Inhibiting periapical lesions through AAV-RNAi silencing of cathepsin K

Atp6i deficient mouse model uncovers transforming growth factor-β1 /Smad2/3 as a key signaling pathway regulating odontoblast differentiation and tooth root formation

The biomolecular mechanisms that regulate tooth root development and odontoblast differentiation are poorly understood. We found that Atp6i deficient mice (Atp6i-/-) arrested tooth root formation, indicated by truncated Hertwig's epithelial root sheath (HERS) progression. Furthermore, Atp6i deficiency significantly reduced the proliferation and differentiation of radicular odontogenic cells responsible for root formation. Atp6i-/- mice had largely decreased expression of odontoblast differentiation marker gene expression profiles (Col1a1, Nfic, Dspp, and Osx) in the alveolar bone. Atp6i-/- mice sample RNA-seq analysis results showed decreased expression levels of odontoblast markers. Additionally, there was a significant reduction in Smad2/3 activation, inhibiting transforming growth factor-β (TGF-β) signaling in Atp6i-/- odontoblasts. Through treating pulp precursor cells with Atp6i-/- or wild-type OC bone resorption-conditioned medium, we found the latter medium to promote odontoblast differentiation, as shown by increased odontoblast differentiation marker genes expression (Nfic, Dspp, Osx, and Runx2). This increased expression was significantly blocked by anti-TGF-β1 antibody neutralization, whereas odontoblast differentiation and Smad2/3 activation were significantly attenuated by Atp6i-/- OC conditioned medium. Importantly, ectopic TGF-β1 partially rescued root development and root dentin deposition of Atp6i-/- mice tooth germs were transplanted under mouse kidney capsules. Collectively, our novel data shows that the prevention of TGF-β1 release from the alveolar bone matrix due to OC dysfunction may lead to osteopetrosis-associated root formation via impaired radicular odontoblast differentiation. As such, this study uncovers TGF-β1 /Smad2/3 as a key signaling pathway regulating odontoblast differentiation and tooth root formation and may contribute to future therapeutic approaches to tooth root regeneration.

Cathepsins in oral diseases: mechanisms and therapeutic implications

Cathepsins are a type of lysosomal globulin hydrolase and are crucial for many physiological processes, including the resorption of bone matrix, innate immunity, apoptosis, proliferation, metastasis, autophagy, and angiogenesis. Findings regarding their functions in human physiological processes and disorders have drawn extensive attention. In this review, we will focus on the relationship between cathepsins and oral diseases. We highlight the structural and functional properties of cathepsins related to oral diseases, as well as the regulatory mechanisms in tissue and cells and their therapeutic uses. Elucidating the associated mechanism between cathepsins and oral diseases is thought to be a promising strategy for the treatment of oral diseases and may be a starting point for further studies at the molecular level.

Emerging Roles of YAP/TAZ in Tooth and Surrounding: from Development to Regeneration

Yes associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are ubiquitous transcriptional co-activators that control organ development, homeostasis, and tissue regeneration. Current in vivo evidence suggests that YAP/TAZ regulates enamel knot formation during murine tooth development, and is indispensable for dental progenitor cell renewal to support constant incisor growth. Being a critical sensor for cellular mechano-transduction, YAP/TAZ lays at the center of the complex molecular network that integrates mechanical cues from the dental pulp chamber and surrounding periodontal tissue into biochemical signals, dictating in vitro cell proliferation, differentiation, stemness maintenance, and migration of dental stem cells. Moreover, YAP/TAZ-mediated cell-microenvironment interactions also display essential regulatory roles during biomaterial-guided dental tissue repair and engineering in some animal models. Here, we review recent advances in YAP/TAZ functions in tooth development, dental pulp, and periodontal physiology, as well as dental tissue regeneration. We also highlight several promising strategies that harness YAP/TAZ activation for promoting dental tissue regeneration.

Recent Advances in Apical Periodontitis Treatment: A Narrative Review

Apical periodontitis is an inflammatory response caused by pulp infection. It induces bone resorption in the apical and periapical regions of the tooth. The most conservative approach to treat this condition is nonsurgical endodontic treatment. However, clinical failure has been reported with this approach; thus, alternative procedures are required. This review highlights recent literature regarding advanced approaches for the treatment of apical periodontitis. Various therapies, including biological medications, antioxidants, specialized pro-resolving lipid mediators, and stem cell therapy, have been tested to increase the success rate of treatment for apical periodontitis. Some of these approaches remain in the in vivo phase of research, while others have just entered the translational research phase to validate clinical application. However, a detailed understanding of the molecular mechanisms that occur during development of the immunoinflammatory reaction in apical periodontitis remains unclear. The aim of this review was to summarize advanced approaches for the treatment of apical periodontitis. Further research can confirm the potential of these alternative nonsurgical endodontic treatment approaches.

GCN5 regulates ZBTB16 through acetylation, mediates osteogenic differentiation, and affects orthodontic tooth movement

In the process of orthodontic tooth movement (OTM), periodontal ligament fibroblasts (PDLFs) must undergo osteogenic differentiation. OTM increased the expression of Zinc finger and BTB domain-containing 16 (ZBTB16), which is implicated in osteogenic differentiation. Our goal was to investigate the mechanism of PDLF osteogenic differentiation mediated by ZBTB16. The OTM rat model was established, and PDLFs were isolated and exposed to mechanical force. Hematoxylin-eosin staining, Alizarin Red staining, immunofluorescence, and immunohistochemistry were carried out. The alkaline phosphatase (ALP) activity was measured. Dual-luciferase reporter gene assay and chromatin immunoprecipitation assay were conducted. In OTM models, ZBTB16 was significantly expressed. Additionally, there was an uneven distribution of PDLFs in the OTM group, as well as an increase in fibroblasts and inflammatory infiltration. ZBTB16 interference hindered PDLF osteogenic differentiation and decreased Wnt and β-catenin levels. Meanwhile, ZBTB16 activated the Wnt/β-catenin pathway. ZBTB16 also enhanced the expression of the osteogenic molecules osterix, osteocalcin (OCN), osteopontin (OPN), and bone sialo protein (BSP) at mRNA and protein levels. The interactions between Wnt1 and ZBTB16, as well as GCN5 and ZBTB16, were also verified. The adeno-associated virus-shZBTB16 injection also proved to inhibit osteogenic differentiation and reduce tooth movement distance in in vivo tests. ZBTB16 was up-regulated in OTM. Through acetylation modification of ZBTB16, GCN5 regulated the Wnt/β-catenin signaling pathway and further mediated PDLF osteogenic differentiation.

