Transient Receptor Potential Melastatin (TRPM) Channels Mediate Clozapine-induced Phenotypes in Caenorhabditis elegans

Abstract

The molecular mechanisms of action of antipsychotic drugs (APDs) are not fully understood. Here, we characterize phenotypes of missense and knockout mutations in the Caenorhabditis elegans transient receptor potential melastatin (TRPM) channel ortholog gtl-2, a candidate APD target identified in a genome-wide RNAi (RNA interference) screen for Suppressors of Clozapine-induced Larval Arrest (scla genes). We then employ the developmental phenotypes of gtl-2(lf) mutants to validate our previous gtl-2(RNAi) result. GTL-2 acts in the excretory canal cell to regulate Mg²⁺ homeostasis. Using exc (excretory canal abnormal) gene mutants, we demonstrate that excretory canal cell function is necessary for clozapine-induced developmental delay and lethality. Moreover, cell-specific promoter-driven expression studies reveal that GTL-2 function in the excretory canal cell is important for its role in the SCLA phenotype. We then investigate the mechanism by which GTL-2 function in the excretory canal cell impacts clozapine-induced phenotypes. gtl-2(lf) mutations cause hypermagnesemia, and we show that exposure of the wild-type strain to high Mg²⁺ phenocopies gtl-2(lf) with respect to suppression of clozapine-induced developmental delay and lethality. Our results suggest that GTL-2 TRPM channel function in the excretory canal cell is important for clozapine's developmental effects. TRP channels are expressed in mammalian brain and are implicated in the pathogenesis of mental illnesses but have not been previously implicated in APD action.

Keywords::

• antipsychotic drug
• Caenorhabditis elegans
• clozapine
• GTL-2
• genome-wide RNAi screen
• schizophrenia
• transient receptor potential melastatin (TRPM) channel

ACKNOWLEDGMENTS

We would like to thank Dr. Taixiang Saur in the Buttner laboratory at McLean Hospital and Drs. Michael Francis and Navonil Banerjee in the Department of Neurobiology at University of Massachusetts Medical School (Worcester, Massachusetts) for assistance with voltage-clamp recordings of Xenopus oocytes. We thank Dr. Kai Sonntag and members of the Buttner laboratory for comments on the manuscript. We thank WormBase. We thank Dr. E. J. Lambie at Ludwig-Maximilians-Universität (Munich, Germany), Dr. Y. Jin at University of California San Diego (La Jolla, California), and Dr. L. Chen at University of Minnesota (Minneapolis, Minnesota) for strains used in this work. Some strains were provided by the Caenorhadbitis Genetics Center, which is funded by National Institutes of Health Office of Research Infrastructure Programs (P40 OD010440). This research was supported by a Shervert Frazier Research Institute Grant to E.A.B. and a Stanley Medical Research Institute Grant to B.M.C.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.