Activation of the acquired immune response reduces coupled bone formation in response to a periodontal pathogen

An update on periodontal inflammation and bone loss

Periodontal disease is a chronic inflammatory condition that affects the supporting structures of the teeth, including the periodontal ligament and alveolar bone. Periodontal disease is due to an immune response that stimulates gingivitis and periodontitis, and its systemic consequences. This immune response is triggered by bacteria and may be modulated by environmental conditions such as smoking or systemic disease. Recent advances in single cell RNA-seq (scRNA-seq) and in vivo animal studies have provided new insight into the immune response triggered by bacteria that causes periodontitis and gingivitis. Dysbiosis, which constitutes a change in the bacterial composition of the microbiome, is a key factor in the initiation and progression of periodontitis. The host immune response to dysbiosis involves the activation of various cell types, including keratinocytes, stromal cells, neutrophils, monocytes/macrophages, dendritic cells and several lymphocyte subsets, which release pro-inflammatory cytokines and chemokines. Periodontal disease has been implicated in contributing to the pathogenesis of several systemic conditions, including diabetes, rheumatoid arthritis, cardiovascular disease and Alzheimer's disease. Understanding the complex interplay between the oral microbiome and the host immune response is critical for the development of new therapeutic strategies for the prevention and treatment of periodontitis and its systemic consequences.

Oxidative Stress and FOXO-1 Relationship in Stage III Periodontitis

OBJECTIVES

8-Hydroxideoxyguanosine (8-OHdG) is a marker of oxidative stress, and Forkhead Box-O1 (FOXO1) is a transcription factor and signaling integrator in cell and tissue homeostasis. This study aims to determine FOXO1 and 8-OHdG levels in serum and saliva samples of periodontitis patients and to evaluate their relationship with clinical periodontal parameters.

MATERIALS AND METHODS

Twenty healthy individuals, twenty generalized Stage III Grade B periodontitis patients, and nineteen generalized Stage III Grade C periodontitis patients were included in the study. Clinical periodontal parameters (plaque index (PI), probing depth (PD), bleeding on probing (BOP), and clinical attachment level (CAL)) were recorded. Salivary and serum 8-OHdG and FOX-O1 levels were analyzed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Clinical periodontal parameters showed a statistically significant increase in periodontitis groups compared to the control group (p < 0.05). 8-OHdG salivary levels were significantly higher in both periodontitis groups compared to the control group. The salivary FOXO1 levels were significantly lower in both periodontitis groups compared to the control group. Salivary FOXO1 level had a low-grade negative correlation with BOP and salivary 8-OHdG level.

CONCLUSIONS

While reactive oxygen species increase in periodontal inflammation, low expression of FOXO1, an important transcription factor for antioxidant enzymes, supports that this molecule plays a vital role in tissue destruction, and FOXO1 can be seen as a potential immune modulator.

CLINICAL RELEVANCE

The role of FOXO1 in supporting antioxidant defense may suggest that FOXO1 is a candidate target for periodontitis treatment.

Bacterial distribution and inflammatory cytokines associated with oral cancer with and without jawbone invasion-a pilot study

OBJECTIVE

To explore the bacterial and inflammatory variations in oral cancer patients with and without jawbone invasion.

MATERIALS AND METHODS

A total of 20 specimens of fresh tumor tissue, including 10 from the tumor-invaded jawbone (JIOC group) and 10 without jawbone invasion (NJIOC group), were collected from oral cancer patients. Meanwhile, 10 specimens from normal oral mucosa were collected from healthy patients (control group). The microbiomic content of each sample was analyzed by 16S rRNA gene sequencing, while the expression of inflammatory cytokines was assessed using protein microarray analysis.

RESULTS

There was a significant difference in β diversity between JIOC and NJIOC groups (P < 0.05), but no difference between NJIOC and control groups. The average relative abundance of Fusobacteria and Spirochaetes was higher, while Firmicutes was lower in the JIOC group than in the NJIOC group (all P < 0.05). The expression of pro-inflammatory cytokines like interleukin (IL)-1α, IL-1β, IL-4, and IL-8 was upregulated in the JIOC group compared with the NJIOC group, while MCP-1 was decreased (all P < 0.05). Slackia spp. and Howardella spp. were positively correlated with IL-4; Odoribacter spp. and Acidaminococcaceae spp. were negatively correlated with IL-4, and Clostridium XIVa spp. was negatively correlated with IL-1α and IL-1β.

CONCLUSION

Bacterial and inflammatory differences were observed in oral cancer patients with and without jawbone invasion, where the relative abundance of the differential bacteria was associated with the expression of the inflammatory cytokines.

CLINICAL RELEVANCE

This study investigated the changes in the flora during jawbone invasion in oral cancer and its effect on inflammatory factors, elucidating the possible mechanisms of jawbone invasion caused by oral cancer, which may lead to new ideas for the clinical prevention and treatment of jawbone invasion in oral cancer.

A novel lncRNA-mediated epigenetic regulatory mechanism in periodontitis

Periodontitis is a highly prevalent chronic inflammatory disease with an exaggerated host immune response, resulting in periodontal tissue destruction and potential tooth loss. The long non-coding RNA, LncR-ANRIL, located on human chromosome 9p21, is recognized as a genetic risk factor for various conditions, including atherosclerosis, periodontitis, diabetes, and cancer. LncR-APDC is an ortholog of ANRIL located on mouse genome chr4. This study aims to comprehend the regulatory role of lncR-APDC in periodontitis progression. Our experimental findings, obtained from lncR-APDC gene knockout (KO) mice with induced experimental periodontitis (EP), revealed exacerbated bone loss and disrupted pro-inflammatory cytokine regulation. Downregulation of osteogenic differentiation occurred in bone marrow stem cells harvested from lncR-APDC-KO mice. Furthermore, single-cell RNA sequencing of periodontitis gingival tissue revealed alterations in the proportion and function of immune cells, including T and B cells, macrophages, and neutrophils, due to lncR-APDC silencing. Our findings also unveiled a previously unidentified epithelial cell subset that is distinctively presenting in the lncR-APDC-KO group. This epithelial subset, characterized by the positive expression of Krt8 and Krt18, engages in interactions with immune cells through a variety of ligand-receptor pairs. The expression of Tff2, now recognized for its role in chronic inflammatory conditions, exhibited a notable increase across various tissue and cell types in lncR-APDC deficient mice. Additionally, our investigation revealed the potential for a direct binding interaction between lncR-APDC and Tff2. Intra-gingival administration of AAV9-lncR-APDC was shown to have therapeutic effects in the EP model. In conclusion, our results suggest that lncR-APDC plays a critical role in the progression of periodontal disease and holds therapeutic potential for periodontitis. Furthermore, the presence of the distinctive epithelial subpopulation and significantly elevated Tff2 levels in the lncR-APDC-silenced EP model offer new perspectives on the epigenetic regulation of periodontitis pathogenesis.

Impact of the host response and osteoblast lineage cells on periodontal disease

Periodontitis involves the loss of connective tissue attachment and alveolar bone. Single cell RNA-seq experiments have provided new insight into how resident cells and infiltrating immune cells function in response to bacterial challenge in periodontal tissues. Periodontal disease is induced by a combined innate and adaptive immune response to bacterial dysbiosis that is initiated by resident cells including epithelial cells and fibroblasts, which recruit immune cells. Chemokines and cytokines stimulate recruitment of osteoclast precursors and osteoclastogenesis in response to TNF, IL-1β, IL-6, IL-17, RANKL and other factors. Inflammation also suppresses coupled bone formation to limit repair of osteolytic lesions. Bone lining cells, osteocytes and periodontal ligament cells play a key role in both processes. The periodontal ligament contains cells that exhibit similarities to tendon cells, osteoblast-lineage cells and mesenchymal stem cells. Bone lining cells consisting of mesenchymal stem cells, osteoprogenitors and osteoblasts are influenced by osteocytes and stimulate formation of osteoclast precursors through MCSF and RANKL, which directly induce osteoclastogenesis. Following bone resorption, factors are released from resorbed bone matrix and by osteoclasts and osteal macrophages that recruit osteoblast precursors to the resorbed bone surface. Osteoblast differentiation and coupled bone formation are regulated by multiple signaling pathways including Wnt, Notch, FGF, IGF-1, BMP, and Hedgehog pathways. Diabetes, cigarette smoking and aging enhance the pathologic processes to increase bone resorption and inhibit coupled bone formation to accelerate bone loss. Other bone pathologies such as rheumatoid arthritis, post-menopausal osteoporosis and bone unloading/disuse also affect osteoblast lineage cells and participate in formation of osteolytic lesions by promoting bone resorption and inhibiting coupled bone formation. Thus, periodontitis involves the activation of an inflammatory response that involves a large number of cells to stimulate bone resorption and limit osseous repair processes.

