Anabolic Actions of Parathyroid Hormone during Bone Growth Are Dependent on c-fos

Abstract PTH has anabolic and catabolic actions in bone that are not clearly understood. The protooncogene c-fos and other activating protein 1 family members are critical transcriptional mediators in bone, and c-fos is up-regulated by PTH. The purpose of this study was to examine the mechanisms of PTH and the role of c-fos in PTH-mediated anabolic actions in bone. Mice with ablation of c-fos (−/−) and their wild-type (+/+) and heterozygous (+/−) littermates were administered PTH for 17 d. The +/+ mice had increased femoral bone mineral density (BMD), whereas −/− mice had reduced BMD after PTH treatment. PTH increased the ash weight of +/+ and +/−, but not −/−, femurs and decreased the calcium content of −/−, but not +/+ or +/−, femurs. Histomorphometric analysis showed that PTH increased trabecular bone volume in c-fos +/+, +/− vertebrae, but, in contrast, decreased trabecular bone in −/− vertebrae. Serum calcium levels in +/+ mice were greater than those in −/− mice, and PTH increased calcium in −/− mice. Histologically, PTH resulted in an exacerbation of the already widened growth plate and zone of hypertrophic chondrocytes but not the proliferating zone in −/− mice. PTH also increased calvarial thickness in +/+ mice, but not −/− mice. The c-fos −/− mice had lower bone sialoprotein and osteocalcin (OCN), but unaltered PTH-1 receptor mRNA expression in calvaria, suggesting an alteration in extracellular matrix. Acute PTH injection (8 h) resulted in a decrease in osteocalcin mRNA expression in wild-type, but unaltered expression in −/−, calvaria. These data indicate that c-fos plays a critical role in the anabolic actions of PTH during endochondral bone growth.

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Gelsolin Deficiency Blocks Podosome Assembly and Produces Increased Bone Mass and Strength

The Journal of Cell Biology ◽

10.1083/jcb.148.4.665 ◽

2000 ◽

Vol 148 (4) ◽

pp. 665-678 ◽

Cited By ~ 173

Author(s):

Meenakshi Chellaiah ◽

Neil Kizer ◽

Matthew Silva ◽

Ulises Alvarez ◽

David Kwiatkowski ◽

...

Keyword(s):

Bone Resorption ◽

Bone Growth ◽

Skeletal Development ◽

Critical Role ◽

Focal Adhesions ◽

Αvβ3 Integrin ◽

Endochondral Bone ◽

Trabecular Thickness ◽

Signaling Complex ◽

Cartilage Proteoglycans

Osteoclasts are unique cells that utilize podosomes instead of focal adhesions for matrix attachment and cytoskeletal remodeling during motility. We have shown that osteopontin (OP) binding to the αvβ3 integrin of osteoclast podosomes stimulated cytoskeletal reorganization and bone resorption by activating a heteromultimeric signaling complex that includes gelsolin, pp60c-src, and phosphatidylinositol 3′-kinase. Here we demonstrate that gelsolin deficiency blocks podosome assembly and αvβ3-stimulated signaling related to motility in gelsolin-null mice. Gelsolin-deficient osteoclasts were hypomotile due to retarded remodeling of the actin cytoskeleton. They failed to respond to the autocrine factor, OP, with stimulation of motility and bone resorption. Gelsolin deficiency was associated with normal skeletal development and endochondral bone growth. However, gelsolin-null mice had mildly abnormal epiphyseal structure, retained cartilage proteoglycans in metaphyseal trabeculae, and increased trabecular thickness. With age, the gelsolin-deficient mice expressed increased trabecular and cortical bone thickness producing mechanically stronger bones. These observations demonstrate the critical role of gelsolin in podosome assembly, rapid cell movements, and signal transduction through the αvβ3 integrin.

