Department of Pathology, University of Alabama at Birmingham, Birmingham, AL 35294;
Department of Pathology, University of Alabama at Birmingham, Birmingham, AL 35294;College of Stomatology, Nanjing Medical University, Nanjing 210029, People's Republic of China;
Proc Natl Acad Sci U S A. 2014 Jun 10;111(23):8482-7. doi: 10.1073/pnas.1310617111. Epub 2014 May 21.
The pathogenesis of cleidocranial dysplasia (CCD) as well as the specific role of core binding factor β (Cbfβ) and the Runt-related transcription factor (RUNX)/Cbfβ complex in postnatal skeletogenesis remain unclear. We demonstrate that Cbfβ ablation in osteoblast precursors, differentiating chondrocytes, osteoblasts, and odontoblasts via Osterix-Cre, results in severe craniofacial dysplasia, skeletal dysplasia, abnormal teeth, and a phenotype recapitulating the clinical features of CCD. Cbfβ(f/f)Osterix-Cre mice have fewer proliferative and hypertrophic chondrocytes, fewer osteoblasts, and almost absent trabecular bone, indicating that Cbfβ may maintain trabecular bone formation through its function in hypertrophic chondrocytes and osteoblasts. Cbfβ(f/f)Collagen, type 1, alpha 1 (Col1α1)-Cre mice show decreased bone mineralization and skeletal deformities, but no radical deformities in teeth, mandibles, or cartilage, indicating that osteoblast lineage-specific ablation of Cbfβ results in milder bone defects and less resemblance to CCD. Activating transcription factor 4 (Atf4) and Osterix protein levels in both mutant mice are dramatically reduced. ChIP assays show that Cbfβ directly associates with the promoter regions of Atf4 and Osterix. Our data further demonstrate that Cbfβ highly up-regulates the expression of Atf4 at the transcriptional regulation level. Overall, our genetic dissection approach revealed that Cbfβ plays an indispensable role in postnatal skeletal development and homeostasis in various skeletal cell types, at least partially by up-regulating the expression of Atf4 and Osterix. It also revealed that CCD may result from functional defects of the Runx2/Cbfβ heterodimeric complex in various skeletal cells. These insights into the role of Cbfβ in postnatal skeletogenesis and CCD pathogenesis may assist in the development of new therapies for CCD and osteoporosis.
克利夫兰颅骨发育不全（CCD）的发病机制以及核心结合因子β（Cbfβ）和 Runt 相关转录因子（RUNX）/Cbfβ复合物在出生后骨骼发生中的特定作用尚不清楚。我们证明，通过 Osterix-Cre 在成骨前体细胞、分化的软骨细胞、成骨细胞和成牙本质细胞中剔除 Cbfβ，会导致严重的颅面骨发育不良、骨骼发育不良、牙齿异常以及一种表型，重现 CCD 的临床特征。Cbfβ（f/f）Osterix-Cre 小鼠的增殖性和肥大性软骨细胞较少，成骨细胞较少，小梁骨几乎不存在，表明 Cbfβ 可能通过其在肥大性软骨细胞和成骨细胞中的功能维持小梁骨形成。Cbfβ（f/f）Collagen, type 1, alpha 1（Col1α1）-Cre 小鼠表现出骨矿物质化减少和骨骼畸形，但牙齿、下颌骨或软骨无明显畸形，表明 Cbfβ 在成骨细胞谱系中被剔除会导致较轻的骨骼缺陷，与 CCD 的相似度较低。两种突变小鼠中的激活转录因子 4（Atf4）和 Osterix 蛋白水平均显著降低。ChIP 分析表明 Cbfβ 直接与 Atf4 和 Osterix 的启动子区域结合。我们的数据进一步表明 Cbfβ 在转录调控水平上高度上调 Atf4 的表达。总的来说，我们的遗传剖析方法表明 Cbfβ 在各种成骨细胞类型的出生后骨骼发育和稳态中发挥不可或缺的作用，至少部分通过上调 Atf4 和 Osterix 的表达。它还表明 CCD 可能是由于各种骨骼细胞中 Runx2/Cbfβ 异二聚体复合物的功能缺陷所致。这些关于 Cbfβ 在出生后骨骼发生和 CCD 发病机制中的作用的见解可能有助于开发 CCD 和骨质疏松症的新疗法。
