Abstract
BACKGROUND: The vulnerable period to neurotoxicity of isoflurane overlaps with a developmental stage characterized by programmed neuronal death. STAT3 has been identified as a crucial molecule involved in survival pathways during this period. We aimed to investigate the role of STAT3 in cellular vulnerability to isoflurane. METHODS: C57/BL6 mice on postnatal day 7 or 21, primary neurons derived from mice embryos at gestational days 14-16 and cultured for 5 or 14 days, as well as human neuroglioma U251 cells were treated with isoflurane. A plasmid containing human wild-type STAT3, STAT3 anti-sense oligonucleotide, STAT3 specific inhibitor STA21, proteasome inhibitor MG-132 and calcineurin inhibitor FK506 were utilized to evaluate the influence of STAT3 levels on isoflurane-induced cytotoxicity. The levels of Western blot results, mRNA, intracellular ROS, apoptotic rate, and calcineurin activity were analyzed using unpaired Student's t-test or one-way ANOVA followed by Bonferroni post hoc test, as appropriate. RESULTS: Elevated levels of STAT3, reduced activity of calcineurin, as well as a diminished response to isoflurane-induced calcineurin activation and neuroapoptosis were observed in more mature brain or neurons. Isoflurane accelerated the degradation of ubiquitin-conjugated proteins but did not facilitate ubiquitin conjugation to proteins. STAT3 was of particular importance in the all ubiquitin-conjugated proteins degraded by isoflurane. Knockdown or inhibition of STAT3 nuclear translocation exacerbated isoflurane-induced oxidative injury and apoptosis, while STAT3 overexpression mitigated these effects. Finally, this study demonstrated that FK506 pretreatment mitigated the apoptosis, ROS accumulation, and the impairment of neurite growth in primary neurons after exposed to isoflurane. CONCLUSIONS: These findings indicate that specific regulation of STAT3 was closely related with the cellular vulnerability to isoflurane via an antioxidative pathway.