Expression of TNF-receptor-associated factor genes in murine tooth development

SMURF1 Regulates Periodontal Stem Cell Injury and Osteogenic Differentiation by Regulating TRAF4

OBJECTIVE

This study aimed to investigate the specific role and mechanistic actions of tumor necrosis factor receptor-associated factor 4 (TRAF4) in periodontitis.

METHODS

Human periodontal ligament stem cells (PDLSCs) were exposed to lipopolysaccharide (LPS). Then, real-time quantitative polymerase chain reaction (RT-qPCR) and western blotting (WB) were carried out to determine the mRNA and protein expression levels of Smad ubiquitination regulator 1 (SMURF1). The relationship between TRAF4 and SMURF1, as predicted by the STRING and GeneMANIA databases, was verified by co-immunoprecipitation (Co-IP). Finally, both TRAF4 and SMURF1 were inhibited in PDLSCs by cell transfection, and the regulatory mechanisms involved were investigated by cell counting kit-8 assays, enzyme linked immunosorbent assay, WB, alkaline phosphatase, and alizarin red staining.

RESULTS

The gene and protein expression levels of SMURF1 in PDLSCs increased following LPS induction (p < 0.001); cell viability was decreased (p < 0.001), TRAF4 expression was decreased (p < 0.001), and cell-mineralized nodules were inhibited. Inhibition of SMURF1 expression increased PDLSCs activity and TRAF4 expression levels (p < 0.001), increased the number of cell-mineralized nodules, and enhanced cellular osteogenic capacity (p < 0.001).

CONCLUSIONS

SMURF1 regulates LPS-stimulated injury and improves the capacity for osteogenic differentiation in PDLSCs by downregulating the expression of TRAF4.

Evaluating predictions of the patterning cascade model of crown morphogenesis in the human lower mixed and permanent dentition

OBJECTIVE

The patterning cascade model of crown morphogenesis has been studied extensively in a variety of organisms to elucidate the evolutionary history surrounding postcanine tooth form. The current research is the first to use a large modern human sample to examine whether the crown configuration of lower deciduous and permanent molars aligns with expectations derived from the model. This study has two main goals: 1) to determine if metameric and antimeric pairs significantly differ in size, accessory trait expression, and relative intercusp spacing, and 2) assess whether the relative distance among early-forming cusps accounts for observed variation in accessory cusp expression.

METHODS

Tooth size, intercusp distance, and morphological trait expression data were collected from 3D scans of mandibular dental casts representing participants of the Harvard Solomon Islands Project. Paired tests were utilized to compare tooth size, accessory trait expression, and relative intercusp distance between diphyodont metameres and permanent antimeres. Proportional odds logistic regression was implemented to investigate how the odds of greater accessory cusp expression vary as a function of the distance between early-developing cusps.

RESULTS/SIGNIFICANCE

Comparing paired molars, significant differences were identified for tooth size and cusp 5 expression. Several relative intercusp distances emerged as important predictors of cusp 6 expression, however, results for cusp 5 and cusp 7 did not match expected patterns. These findings support previous quantitative genetic results and suggest the development of neighboring crown structures represents a zero-sum partitioning of cellular territory and resources. As such, this study contributes to a better understanding of the foundations of deciduous and permanent molar crown variation in humans.

[Effects of post-natal inhibition of RANKL on molar eruption and root formation in C57BL/6 mice]

INTRODUCTION

Recent observations performed in the orthodontic department of La Pitié-Salpêtrière hospital in Paris reported an increase of non-familial eruption defects of permanent molars. Our recent data have evidenced the involvement of osteoclasts (OC) in both the eruption and the dental retention processes through the RANKL/RANK/OPG signaling pathway. These facts are at the origin of the hypothesis of the existence of an environmental etiology for those eruption defects that would correspond to the perturbation of cellular autocrine/paracrine signaling pathways as the RANKL/ RANK/OPG.

MATERIALS AND METHODS

C57BL/6 mice were submitted to repeated injections with anti-RANKL neutralizing antibody during the nine days following birth. A phenotypic comparison with transgenic mice overexpressing RANK was performed for the functional characterization of the RANKL/RANK/OPG pathway. The dento-alveolar complex was analyzed using micro-CT for bone density and Masson's trichrome staining for histological examination.

RESULTS

The RANKL transient invalidation of RANKL stopped the molar root development and tooth eruption contrary to transgenic mice overexpressing RANK. The recruitment and the OC activity were strongly impacted.

DISCUSSION

This research is of direct clinical interest in understanding the pathology of eruption as indirect in establishing orthodontic treatment protocols for particular cases.

Gene expression profile data of the developing small intestine of Id2-deficient mice

This article contains data related to the research article entitled “Id2 determines intestinal identity through repression of the foregut transcription factor, Irx5” [1]. Id2 deficient (Id2^−/−) mice developed gastric tumors and heterotopic squamous epithelium in the small intestine. These tumors and heterotopic tissues were derived from ectopic gastric cells and squamous cells formed in the small intestine respectively during development. In this study, microarray data of the developing small intestine of Id2^−/− mice was analyzed.