Neuropathophysiology of coronavirus disease 2019: neuroinflammation and blood brain barrier disruption are critical pathophysiological processes that contribute to the clinical symptoms of SARS-CoV-2 infection

Coronavirus disease 2019 (COVID-19) is caused by the novel SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) first discovered in Wuhan, Hubei province, China in December 2019. SARS-CoV-2 has infected several millions of people, resulting in a huge socioeconomic cost and over 2.5 million deaths worldwide. Though the pathogenesis of COVID-19 is not fully understood, data have consistently shown that SARS-CoV-2 mainly affects the respiratory and gastrointestinal tracts. Nevertheless, accumulating evidence has implicated the central nervous system in the pathogenesis of SARS-CoV-2 infection. Unfortunately, however, the mechanisms of SARS-CoV-2 induced impairment of the central nervous system are not completely known. Here, we review the literature on possible neuropathogenic mechanisms of SARS-CoV-2 induced cerebral damage. The results suggest that downregulation of angiotensin converting enzyme 2 (ACE2) with increased activity of the transmembrane protease serine 2 (TMPRSS2) and cathepsin L in SARS-CoV-2 neuroinvasion may result in upregulation of proinflammatory mediators and reactive species that trigger neuroinflammatory response and blood brain barrier disruption. Furthermore, dysregulation of hormone and neurotransmitter signalling may constitute a fundamental mechanism involved in the neuropathogenic sequelae of SARS-CoV-2 infection. The viral RNA or antigenic peptides also activate or interact with molecular signalling pathways mediated by pattern recognition receptors (e.g., toll-like receptors), nuclear factor kappa B, Janus kinase/signal transducer and activator of transcription, complement cascades, and cell suicide molecules. Potential molecular targets and therapeutics of SARS-CoV-2 induced neurologic damage are also discussed.

The Roles of FOXO1 in Periodontal Homeostasis and Disease

Periodontitis is an oral chronic inflammatory disease that is initiated by periodontal microbial communities and requires disruption of the homeostatic responses. The prevalence of periodontal disease increases with age; more than 70% of adults 65 years and older have periodontal disease. A pathogenic microbial community is required for initiating periodontal disease. Dysbiotic immune-inflammatory response and bone remodeling are characteristics of periodontitis. The transcription factor forkhead box protein O1 (FOXO1) is a key regulator of a number of cellular processes, including cell survival and differentiation, immune status, reactive oxygen species (ROS) scavenging, and apoptosis. Although accumulating evidence indicates that FOXO1 activity can be induced by periodontal pathogens, the roles of FOXO1 in periodontal homeostasis and disease have not been well documented. The present review summarizes how the FOXO1 signaling axis can regulate periodontal bacteria-epithelial interactions, immune-inflammatory response, bone remodeling, and wound healing.

PERK signaling pathway in bone metabolism: Friend or foe?

Osteoblasts and osteoclasts participate in the process of bone remodelling to meet the needs of normal growth and development or repair pathological damage. Endoplasmic reticulum stress (ER stress) can break the intracellular homeostasis of osteoclasts and osteoblasts, which is closely related to abnormal bone remodelling. The double‐stranded RNA‐dependent protein kinase (PKR)‐like ER kinase (PERK) is a key transmembrane protein that regulates ER stress, and growing evidence suggests that the PERK pathway plays a crucial role in regulating bone metabolism under both physiological and pathological conditions. Based on the current findings, we summarized the main mechanisms involved in bone metabolism downstream of the PERK pathway, among which elF2α, FOXO1, CaN, Nrf2 and DAG play a role in regulating the differentiation of osteoblasts and osteoclasts. Importantly, strategies by the regulation of PERK pathway exert beneficial effects in preclinical trials of several bone‐related diseases. Given the importance and novelty of PERK pathway, we provide an overview and discuss the roles of PERK pathway in regulating bone metabolism and its impact on bone‐related diseases. We hope that the development of research in this field will bring a bright future for the treatment of bone‐related diseases.

Application of specialized pro-resolving mediators in periodontitis and peri-implantitis: a review

Scaling and root planning is a key element in the mechanical therapy used for the eradication of biofilm, which is the major etiological factor for periodontitis and peri‐implantitis. However, periodontitis is also a host mediated disease, therefore, removal of the biofilm without adjunctive therapy may not achieve the desired clinical outcome due to persistent activation of the innate and adaptive immune cells. Most recently, even the resident cells of the periodontium, including periodontal ligament fibroblasts, have been shown to produce several inflammatory factors in response to bacterial challenge. With increased understanding of the pathophysiology of periodontitis, more research is focusing on opposing excessive inflammation with specialized pro‐resolving mediators (SPMs). This review article covers the major limitations of current standards of care for periodontitis and peri‐implantitis, and it highlights recent advances and prospects of SPMs in the context of tissue reconstruction and regeneration. Here, we focus primarily on the role of SPMs in restoring tissue homeostasis after periodontal infection.

Effect of antidepressants on various periodontal parameters: A case-control study

Background:

Various medications are used in the treatment of chronic systemic diseases that affect the periodontium. Antidepressants in mentally depressed patients are prescribed for a long term, but their effect on the periodontium has not been studied adequately. A case–control study was conducted to know the effect of two commonly prescribed antidepressants – venlafaxine (serotonin–norepinephrine reuptake inhibitor [SNRI]) and fluoxetine (selective serotonin reuptake inhibitor [SSRI]). These drugs have been shown to possess anti-inflammatory properties but do not protect the periodontium from insults caused by these medications, which are significantly associated with the presence of destruction of the periodontium. The aim of this study was to clinically evaluate the effect of antidepressants on various periodontal parameters.

Materials and Methods:

The study sample consisted of 182 depressed patients divided into three study groups: Group I – the control group diagnosed as depressed on the first visit, Group II – depressed patients taking fluoxetine 20 mg/day, and Group III – patients taking venlafaxine 75 mg/day. Patients in Groups II and III were on isolated antidepressant medication at least for a period of 3 or more months. Mental depression in patients was assessed with the Patient Health Questionnaire-based Hamilton Depression Rating Scale with scoring of ≤16. All the depressed patients were assessed for periodontal health on the basis of the clinical periodontal parameters.

Results:

The commonly prescribed antidepressants such as fluoxetine and venlafaxine do not protect the periodontium from destruction in spite of possessing anti-inflammatory properties; therefore, these drugs may be considered as a risk factor for periodontal health. The comparative periodontal indices on nonusers of antidepressants or control group (Group I), users of SSRI (fluoxetine) (Group II), and users of antidepressants-SNRI (venlafaxine) (Group III) showed increased periodontal parameters, especially debris index (DI), calculus index (CI), gingival index (GI), periodontal pocket depth (PD), and loss in clinical attachment level. There was no significant difference for CI and GI, probing PD, and clinical attachment levels except DI which was significantly different (P ≤ 0.001).

Conclusion:

The depressed patients receiving fluoxetine or venlafaxine should be regularly evaluated for periodontal health status as these drugs are risk factors for normal periodontal tissues. Further, these medications did not protect the periodontium from periodontal inflammation, although possessing anti-inflammatory properties.

