Type II collagen and TGF-βs in developing and aging porcine mandibular condylar cartilage: immunohistochemical studies

Transforming growth factor-betas (TGF-βs) have been associated with the development and maintenance of articular cartilage. However, no studies have addressed their role in the postnatal development of mandibular condylar cartilage. This investigation represents the first immunohistochemical characterization of TGF-β isoforms and type II collagen in porcine mandibular condylar cartilage from various age groups. Furthermore, it is the first description of possible age-related changes in the expression of these proteins during postnatal development of this tissue. Condylar cartilage was dissected from freshly harvested temporomandibular joints of newborn, 6-, 12-, 24-, and 36-month-old farm swine. TGF-β1, TGF-β2, TGF-β3, and type II collagen were localized via standard immunohistochemical procedures. An immunoblot technique was employed to compare the relative amount of each protein present in the various age groups. Immunoreactivity was detected in mandibular condylar cartilage for all three isoforms of TGF-β and for Type II collagen. All age groups demonstrated some evidence of immunostaining, primarily in the cytoplasm of cells from most zones of the cartilage. Immunoblot results indicated that TGF-β isoforms had individualized patterns of expression. When newborn protein levels were taken as the baseline, TGF-β1 demonstrated a significant increase at ages 24 and 36 months. TGF-β2 significantly increased at 6, 12, 24, and 36 months (peak levels at 24 months; similar levels at 6, 12, and 36 months), whereas TGF-β3 remained stable at all ages. Type II collagen demonstrated increases that paralleled the increased levels of TGF-β1 and TGF-β2 at 24 and 36 months.