Isoflurane Neurotoxicity Involves Activation Of Hypoxia Inducible Factor-1α Via Intracellular Calcium In Neonatal Rodents

Objective:Previousl,we found that the inhaled anesthetic isoflurane up-regulated the transcriptional factor hypoxia inducible factor（HIF）-1αprotein levels during induction of neurodegeneration in the brain of neonatal rats.Here,we investigated the role of HIF-1αand the underlying signaling pathway in the neurodegenration induced by isoflurane in rodent developing brain.Methods:Primary hippocampal neurons were exposed to isoflurane（0.4 mM）for 12h.Neuron injury was analyzed by MTT test and quantification of lactate dehydrogenase release.HIF-1αgene expression and transcriptional activity,cleaved caspase-3 and phosphoinositide phospholipase C（PLC）-γgene expression were quantified.Cytosolic calcium concentration was measured by calcium imagine.The role of HIF-1αon juvenile learning and memory impairment induced by isoflurane was studied by fear conditioning and extinction test and Morris water maze test.Results:Isoflurane induced HIF-1αgene expression and transcriptional activity in vitro.Furthermore,pharmacological inhibition of HIF-1αor knockdown of HIF-1αby siRNA counteracted the neurotoxicity of isoflurane.Ca²⁺signaling pathways involving PLC-γactivation are required for isoflurane-evoked HIF-1αaccumulation.Finally,partial deficiency of HIF-1αattenuated isoflurane-induced neurodegeneration in developing brain,juvenile learning and memory impairment induced by isoflurane.Conclusions:HIF-1αactivation via cytosolic Ca²⁺signaling pathway partially play a role in the mechanism of isoflurane-induced neurodegeneration in neonatal rodents,suggesting HIF-1αas potential therapeutic targets for the prevention of the deleterious effects of prolonged exposures to anesthetics.