Modulation of Wnt/β-catenin Signaling Attenuates Periapical Bone Lesions

Loss of signal transducer and activator of transcription 3 in osteoblasts impaired the bone healing in inflammatory microenvironment

INTRODUCTION

This study aimed to investigate the effect of Stat3 on the osteoblast-mediated bone healing in the inflammatory lesion.

METHODS

The conditional knockout of Stat3 in osteoblasts (Stat3 CKO) was generated via the Cre-loxP recombination system using Osterix-Cre transgenic mice. The calvarial bone inflammatory lesions were established on both Stat3 CKO and wild-type mice, then harvested to assess the bone healing. In response to lipopolysaccharide (LPS) stimulation, osteoblasts from Stat3 CKO and wild-type mice were subjected to examine the formation of calcium deposits, the expression of osteogenic markers (i.e., Runx2, OPN, COL1A1), and osteoclast-related markers (i.e., RANKL, OPG). The EdU and transwell assays were performed to assess the proliferation and migration of the cells.

RESULTS

A decrease in bone mass and an increase in osteolysis were found in the inflammatory lesions on Stat3 CKO mice when compared with the control. More osteoclastic-like cells and an increased expression of RANKL were observed in Stat3 CKO mice. Both mRNA and protein expressions of Stat3 and osteogenic markers in the lesions were significantly decreased in Stat3 CKO mice. After co-cultured with osteogenic medium, the Stat3-deficient osteoblasts were found with a significant decrease in calcium deposits and the expression of osteogenic markers, and with a significant increased expression of RANKL. The impaired ossification of Stat3-deficient osteoblasts was even more pronounced with the presence of lipopolysaccharides in vitro. The most decrease in cell proliferation and migration was found in Stat3-deficient osteoblasts in response to LPS.

CONCLUSIONS

Loss of Stat3 in osteoblasts impaired bone healing in an inflammatory microenvironment.

Wnt signaling in periodontitis

OBJECTIVE

This study aimed to evaluate the Wnt/β-catenin signaling pathway activity in gingival samples obtained from patients with periodontitis.

MATERIALS AND METHODS

Fifteen patients with stage III grade B (SIIIGB) and eleven with stage III grade C (SIIIGC) periodontitis were included and compared to 15 control subjects. β-Catenin, Wnt 3a, Wnt 5a, and Wnt 10b expressions were evaluated by Q-PCR. Topographic localization of tissue β-catenin, Wnt 5a, and Wnt 10b was measured by immunohistochemical analysis. TNF-α was used to assess the inflammatory state of the tissues, while Runx2 was used as a mediator of active destruction.

RESULTS

Wnt 3a, Wnt 5a, and Wnt 10b were significantly higher in gingival tissues in both grades of stage 3 periodontitis compared to the control group (p < 0.05). β-Catenin showed intranuclear staining in connective tissue in periodontitis, while it was confined to intracytoplasmic staining in epithelial tissue and the cell walls in the control group. Wnt5a protein expression was elevated in periodontitis, with the most intense staining observed in the connective tissue of SIIIGC samples. Wnt10b showed the highest density in the connective tissue of patients with periodontitis.

CONCLUSIONS

Our findings suggested that periodontal inflammation disrupts the Wnt/β-catenin signaling pathway.

CLINICAL RELEVANCE

Periodontitis disrupts Wnt signaling in periodontal tissues in parallel with tissue inflammation and changes in morphology. This change in Wnt-related signaling pathways that regulate tissue homeostasis in the immunoinflammatory response may shed light on host-induced tissue destruction in the pathogenesis of the periodontal disease.

Dietary Isoquercetin Ameliorates Bone Loss via Restoration of the Gut Microbiota and Lipopolysaccharide-Triggered Inflammatory Status in Ovariectomy Mice

Osteoporosis is one of the skeletal degenerative diseases accompanied by bone loss and microstructure disruption. Given that the gut-bone signaling axis highly contributes to bone health, here, dietary isoquercetin (IQ) was shown to effectively improve postmenopausal osteoporosis (PMO) in an ovariectomy (OVX) mouse model through the modulation of the gut-bone cross-talk. An in vivo study showed that OVX induced striking disruption of the microbial community, subsequently causing gut leakage and gut barrier dysfunction. As a result, lipopolysaccharide (LPS)-triggered inflammatory cytokines released from the intestine to bone marrow were determined to be associated with bone loss in OVX mice. Long-term dietary IQ effectively improved microbial community and gut barrier function in the OVX mice and thus markedly improved bone loss and host inflammatory status by repressing the NF-κB signaling pathway. An in vitro study further revealed that IQ treatments dose-dependently inhibited LPS-induced inflammation and partly promoted the proliferation and differentiation of osteoblasts. These results provide new evidence that dietary IQ has the potential for osteoporosis treatment.

Protective Actions in Apical Periodontitis: The Regenerative Bioactivities Led by Mesenchymal Stem Cells

Resulting from bacterial infection, apical periodontitis (AP) is a common inflammatory disease of the periapical region of the tooth. The regeneration of the destroyed periapical alveolar bone and the surrounding periodontium tissues has long been a difficult task in clinical practice. These lesions are closely related to pathogen invasion and an overreactive immune response. It is worth noting that the protective healing process occurs simultaneously, in which mesenchymal stem cells (MSCs) have a crucial function in mediating the immune system and promoting regeneration. Here, we review the recent studies related to AP, with a focus on the regulatory network of MSCs. We also discuss the potential therapeutic approaches of MSCs in inflammatory diseases to provide a basis for promoting tissue regeneration and modulating inflammation in AP. A deeper understanding of the protective action of MSCs and the regulatory networks will help to delineate the underlying mechanisms of AP and pave the way for stem-cell-based regenerative medicine in the future.

