Irma Thesleff-Orthodontist who became a developmental biologist.

Irma Thesleff is one of the leading scholars in developmental biology. She and her research group have clarified the mysteries of tooth development. For several decades, her research of very high quality has focused on morphogenesis and resulted in an understanding of the highly complex signaling networks. Irma Thesleff has been duly recognized both in the domestic and international context. Her research continues despite her retirement.

Adipose Tissue as a Strategic Source of Mesenchymal Stem Cells in Bone Regeneration: A Topical Review on the Most Promising Craniomaxillofacial Applications.

Bone regeneration in craniomaxillofacial surgery represents an issue that involves both surgical and aesthetic aspects. The most recent studies on bone tissue engineering involving adipose-derived stromal/stem cells (ASCs) have clearly demonstrated that such cells can play a crucial role in the treatment of craniomaxillofacial defects, given their strong commitment towards the osteogenic phenotype. A deeper knowledge of the molecular mechanisms underlying ASCs is crucial for a correct understanding of the potentialities of ASCs-based therapies in the most complex maxillofacial applications. In this topical review, we analyzed the molecular mechanisms of ASCs related to their support toward angiogenesis and osteogenesis, during bone regeneration. Moreover, we analyzed both case reports and clinical trials reporting the most promising clinical applications of ASCs in the treatment of craniomaxillofacial defects. Our study aimed to report the main molecular and clinical features shown by ASCs, used as a therapeutic support in bone engineering, as compared to the use of conventional autologous and allogeneic bone grafts.

Essential Roles of Dopamine and Serotonin in Tooth Repair: Functional Interplay Between Odontogenic Stem Cells and Platelets.

Characterizing stem cell intrinsic functions is an ongoing challenge for cell therapies. Here, we report that two independent A4 and H8 stem cell lines isolated from mouse molar pulp display the overall functions of bioaminergic cells. Both clones produce neurotrophins and synthesize, catabolize, store, and transport serotonin (5-hydroxytryptamine [5-HT]) and dopamine (DA). They express 5-HT1D,2B,7 and D1,3 autoreceptors, which render pulpal stem cells competent to respond to circulating 5-HT and DA. We show that injury-activated platelets are the source of systemic 5-HT and DA necessary for dental repair since natural dentin reparation is impaired in two rat models with monoamine storage-deficient blood platelets. Moreover, selective inhibition of either D1, D3, 5-HT2B, or 5-HT7 receptor within the pulp of wild-type rat molars after lesion alters the reparative process. Altogether our data argue that 5-HT and DA coreleased by pulp injury-activated platelets are critical for stem cell-mediated dental repair through 5-HT and DA receptor signalings.

Is Pulp Inflammation a Prerequisite for Pulp Healing and Regeneration?

The importance of inflammation has been underestimated in pulpal healing, and in the past, it has been considered only as an undesirable effect. Associated with moderate inflammation, necrosis includes pyroptosis, apoptosis, and nemosis. There are now evidences that inflammation is a prerequisite for pulp healing, with series of events ahead of regeneration. Immunocompetent cells are recruited in the apical part. They slide along the root and migrate toward the crown. Due to the high alkalinity of the capping agent, pulp cells display mild inflammation, proliferate, and increase in number and size and initiate mineralization. Pulp fibroblasts become odontoblast-like cells producing type I collagen, alkaline phosphatase, and SPARC/osteonectin. Molecules of the SIBLING family, matrix metalloproteinases, and vascular and nerve mediators are also implicated in the formation of a reparative dentinal bridge, osteo/orthodentin closing the pulp exposure. Beneath a calciotraumatic line, a thin layer identified as reactionary dentin underlines the periphery of the pulp chamber. Inflammatory and/or noninflammatory processes contribute to produce a reparative dentinal bridge closing the pulp exposure, with minute canaliculi and large tunnel defects. Depending on the form and severity of the inflammatory and noninflammatory processes, and according to the capping agent, pulp reactions are induced specifically.

Deletion of serotonin 2B receptor provokes structural alterations of mouse dental tissues.

Rampant caries and periodontal diseases occur in patients treated with antidepressants such as serotonin reuptake inhibitors (SRIs; e.g., Prozac) which target the serotonin transporter (SERT). As the serotonin 2B receptor (5HT2BR) regulates SERT functionality and capacity to recognize SRIs, we investigated the potential role of 5HT2BR on dental tissues by exploiting 5HT2BR knockout (KO) mice. Compared to wild-type (WT) mice, several structural differences were identified in the teeth of KO mice. In the molar of KO mice, rod curvatures and twisting were altered compared to WT mice, suggesting involvement of 5HT2BR at early stages of enamel formation. The volume of the KO enamel layer was also reduced, and larger porosities were observed in the prismatic enamel, with smaller crystallite thickness. Crystallite pattern disorganization and occlusal abrasion were enhanced in female KO mice, indicating a sexual dimorphism. In the incisor, no difference was detected in the width of the enamel layer between KO and WT mice; however, enamel maturation differed in absence of 5HT2BR. Specifically, the outer aprismatic enamel border was 1.5- to 2-fold larger in KO compared to WT mice, together with a decreased etching pattern. Finally, although no noticeable difference was observed in dentin, the micro-CT three-dimensional pulp reconstruction evidenced a decrease in both length and width of dentin formation in the root canals of the KO versus WT mice. These data provide evidence that 5HT2BR-mediated signaling pathways are involved in enamel formation and dentinogenesis.

