The osteocyte transcriptome is extensively dysregulated in mouse models of Osteogenesis Imperfecta

Osteocytes are long-lived, highly interconnected, terminally differentiated osteoblasts which reside within mineralized bone matrix. They constitute about 95% of adult bone cells and play important functions in the regulation of bone remodeling, phosphate homeostasis, and mechanical stimuli sensing and response. However, the role of osteocytes in the pathogenesis of congenital diseases of bone such as osteogenesis imperfecta (OI) is poorly understood. This study characterized in vivo transcriptional changes in osteocytes from the CrtapKO and oim/oim mouse models of OI, using RNA-sequencing on osteocyte-enriched cortical bone from femur and tibia. These models were chosen because they mimic two types of OI with different genetic mutations which result in distinct type I collagen defects. Hundreds of transcripts were dysregulated in either model of OI compared to WT, but 281 of these were similarly up- or down-regulated in both. Conversely, very few transcripts were differentially expressed between the CrtapKO and oim/oim mice, indicating that distinct alterations in type I collagen can lead to shared pathogenic processes and similar phenotypic outcomes. Bioinformatics analyses identified several critical hubs of dysregulation that were enriched in annotation terms such as development and differentiation, ECM and collagen fibril organization, cell adhesion, signaling, regulatory processes, pattern binding, chemotaxis, and cell projections. The data further indicated alterations in important signaling pathways such as WNT and TGF-β. Overall, our study suggested that the osteocyte transcriptome is broadly dysregulated in OI, that transcriptomic alterations in OI can be strikingly similar despite arising from different genetic mutations, and that the potential consequences of osteocyte dysregulation deserve further investigation. RNA sequencing was performed on mRNA isolated from osteocyte-enriched cortical bone (OT-rich bone) of 3-month old WT, CrtapKO, and oim/oim mice (4 biological replicates of each genotype).骨细胞（Osteocytes）是一类长寿命、高度互联的终末分化成骨细胞，定居于矿化骨基质内部。它们约占成体骨细胞总量的95%，在骨重塑、磷酸盐稳态、机械刺激感知与应答过程中发挥关键功能。然而，骨细胞在成骨不全（osteogenesis imperfecta, OI）这类先天性骨疾病的发病机制中的作用仍未得到充分阐明。本研究针对两种OI小鼠模型——CrtapKO与oim/oim小鼠，通过对其股骨、胫骨中富集骨细胞的皮质骨开展RNA测序（RNA-sequencing），解析了骨细胞体内的转录组变化。选择这两种模型的原因在于，它们分别模拟了两类由不同基因突变引发、具有独特I型胶原缺陷的OI表型。相较于野生型（Wild Type, WT）小鼠，两种OI模型中均有数百个转录本出现表达失调，但其中281个转录本在两种模型中呈现一致的上调或下调趋势。与之相对，CrtapKO与oim/oim小鼠之间差异表达的转录本极少，这表明不同的I型胶原异常可引发共同的致病过程与相似的表型结局。生物信息学分析鉴定出多个核心失调调控节点，其富集的功能注释术语涵盖发育与分化、细胞外基质（extracellular matrix, ECM）与胶原纤维组织、细胞黏附、信号通路、调控过程、模式结合、趋化性以及细胞突起等。研究数据进一步显示，WNT与转化生长因子-β（TGF-β）等重要信号通路亦存在表达异常。总体而言，本研究表明OI状态下骨细胞的转录组存在广泛失调；尽管致病的基因突变不同，OI的转录组改变仍可具有显著的相似性；且骨细胞失调的潜在生物学与临床后果值得进一步深入探究。本研究对3月龄野生型、CrtapKO及oim/oim小鼠的股骨、胫骨中富集骨细胞的皮质骨（OT-rich bone）提取mRNA并完成RNA测序，每个基因型设置4个生物学重复。