Mechanisms of bone remodeling and therapeutic strategies in chronic apical periodontitis

Chronic periapical periodontitis (CAP) is a typical oral disease in which periodontal inflammation caused by an odontogenic infection eventually leads to bone loss. Uncontrolled infections often lead to extensive bone loss around the root tip, which ultimately leads to tooth loss. The main clinical issue in the treatment of periapical periodontitis is the repair of jawbone defects, and infection control is the first priority. However, the oral cavity is an open environment, and the distribution of microorganisms through the mouth in jawbone defects is inevitable. The subversion of host cell metabolism by oral microorganisms initiates disease. The presence of microorganisms stimulates a series of immune responses, which in turn stimulates bone healing. Given the above background, we intended to examine the paradoxes and connections between microorganisms and jaw defect repair in anticipation of new ideas for jaw defect repair. To this end, we reviewed the microbial factors, human signaling pathways, immune cells, and cytokines involved in the development of CAP, as well as concentrated growth factor (CGF) and stem cells in bone defect repair, with the aim of understanding the impact of microbial factors on host cell metabolism to inform the etiology and clinical management of CAP.

Expression of Wnt signaling agonists and antagonists in periodontitis and healthy subjects, before and after non-surgical periodontal treatment: A systematic review

Periodontitis is a preventable and treatable multifactorial chronic inflammatory disease that can lead to irreversible periodontal destruction and tooth loss. Wnt signaling and its regulators play an important role in periodontal inflammation, destruction, regeneration, and reconstruction. This systematic review aimed at investigating the involvement of Wnt signaling agonists and antagonists in periodontitis and healthy subjects, before and after periodontal treatment. Electronic searches were carried out using MEDLINE/PubMed, EMBASE, and Cochrane Library databases in addition to hand searches. Studies having different designs assessing the levels of Wnt signaling antagonist and agonist levels in gingival crevicular fluid, serum, and tissue in patients diagnosed with periodontitis or gingivitis, compared with healthy individuals were included. In addition, studies compared these levels in periodontitis patients before and after non-surgical periodontal therapy were also eligible. Sixteen studies met the eligibility criteria. Sclerostin (SOST) has been mainly investigated in the literature (8 publications). Sclerostin (5 studies), Wnt-5a (2 studies), secreted frizzled-related protein 1 (SFRP1) (3 studies), and β-catenin (3 studies) show increased levels in periodontitis compared with periodontal health. Strong correlations between marker levels and periodontal clinical parameters were identified for SOST (5 studies), SFRP1 (2 studies), and β-catenin (2 studies). SOST (3 studies) and SFRP1 (1 study) levels significantly decrease following non-surgical periodontal treatment. The present systematic review demonstrated an association between Wnt signaling agonist and antagonist levels and periodontitis. Wnt agonists and antagonists may serve as valuable diagnostic and prognostic markers for periodontitis onset and progression. Further case-control and longitudinal studies should be conducted for different Wnt signaling agonists and antagonists.

Oral Osteomicrobiology: The Role of Oral Microbiota in Alveolar Bone Homeostasis

Osteomicrobiology is a new research field in which the aim is to explore the role of microbiota in bone homeostasis. The alveolar bone is that part of the maxilla and mandible that supports the teeth. It is now evident that naturally occurring alveolar bone loss is considerably stunted in germ-free mice compared with specific-pathogen-free mice. Recently, the roles of oral microbiota in modulating host defense systems and alveolar bone homeostasis have attracted increasing attention. Moreover, the mechanistic understanding of oral microbiota in mediating alveolar bone remodeling processes is undergoing rapid progress due to the advancement in technology. In this review, to provide insight into the role of oral microbiota in alveolar bone homeostasis, we introduced the term “oral osteomicrobiology.” We discussed regulation of alveolar bone development and bone loss by oral microbiota under physiological and pathological conditions. We also focused on the signaling pathways involved in oral osteomicrobiology and discussed the bridging role of osteoimmunity and influencing factors in this process. Finally, the critical techniques for osteomicrobiological investigations were introduced.

In vitro evaluation of periapical lesion-derived stem cells for dental pulp tissue engineering

Dental pulp tissue engineering is a promising alternative treatment for pulpitis and periapical periodontitis, and dental pulp stem cells (DPSCs) are considered to be the gold standard for dental seed cell research. Periapical lesions harbor mesenchymal stem cells with the capacity for self-renewal and multilineage differentiation. However, it remains unknown whether these periapical lesion-derived stem cells (PLDSCs) are suitable for dental pulp tissue engineering. To investigate this possibility, PLDSCs and DPSCs were isolated using the tissue outgrowth method and cultured under identical conditions. We then performed in vitro experiments to investigate their biological characteristics. Our results indicate that PLDSCs proliferate actively in vitro and exhibit similar morphology, immunophenotype and multilineage differentiation ability as DPSCs. Simultaneously, PLDSCs exhibit stronger migrative ability and express more vascular endothelial growth factor and glial cell line-derived neurotrophic factor than DPSCs, and PLDSC-derived conditioned medium was more effective in tube formation assay. The mRNA expression levels of immunomodulatory genes HLA-G, IDO and ICAM-1 were also higher in PLDSCs. However, regarding osteo/odontogenic differentiation, PLDSCs showed weaker alkaline phosphatase staining and lower calcified nodule formation compared to DPSCs, as well as lower expression of ALP, RUNX2 and DSPP, as confirmed by a quantitative RT-PCR. The osteo/odontogenic protein expression levels of DSPP, RUNX2, DMP1 and SP7 were also higher in DPSCs. The present study demonstrates that PLDSCs demonstrate potential use as seed cells for dental pulp regeneration, especially for achieving enhanced neurovascularization.

