Investigating the role of the innate immune system, oxidative stress, and cell death in a Drosophila model of epilepsy
Creators: name: Nukala, Krishna Madhav
Publisher: name: University of Iowa
Year: 2022
Subjects: subject: Anti-microbial peptides
subject: Drosophila
subject: Neurodegeneration
subject: Prickle
subject: public abstract
subject: Epilepsy
subject: Genetics
subject: FOS: Biological sciences
subject: Oxidative Stress

description: Epilepsy is a debilitating neurological disorder characterized by recurrent seizures and affectsnearly 1% of the United States population. The underlying disease mechanisms of many epileptic disorders are still unknown and about one-third of patients do not respond to currently available anti-epileptic drugs. Previous work in our laboratory has shown that mutations in the Drosophila isoform of a planar cell polarity gene, prickle-spiny-legs (pksple), lead to spontaneous myoclonic like epilepsy and ataxia, similar to what was observed in human PRICKLE patients. In this work, we show that the spontaneous seizures in pksple mutants are neuronal in origin, and transcriptomic analysis of the brains of pksple mutants revealed a robust upregulation of genes related to the innate immune response (IIR) and oxidative stress pathways. Next, we demonstrated that the glial cells in the brain are the source of IIR upregulation in pksple mutants and that sustained neuronal cell death and exacerbation of seizures occurs across adulthood in pksple mutants. We also provided evidence of increased oxidative stress occurring in the 3rd instar larval developmental stage of pksple mutant brains. Given that brain IIR induction and neuronal cell death has been observed in various fly models of neurological diseases, we decided to test whether inhibiting neuronal cell death and glial IIR might suppress the increase in neuronal cell death and exacerbation of seizures in pksple mutants. Using the Gal4/UAS system in combination with immunohistochemical and behavioral analyses, we first demonstrated that inhibiting neuronal cell death in pksple mutants by expressing an apoptotic inhibitor only in the neurons significantly suppressed spontaneous seizures. Next, genetically ablating either the Toll or Imd arm of the Drosophila IIR pathway specifically in the glia lead to a significant reduction in neuronal cell death as well as spontaneous seizures in pksple mutants, demonstrating that glial IIR significantly contributes to the sustained neuronal cell death and exacerbation of seizures occurring in pksple mutants.
description: After uncovering the role of IIR in pksple mutants, we wanted to understand the biological role of pk isoforms in the Drosophila nervous system and decided to assess the different neurological phenotypes occurring in pkpk mutants and compared them to what we see in our pksple mutant flies. We observed that similar to pksple mutants, pkpk mutants also showed a robust upregulation of IIR and oxidative stress pathway genes in the brain. While both mutants showed a significant increase in neuronal cell death and reduction in lifespan, these phenotypes were more severe in the pkpk mutants. Contrastingly, we also demonstrated that pksple mutants exhibit locomotion, learning and nociception phenotypes while pkpk mutants do not. These data suggest that pkpk could be the major isoform in the Drosophila nervous system and that both pk isoforms could be expressed and/or required in different neuronal populations.
description: In conclusion, we demonstrate the first genetic evidence in any organism that the glial IIR is contributing to the increased neuronal cell death and exacerbation of seizures using a Drosophila model of human epilepsy. We also provide evidence for the role of oxidative stress in leading to increased neuronal cell death and exacerbation of seizures in pksple mutants which suggests that oxidative stress, in combination with IIR and neuronal cell death, is leading to seizure progression in pksple mutants. Furthermore, translating these findings to other fly models of common epilepsy disorders will enable researchers to develop novel strategies to treat epileptic patients.