18F-sodium fluoride positron emission tomography following coronary computed tomography angiography in predicting long-term coronary events: a 5-year follow-up study.

PURPOSE: The predictive value of 18F-sodium fluoride (18F-NaF) positron emission tomography (PET) in combination with coronary computed tomography (CT) angiography (CCTA) for future coronary events has attracted interest. We evaluated the potential of 18F-NaF PET/CT following CCTA to predict major coronary events (MACE) during a 5-year follow-up period. METHODS: Forty patients with coronary atherosclerotic lesions detected on CCTA underwent 18F-NaF PET/CT examination. Each lesion was evaluated for luminal stenosis and high-risk plaque (HRP) with < 30 Hounsfield units and a > 1.1 remodeling index on CCTA. Focal 18F-NaF uptake in each lesion was quantified using the maximum tissue-to-background ratio (TBRmax), and the maximum TBRmax per patient (M-TBRmax) was determined. We followed MACE (cardiac death, acute coronary syndrome, and/or coronary revascularization > 6 months after 18F-NaF PET/CT) for 5 years. RESULTS: In total, 142 coronary lesions were analyzed. Eleven patients experienced any MACE. Patients with MACE showed a higher M-TBRmax than those without (1.40 ± .19 vs. 1.18 ± .18, P = .0011), and the optimal M-TBRmax cutoff to predict MACE was 1.29. Patients with M-TBRmax of ≥ 1.29 had a higher risk of MACE than those with lower values (P = .012, log-rank test), whereas patients with obstructive stenosis and those with HRP did not. Multivariate Cox proportional analysis adjusted for age, sex, coronary risk factors, and CCTA findings showed that M-TBRmax of ≥ 1.29 remained an independent predictor of 5-year MACE (hazard ratio, 5.4; 95% confidence interval, 1.1-25.4; P = .034). CONCLUSION: 18F-NaF PET/CT following CCTA provides useful strategies to predict 5-year MACE.

A longitudinal pilot study to assess temporal changes in coronary arterial 18F-sodium fluoride uptake.

PURPOSE: How coronary arterial 18F-sodium fluoride (18F-NaF) uptake on positron emission tomography changes over the long term and what clinical factors impact the changes remain unclear. We sought to investigate the topics in this study. METHODS: We retrospectively studied 15 patients with ≥1 coronary atherosclerotic lesion/s detected on cardiac computed tomography who underwent baseline and follow-up (interval of >3 years) 18F-NaF positron emission tomography/computed tomography scans. Focal 18F-NaF uptake in each lesion was quantified using maximum tissue-to-background ratio (TBRmax). The temporal change in TBRmax was assessed using a ratio of follow-up to baseline TBRmax (R-TBRmax). RESULTS: A total of 51 lesions were analyzed. Mean R-TBRmax was 0.96 ± 0.21. CT-based lesion features (location, obstructive stenosis, plaque types, features of high-risk plaque) did not correlate with an increase in R-TBRmax. In multivariate analysis, baseline TBRmax significantly correlated with higher follow-up TBRmax (ß = 0.57, P < 0.0001), and the presence of diabetes mellitus significantly correlated with both higher follow-up TBRmax (ß = 0.34, P = 0.001) and elevated R-TBRmax (ß = 0.40, P = 0.003). CONCLUSION: Higher coronary arterial 18F-NaF uptake is likely to remain continuously high. Diabetes mellitus affects the long-term increase in coronary arterial 18F-NaF uptake.

Periodontitis and the outcome of atrial fibrillation ablation: Porphyromonas gingivalis is related to atrial fibrillation recurrence.

