A critical role for suppressors of cytokine signaling 3 in regulating LPS-induced transcriptional activation of matrix metalloproteinase-13 in osteoblasts

Toll-like Receptor 4, Osteoblasts and Leukemogenesis; the Lesson from Acute Myeloid Leukemia

Toll-like receptor 4 (TLR4) is a pattern-recognizing receptor that can bind exogenous and endogenous ligands. It is expressed by acute myeloid leukemia (AML) cells, several bone marrow stromal cells, and nonleukemic cells involved in inflammation. TLR4 can bind a wide range of endogenous ligands that are present in the bone marrow microenvironment. Furthermore, the TLR4-expressing nonleukemic bone marrow cells include various mesenchymal cells, endothelial cells, differentiated myeloid cells, and inflammatory/immunocompetent cells. Osteoblasts are important stem cell supporting cells localized to the stem cell niches, and they support the proliferation and survival of primary AML cells. These supporting effects are mediated by the bidirectional crosstalk between AML cells and supportive osteoblasts through the local cytokine network. Finally, TLR4 is also important for the defense against complicating infections in neutropenic patients, and it seems to be involved in the regulation of inflammatory and immunological reactions in patients treated with allogeneic stem cell transplantation. Thus, TLR4 has direct effects on primary AML cells, and it has indirect effects on the leukemic cells through modulation of their supporting neighboring bone marrow stromal cells (i.e., modulation of stem cell niches, regulation of angiogenesis). Furthermore, in allotransplant recipients TLR4 can modulate inflammatory and potentially antileukemic immune reactivity. The use of TLR4 targeting as an antileukemic treatment will therefore depend both on the biology of the AML cells, the biological context of the AML cells, aging effects reflected both in the AML and the stromal cells and the additional antileukemic treatment combined with HSP90 inhibition.

Anacardic acid-mediated regulation of osteoblast differentiation involves mitigation of inflammasome activation pathways

Disruption of the finely tuned osteoblast-osteoclast balance is the underlying basis of several inflammatory bone diseases, such as osteomyelitis, osteoporosis, and septic arthritis. Prolonged and unrestrained exposure to inflammatory environment results in reduction of bone mineral density by downregulating osteoblast differentiation. Earlier studies from our laboratory have identified that Anacardic acid (AA), a constituent of Cashew nut shell liquid that is used widely in traditional medicine, has potential inhibitory effect on gelatinases (MMP2 and MMP9) which are over-expressed in numerous inflammatory conditions (Omanakuttan et al. in Mol Pharmacol, 2012 and Nambiar et al. in Exp Cell Res, 2016). The study demonstrated for the first time that AA promotes osteoblast differentiation in lipopolysaccharide-treated osteosarcoma cells (MG63) by upregulating specific markers, like osteocalcin, receptor activator of NF-κB ligand, and alkaline phosphatase. Furthermore, expression of the negative regulators, such as nuclear factor-κB, matrix metalloproteinases (MMPs), namely MMP13, and MMP1, along with several inflammatory markers, such as Interleukin-1β and Nod-like receptor protein 3 were downregulated by AA. Taken together, AA expounds as a novel template for development of potential pharmacological therapeutics for inflammatory bone diseases.

The methylation status of TNF-α and SOCS3 promoters and the regulation of these gene expressions in patients with Behçet's disease

Introduction: The aim of this study was to evaluate the methylation status of TNF-α and SOCS3 promoters in patients with BD and compare them with a healthy group.Method: This was a case-control study, in which 47 subjects with BD and 61 individuals as the control participated. Blood samples were collected from all the participants. Then, PBMCs were isolated using the Ficoll method and methylation of considered sites was investigated using the qMS-PCR technique after DNA extraction by the rapid genomic DNA extraction method and its analysis with Nano-drop.Results: The methylation and expression of TNF-α showed that the methylation level significantly declined in the patient in comparison with the healthy (p < 0.05). Moreover, the results on the mean expression showed that it significantly increased in the patient group, as compared with the healthy group (p < 0.05). In addition, the expression of the SOCS3 gene was not significantly different between the patients and healthy subjects while the level of SOCS3 methylation was significantly higher in the patient group than that in the healthy group (p < 0.05).Discussion: The present study revealed that the gene expression of TNF-alpha increased in BD patients, suggesting that TNF-alpha likely has a role in the pathogenesis of BD.

