SDF-1 involvement in orthodontic tooth movement after tooth extraction

The stromal cell-derived factor 1 (SDF-1)/chemokine receptor type 4 (CXCR4) axis plays a key role in alveolar bone metabolism during orthodontic tooth movement (OTM). Herein, the effects of the SDF-1/CXCR4 axis on the regional acceleratory phenomenon (RAP) in OTM velocity and on changes in the surrounding periodontium after adjacent tooth extraction in rats were investigated. Six-week-old male Wistar/ST rats underwent left maxillary first molar (M1) extraction and mesial OTM of the left maxillary second molar (M2) with a 10-g force closed-coil spring. Phosphate-buffered saline, immunoglobulin G (IgG) isotype control antibody, or anti-SDF-1 neutralizing monoclonal antibody were injected at the M1 and M2 interproximal areas (10 μg/0.1 mL) for the first three days. Analyses were performed after 1, 3, and 7 days (n = 7). The results demonstrated a significant increase in SDF-1 expression from day 1, which was effectively blocked via anti-SDF-1 neutralizing monoclonal antibody injection. On day 3, the M2 OTM distance and the number of positively stained osteoclasts significantly reduced alongside a reduction in inflammatory markers in the experimental group. Our results demonstrated that serial local injection of the anti-SDF-1 neutralizing monoclonal antibody reduces M2 OTM, osteoclast accumulation, and localized inflammatory responses in an OTM model with tooth extraction-induced RAP.

Periostin splice variants affect craniofacial growth by influencing chondrocyte hypertrophy

INTRODUCTION

Periostin, an extracellular matrix protein, plays an important role in osteogenesis and is also known to activate several signals that contribute to chondrogenesis. The absence of periostin in periostin knockout mice leads to several disorders such as craniosynostosis and periostitis. There are several splice variants with different roles in heart disease and myocardial infarction. However, little is known about each variant's role in chondrogenesis, followed by bone formation. Therefore, the aim of this study is to investigate the role of several variants in chondrogenesis differentiation and bone formation in the craniofacial region. Periostin splice variants included a full-length variant (Control), a variant lacking exon 17 (ΔEx17), a variant lacking exon 21 (ΔEx21), and another variant lacking both exon 17 and 21 ***(ΔEx17&21).

MATERIALS AND METHODS

We used C56BL6/N mice (n = 6) for the wild type (Control)*** and the three variant type mice (n = 6 each) to identify the effect of each variant morphologically and histologically. Micro-computed tomography demonstrated a smaller craniofacial skeleton in ΔEx17s, ΔEx21s, and ΔEx17&21s compared to Controls, especially the mandibular bone. We, thus, focused on the mandibular condyle.

RESULTS

The most distinctive histological observation was that each defected mouse appeared to have more hypertrophic chondrocytes than Controls. Real-time PCR demonstrated the differences among the group. Moreover, the lack of exon 17 or exon 21 in periostin leads to inadequate chondrocyte differentiation and presents in a diminutive craniofacial skeleton.

DISCUSSION

Therefore, these findings suggested that each variant has a significant role in chondrocyte hypertrophy, leading to suppression of bone formation.

NF-κB Decoy ODN-Loaded Poly(Lactic-co-glycolic Acid) Nanospheres Inhibit Alveolar Ridge Resorption

Residual ridge resorption combined with dimensional loss resulting from tooth extraction has a prolonged correlation with early excessive inflammation. Nuclear factor-kappa B (NF-κB) decoy oligodeoxynucleotides (ODNs) are double-stranded DNA sequences capable of downregulating the expression of downstream genes of the NF-κB pathway, which is recognized for regulating prototypical proinflammatory signals, physiological bone metabolism, pathologic bone destruction, and bone regeneration. The aim of this study was to investigate the therapeutic effect of NF-κB decoy ODNs on the extraction sockets of Wistar/ST rats when delivered by poly(lactic-co-glycolic acid) (PLGA) nanospheres. Microcomputed tomography and trabecular bone analysis following treatment with NF-κB decoy ODN-loaded PLGA nanospheres (PLGA-NfDs) demonstrated inhibition of vertical alveolar bone loss with increased bone volume, smoother trabecular bone surface, thicker trabecular bone, larger trabecular number and separation, and fewer bone porosities. Histomorphometric and reverse transcription-quantitative polymerase chain reaction analysis revealed reduced tartrate-resistant acid phosphatase-expressing osteoclasts, interleukin-1β, tumor necrosis factor-α, receptor activator of NF-κB ligand, turnover rate, and increased transforming growth factor-β1 immunopositive reactions and relative gene expression. These data demonstrate that local NF-κB decoy ODN transfection via PLGA-NfD can be used to effectively suppress inflammation in a tooth-extraction socket during the healing process, with the potential to accelerate new bone formation.

