Inhibition of Ape1 Redox Activity Promotes Odonto/osteogenic Differentiation of Dental Papilla Cells

Hypoxia-inducible factors in postnatal mouse molar dental pulp development: insights into expression patterns, localisation and metabolic pathways

Hypoxia is relevant to several physiological and pathological processes and this also applies for the tooth. The adaptive response to lowering oxygen concentration is mediated by hypoxia-inducible factors (HIFs). Since HIFs were shown to participate in the promotion of angiogenesis, stem cell survival, odontoblast differentiation and dentin formation, they may play a beneficial role in the tooth reparative processes. Although some data were generated in vitro, little is known about the in vivo context of HIFs in tooth development. In order to contribute to this field, the mouse mandibular first molar was used as a model.The expression and in situ localisation of HIFs were examined at postnatal (P) days P0, P7, P14, using RT-PCR and immunostaining. The expression pattern of a broad spectrum of hypoxia-related genes was monitored by customised PCR Arrays. Metabolic aspects were evaluated by determination of the lactate level and mRNA expression of the mitochondrial marker Nd1.The results show constant high mRNA expression of Hif1a, increasing expression of Hif2a, and very low expression of Hif3a during early postnatal molar development. In the examined period the localisation of HIFs in the nuclei of odontoblasts and the subodontoblastic layer identified their presence during odontoblastic differentiation. Additionally, the lower lactate level and higher expression of mitochondrial Nd1 in advanced development points to decreasing glycolysis during differentiation. Postnatal nuclear localisation of HIFs indicates a hypoxic state in specific areas of dental pulp as oxygen demands depend on physiological events such as crown and root dentin mineralization.

Spatiotemporal cellular dynamics and molecular regulation of tooth root ontogeny

Tooth root development involves intricate spatiotemporal cellular dynamics and molecular regulation. The initiation of Hertwig's epithelial root sheath (HERS) induces odontoblast differentiation and the subsequent radicular dentin deposition. Precisely controlled signaling pathways modulate the behaviors of HERS and the fates of dental mesenchymal stem cells (DMSCs). Disruptions in these pathways lead to defects in root development, such as shortened roots and furcation abnormalities. Advances in dental stem cells, biomaterials, and bioprinting show immense promise for bioengineered tooth root regeneration. However, replicating the developmental intricacies of odontogenesis has not been resolved in clinical treatment and remains a major challenge in this field. Ongoing research focusing on the mechanisms of root development, advanced biomaterials, and manufacturing techniques will enable next-generation biological root regeneration that restores the physiological structure and function of the tooth root. This review summarizes recent discoveries in the underlying mechanisms governing root ontogeny and discusses some recent key findings in developing of new biologically based dental therapies.

RORα Regulates Odontoblastic Differentiation and Mediates the Pro-Odontogenic Effect of Melatonin on Dental Papilla Cells

Dental papilla cells (DPCs), precursors of odontoblasts, are considered promising seed cells for tissue engineering. Emerging evidence suggests that melatonin promotes odontoblastic differentiation of DPCs and affects tooth development, although the precise mechanisms remain unknown. Retinoid acid receptor-related orphan receptor α (RORα) is a nuclear receptor for melatonin that plays a critical role in cell differentiation and embryonic development. This study aimed to explore the role of RORα in odontoblastic differentiation and determine whether melatonin exerts its pro-odontogenic effect via RORα. Herein, we observed that RORα was expressed in DPCs and was significantly increased during odontoblastic differentiation in vitro and in vivo. The overexpression of RORα upregulated the expression of odontogenic markers, alkaline phosphatase (ALP) activity and mineralized nodules formation (p < 0.05). In contrast, odontoblastic differentiation of DPCs was suppressed by RORα knockdown. Moreover, we found that melatonin elevated the expression of odontogenic markers, which was accompanied by the upregulation of RORα (p < 0.001). Utilising small interfering RNA, we further demonstrated that RORα inhibition attenuated melatonin-induced odontogenic gene expression, ALP activity and matrix mineralisation (p < 0.01). Collectively, these results provide the first evidence that RORα can promote odontoblastic differentiation of DPCs and mediate the pro-odontogenic effect of melatonin.

