Downregulation of Monocyte Chemoattractant Protein 1 Expression by Prostaglandin E₂ in Human Ocular Surface Epithelium

Elsewhere, we reported that in the tears and serum of patients with acute-stage Stevens-Johnson syndrome or toxic epidermal necrolysis, the levels of interleukin 6 (IL-6), IL-8, and monocyte chemoattractant protein 1 (MCP-1) were dramatically increased.¹ We also reported that Stevens-Johnson syndrome or toxic epidermal necrolysis with severe ocular complications was associated with polymorphism of the prostaglandin E receptor 3 (EP₃) gene (PTGER3).²

Prostanoids are a group of lipid mediators that form in response to various stimuli. They include prostaglandin D₂ (PGD₂), PGE₂, PGF_2α, PGI₂, and thromboxane A₂. There are 4 subtypes of the PGE receptor: EP₁, EP₂, EP₃, and EP₄. We previously reported that PGE₂ suppresses polyinosine–polycytidylic acid (polyI:C)–stimulated cytokine production via EP₂ and/or EP₃ in human ocular surface epithelial cells.^3,4 PolyI:C is a ligand of Toll-like receptor 3, which is strongly expressed in ocular surface epithelium.⁵ We found that PGE₂ suppresses the production of IL-6, chemokine (C-X-C motif) ligand 10, chemokine (C-X-C motif) ligand 11, and chemokine (C-C motif) ligand 5 but not IL-8 by epithelial cells on the human ocular surface³; it remains to be determined whether it also suppresses MCP-1 production. Monocyte chemoattractant protein 1 plays a significant role in the recruitment of monocytes and lymphocytes to the site of cellular immune reactions. In this study, we investigated whether PGE ₂ downregulates polyI:C-induced MCP-1 production.

All experiments were conducted in accordance with the principles set forth in the Declaration of Helsinki. Enzyme-linked immunosorbent assay and quantitative real-time polymerase chain reaction were performed with primary human conjunctival epithelial cells and immortalized human corneal-limbal epithelial cells using previously described methods (eAppendix).³

First, we examined whether PGE₂ downregulated the production and messenger RNA (mRNA) expression of MCP-1 induced by polyI:C stimulation in human conjunctival and corneal epithelial cells. We found that it significantly attenuated the production of MCP-1 (Figure, A). Quantitative real-time polymerase chain reaction confirmed that the mRNA expression of MCP-1 was significantly downregulated by PGE₂ (Figure, A).

Next, we examined which PGE₂ receptor(s) contributed to the downregulation of polyI:C-induced MCP-1. We used the EP₂ agonist ONO-AE-259, the EP₃ agonist ONO-AE-248, and the EP₄ agonist ONO-AE-329. Enzyme-linked immunosorbent assay showed that the EP₂ and EP₃ agonists significantly suppressed the polyI:C-induced production of MCP-1, while the EP₄ agonist did not exert suppression (Figure, B). Quantitative real-time polymerase chain reaction confirmed that the EP₂ and EP₃ agonists significantly downregulated the mRNA expression of MCP-1 (Figure, C). Thus, our results document that PGE₂ attenuated the mRNA expression and production of MCP-1 via both EP₂ and EP₃.

In human macrophages, PGE₂ attenuated the lipopolysaccharide-induced mRNA and protein expression of chemokines including MCP-1 through EP₄.⁶ On the other hand, we demonstrated that in human ocular surface epithelial cells, PGE₂ attenuated the polyI:C-induced mRNA and protein expression of MCP-1 through EP₂ and EP₃ but not EP₄. Our findings suggest that EP₂ and EP₃ play important roles in the regulation of inflammation in epithelial cells, while EP₂ and EP₄ have important roles in immune cells such as macrophages.

In the tears and serum of patients with acute-stage Stevens-Johnson syndrome or toxic epidermal necrolysis, the levels of IL-6, IL-8, and MCP-1 were dramatically increased.¹ Although IL-8 was not regulated by PGE₂, IL-6 was regulated by PGE₂ via EP₃ in human ocular surface epithelial cells.³ Herein, we demonstrated that MCP-1 could be regulated by PGE₂ via EP₂ and EP₃. The regulation of cytokine production by PGE₂ may be associated with the pathogenesis of Stevens-Johnson syndrome or toxic epidermal necrolysis with severe ocular complications because it was associated with polymorphism of the EP₃ gene (PTGER3), one of the PGE receptors (EP₁, EP₂, EP₃, EP₄).²

In summary, our results show that MCP-1 produced by human ocular surface epithelial cells could be downregulated by PGE₂ via EP₂ and EP₃.

Correspondence: Dr Ueta, Department of Ophthalmology, Kyoto Prefectural University of Medicine, 465 Kajiicho, Hirokoji, Kawaramachi, Kamigyoku, Kyoto 602-0841, Japan (mueta@koto.kpu-m.ac.jp).

Author Contributions: Dr Ueta had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Funding/Support: This work was supported in part by grants-in-aid for scientific research from the Japanese Ministry of Health, Labour, and Welfare, the Japanese Ministry of Education, Culture, Sports, Science, and Technology, the Kyoto Foundation for the Promotion of Medical Science, the National Institute of Biomedical Innovation of Japan, the Intramural Research Fund of Kyoto Prefectural University of Medicine, and the Shimizu Foundation for Immunological Research Grant.

Additional Contributions: Chikako Endo provided technical assistance.