Bone metabolism and formation of mice bred in a 2 G environment

Treadmill exercise promotes bone tissue recovery in rats subjected to high + Gz loads

INTRODUCTION

High + Gz loads, the gravitational forces experienced by the body in hypergravity environments, can lead to bone loss in pilots and astronauts, posing significant health risks.

MATERIALS AND METHODS

To explore the effect of treadmill exercise on bone tissue recovery, a study was conducted on 72 male Wistar rats. These rats were subjected to four weeks of varying levels of periodic high + Gz loads (1G, 8G, 20G) experiments, and were subsequently divided into the treadmill group and the control group. The treadmill group underwent a continuous two-week treadmill experiment, while the control group rested during this period. The mechanical properties, microstructure, and molecular markers of their tibial bone tissue were measured using three-point bending, micro-CT, and PCR.

RESULTS

The results showed that treadmill exercise improved the elastic modulus, ultimate deflection, and ultimate load of rat bone tissue. It also increased the number, density, and volume fraction of bone trabeculae, and decreased their separation. Moreover, treadmill exercise enhanced osteogenesis and inhibited osteoclastogenesis.

CONCLUSION

This study demonstrates that treadmill exercise can promote the recovery of bone tissue in rats subjected to high + Gz loads, providing a potential countermeasure for bone loss in pilots and astronauts.

Difference between affected and unaffected sides of forearm bone length in children with congenital terminal transverse deficiencies at the level of carpal bone

The forearm of the affected sideis often shorter than that of the unaffected side in children with congenital terminal transverse deficiencies at the level of proximal or distal carpals. The aim of this study is to clarify the characteristics of forearm bone length in those children, especially to quantify the difference in forearm bone length between affected and unaffected sides. The subjects were children with carpal partial transverse deficiencies. The lengths of the radius and the ulna were measured in the radiographs. The lengths of affected and unaffected sides (A/U) were compared in order to quantify the discrepancy. The A/U ratio was defined as the length of the affected side divided by that of the unaffected side. The A/U ratios ranged from 77.1 to 99.0% in the radii and from 74.1 to 99.6% in the ulnae. In both the radius and ulna, the A/U ratios were significantly lower than the left/right ratios of normal adults. Additionally, the A/U ratios of the ulna were significantly lower than the A/U ratios of the radius. The forearm bones of affected side are significantly shorter than those of unaffected side. Although the cause remains unclear, it is possible that not only congenital factors but also acquired factors such as infrequent use of the affected upper limb are involved. A future longitudinal study is necessary to investigate whether length discrepancies can be reduced by using prostheses to increase the frequency of use on the affected limb.

Hypergravity modulates vitamin D receptor target gene mRNA expression in mice

The possibility of pathological calcium metabolism is a critical health concern introduced by long-term space travel. Because vitamin D plays an important role in calcium homeostasis, we evaluated the effects of hypergravity on the expression of genes involved in vitamin D and calcium metabolism in ICR mice. When exposed to 2G hypergravity for 2 days, the mRNA expression of renal 25-hydroxyvitamin D 24-hydroxylase (Cyp24a1) was increased and that of 25-hydroxyvitamin D 1alpha-hydroxylase (Cyp27b1) was decreased. Although hypergravity decreased food intake and increased the expression of starvation-induced genes, the changes in Cyp24a1 and Cyp27b1 expression were not due to starvation, suggesting that hypergravity affects these genes directly. Hypergravity decreased plasma 1alpha,25-dihydroxyvitamin D(3) levels in ICR mice, suggesting a consequence of decreased Cyp27b1 and increased Cyp24a1 expression. Although 1alpha-hydroxyvitamin D(3) [1alpha(OH)D(3)] treatment induced the expression of vitamin D receptor (VDR) target genes in the kidney of 2G-exposed ICR mice to similar levels as controls, 1alpha(OH)D(3) increased the intestinal expression of Cyp24a1 in ICR mice. Hypergravity-dependent changes of Cyp24a1 and Cyp27b1 expression were diminished in mice exposed to hypergravity for 14 days, which may represent an adaptation to hypergravity stress. Hypergravity exposure also increased Cyp24a1 expression in the kidney of C57BL/6J mice. We examined the effects of hypergravity on VDR-null mice and found that renal Cyp27b1 expression in VDR-null mice was decreased by hypergravity while renal Cyp24a1 expression was not detected in VDR-null mice. Thus hypergravity modifies the expression of genes involved in vitamin D metabolism.