A histomorphometric study of cellular layers after hemiepiphyseal stapling on the physeal plate in rabbits

Authors

Su-Min Son, Il-Hyung Park, Chang-Wug Oh, Hyun-Joo Lee, Byung-Chul Park, Je-Yong Choi

Abstract

Epiphyseal stapling has been widely used to correct angular deformity. The mechanism, however, has not been well determined. To determine the effect of temporary hemiepiphyseal stapling on the cellular layers of the physis, a histomorphometric study was performed using immature rabbits. Distal lateral epiphyseal stapling of the right femur was performed on 6-week-old New Zealand white rabbits. Thirty rabbits were randomly assigned to five groups, and six rabbits in each group were analyzed weekly for up to 5 weeks. The distal femur was deformed into the valgus, and the anatomical lateral distal femoral angle decreased with the passage of time. In the sequential histomorphometry of the operated physeal plate, the area ratio of each layer, compared to the control side, decreased every week. The total area of the physeal plate had decreased up to 60 % at the 5th week compared to the area of the 1st week, and the area of the proliferative layer decreased by the greatest amount among the three layers. Our findings suggest that the proliferation of chondrocytes seemed to be more suppressed by the compression of the stapling, thereby slowing the growth rate, although hypertrophy of the chondrocytes was also suppressed.

Link to Article

http://dx.doi.org/10.1007/s00776-012-0317-6

Deferoxamine Enhances the Vascular Response of Bone Regeneration in Mandibular Distraction Osteogenesis

Authors

Alexis Donneys, Aaron Farberg, Catherine Tchanque-Fossuo, Sagar Deshpande, Steven R. Buchman

Abstract

Bone regeneration during distraction osteogenesis is intricately associated with an enhanced vascular response. Augmenting this response may offer considerable clinical advantages such as optimizing the quality of regenerate formation, decreasing lengthy consolidation periods, or increasing regenerate size and distance. Using deferoxamine, an angiogenic transcriptional activator, the authors posit that substantial increases in vascular volume beyond the normal response to mechanical distraction can be quantified with micro–computed tomography after vessel perfusion during mandibular distraction osteogenesis. Two groups of Sprague-Dawley rats (n = 12) underwent external fixator placement, mandibular osteotomy, and 5.1-mm distraction. During distraction, the experimental group (n = 6) was treated with deferoxamine injections into the distraction gap. After consolidation, the animals were perfused and imaged with micro–computed tomography. Vascular radiomorphometrics were calculated and statistical comparison was conducted with the independent samples t test. A value of p ≤ 0.05 was considered statistically significant. A 40 percent statistically significant increase in the number of vessels (0.82 vessels/mm versus 1.15 vessels/mm; p < 0.012) and a complementary decrease in the space between vessels (1.18 mm versus 0.86 mm; p < 0.012) were calculated in the experimental regenerate when compared with controls. This robust increase in vascularity could also be readily observed with micro–computed tomographic image reconstruction. Gross examination revealed a denser regenerate in the deferoxamine-injected group that is clearly illustrated with Faxitron radiography. The authors' study quantifies the ability of deferoxamine to augment the vascular response of mandibular distraction osteogenesis and establishes correlations between this therapeutic enrichment and enhanced regenerate formation.

Link to Article

http://dx.doi.org/10.1097/PRS.0b013e31824422f2

Prolonged alendronate treatment prevents the decline in serum TGF-β1 levels and reduces cortical bone strength in long-term estrogen deficiency rat model

Authors

Junjing Jia, Wei Yao, Sarah Amugongo, Mohammad Shahnazari, Weiwei Dai, Yu-An E. Lay, Diana Olvera, Elizabeth A. Zimmermann, Robert O. Ritchie, Chin-Shang Li, Tamara Alliston, Nancy E. Lane

Abstract

While the anti-resorptive effects of the bisphosphonates (BPs) are well documented, many questions remain about their mechanisms of action, particularly following long-term use. This study evaluated the effects of alendronate (Ale) treatment on TGF-β1 signaling in mesenchymal stem cells (MSCs) and osteocytes, and the relationship between prolonged alendronate treatment on systemic TGF-β1 levels and bone strength. TGF-β1 expression and signaling were evaluated in MSCs and osteocytic MLO-Y4 cells following Ale treatment. Serum total TGF-β1 levels, a bone resorption marker (DPD/Cr), three-dimensional microCT scans and biomechanical tests from both the trabecular and cortical bone were measured in ovariectomized rats that either received continuous Ale treatment for 360days or Ale treatment for 120days followed by 240days of vehicle. Linear regression tests were performed to determine the association of serum total TGF-β1 levels and both the trabecular (vertebrae) and cortical (tibiae) bone strength. Ale increased TGF-β1 signaling in the MSCs but not in the MLO-Y4 cells. Ale treatment increased serum TGF-β1 levels and the numbers of TGF-β1-positive osteocytes and periosteal cells in cortical bone. Serum TGF-β1 levels were not associated with vertebral maximum load and strength but was negatively associated with cortical bone maximum load and ultimate strength. The increase of serum TGF-β1 levels during acute phase of estrogen deficiency is likely due to increased osteoclast-mediated release of matrix-derived latent TGF-β1. Long-term estrogen-deficiency generally results in a decline in serum TGF-β1 levels that are maintained by Ale treatment. Measuring serum total TGF-β1 levels may help to determine cortical bone quality following alendronate treatment.

