The Serine Protease Inhibitor Trappin-2 Is Present in Cartilage and Synovial Fluid in Osteoarthritis

KANYAKORN JAOVISIDHA, ANN ETIM, KOJI YAMAKAWA, IKUKO MASUDA, CLAUDIA M. GOHR, BASSAM T. WAKIM, NIMARADEE BOONAPATCHAROEN, JAMES NINOMIYA, and ANN K. ROSENTHAL

ABSTRACT.

Objective. Trappins are small serine protease inhibitors bound to extracellular matrix (ECM) through the actions of transglutaminase (TGase) enzymes. Trappin-2 is present in many tissues and is upregulated at sites of injury. In osteoarthritis (OA), serine proteases contribute to articular cartilage destruction, and TGase activity is increased. Yet little is known about matrix-bound serine protease inhibitors or TGase substrates in articular cartilage. Our purpose was to determine if trappin-2 was present in OA cartilage and synovial fluid (SF).

Methods. OA knee articular cartilage and SF were assayed for trappin-2 protein by Western blotting, ELISA, and immunohistochemistry. Trappin-2 mRNA was detected with RT-PCR. The ECM components bound to trappin-2 were identified by 2-D gel electrophoresis and peptide fingerprinting.

Results. Trappin-2 was detectable in OA articular cartilage extracts, cultured chondrocytes, conditioned media, and SF by Western blotting. OA cartilage protein extracts contained significantly higher quantities of trappin-2 than normal cartilage protein extracts (22.98 ± 1.28 ng/mg wet weight vs 14.97 ± 1.92 ng/mg wet weight; p < 0.01). RT-PCR confirmed the presence of trappin-2 mRNA in OA chondrocytes. Immunohistochemical studies of OA cartilage revealed trappin-2 protein in chondrocytes. Peptide mapping of trappin-2 binding partners showed that fibromodulin was bound to trappin-2 in cartilage.

Conclusion. We confirmed the presence of trappin-2 in OA cartilage and SF. Elevated levels of TGase activity in OA cartilage may increase levels of this serine protease inhibitor in response to injury. (J Rheumatol 2006;33:318-25)

Key Indexing Terms:

TRAPPIN
ELAFIN
ARTICULAR CARTILAGE
OSTEOARTHRITIS
TRANSGLUTAMINASE
SERINE PROTEASE INHIBITORS

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From the Division of Rheumatology, Department of Medicine, Medical College of Wisconsin, and the Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin, USA; and Division of Rheumatology, Department of Medicine, Chulalongkorn University Medical School, Bangkok, Thailand.

Supported by a Merit Review Grant from the Veterans Administration Research Service (AKR), NIH–R01-AG15337 (AKR), R29-AR44862 (IM), TRG4680026 from Thailand Research Fund (KJ), and Ratchadapiseksompotch Fund, Faculty of Medicine, Chulalongkorn University (KJ).

K. Jaovisidha, MD; N. Boonapatcharoen, BS, Chulalongkorn University Medical School; A. Etim, BA; K. Yamakawa, MD, PhD; I. Masuda, MD, PhD; C.M. Gohr, BS; A.K. Rosenthal, MD, Division of Rheumatology, Medical College of Wisconsin and Zablocki VA Medical Center; B.T. Wakim, PhD, Department of Biochemistry; J. Ninomiya, MD, Department of Orthopedic Surgery, Medical College of Wisconsin.

Address reprint requests to Dr. A.K. Rosenthal, Rheumatology Section/CC-111W, Zablocki VAMC, 5000 West National Avenue, Milwaukee, WI 53295-1000. E-mail: akrose@mcw.edu

Accepted for publication September 15, 2005.

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