Reduced Function of the Glutathione S-Transferase S1 Suppresses Behavioral Hyperexcitability in Drosophila Expressing Mutant Voltage-Gated Sodium Channels

Voltage-gated sodium (Na_v) channels play a central role in the generation and propagation of action potentials in excitable cells such as neurons and muscles. To determine how the phenotypes of Na_v-channel mutants are affected by other genes, we performed a forward genetic screen for dominant modifiers of the seizure-prone, gain-of-function Drosophila melanogaster Na_v-channel mutant, para^Shu Our analyses using chromosome deficiencies, gene-specific RNA interference, and single-gene mutants revealed that a null allele of glutathione S-transferase S1 (GstS1) dominantly suppresses para^Shu phenotypes. Reduced GstS1 function also suppressed phenotypes of other seizure-prone Na_v-channel mutants, para^GEFS+ and para^bss Notably, para^Shu mutants expressed 50% less GstS1 than wild-type flies, further supporting the notion that para^Shu and GstS1 interact functionally. Introduction of a loss-of-function GstS1 mutation into a para^Shu background led to up- and down-regulation of various genes, with those encoding cytochrome P450 (CYP) enzymes most significantly over-represented in this group. Because GstS1 is a fly ortholog of mammalian hematopoietic prostaglandin D synthase, and in mammals CYPs are involved in the oxygenation of polyunsaturated fatty acids including prostaglandins, our results raise the intriguing possibility that bioactive lipids play a role in GstS1-mediated suppression of para^Shu phenotypes.