孕期地塞米松暴露所致子代骨发育毒性的宫内编程机制

Dexamethasone is one of the most widely used medications for several types of fetal diseases, including preterm delivery, placenta previa and multiple pregnancies. However, there is increasing evidence indicates that prenatal dexamethasone induces low birth weight and bone loss in offspring, which is closely related to high risk of osteoporosis in later life. The underlying mechanisms of this effect remain to be elucidated. Our recent progress demonstrated that prenatal dexamethasone exposure induced long bone growth retardation in rat fetus, significantly reduced the number and diameter of colonies formed by bone marrow mesenchymal stem cells (BMSCs), and up-regulated mitogen-induced gene 6 (Mig6) expression. Based upon our studies and other related work, it can be hypothesized that prenatal dexamethasone may activate myocardin-related transcription factor A (MRTF-A), which stimulates histone methylation in the promoter and the expression of Mig6. The increased expression of Mig6 suppressed the epidermal growth factor receptor signaling accordingly, and inhibited the proliferation and differentiation of BMSCs finally. This project aims to clarify the underlying molecular mechanism by which dexamethasone activates the expression of Mig6 and inhibit the proliferation and differentiation of BMSCs in vitro and in vivo, and finally elucidate the intrauterine programming effect of dexamethasone. The launch of the project will reveal intrauterine programming mechanism of bone developmental toxicity in offspring treated with prenatal dexamethasone, this will eventually lead to a better understanding of the developmental origin of osteoporosis and promote development of early therapeutic strategies.

地塞米松（Dex）被广泛用于产前胎儿疾病治疗（如早产、前置胎盘、多胎妊娠等）。大量研究表明，孕期Dex暴露可致子代低出生体重、骨量减少及骨质疏松易感，其发生机制尚未揭示。我们近期证实，孕期Dex暴露可致子代大鼠骨发育迟缓，且骨髓间充质干细胞（BMSCs）克隆形成单位的数量及直径降低，骨组织的丝裂原诱导基因6（Mig6）表达上调。综合文献，推测：孕期Dex暴露激活胎鼠BMSCs的心肌素相关转录因子A（MRTF-A），通过激活 Mig6表达下调上皮生长因子受体（EGFR）信号，从而抑制BMSCs增殖及成骨定向分化，导致骨发育迟缓。本项目拟在整体动物和细胞水平，证实 Mig6介导孕期Dex暴露所致的BMSCs增殖及成骨定向分化降低，进一步在细胞和分子水平，研究Dex激活Mig6表达的分子机制，以阐明孕期Dex暴露致子代骨发育毒性的宫内编程机制，也为骨质疏松的发育起源及早期防治提供新的研究思路。

地塞米松（dexamethasone, Dex）被广泛用于产前胎儿疾病治疗（如早产、前置胎盘、多胎妊娠等）。大量研究表明，孕期Dex暴露可致子代低出生体重，低骨量和骨质疏松易感，其发生机制尚未揭示。本项目主要研究了孕期Dex暴露的不同剂量、时期及疗程对小鼠胚胎及子代出生后不同阶段长骨发育的影响及对子代骨发育毒性的细胞和分子机制。首先，我们发现孕期Dex暴露引起新生子代小鼠长骨发育毒性的剂量为0.8mg/kg.d，小鼠孕早期（孕第12-14天）为骨发育毒性的敏感暴露时期，且多疗程Dex暴露的骨发育毒性更显著。在出生后早期骨发育中，孕期Dex暴露子代小鼠骨组织中的老化（senescence）细胞增多，其所形成的骨局部老化微环境可抑制骨髓间充质干细胞（BMSCs）增殖与分化，导致小鼠子代出生后持续低骨量。进一步研究表明，孕期Dex暴露可激活胎鼠的成骨细胞和软骨细胞上皮生长因子受体（EGFR）信号的内源性抑制因子即丝裂原诱导基因(Mig-6)表达，下调EGFR信号，引起破骨分化相关基因RANKL和OPG表达失调并抑制破骨细胞分化，导致胎鼠干骺端软骨内成骨障碍和长骨发育迟缓。其次，我们发现衰老小鼠皮质骨内膜骨祖细胞EGFR/ERK信号下调，引起组蛋白甲基转移酶（Ezh2）表达降低，继而引发细胞老化相关基因表达激活，导致骨祖细胞老化和皮骨质退行性变。此外，我们还发现并证明达沙替尼和槲皮素可显著阻断孕期Dex暴露所致子代骨组织细胞的老化，进而改善子代长骨的BMSCs减少和低骨量。本项目的系列研究结果对于指导产科临床糖皮质激素用药提供了较为全面的实验基础，上述骨发育和退变研究提示，发育早期的EGFR信号下调可能引起成年子代小鼠骨量降低和骨质疏松易感。相关的细胞和分子机制研究以及所挖掘的达沙替尼和槲皮素用药对于早期防治产前糖皮质激素用药副作用提供了重要的实验依据，具有重要的临床应用价值。