SIRT1 modulates high-mobility group box 1-induced osteoclastogenic cytokines in human periodontal ligament cells

Sirt1: An Increasingly Interesting Molecule with a Potential Role in Bone Metabolism and Osteoporosis

Osteoporosis (OP) is a common metabolic bone disease characterized by low bone mass, decreased bone mineral density, and degradation of bone tissue microarchitecture. However, our understanding of the mechanisms of bone remodeling and factors affecting bone mass remains incomplete. Sirtuin1 (SIRT1) is a nicotinamide adenine dinucleotide-dependent deacetylase that regulates a variety of cellular metabolisms, including inflammation, tumorigenesis, and bone metabolism. Recent studies have emphasized the important role of SIRT1 in bone homeostasis. This article reviews the role of SIRT1 in bone metabolism and OP and also discusses therapeutic strategies and future research directions for targeting SIRT1.

Peri-implant crevicular fluid SIRT1 levels decrease in patients with peri-implant inflammatory: A prospective observational study

BACKGROUND

A dental Implant is a prosthetic device made of alloplastic materials implanted into the bone to provide retention and support for a dental prosthesis. Sirtuin1 (SIRT1) molecule, a nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylase, regulates a variety of physiological and pathological processes, including oxidative stress, metabolism, cell proliferation, cell differentiation, inflammatory, and apoptosis. We explored whether the expression of SIRT1 correlates in patients receiving implants with peri-implant mucositis (PIM) and peri-implantitis (PI) in comparison to patients with healthy peri-implant area (PIH).

METHODS

A number of 198 patients with dentition defects were enrolled in the study after their implants were functional for at least 6 months. All 198 subjects were divided into 3 groups: 1) control patients with PIH healthy implants; 2) patients with PIM mucositis; and 3) patients with PI implantitis. To distinguish these three groups, peri-implant crevicular fluid (PICF) was collected by inserting a sterile paper strip into the gap around the implant and the levels of SIRT1 and cytokines were measured by the enzyme linked immunosorbent assay (ELISA). Demographic and clinical data included age, sex, Body Mass Index (BMI), probing depth (PD), plaque index (PLI), bleeding on probing (BOP), oral health impact profile (OHIP-14), history of periodontitis and the use time of implants.

RESULTS

The PD, PLI, OHIP-14 evaluation scores in patients with periodontitis of PIM mucositis and PI implantitis were all significantly higher than in patients with PIH healthy implants. Overall, the SIRT1 levels in PICF of the PIM and PI patients were significantly lower than of the PIH patients. In comparison with PIM patients, SIRT1 levels of the PI patients were remarkably lower than the PIH patients. Pearson's analysis showed that SIRT1 levels were negatively correlated with levels of interleukin (IL)-6, C-reactive protein (CRP) and IL-1β in patients with PIM and PI. We suggest that SIRT1 levels could serve as a potential diagnostic biomarker of PI or PIM. The PICF levels of SIRT1, CRP, IL-6, IL-1β and the history of periodontitis were the risk factors for patients with peri-implant inflammatory process.

CONCLUSION

The measurement of SIRT1 expression in PICF may serve as a biomarker for the ongoing inflammatory process in patients with dental implants. The low SIRT1 levels correlated with PI implantitis and PIM mucositis as well as the elevated levels of pro-inflammatory cytokines (CRP, IL-6 and IL-1β).

Selective Upregulation of SIRT1 Expression in Retinal Ganglion Cells by AAV-Mediated Gene Delivery Increases Neuronal Cell Survival and Alleviates Axon Demyelination Associated with Optic Neuritis