Cathepsin K in Pathological Conditions and New Therapeutic and Diagnostic Perspectives

Cathepsin K (CatK) is a part of the family of cysteine proteases involved in many important processes, including the degradation activity of collagen 1 and elastin in bone resorption. Changes in levels of CatK are associated with various pathological conditions, primarily related to bone and cartilage degradation, such as pycnodysostosis (associated with CatK deficiency), osteoporosis, and osteoarthritis (associated with CatK overexpression). Recently, the increased secretion of CatK is being highly correlated to vascular inflammation, hypersensitivity pneumonitis, Wegener granulomatosis, berylliosis, tuberculosis, as well as with tumor progression. Due to the wide spectrum of diseases in which CatK is involved, the design and validation of active site-specific inhibitors has been a subject of keen interest in pharmaceutical companies in recent decades. In this review, we summarized the molecular background of CatK and its involvement in various diseases, as well as its clinical significance for diagnosis and therapy.

Knockout and Double Knockout of Cathepsin K and Mmp9 reveals a novel function of Cathepsin K as a regulator of osteoclast gene expression and bone homeostasis

Cathepsins play a role in regulation of cell function through their presence in the cell nucleus. However, the role of Cathepsin K (Ctsk) as an epigenetic regulator in osteoclasts remains unknown. Our data demonstrated that Ctsk^-/-Mmp9^-/- mice have a striking phenotype with a 5-fold increase in bone volume compared with WT. RNA-seq analysis of Ctsk^-/- , Mmp9^-/- and Ctsk^-/-/Mmp9^-/- osteoclasts revealed their distinct functions in gene expression regulation, including reduced Cebpa expression, increased Nfatc1 expression, and in signaling pathways activity regulation. Western blots and qPCR data validated these changes. ATAC-seq profiling of Ctsk^-/- , Mmp9^-/-, and Ctsk^-/-/Mmp9^-/- osteoclasts indicated the changes resulted from reduced chromatin openness in the promoter region of Cebpa and increased chromatin openness in Nfatc1 promoter in Ctsk^-/-/Mmp9^-/- osteoclasts compared to that in osteoclasts of WT, Ctsk^/- and Mmp9^-/- . We found co-localization of Ctsk with c-Fos and cleavage of H3K27me3 in wild-type osteoclasts. Remarkably, cleavage of H3K27me3 was blocked in osteoclasts of Ctsk^-/- and Ctsk^-/-/Mmp9^-/- mice, suggesting that Ctsk may epigenetically regulate distinctive groups of genes' expression by regulating proteolysis of H3K27me3. Ctsk^-/-/Mmp9^-/- double knockout dramatically protects against ovariectomy induced bone loss. We found that Ctsk may function as an essential epigenetic regulator in modulating levels of H3K27me3 in osteoclast activation and maintaining bone homeostasis. Our study revealed complementary and unique functions of Ctsk as epigenetic regulators for maintaining osteoclast activation and bone homeostasis by orchestrating multiple signaling pathways and targeting both Ctsk and Mmp9 is a novel therapeutic approach for osteolytic diseases such as osteoporosis.

Local immunomodulatory effects of intracanal medications in apical periodontitis

The immune system is an extremely complex biological network that plays a crucial role in the hemostasis of periapical tissue, pathogenesis of apical periodontitis (AP) as well as periapical tissue healing. The successful elimination of microbial infections remains a significant challenge, mostly due to the ever-growing development of antimicrobial-resistant pathogens. The bacterial endurance in the root canal system contributes to features ranging from altered post-treatment healing to exacerbation of chronic periradicular immune response, that compromise the outcome of endodontic treatment. A highly effective strategy for combating infectious diseases and the associated inflammation-mediated tissue damage is to modulate the host immune response in conjunction with antimicrobial therapy. There are several medications currently used in endodontic treatment, however, they suffer various levels of microbial resistance and do not deliver all the required characteristics to simultaneously address both intracanal bacteria and periapical inflammation. Interaction of antimicrobial agents with the immune system can impact its function, leading to immune-suppressive or immune-stimulatory effects. The group of non-conventional antimicrobial medications, such as antimicrobial peptides, propolis, and nanomaterials, are agents that provide strong antimicrobial effectiveness and concomitant immunomodulatory and/or reparative effect, without any host tissue damages. Herein, we provide an overview of local immune modulation in AP and a comprehensive review of the immunomodulatory effect of antimicrobials intracanal medications applied in endodontics with specific emphasis on the antimicrobial nanomaterial-based approaches that provide immunomodulatory potential for successful clinical deployment in endodontics.

Cathepsin K deficiency promotes alveolar bone regeneration by promoting jaw bone marrow mesenchymal stem cells proliferation and differentiation via glycolysis pathway

Objectives

To clarify the possible role and mechanism of Cathepsin K (CTSK) in alveolar bone regeneration mediated by jaw bone marrow mesenchymal stem cells (JBMMSC).

Materials and Methods

Tooth extraction models of Ctsk knockout mice (Ctsk^‐/‐) and their wildtype (WT) littermates were used to investigate the effect of CTSK on alveolar bone regeneration. The influences of deletion or inhibition of CTSK by odanacatib (ODN) on proliferation and osteogenic differentiation of JBMMSC were assessed by CCK‐8, Western blot and alizarin red staining. To explore the differently expressed genes, RNA from WT and Ctsk^‐/‐ JBMMSC was sent to RNA‐seq. ECAR, glucose consumption and lactate production were measured to identify the effect of Ctsk deficiency or inhibition on glycolysis. At last, we explored whether Ctsk deficiency or inhibition promoted JBMMSC proliferation and osteogenic differentiation through glycolysis.

Results

We found out that Ctsk knockout could promote alveolar bone regeneration in vivo. In vitro, we confirmed that both Ctsk knockout and inhibition by ODN could promote proliferation of JBMMSC, up‐regulate expression of Runx2 and ALP, and enhance matrix mineralization. RNA‐seq results showed that coding genes of key enzymes in glycolysis were significantly up‐regulated in Ctsk^‐/‐ JBMMSC, and Ctsk deficiency or inhibition could promote glycolysis in JBMMSC. After blocking glycolysis by 3PO, the effect of Ctsk deficiency or inhibition on JBMMSC’s regeneration was blocked subsequently.

Conclusions

Our findings revealed that Ctsk knockout or inhibition could promote alveolar bone regeneration by enhancing JBMMSC regeneration via glycolysis. These results shed new lights on the regulatory mechanism of CTSK on bone regeneration.

