Ablation of Tnfr1 Gene Impairs Enamel Surface Microhardness and Mineral Composition in Mice

Abstract

While the immune response is increasingly suspected to play a role in dental enamel defects, the specific pathways involved remain unclear. This study investigated the effects of Tnfrsf1a (TNF receptor superfamily member 1A) gene ablation on amelogenesis and enamel biomineralization. Male Tnfrsf1a knockout (Tnfrsf1a^-/-) and wild-type (C57BL/6) mice (n = 6 per group) were evaluated. Lower incisors were analyzed using visual photography, micro-computed tomography (microCT), scanning electron microscopy (SEM), surface microhardness testing, and energy-dispersive X-ray (EDX) spectroscopy. Protein expression of MMP20, RUNX2, and AMBN was assessed via immunohistochemistry, while in situ zymography quantified MMP gelatinolytic activity. Gene expression was analyzed using RT-qPCR. Tnfrsf1a^-/- mice exhibited no macroscopic opacities, though incisors displayed a distinct whitish coloration. While microCT and SEM revealed no significant differences in enamel volume, or prism ultrastructure, the enamel of Tnfrsf1a^-/- mice showed significantly lower calcium and phosphorus content and reduced surface microhardness. Molecular analysis revealed that the Ambn gene was significantly upregulated during both the secretion and maturation stages in Tnfrsf1a^-/- mice compared to wild-type controls. Ablation of Tnfrsf1a results in enamel color change in mice  characterized by altered mineral composition, reduced mechanical hardness, and dysregulated Ambn expression. These findings suggest that TNF signaling acts as a critical modulator during amelogenesis and is essential for achieving the final mineral quality of dental enamel.