Krüppel-like factor 6 promotes odontoblastic differentiation through regulating the expression of dentine sialophosphoprotein and dentine matrix protein 1 genes

AIM

To investigate the potential role of Krüppel-like factor 6 (KLF6) in the odontoblastic differentiation of immortalized dental papilla mesenchymal cells (iMDP-3) cells.

METHODOLOGY

Alizarin Red S (ARS) and Alkaline phosphatase (ALP) staining was used to examine the mineralization effect of iMDP-3 cells after odontoblastic induction. Real-time PCR and Western blotting were employed to analyse dentine sialophosphoprotein (DSPP), dentine matrix protein 1 (DMP1), RUNX family transcription factor 2 (RUNX2), ALP and KLF6 expression during this process. Co-expression of the KLF6 with DMP1, DSPP and RUNX2 was detected by double immunofluorescence staining to explore their local relationship in the cell. To further investigate KLF6 functions, Klf6 gain- and loss-of-function assays followed by ARS and ALP stainings, real-time PCR and Western blotting were performed using Klf6-overexpression plasmids and Klf6 siRNA to investigate whether changes in Klf6 expression affect the odontoblastic differentiation of iMDP-3 cells. Dual-luciferase reporter assays were used to elucidate the mechanistic regulation of Dspp and Dmp1 expression by Klf6. Means were compared using the unpaired t-test and Kruskal-Wallis one-way anova with P < 0.05 and P < 0.01 defined as statistical significance levels.

RESULTS

The expression levels of Klf6 (P < 0.01), Dspp (P < 0.05), Dmp1 (P < 0.01), Runx2 (P < 0.01) and Alp (P < 0.01) were significantly elevated during odontoblastic differentiation of iMDP-3 cells. KLF6 was co-localized with DSPP, DMP1 and RUNX2 in the cytoplasm and nucleus of iMDP-3 cells. Overexpression of Klf6 promoted the odontoblastic differentiation of iMDP-3, whereas the inhibition of Klf6 prevented this procession. Dual-luciferase assays revealed that Klf6 upregulates Dspp and Dmp1 transcription in iMDP-3 cells during odontoblastic differentiation.

CONCLUSION

Klf6 promoted odontoblastic differentiation by targeting the transcription promoter of Dmp1 and Dspp. This study may offer novel insights into strategies for treating injuries to dental pulp tissue.

Small Extracellular Vesicles from Lipopolysaccharide-Preconditioned Dental Follicle Cells Promote Periodontal Regeneration in an Inflammatory Microenvironment

Lipopolysaccharide (LPS)-induced inflammatory microenvironment can enhance the dental follicle cells (DFCs) proliferation, differentiation, and adhesion abilities beneficial to periodontal regeneration, which possibly attributes the success to exosomes according to recent studies. This study aimed to investigate the therapeutic efficacy and underlying mechanisms of LPS-preconditioned DFC-derived small extracellular vesicles (sEVs), which enriched exosomes for periodontal regeneration in an inflammatory microenvironment. LPS preconditioning could significantly increase the secretion of sEVs derived from DFCs. Both LPS-preconditioned dental follicle cell-derived sEV (L-D-sEV) and DFC-derived sEV (D-sEV) promoted the proliferation of periodontal ligament cells from periodontitis (p-PDLCs) with a dose-dependent and saturable manner and also enhanced the migration and differentiation of p-PDLCs. Furthermore, L-D-sEV showed a modest benefit than D-sEV to promote p-PDLCs differentiation. In vivo, an L-D-sEV-loaded hydrogel applied in the treatment of periodontitis was beneficial to repair lost alveolar bone in the early stage of treatment and to maintain the level of alveolar bone in the late stage of treatment in experimental periodontitis rats, which could partly decrease the expression of the RANKL/OPG ratio. In conclusion, L-D-sEV was beneficial to p-PDLCs forming an integrity periodontal tissue. The biological injectable L-D-sEV-loaded hydrogel could be used as a treatment method for experimental periodontitis in rats, promoting periodontal tissue regeneration and providing a new alternative cell therapy method for periodontal tissue regeneration.