Regulation of pathophysiological and tissue regenerative functions of MSCs mediated via the WNT signaling pathway (Review)

Tissues have remarkable natural capabilities to regenerate for the purpose of physiological turnover and repair of damage. Adult mesenchymal stem cells (MSCs) are well known for their unique self-renewal ability, pluripotency, homing potential, paracrine effects and immunomodulation. Advanced research of the unique properties of MSCs have opened up new horizons for tissue regenerative therapies. However, certain drawbacks of the application of MSCs, such as the low survival rate of transplanted MSCs, unsatisfactory efficiency and even failure to regenerate under an unbalanced microenvironment, are concerning with regards to their wider therapeutic applications. The activity of stem cells is mainly regulated by the anatomical niche; where they are placed during their clinical and therapeutic applications. Crosstalk between various niche signals maintains MSCs in homeostasis, in which the WNT signaling pathway plays vital roles. Several external or internal stimuli have been reported to interrupt the normal bioactivity of stem cells. The irreversible tissue loss that occurs during infection at the site of tissue grafting suggests an inhibitory effect mediated by microbial infections within MSC niches. In addition, MSC-seeded tissue engineering success is difficult in various tissues, when sites of injury are under the effects of a severe infection despite the immunomodulatory properties of MSCs. In the present review, the current understanding of the way in which WNT signaling regulates MSC activity modification under physiological and pathological conditions was summarized. An effort was also made to illustrate parts of the underlying mechanism, including the inflammatory factors and their interactions with the regulatory WNT signaling pathway, aiming to promote the clinical translation of MSC-based therapy.

Lithium and Copper Induce the Osteogenesis-Angiogenesis Coupling of Bone Marrow Mesenchymal Stem Cells via Crosstalk between Canonical Wnt and HIF-1α Signaling Pathways

The combination of osteogenesis and angiogenesis dual-delivery trace element-carrying bioactive scaffolds and stem cells is a promising method for bone regeneration and repair. Canonical Wnt and HIF-1α signaling pathways are vital for BMSCs' osteogenic differentiation and secretion of osteogenic factors, respectively. Simultaneously, lithium (Li) and copper (Cu) can activate the canonical Wnt and HIF-1α signaling pathway, respectively. Moreover, emerging evidence has shown that the canonical Wnt and HIF signaling pathways are related to coupling osteogenesis and angiogenesis. However, it is still unclear whether the lithium- and copper-doped bioactive scaffold can induce the coupling of the osteogenesis and angiogenesis in BMSCs and the underlying mechanism. So, we fabricated a lithium- (Li⁺-) and copper- (Cu²⁺-) doped organic/inorganic (Li 2.5-Cu 1.0-HA/Col) scaffold to evaluate the coupling osteogenesis and angiogenesis effects of lithium and copper on BMSCs and further explore its mechanism. We investigated that the sustained release of lithium and copper from the Li 2.5-Cu 1.0-HA/Col scaffold could couple the osteogenesis- and angiogenesis-related factor secretion in BMSCs seeding on it. Moreover, our results showed that 500 μM Li⁺ could activate the canonical Wnt signaling pathway and rescue the XAV-939 inhibition on it. In addition, we demonstrated that the 25 μM Cu²⁺ was similar to 1% oxygen environment in terms of the effectiveness of activating the HIF-1α signaling pathway. More importantly, the combination stimuli of Li⁺ and Cu²⁺ could couple the osteogenesis and angiogenesis process and further upregulate the osteogenesis- and angiogenesis-related gene expression via crosstalk between the canonical Wnt and HIF-1α signaling pathway. In conclusion, this study revealed that lithium and copper could crosstalk between the canonical Wnt and HIF-1α signaling pathways to couple the osteogenesis and angiogenesis in BMSCs when they are sustainably released from the Li-Cu-HA/Col scaffold.

Effects of lipopolysaccharide on proliferation, migration and osteogenic differentiation of apical papilla cells from early and late stage of root development

The aim of this study was to investigate the effects of lipopolysaccharide on cell proliferation, migration and osteogenic differentiation of apical papilla cells from early and late stage of root development. After challenging with various lipopolysaccharide concentrations to apical papilla cells from both stages of root development for 168 h, cell proliferation and migration were investigated. Osteogenic differentiation was examined by Alizarin red staining, and gene expressions of bone/cementum or dentin-related genes were examined by polymerase chain reaction. Lipopolysaccharide did not affect cell proliferation and migration in both groups. Lipopolysaccharide at 1 and 5 µg mL^-1 increased Alizarin red staining in apical papilla cells from early-stage but not the late-stage cells. Bone sialoprotein (bone/cementum marker) gene expression increased in both early and late stage of root development at 5 µg mL^-1 . These results might explain bone/cementum generation in regenerative endodontic procedures.