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Haploinsufficiency of osterix in chondrocytes impairs skeletal growth in mice

Physiological Genomics ◽

10.1152/physiolgenomics.00111.2013 ◽

2013 ◽

Vol 45 (19) ◽

pp. 917-923 ◽

Cited By ~ 12

Author(s):

Shaohong Cheng ◽

Weirong Xing ◽

Xin Zhou ◽

Subburaman Mohan

Keyword(s):

Bone Growth ◽

Skeletal Growth ◽

Endochondral Bone Formation ◽

Volumetric Bone Mineral Density ◽

Mineral Density ◽

Endochondral Bone ◽

Alizarin Red ◽

Adult Mice ◽

Elevated Expression ◽

Skeletal Phenotype

Osterix ( Osx) is essential for both intramembranous or endochondral bone formation. Osteoblast-specific ablation of Osx using Col1α1-Cre resulted in osteopenia, because of impaired osteoblast differentiation in adult mice. Since Osx is also known to be expressed in chondrocytes, we evaluated the role of Osx expressed in chondrocytes by examining the skeletal phenotype of mice with conditional disruption of Osx in Col2α1-expressing chondrocytes. Surprisingly, Cre-positive mice that were homozygous for Osx floxed alleles died after birth. Alcian blue and alizarin red staining revealed that the lengths of skeleton, femur, and vertebrae were reduced by 21, 26, and 14% ( P < 0.01), respectively, in the knockout (KO) compared with wild-type mice. To determine if haploid insufficiency of Osx in chondrocytes influenced postnatal skeletal growth, we compared skeletal phenotype of floxed heterozygous mice that were Cre-positive or Cre-negative. Body length was reduced by 8% ( P < 0.001), and areal BMD of total body, femur, and tibia was reduced by 5, 7, and 8% ( P < 0.05), respectively, in mice with conditional disruption of one allele of Osx in chondrocytes. Micro-CT showed reduced cortical volumetric bone mineral density and trabecular bone volume to total volume in the femurs of Osxflox/+; col2α1-Cre mice. Histological analysis revealed that the impairment of longitudinal growth was associated with disrupted growth plates in the Osxflox/+; col2α1-Cre mice. Primary chondrocytes isolated from KO embryos showed reduced expression of chondral ossification markers but elevated expression of chondrogenesis markers. Our findings indicate that Osx expressed in chondrocytes regulates bone growth in part by regulating chondrocyte hypertrophy.

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Bone Microarchitectural Changes in Hyperthyroid Women Compared to a Normal Canadian Cohort

Journal of the Endocrine Society ◽

10.1210/jendso/bvab048.521 ◽

2021 ◽

Vol 5 (Supplement_1) ◽

pp. A256-A257

Author(s):

Terra G Arnason ◽

David Cooper ◽

Reza Behdani ◽

Saija Kontulainen

Keyword(s):

Thyroid Hormone ◽

Thyroid Hormones ◽

Fracture Risk ◽

Trabecular Bone ◽

Bone Microarchitecture ◽

Critical Role ◽

Primary Objective ◽

Mineral Density ◽

Tsh Suppression ◽

Increased Risk

Abstract Thyroid hormones play a critical role in bone physiology during childhood, but also impacts adult bone metabolism. Hyperthyroidism promotes accelerated bone turnover and bone remodelling which is associated with net loss of bone mineral density over time (BMD) and these changes have been quantitated using the gold standard of measuring BMD, Dual Energy X-ray Absorptiometry (DEXA). Ordinarily, biochemical thyroid hormone normalization restores BMD towards normal, yet an increased risk of fractures remains lifelong. DEXA, therefore, cannot explain the underlying etiology for fracture risk which may be due to undetected changes in bone microarchitecture. Our primary objective was to utilize an investigational 3-dimensional bone imaging technology, High Resolution peripheral Quantitative Tomography (HR-pQCT), to study bone microarchitecture in actively hyperthyroid women to determine if there are changes in cortical and trabecular bone microarchitecture from that of age-matched controls. A subset of women were rescanned using HR-pCT after thyroid hormones had been normalized for at least 6 months to determine if there were cortical/trabecular architectural changes that reversed towards normal in these individual cases. We enrolled 20 hyperthyroid women (age 20–76) for this pilot study who had persistent TSH suppression for >3 months (TSH< 0.5, normal range: 0.5–4.49 mU/L) without secondary causes for bone loss. Their etiology was divided amongst TSH suppression for thyroid carcinoma, Grave’s disease and iatrogenic hyperthyroidism. HR-pQCT scans of the radius were compared to age-matched scans of normal females, available from the robust Canadian Multicentre Osteoporosis Study (CaMOS) control cohort. Four participants were re-scanned after 6 months of TSH normalization to assess reversibility. The observed data showed statistically significant differences in key parameters of bone microarchitecture in hyperthyroidism, independent of etiology. We observed decreased cortical thickness and increased failure load as statistically different from age-matched controls. Increases in cortical bone porosity and decreases in volumetric bone density (cortical, trabecular and total) were notable but did not reach significance in this small study. Repeat scans following normalization of thyroid hormone levels revealed consistent (partial, nonsignificant) normalization of multiple bone microarchitecture elements including increased trabecular number/thickness, and decreased cortical porosity. These findings suggest that there are changes in both cortical and trabecular bone during active hyperthyroidism that may contribute to increased lifelong fracture risk.

