Roles of hemocytes and bioactive lipids in the modulation of neuronal excitability and seizure behavior in Drosophila voltage-gated sodium channel mutants

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PROJECT SUMMARY Local and systemic interactions between the nervous system and immune system play important roles in various physiological and pathological processes. The long-term goal of this project is to obtain a fundamental understanding of how neuroimmune communications contribute to the regulation of neural development, physiology, and behavior using an experimental model organism Drosophila melanogaster possessing the evolutionarily conserved innate immune system. The overall objective in this application is to reveal the roles and mechanisms of functional interactions between innate immune cells and the central nervous system in the modulation of neuronal excitability and behavioral hyperactivity in seizure-prone fly voltage-gated sodium (Nav) channel mutant, paraShu. The project is based on intriguing findings that: 1) paraShu adult seizure severity is significantly suppressed by diet supplemented with -3 polyunsaturated fatty acids (PUFAs) -linolenic acid (ALA); 2) hemocyte (macrophage-like blood cell)-specific knockdown of GstS1, a fly ortholog of mammalian prostaglandin D synthase, mimics the effect of dietary ALA; and 3) both dietary ALA and GstS1 knockdown are effective during development to suppress seizures in adult mutants. The central hypothesis is that the severity of adult paraShu is modulated through neural development by the action of innate immune cells in the biological processes involving bioactive lipid mediators. Two specific aims will be pursued to investigate the hypothesis: 1) Define the roles of hemocytes in modulation of neuronal excitability and behavioral hyperactivity in paraShu mutants; and 2) Identify genes and signaling pathways involved in hemocyte-dependent modulation of adult seizures. For the first aim, hemocyte functions will be genetically perturbed and the effects on neural development, electrophysiological properties, and seizure behavior will be examined in the presence or absence of phenotypic modifiers using freely moving or tethered behaving adult flies as well as dissociated primary neuronal cultures prepared from mutant larval brains. For the second aim, a candidate gene approach will be used to identify genes involved in putative lipid signaling processes, and lipidomics analysis will be carried out to determine the changes in oxylipins, lipid mediators produced from PUFAs, in the mutants in the presence or absence of phenotypic modifiers. The proposed multidisciplinary research is expected to reveal the roles of hemocytes in the diet-dependent modulation of neuronal excitability and behavioral seizures in Nav channel mutants, and provide novel genetic and molecular insights into the largely unexplored lipid signaling pathways that play important roles in the modulation of genetically predisposed neurological phenotypes. The project is scientifically and clinically significant because it will lead to a deeper appreciation of the plastic and interactive nature of the nervous system controlled by the immune system, and is expected to provide valuable insights into future strategies to prevent and treat nervous system disorders associated with aberrant immune function.