1] National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, USA. [2].
Nat Med. 2013 Nov;19(11):1505-12. doi: 10.1038/nm.3314. Epub 2013 Sep 29.
Heterotopic ossification, the pathologic formation of extraskeletal bone, occurs as a common complication of trauma or in genetic disorders and can be disabling and lethal. However, the underlying molecular mechanisms are largely unknown. Here we demonstrate that Gαs restricts bone formation to the skeleton by inhibiting Hedgehog signaling in mesenchymal progenitor cells. In progressive osseous heteroplasia, a human disease caused by null mutations in GNAS, which encodes Gαs, Hedgehog signaling is upregulated in ectopic osteoblasts and progenitor cells. In animal models, we show that genetically-mediated ectopic Hedgehog signaling is sufficient to induce heterotopic ossification, whereas inhibition of this signaling pathway by genetic or pharmacological means strongly reduces the severity of this condition. As our previous work has shown that GNAS gain-of-function mutations upregulate WNT-β-catenin signaling in osteoblast progenitor cells, resulting in their defective differentiation and fibrous dysplasia, we identify Gαs as a key regulator of proper osteoblast differentiation through its maintenance of a balance between the Wnt-β-catenin and Hedgehog pathways. Also, given the results here of the pharmacological studies in our mouse model, we propose that Hedgehog inhibitors currently used in the clinic for other conditions, such as cancer, may possibly be repurposed for treating heterotopic ossification and other diseases caused by GNAS inactivation.
异位骨化，即骨骼外异常骨形成，是创伤或遗传疾病的常见并发症，可导致残疾和死亡。然而，其潜在的分子机制在很大程度上尚不清楚。本研究表明，Gαs 通过抑制间充质祖细胞中的 Hedgehog 信号通路，将骨形成限制在骨骼中。在进行性骨异质增生症（一种由编码 Gαs 的 GNAS 基因无义突变引起的人类疾病）中，Hedgehog 信号在异位成骨细胞和祖细胞中上调。在动物模型中，我们表明，遗传介导的异位 Hedgehog 信号足以诱导异位骨化，而通过遗传或药理学手段抑制该信号通路可强烈降低该疾病的严重程度。由于我们之前的工作表明，GNAS 功能获得性突变会在上皮细胞祖细胞中上调 WNT-β-catenin 信号通路，导致其分化缺陷和纤维结构不良，因此我们将 Gαs 鉴定为通过维持 Wnt-β-catenin 和 Hedgehog 通路之间的平衡来调节成骨细胞分化的关键调节因子。此外，鉴于我们在小鼠模型中的药理学研究结果，我们提出目前在临床上用于治疗其他疾病（如癌症）的 Hedgehog 抑制剂，可能被重新用于治疗异位骨化和其他由 GNAS 失活引起的疾病。
