GATA Binding Protein 4 Regulates Tooth Root Dentin Development via FBP1

Animal models and related techniques for dentin study

The intricate and protracted process of dentin formation has been extensively explored, thanks to the significant advancements facilitated by the use of animal models and related techniques. Despite variations in their effectiveness, taking into account factors such as sensitivity, visibility, and reliability, these models or techniques are indispensable tools for investigating the complexities of dentin formation. This article focuses on the latest advances in animal models and related technologies, shedding light on the key molecular mechanisms that are essential in dentin formation. A deeper understanding of this phenomenon enables the careful selection of appropriate animal models, considering their suitability in unraveling the underlying molecular intricacies. These insights are crucial for the advancement of clinical drugs targeting dentin-related ailments and the development of comprehensive treatment strategies throughout the duration of the disease.

PGC-1α/LDHA signaling facilitates glycolysis initiation to regulate mechanically induced bone remodeling under inflammatory microenvironment

The mechanosensitivity of inflammation can alter cellular mechanotransduction. However, the underlying mechanism remains unclear. This study aims to investigate the metabolic mechanism of inflammation under mechanical force to guide tissue remodeling better. Herein, we found that inflammation hindered bone remodeling under mechanical force, accompanied by a simultaneous enhancement of oxidative phosphorylation (OXPHOS) and glycolysis. The control of metabolism direction through GNE-140 and Visomitin revealed that enhanced glycolysis might act as a compensatory mechanism to resist OXPHOS-induced osteoclastogenesis by promoting osteogenesis. The inhibited osteogenesis induced by inflammatory mechanical stimuli was concomitant with a reduced expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). PGC-1α knockdown impeded osteogenesis under mechanical force and facilitated osteoclastogenesis by enhancing OXPHOS. Conversely, PGC-1α overexpression attenuated the impairment of bone remodeling by inflammatory mechanical signals through promoting glycolysis. This process benefited from the PGC-1α regulation on the transcriptional and translational activity of lactate dehydrogenase A (LDHA) and the tight control of the extracellular acidic environment. Additionally, the increased binding between PGC-1α and LDHA proteins might contribute to the glycolysis promotion within the inflammatory mechanical environment. Notably, LDHA suppression effectively eliminated the bone repair effect mediated by PGC-1α overexpression within inflammatory mechanical environments. In conclusion, this study demonstrated a novel molecular mechanism illustrating how inflammation orchestrated glucose metabolism through glycolysis and OXPHOS to affect mechanically induced bone remodeling.

Ablation of FAM20C caused short root defects via suppressing the BMP signaling pathway in mice

Short root defects are prone to cause various periodontal diseases and lead to tooth loss in some serious cases. Studies about the mechanisms governing the development of the root are needed for a better understanding of the pathogenesis of short root defects. The protein family with sequence similarity 20 group C (FAM20C) is a Golgi casein kinase that has been well studied in the development of tooth crown formation. However, whether FAM20C plays a role in the development of tooth root is still unknown. Thus, we generated Sox2-Cre;Fam20cfl/fl (cKO) mice, in which Fam20c was ablated in both the dental epithelium and dental mesenchyme, and found that the cKO mice showed severe short root defects mainly by inhibiting the development of dental mesenchyme in the root region. In this investigation, we found morphological changes and differentiation defects, with reduced expression of dentin sialophosphoprotein (DSPP) in odontoblasts of the root region in cKO mice. Furthermore, the proliferation rate of apical papillary cells was reduced in the root of cKO mice. In addition, the levels of bone morphogenetic protein 4 (BMP4) and phospho-Smad1/5/8, and that of Osterix and Krüppel-like factor 4 (KLF4), two downstream target molecules of the BMP signaling pathway, were significantly reduced in the root of cKO mice. These results indicate that FAM20C plays an essential role in the development of the root by regulating the BMP signaling pathway.

CDC42-mediated Wnt signaling facilitates odontogenic differentiation of DPCs during tooth root elongation

BACKGROUND

CDC42 is a member of Rho GTPase family, acting as a molecular switch to regulate cytoskeleton organization and junction maturation of epithelium in organ development. Tooth root pattern is a highly complicated and dynamic process that dependens on interaction of epithelium and mesenchyme. However, there is a lack of understanding of the role of CDC42 during tooth root elongation.

METHODS

The dynamic expression of CDC42 was traced during tooth development through immunofluorescence staining. Then we constructed a model of lentivirus or inhibitor mediated Cdc42 knockdown in Herwig's epithelial root sheath (HERS) cells and dental papilla cells (DPCs), respectively. Long-term influence of CDC42 abnormality was assessed via renal capsule transplantation and in situ injection of alveolar socket.