Cystatin-like protein of sweet orange (CsinCPI-2) modulates pre-osteoblast differentiation via β-Catenin involvement

Phytocystatins are endogenous cysteine-protease inhibitors present in plants. They are involved in initial germination rates and in plant defense mechanisms against phytopathogens. Recently, a new phytocystatin derived from sweet orange, CsinCPI-2, has been shown to inhibit the enzymatic activity of human cathepsins, presenting anti-inflammatory potential and pro-osteogenic effect in human dental pulp cells. The osteogenic potential of the CsinCPI-2 protein represents a new insight into plants cysteine proteases inhibitors and this effect needs to be better addressed. The aim of this study was to investigate the performance of pre-osteoblasts in response to CsinCPI-2, mainly focusing on cell adhesion, proliferation and differentiation mechanisms. Together our data show that in the first hours of treatment, protein in CsinCPI-2 promotes an increase in the expression of adhesion markers, which decrease after 24 h, leading to the activation of Kinase-dependent cyclines (CDKs) modulating the transition from G1 to S phases cell cycle. In addition, we saw that the increase in ERK may be associated with activation of the differentiation profile, also observed with an increase in the B-Catenin pathway and an increase in the expression of Runx2 in the group that received the treatment with CsinCPI-2.

Proresolving Mediators in Endodontics: A Systematic Review

INTRODUCTION

Proresolving lipid mediators are specialized molecules (SPMs) involved in the active resolution of the inflammatory process by regulating tissue homeostasis. The aim of this study was to investigate the scientific literature to assess the potential of SPMs as an adjunct in the treatment of endodontic infection.

METHODS

Three electronic databases (PubMed, Web of Science, and Scopus) were searched from their inception until February 2020 (PROSPERO CRD42020164743). Supplemental research was performed by screening the references of the relevant studies eligible for inclusion. A quality assessment of animal studies was performed using the Animal Research: Reporting of In Vivo Experiments guidelines, whereas the Systematic Review Centre for Laboratory animal Experimentation Risk of Bias tool was used to assess the risk of bias.

RESULTS

A total of 3295 records were screened, and 8 articles meeting the criteria were included for this qualitative review. The eligible studies showed a high to moderate overall quality and a low to moderate risk of bias. SPMs positively affected the development of pulpitis and apical periodontitis in experimental animal models. The early treatment of pulpitis with the topical application of SPMs was beneficial to control inflammation within 24 hours from contamination. In addition, SPMs delivered within the root canals after disinfection were found effective in promoting periapical healing.

CONCLUSIONS

Our findings suggest that SPMs may play a role in the inception and treatment of pulpal-periapical diseases, and they should be considered for future research for developing new therapeutics as an adjunct to endodontic treatment.

Silencing of Ac45 Simultaneously Inhibits Osteoclast-Mediated Bone Resorption and Attenuates Dendritic Cell-Mediated Inflammation through Impairing Acidification and Cathepsin K Secretion

Endodontic disease is characterized by inflammation and destruction of periapical tissues, leading to severe bone resorption and tooth loss. ATP6AP1 (Ac45) has been implicated in human immune diseases, yet the mechanism underlying how Ac45 regulates immune response and reaction in inflammatory diseases remains unknown. We generated endodontic disease mice through bacterial infection as an inflammatory disease model and used adeno-associated virus (AAV)-mediated Ac45 RNA interference knockdown to study the function of Ac45 in periapical inflammation and bone resorption. We demonstrated that the AAV small hairpin RNA targeting Ac45 (AAV-sh-Ac45) impaired cellular acidification, extracellular acidification, and bone resorption. Our results showed that local delivery of AAV-sh-Ac45 in periapical tissues in bacterium-induced inflammatory lesions largely reduced bone destruction, inhibited inflammation, and dramatically reduced mononuclear immune cells. T-cell, macrophage, and dendritic cell infiltration in the periapical lesion was dramatically reduced, and the periodontal ligament was protected from inflammation-induced destruction. Furthermore, AAV-sh-Ac45 significantly reduced osteoclast formation and the expression of proinflammatory cytokines, such as tumor necrosis factor alpha, interleukin-10 (IL-10), IL-12, IL-1α, IL-6, and IL-17. Interestingly, AAV-sh-Ac45 impaired mature cathepsin K secretion more significantly than that by AAV-sh-C1 and AAV-sh-CtsK Unbiased genome-wide transcriptome sequencing analysis of Ctsk ^-/- dendritic cells stimulated with lipopolysaccharide demonstrated that the ablation of Ctsk dramatically reduced dendritic cell-mediated inflammatory signaling. Taken together, our results indicated that AAV-sh-Ac45 simultaneously inhibits osteoclast-mediated bone resorption and attenuates dendritic cell-mediated inflammation through impairing acidification and cathepsin K secretion. Thus, Ac45 may be a novel target for therapeutic approaches to attenuate inflammation and bone erosion in endodontic disease and other inflammation-related osteolytic diseases.

Effect of VEGFC on lymph flow and inflammation-induced alveolar bone loss

The lymphatic system plays a crucial role in the maintenance of tissue fluid homeostasis and the immunological response to inflammation. The effects of lymphatic drainage dysfunction on periodontitis have not been well studied. Here we show that lymphatic vessel endothelial receptor 1 (LYVE1)+ /podoplanin (PDPN)+ lymphatic vessels (LVs) are increased in the periodontal tissues, with accumulation close to the alveolar bone surface, in two murine periodontitis models: rheumatoid arthritis (RA)-associated periodontitis and ligature-induced periodontitis. Further, PDPN+ /alpha-smooth muscle actin (αSMA)- lymphatic capillaries are increased, whereas PDPN+ /αSMA+ collecting LVs are decreased significantly in the inflamed periodontal tissues. Both mouse models of periodontitis have delayed lymph flow in periodontal tissues, increased TRAP-positive osteoclasts, and significant alveolar bone loss. Importantly, the local administration of adeno-associated virus for vascular endothelial growth factor C, the major growth factor that promotes lymphangiogenesis, increases the area and number of PDPN+ /αSMA+ collecting LVs, promotes local lymphatic drainage, and reduces alveolar bone loss in both models of periodontitis. Lastly, LYVE1+ /αSMA- lymphatic capillaries are increased, whereas LYVE1+ /αSMA+ collecting LVs are decreased significantly in gingival tissues of patients with chronic periodontitis compared with those of clinically healthy controls. Thus, our findings reveal an important role of local lymphatic drainage in periodontal inflammation-mediated alveolar bone loss. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Cyclic compression emerged dual effects on the osteogenic and osteoclastic status of LPS-induced inflammatory human periodontal ligament cells according to loading force

BACKGROUND

Appropriate mechanical stimulation is essential for bone homeostasis in healthy periodontal tissues. While the osteogenesis and osteoclast differentiation of inflammatory periodontal ligament cells under different dynamic loading has not been yet clear. The aim of this study is to clarify the inflammatory, osteogenic and pro-osteoclastic effects of different cyclic stress loading on the inflammatory human periodontal ligament cells (hPDLCs).

