Abstract
High-mobility group box 1 (HMGB1) was initially discovered as a nuclear protein that interacts with DNA as a chromatin-associated non-histone protein to stabilize nucleosomes and to regulate the transcription of many genes in the nucleus. Once leaked or actively secreted into the extracellular environment, HMGB1 activates inflammatory pathways by stimulating multiple receptors, including Toll-like receptor (TLR) 2, TLR4, and receptor for advanced glycation end products (RAGE), leading to tissue injury. Although HMGB1’s ability to induce inflammation has been well documented, no studies have examined the role of HMGB1 in wound healing in the gastrointestinal field. The aim of this study was to evaluate the role of HMGB1 and its receptors in the healing of gastric ulcers. We also investigated which receptor among TLR2, TLR4, or RAGE mediates HMGB1’s effects on ulcer healing. Gastric ulcers were induced by serosal application of acetic acid in mice, and gastric tissues were processed for further evaluation. The induction of ulcer increased the immunohistochemical staining of cytoplasmic HMGB1 and elevated serum HMGB1 levels. Ulcer size, myeloperoxidase (MPO) activity, and the expression of tumor necrosis factor α (TNFα) mRNA peaked on day 4. Intraperitoneal administration of HMGB1 delayed ulcer healing and elevated MPO activity and TNFα expression. In contrast, administration of anti-HMGB1 antibody promoted ulcer healing and reduced MPO activity and TNFα expression. TLR4 and RAGE deficiency enhanced ulcer healing and reduced the level of TNFα, whereas ulcer healing in TLR2 knockout (KO) mice was similar to that in wild-type mice. In TLR4 KO and RAGE KO mice, exogenous HMGB1 did not affect ulcer healing and TNFα expression. Thus, we showed that HMGB1 is a complicating factor in the gastric ulcer healing process, which acts through TLR4 and RAGE to induce excessive inflammatory responses.
Highlights
High-mobility group box protein 1 (HMGB1), a member of the high-mobility group protein superfamily, is a nuclear protein [1]
HMGB1 Expression following Ulceration We evaluated whether HMGB1 was involved in gastric ulcer healing
We demonstrated that exogenous HMGB1 delays gastric ulcer healing, while inducing tumor necrosis factor α (TNFα) expression and MPO activity
Summary
High-mobility group box protein 1 (HMGB1), a member of the high-mobility group protein superfamily, is a nuclear protein [1]. The best studied HMGB1 receptors are Toll-like receptor (TLR) 2 [6,7], TLR 4 [6,7,8,9], and receptor for advanced glycation end products (RAGE) [6,8]. Triggering TLR2 and TLR4 signaling pathways leads to the activation of nuclear factor κB (NF-κB), through the accessory protein MyD88, and the subsequent regulation of immune and inflammatory genes, including inflammatory cytokines such as tumor necrosis factor α (TNFα), with the activation of mitogen-activated protein kinases [11,12,13]. Receptor for advanced glycation end products (RAGE) is a multi-ligand receptor that belongs to the immunoglobulin superfamily [14]. Multiple experiments have suggested that the ligand-RAGE interaction activates NF-κB and mitogenactivated protein kinases [17,18,19,20]
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