Metabolic dysregulation and decreased capillarization in skeletal muscles of male adolescent offspring rats exposed to gestational intermittent hypoxia

Gestational intermittent hypoxia (IH) is a hallmark of obstructive sleep apnea that occurs frequently during pregnancy, and effects caused by this environmental change during pregnancy may be transmitted to the offspring. In this study, we aimed to clarify the effects of IH in pregnant rats on the skeletal muscle of adolescent offspring rats. Mother rats underwent IH from gestation day 7-21, and their 5-weeks-old male offspring were analyzed. All male offspring rats were born and raised under normoxia conditions. Although no general growth retardation was observed, we found that exposure to gestational IH reduces endurance running capacity of adolescent offspring rats. Both a respiratory muscle (diaphragm; DIA) and a limb muscle (tibialis anterior; TA) showed no histological abnormalities, including fiber size and fiber type distribution. To identify the possible mechanism underlying the reduced running capacity, regulatory factors associated with energy metabolism were analyzed in different parts of skeletal muscles. Compared with rats born under conditions of gestational normoxia, gestational IH offspring rats showed significantly lower expression of genes associated with glucose and lipid metabolism, and lower protein levels of phosphorylated AMPK and AKT. Furthermore, gene expression of adiponectin receptors one and two was significantly decreased in the DIA and TA muscles. In addition, the DIA muscle from adolescent rats had significantly decreased capillary density as a result of gestational IH. However, these changes were not observed in a sucking muscle (geniohyoid) and a masticating muscle (masseter) of these rats. These results suggest that respiratory and limb muscles are vulnerable to gestational IH, which induces altered energy metabolism with decreased aerobic motor function. These changes were partially owing to the decreased expression of adiponectin receptors and decreased capillary density in adolescent offspring rats.

Gestational Intermittent Hypoxia Induces Mitochondrial Impairment in the Geniohyoid Muscle of Offspring Rats

Introduction Gestational intermittent hypoxia (IH), a hallmark of obstructive sleep apnea during gestation, alters respiratory neural control and diaphragm muscle contractile function in the offspring. The geniohyoid (GH) muscle is innervated by the respiratory-related hypoglossal nerve and plays a role in tongue traction and suckling, motor behaviors that then give way to chewing. Here, we aimed to investigate the effects of gestational exposure to IH on the muscle development and metabolism of GH and masseter muscles in male offspring rats. Materials and methods Pregnant Sprague-Dawley rats were exposed to IH (3-min periods of 4-21% O2) for eight hours/day during gestational days 7-20. The GH and masseter muscles from 35-day-old male offspring (n = 6 in each group) were analyzed.  Results Gestational IH induction reduced type IIA fiber size in the GH muscle of the offspring but not in the masseter muscle. Western blot analysis showed that gestational IH-induced significant downregulation of peroxisome proliferator-activated receptor (PPAR)-gamma coactivator 1-alpha (PGC1α) protein in the GH muscle but not in the masseter muscle. Moreover, optic atrophy 1 and mitofusin-2 proteins were decreased and mitochondrial fission 1 protein levels were increased in the GH muscle of the offspring exposed to gestational IH. Mitochondrial adenosine triphosphate (ATP) synthase subunit alpha and transcriptional factor A (TFAM) were decreased in the GH muscle post-gestational IH. Conclusion These findings suggest that gestational IH-induced impaired mitochondrial metabolism and alteration of oxidative myofibers of the GH muscle in the pre-adolescent offspring, but not the masseter muscle, owing to the susceptibility of GH muscular mitochondria to gestational IH.

Intermittent hypoxia retards mandibular growth and alters RANKL expression in adolescent and juvenile rats

OBJECTIVES

Chronic intermittent hypoxia (IH), a common state experienced in obstructive sleep apnoea (OSA), retards mandibular growth in adolescent rats. The aim of this study was to elucidate the differential effects of IH on mandibular growth in different growth stages.

MATERIALS AND METHODS

Three-week-old (juvenile stage) and 7-week-old (adolescent stage) male Sprague-Dawley rats underwent IH for 3 weeks. Age-matched control rats were exposed to room air. Mandibular growth was evaluated by radiograph analysis, micro-computed tomography, real-time polymerase chain reaction and immunohistology. Tibial growth was evaluated as an index of systemic skeletal growth.

RESULTS

IH had no significant impact on the general growth of either the juvenile or adolescent rats. However, it significantly decreased the total mandibular length and the posterior corpus length of the mandible in the adolescent rats and the anterior corpus length in the juvenile rats. IH also increased bone mineral density (BMD) of the condylar head in adolescent rats but did not affect the BMD of the tibia. Immunohistological analysis showed that the expression level of receptor activation of nuclear factor-κB ligand significantly decreased (in contrast to its messenger ribonucleicacid level) in the condylar head of adolescent rats with IH, while the number of osteoprotegerin-positive cells was comparable in the mandibles of adolescent IH rats and control rats.

LIMITATIONS

The animal model could not simulate the pathological conditions of OSA completely and there were differences in bone growth between humans and rodents.

CONCLUSIONS

These results suggest that the susceptibility of mandibular growth retardation to IH depends on the growth stage of the rats.