The Roles of FoxO Transcription Factors in Regulation of Bone Cells Function

Forkhead box class O family member proteins (FoxOs) are evolutionarily conserved transcription factors for their highly conserved DNA-binding domain. In mammalian species, all the four FoxO members, FoxO1, FoxO3, FoxO4, and FoxO6, are expressed in different organs. In bone, the first three members are extensively expressed and more studied. Bone development, remodeling, and homeostasis are all regulated by multiple cell lineages, including osteoprogenitor cells, chondrocytes, osteoblasts, osteocytes, osteoclast progenitors, osteoclasts, and the intercellular signaling among these bone cells. The disordered FoxOs function in these bone cells contribute to osteoarthritis, osteoporosis, or other bone diseases. Here, we review the current literature of FoxOs for their roles in bone cells, focusing on helping researchers to develop new therapeutic approaches and prevent or treat the related bone diseases.

Mucosal Immunity and the FOXO1 Transcription Factors

FOXO1 transcription factors affect a number of cell types that are important in the host response. Cell types whose functions are modulated by FOXO1 include keratinocytes in the skin and mucosal dermis, neutrophils and macrophages, dendritic cells, Tregs and B-cells. FOXO1 is activated by bacterial or cytokine stimulation. Its translocation to the nucleus and binding to promoter regions of genes that have FOXO response elements is stimulated by the MAP kinase pathway and inhibited by the PI3 kinase/AKT pathway. Downstream gene targets of FOXO1 include pro-inflammatory signaling molecules (TLR2, TLR4, IL-1β, and TNF-α), wound healing factors (TGF-β, VEGF, and CTGF) adhesion molecules (integrins-β1, -β3, -β6, α_vβ₃, CD11b, CD18, and ICAM-1), chemokine receptors (CCR7 and CXCR2), B cell regulators (APRIL and BLYS), T-regulatory modulators (Foxp3 and CTLA-4), antioxidants (GPX-2 and cytoglobin), and DNA repair enzymes (GADD45α). Each of the above cell types are found in oral mucosa and modulated by bacteria or an inflammatory microenvironment. FOXO1 contributes to the regulation of these cells, which collectively maintain and repair the epithelial barrier, formation and activation of Tregs that are needed to resolve inflammation, mobilization, infiltration, and activation of anti-bacterial defenses in neutrophils, and the homing of dendritic cells to lymph nodes to induce T-cell and B-cell responses. The goal of the manuscript is to review how the transcription factor, FOXO1, contributes to the activation and regulation of key leukocytes needed to maintain homeostasis and respond to bacterial challenge in oral mucosal tissues. Examples are given with an emphasis on lineage specific deletion of Foxo1 to explore the impact of FOXO1 on cell behavior, inflammation and susceptibility to infection.

Chondrocytes Promote Vascularization in Fracture Healing Through a FOXO1-Dependent Mechanism

Chondrocytes play an essential role in fracture healing by producing cartilage, which forms an anlage for endochondral ossification that stabilizes the healing fracture callus. More recently it has been appreciated that chondrocytes have the capacity to produce factors that may affect the healing process. We examined the role of chondrocytes in angiogenesis during fracture healing and the role of the transcription factor forkhead box-O 1 (FOXO1), which upregulates wound healing in soft tissue. Closed fractures were induced in experimental mice with lineage-specific FOXO1 deletion by Cre recombinase under the control of a collagen-2α1 promoter element (Col2α1Cre+ FOXO1L/L ) and Cre recombinase negative control littermates containing flanking loxP sites (Col2α1Cre- FOXO1L/L ). Experimental mice had significantly reduced CD31+ new vessel formation. Deletion of FOXO1 in chondrocytes in vivo suppressed the expression of vascular endothelial growth factor-A (VEGFA) at both the protein and mRNA levels. Overexpression of FOXO1 in chondrocytes in vitro increased VEGFA mRNA levels and VEGFA transcriptional activity whereas silencing FOXO1 reduced it. Moreover, FOXO1 interacted directly with the VEGFA promoter and a deacetylated FOXO1 mutant enhanced VEGFA expression whereas an acetylated FOXO1 mutant did not. Lastly, FOXO1 knockdown by siRNA significantly reduced the capacity of chondrocytes to stimulate microvascular endothelial cell tube formation in vitro. The results indicate that chondrocytes play a key role in angiogenesis which is FOXO1 dependent and that FOXO1 in chondrocytes regulates a potent angiogenic factor, VEGFA. These studies provide new insight into fracture healing given the important role of vessel formation in the fracture repair process. © 2018 American Society for Bone and Mineral Research.

Costimulation of Murine Osteoblasts with Interferon-γ and Tumor Necrosis Factor-α Induces Apoptosis through Downregulation of Bcl-2 and Release of Cytochrome c from Mitochondria

During chronic inflammation from diseases, such as periodontal disease, the proinflammatory cytokines interferon-gamma (IFNγ) and tumor necrosis factor-α (TNFα) alter bone remodeling. To elucidate the underlying molecular mechanisms, we investigated the effect of IFNγ and TNFα on the proliferation and survival of clonal MC3T3-E1 mouse osteoblasts. We found that although IFNγ or TNFα alone affected cell growth and survival only marginally, costimulation with both synergistically inhibited cell growth and reduced cell viability. The diminished cell viability was due to apoptosis, as indicated by increased TUNEL staining and elevated caspase 3, 8, and 9 activities. Western blot also showed that costimulation with IFNγ and TNFα elicited cytochrome c release and downregulated B cell lymphoma 2 (Bcl-2) expression without affecting Bcl-2-associated X (Bax) protein expression. Furthermore, stable Bcl-2 overexpression significantly alleviated cell death following costimulation. Collectively, these results suggested that IFNγ and TNFα elicited osteoblast apoptosis via cytochrome c release from damaged mitochondria, caspase activation, and Bcl-2 downregulation.

The function of dendritic cells in modulating the host response

Dendritic cells (DCs) are antigen-presenting cells that capture, process, and present antigens to lymphocytes to initiate and regulate the adaptive immune response. DCs detect bacteria in skin and mucosa and migrate into regional lymph nodes, where they stimulate antigen-specific T and B lymphocyte activation and proliferation. DCs direct CD4 T cells to differentiate to T-cell subsets such as T helper cells types 1, 2, and 17, and regulatory T cells. The periodontium is chronically exposed to oral bacteria that stimulate an inflammatory response to induce gingivitis or periodontitis. DCs play both protective and destructive roles through activation of the acquired immune response and are also reported to be a source of osteoclast precursors that promote bone resorption. FOXO1, a member of the forkhead box O family of transcription factors, plays a significant role in the activation of DCs. The function of DCs in periodontal inflammation has been investigated in a mouse model by lineage-specific deletion of FOXO1 in these cells. Deletion of FOXO1 reduces DC protective function and enhances susceptibility to periodontitis. The kinase Akt, phosphorylates FOXO1 to inhibit FOXO activity. Hence the Akt-FOXO1 axis may play a key role in regulating DCs to have a significant impact on periodontal disease.

Effects of polyhexamethylene guanidine phosphate on human gingival fibroblasts

OBJECTIVE

Polyhexamethylene guanidine phosphate (PHMG-P) was compared to chlorhexidine (CHX) in order to determine potential cytotoxic and immune-modulatory effects on human gingival fibroblasts.

MATERIALS AND METHODS

Cytotoxic effects of PHMG-P and CHX on human gingival fibroblasts were assessed using cell viability assay at various time points and concentrations. The effects of PHMG-P and CHX on the secretion of prostaglandin (PG) E₂, interleukin (IL)-6, IL-8 and matrix metalloproteinase (MMP)-1 by non-stimulated or IL-1β stimulated fibroblasts were evaluated by enzyme-linked immunosorbent assays.