Optic neuritis (ON), the most common ocular manifestation of multiple sclerosis, is an autoimmune inflammatory demyelinating disease also characterized by degeneration of retinal ganglion cells (RGCs) and their axons, which commonly leads to visual impairment despite attempted treatments. Although ON disease etiology is not known, changes in the redox system and exacerbated optic nerve inflammation play a major role in the pathogenesis of the disease. Silent information regulator 1 (sirtuin-1/SIRT1) is a ubiquitously expressed NAD+-dependent deacetylase, which functions to reduce/prevent both oxidative stress and inflammation in various tissues. Non-specific upregulation of SIRT1 by pharmacologic and genetic approaches attenuates RGC loss in experimental ON. Herein, we hypothesized that targeted expression of SIRT1 selectively in RGCs using an adeno-associated virus (AAV) vector as a delivery vehicle is an effective approach to reducing neurodegeneration and preserving vision in ON. We tested this hypothesis through intravitreal injection of AAV7m8.SNCG.SIRT1, an AAV2-derived vector optimized for highly efficient SIRT1 transgene transfer and protein expression into RGCs in mice with experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis that recapitulates optic neuritis RGC loss and axon demyelination. Our data show that EAE mice injected with a control vehicle exhibit progressive alteration of visual function reflected by decreasing optokinetic response (OKR) scores, whereas comparatively, AAV7m8.SNCG.SIRT1-injected EAE mice maintain higher OKR scores, suggesting that SIRT1 reduces the visual deficit imparted by EAE. Consistent with this, RGC survival determined by immunolabeling is increased and axon demyelination is decreased in the AAV7m8.SNCG.SIRT1 RGC-injected group of EAE mice compared to the mouse EAE counterpart injected with a vehicle or with control vector AAV7m8.SNCG.eGFP. However, immune cell infiltration of the optic nerve is not significantly different among all EAE groups of mice injected with either vehicle or AAV7m8.SNCG.SIRT1. We conclude that despite minimally affecting the inflammatory response in the optic nerve, AAV7m8-mediated SIRT1 transfer into RGCs has a neuroprotective potential against RGC loss, axon demyelination and vison deficits associated with EAE. Together, these data suggest that SIRT1 exerts direct effects on RGC survival and function.

SIRT1, a promising regulator of bone homeostasis

Sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide-dependent deacetylase, epigenetically regulates various cell metabolisms, including inflammation, tumorigenesis, and bone metabolism. Many clinical studies have found the potential of SIRT1 in predicting and treating bone-related disorders, such as osteoporosis and osteonecrosis, suggesting that SIRT1 might be a regulator of bone homeostasis. In order to identify the mechanisms that underlie the pivotal role of SIRT1 in bone homeostasis, many studies revealed that SIRT1 could maintain the balance between bone formation and absorption via regulating the ratio of osteoblasts to osteoclasts. SIRT1 controls the differentiation of mesenchymal stem cells (MSCs) and bone marrow-derived macrophages, increasing osteogenesis and reducing osteoclastogenesis. Besides, SIRT1 can enhance bone-forming cells' viability, including MSCs and osteoblasts under adverse conditions by resisting senescence, suppressing apoptosis, and promoting autophagy in favor of osteogenesis. Furthermore, the effect on bone vasculature homeostasis enables SIRT1 to become a valuable strategy for ischemic osteonecrosis and senile osteoporosis. The review systemically discusses SIRT1 pathways and the critical role in bone homeostasis and assesses whether SIRT1 is a potential target for manipulation and therapy, to lay a solid foundation for further researches in the future.

High Mobility Group Box 1 Expression in Oral Inflammation and Regeneration

High mobility group box 1 (HMGB1) is a non-histone DNA-binding protein of about 30 kDa. It is released from a variety of cells into the extracellular milieu in response to inflammatory stimuli and acts on specific cell-surface receptors, such as receptors for advanced glycation end-products (RAGE), Toll-like receptor (TLR)2, TLR4, with or without forming a complex with other molecules. HMGB1 mediates various mechanisms such as inflammation, cell migration, proliferation, and differentiation. On the other hand, HMGB1 enhances chemotaxis acting through the C-X-C motif chemokine ligand (CXCL)12/C-X-C chemokine receptor (CXCR)4 axis and is involved in regeneration. In the oral cavity, high levels of HMGB1 have been detected in the gingival tissue from periodontitis and peri-implantitis patients, and it has been shown that secreted HMGB1 induces pro-inflammatory cytokine expression, such as interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α, which prolong inflammation. In contrast, wound healing after tooth extraction or titanium dental implant osseointegration requires an initial acute inflammation, which is regulated by secreted HMGB1. This indicates that secreted HMGB1 regulates angiogenesis and bone remodeling by osteoclast and osteoblast activation and promotes bone healing in oral tissue repair. Therefore, HMGB1 can prolong inflammation in the periodontal tissue and, conversely, can regenerate or repair damaged tissues in the oral cavity. In this review, we highlight the role of HMGB1 in the oral cavity by comparing its function and regulation with its function in other diseases. We also discuss the necessity for further studies in this field to provide more specific scientific evidence for dentistry.

