Effects of Parathyroid Hormone and Calcitonin on Alkaline Phosphatase Activity and Matrix Calcification in Rabbit Growth-Plate Chondrocyte Cultures

Abstract

The effects of PTH and calcitonin (CT) on the expression of mineralization-related phenotypes by chondrocytes were examined. In cultures of pelleted growth-plate chondrocytes. PTH caused 60-90% decreases in alkaline phosphatase activity, the incorporation of 45Ca into insoluble material, and the calcium content during the post-mitotic stage. These effects of PTH were dose-dependent and reversible. In contrast, CT increased alkaline phosphatase activity, 45Ca incorporation into insoluble material, and the calcium content by 1.4- to 1.8-fold. These observations suggest that PTH directly inhibits the expression of the mineralization-related phenotypes by growth-plate chondrocytes, and that CT has the opposite effects.

Effects of interleukin-1 on syntheses of alkaline phosphatase, type X collagen, and 1,25-dihydroxyvitamin D3 receptor, and matrix calcification in rabbit chondrocyte cultures.

“…Thus inhibition of calcification by IL-1 was dissociated from cytokine stimulation ofproteoglycan degradation. Previous studies have shown that PTH inhibits terminal differentiation ofchondrocytes (21 ). Consistent with this finding, treatment with PTH for 6 d delayed subsequent increases in ALPase activity (Fig.…”

“…ALPase activity started to increase after cessation of cell division on day 10, and reached a maximum on day 21 ( Fig. 1 A) (18)(19)(20)(21). The addition of IL-1 beta on day 10 or 16 suppressed the increase in ALPase activity (Fig.…”

“…In these cultures, the DNA content started to increase on day 3, and reached a plateau on day 10 ( 18-21 ). ALPase activity started to increase after cessation of cell division on day 10, and reached a maximum on day 21 ( Fig. 1 A) (18)(19)(20)(21).…”

“…Recently, we found that rabbit growth plate chondrocytes maintained as a pelleted mass in a centrifuge tube produce alkaline phosphatase (ALPase),' a marker of terminal differentiation ( 17), at as a high level as that in growth plates in vivo (18)(19)(20)(21). Furthermore, the extracellular matrix synthesized by these cells is calcified during the hypertrophic stage in the absence of added beta-glycerophosphate or inorganic phosphate ( 18 ).…”

Role of 1,25-dihydroxycholecalciferol in growth-plate cartilage: inhibition of terminal differentiation of chondrocytes in vitro and in vivo.

“…It is unlikely that the effect of 1,25(OH)2D3 on, terminal differentiation is secondary to its effect on extracellular matrix synthesis. Differentiation of chondrocytes to matrixforming stage and terminal differentiation to hypertrophic stage can be separated by manipulation of culture conditions (8,9) or addition of transforming growth factor type (3 (8), fibroblast growth factor (25), or parathyroid hormone (26). Extracellular matrix synthesis and hypertrophy appear to be regulated by different sets of growth factor and hormones.…”