Background Heparan sulfate (HS) degradation mediates pulmonary endothelial hyper-permeability and acute pulmonary edema during acute respiratory distress syndrome (ARDS). The aim of this study was to examine whether histone H4 induced HS degradation by activating heparanase (HPSE) in chlorine gas (Cl2)-induced ARDS. Methods Acute lung injury was induced by Cl2 exposure or histone H4 injection in C57BL/6 mice. Histone H4 in bronchoalveolar lavage fluid (BALF) and plasma was measured by ELISA. HS degradation was measured by immunostaining, ELISA, and flow cytometry. HPSE mRNA and protein were measured by real-time qPCR and western blot analysis, respectively, at preset timepoints. The HPSE inhibitor OGT2115 and specific siRNAs were used to study the role of HPSE during HS degradation caused by Cl2 exposure or histone H4 challenge. Blocking antibodies against TLR1, TLR2, TLR4, or TLR6 were used in vitro to investigate which signaling pathway was involved. The transcriptional regulation of HPSE was studied vis-à-vis NF-κB, which was assessed by nuclear translocation of NF-κB p65 and phosphorylation of I-κBα protein. Results Histone H4 in BALF and plasma increased evidently after Cl2 inhalation. Cl2 exposure or histone H4 challenge caused obvious acute lung injury in mice, and the pulmonary glycocalyx was degraded evidently as observed from endothelial HS staining and measurement of plasma HS fragments. Pretreatment with OGT2115, an HPSE inhibitor, relieved the acute lung injury and HS degradation caused by Cl2 exposure or histone H4 challenge. Targeted knockdown of HPSE by RNA interference (RNAi) significantly inhibited histone H4 induced HS degradation in HPMECs, as measured by immunofluorescence and flow cytometry. By inducing phosphorylation of I-κB α and nuclear translocation of NF-κB p65, histone H4 directly promoted mRNA transcription and protein expression of HPSE in a dose-dependent manner. Additionally, a blocking antibody against TLR4 markedly inhibited both activation of NF-κB and expression of HPSE induced by histone H4. Conclusions Histone H4 is a major pro-inflammatory mediator in Cl2-induced ARDS in mice, and induces HS degradation by activating HPSE via TLRs- and NF-κB-signaling pathways.

Background: Chlorine gas (Cl2) exposure remains a public health concern in household, occupational, and transportation accidents around the world. The death rate associated with acute respiratory distress syndrome (ARDS) caused by high concentrations of Cl2 is very high, mainly because the pathogenesis of ARDS remains unclear. Histone H4 has been identified as an important endogenous pro-inflammatory molecule. The present study aimed to examine the pathogenic role of histone H4 in Cl2-induced ARDS.Methods: ARDS was induced by Cl2 exposure in male C57BL/6 mice. Circulating histone H4, blood gas, pulmonary edema, endothelial activation, and neutrophil infiltration were measured during acute lung injury (ALI). Histone H4 or anti-H4 antibody was administered through the tail vein 1 h prior to Cl2 exposure to study the pathogenic role of histone H4. Toll-like receptor 2 knock-out (Tlr2-KO) and Tlr4-KO mice were used in conjunction with blocking antibody against TLR1, TLR2, TLR4, or TLR6 to explore the mechanism involved in histone H4-mediated injury.Results: Cl2 exposure induced a concentration-dependent ALI. The levels of circulating histone H4 were positively correlated with Cl2 concentrations. Pretreatment with intravenous histone H4 further aggravated lethality rate, blood gas, endothelial activation, and neutrophil infiltration, while anti-H4 antibody showed protective effects. Tlr4 deficiency improved lethality rate, blood gas, and pulmonary edema, and prevented endothelial and neutrophil activation caused by Cl2 exposure. More importantly, Tlr4 gene deletion greatly diminished the effect of histone H4 or anti-H4 antibody observed in wild-type (WT) mice. The impact of Tlr2 on inflammatory injury was not significant. The role of TLRs was also validated by endothelial activation mediated by histone H4 in vitro.Conclusions: Circulating histone H4 played a pro-inflammatory role in ARDS caused by Cl2. TLR4 was closely involved in histone H4-mediated inflammatory injury. Therefore, intervention targeting histone H4 is potentially protective.

