背景:细胞牙骨质(CC)包括牙骨质细胞,怀疑细胞调节CC形成或吸收,如骨细胞在骨骼中的作用。硬化蛋白(SOST)是由骨细胞和牙骨质细胞表达的Wnt/β-连环蛋白信号的分泌性负调节因子。骨细胞SOST表达减少骨形成。我们使用Sost敲除(Sost-/-)小鼠模型研究了SOST在CC中与牙槽骨(AB)相比的功能重要性,以更好地了解牙骨质细胞在CC中的作用。
方法:在出生后42天和120天(dpn)分析Sost-/-和野生型(WT)小鼠的下颌骨和股骨。以42dpn双侧拔除上颌第一磨牙,并在术后21天检查AB愈合(上颌磨牙窝)和CC并置(下颌第一磨牙)。分析包括显微计算机断层扫描,组织学,和免疫组织化学。
结果:在42和/或120dpn时,Sost-/-与WT小鼠相比,股骨皮质和小梁骨以及下颌骨体积相似地增加。与以前的报告相比,CC在任何年龄都没有增加Sost-/-。我们对AB和CC进行了挑战实验,以探索组织特异性反应。Sost缺失改善了提取后AB的愈合。相比之下,实验诱导的磨牙并置未能刺激Sost-/-与WT小鼠的CC形成增加。Wnt通路标志物AXIN2和DKK1在Sost-/-与WTAB骨细胞中增加,在牙骨质细胞中没有变化。
结论:这些数据表明,与AB相比,CC对SOST删除的反应较小。在研究限制范围内,这些结果不支持牙骨质细胞作为指导CC形成增加的关键。
结论:硬化素是一种抑制骨形成的蛋白质,去除硬化蛋白会导致更多的骨形成。牙骨质是覆盖牙齿根部表面的薄层。先前的研究表明,抑制硬骨素可以类似地增加牙骨质的量。我们想比较缺乏硬化素时牙骨质和骨骼的反应,以了解这两种组织之间的异同。在这项研究中,我们删除了小鼠的Sost基因(产生硬化蛋白的基因)。我们发现,没有硬化蛋白的小鼠的腿和下巴有更多的骨头。此外,与正常小鼠相比,没有硬化蛋白的小鼠在拔牙后也能更好地愈合。令人惊讶的是,与以往的研究不同,我们发现,与正常小鼠相比,没有硬化素的小鼠的牙骨质含量没有差异。此外,我们通过取出相对的牙齿来挑战牙骨质,通过建立更多的牙骨质来使第一下颌磨牙向上移动。即使面对这样的挑战,我们发现与正常小鼠相比,缺乏硬化素的小鼠的牙骨质含量没有差异。因此,我们在这里得出的结论是,与骨骼相比,牙骨质对硬化蛋白的缺乏较不敏感。
BACKGROUND: Cellular cementum (CC) includes cementocytes, cells suspected to regulate CC formation or resorption as osteocytes do in bone. Sclerostin (SOST) is a secreted negative regulator of Wnt/β-catenin signaling expressed by osteocytes and cementocytes. Osteocyte SOST expression reduces bone formation. We investigated the functional importance of SOST in CC compared with alveolar bone (AB) using a Sost knockout (Sost-/-) mouse model to better understand the role of cementocytes in CC.
METHODS: Mandibles and femurs of Sost-/- and wild-type (WT) mice were analyzed at 42 and 120 days postnatal (dpn). Maxillary first molars were bilaterally extracted at 42 dpn and both AB healing (maxillary molar sockets) and CC apposition (mandibular first molars) were examined at 21 days post-procedure. Analyses included micro-computed tomography, histology, and immunohistochemistry.
RESULTS: Femur cortical and trabecular bone and mandibular bone volumes were similarly increased in Sost-/- versus WT mice at 42 and/or 120 dpn. In contrast to previous reports, CC was not increased by Sost-/- at either age. We conducted challenge experiments on AB and CC to explore tissue-specific responses. Post-extraction AB healing was improved by Sost deletion. In contrast, experimentally-induced apposition in molars failed to stimulate increased CC formation in Sost-/- versus WT mice. Wnt pathway markers AXIN2 and DKK1, which were increased in Sost-/- versus WT AB osteocytes, were unchanged in cementocytes.
CONCLUSIONS: These data indicate CC is less responsive than AB to SOST deletion. Within the study limitations, these results do not support cementocytes as critical for directing increased CC formation.
CONCLUSIONS: Sclerostin is a protein known to inhibit bone formation, and removing sclerostin leads to more bone formation. Cementum is the thin layer that covers the surface of the tooth\'s root. Previous studies suggest that inhibiting sclerostin can similarly increase the amount of cementum. We wanted to compare the response of cementum and bone when sclerostin is absent to understand similarities and differences between these two tissues. In this study, we removed the Sost gene (the gene which produces sclerostin) in mice. We found that mice without sclerostin have more bone in their legs and jaws. Moreover, mice without sclerostin also healed better after tooth removal compared with normal mice. Surprisingly, unlike previous studies, we found that the amount of cementum was not different in mice without sclerostin compared with normal mice. Additionally, we challenged the cementum by taking out the opposing tooth to cause the first mandibular molar to move up by building more cementum. Even with this challenge, we found no difference in the amount of cementum in mice lacking sclerostin compared with normal mice. Therefore, we conclude here that cementum is less sensitive to the absence of sclerostin compared with bone.