Plithotaxis, a collective cell migration, regulates the sliding of proliferating pulp cells located in the apical niche.

Using the proliferating cell nuclear antigen (PCNA) immunostaining, we previously identified, after pulp exposure, three zones of proliferating cells in the rat molar pulp. Zones I and II were in the crown near the pulp. Zone III was near the apex revealing a recruitment of mitotic cells at distance from the lesion. To gain further insight into the spatio-temporal evolution of proliferating pulp cells of zone III, we performed a longitudinal study of PCNA staining in rat molar mesial root at 3, 8, and 15 d after pulp exposure associated to implantation of unloaded or amelogenin loaded agarose beads. At day 3 after implantation, PCNA-positive cells were located in the central part of the radicular pulp. At day 8, PCNA-labeled cells were aligned in the lateral part of the pulp beneath the odontoblast/sub-odontoblast layer. At day 15, PCNA labeling became undetectable in the root and was located in the coronal pulp. These results suggest that after pulp exposure, PCNA-positive cells may migrate from the central part of the radicular pulp to the sub-odontoblast cell layer and then from the apical root to the crown. Electron microscopy and immunostaining analysis showed that pulpal cells were linked by desmosome-like and gap-junctions. Extracellular matrix was composed of thin collagen fibrils associated with glycosaminoglycans favoring cell mobility. These data suggest that the syncytium-like structure formed by pulp radicular cells may be a pre-request for plithotaxis, a collective cell migration process. This emergent mechanism may govern pulp healing and regeneration after dental lesion.

A deletion in the gene encoding sphingomyelin phosphodiesterase 3 (Smpd3) results in osteogenesis and dentinogenesis imperfecta in the mouse.

The mouse mutation fragilitas ossium (fro) leads to a syndrome of severe osteogenesis and dentinogenesis imperfecta with no detectable collagen defect. Positional cloning of the locus identified a deletion in the gene encoding neutral sphingomyelin phosphodiesterase 3 (Smpd3) that led to complete loss of enzymatic activity. Our knowledge of SMPD3 function is consistent with the pathology observed in mutant mice and provides new insight into human pathologies.

[François Gros, my boss]. / François Gros, mon patron.

This article shares the author's memories of his collaborations with François Gros when the latter was Professor at the University of Paris 7, then Director of the Institut Pasteur, then President of the Pasteur-Weizmann Council. He underlines the major contributions of "his boss" in the exercise of these functions.

Cet article fait part de souvenirs de l'auteur relatifs à ses collaborations avec François Gros lorsque ce dernier était professeur à l'université Paris 7, puis directeur de l'Institut Pasteur, puis président du Conseil Pasteur-Weizmann. Il souligne les contributions majeures de «  son patron  ¼ dans l'exercice de ces fonctions.

Stem Cell and Oxidative Stress-Inflammation Cycle.

Under a variety of physical and experimental settings, stem cells are able to self-renew and differentiate into specialized adult cells. MSCs (mesenchymal stromal/stem cells) are multipotent stem cells present in a wide range of fetal, embryonic, and adult tissues. They are the progenitors of a variety of specialized cells and are considered crucial tools in tissue engineering. MSCs, derived from various tissues, including cord blood, placenta, bone marrow, and dental tissues, have been extensively examined in tissue repair, immune modulation, etc. Increasing the vitality of MSCs and restoring cellular mechanisms are important factors in treatment success. Oxidative stress harms cellular molecules such as DNA, proteins, and lipids due to the overproduction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in cells and tissues or insufficiency of antioxidant systems that can inactivate them. Oxidative stress has a close link with inflammation as a pathophysiological process. ROS can mediate the expression of proinflammatory genes via intracellular signaling pathways and initiate the chronic inflammatory state. At the same time, inflammatory cells secrete a large number of reactive species that cause increased oxidative stress at sites of inflammation. In inflammatory diseases, the differentiation of stem cells and the regenerative and wound healing process can be affected differently by the increase of oxidative stress. Recent studies have indicated that dental pulp stem cells (DPSCs), as a resource of adult stem cells, are an attractive option for cell therapy in diseases such as neurological diseases, diabetes, cardiological diseases, etc., as well as its treatment potential in pulp inflammation. The future of oxidative stressinflammation cycle and/or ageing therapies involves the selective elimination of senescent cells, also known as senolysis, which prevents various age-related diseases. Most pathologies are implicated on the effects of ageing without exerting undesirable side effects.

