Department of Internal Medicine, Chonnam National University Medical School, Gwangju, Korea.
Seoul National University Hospital Biomedical Research Institute, Seoul, Korea.
Endocrinol Metab (Seoul). 2020 Jun;35(2):456-469. doi: 10.3803/EnM.2020.35.2.456. Epub 2020 Jun 24.
We investigated RNA sequencing-based transcriptome profiling and the transformation of mature osteoblasts into bone lining cells (BLCs) through a lineage tracing study to better understand the effect of mechanical unloading on bone loss.
Dmp1-CreERt2(+):Rosa26R mice were injected with 1 mg of 4-hydroxy-tamoxifen three times a week starting at postnatal week 7, and subjected to a combination of botulinum toxin injection with left hindlimb tenotomy starting at postnatal week 8 to 10. The animals were euthanized at postnatal weeks 8, 9, 10, and 12. We quantified the number and thickness of X-gal(+) cells on the periosteum of the right and left femoral bones at each time point.
Two weeks after unloading, a significant decrease in the number and a subtle change in the thickness of X-gal(+) cells were observed in the left hindlimbs compared with the right hindlimbs. At 4 weeks after unloading, the decrease in the thickness was accelerated in the left hindlimbs, although the number of labeled cells was comparable. RNA sequencing analysis showed downregulation of 315 genes in the left hindlimbs at 2 and 4 weeks after unloading. Of these, Xirp2, AMPD1, Mettl11b, NEXN, CYP2E1, Bche, Ppp1r3c, Tceal7, and Gadl1 were upregulated during osteoblastogenic/osteocytic and myogenic differentiation in vitro.
These findings demonstrate that mechanical unloading can accelerate the transformation of mature osteoblasts into BLCs in the early stages of bone loss in vivo. Furthermore, some of the genes involved in this process may have a pleiotropic effect on both bone and muscle.
我们通过谱系追踪研究调查了基于 RNA 测序的转录组谱分析和成熟成骨细胞向骨衬细胞（BLC）的转化，以更好地了解机械去负荷对骨丢失的影响。
在 Dmp1-CreERT2(+):Rosa26R 小鼠出生后第 7 周开始每周注射 1 毫克 4-羟基他莫昔芬 3 次，第 8-10 周开始同时注射肉毒杆菌毒素和左后肢跟腱切断术。动物在出生后第 8、9、10 和 12 周被安乐死。我们在每个时间点定量分析右侧和左侧股骨骨膜上 X-gal(+)细胞的数量和厚度。
去负荷后 2 周，与右侧后肢相比，左侧后肢的 X-gal(+)细胞数量显著减少，厚度略有变化。去负荷 4 周后，左侧后肢的厚度减少加速，尽管标记细胞的数量相当。RNA 测序分析显示，去负荷后 2 和 4 周，左侧后肢有 315 个基因下调。其中，Xirp2、AMPD1、Mettl11b、NEXN、CYP2E1、Bche、Ppp1r3c、Tceal7 和 Gadl1 在体外成骨/成骨细胞和肌源性分化过程中上调。
这些发现表明，机械去负荷可以在体内骨丢失的早期加速成熟成骨细胞向 BLC 的转化。此外，该过程涉及的一些基因可能对骨骼和肌肉具有多效性影响。
