Decreased expression of ATP-binding cassette protein G1 promotes abnormal adipogenesis of condylar chondrocytes in temporomandibular joint osteoarthritis

BACKGROUND

Abnormal lipid metabolism is involved in the development of osteoarthritis (OA). ATP-binding cassette protein G1 (ABCG1) is crucial in mediating the outflow of cholesterol, phosphatidylcholine and sphingomyelin and reducing intracellular lipid accumulation.

OBJECTIVE

This study aimed to evaluate whether ABCG1 participates in the abnormal adipogenesis of chondrocytes in osteoarthritic cartilage of temporomandibular joint.

METHODS

Eight-week-old female rats were subjected to unilateral anterior crossbite (UAC) to induce OA in the temporomandibular joint (TMJ). Histochemical staining, immunohistochemical (IHC) staining, and qRT-PCR were performed. Primary condylar chondrocytes of rats were transfected with ABCG1 shRNA or overexpression lentivirus and then stimulated with fluid flow shear stress (FFSS). Cells were collected for oil red O staining, immunofluorescence staining, and qRT-PCR analysis.

RESULTS

Abnormal adipogenesis, characterized by increased expression of Adiponectin, CCAAT/enhancer-binding protein α (Cebpα), fatty acid binding protein 4 (Fabp4) and Perilipin1, was enhanced in the degenerative cartilage of TMJ OA in rats with UAC, accompanied by decreased expression of ABCG1. After FFSS stimulation, we observed lipid droplets in the cytoplasm of cultured cells with increased expression of Adiponectin, Cebpα, Fabp4 and Perilipin1 and decreased expression of ABCG1. Knockdown of Abcg1 induced abnormal adipogenesis and differentiation of condylar chondrocytes. Overexpression of ABCG1 alleviated the abnormal adipogenesis and differentiation of condylar chondrocytes induced by FFSS.

CONCLUSIONS

Abnormal adipogenesis of chondrocytes and decreased ABCG1 expression were observed in degenerative cartilage of TMJ OA. ABCG1 overexpression effectively inhibits the adipogenesis of chondrocytes and thus alleviates TMJ condylar cartilage degeneration.

Spinal CCK1 Receptors Contribute to Somatic Pain Hypersensitivity Induced by Malocclusion via a Reciprocal Neuron-Glial Signaling Cascade

Recent studies have shown that the incidence of chronic primary pain including temporomandibular disorders (TMD) and fibromyalgia syndrome (FMS) often exhibit comorbidities. We recently reported that central sensitization and descending facilitation system contributed to the development of somatic pain hypersensitivity induced by orofacial inflammation combined with stress. The purpose of this study was to explore whether TMD caused by unilateral anterior crossbite (UAC) can induce somatic pain hypersensitivity, and whether the cholecystokinin (CCK) receptor-mediated descending facilitation system promotes hypersensitivity through neuron-glia cell signaling cascade. UAC evoked thermal and mechanical pain hypersensitivity of the hind paws from day 5 to 70 that peaked at week 4 post UAC. The expression levels of CCK1 receptors, interleukin-18 (IL-18) and IL-18 receptors (IL-18R) were significantly up-regulated in the L4 to L5 spinal dorsal horn at 4 weeks post UAC. Intrathecal injection of CCK1 and IL-18 receptor antagonists blocked somatic pain hypersensitivity. IL-18 mainly co-localized with microglia, while IL-18R mainly co-localized with astrocytes and to a lesser extent with neurons. These findings indicate that the signaling transduction between neurons and glia at the spinal cord level contributes to the descending pain facilitation through CCK1 receptors during the development of the comorbidity of TMD and FMS. PERSPECTIVE: CCK1 receptor-dependent descending facilitation may mediate central mechanisms underlying the development of widespread somatic pain via a reciprocal neuron-glial signaling cascade, providing novel therapeutic targets for the clinical treatment of TMD and FMS comorbidities.

[Mitochondrial calcium overload in the masseter muscle of rats with occlusal interference: ionic changes and regulation by calmodulin kinase II]

OBJECTIVE

To investigate the changes in mitochondrial calcium and extracellular sodium concentrations in the masseter muscle of rats with occlusal interference and the regulatory mechanism of mitochondrial Ca²⁺ overload by calmodulin kinase II (CaMK II).

