MAP kinase phosphatase-1 protects against inflammatory bone loss

Temporal changes of periodontal tissue pathology in a periodontitis animal model

PURPOSE

This study aimed to characterize the early stages of periodontal disease and determine the optimal period for its evaluation in a mouse model. The association between the duration of ligation and its effect on the dentogingival area in mice was evaluated using micro-computed tomography (CT) and histological analysis.

METHODS

Ninety mice were allocated to an untreated control group or a ligation group in which periodontitis was induced by a 6-0 silk ligation around the left second maxillary molar. Mice were sacrificed at 1, 2, 3, 4, 5, 8, 11, and 14 days after ligature placement. Alveolar bone destruction was evaluated using micro-CT. Histological analysis was performed to assess the immune-inflammatory processes in the periodontal tissue.

RESULTS

No significant difference in alveolar bone loss was found compared to the control group until day 3 after ligature placement, and a gradual increase in alveolar bone loss was observed from 4 to 8 days following ligature placement. No significant between-group differences were observed after 8 days. The histological analysis demonstrated that the inflammatory response was evident from day 4.

CONCLUSIONS

Our findings in a mouse model provide experimental evidence that ligature-induced periodontitis models offer a consistent progression of disease with marginal attachment down-growth, inflammatory infiltration, and alveolar bone loss.

The Oral-Gut Axis: Periodontal Diseases and Gastrointestinal Disorders

One of the prospective sequelae of periodontal disease (PD), chronic inflammation of the oral mucosa, is the development of inflammatory gastrointestinal (GI) disorders due to the amplification and expansion of the oral pathobionts. In addition, chronic inflammatory diseases related to the GI tract, which include inflammatory bowel disease (IBD), can lead to malignancy susceptibility in the colon of both animals and humans. Recent studies suggest that dysbiosis of the oral microbiota can alter the microbial composition in relative abundance or diversity of the distal gut, leading to the progression of digestive carcinogenesis. The link between PD and specific GI disorders is also closely associated with the migration and colonization of periodontal pathogens and the subsequent microbe-reactive T cell induction within the intestines. In this review, an in-depth examination of this relationship and the accessibility of different mouse models of IBD and PD may shed light on the current dogma. As such, oral microbiota dysbiosis involving specific bacteria, including Fusobacterium nucleatum and Porphyromonas gingivalis, can ultimately lead to gut malignancies. Further understanding the precise mechanism(s) of the oral-gut microbial axis in PD, IBD, and colorectal cancer pathogenesis will be pivotal in diagnosis, prognosis, and future treatment.

Bombax ceiba Linn. leaf extract rich in phenolic compounds to mitigate non-alcoholic fatty liver-related complications in experimental model

OBJECTIVES

Obesity, diabetes mellitus, insulin resistance (IR), and hypertriglyceridemia are common features observed in non-alcoholic fatty liver diseases (NAFLD). There is a critical medical necessity to find novel therapeutics that can halt the development of NAFLD.

METHODS

Bombax ceiba Linn. leaf extract was prepared and its phytochemical profile was determined. Standard and high carbohydrate high-fat diets (HCHF) were prepared. Rats were fed HCHF for 18 weeks to induce a non-alcoholic fatty liver (NAFL) model. Forty male rats were divided into control, B. ceiba Linn. leaf extract, NAFL, prophylactic, and treated groups. Serum fasting blood sugar (FBS), insulin, insulin resistance (HOMA-IR), cholesterol, high-density lipoprotein (HDL), triglycerides (TG), low density lipoprotein (LDL), alanine aminotransferase (ALT), aspartate aminotransferase (AST), intelectin-1 (ITLN1), p38 MAP kinase (MAPK), peroxisome proliferator-activated receptor alpha (PPAR-α), and interleukin-6 (IL-6) were evaluated.

RESULTS

Data obtained showed that HCHF-induced NAFL resulting in a significant increase in FBS, serum insulin, HOMA-IR, cholesterol, LDL, TG, ALT, AST, and IL-6 and a significant decrease in serum levels of HDL, ITLN1, p38 MAP kinase, and PPAR-α compared to the control group. The analysis of B. ceiba Linn. leaf extract showed high content of phenol compounds which may cause a significant decrease in the levels of FBS, insulin, HOMA-IR values, lipid profile, and levels of IL-6 while a significant increase in serum levels of LDL, ITLN1, p38 MAP kinase, and PPAR-α compared to the NAFL group.

CONCLUSIONS

B. ceiba Linn. Leaf extract is a highly protective and promising therapeutic agent against inflammation and oxidative stress in the NAFLD model induced by HCHF.

GPR40 deficiency worsens metabolic syndrome-associated periodontitis in mice

BACKGROUND AND OBJECTIVE

G protein-coupled receptor 40 (GPR40) is a receptor for medium- and long-chain free fatty acids (FFAs). GPR40 activation improves type 2 diabetes mellitus (T2DM), metabolic syndrome (MetS), and the complications of T2DM and MetS. Periodontitis, a common oral inflammatory disease initiated by periodontal pathogens, is another complication of T2DM and MetS. Since FFAs play a key role in the pathogenesis of MetS which exacerbates periodontal inflammation and GPR40 is a FFA receptor with anti-inflammatory properties, it is important to define the role of GPR40 in MetS-associated periodontitis.

MATERIALS AND METHODS

We induced MetS and periodontitis by high-fat diet and periodontal injection of lipopolysaccharide (LPS), respectively, in wild-type and GPR40-deficient mice and determined alveolar bone loss and periodontal inflammation using micro-computed tomography, histology, and osteoclast staining. We also performed in vitro study to determine the role of GPR40 in the expression of proinflammatory genes.

RESULTS

The primary outcome of the study is that GPR40 deficiency increased alveolar bone loss and enhanced osteoclastogenesis in control mice and the mice with both MetS and periodontitis. GPR40 deficiency also augmented periodontal inflammation in control mice and the mice with both MetS and periodontitis. Furthermore, GPR40 deficiency led to increased plasma lipids and insulin resistance in control mice but had no effect on the metabolic parameters in mice with MetS alone. For mice with both MetS and periodontitis, GPR40 deficiency increased insulin resistance. Finally, in vitro studies with macrophages showed that deficiency or inhibition of GPR40 upregulated proinflammatory genes while activation of GPR40 downregulated proinflammatory gene expression stimulated synergistically by LPS and palmitic acid.

CONCLUSION

GPR40 deficiency worsens alveolar bone loss and periodontal inflammation in mice with both periodontitis and MetS, suggesting that GPR40 plays a favorable role in MetS-associated periodontitis. Furthermore, GPR40 deficiency or inhibition in macrophages further upregulated proinflammatory and pro-osteoclastogenic genes induced by LPS and palmitic acid, suggesting that GPR40 has anti-inflammatory and anti-osteoclastogenic properties.

Protein tyrosine phosphatases in skeletal development and diseases

Skeletal development and homeostasis in mammals are modulated by finely coordinated processes of migration, proliferation, differentiation, and death of skeletogenic cells originating from the mesoderm and neural crest. Numerous molecular mechanisms are involved in these regulatory processes, one of which is protein posttranslational modifications, particularly protein tyrosine phosphorylation (PYP). PYP occurs mainly through the action of protein tyrosine kinases (PTKs), modifying protein enzymatic activity, changing its cellular localization, and aiding in the assembly or disassembly of protein signaling complexes. Under physiological conditions, PYP is balanced by the coordinated action of PTKs and protein tyrosine phosphatases (PTPs). Dysregulation of PYP can cause genetic, metabolic, developmental, and oncogenic skeletal diseases. Although PYP is a reversible biochemical process, in contrast to PTKs, little is known about how this equilibrium is modulated by PTPs in the skeletal system. Whole-genome sequencing has revealed a large and diverse superfamily of PTP genes (over 100 members) in humans, which can be further divided into cysteine (Cys)-, aspartic acid (Asp)-, and histidine (His)-based PTPs. Here, we review current knowledge about the functions and regulatory mechanisms of 28 PTPs involved in skeletal development and diseases; 27 of them belong to class I and II Cys-based PTPs, and the other is an Asp-based PTP. Recent progress in analyzing animal models that harbor various mutations in these PTPs and future research directions are also discussed. Our literature review indicates that PTPs are as crucial as PTKs in supporting skeletal development and homeostasis.

