes that would either reduce or exacerbate the loss of response to light touch [101]. An intriguing observation was that some of the RNAi hits from this C. elegans screen overlapped with striatal gene expression data derived from the CHL2 (Q150/Q150 knock-in) and the transgenic R6/2 mouse models of HD, underscoring the relevance of using invertebrate models for the identification of potential therapeutic targets for human neurodegenerative diseases.…”

“…In particular, the druggable pha gene, which encodes the enzyme phenylalanine-4-hydroxylase, was of interest because of its connection to the tyrosine-dopamine biosynthesis pathway, which is known to be associated with early HD phenotypes [101] In a broader approach, a genome-wide RNAi screen was done in a C. elegans transgenic strain expressing stretches of 35 Q (polyQ35) fused with yellow fluorescent protein specifically in muscle cells [102]. This study yielded 186 genes that, when knocked down, caused premature aggregation of polyQ35 aggregates, including the TCP-1 chaperonin ortholog later confirmed to have a role in aggregation of mHTT in mammalian cells [54,55,103].…”

All the microbiology nematodes can teach us

“…Gerstein et al 2010;Lamm et al 2011;Vergara et al 2014), and the model nematode subjected to many genetic screens (e.g. Lejeune et al 2012;Roy et al 2014). Although less staggering in other model organisms (e.g.…”

Network analysis of human post-mortem microarrays reveals novel genes, microRNAs, and mechanistic scenarios of potential importance in fighting huntington's disease

“…Such models also helped to identify genes that regulate the dysfunction of mutant polyglutamine neurons [15]. Brain-derived neurotrophic factor (BDNF) has been suggested to reduce amyloid-β neurotoxicity in Alzheimer's disease [16], [17], [18].…”