Caenorhabditis elegans provides an efficient drug screening platform for GNAO1-related disorders and highlights the potential role of caffeine in controlling dyskinesia

Abstract

Dominant GNAO1 mutations cause an emerging group of childhood-onset neurological disorders characterized by developmental delay, intellectual disability, movement disorders, drug-resistant seizures, and neurological deterioration. GNAO1 encodes the α-subunit of an inhibitory GTP/GDP-binding protein regulating ion channel activity and neurotransmitter release. The pathogenic mechanisms underlying GNAO1-related disorders remain largely elusive and there are no effective therapies. Here, we assessed the functional impact of two disease-causing variants associated with distinct clinical features, c.139A > G (p.S47G) and c.662C > A (p.A221D), using Caenorhabditis elegans as a model organism. The c.139A > G change was introduced into the orthologous position of the C. elegans gene via CRISPR/Cas9, whereas a knock-in strain carrying the p.A221D variant was already available. Like null mutants, homozygous knock-in animals showed increased egg laying and were hypersensitive to aldicarb, an inhibitor of acetylcholinesterase, suggesting excessive neurotransmitter release by different classes of motor neurons. Automated analysis of C. elegans locomotion indicated that goa-1 mutants move faster than control animals, with more frequent body bends and a higher reversal rate, and display uncoordinated locomotion. Phenotypic profiling of heterozygous animals revealed a strong hypomorphic effect of both variants, with a partial dominant-negative activity for the p.A221D allele. Finally, caffeine was shown to rescue aberrant motor function in C. elegans harboring the goa-1 variants; this effect is mainly exerted through adenosine receptor antagonism. Overall, our findings establish a suitable platform for drug discovery, which may assist in accelerating the development of new therapies for this devastating condition, and highlight the potential role of caffeine in controlling GNAO1-related dyskinesia.

Mouse Models Characterize GNAO1 Encephalopathy as a Neurodevelopmental Disorder Leading to Motor Anomalies: from a Severe G203R to a Milder C215Y Mutation

“…Further, similar modeling has proven successful in Drosophila (Gαo[G203R]/+ model with reduced locomotion and life span, responding to a pharmacological rescue [16]). In contrast, attempts to generate similar heterozygous models in the nematode did not produce clear dominant phenotypes [10,34].…”

Mouse models characterize GNAO1 encephalopathy as a neurodevelopmental disorder leading to motor anomalies: from a severe G203R to a milder C215Y mutation

“…Further, similar modeling has proven successful in Drosophila ( Gαo[G203R]/ + model with reduced locomotion and life span, responding to a pharmacological rescue [ 35 ]). The modeling of GNAO1 encephalopathy has also been performed in C.elegans , with the nematodes heterozygous for S47G or A221D mutations revealing the dominant "unlaid eggs" phenotype indicative of effects in motor neurons, while the heterozygous G42R or R209C mutations produced the dominant aldicarb hypersensitivity effects [ 36 , 37 ]. In contrast to these knock-in modeling, over/mis-expression of mutant Gαo on top of the two wt alleles can be envisioned.…”

Efficacy of Caffeine in ADCY5‐Related Dyskinesia: A Retrospective Study

“…8,9 In addition, caffeine was shown to improve hyperactivity and locomotion in Caenorhabditis elegans mutants harboring mutations causing the closely related disorder of GNAO1-related dyskinesia, which likely result in AC5 activation. 10 Caffeine was therefore tried in other patients, with remarkable efficacy. 11,12 Due to the rarity of ADCY5-related dyskinesia and the fact that caffeine is an everyday consumer product, the conduct of a regular randomized study is extremely challenging: first, for most patients, stopping caffeine and possibly receiving a placebo for weeks was unconceivable; second, there was a risk of not achieving significance due to the high variability in doses and intervals, irrespective of weight, between patients.…”