RESULTS

PHMG-P concentration 0.00009% led to the total loss of fibroblast viability within 24 h, whereas inhibition of fibroblast viability by CHX occurred at significantly higher concentrations of 0.0009% (p < .001). Short-term exposure to 0.005% PHMG-P led to loss of fibroblast viability after 5 min, whilst cells exposed to 0.005% CHX survived 30 min of treatment (p < .001). IL-1β stimulation induced an inflammatory response with a significant increase in the secretion of PGE₂, IL-6, IL-8 and MMP-1. Treatment of IL-1β stimulated fibroblasts in combination with PHMG-P or CHX at concentrations of 0.000045 or 0.0.00009% resulted in significantly decreased PGE₂, IL-6, IL-8 and MMP-1 levels. PHMG-P or CHX alone did not affect the baseline secretion of PGE₂, IL-6, IL-8 or MMP-1 by gingival fibroblasts.

CONCLUSIONS

Cytotoxic effects on gingival fibroblasts were triggered by both PHMG-P and CHX at concentrations below those used in clinical practice. The tested antiseptics did not cause inflammation and reduced IL-1β-induced secretion of inflammatory mediators and collagenase by gingival fibroblasts, which suggests anti-inflammatory properties.

FOXO1 Regulates Bacteria-Induced Neutrophil Activity

Neutrophils play an essential role in the innate immune response to microbial infection and are particularly important in clearing bacterial infection. We investigated the role of the transcription factor FOXO1 in the response of neutrophils to bacterial challenge with Porphyromonas gingivalis in vivo and in vitro. In these experiments, the effect of lineage-specific FOXO1 deletion in LyzM.Cre⁺FOXO1^L/L mice was compared with matched littermate controls. FOXO1 deletion negatively affected several critical aspects of neutrophil function in vivo including mobilization of neutrophils from the bone marrow (BM) to the vasculature, recruitment of neutrophils to sites of bacterial inoculation, and clearance of bacteria. In vitro FOXO1 regulated neutrophil chemotaxis and bacterial killing. Moreover, bacteria-induced expression of CXCR2 and CD11b, which are essential for several aspects of neutrophil function, was dependent on FOXO1 in vivo and in vitro. Furthermore, FOXO1 directly interacted with the promoter regions of CXCR2 and CD11b. Bacteria-induced nuclear localization of FOXO1 was dependent upon toll-like receptor (TLR) 2 and/or TLR4 and was significantly reduced by inhibitors of reactive oxygen species (ROS and nitric oxide synthase) and deacetylases (Sirt1 and histone deacetylases). These studies show for the first time that FOXO1 activation by bacterial challenge is needed to mobilize neutrophils to transit from the BM to peripheral tissues in response to infection as well as for bacterial clearance in vivo. Moreover, FOXO1 regulates neutrophil function that facilitates chemotaxis, phagocytosis, and bacterial killing.

Zanthoxylum piperitum reversed alveolar bone loss of periodontitis via regulation of bone remodeling-related factors

ETHNOPHARMACOLOGICAL RELEVANCE

Zanthoxylum piperitum (ZP) has been used to prevent toothache in East Asia.

AIM OF STUDY

In this study, we investigated the effects of ZP on periodontitis along with alveolar bone loss.

MATERIALS AND METHODS

Twenty-eight male Sprague-Dawley rats were assigned into 4 groups; non-ligated (NOR), ligated and treated vehicle (CTR), ligated and treated 1mg/mL ZP (ZP1), and ligated and treated 100mg/mL ZP (ZP100). Sterilized 3-0 nylon ligature was placed into the subgingival sulcus around the both sides of mandibular first molar. After topical application of 1 and 100mg/mL ZP for 2 weeks, mandibles was removed for histology. In addition, SaOS-2 osteoblast cells were treated 1, 10 and 100μg/mL ZP for 24h to analyze the expressions of alveolar bone-related markers.

RESULTS

Several alveolar bone resorption pits, which indicate cementum demineralization were decreased by ZP treatment. Topical ZP treatment inhibited periodontitis-induced alveolar bone loss. In addition, there were significant reduction of osteoclastic activities following topical ZP treatment in periodontium. The expression of RANKL was decreased in SaOS-2 osteoblast cells by treating ZP, while that of OPG was increased. ZP treatment increased the expressions of Runx2 and Osterix in SaOS-2 cells.

CONCLUSION

In summary, ZP treatment inhibited alveolar bone loss as well as maintained the integrity of periodontal structures via regulation of bone remodeling. ZP may be a therapeutic target for treating periodontitis.

Innate Immune Response of Human Embryonic Stem Cell-Derived Fibroblasts and Mesenchymal Stem Cells to Periodontopathogens

Periodontitis involves complex interplay of bacteria and host immune response resulting in destruction of supporting tissues of the tooth. Toll-like receptors (TLRs) play a role in recognizing microbial pathogens and eliciting an innate immune response. Recently, the potential application of multipotent stem cells and pluripotent stem cells including human embryonic stem cells (hESCs) in periodontal regenerative therapy has been proposed. However, little is known about the impact of periodontopathogens on hESC-derived progenies. This study investigates the effects of heat-killed periodontopathogens, namely, Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, on TLR and cytokine expression profile of hESC-derived progenies, namely, fibroblasts (hESC-Fib) and mesenchymal stem cells (hESC-MSCs). Additionally, the serotype-dependent effect of A. actinomycetemcomitans on hESC-derived progenies was explored. Both hESC-Fib and hESC-MSCs constitutively expressed TLR-2 and TLR-4. hESC-Fib upon exposure to periodontopathogens displayed upregulation of TLRs and release of cytokines (IL-1β, IL-6, and IL-8). In contrast, hESC-MSCs were largely nonresponsive to bacterial challenge, especially in terms of cytokine production. Further, exposure of hESC-Fib to A. actinomycetemcomitans serotype c was associated with higher IL-8 production than serotype b. In contrast, the hESC-MSCs displayed no serotype-dependent response. Differential response of the two hESC progenies implies a phenotype-dependent response to periodontopathogens and supports the concept of immunomodulatory properties of MSCs.

Infection and inflammatory mechanisms

This introductory article examines the potential mechanisms that may play a role in the associations between periodontitis and the systemic conditions being considered in the EFP/AAP Workshop in Segovia, Spain. Three basic mechanisms have been postulated to play a role in these interactions; metastatic infections,inflammation and inflammatory injury, and adaptive immunity. The potential role of each alone and together is considered in in vitro and animal studies and in human studies when available. This is not a systematic or critical review, but rather an overview of the field to set the stage for the critical reviews in each of the working groups.

Osteoblast Lineage Cells Play an Essential Role in Periodontal Bone Loss Through Activation of Nuclear Factor-Kappa B

Bacterial pathogens stimulate periodontitis, the most common osteolytic disease in humans and the most common cause of tooth loss in adults. Previous studies identified leukocytes and their products as key factors in this process. We demonstrate for the first time that osteoblast lineage cells play a critical role in periodontal disease. Oral infection stimulated nuclear localization of NF-κB in osteoblasts and osteocytes in the periodontium of wild type but not transgenic mice that expressed a lineage specific dominant negative mutant of IKK (IKK-DN) in osteoblast lineage cells. Wild-type mice were also susceptible to bacteria induced periodontal bone loss but transgenic mice were not. The lack of bone loss in the experimental group was linked to reduced RANKL expression by osteoblast lineage cells that led to diminished osteoclast mediated bone resorption and greater coupled new bone formation. The results demonstrate that osteoblast lineage cells are key contributors to periodontal bone loss through an NF-κB mediated mechanism.

