Morphohistological Change and Expression of HSP70, Osteopontin and Osteocalcin mRNAs in Rat Dental Pulp Cells with Orthodontic Tooth Movement

The Role of Molecular Chaperones (Hspas/Hsp70S) in Oral Health and Oral Inflammatory Diseases: A Review

Heat shock proteins of the 70kDa family (HSPAs/HSP70s) are major molecular chaperones and cytokines of most cells and microbes, extracellular and interstitial fluids, blood, synovial fluids and secretory body fluids like saliva. The induction of human HSPAs plays an important role at cellular level under most stress conditions; whereas microbial HSPAs improve microbial tolerance to environmental changes, and improve virulence and resistance against antimicrobial peptides. Extracellular HSPAs reveal cytoprotective properties and are involved in numerous physiological and pathological events, including modulation of cytokine release and immunity. Accordingly, HSPAs play a role in the maintenance of pulpal health, and the repair of injured dental hard tissues. HSPAs also play a role in stress adaptation of periodontal tissues, and in the maintenance of periodontal and mucosal health including defense against microbes, prevention of mucosal allergic reactions, and facilitation of healing of ulcers and wounds. Despite their advantageous effects maintaining health of several oral tissues, HSPAs are likely to play a role in the disadvantageous amplification of pulpal inflammatory response to bacteria, and in the formation of several periapical inflammatory lesions. HSPAs may also induce gingivitis under certain conditions, and play a role in the progression of periodontal bone defects. HSPAs may also play a role in atopic-type allergic reactions, autoimmune disorders, and haptenation in certain cases. Based on the above data, it can be assumed that HSPAs play an important role in oral defense under healthy conditions; however, their role is somewhat “Janus-faced” under pathological conditions.

Age-related changes of dental pulp tissue after experimental tooth movement in rats

It is generally accepted that the effect of orthodontic tooth movement on the dental pulp in adolescents is reversible and that it has no long-lasting effect on pulpal physiology. However, it is not clear yet if the same conclusion is also valid for adult subjects. Thus, in two groups of rats, aged 6 and 40 weeks respectively, 3 molars at one side of the maxilla were moved together in a mesial direction with a standardized orthodontic appliance delivering a force of 10 cN. The contralateral side served as a control. Parasagittal histological sections were prepared after tooth movement for 1, 2, 4, 8, and 12 weeks. The pulp tissue was characterized for the different groups, with special emphasis on cell density, inflammatory cells, vascularity, and odontoblasts. Dimensions of dentin and the pulpal horns was determined and related with the duration of orthodontic force application and age ware evaluated. We found that neither in young nor in adult rats, force application led to long-lasting or irreversible changes in pulpal tissues. Dimensional variables showed significant age-related changes. In conclusion, orthodontic tooth movement per se has no long-lasting or irreversible effect on pulpal tissues, neither in the young nor in the adult animals.

Expression and Function of Hypoxia Inducible Factor-1α and Vascular Endothelial Growth Factor in Pulp Tissue of Teeth under Orthodontic Movement

Orthodontic force may lead to cell damage, circulatory disturbances, and vascular changes of the dental pulp, which make a hypoxic environment in pulp. In order to maintain the homeostasis of dental pulp, hypoxia will inevitably induce the defensive reaction. However, this is a complex process and is regulated by numerous factors. In this study, we established an experimental animal model of orthodontic tooth movement to investigate the effects of mechanical force on the expression of VEGF and HIF-1α in dental pulp. Histological analysis of dental pulp and expressions of HIF-1α and VEGF proteins in dental pulp were examined. The results showed that inflammation and vascular changes happened in dental pulp tissue in different periods. Additionally, there were significant changes in the expression of HIF-1α and VEGF proteins under orthodontic force. After application of mechanical load, expression of HIF-1α and VEGF was markedly positive in 1, 3, 7 d, and 2 w groups, and then it weakened in 4 w group. These findings suggested that the expression of HIF-1α and VEGF was enhanced by mechanical force. HIF-1α and VEGF may play an important role in retaining the homeostasis of dental pulp during orthodontic tooth movement.