Bad to the Bone: The Effects of Therapeutic Glucocorticoids on Osteoblasts and Osteocytes

Despite the continued development of specialized immunosuppressive therapies in the form of monoclonal antibodies, glucocorticoids remain a mainstay in the treatment of rheumatological and auto-inflammatory disorders. Therapeutic glucocorticoids are unmatched in the breadth of their immunosuppressive properties and deliver their anti-inflammatory effects at unparalleled speed. However, long-term exposure to therapeutic doses of glucocorticoids decreases bone mass and increases the risk of fractures - particularly in the spine - thus limiting their clinical use. Due to the abundant expression of glucocorticoid receptors across all skeletal cell populations and their respective progenitors, therapeutic glucocorticoids affect skeletal quality through a plethora of cellular targets and molecular mechanisms. However, recent evidence from rodent studies, supported by clinical data, highlights the considerable role of cells of the osteoblast lineage in the pathogenesis of glucocorticoid-induced osteoporosis: it is now appreciated that cells of the osteoblast lineage are key targets of therapeutic glucocorticoids and have an outsized role in mediating their undesirable skeletal effects. As part of this article, we review the molecular mechanisms underpinning the detrimental effects of supraphysiological levels of glucocorticoids on cells of the osteoblast lineage including osteocytes and highlight the clinical implications of recent discoveries in the field.

Application of Ligature-Induced Periodontitis in Mice to Explore the Molecular Mechanism of Periodontal Disease

Periodontitis is an inflammatory disease characterized by the destruction of the periodontium. In the last decade, a new murine model of periodontitis has been widely used to simulate alveolar bone resorption and periodontal soft tissue destruction by ligation. Typically, 3-0 to 9-0 silks are selected for ligation around the molars in mice, and significant bone loss and inflammatory infiltration are observed within a week. The ligature-maintained period can vary according to specific aims. We reviewed the findings on the interaction of systemic diseases with periodontitis, periodontal tissue destruction, the immunological and bacteriological responses, and new treatments. In these studies, the activation of osteoclasts, upregulation of pro-inflammatory factors, and excessive immune response have been considered as major factors in periodontal disruption. Multiple genes identified in periodontal tissues partly reflect the complexity of the pathogenesis of periodontitis. The effects of novel treatment methods on periodontitis have also been evaluated in a ligature-induced periodontitis model in mice. This model cannot completely represent all aspects of periodontitis in humans but is considered an effective method for the exploration of its mechanisms. Through this review, we aimed to provide evidence and enlightenment for future studies planning to use this model.

Silencing matrix metalloproteinase-13 (Mmp-13) reduces inflammatory bone resorption associated with LPS-induced periodontal disease in vivo

OBJECTIVES

The aim of this study was to evaluate the effect of specific inhibition of MMP-13 on inflammation and inflammatory bone resorption in a murine model of lipopolysaccharide (LPS)-induced periodontitis.

MATERIALS AND METHODS

Periodontitis was induced in mice by micro-injections of LPS into the gingival tissues adjacent to the palatal surfaces of maxillary molars twice a week for 15 days. Matrix metalloproteinase-13 (Mmp-13) shRNA or a specific biochemical inhibitor were also injected into the same sites in alternating days with the LPS injections. Efficacy of shRNA-mediated silencing of Mmp-13 was verified by quantitative real-time polymerase chain reaction (qPCR) and immunoblot. Bone resorption was assessed by microcomputed tomography (uCT). Histological sections stained with hematoxylin/eosin (H/E) were used in the stereometric analysis of the inflammatory infiltrate. Gingival tissues were used to evaluate expression of Mmp-13, Il-6, Tnf-α, Ptgs2, and Rankl (qPCR). Protein levels of TGF-β and IL-10 in the tissues were determined by enzyme-linked immunosorbent assays (ELISA) or by MMP-13 and p38 immunoblot.

RESULTS

Silencing Mmp-13 expression reduced bone resorption significantly. Expression of Mmp-13, Il-6, and Tnf-α, as well as the protein levels of IL-6 and TNF-α, was reduced in the animals treated with adenovirus-delivered shRNA; however, these effects were not associated with modulation of p38 MAPK signaling. Interestingly, inhibition Mmp-13 did not affect the severity of inflammatory infiltrate.

CONCLUSIONS

Site-specific inhibition of MMP-13 reduced bone resorption and production of inflammatory mediators associated with periodontal disease.

CLINICAL RELEVANCE

The results suggest that site-specific inhibition of MMP-13 may be an interesting strategy to modulate inflammation and reduce bone resorption in osteolytic inflammatory diseases.

Pam2CSK4 (TLR2 agonist) induces periodontal destruction in mice

Lipoproteins are important bacterial immunostimulating molecules capable of inducing receptor activator of nuclear factor-κB (RANKL) and osteoclast formation in vitro and in vivo . Although these molecules are present in periodontopathogenic bacteria, their role in periodontitis is not known. In this study, we used Pam2CSK4 (PAM2), a synthetic molecule that mimics bacterial lipoprotein, to investigate the effects of lipoproteins on periodontitis in mice. C57BL/6 male mice were randomly divided into three experimental groups: 1) Negative control group: animals received vehicle injection; 2) Positive control group: animals received injection of Escherichia coli lipopolysaccharide (LPS); 3) PAM2 group: animals received PAM2 injection. All the injections were performed bilaterally every other day into the palatal mucosa between first and second molars. After twenty-four days, the animals were euthanized to assess alveolar bone volume (micro-CT), cellular and extracellular composition in the gingiva (stereometric analysis), and osteoclast numbers (TRAP staining). Treatment with either PAM2 or LPS induced gingival inflammation, as demonstrated by increased infiltration of inflammatory cells and enhanced angiogenesis, associated with a smaller number of fibroblasts and decreased extracellular matrix. Importantly, treatment not only with LPS but also with PAM2 resulted in a larger number of TRAP+ multinucleated osteoclasts and significant loss of alveolar bone. Collectively, our data demonstrate that PAM2 can induce gingival inflammation and bone loss in mice, broadening the avenues of investigation into the role of lipoproteins in the pathogenesis of periodontal disease.

Role of Dual-Specificity Phosphatase 1 in Glucocorticoid-Driven Anti-inflammatory Responses

Glucocorticoids (GCs) potently inhibit pro-inflammatory responses and are widely used for the treatment of inflammatory diseases, such as allergies, autoimmune disorders, and asthma. Dual-specificity phosphatase 1 (DUSP1), also known as mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1), exerts its effects by dephosphorylation of MAPKs, i.e., extracellular-signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK). Endogenous DUSP1 expression is tightly regulated at multiple levels, involving both transcriptional and post-transcriptional mechanisms. DUSP1 has emerged as a central mediator in the resolution of inflammation, and upregulation of DUSP1 by GCs has been suggested to be a key mechanism of GC actions. In this review, we discuss the impact of DUSP1 on the efficacy of GC-mediated suppression of inflammation and address the underlying mechanisms.

Functionalized nanoparticles containing MKP-1 agonists reduce periodontal bone loss

BACKGROUND

Progress over of the past several years has elucidated a role for mitogen-activated protein kinase phosphatase to regulate periodontal inflammation yielding new possibilities for treatment of periodontal diseases. These studies aimed to determine if nanoparticles (NPs) loaded with a pharmacological agent that induces mitogen-activated protein kinase phosphatase have potential clinical utility for management of periodontal inflammation and alveolar bone.

METHODS

Polyethylene glycol (PEG)-polylactide (PLA) (PEG-PLA) NPs were loaded with auranofin (ARN), an antirheumatic drug, to induce mitogen-activated protein kinase phosphatase (MKP)-1 expression in vitro and in vivo. Release kinetics of ARN from NPs was performed by high performance liquid chromatography (HPLC). Fluorescent-labeled NPs were used to show uptake into macrophages by flow cytometry. Real-time quantitative polymerase chain reaction (qPCR) was used to determine dual specificity protein phosphatase (Dusp)-1 mRNA induction by Auranofin-loaded nanoparticles (ARN-NPs) and viability of ARN-NPs was determined by colorimetric in vitro assays. Functional in vitro assays were used to measure functional MKP-1 induction and preclinical models using Aggregatibacter actinomycetemcomitans lipopolysaccharide-induced alveolar bone loss and microcomputed tomography was used to determine in vivo efficacy of functionalized ARN-NPs.

RESULTS

Data indicated that ARN-NPs had reduced cytotoxicity compared with free ARN and Dusp1 mRNA and MKP-1 activity was significantly increased by ARN-NPs in vitro. Flow cytometry indicated rapid uptake into macrophages. Finally, significant bone loss reduction was observed with ARN-NPs compared with control NPs in vivo using an lipopolysaccharide-induced rat model of periodontitis.

CONCLUSION

Results from these studies suggest that developing NPs functionalized with ARN have anti-inflammatory activities and may be a novel adjuvant therapeutic strategy to significantly improve periodontitis therapy and outcomes.

