The transcription factor NF-(B is essential for osteoclastogenesis and is considered a key modulator of inflammatory responses. Activation of NF-(B entails induction of a large I(B kinase (IKK) complex that comprises IKK1, IKK2, and IKK(/NEMO. IKK2 and IKK1 activate the canonical (p50/p65) and non- canonical (p52/relB) NF-(B pathways, respectively. Recent studies implicate IKK2 and IKK1 as essential for osteoclastogenesis, yet the mechanisms underling this function, remain unclear. In addition, IKK2 is considered as a key mediator of inflammatory events induced by TNF, LPS, and other pro-inflammatory agents (through the classical NF-(B pathway), whereas less is known about the role of IKK1 is such responses. In the past few years we have investigated molecular pathways regulating osteoclast activity in osteolytic responses, such as inflammatory osteolysis and arthritic bone erosion, and unveiled critical regulatory steps modulating NF-(B activation in osteoclast precursors. In this regard, we find that disruption of NF-(B activation at multiple levels attenuates osteoclastogenesis and inflammatory bone erosion. Specifically, we have shown that administration of dominant-negative forms of I(B(, that resist phosphorylation by IKK2; and most recently inhibition of IKK assembly with NEMO, using a decoy NEMO binding domain (NBD) peptide, all are successful approaches to inhibit osteoclastogenesis and bone erosion, in vitro and in vivo. Most importantly, we have preliminary evidence that, 1) failure of RANKL-induced osteoclastogenesis by IKK1-null OCPs is rescued by re-introduction of IKK1 cDNA constructs, and that 2) tissue-specific deletion of IKK2 in OCPs (using CD11b-cre) results with skeletally deformed mice. It is evident that osteoclastogenesis is impaired in the absence of IKK1 or IKK2, however, the precise mechanism(s) underlying signaling of IKKs in basal and inflammatory osteoclastogenesis remain scarce. Moreover, the relative contribution of either protein to these responses is indefinite. It is also known that IKK1 and IKK2 share considerable sequence and domain similarities, albeit they maintain distinct and non-overlapping functions. Thus, we hypothesize that IKK1 and IKK2 differentially regulate basal and inflammatory osteoclastogenesis through the alternative and classical NF-(B activation pathways. Hence, clarifying the individual roles of IKKs in osteoclastogenesis by investigating the details of their molecular signaling in osteoclasts, utilizing germ-line and specific tissue deletions of the relevant genes, will enable us to design strategies and selective inhibitors directed against IKK1 and IKK2 that may be useful for regulating osteoclastogenesis and alleviating inflammatory osteolysis in various bone resorptive disorders. Thus, we propose to investigate the following specific aims: 1) Determine the molecular role of IKK1 and IKK2 in basal and inflammatory osteoclastogenesis. 2) Determine the mechanism by which tyrosine phosphorylation regulates the fate and activity of IKK2 in the osteoclast lineage and it's impact on osteoclastogenesis. 3) Determine the role of IKK1 and IKK2 in inflammatory osteolysis, in vivo.

Public Health Relevance

The transcription factor NF-(B is essential for osteoclastogenesis and modulates inflammatory responses. NF-(B is activated by the serine kinases, I(B kinase (IKK)-1, IKK-2, and IKK(/NEMO. Gene deletions of IKK1 or IKK2 led to defects in osteoclasts and inflammatory responses. Using IKK1 and IKK2-null mice, we propose to investigate the molecular domain contributions of IKK1 and IKK2 to osteoclastogenesis and inflammatory osteolysis, as is the case in inflammatory arthritis. Our proposal holds promise to identify novel selective anti-osteolytic therapies. ? ? ?

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
1R01AR054326-01A2
Application #
7461161
Study Section
Skeletal Biology Development and Disease Study Section (SBDD)
Program Officer
Sharrock, William J
Project Start
2008-07-07
Project End
2013-03-31
Budget Start
2008-07-07
Budget End
2009-03-31
Support Year
1
Fiscal Year
2008
Total Cost
$334,400
Indirect Cost
Name
Washington University
Department
Orthopedics
Type
Schools of Medicine
DUNS #
068552207
City
Saint Louis
State
MO
Country
United States
Zip Code
63130
Rohatgi, Nidhi; Zou, Wei; Collins, Patrick L et al. (2018) ASXL1 impairs osteoclast formation by epigenetic regulation of NFATc1. Blood Adv 2:2467-2477
Wang, Chun; Hockerman, Susan; Jacobsen, E Jon et al. (2018) Selective inhibition of the p38? MAPK-MK2 axis inhibits inflammatory cues including inflammasome priming signals. J Exp Med 215:1315-1325
Wang, Cuicui; Abu-Amer, Yousef; O'Keefe, Regis J et al. (2018) Loss of Dnmt3b in Chondrocytes Leads to Delayed Endochondral Ossification and Fracture Repair. J Bone Miner Res 33:283-297
Wang, Chun; Xu, Can-Xin; Alippe, Yael et al. (2017) Chronic inflammation triggered by the NLRP3 inflammasome in myeloid cells promotes growth plate dysplasia by mesenchymal cells. Sci Rep 7:4880
Alippe, Yael; Wang, Chun; Ricci, Biancamaria et al. (2017) Bone matrix components activate the NLRP3 inflammasome and promote osteoclast differentiation. Sci Rep 7:6630
Swarnkar, Gaurav; Chen, Tim Hung-Po; Arra, Manoj et al. (2017) NUMBL Interacts with TAK1, TRAF6 and NEMO to Negatively Regulate NF-?B Signaling During Osteoclastogenesis. Sci Rep 7:12600
Zou, Wei; Rohatgi, Nidhi; Chen, Timothy Hung-Po et al. (2016) PPAR-? regulates pharmacological but not physiological or pathological osteoclast formation. Nat Med 22:1203-1205
Wang, C; Qu, C; Alippe, Y et al. (2016) Poly-ADP-ribosylation-mediated degradation of ARTD1 by the NLRP3 inflammasome is a prerequisite for osteoclast maturation. Cell Death Dis 7:e2153
Swarnkar, Gaurav; Shim, Kyuhwan; Nasir, Amjad M et al. (2016) Myeloid Deletion of Nemo Causes Osteopetrosis in Mice Owing to Upregulation of Transcriptional Repressors. Sci Rep 6:29896
Swarnkar, Gaurav; Karuppaiah, Kannan; Mbalaviele, Gabriel et al. (2015) Osteopetrosis in TAK1-deficient mice owing to defective NF-?B and NOTCH signaling. Proc Natl Acad Sci U S A 112:154-9

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