Nuclear factor-kappa B (NF-κB) decoy oligodeoxynucleotide-loaded poly lactic-co-glycolic acid (PLGA) nanospheres promote periodontal tissue healing after tooth replantation in rats

BACKGROUND

Excessive inflammation in the periodontal tissue after tooth replantation can lead to inflammatory root resorption and interrupt periodontal tissue regeneration. We tested the hypothesis that NF-κB decoy oligodeoxynucleotide-loaded poly lactic-co-glycolic acid nanospheres (NF-PLGA) inhibit excessive inflammation and promote healing of periodontal tissue after replantation in rats.

METHODS

The upper right incisors of rats were extracted, immersed in different specific solutions, and replanted. The rats were euthanized at 7, 14, and 28 days after replantation. Morphological evaluation with micro-CT and histological assessment with hematoxylin and eosin and tartrate-resistant acid phosphatase (TRAP) staining was performed. Additionally, we examined the expression of interleukin (IL)-1β, IL-6, transforming growth factor-β1 (TGF-β1), and fibroblast growth factor-2 (FGF-2) in the periodontal ligament (PDL) by performing immunohistological assessment.

RESULTS

The NF-PLGA group showed significantly greater dental root thickness than the other experimental groups. Root resorption was not observed after the application of NF-PLGA on day 7. The application of NF-PLGA also resulted in a significantly lower number of TRAP-positive osteoclasts on days 7 and 14 after replantation. Significantly lower expression of IL-1β and IL-6 and higher expression of TGF-β1 and FGF-2 were observed under the application of NF-PLGA in the PDL.

CONCLUSIONS

NF-PLGA promoted the healing process by inhibiting the initial excessive inflammatory response in the PDL, preventing root resorption, and promoting periodontal tissue regeneration. The findings also suggested that the PLGA nanospheres-mediated transfection of the decoy oligodeoxynucleotides can be useful for the clinical application of replanted tooth root surfaces. This article is protected by copyright. All rights reserved.

Selective β2-Adrenoceptor Blockade Rescues Mandibular Growth Retardation in Adolescent Rats Exposed to Chronic Intermittent Hypoxia

Activation of the sympathoadrenal system is associated with sleep apnea-related symptoms and metabolic dysfunction induced by chronic intermittent hypoxia (IH). IH can induce hormonal imbalances and growth retardation of the craniofacial bones. However, the relationship between IH and β2-adrenergic receptor signaling in the context of skeletal growth regulation is unclear. This study aimed to investigate the role of β2-adrenergic receptors in IH-induced mandibular growth retardation and bone metabolic alterations. Male 7-week-old Sprague–Dawley rats were subjected to IH for 3 weeks. IH conditions were established using original customized hypoxic chambers; IH was induced at a rate of 20 cycles per hour (oxygen levels changed from 4 to 21% in one cycle) for 8 h per day during the 12 h “lights on” period. The rats received intraperitoneal administration of a β2-adrenergic antagonist (butoxamine) or saline. To exclude dietary effects on general growth, the normoxic rats with saline, normoxic rats with butoxamine, and IH rats with butoxamine were subjected to food restriction to match the body weight gains between IH and other three groups. Body weight, heart rate, blood pressure, and plasma concentrations of leptin, serotonin, and growth hormone were measured. Bone growth and metabolism were evaluated using radiography, microcomputed tomography, and immunohistochemical staining. Plasma leptin levels were significantly increased, whereas that of serotonin and growth hormone were significantly decreased following IH exposure. Leptin levels recovered following butoxamine administration. Butoxamine rescued IH-induced mandibular growth retardation, with alterations in bone mineral density at the condylar head of the mandible. Immunohistochemical analysis revealed significantly lower expression levels of receptor activator of nuclear factor-kappa B ligand (RANKL) in the condylar head of IH-exposed rats. Conversely, recovery of RANKL expression was observed in IH-exposed rats administered with butoxamine. Collectively, our findings suggest that the activation of β2-adrenergic receptors and leptin signaling during growth may be involved in IH-induced skeletal growth retardation of the mandible, which may be mediated by concomitant changes in RANKL expression at the growing condyle.

Intermittent hypoxia inhibits mandibular cartilage growth with reduced TGF-β and SOX9 expressions in neonatal rats

Intermittent hypoxia (IH) has been associated with skeletal growth. However, the influence of IH on cartilage growth and metabolism is unknown. We compared the effects of IH on chondrocyte proliferation and maturation in the mandibular condyle fibrocartilage and tibial hyaline cartilage of 1-week-old male Sprague-Dawley rats. The rats were exposed to normoxic air (n = 9) or IH at 20 cycles/h (nadir, 4% O₂; peak, 21% O₂; 0% CO₂) (n = 9) for 8 h each day. IH impeded body weight gain, but not tibial elongation. IH also increased cancellous bone mineral and volumetric bone mineral densities in the mandibular condylar head. The mandibular condylar became thinner, but the tibial cartilage did not. IH reduced maturative and increased hypertrophic chondrocytic layers of the middle and posterior mandibular cartilage. PCR showed that IH shifted proliferation and maturation in mandibular condyle fibrocartilage toward hypertrophic differentiation and ossification by downregulating TGF-β and SOX9, and upregulating collagen X. These effects were absent in the tibial growth plate hyaline cartilage. Our results showed that neonatal rats exposed to IH displayed underdeveloped mandibular ramus/condyles, while suppression of chondrogenesis marker expression was detected in the growth-restricted condylar cartilage.

