Parathyroid Hormone (1-34) Receptor-Binding and Second-Messenger Response in Rat Incisor Odontoblasts (original) (raw)
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Disturbed tooth development in parathyroid hormone-related protein (PTHrP)-gene knockout mice
Bone, 2002
In tooth germs, PTHrP is expressed in the enamel organ (epithelial component), whereas its major receptor, the type I PTH/PTHrP receptor is expressed in cells of the alveolar bone and dental follicle (mesenchymal components). To clarify the role of PTHrP during fetal tooth germ development, PTHrP gene-knockout mice were used for histochemical and ultrastructural analysis. In wild-type mice, osteoclastic cells were aligned predominantly in the inner aspects of the alveolar bone surrounding the developing tooth germs throughout the late embryonic (after embryonic, 17.5 days) and neonatal animals examined. In contrast, osteoblasts were predominant in corresponding areas of fetal homozygous PTHrP-gene knockout mice with only occasional osteoclasts. In such areas, cell-free surfaces showing cement line-like tartrate-resistant acid phosphatase (TRAP) reactions were frequently observed. In neonatal homozygous mice, bone spicules were often shown to penetrate and/or compress the enamel organ and caused partial destruction of the tooth germs. Osteoclasts were few in number in the inner aspects of the alveolar bone, and had poorly developed ruffled border. No morphological abnormality was noted in cells of the tooth germs proper. On bone surfaces away from developing tooth germs, functional osteoclasts with structural features similar to those in wild-type mice were observed in homozygous mice. These observations suggest that PTHrP is required to maintain an appropriate spatiotemporal arrangement of bone cells and osteoclast function, which are necessary for the normal development of tooth germ and alveolar bone encasing the tooth germ. The observation also demonstrates that PTHrP deficiency affects the structure and function of osteoclasts exclusively those located in the vicinity of the growing tooth germ. (Bone 30: 48 -56; 2002)
Archives of Oral Biology, 2002
In a previous study, it was shown that tooth germs of neonatal homozygous parathyroid hormone-related protein (PTHrP)knockout mice are penetrated or compressed by the surrounding alveolar bone, suggesting an important role for PTHrP in the formation and activation of osteoclasts around growing tooth germs. In order to elucidate the role of PTHrP during the development of the tooth germ and related structures, mandibular explants containing cap stage tooth germs of embryonic day 14, homozygous mice were here cultured with or without surrounding alveolar bone. There was no difference in the number of tartrate-resistant acid phosphatase-positive multinucleated osteoclastic cells around the first molars of homozygous and wild-type mice. After 10 days of culture, osteoclastic cells were rarely present in explants from homozygous mice and penetration of alveolar bone into the dental papilla was observed. The decline in osteoclast number was partly restored by the addition of PTHrP to the culture. Tooth germs of both wild-type and homozygous mice cultured without alveolar bone developed well, with no apparent structural abnormality; dentine formation was evident after 10 days. These data suggest that PTHrP is not required for the development of the tooth germ proper but is indispensable in promoting the osteoclast formation required to accommodate that development.
Cell Calcium, 1985
It has been suggested that intracellular Ca2+, in addition to CAMP, plays an important role in PTH-stimulated bone resorption. There is now strong evidence indicating that the osteoblast is the main target cell for PTH action, regulating indirectly, via cell-cell communication , osteoclastic bone resorption. In order to investigate the possible role of free cytosolic calcium in stimulated bone resorption, we studied the effects of the intact hormone (bPTH l-84) and some of its fragments (bPTH(l-34), bPTH(3-34,) (Nle-8, Nle-18,Tyr-34)bPTH q-34)amide) on ;! their capacity to modify the cytosolic Ca concentration in rat osteoblast-like cells. The experiments were performed using Quin-2, a fluorescent indicator of free calcium. We found an excellent correlation between the ability of PTH and PTH transiently increase cytosolic Ca2+ concentra~f~~me4~s rL"t osteoblast-like cells and their ability to stimulate bone resorption in embryonic rat calvaria in vitro. On the other hand, no direct correlation was found for the CAMP and boneresorbing responses. On the ground of these data we propose a two-receptor model for PTH action in osteoblasts, in which one receptor is coupled to the production of CAMP, whereas the other is involved in the increase of cytosolic Ca2+. Activation of both receptors by PTH (l-84) or PTH (l-34) leads to the full physiological response in osteoblasts, most probably the release of one or more factors which stimulate the activity of existing osteoclasts and others which stimulate the recruitment of additional osteoclasts.
