N-cadherin Restrains PTH Activation of Lrp6/β-catenin Signaling and Osteoanabolic Action

Authors

Leila Revollo, Jacqueline Kading, Sung Yeop Jeong, Jiemin Li, Valerie Salazar, Gabriel Mbalaviele and Roberto Civitell

Abstract

Interaction between parathyroid hormone/parathyroid hormone-related peptide receptor 1 (PTHR1) and low density lipoprotein receptor-related protein 6 (Lrp6) is important for parathyroid hormone (PTH) signaling and anabolic action. Since N-cadherin has been shown to negatively regulate canonical Wnt/β-catenin signaling, we asked whether N-cadherin alters PTH signaling and stimulation of bone formation. Ablation of the N-cadherin gene (Cdh2) in primary osteogenic lineage cells resulted in increased Lrp6/PTHR1 interaction in response to PTH1-34, associated with enhanced PTH-induced PKA signaling and PKA-dependent β-catenin C-terminus phosphorylation, which promotes β-catenin transcriptional activity. β-catenin C-terminus phosphorylation was abolished by Lrp6 knockdown. Accordingly, PTH1-34 stimulation of Tcf/Lef target genes, Lef1 and Axin2, was also significantly enhanced in Cdh2 deficient cells. This enhanced responsiveness to PTH extends to the osteo-anabolic effect of PTH, as mice with a conditional Cdh2 deletion in Osx+ cells treated with intermittent doses of PTH1-34 exhibited significantly larger gains in trabecular bone mass relative to control mice, the result of accentuated osteoblast activity. Therefore, N-cadherin modulates Lrp6/PTHR1 interaction, restraining the intensity of PTH-induced β-catenin signaling, and ultimately influencing bone formation in response to intermittent PTH administration.

Link To Article

http://dx.doi.org/10.1002/jbmr.2323

Comparative study of the osseous healing process following three different techniques of bone augmentation in the mandible: an experimental study

Authors

M.E. Benlidayi, A. Gaggl, H. Buerger, O.E. Kahraman, L. Sencar, C. Brandtner, M. Kurkcu, S. Polat, F. Borumandi

Abstract

The aim of this study was to evaluate the osseointegration of three different bone grafting techniques. Forty-eight mature New Zealand rabbits were divided randomly into three groups of 16 each. Horizontal augmentation was performed on the corpus of the mandible using three different techniques: free bone graft (FBG), free periosteal bone graft (PBG), pedicled bone flap (BF). The animals were sacrificed at postoperative weeks 1, 3, or 8. Specimens were decalcified for histological examination, and histomorphometric measurements were performed. The histological evaluation demonstrated bony fusion between the grafts and the augmented mandibular bone after 8 weeks in all groups. At week 8, the bone volume was significantly greater in the BF group than in the FBG (P<0.001) and PBG (P=0.001) groups, and also the trabecular thickness was significantly greater than in the FBG (P=0.015) and PBG (P=0.015) groups. Trabecular separation was significantly lower in the BF group than in the FBG group at week 8 (P=0.015). BF demonstrated greater osseous healing capacity compared to FBG and PBG. The preserved vascularization in BF improves the bone quality in mandibular bone augmentations.

Link To Article

http://dx.doi.org/10.1016/j.ijom.2014.07.004

Effect of isolated hyperglycemia on native mechanical and biologic shoulder joint properties in a rat model

Authors

Stephen J. Thomas, Joseph J. Sarver, Sarah M. Yannascoli, Jennica J. Tucker, John D. Kelly IV, Rexford S. Ahima, Mary F. Barbe and Louis J. Soslowsky

Abstract

Recently, diabetes has been linked to rotator cuff disease and adhesive capsulitis, conditions with increased stiffness and inflammation. Unfortunately, limited research exists examining how hyperglycemia affects the native shoulder (tendon and capsule) properties. Therefore, the objectives of this study were to compare shoulder joint mechanics, tendon properties (mechanics and immunohistochemistry), and capsule of healthy control and hyperglycemic rats 8 weeks following induction of hyperglycemia with a submaximal dose of streptozotocin (STZ). Eighteen rats were injected with STZ to induce hyperglycemia or citrate buffer (control) and underwent normal cage activity for 8 weeks. Passive joint mechanics demonstrated significantly less external rotation in the hyperglycemic group compared to controls, with no other group differences. Tendon mechanical properties (stiffness and modulus) were not significantly different between groups at both the insertion site and mid-substance. Immunohistochemistry staining of the tendon and capsule demonstrated significantly increased interleukin 1-beta (IL1-β) and advanced glycated end-products (AGE) staining localized to the insertion and mid-substance of the tendon but not the capsule. In addition, tumor necrosis factor alpha (TNF-α) staining was significantly increased in the superior capsule but not the supraspinatus tendon. This study demonstrates that isolated hypergylcemia does not diminish shoulder mechanical properties but does induce a chronic inflammatory response.