METHODS

hPDLCs were isolated from healthy premolars and cultured in alpha minimum Eagle's medium (α-MEM). Lipopolysaccharides (LPS) were used to induce the inflammation state of hPDLCs in vitro. Determination of LPS concentration for the model of inflammatory periodontium was based on MTT and genes expression analysis. Then the cyclic stress of 0, 0-50, 0-90 and 0-150 kPa was applied to the inflammatory hPDLCs for 5 days respectively. mRNA and protein levels of osteogenic, osteoclastic and inflammation-related markers were examined after the treatment.

RESULTS

MTT and RT-PCR results showed that 10 μg/ml LPS up-regulated TNF-α, IL-1β, IL-6, IL-8 and MCP-1 mRNA levels (P < 0.05) and did not affect the cell viability (P > 0.05). The excessive loading of stress (150 kPa) with or without LPS strongly increased the expression of inflammatory-related markers TNF-α, IL-1β, IL-6, IL-8, MCP-1 (P < 0.05) and osteoclastic markers RANKL, M-CSF, PTHLH and CTSK compared with other groups (P < 0.05), but had no significant effect on osteogenic genes. While 0-90 kPa cyclic pressure could up-regulate the expression of osteogenic genes ALP, COL-1, RUNX2, OCN, OPN and OSX in the healthy hPDLSCs.

CONCLUSIONS

Collectively, it could be concluded that 0-150 kPa was an excessive stress loading which accelerated both inflammatory and osteoclastic effects, while 0-90 kPa may be a positive factor for the osteogenic differentiation of hPDLCs in vitro.

C1 Silencing Attenuates Inflammation and Alveolar Bone Resorption in Endodontic Disease

INTRODUCTION

Endodontic disease, 1 of the most prevalent chronic infectious diseases worldwide, occurs when the dental pulp becomes infected and inflamed, leading to bone destruction around the tooth root, severe pain, and tooth loss. Although many studies have tried to develop therapies to alleviate the bone erosion and inflammation associated with endodontic disease, there is an urgent need for an effective treatment.

METHODS

In this study, we used a gene-based therapy approach by administering recombinant adeno-associated virus (AAV)-mediated Atp6v1c1 knockdown to target both periapical bone resorption and inflammation in the mouse model of endodontic disease.

RESULTS

The results showed that Atp6v1c1 knockdown is simultaneously capable of reducing bone resorption by 70% through impaired osteoclast activation, inhibiting inflammation by decreasing T-cell infiltration in the periapical lesion by 75%, and protecting the periodontal ligament from destruction caused by inflammation. Notably, AAV-mediated gene therapy of Atp6v1c1 knockdown significantly reduced proinflammatory cytokine expression, including tumor necrosis factor α, interleukin 1α, interleukin 17, interleukin 12, and interleukin 6 levels in periapical tissues caused by bacterial infection. Quantitative real-time polymerase chain reaction revealed that Atp6v1c1 knockdown reduced osteoclast-specific functional genes (ie, Ctsk) in periapical tissues.

CONCLUSIONS

Our results showed that AAV-mediated Atp6v1c1 knockdown in periapical tissues slowed endodontic disease progression, prevented bone erosion, and alleviated inflammation in the periapical tissues and periodontal ligament potentially through regulation of toll-like receptor signaling, indicating that targeting Atp6v1c1 may facilitate the design of novel therapeutic approaches to reduce inflammation and bone erosion in endodontic disease.

Inhibition of Ctsk alleviates periodontitis and comorbid rheumatoid arthritis via downregulation of the TLR9 signalling pathway

AIM

In this study, we investigate the mechanistic link between rheumatoid arthritis (RA) and periodontitis to identify a novel target (cathepsin K; Ctsk) for the treatment of comorbid periodontitis and RA.

METHODS

An experimental model of periodontitis with arthritis was established in DBA/1 mice. We then tested the effect of BML-244, a specific inhibitor of Ctsk, by quantifying several inflammatory markers of TLR9 signalling both in vivo and in vitro.

RESULTS

Our results showed that periodontitis-rheumatoid arthritis comorbidity causes severer periodontal bone and joint cartilage destruction than either disease alone. Inhibition of Ctsk reduced infiltration by dendritic cells and T cells and inflammatory cytokine production; these improvements alleviated the hard-tissue erosion in periodontitis and RA as measured by bone erosion in periodontal lesions and cartilage destruction in knee joints. Inhibition of Ctsk also decreased the expression of TLR4 and TLR9 in vivo, whereas in vitro experiments indicated that Ctsk is involved specifically in the production of cytokines in response to TLR9 engagement.

CONCLUSION

Our data reveal that periodontitis and RA may have additive pathological effects through dysregulation of the TLR9 pathway and that Ctsk is a critical mediator of this pathway and contributes to the pathogenesis of RA and periodontitis.

Bone resorption deficiency affects tooth root development in RANKL mutant mice due to attenuated IGF-1 signaling in radicular odontoblasts

The tooth root is essential for normal tooth physiological function. Studies on mice with mutations or targeted gene deletions revealed that osteoclasts (OCs) play an important role in tooth root development. However, knowledge on the cellular and molecular mechanism underlying how OCs mediate root formation is limited. During bone formation, growth factors (e.g. Insulin-like growth factor-1, IGF-1) liberated from bone matrix by osteoclastic bone resorption stimulate osteoblast differentiation. Thus, we hypothesize that OC-osteoblast coupling may also apply to OC-odontoblast coupling; therefore OCs may have a direct impact on odontoblast differentiation through the release of growth factor(s) from bone matrix, and consequently regulate tooth root formation. To test this hypothesis, we used a receptor activator of NF-κB ligand (RANKL) knockout mouse model in which OC differentiation and function was entirely blocked. We found that molar root formation and tooth eruption were defective in RANKL^-/- mice. Disrupted elongation and disorganization of Hertwig's epithelial root sheath (HERS) was observed in RANKL^-/- mice. Reduced expression of nuclear factor I C (NFIC), osterix, and dentin sialoprotein, markers essential for radicular (root) odontogenic cell differentiation indicated that odontoblast differentiation was disrupted in RANKL deficient mice likely contributing to the defect in root formation. Moreover, down-regulation of IGF/AKT/mTOR activity in odontoblast indicated that IGF signaling transduction in odontoblasts of the mutant mice was impaired. Treating odontoblast cells in vitro with conditioned medium from RANKL^-/- OCs cultured on bone slices resulted in inhibition of odontoblast differentiation. Moreover, depletion of IGF-1 in bone resorption-conditioned medium (BRCM) from wild-type (WT) OC significantly compromised the ability of WT osteoclastic BRCM to induce odontoblast differentiation while addition of IGF-1 into RANKL^-/- osteoclastic BRCM rescued impaired odontoblast differentiation, confirming that root and eruption defect in RANKL deficiency mice may result from failure of releasing of IGF-1 from bone matrix through OC bone resorption. These results suggest that OCs are important for odontoblast differentiation and tooth root formation, possibly through IGF/AKT/mTOR signaling mediated by cell-bone matrix interaction. These findings provide significant insights into regulatory mechanism of tooth root development, and also lay the foundation for root regeneration studies.

