Studies On Mechanism Of HIF-1α Expression Increase In Murine Tissues With Acute Imflammation Induced By Lipopolysaccharide

Objective To explore the effects of nuclear factor-κB inhibitor, N-acetylcysteine on inflammatory injury induced by lipopolysaccharide (LPS) and their molecular mechanisms.Methods Balb/c mice were divided into three groups: inflammation group, administrating group, and control group. The mouse model of acute inflammatory injuries was set up by tail vein injection with the bacillus calmette-guerin (BCG) and LPS respectively prior and posterior to administration of nuclear factor-κB inhibitor, N-acetylcysteine. The pathological changes in the hepatic and pulmonic tissues were observed and compared by common histopathological methods. The semi-quantitive RT-PCR was performed to detect the expression of HIF-1αand VEGF mRNA. The immunohistochemistry SP method was performed to detect the expression of HIF-1αand VEGF proteins. The ELISA method was performed to detect the protein level of TNF-αin the blood serum .The peritoneal macrophages from normal Balb/c mice were collected and the cells were incubated after adding NAC and LPS (NAC+LPS group) or LPS (experimental group) or PBS (control group) for 10 hours. The mRNA expressions of HIF-1αand TNF-αin the cells were measured by semi-quantitive RT-PCR. The protein expression of HIF-1αand VEGF was detected by method of immunocytochemistry.Result In vivo, the protein level of TNF-αin the blood serum of inflammation group was obviously higher than that of control group (p<0.01). The expression level of HIF-1αprotein, VEGF mRNA and its protein in the hepatic and pulmonic tissues of administrating group was significantly lower than that of inflammation group (p<0.01). In the blood serum of administrating group, the protein level of TNF-αwas lower than in the inflammation group (p<0.01), though the mRNA level of HIF-1αin the hepatic and pulmonic tissues of administrating group was not altered (P>0.05). In vitro under normoxic environment, the protein level of HIF-1αand VEGF, and the mRNA level of TNF-αwere down-regulated by NAC (p<0.01), but the mRNA level of HIF-1αin the LPS-stimulated macrophages had no changed (P>0.05).Conclusion Compared with inflammation group, the protein level of HIF-1α, VEGF and TNF-αdecreased obviously in administrating group, but the mRNA level of HIF-1αhad no changed. As it decreased the mRNA level of TNF-αinduced by LPS in vitro, NAC can down-regulate the protein level of HIF-1αin macrophages by post-transcription mechanism, and then the expression of VEGF which is a target gene of HIF-1 was decreased. These data indicate that NF-κB signal transduction pathway may participate in LPS inducing the HIF-1αaccumulation by up-regulation the TNF-αexpression.