Inhibition of osteoclastogenesis and inflammatory bone resorption by targeting BET proteins and epigenetic regulation

Authors

Kyung-Hyun Park-Min, Elisha Lim, Min Joon Lee, Sung Ho Park, Eugenia Giannopoulou, Anna Yarilina, Marjolein van der Meulen, Baohong Zhao, Nicholas Smithers, Jason Witherington, Kevin Lee, Paul P. Tak, Rab K. Prinjha & Lionel B Ivashkiv

Abstract

Emerging evidence suggests that ANKL-induced changes in chromatin state are important for osteoclastogenesis, but these epigenetic mechanisms are not well understood and have not been therapeutically targeted. In this study, we find that the small molecule -BET151 that targets bromo and extra-terminal (BET) proteins that ‘read’ chromatin states by binding to acetylated histones strongly suppresses osteoclastogenesis. -BET151 suppresses pathologic bone loss in NF-induced inflammatory osteolysis, inflammatory arthritis and post-ovariectomy models. Transcriptome analysis identifies a YC-NFAT axis important for osteoclastogenesis. Mechanistically, -BET151 inhibits expression of the master osteoclast regulator FATC1 by suppressing expression and recruitment of its newly identified upstream regulator YC. YC is elevated in rheumatoid arthritis macrophages and its induction by ANKL is important for osteoclastogenesis and NF-induced bone resorption. These findings highlight the importance of an -BET151-inhibited YC-NFAT axis in osteoclastogenesis, and suggest targeting epigenetic chromatin regulators holds promise for treatment of inflammatory and oestrogen deficiency-mediated pathologic bone resorption.

Link to Article

http://dx.doi.org/10.1038/ncomms6418

Covalently immobilised type I collagen facilitates osteoconduction and osseointegration of titanium coating implants

Authors

Haiyong Ao, Youtao Xie, Shengbin Yang, Xiaodong Wu, Kai Li, Xuebin Zheng, Tingting Tang

Abstract

Background/Objective

Plasma-sprayed titanium coating (TC) with rough surfaces has been successfully applied in hip or knee prostheses. This study aimed to investigate the osteoconduction and osseointegration of Type I collagen covalently immobilised on TC (TC-AAC) compared with those of TC.

Methods

In vitro, the migration of human mesenchymal stem cells (hMSCs) on TC and TC-AAC was observed by scanning electron microscopy and visualised fluorescent live/dead assay. In vivo, a rabbit model with femur condyle defect was employed, and implants of TC and TC-AAC were embedded into the femur condyles.

Results

Collagen immobilised on TC could promote hMSCs' migration into the porous structure of the TC. Micro computed tomography images showed that bone trabeculae were significantly more abundant around TC-AAC implants than around TC implants. Fluorescence micrographs indicated more active new-bone formation around implants in the TC-AAC group than in the TC group. The measurement of bone–implant contact on histological sections indicated significantly greater osteointegration around TC-AAC implants than around TC ones.

Conclusion

Immobilised Type I collagen could improve the osteoconduction and osseointegration of TC implants.

Link to Article

http://dx.doi.org/10.1016/j.jot.2015.08.005

C-Mpl Is Expressed on Osteoblasts and Osteoclasts and Is Important in Regulating Skeletal Homeostasis

Authors

Tomas E. Meijome,Jenna T. Baughman,R. Adam Hooker,Ying-Hua Cheng,Wendy A. Ciovacco,Sanjeev M. Balamohan,Trishya L. Srinivasan,Brahmananda R. Chitteti, Pierre P. Eleniste,Mark C. Horowitz,Edward F. Srour,Angela Bruzzaniti,Robyn K. Fuchs,Melissa A. Kacena

Abstract

C-Mpl is the receptor for thrombopoietin (TPO), the main megakaryocyte (MK) growth factor, and c-Mpl is believed to be expressed on cells of the hematopoietic lineage. As MKs have been shown to enhance bone formation, it may be expected that mice in which c-Mpl was globally knocked out (c-Mpl-/- mice) would have decreased bone mass because they have fewer MKs. Instead, c-Mpl-/- mice have a higher bone mass than WT controls. Using c-Mpl-/- mice we investigated the basis for this discrepancy and discovered that c-Mpl is expressed on both osteoblasts (OBs) and osteoclasts (OCs), an unexpected finding that prompted us to examine further how c-Mpl regulates bone. Static and dynamic bone histomorphometry parameters suggest that c-Mpl deficiency results in a high bone turnover state with a net gain in bone volume. In vitro, a higher percentage of c-Mpl-/- OBs were in active phases of the cell cycle, leading to an increased number of OBs. No difference in OB differentiation was observed in vitro as examined by real-time PCR and functional assays. In co-culture systems, which allow for the interaction between OBs and OC progenitors, c-Mpl-/- OBs enhanced osteoclastogenesis. Two of the major signaling pathways by which OBs regulate osteoclastogenesis, MCSF/OPG/RANKL and EphrinB2-EphB2/B4, were unaffected in c-Mpl-/- OBs. These data provide new findings for the role of MKs and c-Mpl expression in bone and may provide insight into the homeostatic regulation of bone mass as well as bone loss diseases such as osteoporosis.

Link to Article

http://dx.doi.org/10.1002/jcb.25380

Sclerostin-antibody treatment of glucocorticoid-induced osteoporosis maintained bone mass and strength

Authors

W. Yao, W. Dai, L. Jiang, E. Y.-A. Lay, Z. Zhong, R. O. Ritchie, X. Li, H. Ke, N. E. Lane

Abstract

Summary

This study was to determine if antibody against sclerostin (Scl-Ab) could prevent glucocorticoid (GC)-induced osteoporosis in mice. We found that Scl-Ab prevented GC-induced reduction in bone mass and bone strength and that the anabolic effects of Scl-Ab might be partially achieved through the preservation of osteoblast activity through autophagy.

