Inhibition of relaxin-induced pubic symphyseal "relaxation" in guinea pigs by glycosaminoglycan polysulfates and pentosan polysulfate

Immunohistochemical detection of relaxin binding to the volar oblique ligament

PURPOSE

Excess laxity in the volar oblique ligament may predispose the thumb to trapeziometacarpal joint osteoarthritis. A greater prevalence of trapeziometacarpal joint osteoarthritis in women suggests a hormonal cause and relaxin is a hormone that may have some involvement. This conclusion emerges from relaxin's diverse tissue tropism, stimulation of collagenase production in cultured fibroblasts, and reports of increased joint laxity during pregnancy. We used immunohistochemistry to assess the potential of the volar oblique ligament to bind relaxin.

METHODS

Eight volar oblique ligaments were obtained intraoperatively from perimenopausal women having basal joint arthroplasty with ligament reconstruction using the flexor carpi radialis tendon. Tissue specimens were snap-frozen in liquid nitrogen and stored at -80 degrees C until processing. Specimens then were cryosectioned, treated with a chelating rinse, incubated overnight with recombinant human relaxin, fixed, blocked, and exposed to antirelaxin antibody. Treatment with a universal aminoethylcarbizole staining kit was used to visualize areas of ligament-ligand binding. Both tissue and procedural controls served to establish binding specificity.

RESULTS

Abundant staining was observed with the positive control (cervix) and all 8 volar oblique ligaments. Little or no staining was present in fibrocartilage (negative control) or procedural controls.

CONCLUSIONS

Relaxin binds to the volar oblique ligament with specificity, implying a receptor-mediated process. Limitations of the procedure could not confirm binding saturability, necessitating additional study.

Biology of Fibrocartilage Cells

Fibrocartilage is an avascular tissue that is best documented in menisci, intervertebral discs, tendons, ligaments, and the temporomandibular joint. Several of these sites are of particular interest to those in the emerging field of tissue engineering. Fibrocartilage cells frequently resemble chondrocytes in having prominent rough endoplasmic reticulum, many glycogen granules, and lipid droplets, and intermediate filaments together with and actin stress fibers that help to determine cell organization in the intervertebral disc. Fibrocartilage cells can synthesize a variety of matrix molecules including collagens, proteoglycans, and noncollagenous proteins. All the fibrillar collagens (types I, II, III, V, and XI) have been reported, together with FACIT (types IX and XII) and network-forming collagens (types VI and X). The proteoglycans include large, aggregating types (aggrecan and versican) and small, leucine-rich types (decorin, biglycan, lumican, and fibromodulin). Less attention has been paid to noncollagenous proteins, although tenascin-C expression may be modulated by mechanical strain. As in hyaline cartilage, matrix metalloproteinases are important in matrix turnover and fibrocartilage cells are capable of apoptosis.