Immune cell profile of dental pulp tissue treated with zoledronic acid

AIM

To characterize the pulp immune cell profile in the teeth of rats treated with zoledronic acid (ZA).

METHODOLOGY

Male Wistar rats (n = 6 per group) received four intravenous infusions of ZA at doses of 0.04, 0.20 or 1.00 mg kg^-1 ZA or saline (control). On the 70th experimental day, they were euthanized. The first right molar was examined microscopically and submitted to toluidine blue reaction and immunohistochemical for CD68, tumour necrosis Factor (TNF)-α, interleukin (IL)-1β, inducible nitric oxide synthase (iNOS), nuclear factor kappa B (NF-kB) and IL-18 binding protein (IL-18 bp). The presence of ectasic/dilated vessels and inflammatory cells was analysed, and mast cells and mononuclear CD68-positive cells were counted along with the intensity of immunostaining (0-3) for inflammatory markers in odontoblasts and nonodontoblasts pulp cells. The Kruskal-Wallis/Dunn's test (scores or quantitative data) and the chi-squared test (categorical data) were used (GraphPad Prism 5.0, P < 0.05).

RESULTS

There was no differences in the number of animals exhibiting dilated/ectasic blood vessels (P = 0.242) and inflammatory cells (P = 0.489) or in the number of mast cells (P = 1.000). However, there was an increase in mononuclear CD68-positive cells (P = 0.026), immunostaining of TNF-α (P = 0.020), IL-1β (P = 0.027) and iNOS (P = 0.001) in odontoblasts, and IL-1β (P = 0.013) in nonodontoblast pulp cells dose-dependently. NFkB (nucleus and cytoplasm) and IL-18 bp did not differ between groups.

CONCLUSION

ZA modified the immune cell profile in the dental pulp, increasing the number of macrophages and expression of pro-inflammatory markers independent of NFkB.

Opg, Rank, and Rankl in Tooth Development: Co-ordination of Odontogenesis and Osteogenesis

Osteoprotegerin (OPG), receptor activator of nuclear factor-κB (RANK), and RANK ligand (RANKL) are mediators of various cellular interactions, including bone metabolism. We analyzed expression of these three genes during murine odontogenesis from epithelial thickening to cytodifferentiation stages. Opg showed expression in the thickening and bud epithelium. Expression of Opg and Rank was observed in both the internal and the external enamel epithelium as well as in the dental papilla mesenchyme. Although Rankl expression was not detected in tooth epithelium or mesenchyme, it was expressed in pre-osteogenic mesenchymal cells close to developing tooth germs. All three genes were detected in developing dentary bone at P0. The addition of exogenous OPG to explant cultures of tooth primordia produced a delay in tooth development that resulted in reduced mineralization. We propose that the spatiotemporal expression of these molecules in early tooth and bone primordia cells has a role in co-ordinating bone and tooth development.

Congenital tracheal malformation in cystic fibrosis transmembrane conductance regulator-deficient mice

In cystic fibrosis (CF) patients, the major alteration in pulmonary function is due to peripheral airway obstruction. In the present study, we investigated the possibility that alterations in the extrathoracic airways, particularly in the trachea that expresses high levels of CFTR (CF transmembrane conductance regulator), may contribute to respiratory dysfunction. We performed morphological analyses of the trachea and airway functional studies in adult Cftr knockout (Cftr(-/-)) and F508del-CFTR mice and their controls. Macroscopic and histological examination of the trachea showed the presence of one to seven disrupted or incomplete cartilage rings in Cftr(-/-) mice (23/25) while only a few Cftr(+/+) mice (6/25) had one abnormal ring. Tracheal defects were mainly localized in the proximal trachea. In 14 Cftr(-/-) mice, frontal disruption of the first three to six rings below the cricoid cartilage were associated with upper tracheal constriction. Similar tracheal abnormalities were detected in adult F508del-CFTR and in newborn Cftr(-/-) and F508del-CFTR mice. Tracheal and ventilatory function analyses showed in Cftr(-/-) mice a decreased contractile response of the proximal trachea and a reduced breathing rate due to an increase in the inspiratory and expiratory times. In F508del-CFTR mice, the expiratory time was longer than in controls. Therefore, these structural and functional abnormalities detected in adult and newborn CF mouse models may represent congenital malformations related to CFTR dysfunction. These results raise important questions concerning the mechanisms governing tracheal development within the context of CFTR protein dysfunction and the implication of such abnormalities in the pathogenesis of airway disease in CF.