Intermittent hypoxia induces turbinate mucosal hypertrophy via upregulating the gene expression related to inflammation and EMT in rats

PURPOSE

Chronic intermittent hypoxia (IH) plays a pivotal role in the consequences of obstructive sleep apnea (OSA). It has been demonstrated that IH impairs nasomaxillary complex growth to reduce nasal airway cavity size in rodent models. Although turbinate dysfunction with inflammatory mucosal hypertrophy is related to OSA, the role of IH in turbinate hypertrophy with inflammation-driven fibrosis is unknown. Here, we aimed to clarify the pathogenesis of inflammatory mucosal hypertrophy and epithelial-mesenchymal transition (EMT) in the nasal turbinate under IH.

METHODS

Seven-week-old male Sprague-Dawley rats were exposed to IH (4% O₂ to 21% O₂ with 0% CO₂) at a rate of 20 cycles/h.

RESULTS

Hypertrophy of the turbinate mucosa occurred after 3 weeks, with the turbinate mucosa of the experimental group becoming significantly thicker than in the control group. Immunostaining showed that IH increased the expression of TGFβ and N-cadherin and decreased E-cadherin expression in the turbinate mucosa. Quantitative PCR analysis demonstrated that IH enhanced the expression of not only the inflammatory markers Tnf-a, Il-1b, and Nos2 but also the EMT markers Tgf-b1, Col1a1, and Postn.

CONCLUSIONS

Collectively, these results suggest that IH induced turbinate hypertrophy via upregulation of gene expression related to inflammation and EMT in the nasal mucosa.

Differential growth of craniofacial and tibial bones to sympathetic hyperactivity-related hypertension in rats

OBJECTIVE

To evaluate the effect of sympathetic nervous system hyperactivity on craniofacial skeletal growth in growing spontaneously hypertensive rats (SHRs).

DESIGN

Craniofacial skeletal growth was compared between male SHR and Wistar-Kyoto rats (WKR) using linear measurements on lateral and transverse cephalometric radiographs at the age of 12 weeks. Tibia length was measured as an index of whole body growth. Body weight　and blood pressure were measured from 3 to 12 weeks of age. Bone microstructure in the mandibular condyle and tibia between the two groups was compared at the age of 12 weeks using microcomputed tomography.

RESULTS

The SHRs had a significantly lower body weight than WKRs from 7 weeks of age, and tibial length was significantly smaller in the SHRs than in the WKR at 12 weeks of age. In all SHRs, blood pressure was significantly higher than in WKRs from 3 to 12 weeks of age. Cephalometric analyses revealed decreased measurements of the neurocranium, viscerocranium, and mandible in SHRs, and mandibular growth was most negatively affected in this group. Lastly, in SHRs, microcomputed tomography analyses revealed decreased bone mineral density and bone volume/tissue volume in the mandibular condyle but not in the tibia.

CONCLUSION

In growing SHRs, hypertension related to the hyperactivity of the sympathetic nervous system reduced craniofacial skeletal growth more than the growth of the tibia.

Optogenetic manipulation of intracellular calcium by BACCS promotes differentiation of MC3T3-E1 cells

Bone remodeling is maintained through the balance between bone formation by osteoblasts and bone resorption by osteoclasts. Previous studies suggested that intracellular Ca²⁺ signaling plays an important role in the differentiation of osteoblasts; however, the molecular mechanism of Ca²⁺ signaling in the differentiation of osteoblasts remains unclear. To elucidate the effect of Ca²⁺ signaling in osteoblasts, we employed an optogenetic tool, blue light-activated Ca²⁺ channel switch (BACCS). BACCS was used to spatiotemporally control intracellular Ca²⁺ with blue light stimulation. MC3T3-E1 cells, which have been used as a model of differentiation from preosteoblast to osteoblast, were promoted to differentiate by BACCS expression and rhythmical blue light stimulation. The results indicated that intracellular Ca²⁺ change from the outside of the cells can regulate signaling for differentiation of MC3T3-E1 cells. Our findings provide evidence that Ca²⁺ could cause osteoblast differentiation.

Effects of unilateral nasal obstruction on the characteristics of jaw-closing muscles in growing rats

OBJECTIVES

Mouth breathing caused by nasal obstruction (owing to abnormal pressure of masticatory muscles) affects craniofacial growth and development. The influence of unilateral nasal obstruction on jaw-closing muscles was investigated in rats to reveal one of the etiologic mechanisms.

MATERIALS AND METHODS

Forty 8-day-old male Wistar rats were used in this study. Experimental rats were subjected to left-sided nasal obstruction by burning the external nostril tissue at the age of 8 days. Pulse oxygen saturation was recorded each week. Morphologic changes were evaluated by staining with hematoxylin and eosin (to assess the cross-sectional area) and by adenosine triphosphatase activity staining (to assess the myosin heavy chain isoform composition). Immunohistochemical and reverse transcription quantitative real-time polymerase chain reaction analyses of tumor necrosis factor-α and glucose transporter 4 were carried out at 5 and 9 weeks of age.

