title: cGMP-Dependent Protein Kinase Inhibition Extends the Upper Temperature Limit of Stimulus-Evoked Calcium Responses in Motoneuronal Boutons of Drosophila melanogaster Larvae.
abstract: While the mammalian brain functions within a very narrow range of oxygen concentrations and temperatures, the fruit fly, Drosophila melanogaster, has employed strategies to deal with a much wider range of acute environmental stressors. The foraging (for) gene encodes the cGMP-dependent protein kinase (PKG), has been shown to regulate thermotolerance in many stress-adapted species, including Drosophila, and could be a potential therapeutic target in the treatment of hyperthermia in mammals. Whereas previous thermotolerance studies have looked at the effects of PKG variation on Drosophila behavior or excitatory postsynaptic potentials at the neuromuscular junction (NMJ), little is known about PKG effects on presynaptic mechanisms. In this study, we characterize presynaptic calcium ([Ca2+]i) dynamics at the Drosophila larval NMJ to determine the effects of high temperature stress on synaptic transmission. We investigated the neuroprotective role of PKG modulation both genetically using RNA interference (RNAi), and pharmacologically, to determine if and how PKG affects presynaptic [Ca2+]i dynamics during hyperthermia. We found that PKG activity modulates presynaptic neuronal Ca2+ responses during acute hyperthermia, where PKG activation makes neurons more sensitive to temperature-induced failure of Ca2+ flux and PKG inhibition confers thermotolerance and maintains normal Ca2+ dynamics under the same conditions. Targeted motoneuronal knockdown of PKG using RNAi demonstrated that decreased PKG expression was sufficient to confer thermoprotection. These results demonstrate that the PKG pathway regulates presynaptic motoneuronal Ca2+ signaling to influence thermotolerance of presynaptic function during acute hyperthermia.
authors.affiliation: Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida, United States of America.
authors.forename: Jennifer L
authors.identifier: http://orcid.org/0000-0002-4598-1450
authors.initials: JL
authors.lastname: Krill
authors.affiliation: Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida, United States of America.
authors.forename: Ken
authors.initials: K
authors.lastname: Dawson-Scully
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000172:deficiency / Q000235:genetics*; D029721:Drosophila Proteins / Q000172:deficiency / Q000235:genetics; D004331:Drosophila melanogaster / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D007814:Larva / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D009046:Motor Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D034622:RNA Interference; D009435:Synaptic Transmission / Q000187:drug effects / Q000235:genetics; D013696:Temperature; D000071436:Thermotolerance / Q000187:drug effects / Q000235:genetics
chemical_list: D029721:Drosophila Proteins; D047428:Protein Kinase Inhibitors; D017869:Cyclic GMP-Dependent Protein Kinases; C528566:for protein, Drosophila; D002118:Calcium