Therapeutic potential of HERS spheroids in tooth regeneration

Hertwig's epithelial root sheath (HERS) plays indispensable roles in tooth root development, including controlling the shape and number of roots, dentin formation, and helping generate the cementum. Based on these characteristics, HERS cell is a potential seed cell type for tooth-related tissue regeneration. However, the application is severely limited by a lack of appropriate culture methods and small cell numbers. Methods: Here, we constructed a 3D culture method to expand functional HERS cells into spheroids, and investigated characteristics and application of dental tissue regeneration of these spheroids. HERS spheroids and HERS cells (2D monolayer culture) were compared in terms of biological characteristics (such as proliferation, self-renewal capacity, and stemness) in vitro and functions (including differentiation potential and inductive ability of dentin formation) both in vitro and in vivo. Further, transcriptome analysis was utilized to reveal the molecular mechanisms of their obvious differences. Results: HERS spheroids showed obvious superiority in biological characteristics and functions compared to 2D monolayers of HERS cells in vitro. In vivo, HERS spheroids generated more mineralized tissue; when combined with dental papilla cells (DPCs), HERS spheroids contributed to dentin-like tissue formation. Moreover, the generation and expansion of HERS spheroids rely to some degree on the HIF-1 pathway. Conclusion: HERS spheroid generation is beneficial for functional HERS cell expansion and can provide a useful cell source for further tooth regeneration and mechanistic research. Notably, HIF-1 pathway plays a critical role in HERS spheroid formation and function.

Immunoexpression of DNA base excision repair and nucleotide excision repair proteins in ameloblastomas, syndromic and non-syndromic odontogenic keratocysts and dentigerous cysts

OBJECTIVE

To evaluate the immunoexpression of DNA base excision repair (BER) [apurinic/apyrimidinic endonuclease 1 (APE-1), X-ray repair cross complementing 1 (XRCC-1)] and nucleotide excision repair (NER) [xeroderma pigmentosum complementation group (XPF)] proteins in benign epithelial odontogenic lesions with different biological behaviors.

DESIGN

Thirty solid ameloblastomas, 30 non-syndromic odontogenic keratocysts (NSOKCs), 29 syndromic odontogenic keratocysts (SKOCs), 30 dentigerous cysts (DCs) and 20 dental follicles (DFs) were evaluated quantitatively for APE-1, XRCC-1 and XPF through immunohistochemistry.

RESULTS

Nuclear expression of APE-1 was significantly higher in NSOKCs, SOKCs, and ameloblastomas in comparison to DCs (p < 0.001). Nuclear expression of XRCC-1 was higher in NSOKCs and SOKCs than in DCs (p < 0.05). At the nuclear level, XPF expression was higher in NSOKCs and SOKCs than in DCs and ameloblastomas (p < 0.05). A statistically significant higher expression of APE-1 (nuclear), XRCC-1 (nuclear), and XPF (nuclear and cytoplasmic) was found in all odontogenic lesion samples as compared to DFs (p < 0.05). For all lesions, there was a positive correlation between nuclear expression of APE-1 and XRCC-1 or XPF (p < 0.05).

CONCLUSIONS

Our results suggest a potential involvement of APE-1, XRCC-1 and XPF proteins in the pathogenesis of benign epithelial odontogenic lesions, especially in those with more aggressive biological behavior, such as ameloblastomas, NSOKCs, and SOKCs. We also showed that the expression of APE-1 was positively correlated with the nuclear expression of XRCC-1 and XPF, which may suggest an interaction between the BER and NER pathways in all odontogenic lesions studied herein.

