Endoplasmic reticulum stress is upregulated in inflammatory bowel disease and contributed TLR2 pathway-mediated inflammatory response.

Objective: Endoplasmic reticulum stress (ERS) and Toll-like receptor 2 (TLR2) signaling play an important role in inflammatory bowel disease (IBD); however, the link between TLR2 and ERS in IBD is unclear. This study investigated whether Thapsigargin (TG) -induced ER protein expression levels contributed to TLR2-mediated inflammatory response.

Methods: The THP-1 cells were treated with TLR2 agonist (Pam3CSK4), ERS inducer Thapsigargin (TG) or inhibitor (TUDCA). The mRNA expressions of TLR1-TLR10 were detected by qPCR. The production and secretion of inflammatory factors were detected by PCR and ELISA. Immunohistochemistry was used to detect the expressions of GRP78 and TLR2 in the intestinal mucosa of patients with Crohn's disease (CD). The IBD mouse model was established by TNBS in the modeling group. ERS inhibitor (TUDCA) was used in the treatment group.

Results: The expression of TLRs was detected via polymerase chain reaction (PCR) in THP-1 cells treated by ERS agonist Thapsigargin (TG). According to the findings, TG could promote TLR2 and TLR5 expression. Subsequently, in TLR2 agonist Pam3CSK4 induced THP-1 cells, TG could lead to increased expression of the inflammatory factors such as TNF-α, IL-1β and IL-8, and ERS inhibitor (TUDCA) could block this effect. However, Pam3CSK4 did not significantly impact the GRP78 and CHOP expression. Based upon the immunohistochemical results, TLR2 and GRP78 expression were significantly increased in the intestinal mucosa of patients with Crohn's disease (CD). For in vivo experiments, TUDCA displayed the ability to inhibit intestinal mucosal inflammation and reduce GRP78 and TLR2 proteins.

Conclusions: ERS and TLR2 is upregulated in inflammatory bowel disease, ERS may promote TLR2 pathway-mediated inflammatory response. Moreover, ERS and TLR2 signaling could be novel therapeutic targets for IBD.