Smad2 overexpression reduces the proliferation of the junctional epithelium

Junctional epithelium and hemidesmosomes: Tape and rivets for solving the "percutaneous device dilemma" in dental and other permanent implants

The percutaneous device dilemma describes etiological factors, centered around the disrupted epithelial tissue surrounding non-remodelable devices, that contribute to rampant percutaneous device infection. Natural percutaneous organs, in particular their extracellular matrix mediating the "device"/epithelium interface, serve as exquisite examples to inspire longer lasting long-term percutaneous device design. For example, the tooth's imperviousness to infection is mediated by the epithelium directly surrounding it, the junctional epithelium (JE). The hallmark feature of JE is formation of hemidesmosomes, cell/matrix adhesive structures that attach surrounding oral gingiva to the tooth's enamel through a basement membrane. Here, the authors survey the multifaceted functions of the JE, emphasizing the role of the matrix, with a particular focus on hemidesmosomes and their five main components. The authors highlight the known (and unknown) effects dental implant - as a model percutaneous device - placement has on JE regeneration and synthesize this information for application to other percutaneous devices. The authors conclude with a summary of bioengineering strategies aimed at solving the percutaneous device dilemma and invigorating greater collaboration between clinicians, bioengineers, and matrix biologists.

Role of Inhibitor SMADs in Stage 3 Grade B periodontitis before and after periodontal treatment

OBJECTIVE

This study aimed to examine the levels of transforming growth factor-beta (TGF-β) and inhibitory-Smads (I-Smads) in saliva and gingival crevicular fluid (GCF) in patients with Stage 3 Grade B periodontitis before and after non-surgical periodontal treatment.

BACKGROUND

Recently, it has been stated that Smads play an active role in all conditions where TGF-β is involved, including periodontal inflammation.

METHODS

Twenty healthy participants (control) and 20 patients with Stage 3, Grade B periodontitis were recruited. GCF and saliva samples and clinical periodontal recordings were investigated at the baseline and 1 month after treatment. TGF-β and I-Smads (Smads 6 and 7) were determined by ELISA.

RESULTS

Salivary Smad6 and Smad7 levels were significantly lower in the periodontitis group than healthy controls (p < .05), while there was no difference in salivary TGF-β levels between groups at baseline (p > .05). The total amounts and concentrations of GCF TGF-β, Smad6, and Smad7 were significantly lower in the periodontitis group than healthy controls at baseline (p < .05), and then decreased in concentration levels with treatment (p < .001). Positive correlations were found between total amounts and concentrations of GCF TGF-β, Smad6, and Smad7 (p < .05).

CONCLUSION

Our findings revealed that Smad6 and Smad7 in GCF and saliva decreased in periodontitis and then increased after periodontal treatment. Our study suggests that I-Smads act in parallel with TGF-β in periodontal inflammation and may have a role in the development of periodontitis.

Dual roles of TGF-β signaling in the regulation of dental epithelial cell proliferation

The purpose of this study is to investigate the molecular mechanisms and biological function of TGF-β-activated Smad1/5 in dental epithelium. Immunohistochemistry was used to detect the expressions of TGF-β signaling-related gene in mice molar germ. Primary dental epithelial cells were cultured and treated with TGF-β1 at a concentration of 0.5 or 5 ng/mL. Small molecular inhibitors, SB431542 and ML347, was used to inhibite ALK5 and ALK1/2, respectively. Small interfering RNA was used to knock down Smad1/5 or Smad2/3. The proliferation rate of cells was evaluated by EdU assay. In the basal layer of dental epithelial bud TGF-β1 and p-Smad1/5 were highly expressed, and in the interior of the epithelial bud TGF-β1 was lowly expressed, whereas p-Smad2/3 was highly expressed. In primary cultured dental epithelial cells, low concentration of TGF-β1 activated Smad2/3 but not Smad1/5, while high concentration of TGF-β1 was able to activate both Smad2/3 and Smad1/5. SB431542 but not ML347 was able to block the phosphorylation of Smad2/3 by TGF-β1. Either SB431542 or ML347 was able to block the phosphorylation of Smad1/5 by TGF-β1. EdU staining showed that high concentration of TGF-β1 promoted dental epithelial cell proliferation, which was reversed by silencing Smad1/5, whereas low concentration of TGF-β1 inhibited cell proliferation, which was reversed by silencing Smad2/3. In conclusions, TGF-β exhibits dual roles in the regulation of dental epithelial cell proliferation through two pathways. On the one hand, TGF-β activates canonical Smad2/3 signaling through ALK5, inhibiting the proliferation of internal dental epithelial cells. On the other hand, TGF-β activates noncanonical Smad1/5 signaling through ALK1/2-ALK5, promoting the proliferation of basal cells in the dental epithelial bud.

