Localization of insulin-like growth factor binding protein-2 in chondrocytes of bovine articular cartilage.
OBJECTIVE
Previous work indicated that transforming growth factor (TGF-beta) treatment of bovine articular cartilage resulted in an accumulation of insulin-like growth factor binding protein-2 (IGF-BP-2). The purpose of the work presented in this paper was to define the localization of the IGF-BP-2 in freshly excised articular cartilage and in slices cultured in the presence and absence of TGF-beta.


METHODS
Newborn calf articular cartilage was dissected and immediately fixed or maintained in organ culture for five days under basal conditions (media without added serum or growth factors) or with basal media containing 15 ng/ml of TGF-beta1. Frozen or paraffin embedded sections were prepared, and immunohistochemistry using anti-IGF-BP-2 performed.


RESULTS
The paraffin sections provided the best preservation of morphology and consistency of immunohistochemical staining patterns. In fresh cartilage slices, IGF-BP-2 was associated with most of the chondrocytes. The basal cultured cartilage showed positive immunostaining in some areas, but not others: the most consistently stained area was the upper radial zone. In all cases where a positive reaction was observed, it was associated mostly with chondrocytes. On the other hand, all the TGF-beta treated samples that were examined in this study were evenly stained, and most chondrocytes were positive in all areas from superficial to deep zones, thus closely resembling the pattern of fresh tissue.


CONCLUSIONS
It is concluded that IGF-BP-2 is closely cell associated in bovine articular cartilage. Following culture of cartilage slices, TGF-beta increases the number of cells with positive immunostaining. These data help to support the postulate that TGF-beta exerts at least some of its actions in articular cartilage via cross-talk mechanisms involving the IGF-BP-2 system.
Morales
Teresa I
TI
Department of Orthopaedic Surgery, Massachusetts General Hospital and Harvard Medical School, Jackson 1223, 55 Fruit Street, Boston, MA 02114, USA. tmorales@partners.org
Hunziker
Ernst B
EB
D000818:Animals; D000831:Animals, Newborn; D002358:Cartilage, Articular / Q000166:cytology / Q000378:metabolism*; D002417:Cattle; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism*; D007124:Immunoenzyme Techniques; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000378:metabolism*; D009924:Organ Culture Techniques; D015398:Signal Transduction
D018971:Insulin-Like Growth Factor Binding Protein 2