IADR Abstract Archives
Glycosaminoglycans in the Dental Epithelium are Essential for Amelogenesis
Objectives: Recent studies indicate that proteoglycans, once viewed as structural proteins in extracellular matrix, have roles in signaling mediation. Our lab, and others, found that proteoglycans are present in early-stage dental epithelium, stellate reticulum of enamel organs, and ameloblasts. Proteoglycan involvement in amelogenesis remains unclear and warrants investigation.
Methods: To investigate proteoglycans’ role in amelogenesis, we generated a floxed allele of Fam20B, a xylose kinase essential for glycosaminoglycan (GAG) assembly, and crossbred Fam20B-flox mice with K14-CreER transgenic mice to induce Fam20B inactivation in the dental epithelium at E10.5 and E16.5 by administrating tamoxifen. Total thickness of incisor enamel and crystal structure were examined by scanning electron microscopy (SEM). Knoop hardness of enamel was assessed by microhardness measurements. Expression pattern of critical enamel matrix proteins was examined by immunochemistry (IHC) and in situ hybridization (ISH).
Results: Inactivation of dental epithelial Fam20B at E10.5 led to white incisors in knockout mice. Those induced at E16.5 lacked apparent enamel defects, suggesting the defects are associated with aberrant differentiation of ameloblasts at early stages, not with biological events ensuing ameloblast maturation. SEM analysis on E10.5-induced knockout mice lacked apparent difference from the wild type (WT) in enamel thickness, while enamel crystal density of knockout mice was significantly reduced (P<0.01) compared to the WT. The enamel Knoop microhardness of knockout mice was significantly lower than in WT mice (P<0.01). IHC and ISH analyses of ameloblastin and amelogenin showed significantly lower expression levels in E10.5-induced knockout mice than in WT mice.
Conclusions: Our results indicate that proteoglycans are essential for amelogenesis; GAG deficiency in early-stage dental epithelium leads to lower enamel hardness, reduced enamel crystal density, and aberrant expression of enamel matrix proteins. Proteoglycans are likely involved in amelogenesis through mediating early-stage ameloblast differentiation, not the biological events ensuing ameloblast maturation.
Supported by NIDCR DE026461(XW).
Methods: To investigate proteoglycans’ role in amelogenesis, we generated a floxed allele of Fam20B, a xylose kinase essential for glycosaminoglycan (GAG) assembly, and crossbred Fam20B-flox mice with K14-CreER transgenic mice to induce Fam20B inactivation in the dental epithelium at E10.5 and E16.5 by administrating tamoxifen. Total thickness of incisor enamel and crystal structure were examined by scanning electron microscopy (SEM). Knoop hardness of enamel was assessed by microhardness measurements. Expression pattern of critical enamel matrix proteins was examined by immunochemistry (IHC) and in situ hybridization (ISH).
Results: Inactivation of dental epithelial Fam20B at E10.5 led to white incisors in knockout mice. Those induced at E16.5 lacked apparent enamel defects, suggesting the defects are associated with aberrant differentiation of ameloblasts at early stages, not with biological events ensuing ameloblast maturation. SEM analysis on E10.5-induced knockout mice lacked apparent difference from the wild type (WT) in enamel thickness, while enamel crystal density of knockout mice was significantly reduced (P<0.01) compared to the WT. The enamel Knoop microhardness of knockout mice was significantly lower than in WT mice (P<0.01). IHC and ISH analyses of ameloblastin and amelogenin showed significantly lower expression levels in E10.5-induced knockout mice than in WT mice.
Conclusions: Our results indicate that proteoglycans are essential for amelogenesis; GAG deficiency in early-stage dental epithelium leads to lower enamel hardness, reduced enamel crystal density, and aberrant expression of enamel matrix proteins. Proteoglycans are likely involved in amelogenesis through mediating early-stage ameloblast differentiation, not the biological events ensuing ameloblast maturation.
Supported by NIDCR DE026461(XW).