Monocyte-Specific Knockout of C/ebpα Results in Osteopetrosis Phenotype, Blocks Bone Loss in Ovariectomized Mice, and Reveals an Important Function of C/ebpα in Osteoclast Differentiation and Function

CCAAT/enhancer-binding protein α (C/ebpα) is critical for osteoclastogenesis by regulating osteoclast (OC) lineage commitment and is also important for OC differentiation and function in vitro. However, the role of C/ebpα in postnatal skeletal development has not been reported owing to lethality in C/ebpα-/- mice from hypoglycemia within 8 hours after birth. Herein, we generated conditional knockout mice by deleting the C/ebpα gene in monocyte via LysM-Cre to examine its role in OC differentiation and function. C/ebpαf/f LysM-Cre mice exhibited postnatal osteopetrosis due to impaired osteoclastogenesis, OC lineage priming defects, as well as defective OC differentiation and activity. Furthermore, our ex vivo analysis demonstrated that C/ebpα conditional deletion significantly reduced OC differentiation, maturation, and activity while mildly repressing macrophage development. At the molecular level, C/ebpα deficiency significantly suppresses the expressions of OC genes associated with early stages of osteoclastogenesis as well as genes associated with OC differentiation and activity. We also identified numerous C/ebpα critical cis-regulatory elements on the Cathepsin K promoter that allow C/ebpα to significantly upregulate Cathepsin K expression during OC differentiation and activity. In pathologically induced mouse model of osteoporosis, C/ebpα deficiency can protect mice against ovariectomy-induced bone loss, uncovering a central role for C/ebpα in osteolytic diseases. Collectively, our findings have further established C/ebpα as a promising therapeutic target for bone loss by concurrently targeting OC lineage priming, differentiation, and activity. © 2017 American Society for Bone and Mineral Research.

C/ebpα controls osteoclast terminal differentiation, activation, function, and postnatal bone homeostasis through direct regulation of Nfatc1

Osteoclast lineage commitment and differentiation have been studied extensively, although the mechanism by which transcription factor(s) control osteoclast terminal differentiation, activation, and function remains unclear. CCAAT/enhancer-binding protein α (C/ebpα) has been reported to be a key regulator of osteoclast cell lineage commitment, yet C/ebpα's roles in osteoclast terminal differentiation, activation and function, and bone homeostasis, under physiological or pathological conditions, have not been studied because newborn C/ebpα-null mice die within several hours after birth. Furthermore, the function of C/ebpα in osteoclast terminal differentiation, activation, and function is largely unknown. Herein, we generated and analyzed an osteoclast-specific C/ebpα conditional knockout (CKO) mouse model via Ctsk-Cre mice and found that C/ebpα-deficient mice exhibited a severe osteopetrosis phenotype due to impaired osteoclast terminal differentiation, activation, and function, including mildly reduced osteoclast number, impaired osteoclast polarization, actin formation, and bone resorption, which demonstrated the novel function of C/ebpα in cell function and terminal differentiation. Interestingly, C/ebpα deficiency did not affect bone formation or monocyte/macrophage development. Our results further demonstrated that C/ebpα deficiency suppressed the expression of osteoclast functional genes, e.g. encoding cathepsin K (Ctsk), Atp6i (Tcirg1), and osteoclast regulator genes, e.g. encoding c-fos (Fos), and nuclear factor of activated T-cells 1 (Nfatc1), while having no effect on Pu.1 (Spi1) expression. Promoter activity mapping and ChIP assay defined the critical cis-regulatory element (CCRE) in the promoter region of Nfatc1, and also showed that the CCREs were directly associated with C/ebpα, which enhanced the promoter's activity. The deficiency of C/ebpα in osteoclasts completely blocked ovariectomy-induced bone loss, indicating that C/ebpα is a promising new target for the treatment of osteolytic diseases. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

5-Lipoxygenase Knockout Aggravated Apical Periodontitis in a Murine Model

5-Lipoxygenase (5-LO) plays a vital role in the host innate immune response, including bacteria-induced inflammation. Apical periodontitis (AP) is due to immune disorders caused by imbalances between bacterial invasion and subsequent host defense response. In this work, we investigated the role of 5-lipoxygenase in AP by using 5- lo knockout mice (5- lo-/- mice). Results showed that 5- lo-/- mice had greater periapical bone loss and more osteoclasts positive for tartrate-resistant acid phosphatase staining than did wild-type mice, as determined by micro-computed tomography and histologic staining. The inflammation- and osteoclastogenesis-related factors IL-1β, TNF-α, RANK, and RANKL were also significantly elevated in 5- lo-/- mice, whereas osteoprotegerin was reduced. Furthermore, peritoneal macrophages from 5- lo-/- mice revealed an obviously impaired ability to phagocytose the AP pathogenic bacteria Fusobacterium nucleatum. In vivo experiments confirmed that 5- lo knockout led to decreased macrophage recruitment and increased F. nucleatum infection around the periapical area due to decreased leukotriene B₄ and LXA4 production. All these results showed that 5- lo knockout impaired the host innate immune system to promote the release of bone resorption-related factors. Therefore, 5- lo deficiency aggravated AP in an experimental murine AP model.

Participation of osteoclastogenic factors in immunopathogenesis of human chronic periapical lesions

BACKGROUND

Chronic periapical lesions (CPLs) are common lesions of the oral cavity and are the result of caries, tooth fracture, iatrogenic causes, or factors causing contamination and pulp necrosis. Inflammatory cells participate in the expansion of CPLs by releasing factors that stimulate or inhibit osteolytic activity. The objective of this study was to investigate the participation of RANKL, TNF-α, cathepsin K, IL-33, and OPG in the development of radicular cysts (RCs) and periapical granulomas (PGs).

METHODS

Paraffin-embedded sections of 30 RCs and 22 PGs were submitted to immunohistochemistry.

