Microtubule-associated protein tau (Mapt) is expressed in terminally differentiated odontoblasts and severely down-regulated in morphologically disturbed odontoblasts of Runx2 transgenic mice

Cpne7 deficiency induces cellular senescence and premature aging of dental pulp

Once tooth development is complete, odontoblasts and their progenitor cells in the dental pulp play a major role in protecting tooth vitality from external stresses. Hence, understanding the homeostasis of the mature pulp populations is just as crucial as understanding that of the young, developing ones for managing age-related dentinal damage. Here, it is shown that loss of Cpne7 accelerates cellular senescence in odontoblasts due to oxidative stress and DNA damage accumulation. Thus, in Cpne7-null dental pulp, odontoblast survival is impaired, and aberrant dentin is extensively formed. Intraperitoneal or topical application of CPNE7-derived functional peptide, however, alleviates the DNA damage accumulation and rescues the pathologic dentin phenotype. Notably, a healthy dentin-pulp complex lined with metabolically active odontoblasts is observed in 23-month-old Cpne7-overexpressing transgenic mice. Furthermore, physiologic dentin was regenerated in artificial dentinal defects of Cpne7-overexpressing transgenic mice. Taken together, Cpne7 is indispensable for the maintenance and homeostasis of odontoblasts, while promoting odontoblastic differentiation of the progenitor cells. This research thereby introduces its potential in oral disease-targeted applications, especially age-related dental diseases involving dentinal loss.

CPNE7 regenerates periodontal ligament via TAU-mediated alignment and cementum attachment protein-mediated attachment

AIM

Once the periodontal ligament (PDL) is damaged, it is difficult to regenerate its characteristic structure. Copine7 (CPNE7) reportedly plays a functional role in supporting periodontal attachment and PDL alignment. Here we demonstrate the regulatory mechanism of CPNE7 coordination with cytoskeleton reorganization and cementum attachment protein (CAP)-mediated attachment in PDL regeneration.

MATERIALS AND METHODS

The expression and localization of CPNE7, α-TUBULIN, ACTIN, and microtubule associated protein tau (TAU) were investigated in vitro. The effects of recombinant CPNE7 (rCPNE7) and CPNE7-derived peptides (CPNE7-DP) on the regulation of CAP were analysed in vitro, and PDL repair capacity was analysed in vivo.

RESULTS

CPNE7 co-localized with F-ACTIN and induced α-TUBULIN expansion to the edge of human PDL cells (hPDLCs). ACTIN and α-TUBULIN protein expressions were not elevated in rCPNE7-treated hPDLCs. rCPNE7 elevated the protein expression of TAU, which co-localized with F-ACTIN and α-TUBULIN. Replantation studies on mice revealed that well-attached and well-aligned PDLs were repaired in the rCPNE7 group. CPNE7-DP directly up-regulate the expression of CAP in vitro and promote PDL regeneration in three-wall defect canine models in vivo.

CONCLUSIONS

Our findings suggest that CPNE7 helps in PDL repair by supporting PDL alignment through TAU-mediated cytoskeleton reorganization and direct regulation of CAP-mediated PDL attachments of PDLCs.

Tubular dentin formation by TGF-β/BMP signaling in dental epithelial cells

OBJECTIVES

This study aimed to identify formation of tubular dentin induced by Transforming growth factor-β (TGF-β) and bone morphogenic protein (BMP) signaling pathway in dental epithelial cells.

METHODS

We collected conditioned medium (CM) of rTGF-β1/rBMP-2 treated HAT-7 and treated to MDPC-23 cells. The expression levels of odontoblast differentiation markers, KLF4, DMP1, and DSP were evaluated by real-time PCR and western blot analysis. To evaluate whether CM of rTGF-β1/rBMP-2 induces tubular dentin formation, we made a beagle dog tooth defect model.

RESULTS

Here, we show that Cpne7 is regulated by Smad4-dependent TGF-β1/BMP2 signaling pathway in dental epithelial cells. CM of rTGF-β1/rBMP-2 treated HAT-7, or rCPNE7 raises the expression levels of KLF4, DMP1, and DSP in MDPC-23 cells. When rTGF-β1 or rBMP-2 is directly treated to MDPC-23 cells, however, expression levels of Cpne7-regulated genes remain unchanged. In a beagle dog defect model, application of rTGF-β1/BMP2 treated CM resulted in tubular tertiary dentin mixed with osteodentin at cavity-prepared sites, while rTGF-β1 group exhibited homogenous osteodentin.

CONCLUSIONS

Taken together, Smad4-dependent TGF-β1/BMP2 signaling regulates Cpne7 in dental epithelial cells, and CPNE7 protein secreted from pre-ameloblasts mediates odontoblast differentiation via epithelial-mesenchymal interaction.