Smad7 Regulates Dental Epithelial Proliferation during Tooth Development

Tooth morphogenesis involves dynamic changes in shape and size as it proceeds through the bud, cap, and bell stages. This process requires exact regulation of cell proliferation and differentiation. Smad7, a general antagonist against transforming growth factor-β (TGF-β) signaling, is necessary for maintaining homeostasis and proper functionality in many organs. While TGF-β signaling is widely involved in tooth morphogenesis, the precise role of Smad7 in tooth development remains unknown. In this study, we showed that Smad7 is expressed in the developing mouse molars with a high level in the dental epithelium but a moderate to weak level in the dental mesenchyme. Smad7 deficiency led to a profound decrease in tooth size primarily due to a severely compromised cell proliferation capability in the dental epithelium. Consistent with the tooth shrinkage phenotype, RNA sequencing (RNA-seq) analysis revealed that Smad7 ablation downregulated genes referred to epithelial cell proliferation and cell cycle G1/S phase transition, whereas the upregulated genes were involved in responding to TGF-β signaling and cell cycle arrest. Among these genes, the expression of Cdkn1a (encoding p21), a negative cell proliferation regulator, was remarkably elevated in parallel with the diminution of Ccnd1 encoding the crucial cell cycle regulator cyclin D1 in the dental epithelium. Meanwhile, the expression level of p-Smad2/3 was ectopically elevated in the developing tooth germ of Smad7 null mice, indicating the hyperactivation of the canonical TGF-β signaling. These effects were reversed by addition of TGF-β signaling inhibitor in cell cultures of Smad7^-/- molar tooth germs, with rescued expression of cyclin D1 and cell proliferation rate. In sum, our studies demonstrate that Smad7 functions primarily as a positive regulator of cell proliferation via inhibition of the canonical TGF-β signaling during dental epithelium development and highlight a crucial role for Smad7 in regulating tooth size.

Modulation of microenvironment for controlling the fate of periodontal ligament cells: the role of Rho/ROCK signaling and cytoskeletal dynamics

Cells behave in a variety of ways when they perceive changes in their microenvironment; the behavior of cells is guided by their coordinated interactions with growth factors, niche cells, and extracellular matrix (ECM). Modulation of the microenvironment affects the cell morphology and multiple gene expressions. Rho/Rho-associated coiled-coil-containing protein kinase (ROCK) signaling is one of the key regulators of cytoskeletal dynamics and actively and/or passively determines the cell fate, such as proliferation, migration, differentiation, and apoptosis, by reciprocal communication with the microenvironment. During periodontal wound healing, it is important to recruit the residential stem cells into the defect site for regeneration and homeostasis of the periodontal tissue. Periodontal ligament (PDL) cells contain a heterogeneous fibroblast population, including mesenchymal stem cells, and contribute to the reconstruction of tooth-supporting tissues. Therefore, bio-regeneration of PDL cells has been the ultimate goal of periodontal therapy for decades. Recent stem cell researches have shed light on intrinsic ECM properties, providing paradigm shifts in cell fate determination. This review focuses on the role of ROCK activity and the effects of Y-27632, a specific inhibitor of ROCK, in the modulation of ECM-microenvironment. Further, it presents the current understanding of how Rho/ROCK signaling affects the fate determination of stem cells, especially PDL cells. In addition, we have also discussed in detail the underlying mechanisms behind the reciprocal response to the microenvironment.

Regulation of defensive function on gingival epithelial cells can prevent periodontal disease

Periodontal disease is a bacterial biofilm-associated inflammatory disease that has been implicated in many systemic diseases. A new preventive method for periodontal disease needs to be developed in order to promote the health of the elderly in a super-aged society. The gingival epithelium plays an important role as a mechanical barrier against bacterial invasion and a part of the innate immune response to infectious inflammation in periodontal tissue. The disorganization of cell–cell interactions and subsequent inflammation contribute to the initiation of periodontal disease. These make us consider that regulation of host defensive functions, epithelial barrier and neutrophil activity, may become novel preventive methods for periodontal inflammation. Based on this concept, we have found that several agents regulate the barrier function of gingival epithelial cells and suppress the accumulation of neutrophils in the gingival epithelium. We herein introduce the actions of irsogladine maleate, azithromycin, amphotericin B, and Houttuynia cordata (dokudami in Japanese), which is commonly used in traditional medicine, on the epithelial barrier and neutrophil migration in gingival epithelial cells in vivo and in vitro, in order to provide support for the clinical application of these agents to the prevention of periodontal inflammation.