Introduction

Glucocorticoids (GCs) inhibit bone formation by altering osteoblast and osteocyte cell activity and lifespan. A monoclonal antibody against sclerostin, Scl-Ab, increased bone mass in both preclinical animal and clinical studies in subjects with low bone mass. The objectives of this study were to determine if treatment with the Scl-Ab could prevent loss of bone mass and strength in a mouse model of GC excess and to elucidate if Scl-Ab modulated bone cell activity through autophagy.

Methods

We generated reporter mice that globally expressed dsRed fused to LC3, a protein marker for autophagosomes, and evaluated the dose-dependent effects of GCs (0, 0.8, 2.8, and 4 mg/kg/day) and Scl-Ab on autophagic osteoblasts, bone mass, and bone strength.

Results

GC treatment at 2.8 and 4 mg/kg/day of methylprednisolone significantly lowered trabecular bone volume (Tb-BV/TV) at the lumbar vertebrae and distal femurs, cortical bone mass at the mid-shaft femur (FS), and cortical bone strength compared to placebo (PL). In mice treated with GC and Scl-Ab, Tb-BV/TV increased by 60–125 %, apparent bone strength of the lumbar vertebrae by 30–70 %, FS-BV by 10–18 %, and FS-apparent strength by 13–15 %, as compared to GC vehicle-treated mice. GC treatment at 4 mg/kg/day reduced the number of autophagic osteoblasts by 70 % on the vertebral trabecular bone surface compared to the placebo group (PL, GC 0 mg), and GC + Scl-Ab treatment.

Conclusions

Treatment with Scl-Ab prevented GC-induced reduction in both trabecular and cortical bone mass and strength and appeared to maintain osteoblast activity through autophagy.

Link to Article

http://dx.doi.org/10.1007/s00198-015-3308-6

Alexidine Dihydrochloride Attenuates Osteoclast Formation and Bone Resorption and Protects Against LPS-Induced Osteolysis

Authors

Xiang Zhu MD, Junjie Gao BSc, Pei Y. Ng PhD, An Qin MD, PhD, James H. Steer BSc, Nathan J. Pavlos PhD, Ming H. Zheng MD, PhD, ARCPA, FRACSPath, Yang Dong MD and Tak S. Cheng PhD

Abstract

Aseptic loosening and periprosthetic infection leading to inflammatory osteolysis is a major complication associated with total joint arthroplasty (TJA). The liberation of bacterial products and/or implant-derived wear particles activates immune cells which produce pro-osteoclastogenic cytokines that enhances osteoclast recruitment and activity leading to bone destruction and osteolysis. Therefore agents which prevent the inflammatory response and/or attenuate excessive osteoclast (OC) formation and bone resorption offer therapeutic potential by prolonging the life of TJA implants. Alexidine dihydrochloride (AD) is a bisbiguanide compound commonly used as an oral disinfectant and in contact lens solutions. It possesses anti-microbial, anti-inflammatory and anti-cancer properties however its effects on OC biology are poorly described. Here, we demonstrate that AD inhibits OC formation and bone resorption in vitro and exert prophylatic protection against LPS-induced osteolysis in vivo. Biochemical analysis demonstrated that AD suppressed RANKL-induced activation of MAPKs (ERK, p38 and JNK) leading to the downregulation of NFATc1. Furthermore, AD disrupted F-actin ring formation and attenuated the ability of mature OC to resorb bone. Collectively our findings suggest that AD may be a promising prophylactic anti-osteoclastic/resorptive agent for the treatment of osteolytic diseases caused by excessive OC formation and function.

Link to Article

http://dx.doi.org/10.1002/jbmr.2710

A resorbable antibiotic eluting bone void filler for periprosthetic joint infection prevention

Authors

Zachary Jones, Amanda E. Brooks, Zachary Ferrell, David W. Grainger and Kristofer D. Sinclair

Abstract

Periprosthetic joint infection (PJI) following total knee arthroplasty is a globally increasing procedural complication. These infections are difficult to treat and typically require revision surgery. Antibiotic-loaded bone cement is frequently utilized to deliver antibiotics to the site of infection; however, bone cement is a nondegrading foreign body and known to leach its antibiotic load, after an initial burst release, at subtherapeutic concentrations for months. This work characterized a resorbable, antibiotic-eluting bone void filler designed to restore bone volume and prevent PJI. Three device formulations were fabricated, consisting of different combinations of synthetic inorganic bone graft material, degradable polymer matrices, salt porogens, and antibiotic tobramycin. These formulations were examined to determine the antibiotic's elution kinetics and bactericidal potential, the device's degradation in vitro, as well as osteoconductivity and device resorption in vivo using a pilot rabbit bone implant model. Kirby-Bauer antibiotic susceptibility tests assessed bactericidal activity. Liquid chromatography with tandem mass spectrometry measured antibiotic elution kinetics, and scanning electron microscopy was used to qualitatively assess degradation. Results indicated sustained antibiotic release from all three formulations above the Staphylococcus aureus minimum inhibitory concentration for a period of 5 to 8 weeks. Extensive degradation was observed with the Group 3 formulation after 90 days in phosphate-buffered saline, with a lesser degree of degradation observed in the other two formulations. Results from the pilot rabbit study showed the Group 3 device to be biocompatible, with minimal inflammatory response and no fibrous encapsulation in bone. The device was also highly osteoconductive—exhibiting an accelerated mineral apposition rate.

Link to Article

http://dx.doi.org/10.1002/jbm.b.33513