The Effect And Receptor Mechanism Of Distinct Redox States Of HMGB1 In Depressive-like Behavior

Depression disorder is a common,chronic and life debilitating mental illness and the pathogenesis has not yet been fully elucidated.On the basis of inflammatory hypothesis,we aim to investigate the role and potential mechanisms of HMGB1 on the induction of depressive behavior.High mobility group box 1(HMGB1)plays an important role in some of the pathogenesis of autoimmune diseases as a late inflammatory mediator.Increasing evidence has indicated that HMGB1 is widely involved in the mediation of neuroinflammatory process.Our previous study suggested that the release of central HMGB1 acts as a late-phase mediator in lipopolysaccharide(LPS)-induced depression.As a ubiquitous nonhistone chromosomal protein,HMGB1 is mainly located in the nucleus under physiological condition.When subjected to various stressors,biologically active HMGB1 may be transported to the cytosol,further excreted into the extracelluar space and cause a series of reactions.In this process,the cysteines at positions 23,45,and 106 within a protein are oxidized to form different redox forms of HMGB1,namely,fully reduced HMGB1(fr-HMGB1),disulfide HMGB1(ds-HMGB1)and fully oxidized HMGB1(ox-HMGB1).Fr-HMGB1 functions as a chemotactic factor via interactions with the RAGE receptor and potentiates chemotactic activity via interactions with CXC-chemokine receptor 4(CXCR4)and the formation of a heterocomplex with CXC chemokine ligand 12(CXCL12)chemokine.In contrast,ds-HMGB1 exerts proinflammatory effects via binding to TLRs.Ox-HMGB1 is not associated with an in vivo function.Recent findings indicate that the redox state of HMGB1 is a critical determinant of its immunomodulatory properties.Here,we aimed to investigate the potential mechanisms that link the redox states of HMGB1 to depression in mice.To further confirm this finding,the HMGB1 level in the chronic unpredictable mild stress(CUMS)depression model was measured.Following the 4-week CUMS exposure,the sucrose preference test(SPT)and tail suspension test(TST)were performed to assess the depressive status of the mice.The serum and cortex HMGB1 proteins were measured by enzyme-linked immunosorbent assay(ELISA)and western blot(WB),respectively.Next,distinct redox forms of recombinant HMGB1(rHMGB1)were used that included fr-HMGB1,which acted as a chemokine,and ds-HMGB1,which possessed cytokine activity.Fr-HMGB1 in vivo was partially oxidized into ds-HMGB1;thus,the mutant protein non-oxidizable chemokine-HMGB(nonoxid-HMGB1)was applied.A single dose of rHMGB1(200ng/5μl/mice)or vehicle was administered to mice via intracerebroventricular(i.c.v.)injection.The receptor inhibitors of TLR4/RAGE/CXCR4(TAK-242/FPS-ZM1/AMD3100)(3 mg/kg)were intraperitoneally injected 30 min prior to rHMGB1 treatment.Depressive-like behavior was measured 20 h post i.c.v.injection.We also assessed the neuroinflammation status following rHMGB1 administration and expression of myelin basic protein(MBP)was assayed for further mechanistic investigation.Concurrent with depressive behavior induced by four-week stress exposure,the HMGB1 concentrations in the serum and cerebral cortex substantially increased.Administration of fr-HMGB1 prolonged the immobility duration in the TST and decreased sucrose preference.In addition to depressive behavior,the hippocampal TNF-? protein slightly increased.These depressive behaviors and upregulation of hippocampal TNF-? were alleviated or abrogated by pretreatment with the inhibitors AMD3100,FPS-ZM1,and TAK-242.Alternatively,nonoxid-HMGB1 failed to induce TNF-? protein or prolong the immobility duration.As expected,ds-HMGB1 administration substantially upregulated hippocampal TNF-? protein,increased the immobility time in the TST and decreased sucrose preference.Moreover,both glycyrrhizin and TAK-242 improved ds-HMGB1 induced depressive behavior.Furthermore,TAK-242 significantly blocked the upregulation of hippocampal TNF-? protein and protected hippocampal myelin basic protein from ds-HMGB1-induced reduction.These drugs had no effect on the total or central distance in the open field test.Collectively,this initial experiment demonstrates the role and receptor mechanisms of HMGB1 under different redox states on the induction of depressive-like behavior.Both ds-HMGB1 and fr-HMGB1 may induce depressive-like behavior in vivo mainly via neuroinflammatory response activation.