Biofilm-induced profiles of immune response gene expression by oral epithelial cells

This study examined the oral epithelial immunotranscriptome response patterns modulated by oral bacterial planktonic or biofilm challenge. We assessed gene expression patterns when epithelial cells were challenged with a multispecies biofilm composed of Streptococcus gordonii, Fusobacterium nucleatum, and Porphyromonas gingivalis representing a type of periodontopathic biofilm compared to challenge with the same species of planktonic bacteria. Of the 579 human immunology genes, a substantial signal of the epithelial cells was observed to 181 genes. Biofilm challenged stimulated significant elevations compared to planktonic bacteria for IL32, IL8, CD44, B2M, TGFBI, NFKBIA, IL1B, CD59, IL1A, CCL20 representing the top 10 signals comprising 55% of the overall signal for the epithelial cell responses. Levels of PLAU, CD9, IFITM1, PLAUR, CD24, TNFSF10, and IL1RN were all elevated by each of the planktonic bacterial challenge vs the biofilm responses. While the biofilms up-regulated 123/579 genes (>2-fold), fewer genes were increased by the planktonic species (36 [S gordonii], 30 [F nucleatum], 44 [P gingivalis]). A wide array of immune genes were regulated by oral bacterial challenge of epithelial cells that would be linked to the local activity of innate and adaptive immune response components in the gingival tissues. Incorporating bacterial species into a structured biofilm dramatically altered the number and level of genes expressed. Additionally, a specific set of genes were significantly decreased with the multispecies biofilms suggesting that some epithelial cell biologic pathways are down-regulated when in contact with this type of pathogenic biofilm.

Dual micelles-loaded gelatin nanofibers and their application in lipopolysaccharide-induced periodontal disease

INTRODUCTION

Combined therapies utilizing inhibitors to remove pathogens are needed to suppress lipopolysaccharide (LPS)-induced periodontal disease. We prepared a novel, multi-agent delivery scaffold for periodontal treatment.

METHODS

In this study, we synthesized SP600125 (a JNK inhibitor) and SB203580 (a p38 inhibitor) drug-loaded poly(ethylene glycol)-block-caprolactone copolymer via dialysis method. The physical property of micelles was characterized through dynamic light scattering and transmission electron microscopy. The cell growth and LPS-induced MMP-2 and MMP-13 expression were evaluated through CCK-8, real-time PCR and Western blot assay. The release of SP600125 and SB203580 from different scaffolds was estimated. Microcomputed tomography and histology were used for evaluating the effect of the micelles-loaded nanofibers on the treatment of class II furcation defects in dogs.

RESULTS

The drug was then successfully incorporated into gelatin fibers during electrospinning process. We confirmed that the micelles had spherical structure and an average particle size of 160 nm for SP600125-micelles (SP-Ms) and 150 nm for SB203580-micelles (SB-Ms). The nanofiber scaffold showed excellent encapsulation capability, in vitro drug-release behavior, and cell compatibility. Real-time PCR and Western blot assay further indicated that LPS-induced MMP-2 and MMP-13 expression was significantly inhibited by the scaffold.

CONCLUSION

The results suggested that the dual drug-loaded system developed in this study might become a highly effective therapy for periodontal disease.

