McGuire J D, Gorski J P, Dusevich V, Wang Y, Walker M P
Department of Oral and Craniofacial Sciences, School of Dentistry
Department of Oral and Craniofacial Sciences, School of Dentistry Center of Excellence in Musculoskeletal and Dental Tissues, University of Missouri-Kansas City, Kansas City, MO 64108, USA.
J Dent Res. 2014 Oct;93(10):1028-34. doi: 10.1177/0022034514548221. Epub 2014 Aug 21.
The dental basement membrane (BM) is composed of collagen types IV, VI, VII, and XVII, fibronectin, and laminin and plays an inductive role in epithelial-mesenchymal interactions during tooth development. The BM is degraded and removed during later-stage tooth morphogenesis; however, its original position defines the location of the dentin-enamel junction (DEJ) in mature teeth. We recently demonstrated that type VII collagen is a novel component of the inner enamel organic matrix layer contiguous with the DEJ. Since it is frequently co-expressed with and forms functional complexes with type VII collagen, we hypothesized that type IV collagen should also be localized to the DEJ in mature human teeth. To identify collagen IV, we first evaluated defect-free erupted teeth from various donors. To investigate a possible stabilizing role, we also evaluated extracted teeth exposed to high-dose radiotherapy--teeth that manifest post-radiotherapy DEJ instability. We now show that type IV collagen is a component within the morphological DEJ of posterior and anterior teeth from individuals aged 18 to 80 yr. Confocal microscopy revealed that immunostained type IV collagen was restricted to the 5- to 10-µm-wide optical DEJ, while collagenase treatment or previous in vivo tooth-level exposure to > 60 Gray irradiation severely reduced immunoreactivity. This assignment was confirmed by Western blotting with whole-tooth crown and enamel extracts. Without reduction, type IV collagen contained macromolecular α-chains of 225 and 250 kDa. Compositionally, our results identify type IV collagen as the first macromolecular biomarker of the morphological DEJ of mature teeth. Given its network structure and propensity to stabilize the dermal-epidermal junction, we propose that a collagen-IV-enriched DEJ may, in part, explain its well-known fracture toughness, crack propagation resistance, and stability. In contrast, loss of type IV collagen may represent a biochemical rationale for the DEJ instability observed following oral cancer radiotherapy.
牙本质基底膜（BM）由IV型、VI型、VII型和XVII型胶原蛋白、纤连蛋白和层粘连蛋白组成，在牙齿发育过程中的上皮-间充质相互作用中起诱导作用。在牙齿后期形态发生过程中，基底膜会降解并被去除；然而，其原始位置决定了成熟牙齿中牙本质-釉质界（DEJ）的位置。我们最近证明VII型胶原蛋白是与DEJ相邻的内釉质有机基质层的一种新成分。由于它经常与VII型胶原蛋白共表达并形成功能复合物，我们推测IV型胶原蛋白在成熟人类牙齿中也应定位于DEJ。为了鉴定IV型胶原蛋白，我们首先评估了来自不同供体的无缺陷萌出牙齿。为了研究其可能的稳定作用，我们还评估了接受高剂量放疗的拔除牙齿——这些牙齿在放疗后表现出DEJ不稳定。我们现在表明，IV型胶原蛋白是18至80岁个体前后牙形态学DEJ中的一种成分。共聚焦显微镜显示，免疫染色的IV型胶原蛋白局限于5至10μm宽的光学DEJ，而胶原酶处理或先前在体内牙齿水平暴露于>60格雷辐射会严重降低免疫反应性。用全牙冠和釉质提取物进行的蛋白质印迹证实了这一结果。未经还原时，IV型胶原蛋白包含225和250 kDa的大分子α链。在组成上，我们的结果确定IV型胶原蛋白是成熟牙齿形态学DEJ的首个大分子生物标志物。鉴于其网络结构和稳定真皮-表皮连接的倾向，我们提出富含IV型胶原蛋白的DEJ可能部分解释了其众所周知的断裂韧性、抗裂纹扩展能力和稳定性。相比之下，IV型胶原蛋白的缺失可能代表了口腔癌放疗后观察到的DEJ不稳定的生化原因。