RESULTS

The cross-sectional area of the jaw-closing muscles was lower in the experimental group at 9 weeks of age. The percentage of myosin heavy chain-2a in masseter muscles was increased in the experimental group compared with the control group. An increase in the tumor necrosis factor-α messenger RNA and protein levels and a decrease in the glucose transporter 4 messenger RNA and protein levels at 5 and 9 weeks of age in the jaw-closing muscles in the experimental group were noted.

CONCLUSIONS

Unilateral nasal obstruction could affect the morphology and contractile characteristics of jaw-closing muscles during growth in rats.

Intermittent hypoxia causes mandibular growth retardation and macroglossia in growing rats

INTRODUCTION

In this study, we aimed to examine the role of intermittent hypoxia (IH) in dentofacial morphologic changes in growing rats.

METHODS

Seven-week-old male rats were exposed to IH at 20 cycles per hour (nadir of 4% oxygen to peak of 21% oxygen) for 8 hours per day for 6 weeks. Control rats were exposed to normoxia (N). Maxillofacial growth was compared between the 2 groups by linear measurements on cephalometric radiographs. To examine the dental arch morphology, study models and microcomputed tomography images of the jaws were taken. Additionally, tongue size was measured.

RESULTS

The gonial angle and the ramus of the mandible were smaller in the IH group than in the N group, whereas the body weights were not different between the 2 groups. Morphometric analysis of the dentition showed a significantly wider mandibular dentition and narrower maxillary dentition in the IH than in the N group. The relative width (+4.2 %) and length (tongue apex to vallate papillae, +3.5 %) of the tongue to the mandible were significantly greater in the IH group than in the N group.

CONCLUSIONS

IH induced dentofacial morphologic discrepancies in growing rats.

The chemokine receptor type 4 antagonist, AMD3100, interrupts experimental tooth movement in rats

OBJECTIVE

The aim of this study was to clarify the role of the stromal cell-derived factor-1 (SDF-1)/C-X-C chemokine receptor type 4 (CXCR4) axis in osteoclast accumulation, and the influence of orthodontic tooth movement (OTM) under mechanical force application to periodontal tissues, by administration of the CXCR4 antagonist AMD3100.

DESIGN

The upper right first molar (M1) of rats was moved mesially with a 10-g force titanium-nickel closed coil spring. Rats were treated with phosphate-buffered saline or AMD3100 (5mg/kg), which is a SDF-1 antagonist. After 0, 1, 3, and 7days, alveolar bones in all groups were examined at each time point by micro-computed tomography and histological analysis.

RESULTS

Tooth movement was decreased significantly in the AMD3100-treated group at 1, 3, and 7days after beginning OTM. The numbers of tartrate-resistant acid phosphatase-positive multinucleated cells in the periodontal ligament around the maxillary M1 were decreased significantly in the treated as compared to the control group on Days 1 and 3.

CONCLUSION

Administration of AMD3100 decreases OTM and osteoclast accumulation in rat molars under orthodontic force application. These findings suggest that the SDF-1/CXCR4 axis plays an important role in alveolar bone metabolism during OTM.

Low-intensity pulsed ultrasound reduces periodontal atrophy in occlusal hypofunctional teeth

OBJECTIVE

To clarify whether low-intensity pulsed ultrasound (LIPUS) exposure has recovery effects on the hypofunctional periodontal ligament (PDL) and interradicular alveolar bone (IRAB).

MATERIALS AND METHODS

Twelve-week-old male Sprague-Dawley rats were divided into three groups (n = 5 each): a normal occlusion (C) group, an occlusal hypofunction (H) group, and an occlusal hypofunction group subjected to LIPUS (HL) treatment. Hypofunctional occlusion of the maxillary first molar (M1) of the H and HL groups was induced by the bite-raising technique. Only the HL group was irradiated with LIPUS for 5 days. The IRAB and PDL of M1 were examined by microcomputed tomography (micro-CT) analysis. To quantify mRNA expression of cytokines involved in PDL proliferation and development, real-time reverse transcription quantitative PCR (qRT-PCR) was performed for twist family bHLH transcription factor 1 (Twist1), periostin, and connective tissue growth factor (CTGF) in the PDL samples.

RESULTS

Micro-CT analysis showed that the PDL volume was decreased in the H group compared with that of the C and HL groups. Both bone volume per tissue volume (BV/TV) of IRAB was decreased in the H group compared with that in the C group. LIPUS exposure restored BV/TV in the IRAB of the HL group. qRT-PCR analysis showed that Twist1, periostin, and CTGF mRNA levels were decreased in the H group and increased in the HL group.

CONCLUSION

LIPUS exposure reduced the atrophic changes of alveolar bone by inducing the upregulation of periostin and CTGF expression to promote PDL healing after induction of occlusal hypofunction.

