The Mechanism Study Of HMGB1 Mediating Depressive Behavior Induced By Chronic Stress

Depression is a global neuropsychiatric disorder accompanying by low mood,loss of interest and enjoyment,reduced energy and poor concentration.Until now,traditional medicine has been applied in the clinic,but unfortunately,not all the patients can recover from this disease.Numerous efforts have been devoted to exploring the mechanism underlying the course of depression and recently found that the inflammatory system was one of the major contributors.High-mobility group box 1(HMGB1),known as a late inflammatory cytokine,belongs to damage associated molecular patterns(DAMPs),is rolled in some emotional and cognitive dysfunctions.Our previous study implied that the proactive secretion and role of central high mobility group box 1(HMGB1)in lipopolysaccharide(LPS)-induced depressive behavior.Some laboratories and we had also discovered that the kynurenine pathway(KP),activated by early inflammatory factors such as tumor necrosis factor ?(TNF-?),affected the metabolism of the raw tryptophan(Trp),which had become one of the new important mechanisms of depression.Here,we further explored the potential mechanism of HMGB1 mediating chronic-stress-induced depression through the kynurenine pathway(KP)both in vivo and in vitro.Depression model was established with the 4-week chronic unpredictable mild stress(CUMS).Sucrose preference,tail suspension and Barnes maze test were performed to reflect depressive behaviors.Enzyme activity of indoleamine-2,3-dioxygenase(IDO)was reflected with the ratio of kynurenine(KYN)/ tryptophan(Trp),which were determined by combination of ultra high pressure liquid chromatography-tandem mass spectrometer(UHPLC-MS/MS).Gene transcription and protein expression were assayed by real-time RT-PCR and western-blot or ELISA kit respectively.We also use two inhibitors of HMGB1,ethyl pyruvate(EP)and glycyrrhizic acid(GZA),administering daily by intraperitoneal injection at a dose of 40/20 mg/kg respectively.At last,we would use immunofluorescence to detect the microglia marker IBA1,astrocyte marker GFAP and neuron marker NeuN within the hippocampal cell layer in order to analysis the source of HMGB1 in the CUMS mice.In addition,due to its abilities to inhibit the activation of microglia and penetrate the blood-brain barrier(BBB),minocycline(30 mg/kg)was injected intraperitoneally to conduct interference treatment in this study as well.Along with depressive behavior,HMGB1 concentrations in the hippocampus and serum substantially increased post 4-week CUMS exposure.Concurrent with the upregulated HMGB1 protein,the regulator of translocation of HMGB1,sirtuin 1(SIRT1)concentration in the hippocampus remarkably increased.In addition to HMGB1 and SIRT1,IDO,the rate limiting enzyme of KP,was upregulated at the level of mRNA expression and enzyme activity in stressed hippocampi and LPS-treated hippocampal slices.The gene transcription of kynurenine monooxygenase(KMO)and kynureninase(KYNU)in the downstream of KP also increased both in vivo and in vitro.There was no significant effect on the transcripts of 3-hydroxyanthranilate 3,4-dioxygenase(3-HAO)and kynurenine aminotransferase 2(KAT2).Treatment of mice with EP and GZA,prevented the development of depressive behaviors and the activated enzymes in KP.In addition,we found that after four-week CUMS exposure,the release of HMBG1 in hippocampus was mainly derived from microglia and neurons,and minocycline could inhibit the translocation of HMGB1 from both microglia and neurons inducing the important role of microglia.All of these experiments demonstrate that the cell soure of central HMGB1 release and the role of HMGB1 on the induction of depressive behavior is mediated by KP activation.