It was previously reported that the loss of the transcription factor nuclear factor I/X (NFIX) gene in mice impaired endochondral ossification and mineralization in bone. However, the cellular and molecular basis for the defect remains unexplored. In this study, we investigated if and how NFIX regulates osteoblast differentiation. Nfix mRNA was induced during osteogenic and adipogenic differentiation of progenitor cells. Loss-of-function and gain-of-function studies revealed that NFIX induced osteoblast differentiation and impaired adipocyte formation from progenitor cells. RNA-seq and promoter analysis revealed that NFIX transcriptionally stimulated the expression of high-mobility group AT-Hook 1 (HMGA1). We then demonstrated that HMGA1 stimulated osteogenic differentiation of progenitor cells at the expense of adipogenic differentiation. The effect of Nfix siRNA on the differentiation of progenitor cells could be attenuated when HMGA1 was simultaneously overexpressed. Further investigations revealed the stimulatory effect of NFIX and HMGA1 on canonical wingless-type MMTV integration site family (Wnt) signaling. HMGA1 transcriptionally activates the expression of low-density lipoprotein receptor-related protein 5. Finally, in vivo transfection of Nfix siRNA to the marrow of mice reduced osteoblasts and increased fat accumulation in the marrow, and inactivated HMGA1/β-catenin signaling in bone marrow mesenchymal stem cells. This study suggests that HMGA1 plays a role in osteoblast commitment and mediates the function of NFIX through transcriptionally activating canonical Wnt signaling.

中文翻译：

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高迁移率基团 AT-Hook 1 通过激活经典 Wnt 信号介导核因子 I/X 在成骨分化中的作用

此前有报道称，小鼠中转录因子核因子 I/X (NFIX) 基因的缺失会损害骨骼中的软骨内骨化和矿化。然而，该缺陷的细胞和分子基础仍未探索。在这项研究中，我们研究了 NFIX 是否以及如何调节成骨细胞分化。Nfix mRNA 在祖细胞的成骨和成脂分化过程中被诱导。功能丧失和功能获得研究表明，NFIX 诱导成骨细胞分化并损害祖细胞的脂肪细胞形成。RNA-seq 和启动子分析显示，NFIX 在转录上刺激了高迁移率基团 AT-Hook 1 (HMGA1) 的表达。然后，我们证明 HMGA1 以脂肪形成分化为代价刺激了祖细胞的成骨分化。当HMGA1同时过表达时，Nfix siRNA对祖细胞分化的影响可能会减弱。进一步的研究揭示了 NFIX 和 HMGA1 对典型的无翼型 MMTV 整合位点家族 (Wnt) 信号传导的刺激作用。HMGA1 转录激活低密度脂蛋白受体相关蛋白 5 的表达。最后，将 Nfix siRNA 体内转染至小鼠骨髓减少了成骨细胞并增加了骨髓中的脂肪积累，并使骨髓中的 HMGA1/β-连环蛋白信号失活间充质干细胞。该研究表明 HMGA1 在成骨细胞定型中发挥作用，并通过转录激活经典 Wnt 信号传导介导 NFIX 的功能。