METHODS

SD rat models of occlusal interference were established by placing a stainless steel segments (0.8 mm in diameter) to raise the occlusal surface of the upper right first molar. At 3, 7, 14, and 21 days after occlusal interference and at 3 days after removal of occlusal interference, HE staining was used to observe the histomorphological changes of the masseter muscle. Mitochondrial calcium concentration in the masseter muscle was detected using fluorescence spectrophotometry, and direct turbidimetry with potassium pyroantimonate was used to detect the extracellular sodium concentration; the expression levels of masseter muscle p-CaMK II (Thr287) and CaMK II were detected using Western blotting.

RESULTS

Compared with those in the corresponding control groups, mitochondrial Ca²⁺ concentration in the masseter muscle on occlusal interference side increased significantly at 3, 7, 14 and 21 days after occlusal interference (P<0.05), but was significantly lowered at 3 days after removal of the interference (P<0.05). The concentration of extracellular Na⁺ increased progressively with time at 3, 7, 14 and 21 days after occlusal interference (P<0.05), and was significantly decreased at 3 days after interference removal (P<0.05). Occlusal interference for 3, 7 and 14 days resulted in significantly increased expressions of p-CaMK II (Thr287) and CaMK II (P<0.05), which was significantly decreased at 21 days compared with those in the control groups (P<0.05) and further decreased after removal of occlusal interference (P<0.05). Similar changes were also observed on the side without interference, but the changes on the interference side were more obvious (P<0.05).

CONCLUSION

Occlusal interference causes elevated mitochondrial Ca²⁺ and extracellular Na⁺ concentrations in the masseter muscle of rats to lead to calcium overload; the increase in mitochondrial Ca²⁺ concentration is correlated with the phosphorylation level of CaMK II signaling pathway, suggesting a negative feedback regulation mechanism by the CaMK II signal pathway.

Alterations in the masseter muscle and plasma IL-6 level following experimentally induced occlusal interference and chronic stress--a study in rats

This study was undertaken to examine the alteration of masseter and plasma interleukin-6 after inducing occlusal interference and chronic stress. Male Wistar rats were submitted to chronic stress procedure, exposed to occlusal interference, or exposed to both mentioned procedures. Whole blood and masseter tissue were collected to determine interleukin-6 level, measured by means of ELISA. Masseter pain was evaluated using the orofacial formalin test. Masseter interleukin-6 level was significantly higher in animals submitted to combination of occlusal interference and chronic stress than in the control group (p<0.05). There was positive and significant correlation between pain response and masseter interleukin-6 level (r=0.5741; p<0.0003). No significant differences in plasma interleukin-6 level were found between groups (p>0.05), as well as no correlation with pain (p>0.05). Combination of occlusal interference and chronic stress leads to strong local reaction characterized by high levels of masseter interleukine-6. High concentrations of muscle interleukin-6 and its correlation with pain point to inflammatory background of masticatory muscle pain.

Malocclusion induces chronic stress

We examined the effect of occlusal disharmony in senescence-accelerated (SAMP8) mice on plasma corticosterone levels, spatial learning in the water maze, fos induction, hippocampal neuron number, expression of glucocorticoid receptors (GR) and glucocorticoid receptor messenger ribonucleic acid (GRmRNA) in hippocampus and inhibitor of glucocorticoid (metyrapone). Bite-raised aged mice had significantly greater plasma corticosterone levels than age-matched control mice as well as impaired spatial memory and decreased Fos induction and a number of neurons in hippocampus. GR and GRmRNA expressions were significantly decreased in aged bite-raised mice compared with age-matched control mice. Pretreatment with metyrapone inhibited not only the bite-raised induced increase in plasma corticosterone levels, but also the reduction in the number of hippocampal neurons and impaired spatial learning. These datas suggest that the bite-raised condition may enhance the aging process in hippocampus, thereby leading to impairment of spatial memory by stress.

[A study on the levels of soluble intercellular adhesion molecule-1 in the gingival crevicular fluid of the malocclusion patients with fixed appliances]

OBJECTIVE

To investigate the levels of soluble intercellular adhesion molecule-1(sICAM-1) shed into the gingival crevicular fluid (GCF) of 31 malocclusion cases, who received fixed appliances orthodontic treatment in period of pre-treatment, 1,4,8 weeks of treatment. To determine if the fixed appliance will affect the periodontal health.

