Oxidative phosphorylation is a pivotal therapeutic target of fibrodysplasia ossificans progressiva

Heterotopic ossification (HO) is a non-physiological process of bone formation in which progenitor cells in soft tissues differentiate into chondrogenic cells. In the case of fibrodysplasia ossificans progressiva (FOP), a rare genetic disease characterized by progressive and systemic HO, the Activin A/mutated-ACVR1/mTORC1 cascade induces HO in progenitors, one of which is the fibro/adipogenic progenitors (FAPs) in muscle tissues. The relevant biological processes aberrantly regulated by activated mTORC1 remain unclear, however. RNA sequencing analyses revealed the enrichment of genes involved in oxidative phosphorylation (OXPHOS) during Activin A-induced chondrogenesis of mesenchymal stem cells derived from induced pluripotent stem cells (iPSCs) of FOP patients. Functional analyses showed a metabolic transition from glycolysis to OXPHOS during chondrogenesis, in conjunction with an upregulation of mitochondrial biogenesis. mTORC1 inhibition by rapamycin suppressed OXPHOS, and IACS-010759, an inhibitor of OXPHOS, inhibited cartilage matrix formation in vitro, indicating that OXPHOS is principally involved in mTORC1-induced chondrogenesis. Furthermore, IACS-010759 inhibited the muscle injury-induced enrichment of FAP genes and HO in transgenic mice carrying the mutated human ACVR1. These data indicated that OXPHOS is a critical downstream mediator of mTORC1 signaling in chondrogenesis and therefore is a potential FOP therapeutic target. Overall design: Gene expression at day 0 and day 6 after Activin-A-induced chondrogenesis.

异位骨化（Heterotopic ossification, HO）是一种非生理性骨形成过程，指软组织中的祖细胞分化为软骨生成细胞。进行性骨化性纤维发育不良（fibrodysplasia ossificans progressiva, FOP）是一种以进行性、全身性异位骨化为特征的罕见遗传病，其发病过程中，激活素A（Activin A）/突变型ACVR1（mutated-ACVR1）/哺乳动物雷帕霉素靶蛋白复合物1（mTORC1）信号级联可诱导祖细胞发生异位骨化，其中一类祖细胞即为肌肉组织中的成纤维/脂肪祖细胞（fibro/adipogenic progenitors, FAPs）。然而，激活的mTORC1异常调控的相关生物学过程仍未明确。RNA测序（RNA sequencing）分析显示，在FOP患者诱导多能干细胞（induced pluripotent stem cells, iPSCs）来源的间充质干细胞经激活素A诱导的软骨生成过程中，氧化磷酸化（oxidative phosphorylation, OXPHOS）相关基因呈现富集特征。功能实验表明，软骨生成过程中伴随线粒体生物发生上调的同时，发生了从糖酵解到氧化磷酸化的代谢转变。雷帕霉素介导的mTORC1抑制可阻断氧化磷酸化；而氧化磷酸化抑制剂IACS-010759可在体外抑制软骨基质形成，这提示氧化磷酸化主要参与了mTORC1诱导的软骨生成过程。此外，在携带突变型人ACVR1的转基因小鼠中，IACS-010759可抑制肌肉损伤诱导的FAP基因富集与异位骨化形成。上述数据表明，氧化磷酸化是mTORC1信号通路在软骨生成过程中的关键下游介导因子，因此可作为FOP潜在的治疗靶点。整体实验设计：激活素A诱导软骨生成后第0天与第6天的基因表达水平。