Smad2 Decelerates Re-epithelialization during Gingival Wound Healing

Abstract

During periodontal regeneration, inhibition of gingival downgrowth is necessary to promote migration of mesenchymal cells into the defects. Transforming growth factor (TGF)-β 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-β, 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-β/Smad2 signaling mediating alteration of K16 expression must be tightly regulated during periodontal regeneration.

Bone Morphogenetic Protein Signaling Suppresses Wound-Induced Skin Repair by Inhibiting Keratinocyte Proliferation and Migration

“…These data are consistent with previous studies showing that other components of the TGF-beta signalling pathways, such as Smad2/3 and Smad4 negatively regulate skin repair (Ashcroft et al , 1999; Flanders et al , 2003; Hosokawa et al , 2005; Tomikawa et al , 2012; Yang et al , 2012). Our data provide evidence that Smad1, a crucial downstream regulator of the BMP-Smad pathway (Botchkarev and Sharov, 2004), slows wound healing by attenuating keratinocyte proliferation and migration and augmenting wound epithelial apoptosis.…”

Overexpression of Smad2 inhibits proliferation of gingival epithelial cells

“…To determine the consistency of our in vitro data with the gingival junctional epithelium in vivo, the localization and expression levels of p15 and p21 were examined immunohistochemically. As reported previously (22), Smad2 was expressed in epithelium except in the basal layer, while P-Smad2 was highly expressed in the basal layer of gingival junctional epithelium and sulcus epithelium. The intensities of both Smad2 and P-Smad2 expression were significantly increased in TG compared to WT.…”

“…Re‐epithelialization is initiated by activation of keratinocyte migration at wound margins . It has been reported that K14‐Smad2 TG mice exhibited inhibition of migration in gingival epithelia . However, in the scratch assay, there were no significant differences between cell movement of TG and WT (Fig.…”

Transforming Growth Factor Beta Signaling in Cutaneous Wound Healing: Lessons Learned from Animal Studies

“…Similar results showing a delay in wound healing due to inhibition of epithelial cell migration in K14-Smad2 mice were obtained using a gingival wound-healing model. 82 These results are corroborated in a recent study showing that keratinocyte-specific Smad2 KO mice display the opposite effect-accelerated reepithelialization with enhanced keratinocyte migration. 83 Taken together, these studies suggest that epidermal Smad2 plays an important role in wound re-epithelialization.…”