Background: Chlorine gas (Cl 2 ) exposure remains a public health concern in household, occupational, and transportation accidents around the world. The death rate associated with acute respiratory distress syndrome (ARDS) caused by high concentrations of Cl 2 is very high, mainly because the pathogenesis of ARDS remains unclear. Histone H4 has been identified as an important endogenous pro-inflammatory molecule. The present study aimed to examine the pathogenic role of histone H4 in Cl 2 -induced ARDS.Methods: ARDS was induced by Cl 2 exposure in male C57BL/6 mice. Circulating histone H4, blood gas, pulmonary edema, endothelial activation, and neutrophil infiltration were measured during acute lung injury (ALI). Histone H4 or anti-H4 antibody was administered through the tail vein 1 h prior to Cl 2 exposure to study the pathogenic role of histone H4. Toll-like receptor 2 knock-out ( Tlr2 -KO) and Tlr4 -KO mice were used in conjunction with blocking antibody against TLR1, TLR2, TLR4, or TLR6 to explore the mechanism involved in histone H4-mediated injury. Results: Cl 2 exposure induced a concentration-dependent ALI. The levels of circulating histone H4 were positively correlated with Cl 2 concentrations. Pretreatment with intravenous histone H4 further aggravated lethality rate, blood gas, endothelial activation, and neutrophil infiltration, while anti-H4 antibody showed protective effects. Tlr4 deficiency improved lethality rate, blood gas, and pulmonary edema, and prevented endothelial and neutrophil activation caused by Cl 2 exposure. More importantly, Tlr4 gene deletion greatly diminished the effect of histone H4 or anti-H4 antibody observed in wild-type (WT) mice. The impact of Tlr2 on inflammatory injury was not significant. The role of TLRs was also validated by endothelial activation mediated by histone H4 in vitro. Conclusions: Circulating histone H4 played a pro-inflammatory role in ARDS caused by Cl 2 . TLR4 was closely involved in histone H4-mediated inflammatory injury. Therefore, intervention targeting histone H4 is potentially protective.

Background: Chlorine gas (Cl2) exposure remains a public health concern in household, occupational, and transportation accidents around the world. The death rate associated with acute respiratory distress syndrome (ARDS) caused by high concentrations of Cl2 is very high, mainly because the pathogenesis of ARDS is still not very clear. Histone H4 has been identified as an important endogenous pro-inflammatory molecule. The present work aimed to study the pathogenic role of histone H4 in Cl2 induced ARDS. Methods: ARDS was induced by Cl2 exposure in male C57BL/6 mice. Circulating histone H4, blood gas, pulmonary edema, endothelial activation, and neutrophil infiltration were measured during acute lung injury. Histone H4 or anti-H4 antibody was administered through tail vein 1h prior to Cl2 exposure to study the pathogenic role of histone H4. The Toll-like receptor 2 knock-out (Tlr2-KO), Tlr4-KO mice and the blocking antibody against TLR1, TLR2, TLR4 or TLR6 were used to explore the mechanism involved in histone H4 mediated injury. Results: Cl2 exposure induced a concentration dependent acute lung injury. The levels of circulating histone H4 were positively correlated with the concentrations of Cl2. Pretreatment with intravenous histone H4 further aggravated lethality rate, blood gas, endothelial activation, and neutrophil infiltration while the anti-H4 antibody showed protective effects. The deficiency of Tlr4 improved lethality rate, blood gas, and pulmonary edema; prevented endothelial and neutrophil activation caused by Cl2 exposure. More importantly, the gene deletion of Tlr4 diminished greatly the effect of histone H4 or anti-H4 antibody observed in the wild-type (WT) mice. The impact of Tlr2 on inflammatory injury was not significant. The role of TLRs was also validated by endothelial activation mediated by histone H4 in vitro. Conclusions: Circulating histone H4 played a pro-inflammatory role in ARDS caused by Cl2. TLR4 was closely involved in histone H4 mediated inflammatory injury. The intervention targeted at histone H4 is potentially protective.