The Large Zinc Finger Protein ZAS3 Is a Critical Modulator of Osteoclastogenesis

Abstract

BackgroundMice deficient in the large zinc finger protein, ZAS3, show postnatal increase in bone mass suggesting that ZAS3 is critical in the regulation of bone homeostasis. Although ZAS3 has been shown to inhibit osteoblast differentiation, its role on osteoclastogenesis has not been determined. In this report we demonstrated the role of ZAS3 in bone resorption by examining the signaling mechanisms involved in osteoclastogenesis.Methodology/Principal FindingsComparison of adult wild-type and ZAS3 knockout (ZAS3−/−) mice showed that ZAS3 deficiency led to thicker bones that are more resistant to mechanical fracture. Additionally, ZAS3−/− bones showed fewer osteoclasts and inefficient M-CSF/sRANKL-mediated osteoclastogenesis ex vivo. Utilizing RAW 264.7 pre-osteoclasts, we demonstrated that overexpression of ZAS3 promoted osteoclastogenesis and the expression of crucial osteoclastic molecules, including phospho-p38, c-Jun, NFATc1, TRAP and CTSK. Contrarily, ZAS3 silencing by siRNA inhibited osteoclastogenesis. Co-immunoprecipitation experiments demonstrated that ZAS3 associated with TRAF6, the major receptor associated molecule in RANK signaling. Furthermore, EMSA suggested that nuclear ZAS3 could regulate transcription by binding to gene regulatory elements.Conclusion/SignificanceCollectively, the data suggested a novel role of ZAS3 as a positive regulator of osteoclast differentiation. ZAS3 deficiency caused increased bone mass, at least in part due to decreased osteoclast formation and bone resorption. These functions of ZAS3 were mediated via activation of multiple intracellular targets. In the cytoplasmic compartment, ZAS3 associated with TRAF6 to control NF-kB and MAP kinase signaling cascades. Nuclear ZAS3 acted as a transcriptional regulator for osteoclast-associated genes. Additionally, ZAS3 activated NFATc1 required for the integration of RANK signaling in the terminal differentiation of osteoclasts. Thus, ZAS3 was a crucial molecule in osteoclast differentiation, which might potentially serve as a target in the design of therapeutic interventions for the treatment of bone diseases related to increased osteoclast activity such as postmenopausal osteoporosis, Paget's disease, and rheumatoid arthritis.

Control of bone resorption in mice by Schnurri-3

“…Consistent with our findings, these authors observed increased bone mass with increased fracture resistance in an independent model of germline Shn3 deletion. Similar to our findings, Liu et al (33) observed decreased numbers of osteoclasts in vivo. However, we believe that our current findings of persistent high bone mass phenotype in WT animals receiving Shn3-deficient BM transplantation (Fig.…”

“…Recently, it has been suggested that Shn3 (also known as ZAS3) may play a cell-intrinsic role in regulating osteoclastogenesis by regulating receptor activator of nuclear factor-κB signaling (33). Consistent with our findings, these authors observed increased bone mass with increased fracture resistance in an independent model of germline Shn3 deletion.…”

Novel estrogen target gene ZAS3 is overexpressed in systemic lupus erythematosus

“…We have previously shown that ZAS3 is a critical mediator of osteoclastogenesis as ZAS3 knockout mice have dramatically increased bone mass [37]. Further, osteoclastogenesis has recently been shown to be impaired in a murine lupus model by shifting monocyte development toward myeloid dendritic cells and away from osteoclasts [38].…”

Human Immunodeficiency Virus Type 1 Enhancer-binding Protein 3 Is Essential for the Expression of Asparagine-linked Glycosylation 2 in the Regulation of Osteoblast and Chondrocyte Differentiation

“…In addition, they showed that bone formation, as well as bone resorption, decreased in the bones of Hivep2-null mice, resulting in osteopenia due to the low turnover of bone remodeling. Recently, Hivep3 was also found to promote osteoclastogenesis (14,15). Taken together, the defects in osteoclastogenesis induced by loss of the Hivep genes seem to be mainly responsible for the additively increased bone volume in Hivep2/Hivep3 double knock-out mice.…”

“…In addition, Hivep3 indirectly promotes osteoclastogenesis by promoting osteoblastic expression of receptor activator of nuclear factor-B ligand (Rankl), a crucial factor for osteoclast differentiation (14). Hivep3 also cell-autonomously promotes osteoclastogenesis by inducing the expression of Nfatc1, a master transcription factor in osteoclast differentiation, by interacting with Traf6 to enhance its activity while forming a complex with c-Jun to activate the Nfatc1 promoter (15). Thus, Hivep3 controls both bone formation and resorption at multiple steps to maintain normal bone mass.…”