Immunolocalization of connective tissue growth factor, transforming growth factor-beta1 and phosphorylated-SMAD2/3 during the postnatal tooth development and formation of junctional epithelium

Connective tissue growth factor (CTGF) is a downstream mediator of transforming growth factor-beta 1 (TGF-β₁) and TGF-β₁-induced CTGF expression is regulated through SMAD pathway. However, there is no literature showing the expression of TGF-β₁-SMAD2/3-CTGF signaling pathway during postnatal tooth development and the formation of junctional epithelium (JE). Hence, we aimed to analyze the localization of TGF-β₁, CTGF and phosphorylated SMAD2/3 (p-SMAD2/3) in the developing postnatal rat molars. Wistar rats were killed at postnatal (PN) 0.5, 3.5, 7, 14 and 21days and the upper jaws were processed for immunohistochemistry. At PN0.5 and PN3.5, weak staining for TGF-β₁ and CTGF was evident in preameloblasts (PA), while moderate to strong staining was seen in odontoblasts (OD), dental papilla (DPL), secretary ameloblasts (SA), preodontoblasts (PO) and polarized odontoblasts (PoO). There was no staining for p-SMAD2/3 in PA, SA, PO and PoO, although strong staining was localized in DPL. OD was initially moderately positive and then negative for p-SMAD2/3. At PN7, intense staining for TGF-β₁ and CTGF was observed in SA, OD, dental pulp (DP) and predentin respectively. p-SMAD2/3 was strongly expressed in DP and moderately expressed in SA and OD. At PN14 and PN21, both reduced enamel epithelium (REE) and JE showed a strong reaction for TGF-β₁ and CTGF. p-SMAD2/3 was intensely and weakly expressed in REE and JE respectively. These data demonstrate that the expression of CTGF, TGF-β₁ and p-SNAD2/3 is tissue-specific and stage-specific, and indicate a regulatory role for a TGF-β₁-SMAD2/3-CTGF signaling pathway in amelogenesis, dentinogenesis and formation of JE.

Hypoxia-induced ANGPTL4 sustains tumour growth and anoikis resistance through different mechanisms in scirrhous gastric cancer cell lines

Patients with scirrhous gastric cancer (SGC) frequently develop peritoneal dissemination, which leads to poor prognosis. The secreted protein angiopoietin-like-4 (ANGPTL4), which is induced by hypoxia, exerts diverse effects on cancer progression. Here, we aimed to determine the biological function of ANGPTL4 in SGC cells under hypoxia. ANGPTL4 levels were higher in SGC cells under hypoxia than in other types of gastric cancer cells. Hypoxia-induced ANGPTL4 mRNA expression was regulated by hypoxia-inducible factor-1α (HIF-1α). Under hypoxic conditions, monolayer cultures of ANGPTL4 knockdown (KD) 58As9 SGC (58As9-KD) cells were arrested in the G₁ phase of the cell cycle through downregulation of c-Myc and upregulation of p27, in contrast to control 58As9-SC cells. Moreover, the ability of 58As9-KD xenografts to form tumours in nude mice was strongly suppressed. When 58As9-KD cells were cultured in suspension, hypoxia strongly increased their susceptibility to anoikis through suppression of the FAK/Src/PI3K-Akt/ERK pro-survival pathway, followed by activation of the apoptotic factors caspases-3, -8 and -9. The development of peritoneal dissemination by 58As9-KD cells was completely inhibited compared with that by 58As9-SC cells. In conclusion, ANGPTL4 is uniquely induced by hypoxia in cultured SGC cells and is essential for tumour growth and resistance to anoikis through different mechanisms.

