Insulin-like growth factor-1 receptor in mature osteoblasts is required for periosteal bone formation induced by reloading

Authors

Takuo Kubota, Hashem Z. Elalieh, Neema Saless, Chak Fong, Yongmei Wang, Muriel Babey, Zhiqiang Cheng, Daniel D. Bikle

Abstract

Skeletal loading and unloading has a pronounced impact on bone remodeling, a process also regulated by insulin-like growth factor-1 (IGF-1) signaling. Skeletal unloading leads to resistance to the anabolic effect of IGF-1, while reloading after unloading restores responsiveness to IGF-1. However, a direct study of the importance of IGF-1 signaling in the skeletal response to mechanical loading remains to be tested. In this study, we assessed the skeletal response of osteoblast-specific Igf-1 receptor deficient (Igf-1r−/−) mice to unloading and reloading. The mice were hindlimb unloaded for 14 days and then reloaded for 16 days. Igf-1r−/− mice displayed smaller cortical bone and diminished periosteal and endosteal bone formation at baseline. Periosteal and endosteal bone formation decreased with unloading in Igf-1r+/+ mice. However, the recovery of periosteal bone formation with reloading was completely inhibited in Igf-1r−/− mice, although reloading-induced endosteal bone formation was not hampered. These changes in bone formation resulted in the abolishment of the expected increase in total cross-sectional area with reloading in Igf-1r−/− mice compared to the control mice. These results suggest that the Igf-1r in mature osteoblasts has a critical role in periosteal bone formation in the skeletal response to mechanical loading.

Link to Article

http://dx.doi.org/10.1016/j.actaastro.2012.08.007

Skeletal effects of zoledronic acid in an animal model of chronic kidney disease

Authors

M. R. Allen, N. X. Chen, V. H. Gattone II, X. Chen, A. J. Carr, P. LeBlanc, D. Brown and S. M. Moe

Abstract

Bisphosphonates reduce skeletal loss and fracture risk, but their use has been limited in patients with chronic kidney disease. This study shows skeletal benefits of zoledronic acid in an animal model of chronic kidney disease. Bisphosphonates are routinely used to reduce fractures but limited data exists concerning their efficacy in non-dialysis chronic kidney disease. The goal of this study was to test the hypothesis that zoledronic acid produces similar skeletal effects in normal animals and those with kidney disease. At 25 weeks of age, normal rats were treated with a single dose of saline vehicle or 100 μg/kg of zoledronic acid while animals with kidney disease (approximately 30 % of normal kidney function) were treated with vehicle, low dose (20 μg/kg), or high dose (100 μg/kg) zoledronic acid, or calcium gluconate (3 % in the drinking water). Skeletal properties were assessed 5 weeks later using micro-computed tomography, dynamic histomorphometry, and mechanical testing. Animals with kidney disease had significantly higher trabecular bone remodeling compared to normal animals. Zoledronic acid significantly suppressed remodeling in both normal and diseased animals yet the remodeling response to zoledronic acid was no different in normal and animals with kidney disease. Animals with kidney disease had significantly lower cortical bone biomechanical properties; these were partially normalized by treatment. Based on these results, we conclude that zoledronic acid produces similar amounts of remodeling suppression in animals with high turnover kidney disease as it does in normal animals, and has positive effects on select biomechanical properties that are similar in normal animals and those with chronic kidney disease.

Link to Article

http://dx.doi.org/10.1007/s00198-012-2103-x

Negative regulation of osteoclast precursor differentiation by CD11b and β2 integrin-BCL6 signaling

Authors

Kyung-Hyun Park-Min, Eun Young Lee, Neal K. Moskowitz, Elisha Lim,Sun-Kyeong Lee, Joseph A. Lorenzo, Chuanxin Huang, Ari M. Melnick, P. Edward Purdue, Steven R. Goldring, Lionel B. Ivashkiv