MKP-1 promotes anti-inflammatory M(IL-4/IL-13) macrophage phenotype and mediates the anti-inflammatory effects of glucocorticoids

Macrophage polarization refers to the ability of these cells to adopt different functional phenotypes according to their environment. Mitogen-activated protein kinase phosphatase-1 (MKP-1) is known to regulate the classical lipopolysaccharide (LPS)-induced pro-inflammatory macrophage activation and the inflammatory response. Here, we investigated the effects of MKP-1 on the anti-inflammatory and healing-promoting macrophage phenotype induced by cytokines IL-4 and IL-13 and examined the potential mediator role of MKP-1 in glucocorticoid effects on the two macrophage phenotypes. In MKP-1-deficient macrophages treated with IL-4 and IL-13 to induce the anti-inflammatory phenotype, the expression of phenotypic markers arginase 1, Ym-1 and FGF2 was reduced as compared to wild-type cells. In contrast, LPS-induced expression of the pro-inflammatory factors IL-6 and iNOS was significantly higher in MKP-1-deficient macrophages. Dexamethasone suppressed the pro-inflammatory phenotype and enhanced the anti-inflammatory phenotype. Interestingly, both of these glucocorticoid effects were attenuated in macrophages from MKP-1-deficient mice. Accordingly, dexamethasone increased MKP-1 expression in both LPS- and IL4+13-treated wild-type cells. In conclusion, the findings support MKP-1 as an endogenous mechanism able to shift macrophage activation from the classical pro-inflammatory state towards the anti-inflammatory and healing-promoting phenotype. In addition, MKP-1 was found to mediate the anti-inflammatory effects of dexamethasone in a dualistic manner: by suppressing the pro-inflammatory macrophage activation and by enhancing the healing-promoting macrophage phenotype.

Geniposide regulates the miR-101/MKP-1/p38 pathway and alleviates atherosclerosis inflammatory injury in ApoE-/- mice

Atherosclerosis (AS) is the common pathological basis of chronic cardiovascular diseases and is associated with inflammation and lipid metabolism dysfunction. Geniposide, the main active ingredient of Gardenia jasminoides Ellis fruit, exhibits a variety of anti-inflammatory and anti-oxidative functions; however, its role in AS remains unclear. The aim of this study was to investigate the mechanisms of geniposide in alleviating inflammation and thereby attenuating the development of AS. ApoE^-/- mice were fed a high fat diet to induce AS and were treated with geniposide (50 mg/kg) for 12 weeks. Blood glucose and lipid levels were measured by biochemical analysis. H&E, Masson and Oil red O staining were performed to observe morphological changes and lipid deposition in the aorta and liver. Serum inflammatory cytokines were detected by ELISA. Dual-luciferase reporter gene assay was used to verify the target relationship between microRNA-101 (miR-101) and mitogen-activated protein kinase phosphatase-1 (MKP-1). The levels of miR-101, p-p38, and MKP-1 in the aorta were detected by qPCR and western blotting. The anti-inflammatory effect of geniposide in vitro was investigated in the RAW264.7 macrophage cell line. A miR-101 mimic and an inhibitor were used to study the effect of miR-101 on regulating the expression of the target MKP-1 and the downstream inflammatory cytokines. Geniposide treatment reduced lipid levels and plaque size in the mouse model of AS. Geniposide downregulated miR-101 to upregulate MKP-1 and suppress the production of inflammatory factors in vitro and in vivo. Geniposide suppressed the levels of inflammatory factors in the presence of the miR-101 mimic, whereas no obvious effect was observed in the miR-101 inhibitor group. We concluded that geniposide reduced the plaque size and alleviated inflammatory injury in ApoE^-/- mice and RAW264.7 cells. The specific anti-inflammatory mechanism was related to the miR-101/ MKP-1/p38 signaling pathway.

Roles of Mitogen-Activated Protein Kinases in Osteoclast Biology

Bone undergoes continuous remodeling, which is homeostatically regulated by concerted communication between bone-forming osteoblasts and bone-degrading osteoclasts. Multinucleated giant osteoclasts are the only specialized cells that degrade or resorb the organic and inorganic bone components. They secrete proteases (e.g., cathepsin K) that degrade the organic collagenous matrix and establish localized acidosis at the bone-resorbing site through proton-pumping to facilitate the dissolution of inorganic mineral. Osteoporosis, the most common bone disease, is caused by excessive bone resorption, highlighting the crucial role of osteoclasts in intact bone remodeling. Signaling mediated by mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38, has been recognized to be critical for normal osteoclast differentiation and activation. Various exogenous (e.g., toll-like receptor agonists) and endogenous (e.g., growth factors and inflammatory cytokines) stimuli contribute to determining whether MAPKs positively or negatively regulate osteoclast adhesion, migration, fusion and survival, and osteoclastic bone resorption. In this review, we delineate the unique roles of MAPKs in osteoclast metabolism and provide an overview of the upstream regulators that activate or inhibit MAPKs and their downstream targets. Furthermore, we discuss the current knowledge about the differential kinetics of ERK, JNK, and p38, and the crosstalk between MAPKs in osteoclast metabolism.

Differential Mechanism of Periodontitis Progression in Postmenopause

Over the past four decades, it has become accepted that periodontal disease is caused by specific bacterial infections and that individuals are uniformly susceptible neither to these infections nor to the damage caused by them. The specific bacterial infections and the composition of the environment in which these bacteria easily settle cause an immune response. The immune cells involved in pathogenesis of periodontitis migrate into the periodontitis lesion and advance the disease. The purpose of the present study is to investigate the correlation between immune cell migration and progression of periodontal disease by inducing estrogen deficiency through ovariectomy (OVX) to mimic postmenopausal women and treatment with lipopolysaccharide (LPS). The LPS derived from Porphyromonas gingivalis induced periodontitis and absorption of the alveolar bone dose-dependently. However, the alveolar crest level reduction after LPS injection between OVX and Sham operated mice did not show a significant difference. Matrix metallopeptidase-9 (MMP-9), which is known to be able to detect the progression of periodontitis in general, was not significantly different between OVX and Sham groups. However, immune cells such as T-lymphocytes and neutrophils migrated less overall in OVX groups than Sham operated groups. These findings can be a topic of debate on the old controversy regarding the relationship between periodontal disease and hormonal change. Currently, in clinical practice, menopause is not a major consideration in the treatment of periodontal disease. This study suggests that treatment methods and medication should be considered in the treatment of infectious periodontal disease in postmenopausal women.

Genomewide Association Study Identifies Cxcl Family Members as Partial Mediators of LPS-Induced Periodontitis

Periodontitis (PD) is characterized by bacterial infection and inflammation of tooth-supporting structures and can lead to tooth loss. PD affects ∼47% of the US population over age 30 years and has a heritability of about 50%. Although the host immunoinflammatory response and genetic background play a role, little is known of the underlying genetic factors. We examined natural genetic variation in lipopolysaccharide (LPS)-induced PD across a panel of inbred mouse strains, the hybrid mouse diversity panel (HMDP). We observed a strain-dependent sixfold difference in LPS-induced bone loss across the HMDP with a heritability of 53%. We performed a genomewide association study (GWAS) using FAST-LMM, which corrects for population structure, and identified loci significantly associated with PD. We examined candidate genes at a locus on chromosome 5, which suggested a relationship between LPS-induced bone loss and, together with expression data, identified Cxcl family members as associated with PD. We observed an increase in Cxcl10 protein, as well as immune cells and pro-inflammatory cytokines in C57BL/6J (high bone loss strain) but not in A/J (low bone loss strain) after LPS injections. Genetic deletion of CXCR3 (Cxcl9 and10 receptor) demonstrated a ∼50% reduction in bone loss and reduced osteoclasts after LPS injections. Furthermore, WT mice treated with AMG-487 (a CXCR3 antagonist) showed a ∼45% reduction in bone loss and decreased osteoclasts after LPS injections. We conclude that CXCR3 is a strong candidate for modulating the host response in individuals susceptible to PD. © 2018 American Society for Bone and Mineral Research.

A Chemically Modified Curcumin (CMC 2.24) Inhibits Nuclear Factor κB Activation and Inflammatory Bone Loss in Murine Models of LPS-Induced Experimental Periodontitis and Diabetes-Associated Natural Periodontitis

The purpose of this study was to assess the effect of a novel chemically modified curcumin (CMC 2.24) on NF-κB and MAPK signaling and inflammatory cytokine production in two experimental models of periodontal disease in rats. Experimental model I: Periodontitis was induced by repeated injections of LPS into the gingiva (3×/week, 3 weeks); control rats received vehicle injections. CMC 2.24, or the vehicle, was administered by daily oral gavage for 4 weeks. Experimental model II: Diabetes was induced in adult male rats by streptozotocin injection; periodontal breakdown then results as a complication of uncontrolled hyperglycemia. Non-diabetic rats served as controls. CMC 2.24, or the vehicle, was administered by oral gavage daily for 3 weeks to the diabetics. Hemimaxillae and gingival tissues were harvested, and bone loss was assessed radiographically. Gingival tissues were pooled according to the experimental conditions and processed for the analysis of matrix metalloproteinases (MMPs) and bone-resorptive cytokines. Activation of p38 MAPK and NF-κB signaling pathways was assessed by western blot. Both LPS and diabetes induced an inflammatory process in the gingival tissues associated with excessive alveolar bone resorption and increased activation of p65 (NF-κB) and p38 MAPK. In both models, the administration of CMC 2.24 produced a marked reduction of inflammatory cytokines and MMPs in the gingival tissues, decreased bone loss, and decreased activation of p65 (NF-κB) and p38 MAPK. Inhibition of these cell signaling pathways by this novel tri-ketonic curcuminoid (natural curcumin is di-ketonic) may play a role in its therapeutic efficacy in locally and systemically associated periodontitis.