Journal of Bone and Mineral Research, 2009
PTH is regarded conventionally as a catabolic hormone that stimulates osteoclastic resorption of bone. However, it has been known since 1932 that intermittent pulses of PTH stimulate bone formation in animals and humans. PTH independently activates two signal mechanisms: one that stimulates adenylyl cyclase and one that stimulates protein kinase C (PKC). The goal of this study was to use the 3- to 5-month-old ovariectomized (OVX) rat model to determine which of the two signal mechanisms is responsible for the anabolic action of PTH on bone. OVX triggered a large loss of trabecular bone without significantly affecting the normal slow growth of cortical bone in the distal halves of the femora. Daily injections of human hPTH(1-34) fragment (1 nmol/100 g body weight), which stimulated both adenylyl cyclase and membrane-associated PKC activity in osteoblast-like ROS 17/2 rat osteosarcoma cells, stimulated the growth of both cortical and trabecular bone in the OVX rats. Daily injections of the same dose of hPTH(1-31), which stimulated adenylyl cyclase but not PKC in ROS 17/2 cells, stimulated trabecular bone growth in the OVX rats less effectively than hPTH(1-34), but it stimulated cortical bone growth as rapidly and as dramatically as hPTH(1-34). Injections of equimolar amounts of desamino-hPTH(1-34) [N-propionyl(2-3)hPTH-amide], which stimulated PKC as strongly as hPTH(1-34) in ROS 17/2 cells but had a drastically reduced ability to stimulate adenylyl cyclase, or injections of recombinant hPTH(8-84) which stimulated PKC only in the ROS 17/2 cells, did not stimulate cortical or trabecular bone growth in the OVX animals. Thus, cyclic AMP and cyclic AMP-dependent protein kinases may be the primary mediators of the anabolic action of intermittent pulses of PTH on bone in OVX rats.
Short-term PTH administration increases dentine apposition and microhardness in mice
Archives of oral biology, 2012
The purpose of this study is to investigate the effects of intermittent parathyroid hormone (PTH) administration on the apposition rate and structural features of dentine from mouse incisors. Young male A/J Unib mice were treated daily for 6 and 10 days with 40 μg/kg of hPTH 1-34 or a vehicle. Dentine apposition rates measured by fluorescent labels (tetracycline and calcein) and alkaline phosphatase (ALP) plasma levels were evaluated after 6 days of treatment. Knoop microhardness testing and element content measurements in at.% of calcium (Ca), phosphorus (P), oxygen (O), and magnesium (Mg) in the peritubular and intertubular dentine were performed by Energy Dispersive X-ray (EDX) microanalysis via Scanning Electron Microscopy (SEM) after 10 days of treatment. Histometric analysis revealed an increase of 5% in the apposition rate of dentine and 25% in the ALP plasma levels in the PTH treated group. In addition, knoop microhardness testing revealed that the animals treated with PTH h...
Hormonal reactivity in tooth germsin vitro: Effects of parathyroid hormone and calcitonin
Calcified Tissue Research, 1976
For many years it had been generally accepted that the ameloblasts secrete minerals which enter the matrix during maturation. With radioactive tracers it has been shown that substances may enter the enamel from dentine via the odontoblastic processes. Studies have clearly demonstrated that the odontoblasts and osteoblasts undergo a common pathway of development involving proliferating and sequential cytodifferentiation of mesenchyneal precursors . It is the purpose of this paper to describe some findings from studies on calcium release from tooth germs in contact with the principal hormones responsible for the stimulation and inhibition of movement of calcium in living hard tissue.
Journal of Clinical Investigation, 1985
To determine the structural requirements for parathyroid hormone (PTH) activity in mature bone, we perfused the surgically isolated hindquarters of adult male rats with either native bovine PTH-(1-84) IbPTH-(1-84)i or the synthetic amino-terminal fragment, bovine PTH-(1-34) j. Changes in the release of cyclic AMP (cAMP) and bone Gla protein (BGP) were monitored as evidence of bone-specific response to PTH; tissue specificity of the cAMP response was confirmed through in vitro examination of nonskeletal tissue response to PTH. Biologically active, monoiodinated "I-bbPTH-(1-84) was administered to determine if mature murine bone cleaves native hormone. We found that perfused rat bone continuously releases BGP, and that both bPTH41-84) and bPTH41-34) acutely suppress this release. In addition, both hormones stimulate cAMP release from perfused rat hindquarters. When examined on a molar basis, the magnitude ofthe cAMP response was dose-dependent and similar for both hormones, with doses yielding half-maximal cAMP responses. The response for bPTH41-34) was 0.5 nmol and for bPTH-(1-84) was 0.7 nntol. Moreover, biologically active "SI-bPTH41-84) was not metabolized in our hindquarter perfusion system. These findings indicate that PTH41-84) does not require extraskeletal or skeletal cleavage to an amino-terminal fragment in order to stimulate cAMP generation in, or suppress BGP release from, mature rat bone.