Amelogenin exons 8 and 9 encoded peptide enhances leucine rich amelogenin peptide mediated dental pulp repair.

Amelogenins containing exons 8 and 9 are alternatively spliced variants of amelogenin. Some amelogenin spliced variants have been found to promote pulp regeneration following pulp exposure. The function of the amelogenin spliced variants with the exons 8 and 9 remains unknown. In this study, we synthesized recombinant leucine rich amelogenin peptide (LRAP, A-4), LRAP plus exons 8 and 9 peptide (LRAP 8, 9) or exons 8 and 9 peptide (P89), to determine their effects on odontoblasts. In vivo analyses were completed following the insertion of agarose beads containing LRAP or LRAP 8, 9 into exposed cavity preparations of rat molars. After 8, 15 or 30 days' exposure, the pulp tissues were analyzed for changes in histomorphometry and cell proliferation by PCNA stainings. In vitro analyses included the effects of the addition of the recombinant proteins or peptide on cell proliferation, differentiation and adhesion of postnatal human dental pulp cells (DPCs). These studies showed that in vivo LRAP 8, 9 enhanced the reparative dentin formation as compared to LRAP. In vitro LRAP 8, 9 promoted DPC proliferation and differentiation to a greater extent than LRAP. These data suggest that amelogenin exons 8 and 9 may be useful in amelogenin-mediated pulp repair.

Differential effects of fibromodulin deficiency on mouse mandibular bones and teeth: a micro-CT time course study.

Fibromodulin (Fmod) is a keratan sulfate small leucine-rich proteoglycan which is enriched in bones and teeth. In order to determine its functions on bone and tooth mineralization we characterized the phenotype of Fmod-deficient (Fmod-KO) mice using a new-generation microfocus computerized tomography system (micro-CT) and software allowing advanced visualization of 3-D data. Three-week-old and 10- week-old Fmod-KO mandibles and teeth were compared with those of age-matched wild-type (WT) mice. In both young and mature mice the Fmod-KO mandibles were hypomineralized, especially the posterior (proximal) part of the mandible as it appeared to be the main target of the molecule deficiency whereas less extensive alterations were found in the alveolar bone. In transverse sections, larger marrow spaces were observed in the Fmod-KO mice compared with age-matched young or mature WT mice. Quantitative evaluation of the pulp volume of the first molar and 3-D reconstructions suggested that dentinogenesis was diminished in 3-week-old Fmod-KO teeth. In contrast, increased dentin formation was found in 10-week-old Fmod-KO mice and it was accompanied by a reduced pulp volume. Thus, the differential effects of Fmod deficiency on bones and teeth appear to diverge in adult mice. This may result from the previously reported differences in the molecular weight of Fmod in the 2 tissues or from compensatory mechanisms due to the overexpression of DSP and DMP-1 in the dental pulp of Fmod-KO. It is also possible that a single molecule plays diverging roles in a tissue-specific or region-specific manner.

Enamel alterations in serotonin 2B receptor knockout mice.

The role of the serotonin 2B receptor (5-HT(2B) R) in enamel formation and mineralization was explored in adult 5HT(2B) R knockout (KO) mice compared with wild-type (WT) mice. In the molar, quantitative data obtained by micro-computed tomography imaging showed that the overall volume of the enamel layer was firmly reduced in KO mice. Defective mineralization was ascertained by energy-dispersive X-ray microanalysis. We also observed, using scanning electron microscopy, that parazones in the KO mice included two or three helicoidally twisted rods within Hunter-Schreger bands, instead of a single rod, as found in the WT mice. Minor disturbances were also detected in the incisors of KO mice. Structural modifications, thinner enamel crystallites, and porosities observed in KO mice indicate that the 5-HT(2B) R-mediated signaling pathways as part of the enamel formation process. These data provide a basis for evaluating the role of 5-HT(2B) R in ameloblast functions. Defects observed in the mineralization and structure of enamel in KO mice highlight that the 5-HT(2B) R interferes with the mechanisms directing amelogenesis.

Undesirable and adverse effects of tooth-whitening products: a review.

