A novel role for interferon regulatory factor 1 (IRF1) in regulation of bone metabolism

Authors

Sandra Salem, Chan Gao, Ailian Li, Huifen Wang, Loan Nguyen-Yamamoto, David Goltzman, Janet E. Henderson, and Philippe Gros

Abstract

Increased risk of bone fractures is observed in patients with chronic inflammatory conditions, such as inflammatory bowel disease and rheumatoid arthritis. Members of the Interferon Response Factor family of transcriptional regulators, IRF1 and IRF8, have been identified as genetic risk factors for several chronic inflammatory and autoimmune diseases. We have investigated a potential role for the Irf1 gene in bone metabolism. Here, we report that Irf1−/−mutant mice show altered bone morphology in association with altered trabecular bone architecture and increased cortical thickness and cellularity. Ex vivo studies on cells derived from bone marrow stimulated with Rank ligand revealed an increase in size and resorptive activity of tartrate-resistant acid-positive cells from Irf1−/− mutant mice compared with wild-type control mice. Irf1 deficiency was also associated with decreased proliferation of bone marrow-derived osteoblast precursors ex vivo, concomitant with increased mineralization activity compared with control cells. We show that Irf1 plays a role in bone metabolism and suggest that Irf1 regulates the maturation and activity of osteoclasts and osteoblasts. The altered bone phenotype of Irf1−/− mutants is strikingly similar to that of Stat1−/− mice, suggesting that the two interacting proteins play a critical enabling role in the common regulation of these two cell lineages.

Link To Article

http://dx.doi.org/10.1111/jcmm.12327

Tissue-engineered bone constructed in a bioreactor for repairing critical-sized bone defects in sheep

Authors

Deqiang Li, Ming Li, Peilai Liu, Yuankai Zhang, Jianxi Lu, Jianmin Li

Abstract

Purpose Repair of bone defects, particularly critical-sized bone defects, is a considerable challenge in orthopaedics. Tissue-engineered bones provide an effective approach. However, previous studies mainly focused on the repair of bone defects in small animals. For better clinical application, repairing critical-sized bone defects in large animals must be studied. This study investigated the effect of a tissue-engineered bone for repairing critical-sized bone defect in sheep.

Methods A tissue-engineered bone was constructed by culturing bone marrow mesenchymal-stem-cell-derived osteoblast cells seeded in a porous β-tricalcium phosphate ceramic (β-TCP) scaffold in a perfusion bioreactor. A critical-sized bone defect in sheep was repaired with the tissue-engineered bone. At the eighth and 16th week after the implantation of the tissue-engineered bone, X-ray examination and histological analysis were performed to evaluate the defect. The bone defect with only the β-TCP scaffold served as the control.

Result X-ray showed that the bone defect was successfully repaired 16 weeks after implantation of the tissue-engineered bone; histological sections showed that a sufficient volume of new bones formed in β-TCP 16 weeks after implantation. Eight and 16 weeks after implantation, the volume of new bones that formed in the tissue-engineered bone group was more than that in the β-TCP scaffold group (P < 0.05).

Conclusion Tissue-engineered bone improved osteogenesis in vivo and enhanced the ability to repair critical-sized bone defects in large animals.

Link To Article

http://dx.doi.org/10.1007/s00264-014-2389-8

Targeting angiogenesis as a therapeutic means to reinforce osteocyte survival and prevent non-unions in the aftermath of radiotherapy

Authors

Alexis Donneys, Noah S. Nelson, Erin E. Page, Sagar S. Deshpande, Peter A. Felice, Catherine N. Tchanque-Fossuo, Joshua P. Spiegel and Steven R. Buchman

Abstract

Background: Radiotherapy exerts detrimental collateral effects on bone tissue through mechanisms of vascular damage and impediments to osteocytes, ultimately predisposing patients to the debilitating problems of late pathologic fractures and non-unions. We posit that angiogenic therapy will reverse these pathologic effects in a rat model of radiated fracture healing.

Methods: Three groups of rats underwent mandibular osteotomy. Radiated groups received a fractionated 35Gy dose prior to surgery. The deferoxamine group received local injections postoperatively. A 40-day healing period was allowed prior to histology. ANOVA (p<0.05) was used for group comparisons.

Results: Radiated fractures revealed a significantly decreased osteocyte count and corresponding increase in empty lacunae when compared to non-radiated fractures (p=0.001). With the addition of deferoxamine, these differences were not appreciated. Further, a 42% increase in bony unions was observed after deferoxamine therapy.

Conclusions: Targeting angiogenesis is a useful means for promoting osteocyte survival and preventing bone pathology after radiotherapy

Link To Article

http://dx.doi.org/10.1002/hed.23744

How does the amount of surgical insult affect bone around moving teeth?

Authors

Matthew D. McBride, Phillip M. Campbell, Lynne A. Opperman, Paul C. Dechow, Peter H. Buschang

Abstract

Introduction

The purpose of this study was to determine how the amount of surgical insult affects the quantity and maturity of dentoalveolar bone around teeth that have been orthodontically moved.