RESULTS

Immunoexpression of the proteins studied was observed in the epithelium and capsule of RCs, as well as in connective tissue of PGs. The expression of the osteoclastogenic factors studied differed significantly in RCs and PGs (P < .001), with lower expression of OPG in RCs. In PGs, the lowest expression was observed for cathepsin K. Comparison of the 2 lesions showed a similar participation of RANKL and IL33, while a significant difference was observed for OPG (P < .001), TNF-α (P = .002), and cathepsin K (P = .016). No association of the expression of the proteins with lesions size was observed.

CONCLUSIONS

This study demonstrated the participation of RANKL, TNF-α, IL-33, cathepsin K, and OPG in the development of RCs and PGs, with emphasis on the highest immunoreactivity of cathepsin in RCs and TNF-α and OPG in PGs. OPG possibly determines the slower growth of PGs compared to RCs.

High-mobility Group Box 1 Is Associated with the Inflammatory Infiltration and Alveolar Bone Destruction in Rats Experimental Periapical Lesions

INTRODUCTION

This study was conducted to observe the immunohistochemical localization of high-mobility group box 1 (HMGB1) and its receptor, Toll-like receptor 4 (TRL4), in the development of periapical lesions induced in rats. The possible role of these molecules in the pathogenesis of periapical lesions was also explored.

METHODS

Periapical lesions developed within 35 days after mandibular first molar pulp exposure in Wistar rats. The animals were randomly killed at 0, 7, 14, 21, 28, and 35 days after pulp exposure. The jaws that contained the first molar were obtained and prepared for histologic analysis, enzyme histochemistry, immunohistochemistry, and double immunofluorescence staining.

RESULTS

From day 0 to 35, the areas of periapical bone loss increased and appeared to be stabilized on day 35. A few HMGB1-positive, TLR4-positive cells and osteoclasts could be observed on day 7. From day 7 to 28, the HMGB1 and TLR4 protein expression increased and subsequently remained stable. The number of osteoclasts multiplied from day 0 to 14 and then gradually decreased from day 14 to 35. Double immunofluorescence staining results showed HMGB1-positive, TLR4-positive cells around periapical lesions surrounding the apical foramen.

CONCLUSIONS

Thus, HMGB1 and TLR4 may be associated with the pathogenesis of the periapical lesions.

Role of odanacatib in reducing bone loss due to endodontic disease: An overview

Aims and Objectives:

Through a comprehensive literature review, this article provides an overview of the potential role of odanacatib (ODN) in reducing bone loss due to endodontic disease.

Materials and Methods:

A literature review was performed in PubMed Central, MEDLINE, Cochrane Library, and EBSCO databases. The articles identified included those published between 2002 and 2016. Based on the predetermined inclusion and exclusion criteria, out of 237 articles found, 50 were selected for this review.

Results:

Cathepsin K (CstK), which is indispensible to the immune system, also plays an important role in osteoclastic bone resorption. ODN, which is an orally active, selective, and effective inhibitor of CstK, decreases bone resorption by selectively inhibiting proteolysis of matrix proteins by CstK, without affecting other osteoclastic activity or osteoblast viability.

Conclusion:

The goal of endodontic treatment is to achieve a clinically asymptomatic state along with formation of reparative bone. This process could take 6 months or longer, hence, an earlier reversal of the resorption process could lead to faster healing and resolution of the periapical lesion. Use of ODN can be of help in achieving this goal.

The silencing of cathepsin K used in gene therapy for periodontal disease reveals the role of cathepsin K in chronic infection and inflammation

BACKGROUND AND OBJECTIVE

Periodontitis is a severe chronic inflammatory disease and one of the most prevalent non-communicable chronic diseases that affects the majority of the world's adult population. While great efforts have been devoted toward understanding the pathogenesis of periodontitis, there remains a pressing need for developing potent therapeutic strategies for targeting this dreadful disease. In this study, we utilized adeno-associated virus (AAV) expressing cathepsin K (Ctsk) small hairpin (sh)RNA (AAV-sh-Ctsk) to silence Ctsk in vivo and subsequently evaluated its impact in periodontitis as a potential therapeutic strategy for this disease.

MATERIAL AND METHODS

We used a known mouse model of periodontitis, in which wild-type BALB/cJ mice were infected with Porphyromonas gingivalis W50 in the maxillary and mandibular periodontium to induce the disease. AAV-sh-Ctsk was then administrated locally into the periodontal tissues in vivo, followed by analyses to assess progression of the disease.

RESULTS

AAV-mediated Ctsk silencing drastically protected mice (> 80%) from P. gingivalis-induced bone resorption by osteoclasts. In addition, AAV-sh-Ctsk administration drastically reduced inflammation by impacting the expression of many inflammatory cytokines as well as T-cell and dendritic cell numbers in periodontal lesions.

CONCLUSION

AAV-mediated Ctsk silencing can simultaneously target both the inflammation and bone resorption associated with periodontitis through its inhibitory effect on immune cells and osteoclast function. Thereby, AAV-sh-Ctsk administration can efficiently protect against periodontal tissue damage and alveolar bone loss, establishing this AAV-mediated local silencing of Ctsk as an important therapeutic strategy for effectively treating periodontal disease.

CCAAT/Enhancer-binding Protein α (C/EBPα) Is Important for Osteoclast Differentiation and Activity

CCAAT/enhancer-binding protein (C/EBPα) can appoint mouse bone marrow (MBM) cells to the osteoclast (OC) lineage for osteoclastogenesis. However, whether C/EBPα is also involved in OC differentiation and activity is unknown. Here we demonstrated that C/EBPα overexpression in MBM cells can promote OC differentiation and strongly induce the expression of the OC genes encoding the nuclear factor of activated T-cells, c1 (NFATc1), cathepsin K (Cstk), and tartrate-resistant acid phosphatase 5 (TRAP) with receptor activator of NF-κB ligand-evoked OC lineage priming. Furthermore, while investigating the specific stage of OC differentiation that is regulated by C/EBPα, our gene overexpression studies revealed that, although C/EBPα plays a stronger role in the early stage of OC differentiation, it is also involved in the later stage. Accordingly, C/EBPα knockdown drastically inhibits osteoclastogenesis and markedly abrogates the expression of NFATc1, Cstk, and TRAP during OC differentiation. Consistently, C/EBPα silencing revealed that, although lack of C/EBPα affects all stages of OC differentiation, it has more impact on the early stage. Importantly, we showed that ectopic expression of rat C/EBPα restores osteoclastogenesis in C/EBPα-depleted MBM cells. Furthermore, our subsequent functional assays showed that C/EBPα exhibits a dispensable role on actin ring formation by mature OCs but is critically involved in bone resorption by stimulating extracellular acidification and regulating cell survival. We revealed that C/EBPα is important for receptor activator of NF-κB ligand-induced Akt activation, which is crucial for OC survival. Collectively, these results indicate that C/EBPα functions throughout osteoclastogenesis as well as in OC function. This study provides additional understanding of the roles of C/EBPα in OC biology.