Susceptibility of different mouse strains to peri-implantitis

BACKGROUND AND OBJECTIVE

Peri-implantitis (PI) is an inflammatory condition that affects the tissues surrounding dental implants. Although the pathogenesis of PI is not fully understood, evidence suggests that the etiology is multifactorial and may include a genetic component. The aim of this study was to investigate the role of genetics in the development of peri-implantitis.

MATERIAL AND METHODS

Four-week-old C57BL/6J, C3H/HeJ and A/J male mice had their left maxillary molars extracted. Implants were placed in the healed extraction sockets. Upon osseointegration, ligatures were placed around the implant head for 1 or 4 weeks to induce PI. Micro-computed tomography scanning was used to measure volumetric bone loss. Histological analyses were also performed to evaluate collagen organization and the presence of neutrophils and osteoclasts.

RESULTS

Radiographically, comparing the ligature-treated mice, C57BL/6J displayed the greatest amount of bone loss, followed by C3H/HeJ and A/J mice at 1 and 4 weeks. Histologically, at 1 week, C57BL/6J mice presented with the highest numbers of neutrophils and osteoclasts. At 4 weeks, C57BL/6J mice presented with the most active bone remodeling compared with the other two strains.

CONCLUSION

There were significant differences in the severity of peri-implantitis among the different mouse strains, suggesting that the genetic framework can affect implant survival and success. Future work is needed to dissect the genetic contribution to the development of peri-implantitis.

Metal ions from S-PRG filler have the potential to prevent periodontal disease

The surface pre-reacted glass ionomer (S-PRG) filler, a component of composite resin, is capable of releasing metal ions that possess antibacterial activity against caries and periodontal pathogens. Although S-PRG has been suggested to be involved in oral disease prevention, no reports have been published regarding its preventive effect on periodontal disease in vivo. The present study investigated whether the eluate from S-PRG (S-PRG eluate) has a suppressive effect on tissue destruction induced in a mouse model of ligature-induced periodontal disease. Twenty-seven C57BL/6 mice were divided into three groups of nine animals each, no ligature group (Lig(-)), ligature group (Lig(+)S-PRG(-)) and ligature with S-PRG eluate group (Lig(+)S-PRG(+)). Alveolar bone loss was evaluated using micro-computed tomography scanning. Histologic changes were detected by hematoxylin and eosin staining. The infiltration of inflammatory cells was assessed by Ly6G and F4/80 staining immunohistochemically. The distribution of metal ions was detected by time-of-flight secondary ion mass spectrometry. S-PRG eluate clearly inhibited alveolar bone loss and bone density. The histological analysis revealed that S-PRG eluate reduced destruction of the collagen bundle in the periodontal ligament and the infiltration of inflammatory cells. Immunohistochemical analysis showed that the S-PRG eluate significantly suppressed the number of infiltrating neutrophils and macrophages. Time-of-flight secondary ion mass spectrometry analysis revealed that more boron ions were present in the Lig(+)S-PRG(+) group than in the Lig(+)S-PRG(-) group. Our results suggest that the S-PRG eluate has a preventive effect against tissue destruction in periodontal disease through its anti-inflammatory effects in vivo.

Production of Osteoclasts for Studying Protein Tyrosine Phosphatase Signaling

Osteoclasts, specialized cells that degrade bone, are key components of the cellular system that regulates and maintains bone homeostasis. Aberrant function of osteoclasts can lead to pathological loss or gain of bone mass, such as in osteopetrosis, osteoporosis, and several types of cancer that metastasize to bone. Phosphorylation of osteoclast proteins on tyrosine residues is critical for formation of osteoclasts and for their proper function and responses to physiological signals. Here we describe preparation and growth of osteoclasts from bone marrow of mice, use of viral vectors to downregulate expression of endogenous proteins and to express exogenous proteins in osteoclasts, and analysis of signaling processes triggered by M-CSF, estrogen, and physical contact with matrix in these cells.

Sex-based differential regulation of bacterial-induced bone resorption

BACKGROUND AND OBJECTIVE

Periodontal disease pathogenesis is comprised of the complex inflammatory immune response to oral bacterial dysbiosis. Like other inflammatory diseases, there is sexual dimorphism evident in periodontal diseases. During periodontitis, inflammatory chemokines direct neutrophils to migrate to the site of infection to neutralize the pathogen. Interestingly, these same chemokines are also involved in regulating pathogen-induced osteoclast formation. Previous reports show differences in bone turnover and lymphocyte recruitment between sexes. We hypothesize that chemokine expression is differentially regulated by sex and thus results in differential osteoclast formation.

MATERIAL AND METHODS

Male and female mice were utilized to isolate neutrophils based on expression of Ly6G-specific, as well as defined osteoclast progenitors. Cells were stimulated with lipopolysaccharide (LPS; 100 ng/mL) then analyzed for neutrophil infiltration and gene expression. Defined osteoclast progenitors were primed: macrophage-colony stimulating factor (25 ng/mL), receptor activator of NF-κB ligand (50 ng/mL), then stimulated with LPS. Osteoclasts were enumerated via TRAP stain and mRNA isolated for gene expression analysis via quantitative polymerase chain reaction.

RESULTS

In response to LPS, male neutrophils in vitro respond with increased chemokine expression and significantly more osteoclast formed in response to LPS compared to females.

CONCLUSIONS

Findings support observations in humans regarding a sexual dimorphism in oral bacterial infections of alveolar bone loss. Males have a strong inflammatory response to bacterial infection, resulting in increased inflammatory microenvironment, reduced pathogenic bacteria clearance and increased osteoclast-driven bone loss in response to differential expression of key chemokines.

Mitogen-activated protein kinase phosphatase-1: function and regulation in bone and related tissues

In this review, we have highlighted work that has clearly demonstrated that mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1), a negative regulator of MAPKs, is an important signaling mediator in bone, muscle, and fat tissue homeostasis and differentiation. Further, we examined recent studies with particular focus on MKP-1 overexpression or deletion and its impact on tissues connected to bone. We also summarized regulation of MKP-1 by known skeletal regulators like parathyroid hormone (PTH)/PTH-related peptide (PTHrP) and bone morphogenic proteins. MKP-1's integration into the pathophysiological state of osteoporosis, osteoarthritis, rheumatoid arthritis, obesity, and muscular dystrophy are examined to emphasize possible involvement of MKP-1 both at the molecular level and in disease complications such as sarcopenia- or diabetes-related osteoporosis. We predict that understanding the mechanism of MKP-1-mediated signaling in bone-muscle-fat crosstalk will be a key in coordinating their activities and developing therapeutics to improve clinical outcomes for diseases associated with advanced age.

Role of indoleamine 2,3-dioxygenase in an inflammatory model of murine gingiva

BACKGROUND AND OBJECTIVE

Indoleamine 2,3-dioxygenase (IDO) is one of the major pathways for metabolism of tryptophan in a variety of cells, including immune cells. Increasing evidence indicates that IDO is a critical player in establishing the balance between immunity and tolerance and ultimately in the maintenance of homeostasis. By inducing inflammation in gingival tissue, we tested the hypothesis that IDO is a pivotal player in regulating the immune and inflammatory responses of gingiva.

MATERIAL AND METHODS

We utilized the IDO knockout mouse model in conjunction with lipopolysaccharide (LPS)-induced inflammation. Accordingly, wild-type and IDO knockout mice were injected with LPS or vehicle in the anterior mandibular gingiva, twice over a 2-wk period, which was followed by procurement of gingival tissue for histopathology and preparation of tissue for flow cytometry-based studies.

RESULTS

Clinical and histological examinations revealed a marked adverse impact of IDO deficiency on gingival inflammation. These observations were consistent with a more marked increase in the number of cells positive for the proinflammatory cytokine interleukin (IL)-17, but no significant change in the number of cells positive for the anti-inflammatory cytokine IL-10, in LPS-treated IDO knockout mice. Consistent with the more marked proinflammatory impact of IDO deficiency, the percentage of regulatory T cells was much reduced in gingival tissue of LPS-treated IDO knockout mice than in gingival tissue of wild-type mice. These proinflammatory changes were accompanied with a prominent increase in apoptotic and necrotic cell death in gingival tissue of IDO knockout mice compared with wild-type mice.

CONCLUSION

Collectively, our findings support a major role for IDO in the development of gingival inflammation, as an example of an inflammatory condition, and lay the foundation for subsequent studies to explore it as a novel immunotherapy target.