INTRODUCTION: Inflammation is one of the main causes of atrial fibrillation (AF) recurrence after ablation. Porphyromonas gingivalis is a key periodontal pathogen in the oral-systemic disease connection and serum immunoglobulin G (IgG) antibody titers against P. gingivalis reflect the clinical status of periodontitis. This study aimed to investigate the relationship between late recurrence of AF after radiofrequency catheter ablation (RFCA) and serum IgG antibody titers against P. gingivalis. METHODS: A total of 596 AF patients (mean age, 64.9 ± 10.0 years; 69% male; 61% paroxysmal AF) who underwent a first session of RFCA were enrolled. Patients were carefully examined for late recurrence during a mean follow-up period of 17.1 ± 14.5 months. Serum IgG antibody titers against P. gingivalis (types I-IV) were measured using enzyme-linked immunosorbent assay. The results of serum antibody titers were divided into a high-value and a low-value group. RESULTS: Among the five P. gingivalis subtypes, serum antibody titer against P. gingivalis type IV was associated with late recurrence (odds ratio, 1.937; 95% confidence interval [CI], 1.301-2.884; p = .002). Multivariate Cox proportional-hazards regression analysis revealed that high-value serum antibody titer against P. gingivalis type IV independently predicted late recurrence (paroxysmal AF: adjusted hazard ratio [HR], 1.569; 95% CI, 1.010-2.427; p = .04; non-paroxysmal AF: adjusted HR, 1.909; 95% CI, 1.213-3.005; p = .004). CONCLUSION: Periodontitis was related to the late recurrence of AF after RFCA. P. gingivalis type IV may be pathogenic for AF recurrence after RFCA.

Porphyromonas gingivalis and left atrial appendage spontaneous echo contrast in atrial fibrillation ablation candidates.

Atrial fibrillation (AF) is associated with a fivefold risk of stroke and thrombotic embolism, which are usually derived from the left atrial appendage (LAA). Spontaneous echo contrast (SEC) is known as a risk factor for thrombosis. Porphyromonas gingivalis (P. gingivalis) has some prothrombotic effects and plays a key role in periodontitis and oral-systemic disease connection. We aimed to clarify the relationship between P. gingivalis and LAA SEC among AF patients. A total of 569 AF ablation candidates were enrolled in the present study. LAA SEC was categorized into nondense SEC and dense SEC based on transesophageal echocardiography. Serum immunoglobulin G antibody titers of P. gingivalis fimA subtypes (types I-IV) were measured with an enzyme-linked immunosorbent assay. The levels of antibody titers were categorized into high (> mean + 3 standard deviation) and low values. A total of 513 (90%) patients were included in the nondense SEC group, and 56 (10%) were included in the dense SEC group. Multivariate regression analysis revealed that the high-value serum antibody titers of P. gingivalis types II and IV were independently associated with dense SEC [type II: adjusted odds ratio (OR) 2.220; 95% confidence interval (CI) 1.062-4.643; P = 0.02; and type IV: adjusted OR 3.169; 95% CI 1.058-6.657; P = 0.002]. The results revealed that P. gingivalis types II and IV are related to LAA SEC severity among AF patients who receive appropriate anticoagulation therapy.

Periodontal Treatment During the Blanking Period Improves the Outcome of Atrial Fibrillation Ablation.

BACKGROUND: Periodontitis has not been recognized as a modifiable risk factor for atrial fibrillation (AF). This prospective nonrandomized study investigated whether periodontal treatment improves the AF ablation outcome. METHODS AND RESULTS: We prospectively enrolled 288 AF patients scheduled to undergo initial radiofrequency catheter ablation. Each patient underwent periodontal inflamed surface area (PISA; a quantitative index of periodontal inflammation) measurement. All eligible patients were recommended to receive periodontal treatment within the blanking period, and 97 consented. During the mean follow-up period of 507±256 days, 70 (24%) AF recurrences were documented. Patients who exhibited AF recurrences had a higher PISA than those who did not (456.8±403.5 versus 277.7±259.0 mm2, P=0.001). These patients were categorized into high-PISA (>615 mm2) and low-PISA (<615 mm2) groups according to the receiver operating characteristic analysis for AF recurrence (area under the curve, 0.611; sensitivity, 39%; specificity, 89%). A high PISA, as well as female sex, AF duration, and left atrial volume, were the statistically significant predicter for AF recurrence (hazard ratio [HR], 2.308 [95% CI, 1.234-4.315]; P=0.009). In patients with a high PISA, those who underwent periodontal treatment showed significantly fewer AF recurrences (P=0.01, log-rank test). The adjusted HR of periodontal treatment for AF recurrence was 0.393 (95% CI, 0.215-0.719; P=0.002). CONCLUSIONS: Periodontitis may serve as a modifiable risk factor for AF. PISA is a hallmark of AF recurrence, and periodontal treatment improves the AF ablation outcome, especially for those with poor periodontal condition.