FOXO1 deletion reduces dendritic cell function and enhances susceptibility to periodontitis

The host response plays both protective and destructive roles in periodontitis. FOXO1 is a transcription factor that is activated in dendritic cells (DCs), but its function in vivo has not been examined. We investigated the role of FOXO1 in activating DCs in experimental (CD11c.Cre(+).FOXO1(L/L)) compared with matched control mice (CD11c.Cre(-).FOXO1(L/L)) in response to oral pathogens. Lineage-specific FOXO1 deletion reduced the recruitment of DCs to oral mucosal epithelium by approximately 40%. FOXO1 was needed for expression of genes that regulate migration, including integrins αν and β3 and matrix metalloproteinase-2. Ablation of FOXO1 in DCs significantly decreased IL-12 produced by DCs in mucosal surfaces. Moreover, FOXO1 deletion reduced migration of DCs to lymph nodes, reduced capacity of DCs to induce formation of plasma cells, and reduced production of bacteria-specific antibody. The decrease in DC function in the experimental mice led to increased susceptibility to periodontitis through a mechanism that involved a compensatory increase in osteoclastogenic factors, IL-1β, IL-17, and RANKL. Thus, we reveal a critical role for FOXO1 in DC recruitment to oral mucosal epithelium and activation of adaptive immunity induced by oral inoculation of bacteria.

Bone Remodeling Under Pathological Conditions

Bone is masterfully programmed to repair itself through the coupling of bone formation following bone resorption, a process referred to as coupling. In inflammatory or other conditions, the balance between bone resorption and bone formation shifts so that a net bone loss results. This review focuses on four pathologic conditions in which remodeling leads to net loss of bone, postmenopausal osteoporosis, arthritis, periodontal disease, and disuse bone loss, which is similar to bone loss associated with microgravity. In most of these there is an acceleration of the resorptive process due to increased formation of bone metabolic units. This initially leads to a net bone loss since the time period of resorption is much faster than the time needed for bone formation that follows. In addition, each of these processes is characterized by an uncoupling that leads to net bone loss. Mechanisms responsible for increased rates of bone resorption, i.e. the formation of more bone metabolic units, involve enhanced expression of inflammatory cytokines and increased expression of RANKL. Moreover, the reasons for uncoupling are discussed which range from a decrease in expression of growth factors and bone morphogenetic proteins to increased expression of factors that inhibit Wnt signaling.

Inflammatory and immune pathways in the pathogenesis of periodontal disease

The pathogenesis of periodontitis involves a complex immune/inflammatory cascade that is initiated by the bacteria of the oral biofilm that forms naturally on the teeth. The susceptibility to periodontitis appears to be determined by the host response; specifically, the magnitude of the inflammatory response and the differential activation of immune pathways. The purpose of this review was to delineate our current knowledge of the host response in periodontitis. The role of innate immunity, the failure of acute inflammation to resolve (thus becoming chronic), the cytokine pathways that regulate the activation of acquired immunity and the cells and products of the immune system are considered. New information relating to regulation of both inflammation and the immune response will be reviewed in the context of susceptibility to, and perhaps control of, periodontitis.

Diabetes mellitus related bone metabolism and periodontal disease

Diabetes mellitus and periodontal disease are chronic diseases affecting a large number of populations worldwide. Changed bone metabolism is one of the important long-term complications associated with diabetes mellitus. Alveolar bone loss is one of the main outcomes of periodontitis, and diabetes is among the primary risk factors for periodontal disease. In this review, we summarise the adverse effects of diabetes on the periodontium in periodontitis subjects, focusing on alveolar bone loss. Bone remodelling begins with osteoclasts resorbing bone, followed by new bone formation by osteoblasts in the resorption lacunae. Therefore, we discuss the potential mechanism of diabetes-enhanced bone loss in relation to osteoblasts and osteoclasts.

FOXO1 regulates dendritic cell activity through ICAM-1 and CCR7

The transcription factor FOXO1 regulates cell function and is expressed in dendritic cells (DCs). We investigated the role of FOXO1 in activating DCs to stimulate a lymphocyte response to bacteria. We show that bacteria induce FOXO1 nuclear localization through the MAPK pathway and demonstrate that FOXO1 is needed for DC activation of lymphocytes in vivo. This occurs through FOXO1 regulation of DC phagocytosis, chemotaxis, and DC-lymphocyte binding. FOXO1 induces DC activity by regulating ICAM-1 and CCR7. FOXO1 binds to the CCR7 and ICAM-1 promoters, stimulates CCR7 and ICAM-1 transcriptional activity, and regulates their expression. This is functionally important because transfection of DCs from FOXO1-deleted CD11c.Cre(+)FOXO1(L/L) mice with an ICAM-1-expressing plasmid rescues the negative effect of FOXO1 deletion on DC bacterial phagocytosis and chemotaxis. Rescue with both CCR7 and ICAM-1 reverses impaired DC homing to lymph nodes in vivo when FOXO1 is deleted. Moreover, Ab production following injection of bacteria is significantly reduced with lineage-specific FOXO1 ablation. Thus, FOXO1 coordinates upregulation of DC activity through key downstream target genes that are needed for DCs to stimulate T and B lymphocytes and generate an Ab defense to bacteria.

FOXO1 mediates RANKL-induced osteoclast formation and activity

We have previously shown that the transcription factor FOXO1 is elevated in conditions with high levels of bone resorption. To investigate the role of FOXO1 in the formation of osteoclasts, we examined mice with lineage-specific deletion of FOXO1 in osteoclast precursors and by knockdown of FOXO1 with small interfering RNA. The receptor activator for NF-κB ligand (RANKL), a principal bone-resorbing factor, induced FOXO1 expression and nuclear localization 2 d after stimulation in bone marrow macrophages and RAW264.7 osteoclast precursors. RANKL-induced osteoclast formation and osteoclast activity was reduced in half in vivo and in vitro with lineage-specific FOXO1 deletion (LyzM.Cre(+)FOXO1(L/L)) compared with matched controls (LyzM.Cre(-)FOXO1(L/L)). Similar results were obtained by knockdown of FOXO1 in RAW264.7 cells. Moreover, FOXO1-mediated osteoclast formation was linked to regulation of NFATc1 nuclear localization and expression as well as a number of downstream factors, including dendritic cell-specific transmembrane protein, ATP6vod2, cathepsin K, and integrin αv. Lastly, FOXO1 deletion reduced M-CSF-induced RANK expression and migration of osteoclast precursors. In the present study, we provide evidence that FOXO1 plays a direct role in osteoclast formation by mediating the effect of RANKL on NFATc1 and several downstream effectors. This is likely to be significant because FOXO1 and RANKL are elevated in osteolytic conditions.

Effect of the interaction between periodontitis and type 1 diabetes mellitus on alveolar bone, mandibular condyle and tibia

OBJECTIVE

This study examined the effect of the interaction between periodontitis and type 1 diabetes mellitus on alveolar bone, mandibular condyle and tibia in animal models.

MATERIALS AND METHODS

Rats were divided into normal, periodontitis, diabetic and diabetic with periodontitis groups. After injection of streptozotocin to induce diabetes, periodontitis was induced by ligation of both lower-side first molars for 30 days. Alveolar bone loss and trabecular bone volume fraction (BVF) of the mandibular condyle and tibia were estimated via hematoxylin and eosin staining and micro-computed tomography, respectively. Osteoclastogenesis of bone marrow cells isolated from tibia and femur was assayed using tartrate-resistant acid phosphatase staining.

RESULTS

The cemento-enamel junction to the alveolar bone crest distance and ratio of periodontal ligament area in the diabetic with periodontitis group were significantly increased compared to those of the periodontitis group. Mandibular condyle BVF did not differ among groups. The BVF of tibia in the diabetic and diabetic with periodontitis groups was lower than that of the normal and periodontitis groups. Osteoclastogenesis of bone marrow cells in the diabetic groups was higher than that in the non-diabetic groups. However, the BVF of tibia and osteoclastogenesis in the diabetic with periodontitis group were not significantly different than those in the diabetic group.

CONCLUSIONS

Type 1 diabetes mellitus aggravates alveolar bone loss induced by periodontitis, but periodontitis does not alter the mandibular condyle and tibia bone loss induced by diabetes. Alveolar bone, mandibular condyle and tibia may have different responses to bone loss stimuli in the diabetic environment.