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Endochondral bone growth, bone calcium accretion, and bone mineral density: how are they related?

The Journal of Physiological Sciences ◽

10.1007/s12576-012-0212-0 ◽

2012 ◽

Vol 62 (4) ◽

pp. 299-307 ◽

Cited By ~ 21

Author(s):

Kannikar Wongdee ◽

Nateetip Krishnamra ◽

Narattaphol Charoenphandhu

Keyword(s):

Bone Mineral Density ◽

Bone Mineral ◽

Bone Growth ◽

Mineral Density ◽

Endochondral Bone ◽

Bone Calcium

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Differential Expression of Alkaline Phosphatase and PHOSPHO1 in Bone from a Murine Model of Chronic Kidney Disease

10.1101/2021.08.06.455411 ◽

2021 ◽

Author(s):

Shun-Neng Hsu ◽

Louise A Stephen ◽

Scott Dillon ◽

Elspeth Milne ◽

Amanda Novak ◽

...

Keyword(s):

Chronic Kidney Disease ◽

Alkaline Phosphatase ◽

Kidney Disease ◽

Trabecular Bone ◽

Mrna Expression ◽

Cortical Bone ◽

Murine Model ◽

Dependent Manner ◽

Mineral Density ◽

Concentration Dependent Manner

Chronic kidney disease-mineral bone disorder (CKD-MBD) is a systemic disorder characterized by altered mineral and bone metabolism. The role of PHOSPHO1 and tissue-nonspecific alkaline phosphatase (TNAP) in controlling bone mineralization in CKD-MBD is unclear. We utilized the adenine-induced murine model of CKD-MBD in which mice present with hyperphosphatemia, hyperparathyroidism, and elevated FGF23 levels, and bone turnover markers. Micro-CT and histomorphometric analysis revealed microarchitectural changes to the trabecular and cortical bone of CKD mice. Furthermore, CKD cortical bone mineral density (BMD) was increased (p < 0.05) whereas CKD trabecular bone BMD was decreased (p < 0.05). These changes were accompanied by decreased Alpl mRNA expression (p < 0.001) and increased Phospho1 mRNA expression (p < 0.01) in CKD bones, which were confirmed at the protein level. Cortical bone BMD was unchanged in Phospho1 knockout (P1KO) CKD mice suggesting that the increased cortical BMD noted in CKD was driven by the increased PHOSPHO1 expression. Intriguingly, other structural parameters were improved in P1KO CKD mice. In an attempt to determine the causes of the mineralization defects noted in the CKD mice, we investigated the direct effects of FGF23, PTH, and phosphate (Pi) administration on PHOSPHO1 and TNAP expression by primary murine osteoblasts. PHOSPHO1 and TNAP expression were down-regulated in a concentration-dependent manner by Pi and PTH whereas the effects of FGF23 treatment, with or without klotho, were less marked. Osteoblast matrix mineralization was increased with Pi, decreased with PTH in a concentration-dependent manner and FGF23 had no effect. In summary, this pre-clinical model of CKD presented with hypomineralization of trabecular bone but hypermineralisation of cortical bone. Similarly, divergent expression levels of TNAP and PHOSPHO1 were noted in CKD. These novel observations implicate these key phosphatases in the etiology of CKD-MBD and may help explain the disordered skeletal mineralization characteristic of this progressive disorder.

