UCLA

Mouse molars resemble human teeth, as their roots develop and stop growing. In contrast, mouse incisors grow and erupt continuously due to the presence of a persistent stem cell niche identified as the labial cervical loop, which actively gives rise to dentin-forming odontoblasts to support tooth homeostasis and injury repair. Autophagy (ATG), a cellular degradation process whereby macromolecules and organelles are sequestered to be recycled, has been shown to play a role in mineralized tissue-forming cells including odontoblasts. However, the precise role of ATG in odontoblasts in vivo remains unclear. Beclin1 is an indispensable ATG-related protein involved in ATG initiation. Therefore, we conditionally deleted Beclin1 in odontoblast-specific manner and generated Becn1f/f;Dmp1Cre/+ (Becn1 cKO) mice. From these mice, molars and incisors were evaluated radiographically and histologically. MicroCT scanning was employed to observe dentin formation and measure pulp tissue volume, histological analysis to examine dentin formation and dental pulp cells, and RNAscope in situ hybridization to identify odontoblast differentiation in the incisor stem cell niche and mesenchymal tissue in molars. We further evaluated the mRNA expression of FGF signaling genes in human dental pulp stem cells in vitro using Becn1 knocked down dental pulp cells (DPCs). Becn1 cKO mice were born at the expected Mendalian ratio. However, Becn1 cKO mice at the 6th month mark exhibited increased obliteration of the pulp chamber in both molar and incisors. Interestingly, both Becn1 wildtype (WT) and Becn1 ckO mice a normal laCL histology. When Becn1 was knocked down in DPCs, Etv4, a downstream target gene of FGF signaling pathway, was significantly upregulated. Our study highlights the possible role of Beclin1 in pulp calcification of molars, as Beclin1 KO mice molars were characterized by a completely obliteration and calcification of the pulp space, and suggests that Beclin1 may play a role in developed teeth, but not in developing teeth.