MiR-21/STAT3 Signal Is Involved in Odontoblast Differentiation of Human Dental Pulp Stem Cells Mediated by TNF-α

Dental pulp stem cells (DPSCs), as one type of mesenchymal stem cells (MSCs), have the capability of self-renewal and multipotency to differentiate into several cell lineages, including osteogenesis, odontoblasts, chondrogenesis, neurogenesis, and adipogenesis. It has found that tumor necrosis factor-α (TNF-α) can promote osteogenic differentiation of human DPSCs in our previous studies. Other experimentation revealed that signal transducer and activator of transcription 3 (STAT3) underwent a rapid activation both in osteogenesis and inflammation microenvironment of MSCs in vitro. MicroRNAs (miRNAs or miRs) have been proved in previous studies to regulate MSCs differentiation in vitro. In this study, we identified miR-21 as a key miRNA contributed the functional axis of odontoblast differentiation induced by STAT3. It is observed that the expression of miR-21 and STAT3 increased gradually in low concentration (1-10 ng/mL) of TNF-α, while they were suppressed in high concentration (50-100 ng/mL). The upregulation of miR-21 may facilitate the odontoblast differentiation of DPSCs coordinating with STAT3. SiSTAT3 or treated by the inhibitor of STAT3, cucurbitacin I (Cuc I), significantly increased primary miR-21 expression along with decreased mature miR-21 expression. Meanwhile, the inhibition of miR-21 (anti-miR-21) decreased the activation of STAT3 as well as suppressed the marker proteins of odontoblast differentiation. The results revealed a new function of miR-21, suggesting that miR-21/STAT3 signal may act as a modulator within a complex network of factors to regulate odontoblast differentiation of human DPSCs. It may provide a novel therapeutic strategy to regulate the odontoblast differentiation of DPSCs.

Changes of mitochondrial respiratory function during odontogenic differentiation of rat dental papilla cells

Dental papilla cells (DPCs) belong to precursor cells differentiating to odontoblasts and play an important role in dentin formation and reproduction. This study aimed to explore the changes and and involvement of mitochondrial respiratory function during odontogenic differentiation. Primary DPCs were obtained from first molar dental papilla of neonatal rats and cultured in odontogenic medium for 7, 14, 21 days. DPCs, which expressed mesenchymal surface markers CD29, CD44 and CD90, had the capacity for self-renewal and multipotent differentiation. Odontoblastic induction increased mineralized matrix formation in a time-dependent manner, which was accompanied by elevated alkaline phosphatase (ALP), dentin sialophosphoprotein and dentin matrix protein 1 expression at mRNA and protein levels. Notably, odontogenic medium led to an increase in adenosine-5'-triphosphate content and mitochondrial membrane potential, whereas a decrease in intercellular reactive oxygen species production and NAD⁺/NADH ratio. Furthermore, odontogenic differentiation was significantly suppressed by treatment with rotenone, an inhibitor of mitochondrial respiratory chain. These results demonstrate that enhanced mitochondrial function is crucial for odontogenic differentiation of DPCs.

APE1/Ref-1 Inhibits Phosphate-Induced Calcification and Osteoblastic Phenotype Changes in Vascular Smooth Muscle Cells