Resveratrol Suppresses Matrix Metalloproteinase-2 Activation Induced by Lipopolysaccharide in Mouse Osteoblasts via Interactions with AMP-Activated Protein Kinase and Suppressor of Cytokine Signaling 1

Porphyromonas endodontalis (P. endodontalis) lipopolysaccharide (LPS) is associated with the progression of bone resorption in periodontal and periapical diseases. Matrix metalloproteinase-2 (MMP-2) expression and activity are elevated in apical periodontitis and have been suggested to participate in bone resorption. Therefore, inhibiting MMP-2 activation may be considered a therapeutic strategy for treating apical periodontitis. Resveratrol is a natural non-flavonoid polyphenol that has been reported to have antioxidant, anti-cancer, and anti-inflammatory properties. However, the capacity of resveratrol to protect osteoblast cells from P. endodontalis LPS insults and the mechanism of its inhibitory effects on MMP-2 activation is poorly understood. Here, we demonstrate that cell viability is unchanged when 10 mg L⁻¹P. endodontalis LPS is used, and MMP-2 expression is drastically induced by P. endodontalis LPS in a concentration- and time-dependent manner. Twenty micromolar resveratrol did not reduce MC3T3-E1 cell viability. Resveratrol increased AMP-activated protein kinase (AMPK) phosphorylation, and Compound C, a specific AMPK inhibitor, partially abolished the resveratrol-mediated phosphorylation of AMPK. In addition, AMPK inhibition blocked the effects of resveratrol on MMP-2 expression and activity in LPS-induced MC3T3-E1 cells. Treatment with resveratrol also induced suppressor of cytokine signaling 1 (SOCS1) expression in MC3T3-E1 cells. SOCS1 siRNA negated the inhibitory effects of resveratrol on LPS-induced MMP-2 production. Additionally, resveratrol-induced SOCS1 upregulation was reduced by treatment with compound C. These results demonstrate that AMPK and SOCS1 activation are important signaling events during resveratrol-mediated inhibition of MMP-2 production in response to LPS in MC3T3-E1 cells, and there is crosstalk between AMPK and SOCS1 signaling.

Role of Toll-Like Receptor 4 on Osteoblast Metabolism and Function

Inflammation is a process whose main function is to fight against invading pathogens or foreign agents. Nonetheless, it is widely accepted that inflammation takes part in multiple processes in a physiological or pathophysiological context. Among these processes the inflammation has been closely related to bone metabolism. It is well-known that in systemic inflammatory diseases such as rheumatoid arthritis the inflammatory environment contributes to the reduction of the bone mineral density. This has been further evidenced in different animals models of osteoporosis where the deletion of key inflammatory molecules dramatically reduced the bone loss. On the contrary, it is also well-known that certain degree of inflammation is required to allow bone fractures healing. In fact, excessive use of anti-inflammatory drugs inhibits bone fracture consolidation. The innate immune responses (IIRs) contribute to the development and maintenance of the inflammation. These responses have been observed in cells of the musculoskeletal system. Chondrocytes and osteoblasts are equipped with the molecular repertoire necessary to setting up these IIR, including the expression of several toll-like receptors. Specifically, toll-like receptor 4 (TLR4) activation in mesenchymal stem cells, osteoblasts, and osteocytes has been involved in catabolic and anabolic process. Accordingly, in this review we have summarized the current knowledge about the physiology of TLR4, including its signaling, and its endogenous agonists. In addition we have focused on its role on osteoblast metabolism and function.

Sirtuin 1 regulates matrix metalloproteinase-13 expression induced by Porphyromonas endodontalis lipopolysaccharide via targeting nuclear factor-κB in osteoblasts