Relationship Between Periodontitis and Atrial Fibrosis in Atrial Fibrillation: Histological Evaluation of Left Atrial Appendages.

BACKGROUND: Atrial fibrosis contributes to the onset and persistence of atrial fibrillation (AF) and AF-related stroke. Periodontitis, a common infectious and inflammatory disease, aggravates some systemic diseases. However, the association of periodontitis with AF and with atrial fibrosis has remained unclarified. OBJECTIVES: The authors aimed to elucidate the relationship between periodontitis and atrial fibrosis by studying resected left atrial appendages (LAAs). METHODS: Seventy-six patients with AF (55 with nonparoxysmal AF, 25 with mitral valve regurgitation, 18 with LAA thrombus) who were scheduled to undergo LAA excision during cardiac surgery were prospectively enrolled. All patients underwent an oral examination, and the remaining number of teeth, bleeding on probing, periodontal probing depth, and periodontal inflamed surface area (PISA) were evaluated as parameters of periodontitis. The degree of fibrosis in each LAA was quantified by Azan-Mallory staining. RESULTS: Bleeding on probing (R = 0.48; P < 0.0001), periodontal probing depth of ≥4 mm (R = 0.26; P = 0.02), and PISA (R = 0.46; P < 0.0001) were positively correlated with atrial fibrosis. Among patients with >10 remaining teeth, PISA was positively and strongly correlated with atrial fibrosis (R = 0.57; P < 0.0001). After adjustments for age, AF duration, BMI, mitral valve regurgitation, and CHADS2 (congestive heart failure, hypertension, age, diabetes, previous stroke/transient ischemic attack) score, PISA was significantly associated with atrial fibrosis (ß = 0.016; P = 0.0002). CONCLUSIONS: The authors histologically revealed the association of periodontitis with atrial fibrosis. This indicates that periodontitis, which is modifiable, is likely a risk factor for AF.

Comparative temporospatial expression profiling of murine amelotin protein during amelogenesis.

Tooth enamel is formed in a typical biomineralization process under the guidance of specific organic components. Amelotin (AMTN) is a recently identified, secreted protein that is transcribed predominantly during the maturation stage of enamel formation, but its protein expression profile throughout amelogenesis has not been described in detail. The main objective of this study was to define the spatiotemporal expression profile of AMTN during tooth development in comparison with other known enamel proteins. A peptide antibody against AMTN was raised in rabbits, affinity purified and used for immunohistochemical analyses on sagittal and transverse paraffin sections of decalcified mouse hemimandibles. The localization of AMTN was compared to that of known enamel proteins amelogenin, ameloblastin, enamelin, odontogenic ameloblast-associated/amyloid in Pindborg tumors and kallikrein 4. Three-dimensional images of AMTN localization in molars at selected ages were reconstructed from serial stained sections, and transmission electron microscopy was used for ultrastructural localization of AMTN. AMTN was detected in ameloblasts of molars in a transient fashion, declining at the time of tooth eruption. Prominent expression in maturation stage ameloblasts of the continuously erupting incisor persisted into adulthood. In contrast, amelogenin, ameloblastin and enamelin were predominantly found during the early secretory stage, while odontogenic ameloblast-associated/amyloid in Pindborg tumors and kallikrein 4 expression in maturation stage ameloblasts paralleled that of AMTN. Secreted AMTN was detected at the interface between ameloblasts and the mineralized enamel. Recombinant AMTN protein did not mediate cell attachment in vitro. These results suggest a primary role for AMTN in the late stages of enamel mineralization.

WDR72 regulates vesicle trafficking in ameloblasts.