RESULTS

CDC42 displayed a dynamic spatiotemporal pattern, with abundant expression in HERS cells and apical DPCs in developing root. Lentivirus-mediated Cdc42 knockdown in HERS cells didn't disrupt cell junctions as well as epithelium-mesenchyme transition. However, inhibition of CDC42 in DPCs undermined cell proliferation, migration and odontogenic differentiation. Wnt/β-catenin signaling as the downstream target of CDC42 modulated DPCs' odontogenic differentiation. The transplantation and in situ injection experiments verified that loss of CDC42 impeded root extension via inhibiting the proliferation and differentiation of DPCs.

CONCLUSIONS

We innovatively revealed that CDC42 was responsible for guiding root elongation in a mesenchyme-specific manner. Furthermore, CDC42-mediated canonical Wnt signaling regulated odontogenic differentiation of DPCs during root formation.

Molecular mechanism of hyperactive tooth root formation in oculo-facio-cardio-dental syndrome

Mutations in the B-cell lymphoma 6 (BCL6) interacting corepressor (BCOR) cause oculo-facio-cardio-dental (OFCD) syndrome, a rare X-linked dominant condition that includes dental radiculomegaly among other characteristics. BCOR regulates downstream genes via BCL6 as a transcriptional corepressor. However, the molecular mechanism underlying the occurrence of radiculomegaly is still unknown. Thus, this study was aimed at identifying BCOR-regulated genetic pathways in radiculomegaly. The microarray profile of affected tissues revealed that the gene-specific transcriptional factors group, wherein nucleus factor 1B, distal-less homeobox 5, and zinc finger protein multitype 2 (ZFPM2) were the most upregulated, was significantly expressed in periodontal ligament (PDL) cells of the diseased patient with a frameshift mutation (c.3668delC) in BCOR. Wild-type BCOR overexpression in human periodontal ligament fibroblasts cells significantly hampered cellular proliferation and ZFPM2 mRNA downregulation. Promoter binding assays showed that wild-type BCOR was recruited in the BCL6 binding of the ZFPM2 promoter region after immunoprecipitation, while mutant BCOR, which was the same genotype as of our patient, failed to recruit these promoter regions. Knockdown of ZFPM2 expression in mutant PDL cells significantly reduced cellular proliferation as well as mRNA expression of alkaline phosphatase, an important marker of odontoblasts and cementoblasts. Collectively, our findings suggest that BCOR mutation-induced ZFPM2 regulation via BCL6 possibly contributes to hyperactive root formation in OFCD syndrome. Clinical data from patients with rare genetic diseases may aid in furthering the understanding of the mechanism controlling the final root length.

Mesenchymal Mycn participates in odontoblastic lineage commitment by regulating Krüppel-like Factor 4 (Klf4) in mice

Background

Commitment of mouse dental papilla cells (mDPCs) to the odontoblast lineage is critical for dentin formation, and this biological process is regulated by a complex transcription factor network. The transcription factor Mycn is a proto-oncogene that plays an important role in tumorigenesis and normal embryonic development. An early study revealed that Mycn is exclusively expressed in dental mesenchymal cells at E15.5, which implies a potential role of Mycn in dentinogenesis. However, the role of Mycn in dentin formation remains elusive. Thus, it is of considerable interest to elucidate the role of Mycn in dentin formation.

Methods

Mycn^fl/fl; Osr2^IresCre (Mycn^Osr2) and Mycn^fl/fl; K14^Cre (Mycn^K14) transgenic mice were generated, and micro-CT scans were performed to quantitatively analyse the volumetric differences in the molars and incisors of the mutants and their littermates. Mycn was also knocked down in vitro, and alkaline phosphatase (ALP) and alizarin red staining (ARS) were conducted. Cleavage under targets and tagmentation (CUT&Tag) analysis and dual luciferase assays were performed to identify direct downstream targets of Mycn. Immunofluorescence and immunochemistry staining and western blotting (WB) were performed to analyse the expression levels of potential targets. Quantitative PCR, WB, ALP and ARS were performed to test the rescue efficiency.

Results

Mesenchymal ablation of Mycn (Mycn^Osr2) led to defective dentin formation, while epithelial deletion (Mycn^K14) had no obvious effects on tooth development. ALP and ARS staining revealed that the commitment capacity of mDPCs to the odontoblast lineage was compromised in Mycn^Osr2 mice. CUT&Tag analysis identified Klf4 as a potential direct target of Mycn, and a dual luciferase reporter assay verified that Mycn could bind to the promotor region of Klf4 and directly activate its transcription. Reciprocally, forced expression of Klf4 partially recovered the odontoblastic differentiation capacity of mDPCs with Mycn knockdown.

Conclusions

Our results elucidated that mesenchymal Mycn modulates the odontoblastic commitment of dental papilla cells by directly regulating Klf4. Our study illustrated the role of Mycn in dentin development and furthers our general comprehension of the transcription factor networks involved in the dentinogenesis process. Thus, these results may provide new insight into dentin hypoplasia and bioengineered dentin regeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02749-8.