Porphyromonas endodontalis lipopolysaccharide (P.e LPS) is an important initiating factor for periapical inflammation and bone destruction. Matrix metalloproteinase-13 (MMP-13) has been shown to participate in the formation and diffusion of periapical bone lesion in chronic apical periodontitis. Sirtuin 1 (SIRT1) is a key regulator of inflammation in mammalian cells which suppresses the release of inflammatory mediators. This study aimed to explore the role of SIRT1 in regulating MMP-13 expression induced by P.e LPS in osteoblasts. P.e LPS stimulated MMP-13 expression in MC3T3-E1 cells. Knockdown of SIRT1 reinforced the increase of MMP-13mRNA expression induced by P.e LPS. SIRT1 activator resveratrol significantly reduced the expression of MMP-13 and SIRT1 inhibitor EX-527 enhanced the expression of MMP-13. Moreover, SIRT1 activation with resveratrol inhibited acetylation of NF-κB p65 and NF-κB transcriptional activity, which were enhanced by P.e LPS. In addition, NF-κB p65 was involved in P.e LPS-induced MMP-13 expression via directly binding to the MMP-13 promoter. However, SIRT1 activation significantly interfered with this binding. These findings strongly suggest that P.e LPS induces MMP-13 expression in osteoblasts, and SIRT1 suppresses this expression of MMP-13 through targeting NF-κB p65. This provides new insights into understanding the actions of SIRT1 on anti-inflammatory and anti-bone resorption activity.

Enhanced SOCS3 in osteoarthiritis may limit both proliferation and inflammation

Osteoarthritis (OA) is a degenerative joint disease that is characterized by localized inflammatory and secondary proliferative changes. Suppressor of cytokine signaling 3 (SOCS3) is elevated during OA development. We investigated the effects of this protein on human chondrocyte survival in OA and the inflammatory response together with the mechanisms of these effects. Small interfering RNA (siRNA) was used to knock down the expression of SOCS3 in interleukin(IL)-1β-induced primary human osteoarthritic chondrocytes. We found that siRNA-mediated SOCS3 knock-down in human osteoarthritic chondrocytes increased production of IL-1β-induced prostaglandin E₂, cell growth, transcript level and nuclear translocation of cyclin D1. Silencing of SOCS3 resulted in altered expression of nuclear factor-kappa-B (NF-κB) and cyclooxygenase (COX2). Our findings indicate that enhanced SOCS3 could have contradictory influences on OA development. SOCS3 might protect damaged joints by its anti-inflammatory effect and by inhibition of over-augmented cartilage tissue repair, which could exhibit inhibitory properties for joint inflammation, abnormal chondrocyte clustering and osteophyte formation in OA. On the other hand, SOCS3 might reduce chondrocyte growth response, which would delay repair of subchondral cancellous bone damage in OA owing to its anti-proliferation effect. The anti-inflammation and growth inhibition effects exhibited by enhanced SOCS3 in OA appear to be related to its capacity to down-regulate expression levels of NF-κB and COX2.

Strain differences in the attenuation of bone accrual in a young growing mouse model of insulin resistance

Skeletal fractures are considered a chronic complication of type 2 diabetes mellitus (T2DM), but the etiology of compromised bone quality that develops over time remains uncertain. This study investigated the concurrent alterations in metabolic and skeletal changes in two mouse strains, a responsive (C57BL/6) and a relatively resistant (C3H/HeJ) strain, to high-fat diet-induced glucose intolerance. Four-week-old male C57BL/6 and C3H/HeJ mice were randomized to a control (Con = 10 % kcal fat) or high-fat (HF = 60 % kcal fat) diet for 2, 8, or 16 weeks. Metabolic changes, including blood glucose, plasma insulin and leptin, and glucose tolerance were monitored over time in conjunction with alterations in bone structure and turn over. Elevated fasting glucose occurred in both the C57BL/6 and C3H/HeJ strains on the HF diet at 2 and 8 weeks, but only in the C57BL/6 strain at 16 weeks. Both strains on the HF diet demonstrated impaired glucose tolerance at each time point. The C57BL/6 mice on the HF diet exhibited lower whole-body bone mineral density (BMD) by 8 and 16 weeks, but the C3H/HeJ strain had no evidence of bone loss until 16 weeks. Analyses of bone microarchitecture revealed that trabecular bone accrual in the distal femur metaphysis was attenuated in the C57BL/6 mice on the HF diet at 8 and 16 weeks. In contrast, the C3H/HeJ mice were protected from the deleterious effects of the HF diet on trabecular bone. Alterations in gene expression from the femur revealed that several toll-like receptor (TLR)-4 targets (Atf4, Socs3, and Tlr4) were regulated by the HF diet in the C57BL/6 strain, but not in the C3H/HeJ strain. Structural changes observed only in the C57BL/6 mice were accompanied with a decrease in osteoblastogenesis after 8 and 16 weeks on the HF diet, suggesting a TLR-4-mediated mechanism in the suppression of bone formation. Both the C57BL/6 and C3H/HeJ mice demonstrated an increase in osteoclastogenesis after 8 weeks on the HF diet; however, bone turnover was decreased in the C57BL/6 with prolonged hyperglycemia. Further investigation is needed to understand how hyperglycemia and hyperinsulinemia suppress bone turnover in the context of T2DM and the role of TLR-4 in this response.

