Department of Orofacial Sciences, School of Dentistry, University of California, San Francisco, CA, USA.
Matrix Biol. 2013 Oct-Nov;32(7-8):432-42. doi: 10.1016/j.matbio.2013.05.004. Epub 2013 Jun 4.
Highly mineralized tooth enamel develops from an extracellular matrix chiefly comprised of amelogenins formed by splicing of 7 (human) or 9 (rodent) exons secreted from specialized epithelial cells known as ameloblasts. Here we examined the role of the 59 amino acid alternatively spliced amelogenin known as leucine rich amelogenin peptide (LRAP) on enamel formation, using transgenic murine models in which LRAP overexpression is driven by an amelogenin promoter (TgLRAP). Beginning in the secretory stage of mouse amelogenesis, we found a reduced thickness of enamel matrix and a loss of Tomes' processes, followed by upregulated amelogenin mRNA expression, inhibited amelogenin secretion and loss of cell polarity. In the presecretory stage (P0) amelogenin m180 mRNA expression was increased 58 fold along with a 203 fold increase in MMP-20 expression and 3.5 and 3.2 fold increased in respectively enamelin and ameloblastin. When LRAP was overexpressed on an amelogenin knockout mouse model, the ameloblasts were not affected. Further, expression of the global chromatin organizer and transcription factor SATB1 was reduced in secretory stage TgLRAP ameloblasts. These findings identify a cellular role for LRAP in enamel formation that is not directly related to directing enamel crystal formation as is reported to be the primary function of full length amelogenins. The effect of LRAP overexpression in upregulating amelogenins, MMP-20 and SATB1, suggests a role in protein regulation critical to ameloblast secretion and matrix processing, to form a mineralized enamel matrix.
高度矿化的牙釉质由主要由来自称为成釉细胞的特殊上皮细胞分泌的 7 个（人类）或 9 个（啮齿动物）外显子拼接而成的细胞外基质组成。在这里，我们使用由成釉蛋白启动子驱动的 LRAP 过表达的转基因鼠模型研究了 59 个氨基酸的可选拼接釉原蛋白，即富含亮氨酸的釉原蛋白肽（LRAP）在釉质形成中的作用（TgLRAP）。从鼠釉质形成的分泌阶段开始，我们发现釉质基质变薄，汤姆氏突消失，随后釉原蛋白 mRNA 表达上调，釉原蛋白分泌抑制和细胞极性丧失。在分泌前期（P0），m180mRNA 表达增加了 58 倍，MMP-20 表达增加了 203 倍，牙本质蛋白和釉原蛋白分别增加了 3.5 倍和 3.2 倍。当 LRAP 在釉原蛋白敲除鼠模型中过表达时，成釉细胞不受影响。此外，在分泌阶段的 TgLRAP 成釉细胞中，全局染色质组织者和转录因子 SATB1 的表达减少。这些发现确定了 LRAP 在釉质形成中的细胞作用，与全长釉原蛋白报告的主要功能即直接指导釉质晶体形成无关。LRAP 过表达上调釉原蛋白、MMP-20 和 SATB1 的作用表明，其在蛋白质调节中起关键作用，对成釉细胞分泌和基质加工至关重要，以形成矿化的牙釉质基质。