Autophagy was involved in tumor necrosis factor-α-inhibited osteogenic differentiation of murine calvarial osteoblasts through Wnt/β-catenin pathway

Periodontitis is an inflammatory disease with a high incidence characterized by irreversible destruction of alveolar bone. This study aimed to investigate the effect of tumor necrosis factor-α (TNF-α) on osteogenic differentiation and its molecular mechanism. TNF-α inhibited osteogenic differentiation as revealed by the lower accumulation of osteoblastic genes like runt-related transcription factor (Runx2), alkaline phosphatase (ALP), osteoprotegerin (OPG), and osteocalcin (OCN). Moreover, TNF-α down-regulated the expressions of LC3II, ATG7, and beclin 1 (BECN1); suggesting that autophagy was inhibited during the process of osteogenic differentiation. Consistently, Wnt/β-catenin signaling pathway members such as low-density lipoprotein receptor-related protein 5 (LRP5), β-catenin, and phosphorylated-β-catenin (p-β-catenin) were reduced by TNF-α. Furthermore, the inhibitory effect of TNF-α on osteogenic differentiation and the Wnt/β-catenin signaling pathway could be abated by autophagy inducers but exacerbated by autophagy inhibitors. The most intriguing finding of all was that TNF-α inhibited osteoblastic differentiation and the Wnt/β-catenin signaling pathway by down-regulating autophagy, and autophagy positively regulated the Wnt/β-catenin pathway and thus influenced osteoblastic differentiation. Our study provides a theoretical basis for autophagy-inducer therapy for the alveolar bone loss caused by periodontitis.

METTL3 Regulates Osteoblast Differentiation and Inflammatory Response via Smad Signaling and MAPK Signaling

Osteoblasts are crucial bone-building cells that maintain bone homeostasis, whereas inflammatory stimuli can inhibit osteogenesis and activate inflammatory response. N6-methyladenosine (m⁶A) is the most abundant mRNA modification in eukaryotes and plays important roles in multiple biological processes. However, whether m⁶A modification affects osteoblast differentiation and inflammatory response remains unknown. To address this issue, we investigated the expression of the N6-adenosine methyltransferase METTL3 and found that it was upregulated during osteoblast differentiation and downregulated after LPS stimulation. We then knocked down METTL3 and observed decreased levels of osteogenic markers, ALP activity, and mineralized nodules, as well as Smad1/5/9 phosphorylation, in LPS-induced inflammation. METTL3 knockdown promoted the mRNA expression and stability of negative regulators of Smad signaling, Smad7 and Smurf1, the same regulatory pattern identified when the m⁶A-binding protein YTHDF2 was silenced. Moreover, METTL3 depletion enhanced proinflammatory cytokine expression and increased the phosphorylation of ERK, p38, JNK, and p65 in MAPK and NF-κB signaling pathways. The increase in cytokine expression was inhibited after MAPK signaling inhibitor treatment. All data suggest that METTL3 knockdown inhibits osteoblast differentiation and Smad-dependent signaling by stabilizing Smad7 and Smurf1 mRNA transcripts via YTHDF2 involvement and activates the inflammatory response by regulating MAPK signaling in LPS-induced inflammation.

WNT gene polymorphisms and predisposition to apical periodontitis

Single nucleotide polymorphisms (SNPs) in WNT genes may impact gene/protein function and contribute to individual predisposition to apical periodontitis (AP). Here, we investigated the association of SNPs in/nearby WNT3, WNT3A, WNT5A, WNT8A, WNT9B and WNT11 genes with AP using a case-control dataset. Cases were defined as individuals with deep caries and AP (n = 188); controls had deep caries and no AP (n = 230). Genotyping was performed using Taqman chemistry in real time PCR. Data analyses was performed using Fisher Exact tests assuming a Bonferroni correction threshold value of 0.005. Single-SNP association analysis revealed a trend for association with WNT3 rs9890413 genotypes (P = 0.009) under a dominant model and allelic association for WNT3A rs1745420 (P = 0.009). Haplotypes involving WNT3-WNT9B-WNT3A alleles were also significantly associated with AP (P ≤ 0.003). Luciferase reporter assays showed higher transcriptional activity (1.4-fold) with the alternate G allele in rs1745420. Expression of WNT3, WNT3A and WNT5A in AP tissues was significantly higher than in control tissues, and inversely correlated with the expression of SERPINB1, COL1A1 and TIMP1 (P < 0.05). Our results suggest that WNT genes have a role in modulating AP and polymorphisms in these genes may increase susceptibility to AP.

Wnt5a is involved in LOX-1 and TLR4 induced host inflammatory response in peri-implantitis

BACKGROUND AND OBJECTIVE

Peri-implantitis is a plaque-associated pathological condition occurring in tissues around dental implants, characterized by inflammation in the peri-implant mucosa and subsequent progressive loss of supporting bone. Wnt5a is the activating ligand of the non-canonical Wnt signaling pathways and plays important roles in leukocyte infiltration and cytokine/ chemokine production in inflammatory disorders. Previous studies showed that Wnt5a was significantly up-regulated in gingival tissues of chronic and aggressive periodontitis. However, the roles and the regulatory mechanisms of Wnt5a in peri-implantitis are not well known.

METHODS

The expression of Wnt5a in gingival tissues collected from 8 healthy implant patients and 8 peri-implantitis patients was analyzed by Western blotting and immunofluorescence. Porphyromonas gingivalis infected macrophages isolated from the peripheral blood of healthy volunteers were used as an in vitro cellular model of peri-implantitis. Using neutralizing antibodies, inhibitors and siRNA, the production and roles of Wnt5a in peri-implantitis were assessed by immunofluorescence, quantitative polymerase chain reaction (RT-PCR) and Western blotting. Unpaired two-tailed Student's t test was used to compare qRT-PCR and Western blotting results. P ≤ .05 was considered statistically significant.