Link To Article

http://dx.doi.org/10.1002/jor.22695

Loss of Runx2 in Committed Osteoblasts Impairs Postnatal Skeletogenesis

Authors

Mitra D. Adhami BS, Harunur Rashid MSc, Haiyan Chen PhD, John C. Clarke BS, Yang Yang MD and Amjad Javed PhD

Abstract

The Runx2 transcription factor is critical for commitment to the osteoblast lineage. However, its role in committed osteoblasts and its functions during postnatal skeletogenesis remain unclear. We established a Runx2-floxed line with insertion of loxP sites around exon 8 of the Runx2 gene. Runx2 protein lacking the region encoded by exon 8 is imported into the nucleus and binds target DNA, but exhibits diminished transcriptional activity. We specifically deleted the Runx2 gene in committed osteoblasts using 2.3kb col1a-Cre transgenic mice. Surprisingly, the homozygous Runx2 mutant mice were born alive. The Runx2 heterozygous and homozygous null were grossly indistinguishable from wild-type littermates at birth. Runx2 deficiency did not alter proliferative capacity of osteoblasts during embryonic development (E18). Chondrocyte differentiation and cartilage growth in mutants was similar to wild-type mice from birth to 3 months of age. Analysis of the embryonic skeleton revealed poor calcification in homozygous mutants, which was more evident in bones formed by intramembranous ossification. Runx2 mutants showed progressive retardation in postnatal growth and exhibited significantly low bone mass by 1 month of age. Decreased bone formation was associated with decreased gene expression of osteoblast markers and impaired collagen assembly in the extracellular matrix. Consequently, Runx2 mutant bones exhibited decreased stiffness and structural integrity. By 3 months of age, bone acquisition in mutant mice was roughly half that of wild-type littermates. In addition to impaired osteoblast function, mutant mice showed markedly decreased osteoclast number and postnatal bone resorption. Taken together, functional deficiency of Runx2 in osteoblasts does not result in failed embryonic skeletogenesis, but disrupts postnatal bone formation.

Link To Article

http://dx.doi.org/10.1002/jbmr.2321

Genetic manipulation of the ghrelin signaling system in male mice reveals bone compartment specificity of acylated and unacylated ghrelin in the regulation of bone remodeling

Authors

Patric JD Delhanty, Martijn van der Velde, Bram CJ van der Eerden, Yuxiang Sun, Julia MM Geminn, Aart-Jan van der Lely, Roy G Smith, and Johannes PTM van Leeuwen

Abstract

Ghrelin receptor deficient (Ghsr-/-) mice, which lack acylated ghrelin (AG) signaling, retain a metabolic response to unacylated ghrelin (UAG). Recently, we showed that Ghsr-deficiency affects bone metabolism. The aim of this study was to further establish the impact of AG and UAG on bone metabolism. We compared bone metabolism in Ghsr-/- (lacking only AG signaling) and ghrelin deficient (Ghrl-/-; both AG and UAG deficient) male mice. Ghrl-/- mice had lower cortical bone mass, while Ghsr-/- mice had lower trabecular bone mass. This demonstrates bone compartment-specific effects of AG and a role for UAG in bone metabolism. Also, Ghrl-/- but not Ghsr-/- mice had increased bone formation rate and increased osteogenic stem cell numbers in their bone marrow. In ex vivo bone marrow cultures both AG and UAG inhibited osteoblast differentiation. This indicated that bone resorption must be increased in these mice. Accordingly, osteoclastogenesis rate was faster in bone marrow cultures from Ghsr-/- and Ghrl-/- mice, and osteoclast formation was inhibited by AG signaling and partially suppressed by UAG. In osteoblast cultures, AG markedly induced osteoprotegerin gene expression and both peptides reduced RANKL/osteoprotegerin ratio. These data describe unique cell-type specific effects of AG and UAG within a single tissue, supporting a tight and complex control of bone formation and resorption as well as a link between nutrition and bone metabolism. The balance between AG and UAG actions in the bone marrow may lead to bone compartmental specific effects.

Link To Article

http://dx.doi.org/10.1210/en.2013-2055

Immobilization contributes to exaggerated neuropeptide signaling, inflammatory changes, and nociceptive sensitization after fracture in rats

Authors

Tian-Zhi Guo, Tzuping Wei, Wen-Wu Li, Xiang-Qi Li, J. David Clark, Wade S. Kingery

Abstract

A tibia fracture cast immobilized for 4 weeks can induce exaggerated substance P (SP) and CGRP signaling and neuropeptide-dependent nociceptive and inflammatory changes in the hindlimbs of rats similar to those seen in complex regional pain syndrome (CRPS). Four weeks of hindlimb cast immobilization can also induce nociceptive and vascular changes resembling CRPS. To test our hypothesis that immobilization alone could cause exaggerated neuropeptide signaling and inflammatory changes we tested 5 cohorts of rats; 1) controls, 2) tibia fracture and hindlimb casted, 3) hindlimb casted, no fracture, 4) tibia fracture with intrameduallary pinning, no cast, and 5) tibia fracture with intrameduallary pinning and hindlimb casting. After 4 weeks the casts were removed and hindlimb allodynia, unweighting, warmth, edema, sciatic nerve neuropeptide content, cutaneous and spinal cord inflammatory mediator levels, and spinal c-Fos activation were measured. After fracture with casting there was allodynia, unweighting, warmth, edema, increased sciatic nerve SP and CGRP, increased skin NK1 receptors and keratinocyte proliferation, increased in inflammatory mediator expression in the hindpaw skin (TNF-α, IL-1β, IL-6, NGF) and cord (IL-1β, NGF), and increased spinal c-Fos activation. These same changes were observed after cast immobilization alone, except spinal IL-1β levels were not increased. Treating cast only rats with an NK1 receptor antagonist inhibited development of nociceptive and inflammatory changes. Four weeks after fracture with pinning all nociceptive and vascular changes had resolved and there were no increases in neuropeptide signaling or inflammatory mediator expression.

Link To Article

http://dx.doi.org/10.1016/j.jpain.2014.07.004