A novel mutation of MSX1 in oligodontia inhibits odontogenesis of dental pulp stem cells via the ERK pathway

Orodental malformations associated with human MSX1 sequence variants

BACKGROUND

MSX1 sequence variants have been known to cause human tooth agenesis (TA) with or without orofacial clefts. However, their roles during the whole processes of tooth development are not fully understood. This study aimed to characterize a 4-membered family with TA carrying a novel MSX1 pathogenic variant and investigate the disease mechanism.

METHODS

The authors conducted whole exome analysis to define the disease-causing sequence variant. They performed microcomputed tomography, morphometric analyses, transcriptome profiling, and molecular characterization to study the affected teeth and the gene variant.

RESULTS

The authors identified an MSX1 pathogenic variant, p.Glu232∗, in affected family members with TA and concomitant orodental anomalies, namely, prominent maxillary labial frenum, central incisor diastema, median maxillary anterior alveolar cleft, tooth fusion, mandibular molar dysmorphology, thin dentin layer, and slender dental roots. MSX1-defective teeth were not apparently microdontic but had thin dentin layers. The mandibular molars showed a homeotic transformation to maxillary counterparts. Genes involved in extracellular matrix organization and dentinogenesis, such as DMP1 and MMP20, were downregulated in dental pulp tissues of MSX1-defective teeth. The p.Glu232∗-truncated MSX1 properly localized to the nucleus but partially lost its transactivation ability. Analyzing reported cases indicated that truncation sequence variants within the homeobox domain of MSX1 caused a more severe TA phenotype than those outside of the homeobox domain, probably due to dominant negativity compared with haploinsufficiency.

CONCLUSIONS

This study provides in vivo evidence that MSX1 contributes to developmental processes of various orodental tissues in humans.

PRACTICAL IMPLICATIONS

Clinically, hypertrophic labial frenum, incisor diastema, and median maxillary anterior alveolar cleft might be considered diagnostic for MSX1-associated TA.

Characterization of novel MSX1 variants causally associated with non-syndromic oligodontia in Chinese families

BACKGROUND

MSX1 (OMIM #142983) is crucial to normal dental development, and variants in MSX1 are associated with dental anomalies. The objective of this study was to characterize the pathogenicity of novel MSX1 variants in Chinese families with non-syndromic oligodontia (NSO).

METHODS

Genomic DNA was extracted from individuals representing 35 families with non-syndromic oligodontia and was analyzed by Sanger sequencing and whole-exome sequencing. Pathogenic variants were screened via analyses involving PolyPhen-2, Sorting-Intolerant from Tolerant, and MutationTaster, and conservative analysis of variants. Patterns of MSX1-related NSO were analyzed. MSX1 structural changes suggested functional consequences in vitro.

RESULTS

Three previously unreported MSX1 heterozygous variants were identified: one insertion variant (c.576_577insTAG; p.Gln193*) and two missense variants (c. 871T>C; p.Tyr291His and c. 644A>C; p.Gln215Pro). Immunofluorescence analysis revealed abnormal subcellular localization of the p.Gln193* MSX1 variant. In addition, we found that these MSX1 variants likely lead to the loss of second premolars.

CONCLUSION

Three novel MSX1 variants were identified in Chinese Han families with NSO, expanding the MSX1 variant spectrum and presenting a genetic origin for the pathogenesis detected in patients and their families.

Exploring Various Transfection Approaches and Their Applications in Studying the Regenerative Potential of Dental Pulp Stem Cells

Transfection is a contemporary approach for introducing foreign genetic material into target cells. The effective transport of genetic materials into cells is mostly influenced by (a) the characteristics of the genetic material (quantity and quality), (b) the transfection procedure (incubation time, ratio of the reagents to the introduced genetic material, and components of cell culture), and (c) targeted cells for transfection (cell origin and cell type). This review summarizes the findings of different studies focusing on various transfection approaches and their applications to explore the regenerative potential of dental pulp stem cells (DPSCs). Several databases, including Scopus, Google Scholar, and PubMed, were searched to obtain the literature for the current review. Different keywords were used as key terms in the search. Approximately 200 articles were retained after removing duplicates from different databases. Articles published in English that discussed different transfection approaches were included. Several sources were excluded because they did not meet the inclusion criteria. Approximately 70 relevant published sources were included in the final stage to achieve the study objectives. This review demonstrated that no single transfection system is applicable to all cases and the various cell types with no side effects. Further studies are needed to focus on optimizing process parameters, decreasing the toxicity and side effects of available transfection techniques, and increasing their efficiencies. Moreover, this review sheds light on the impact of using different valuable transfection approaches to investigate the regenerative potential of DPSCs.