FOXO transcription factors: their clinical significance and regulation

Members of the class O of forkhead box transcription factors (FOXO) have important roles in metabolism, cellular proliferation, stress resistance, and apoptosis. The activity of FOXOs is tightly regulated by posttranslational modification, including phosphorylation, acetylation, and ubiquitylation. Activation of cell survival pathways such as phosphoinositide-3-kinase/AKT/IKK or RAS/mitogen-activated protein kinase phosphorylates FOXOs at different sites which regulate FOXOs nuclear localization or degradation. FOXO transcription factors are upregulated in a number of cell types including hepatocytes, fibroblasts, osteoblasts, keratinocytes, endothelial cells, pericytes, and cardiac myocytes. They are involved in a number of pathologic and physiologic processes that include proliferation, apoptosis, autophagy, metabolism, inflammation, cytokine expression, immunity, differentiation, and resistance to oxidative stress. These processes impact a number of clinical conditions such as carcinogenesis, diabetes, diabetic complications, cardiovascular disease, host response, and wound healing. In this paper, we focus on the potential role of FOXOs in different disease models and the regulation of FOXOs by various stimuli.

Diabetic characteristics and alveolar bone loss in streptozotocin- and streptozotocin-nicotinamide-treated rats with periodontitis

BACKGROUND AND OBJECTIVE

Experimental models showing variable diabetic status are necessary to understand the relationship between diabetes and periodontitis. The streptozotocin (STZ)-induced diabetes model allows control of diabetic status by nicotinamide (NA), which protects against STZ-induced β-cell necrosis. Therefore, we compared diabetic characteristics and alveolar bone loss in STZ- and STZ-NA-treated rats with periodontitis.

MATERIAL AND METHODS

STZ-treated rats were generated by intravenous (IV) administration of STZ (50 mg/kg). STZ-NA-treated rats were induced by intraperitoneal administration of NA (270 mg/kg) 15 min before IV administration of STZ (65 mg/kg). Periodontitis was induced by ligature around the left mandibular first molar 1 wk after injection. Blood glucose level, glucose tolerance and serum insulin levels were determined at day 0 and/or 20 after ligature. At day 20, tibia bone loss was assessed using micro-computed tomography and hematoxylin and eosin staining. Alveolar bone loss was histologically measured as the distance of the cementoenamel junction to the alveolar bone crest in distal and the percentage of periodontal ligament area in the first molar furcation, respectively. The number of inflammatory cells, receptor activator of nuclear factor kappa-B ligand (RANKL)-positive cells and the area of osteoid were determined.

RESULTS

In STZ-treated rats, obvious hyperglycemia over 300 mg/dL and severe body weight loss were observed. The insulin level was approximately 14% compared to that of control rats. STZ-NA-treated rats were impaired in glucose tolerance compared to control rats; however, body weight and insulin levels were not significantly different. Tibia bone loss was increased in STZ-treated rats, but significant change was not observed in STZ-NA-treated rats compared to control rats. In ligatured teeth, alveolar bone loss was increased in both STZ- and STZ-NA-treated rats compared to control rats. Alveolar bone loss, the number of inflammatory cells and RANKL-positive cells in STZ-treated rats were greater than in STZ-NA-treated rats. The area of osteoid decreased in STZ-treated rats compared to control, but not STZ-NA-treated rats.

CONCLUSION

These results indicate that STZ- and STZ-NA-treated rats exhibit diabetic characteristics similar to type 1 diabetes mellitus and a pre-diabetic state, respectively. In addition, alveolar bone loss in response to periodontitis and tibia loss depend on diabetic status. Diabetic status-dependent bone remodeling imbalance and inflammation could affect the alveolar bone loss in the two models. Both STZ- and STZ-NA-treated rats may be useful to investigate differences in periodontitis sensitivity associated with diabetic status and to develop therapeutic agents for periodontitis in patients with diabetes.

PI3K/Akt/FoxO: a novel participant in signal transduction in bone cells under mechanical stimulation

FoxO (forkhead box O) transcription factors, one of the main downstream mediators of PI3K (phosphatidylinositol-3 kinase)/Akt [also known as PKB (protein kinase B)] signal transduction pathway, play an important role in modulating cellular homoeostasis. Recent studies have revealed the significance of FoxO in bone, the interaction of FoxO with β-catenin, along with mechanical stress-induced inactivation of FoxO via PI3K/Akt. We hypothesize that FoxO is a novel participant in mechanotransduction of bone cells in a PI3K/Akt-dependent way. After describing downstream targets of FoxO, we speculate that FoxO would be involved in the positive effects of mechanical stimulation on bone cells directly through its target genes. We have also concisely represented the cross-talk between ROS (reactive oxygen species) and Wnt/β-catenin pathway, which leads us to hypothesize that the inhibition of FoxO caused by mechanical stress acts at the cross-roads between ROS and Wnt/β-catenin to regulate indirectly bone metabolism.

Oral inflammatory diseases and systemic inflammation: role of the macrophage

Inflammation is a complex reaction to injurious agents and includes vascular responses, migration, and activation of leukocytes. Inflammation starts with an acute reaction, which evolves into a chronic phase if allowed to persist unresolved. Acute inflammation is a rapid process characterized by fluid exudation and emigration of leukocytes, primarily neutrophils, whereas chronic inflammation extends over a longer time and is associated with lymphocyte and macrophage infiltration, blood vessel proliferation, and fibrosis. Inflammation is terminated when the invader is eliminated, and the secreted mediators are removed; however, many factors modify the course and morphologic appearance as well as the termination pattern and duration of inflammation. Chronic inflammatory illnesses such as diabetes, arthritis, and heart disease are now seen as problems that might have an impact on the periodontium. Reciprocal effects of periodontal diseases are potential factors modifying severity in the progression of systemic inflammatory diseases. Macrophages are key cells for the inflammatory processes as regulators directing inflammation to chronic pathological changes or resolution with no damage or scar tissue formation. As such, macrophages are involved in a remarkably diverse array of homeostatic processes of vital importance to the host. In addition to their critical role in immunity, macrophages are also widely recognized as ubiquitous mediators of cellular turnover and maintenance of extracellular matrix homeostasis. In this review, our objective is to identify macrophage-mediated events central to the inflammatory basis of chronic diseases, with an emphasis on how control of macrophage function can be used to prevent or treat harmful outcomes linked to uncontrolled inflammation.

Role of forkhead transcription factors in diabetes-induced oxidative stress

Diabetes is a chronic metabolic disorder, characterized by hyperglycemia resulting from insulin deficiency and/or insulin resistance. Recent evidence suggests that high levels of reactive oxygen species (ROS) and subsequent oxidative stress are key contributors in the development of diabetic complications. The FOXO family of forkhead transcription factors including FOXO1, FOXO3, FOXO4, and FOXO6 play important roles in the regulation of many cellular and biological processes and are critical regulators of cellular oxidative stress response pathways. FOXO1 transcription factors can affect a number of different tissues including liver, retina, bone, and cell types ranging from hepatocytes to microvascular endothelial cells and pericytes to osteoblasts. They are induced by oxidative stress and contribute to ROS-induced cell damage and apoptosis. In this paper, we discuss the role of FOXO transcription factors in mediating oxidative stress-induced cellular response.

Animal models to study host-bacteria interactions involved in periodontitis

Animal models have distinct advantages because they can mimic cellular complexities that occur in humans in vivo and are often more accurate than in vitro studies that take place on plastic surfaces with limited numbers of cell types present. Furthermore, cause and effect relationships can be established by applying inhibitors or activators or through the use of genetically modified animals. Such gain or loss of function studies are often difficult to achieve in human clinical studies, particularly in obtaining target tissue due to important ethical considerations. Animal models in periodontal disease are particularly important at this point in the development of the scientific basis for understanding the predominant pathological processes. Periodontal disease can be broken down into discrete steps, each of which may be studied separately depending upon the animal model. These steps involve the development of a pathogenic biofilm, invasion of connective tissue by bacteria or their products, induction of a destructive host response in connective tissue and limitation of are pair process that follows tissue breakdown. Animal studies can test hypotheses related to each of these steps, and should be evaluated by their capacity to test a specific hypothesis rather than recapitulating all aspects of periodontal disease. Thus, each of the models described below can be adapted to test discrete components of the pathological process of periodontal disease, but not necessarily all of them.

