Vascular expression of the chemokine CX3CL1 promotes osteoclast recruitment and exacerbates bone resorption in an irradiated murine model

Authors

Ki Hoon Han, Jae Won Ryu, Kyung-Eun Lim, Soo-Han Lee, Yuna Kim, Chang Sun Hwang, Je-Yong Choi, Ki Ok Han

Abstract

Circulating osteoclast precursor cells highly express CX3C chemokine receptor 1 (CX3CR1), which is the only receptor for the unique CX3C membrane-anchored chemokine, fractalkine (CX3CL1). An irradiated murine model was used to evaluate the role of the CX3CL1–CX3CR1 axis in osteoclast recruitment and osteoclastogenesis. Ionizing radiation (IR) promoted the migration of circulating CD11b + cells to irradiated bones and dose-dependently increased the number of differentiated osteoclasts in irradiated bones. Notably, CX3CL1 was dramatically upregulated in the vascular endothelium after IR. IR-induced production of CX3CL1 by skeletal vascular endothelium promoted chemoattraction of circulating CX3CR1 +/CD11b + cells and triggered homing of these osteoclast precursor cells toward the bone remodeling surface, a specific site for osteoclast differentiation. CX3CL1 also increased the endothelium-derived expression of other chemokines including stromal cell-derived factor-1 (CXCL12) and macrophage inflammatory protein-2 (CXCL2) by activating the hypoxia-inducible factor-1 α pathway. These effects may further enhance osteoclastogenesis. A series of in vivo experiments confirmed that knockout of CX3CR1 in bone marrow-derived cells and functional inhibition of CX3CL1 using a specific neutralizing antibody significantly ameliorated osteoclastogenesis and prevented bone loss after IR. These results demonstrate that the de novo CX3CL1–CX3CR1 axis plays a pivotal role in osteoclast recruitment and subsequent bone resorption, and verify its therapeutic potential as a new target for anti-resorptive treatment.

Link To Article

http://dx.doi.org/10.1016/j.bone.2013.12.032

The Rho-GEF Kalirin regulates bone mass and the function of osteoblasts and osteoclasts

Authors

Su Huang, Pierre P. Elensite, Kornchanok Wayakanon, Prashant Mandela, Betty A. Eipper, Richard E. Mains, Matthew R. Allen, Angela Bruzzaniti

Abstract

Bone homeostasis is maintained by the balance between bone resorption by osteoclasts and bone formation by osteoblasts. Dysregulation in the activity of the bone cells can lead to osteoporosis, a disease characterized by low bone mass and an increase in bone fragility and risk of fracture. Kalirin is a novel GTP-exchange factor protein that has been shown to play a role in cytoskeletal remodeling and dendritic spine formation in neurons. We examined Kalirin expression in skeletal tissue and found that it was expressed in osteoclasts and osteoblasts. Furthermore, micro-CT analyses of the distal femur of global Kalirin knockout (Kal-KO) mice revealed significantly reduced trabecular and cortical bone parameters in Kal-KO mice, compared to WT mice, with significantly reduced bone mass in 8, 14 and 36 week-old female Kal-KO mice. Male mice also exhibited a decrease in bone parameters but not the level seen in female mice. Histomorphometric analyses also revealed decreased bone formation rate in 14 week-old female Kal-KO mice, as well as decreased osteoblast number/bone surface and increased osteoclast surface/bone surface. Consistent with our in vivo findings, the bone resorbing activity and differentiation of Kal-KO osteoclasts was increased in vitro. Although alkaline phosphatase activity by Kal-KO osteoblasts was increased in vitro, Kal-KO osteoblasts showed decreased mineralizing activity, as well as decreased secretion of OPG, which was inversely correlated with ERK activity. Taken together, our findings suggest that deletion of Kalirin directly affects osteoclast and osteoblast activity, leading to decreased OPG secretion which is likely to alter the RANKL/OPG ratio, promoting osteoclastogenesis. Therefore, Kalirin may play a role in paracrine and/or endocrine signaling events that control skeletal bone remodeling and the maintenance of bone mass.

Link To Article

http://dx.doi.org/10.1016/j.bone.2013.12.023

Biceps Detachment Decreases Joint Damage in a Rotator Cuff Tear Rat Model

Authors

Stephen J. Thomas PhD, ATC, Katherine E. Reuther BS, Jennica J. Tucker BS, Joseph J. Sarver PhD, Sarah M. Yannascoli MD, Adam C. Caro DVM, Pramod B. Voleti MD, Sarah I. Rooney MSE, David L. Glaser MD, Louis J. Soslowsky PhD

Abstract

Background

Pathology in the long head of the biceps tendon often occurs in patients with rotator cuff tears. Arthroscopic tenotomy is the most common treatment. However, the role of the long head of the biceps at the shoulder and the consequences of surgical detachment on the remaining shoulder structures remain unknown.

Questions/purposes

We hypothesized that detachment of the long head of the biceps, in the presence of supraspinatus and infraspinatus tears, would decrease shoulder function and decrease mechanical and histologic properties of both the subscapularis tendon and the glenoid articular cartilage.

