Determining the mechanism of anesthetic-induced neurotoxicity in a Drosophila model of mitochondrial disease
Authors: Zachariah Olufs; David Wassarman; Misha Perouansky
Affiliation: University of Wisconsin - Madison, Madison, WI
Keywords: h. mitochondria; a. stress responses
General anesthetics are broadly used and are safe in healthy individuals. However, adverse sequelae collectively referred to as anesthetic-induced neurotoxicity (AiN) have been reported in pre-clinical animal models and clinical studies of mitochondrial disease. Leigh Syndrome (LS) is the most common pediatric manifestation of mitochondrial disease. Over 75 distinct genes underlie LS, including mutations in Complex I of the mitochondrial electron transport chain. To investigate the mechanism of AiN, we have characterized flies carrying a mutation in ND23, which encodes a core subunit of Complex I and is orthologous to mammalian NDUFS8. We previously found that ND23 mutants are behaviorally sensitive to two volatile general anesthetics (VGAs), isoflurane (Iso) and sevoflurane (Sevo). Furthermore, Iso, but not Sevo, causes mortality within 24 hours of exposure, the extent of which is dependent on oxygen concentration ([O2]) during exposure; low [O2] (hypoxia) reduces mortality and high [O2] (hyperoxia) increases mortality. To identify genes involved in the differential response of ND23 mutants to different anesthetics and to different oxygen concentrations, we performed RNA-seq analysis of fly heads. We found that Iso and Sevo differentially affected expression of chaperone and antioxidant genes, but high and low [O2] did not appreciably influence gene expression. To test whether differential expression of chaperones or antioxidant genes is responsible for the difference in mortality between Iso- and Sevo-exposed flies, we used orthologous approaches to induce the transcriptional responses prior to anesthesia exposure, since exposure to a non-injurious stress might initiate protective mechanisms that would result in a state of tolerance to the subsequence injurious stress. We found that pre-exposure to Sevo or heat shock did not reduce mortality from a subsequent exposure to Iso. These data argue against a role for transcriptional activation of chaperone and antioxidant genes in the mortality mechanism. We are currently testing other non-injurious stressors as well as using loss-of-function genetic approaches to test whether the transcriptional response or excess oxygen are necessary for Iso-induced mortality in the context of the ND23 mutant.