Hepatic soluble epoxide hydrolase mediates osteoclastogenesis by suppressing the Nrf2 signaling pathway: a novel mechanism of redox imbalance in osteoporosis.

OBJECTIVE

This study aimed to investigate whether liver-specific soluble epoxide hydrolase (sEH) mediates osteoclast differentiation by regulating the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway, thereby contributing to molecular mechanisms underlying bone homeostasis imbalance.

METHODS

Clinical samples, an ovariectomy (OVX)-induced mouse osteoporosis model, and in vitro osteoclast induction experiments were systematically employed to evaluate the role of sEH in osteoclast differentiation.

RESULTS

Osteoporosis patients exhibited decreased plasma levels of 14,15-epoxyeicosatrienoic acid (14,15-EET), increased levels of 14,15-dihydroxyeicosatrienoic acid (14,15-DHET), and elevated pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β). OVX mice demonstrated enhanced osteoclast differentiation associated with upregulated hepatic sEH expression, decreased plasma 14,15-EET, increased 14,15-DHET, and elevated pro-inflammatory cytokines (TNF-α, IL-6, IL-1β). Treatment with sEH inhibitors or liver-specific sEH knockdown ameliorated osteoclast differentiation by restoring 14,15-EET and 14,15-DHET levels and reducing pro-inflammatory cytokine concentrations. Transcriptome sequencing revealed that sEH inhibitors suppress osteoclast differentiation by activating the Nrf2-antioxidant response element (ARE) signaling pathway. Furthermore, 14,15-EET directly inhibited osteoclast differentiation in an Nrf2-dependent manner, underscoring a direct link between the metabolite and the antioxidant transcription factor.

CONCLUSION

This study reveals, for the first time, a novel regulatory mechanism of bone metabolism mediated by the "liver-bone axis." Liver-derived sEH remotely modulates the Nrf2-ARE signaling pathway in bone tissue by controlling circulating levels of 14,15-EET, 14,15-DHET, and pro-inflammatory cytokines, thereby influencing osteoclast differentiation and bone homeostasis. These findings provide new insights into the pathogenesis of osteoporosis.