Katsurou Iwasaki

Expression of parathyroid hormone-related protein in rat articular cartilage

Expression and localization of parathyroid hormone-related protein (PTHrP) in rat articular cartilage during fetal and postnatal periods were investigated by immunohistochemistry and in situ hybridization. PHTrP displayed distinct distribution and intensity of staining at different ages. In fetal (18-day-old) and young (3-week-old) rats, articular chondrocytes expressed abundant PTHrP throughout the entire thickness of cartilage. In contrast, in 60-week-old rats, PTHrP was expressed in a few articular chondrocytes of superficial and middle layers. Regulation of PTHrP and PTH/PTHrP receptor mRNA was also studied in cultured rat articular chondrocytes. Northern blot analysis revealed that both transforming growth factor-β (TGF-β), an important stimulator for chondrocyte proliferation and differentiation, and 10% fetal bovine serum (FBS) stimulated the expression of PTHrP mRNA with down-regulation of its receptor mRNA. In contrast, 12-O-tetradecanoylphorbol-13-acetate (TPA) down-regulated the expression of receptor without changes of PTHrP mRNA level. These results suggest that the changes in abundance and localization of PTHrP and its receptor may be directly involved in the cell growth and differentiation of articular cartilage.

Peculiar structures of the blood vessels forming the secondary ossification center in the rat femoral heads

To investigate the development of the blood vessels forming the secondary ossification center in the femoral heads of growing rats, we observed the specimens of the proximal femurs having vascular casts using both an optical and a scanning electron microscopy (SEM). Histologically, the vascular invasion occurred from the lateral part of the cartilaginous epiphysis, prior to the appearance of the ossification center. The vascular casts were prominent within the cellular spaces consisting of a few hypertrophic chondrocytes. The SEM study suggested that the vascular buds had peculiar structures and invaded the cartilaginous epithysis by breaking through the cellular spaces. The blood vessels budded out from the arch of the lateral epiphyseal vessels toward the femoral heads. The sizes of the large-caliber vascular buds of about 50 μm in diameter were similar to those of the cellular spaces, and they penetrated into the epiphysis by repeated merging and branching. Many deep impressions were noted on the surface of the vascular buds, and the tips showed the peculiar shape similar to a suction cup.