Excessive retinoic acid inhibit mouse embryonic palate mesenchymal cell growth through involvement of Smad signaling

All-trans retinoic acid (atRA), the oxidative metabolite of retinoic acid (RA), is essential for palatogenesis. Overdose RA is capable of inducing cleft palate in mice and humans. Normal embryonic palatal mesenchymal (EPM) cell growth is crucial for shelf growth. Smad signaling is involved in many biological processes. However, it is not much clear if atRA could affect Smad signaling during EPM cells growth. In this study, the timed pregnant mice with maternal administration of 100 mg/kg body weight of RA by gastric intubation were cervical dislocation executed to evaluate growth changes of palatal shelves by hematoxylin and eosin (H&E) staining. At the same time, a primary mouse EPM (MEPM) cell culture model was also established. MEPM cells were treated with atRA (0.1, 0.5, 1, 5 and 10 μM) for 24, 48 and 72 h. The results indicated that the sizes of the shelves were smaller than those in control. AtRA inhibited MEPM cell growth with both increasing concentration and increasing incubation time, especially at 72 h in vitro. Moreover, atRA significantly increased the mRNA and protein expression levels of Smad7 (P < .05), but the mRNA and protein expression levels of PCNA were reduced (P < .05). We also found atRA inhibited phosphorylation of Smad2 compared with untreated group (P < .05). However, the protein and mRNA levels of Smad2 did not change both in atRA-treated and untreated group (P > .05). We demonstrated that RA induced inhibition of MEPM cell growth that could cause cleft palate partly by down-regulation of Smad pathway.

Smad2 overexpression enhances adhesion of gingival epithelial cells

OBJECTIVE

Gingival epithelial cells play an important role in preventing the initiation of periodontitis, by their hemidesmosomal adhesion to the tooth root surface. Adhesion requires integrin-extracellular matrix (ECM) interactions that are intricately regulated by transforming growth factor-β (TGF-β) signaling. However, the mechanisms underlying the interplay between adhesion molecules and TGF-β, especially the respective roles of Smad2 and Smad3, remain elusive. In this study, we examined the effects of Smad overexpression on gingival epithelial cell adhesion and expression profiles of integrin and ECM-related genes.

METHODS

Human gingival epithelial cells immortalized by the SV40 T-antigen were transfected with Smad2- and Smad3-overexpression vectors. A cell adhesion assay involving fluorescence detection of attached cells was performed using the ArrayScan imaging system. Real-time PCR was performed to examine the kinetics of integrin and ECM gene expression. In vitro and in vivo localization of adhesion molecules was examined by immunofluorescence analysis.

RESULTS

By using SB431542, a specific inhibitor of the TGF-β type I receptor, Smad2/3 signaling was confirmed to be dominant in TGF-β1-induced cell adhesion. The Smad2-transfectant demonstrated higher potency for cell adhesion and integrin expression (α2, α5, β4, and β6) than the Smad3-transfectant, whereas little or no change in ECM expression was observed in either transfectant. Moreover, the gingival epithelium of transgenic mice that overexpressed Smad2 driven by the keratin 14 promoter showed increased integrin α2 expression.

CONCLUSION

These findings indicate the crucial role of Smad2 in increased adhesion of gingival epithelial cells via upregulation of integrin α2.

Smad2 overexpression induces alveolar bone loss and up regulates TNF-α, and RANKL

OBJECTIVE

The aim of the current study was to investigate whether Smad2 overexpression in JE cells induced alveolar bone loss, and to understand the mechanisms regulating the bone loss.

METHODS

A mouse line was created that used a cytokeratin 14 (K14) promoter to overexpress Smad2 in the epithelium of the transgenic mice (K14-Smad2). Micro CT radiographs (μCT) were used to assess bone loss, bone volume, and bone density. The expression of Tnfα, Il1-β, Ifγ, Rankl, and Opg were assessed by RT-PCR. Western blots were used to detect the protein levels of TNF-α and IL1-β. Tartrate-resistant acid phosphatase (TRAP) was used as a marker for osteoclasts. Wild type (WT) mice were used as controls in all steps of the current study.

RESULTS

K14-Smad2 mice had 52.5% (±4.2) root exposed compared to 32.4%(±3.2) in the WT mice. There was a significant difference in alveolar bone volume in the K14-Smad2 mice when compared to WT mice 2.65mm³ (±0.3) and 4.3mm³ (±0.35) respectively. K14-Smad2 mice also had reduced bone density 696.8mg/cc (±70) at 12 months when compared to WT mice 845.9mg/cc(±10). The mRNA levels of Tnfα and Rankl increased by 3.26- and 2.5-fold respectively in the K14-Smad2 mice when compared to controls. The protein level of TNF-α was also significantly increased to 2.8-fold in K14-Smad2 mice when compared to WT mice. Smad2 overexpression increased the total numbers of osteoclasts in K14-Smad2 mice (3.4±0.2)-fold when compared to WT mice.

CONCLUSION

Smad2 overexpression induces alveolar bone loss and increases the numbers of osteoclasts. Also, Smad2 overexpression up-regulates TNF-α and RANKL.