Regulation of human osteoclast differentiation by thioredoxin binding protein-2 and redox-sensitive signaling.
Differential expression of TBP-2 and Trx-1 occurs during osteoclastogenesis. Adenoviral overexpression of TBP-2 in osteoclast precursors inhibits Trx-1 expression, osteoclast formation, and AP-1 binding activity. TBP-2 and Trx-1 are key regulators of osteoclastogenesis.


BACKGROUND
Thioredoxin binding protein-2 (TBP-2) negatively regulates thioredoxin-1 (Trx-1), a key endogenous modulator of cellular redox and signaling. In gene array analysis, we found that TBP-2 expression was reduced during human osteoclast differentiation compared with macrophage differentiation. Our aim was to determine the roles of TBP-2 and Trx-1 in human osteoclastogenesis and RANKL signaling.


METHODS
Osteoclasts or macrophages were generated from colony-forming unit-granulocyte macrophage (CFU-GM) precursors treated with sRANKL and macrophage-colony-stimulating factor (M-CSF), or M-CSF alone, respectively. Expression of TBP-2 and Trx-1 was quantified by real-time PCR and Western analysis. Adenoviral gene transfer was used to overexpress TBP-2 in precursors. NF-kappaB and activator protein 1 (AP-1) signaling was assessed with EMSA.


RESULTS
In the presence of sRANKL, expression of TBP-2 was decreased, whereas Trx-1 expression was increased. The antioxidant N-acetylcysteine reversed this pattern and markedly inhibited osteoclastogenesis. Adenoviral overexpression of human TBP-2 in precursors inhibited osteoclastogenesis and Trx-1 expression, inhibited sRANKL-induced DNA binding of AP-1, but enhanced sRANKL-induced DNA binding of NF-kappaB.


CONCLUSIONS
These data support significant roles for TBP-2 and the Trx system in osteoclast differentiation that are mediated by redox regulation of AP-1 transcription. A likely mechanism of stress signal induction of bone resorption is provided. Modulators of the Trx system such as antioxidants have potential as antiresorptive therapies.
Aitken
Cathy J
CJ
Department of Clinical and Biomedical Sciences: Barwon Health, The University of Melbourne, Geelong, Victoria 3220, Australia.
Hodge
Jason M
JM
Nishinaka
Yumiko
Y
Vaughan
Tanya
T
Yodoi
Junji
J
Day
Christopher J
CJ
Morrison
Nigel A
NA
Nicholson
Geoffrey C
GC
D000256:Adenoviridae / Q000235:genetics; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D002454:Cell Differentiation; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation; D018014:Gene Transfer Techniques; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000096:biosynthesis; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D010010:Osteoclasts / Q000166:cytology* / Q000378:metabolism; D010084:Oxidation-Reduction; D011485:Protein Binding; D053245:RANK Ligand; D012333:RNA, Messenger / Q000378:metabolism; D053246:Receptor Activator of Nuclear Factor-kappa B; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013879:Thioredoxins / Q000378:metabolism; D013997:Time Factors; D018808:Transcription Factor AP-1 / Q000378:metabolism
D000975:Antioxidants; D002352:Carrier Proteins; D018950:Lipopolysaccharide Receptors; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D053245:RANK Ligand; D012333:RNA, Messenger; D053246:Receptor Activator of Nuclear Factor-kappa B; C505686:TNFRSF11A protein, human; C505688:TNFSF11 protein, human; C486715:TXNIP protein, human; D018808:Transcription Factor AP-1; D013879:Thioredoxins