FOXO1 Mediates RANKL-Induced Osteoclast Formation and Activity

Abstract

We have previously shown that the transcription factor FOXO1 is elevated in conditions with high levels of bone resorption. To investigate the role of FOXO1 in the formation of osteoclasts we examined mice with lineage specific deletion of FOXO1 in osteoclast precursors and by knockdown of FOXO1 with siRNA. The receptor activator of NF-kappa B ligand (RANKL), a principal bone resorbing factor, induced FOXO1 expression and nuclear localization two days after stimulation in bone marrow macrophages (BMMs) and RAW264.7 osteoclast precursors. RANKL- induced osteoclast formation and osteoclast activity was reduced in half in vivo and in vitro with lineage specific FOXO1 deletion (LyzM.Cre+FOXO1L/L) compared to matched controls (LyzM.Cre−FOXO1L/L). Similar results were obtained by knockdown of FOXO1 in RAW264.7 cells. Moreover, FOXO1-mediated osteoclast formation was linked to regulation of NFATc1 nuclear localization and expression as well as a number of downstream factors including dendritic cell-specific transmembrane protein (DC-STAMP), ATP6vod2, cathepsin K and integrin αν Lastly, FOXO1 deletion reduced M-CSF induced RANK expression and migration of osteoclast precursors. Studies presented here provide the evidence that FOXO1 plays a direct role in osteoclast formation by mediating the effect of RANKL on NFATc1 and several downstream effectors. This is likely to be significant since FOXO1 and RANKL are elevated in osteolytic conditions.

RBP-J–Regulated miR-182 Promotes TNF-α–Induced Osteoclastogenesis

“…In this group of genes, Forkhead box class O 3a ( Foxo3a encoding Foxo3), a member of the Foxo family of transcription factors, has been reported as a direct target of miR-182 in literature (45). Foxo proteins regulate RANKL-induced osteoclastogenesis (47, 48) and FOXO3 activity is associated with outcomes in infectious and inflammatory diseases including RA (49, 50), which suggest its possible relevance in TNF-α-driven osteoclastogenesis. We also selected Mastermind-like 1 ( Maml1 ) as a gene of interest because of its role as a cotranscriptional regulator that is essential for RBP-J signaling (51), which suggests a potential function of Maml1 in osteoclast biology.…”

“…We found that Foxo3 is also a key miR-182 target in TNF-α-mediated osteoclast differentiation. Despite different functions for different Foxo family members, Foxo1, 3, and 4 proteins have been reported to regulate RANKL induced osteoclast differentiation (47, 48). Our study is the first one investigating the role of Foxo3 in TNF-α mediated osteoclastogenesis.…”

Diabetes and Its Effect on Bone and Fracture Healing

“…Deletion of FOXO1, FOXO3 and FOXO4 results in reduced expression of antioxidant enzymes and failure to protect against oxidative stress [50]. Interestingly, FOXO1 is induced by RANKL stimulation and has a direct effect in stimulating osteoclast formation [51]. The long-term effects of oxidative stress may be particularly important for long-lived cells such as osteocytes and mesenchymal stem cells.…”

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

“…Some studies show that FoxO1, 3, and 4 proteins are inhibitors of osteoclastogenesis, 57 whereas others found FoxO1 as a positive regulator. 58 These data indicate that the FoxO family plays an important but complex role in osteoclastogenesis. We found that FoxO3 is an important miR182 target in TNF-mediated osteoclast differentiation.…”

“…46 FoxO1 and FoxO3 are well-defined miR182 targets in several biological settings. 55,56 FoxO family members, FoxO1, 3, and 4 proteins, are involved in osteoclast differentiation, 45,57,58 but reported with different functions and mechanisms. Some studies show that FoxO1, 3, and 4 proteins are inhibitors of osteoclastogenesis, 57 whereas others found FoxO1 as a positive regulator.…”