As the hardest tissue in the human body, tooth enamel formation is a highly regulated process involving several stages of differentiation and key regulatory genes. One such gene, tryptophan-aspartate repeat domain 72 (WDR72), has been found to cause a tooth enamel defect when deleted or mutated, resulting in a condition called amelogenesis imperfecta. Unlike the canonical genes regulating tooth development, WDR72 remains intracellularly and is not secreted to the enamel matrix space to regulate mineralization, and is found in other major organs of the body, namely the kidney, brain, liver, and heart. To date, a link between intracellular vesicle transport and enamel mineralization has been suggested, however identification of the mechanistic regulators has yet to be elucidated, in part due to the limitations associated with studying highly differentiated ameloblast cells. Here we show compelling evidence that WDR72 regulates endocytosis of proteins, both in vivo and in a novel in vitro ameloblast cell line. We elucidate WDR72's function to be independent of intracellular vesicle acidification while still leading to defective enamel matrix pH extracellularly. We identify a vesicle function associated with microtubule assembly and propose that WDR72 directs microtubule assembly necessary for membrane mobilization and subsequent vesicle transport. Understanding WDR72 function provides a mechanistic basis for determining physiologic and pathologic tissue mineralization.

Effects of Early Life Adversity on Tooth Enamel Formation.

In a systemic effort to survive environmental stress, organ systems fluctuate and adapt to overcome external pressures. The evolutionary drive back toward homeostasis makes it difficult to determine if an organism experienced a toxic exposure to stress, especially in early prenatal and neonatal periods of development. Previous studies indicate that primary human teeth may provide historical records of experiences related to stressors during that early time window. To assess the molecular effects of early life adversity on enamel formation, we used a limited bedding and nesting (LBN) mouse model of early life adversity (ELA) to assess changes in the enamel organ gene expression and enamel matrix mineralization. On average, postnatal day 12 (P12) ELA mice weighed significantly less than the controls. When adjusted for animal weight, ELA molar enamel volume was reduced as compared with the controls, and the relative mineral density of molar enamel was significantly increased. There were no obvious changes in enamel matrix crystal morphology or structure in ELA as compared with the control mouse enamel. RNAseq showed extracellular matrix organization to be the most significantly affected GO and reactome pathways, whereas butanote metabolism was the most significantly altered KEGG pathway. Transcripts expressing the enamel matrix proteins amelogenin (Amelx) and enamelin (Enam) were among the top 4 most differentially expressed genes. When evaluating molecular mechanisms for the changes in gene expression in ELA enamel organs, we found significantly increased expression of Dlx3, while transcripts for clock genes Per1 and Nrd1 were downregulated. These findings support the possibility that the developing enamel organ is sensitive to the pressures of early life adversity and produces molecular and structural biomarkers reflecting these challenges.

Fluoride Alters Signaling Pathways Associated with the Initiation of Dentin Mineralization in Enamel Fluorosis Susceptible Mice.

Fluoride can alter the formation of mineralized tissues, including enamel, dentin, and bone. Dentin fluorosis occurs in tandem with enamel fluorosis. However, the pathogenesis of dentin fluorosis and its mechanisms are poorly understood. In this study, we report the effects of fluoride on the initiation of dentin matrix formation and odontoblast function. Mice from two enamel fluorosis susceptible strains (A/J and C57BL/6J) were given either 0 or 50 ppm fluoride in drinking water for 4 weeks. In both mouse strains, there was no overall change in dentin thickness, but fluoride treatment resulted in a significant increase in the thickness of the predentin layer. The lightly mineralized layer (LL), which lies at the border between predentin and fully mineralized dentin and is associated with dentin phosphoprotein (DPP), was absent in fluoride exposed mice. Consistent with a possible reduction of DPP, fluoride-treated mice showed reduced immunostaining for dentin sialoprotein (DSP). Fluoride reduced RUNX2, the transcription regulator of dentin sialophosphoprotein (DSPP), that is cleaved to form both DPP and DSP. In fluoride-treated mouse odontoblasts, the effect of fluoride was further seen in the upstream of RUNX2 as the reduced nuclear translocation of ß-catenin and phosphorylated p65/NFκB. In vitro, MD10-F2 pre-odontoblast cells showed inhibition of the Dspp mRNA level in the presence of 10 µM fluoride, and qPCR analysis showed a significantly downregulated level of mRNAs for RUNX2, ß-catenin, and Wnt10b. These findings indicate that in mice, systemic exposure to excess fluoride resulted in reduced Wnt/ß-catenin signaling in differentiating odontoblasts to downregulate DSPP production via RUNX2.