Genome-wide screening for deubiquitinase subfamily identifies ubiquitin-specific protease 49 as a novel regulator of odontogenesis

Proteins expressed by the paired box gene 9 (PAX9) and Msh Homeobox 1 (MSX1) are intimately involved in tooth development (odontogenesis). The regulation of PAX9 and MSX1 protein turnover by deubiquitinating enzymes (DUBs) plausibly maintain the required levels of PAX9 and MSX1 during odontogenesis. Herein, we used a loss-of-function CRISPR-Cas9-mediated DUB KO library kit to screen for DUBs that regulate PAX9 and MSX1 protein levels. We identify and demonstrate that USP49 interacts with and deubiquitinates PAX9 and MSX1, thereby extending their protein half-lives. On the other hand, the loss of USP49 reduces the levels of PAX9 and MSX1 proteins, which causes transient retardation of odontogenic differentiation in human dental pulp stem cells and delays the differentiation of human pluripotent stem cells into the neural crest cell lineage. USP49 depletion produced several morphological defects during tooth development, such as reduced dentin growth with shrunken enamel space, and abnormal enamel formation including irregular mineralization. In sum, our results suggest that deubiquitination of PAX9 and MSX1 by USP49 stabilizes their protein levels to facilitate successful odontogenesis.

Non-syndromic familial congenital dental deficiency: two cases report

Congenital dental deficiency can lead to aesthetic and masticatory dysfunction, which have a great effect on the quality of life of patients. Genetic inheritance is the determining factor of congenital dental deficiency, which may follow the pattern of autosomal dominant, recessive, or sex chromosome inheritance. However, the specific genetic mechanisms are not clear. The prevalence of congenital absence of permanent teeth in the general population worldwide are not high, and familial oligodontia in clinically healthy patients is rare. This paper reported two cases of familial non-syndromic congenital teeth loss and included a review of literature referring to the etiology, clinical manifestations, and treatment of congenital dental deficiency.

BMP Signaling Pathway in Dentin Development and Diseases

BMP signaling plays an important role in dentin development. BMPs and antagonists regulate odontoblast differentiation and downstream gene expression via canonical Smad and non-canonical Smad signaling pathways. The interaction of BMPs with their receptors leads to the formation of complexes and the transduction of signals to the canonical Smad signaling pathway (for example, BMP ligands, receptors, and Smads) and the non-canonical Smad signaling pathway (for example, MAPKs, p38, Erk, JNK, and PI3K/Akt) to regulate dental mesenchymal stem cell/progenitor proliferation and differentiation during dentin development and homeostasis. Both the canonical Smad and non-canonical Smad signaling pathways converge at transcription factors, such as Dlx3, Osx, Runx2, and others, to promote the differentiation of dental pulp mesenchymal cells into odontoblasts and downregulated gene expressions, such as those of DSPP and DMP1. Dysregulated BMP signaling causes a number of tooth disorders in humans. Mutation or knockout of BMP signaling-associated genes in mice results in dentin defects which enable a better understanding of the BMP signaling networks underlying odontoblast differentiation and dentin formation. This review summarizes the recent advances in our understanding of BMP signaling in odontoblast differentiation and dentin formation. It includes discussion of the expression of BMPs, their receptors, and the implicated downstream genes during dentinogenesis. In addition, the structures of BMPs, BMP receptors, antagonists, and dysregulation of BMP signaling pathways associated with dentin defects are described.

A novel mutation of SATB2 inhibits odontogenesis of human dental pulp stem cells through Wnt/β-catenin signaling pathway

BACKGROUND

SATB2-associated syndrome (SAS) is a multisystem disorder caused by mutation of human SATB2 gene. Tooth agenesis is one of the most common phenotypes observed in SAS. Our study aimed at identifying novel variant of SATB2 in a patient with SAS, and to investigate the cellular and molecular mechanism of tooth agenesis caused by SATB2 mutation.

METHODS

We applied whole exome sequencing (WES) to identify the novel mutation of SATB2 in a Chinese patient with SAS. Construction and overexpression of wild-type and the mutant vector was performed, followed by functional analysis including flow cytometry assay, fluorescent immunocytochemistry, western blot, quantitative real-time PCR and Alizarin Red S staining to investigate its impact on hDPSCs and the underlying mechanisms.

RESULTS

As a result, we identified a novel frameshift mutation of SATB2 (c. 376_378delinsTT) in a patient with SAS exhibiting tooth agenesis. Human DPSCs transfected with mutant SATB2 showed decreased cell proliferation and odontogenic differentiation capacity compared with hDPSCs transfected with wild-type SATB2 plasmid. Mechanistically, mutant SATB2 failed to translocate into nucleus and distributed in the cytoplasm, failing to activate Wnt/β-catenin signaling pathway, whereas the wild-type SATB2 translocated into the nucleus and upregulated the expression of active β-catenin. When we used Wnt inhibitor XAV939 to treat hDPSCs transfected with wild-type SATB2 plasmid, the increased odontogenic differentiation capacity was attenuated. Furthermore, we found that SATB2 mutation resulted in the upregulation of DKK1 and histone demethylase JHDM1D to inhibit Wnt/β-catenin signaling pathway.