Prospective, case-controlled study evaluating serum concentration of sirtuin-1 and mannose-binding lectin in patients with and without periodontal and coronary artery disease

Background:

Atherosclerosis and periodontal disease (PD) are inflammatory diseases that have been shown in studies to have a direct association. Mannose-binding lectin (MBL) is an immune system protein that binds to periodontal pathogens favoring phagocytosis. Conversely, increased serum sirtuin-1 (SIRT1) concentration reduces the inflammatory process.

Methods:

This was a prospective, case-controlled study that analyzed serum concentration of biomarkers in patients with or without coronary artery disease (CAD) and PD. A total of 78 patients were evaluated: 20 healthy individuals, 18 patients with CAD, 20 patients with PD, and 20 patients with both PD and CAD. Clinical and laboratory characteristics were analyzed before and after nonsurgical treatment of PD and also at two equivalent times in patients without PD. Serum MBL and SIRT1 concentration were analyzed by enzyme-linked immunosorbent assay.

Results:

A negative correlation was observed between changes in serum concentration of MBL and SIRT1 (r = −0.30; p = 0.006). Comparison between pre- and post-treatment of PD showed a reduction in MBL levels (886.27 ± 906.72 versus 689.94 ± 808.36; p = 0.002) and an increase in SIRT1 values (0.80 ± 1.01 versus 1.49 ± 1.55; p = 0.005) in patients with PD and without CAD. The same result was observed in patients with PD and CAD for MBL and SIRT1, respectively, of 1312.43 ± 898.21 versus 1032.90 ± 602.52 (p = 0.010) and 1.32 ± 1.0 versus 1.82 ± 1.75 (p = 0.044).

Conclusion:

PD treatment reduced MBL serum concentration and increased SIRT1 serum concentration in patients with and without CAD.

Influence of the treatment of periodontal disease in serum concentration of sirtuin 1 and mannose-binding lectin

BACKGROUND

Increased levels of periodontal pathogens disrupt the homeostasis between the host and its microbiota and increase susceptibility to periodontal diseases. Periodontitis increases the serum concentration of mannose-binding lectin (MBL), which exacerbates local inflammatory processes. In animal studies, sirtuin 1 (SIRT1) was associated with protection against inflammation. This study analyzed the influence of non-surgical periodontal treatment on serum levels of MBL and SIRT1.

METHODS

Forty patients with periodontitis and 38 periodontally healthy individuals (aged 45 to 79 years) were included. Periodontitis patients received scaling and root planing using machine driven and hand instruments. Clinical parameters, inflammatory biomarkers, MBL, and SIRT1 levels were measured at baseline and at post-treatment.

RESULTS

For all patients, an inverse correlation was observed between serum concentrations of MBL and SIRT1 (r = -0.30; P = 0.006). Periodontal treatment reduced serum concentrations of MBL (1,099.35 ± 916.59 to 861.42 ± 724.82 ng/mL; P < 0.001) and C-reactive protein (6.05 ± 8.99 to 2.49 ± 2.89 mg/L; P = 0.009). By contrast, SIRT1 serum levels increased (1.06 ± 1.03 to 1.66 ± 1.64 ng/mL; P < 0.001) following periodontal treatment.

CONCLUSIONS

Periodontal treatment was associated with decreased serum concentrations of MBL and CRP and increased serum levels of SIRT1. Prospective studies are needed to assess the impact of these biomarkers on pathophysiology of periodontitis.