Intermittent Hypoxia Influences Alveolar Bone Proper Microstructure via Hypoxia-Inducible Factor and VEGF Expression in Periodontal Ligaments of Growing Rats

Intermittent hypoxia (IH) recapitulates morphological changes in the maxillofacial bones in children with obstructive sleep apnea (OSA). Recently, we found that IH increased bone mineral density (BMD) in the inter-radicular alveolar bone (reflecting enhanced osteogenesis) in the mandibular first molar (M1) region in the growing rats, but the underlying mechanism remains unknown. In this study, we focused on the hypoxia-inducible factor (HIF) pathway to assess the effect of IH by testing the null hypothesis of no significant differences in the mRNA-expression levels of relevant factors associated with the HIF pathway, between control rats and growing rats with IH. To test the null hypothesis, we investigated how IH enhances mandibular osteogenesis in the alveolar bone proper with respect to HIF-1α and vascular endothelial growth factor (VEGF) in periodontal ligament (PDL) tissues. Seven-week-old male Sprague-Dawley rats were exposed to IH for 3 weeks. The microstructure and BMD in the alveolar bone proper of the distal root of the mandibular M1 were evaluated using micro-computed tomography (micro-CT). Expression of HIF-1α and VEGF mRNA in PDL tissues were measured, whereas osteogenesis was evaluated by measuring mRNA levels for alkaline phosphatase (ALP) and bone morphogenetic protein-2 (BMP-2). The null hypothesis was rejected: we found an increase in the expression of all of these markers after IH exposure. The results provided the first indication that IH enhanced osteogenesis of the mandibular M1 region in association with PDL angiogenesis during growth via HIF-1α in an animal model.

Intermittent hypoxia induces disturbances in craniofacial growth and defects in craniofacial morphology

OBJECTIVES

To investigate intermittent hypoxia (IH) induced changes in craniofacial morphology and bone mineral density (BMD) in the mandible of growing rats.

DESIGN

Seven-week-old male Sprague-Dawley rats were exposed to IH for 4 days or 3 weeks. Sham-operated rats simultaneously breathed room air. Lateral and transverse cephalometric radiographs of the craniofacial region were obtained, and the linear distances between cephalometric landmarks were statistically analyzed. BMD and bone microstructure of the mandible were evaluated using micro-computed tomography (micro-CT).

RESULTS

Cephalometric analyses demonstrated that exposure to IH only in the two groups for 3 weeks decreased the size of the mandibular and viscerocranial bones, but not that of the neurocranial bones, in early adolescent rats. These findings are consistent with upper airway narrowing and obstructive sleep apnea (OSA). Micro-CT showed that IH increased the BMD in the cancellous bone of the mandibular condyle and the inter-radicular alveolar bone in the mandibular first molar (M1) region.

CONCLUSIONS

This study is the first to identify growth retardation of the craniofacial bones in an animal model of sleep apnea. Notably, 3 weeks of IH can induce multiple changes in the bones around the upper airway in pubertal rats, which can enhance upper airway narrowing and the development of OSA. The reproducibility of these results supports the validity and usefulness of this model. These findings also emphasize the critical importance of morphometric evaluation of patients with OSA.

Immortalization and characterization of mouse temporomandibular joint disc cell clones with capacity for multi-lineage differentiation

OBJECTIVE

Despite the importance of temporomandibular joint (TMJ) disc in normal function and disease, studying the responses of its cells has been complicated by the lack of adequate characterization of the cell subtypes. The purpose of our investigation was to immortalize, clone, characterize and determine the multi-lineage potential of mouse TMJ disc cells.

DESIGN

Cells from 12-week-old female mice were cultured and immortalized by stable transfection with human telomerase reverse transcriptase (hTERT). The immortalized cell clones were phenotyped for fibroblast- or chondrocyte-like characteristics and ability to undergo adipocytic, osteoblastic and chondrocytic differentiation.

RESULTS

Of 36 isolated clones, four demonstrated successful immortalization and maintenance of stable protein expression for up to 50 passages. Two clones each were initially characterized as fibroblast-like and chondrocyte-like on the basis of cell morphology and growth rate. Further the chondrocyte-like clones had higher mRNA expression levels of cartilage oligomeric matrix protein (COMP) (>3.5-fold), collagen X (>11-fold), collagen II expression (2-fold) and collagen II:I ratio than the fibroblast-like clones. In contrast, the fibroblast-like clones had higher mRNA expression level of vimentin (>1.5-fold), and fibroblastic specific protein 1 (>2.5-fold) than the chondrocyte-like clones. Both cell types retained multi-lineage potential as demonstrated by their capacity to undergo robust adipogenic, osteogenic and chondrogenic differentiation.

CONCLUSIONS

These studies are the first to immortalize TMJ disc cells and characterize chondrocyte-like and fibroblast-like clones with retained multi-differentiation potential that would be a valuable resource in studies to dissect the behavior of specific cell types in health and disease and for tissue engineering.

Micro-computed tomography analysis of changes in the periodontal ligament and alveolar bone proper induced by occlusal hypofunction of rat molars

Objective

To three-dimensionally elucidate the effects of occlusal hypofunction on the periodontal ligament and alveolar bone proper of rat molars by micro-computed tomography (micro-CT).