Hydrogen peroxide (H(2)O(2)) is a powerful oxidising agent. It gives rise to agents known to be effective bleaching agents. The mechanisms of bleaching involve the degradation of the extracellular matrix and oxidation of chromophores located within enamel and dentin. However, H(2)O(2) produces also local undesirable effects on tooth structures and oral mucosa. In clinical conditions, the daily low-level doses used to produce tooth whitening never generate general acute and sub-acute toxic effects. Genotoxicity and carcinogenicity only occur at concentrations that are never reached during dental treatments. Some transient adverse effects have been reported on the oral mucosa and the digestive tract if the product is swallowed. Local effects may occur on the oral mucosa and dental tissues during whitening, namely, pulp sensitivity, cervical resorption, release of selected components of dental restorative materials, and alteration of the enamel surface. Most of the local effects are dependent of the technique and concentration of the product so far used, but as the results of bleaching obtained are not stable, repeated treatments add to the adverse effects. The informed decision to administer or not and the control of bleaching effects should stand in the hand of dental surgeons and certainly not as it appears at present, as cosmetics sold without any restriction despite the potential health hazards of peroxides.

Adaptive amelogenesis during unimpeded eruption of rat mandibular incisor.

The aim of the study was to see whether the length of the enamel secretion zone in unimpeded rat incisors, measured precisely, is in agreement with the observed decrease in enamel thickness. Unimpeded eruption of mandibular incisors of five experimental and two control rats was induced by cutting off the erupted part of the incisors three times per week for 5 weeks. The length of the zone of enamel secretion in unimpeded and impeded control incisors was measured on longitudinal and serial transverse histological sections of fixed, demineralised and embedded hemimandibles. Impeded contralateral incisors were also included in the study. The length of the zone of enamel secretion in unimpeded incisors showed an increase to 8,398 ± 558 µm, that is 161% of the length in control incisors (5,213 ± 95 µm). The contralateral incisor showed a reduction in eruption rate, in length of the secretion zone, and the whole tooth was shifted somewhat apically. The measured length of the secretion zone is in agreement with the observed thickness of enamel (98 µm) in unimpeded incisors. The reduced eruption rate and the apical shift of the contralateral incisor are probably due to an increased occlusal load.

Fibromodulin-deficient mice reveal dual functions for fibromodulin in regulating dental tissue and alveolar bone formation.

The extracellular matrix of newborn, 7- and 21-day-old fibromodulin-deficient (Fmod KO) mice was compared with age-matched wild-type (WT) mice. Western blotting of proteins from 21-day-old WT mice revealed that the molecular weight of Fmod is smaller in dental tissues (approx. 40 kDa) compared to alveolar bone extracts (approx. 52 kDa). Dentin matrix protein1 (DMP1) was slightly increased in Fmod KO versus WT tooth extracts. After chondroitinase ABC digestion, dentin sialophosphoprotein (DSPP) appeared as 2 strong bands (approx. 150 and 70 kDa) in incisors from 21-day-old Fmod KO mice, whereas the smaller-sized species of DSPP was nearly absent in WT molars and no difference was detected between WT and KO mice in molars. Dentin mineralization was altered in newborn and 7-day-old KO mice, but seemed normal in 21-day-old KO mice. DMP1 and DSPP may be involved in compensatory mechanisms. The enamel had a twisted appearance and looked porous at day 21 in KO incisor, and the outer aprismatic layer was missing in the molar. Alveolar bone formation was enhanced in Fmod KO mice at days 0 and 7, whereas no difference was detected at day 21. We conclude that Fmod may control dental tissue formation and early maturation, where it acts mostly as an inhibitor in alveolar bone accumulation, excerpting its effects only at early developing stages. These dual functions may be related to the different forms of Fmod found in bone versus teeth.

Dentin noncollagenous matrix proteins in familial hypophosphatemic rickets.

Familial hypophosphatemic rickets is transmitted in most cases as an X-linked dominant trait and results from the mutation of the PHEX gene predominantly expressed in osteoblast and odontoblast. Patients with rickets have been reported to display important dentin defects. Our purpose was to explore the structure, composition and distribution of noncollagenous proteins (NCPs) of hypophosphatemic dentin. We collected teeth from 10 hypophosphatemic patients whose mineralization occurred either in a hypophosphatemic environment or in a corrected phosphate and vitamin environment. Teeth were examined by scanning electron microscopy, immunohistochemistry and Western blot analysis. An abnormal distribution (accumulation in interglobular spaces) and cleavage of the NCPs and particularly of matrix extracellular phosphoglycoprotein were observed in deciduous dentin. In contrast, it was close to normal in permanent dentin mineralized under corrected conditions. In conclusion, dentin mineralization in a corrected phosphate and vitamin D environment compensates the adverse effect of PHEX mutation.

Infrared imaging microscopy of bone: illustrations from a mouse model of Fabry disease.

Bone is a complex tissue whose composition and properties vary with age, sex, diet, tissue type, health and disease. In this review, we demonstrate how infrared spectroscopy and infrared spectroscopic imaging can be applied to the study of these variations. A specific example of mice with Fabry disease (a lipid storage disease) is presented in which it is demonstrated that the bones of these young animals, while showing typical spatial variation in mineral content, mineral crystal size, and collagen maturity, do not differ from the bones of age- and sex-matched wild type animals.