Regulatory network mediated by RBP‐J/NFATc1‐miR182 controls inflammatory bone resorption

Abstract

Abbreviations: Blimp1, B lymphocyte-induced maturation protein-1; BMM, bone marrow-derived macrophage; ChIP, chromatin immunoprecipitation; FAIRE, formaldehyde-assisted isolation of regulatory elements; FOXO3, Forkhead box class O 3; MNC, multinucleated cell; M-CSF, macrophage colony-stimulating factor; NFATc1, nuclear factor of activated T cells c1; PBMCs, peripheral blood monocytes; PKR, protein kinase double-stranded RNA dependent; RA, rheumatoid arthritis; RANKL, receptor activator for NF-kB ligand; RBP-J, recombination signal binding protein for immunoglobulin kappa J region; TNFα, tumor necrosis factor-α; TNFi, TNF inhibitor; TRAP, tartrate-resistant acid phosphatase; WT, wild-type; μCT, microcomputed tomography. AbstractBone resorption is a severe consequence of inflammatory diseases associated with osteolysis, such as rheumatoid arthritis (RA), often leading to disability in patients.In physiological conditions, the differentiation of bone-resorbing osteoclasts is delicately regulated by the balance between osteoclastogenic and anti-osteoclastogenic mechanisms. Inflammation has complex impact on osteoclastogenesis and bone destruction, and the underlying mechanisms of which, especially feedback inhibition, are underexplored. Here, we identify a novel regulatory network mediated by RBP-J/NFATc1-miR182 in TNF-induced osteoclastogenesis and inflammatory bone resorption. This network includes negative regulator RBP-J and positive regulators, NFATc1 and miR182, of osteoclast differentiation. In this network, miR182 is a direct target of both RBP-J and NFATc1. RBP-J represses, while NFATc1 activates miR182 expression through binding to specific open chromatin regions in the miR182 promoter. Inhibition of miR182 by RBP-J servers as a critical mechanism that limits TNF-induced osteoclast differentiation and inflammatory bone resorption. Inflammation, such as that which occurs in RA, shifts the expression levels of the components in this network mediated by RBP-J/NFATc1-miR182-FoxO3/ PKR (previously identified miR182 targets) towards more osteoclastogenic, rather than healthy conditions. Treatment with TNF inhibitors in RA patients reverses the expression changes of the network components and osteoclastogenic potential. Thus, this network controls the balance between activating and repressive signals that determine the extent of osteoclastogenesis. These findings collectively highlight the biological significance and translational implication of this newly identified intrinsic regulatory network in inflammatory osteoclastogenesis and osteolysis. K E Y W O R D Sinflammatory bone resorption, osteoclast, osteoimmunology, rheumatoid arthritis | 2393 INOUE Et al.

Sulforaphane Inhibits Osteoclastogenesis via Suppression of the Autophagic Pathway

“…Throughout life, bone remodeling is precisely regulated by the balance between osteoblastic bone formation and osteoclastic bone resorption. This balance is often disturbed by diseases associated with excessive bone resorption, such as osteoporosis, rheumatoid arthritis (RA), periodontitis, and bone metastasis [ 1 , 2 , 3 ]. Osteoclasts, multinucleated cells that derive from the monocyte–macrophage lineage of hematopoietic stem cells, are responsible for bone destruction in these diseases.…”

Intrinsic Restriction of TNF-Mediated Inflammatory Osteoclastogenesis and Bone Resorption

“…Through genome-wide miRNA expression profiling, our group identified miR-182 as a TNF-induced miRNA that is directly targeted and suppressed by RBP-J in bone marrow macrophages and osteoclast precursors ( 46 , 47 ). RBP-J inhibits the expression and function of NFATc1 ( 25 ), which in turn acts as an upstream regulator activating miR-182, pointing to a novel regulatory network ( 48 ). Both in vitro and in vivo evidence supports the role of miR-182 as a positive regulator of TNF-mediated osteoclastogenesis.…”

“…Potential long-term side effects on physiological bone remodeling by targeting these mechanisms should especially be given attention. Recent studies identified novel TNF-induced intrinsic inhibitory mechanisms of osteoclastogenesis, which are unique from RANKL-mediated mechanisms ( 25 , 32 , 48 ). Exploring these mechanisms would shed insight into developing selective therapeutic approaches to prevent TNF-mediated bone resorption associated with inflammatory diseases, without undesirably impacting physiological bone remodeling.…”

“…The identification of miR-182 as a key downstream target of RBP-J lead to the finding of a novel RBP-J/NFATc1-miR182 regulatory network ( 47 , 48 ). Positive osteoclastogenic regulators NFATc1 and miR-182 levels were elevated, while negative regulators RBP-J, FOXO3, PKR and IFN- β levels were repressed in PBMCs isolated from RA patients compared to healthy donors ( Figure 3 ).…”

The Expression Level of FOXO3a in Patients With Autoimmune Diseases

“…It has been reported that FOXO3a levels were significantly decreased in RA patients compared with healthy individuals. 21,[23][24][25][26] However, Kuo and Lin 20 and Grabiec et al 22 showed the opposite results and found no significant difference in FOXO3a levels between RA patients and healthy controls. In addition, Min et al 18,27 and Kim et al 28 observed that FOXO3a levels in IBD patients were different from controls, whereas other studies 20,29 reported that there were no significant differences between SLE patients and healthy individuals.…”