Expression and localization of plasma transglutaminase factor XIIIA in bone.

Transglutaminases (TGs) are protein crosslinking enzymes involved in cell adhesion and signaling and matrix stabilization and maturation, in many cell types and tissues. We previously described that in addition to transglutaminase 2 (TG2), cultured MC3T3-E1 osteoblasts also express the plasma TG Factor XIIIA (FXIIIA). Here we report on the expression and localization of FXIIIA in bone in vivo and provide confirmatory in vitro data. Immunohistochemistry and in situ hybridization demonstrated that FXIIIA is expressed by osteoblasts and osteocytes in long bones formed by endochondral ossification (femur) and flat bones formed primarily by intramembranous ossification (calvaria and mandible). FXIIIA immunoreactivity was localized to osteoblasts, osteocytes, and the osteoid. RT-PCR analysis revealed FXIIIA expression by both primary osteoblasts and by the MC3T3-E1 osteoblast cell line. Western blot analysis of bone and MC3T3-E1 culture extracts demonstrated that FXIIIA is produced mainly as a small, 37-kDa form. Sequential RT-PCR analysis using overlapping PCR primers spanning the full FXIIIA gene showed that the entire FXIIIA gene is expressed, thus indicating that the 37-kDa FXIIIA is not a splice variant but a product of posttranslational proteolytic processing. Forskolin inhibition of osteoblast differentiation revealed that FXIIIA processing is regulated by the protein kinase A pathway.

Opisa takafuminakanoi, a new species of Opisidae from Hokkaido, Japan (Crustacea: Amphipoda).

Opisa is a small amphipod genus including three species: O. eschrichtii (Krøyer, 1842) from the North Atlantic Ocean (Sars 1895; Bousfield 1987), the Arctic Ocean (Bousfield 1987), and the western Pacific Ocean (Stebbing 1906; Derzhavin 1929); O. odontochela Bousfield, 1987 from the southeast Alaska (Bousfield 1987); and O. tridentata Hurley, 1963 from the Pacific coasts of North America (Bousfield 1987). During field survey of the marine benthic fauna of Hokkaido, Japan, one of the authors (KK) collected an undescribed species of Opisa from off the southeast of Akkeshi Bay using a sledge net. This paper describes and illustrates the new species in detail.

A Critical Role of TRPM7 As an Ion Channel Protein in Mediating the Mineralization of the Craniofacial Hard Tissues.

Magnesium ion (Mg(2+)) is the fourth most common cation in the human body, and has a crucial role in many physiological functions. Mg(2+) homeostasis is an important contributor to bone development, however, its roles in the development of dental mineralized tissues have not yet been well known. We identified that transient receptor potential cation channel, subfamily M, member 7 (TRPM7), was significantly upregulated in the mature ameloblasts as compared to other ameloblasts through our whole transcript microarray analyses of the ameloblasts. TRPM7, an ion channel for divalent metal cations with an intrinsic serine/threonine protein kinase activity, has been characterized as a key regulator of whole body Mg(2+) homeostasis. Semi-quantitative PCR and immunostaining for TRMP7 confirmed its upregulation during the maturation stage of enamel formation, at which ameloblasts direct rapid mineralization of the enamel matrix. The significantly hypomineralized craniofacial structures, including incisors, molars, and cranial bones were demonstrated by microCT analysis, von Kossa and trichrome staining in Trpm7 (Δkinase∕+) mice. A previously generated heterozygous mouse model with the deletion of the TRPM7 kinase domain. Interestingly, the skeletal phenotype of Trpm7 (Δkinase∕+) mice resembled those found in the tissue-nonspecific alkaline phosphatase (Alpl) KO mice, thus we further examined whether ALPL protein content and alkaline phosphatase (ALPase) activity in ameloblasts, odontoblasts and osteoblasts were affected in those mice. While ALPL protein in Trpm7 (Δkinase∕+) mice remained at the similar level as that in wt mice, ALPase activities in the Trpm7 (Δkinase∕+) mice were almost nonexistent. Supplemented magnesium successfully rescued the activities of ALPase in ameloblasts, odontoblasts and osteoblasts of Trpm7 (Δkinase∕+) mice. These results suggested that TRPM7 is essential for mineralization of enamel as well as dentin and bone by providing sufficient Mg(2+) for the ALPL activity, underlining the key importance of ALPL for biomineralization.