Alveolar bone loss: mechanisms, potential therapeutic targets, and interventions

This article reviews recent research into mechanisms underlying bone resorption and highlights avenues of investigation that may generate new therapies to combat alveolar bone loss in periodontitis. Several proteins, signaling pathways, stem cells, and dietary supplements are discussed as they relate to periodontal bone loss and regeneration. RGS12 is a crucial protein that mediates osteoclastogenesis and bone destruction, and a potential therapeutic target. RGS12 likely regulates osteoclast differentiation through regulating calcium influx to control the calcium oscillation-NFATc1 pathway. A working model for RGS10 and RGS12 in the regulation of Ca(2+) oscillations during osteoclast differentiation is proposed. Initiation of inflammation depends on host cell-microbe interactions, including the p38 mitogen-activated protein kinase (MAPK) signaling pathway. Oral p38 inhibitors reduced lipopolysaccharide (LPS)-induced bone destruction in a rat periodontitis model but showed unsatisfactory safety profiles. The p38 substrate MK2 is a more specific therapeutic target with potentially superior tolerability. Furthermore, MKP-1 shows anti-inflammatory activity, reducing inflammatory cytokine biosynthesis and bone resorption. Multipotent skeletal stem cell (SSC) populations exist within the bone marrow and periosteum of long bones. These bone-marrow-derived SSCs and periosteum-derived SSCs have shown therapeutic potential in several applications, including bone and periodontal regeneration. The existence of craniofacial bone-specific SSCs is suggested based on existing studies. The effects of calcium, vitamin D, and soy isoflavone supplementation on alveolar and skeletal bone loss in post-menopausal women were investigated. Supplementation resulted in stabilization of forearm bone mass density and a reduced rate of alveolar bone loss over 1 yr, compared with placebo. Periodontal attachment levels were also well-maintained and alveolar bone loss suppressed during 24 wk of supplementation.

Deletion of Dual Specificity Phosphatase 1 Does Not Predispose Mice to Increased Spontaneous Osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a degenerative joint disease with poorly understood etiology and pathobiology. Mitogen activated protein kinases (MAPKs) including ERK and p38 play important roles in the mediation of downstream pathways involved in cartilage degenerative processes. Dual specificity phosphatase 1 (DUSP1) dephosphorylates the threonine/serine and tyrosine sites on ERK and p38, causing deactivation of downstream signalling. In this study we examined the role of DUSP1 in spontaneous OA development at 21 months of age using a genetically modified mouse model deficient in Dusp1 (DUSP1 knockout mouse).

RESULTS

Utilizing histochemical stains of paraffin embedded knee joint sections in DUSP1 knockout and wild type female and male mice, we showed similar structural progression of cartilage degeneration associated with OA at 21 months of age. A semi-quantitative cartilage degeneration scoring system also demonstrated similar scores in the various aspects of the knee joint articular cartilage in DUSP1 knockout and control mice. Examination of overall articular cartilage thickness in the knee joint demonstrated similar results between DUSP1 knockout and wild type mice. Immunostaining for cartilage neoepitopes DIPEN, TEGE and C1,2C was similar in the cartilage lesion sites and chondrocyte pericellular matrix of both experimental groups. Likewise, immunostaining for phosphoERK and MMP13 showed similar intensity and localization between groups. SOX9 immunostaining demonstrated a decreased number of positive cells in DUSP1 knockout mice, with correspondingly decreased staining intensity. Analysis of animal walking patterns (gait) did not show a discernable difference between groups.

CONCLUSION

Loss of DUSP1 does not cause changes in cartilage degeneration and gait in a mouse model of spontaneous OA at 21 months of age. Altered staining was observed in SOX9 immunostaining which may prove promising for future studies examining the role of DUSPs in cartilage and OA, as well as models of post-traumatic OA.

Expression Profiles of TGF-β and TLR Pathways in Porphyromonas gingivalis and Prevotella intermedia Challenged Osteoblasts

BACKGROUND

The presence of certain oral pathogens at implant sites can hinder the osseointegration process. However, it is unclear how and by what microorganisms it happens.

OBJECTIVES

This study investigated whether the presence of oral pathogens of Porphyromonas gingivalis and Prevotella intermedia individually, play a role in the failure of bone formation by determining the expression profiles of Transforming Growth Factor Beta (TGF-β/Bone Morphogenic Protein (BMP) and Toll-Like Receptor (TLR) pathways in challenged osteoblasts.

MATERIALS AND METHODS

Cell viability of P. gingivalis and P. intermedia challenged osteoblasts were determined by WST assay. Changes in osteoblast morphology and inhibition of mineralization were observed by Scanning Electron Microscopy (SEM) and Von Kossa staining, respectively. Expression of TGF-β and TLR pathway genes on challenged cells were identified by RT profiler array. Both P. gingivalis and P. intermedia challenges resulted in reduced viability and mineralization of osteoblasts.

RESULTS

Viability was reduced to 56.8% (P. gingivalis) and 52.75% (P. intermedia) at 1000 multiplicity. Amongst 48 genes examined, expressions of BMPER, SMAD1, IL8 and NFRKB were found to be highly upregulated by both bacterial challenges (Fold Change > 4).

CONCLUSIONS

P. gingivalis and P. intermedia could play a role in implant failure by changing the expression profiles of genes related to bone formation and resorption.

Dual-Specificity Phosphatase 1 and Tristetraprolin Cooperate To Regulate Macrophage Responses to Lipopolysaccharide

Dual-specificity phosphatase (DUSP) 1 dephosphorylates and inactivates members of the MAPK superfamily, in particular, JNKs, p38α, and p38β MAPKs. It functions as an essential negative regulator of innate immune responses, hence disruption of the Dusp1 gene renders mice extremely sensitive to a wide variety of experimental inflammatory challenges. The principal mechanisms behind the overexpression of inflammatory mediators by Dusp1(-/-) cells are not known. In this study, we use a genetic approach to identify an important mechanism of action of DUSP1, involving the modulation of the activity of the mRNA-destabilizing protein tristetraprolin. This mechanism is key to the control of essential early mediators of inflammation, TNF, CXCL1, and CXCL2, as well as the anti-inflammatory cytokine IL-10. The same mechanism also contributes to the regulation of a large number of transcripts induced by treatment of macrophages with LPS. These findings demonstrate that modulation of the phosphorylation status of tristetraprolin is an important physiological mechanism by which innate immune responses can be controlled.

Licochalcone F alleviates glucose tolerance and chronic inflammation in diet-induced obese mice through Akt and p38 MAPK

BACKGROUND & AIMS

Licochalcone (lico) F is a novel synthetic retrochalcone. In this study, we investigated the anti-inflammatory effects of lico F in vitro, and its effects on obesity-induced chronic inflammation, glucose intolerance, and fatty liver in vivo.

METHODS

The inhibitory effects of lico F on TNFα-induced inflammation were investigated using NF-κB luciferase reporter assay and RT-PCR. Diet-induced obese mice were treated orally, once per day, with vehicle or lico F (10 mg/kg/day), for 3 weeks, and blood, liver, and adipose tissues were analyzed.

RESULTS

Lico F inhibited TNFα-induced NF-κB activation and mRNA expression of TNFα, COX-2, IL-6, IL-1β, and NOS2. In obese mice, lico F administration significantly alleviated glucose tolerance without changes in body weight gain and food intake. Lico F reduced adipocyte size and macrophage infiltration into white adipose tissue and improved hepatic lesions, by decreasing fat droplets and glycogen deposition. The mRNA expression levels of TNFα, MCP-1, and CD68 in white adipose tissue also decreased markedly. Moreover, lico F enhanced Akt signaling, but reduced p38 MAPK signaling in white adipose tissue.

CONCLUSIONS

Lico F had anti-inflammatory effects and showed beneficial effects on glucose metabolism, which could be partially caused by activation of the Akt signal pathway and obesity-induced chronic inflammation, probably by downregulating p38 signal pathway. Moreover, lico F could be used as a potential novel therapeutic compound against type 2 diabetes and obesity-induced chronic inflammation without the deleterious effects of body weight gain and fatty liver.

Heritability of periodontal bone loss in mice

BACKGROUND

Periodontitis is an inflammatory disease of the periodontal tissues that compromises tooth support and can lead to tooth loss. Although bacterial biofilm is central in disease pathogenesis, the host response plays an important role in the progression and severity of periodontitis. Indeed, clinical genetic studies indicate that periodontitis is 50% heritable. In this study, we hypothesized that lipopolysaccharide (LPS) injections lead to a strain-dependent periodontal bone loss pattern.

MATERIAL AND METHODS

We utilized five inbred mouse strains that derive the recombinant strains of the hybrid mouse diversity panel. Mice received Porphyromonas gingivalis-LPS injections for 6 wk.

