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Objectives: RhoE and regulator of G-proteins signalling (RGS) 2 were identified as the up-regulated genes in human periodontal ligament (PDL) cells under compression. RhoE belongs to the Rho GTPase family, and RGS2, a novel family of GTPase-activating proteins, turns off the G-protein signalling. Rho family proteins have recently been known to regulate actin cytoskeleton dynamics in various cell types. In this study, we investigated the involvement of RhoE and RGS2 in the regulation of actin filament organization in the PDL cells under mechanical stress., Methods: Human PDL cells were cultured and subjected to a static compressive force (3.0g/cm(2)) for 48h. To observe changes in the actin cytoskeleton and the expression of RhoE and RGS2 in response to mechanical stress, immunofluorescence analysis was performed. To examine the role of RhoE and RGS2 in actin filament organization, cells were transfected with antisense S-oligonucleotides (ODNs) to RhoE and RGS2., Results: Compressive force caused a loss and disassembly of actin stress fibres leading to cell spreading. Immunocytochemical study revealed that RhoE and RGS2 expressions were induced by mechanical stress and localized in the perinuclear and in the cell membrane, respectively. The impaired formation of stress fibres caused by compressive forces was recovered by treatment with antisense S-ODN to RhoE to the control levels. However, addition of antisense S-ODN to RGS2 did not affect the stress fibre formation., Conclusions: These results indicate that the loss and disassembly of stress fibres due to mechanical stress are mediating RhoE signalling, without the exertion of RGS2., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Mechanical stress is thought to regulate the expression of genes in the periodontal ligament (PDL) cells. Using a microarray approach, we recently identified a regulator of G-protein signaling 2 (RGS2) as an up-regulated gene in the PDL cells under compressive force. The RGS protein family is known to turn off G-protein signaling. G-protein signaling involves the production of cAMP, which is thought to be one of the biological mediators in response to mechanical stress. Here, we investigated the role of RGS2 in the PDL cells under mechanical stress. PDL cells derived from the ligament tissues of human premolar teeth were cultured in collagen gels and subjected to static compressive force. Compressive force application time-dependently enhanced RGS2 expression and intracellular cAMP levels. To examine the interrelationship between RGS2 and cAMP, the PDL cells were treated with 2',5'-dideoxyadenosine (DDA), an inhibitor of adenyl cyclase, or antisense S-oligonucleotide (S-ODN) to RGS2 under compressive force. DDA dose-dependently inhibited RGS2 stimulated by compressive force. Blockage of RGS2 by antisense S-ODN elevated the cAMP levels compared with controls. These results indicate that cAMP stimulates RGS2 expression, which in turn leads to a decrease in the cAMP production by inactivating the G-protein signaling in the mechanically stressed PDL cells., (Copyright (c) 2007 John Wiley & Sons, Ltd.)

Periostin, which is a secreted protein that supports cell adhesion, is highly expressed in the periodontal ligament (PDL). Twist, a basic helix-loop-helix (bHLH) transcription factor and a negative regulator of osteoblast differentiation, has been found to regulate the periostin gene transcription. Since occlusal force is thought to be important in the homeostasis of the PDL, in this study we investigated the expression of periostin and Twist mRNA in the mouse periodontal tissue following removal of antagonizing teeth. Unilateral maxillary tooth extraction was performed in 3-week-old male mice to produce occlusal hypofunction of the right mandibular molars. The expressions of periostin and Twist mRNA were examined by real time-PCR and in situ hybridization at 12, 24, 72 and 168 h after the tooth extraction. The real-time PCR analysis showed that periostin and Twist mRNA significantly decreased at 24 h to 14.5 and 49.9% of those in control group, respectively. But the recovery began at 72 and 168 h, no significant difference was observed. As determined by in situ hybridization analysis, the number of periostin and Twist mRNA-expressing PDL cells showed a marked decrease at 24 h, although an increase was observed from 72 h until the distribution was almost similar to that of the control group at 168 h. These results suggested that occlusal force might have putative roles in periostin and Twist gene expression in the PDL and the changes in their expression level during hypofunction may be considered a form of adaptation to environmental changes.