Link to Article

Negative regulation of osteoclastogenesis is important for bone homeostasis and prevention of excessive bone resorption in inflammatory and other diseases. Mechanisms that directly suppress osteoclastogenesis are not well understood. In this study we investigated regulation of osteoclast differentiation by the β2 integrin CD11b/CD18 that is expressed on myeloid lineage osteoclast precursors. CD11b-deficient mice exhibited decreased bone mass that was associated with increased osteoclast numbers and decreased bone formation. Accordingly, CD11b and β2 integrin signaling suppressed osteoclast differentiation by preventing RANKL-induced induction of the master regulator of osteoclastogenesis NFATc1 and of downstream osteoclast-related NFATc1 target genes. CD11b suppressed induction of NFATc1 by the complementary mechanisms of downregulation of RANK expression and induction of recruitment of the transcriptional repressor BCL6 to the NFATC1 gene. These findings identify CD11b as a negative regulator of the earliest stages of osteoclast differentiation, and provide an inducible mechanism by which environmental cues suppress osteoclastogenesis by activating a transcriptional repressor that makes genes refractory to osteoclastogenic signaling.

Link to Article

http://dx.doi.org/10.1002/jbmr.1739

Bone remodelling and aposition onto calcium phosphate coated polymer surfaces in the spine: an in vivo animal model

Authors

T Steffen, BJC Freeman and M Aebi

Abstract

Long term, secondary implant fixation of Total Disc Replacements (TDR) can be enhanced by hydroxyapatite or similar osseo-conductive coatings. These coatings are routinely applied to metal substrates. The objective of this in vivo study was to investigate the early stability and subsequent bone response adjacent to an all polymer TDR implant over a period of six months in an animal model. Six skeletally mature male baboons (Papio annubis) were followed for a period of 6 months. Using a transperitoneal exposure, a custom-sized Cadisc L device was implanted into the disc space one level above the lumbo-sacral junction in all subjects. Radiographs of the lumbar spine were acquired prior to surgery, and post-operatively at intervals up to 6 months to assess implant stability. Flourochrome markers (which contain molecules that bind to mineralization fronts) were injected at specified intervals in order to investigate bone remodeling with time. Animals were humanely euthanized six months after index surgery. Test and control specimens were retrieved, fixed and subjected to histological processing to assess the bone-implant-bone interface. Fluorescence microscopy and confocal scanning laser microscopy were utilized with BioQuant image analysis to determine the bone mineral apposition rates and gross morphology. Radiographic evaluation revealed no loss of disc height at the operative level or adjacent levels. No evidence of subsidence or significant migration of the implant up to 6 months. Heterotopic ossification was observed to varying degrees at the operated level. Histology revealed the implant primary fixation features embedded within the adjacent vertebral endplates. Flourochrome distribution revealed active bone remodeling occurring adjacent to the polymeric end-plate with no evidence of adverse biological responses. Mineral apposition rates of between 0.7 and 1.7 microns / day are in keeping with literature values for hydroxyapatite coated implants in cancellous sites of various species. Radiographic assessment demonstrates that the Cadisc L implant remains stable in vivo with no evidence of subsidence or significant migration. Histological analysis suggests the primary fixation features are engaged, and in close apposition with the adjacent vertebral bone. Flourochrome markers provide evidence of a positive bone remodelling response in the presence of the implant.

Link to Article

http://www.bjjprocs.boneandjoint.org.uk/content/94-B/SUPP_XXXVI/85.short

Quantitative Histologic Evidence of Amifostine Induced Cytoprotection in an Irradiated Murine Model of Mandibular Distraction Osteogenesis

Authors

Tchanque-Fossuo, Catherine N. MD, MS; Donneys, Alexis MD, MS; Razdolsky, Elizabeth R. BS; Monson, Laura; Farberg, Aaron S. BS; Deshpande, Sagar S. BS; Sarhaddi, Deniz BA; Poushanchi, Behdod BS; Goldstein, Steven A. PhD; Buchman, Steven R. MD

