Published online Sep 28, 2019. doi: 10.3748/wjg.v25.i36.5434
Peer-review started: April 26, 2019
First decision: May 24, 2019
Revised: August 7, 2019
Accepted: August 19, 2019
Article in press: August 19, 2019
Published online: September 28, 2019
High mobility group box-1 (HMGB1) released by injured/dying cells becomes a key of damage-associated molecular patterns molecule to trigger inflammation responses leading to a series of tissue and organ damage, even diseases. But the details on how the injured hepatocytes released HMGB1 are to be elicited.
Hepatocytes are the most abundant cell type in the liver and the most easily attacked target, and loss of hepatocytes would contribute to various hepatic diseases. So, it is important to investigate the mechanism of HMGB1 release during hepatocyte injury or death.
To elicit HMGB1 release regulated by Sirt1 in injured/ dying hepatocytes, male C57BL/6J mice fed a high-fat diet (HFD) plus ethyl alcohol (etOH) were employed to assess the HMGB1 release and translocation from the nuclues to cytoplasm in injured hepatocytes. In vitro, mouse embryonic hepatocyte cell line BNL.CL2 incubated with H2O2 was further investigate the regulatory effect of Sirt1 on HMGB1 release. The main aim ofthis study was to understand HMGB1 release and its regulatory factors during hepatocyte injury/death, which would be a potential target for clinical therapy.
Male C57BL/6J mice were fed an HFD plus etOH to establish a model of hepatocytes injury/death. Meanwhile, mouse embryonic hepatocyte cell line BNL.CL2 was cultured in vitro and treated with H2O2. Serum ALT, liver H2O2 content and catalase activity, lactate dehydrogenase and 8-hydroxy-2-deoxyguanosine content, NAD+ levels, Sirt1 activity were detected by spectrophotometry. HMGB1 release was measured by ELISA and its translocation was detected by immunohistochemistry/immunofluorescence or Western blot. The mRNA and protein levels were assayed by qPCR and Western blot, respectively. Acetylated HMGB1 and Parp1 were analyzed by immunoprecipitation.
After treatment with an HFD plus etOH in vivo or H2O2in vitro toinduce hepatocyte injury, HMGB1 was translocated from the nucleus to the cytoplasm and passively released outside. This process occured because HMGB1 was hyperacetylated owing to both Sirt1 protein and activity suppression. After treatment with Sirt1-siRNA or Sirt1 inhibitor EX527, hyperacetylated HMGB1 increased (P < 0.01). Further, Sirt1 activity was suppressed by H2O2, which could be reversed by the Parp1 inhibitor DIQ (P < 0.01).
When hepatocytes injured/die, HMGB1 is translocated from the nucleus to the cytoplasm and finally released, which is related with hyperacetylated HMGB1 due to Sirt1 activity inhibition by NAD+ depletion caused by Parp1 overactivation.
The future research will focus on herbs affecting this process to investigate the recovery of injured hepatocyte.