Mitochondrial biogenesis of astrocytes is increased under experimental septic conditions

Background Mitochondrial dysfunction has been reported to be one of the contributing factors of sepsis-associated encephalopathy （SAE）.Mitochondrial biogenesis controls mitochondrial homeostasis and responds to changes in cellular energy demand.In addition,it is enhanced or decreased due to mitochondrial dysfunction during SAE.The aim of this study was to explore the changes of mitochondrial biogenesis of astrocytes under septic conditions.Methods Lipopolysaccharide （LPS; 50 ng/ml） and interferon-γ （IFN-γ; 200 U/ml） were incubated with astrocytes to model the effects of a septic insult on astrocytes in vitro.The mitochondrial ultrastructure and volume density were evaluated by transmission electron microscopy.Intracellular adenosine triphosphate （ATP） levels were detected by the firefly luciferase system.The expression of protein markers of mitochondrial biogenesis and the binding ability of mitochondrial transcription factor A （TFAM） were determined by western blot and electrophoretic mobility shift assays,respectively.The mitochondrial DNA （mtDNA） content was detected by real-time polymerase chain reaction.Results The number of mildly damaged mitochondria was found to be significantly greater after treatment for 6 hours,as compared with at 0 hour （P＜0.05）.The mitochondrial volume density was significantly elevated at 24 hours,as compared with at 0 hour （P＜0.05）.The ATP levels at 6 hours,12 hours,and 24 hours were significantly greater than those at 0 hour （P＜0.05）.The protein markers of mitochondrial biogenesis were significantly increased at 6 hours and 12 hours,as compared with at 0 hour （P＜0.05）.The TFAM binding activity was not significantly changed among the four time points analyzed.The mtDNA contents were significantly increased at 12 hours and 24 hours,as compared with at 0 hour （P＜0.05）.Conclusions Under septic conditions,mitochonddal biogenesis of astrocytes increased to meet the high-energy demand and to promote mitochondrial recovery.Furthermore,the TFAM-DNA binding ability was not sensitive to sepsis-induced injury.