RESULTS

Wnt5a was highly expressed in the gingival tissues of peri-implantitis patients. Compared to controls, Wnt5a increased in P gingivalis infected macrophages. Wnt5a production in response to P gingivalis infection was dependent on LOX-1 and TLR4. Compared to controls, Wnt5a knockdown impaired IL-1β, MCP-1, and MMP2 production induced by P gingivalis infection.

CONCLUSION

Our results indicate that Wnt5a is involved in LOX-1 and TLR4 induced inflammatory signature via inflammatory cytokines production in response to P gingivalis infection. These findings demonstrate that Wnt5a maybe an important component of the host immune response in peri-implantitis.

Involvement of GSK3/β-catenin in the action of extracellular ATP on differentiation of primary cultures from rat calvaria into osteoblasts

Modulation of purinergic receptors play an important role in the regulation of osteoblasts differentiation and bone formation. In this study, we investigated the involvement of the GSK3/βcatenin signaling in the action of ATPγ-S on osteogenic differentiation of primary cell cultures from rat calvaria. Our results indicate that the cell treatment with 10 or 100 µM ATPγ-S for 96 h increase the cytoplasmic levels of β-catenin and its translocation to nucleus respect to control. A similar effect was observed after cell treatment with the GSK3 inhibitor LiCl (10 mM). Cell treatments with 4-10 mM LiCl significantly stimulated ALP activity respect to control at 4 and 7 days, suggesting that inhibition of GSK-3 mediates osteoblastic differentiation of rat calvarial cells. Effects comparison between ATP and LiCl shown that ALP activity was significantly increased by 10 µM ATPγ-S and decreased by 10 mM LiCl at 10 day of treatment, respect to control, suggesting that the effect of ATPγ-S was less potent but more persistent than of LiCl in stimulating this osteogenic marker in calvarial cells. Cell culture mineralization was significantly increased by treatment with 10 µM ATPγ-S and decreased by 10 mM LiCl, respect to control. In together, these results suggest that GSK3 inhibition is involved in ATPγ-S action on rat calvarial cell differentiation into osteoblasts at early steadies. In addition such inhibition by LiCl appear promote osteoblasts differentiation at beginning but has a deleterious effect on its function at later steadies as the extracellular matrix mineralization.

MicroRNA-99a is a novel regulator of KDM6B-mediated osteogenic differentiation of BMSCs

Skeletal tissue originates from mesenchymal stem cells (MSCs) with differentiation potential into the osteoblast lineage regulated by essential transcriptional and post‐transcriptional mechanisms. Recently, miRNAs and histone modifications have been identified as novel key regulators of osteogenic differentiation of MSCs. Here, we identified miR‐99a and its target lysine (K)‐specific demethylase 6B (KDM6B) gene as novel modulators of osteogenic differentiation of bone mesenchymal stem cells (BMSCs). Microarray profiling and further validation by quantitative real‐time RT‐PCR revealed that miR‐99a was up‐regulated during osteoblastic differentiation of BMSCs, and decreased in differentiated osteoblasts. Transfection of miR‐99a mimics inhibited osteoblastic commitment and differentiation of BMSCs, whereas inhibition of miR‐99a by inhibitors enhances these processes. KDM6B was determined as one of important targets of miR‐99a, which was further confirmed by luciferase assay of 3′‐UTR of KDM6B. Moreover, HOX gene level decreased after transfection of miR‐99a mimics in BMSCs, which indicated that KDM6B is a bona fide target of miR‐99a. Furthermore, in a model of in vivo bone regeneration, osteoblast‐specific gain‐ and loss‐of‐function experiments performed using cranial bone defects revealed that miR‐99a mimics‐transfected BMSCs reduced bone formation, and conversely, miR‐99a inhibitors‐transfected BMSCs increased in vivo bone formation. Tissue‐specific inhibition of miR‐99a may be a potential novel therapeutic approach for enhancing BMSCs‐based bone formation and regeneration.

Dickkopf-1 may regulate bone coupling by attenuating wnt/β-catenin signaling in chronic apical periodontitis

OBJECTIVE

Alveolar bone loss is a common outcome of chronic apical periodontitis. In this study, we investigated the involvement of the Dickkopf-1-Wnt/β-catenin signaling pathway in the attenuation of osteogenic differentiation induced by Escherichia coli lipopolysaccharide, and we evaluated the use of Dickkopf-1 inhibitor and Dickkopf-1 recombinant protein to reverse bone loss in different phases of osteogenic differentiation.

METHODS

MC3T3-E1 cells grown in osteogenic medium were treated with Escherichia coli lipopolysaccharide for 24h during osteogenic induction on days 0, 1, 7, 14 and 21. Dickkopf-1 siRNA was added on days 0 and 1, and Dickkopf-1 recombinant was added on days 7, 14, and 21. Quantitative real-time PCR, Western blotting and alkaline phosphatase activity assays were performed to measure osteogenic marker expression and Wnt/β-catenin signaling. A rat apical periodontitis model was used to further evaluate the function of Dickkopf-1 in relation to bone loss.

RESULTS

MC3T3-E1 cells treated with Escherichia coli lipopolysaccharide showed decreased mRNA expression of osteogenic markers. Wnt/β-catenin signaling was also inhibited, and Dickkopf-1 showed corresponding variations as quantified by Western blotting. Using Dickkopf-1 inhibitor or Dickkopf-1 recombinant protein at different phases of osteogenic differentiation in vitro partially reversed the decrease in osteogenic marker expression. The rat apical periodontitis model indicated that the Dickkopf-1 inhibitor could restore bone loss in the periapical area in vivo.

