BACKGROUND
High mobility group box-1 (HMGB1), recognized as a representative of damage-associated molecular patterns, is released during cell injury/death, triggering the inflammatory response and ultimately resulting in tissue damage. Downs of studies have shown that HMGB1 is involved in certain diseases, but the details on how injured hepatocytes release HMGB1 need to be elicited.
AIM
To reveal HMGB1 release mechanism in hepatocytes undergoing oxidative stress.
METHODS
C57BL6/J male mice were fed a high-fat diet for 12 wk plus a single binge of ethanol to induce severe steatohepatitis. Hepatocytes treated with H(2)O(2)( )were used to establish an in vitro model. Serum alanine aminotransferase, liver H2O2 content and catalase activity, lactate dehydrogenase and 8-hydroxy-2-deoxyguanosine content, nicotinamide adenine dinucleotide (NAD(+)) levels, and Sirtuin 1 (Sirt1) activity were detected by spectrophotometry. HMGB1 release was measured by enzyme linked immunosorbent assay. HMGB1 translocation was observed by immunohistochemistry/immunofluorescence or Western blot. Relative mRNA levels were assayed by qPCR and protein expression was detected by Western blot. Acetylated HMGB1 and poly(ADP-ribose)polymerase 1 (Parp1) were analyzed by Immunoprecipitation.
RESULTS
When hepatocytes were damaged, HMGB1 translocated from the nucleus to the cytoplasm because of its hyperacetylation and was passively released outside both in vivo and in vitro. After treatment with Sirt1-siRNA or Sirt1 inhibitor (EX527), the hyperacetylated HMGB1 in hepatocytes increased, and Sirt1 activity inhibited by H2O2 could be reversed by Parp1 inhibitor (DIQ). Parp1 and Sirt1 are two NAD(+)-dependent enzymes which play major roles in the decision of a cell to live or die in the context of stress . We showed that NAD(+) depletion attributed to Parp1 activation after DNA damage was caused by oxidative stress in hepatocytes and resulted in Sirt1 activity inhibition. On the contrary, Sirt1 suppressed Parp1 by negatively regulating its gene expression and deacetylation.
CONCLUSION
The functional inhibition between Parp1 and Sirt1 leads to HMGB1 hyperacetylation, which leads to its translocation from the nucleus to the cytoplasm and finally outside the cell.
[1]Shanghai Univ Tradit Chinese Med, Sch Basic Med Sci, Dept Biol, 1200 Cailun Rd, Shanghai 201203, Peoples R China.
[2]Shanghai Univ Tradit Chinese Med, Longhua Hosp, Dept Oncol, Shanghai 200032, Peoples R China.
[3]Shanghai Univ Tradit Chinese Med, Longhua Hosp, Inst Tradit Chinese Med Oncol, Shanghai 200032, Peoples R China.
(8.0+极速模式)