Interferon regulatory factor 8 (IRF8), a transcription factor expressed in immune cells, functions as a negative regulator of osteoclasts and helps maintain dental and skeletal homeostasis. Previously, we reported that a novel mutation in the IRF8 gene increases susceptibility to multiple idiopathic cervical root resorption (MICRR), a form of tooth root resorption mediated by increased osteoclast activity. The IRF8 G388S variant in the highly conserved C-terminal motif is predicted to alter the protein structure, likely impairing IRF8 function. To investigate the molecular basis of MICRR and IRF8 function in osteoclastogenesis, we generated Irf8 knock-in ( KI) mice using CRISPR/Cas9 technique modeling the human IRF8 G388S mutation. The heterozygous (Het) and homozygous (Homo) Irf8 KI mice showed no gross morphological defects, and the development of hematopoietic cells was unaffected and similar to wild-type (WT) mice. The Irf8 KI Het and Homo mice showed no difference in macrophage gene signatures important for antimicrobial defenses and inflammatory cytokine production. Consistent with the phenotype observed in MICRR patients, Irf8 KI Het and Homo mice demonstrated significantly increased osteoclast formation and resorption activity in vivo and in vitro when compared to WT mice. The oral ligature–inserted Het and Homo mice displayed significantly increased root resorption and osteoclast-mediated alveolar bone loss compared to WT mice. The increased osteoclastogenesis noted in KI mice is due to the inability of IRF8 G388S mutation to inhibit NFATc1-dependent transcriptional activation and downstream osteoclast specific transcripts, as well as its impact on autophagy-related pathways of osteoclast differentiation. This translational study delineates the IRF8 domain important for osteoclast function and provides novel insights into the IRF8 mutation associated with MICRR. IRF8 G388S mutation mainly affects osteoclastogenesis while sparing immune cell development and function. These insights extend beyond oral health and significantly advance our understanding of skeletal disorders mediated by increased osteoclast activity and IRF8’s role in osteoclastogenesis.

中文翻译：

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小鼠 IRF8 突变为破骨细胞和牙根吸收提供了新的见解

干扰素调节因子 8 (IRF8) 是一种在免疫细胞中表达的转录因子，作为破骨细胞的负调节因子发挥作用，有助于维持牙齿和骨骼的稳态。此前，我们报道了IRF8基因的一个新突变增加了对多发性特发性颈根吸收（MICRR）的易感性，MICRR是一种由破骨细胞活性增加介导的牙根吸收形式。高度保守的 C 端基序中的 IRF8 G388S 变体预计会改变蛋白质结构，可能损害 IRF8 功能。为了研究 MICRR 和 IRF8 在破骨细胞生成中功能的分子基础，我们使用 CRISPR/Cas9 技术模拟人类 IRF8 生成了 Irf8 敲入 (KI) 小鼠G388S突变。杂合子（Het）和纯合子（Homo）Irf8 KI小鼠没有表现出明显的形态缺陷，造血细胞的发育不受影响，与野生型（WT）小鼠相似。Irf8 KI Het 和 Homo 小鼠在巨噬细胞基因特征上没有表现出差异，而巨噬细胞基因特征对于抗菌防御和炎症细胞因子的产生很重要。与 MICRR 患者中观察到的表型一致，与 WT 小鼠相比，Irf8 KI Het 和 Homo 小鼠在体内和体外表现出破骨细胞形成和吸收活性显着增加。与 WT 小鼠相比，插入口腔结扎线的 Het 和 Homo 小鼠显示牙根吸收和破骨细胞介导的牙槽骨丢失显着增加。KI 小鼠中破骨细胞生成增加是由于 IRF8 的缺失G388S突变抑制 NFATc1 依赖性转录激活和下游破骨细胞特异性转录本，及其对破骨细胞分化的自噬相关途径的影响。这项转化研究描绘了对破骨细胞功能重要的 IRF8 结构域，并为与 MICRR 相关的 IRF8 突变提供了新的见解。IRF8G388S突变主要影响破骨细胞生成，同时影响免疫细胞的发育和功能。这些见解不仅限于口腔健康，还显着增进了我们对破骨细胞活性增加介导的骨骼疾病以及 IRF8 在破骨细胞生成中的作用的理解。