CONCLUSIONS

Dickkopf-1 may play a key regulatory role in determining the outcome for bone in inflammatory environments, and modulating the Wnt/β-catenin signaling pathway via Dickkopf-1 inhibitor or recombinant protein may provide a potential therapeutic option to prevent bone destruction in endodontic disease.

Extracorporeal Shock Wave Rebuilt Subchondral Bone In Vivo and Activated Wnt5a/Ca2+ Signaling In Vitro

Background

This study aimed to identify the optimal extracorporeal shock wave (ESW) intensity and to investigate its effect on subchondral bone rebuilt in vivo and Wnt5a/Ca²⁺ signaling in vitro using an osteoarthritis (OA) rat model and bone marrow mesenchymal stem cells (BMMSCs), respectively.

Methods

OA rats treated with (OA + ESW group) or without (OA group) ESW (n = 12/group) were compared with healthy controls (control group, n = 12). Gait patterns and subchondral trabecular bone changes were measured. Western blot and quantitative real-time polymerase chain reaction detected protein expression and gene transcription, respectively.

Results

The gait disturbances of OA + ESW group were significantly improved compared with the OA group at 6th and 8th weeks. The micro-CT analysis indicated that the BMD, BSV/BV, BV/TV, Tr.S, and Tr.Th are significantly different between OA group and OA + ESW group. Expression of Wnt5a was increased rapidly after ESW treatment at 0.6 bar and peaked after 30 min.

Conclusions

ESW were positive for bone remodeling in joint tibial condyle subchondral bone of OA rat. ESW prevented histological changes in OA and prevented gait disturbance associated with OA progression. Optimal intensity of ESW induced changes in BMMSCs via activation of the Wnt5a/Ca²⁺ signaling pathway.

Lithium enhances alveolar bone formation during orthodontic retention in rats

OBJECTIVE

To investigate the effect of lithium on alveolar bone formation during orthodontic retention in rats.

MATERIALS AND METHODS

After 2 weeks of orthodontic tooth movement (OTM), 42 8-week-old male Wistar rats were randomly divided into two orthodontic retention groups: one without (control) and the other with LiCl treatment (LiCl group). Samples were collected on days 0, 3, 7 and 14 during the retention period. We evaluated the bone volume/total volume (BV/TV) ratio and new bone formation in the region of interests (ie, the root, the periodontal ligament and the adjacent alveolar bone around the distal buccal surface of the distal root of the maxillary first molar). We performed quantitative analyses, including histology, histomorphometry and immunohistochemistry to identify Runx2 and Osterix expression.

RESULTS

The density of trabecular bone, the quantity of osteoblasts and the expression of osteogenic markers, Runx2 and Osterix, were significantly higher in the LiCl group than in the control group during the orthodontic retention period.

CONCLUSION

LiCl enhances alveolar bone formation during orthodontic retention in rats.

Wnt3α and transforming growth factor-β induce myofibroblast differentiation from periodontal ligament cells via different pathways

Myofibroblasts are specialized cells that play a key role in connective tissue remodeling and reconstruction. Alpha-smooth muscle actin (α-SMA), vimentin and tenascin-C are myofibroblast phenotype, while α-SMA is the phenotypic marker. The observation that human periodontal ligament cells (hPDLCs) differentiate into myofibroblasts under orthodontic force has provided a new perspective for understanding of the biological and biomechanical mechanisms involved in orthodontic tooth movement. However, the cell-specific molecular mechanisms leading to myofibroblast differentiation in the periodontal ligament (PDL) remain unclear. In this study, we found that expression of Wnt3α, transforming growth factor-β1 (TGF-β1), α-SMA and tenascin-C increased in both tension and compression regions of the PDL under orthodontic load compared with unloaded control, suggesting that upregulated Wnt3α and TGF-β1 signaling might have roles in myofibroblast differentiation in response to orthodontic force. We reveal in vitro that both Wnt3α and TGF-β1 promote myofibroblast differentiation from hPDLCs. Dickkopf-1 (DKK1) impairs Wnt3α-induced myofibroblast differentiation in a β-catenin-dependent manner. TGF-β1 stimulates myofibroblast differentiation via a JNK-dependent mechanism. DKK1 has no significant effect on TGF-β1-induced myofibroblastic phenotype.

Analysis of the expression of the Wnt family of proteins and its modulatory role on cytokine expression in non activated and activated astroglial cells

Despite the essential functions of astrocytes and the emerging relevance of the Wnt family of proteins in the CNS under physiological and pathological conditions, the astroglial expression of this family of proteins and its potential modulatory role on astroglial activation is almost unknown. Thus, we have evaluated the expression of all Wnt ligands, receptors and regulators, and the activation state of Wnt-related signaling pathways in non-activated and differentially activated astroglial cultures. We found that numerous Wnt ligands, receptors and regulators were expressed in non-activated astrocytes, while the Wnt-dependent pathways were constitutively active. Moreover, the expression of most detectable Wnt-related molecules and the activity of the Wnt-dependent pathways suffered post-activation variations which frequently depended on the activation system. Finally, the analysis of the effects exerted by Wnt1 and 5a on the astroglial expression of prototypical genes related to astroglial activation showed that both Wnt ligands increased the astroglial expression of interleukin 1β depending on the experimental context, while did not modulate tumor necrosis factor α, interleukin 6, transforming growth factor β1 and glial fibrillary acidic protein expression. These results strongly suggest that the Wnt family of proteins is involved in how astrocytes modulate and respond to the physiological and pathological CNS.

