Scientists funded in part by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) have demonstrated that the large-protein molecule known as SZP (superficial zone protein) functions to lubricate the jaw.

SZP is known to be synthesized and expressed on the surface layer of cartilage in the limb joints. In these joints, SZP serves as a lubricant. However, until now, the role of SZP in the function of the temporomandibular joint has been less clear.

Unlike the surface layer of cartilage found in the limb joints, the corresponding surface in the temporomandibular joint is made up of thick, fibrous tissue. Researchers at Rush Medical College in Chicago and Hiroshima University Graduate School of Biomedical Sciences in Japan sought to determine whether, despite the differences in cartilage structure, SZP is expressed on the surface layer of cartilage in the jaw. To do this, they examined temporomandibular joint cartilage samples taken from the heads of 18-month-old steers.

The scientists found that SZP is locally synthesized and expressed on the surface layer of cartilage in the temporomandibular joint. They also discovered that SZP in the temporomandibular joint is regulated by several well-known cell mediators: transforming growth factor-beta and interleukin-1beta.

Reduced expression of a lubricant such as SZP is associated with cartilage damage. Interleukin-1beta (IL-1beta) is known to reduce the capacity of tissues to synthesize and retain SZP. Researchers in this study found that when the surface of the cartilage samples was treated with the cell mediator IL-1beta, expression of SZP was reduced. They theorized that reduced SZP expression in the temporomandibular joint would lead to progression of osteoarthritis.

On the other hand, enhanced expression of SZP has been shown to improve smooth joint movement without tissue adhesion. Researchers in this study found that when the surface of the cartilage samples was treated with the cell mediator transforming growth factor-beta (TGF-beta), expression of SZP was enhanced. They concluded that TGF-beta could have potential as a therapeutic strategy for temporomandibular joint diseases.

NIAMS grantees involved in the study included Drs. Warren Knudson, Cheryl B. Knudson, Theodore R. Oegema and Thomas M. Schmid at Rush Medical College.

The mission of the National Institute of Arthritis and Musculoskeletal and Skin Diseases a part of the Department of Health and Human Services' National Institutes of Health, is to support research into the causes, treatment and prevention of arthritis and musculoskeletal and skin diseases; the training of basic and clinical scientists to carry out this research; and the dissemination of information on research progress in these diseases. For more information about NIAMS, call the information clearinghouse at (301) 495-4484 or (877) 22-NIAMS (free call) or visit the NIAMS Web site at http://www.niams.nih.gov.

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Ohno S, et al. Expression of SZP in Mandibular Condyle Cartilage. Osteoarthritis and Cartilage 2006; 14; 807-813.