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CNC-bZIP protein NFE2L1 regulates osteoclast differentiation in antioxidant-dependent and independent manners

ABSTRACT: Fine-tuning of osteoclast differentiation (OD) and bone remodeling is crucial for bone homeostasis. Dissecting the mechanisms regulating osteoclastogenesis is fundamental to understanding the pathogenesis of various bone disorders including osteoporosis and arthritis. Nuclear factor erythroid 2-related factor 1 (NFE2L1, also known as NRF1), which belongs to the CNC-bZIP family of transcription factors, orchestrates a variety of physiological processes and stress responses. While Nfe2l1 gene may be transcribed into multiple alternatively spliced isoforms, the biological function of the different isoforms of NFE2L1 in bone metabolism, osteoclastogenesis in particular, has not been reported. Here we demonstrate that knockout of all isoforms of Nfe2l1 transcripts specifically in the myeloid lineage in mice [Nfe2l1(M)-KO] results in increased activity of osteoclasts, decreased bone mass and worsening of osteoporosis induced by ovariectomy and aging. In comparison, LysM-Cre-mediated Nfe2l1 deletion has no significant effect on the osteoblast and osteocytes. Mechanistic investigations using bone marrow cells and RAW 264.7 cells revealed that deficiency of Nfe2l1 leads to accelerated and elevated OD, which is attributed, at least in part, to enhanced accumulation of ROS in the early stage of OD and expression of nuclear factor of activated T cells, cytoplasmic, calcineurin dependent 1α (Nfatc1/α). In addition, NFE2L1 regulates the transcription of multiple antioxidant genes and Nfatc1/α and OD in an isoform-specific manner. While long isoforms of NFE2L1 function as accelerators of induction of Nfatc1/α and antioxidant genes and OD, the short isoform NFE2L1-453 serves as a brake that keeps the long isoforms’ accelerator effects in check. These findings provide a novel insight into the regulatory roles of NFE2L1 in osteoclastogenesis and highlight that NFE2L1 is essential in regulating bone remodeling and thus may be a valuable therapeutic target for bone disorders. Graphical abstract Image 1 Highlights • Nfe2l1(M)-KO mice exhibit reduced bone mass and elevated osteoclast activity.• Lack of Nfe2l1 in myeloid lineage cells results in elevated osteoclastogenesis.• Lack of Nfe2l1 leads to ROS accumulation accelerating osteoclastogenesis.• Long isoforms of NFE2L1 positively regulate Nfatc1/α and osteoclastogenesis.• S-NFE2L1-453 functions as a brake on Nfatc1/α transcription and osteoclastogenesis.

SUBMITTER: Liu Z

PROVIDER: S-EPMC8591424 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Mitochondrial biogenesis, the generation of new mitochondrial DNA and proteins, has been linked to osteoclast (OC) differentiation and function. In this study we used mice with mutations in key alternative NF-?B pathway proteins, RelB and NF-?B-inducing kinase (NIK), to dissect the complex relationship between mitochondrial biogenesis and osteoclastogenesis. In OC precursors lacking either NIK or RelB, receptor activator of NF-?B ligand (RANKL) was unable to increase mitochondrial DNA or oxidative phosphorylation (OxPhos) protein expression, which was associated with lower oxygen consumption rates. Transgenic OC precursors expressing constitutively active NIK showed normal RANKL-induced mitochondrial biogenesis (OxPhos expression and mitochondria copy number) compared to controls, but larger mitochondrial dimensions and increased oxygen consumption rates, suggesting increased mitochondrial function. To deduce the mechanism for mitochondrial biogenesis defects in NIK-deficient and RelB-deficient precursors, we examined expression of genes known to control this process. PGC-1? (Ppargc1b) expression, but not PGC-1?, PPRC1, or ERR?, was significantly reduced in RelB(-/-) and NIK(-/-) OCs. Because PGC-1? has been reported to positively regulate both mitochondrial biogenesis and differentiation in OCs, we retrovirally overexpressed PGC-1? in RelB(-/-) cells, but surprisingly found that it did not affect differentiation, nor did it restore RANKL-induced mitochondrial biogenesis. To determine whether the blockade in osteoclastogenesis in RelB-deficient cells precludes mitochondrial biogenesis, we rescued RelB(-/-) differentiation via overexpression of NFATc1. Mitochondrial parameters in neither WT nor RelB-deficient cultures were affected by NFATc1 overexpression, and bone resorption in RelB(-/-) was not restored. Furthermore, NFATc1 co-overexpression with PGC-1?, although allowing OC differentiation, did not rescue mitochondrial biogenesis or bone resorption in RelB(-/-) OCs, by CTX-I levels. Thus, our results indicate that the alternative NF-?B pathway plays dual, but distinct, roles in controlling the independent processes of OC differentiation and OC mitochondrial biogenesis. Furthermore, the inability of PGC-1? to drive mitochondrial biogenesis in OCs without RelB indicates a cell-type specificity in mitochondria regulation.

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CNC-bZIP protein NFE2L1 regulates osteoclast differentiation in antioxidant-dependent and independent manners

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