RESULTS AND CONCLUSION

Micro-computed tomography analysis demonstrated a statistically significant strain-dependent bone loss. The most susceptible strain, C57BL/6J, had a fivefold higher LPS-induced bone loss compared to the most resistant strain, A/J. More importantly, periodontal bone loss revealed 49% heritability, which closely mimics periodontitis heritability for patients. To evaluate further the functional differences that underlie periodontal bone loss, osteoclast numbers of C57BL/6J and A/J mice were measured in vivo and in vitro. In vitro analysis of osteoclastogenic potential showed a higher number of osteoclasts in C57BL/6J compared to A/J mice. In vivo LPS injections statistically significantly increased osteoclast numbers in both groups. Importantly, the number of osteoclasts was higher in C57BL/6J vs. A/J mice. These data support a significant role of the genetic framework in LPS-induced periodontal bone loss and the feasibility of utilizing the hybrid mouse diversity panel to determine the genetic factors that affect periodontal bone loss. Expanding these studies will contribute in predicting patients genetically predisposed to periodontitis and in identifying the biological basis of disease susceptibility.

DUSP1 phosphatase regulates the proinflammatory milieu in head and neck squamous cell carcinoma

DUSP1 is a dual-specificity phosphatase that regulates mitogen-activated protein (MAP) kinase activity. Studies have associated loss of DUSP1 expression with certain cancers, but there has been no report of a mechanism by which this supports tumor progression. In this study, we found DUSP1 mRNA and protein decreased in human head and neck squamous cell carcinoma tissues compared with adjacent nontumor controls. To evaluate the impact of this difference, we compared the susceptibility of Dusp1-deficient mice with oral squamous carcinogenesis induced by 4-nitroquinoline 1-oxide. Dusp1-deficient mice displayed enhanced disease progression, characterized by advanced onset, histologic stage, and tumor burden. In a syngeneic model of tumor progression, subcutaneous injection of EO771 cells formed faster-growing tumors in Dusp1-deficient mice, an effect abrogated by inhibition of p38 MAP kinase with SB203580. Histologic and quantitative assessments demonstrated increased inflammation and deregulated chemokine and cytokine expression in Dusp1-deficient tumor tissues. Specifically, proinflammatory cytokine IL1β was elevated. IL1β production was recapitulated ex vivo in primary bone marrow-derived macrophages from Dusp1-deficient mice. Together, our results clearly establish the role of Dusp1 as a tumor suppressor gene that regulates cancer-associated inflammation.

Critical role of MKP-1 in lipopolysaccharide-induced osteoclast formation through CXCL1 and CXCL2

Osteoclast (OC) progenitors (OCP) have been defined in the bone marrow (BM) as CD3(-)CD45R(B220)(-)GR1(-)CD11b(lo/)(-)CD115(+) (dOCP) and more recently in the peripheral blood (PB) as Lym(-)Ly6G(-)CD11b(+)Ly6C(+). These progenitors respond to stimuli, including LPS from periopathogenic Aggregatibacter actinomycetemcomitans, activating MAPK signaling, resulting in cytokine/chemokine-mediated osteoclastogenesis. Intracellular negative signaling pathways, including MAPK phosphatase-1 (MKP-1, gene Dusp1) deactivate MAPK pathways (p-p38 and p-JNK) and reduce inflammatory cytokines/chemokines.

OBJECTIVE

To delineate the role of MKP-1 in chemokine-mediated OC formation using defined OC progenitor populations. Given its role in innate immune inflammatory signaling, we hypothesize that MKP-1 regulates LPS-induced OC formation from BM OCP through deregulated chemokines.

METHODS

BM and PB from WT and Dusp1(-/-) female mice (8-12weeks) was obtained and sorted into defined progenitor populations. BM sorted dOCP were primed with MCSF and RANKL (48h), blocked with vehicle or chemokine blocking antibodies and stimulated with LPS (48-96h). TRAP assay and OC activity were measured for OC formation and activity following treatments. NanoString Array and qPCR were utilized for gene expression analysis.

RESULTS

Dusp1(-/-) dOCPs formed more and larger osteoclasts from CD11b(hi) and dOCP compared to matched WT (P<0.05 each). PB-derived dOCP produced larger and more functional osteoclasts from Dusp1(-/-) mice compared to WT controls. NanoString array data revealed significant deregulation in chemokine expression from Dusp1(-/-) versus WT cells. qPCR validation of target genes revealed that Dusp1 deficient CD11b(+) populations display 1.5-3.5-fold greater expression of CXCL1 and 2-3-fold greater expression of CXCL2 compared to WT in CD11b(hi) and dOCP (P<0.05 each). Antibody blocking studies using anti-CXCL1 and CXCL2 antibodies blunted osteoclastogenesis in Dusp1(-/-) cells.

CONCLUSION

MKP-1 negatively regulates chemokine-driven OC formation and subsequent bone resorption in response to LPS stimulation. Collectively, these data provide useful insight into mechanisms potentially leading to the development of therapeutic treatment of periodontal disease.

A Murine Model of Lipopolysaccharide-Induced Peri-Implant Mucositis and Peri-Implantitis

Dental implants are a widely used treatment option for tooth replacement. However, they are susceptible to inflammatory diseases such as peri-implant mucositis and peri-implantitis, which are highly prevalent and may lead to implant loss. Unfortunately, the understanding of the pathogenesis of peri-implant mucositis and peri-implantitis is fragmented and incomplete. Therefore, the availability of a reproducible animal model to study these inflammatory diseases would facilitate the dissection of their pathogenic mechanisms. The objective of this study is to propose a murine model of experimental peri-implant mucositis and peri-implantitis. Screw-shaped titanium implants were placed in the upper healed edentulous alveolar ridges of C57BL/6J mice 8 weeks after tooth extraction. Following 4 weeks of osseointegration, Porphyromonas gingivalis -lipolysaccharide (LPS) injections were delivered to the peri-implant soft tissues for 6 weeks. No-injections and vehicle injections were utilized as controls. Peri-implant mucositis and peri-implantitis were assessed clinically, radiographically (microcomputerized tomograph [CT]), and histologically following LPS-treatment. LPS-injections resulted in a significant increase in soft tissue edema around the head of the implants as compared to the control groups. Micro-CT analysis revealed significantly greater bone loss in the LPS-treated implants. Histological analysis of the specimens demonstrated that the LPS-group had increased soft tissue vascularity, which harbored a dense mixed inflammatory cell infiltrate, and the bone exhibited noticeable osteoclast activity. The induction of peri-implant mucositis and peri-implantitis in mice via localized delivery of bacterial LPS has been demonstrated. We anticipate that this model will contribute to the development of more effective preventive and therapeutic approaches for these 2 conditions.

Protein tyrosine phosphatases ε and α perform nonredundant roles in osteoclasts

The closely related tyrosine phosphatases PTPa and PTPe fulfill distinct roles in osteoclasts. The various effects of each PTP on podosome organization in osteoclasts are caused by their distinct N-termini. The function of PTPe in these cells requires the presence of its 12 N-terminal residues, in particular serine 2.

Female mice lacking protein tyrosine phosphatase ε (PTP ε) are mildly osteopetrotic. Osteoclasts from these mice resorb bone matrix poorly, and the structure, stability, and cellular organization of their podosomal adhesion structures are abnormal. Here we compare the role of PTP ε with that of the closely related PTP α in osteoclasts. We show that bone mass and bone production and resorption, as well as production, structure, function, and podosome organization of osteoclasts, are unchanged in mice lacking PTP α. The varying effects of either PTP on podosome organization in osteoclasts are caused by their distinct N-termini. Osteoclasts express the receptor-type PTP α (RPTPa), which is absent from podosomes, and the nonreceptor form of PTP ε (cyt-PTPe), which is present in these structures. The presence of the unique 12 N-terminal residues of cyt-PTPe is essential for podosome regulation; attaching this sequence to the catalytic domains of PTP α enables them to function in osteoclasts. Serine 2 within this sequence regulates cyt-PTPe activity and its effects on podosomes. We conclude that PTPs α and ε play distinct roles in osteoclasts and that the N-terminus of cyt-PTPe, in particular serine 2, is critical for its function in these cells.

MKP-1 signaling events are required for early osteoclastogenesis in lineage defined progenitor populations by disrupting RANKL-induced NFATc1 nuclear translocation

Cytokine-directed osteoclastogenesis is initiated in response to macrophage colony stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL) to drive formation of osteoclasts (OC), large bone resorptive cells of hematopoietic origin. RANKL-induced signaling activates the MAPK pathways, which initiates nuclear translocation of the master regulator of osteoclast formation, transcription factor NFATc1. Proper control over these signaling events is essential to normal OC formation response to stimuli. MAPK phosphatase 1 (MKP-1), a serine and tyrosine phosphatase encoded by the gene Dusp1, functions to dephosphorylate and subsequently inactivate MAPK (p38 and JNK) signaling essential in osteoclastogenesis. Here, we explored the role of MKP-1 during RANKL-driven osteoclastogenesis from defined (B220/CD45(-)GR1(-)CD11b(lo/-)CD115(+)) OC progenitor (dOCP) populations using WT and Dusp1(-/-) global knockout mice. Sorted cells were driven to OC by M-CSF pre-treatment followed by RANKL stimulation for 3days. OC formation and qPCR products were analyzed for maturation. Results indicate that Dusp1(-/-) dOCP form less numerous, significantly smaller and less functional OC compared to WT controls. These data were corroborated by mRNA expression of the key OC genes, Nfatc1 and Tm7sf4 (DC-STAMP), which were significantly reduced in early osteoclastogenesis in OC progenitor from Dusp1(-/-) mice. Intriguingly, our data reveals that MKP-1 may positively control OC formation in response to RANKL by regulating NFATc1 nuclear translocation. Collectively, this report supports the idea that MKP-1 signaling is essential in early osteoclastogenesis in response to RANKL-induced signaling.