Cigarette smoking and inflammation: cellular and molecular mechanisms

Cigarette smoke (CS) causes considerable morbidity and mortality by inducing cancer, chronic lung and vascular diseases, and oral disease. Despite the well-recognized risks associated with smoking, the habit remains unacceptably prevalent. Several toxins present in CS have immunomodulatory effects. CS also contains trace amounts of microbial cell components, including bacterial lipopolysaccharide. These and other CS constituents induce chronic inflammation at mucosal surfaces and modify host responses to exogenous antigens. The effects of CS on immunity are far-reaching and complex; both pro-inflammatory and suppressive effects may be induced. The net effect of CS on immunity depends on many variables, including the dose and type of tobacco, the route and chronicity of exposure, and the presence of other factors at the time of immune cell stimulation, such as Toll receptor ligands or other inflammatory mediators. CS impairs innate defenses against pathogens, modulates antigen presentation, and promotes autoimmunity. CS also impairs immunity in the oral cavity and promotes gingival and periodontal disease and oral cancer. The recognition of specific mechanisms by which CS affects host immunity is an important step toward elucidating mechanisms of tobacco-induced disease and may identify novel therapeutic approaches for the management of diseases that afflict smokers.

FOXO1 modulates osteoblast differentiation

Forkhead box O1 (FOXO1) is upregulated during bone formation and in response to stimulation by bone morphogenetic proteins. Studies presented here examined the functional role of FOXO1 in a well defined culture system in which pre-osteoblastic cells undergo terminal differentiation in vitro. Mineralizing cultures of MC3T3-E1 cells were examined with or without FOXO1 knockdown by RNAi. Normal cells show the upregulation of FOXO1 and RUNX2 DNA binding activity, alkaline phosphatase activity, and mRNA levels of FOXO1, RUNX2, type 1 collagen, osteocalcin and MMP13 during formation of mineralizing nodules. In FOXO1 depleted cells each of these measurements was significantly reduced compared to values in control cells transfected with scrambled siRNA (P<0.05). Depletion of FOXO1 also reduced the number of mineralized nodules formed. Moreover, chromatin immunoprecipitation assays revealed a direct interaction of FOXO1 with the RUNX2 promoter. Overexpression of FOXO1 reduced the MC3T3-E1 cell number and the number of PCNA positive cells with little effect on apoptosis. These findings indicate that FOXO1 plays an important role in promoting osteoblast differentiation and suppressing proliferation in differentiating cells.

Relationship between the Pathogenic Representatives of Periodontal Pockets Microbiocenosis in Patients with Periodontitis with Varying Degrees of Severity

Periodontitis is a common disease that is considered to be a manifestation of the distortion of the ratio between the normal and conditionally pathogenic microflora of periodontal pockets. In this study, the ratio between the six most important periodontal pathogens and the total microflora of the periodontal pocket in healthy individuals and patients with varying severity of periodontitis was ascertained by quantitative real-time PCR. It was ascertained that the relative content ofPorphyromonas gingivalis,Prevotella intermedia, andTannerella forsythensis(Bacteroides forsythus) persistently develops in the total microflora of the periodontal pocket upon progressing periodontitis; this value is higher than that in the control group by more than two orders of magnitude upon a severe degree of chronic generalized periodontitis.

A controversial role for IL-12 in immune response and bone resorption at apical periodontal sites

Periapical lesions are inflammatory conditions of tooth periapical tissues, triggered by dental pulp infection and characterized by exudation of immune cells to the affected tissues and production of inflammatory mediators such as cytokines. The inflammatory periapical reaction is mainly driven by Th1, Th2, and Th17 responses, and such polarization may modulate progression of the disease and expression of bone proresorptive cytokines. IL-12 is a potent inducer of IFN-γ production, which stimulates Th1 effector cells. Many evidences have shown a positive correlation between the bone resorptive cytokine IL-1β and the production of IL-12 and IFN-γ. Furthermore, IL-12 may have a potential role in the release of bone resorptive mediators and blockade of Th2 cytokines, affecting the progression of periapical bone loss. Nevertheless, IL-12 and IFN-γ have also been described as suppressors of osteoclast differentiation and activation, favoring bone maintenance. This paper focuses on the controversial roles of IL-12 in periapical lesions.

Review of osteoimmunology and the host response in endodontic and periodontal lesions

Both lesions of endodontic origin and periodontal diseases involve the host response to bacteria and the formation of osteolytic lesions. Important for both is the upregulation of inflammatory cytokines that initiate and sustain the inflammatory response. Also important are chemokines that induce recruitment of leukocyte subsets and bone-resorptive factors that are largely produced by recruited inflammatory cells. However, there are differences also. Lesions of endodontic origin pose a particular challenge since that bacteria persist in a protected reservoir that is not readily accessible to the immune defenses. Thus, experiments in which the host response is inhibited in endodontic lesions tend to aggravate the formation of osteolytic lesions. In contrast, bacteria that invade the periodontium appear to be less problematic so that blocking arms of the host response tend to reduce the disease process. Interestingly, both lesions of endodontic origin and periodontitis exhibit inflammation that appears to inhibit bone formation. In periodontitis, the spatial location of the inflammation is likely to be important so that a host response that is restricted to a subepithelial space is associated with gingivitis, while a host response closer to bone is linked to bone resorption and periodontitis. However, the persistence of inflammation is also thought to be important in periodontitis since inflammation present during coupled bone formation may limit the capacity to repair the resorbed bone.

Inflammation and uncoupling as mechanisms of periodontal bone loss

Periodontal disease is characterized by both inflammation and bone loss. Advances in research in both these areas have led to a new appreciation of not only each field but also the intimate relationship between inflammation and bone loss. This relationship has resulted in a new field of science called osteoimmunology and provides a context for better understanding the pathogenesis of periodontal disease. In this review, we discuss several aspects of the immuno-inflammatory host response that ultimately results in loss of alveolar bone. A proposal is made that periodontal inflammation not only stimulates osteoclastogenesis but also interferes with the uncoupling of bone formation and bone resorption, consistent with a pathologic process. Furthermore, arguments based on experimental animal models suggest a critical role of the spatial and temporal aspects of inflammation in the periodontium. A review of these findings leads to a new paradigm to help explain more fully the impact of inflammation on alveolar bone in periodontal disease so that it includes the effects of inflammation on uncoupling of bone formation from resorption.

Adaptive immune response in osteoclastic bone resorption induced by orally administered Aggregatibacter actinomycetemcomitans in a rat model of periodontal disease

There is mounting evidence that innate and adaptive immunity are critical for periodontal disease-mediated bone resorption. These studies examined the role of B and CD4 T cells in adaptive immunity of rats infected with Aggregatibacter actinomycetemcomitans (Aa). Sprague-Dawley male rats were fed Aa-containing mash or control-mash for 2 weeks. B and CD4 T cells were obtained from draining lymph nodes at 2, 4 and 12 weeks, postinoculation. Quantitative polymerase chain reaction-based messenger RNA expression was conducted for 89 cytokine family genes. Disease-relevance of the differentially expressed genes was assessed using a biological interaction pathway analysis software. B and CD4 T cells of Aa-infected rats increased and were activated, resulting in enhanced isotype-switched serum immunoglobulin G by 2 weeks postinoculation. Bone resorption was evident 12 weeks after Aa-feeding. In B cells, interleukin-2 (IL-2), macrophage-inhibiting factor, IL-19, IL-21, tumor necrosis factor (TNF), CD40 ligand (CD40L), CD70, bone morphogenetic protein 2 (BMP2), BMP3, and BMP10 were upregulated early; while IL-7, Fas ligand (FasL), small inducible cytokine subfamily E1, and growth differentiation factor 11 (GDF11; BMP11) were upregulated late (12 weeks). BMP10 was sustained throughout. In CD4 T cells, IL-10, IL-16, TNF, lymphotoxin-beta (LTbeta), APRIL, CD40L, FasL, RANKL and osteoprotegerin were upregulated early, whereas IL-1beta, IL-1RN, IL-1F8, IL-24, interferon-alpha1, GDF11 (BMP11), and GDF15 were upregulated late (12 weeks). Adaptive immunity appears crucial for bone resorption. Several of the deregulated genes are, for the first time, shown to be associated with bone resorption, and the results indicate that activated B cells produce BMP10. The study provides a rationale for a link between periodontal disease and other systemic diseases.

