VS and MA contributed equally to this work.
EphA4 Receptor Is a Novel Negative Regulator of Osteoclast Activity
Version of Record online: 19 MAR 2014
© 2014 American Society for Bone and Mineral Research
Journal of Bone and Mineral Research
Volume 29, Issue 4, pages 804–819, April 2014
How to Cite
Stiffel, V., Amoui, M., Sheng, M. H.-C., Mohan, S. and Lau, K.-H. W. (2014), EphA4 Receptor Is a Novel Negative Regulator of Osteoclast Activity. J Bone Miner Res, 29: 804–819. doi: 10.1002/jbmr.2084
Preliminary results presented at: 31st Annual Meeting of the American Society of Bone and Mineral Research, September 11–15, 2009, Denver, CO, USA. Abstract 1004.
- Issue online: 19 MAR 2014
- Version of Record online: 19 MAR 2014
- Accepted manuscript online: 26 AUG 2013 08:04AM EST
- Manuscript Accepted: 20 AUG 2013
- Manuscript Revised: 7 AUG 2013
- Manuscript Received: 15 MAR 2013
- Office of Research and Development, Medical Research Service, Department of Veteran Affairs
- MOLECULAR PATHWAYS, REMODELING;
- CELL/TISSUE SIGNALING, PARACRINE PATHWAY, OTHERS (EPHA4 SIGNALING);
- GENETIC ANIMAL MODELS
Of the ephrin (Eph) receptors, mature osteoclasts express predominantly EphA4. This study sought to determine if EphA4 has a regulatory role in osteoclasts. Treatment of RAW/C4 cells with Epha4 small interfering RNAs (siRNAs) increased average size, Ctsk mRNA expression level, and bone resorption activity of the derived osteoclast-like cells. Activation of the EphA4 signaling in osteoclast precursors with EfnA4-fc chimeric protein reduced cell size and resorption activity of the derived osteoclasts. Homozygous Epha4 null mice had substantially less trabecular bone in femur and vertebra compared to wild-type controls. The bone loss was due to a decrease in trabecular number and an increase in trabecular spacing, but not to an increase in osteoclast-lined bone surface or an increase in the number of osteoclasts on bone surface. Dynamic histomorphometry and serum biomarker analyses indicate that bone formation in Epha4 null mice was reduced slightly but not significantly. Osteoclasts of Epha4 null mice were also larger, expressed higher levels of Mmp3 and Mmp9 mRNAs, and exhibited greater bone resorption activity than wild-type osteoclasts in vitro. Deficient Epha4 expression had no effects on the total number of osteoclast formed in response to receptor activator of NF-κB ligand nor on apoptosis of osteoclasts in vitro. It also did not affect the protein-tyrosine phosphorylation status of its ligands, EfnB2, EfnA2, and EfnA4, in osteoclasts. Deficient Epha4 expression in Epha4 null osteoclasts activated the β3-integrin signaling through reduced phosphorylation of the tyr-747 residue, which led to increased binding of the stimulatory talin and reduced binding of the inhibitory Dok1 to β3-integrin. This in turn activated Vav3 and the bone resorption activity of osteoclasts. In conclusion, we demonstrate for the first time that EphA4 is a potent negative regulator of osteoclastic activity, mediated in part through increased Dok1 binding to β3-integrin via an increase in EphA4-dependent tyr-747 phosphorylation. © 2014 American Society for Bone and Mineral Research.