Local application of Usag-1 siRNA can promote tooth regeneration in Runx2-deficient mice

Resilience of the replacing dentition in adult reptiles

The dentition is critical to animal survival and teeth are present in modern vertebrates including teleost fish, sharks, amphibians, mammals and reptiles. The developmental processes that give rise to teeth are not just preserved through evolution but also share high level of similarity with the embryogenesis of other ectodermal organs. In this review we go beyond the embryonic phase of tooth development to life-long tooth replacement. We will address the origins of successional teeth, the location of putative tissue-resident stem cells, how de novo tooth formation continues throughout life and how teeth are shed in a spatially and temporally controlled manner. We review the evidence that the dental epithelium, which is the earliest recognizable dental structure in the reptilian dentition, serves as a putative niche for tissue-resident epithelial stem cells and recent molecular findings from transcriptomics carried out in reptilian dentitions. We discuss how odontoclasts resorb the primary tooth allowing eruption of the successional tooth. The reptiles, particularly lizards, are emerging as some of the most accessible animals to study tooth replacement which has relevance to evolution of the dentition and human dental disorders.

Development of a new antibody drug to treat congenital tooth agenesis

BACKGROUND

This study aimed to develop a therapeutic agent promoting teeth regeneration from autologous tissues for congenital tooth agenesis, specifically for hypodontia (≤ 5 missing congenital teeth, 10% prevalence) and oligodontia (≥ 6 missing congenital teeth, 0.1% prevalence).

HIGHLIGHT

We studied mice genetically deficient in the USAG-1 protein, an antagonist of BMP/Wnt which forms excessive teeth. We identified USAG-1 as a target molecule for increasing the number of teeth. Crossing USAG-1-deficient mice with a congenital tooth agenesis model restored tooth formation. We produced anti-USAG-1 neutralizing antibodies as potential therapeutic agents for the treatment of congenital tooth agenesis. Mice anti-USAG-1 neutralizing antibodies can potentially rescue the developmentally arrested tooth germ programmed to a certain tooth type. A humanized anti-USAG-1 antibody was developed as the final candidate.

CONCLUSION

Targeting USAG-1 shows promise for treating missing congenital tooth. Anti-USAG-1 neutralizing antibodies have been developed and will progress towards clinical trials, which may regenerate missing congenital teeth in conditions, such as hypodontia and oligodontia. The protocol framework for a phase 1 study has been finalized, and preparation for future studies is underway.

Current Trends, Advances, and Challenges of Tissue Engineering-Based Approaches of Tooth Regeneration: A Review of the Literature

INTRODUCTION

Tooth loss is a significant health issue. Currently, this situation is often treated with the use of synthetic materials such as implants and prostheses. However, these treatment modalities do not fully meet patients' biological and mechanical needs and have limited longevity. Regenerative medicine focuses on the restoration of patients' natural tissues via tissue engineering techniques instead of rehabilitating with artificial appliances. Therefore, a tissue-engineered tooth regeneration strategy seems like a promising option to treat tooth loss.

OBJECTIVE

This review aims to demonstrate recent advances in tooth regeneration strategies and discoveries about underlying mechanisms and pathways of tooth formation.

RESULTS AND DISCUSSION

Whole tooth regeneration, tooth root formation, and dentin-pulp organoid generation have been achieved by using different seed cells and various materials for scaffold production. Bioactive agents are critical elements for the induction of cells into odontoblast or ameloblast lineage. Some substantial pathways enrolled in tooth development have been figured out, helping researchers design their experiments more effectively and aligned with the natural process of tooth formation.

CONCLUSION

According to current knowledge, tooth regeneration is possible in case of proper selection of stem cells, appropriate design and manufacturing of a biocompatible scaffold, and meticulous application of bioactive agents for odontogenic induction. Understanding innate odontogenesis pathways play a crucial role in accurately planning regenerative therapeutic interventions in order to reproduce teeth.

