Ras guanine nucleotide-releasing protein 4 is aberrantly expressed in the fibroblast-like synoviocytes of patients with rheumatoid arthritis and controls their proliferation.

Abstract

OBJECTIVE:

Ras guanine nucleotide-releasing protein 4 (RasGRP-4) is a calcium-regulated guanine nucleotide exchange factor and diacylglycerol/phorbol ester receptor not normally expressed in fibroblasts. While RasGRP-4-null mice are resistant to arthritis induced by anti-glucose-6-phosphate isomerase autoantibodies, the relevance of these findings to humans is unknown. We undertook this study to evaluate the importance of RasGRP-4 in the pathogenesis of human and rat arthritis.

METHODS:

Synovial tissue from patients with rheumatoid arthritis (RA) and osteoarthritis (OA) were evaluated immunohistochemically for the presence of RasGRP-4 protein. Fibroblast-like synoviocytes (FLS) were isolated from synovial samples, and expression of RasGRP-4 was evaluated by real-time quantitative reverse transcription-polymerase chain reaction analyses. The proliferation potency of FLS was evaluated by exposing the cells to a RasGRP-4-specific small interfering RNA (siRNA). Finally, the ability of RasGRP-4-specific siRNAs to hinder type II collagen-induced arthritis in rats was evaluated to confirm the importance of the signaling protein in the disease.

RESULTS:

Unexpectedly, RasGRP-4 protein was detected in the synovial hyperplastic lining, where proliferating FLS preferentially reside. FLS isolated from tissues obtained from a subpopulation of RA patients expressed much more RasGRP-4 than did FLS from examined OA patients. Moreover, the level of RasGRP-4 transcript was correlated with the FLS proliferation rate. The ability of cultured FLS to divide was diminished when they were treated with RasGRP-4-specific siRNAs. The intraarticular injection of RasGRP-4-specific siRNAs also dampened experimental arthritis in rats.

CONCLUSION:

RasGRP-4 is aberrantly expressed in FLS and helps regulate their growth. This intracellular signaling protein is therefore a candidate target for dampening proliferative synovitis and joint destruction.

• Authors: Michihito Kono, Shinsuke Yasuda, Richard L Stevens, Hideyuki Koide, Takashi Kurita, Yuka Shimizu, Yusaku Kanetsuka, Kenji Oku, Toshiyuki Bohgaki, Olga Amengual, Tetsuya Horita, Tomohiro Shimizu, Tokifumi Majima, Takao Koike, Tatsuya Atsumi
• Journal: Arthritis & rheumatology (Hoboken, N.J.) (Arthritis Rheumatol) Vol. 67 Issue 2 Pg. 396-407 (Feb 2015) ISSN: 2326-5205 [Electronic] United States
• PMID: 25330932 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2015 by the American College of Rheumatology.

Chemical References

• RASGRP4 protein, human
• RNA, Small Interfering
• ras Guanine Nucleotide Exchange Factors

Topics

• Adult
• Aged
• Aged, 80 and over
• Animals
• Arthritis, Experimental (metabolism, pathology)
• Arthritis, Rheumatoid (metabolism, pathology)
• Cell Proliferation (drug effects, physiology)
• Cells, Cultured
• Disease Models, Animal
• Female
• Fibroblasts (metabolism, pathology)
• Humans
• In Vitro Techniques
• Male
• Middle Aged
• Osteoarthritis (metabolism, pathology)
• RNA, Small Interfering (pharmacology)
• Rats
• Rats, Inbred Lew
• Synovial Membrane (metabolism, pathology)
• Time Factors
• ras Guanine Nucleotide Exchange Factors (metabolism)