Abstract

Head and neck cancer (HNC) management requires adjuvant radiation therapy (XRT). The authors have previously demonstrated the damaging effect of a human equivalent dose of radiation (HEDR) on a murine mandibular model of distraction osteogenesis (DO). Utilizing quantitative histomorphometry (QHM), our specific aim is to objectively measure the radio-protective effects of Amifostine (AMF) on the cellular integrity and tissue quality of an irradiated and distracted regenerate. Sprague Dawley rats were randomly assigned into 2 groups: XRT/DO and AMF/XRT/DO, which received AMF prior to XRT. Both groups were given HEDR in 5 fractionated doses and underwent a left mandibular osteotomy with bilateral fixator placement. Distraction to 5.1mm was followed by a 28-day consolidation period. Left hemimandibles were harvested. QHM was performed for osteocyte count (Oc), empty lacunae (EL), Bone Volume/Tissue Volume (BV/TV) and Osteoid Volume/Tissue Volume (OV/TV) ratios. AMF/XRT/DO exhibited bony bridging as opposed to XRT/DO fibrous unions. QHM analysis revealed statistically significant higher Oc and BV/TV ratio in AMF-treated mandibles compared with irradiated mandibles. There was a corresponding decrease in EL and the ratio of OV/TV between AMF/XRT/DO and XRT/DO. We have successfully established the significant osseous cytoprotective and histoprotective capacity of AMF on DO in the face of XRT. AMF-sparing effect on bone cellularity correlated with an increase in bony union and elimination of fibrous union. We posit that the demonstration of similar efficacy of AMF in the clinic may allow the successful implementation of DO as a viable reconstructive option for HNC in the future.

Link to Article

http://dx.doi.org/10.1097/PRS.0b013e31826d2201

Hexa-D-Arginine treatment increases 7B2•PC2 activity in hyp-mouse osteoblasts and rescues the HYP phenotype

Authors

Baozhi Yuan, Jian Q. Feng, Stephen Bowman, Ying Liu, Robert D. Blank, Iris Lindberg, Marc K. Drezner

Abstract

Inactivating mutations of PHEX/Phex underlie disease in patients with X-linked hypophosphatemia (XLH) and the hyp-mouse, a murine homologue of the human disorder. Although increased serum FGF-23 underlies the HYP phenotype, the mechanism(s) by which PHEX mutations inhibit FGF-23 degradation and/or enhance production remains unknown. Here we show that treatment of wild type mice with the proprotein convertase (PC) inhibitor, Decanoyl-Arg-Val-Lys-Arg-chloromethyl ketone, increases serum FGF-23 and produces the HYPphenotype. Since PC2 is uniquely co-localized with PHEX in osteoblasts/bone, we examined if PC2 regulates PHEX-dependent FGF-23 cleavage and production. Transfection of murine osteoblasts with PC2 and its chaperone protein 7B2 cleaved FGF-23, while Signe1 (7B2) RNAi transfection, which limited 7B2 protein production, decreased FGF-23 degradation and increased Fgf-23 mRNA and protein. The mechanism by which decreased 7B2•PC2 activity influences Fgf-23 mRNA was linked to reduced conversion of proBMP1 to active BMP1, which resulted in limited cleavage of DMP1, and consequent increased Fgf-23 mRNA. The significance of decreased 7B2•PC2 activity in XLH was confirmed by studies of hyp-mouse bone, which revealed significantly decreased Sgne1 (7B2) mRNA and 7B2 protein, and limited cleavage of proPC2 to active PC2. The expected downstream effects of these changes included decreased FGF-23 cleavage and increased FGF-23 synthesis, secondary to decreased BMP1-mediated degradation of DMP1. Subsequent Hexa-D-Arginine treatment of hyp-mice enhanced bone 7B2•PC2 activity, normalized FGF-23 degradation and production, and rescued the HYP phenotype. These data suggest decreased PHEX-dependent 7B2•PC2 activity is central to the pathogenesis of XLH.

Link to Article

http://dx.doi.org/10.1002/jbmr.1738