The Effects of Poly [Adp-Ribose] Polymerase 1 (PARP1) on the High Mobility Group Box 1 (HMGB1) Protein in Promoting Colonic Inflammation

Abstract

Inflammatory bowel disease (IBD) affects millions of individuals around the world. High-mobility group box 1 (HMGB1) protein is identified as an important inflammatory mediator and a fecal biomarker in IBD. HMGB1 is a nuclear protein that can act as a danger-associated molecular pattern (DAMP) to activate inflammatory responses. Oxidative stress stimulates the release of HMGB1 from injured/dead cells and the release is mediated by poly (ADP-ribose) polymerase 1 (PARP1). However, the mechanism of HMGB1 release in colonic epithelial cells is unclear. In this study, hydrogen peroxide (H2O2) was used to mimic oxidative stress. H2O2-induced HMGB1 release, translocation, and expression were explored in young adult mouse colon (YAMC) cells in the presence or absence of PARP1 inhibitors. The released/secreted HMGB1 in the cell culture supernatants was measured by ELISA. The intracellular expression of HMGB1 was detected by western blot after H2O2 treatments. The nuclear and cytoplasmic HMGB1 were evaluated by nuclear and cytoplasmic extraction kit. Lastly, quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect HMGB1 mRNA level. Here, we demonstrated that H2O2 induced the release of HMGB1 from YAMC cells in a dose-dependent manner and PARP1 inhibition decreased the HMGB1 release. In addition, PARP1 regulated the translocation of HMGB1 from the nucleus to the cytoplasm. Extracellular HMGB1 was PARylated after H2O2 treatment. H2O2 enhanced the mRNA level of HMGB1, but no significant change was observed in the mRNA level in the presence of PARP1 inhibitors. Our data provide insight of the potential role of PARP1 in the mechanism of HMGB1 localization in colonic epithelial cells. Our findings also establish an important role for H2O2 in inducing HMGB1 release, expression, and translocation and suggest that HMGB1 is an important target for the treatment of inflammatory diseases. Targeting the central players of inflammatory responses in IBD can reduce tissue damage and prevent the progression of the disease.