Link to Article

http://dx.doi.org/10.1016/j.bone.2012.10.017

Histone deacetylase 3 is required for maintenance of bone mass during aging

Authors

Meghan E. McGee-Lawrence, Elizabeth W. Bradley, Amel Dudakovic, Samuel W. Carlson, Zachary C. Ryan, Rajiv Kumar, Mahrokh Dadsetan, Michael J. Yaszemski, Qingshan Chen, Kai-Nan An, Jennifer J. Westendorf

Abstract

Histone deacetylase 3 (Hdac3) is a nuclear enzyme that removes acetyl groups from lysine residues in histones and other proteins to epigenetically regulate gene expression. Hdac3 interacts with bone-related transcription factors and co-factors such as Runx2 and Zfp521, and thus is poised to play a key role in the skeletal system. To understand the role of Hdac3 in osteoblasts and osteocytes, Hdac3 conditional knockout (CKO) mice were created with the osteocalcin (OCN) promoter driving Cre expression. Hdac3 CKOOCN mice were of normal size and weight, but progressively lost trabecular and cortical bone mass with age. The Hdac3 CKOOCN mice exhibited reduced cortical bone mineralization and material properties and suffered frequent fractures. Bone resorption was lower, not higher, in the Hdac3 CKOOCN mice, suggesting that primary defects in osteoblasts caused the reduced bone mass. Indeed, reductions in bone formation were observed. Osteoblasts and osteocytes from Hdac3 CKOOCN mice showed increased DNA damage and reduced functional activity in vivo and in vitro. Thus, Hdac3 expression in osteoblasts and osteocytes is essential for bone maintenance during aging.

Link to Article

http://dx.doi.org/10.1016/j.bone.2012.10.015

Osteogenesis and angiogenesis induced by porous β-CaSiO3/PDLGA composite scaffold via activation of AMPK/ERK1/2 and PI3K/Akt pathways

Authors

Chen Wang, Kaili Lin, Jiang Chang, Jiao Sun

Abstract

As a potential bioactive material, β-calcium silicate (β-CS) has attracted particular attention in the field of bone regeneration. In this study, porous β-CS/Poly-d,l-Lactide-Glycolide (PDLGA) composite scaffolds were developed with the goals of controlling the degradation rate and improving the mechanical and biological properties. The compressive strength and toughness were significantly enhanced by PDLGA modification of porous β-CS ceramic scaffolds. The effects of the ionic extract from β-CS/PDLGA composite scaffolds on osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (rBMSCs), proliferation of human umbilical vein endothelial cells (HUVECs) and the related mechanisms were investigated. It was shown that bioactive ions from β-CS/PDLGA scaffolds could enhance cell viability, alkaline phosphatase (ALP) activity, calcium mineral deposition, and mRNA expression levels of osteoblast-related genes of rBMSCs without addition of extra osteogenic reagents. The activation in AMP-activated protein kinase (AMPK), extracellular signal-related kinases (ERK) 1/2 and RUNX-2 were observed in rBMSCs cultured in the extract of β-CS/PDLGA, and these effects could be blocked by AMPK inhibitor Compound C. The extracts of β-CS/PDLGA composites stimulated HUVECs proliferation that was associated with phosphorylation of protein kinase B (Akt) and endothelial nitric oxide synthase (eNOS) as well as an increase in nitric oxide (NO) production and secretion of vascular endothelial growth factor (VEGF). The inductions were abolished by the addition of phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002. The composite scaffolds were implanted in critical sized rabbit femur defects (6 × 10 mm) for 4, 12 and 20 weeks with β-tricalcium phosphate (β-TCP) as controls. Sequential histological evaluations and radiographs revealed that β-CS/PDLGA dramatically stimulated new bone formation and angiogenesis. The biodegradation rate of the β-CS/PDLGA scaffolds was lower than that of β-TCP at each time point examined, and matched the new bone formation rates. These data suggest that β-CS/PDLGA could promote bone regeneration in vivo, which might be ascribed to the enhanced osteogenic differentiation of mesenchymal stem cells (MSCs) and increased angiogenic activity of endothelial cells (ECs).

Link to Article

http://dx.doi.org/10.1016/j.biomaterials.2012.09.021

The Skeletal site-specific role of connective tissue growth factor in prenatal osteogenesis

Authors

Alex G. Lambi, Talia L. Pankratz, Christina Mundy, Maureen Gannon, Mary F. Barbe, Joan T. Richtsmeier, Steven N. Popoff

Abstract

Background: Connective tissue growth factor (CTGF/CCN2) is a matricellular protein that is highly expressed during bone development. Mice with global CTGF ablation (knockout, KO) have multiple skeletal dysmorphisms and perinatal lethality. A quantitative analysis of the bone phenotype has not been conducted. Results: We demonstrated skeletal site-specific changes in growth plate organization, bone microarchitecture, and shape and gene expression levels in CTGF KO compared with wild-type mice. Growth plate malformations included reduced proliferation zone and increased hypertrophic zone lengths. Appendicular skeletal sites demonstrated decreased metaphyseal trabecular bone, while having increased mid-diaphyseal bone and osteogenic expression markers. Axial skeletal analysis showed decreased bone in caudal vertebral bodies, mandibles, and parietal bones in CTGF KO mice, with decreased expression of osteogenic markers. Analysis of skull phenotypes demonstrated global and regional differences in CTGF KO skull shape resulting from allometric (size-based) and nonallometric shape changes. Localized differences in skull morphology included increased skull width and decreased skull length. Dysregulation of the transforming growth factor-β-CTGF axis coupled with unique morphologic traits provides a potential mechanistic explanation for the skull phenotype. Conclusions: We present novel data on a skeletal phenotype in CTGF KO mice, in which ablation of CTGF causes site-specific aberrations in bone formation.

Link to Article

http://dx.doi.org/10.1002/dvdy.23888