Methods

We detached the supraspinatus and infraspinatus or the supraspinatus, infraspinatus, and long head of the biceps after 4 weeks of overuse in a rat model. Animals were gradually returned to overuse activity after detachment. At 8 weeks, the subscapularis and glenoid cartilage biomechanical and histologic properties were evaluated and compared.

Results

The group with the supraspinatus, infraspinatus, and long head of the biceps detached had greater medial force and decreased change in propulsion, braking, and vertical force. This group also had an increased upper and lower subscapularis modulus but without any differences in glenoid cartilage modulus. Finally, this group had a significantly lower cell density in both the upper and lower subscapularis tendons, although cartilage histology was not different.

Conclusions

Detachment of the long head of the biceps tendon in the presence of a posterior-superior cuff tear resulted in improved shoulder function and less joint damage in this animal model.

Clinical Relevance

This study provides evidence in an animal model that supports the use of tenotomy for the management of long head of the biceps pathology in the presence of a two-tendon cuff tear. However, long-term clinical trials are required.

Link To Article

http://dx.doi.org/10.1007/s11999-013-3422-8

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

Cartilage-Specific Overexpression of ERRγ Results in Chondrodysplasia and Reduced Chondrocyte Proliferation

Authors

Marco Cardelli, Ralph A. Zirngibl, Jonathan F. Boetto, Kristen P. McKenzie, Tammy-Claire Troy, Kursad Turksen, Jane E. Aubin

Abstract

While the role of estrogen receptor-related receptor alpha (ERRα) in chondrogenesis has been investigated, the involvement of ERR gamma (ERRγ) has not been determined. To assess the effect of increased ERRγ activity on cartilage development in vivo, we generated two transgenic (Tg) lines overexpressing ERRγ2 via a chondrocyte-specific promoter; the two lines exhibited ~3 and ~5 fold increased ERRγ2 protein expression respectively in E14.5 Tg versus wild type (WT) limbs. On postnatal day seven (P7), we observed a 4–10% reduction in the size of the craniofacial, axial and appendicular skeletons in Tg versus WT mice. The reduction in bone length was already present at birth and did not appear to involve bones that are derived via intramembranous bone formation as the bones of the calvaria, clavicle, and the mandible developed normally. Histological analysis of P7 growth plates revealed a reduction in the length of the Tg versus WT growth plate, the majority of which was attributable to a reduced proliferative zone. The reduced proliferative zone paralleled a decrease in the number of Ki67-positive proliferating cells, with no significant change in apoptosis, and was accompanied by large cell-free swaths of cartilage matrix, which extended through multiple zones of the growth plate. Using a bioinformatics approach, we identified known chondrogenesis-associated genes with at least one predicted ERR binding site in their proximal promoters, as well as cell cycle regulators known to be regulated by ERRγ. Of the genes identified, Col2al, Agg, Pth1r, and Cdkn1b (p27) were significantly upregulated, suggesting that ERRγ2 negatively regulates chondrocyte proliferation and positively regulates matrix synthesis to coordinate growth plate height and organization.

Link To Article

http://dx.doi.org/10.1371/journal.pone.0081511

Deleterious effects of osteoarthritis on the structure and function of the meniscal enthesis

Authors

Adam C. Abraham, Hannah M. Pauly, Tammy L. Haut Donahue

Abstract

Objective

The ability of menisci to prevent osteoarthritis (OA) is dependent on the integrity of the complex meniscal entheses, the attachments of the menisci to the underlying subchondral bone. The goal of this study was to determine mechanical and structural changes in meniscal entheses after the onset of osteoarthritis.

Design

Healthy and osteoarthritic meniscal entheses were evaluated for changes in histomorphological characteristics, mineralization, and mechanical properties. GAG and calcium in the insertion were evaluated with histological staining techniques. The extent of calcium deposition was assessed and tidemark integrity was quantified. Changes in the mineralized zone of the insertion was examined using micro-computed tomography to determine bone mineral density, cortical zone thickness, and mineralization gradient. Mechanical properties of the entheses were measured using nanoindentation techniques to obtain material properties based on viscoelastic analysis.

Results

GAG thickness in the calcified fibrocartilage zone and calcium content were significantly greater in osteoarthritic anterior meniscal entheses. Tidemark integrity was significantly decreased in OA tissue, particularly in the medial anterior enthesis. The mineralized zone of osteoarthritic meniscal entheses was significantly thicker than in healthy entheses and showed decreased bone mineral density. Fitting of mineralization data to a sigmoidal Gompertz function revealed a lower rate of increase in mineralization in osteoarthritic tissue. Analysis of viscoelastic mechanical properties revealed increased compliance in osteoarthritic tissue.

Conclusions

These data suggest that significant changes occur at meniscal enthesis sites with the onset of osteoarthritis. Mechanical and structural changes in meniscal entheses may contribute to meniscal extrusion, which has been show to increase the progression of OA.

Link To Article

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