The Transcriptional Response of Caenorhabditis elegans to Ivermectin Exposure Identifies Novel Genes Involved in the Response to Reduced Food Intake

Steven T Laing,Roz Laing,John S Gilleard,Debra J Woods,Sai P Ravikumar,Victoria Butler,Al Ivens,Clotilde K Carlow

doi:10.1371/journal.pone.0031367

Steven T Laing, Roz Laing + Show 6 more

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https://doi.org/10.1371/journal.pone.0031367

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Abstract

We have examined the transcriptional response of Caenorhabditis elegans following exposure to the anthelmintic drug ivermectin (IVM) using whole genome microarrays and real-time QPCR. Our original aim was to identify candidate molecules involved in IVM metabolism and/or excretion. For this reason the IVM tolerant strain, DA1316, was used to minimise transcriptomic changes related to the phenotype of drug exposure. However, unlike equivalent work with benzimidazole drugs, very few of the induced genes were members of xenobiotic metabolising enzyme families. Instead, the transcriptional response was dominated by genes associated with fat mobilization and fatty acid metabolism including catalase, esterase, and fatty acid CoA synthetase genes. This is consistent with the reduction in pharyngeal pumping, and consequential reduction in food intake, upon exposure of DA1316 worms to IVM. Genes with the highest fold change in response to IVM exposure, cyp-37B1, mtl-1 and scl-2, were comparably up-regulated in response to short–term food withdrawal (4 hr) independent of IVM exposure, and GFP reporter constructs confirm their expression in tissues associated with fat storage (intestine and hypodermis). These experiments have serendipitously identified novel genes involved in an early response of C. elegans to reduced food intake and may provide insight into similar processes in higher organisms.

Highlights

The macrocyclic lactone ivermectin (IVM) is one of the most important drugs used for the control of animal and human parasites [1,2]
The transcriptional response of C. elegans strain DA1316 exposed to IVM is dominated by genes associated with fat mobilization and fatty acid metabolism
The transcriptional response of the C. elegans strain DA1316 (avr14(ad1302); avr-15(vu227); glc-1(pk54)) to IVM appears to be dominated by genes associated with the consequences of food deprivation, such as changes to fatty acid metabolism, many of which are conserved in higher mammals

Summary

Introduction

The macrocyclic lactone ivermectin (IVM) is one of the most important drugs used for the control of animal and human parasites [1,2]. It acts by irreversibly binding to, and activating, ligand-gated ion channels, glutamate-gated chloride channels (GluCls), resulting in paralysis of the body wall and pharyngeal muscles [14,15,16]. In order to minimise nonspecific, stress-related changes in the transcriptome following drug exposure, we made use of the strain DA1316, which has a null mutation in three subunits of the glutamate-gated chloride channel target of IVM. This strain is largely resistant to the paralytic effects of IVM on the body wall, we found that following four hours exposure to high doses of the drug there is a significant decrease in pharyngeal function. To the authors’ knowledge this is the first unbiased, wholegenome investigation of the immediate effects of food deprivation in C. elegans and in any whole organism

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Methods