Fluorosed mouse ameloblasts have increased SATB1 retention and Gαq activity.

Dental fluorosis is characterized by subsurface hypomineralization and increased porosity of enamel, associated with a delay in the removal of enamel matrix proteins. To investigate the effects of fluoride on ameloblasts, A/J mice were given 50 ppm sodium fluoride in drinking water for four weeks, resulting serum fluoride levels of 4.5 µM, a four-fold increase over control mice with no fluoride added to drinking water. MicroCT analyses showed delayed and incomplete mineralization of fluorosed incisor enamel as compared to control enamel. A microarray analysis of secretory and maturation stage ameloblasts microdissected from control and fluorosed mouse incisors showed that genes clustered with Mmp20 appeared to be less downregulated in maturation stage ameloblasts of fluorosed incisors as compared to control maturation ameloblasts. One of these Mmp20 co-regulated genes was the global chromatin organizer, special AT-rich sequence-binding protein-1 (SATB1). Immunohistochemical analysis showed increased SATB1 protein present in fluorosed ameloblasts compared to controls. In vitro, exposure of human ameloblast-lineage cells to micromolar levels of both NaF and AlF3 led to a significantly increase in SATB1 protein content, but not levels of Satb1 mRNA, suggesting a fluoride-induced mechanism protecting SABT1 from degradation. Consistent with this possibility, we used immunohistochemistry and Western blot to show that fluoride exposed ameloblasts had increased phosphorylated PKCα both in vivo and in vitro. This kinase is known to phosphorylate SATB1, and phosphorylation is known to protect SATB1 from degradation by caspase-6. In addition, production of cellular diacylglycerol (DAG) was significantly increased in fluorosed ameloblasts, suggesting that the increased phosphorylation of SATB1 may be related to an effect of fluoride to enhance Gαq activity of secretory ameloblasts.

Leucine rich amelogenin peptide alters ameloblast differentiation in vivo.

Highly mineralized tooth enamel develops from an extracellular matrix chiefly comprised of amelogenins formed by splicing of 7 (human) or 9 (rodent) exons secreted from specialized epithelial cells known as ameloblasts. Here we examined the role of the 59 amino acid alternatively spliced amelogenin known as leucine rich amelogenin peptide (LRAP) on enamel formation, using transgenic murine models in which LRAP overexpression is driven by an amelogenin promoter (TgLRAP). Beginning in the secretory stage of mouse amelogenesis, we found a reduced thickness of enamel matrix and a loss of Tomes' processes, followed by upregulated amelogenin mRNA expression, inhibited amelogenin secretion and loss of cell polarity. In the presecretory stage (P0) amelogenin m180 mRNA expression was increased 58 fold along with a 203 fold increase in MMP-20 expression and 3.5 and 3.2 fold increased in respectively enamelin and ameloblastin. When LRAP was overexpressed on an amelogenin knockout mouse model, the ameloblasts were not affected. Further, expression of the global chromatin organizer and transcription factor SATB1 was reduced in secretory stage TgLRAP ameloblasts. These findings identify a cellular role for LRAP in enamel formation that is not directly related to directing enamel crystal formation as is reported to be the primary function of full length amelogenins. The effect of LRAP overexpression in upregulating amelogenins, MMP-20 and SATB1, suggests a role in protein regulation critical to ameloblast secretion and matrix processing, to form a mineralized enamel matrix.

The existence of CD11c+ sentinel and F4/80+ interstitial dendritic cells in dental pulp and their dynamics and functional properties.