Effects of Atorvastatin on Periodontitis of Rats Subjected to Glucocorticoid-Induced Osteoporosis

BACKGROUND

Atorvastatin (ATV) has shown pleiotropic effects on bone tissue, and osteoporosis can aggravate periodontitis. Thus, the effects of ATV on experimental periodontitis (EP) in rats subjected to glucocorticoid-induced osteoporosis (GIOP) was assessed.

METHODS

Male Wistar rats were divided into the following groups: 1) naive; 2) EP; 3) GIOP + EP; and 4) ATV. Groups GIOP + EP and ATV received 7 mg/kg dexamethasone intramuscularly once per week for 5 weeks, and the others received saline (SAL). Groups EP, GIOP + EP, and ATV were submitted to EP by ligature around the maxillary left second molars for 11 days. Group ATV received 27 mg/kg ATV orally, and the others received SAL 30 minutes before EP. Periodontium was analyzed by macroscopy, microtomography, and histopathology; by immunohistochemical examination of receptor activator of nuclear factor-κB ligand (RANKL), osteoprotegerin (OPG), wingless (WNT) 10b, dickkopf-related protein 1 (DKK-1), and β-catenin; and by enzyme-linked immunosorbent assay analysis of myeloperoxidase (MPO), tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-8, IL10, reduced glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT). Leukogram, liver and kidney enzymes, and bone-specific alkaline phosphatase (BALP) serum levels were evaluated.

RESULTS

ATV decreased bone loss, reduced MPO, TNF-α, IL-1β, IL-6, and IL-8, and increased IL-10, GSH, SOD, and CAT levels. ATV reduced RANKL and DKK-1 and increased OPG, WNT10b, and β-catenin expressions and BALP activity.

CONCLUSION

ATV reduced inflammation, oxidative stress, and bone loss in rats with EP and GIOP, with participation of the WNT signaling pathway.

Use of micro-computed tomography for the assessment of periapical lesions in small rodents: a systematic review

This systematic review aimed to evaluate the literature on the acquisition-, reconstruction- and analysis parameters of micro-computed tomography (micro-CT) for the assessment of periapical lesions in rats and mice, and to illustrate the effect of variation in these parameters. The PubMed database was searched from 2000 to January 2015 (English-language publications) for reports on the use of micro-CT to evaluate periapical lesions in rats and mice. QUADAS criteria were used to rate the quality of the studies. To illustrate the effect of variations in acquisition-, reconstruction-, and analysis parameters on images of periapical lesions, micro-CT examination of two hemi-mandibles of mice, with periapical lesions around the first molar was undertaken. Twenty-one studies were identified, which analysed periapical lesions in rats or mice using micro-CT. According to the QUADAS, no study was classified as high-, seven were classified as moderate-, and 14 as low quality. The effect of variation in parameters was that voxel size may interfere with image sharpness, reconstruction may interfere with image sharpness and contrast, and inadequate plane orientation may alter the size of the periapical lesion. Nonpersonalized ROIs resulted in areas that were not part of the periapical lesion. Changing the limits of the threshold for bone-tissue visualization increased lesion size. There is no defined protocol for acquiring and analysing micro-CT images of periapical lesions in rats and mice. Furthermore, acquisition-, reconstruction- and analysis parameters are not adequately explained, which may compromise the scientific impact of the studies.

Expression of Wnt3a, Wnt10b, β-catenin and DKK1 in periodontium during orthodontic tooth movement in rats

OBJECTIVE

To investigate the expression of Wnt3a, Wnt10b, β-catenin and DKK1 in the periodontal ligament (PDL) during orthodontic tooth movement (OTM) in rats.

MATERIALS AND METHODS

Nickel-titanium closed-coil springs were used to deliver an initial 50 g mesial force to the left maxillary first molars in 30 rats. The force was kept constant for 1, 3, 5, 7, 10 and 14 days until the animals were sacrificed. The right maxillary molars without force application served as control. Paraffin-embedded sections of the upper jaws were prepared for histological and immunohistochemical analyses to detect Wnt3a, Wnt10b, β-catenin and DKK1 expression in PDL.

RESULTS

Wnt3a, Wnt10b, β-catenin and DKK1 were expressed on both the ipsilateral and contralateral sides of PDL in each group. After the application of orthodontic force, the expression of β-catenin and DKK1 was initially increased and then decreased on both sides, with maximal levels of expression at day 7 and day 10, respectively. On the compression side, Wnt3a and Wnt10b levels started to increase at day 5, while on the tension side, these two molecules began to increase at day 1. Furthermore, the expression levels of Wnt3a, Wnt10b, and β-catenin were much stronger on the tension side than on the compression side at any of the observation points, while DKK1 level was much higher on the compression side.

CONCLUSION

Wnt3a, Wnt10b, β-catenin and DKK1 expression may be related to the periodontal tissue remodeling following the application of an orthodontic force in rats. These observations suggest that the Wnt/β-catenin signaling pathway may play a crucial role in periodontal tissue remodeling during OTM.