Methods

Occlusal function in the molar area was restricted by attaching an anterior bite plate on the maxillary incisors and a metal cap on the mandibular incisors of 5-week-old male Wistar rats for 1 week. The periodontal ligament space and alveolar bone proper around roots of the mandibular first molar were assessed by histology and micro-CT.

Results

The periodontal ligament space was narrower and the alveolar bone proper was sparser and less continuous in the hypofunction group than in the control group. Further, both the volume of the periodontal ligament and the volumetric ratio of the alveolar bone proper to the total tissue in the region of interest were significantly lower in the hypofunction group (p < 0.05).

Conclusions

Occlusal hypofunction induces atrophic changes in the periodontal ligament and alveolar bone proper of rat molars.

Impairment of nasal airway under intermittent hypoxia during growth period in rats

OBJECTIVE

To clarify the influences of intermittent hypoxia (IH) on the growth and development of the midfacial area, including the nasal cavity, in growing rats.

DESIGN

Seven-week-old male Sprague-Dawley rats were divided into two groups: the experimental group (n=5), which was exposed to IH for 8h during light periods at a rate of 20 cycles/h (nadir, 4% O₂ to peak, 21% O₂ with 0% CO₂), and the control group (n=5), which was exposed to room air. After 3 weeks, the maxillofacial structures in both groups were evaluated with respect to the height, width, length, surface area, cross-sectional area, and volume of the nasal cavity using soft X-ray and micro-CT.

RESULTS

The experimental group showed a significantly smaller cross-sectional area and volume than did the control group. The surface area exhibited no significant differences between the two groups, although it tended to be smaller in the experimental group than in the control group. The nasal volume divided by the length of the tibia (for comparison with whole-body growth) was significantly smaller in the experimental group than in the control group.

CONCLUSIONS

These data suggest that IH exposure suppresses growth and development of the nasal cavity and may result in nasal breathing disturbance.

Soft diet causes greater alveolar osteopenia in the mandible than in the maxilla

OBJECTIVE

To investigate changes in the bony microstructure of the upper and lower alveolar bone during masticatory loading induced by soft diet feeding in growing rats.

DESIGN

Three-week-old male Wistar rats were randomly divided into two groups. Rats were fed with either pellets [control group (n=6)] or a soft diet [experimental group (n=6)] for nine weeks. 3D-microstructure of the alveolar bone of the first molar region (M1) was examined by micro-CT analysis.

RESULTS

Micro-CT images showed increased marrow spaces of the inter-radicular alveolar bone around the rat mandibular M1 in the experimental group compared with that in the control group. The bone volume/tissue volume ratio, trabecular thickness, trabecular number, mean intercept length, trabecular width and trabecular star volume for the mandibular M1 inter-radicular alveolar bone were lower in the experimental group than in the control group. Marrow space star volume was increased in the experimental group compared with the control group.

CONCLUSIONS

These results suggest that alveolar osteopenia is more extensive in the mandible than the maxilla in rats that experience low masticatory loading during growth.

Occlusal hypofunction causes periodontal atrophy and VEGF/VEGFR inhibition in tooth movement

OBJECTIVE

To examine changes in microvasculature and the expression of vascular endothelial growth factor A (VEGF-A) and VEGF receptor 2 (VEGFR-2) in rat hypofunctional periodontal ligament (PDL) during experimental tooth movement.

MATERIALS AND METHODS

Twelve-week-old male Sprague-Dawley rats were divided into normal occlusion and occlusal hypofunction groups. After a 2-week bite-raising period, rat first molar was moved mesially using a 10-gf titanium-nickel alloy closed coil spring in both groups. On days 0, 1, 2, 3, and 7 after tooth movement, histologic changes were examined by micro-computed tomography and immunohistochemistry using CD31, VEGF-A, VEGFR-2, and the terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) method.

RESULTS

Hypofunctional molars inclined more than normal molars and did not move notably after day 1 of tooth movement. Blood vessels increased on the tension side of the PDL in normal teeth. Immunoreactivities for VEGF-A and VEGFR-2 in normal teeth were greater than those in hypofunctional teeth during tooth movement. Compressive force rapidly caused apoptosis of the PDL and vascular endothelial cells in hypofunctional teeth, but not in normal teeth.

CONCLUSIONS

Occlusal hypofunction induces vascular constriction through a decrease in the expression of VEGF-A and VEGFR-2, and apoptosis of the PDL and vascular cells occurs during tooth movement.

Influence of occlusal stimuli on the microvasculature in rat dental pulp

OBJECTIVE

To examine the influence of occlusal stimuli on the vasculature in the dental pulp, using an occlusal hypofunction model.

MATERIALS AND METHODS

Twenty 7-week-old male Sprague-Dawley rats were divided into two groups. To produce occlusal hypofunction, the appliances were attached to the maxillary and mandibular incisors. Untreated rats served as controls. Serial horizontal paraffin sections of the mandibular first molar were processed by conventional methods. To evaluate the microvasculature in the dental pulp, sections of each specimen were stained with hematoxylin-eosin.