Extracellular vesicles secreted from mouse muscle cells improve delayed bone repair in diabetic mice

Humoral factors that are secreted from skeletal muscles can regulate bone metabolism and contribute to muscle-bone relationships. Although extracellular vesicles (EVs) play important roles in physiological and pathophysiological processes, the roles of EVs that are secreted from skeletal muscles in bone repair have remained unclear. In the present study, we investigated the effects of the local administration of muscle cell-derived EVs on bone repair in control and streptozotocin-treated diabetic female mice. Muscle cell-derived EVs (Myo-EVs) were isolated from the conditioned medium from mouse muscle C2C12 cells by ultracentrifugation, after which Myo-EVs and gelatin hydrogel sheets were transplanted on femoral bone defect sites. The local administration of Myo-EVs significantly improved delayed bone repair that was induced by the diabetic state in mice 9 days after surgery. Moreover, this administration significantly enhanced the ratio of bone volume to tissue volume at the damaged sites 9 days after surgery in the control mice. Moreover, the local administration of Myo-EVs significantly blunted the number of Osterix-positive cells that were suppressed by the diabetic state at the damage sites after bone injury in mice. Additionally, Myo-EVs significantly blunted the mRNA levels of Osterix and alkaline phosphatase (ALP), and ALP activity was suppressed by advanced glycation end product 3 in ST2 cells that were treated with bone morphogenetic protein-2. In conclusion, we have shown for the first time that the local administration of Myo-EVs improves delayed bone repair that is induced by the diabetic state through an enhancement of osteoblastic differentiation in female mice.

Advances in tooth agenesis and tooth regeneration

The lack of treatment options for congenital (0.1%) and partial (10%) tooth anomalies highlights the need to develop innovative strategies. Over two decades of dedicated research have led to breakthroughs in the treatment of congenital and acquired tooth loss. We revealed that by inactivating USAG-1, congenital tooth agenesis can be successfully ameliorated during early tooth development and that the inactivation promotes late-stage tooth morphogenesis in double knockout mice. Furthermore, Anti- USAG-1 antibody treatment in mice is effective in tooth regeneration and can be a breakthrough in treating tooth anomalies in humans. With approximately 0.1% of the population suffering from congenital tooth agenesis and 10% of children worldwide suffering from partial tooth loss, early diagnosis will improve outcomes and the quality of life of patients. Understanding the role of pathogenic USAG-1 variants, their interacting gene partners, and their protein functions will help develop critical biomarkers. Advances in next-generation sequencing, mass spectrometry, and imaging technologies will assist in developing companion and predictive biomarkers to help identify patients who will benefit from tooth regeneration.

Tooth number abnormality: from bench to bedside

Tooth number abnormality is one of the most common dental developmental diseases, which includes both tooth agenesis and supernumerary teeth. Tooth development is regulated by numerous developmental signals, such as the well-known Wnt, BMP, FGF, Shh and Eda pathways, which mediate the ongoing complex interactions between epithelium and mesenchyme. Abnormal expression of these crutial signalling during this process may eventually lead to the development of anomalies in tooth number; however, the underlying mechanisms remain elusive. In this review, we summarized the major process of tooth development, the latest progress of mechanism studies and newly reported clinical investigations of tooth number abnormality. In addition, potential treatment approaches for tooth number abnormality based on developmental biology are also discussed. This review not only provides a reference for the diagnosis and treatment of tooth number abnormality in clinical practice but also facilitates the translation of basic research to the clinical application.

