Mechanism of action of parathyroid hormone‐induced proteoglycan synthesis in the growth plate chondrocyte

During embryogenesis, the expression of mammalian stanniocalcin (STC1) in the appendicular skeleton suggests its involvement in the regulation of longitudinal bone growth. Such a role is further supported by the presence of dwarfism in mice overexpressing STC1. Yet, the STC 1 inhibitory effect on growth may be related to both postnatal metabolic abnormalities and prenatal defective bone formation. In our study, we used an organ culture system to evaluate the effects of STC on growth plate chondrogenesis, which is the primary determinant of longitudinal bone growth. Fetal rat metatarsal bones were cultured in the presence of recombinant human STC (rhSTC). After 3 days, rhSTC suppressed metatarsal growth, growth plate chondrocyte proliferation and hypertrophy/differentiation, and extracellular matrix synthesis. In addition, rhSTC increased the number of apoptotic chondrocytes in the growth plate. In cultured chondrocytes, rhSTC increased phosphate uptake, reduced chondrocyte proliferation and matrix synthesis, and induced apoptosis. All these effects were reversed by culturing chondrocytes with rhSTC and phosphonoformic acid, an inhibitor of phosphate transport. The rhSTC-mediated inhibition of metatarsal growth and growth plate chondrocyte proliferation and hypertrophy/differentiation was abolished by culturing metatarsals with rhSTC and phosphonoformic acid. Taken together, our findings indicate that STC1 inhibits longitudinal bone growth directly at the growth plate. Such growth inhibition, likely mediated by an increased chondrocyte phosphate uptake, results from suppressed chondrocyte proliferation, hypertrophy/differentiation, and matrix synthesis and by increased apoptosis. Last, the expression of both STC1 and its binding site in the growth plate would support an autocrine/paracrine role for this growth factor in the regulation of growth plate chondrogenesis. Stanniocalcin (STC)2 is a glycoprotein first identified as a secretory product of the corpuscles of Stannius, an endocrine gland unique to bony fish (1, 2). The primary function of STC in fish is to prevent hypercalcemia (3) by inhibiting calcium uptake by the gills and gut and stimulating phosphate reabsorption by the kidneys (1, 4).The mammalian homolog of STC (STC1) has been found in humans, rats, and mice (5-7). Human and mouse STC1 proteins are closely related to each other (98% amino acid identity) and share 80% amino acid identity with fish STC (5). Compared with fish STC, STC1 seems to have a preferential effect on phosphate metabolism than on calcium metabolism (8, 9), with evidence suggesting that sodium-dependent P i (NaP i ) transporter(s) may be a target of STC1 activity (10). Although fish STC is primarily expressed in one organ (the corpuscle of Stannius), mammalian STC1 is virtually ubiquitous. The distribution of STC protein and/or mRNA in multiple organs such as kidney, intestine, heart, thyroid, lung, placenta, brain (11-15), and bone (with virtually undetectable serum levels) (11) would suggest a paracrine rather than an endocrine ...

Section: Stanniocalcin (Stc)mentioning

confidence: 99%

mentioning

confidence: 99%

Stanniocalcin 1 Acts as a Paracrine Regulator of Growth Plate Chondrogenesis

Yoshiko

Luca

2006

“…The role of IGF-I in chondrocyte proteoglycan synthesis has been well documented (27)(28)(29)(30). Furthermore, PTH has been shown to alter local IGF-I levels in calvaria (21,22).…”

Section: Fig 8 Reciprocal Relationship Between Aggrecan and Ig-fbp-mentioning

confidence: 99%

Parathyroid Hormone-(1–34) Enhances Aggrecan Synthesis via an Insulin-like Growth Factor-I Pathway

Frolik

Chandrasekhar

1999

During endochondral bone formation, the growth plate chondrocytes proliferate, become hypertrophic, lose the cartilage phenotype, undergo mineralization, and provide a scaffold upon which subsequent longitudinal bone growth occurs. Parathyroid hormone (PTH), a calcium-regulating hormone, and parathyroid hormone-related peptide (PTHrP), which shares several properties with PTH, have profound effects on skeletal growth and new bone formation. In order to define further the mechanism by which PTH/PTHrP promotes the cartilage phenotype, chondrocytes isolated from the rib cages of developing rat embryos were evaluated for the biosynthesis of aggrecan. Cells treated with PTH-(1-34) for a 4-h period followed by a 20-h recovery period showed a significant increase in cartilage proteoglycan (aggrecan) synthesis in a dose-dependent manner. Only N-terminally intact PTH and PTHrP were effective in stimulating aggrecan synthesis. Addition of a neutralizing antibody to insulin-like growth factor-I (IGF-I) during PTH treatment resulted in the inhibition of PTHstimulated aggrecan synthesis, whereas the addition of a neutralizing antibody to insulin-like growth factorbinding protein-2 (IGFBP-2) resulted in an increase in synthesis in both the control and PTH-treated cells. In addition, PTH treatment resulted in an increase in the mRNA for aggrecan, a reduction in IGFBP-3 mRNA, and no discernible changes in IGF-I mRNA levels, which was complemented by quantitative changes in IGFBP-3 and free IGF-I levels. The reciprocal relationship in the expression of aggrecan and IGFBP was further confirmed in chondrocytes from various gestational stages during normal development. Collectively, our results indicate that the effect of PTH may be mediated at least in part through the regulation of the IGF/IGFBP axis, by a decrease in the level of IGFBP-3, and an increase in free IGF-I levels. It is likely that the local increase in IGF-I may lead to an increase in cartilage type proteoglycan synthesis and maintenance of the cartilage phenotype.

