Endothelin-1 drives COX-2 and prostaglandin E₂ expression in osteoblasts through MAPK/AP-1 signaling during...

Endothelin-1 (ET-1) has been implicated in inflammatory tissue responses, but its role in osteoblast-mediated inflammation during periodontal inflammation remains unclear. This study investigated whether ET-1 induces cyclooxygenase-2 (COX-2) expression and prostaglandin E₂ (PGE₂) release in osteoblasts and explored the underlying signaling mechanisms.

Murine osteoblast-like MC3T3-E1 cells were stimulated with ET-1. COX-2 protein and mRNA expression, promoter activity, and PGE₂ release were assessed by Western blotting, real-time RT-PCR, luciferase reporter assay, and ELISA, respectively. Pharmacological inhibitors and siRNA knockdown were used to examine the roles of ET_A/ET_B receptors, G_q/G_i proteins, ERK1/2, p38 MAPK, JNK1/2, and AP-1 signaling.

ET-1 increased COX-2 protein and mRNA expression, COX-2 promoter activity, and PGE₂ release in MC3T3-E1 cells in a time-dependent manner. Actinomycin D and cycloheximide significantly reduced ET-1-induced COX-2 expression and PGE₂ release, indicating transcriptional and translational regulation. Pharmacological blockade or knockdown of ET_A and ET_B receptors attenuated these responses. Inhibition or silencing of G_q and G_i also suppressed ET-1-induced COX-2 expression and PGE₂ release. Moreover, inhibition or knockdown of ERK1/2, p38 MAPK, or JNK1/2 reduced these effects. ET-1 also promoted c-Jun phosphorylation, nuclear accumulation, AP-1 binding activity, and COX-2 promoter transactivation, whereas AP-1 inhibition or c-Jun knockdown reduced COX-2 expression and downstream PGE₂ production.

ET-1 drives COX-2 expression and PGE₂ release in osteoblasts through ET_A/ET_B dependent G_i/G_q, MAPK, and AP-1 signaling, supporting a potential role of ET-1 in osteoblast-associated inflammatory responses and inflammatory bone microenvironment changes under periodontal inflammatory conditions.