Mitogen-activated protein kinase phosphatase 1 as an inflammatory factor and drug target

Mitogen-activated protein kinases (MAPKs) are signaling proteins that are activated through phosphorylation, and they regulate many physiological and pathophysiological processes in cells. Mitogen-activated protein kinase phosphatase 1 (MKP-1) is an inducible nuclear phosphatase that dephosphorylates MAPKs, and thus, it is a negative feedback regulator of MAPK activity. MKP-1 has been found as a key endogenous suppressor of innate immune responses, as well as a regulator of the onset and course of adaptive immune responses. Altered MKP-1 signaling is implicated in chronic inflammatory diseases in man. Interestingly, MKP-1 expression and protein function have been found to be regulated by certain anti-inflammatory drugs, namely by glucocorticoids, antirheumatic gold compounds and PDE4 inhibitors, and MKP-1 has been shown to mediate many of their anti-inflammatory effects. In this Mini Review, we summarize the effect of MKP-1 in the regulation of innate and adaptive immune responses and its role as a potential anti-inflammatory drug target and review recent findings concerning the role of MKP-1 in certain anti-inflammatory drug effects.

The effect of orally administered epigallocatechin-3-gallate on ligature-induced periodontitis in rats

BACKGROUND AND OBJECTIVE

Epigallocatechin-3-gallate (EGCG) is known for its beneficial properties, including anti-inflammatory and anti-oxidative activities. Recently, reports have suggested that EGCG plays a pivotal role in regulating cytokine expression and osteoclastic activity. In the present study, we investigated whether orally administered EGCG has a therapeutic effect on ligature-induced periodontitis.

MATERIALS AND METHODS

Forty-eight Sprague-Dawley rats were treated with EGCG or phosphate-buffered saline. Periodontitis was induced by tying a ligature for 7 d. After removing ligation, EGCG (200 mg/kg) or phosphate-buffered saline was administered via oral gavage on a daily basis. Rats were killed after 1, 2 and 4 wk of administration. Histologic and histomorphometric analyses, tartrate resistant acid phosphatase staining and immunohistochemistry were carried out.

RESULTS

In the control group, bone loss did not recover even after the causative factor of periodontitis was eliminated. On the other hand, distance from cemento-enamel junction to alveolar bone crest, long junctional epithelium and collagen destruction were reduced in the EGCG group. Decreased interleukin (IL)-6 expression was shown from the early stage of EGCG administration, followed by reduced tumor necrosis factor (TNF) expression at week 4 EGCG group. The CT area showed a higher decrease of IL-6 expression between the control and EGCG group than alveolar bone area. Downregulation of TNF and IL-6 expression led to a decrease in osteoclast number and activity, which resulted in reduced bone loss.

CONCLUSIONS

Systemic administration of EGCG could have a therapeutic effect on damaged periodontal tissue. Inhibited cytokine expression, including TNF and IL-6 is responsible for the reduction in osteoclast formation, osteoclastic activity and collagen destruction.

New insights into the anti-inflammatory mechanisms of glucocorticoids: an emerging role for glucocorticoid-receptor-mediated transactivation

Glucocorticoids are anti-inflammatory drugs that are widely used for the treatment of numerous (autoimmune) inflammatory diseases. They exert their actions by binding to the glucocorticoid receptor (GR), a member of the nuclear receptor family of transcription factors. Upon ligand binding, the GR translocates to the nucleus, where it acts either as a homodimeric transcription factor that binds glucocorticoid response elements (GREs) in promoter regions of glucocorticoid (GC)-inducible genes, or as a monomeric protein that cooperates with other transcription factors to affect transcription. For decades, it has generally been believed that the undesirable side effects of GC therapy are induced by dimer-mediated transactivation, whereas its beneficial anti-inflammatory effects are mainly due to the monomer-mediated transrepressive actions of GR. Therefore, current research is focused on the development of dissociated compounds that exert only the GR monomer-dependent actions. However, many recent reports undermine this dogma by clearly showing that GR dimer-dependent transactivation is essential in the anti-inflammatory activities of GR. Many of these studies used GR(dim/dim) mutant mice, which show reduced GR dimerization and hence cannot control inflammation in several disease models. Here, we review the importance of GR dimers in the anti-inflammatory actions of GCs/GR, and hence we question the central dogma. We summarize the contribution of various GR dimer-inducible anti-inflammatory genes and question the use of selective GR agonists as therapeutic agents.

Kaposi's sarcoma-associated herpesvirus suppression of DUSP1 facilitates cellular pathogenesis following de novo infection

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi's sarcoma (KS), and KSHV activation of mitogen-activated protein kinases (MAPKs) initiates a number of key pathogenic determinants of KS. Direct inhibition of signal transduction as a therapeutic approach presents several challenges, and a better understanding of KSHV-induced mechanisms regulating MAPK activation may facilitate the development of new treatment or prevention strategies for KS. MAPK phosphatases, including dual-specificity phosphatase-1 (DUSP1), negatively regulate signal transduction and cytokine activation through MAPK dephosphorylation or interference with effector molecule binding to MAPKs, including the extracellular signal-regulated kinase (ERK). We found that ERK-dependent latent viral gene expression, the induction of promigratory factors, and cell invasiveness following de novo infection of primary human endothelial cells are in part dependent on KSHV suppression of DUSP1 expression during de novo infection. KSHV-encoded miR-K12-11 upregulates the expression of xCT (an amino acid transporter and KSHV fusion/entry receptor), and existing data indicate a role for xCT in the regulation of 14-3-3β, a transcriptional repressor of DUSP1. We found that miR-K12-11 induces endothelial cell secretion of promigratory factors and cell invasiveness through upregulation of xCT-dependent, 14-3-3β-mediated suppression of DUSP1. Finally, proof-of-principle experiments revealed that pharmacologic upregulation of DUSP1 inhibits the induction of promigratory factors and cell invasiveness during de novo KSHV infection. These data reveal an indirect role for miR-K12-11 in the regulation of DUSP1 and downstream pathogenesis.

Dual-specificity phosphatase 1-null mice exhibit spontaneous osteolytic disease and enhanced inflammatory osteolysis in experimental arthritis

OBJECTIVE

Bone formation and destruction are usually tightly linked; however, in disorders such as rheumatoid arthritis, periodontal disease, and osteoporosis, elevated osteoclast activity leads to bone destruction. Osteoclast formation and activation are controlled by many signaling pathways, including p38 MAPK. Dual-specificity phosphatase 1 (DUSP-1) is a factor involved in the negative regulation of p38 MAPK. The purpose of this study was to examine the effect of Dusp1 deficiency on bone destruction.

METHODS

Penetrance, onset, and severity of collagen-induced arthritis were recorded in DUSP-1+/+ and DUSP-1-/- mice. Bone destruction was assessed by histologic and micro-computed tomographic examination of the joints. The in vitro formation and activation of osteoclasts from DUSP-1+/+ and DUSP-1-/- precursors were assessed in the absence or presence of tumor necrosis factor (TNF).

RESULTS

The formation and activation of osteoclasts in vitro in the presence of TNF were enhanced by Dusp1 gene disruption. DUSP-1-/- mice exhibited higher penetrance, earlier onset, and increased severity of experimental arthritis, accompanied by greater numbers of osteoclasts in inflamed joints and more extensive loss of bone. A DUSP-1-/- mouse colony of mixed genetic background also demonstrated striking spontaneous osteolytic destruction of distal phalanges.

CONCLUSION

DUSP-1 is a critical regulator of osteoclast activity and limits bone destruction in an experimental model of rheumatoid arthritis. Defects in the expression or activity of DUSP1 in humans may correlate with a propensity to develop osteolytic lesions in arthritis.