METHODS

The soluble intercellular adhesion molecule-1 in gingival crevicular fluid carefully collected with standardized filter strips from 31 patients with fixed appliance were measured,using an ELISA technique. The relation between the level of GCF and sICAM-1 during treatment was analyzed.

RESULTS

After one week of treatment, the levels of sICAM-1 in GCF increased significantly.

CONCLUSION

Using fixed appliances will affect the periodontal health. The levels of soluble intercellular adhesion molecule-1 in GCF can be used as an efficient method for monitoring periodontal health during orthodontic treatment.

[The biological effects of recombinant human bone morphogenetic protein 2 on human periodontal ligament fibroblasts]

OBJECTIVE

The purpose of this study is to study the biological effects of recombinant human bone morphogenetic protein 2 (rhBMP2) on human periodontal ligament fibroblasts (HPDLFs).

METHODS

Human periodontal ligament fibroblasts were primary cultured and detected the different doses of rhBMP2 on their proliferation, alkaline phosphatase (ALP) activity, osteocalcin (OC) synthesis and formation of the mineralized nodules.

RESULTS

rhBMP2 (0.25-2 mg/ml) had no remarkable effect on the proliferation of HPDLFs. The ALP activity, OC synthesis and formation of the mineralized nodules of HPDLFs were significantly stimulated by 0.5-2 mg/ml rhBMP2.

CONCLUSION

The effects of rhBMP2 on HPDLFs are dose-dependent. Not only can rhBMP2 stimulate the expression but also promote the maturation of osteoblastic phenotype of HPDLFs.

Occlusal disharmonies modulate central catecholaminergic activity in the rat

Occlusal disharmonies have classically been thought to be involved in the etiopathogenesis of bruxism, as have, more recently, alterations in central neurotransmission, particularly dopaminergic neurotransmission. However, the connection between these two factors has still not been established. In this study, we assessed the effects of diverse occlusal disharmonies, maintained for either 1 day or 14 days, on neurochemical indices of dopaminergic and noradrenergic activity in the striatum, frontal cortex, and hypothalamus of the rat. The in vivo activity of tyrosine hydroxylase, determined as the accumulation of 3,4-dihydroxyphenylalanine (DOPA), 30 min after the administration of 3-hydroxybenzylhydrazine, a DOPA decarboxylase inhibitor, and dopamine and noradrenaline contents were quantified by high-performance liquid chromatography with electrochemical detection. The wearing of an acrylic cap on both lower incisors for 1 day induced a significant increase in DOPA accumulation in the regions analyzed, with parallel increases in dopamine levels in the hypothalamus and dopamine and noradrenaline in the frontal cortex. After the cap was maintained for 14 days, DOPA accumulation tended to return to control values, except in the left striatum, thereby causing an imbalance between hemispheres. In contrast, 1 or 14 days after the lower left and the upper right incisors were cut, less pronounced changes in catecholaminergic neurotransmission were found in the brain areas studied. Moreover, the cutting of one lower incisor did not modify either DOPA accumulation or dopamine and noradrenaline contents in the striatum or hypothalamus. These results provide experimental evidence of a modulation of central catecholaminergic neurotransmission by occlusal disharmonies, being dependent on the nature of the incisal alteration and on the time during which it was maintained.

Adaptation of guinea-pig superficial masseter muscle to an increase in occlusal vertical dimension

