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Skeletal Phenotype Analysis of a Conditional Stat3 Deletion Mouse Model
Published on: July 3, 2020
Tail-suspended mice lacking calponin H1 experience decreased bone loss
Naoki Yotsumoto1, Michiko Takeoka, Minesuke Yokoyama
1Shinkatsushika Hospital, Tokyo, Japan.
Abstract:
Calponin h1 (CNh1) is an actin-binding protein originally isolated from vascular smooth muscle and has been reported to suppress bone formation. We are therefore curious how CNh1 is involved in bone loss that is caused by space flight in microgravity. We assessed the effects of tail suspension (TS) in C57BL/6J wild (CN+/+) and CNh1-deleted (CN-/-) mice to elucidate the role of CNh1 in bone loss under weightless conditions. Bone mineral density (BMD) of tibiae was measured by single energy X-ray absorptiometry, and bone volume fraction (BV/TV), mineral apposition rate (MAR), and bone formation rate (BFR/BS) were measured by bone histomorphometry. BMD, BV/TV, MAR, and BFR/BS were lower in CN+/+ mice with TS than in those without. In the CN-/- group, however, the decrease in each of these parameters by TS was ameliorated. Decreases in serum osteocalcin levels by TS in CN+/+ mice were attenuated in CN-/- mice. Furthermore, urinary deoxypyridinolin (DPD), an indicator of bone resorption, was increased in CN+/+ mice following TS, but not in CN-/- mice. In transfection experiments, the degree of induction of bone formation markers, alkaline phosphatase (ALP) activity and bone morphogenetic protein (BMP)-4 mRNA expression, under stimulation with BMP-2, was lower in MC3T3-E1 mouse osteoblast-like cells expressing CNh1 than that in mock transfected cells. Notably, the BMP-2-induced ALP activity was decreased by CNh1 expression, which was partially rescued by treatment with the Rho kinase inhibitor Y27632. Taken together, these results indicate that CNh1 is responsible for weightlessness-induced bone loss in part through Rho signaling pathway.
Insights
Calponin h1 (CNh1) protein exacerbates bone loss during simulated weightlessness. Deleting CNh1 in mice protected against microgravity-induced decreases in bone density and formation, suggesting CNh1
Area of Science:
- Bone biology
- Spaceflight physiology
- Molecular mechanisms of bone loss
Background:
- Calponin h1 (CNh1) is an actin-binding protein known to inhibit bone formation.
- Spaceflight leads to significant bone loss, a critical concern for astronaut health.
- The specific role of CNh1 in microgravity-induced bone loss remains unclear.
Purpose of the Study:
- To investigate the role of Calponin h1 (CNh1) in bone loss experienced under simulated weightless conditions.
- To determine if CNh1 contributes to the decrease in bone mineral density and formation caused by tail suspension (TS).
Main Methods:
- Tail suspension (TS) model in wild-type (CN+/+) and CNh1-deleted (CN-/-) mice.
- Assessment of bone mineral density (BMD) using X-ray absorptiometry.
- Bone histomorphometry to measure bone volume fraction (BV/TV), mineral apposition rate (MAR), and bone formation rate (BFR/BS).
- Analysis of serum osteocalcin and urinary deoxypyridinolin (DPD) levels.
- In vitro studies using MC3T3-E1 osteoblast-like cells to assess the impact of CNh1 on bone formation markers (ALP, BMP-4 mRNA) and Rho kinase signaling.
Main Results:
- Tail suspension (TS) significantly reduced BMD, BV/TV, MAR, and BFR/BS in wild-type (CN+/+) mice.
- CNh1-deleted (CN-/-) mice showed ameliorated decreases in these bone parameters following TS compared to wild-type mice.
- TS-induced reduction in serum osteocalcin was attenuated in CN-/- mice.
- Urinary deoxypyridinolin (DPD), a marker of bone resorption, increased with TS in CN+/+ mice but not in CN-/- mice.
- CNh1 expression in osteoblast-like cells suppressed BMP-2-induced alkaline phosphatase (ALP) activity and BMP-4 mRNA expression, an effect partially mediated by Rho kinase.
Conclusions:
- Calponin h1 (CNh1) plays a significant role in weightlessness-induced bone loss.
- CNh1 contributes to microgravity-related bone loss, potentially through the Rho signaling pathway.
- Targeting CNh1 or the Rho pathway may offer therapeutic strategies to prevent bone loss during spaceflight.
