Effects of parathyroid hormone fragments on the growth of murine mandibular condylar cartilage in vitro

Abstract

The present study showed that the fragment hPTH (1-34) is mitogenic in organ cultures of neonatal mandibular condylar cartilage, and even more so in late fetal condyles. Three fragments of hPTH were used to clarify which part of the molecule possesses a mitogenic effect alike that of the native hormone: hPTH (1-34), and (53-84). [3H]thymidine incorporation into trichloracetic acid insoluble material and quantitative autoradiography were employed in a serum-free medium to assess the effects of these fragments while light and electron microscopy studies served for morphological evaluations. It became evident that the fragment hPTH (1-34) enhanced the incorporation of [3H]thymidine, a fact that could be noted only in serum-free medium. The putative target cells for the effects of hPTH (1-34) were the chondroporogenitor cells which also appeared to have experienced a blockage in their differentiation into chondroblasts. Ultrastructurally, the latter cells responded in the formation of adherent profiles of plasma membranes, whereas the differentiated zone of the cartilage reduced its size. Using serum-free medium, hPTH (1-34) also brought about an inhibition in alkaline phosphatase activity, a fact that was not encountered in medium containing serum. By contrast, hPTH (28-48) had no mitogenic effect, although treated specimens revealed morphological changes in the chondroprogenitor cell zone along with an enhancement of cartilage cells hypertrophy. No significant effects on either mitogenecity or morphology could be noted in hPTH (53-84)-treated cultures.Various in vivo studies with parathyroid hormone have shown that the epiphyseal growth plate usu¬ ally responds in a marked widening and in an in¬ crease in the number of chondroclasts along its ossification zone (1,2). These findings, along with others in earlier studies, appeared to suggest that PTH possesses a growth-stimulating effect on car¬ tilage. However, in order to gain further under¬ standing as to the mechanisms involved in the ac¬ tivity of PTH, one had to turn to in vitro studies. Kawashima et al. (3) carried out a series of organculture studies whereby the growth of cartilage of 9-day-old chick embryo femur was stimulated by PTH (500 U/l). In a subsequent study, Kawashima et al. (4) indicated that the stimulatory effects of PTH were exerted selectively upon the more mature, non-dividing hypertrophie chondrocytes, whereas younger cells did not respond to this hor¬ mone. Suzuki et al. (5) were the first to investigate the effects of PTH in tissue cultures of chon¬ drocytes isolated from growth cartilage of young male rats, finding that the hormone (100 (tg/1) in¬ duced a marked stimulatory effect upon the syn¬ thesis of proteoglycans. Takigawa et al. (6), who extended the original studies of Suzuki et al.,showed that PTH also increased the level of cAMP in chondrocytes, but had no effect upon DNA syn¬ thesis in cultured chondrocytes. Burch 8c Lebovitz (7) using chick pelvic cartilage in vitro, reported that PTH (10 nmol/1) increased the DNA content by 5...

In VivoAnabolic Effects of Parathyroid Hormone (PTH) 28–48 and N-Terminal Fragments of PTH and PTH-Related Protein on Neonatal Mouse Bones1

“…3), which means that the stimulation to proliferation could be maintained also by the somewhat older condyles. In our previous in vitro study, we observed that the midregion fragment enhanced maturation, hypertrophy, and mineralization of the chondrocytes (23). This earlier observation is in agreement with the results obtained in the present study, which showed that the proliferative effect of PTH (28 -48) was also accompanied by a rise in protein content.…”

Effect of 1–34 human parathyroid hormone upon first trimester placental human chorionic gonadotrophin secretion in vitro: potentiation by epidermal growth factor

“…The involvement of 1-34 PTH, a calciotrophic fragment, in promoting calcified tissue growth has been recently demonstrated (Shurtz-Swirski et al, 1990). Our data provide evidence that this fragment of PTH also has an endocrine effect by stimulating HCG secretion by first trimester placental explants in vitro.…”

“…The secretion of a lower molecular weight fragment, namely 1-34 PTH, has also been described. This fragment, when compared to the whole molecule, acts as a mitogen on murine mandibular condylar cartilage in vitro, in addition to its calciotrophic effects which are also ascribed to the whole hormone (Milstone et al, 1989;Shurtz-Swirski et al, 1990). Recently specific binding sites for PTH were identified in the human placenta (Lafond et al, 1988).…”

Individual and combined effects of calciotropic hormones and growth factors on mineral metabolism in embryonic chick tibiae

“…Furthermore, PTH is rapidly degraded and has a biological half-life only of minutes in vivo. The presence of FCS abolished the inhibitory, effect of PTH on ALP activity, as was reported in the condylar organ system (28). Therefore, the influence of FCS on FFH activity was assayed.…”

“…Bone organ cultures have been used extensively to investigate the actions of vitamins, hormones, and growth factors individually on bone calcium turnover (8,20,21,23,25,26,28,33). However, in rive these agents never occur in isolation, and to realistically describe their role in the complex process of bone growth and remodeling, it is necessary to study the interactions of ealciotropic hormones and multiple mediators in vitro.…”