Deficiency of optineurin enhances osteoclast differentiation by attenuating the NRF2-mediated antioxidant response

Peng Xue,Emily Chang,Ching-Chang Ko,Xiangxiang Hu,Minghui Chen,Tai-Hsien Wu,Henry C Tseng,Lufei Wang,Dong-Joon Lee,Brian L Foster

doi:10.1038/s12276-021-00596-w

Abstract

Abnormally increased resorption contributes to bone degenerative diseases such as Paget’s disease of bone (PDB) through unclear mechanisms. Recently, the optineurin (OPTN) gene has been implicated in PDB, and global OPTN knockout mice (Optn−/−) were shown to exhibit increased formation of osteoclasts (osteoclastogenesis). Growing evidence, including our own, has demonstrated that intracellular reactive oxygen species (ROS) stimulated by receptor activator of nuclear factor kappa-B ligand (RANKL) can act as signaling molecules to promote osteoclastogenesis. Here, we report that OPTN interacts with nuclear factor erythroid-derived factor 2-related factor 2 (NRF2), the master regulator of the antioxidant response, defining a pathway through which RANKL-induced ROS could be regulated for osteoclastogenesis. In this study, monocytes from Optn−/− and wild-type (Optn+/+) mice were utilized to differentiate into osteoclasts, and both qRT-PCR and tartrate-resistant acid phosphatase (TRAP) staining showed that the Optn−/− monocytes exhibited enhanced osteoclastogenesis compared to the Optn+/+ cells. CellROX® staining, qRT-PCR, and Western blotting indicated that OPTN deficiency reduced the basal expression of Nrf2, inhibited the expression of NRF2-responsive antioxidants, and increased basal and RANKL-induced intracellular ROS levels, leading to enhanced osteoclastogenesis. Coimmunoprecipitation (co-IP) showed direct interaction, and immunofluorescence staining showed perinuclear colocalization of the OPTN-NRF2 granular structures during differentiation. Finally, curcumin and the other NRF2 activators attenuated the hyperactive osteoclastogenesis induced by OPTN deficiency. Collectively, our findings reveal a novel OPTN-mediated mechanism for regulating the NRF2-mediated antioxidant response in osteoclasts and extend the therapeutic potential of OPTN in the aging process resulting from ROS-triggered oxidative stress, which is associated with PDB and many other degenerative diseases.

Highlights

During skeletal remodeling, bone formation by osteoblasts is balanced with bone degradation by osteoclasts to meet the functional demands of the skeletal system[1,2]
OPTN deficiency enhances osteoclastogenesis To test the effects of OPTN ablation on osteoclastogenesis, we determined the gene expression of Optn and osteoclast markers in osteoclast precursors under basal conditions
Optineurin (OPTN) has been recently implicated in the differentiation of osteoclasts; the mechanisms identified to date by which OPTN deficiency results in elevated osteoclastogenesis have been limited to the NFkB and interferon signaling pathways[36,52]

Summary

Introduction

Bone formation by osteoblasts is balanced with bone degradation by osteoclasts to meet the functional demands of the skeletal system[1,2]. Mature osteoclasts are derived from differentiating osteoclast precursors. This process, called osteoclastogenesis, is Official journal of the Korean Society for Biochemistry and Molecular Biology. Xue et al Experimental & Molecular Medicine (2021) 53:667–680 triggered by the binding of receptor activator of nuclear factor kappa-B ligand (RANKL) to its receptor on osteoclastic progenitors (preosteoclasts), which activate multiple downstream signaling pathways[11], in which intracellular reactive oxidative species (ROS) have recently been demonstrated to serve as critical secondary messengers[12,13,14,15]. In contrast to physiological levels of ROS, which serve as signaling molecules[16,17,18], excess ROS levels may result in abnormally elevated osteoclastogenesis, oxidative stress, and cellular damage over time[19,20]. ROS have been broadly associated with age-dependent cellular degeneration in other tissues[30,31,32]

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Results

Conclusion