Vascular calcification plays a role in the pathogenesis of atherosclerosis, diabetes, and chronic kidney disease; however, the role of apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE1/Ref-1) in inorganic phosphate (Pi)-induced vascular smooth muscle cell (VSMC) calcification remains unknown. In this study, we investigated the possible role of APE1/Ref-1 in Pi-induced VSMC calcification. We observed that Pi decreased endogenous APE1/Ref-1 expression and promoter activity in VSMCs, and that adenoviral overexpression of APE1/Ref-1 inhibited Pi-induced calcification in VSMCs and in an ex vivo organ culture of a rat aorta. However, a redox mutant of APE1/Ref-1(C65A/C93A) did not reduce Pi-induced calcification in VSMCs, suggesting APE1/Ref-1-mediated redox function against vascular calcification. Additionally, APE1/Ref-1 overexpression inhibited Pi-induced intracellular and mitochondrial reactive oxygen species production, and APE1/Ref-1 overexpression resulted in decreased Pi-induced lactate dehydrogenase activity, pro-apoptotic Bax levels, and increased anti-apoptotic Bcl-2 protein levels. Furthermore, APE1/Ref-1 inhibited Pi-induced osteoblastic differentiation associated with alkaline phosphatase activity and inhibited Pi-exposure-induced loss of the smooth muscle phenotype. Our findings provided valuable insights into the redox function of APE1/Ref-1 in preventing Pi-induced VSMC calcification by inhibiting oxidative stress and osteoblastic differentiation, resulting in prevention of altered osteoblastic phenotypes in VSMCs.

Maternal diabetes modulates dental epithelial stem cells proliferation and self-renewal in offspring through apurinic/apyrimidinicendonuclease 1-mediated DNA methylation

Maternal gestational diabetes mellitus (GDM) has many adverse effects on the development of offspring. Aberrant DNA methylation is a potential mechanism associated with these effects. However, the effects of GDM on tooth development and the underlying mechanisms have not been thoroughly investigated. In the present study, a GDM rat model was established and incisor labial cervical loop tissue and dental epithelial stem cells (DESCs) were harvested from neonates of diabetic and control dams. GDM significantly suppressed incisor enamel formation and DESCs proliferation and self-renewal in offspring. Gene expression profiles showed that Apex1 was significantly downregulated in the offspring of diabetic dams. In vitro, gain and loss of function analyses showed that APEX1 was critical for DESCs proliferation and self-renewal and Oct4 and Nanog regulation via promoter methylation. In vivo, we confirmed that GDM resulted in significant downregulation of Oct4 and Nanog and hypermethylation of their promoters. Moreover, we found that APEX1 modulated DNA methylation by regulating DNMT1 expression through ERK and JNK signalling. In summary, our data suggest that GDM-induced APEX1 downregulation increased DNMT1 expression, thereby inhibiting Oct4 and Nanog expression, through promoter hypermethylation, resulting in suppression of DESCs proliferation and self-renewal, as well as enamel formation.

DNA Demethylation Rescues the Impaired Osteogenic Differentiation Ability of Human Periodontal Ligament Stem Cells in High Glucose

Diabetes mellitus, characterized by abnormally high blood glucose levels, gives rise to impaired bone remodeling. In response to high glucose (HG), the attenuated osteogenic differentiation capacity of human periodontal ligament stem cells (hPDLSCs) is associated with the loss of alveolar bone. Recently, DNA methylation was reported to affect osteogenic differentiation of stem cells in pathological states. However, the intrinsic mechanism linking DNA methylation to osteogenic differentiation ability in the presence of HG is still unclear. In this study, we found that diabetic rats with increased DNA methylation levels in periodontal ligaments exhibited reduced bone mass and density. In vitro application of 5-aza-2′-deoxycytidine (5-aza-dC), a DNA methyltransferase inhibitor, to decrease DNA methylation levels in hPDLSCs, rescued the osteogenic differentiation capacity of hPDLSCs under HG conditions. Moreover, we demonstrated that the canonical Wnt signaling pathway was activated during this process and, under HG circumstances, the 5-aza-dC-rescued osteogenic differentiation capacity was blocked by Dickkopf-1, an effective antagonist of the canonical Wnt signaling pathway. Taken together, these results demonstrate for the first time that suppression of DNA methylation is able to facilitate the osteogenic differentiation capacity of hPDLSCs exposed to HG, through activation of the canonical Wnt signaling pathway.