RESULTS

In the experimental group, the arterioles in the tooth pulp tissue ran convergently, and their inside diameter was significantly smaller than that of the control group.

CONCLUSION

This study suggests that occlusal stimuli influence the periodontal ligament throughout the microvasculature of the dental pulp.

Occlusal stimuli influence on the expression of IGF-1 and the IGF-1 receptor in the rat periodontal ligament

OBJECTIVE

To test the hypothesis that hypofunction/recovered occlusal function has no effect on the changes in insulin-like growth factor-1 (IGF-1) and IGF-1 receptor expressions and cell proliferation of periodontal ligament (PDL) cells.

MATERIALS AND METHODS

To produce occlusal hypofunction, the appliances were attached to the rats' maxillary and mandibular incisors. Subsequently, occlusal contact of the molar area was thoroughly recovered by removal of the appliances.

RESULTS

In periodontal sections, localization of IGF-1, the IGF-1 receptor, and proliferating cell nuclear antigen (PCNA) immunoreactive cells was significantly more expressed in the control group compared with the hypofunctional group (P < .01). In addition, after the recovery of the occlusion, IGF-1, IGF-1 receptor, and PCNA were detected significantly much more than in the hypofunction group (P < .01).

CONCLUSION

The hypothesis was rejected. This study suggests that occlusal stimuli induce cell proliferation of PDL cells by increasing IGF-1 and IGF-1 receptor expression.

The influence of occlusal stimuli on basic fibroblast growth factor expression in the periodontal healing of replanted teeth

Occlusal stimuli and the periodontal healing of replanted teeth have been reported to be related. However, the mechanism for preventing dentoalveolar ankylosis remains unclear. Basic fibroblast growth factor (bFGF/FGF-2) is considered as a key factor in wound healing. The purpose of this study was to evaluate the relationship between occlusal stimuli, bFGF, and the periodontal healing after tooth replantation. Five-week-old male rats were divided into non-occluded, occluded, and recovery groups. The right maxillary first molars were replanted in all groups, and the left maxillary first molars in the 2-week occluded group without replantation were served as nontreated. An anterior bite plate was attached to the maxillary and mandibular incisors to produce occlusal hypofunction in the non-occluded group and was then removed after 1 week in the recovery group. Histological observations were performed after 1 and 2 weeks of the experimental period. After 2 weeks, the non-occluded group had detectable ankylosis and obvious periodontal tissue stricture. Meanwhile, the occluded and recovery groups showed enlarged and thickened periodontia without ankylosis. The number of bFGF-positive cells in the occluded and recovery groups significantly increased as compared to in the non-occluded group. These results suggest that occlusal stimuli enhance the production of bFGF in the periodontal healing of replanted teeth and prevent dentoalveolar ankylosis.

Influence of estrogen cycle on temporomandibular joint synovial membrane in rat with deviated mandible

Temporomandibular disorders (TMD) are known to be more prevalent and severe in women than in men, especially in those who are in their reproductive age. In those patients reproductive hormones may play a vital role in the host adaptive capacity of the temporomandibular joint (TMJ). In order to clarify the relationship between TMD prevalence and estrogen cycle, a mandible deviated animal model was carried out, and the expression of inducible nitric oxide synthase (iNOS), an essential enzyme in the pathogenesis of inflammatory arthritis, was investigated in the rat's synovial tissue. An appliance was attached to the rat's incisors to produce a lateral deviation of the mandible during the metestrus phase, and the animals were sacrificed in the proestrus and estrus phase, when the estrogen was at the highest and lowest level, respectively. Immunostaining was then performed for 2 consecutive estrous cycles to demonstrate iNOS expression in the synovial membrane of the TMJ. The immunoreactivity for iNOS was more intense in the synovial membrane on the contralateral side in the proestrus phase (estrogen peak phase). These observations suggest that iNOS expression in the synovial membrane with mandibular deviation may be exacerbated in the presence of estrogen.

Involvement of the collagen I-binding motif in the anti-angiogenic activity of pigment epithelium-derived factor

Pigment epithelium-derived factor (PEDF) is the most potent endogenous inhibitor of angiogenesis in age-related macular degeneration and tumors. However, the molecular mechanism of the anti-angiogenic activity of PEDF is poorly understood. PEDF interacts with the extracellular matrix (ECM) in vitro. Here, we investigated the possible involvement of the motif for ECM interaction in the anti-angiogenic activity of PEDF. The growth rates of HeLa cells in culture were not affected by transfection of PEDF, indicating that PEDF did not suppress tumor cell growth directly. In tumor xenografts, the overexpression of wild-type PEDF significantly suppressed tumor growth, whereas a mutant of the collagen I-binding site of PEDF (Col-mut PEDF) did not inhibit tumor growth. A mutant of the heparin-binding site of PEDF (Hep-mut PEDF) suppressed tumor growth. Histological analysis showed that the density and area of microvasculatures in either PEDF or Hep-mut PEDF were suppressed when compared with those in either vector or Col-mut PEDF. Our data indicate that PEDF inhibits tumor growth via its anti-angiogenic activity, and the collagen I-binding motif of PEDF is involved in the biological activity.