CONCLUSION

We identified a novel frameshift mutation of SATB2 (c.376_378delinsTT, p.Leu126SerfsX6) in a Chinese patient with SATB2-associated syndrome (SAS) exhibiting tooth agenesis. Mechanistically, SATB2 regulated osteo/odontogenesis of human dental pulp stem cells through Wnt/β-catenin signaling pathway by regulating DKK1 and histone demethylase JHDM1D.

Case Report: A Novel COL1A1 Missense Mutation Associated With Dentineogenesis Imperfecta Type I

Background: Osteogenesis imperfecta (OI) is a clinical and genetic disorder that results in bone fragility, blue sclerae and dentineogenesis imperfecta (DGI), which is mainly caused by a mutation in the COL1A1 or COL1A2 genes, which encode type I procollagen. Case Report: A missense mutation (c.1463G > C) in exon 22 of the COL1A1 gene was found using whole-exome sequencing. However, the cases reported herein only exhibited a clinical DGI-I phenotype. There were no cases of bone disease or any other common abnormal symptom caused by a COL1A1 mutation. In addition, the ultrastructural analysis of the tooth affected with non-syndromic DGI-I showed that the abnormal dentine was accompanied by the disruption of odontoblast polarization, a reduced number of odontoblasts, a reduction in hardness and elasticity, and the loss of dentinal tubules, suggesting a severe developmental disorder. We also investigated the odontoblast differentiation ability using dental pulp stem cells (DPSCs) that were isolated from a patient with DGI-I and cultured. Stem cells isolated from patients with DGI-I are important to elucidate their pathogenesis and underlying mechanisms to develop regenerative therapies. Conclusion: This study can provide new insights into the phenotype-genotype association in collagen-associated diseases and improve the clinical diagnosis of OI/DGI-I.

Novel MSX1 variants identified in families with nonsyndromic oligodontia

The goal of this study was to identify MSX1 gene variants in multiple Chinese families with nonsyndromic oligodontia and analyse the functional influence of these variants. Whole-exome sequencing (WES) and Sanger sequencing were performed to identify the causal gene variants in five families with nonsyndromic oligodontia, and a series of bioinformatics databases were used for variant confirmation and functional prediction. Phenotypic characterization of the members of these families was described, and an in vitro analysis was performed for functional evaluation. Five novel MSX1 heterozygous variants were identified: three missense variants [c.662A>C (p.Q221P), c.670C>T (p.R224C), and c.809C>T (p.S270L)], one nonsense variant [c.364G>T (p.G122*)], and one frameshift variant [c.277delG (p.A93Rfs*67)]. Preliminary in vitro studies demonstrated that the subcellular localization of MSX1 was abnormal with the p.Q221P, p.R224C, p.G122*, and p.A93Rfs*67 variants compared to the wild type. Three variants (p.Q221P, p.G122*, and p.A93Rfs*67) were classified as pathogenic or likely pathogenic, while p.S270L and p.R224C were of uncertain significance in the current data. Moreover, we summarized and analysed the MSX1-related tooth agenesis positions and found that the type and variant locus were not related to the severity of tooth loss. Our results expand the variant spectrum of nonsyndromic oligodontia and provide valuable information for genetic counselling.

Phosphorylation of Msx1 promotes cell proliferation through the Fgf9/18-MAPK signaling pathway during embryonic limb development

Msh homeobox (Msx) is a subclass of homeobox transcriptional regulators that control cell lineage development, including the early stage of vertebrate limb development, although the underlying mechanisms are not clear. Here, we demonstrate that Msx1 promotes the proliferation of myoblasts and mesenchymal stem cells (MSCs) by enhancing mitogen-activated protein kinase (MAPK) signaling. Msx1 directly binds to and upregulates the expression of fibroblast growth factor 9 (Fgf9) and Fgf18. Accordingly, knockdown or antibody neutralization of Fgf9/18 inhibits Msx1-activated extracellular signal-regulated kinase 1/2 (Erk1/2) phosphorylation. Mechanistically, we determined that the phosphorylation of Msx1 at Ser136 is critical for enhancing Fgf9 and Fgf18 expression and cell proliferation, and cyclin-dependent kinase 1 (CDK1) is apparently responsible for Ser136 phosphorylation. Furthermore, mesenchymal deletion of Msx1/2 results in decreased Fgf9 and Fgf18 expression and Erk1/2 phosphorylation, which leads to serious defects in limb development in mice. Collectively, our findings established an important function of the Msx1-Fgf-MAPK signaling axis in promoting cell proliferation, thus providing a new mechanistic insight into limb development.

