Parathyroid hormone-related peptide-depleted mice show abnormal epiphyseal cartilage development and altered endochondral bone formation.

Abstract

Abstract. To elucidate the role of PTHrP in skeletal development, we examined the proximal tibial epiphysis and metaphysis of wild-type (PTHrP-normal) 18-19-d-old fetal mice and of chondrodystrophic litter mates homozygous for a disrupted PTHrP allele generated via homologous recombination in embryonic stem cells (PTHrP-depleted). In the PTHrP-normal epiphysis, immunocytochemistry showed PTHrP to be localized in chondrocytes within the resting zone and at the junction between proliferative and hypertrophic zones. In PTHrP-depleted epiphyses, a diminished [3H]thymidine-labeling index was observed in the resting and proliferative zones accounting for reduced numbers of epiphyseal chondrocytes and for a thinner epiphyseal plate. In the mutant hypertrophic zone, enlarged chondrocytes were interspersed with clusters of cells that did not hypertrophy, but resembled resting or proliferative chondrocytes. Although the overall content of type II collagen in the epiphyseal plate was diminished, the lacunae of these non-hypertrophic chondrocytes did react for type II collagen. Moreover, cell membrane-associated chondroitin sulfate immunoreactivity was evident on these cells. Despite the presence of alkaline phosphatase activity on these nonhypertrophic chondrocytes, the adjacent cartilage matrix did not calcify and their persistence accounted for distorted chondrocyte columns and sporadic distribution of calcified cartilage. Consequently, in the metaphysis, bone deposited on the irregular and sparse scaffold of calcified cartilage and resulted in mixed spicules that did not parallel the longitudinal axis of the tibia and were, therefore, inappropriate for bone elongation. Thus, PTHrP appears to modulate both the proliferation and differentiation of chondrocytes and its absence alters the temporal and spatial sequence of epiphyseal cartilage development and of subsequent endochondral bone formation necessary for normal elongation of long bones. p ARATHYROID hormone-related peptide (PTHrP) ~ was originally identified as a pathogenetic factor for malignancy-associated hypercalcemia (Suva et al., 1987;Burtis et al., 1987;Strewler et al., 1987). The homology of the NH2-terminal region of PTHrP with the corresponding domain of parathyroid hormone (PTH), and the resultant capacity of both molecules to interact with a common receptor (Jiippner et al., 1991) appear to account for the ability of

Rapamycin retards growth and causes marked alterations in the growth plate of young rats

“…Morphological distortion of the maturation zone and presence of PAS-positive glycogen granules in distal hypertrophic chondrocytes have been previously interpreted as a disruption of the orderly process of maturation of chondrocytes in a model of parathyroid-hormone-related peptide (PTHrP)-depleted mice [26]. Therefore, our results encourage the further study of rapamycin interaction with the Indian hedgehog (Ihh)/PTHrP feedback loop [27], so far not explored.…”

An in vivo model of melanoma: treatment with ATP

“…Three-dimensional tumour measurements were performed using callipers and the tumour volume was calculated using the formula: 4/3Π(L/2×W/2) 3 where L is long axis and W is mean midaxis width [20]. The animals were weighed at regular intervals.…”

Ossification of the mouse metatarsal: Differentiation and proliferation in the presence/absence of a defined growth plate

“…For instance, patterning mechanisms such as Hox genes have been shown to affect growth plate formation and behavior and chondrocyte proliferation (Yokouchi et al, 1995;Goff and Tabin, 1997;Papenbrock et al, 2000;Boulet and Capecchi, 2002). In addition, mice with ablated PTHrP or PTH/PTHrP receptor (PPR) genes have shortened, disorganized growth plates in the embryonic skele-ton as a consequence of accelerated differentiation of their columnar chondrocytes (Amizuka et al, 1994;Lanske et al, 1996). Mice haploinsufficient for PTHrP (Amizuka et al, 1996) have smaller epiphyses and growth plates.…”