To study the effect of increased occlusal vertical dimension on the fibre phenotypes of the superficial masseter muscle, the composition of myosin heavy-chains (MHC), myosin light-chains (MLC) and tropomyosin was investigated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and two-dimensional gel electrophoresis in conjunction with densitometric analysis in normal (control) and bite-opened (5.7 mm increase in the vertical dimension for 1 week) guinea-pigs. The superficial masseter contained two fast-type MHC isoforms, II-1 and II-2, in both the bite-opened and control groups; their relative content (mean+/-SD, n = 7) was 47.8+/-2.9% and 52.2+/-2.9%, in the bite-opened and 44.4+/-3.0% and 55.6+3.0% in control preparations, indicating no significant (p>0.05) changes in MHC composition in association with the bite opening. On the other hand, significant differences in MLC and tropomyosin composition were found between the two preparations. Although the MLC consisted of three components, LC1f, LC2f and LC3f, in both preparations, their relative content (mean+/-SD, n = 7) was 37.1+/-2.4%, 49.6+/-1.6% and 13.2+/-3.2%, respectively, in the bite-opened and 28.1+/-3.1%, 50.9+/-1.6% and 21.0+/-3.5% in the control preparations, indicating that the bite opening induced a significant (p < 0.0001) increase in the relative content of LC1f at the expense of that of LC3f. Although the tropomyosin consisted of two components, TM-alpha and TM-beta, in both preparations, their relative content (mean+/-SD, n = 7) was 91.8%+/-1.9% and 8.2+/-1.9%, respectively, in the bite-opened and 95.9+/-0.7% and 4.1+/-0.7% in the control preparations, showing a significant (p < 0.001) increase in the relative content of TM-beta in relation to the bite opening. These results indicate that in guinea-pigs an increase in occlusal vertical dimension for 1 week changes the composition of MLC and tropomyosin, with no significant change in MHC, in the masseter muscle. These changes might be required to meet altered functional demands.

Expression of an embryonic fibronectin splicing variant in human masseter muscle

Fibronectin is an extracellular matrix protein that is a key constituent of all skeletal muscles. Its deposition increases in a number of pathological conditions, including some muscular dystrophies in which a progressive increase in lower-face height is often noted. It has been shown in other organ systems that increased deposition of fibronectin is associated with changes in the expression of differentially spliced isoforms of the molecule. This investigation documents the expression of mRNA coding for fibronectin and its splicing variants, EIIIA and EIIIB, in biopsies of masseter muscle from normal and long-face patients, using reverse transcriptase-polymerase chain reaction. Expression was compared with that occurring in anatomically and embryologically differing somatic skeletal muscle. Masseter expressed fibronectin mRNA containing the EIIIA but not the EIIIB splicing variant. Conversely, somatic skeletal muscle expressed neither the EIIIA nor EIIIB variants. There were no differences between expression of fibronectin containing the EIIIA splicing variants in masseter from normal and long faces. These results suggest that variations in fibronectin expression reflect the differing functional demands of muscles from different anatomical locations and indicate that jaw and somatic muscle belong to different allotypes.

Proteoglycan expression in the rat temporomandibular joint in response to unilateral bite raise

The vertebrate articular tissue consists of collagen fibers embedded in a ground substance. Collagen resists tensile forces, while proteoglycans in the ground substance provide resilience and resistance to compression. It was hypothesized that unilateral bite raise would induce increasing expression of proteoglycans in TMJ articular tissues. As a test of this hypothesis, six- and nine-week-old Sprague-Dawley rats received unilateral bite-raising appliances bonded to their right upper molars for 4 wks. A group of nine-week-old rats was housed for an additional 4 wks after removal of the appliances they had worn for 4 wks. Proteoglycans that carry abundant chondroitin sulfate and keratan sulfate side-chains, most likely aggrecans, were detected by safranin O in the fibrocartilaginous zone of the condyle in parasagittal sections. A monoclonal antibody against a large chondroitin sulfate proteoglycan related to versican reacted strongly in the surface fibrous layer of the mandibular condyle and moderately in the discs of the treated specimens. Computer quantification for safranin O and anti-versican antibody staining revealed that the average intensities of the treated specimens were significantly higher than those of their corresponding sham-operated controls, and the average intensities of the treatment-reversal specimens had no significant differences from their corresponding sham-operated controls. Thus, unilateral bite raise appeared to have induced an increase in the expression of aggrecan in the condylar cartilage and a proteoglycan related to versican in the TMJ disc and the articular surface of the condyle. The elevated proteoglycan expression is interpreted to suggest that unilateral bite raise leads to an increase in the magnitude of compressive forces in the rat temporomandibular joint.