Making a tooth: growth factors, transcription factors, and stem cells

Mammalian tooth development is largely dependent on sequential and reciprocal epithelial-mesenchymal interactions. These processes involve a series of inductive and permissive interactions that result in the determination, differentiation, and organization of odontogenic tissues. Multiple signaling molecules, including BMPs, FGFs, Shh, and Wnt proteins, have been implicated in mediating these tissue interactions. Transcription factors participate in epithelial-mesenchymal interactions via linking the signaling loops between tissue layers by responding to inductive signals and regulating the expression of other signaling molecules. Adult stem cells are highly plastic and multipotent. These cells including dental pulp stem cells and bone marrow stromal cells could be reprogrammed into odontogenic fate and participated in tooth formation. Recent progress in the studies of molecular basis of tooth development, adult stem cell biology, and regeneration will provide fundamental knowledge for the realization of human tooth regeneration in the near future.

TRAF4, the unique family member

The fourth member of the TRAF protein family (TRAF4) presents several characteristics that distinguish it from the other members of the family. These characteristics concern the primary sequence of the protein, a strong evolutionary conservation, and a tightly regulated physiological expression during development. The subcellular localization of TRAF4 is controversial as it has been detected at the cell membrane, in the cytoplasm and in the nucleus. Using mouse and fly models, it has been established that TRAF4 is a key molecule in diverse ontogenic processes, particularly in the nervous system. However, the molecular mechanisms of action of TRAF4 remain evasive as it was found to interact with diverse types of proteins, leading either to pro-apoptotic or anti-apoptotic functions. Finally, few studies implicated TRAF4 in human diseases.

The Ectodysplasin and NFkappaB signalling pathways in odontogenesis

Hypohidrotic ectodermal dysplasia (HED) is a congenital disorder affecting organs of ectodermal origin including teeth, hair and sweat glands. Defects in Ectodysplasin (tabby), Edar (downless) and Edar associated death domain (Edaradd) (crinkled) cause HED in both humans and mice. Ectodysplasin is a tumour necrosis factor (TNF) superfamily member whose downstream signalling is transduced by the inhibitor of kappaB kinase (IKK) complex and inhibitors of kappaB (IkappaB) to activate the transcription factor NFkappaB. NFkappaB signalling is involved in a wide range of cellular processes and at each stage the different family members must be tightly regulated for each function. Recent data have demonstrated the importance of this signalling pathway in odontogenesis, particularly in the formation of cusps. Here we review recent advances in our understanding of Ectodysplasin/NFkappaB signalling in tooth development and in particular the central role of the IKK complex.

Mouse tooth development time sequence determination for the ICR/Jcl strain

To establish the normal dental development pattern of the ICR/Jcl strain of mouse, we analyzed a significant number of observations of the different developmental stages of the first mandibular molar, accurately recording the chronology of their daily embryonic development. Proliferation of the dental sheet began at day 12.5 in utero (E-12.5), the bud stage appeared at days E-13.5 and E-14.5, the cap stage was observed at days E-14.5, E-15.5 and E-16.5 and the early bell stage at day E-17.5. The presence of predentin was observed at day E-18.5 and dentin was observed 1 and 2 days after birth (D-1 and D-2). The late bell stage with presence of enamel was detected more than 3 days after birth. Embryonic and dental development in the ICR/Jcl strain of mouse is faster than in other well-known strains. The establishment of this developmental pattern will be useful for future investigations of transgenic mice.

TNF signalling in tooth development

Mammalian tooth development has served as an excellent model system to investigate the intricate, interactive mechanisms of patterning, morphogenesis and cytodifferentiation during organogenesis. Teeth develop from interactions between epithelium and neural crest-derived (ecto)mesenchyme that are largely mediated by ligand-receptor signalling. It is well-established that signalling molecules of the Bmp, Fgf, Wnt and Hedgehog families, are involved at multiple stages of tooth development. Recently, however, a specific role for molecules belonging to the TNF-family of ligands in tooth morphogenesis has been identified, suggesting that this pathway, acting to activate NF-kappaB, has played an important role in the development and evolution of tooth number and shape.

Traf6 is essential for murine tooth cusp morphogenesis

Ectodermal appendages such as skin, hair, teeth, and sweat glands are affected in patients with hypohidrotic (anhydrotic) ectodermal dysplasia (HED). It has been established that mutations in the tumor necrosis factor (TNF) superfamily of molecules, i.e., ectodysplasin (EDA), EDA receptor (EDAR), and EDAR-associated death domain (EDARADD; the intracellular adaptor for EDAR), are responsible for several forms of HED in humans and mice. We show here by in situ hybridisation that another TNF family (orphan) receptor, TROY (also known TAJ, TAJ-alpha, TRADE, and TNFRSF19), is strongly coexpressed with Edar in the epithelial enamel knot signalling centres that are believe to regulate cuspal morphogenesis during murine tooth development. Traf6 is known to function as an intracellular adaptor protein for Troy and examination of Traf6 mutant mice revealed abnormalities in molar teeth that are similar but more severe than those produced by mutations in Eda signalling molecules. This finding suggests that, in additional to ectodysplasin, another TNF pathway involving Troy/Traf6 is involved in molar tooth cusp formation and identifies an essential role for a Traf in tooth development. Developmental Dynamics 229:131-135, 2004.