Dental caries and pulpitis are the most common bacterial infections in humans. However, the immune responses against bacterial stimulation in dental pulp that is bounded by special hard tissues are poorly understood. We examined the initial immune responses in mouse dental pulp after cusp trimming and acid treatment. Using fluorescence immunohistochemistry, two distinct cell populations were identified in the intact pulp; CD11c+F4/80- and CD11c-F4/80+ cells. CD11c+F4/80- cells were localized in the pulp-dentin (P-D) border of the central pulp beneath the dental fissure, whereas CD11c-F4/80+ cells with dendritic morphology were distributed in the perivascular region of the inner pulp and the sub-odontoblastic layer. CD11c+F4/80- cells, but not CD11c-F4/80+ cells, constitutively expressed toll-like receptors 2 and 4 and CD205, and migrated to the P-D border of the treated side within 2 h after the treatment. In parallel, some of the F4/80+ cells migrated to the inner pulp of the treated side, increased in size and enhanced CD86 expression. At 24 h, the CD86+ cells with high fluorescence intensity had disappeared entirely from the pulp. Concurrently, CD86high cells expressing intermediate levels of CD11c and high levels of MHC class II and F4/80, assessed by using flow cytometry, increased significantly in the regional lymph nodes, suggesting migration of these cells from the dental pulp. Our results are the first to demonstrate the existence of at least two types of dendritic cells (DCs) in dental pulp. The CD11c+ sentinel and F4/80+ interstitial DCs might have distinct territories and unique roles in responding to external stimuli via the dentinal tubules.

Formation of acellular cementum-like layers, with and without extrinsic fiber insertion, along inert bone surfaces of aging c-Src gene knockout mice.

To investigate the long-term effects of c-src deficiency on skeletal and dental tissues, we examined the lower jaws and long bones of c-src gene knockout (c-src KO) mice by histological and histochemical methods. Numerous multinucleated osteoclasts were distributed throughout the mandible in 5-wk-old c-src KO mice, but by 14 wk they had almost completely disappeared from the alveolar bone, leaving tartrate-resistant acid phosphatase (TRAP)-positive layers along the bone surface. Deposition of osteopontin-positive mineralized tissue, reminiscent of acellular afibrillar cementum (AAC), was confirmed along the TRAP-positive bone surface at 14 wk. The layer progressively thickened up to 21 months. A comparable mineralized layer was noted along the trabeculae of long bones as thickened cement lines. In the periostin-rich areas of jaw bones, but not in the long bones, portions of AAC-like mineralized layers were often replaced with and/or covered by acellular extrinsic fiber cementum (AEFC)-like tissue. These data suggest that the deposition of AAC-like mineralized tissue is a general phenomenon that may occur along inert or slowly remodeling bone surfaces under conditions characterized by reduced bone-resorbing activity, whereas the induction of AEFC-like tissue seems to be associated with the expression of certain molecules that are particularly abundant in the microenvironment of the periodontal ligament.

The induction of enamel and dentin complexes by subcutaneous implantation of reconstructed human and murine tooth germ elements.

Tooth induction by xenogenic graft of reconstructed human tooth germ components has never been attempted. Here we report our first attempt at a transplantation of human tooth germ components, heterologously recombined with mouse dental epithelia, into immunocompromised animals. Human third molar tooth germs enucleated from young patients as prophylactic treatment for orthodontic reasons were collected. The whole or minced human dental papilla was reconstructed with human- or mouse molar enamel epithelium, and transplanted in the dorsal aspect of C.B-17/Icr-scid Jcl mice. The transplant of human dental papilla reconstructed with human enamel epithelium formed thin dentin and immature enamel layers by 3 to 4 weeks, but remained extremely small in quantity due to a shortage of epithelial components in the graft. The addition of E16 mouse molar enamel organs (n=10-12) to each graft augmented the formation of tooth germ-like structures, but the differentiation of mouse molar ameloblasts was suppressed. However, once a solid layer of mineralized dentin was established, mouse ameloblasts accelerated their differentiation, and completed the enamel matrix formation and maturation within the following 4 weeks, whereas human ameloblasts, which had interacted with human dental papilla, remained in the stage of matrix formation during the same period. These data imply that, in reconstructed transplants, the differentiation of mouse dental epithelia is restrained by putative suppressive factors derived from human dental papilla until they are separated by mineralized dentin layers that serve as a diffusion barrier. The mouse enamel organ nevertheless retains its own phenotypic characteristics and intrinsic timing of cell differentiation and function.