Methods

A split-mouth design with 8 foxhound dogs was used to evaluate bone surrounding maxillary second premolars that were protracted for 15 days and retained for 7 weeks. The maxillary first premolars were extracted, and the interseptal bone was removed to within 1 mm of the second premolars; on the insult (lesser surgical insult) side, buccal and lingual vertical grooves were made in the extraction socket to undermine the mesial root of the second premolar; the insult+ (greater surgical insult) side was flapped and had modified corticotomies extending to, but not through, the lingual cortex 1 mm distal to the distal root, and 3 to 5 mm apical to both roots. Microcomputed tomography analyses were used to evaluate the material density, bone volume fraction, and trabecular characteristics of surrounding bone. Hematoxylin and eosin sections were used to determine osteoclast numbers, bone surface areas, and bone volumes.

Results

After 7 weeks of consolidation, there was significantly (P <0.05) less bone on the insult+ side; it was less dense and less mature than the bone on the insult side. Relative to the control bone, bone on the insult+ side was significantly less dense but showed no differences in bone volume. Preliminary histologic evaluations indicated increased numbers of osteoclasts and greater bone surface areas on the insult+ side than the insult side, but no differences in bone volume.

Conclusions

Increased surgical insults produce less dense and less mature bone but have no effect on bone volume at 9 weeks after surgery.

Link To Article

http://dx.doi.org/10.1016/j.ajodo.2013.10.020

Vitamin A Is a Negative Regulator of Osteoblast Mineralization

Authors

Thomas Lind, Anders Sundqvist, Lijuan Hu, Gunnar Pejler, Göran Andersson, Annica Jacobson, Håkan Melhus

Abstract

An excessive intake of vitamin A has been associated with an increased risk of fractures in humans. In animals, a high vitamin A intake leads to a reduction of long bone diameter and spontaneous fractures. Studies in rodents indicate that the bone thinning is due to increased periosteal bone resorption and reduced radial growth. Whether the latter is a consequence of direct effects on bone or indirect effects on appetite and general growth is unknown. In this study we therefore used pair-feeding and dynamic histomorphometry to investigate the direct effect of a high intake of vitamin A on bone formation in rats. Although there were no differences in body weight or femur length compared to controls, there was an approximately halved bone formation and mineral apposition rate at the femur diaphysis of rats fed vitamin A. To try to clarify the mechanism(s) behind this reduction, we treated primary human osteoblasts and a murine preosteoblastic cell line (MC3T3-E1) with the active metabolite of vitamin A; retinoic acid (RA), a retinoic acid receptor (RAR) antagonist (AGN194310), and a Cyp26 inhibitor (R115866) which blocks endogenous RA catabolism. We found that RA, via RARs, suppressed in vitro mineralization. This was independent of a negative effect on osteoblast proliferation. Alkaline phosphatase and bone gamma carboxyglutamate protein (Bglap, Osteocalcin) were drastically reduced in RA treated cells and RA also reduced the protein levels of Runx2 and Osterix, key transcription factors for progression to a mature osteoblast. Normal osteoblast differentiation involved up regulation of Cyp26b1, the major enzyme responsible for RA degradation, suggesting that a drop in RA signaling is required for osteogenesis analogous to what has been found for chondrogenesis. In addition, RA decreased Phex, an osteoblast/osteocyte protein necessary for mineralization. Taken together, our data indicate that vitamin A is a negative regulator of osteoblast mineralization.

Link To Article

http://dx.doi.org/10.1371/journal.pone.0082388

Modulation of endochondral ossification by MEK inhibitors PD0325901 and AZD6244 (Selumetinib)

Authors

J. El-Hossa, M. Kolind, M.T. Jackson, N. Deo, K. Mikuleca, M.M. McDonald, C.B. Little, D.G. Little, A. Schindeler

Abstract

MEK inhibitors (MEKi) PD0325901 and AZD6244 (Selumetinib) are drugs currently under clinical investigation for cancer treatment, however the Ras–MAPK pathway is also an important mediator of normal bone cell differentiation and function. In this study we examined the effects of these compounds on endochondral processes using both in vitro and in vivo models. Treatment with PD0325901 or AZD6244 significantly increased Runx2 and Alkaline phosphate gene expression in calvarial osteoblasts and decreased TRAP + cells in induced osteoclast cultures. To test the effects of these drugs on bone healing, C57/Bl6 mice underwent a closed tibial fracture and were treated with PD0325901 or AZD6244 at 10 mg/kg/day. Animals were culled at day 10 and at day 21 post-fracture for analysis of the fracture callus and the femoral growth plate in the contralateral leg. MEKi treatment markedly increased cartilage volume in the soft callus at day 10 post-fracture (+ 60% PD0325901, + 20% AZD6244) and continued treatment led to a delay in cartilage remodeling. At the growth plate, we observed an increase in the height of the hypertrophic zone relative to the proliferative zone of + 78% in PD0325901 treated mice. Osteoclast surface was significantly decreased both at the terminal end of the growth plate and within the fracture calluses of MEKi treated animals. The mechanistic effects of MEKi on genes encoding cartilage matrix proteins and catabolic enzymes were examined in articular chondrocyte cultures. PD0325901 or AZD6244 led to increased matrix protein expression (Col2a1 and Agc1) and decreased expression of catabolic factors (Mmp13 and Adamts-5). Taken together, these data support the hypothesis that MEKi treatment can impact chondrocyte hypertrophy, matrix resorption, and fracture healing. These compounds can also affect bone architecture by expanding the hypertrophic zone of the growth plate and reducing osteoclast surface systemically.

Link To Article

http://dx.doi.org/10.1016/j.bone.2013.11.013