Effect of an increase in occlusal vertical dimension on the rate of cyclic actin-myosin interaction in guinea-pig masseter muscle

To study the effects of increased occlusal vertical dimension on these kinetics, the actin-filament sliding velocity on masseter myosins in an in vitro motility assay and the ATPase activity of masseter myosins from normal (control) and bite-opened (5.6 mm increase in the vertical dimension for 1 week) guinea-pigs were measured. In control myosin preparations, the average value (mean +/- SD, n = 5) for the actin-filament sliding velocity at 25 degrees C was 4.0 +/- 0.3 microns/sec. In bite-opened myosin preparations (n = 5), it was 3.4 +/- 0.3 microns/sec, a significant (p < 0.01) decrease. Myosin ATPase activity was also decreased significantly (p < 0.01) from 1.0 +/- 0.1 to 0.7 +/- 0.1 mumol Pi mg per min (mean +/- SD, n = 5) after the bite opening. These results strongly suggest that in guinea-pigs an increase in occlusal vertical dimension for 1 week decreases the turnover rate of actin-myosin interaction in the masseter through changes in the myosin isozyme. These changes may result in a slowing of the rate of detachment of myosin cross-bridges from actin filaments.

Influence of diet composition and malocclusion on masticatory organs in rats

The present study was undertaken to determine the effects of different dietary consistencies and malocclusion induced by extraction of molar teeth on the masticatory organs of weaning and adult rats, by determining the biochemical properties of masseter muscle, and also Ca and P levels in mandibular bone. Male SD rats, 3 and 20 weeks old, were divided into 3 groups. Group one (G-1) was maintained on a solid diet, and Groups two (G-2) and three (G-3) on a semi-solid diet. Furthermore, the mandibular molar teeth of G-3 rats were extracted. The experimental period was 120 days. The masseter muscle and mandibular bone weights of G-1 in weaning rats were increased significantly in comparison with G-3, but not in adult rats. The CPK activities in weaning and adult rats of G-1 were higher than those in the other two groups. The order of LDH activity in weaning and adult rats was G-3 > G-2 > G-1. G-2 and particularly G-3 showed significantly lower glycogen contents than G-1. The Ca and P contents of the mandibular bone in G-2 and G-3 were lower than those in G-1. These results suggest that a different dietary consistency and malocclusion induced by extraction of mandibular molar teeth have a considerable influence on the development of masticatory organs, mandibular bone and masseter muscle.

[Involvement in morphological changes of the articular cartilage of rat temporomandibular joint induced by experimental malocclusion]

The effect of malocclusion induced by increase in unilateral occlusal vertical dimension on the articular cartilage of rat mandibular condyle was histologically and immunohistologically examined. WKA rats (8 weeks) were divided into three group A: untreated (control) rats, group B: rats forced to mouth open just for 20 min, and group C: rats given malocclusion by putting the 1 mm diameter wire on the right upper molar continuously. After treatment, each rat was sacrificed periodically up to 9 weeks, and the morphological changes of condylar cartilage (articular, embryonic and transitional zones of cartilage layer) were histologically investigated. The thickness of articular cartilage in all groups was decreased in a time-dependent manner (up to 9 weeks after treatment). In group C rats, whose articular cartilage was thinnest in three groups, the reduced thickness of cartilage in the non-treated side (the left side) was same as that in the treated side which was presented with excessive molar contact. But, its occurrence in the treated side was seen 2 weeks earlier than that in the non-treated side. Even in group B rats which were only forced to open the mouth for 20 min without setting of permanent malocclusion, the thickness of condylar cartilage was decreased more than that of group A rats. When the condylar cartilages of all three groups were immunohistologically examined with anti-interleukin-1 (IL-1) antibody in order to investigate the pathophysiological involvement of IL-1, which is well-known catabolic factor to cartilage, some chondrocytes in articular cartilage were positively stained. The ratio of IL-1 positive cells increased time-dependently. IL-1-producing cells in group B and the non-treated side of group C reached to the maximal ratio at the same time when the condylar cartilage markedly decreased in thickness. However, the ratio of IL-1-positive chondrocytes in the treated side of group C was maximal four weeks after the decrease of cartilage thickness. In respect with the size of cells in cartilage, the occurrence of decreased thickness in condylar cartilage corresponded to that of the reduction of cellular size, especially in the embryonic zone of group C. These results described above suggest that malocclusion, unilateral immature occlusion, can induce the thinning of condylar cartilage which may result from the reducing size of articular chondrocytes (differentiated chondrocytes) and the accompanying decreased cartilage matrix. This change of cartilage may be caused by IL -1 that articular chondrocyte seemed to produce.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of rate of eruption on periodontal ligament glycosylaminoglycan content and enamel formation in the rat incisor

