Overexpression of Smad2 inhibits proliferation of gingival epithelial cells.

BACKGROUND AND OBJECTIVE: Spatiotemporal inhibition of apical migration and proliferation of gingival epithelium are significant factors involved in periodontal regeneration. Transforming growth factor ß (TGF-ß) is important in multiple aspects of wound healing, and Smad2, a downstream transcription factor of TGF-ß, has an inhibitory effect on re-epithelialization during gingival wound healing. Therefore, we investigated the effects on migration and proliferation status, and intra/extracellular signaling regulated by Smad2 overexpression in gingival epithelial cells. MATERIAL AND METHODS: Gingival epithelial cells were isolated from the palatal gingival tissue of transgenic mice overexpressing Smad2 driven by the Keratin14 promoter. Smad2 expression was identified by western blotting and immunofluorescence analysis. Scratch assay and 5-bromo-2'-deoxyuridine staining were performed to assess cell migration and proliferation. To inactivate TGF-ß type I receptor, the cultures were supplemented with SB431542. Secreted TGF-ß was quantified by ELISA. Smad2 target gene expression was examined by real-time RT-PCR and in vivo immunofluorescence analysis of gingival junctional epithelium. RESULTS: Smad2-overexpressing cells were confirmed to have significant phosphorylated Smad2 in the nucleus. Scratch assay and 5-bromo-2'-deoxyuridine staining indicated that Smad2-overexpressing cells showed no significant differences in migration, but had reduced proliferation rates compared to wild-type controls. SB431542 significantly inhibited Smad2 phosphorylation, which coincided with restoration of the proliferation rate in Smad2-overexpressing cells. ELISA of TGF-ß release did not show any differences between genotypes. The cell cycle inhibitors, p15 and p21, showed significant upregulation in Smad2-overexpressing cells compared to wild-type controls. Moreover, junctional epithelium of the transgenic mice showed increased expression of P-Smad2, p15 and p21. CONCLUSION: The signaling activation triggered by overexpression of Smad2 was dependent on TGF-ß type I receptor, and the activated Smad2 increased p15 and p21 expression, responsible for inhibiting cell cycle entry, resulting in antiproliferative effects on gingival epithelial cells. Understanding of Smad2-induced signaling would be useful for possible clinical application to regulate gingival epithelial downgrowth.

Smad2 decelerates re-epithelialization during gingival wound healing.

During periodontal regeneration, inhibition of gingival downgrowth is necessary to promote migration of mesenchymal cells into the defects. Transforming growth factor (TGF)-ß is a pleiotropic cytokine that has numerous cell functions, including regulation of epithelial growth. Recent studies have shown that Smad2, a downstream transcription factor of TGF-ß, plays crucial roles in wound healing in the epithelia. Therefore, we investigated the effects of Smad2 overexpression on re-epithelialization of gingival wounds. Transgenic mice overexpressing smad2 driven by the keratin 14 promoter (k14-smad2) were confirmed to have significant Smad2 phosphorylation in gingival basal epithelia. Punch wounds were made in the palatal gingiva, and wound healing was assessed histologically for 7 days. Re-epithelialization was significantly retarded on day 2, while collagen deposition was enhanced on day 7 in k14-smad2 compared with wild-type mice. Moreover, expression of keratin 16 (K16), an indicator of keratinocyte migration, was significantly inhibited in wound-edge keratinocytes in k14-smad2. The inhibition of K16 coincided with the induction of Smad2 in the corresponding epithelia, while BrdU incorporation was unaffected. These results indicated that Smad2 has inhibitory effects in regulating keratinocyte migration during gingival wound healing. TGF-ß/Smad2 signaling mediating alteration of K16 expression must be tightly regulated during periodontal regeneration.

Simultaneous determination of glycyrrhizin, glycyrrhetic acid and glycyrrhetic acid mono-glucuronide in Shakuyaku-kanzo-to incubated with rat feces by semi-micro high-performance liquid chromatography.

A method for semi-micro high-performance liquid chromatography (HPLC) has been established for the simultaneous determination of glycyrrhizin (GL), glycyrrhetic acid (GA) and glycyrrhetic acid mono-glucuronide (GAMG) in incubation mixtures of rat feces with Shakuyaku-kanzo-to decoction (combination of licorice root and peony root). The analysis could be accomplished within 20 min with a TSKgel ODS-80TsQA (150 x 2.0 mm i.d.) column by linear gradient elution using a mobile phase containing aqueous phosphoric acid and acetonitrile at a flow rate of 0.2 ml x min(-1), a thermostatic oven at 25 degrees C, and detection at 254 nm. The detection limits of these compounds were 0.1-0.85 pmol per injection (5 microl). The concentrations of GL and its metabolites in the incubation mixture after continuous consumption of Shakuyaku-kanzo-to were significantly different compared with those of untreated control. GL-hydrolysis of rat feces was enhanced by pre-consumption of Shakuyaku-kanzo-to.