The Genes Involved in Dentinogenesis

The development and repair of dentin are strictly regulated by hundreds of genes. Abnormal dentin development is directly caused by gene mutations and dysregulation. Understanding and mastering this signal network is of great significance to the study of tooth development, tissue regeneration, aging, and repair and the treatment of dental diseases. It is necessary to understand the formation and repair mechanism of dentin in order to better treat the dentin lesions caused by various abnormal properties, whether it is to explore the reasons for the formation of dentin defects or to develop clinical drugs to strengthen the method of repairing dentin. Molecular biology of genes related to dentin development and repair are the most important basis for future research.

GATA4-driven miR-206-3p signatures control orofacial bone development by regulating osteogenic and osteoclastic activity

Growth disorders in the orofacial bone development process may lead to orofacial deformities. The balance between bone matrix formation by mesenchymal lineage osteoblasts and bone resorption by osteoclasts is vital for orofacial bone development. Although the mechanisms of orofacial mesenchymal stem cells (OMSCs) in orofacial bone development have been studied intensively, the communication between OMSCs and osteoclasts remains largely unclear. Methods: We used a neural crest cell-specific knockout mouse model to investigate orofacial bone development in GATA-binding protein 4 (GATA4) morphants. We investigated the underlying mechanisms of OMSCs-derived exosomes (OMExos) on osteoclastogenesis and bone resorption activity in vitro. miRNAs were extracted from OMExos, and differences in miRNA abundances were determined using an Affymetrix miRNA array. Luciferase reporter assays were used to validate the binding between GATA4 and miR-206-3p in OMSCs and to confirm the putative binding of miR-206-3p and its target genes in OMSCs and osteoclasts. The regulatory mechanism of the GATA4-miR-206-3p axis in OMSC osteogenic differentiation and osteoclastogenesis was examined in vitro and in vivo. Results: Wnt1-Cre;Gata4^fl/fl mice (cKO) not only presented inhibited bone formation but also showed active bone resorption. Osteoclasts cocultured in vitro with cKO OMSCs presented an increased capacity for osteoclastogenesis, which was exosome-dependent. Affymetrix miRNA array analysis showed that miR-206-3p was downregulated in exosomes from shGATA4 OMSCs. Moreover, the transcriptional activity of miR-206-3p was directly regulated by GATA4 in OMSCs. We further demonstrated that miR-206-3p played a key role in the regulation of orofacial bone development by directly targeting bone morphogenetic protein-3 (Bmp3) and nuclear factor of activated T -cells, cytoplasmic 1 (NFATc1). OMExos and agomiR-206-3p enhanced bone mass in Wnt1-cre;Gata4^fl/fl mice by augmenting trabecular bone structure and decreasing osteoclast numbers. Conclusion: Our findings confirm that miR-206-3p is an important downstream factor of GATA4 that regulates the functions of OMSCs and osteoclasts. These results demonstrate the efficiency of OMExos and microRNA agomirs in promoting bone regeneration, which provide an ideal therapeutic tool for orofacial bone deformities in the future.

Triptolide impairs glycolysis by suppressing GATA4/Sp1/PFKP signaling axis in mouse Sertoli cells

Triptolide (TP), a primary bioactive ingredient isolated from the traditional Chinese herbal medicine Tripterygium wilfordii Hook. F. (TWHF), has attracted great interest for its therapeutic biological activities in inflammation and autoimmune disease. However, its clinical use is limited by severe testicular toxicity, and the underlying mechanism has not been elucidated. Our preliminary evidence demonstrated that TP disrupted glucose metabolism and caused testicular toxicity. During spermatogenesis, Sertoli cells (SCs) provide lactate as an energy source to germ cells by glycolysis. The transcription factors GATA-binding protein 4 (GATA4) and specificity protein 1 (Sp1) can regulate glycolysis. Based on this evidence, we speculate that TP causes abnormal glycolysis in SCs by influencing the expression of the transcription factors GATA4 and Sp1. The mechanism of TP-induced testicular toxicity was investigated in vitro and in vivo. The data indicated that TP decreased glucose consumption, lactate production, and the mRNA levels of glycolysis-related transporters and enzymes. TP also downregulated the protein expression of the transcription factors GATA4 and Sp1, as well as the glycolytic enzyme phosphofructokinase platelet (PFKP). Phosphorylated GATA4 and nuclear GATA4 protein levels were reduced in a dose- and time-dependent manner after TP incubation. Similar effects were observed in shGata4-treated TM4 cells and BALB/c mice administered 0.4 mg/kg TP for 28 days, and glycolysis was also inhibited. Gata4 knockdown downregulated Sp1 and PFKP expression. Furthermore, the Sp1 inhibitor plicamycin inhibited PFKP protein levels in TM4 cells. In conclusion, TP inhibited GATA4-mediated glycolysis by suppressing Sp1-dependent PFKP expression in SCs and caused testicular toxicity.