Uroporphyrinogen Ⅲ synthase promotes bone loss by increasing osteoclast activity in mouse bone tissue under weightlessness
Objective To investigate the impact of uroporphyrinogen Ⅲ synthase(UROS)on bone loss induced by weightlessness.Methods Eight male C57BL/6J mice aged 9 weeks were randomly assigned to a control group and a tail suspension group,with four mice in each.Following a 28-day period of tail suspension,the hind limbs of the mice underwent micro-CT and mechanical testing,respectively.A microgravity osteoclast model was established using the cell cyclotron device(RCCS).Changes in osteoclast differentiation activity induced by microgravity were assessed via real-time quantitative PCR(qPCR)and tartrate-resistant acid phosphatase(TRAP)staining.Additionally,alterations in UROS expression levels were detected using qPCR and Western blotting analysis.The protein expression of UROS was also determined via Western blotting.A UROS knockout RAW264.7 stable strain was generated.qPCR and TRAP staining were employed to confirm the downregulation of osteoclast differentiation activity upon UROS deficiency.Results After hindlimb unloading in mice,a marked decrease in bone mass was observed in the bone tissue,which was accompanied by a pronounced upregulation of UROS protein expression.Upon exposure to microgravity,osteoclasts exhibited an upregulation of UROS protein expression,along with increased levels of osteoclast differentiation markers including matrix metalloproteinase 9(MMP-9)and tartrate-resistant acid phosphatase(TRAP).Knockdown of UROS significantly downregulated the expression levels of osteoclast differentiation-related markers,indicating its crucial role in osteoclast differentiation and bone metabolism.Conclusion Under weightlessness stress,the expression level of UROS in osteoclasts is upregulated,leading to enhanced osteoclast activity and an imbalance between bone resorption and bone formation,with bone resorption exceeding bone formation,which ultimately results in bone loss.
uroporphyrinogen Ⅲ synthasemicemicrogravityosteoclastbone loss
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