SOCS-3 Regulates Alveolar Bone Loss in Experimental Periodontitis

The host immune response plays a key role in bacteria-induced alveolar bone resorption. Endogenous control of the magnitude and duration of inflammatory signaling is considered an important determinant of the extent of periodontal pathology. Suppressor of cytokine signaling (SOCS) proteins are inhibitors of cytokine signaling pathways and may play a role in restraining periodontal inflammation. We hypothesized that SOCS-3 regulates alveolar bone loss in experimental periodontitis. Periodontal bone loss was induced in 16-wk-old myeloid-specific SOCS-3-knockout and wild-type (WT) C57Bl6-B.129 mice by oral inoculation 9 times with 10(9) colony-forming units of Porphyromonas gingivalis A7436 through an oral gavage model for periodontitis. Sham controls for both types of mice received vehicle without bacteria. The mice were euthanized 6 wk after the last oral inoculation. Increased bone loss was demonstrated in P. gingivalis-infected SOCS-3-knockout mice as compared with P. gingivalis-infected WT mice by direct morphologic measurements, micro-computed tomography analyses, and quantitative histology. Loss of SOCS-3 function resulted in an increased number of alveolar bone osteoclasts and increased RANKL expression after P. gingivalis infection. SOCS-3 deficiency in myeloid cells also promotes a higher P. gingivalis lipopolysaccharide-induced inflammatory response with higher secretion of IL-1β, IL-6, and KC (IL-8) by peritoneal macrophages as compared with WT controls. Our data implicate SOCS-3 as a critical negative regulator of alveolar bone loss in periodontitis.

A novel role of MMP-13 for murine DC function: its inhibition dampens T-cell activation

Dendritic cells (DCs) have been shown to express matrix metalloproteinase 13 (MMP-13), but little is known about its specific function in DCs and its role in inflammatory conditions. In the present study, we describe a novel role of MMP-13 in regulating the immunostimulatory function of murine DCs through moderating MHC-I surface presentation, endocytosis and cytokine/chemokine secretion. MMP-13 expression was confirmed in bone marrow-derived DCs at both the mRNA and the protein level and, furthermore, at the activity level. Remarkably, LPS treatment strongly enhanced MMP-13 mRNA expression as well as MMP-13 activity, indicating an important role of MMP-13 in inflammatory processes. Functionally, MMP-13 inhibition did not influence the DC migratory capacity, while endocytosis of ovalbumin was significantly decreased. Inhibition of MMP-13 lowered the capability of murine DCs to activate CD8⁺ T cells, apparently through reducing MHC-I surface presentation. Decreased surface expression of CD11c on DCs, as well as changes in the DC cytokine/chemokine profile after MMP-13 inhibition, emphasizes the influence of MMP-13 on DC function. Moreover, T-cell-targeting cytokines such as IL-12, IL-23 and IL-6 were significantly reduced. Collectively, our data reveal a novel involvement of MMP-13 in regulating DC immunobiology through moderating MHC-I surface presentation, endocytosis and cytokine/chemokine secretion. Furthermore, the reduced MHC-I surface presentation by DCs resulted in a poor CD8⁺ T-cell response in vitro This novel finding indicates that MMP-13 might be a promising target for therapeutic intervention in inflammatory diseases.