Orthodontic cell stress modifies proinflammatory cytokine expression in human PDL cells and induces immunomodulatory effects via TLR-4 signaling in vitro

OBJECTIVE

Biomechanical orthodontics loading of the periodontium initiates a cascade of inflammatory signaling events that induce periodontal remodeling and finally facilitate orthodontic tooth movement. Pattern recognition receptors such as toll-like receptors (TLRs) have been well characterized for their ability to induce the activation of inflammatory, immunomodulatory cytokines. Here, we examined whether the cellular response of human periodontal ligament (hPDL) cells to mechanical stress involves TLR-4 signaling in vitro.

MATERIALS AND METHODS

Confluent hPDL cells were cultured in the presence of 5 μg/ml TLR-4 antibody (TLR-4ab) for 1 h prior to the induction of compressive forces by the use of round glass plates for 24 h. At harvest, interleukin-6 and interleukin-8 (IL-6, IL-8) mRNA and protein expression were analyzed by real-time PCR and ELISA. The immunomodulatory role of mechanical cell stress and TLR-4 signaling was addressed in co-culture experiments of hPDL and THP-1 cells targeting monocyte adhesion and by culturing osteoclastic precursors (RAW 264.7) in the presence of the conditioned medium of hPDL cells that had been mechanically loaded before.

RESULTS

Basal expression of IL-6 and IL-8 was not affected by TLR-4ab, but increased significantly upon mechanical loading of hPDL cells. When cells were mechanically stressed in the presence of TLR-4ab, the effect seen for loading alone was markedly reduced. Likewise, monocyte adhesion and osteoclastic differentiation were enhanced significantly by mechanical stress of hPDL cells and this effect was partially inhibited by TLR-4ab.

CONCLUSIONS

The results of the present study indicate a proinflammatory and immunomodulatory influence of mechanical loading on hPDL cells. Intracellular signaling involves a TLR-4-dependent pathway.

CLINICAL RELEVANCE

These findings hold out the prospect of interfering with the cellular response to mechanical cell stress in order to minimize undesired side effects of orthodontic tooth movement.

Heat shock protein 70 dampens the inflammatory response of human PDL cells to mechanical loading in vitro

BACKGROUND AND OBJECTIVE

Previously, we demonstrated an inflammatory response of human PDL (hPDL) cells to mechanical loading. The cellular reaction was dampened by heat pre-treatment suggesting a protective role for heat shock proteins (HSP) during stress-induced ischemia. Here we explored if HSP70, which has already been documented in the pressure zone of tooth movement, might be regulatorily involved in the attenuation of the inflammatory response.

MATERIALS AND METHODS

Fifth passage hPDL cells were mechanically loaded in the presence of the HSP70 inhibitor VER155008. Cell morphology, HSP70 expression, viability, IL-6 and IL-8 expression were determined by means of microscopy, realtime-PCR and ELISA. The conditioned medium of mechanically loaded and pre-treated hPDL cells was used to culture monocytes to identify a potential impact on adhesion and osteoclastic differentiation capacity.

RESULTS

Mechanical cell stress resulted in a significant increase of pro-inflammatory parameters. HSP70 inhibition led to a further enhancement of cytokine expression. The conditioned medium of mechanically loaded hPDL cells significantly increased monocyte adhesion and differentiation along the osteoclastic pathway. VER155008 pronounced this effect significantly.

CONCLUSION

The results indicate a regulatory role for HSP70 in the control of the inflammatory hPDL cell response to mechanical loading and identify HSP70 as a target in the attempt to attenuate tissue damage during orthodontic tooth movement. Furthermore, the present findings point to the risk of increased periodontal destruction when medication targeting HSP70 is applied for severe medical conditions during orthodontic tooth movement.

