RESUMEN
BACKGROUND: High mobility group proteins 1 and 2 (HMGB1 and HMGB2) are 80% conserved in amino acid sequence. The function of HMGB1 in inflammation and fibrosis has been extensively characterized. However, an unaddressed central question is the role of HMGB2 on liver fibrosis. In this study, we provided convincing evidence that the HMGB2 expression was significantly upregulated in human liver fibrosis and cirrhosis, as well as in several mouse liver fibrosis models. METHODS: The carbon tetrachloride (CCl4) induced liver fibrosis mouse model was used. AAV8-Hmgb2 was utilized to overexpress Hmgb2 in the liver, while Hmgb2-/- mice were used for loss of function experiments. The HMGB2 inhibitor inflachromene and liposome-shHMGB2 (lipo-shHMGB2) were employed for therapeutic intervention. RESULTS: The serum HMGB2 levels were also markedly elevated in patients with liver fibrosis and cirrhosis. Deletion of Hmgb2 in Hmgb2-/- mice or inhibition of HMGB2 in mice using a small molecule ICM slowed the progression of CCl4-induced liver fibrosis despite constant HMGB1 expression. In contrast, AAV8-mediated overexpression of Hmgb2 enchanced CCl4-incuded liver fibrosis. Primary hepatic stellate cells (HSCs) isolated from Hmgb2-/- mice showed significantly impaired transdifferentiation and diminished activation of α-SMA, despite a modest induction of HMGB1 protein. RNA-seq analysis revealed the induction of top 45 CCl4-activated genes in multiple signaling pathways including integrin signaling and inflammation. The activation of these genes by CCl4 were abolished in Hmgb2-/- mice or in ICM-treated mice. These included C-X3-C motif chemokine receptor 1 (Cx3cr1) associated with inflammation, cyclin B (Ccnb) associated with cell cycle, DNA topoisomerase 2-alpha (Top2a) associated with intracellular component, and fibrillin (Fbn) and fibromodulin (Fmod) associated with extracellular matrix. CONCLUSION: We conclude that HMGB2 is indispensable for stellate cell activation. Therefore, HMGB2 may serve as a potential therapeutic target to prevent HSC activation during chronic liver injury. The blood HMGB2 level may also serve as a potential diagnostic marker to detect early stage of liver fibrosis and cirrhosis in humans.
Asunto(s)
Proteína HMGB1 , Humanos , Ratones , Animales , Proteína HMGB1/genética , Proteína HMGB2/genética , Cirrosis Hepática/diagnóstico , Cirrosis Hepática/genética , Cirrosis Hepática/inducido químicamente , Factores de Transcripción , Modelos Animales de Enfermedad , Inflamación , FibromodulinaRESUMEN
High-mobility-group protein 2 (HMGB2) expression is upregulated in human liver cancer. However, little is known about its regulatory function. Here we establish HMGB2 as a new modulator of the pluripotency of mouse embryonic stem cells (ESCs). Similar to OCT4 and SOX2, HMGB2 protein is highly expressed in undifferentiated CGR8 cells, whereas it undergoes rapid decline during embryonic body (EB) formation. HMGB2 interacts with OCT4, increases protein expression of OCT4 and SOX2, and enhances their transcriptional activities. We also show that miRNA-127 is a translational repressor of HMGB2 protein expression by targeting its 3'UTR. We further elucidate a trancrptional mechanism controlling HMGB2 mRNA expression by nuclear receptor SHP and transcription factor E2F1. Diminishing HMGB2 expression by ectopic expression of miR-127 or SHP, or treatment with a small molecule inhibitor inflachromene (ICM), decreases OCT4 and SOX2 expression and facilitates CGR8 differentiation. In addition, HMGB2 is markedly induced in liver tumor initiating cells (TICs). Diminishing HMGB2 expression by shHMGB2, miR-127 or SHP impaires spheroid formation. Importantly, HMGB2 expression is elevated in various human cancers. Conclusion: HMGB2 acts upstream of the OCT4/SOX2 signaling to control ESCs pluripotency. Diminishing HMGB2 expression by miR-127 or SHP may provide a potential means to decrease the pluripotency of tumor initiating cells.