Pathogenic potential of Escherichia coli clinical strains from orthopedic implant infections towards human osteoblastic cells

Escherichia coli is one of the first causes of Gram-negative orthopedic implant infections (OII), but little is known about the pathogenicity of this species in such infections that are increasing due to the ageing of the population. We report how this pathogen interacts with human osteoblastic MG-63 cells in vitro, by comparing 20 OII E. coli strains to two Staphylococcus aureus and two Pseudomonas aeruginosa strains. LDH release assay revealed that 6/20 (30%) OII E. coli induced MG-63 cell lysis whereas none of the four control strains was cytotoxic after 4 h of coculture. This high cytotoxicity was associated with hemolytic properties and linked to hlyA gene expression. We further showed by gentamicin protection assay and confocal microscopy that the non-cytotoxic E. coli were not able to invade MG-63 cells unlike S. aureus strains (internalization rate <0.01% for the non-cytotoxic E. coli versus 8.88 ± 2.31% and 4.60 ± 0.42% for both S. aureus). The non-cytotoxic E. coli also demonstrated low adherence rates (<7%), the most adherent E. coli eliciting higher IL-6 and TNF-α mRNA expression in the osteoblastic cells. Either highly cytotoxic or slightly invasive OII E. coli do not show the same infection strategies as S. aureus towards osteoblasts.

Testosterone regulates bone response to inflammation

This study evaluated the alveolar bone response to testosterone and the impact of Resolvin D2 (RvD2) on testosterone-induced osteoblast function. For the in vivo characterization, 60 male adult rats were used. Treatments established sub-physiologic (L), normal (N), or supra-physiologic (H) concentrations of testosterone. Forty rats were subjected to orchiectomy; 20 rats received periodical testosterone injections while 20 rats received testicular sham-operation. Four weeks after the surgeries, 10 rats in each group received a subgingival ligature around the lower first molars to induce experimental periodontal inflammation and bone loss. In parallel, osteoblasts were differentiated from neonatal mice calvariae and treated with various doses of testosterone for 48 h. Cell lysates and conditioned media were used for the determination of alkaline phosphatase, osteocalcin, RANKL, and osteoprotegerin. Micro-computed tomography linear analysis demonstrated that bone loss was significantly increased for both L and H groups compared to animals with normal levels of testosterone. Gingival IL-1β expression was increased in the L group (p<0.05). Ten nM testosterone significantly decreased osteocalcin, RANKL, and OPG levels in osteoblasts; 100 nM significantly increased the RANKL:OPG ratio. RvD2 partially reversed the impact of 10 nM testosterone on osteocalcin, RANKL, and OPG. These findings suggest that both L and H testosterone levels increase inflammatory bone loss in male rats. While low testosterone predominantly increases the inflammatory response, high testosterone promotes a higher osteoblast-derived RANKL:OPG ratio. The proresolving mediator RvD2 ameliorates testosterone-derived downregulation of osteocalcin, RANKL, and OPG in primary murine osteoblasts suggesting a direct role of inflammation in osteoblast function.

Role of suppressors of cytokine signaling 3 in bone inflammatory responses

Suppressor of cytokine signaling 3 (SOCS3) is a potent regulator of cytokine signaling in macrophages and T cells. In recent studies, evidence has been provided for SOCS3 activation in all major bone cells including osteoclasts, chondrocytes, synoviocytes, and osteoblasts. The investigation of SOCS3 function in bone remodeling systems implicates SOCS3 as a key signaling molecule in bone cell-mediated inflammatory responses. Both pro- and anti-inflammatory functions of SOCS3 have been demonstrated in different types of bone cells. This review provides an overview of the important role of SOCS3 in inflammatory responses of various bone cells and in bone inflammatory disorders such as periodontal disease and arthritis. Understanding the roles of SOCS3 in inflammatory diseases of bone and joints such as arthritis, osteomyelitis, and periodontal diseases is critical to revealing insights into signaling pathways that can be manipulated in potential therapeutic approaches.