Interleukin-17/T-helper 17 cells in an atopic dermatitis mouse model aggravate orthodontic root resorption in dental pulp

Interleukin (IL)-17 is an important mediator of orthodontically induced inflammatory root resorption (OIIRR). However, its role in the dental pulp (DP) has not been studied. The aim of this study was to investigate, using an atopic dermatitis (AD) model, how IL-17 contributes to OIIRR in DP. Atopic dermatitis is the most common IL-17-associated allergic disease. Atopic dermatitis model mice (AD group) and wild-type mice (control group) were subjected to an excessive orthodontic force. The localization of T-helper (Th)17 cells, IL-17, IL-6, and keratinocyte chemoattractant (KC; an IL-8-related protein in rodents) were determined in DP. In addition, CD4+ T cells, including IL-17 production cells, were obtained from patients with AD and from healthy donors, and the effects of IL-17 on the production of IL-6 and IL-8 were investigated using a co-culture of CD4+ T cells with human dental pulp (hDP) cells stimulated with substance P (SP). Immunoreactivity for Th17 cells, IL-17, IL-6, and KC was increased in DP tissue subjected to orthodontic force in the AD group compared with DP tissue subjected to orthodontic force in the control group. The cells obtained from the AD patients displayed increased IL-6 and IL-8 production. These results suggest that IL-17 may aggravate OIIRR in DP.

Immunohistochemical expression of heat shock protein27 in the mouse dental pulp after immediate teeth separation

Aim

After immediate teeth separation, expression of HSP27 in the mouse dental pulp was examined. Immunohistochemistry was performed to examine the incidence of HSP27 expression.

Materials and methods

A total of 36 8-week-old ddY mice were used as experimental subjects and a wedge was inserted in between maxillary right molars. The wedge was removed 30 min or 3 h after insertion. Animals were immediately sacrificed after the removal of wedge or until 1 week later and serial sections from paraffin-embedded tissues were prepared. Immunohistochemistry was carried out to examine the expression of HSP27. The untreated side served as the control.

Results

In the control group, the endothelial cells and some pulp fibroblasts weakly expressed HSP27 suggesting that the expression is due to mechanical stress brought about by physiological masticatory force and pressure from the tongue. In both 30 min and 3 h experimental groups, HSP27 expression was highest at 24 h after wedge removal and the expression remained the same or started to decrease thereafter. The expression decreased at the same level as that of the control group 1 week after wedge removal.

Conclusion

HSP27 may serve as an indicator of stimulus strong enough to show its expression.

Immunohistochemical expression of hard tissue related factors in the mouse dental pulp after immediate teeth separation

We examined change of Runx2 and ALP expression in mouse tooth pulp which exposed to teeth separation experiment by immunohistochemistry as a model for conservative dentistry treatment. 8-week-old 36 male ddY mice were used and wedge was inserted between upper 1st and 2nd molars. The wedge was removed 30 minutes as well as 3 hours after the insertion and the samples were prepared extending up to 1 week of time period for regular histopathological and immunohistochemical examinations for ALP and Runx2 expression. The opposite sides without wedge insertion were taken as controls. In the control group pulp, weak expressions of Runx2 and ALP in the vessel endothelial cells as well as the pulp cells were revealed, suggesting the appearance of these genes upon mechanical stress induced by mastication and tongue pressure etc. On the other hand in the experiment group, Runx2 expression increased both in 30-minute and 3-hour teeth separation group. The expression became maximum at 24 hours. Then it gradually decreased and became similar level with the control group at 1-week after the wedge insertion. Similarly ALP expression increased after the wedge insertion and was maximum at 24 hours and then gradually decreased to the levels similar with the control group. These results suggest that when immunohistochemical expression of Runx2 as well as ALP was used as an index, no severe damage occur upon clinical application of wedge insertion.