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.

The role of cathepsin K in oral and maxillofacial disorders

Cathepsin K (CTSK) was thought to be a collagenase, specifically expressed by osteoclasts, and played an important role in bone resorption. However, more and more research found that CTSK was expressed in more extensive cells, tissues, and organs. It may not only participate in regulating human physiological activity, but also be closely related to a variety of disease. In this review, we highlight the relationship between CTSK and oral and maxillofacial disorders on the following three aspects: oral and maxillofacial abnormities in patients with pycnodysostosis caused by CTSK mutations, oral and maxillofacial abnormities in Ctsk(-/-) mice, and the role of CTSK in oral and maxillofacial diseases, including periodontitis, peri-implantitis, tooth movement, oral and maxillofacial tumor, root resorption, and periapical disease.

Targeting Atp6v1c1 Prevents Inflammation and Bone Erosion Caused by Periodontitis and Reveals Its Critical Function in Osteoimmunology

Periodontal disease (Periodontitis) is a serious disease that affects a majority of adult Americans and is associated with other systemic diseases, including diabetes, rheumatoid arthritis, and other inflammatory diseases. While great efforts have been devoted toward understanding the pathogenesis of periodontitis, there remains a pressing need for developing potent therapeutic strategies for targeting this pervasive and destructive disease. In this study, we utilized novel adeno-associated virus (AAV)-mediated Atp6v1c1 knockdown gene therapy to treat bone erosion and inflammatory caused by periodontitis in mouse model. Atp6v1c1 is a subunit of the V-ATPase complex and regulator of the assembly of the V0 and V1 domains of the V-ATPase complex. We demonstrated previously that Atp6v1c1 has an essential function in osteoclast mediated bone resorption. We hypothesized that Atp6v1c1 may be an ideal target to prevent the bone erosion and inflammation caused by periodontitis. To test the hypothesis, we employed AAV RNAi knockdown of Atp6v1c1 gene expression to prevent bone erosion and gingival inflammation simultaneously. We found that lesion-specific injection of AAV-shRNA-Atp6v1c1 into the periodontal disease lesions protected against bone erosion (>85%) and gingival inflammation caused by P. gingivalis W50 infection. AAV-mediated Atp6v1c1 knockdown dramatically reduced osteoclast numbers and inhibited the infiltration of dendritic cells and macrophages in the bacteria-induced inflammatory lesions in periodontitis. Silencing of Atp6v1c1 expression also prevented the expressions of osteoclast-related genes and pro-inflammatory cytokine genes. Our data suggests that AAV-shRNA-Atp6v1c1 treatment can significantly attenuate the bone erosion and inflammation caused by periodontitis, indicating the dual function of AAV-shRNA-Atp6v1c1 as an inhibitor of bone erosion mediated by osteoclasts, and as an inhibitor of inflammation through down-regulation of pro-inflammatory cytokine expression. This study demonstrated that Atp6v1c1 RNAi knockdown gene therapy mediated by AAV-shRNA-Atp6v1c1 is a promising novel therapeutic approach for the treatment of bone erosion and inflammatory related diseases, such as periodontitis and rheumatoid arthritis.

Sirtuin 6 Modulates Hypoxia-induced Apoptosis in Osteoblasts via Inhibition of Glycolysis: Implication for Pathogenesis of Periapical Lesions

INTRODUCTION

Osteoblast apoptosis is important in the regulation of inflammatory bone resorption. Hypoxia resulting from inflammation enhances glycolysis and apoptosis. Sirtuin 6 (SIRT6) is a modulator of glucose metabolism and apoptosis. In the study we assessed the role of SIRT6 in hypoxia-induced glycolysis and apoptosis in osteoblasts, with special attention on the significance of these cellular processes in periapical lesions.

METHODS

Human bone marrow-derived osteoblasts were cultured under hypoxia. Expression of lactate dehydrogenase A was examined by Western blot, and production of lactate was measured by colorimetric assay. Cleavage of poly (adenosine diphosphate ribose) polymerase was used as an apoptosis marker and assessed by Western blot. SIRT6 was overexpressed in osteoblasts by lentiviral gene transduction, and then glycolytic and apoptotic responses were studied. In a rat model of bacteria-induced periapical lesions, expressions of SIRT6 and markers of glycolysis and apoptosis in osteoblasts were examined.

RESULTS

Hypoxia enhanced lactate dehydrogenase A expression and lactate production in osteoblasts. Poly (adenosine diphosphate ribose) polymerase cleavage was induced by hypoxia or lactate treatment. SIRT6 suppressed hypoxia-augmented glycolysis and inhibited apoptosis induced by hypoxia or lactate treatment. Expression of SIRT6 in osteoblasts was downregulated by hypoxia and inflammatory mediators. Development of periapical lesions in rats was associated with decreased expression of SIRT6 and increased glycolysis and apoptosis in osteoblasts.

CONCLUSIONS

Our study suggested that hypoxia-induced apoptosis of osteoblasts is dependent on glycolytic activity. SIRT6 is a negative regulator of inflammation and may alleviate periapical lesions by suppressing osteoblastic glycolysis and apoptosis.

Ac45 silencing mediated by AAV-sh-Ac45-RNAi prevents both bone loss and inflammation caused by periodontitis

AIM

Periodontitis induced by oral pathogens leads to severe periodontal tissue damage and osteoclast-mediated bone resorption caused by inflammation. On the basis of the importance of Ac45 in osteoclast formation and function, we performed this study to evaluate the therapeutic potential of periodontitis by local adeno-associated virus (AAV)-mediated Ac45 gene knockdown.

MATERIAL AND METHODS

We used AAV-mediated short hairpin RNAi knockdown of Ac45 gene expression (AAV-sh-Ac45) to inhibit bone erosion and gingival inflammation simultaneously in a well-established periodontitis mouse model induced by Porphyromonas gingivalis W50. Histological studies were performed to evaluate the bone protection of AAV-sh-Ac45. Immunochemistry, ELISA and qRT-PCR were performed to reveal the role of Ac45 knockdown on inflammation, immune response and expression of cytokine.

RESULTS

We found that Ac45 knockdown impaired osteoclast-mediated extracellular acidification and bone resorption in vitro and in vivo. Furthermore, local administration of AAV-sh-Ac45 protected mice from bone erosion by >85% and attenuated inflammation and decreased infiltration of T cells, dendritic cells and macrophages in the periodontal lesion. Notably, the expression of pro-inflammatory cytokines was also reduced.