High-Fat Diet/Low-Dose Streptozotocin-Induced Type 2 Diabetes in Rats Impacts Osteogenesis and Wnt Signaling in Bone Marrow Stromal Cells

Bone regeneration disorders are a significant problem in patients with type 2 diabetes mellitus. Bone marrow stromal cells (BMSCs) are recognized as ideal seed cells for tissue engineering because they can stimulate osteogenesis during bone regeneration. Therefore, the aim of this study was to investigate the osteogenic potential of BMSCs derived from type 2 diabetic rats and the pathogenic characteristics of dysfunctional BMSCs that affect osteogenesis. BMSCs were isolated from normal and high-fat diet+streptozotocin-induced type 2 diabetic rats. Cell metabolic activity, alkaline phosphatase (ALP) activity, mineralization and osteogenic gene expression were reduced in the type 2 diabetic rat BMSCs. The expression levels of Wnt signaling genes, such as β-catenin, cyclin D1 and c-myc, were also significantly decreased in the type 2 diabetic rat BMSCs, but the expression of GSK3β remained unchanged. The derived BMSCs were cultured on calcium phosphate cement (CPC) scaffolds and placed subcutaneously into nude mice for eight weeks; they were detected at a low level in newly formed bone. The osteogenic potential of the type 2 diabetic rat BMSCs was not impaired by the culture environment, but it was impaired by inhibition of the Wnt signaling pathway, likely due to an insufficient accumulation of β-catenin rather than because of GSK3β stimulation. Using BMSCs derived from diabetic subjects could offer an alternative method of regenerating bone together with the use of supplementary growth factors to stimulate the Wnt signaling pathway.

Noncanonical activation of β-catenin by Porphyromonas gingivalis

Porphyromonas gingivalis is an established pathogen in periodontal disease and an emerging pathogen in serious systemic conditions, including some forms of cancer. We investigated the effect of P. gingivalis on β-catenin signaling, a major pathway in the control of cell proliferation and tumorigenesis. Infection of gingival epithelial cells with P. gingivalis did not influence the phosphorylation status of β-catenin but resulted in proteolytic processing. The use of mutants deficient in gingipain production, along with gingipain-specific inhibitors, revealed that gingipain proteolytic activity was required for β-catenin processing. The β-catenin destruction complex components Axin1, adenomatous polyposis coli (APC), and GSK3β were also proteolytically processed by P. gingivalis gingipains. Cell fractionation and Western blotting demonstrated that β-catenin fragments were translocated to the nucleus. The accumulation of β-catenin in the nucleus following P. gingivalis infection was confirmed by immunofluorescence microscopy. A luciferase reporter assay showed that P. gingivalis increased the activity of the β-catenin-dependent TCF/LEF promoter. P. gingivalis did not increase Wnt3a mRNA levels, a finding consistent with P. gingivalis-induced proteolytic processing causing the increase in TCF/LEF promoter activity. Thus, our data indicate that P. gingivalis can induce the noncanonical activation of β-catenin and disassociation of the β-catenin destruction complex by gingipain-dependent proteolytic processing. β-Catenin activation in epithelial cells by P. gingivalis may contribute to a proliferative phenotype.

TRIB3 mediates the expression of Wnt5a and activation of nuclear factor-κB in Porphyromonas endodontalis lipopolysaccharide-treated osteoblasts

Porphyromonas endodontalis lipopolysaccharide (LPS) is considered to be correlated with the progression of bone resorption in periodontal and periapical diseases. Wnt5a has recently been implicated in inflammatory processes, but its role is unclear as a P. endodontalis LPS-induced mediator in osteoblasts. Tribbles homolog 3 (TRIB3) encodes a pseudokinase and has been linked to inflammation in certain situations. Here, we found that P. endodontalis LPS induced Wnt5a expression in a dose- and time-dependent manner and it also upregulated translocation, phosphorylation and transcriptional activity of nuclear factor-κB (NF-κB) in MC3T3-E1 cells. Bay 11-7082 blocked the translocation of NF-κB and Wnt5a expression induced by P. endodontalis LPS. Chromatin immunoprecipitation assay further established that induction of Wnt5a by P. endodontalis LPS was mediated through the NF-κB p65 subunit. Additionally, P. endodontalis LPS increased expression of TRIB3 in osteoblasts after 10 h simulated time. Overexpression of TRIB3 enhanced NF-κB phosphorylation and Wnt5a induction, whereas knockdown of TRIB3 inhibited NF-κB phosphorylation and Wnt5a expression in P. endodontalis LPS-stimulated osteoblasts. These results suggest that P. endodontalis LPS has the ability to promote the expression of Wnt5a in mouse osteoblasts, and this induction is mainly mediated by NF-κB pathway. TRIB3 seems to modulate the sustained expression of Wnt5a in osteoblasts stimulated by P. endodontalis LPS, as well as regulating NF-κB phosphorylation.

Histochemical localization of Dickkopf-1 in induced rat periapical lesions

INTRODUCTION

The purpose of this study was to evaluate the expression of Dickkopf-1 (DKK-1), a secreted antagonist of the Wnt (wingless)/beta-catenin signaling pathway, during the development of periapical lesions in rats.

METHODS

Periapical lesions were induced in Wistar rats by occlusal exposure of the pulp of their mandibular first molars. The animals were sacrificed randomly at 0, 7, 14, 21, and 28 day after pulpal exposure. Jaws containing the first molar were obtained and routinely prepared for histologic, immunohistochemical, and enzyme histochemical double immunofluorescence analyses. Data were analyzed using 1-way analysis of variance and Pearson correlation test.

RESULTS

The expansion of the area of periapical lesions was visible from days 7-21 and slowed down thereafter. A few DKK-1- and receptor activator of nuclear factor kappa B ligand (RANKL)-positive cells and osteoclasts were observed on day 7. All positive samples peaked in number on day 14. The expression levels of DKK-1 and RANKL and the number of osteoclasts decreased on days 21 and 28. DKK-1 expression was positively correlated with RANKL expression and osteoclast number from days 7-28.

CONCLUSIONS

DKK-1 expression was up-regulated during periapical lesion development. DKK-1 may be associated with the inflammatory response and bone resorption in periapical lesions.