Effect of stretching stress on gene transcription related to early-phase differentiation in rat periodontal ligament cells

Mechanical stress such as occlusal and orthodontic loading has been suggested to induce a homeostatic and regenerative response in periodontal ligament (PDL), but the underlying mechanism remains to be clarified. The purpose of this study was to investigate expression of mRNAs encoding proteins involved in osteogenesis and homeostasis by PDL cells following application of tensile stress and characterize the relationship between such expression and the regenerative and homeostatic functions of the PDL. PDL cells were obtained from rats and stretched by 9% or 18% at a frequency of 6 cycles/min for 12 hr to 5 days in a FX-4000T&trade; culture system. After stretching, expression of mRNAs encoding collagen type I (Col-I), alkaline phosphatase (ALP), bone morphogenetic protein-2 (BMP-2), bone morphogenetic protein-4 (BMP-4), heat shock protein 70 (HSP70) and basic fibroblast growth factor (bFGF) was investigated. The highest levels of Col-I, ALP and BMP-2 mRNA expression occurred at 12 hr, while those of BMP-4 and HSP70 occurred at 1 day and 5 days, respectively. Expression levels of Col-I, ALP, BMP-2, BMP-4 and HSP70 increased magnitude-dependently with stretching force in the stretching groups. In contrast, expression of bFGF mRNA showed statistically significant reduction in both stretching groups, with the largest reduction seen in the 9% stretching group (p<0.01). These results suggest that stretching of PDL cells provokes significant increases in expression of factors promoting osteogenic differentiation and HSP70, which protects PDL cells undergoing mechanical stress and contributes to maintenance of PDL homeostasis. However, expression of bFGF was restrained. Reduced expression of bFGF mRNA suggested that there was an optimum magnitude of stretching force for increasing expression.

Immunohistochemical expression of heat shock proteins in the mouse periodontal tissues due to orthodontic mechanical stress

The histopathology of periodontal ligament of the mouse subjected to mechanical stress was studied. Immunohistochemical expressions of HSP27 and pHSP27 were examined. Experimental animals using the maxillary molars of ddY mouse by Waldo method were used in the study. A separator was inserted to induce mechanical stress. After 10 minutes, 20 minutes, 1 hour, 3 hours, 9 hours and 24 hours, the regional tissues were extracted, fixed in 4% paraformaldehyde and 0.05 M phosphate-buffered fixative solution. Paraffin sections were made for immunohistochemistry using HSP27 and p-HSP27. In the control group, the periodontal ligament fibroblasts expressed low HSP27 and p-HSP27. However, in the experimental group, periodontal ligament fibroblasts expressed HSP27 10 minutes after mechanical load application in the tension side. The strongest expression was detected 9 hours after inducing mechanical load. p-HSP27 was also expressed in a time-dependent manner though weaker than HSP27. The findings suggest that HSP27 and p-HSP27 were expressed for the maintenance of homeostasis of periodontal ligament by the activation of periodontal ligament fibroblasts on the tension side. It also suggests that these proteins act as molecular chaperones for osteoblast activation and maintenance of homeostasis.

The expression of heat shock protein 70 in the dental pulp following trauma

BACKGROUND/AIM

Traumatic dental injuries vary in severity from mild concussion to avulsion. All organisms respond to stress by inducing the synthesis of a group of proteins known generically as heat shock proteins. The activation of these proteins is an essential cellular mechanism designed to protect against a variety of environmental stresses. It is probable that the production of these proteins is increased in the cells of the traumatized dental pulp, however, this has not as yet been demonstrated. The degree of heat shock proteins expression may be related to the severity of the trauma such that estimating the extent of heat shock proteins expression may provide a practicable way of quantifying these injuries.

MATERIALS AND METHODS

Twenty adult male ferrets were divided into four groups. Each maxillary and mandibular right canine was traumatized with the contralateral canines acting as undamaged controls. The trauma was a simulated concussion injury applied using a uniform force. Animals were killed at 24, 48, 72 and 168 h after the injury. The canines were extracted, sectioned and processed for immunohistochemistry using a mouse monoclonal antibody specific for Hsp70.

RESULTS

There was a statistically significant difference in Hsp70 staining between traumatized and non-traumatized teeth only in the group observed 24 h after the trauma. The expression of heat shock proteins form part of the early pulpal response to trauma.