Prostaglandin E₂-Transporting Pathway and Its Roles via EP2/EP4 in Cultured Human Dental Pulp

Prostaglandin E₂ (PGE₂) exerts biological actions through its transport pathway involving intracellular synthesis, extracellular transport, and receptor binding. This study aimed to determine the localization of the components of the PGE₂-transporting pathway in human dental pulp and explore the relevance of PGE₂ receptors (EP2/EP4) to angiogenesis and dentinogenesis.

Protein localization of microsomal PGE₂ (mPGES)synthase, PGE₂ transporters (multidrug resistance-associated protein-4 [MRP4] and prostaglandin transporter [PGT]), and EP2/EP4 was analyzed using double immunofluorescence staining. Tooth slices from human third molars were cultured with or without butaprost (EP2 agonist) or rivenprost (EP4 agonist) for 1 week. Morphometric analysis of endothelial cell filopodia was performed to evaluate angiogenesis, and real-time polymerase chain reaction was performed to evaluate angiogenesis and odontoblast differentiation markers.

MRP4 and PGT were colocalized with mPGES and EP2/EP4 in odontoblasts and endothelial cells. Furthermore, MRP4 was colocalized with mPGES and EP4 in human leukocyte antigen-DR-expressing dendritic cells. In the tooth slice culture, EP2/EP4 agonists induced significant increases in the number and length of filopodia and mRNA expression of angiogenesis markers (vascular endothelial growth factor and fibroblast growth factor-2) and odontoblast differentiation markers (dentin sialophosphoprotein and collagen type 1).

PGE₂-producing enzyme (mPGES), transporters (MRP4 and PGT), and PGE₂-specific receptors (EP2/EP4) were immunolocalized in various cellular components of the human dental pulp. EP2/EP4 agonists promoted endothelial cell filopodia generation and upregulated angiogenesis- and odontoblast differentiation-related genes, suggesting that PGE₂ binding to EP2/EP4 is associated with angiogenic and dentinogenic responses.