Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


The TRAF6 Binding Molecule p62/SQSTM1 Controls Inflammatory Bone Destruction in hTNFtg Mice.

Korb7,  Adelheid, Niedermeier3,  Marianne, Hillmann7,  Anja, Burgis1,  Susanne, Kollias5,  George, Herrmann2,  Sven, Pap4,  Thomas

Department of Immunology, University Erlangen, Erlangen, Germany
European Institute of Molecular Imaging, University Muenster, Germany
Institute for Experimental Musculoskeletal Medicine, University Hospital Muenster, Muenster, Germany
Institute for Experimental Musuculoskeletal Medicine, University Hospital Muenster, Muenster, Germany
Institute of Immunology, Biomedical Science Research Center, Vari, Greece
Institute of Microbiology - Clinical Microbiology, Immunology and Hygiene, University Hospital Erlangen, Erlangen, Germany
Internal Medicine D, Department of Nephrology and Rheumatology, University Hospital Muenster, Muenster, Germany

Background:

Activation of NF-kappaB via RANK is essential in regulating osteoclastogenesis. This process is enhanced by pro-inflammatory cytokines such as TNFalpha. P62/SQSTM1 directly modulates these pathways through complex formation with TRAF6, aPKCs and ubiquitin. However, the function of p62/SQSTM1 in regulating bone turnover under inflammatory conditions and specifically the role of the signal transduction domains of p62/SQSTM1 in this process is not known.

Methods:

Mice carrying a mutant of p62 with functional ubiquitin- binding but defective signal transduction domains (p62aaD69–251) were interbreed with arthritic hTNFtg mice. All resulting genotypes were scored for clinical parameters for 14 weeks. For quantification of inflammation, cartilage degradation and number of osteoclasts, joints of 14 wks old mice were stained with toluidin-blue and TRAP. To identify abnormalities in bone metabolism and bone structure high resolution micro-CT and Fluoride/FDG-PET analyses were performed. In addition, bone marrow derived monocytes (BMDMs) of wt and p62aaD69–251 mice were isolated and osteoclastogenesis was studied using an established osteoclast formation assay. To investigate the underlying signalling pathways, cells were treated with TNFalpha and RANKL at different time points, and the activation of MAPKs was studied by Western Blot analysis.

Results:

Histology and in vivo PET/CT studies revealed an increase in bone metabolism and bone mass in the hind paws, knees and vertebrae of p62aaD69–251 mice, but the number and size of osteoclasts of p62aaD69–251 and wt animals showed only minor changes suggesting that under physiological conditions the lack of the signal transduction domains of p62 is compensated by regulatory mechanisms. Compared to wt cells, however, BMDMs of p62aaD69–251 mice showed a significantly increased osteoclastogenesis, especially when stimulated with TNFalpha. Crossing of p62aaD69–251 mice with hTNFtg animals resulted in a dramatic increase in the severity of joint damage in the hTNFtg/p62aaD69–251/wt mice as determined clinically, by histomorphometry and PET/CT analysis. This was accompanied by an increase in the number and size of osteoclasts in vivo. During osteoclastogenesis, BMDMs from p62aaD69–251 mice showed an enhanced TNFalpha- induced ERK1/2 and p38 MAPK phosphorylation compared to that of wt mice.

Conclusion:

In summary, our data suggest that p62 plays a relevant role in regulating TNFalpha mediated joint damage. They indicate that the loss of the TRAF6 and aPKCs binding domains has essential consequences for osteoclastogenesis under inflammatory conditions.

To cite this abstract, please use the following information:
Korb, Adelheid, Niedermeier, Marianne, Hillmann, Anja, Burgis, Susanne, Kollias, George, Herrmann, Sven, et al; The TRAF6 Binding Molecule p62/SQSTM1 Controls Inflammatory Bone Destruction in hTNFtg Mice. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :2237
DOI: 10.1002/art.30000

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