CONCLUSIONS

Local AAV-sh-Ac45 gene therapy efficiently protects against periodontal tissue damage and bone erosion through both inhibition of osteoclast function and attenuating inflammation, and may represent a powerful new treatment strategy for periodontitis.

Odanacatib, A Cathepsin K-Specific Inhibitor, Inhibits Inflammation and Bone Loss Caused by Periodontal Diseases

BACKGROUND

Periodontitis is a bacteria-induced inflammatory disease mainly affecting periodontal tissues, leading to periodontal inflammation, bone breakdown, and loss of the tooth. The main obstacle for treating periodontitis effectively is the difficulty in finding a target that can inhibit bone loss and inflammation simultaneously. Recent studies showed that cathepsin K (CTSK) might have functions in the immune system besides its role in osteoclasts. Thus, targeting CTSK would have a potential therapeutic effect in both the bone system and the immune system during the progression of periodontitis.

METHODS

In the current study, a small molecular inhibitor (odanacatib [ODN]) is explored to inhibit the function of CTSK in a bacteria-induced periodontitis mouse model.

RESULTS

The application of ODN decreased the number of osteoclasts, macrophages, and T cells, as well as the expression of Toll-like receptors (TLRs) in the periodontitis lesion area. Furthermore, lack of CTSK inhibited the expression of TLR4, TLR5, and TLR9 and their downstream cytokine signaling in the gingival epithelial cells in periodontitis lesions, demonstrating that the innate immune response was inhibited in periodontitis.

CONCLUSION

The present results show that inhibition of CTSK can prevent bone loss and the immune response during the progression of periodontitis, indicating that CTSK is a promising target for treating inflammatory diseases such as periodontitis by affecting both osteoclasts and the immune system.

A small molecule, odanacatib, inhibits inflammation and bone loss caused by endodontic disease

Periapical disease, an inflammatory disease mainly caused by dental caries, is one of the most prevalent infectious diseases of humans, affecting both children and adults. The infection travels through the root, leading to inflammation, bone destruction, and severe pain for the patient. Therefore, the development of a new class of anti-periapical disease therapies is necessary and critical for treatment and prevention. A small molecule, odanacatib (ODN), which is a cathepsin K (Ctsk) inhibitor, was investigated to determine its ability to treat this disease in a mouse model of periapical disease. While Ctsk was originally found in osteoclasts as an osteoclast-specific lysosomal protease, we were surprised to find that ODN can suppress the bacterium-induced immune response as well as bone destruction in the lesion area. X rays and microcomputed tomography (micro-CT) showed that ODN treatment had significant bone protection effects at different time points. Immunohistochemical and immunofluorescent staining show that ODN treatment dramatically decreased F4/80+ macrophages and CD3+ T cells in the lesion areas 42 days after infection. Consistent with these findings, quantitative real-time PCR (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA) analysis showed low levels of proinflammatory mRNAs (for tumor necrosis factor alpha, interleukin 6, and interleukin 23α) and corresponding cytokine expression in the ODN-treated disease group. The levels of mRNA for Toll-like receptors 4, 5, and 9 also largely decreased in the ODN-treated disease group. Our results demonstrated that ODN can inhibit endodontic disease development, bone erosion, and immune response. These results indicate that application of this small molecule offers a new opportunity to design effective therapies that could prevent periapical inflammation and revolutionize current treatment options.

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

Wnt/β-catenin signaling plays an important role in bone biology. The present study investigated the involvement of Wnt/β-catenin signaling in rat periapical bone destruction and whether lithium chloride (LiCl), a glycogen synthase kinase-3β (GSK-3β) inhibitor, promotes bone restoration. Rat bone marrow mesenchymal cells (BMMSCs) treated with Porphyromonas gingivalis lipopolysaccharide ( Pg LPS) showed decreased osteogenic potential through inhibited Wnt/β-catenin signaling as quantified by Western blot, immunofluorescence, and luciferase reporter assay. Transient Wnt3a treatment in vitro partially restored mineralization and Runx2/Osx and osteocalcin expression in cultures with Pg LPS-induced osteogenic arrest. Prolonged Wnt3a treatment impaired osteogenic commitment. X-ray microtomography showed dramatically enhanced periapical bone formation in rats gavage-fed with LiCl for 2 wks, while continuous LiCl treatment for 4 wks impaired periapical bone healing. LiCl treatment also increased GSK-3β phosphorylation and osteocalcin expression in periapical tissue. Collectively, these results indicate that Wnt/β-catenin has dichotomous functions in bone homeostasis. Modulation of this signaling pathway by LiCl may be a potential therapeutic option for bone destruction in endodontic disease.

Periapical disease and bisphosphonates induce osteonecrosis of the jaws in mice

Osteonecrosis of the jaw (ONJ) is a well-recognized complication of antiresorptive medications, such as bisphosphonates (BPs). Although ONJ is most common after tooth extractions in patients receiving high-dose BPs, many patients do not experience oral trauma. Animal models using tooth extractions and high BP doses recapitulate several clinical, radiographic, and histologic findings of ONJ. We and others have reported on rat models of ONJ using experimental dental disease in the absence of tooth extraction. These models emphasize the importance of dental infection/inflammation for ONJ development. Here, we extend our original report in the rat, and present a mouse model of ONJ in the presence of dental disease. Mice were injected with high dose zoledronic acid and pulpal exposure of mandibular molars was performed to induce periapical disease. After 8 weeks, quantitative and qualitative radiographic and histologic analyses of mouse mandibles were done. Periapical lesions were larger in vehicle-treated versus BP-treated mice. Importantly, radiographic features resembling clinical ONJ, including thickening of the lamina dura, periosteal bone deposition, and increased trabecular density, were seen in the drilled site of BP-treated animals. Histologically, osteonecrosis, periosteal thickening, periosteal bone apposition, epithelial migration, and bone exposure were present in the BP-treated animals in the presence of periapical disease. No difference in tartrate-resistant acid phosphatase (TRAP)+ cell numbers was observed, but round, detached, and removed from the bone surface cells were present in BP-treated animals. Although 88% of the BP-treated animals showed areas of osteonecrosis in the dental disease site, only 33% developed bone exposure, suggesting that osteonecrosis precedes bone exposure. Our data further emphasize the importance of dental disease in ONJ development, provide qualitative and quantitative measures of ONJ, and present a novel mouse ONJ model in the absence of tooth extraction that should be useful in further exploring ONJ pathophysiological mechanisms.