The rate of eruption of rat mandibular incisors was either increased by cutting one tooth out of occlusion or eliminated by means of pinning. The effects of such changes in eruption rate on the sulphated glycosylaminoglycan content of the periodontal ligaments was analysed. The length of the enamel secretory zone and the composition of the developing enamel matrix protein was also compared. Sulphated glycosylaminoglycan content of the periodontal ligament increased fourfold (P < 0.001) during accelerated eruption but decreased to a corresponding extent (P < 0.001) in the absence of eruption, when compared with controls. The length of the enamel secretory zone was also significantly reduced in the immobilised teeth, although the protein content was similar compared with controls. The results demonstrate the differential response to varied eruption rates of the periodontal ligament and enamel, particularly in respect of the extracellular matrix. The data are consistent with the view that the ground substance of the periodontal ligament plays a role in the generation of the eruptive force.

Influence of occlusion on the fluoride distribution in rat molar cementum

This study was undertaken to examine the influence of occlusion on the fluoride distribution in cementum following an experiment in which the occlusion in rats was locally altered by extracting the upper left molar. These and control rats with normal occlusion were given water containing 0 or 100 ppm fluoride for 12 weeks. The fluoride distributions in cementum from both first lower molars of the same animal were compared. The fluoride concentrations had increased throughout the tissue as a result of increased fluoride administration, irrespective of any changes in occlusion. They were, as usual, generally highest at or near the cementum surface and decrease towards the interior of the tissue. Where there had been a change in occlusion, the thickness of cementum was less than that of the contralateral tooth, but, despite this, the fluoride profiles in contralateral teeth were similar in both experimental and control rats. In the experimental rats, on the other hand, the total fluoride tended to be lower, and the mean fluoride tended to be higher in left molars without antagonists. These findings were never seen in the control rats. It was concluded that the alteration in occlusion influenced the fluoride distribution in the cementum through its effect on the rate of cementum formation.

[Problems and characteristics of the orthodontic treatment of a patient with adrenogenital syndrome]

This article describes biochemical relationships accompanying pathological symptoms of C-21-hydroxylase deficiency (adrenogenital syndrome). Disturbances of bone growth and development have been observed, even during medical treatment. A discrepancy of 2 1/2 years was noted between the patients chronological age and his bone development. The patient reaches a maximum height of 155 to 160 cm. Supernumeraries and delayed mineralisation are to be expected. Surgical procedures require an increase in cortisone dosage. When considering orthodontic treatment, one must determine the most appropriate time to start, take into account the long retention period and pay particular attention to oral hygiene.

Histochemical and immunohistochemical studies on the articular disk of the temporomandibular joint in rats

The effects of surgically induced malocclusion upon the articular disk of the temporomandibular joint in adult male rats were investigated histochemically and immunohistochemically using antibody against type II collagen. In the intermediate portion of the articular disk, the number of collagen fibers and chondrocytes was much less and the collagen fibers became more wavy, rough and irregular in surgically operated rats than in control rats. Clusters of chondrocytes were found in some experimental rats. The present experiments revealed that surgically induced malocclusion causes noticeable changes in collagen fibers and chondrocytes within the extracellular matrix of the articular disk of the temporomandibular joint.

Histochemical study of the masseter muscle in patients with vertical maxillary excess

This study was designed to examine the morphologic properties of the masseter muscle in individuals with vertical maxillary excess (VME). The deep surface of the anterior aspect of the superficial masseter was biopsied in nine patients at the time of corrective surgery. Individual muscle fibers were classified as slow-twitch-oxidative (SO), fast-twitch-oxidative-glycolytic (FOG), or fast-twitch-glycolytic (FG) based on staining characteristics using a battery of histochemical procedures. Most patients had normal tissue, although there were considerable differences in size and distribution of the three fiber types. Generally, SO fibers were the largest and most prevalent type of fiber. Two individuals, however, demonstrated evidence of muscle pathology that primarily affected the FG fiber population. Histochemical evidence of muscle pathology has not previously been reported in patients with VME, and the pattern of SO dominance observed in these patients may be different from the distribution that would be seen in the masseter of a person free of craniofacial deformities.