Endothelial protein C receptor is over-expressed in rheumatoid arthritic (RA) synovium and mediates the anti-inflammatory effects of activated protein C in RA monocytes

Meilang Xue ^1*, Lyn March ¹, Philip N Sambrook ¹, Fenji Fukudome ² and Christopher J Jackson ¹

¹ The University of Sydney, Australia
² Saga Medical School, Japan

^* To whom correspondence should be addressed. E-mail: mlxue{at}med.usyd.edu.au.

Accepted 19 April 2007

Abstract

Objectives: i) To investigate whether inflammatory synovial tissues from patients with rheumatoid arthritis (RA) express endothelial protein C receptor (EPCR) and ii) to determine the major cell type (s) that EPCR is associated with and whether EPCR functions to mediate the effects of activated protein C (APC) on these cells.

Methods: EPCR, CD68 and PC/APC in synovial tissues were detected by immunostaining and in situ PCR. Monocytes were isolated from peripheral blood of patients with RA and treated with APC, lipopolysaccharide (LPS), and/or EPCR blocking antibody RCR252. Cells and supernatants were collected for RT-PCR, western blotting, enzyme-linked immuosorbent assay and chemotaxis assay.

Results: EPCR was expressed by both OA and RA synovial tissues but was markedly increased in RA synovium. EPCR was colocalized with PC/APC mostly on CD68 positive cells in synovium. In RA monocytes, APC upregulated EPCR expression and reduced monocyte chemoattractant protein-1-induced chemotaxis of monocytes by approximately 50%. APC also completely suppressed LPS-stimulated NF-B activation and attenuated TNF- protein by more than 40% in RA monocytes. The inhibitory effects of APC were reversed by RCR252, indicating that EPCR is required.

Conclusions: Our results demonstrate for the first time that EPCR is expressed by synovial tissues, particularly in RA, where it co-localizes with PC/APC on monocytes/macrophages. In addition, APC inhibits the migration and activation of RA monocytes via EPCR. These inhibitory effects on RA monocytes suggest that PC pathway may have a beneficial therapeutic effect in RA.

Keywords: activated protein C, endothelial protein C receptor, migration and activation, monocytes, rheumatoid arthritis

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