Journal of Biological Chemistry, 2001
The regulation of tissue turnover requires the coordinated activity of both local and systemic factors. Nucleotides exist transiently in the extracellular environment, where they serve as ligands to P2 receptors. Here we report that the localized release of these nucleotides can sensitize osteoblasts to the activity of systemic factors. We have investigated the ability of parathyroid hormone (PTH), a principal regulator of bone resorption and formation, to potentiate signals arising from nucleotide stimulation of UMR-106 clonal rat osteoblasts. PTH receptor activation alone did not lead to [Ca(2+)](i) elevation in these cells, indicating no G(q) coupling, however, activation of G(q)-coupled P2Y(1) receptors resulted in characteristic [Ca(2+)](i) release. PTH potentiated this nucleotide-induced Ca(2+) release, independently of Ca(2+) influx. PTH-(1-31), which activates only G(s), mimicked the actions of PTH-(1-34), whereas PTH-(3-34), which only activates G(q), was unable to potentiate nucleotide-induced [Ca(2+)](i) release. Despite this coupling of the PTHR to G(s), cAMP accumulation or protein kinase A activation did not contribute to the potentiation. 3-Isobutyl-1-methylxanthine, but not forskolin effectively potentiated nucleotide-induced [Ca(2+)](i) release, however, further experiments proved that cyclic monophosphates were not involved in the potentiation mechanism. Costimulation of UMR-106 cells with P2Y(1) agonists and PTH led to increased levels of cAMP response element-binding protein phosphorylation and a synergistic effect was observed on endogenous c-fos gene expression following costimulation. In fact the calcium responsive Ca/cAMP response element of the c-fos promoter alone was effective at driving this synergistic gene expression. These findings demonstrate that nucleotides can provide a targeted response to systemic factors, such as PTH, and have important implications for PTH-induced signaling in bone.
Parathyroid hormone-related peptide as an endogenous inducer of parietal endoderm differentiation
The Journal of cell biology, 1993
Parathyroid hormone related peptide (PTHrP), first identified in tumors from patients with the syndrome of "Humoral Hypercalcemia of Malignancy," can replace parathyroid hormone (PTH) in activating the PTH-receptor in responsive cells. Although PTHrP expression is widespread in various adult and fetal tissues, its normal biological function is as yet unknown. We have examined the possible role of PTHrP and the PTH/PTHrP-receptor in early mouse embryo development. Using F9 embryonal carcinoma (EC) cells and ES-5 embryonic stem (ES) cells as in vitro models, we demonstrate that during the differentiation of these cells towards primitive and parietal endoderm-like phenotypes, PTH/PTHrP-receptor mRNA is induced. This phenomenon is correlated with the appearance of functional adenylate cyclase coupled PTH/PTHrP-receptors. These receptors are the mouse homologues of the recently cloned rat bone and opossum kidney PTH/PTHrP-receptors. Addition of exogenous PTH or PTHrP to RA-trea...
Journal of Biological …, 2001
The regulation of tissue turnover requires the coordinated activity of both local and systemic factors. Nucleotides exist transiently in the extracellular environment, where they serve as ligands to P2 receptors. Here we report that the localized release of these nucleotides can sensitize osteoblasts to the activity of systemic factors. We have investigated the ability of parathyroid hormone (PTH), a principal regulator of bone resorption and formation, to potentiate signals arising from nucleotide stimulation of UMR-106 clonal rat osteoblasts. PTH receptor activation alone did not lead to [Ca 2؉ ] i elevation in these cells, indicating no G q coupling, however, activation of G q-coupled P2Y 1 receptors resulted in characteristic [Ca 2؉ ] i release. PTH potentiated this nucleotide-induced Ca 2؉ release, independently of Ca 2؉ influx. PTH-(1-31), which activates only G s , mimicked the actions of PTH-(1-34), whereas PTH-(3-34), which only activates G q , was unable to potentiate nucleotide-induced [Ca 2؉ ] i release. Despite this coupling of the PTHR to G s , cAMP accumulation or protein kinase A activation did not contribute to the potentiation. 3-Isobutyl-1methylxanthine, but not forskolin effectively potentiated nucleotide-induced [Ca 2؉ ] i release, however, further experiments proved that cyclic monophosphates were not involved in the potentiation mechanism. Costimulation of UMR-106 cells with P2Y 1 agonists and PTH led to increased levels of cAMP response elementbinding protein phosphorylation and a synergistic effect was observed on endogenous c-fos gene expression following costimulation. In fact the calcium responsive Ca/cAMP response element of the c-fos promoter alone was effective at driving this synergistic gene expression. These findings demonstrate that nucleotides can provide a targeted response to systemic factors, such as PTH, and have important implications for PTH-induced signaling in bone.