Role of Wnt/β-catenin signaling pathway in ameloblast differentiation in relevance to dental fluorosis

Excess consumption of fluoride during the development of tooth enamel will cause dental fluorosis, but the exact molecular mechanisms remain to be elucidated. Circadian rhythm is implicated in many physiological processes and various diseases. There is increasing evidence indicates that ameloblast differentiation is under the control of clock genes. However, it has not been reported whether fluoride regulates ameloblast differentiation through clock genes and the downstream PPARγ. To explore the effect of fluoride on ameloblast differentiation and the underlying regulatory mechanism, we used both rat dental fluorosis model and an ameloblast cell line LS8 to conduct a series of experiments. Our results showed that fluoride significantly reduced the expression of PCNA, RUNX2 and MMP9 in rat ameloblasts and LS8 cells (P < 0.05). Fluoride increased nuclear translocation of β-catenin in vivo and in vitro, and 0.1 μg/ml Dkk1 pretreatment ameliorated the decreased expression of CXXC5, RUNX2 and MMP9 induced by fluoride. Furthermore, we found fluoride significantly inhibited the expression of Clock, Bmal1, Per2 and PPARγ in rat mandibular ameloblasts and LS8 cells by immunostaining, qPCR and Western blot (P < 0.05). Flow cytometry analysis showed that fluoride promoted ROS generation. Remarkably, 50 μM resveratrol significantly ameliorated the inhibitory effect of fluoride on ameloblast differentiation markers, clock genes and PPARγ, and inhibited the Wnt/β-catenin signaling (P < 0.05). Taken together, these findings suggested that excessive fluoride promoted ROS generation, leading to the inhibition of clock genes, which resulted in reduced PPARγ and activated Wnt/β-catenin signaling pathway, thus inhibiting ameloblast differentiation and matrix degradation. This study provides a better understanding of the molecular mechanism of enamel defects in dental fluorosis.

Irisin improves delayed bone repair in diabetic female mice

INTRODUCTION

Irisin is a proteolytic product of fibronectin type II domain-containing 5, which is related to the improvement in glucose metabolism. Numerous studies have suggested that irisin is a crucial myokine linking muscle to bone in physiological and pathophysiological states.

MATERIALS AND METHODS

We examined the effects of local irisin administration with gelatin hydrogel sheets and intraperitoneal injection of irisin on the delayed femoral bone repair caused by streptozotocin (STZ)-induced diabetes in female mice. We analyzed the femurs of mice using quantitative computed tomography and histological analyses and then measured the mRNA levels in the damaged mouse tissues.

RESULTS

Local irisin administration significantly blunted the delayed bone repair induced by STZ 10 days after a femoral bone defect was generated. Local irisin administration significantly blunted the number of Osterix-positive cells that were suppressed by STZ at the damaged site 4 days after a femoral bone defect was generated, although it did not affect the mRNA levels of chondrogenic and adipogenic genes 4 days after bone injury in the presence or absence of diabetes. On the other hand, intraperitoneal injection of irisin did not affect delayed bone repair induced by STZ 10 days after bone injury. Irisin significantly blunted the decrease in Osterix mRNA levels induced by advanced glycation end products or high-glucose conditions in ST2 cells in the presence of bone morphogenetic protein-2.

CONCLUSIONS

We first showed that local irisin administration with gelatin hydrogel sheets improves the delayed bone repair induced by diabetic state partially by enhancing osteoblastic differentiation.

Exosome mediated biological functions within skeletal microenvironment

Exosomes are membranous lipid vesicles fused with intracellular multicellular bodies that are released into the extracellular environment. They contain bioactive substances, including proteins, RNAs, lipids, and cytokine receptors. Exosomes in the skeletal microenvironment are derived from a variety of cells such as bone marrow mesenchymal stem cells (BMSCs), osteoblasts, osteoclasts, and osteocytes. Their biological function is key in paracrine or endocrine signaling. Exosomes play a role in bone remodeling by regulating cell proliferation and differentiation. Genetic engineering technology combined with exosome-based drug delivery can therapy bone metabolic diseases. In this review, we summarized the pathways of exosomes derived from different skeletal cells (i.e., BMSCs, osteoblasts, osteocytes, and osteoclasts) regulate the skeletal microenvironment through proteins, mRNAs, and non-coding RNAs. By exploring the role of exosomes in the skeletal microenvironment, we provide a theoretical basis for the clinical treatment of bone-related metabolic diseases, which may lay the foundation to improve bone tumor microenvironments, alleviate drug resistance in patients.