Plumbagin ameliorates hepatic ischemia-reperfusion injury in rats: Role of high mobility group box 1 in inflammation, oxidative stress and apoptosis

Ischemia-reperfusion (I/R) injury is a pathological process which magnifies with the ensuing inflammatory response and endures with the increase of oxidants especially during reperfusion. The present study was conducted to assess the possible modulatory effects of plumbagin, the active constituent extracted from the roots of traditional medicinal plant Plumbago zeylanica L., on the dire role of high mobility group box 1 (HMGB1) as well as the associated inflammation, oxidative stress and apoptotic cell death following hepatic I/R. Four groups of rats were included: sham-operated, sham-operated treated with plumbagin, I/R (30 min ischemia and 1 h reperfusion) and I/R treated with plumbagin. Pretreatment with plumbagin markedly improved hepatic function and structural integrity compared to the I/R group, as manifested by depressed plasma transaminases and lactate dehydrogenase (LDH) activities as well as alleviated tissue pathological lesions. Plumbagin prominently hampered HMGB1 expression and subsequently quelled inflammatory cascades, as nuclear factor κB (NF-κB), tumor necrosis factor-alpha (TNF-α) and myeloperoxidase (MPO) activity. It also interrupted reactive oxygen species (ROS)-HMGB1loop as evident by restored liver reduced glutathione (GSH), elevated glutathione peroxidase (GPx) activity, along with decreased liver lipid peroxidation. Simultaneously, plumbagin significantly ameliorated apoptosis by amending the mRNA expressions of both anti-apoptotic (Bcl-2) and pro-apoptotic (Bax). The present results revealed that plumbagin is endowed with hepatoprotective activity ascribed to its antioxidant, anti-inflammatory and anti-apoptotic properties which are partially mediated through dampening of HMGB1 expression.

Role of HSP70 protein in human periodontal ligament cell function and physiology

OBJECTIVE

Heat pre-treatment of mechanically loaded human periodontal ligament cells (hPDL) dampens the inflammatory cellular response, as evidenced by a reduced expression of pro-inflammatory cytokines, inhibition of monocyte adhesion and osteoclastic differentiation. These findings imply heat shock proteins (HSP) as cell protective molecules acting in the PDL that are up-regulated upon ischemia caused by mechanical loading. HSP70 and its inhibition by VER155008 as the active agent in several pharmaceuticals are established targets and strategies, respectively, in the treatment of neoproliferative diseases. However, the effect of both players on periodontal remodeling in unknown. Therefore, we analyzed the role of HSP70 and its frequently used inhibitor VER155008 in the regulation of physiological hPDL cell functions and immune cell interaction.

MATERIALS AND METHODS

Fifth passage hPDL cells were cultured in the presence of 25μm HSP70 inactivating agent VER155008. At harvest, HSP70 expression, cell proliferation, and parameters of cell interaction, colony formation and wound healing were analyzed by means of real-time PCR, immunohistochemistry, Western blot, biochemical MTS assay, microscopy, and functional assays for monocyte adhesion and differentiation.

RESULTS

Basal HSP70 expression and hPDL cell morphology were not affected by HSP70 inhibitor VER155008. In contrast, cell proliferation, tissue defect healing, and colony formation were reduced significantly following HSP70 inhibition, whereas apoptosis and necrosis, monocyte adhesion and osteoclastic differentiation were markedly increased.

CONCLUSIONS

The present data indicate a regulatory role for HSP70 protein in hPDL cell biology.

CLINICAL RELEVANCE

These findings identify HSP70 as a promising target in the attempt to modify periodontal remodeling and point to potential periodontal side effects of HSP70 pharmaceutical usage.

