The bony skeleton is continuously renewed throughout adult life by the bone remodeling process, in which old or damaged bone is removed by osteoclasts via largely unknown mechanisms. Osteocytes regulate bone remodeling by producing the osteoclast differentiation factor RANKL (encoded by the TNFSF11 gene). However, the precise mechanisms underlying RANKL expression in osteocytes are still elusive. Here, we explored the epigenomic landscape of osteocytic cells and identified a hitherto-undescribed osteocytic cell-specific intronic enhancer in the TNFSF11 gene locus. Bioinformatics analyses showed that transcription factors involved in cell death and senescence act on this intronic enhancer region. Single-cell transcriptomic data analysis demonstrated that cell death signaling increased RANKL expression in osteocytic cells. Genetic deletion of the intronic enhancer led to a high-bone-mass phenotype with decreased levels of RANKL in osteocytic cells and osteoclastogenesis in the adult stage, while RANKL expression was not affected in osteoblasts or lymphocytes. These data suggest that osteocytes may utilize a specialized regulatory element to facilitate osteoclast formation at the bone surface to be resorbed by linking signals from cellular senescence/death and RANKL expression.

在整个成年过程中，骨骨骼通过骨重塑过程不断更新，破骨细胞通过很大程度上未知的机制去除旧骨或受损骨。骨细胞通过产生破骨细胞分化因子 RANKL（由TNFSF11基因编码）来调节骨重塑。然而，骨细胞中 RANKL 表达的精确机制仍不清楚。在这里，我们探索了骨细胞的表观基因组景观，并在TNFSF11基因位点中鉴定了迄今为止未描述的骨细胞特异性内含子增强子。生物信息学分析表明，参与细胞死亡和衰老的转录因子作用于该内含子增强子区域。单细胞转录组数据分析表明，细胞死亡信号传导增加了骨细胞中 RANKL 的表达。内含子增强子的基因缺失导致高骨量表型，成年阶段骨细胞中的RANKL水平和破骨细胞生成水平降低，而成骨细胞或淋巴细胞中的RANKL表达不受影响。这些数据表明，骨细胞可能利用特殊的调节元件，通过连接细胞衰老/死亡和 RANKL 表达的信号，促进破骨细胞在骨表面形成，并被再吸收。