“…Longitudinal growth occurs at the growth plate by endochondral ossification, a process in which cartilage is formed and then remodeled into bone (1,2). The multistep process of chondrogenesis involves: 1) the aggregation of mesenchymal cells into prechondrogenic condensations, 2) differentiation of the condensed prechondrogenic mesenchyme into small immature chondrocytes, and 3) chondrocyte maturation followed by ossification, starting in the center of the element.…”

mentioning

confidence: 99%

“…Bone morphogenetic proteins (BMPs) 1 play an important role in skeletal development (3)(4)(5). At the early stage of bone development, BMP-2 and BMP-4 are expressed in specific areas of the limb bud 3 and misexpression of noggin, a glycoprotein that blocks actions of BMP-2 and BMP-4, prior to the onset of chondrogenesis leads to the total absence of skeletal elements (6), suggesting that BMP signaling is absolutely required for prechondrogenic condensations.…”

mentioning

confidence: 99%

NF-κB Specifically Activates BMP-2 Gene Expression in Growth Plate Chondrocytes in Vivo and in a Chondrocyte Cell Line in Vitro

Feng

Xing

Zhang

et al. 2003

111

102

In long bones, morphogenesis is followed by an extended period of growth. Longitudinal growth occurs at the growth plate by endochondral ossification, a process in which cartilage is formed and then remodeled into bone (1, 2). The multistep process of chondrogenesis involves: 1) the aggregation of mesenchymal cells into prechondrogenic condensations, 2) differentiation of the condensed prechondrogenic mesenchyme into small immature chondrocytes, and 3) chondrocyte maturation followed by ossification, starting in the center of the element.Bone morphogenetic proteins (BMPs) 1 play an important role in skeletal development (3-5). At the early stage of bone development, BMP-2 and BMP-4 are expressed in specific areas of the limb bud 3 and misexpression of noggin, a glycoprotein that blocks actions of BMP-2 and BMP-4, prior to the onset of chondrogenesis leads to the total absence of skeletal elements (6), suggesting that BMP signaling is absolutely required for prechondrogenic condensations. At the late stage, BMP-2, expressed in the growth plate of long bone, accelerates longitudinal bone growth by stimulating growth plate chondrocyte proliferation and hypertrophy (7,8).To understand the regulatory mechanism of BMP-2 gene, we have previously characterized the BMP-2 promoter and identified control elements in osteoblasts and chondrocytes in BMP-2 gene (9). BMP-2 autoregulates its own expression through its proximal promoter (10) in a similar fashion that the decapentaplegic (dpp) gene is regulated in drosophila. dpp is a drosophila homologue of BMP-2. In drosophila, expression of dpp is regulated by dorsal, a homologue of mammalian NF-B (11, 12). In chick embryo, overexpression of a mutated form of I-B␣ protein, which blocks NF-B activation, leads to abnormality in limb bud development, and changes in downstream signals include BMP-4 (13). These findings suggest that NF-B may participate in the regulatory process of the BMP-2 gene.NF-B is a group of transcription factors including five members, p65, c-Rel, RelB, p50, and p52. They form homodimers or heterodimers to regulate expression of a variety of genes and are involved in many biological functions (14). It has been demonstrated previously that NF-B family members p50 and p52 are absolutely required for osteoclast development and p50/p52 double knock-out (dKO) mice failed to form osteoclasts and developed severe osteopetrosis (15).The role of NF-B in BMP-2 gene expression and functions of NF-B in other bone cells, such as chondrocytes, have not been reported. In the present studies, we have examined the regulatory mechanism of BMP-2 by NF-B in chondrocytes in vitro and in vivo. We searched the Ϫ2712/ϩ165 region of BMP-2 gene and found two putative NF-B response elements. Using different experimental approaches, we demonstrate that these NF-B response elements are functional in chondrocytes and NF-B positively regulates BMP-2 gene transcription through these response elements. We also show that in growth plate chondrocytes of 2-week-old NF-B p50/p52 dKO mice, BMP-...