MKP-1 is essential for canonical vitamin D-induced signaling through nuclear import and regulates RANKL expression and function

Vitamin D(3,) and its most active form, 1,25(OH)(2)D(3), are well known to stimulate osteoclastogenesis through stromal cell induction of the receptor activator of nuclear factor-κB ligand (RANKL). MAPK phosphatase-1 (MKP-1) is a phosphatase classically known to negatively regulate the innate immune response through dephosphorylation of p38, ERK, and c-Jun N-terminal kinase activity. This paper describes a new function of MKP-1 in permitting genomic 1,25(OH)(2)D(3) signaling and downstream osteoclastogenesis through RANKL. Initially, quantitative RT-PCR (qRT-PCR) and immunoblot analysis comparing bone marrow stromal cells (BMSC) revealed that 1,25(OH)(2)D(3)-induced vitamin D receptor (VDR), cytochrome P 45024a1, and RANKL mRNA expression and protein were significantly attenuated or absent in MKP-1(-/-) BMSC. Immunoblot analysis from cellular fractions of wild type and MKP-1(-/-) BMSC stimulated with 10(-7) m 1,25(OH)(2)D(3) revealed retinoid X receptor (RXR)α nuclear import was impaired in MKP-1(-/-) BMSC, whereas VDR import was not. Proximity ligation assays revealed that baseline VDR-RXRα heterodimer translocation was unchanged, yet 1,25(OH)(2)D(3)-induced nuclear translocation of VDR-RXRα heterodimers was reduced in MKP-1(-/-) BMSC. A functional consequence was observed as BMSC from MKP-1(-/-) mice treated with 1,25(OH)(2)D(3) and cocultured with RAW 264.7 cells had a 91% decrease in osteoclastogenesis and a 94.5% decrease in mineralized matrix resorption compared with wild-type cocultures (P < 0.01). These results reveal an unexpected, permissive role for MKP-1 in canonical 1,25(OH)(2)D(3) signaling via VDR-RXRα heterodimer nuclear import and downstream osteoclastogenesis through stromal cell RANKL expression.

Sustained mitogen-activated protein kinase activation with Aggregatibacter actinomycetemcomitans causes inflammatory bone loss

Aggregatibacter actinomycetemcomitans is a gram-negative facultative capnophile involved in pathogenesis of aggressive forms of periodontal disease. In the present study, we interrogated the ability of A. actinomycetemcomitans to stimulate innate immune signaling and cytokine production and established that A. actinomycetemcomitans causes bone loss in a novel rat calvarial model. In vitro studies indicated that A. actinomycetemcomitans stimulated considerable production of soluble cytokines, tumor necrosis factor-α, interleukin-6 and interleukin-10 in both primary bone marrow-derived macrophages and NR8383 macrophages. Immunoblot analysis indicated that A. actinomycetemcomitans exhibits sustained activation of all major mitogen-activated protein kinase (MAPK) pathways, as well as the negative regulator of MAPK signaling, MAPK phosphatase-1 (MKP-1), for at least 8 h. In a rat calvarial model of inflammatory bone loss, high and low doses of formalin-fixed A. actinomycetemcomitans were microinjected into the supraperiosteal calvarial space for 1-2 weeks. Histological staining and micro-computed tomography of rat calvariae revealed a significant increase of inflammatory and fibroblast infiltrate and increased bone resorption as measured by total lacunar pit formation. From these data, we provide new evidence that fixed whole cell A. actinomycetemcomitans stimulation elicits a pro-inflammatory host response through sustained MAPK signaling, leading to enhanced bone resorption within the rat calvarial bone.

Diversity and specificity of the mitogen-activated protein kinase phosphatase-1 functions

The balance of protein phosphorylation is achieved through the actions of a family of protein serine/threonine kinases called the mitogen-activated protein kinases (MAPKs). The propagation of MAPK signals is attenuated through the actions of the MAPK phosphatases (MKPs). The MKPs specifically inactivate the MAPKs by direct dephosphorylation. The archetypal MKP family member, MKP-1 has garnered much of the attention amongst its ten other MKP family members. Initially viewed to play a redundant role in the control of MAPK signaling, it is now clear that MKP-1 exerts profound regulatory functions on the immune, metabolic, musculoskeletal and nervous systems. This review focuses on the physiological functions of MKP-1 that have been revealed using mouse genetic approaches. The implications from studies using MKP-1-deficient mice to uncover the role of MKP-1 in disease will be discussed.

Sexual dimorphism in periapical inflammation and bone loss from mitogen-activated protein kinase phosphatase-1 deficient mice

INTRODUCTION

Mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) has been shown to be a key negative regulator of the MAPK pathways of the innate immune system. The impact of MKP-1 in an endodontic model has yet to be studied. Thus, the purpose of this study was to determine the role of MKP-1 in a bacterial-driven model of pathologic endodontic bone loss.

METHODS

Pulps were exposed in both lower first molars of 10-week-old mkp-1(+/+) and mkp-1(-/-) mice and left open to the oral environment for either 3 or 8 weeks. At death, mandibles were harvested and scanned by micro-computed tomography (μCT) to determine periapical bone loss. Histopathologic scoring was then performed on the samples to determine the amount of inflammatory infiltrate within the periapical microenvironment.

RESULTS

Significant bone loss and inflammatory infiltrate were found in all experimental groups when compared with control. No statistical difference was found between mkp-1(+/+) and mkp-1(-/-) at either time point with respect to bone loss or inflammatory infiltrate. At 8 weeks, male mkp-1(-/-) mice were found to have significantly more bone loss and inflammatory infiltrate when compared with female mkp-1(-/-) mice. There was also a significant correlation between an increase in bone loss and increase in inflammatory infiltrate.

CONCLUSIONS

A sexual dimorphism exists in the periapical inflammatory process, where male mkp-1(-/-) mice have more inflammation than female mkp-1(-/-) mice. The increase in inflammatory infiltrate correlates to more bone loss in the male mice.

Mitogen-activated protein kinase phosphatase (MKP)-1 in immunology, physiology, and disease

Mitogen-activated protein kinases (MAPKs) are key regulators of cellular physiology and immune responses, and abnormalities in MAPKs are implicated in many diseases. MAPKs are activated by MAPK kinases through phosphorylation of the threonine and tyrosine residues in the conserved Thr-Xaa-Tyr domain, where Xaa represents amino acid residues characteristic of distinct MAPK subfamilies. Since MAPKs play a crucial role in a variety of cellular processes, a delicate regulatory network has evolved to control their activities. Over the past two decades, a group of dual specificity MAPK phosphatases (MKPs) has been identified that deactivates MAPKs. Since MAPKs can enhance MKP activities, MKPs are considered as an important feedback control mechanism that limits the MAPK cascades. This review outlines the role of MKP-1, a prototypical MKP family member, in physiology and disease. We will first discuss the basic biochemistry and regulation of MKP-1. Next, we will present the current consensus on the immunological and physiological functions of MKP-1 in infectious, inflammatory, metabolic, and nervous system diseases as revealed by studies using animal models. We will also discuss the emerging evidence implicating MKP-1 in human disorders. Finally, we will conclude with a discussion of the potential for pharmacomodulation of MKP-1 expression.

MAPK usage in periodontal disease progression

In periodontal disease, host recognition of bacterial constituents, including lipopolysaccharide (LPS), induces p38 MAPK activation and subsequent inflammatory cytokine expression, favoring osteoclastogenesis and increased net bone resorption in the local periodontal environment. In this paper, we discuss evidence that the p38/MAPK-activated protein kinase-2 (MK2) signaling axis is needed for periodontal disease progression: an orally administered p38α inhibitor reduced the progression of experimental periodontal bone loss by reducing inflammation and cytokine expression. Subsequently, the significance of p38 signaling was confirmed with RNA interference to attenuate MK2-reduced cytokine expression and LPS-induced alveolar bone loss. MAPK phosphatase-1 (MKP-1), a negative regulator of MAPK activation, was also critical for periodontal disease progression. In MPK-1-deficient mice, p38-sustained activation increased osteoclast formation and bone loss, whereas MKP-1 overexpression dampened p38 signaling and subsequent cytokine expression. Finally, overexpression of the p38/MK2 target RNA-binding tristetraprolin (TTP) decreased mRNA stability of key inflammatory cytokines at the posttranscriptional level, thereby protecting against periodontal inflammation. Collectively, these studies highlight the importance of p38 MAPK signaling in immune cytokine production and periodontal disease progression.

Enhanced alveolar bone loss in a model of non-invasive periodontitis in rice rats

OBJECTIVE

The rice rat (Oryzomys palustris) develops periodontitis-like lesions when fed a diet rich in sucrose and casein (H-SC). We aimed to establish whether this model can accurately mimic the development of human periodontitis.

MATERIALS AND METHODS

For this purpose, 28-day-old rice rats (15/group) were assigned to standard (STD) or H-SC diets and sacrificed after 6, 12, and 18 weeks. Jaws were processed for morphometric, histometric, histologic, histomorphometric, and micro-CT analyses.

RESULTS

We found a progressive increase in horizontal alveolar bone loss (ABL) with age in maxillae of rats fed the STD diet as determined by morphometry. The H-SC diet exacerbated horizontal ABL at the palatal surface at 12 and 18 weeks. Furthermore, increased vertical ABL was detected in mandibles and maxillae of rats fed the H-SC diet for 12 and/or 18 weeks by histometry and micro-CT. Remarkably, the H-SC diet significantly increased bone remodeling at the interproximal alveolar bone of mandibles from rats fed for 6 weeks, but not in those fed for longer periods.

CONCLUSIONS

These findings indicate that the H-SC diet induced a transient increase in alveolar bone remodeling, which is followed by ABL characteristic of moderate periodontitis.