Destructive and protective roles of cytokines in periodontitis: a re-appraisal from host defense and tissue destruction viewpoints

Periodontal diseases (PD) are chronic infectious inflammatory diseases characterized by the destruction of tooth-supporting structures, being the presence of periodontopathogens required, but not sufficient, for disease development. As a general rule, host inflammatory mediators have been associated with tissue destruction, while anti-inflammatory mediators counteract and attenuate disease progression. With the discovery of several T-cell subsets bearing distinct immunoregulatory properties, this pro- vs. anti-inflammatory scenario became more complex, and a series of studies has hypothesized protective or destructive roles for Th1, Th2, Th17, and Treg subpopulations of polarized lymphocytes. Interestingly, the "protective vs. destructive" archetype is usually considered in a framework related to tissue destruction and disease progression. However, it is important to remember that periodontal diseases are infectious inflammatory conditions, and recent studies have demonstrated that cytokines (TNF-α and IFN-γ) considered harmful in the context of tissue destruction play important roles in the control of periodontal infection. Therefore, in this review, the state-of-the-art knowledge concerning the protective and destructive roles of host inflammatory immune response will be critically evaluated and discussed from the tissue destruction and control-of-infection viewpoints.

TNF-alpha mediates diabetes-enhanced chondrocyte apoptosis during fracture healing and stimulates chondrocyte apoptosis through FOXO1

To gain insight into the effect of diabetes on fracture healing, experiments were carried out focusing on chondrocyte apoptosis during the transition from cartilage to bone. Type 1 diabetes was induced in mice by multiple low-dose streptozotocin injections, and simple transverse fractures of the tibia or femur was carried out. Large-scale transcriptional profiling and gene set enrichment analysis were performed to examine apoptotic pathways on total RNA isolated from fracture calluses on days 12, 16, and 22, a period of endochondral bone formation when cartilage is resorbed and chondrocyte numbers decrease. Tumor necrosis factor alpha (TNF-alpha) protein levels were assessed by ELISA and caspase-3 by bioactivity assay. The role of TNF was examined by treating mice with the TNF-specific inhibitor pegsunercept. In vitro studies investigated the proapoptotic transcription factor FOXO1 in regulating TNF-induced apoptosis of chondrogenic ATDC5 and C3H10T1/2 cells as representative of differentiated chondrocytes, which are important during endochondral ossification. mRNA profiling revealed an upregulation of gene sets related to apoptosis in the diabetic group on day 16 when cartilage resorption is active but not day 12 or day 22. This coincided with elevated TNF-alpha protein levels, chondrocyte apoptosis, enhanced caspase-3 activity, and increased FOXO1 nuclear translocation (p < .05). Inhibition of TNF significantly reduced these parameters in the diabetic mice but not in normoglycemic control mice (p < .05). Silencing FOXO1 using siRNA in vitro significantly reduced TNF-induced apoptosis and caspase activity in differentiated chondrocytes. The mRNA levels of the proapoptotic genes caspase-3, caspase-8, caspase-9, and TRAIL were significantly reduced with silencing of FOXO1 in chondrocytic cells. Inhibiting caspase-8 and caspase-9 significantly reduced TNF-induced apoptosis in chondrogenic cells. These results suggest that diabetes causes an upregulation of proapoptotic genes during the transition from cartilage to bone in fracture healing. Diabetes increased chondrocyte apoptosis through a mechanism that involved enhanced production of TNF-alpha, which stimulates chondrocyte apoptosis and upregulates mRNA levels of apoptotic genes through FOXO1 activation.

Effect of venlafaxine on bone loss associated with ligature-induced periodontitis in Wistar rats

Background

The present study investigated the effects of venlafaxine, an antidepressant drug with immunoregulatory properties on the inflammatory response and bone loss associated with experimental periodontal disease (EPD).

Materials and Methods

Wistar rats were subjected to a ligature placement around the second upper left molar. The treated groups received orally venlafaxine (10 or 50 mg/kg) one hour before the experimental periodontal disease induction and daily for 10 days. Vehicle-treated experimental periodontal disease and a sham-operated (SO) controls were included. Bone loss was analyzed morphometrically and histopathological analysis was based on cell influx, alveolar bone, and cementum integrity. Lipid peroxidation quantification and immunohistochemistry to TNF-α and iNOS were performed.

Results

Experimental periodontal disease rats showed an intense bone loss compared to SO ones (SO = 1.61 ± 1.36; EPD = 4.47 ± 1.98 mm, p < 0.001) and evidenced increased cellular infiltration and immunoreactivity for TNF-α and iNOS. Venlafaxine treatment while at low dose (10 mg/kg) afforded no significant protection against bone loss (3.25 ± 1.26 mm), a high dose (50 mg/kg) caused significantly enhanced bone loss (6.81 ± 3.31 mm, p < 0.05). Venlafaxine effectively decreased the lipid peroxidation but showed no significant change in TNF-α or iNOS immunoreactivity.

Conclusion

The increased bone loss associated with high dose venlafaxine may possibly be a result of synaptic inhibition of serotonin uptake.

Association of periodontitis with rheumatoid arthritis and atherosclerosis: Novel paradigms in etiopathogeneses and management?

There is increasing documentation of a link between inflammatory periodontal disease affecting the supporting structure of teeth, rheumatoid arthritis, and coronary artery disease. Periodontitis is initiated predominantly by Gram-negative bacteria and progresses as a consequence of the host inflammatory response to periodontal pathogens. Lipopolysaccharide, a cell wall constituent stimulates the production of inflammatory cytokines via the activation of signaling pathways perpetuating inflammatory pathogenesis in a cyclical manner in susceptible individuals; with an element of autoimmune stimulation, not dissimilar to the sequential events seen in RA. Periodontitis, also implicated as a risk factor for cardiovascular disease, promotes mechanisms for atherosclerosis by enhancing an imbalance in systemic inflammatory mediators; more direct mechanisms attributed to microbial products are also implicated in both RA and atherogenesis. Severe periodontal disease characterized by clinical and radiographic parameters has been associated with ischemic stroke risk, significant levels of C-reactive protein and serum amyloid A, amongst others common to both periodontitis and atherosclerosis. Existing data supports the hypothesis that persistent localized infection in periodontitis may influence systemic levels of inflammatory markers and pose a risk for RA and atherosclerosis. A common nucleus of activity in their pathogeneses provides novel paradigms of therapeutic targeting for reciprocal benefit.

Altered fibroblast proliferation and apoptosis in diabetic gingival wounds

Although it is known that diabetes impairs oral wound healing, relatively little is known about the cellular parameters affected, particularly in connective tissue. This study investigated the hypothesis that diabetes impairs connective tissue formation in healing gingiva, and that impaired healing is associated with factors that decrease fibroblast numbers. Full-thickness wounds were created in the palatal gingiva of type 1 and type 2 diabetic and normoglycemic mice. Five days after wounding, diabetic mice had less epithelial wound coverage, less new connective tissue formation, and reduced fibroblast density (p < 0.05). This occurred with increased numbers of caspase-3- and TUNEL-positive fibroblasts, decreased fibroblast proliferation, increased nuclear translocation of the pro-apoptotic transcription factor FOXO1, and increased numbers of polymorphonuclear leukocytes, all of which were significant (p < 0.05). The results suggest that diabetes may decrease fibroblast numbers through increased apoptosis and reduced proliferation, both of which may be mediated through increased activation of FOXO1.