Hepcidin inhibits osteoclast differentiation to alleviate osteoporosis by modulating the p53/miR-34a/Trem2 axis.

Abstract

BACKGROUND: The relationship between iron accumulation and osteoporosis (OP) progression has received attention in recent years. Hepcidin is a key regulator of iron homeostasis and may contribute to the treatment of OP. However, the underlying molecular mechanism of hepcidin in OP remains unclear. METHODS: Transgenic mice were constructed, including hepcidin overexpression (Hamp) mice and Trem2 overexpression (Trem2) mice, followed by performed ovariectomy (OVX) procedure. Trem2-OVX mice and Hamp mice were used to construct parabiosis model, which was named as Hamp+Trem2-OVX parabiosis mice. Serum hepcidin and ferritin levels were tested by ELISA. Bone microstructure and related parameters were evaluated by Micro-CT. Bone mass and osteoclast ratio in mice were assessed by tartrate-resistant acid phosphatase (TRAP) staining and hematoxylin and eosin staining. Bone marrow-derived macrophages (BMMs) were isolated from OVX mice and Hamp-OVX mice, and then treated with RANKL to induce osteoclast differentiation. Osteoclast formation and differentiation were assessed by TRAP staining, western blot and immunofluorescence staining assay. The protein levels of osteoclast differentiation-related markers, p53 and Trem2 were examined by western blot. Quantitative real-time PCR was used to measure miR-34a and Trem2 mRNA expression. The interaction between miR-34a and p53 or Trem2 was confirmed by ChIP assay, dual-luciferase reporter assay and RIP assay. RESULTS: Serum hepcidin level was decreased in OP women and mice, and its overexpression attenuated OP progression in OVX mice. Hepcidin overexpression inhibited osteoclast formation and differentiation in RANKL-induced BMMs. Hepcidin activated p53 to promote miR-34a transcription, and miR-34a targeted Trem2. Inhibition of miR-34a reversed the inhibitory effect of hepcidin on osteoclast formation and differentiation in RANKL-induced BMMs. Furthermore, Trem2 overexpression promoted bone loss and osteoclast formation in OVX mice, and these effects were abolished in Hamp+Trem2-OVX parabiosis mice. CONCLUSION: Hepcidin alleviated OP progression by inhibiting osteoclast differentiation via regulating the p53/miR-34a/Trem2 axis.