CPNE7-Induced Autophagy Restores the Physiological Function of Mature Odontoblasts

Dentin, which composes most of the tooth structure, is formed by odontoblasts, long-lived post-mitotic cells maintained throughout the entire life of the tooth. In mature odontoblasts, however, cellular activity is significantly weakened. Therefore, it is important to augment the cellular activity of mature odontoblasts to regenerate physiological dentin; however, no molecule regulating the cellular activity of mature odontoblasts has yet been identified. Here, we suggest that copine-7 (CPNE7) can reactivate the lost functions of mature odontoblasts by inducing autophagy. CPNE7 was observed to elevate the expression of microtubule-associated protein light chain 3-II (LC3-II), an autophagy marker, and autophagosome formation in the pre-odontoblast and mature odontoblast stages of human dental pulp cells. CPNE7-induced autophagy upregulated DSP and DMP-1, odontoblast differentiation and mineralization markers, and augmented dentin formation in mature odontoblasts. Furthermore, CPNE7 also upregulated NESTIN and TAU, which are expressed in the physiological odontoblast process, and stimulated the elongation of the odontoblast process by inducing autophagy. Moreover, lipofuscin, which progressively accumulates in long-lived post-mitotic cells and hinders their proper functions, was observed to be removed in recombinant CPNE7-treated mature odontoblasts. Thus, CPNE7-induced autophagy reactivated the function of mature odontoblasts and promoted the formation of physiological dentin in vivo. On the other hand, the well-known autophagy inducer, rapamycin, promoted odontoblast differentiation in pre-odontoblasts but did not properly reactivate the function of mature odontoblasts. These findings provide evidence that CPNE7 functionally reactivates mature odontoblasts and introduce its potential for dentinal loss-targeted clinical applications.

Baba T, Mori M, Komori T. Collapsin Response Mediator Protein 1, a Novel Marker Protein for Differentiated Odontoblasts

We previously reported that the terminal differentiation of odontoblasts was inhibited in Runx2 transgenic {Tg(Col1a1-Runx2)} mice under the control of the 2.3-kb Col1a1 promoter. Odontoblasts in Tg(Col1a1-Runx2) mice lose their characteristic long cellular processes, and show marked reductions in the protein levels of markers for odontoblasts, such as dentin sialophosphoprotein, nestin, and microtubule-associated protein tau (Mapt). We herein demonstrated that collapsin response mediator protein 1 (CRMP1), a neuronal phosphoprotein that participates in various aspects of neuronal development, was specifically expressed in the differentiated odontoblasts of wild-type, but not Tg(Col1a1-Runx2) tooth germs by comparing expression profiles in wild-type and Tg(Col1a1-Runx2) mouse molars using microarray and immunohistochemical analyses. CRMP1 expression was detected at a slightly later differentiation stage in odontoblasts than type 1 collagen, nestin, and Mapt expression, which was observed from the onset of dentinogenesis. Among these proteins, CRMP1 was the most specifically localized in odontoblasts in the tooth germ. In erupted molars, odontoblast-specific CRMP1 expression decreased with age. These results indicate that CRMP1 is a novel marker protein for differentiated odontoblasts in mouse tooth germs, and suggest that CRMP1 participates in the morphogenesis of functioning odontoblasts.

Suppression of AKT-mTOR signal pathway enhances osteogenic/dentinogenic capacity of stem cells from apical papilla

BACKGROUND

Stem cells from apical papilla (SCAP) are a subpopulation of mesenchymal stem cells (MSCs) isolated from the apical papilla of the developing tooth root apex of human teeth. Because of their osteogenic/dentinogenic capacity, SCAP are considered as a source for bone and dentin regeneration. However, little is understood about the molecular mechanism of osteogenic/dentinogenic differentiation of SCAP. Phosphoinositide 3 kinase (PI3K)-AKT-mammalian target of rapamycin (mTOR) signal pathway participates in regulating the differentiation of various cell types, such as MSCs. In this study, we examined the role of the PI3K-AKT-mTOR signal pathway in the osteogenic/dentinogenic differentiation of SCAP. Moreover, we challenge to fabricate scaffold-free SCAP-based spheroidal calcified constructs.

METHODS

SCAP were pretreated with or without small interfering RNA for AKT (AKT siRNA), PI3K inhibitor LY294402, and mTOR inhibitor rapamycin and were cultured under osteogenic/dentinogenic differentiation to examine in vitro and in vivo calcified tissue formation. Moreover, SCAP-based cell aggregates were pretreated with or without LY294402 and rapamycin. The cell aggregates were cultured under osteogenic/dentinogenic condition and were analyzed the calcification of the aggregates.

RESULTS

Pretreatment with AKT siRNA, LY294402, and rapamycin enhances the in vitro and in vivo calcified tissue-forming capacity of SCAP. SCAP were fabricated as scaffold-free spheroids and were induced into forming calcified 3D constructs. The calcified density of the spheroidal constructs was enhanced when the spheroids were pretreated with LY294402 and rapamycin.

CONCLUSIONS

Our findings indicate that the suppression of PI3K-AKT-mTOR signal pathway plays a role in not only enhancing the in vivo and in vitro osteogenic/dentinogenic differentiation of SCAP, but also promoting the calcification of scaffold-free SCAP-based calcified constructs. These findings suggest that a suppressive regulation of PI3K-AKT-mTOR signal pathway is a novel approach for SCAP-based bone and dentin regeneration.