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Effects of hypothyroidism on the structure and mechanical properties of bone in the ovine fetus

Journal of Endocrinology ◽

10.1530/joe-11-0138 ◽

2011 ◽

Vol 210 (2) ◽

pp. 189-198 ◽

Cited By ~ 11

Author(s):

S A Lanham ◽

A L Fowden ◽

C Roberts ◽

C Cooper ◽

R O C Oreffo ◽

...

Keyword(s):

Thyroid Hormone ◽

Thyroid Hormones ◽

Trabecular Bone ◽

Growth And Development ◽

Bone Growth ◽

Bone Structure ◽

Metatarsal Bone ◽

Postnatal Life ◽

Type I ◽

Mineral Density

Thyroid hormones are important for normal bone growth and development in postnatal life. However, little is known about the role of thyroid hormones in the control of bone development in the fetus. Using computed tomography and mechanical testing, the structure and strength of metatarsal bones were measured in sheep fetuses in which thyroid hormone levels were altered by thyroidectomy or adrenalectomy. In intact fetuses, plasma concentrations of total calcium and the degradation products of C-terminal telopeptides of type I collagen increased between 100 and 144 days of gestation (term 145±2 days), in association with various indices of bone growth and development. Thyroid hormone deficiency induced by thyroidectomy at 105–110 days of gestation caused growth retardation of the fetus and significant changes in metatarsal bone structure and strength when analyzed at both 130 and 144 days of gestation. In hypothyroid fetuses, trabecular bone was stronger with thicker, more closely spaced trabeculae, despite lower bone mineral density. Plasma osteocalcin was reduced by fetal thyroidectomy. Removal of the fetal adrenal gland at 115–120 days of gestation, and prevention of the prepartum rises in cortisol and triiodothyronine, had no effect on bodyweight, limb lengths, metatarsal bone structure or strength, or circulating markers of bone metabolism in the fetuses studied near term. This study demonstrates that hypothyroidism in utero has significant effects on the structure and strength of bone, with different consequences for cortical and trabecular bone.

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Pathophysiology of Growth Hormone Secretion Disorders and Their Impact on Bone Microstructure as Measured by Trabecular Bone Score

Physiological Research ◽

10.33549/physiolres.934303 ◽

2019 ◽

pp. S121-S129 ◽

Cited By ~ 1

Author(s):

M. KUŽMA ◽

Z. KILLINGER ◽

P. JACKULIAK ◽

P. VAŇUGA ◽

D. HANS ◽

...

Keyword(s):

Growth Hormone ◽

Fracture Risk ◽

Trabecular Bone ◽

Bone Quality ◽

Bone Growth ◽

Trabecular Bone Score ◽

Bone Matrix ◽

Hormone Secretion ◽

Growth Hormone Secretion ◽

Mineral Density

This article is focused on endocrine-mediated osteoporosis caused by growth hormone (GH) disorders; adult GH deficiency and acromegaly. GH and insulin like growth factor-1 (IGF-1) stimulate linear bone growth through complex hormonal interactions and activates epiphyseal prechondrocytes. GH, via receptor activator of nuclear factor-kappaB (RANK), its ligand (RANK-L), and the osteoprotegerin system, stimulates production of osteoprotegerin and its accumulation in bone matrix. Malfunction of this mechanism, could lead to specific bone impairment. However, the primary problem of bone disease in GH secretion disorders is the primary prevention of osteoporotic fractures, so it is important to determine bone quality that better reflects the patient's actual predisposition to fracture. A method estimating bone quality from lumbar spine dual X-ray absorptiometry (DXA) scans is trabecular bone score (TBS). TBS in addition to bone mineral density (BMD) is a promising predictor of the osteoporotic fracture risk in women with postmenopausal osteopenia. In acromegaly TBS better defines risk of fracture because BMD is normal or even increased. TBS helps to monitor the effect of growth hormone therapy. Despite these findings, TBS shouldn´t be used alone, but a comprehensive consideration of all fracture risk factors, BMD and bone turnover markers is necessary.

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