DPSCs Attenuate Experimental Progressive TMJ Arthritis by Inhibiting the STAT1 Pathway

Severe inflammation, progressive cartilage, and bone destruction are typical pathologic changes in temporomandibular joint (TMJ) arthritis and lead to great difficulty for treatment. However, current therapy is inefficient to improve degenerative changes in progressive TMJ arthritis. This study investigated the therapeutic effects of human dental pulp stem cells (DPSCs) on severe inflammatory TMJ diseases. Progressive TMJ arthritis in rats was induced by intra-articular injection of complete Freund's adjuvant and monosodium iodoacetate. DPSCs were injected into the articular cavity to treat rat TMJ arthritis, with normal saline injection as control. Measurement of head withdrawal threshold, micro-computed tomography scanning, and histologic staining were applied to evaluate the severity of TMJ arthritis. Results showed that local injection of DPSCs in rats with TMJ arthritis relieved hyperalgesia and synovial inflammation, attenuated cartilage matrix degradation, and induced bone regeneration. Inflammatory factors TNF-α and IFN-γ were elevated in progressive TMJ arthritis and partially decreased by local injection of DPSCs. MMP3 and MMP13 were elevated in the arthritis + normal saline group and decreased in the arthritis + DPSCs group, which indicated amelioration of matrix degradation. The isolated primary synoviocytes were cocultured with DPSCs after inflammatory factors stimulated to explore the possible biological mechanisms. The expression of MMP3 and MMP13 in synoviocytes was elevated after TNF-α and IFN-γ stimulation and partially reversed by DPSC treatment in the in vitro study. The signal transducer and activator of transcription 1 (STAT1) was activated by inflammatory stimulation and suppressed by DPSC coculture. The upregulation of MMP3 and MMP13 triggered by inflammation was blocked by STAT1-specific inhibitor, suggesting that STAT1 regulated the expression of MMP3 and MMP13. In conclusion, this study demonstrated the possible therapeutic effects of local injection of DPSCs on progressive TMJ arthritis by inhibiting the expression of MMP3 and MMP13 through the STAT1 pathway.

Two novel mutations in MSX1 causing oligodontia

Tooth agenesis is one of the most common developmental anomalies in humans and can affect dental occlusion and speech pronunciation. Research has identified an association between mutations in MSX1, PAX9, EDA, AXIN2, WNT10A, WNT10B and LRP6 and human tooth agenesis. Two unrelated individuals with non-syndromic tooth agenesis and their families were enrolled in this study. Using Sanger sequencing of the candidate genes, we identified two novel mutations: a missense mutation c.572 T>C and a frameshift mutation c.590_594 dup TGTCC, which were both detected in the homeodomain of MSX1. After identifying the mutations, structural modeling and bioinformatics analysis were used to predict the resulting conformational changes in the MSX1 homeodomain. Combined with 3D-structural analysis of other MSX1 mutations, we propose that there is a correlation between the observed phenotypes and alterations in hydrogen bond formation, thereby potentially affecting protein binding.

Loss of homeoprotein Msx1 and Msx2 leading to athletic and kinematic impairment related to the increasing neural excitability of neurons in aberrant neocortex in mice

Although homeoproteins Msx1 and Msx2, the cell-specific transcription regulators, have been proven to play multiple roles in the embryogenesis of bone, muscle and tooth, the functions and mechanisms of Msx1 and Msx2 in the development of the central nervous system of mice after birth are not clear because of the death of Msx1 and Msx1/2 germline-deleted embryo at late gestation of mouse. In current research, Nestin-Cre mice was introduced to generate the central nervous system-specific knockout mice (Nestin-Cre;Msx1,Msx2^fl/fl). We found that besides the falling of the body mass and the brain volume, the cortical tissue sections and staining showed the decreasing thickness of layer II-IV and declining number of vertebral cells in layer V resulting from Msx1/2 deletion. In addition, electrophysiological tests revealed the aberrant action potential parameters of deep pyramidal neurons in Nestin-Cre;Msx1,2^fl/fl mice, which may be related with the ethology impairment displayed in further experiments. We discovered Nestin-Cre;Msx1,2^fl/fl mice had severe impairment in their athletic ability and kinematic learning ability in rotate test, and exhibited hyperactivity in open-field test. Above all, our results revealed that deletion of homeoproteins Msx1 and Msx2 could lead to behavioral disorders and suggested that Msx1 and Msx2 played a crucial role in regulating the development and function of the neocortex. In addition, our current research provided a new mouse model for understanding the pathogenesis of human central nervous system disease.