Reduced Orthodontic Tooth Movement in Enpp1 Mutant Mice with Hypercementosis

Previous studies revealed that cementum formation is tightly regulated by inorganic pyrophosphate (PPi), a mineralization inhibitor. Local PPi concentrations are determined by regulators, including ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), which increases PPi concentrations by adenosine triphosphate hydrolysis. Orthodontic forces stimulate alveolar bone remodelling, leading to orthodontic tooth movement (OTM). To better understand how disturbed mineral metabolism and the resulting altered periodontal structures affect OTM, we employed Enpp1 mutant mice that feature reduced PPi and increased cervical cementum in a model of OTM induced by a stretched closed-coil spring ligated between the maxillary left first molar and maxillary incisors. We analyzed tooth movement, osteoclast/odontoclast response, and tooth root resorption by micro-computed tomography, histology, histomorphometry, and immunohistochemistry. Preoperatively, we noted an altered periodontium in Enpp1 mutant mice, with significantly increased periodontal ligament (PDL) volume and thickness, as well as increased PDL-bone/tooth root surface area, compared to wild-type (WT) controls. After 11 d of orthodontic treatment, Enpp1 mutant mice displayed 38% reduced tooth movement versus WT mice. Molar roots in Enpp1 mutant mice exhibited less change in PDL width in compression and tension zones compared to WT mice. Root resorption was noted in both groups with no difference in average depths, but resorption lacunae in Enpp1 mutant mice were almost entirely limited to cementum, with 150% increased cementum resorption and 92% decreased dentin resorption. Osteoclast/odontoclast cells were reduced by 64% in Enpp1 mutant mice, with a predominance of tartrate-resistant acid phosphatase (TRAP)-positive cells on root surfaces, compared to WT mice. Increased numbers of TRAP-positive cells on root surfaces were associated with robust immunolocalization of osteopontin (OPN) and receptor-activator of NF-κB ligand (RANKL). Collectively, reduced response to orthodontic forces, decreased tooth movement, and altered osteoclast/odontoclast distribution suggests Enpp1 loss of function has direct effects on clastic function/recruitment and/or indirect effects on periodontal remodeling via altered periodontal structure or tissue mineralization.

tBHQ Suppresses Osteoclastic Resorption in Xenogeneic-Treated Dentin Matrix-Based Scaffolds

Extracellularmatrix (ECM)-based scaffolds are important for their potential therapeutic application. Treated dentin matrix (TDM), a kind of ECM, seeded with allogeneic dental follicle stem cells (TDM/aDFC) provides a suitable inductive microenvironment for tooth root regeneration. Considering the limited sources, xenogeneic TDM (xTDM) is a possible alternative to allogeneic TDM; however, xTDM-based scaffold presents severe osteolysis and resorption lacunae causing regenerated tooth root failure. Immune response-induced excessive osteoclastogenesis plays a critical role in xenogeneic scaffold osteolysis and resorption. The impact of antioxidant, tert-butylhydroquinone (tBHQ), on xTDM/aDFCs-induced osteoclastogenesis and osteoclastic resorption in vivo and in vitro are investigated. tBHQ upregulates heme oxygenase-1 release and downregulates high mobility group box 1 mRNA expression. mRNA expression of other osteoclast-related genes including nuclear factor-kappa Bp65, receptor activator of nuclear factor kappa-B, nuclear factor of activated T-cells cytoplasmic 1, cathepsin K, and integrin β3, also decreases significantly. Furthermore, tBHQ-treated xTDM/aDFCs scaffolds implanted into rhesus macaques show reduced osteolysis and osteoclastic resorption by microcomputed tomography and tartrate-resistant acid phosphatase staining. tBHQ-induced suppression of xTDM/aDFC-induced osteoclastogenesis and osteoclastic resorption presents a new strategy for the regeneration of biological tooth root and could be applied to the regeneration of other complex tissues and organs.

Periodontal Ligament Stem Cells in the Periodontitis Microenvironment Are Sensitive to Static Mechanical Strain

During orthodontic treatment, periodontium remodeling of periodontitis patients under mechanical force was abnormal. We have previously confirmed the function impairment of periodontal ligament stem cells (PDLSCs) in the periodontitis microenvironment which might be involved in this pathological process. However, the response of PDLSCs in periodontitis microenvironment to mechanical force remains unclear. Therefore, in the present study, we introduced a Flexcell tension apparatus and investigated the response of PDLSCs obtained from periodontal tissues of periodontitis patients (PPDLSCs) and of those obtained from healthy periodontal tissues (HPDLSCs) to different magnitudes of static mechanical strain (SMS). PPDLSCs showed increased proliferation, decreased osteogenic activity, activated osteoclastogenesis, and greater secretion of inflammatory cytokines. Different magnitudes of SMS exerted distinct effects on HPDLSCs and PPDLSCs. An SMS of 12% induced optimal effects in HPDLSCs, including the highest proliferation, the best osteogenic ability, the lowest osteoclastogenesis, and the lowest secretion of inflammatory cytokines, while the optimal SMS for PPDLSCs was 8%. Excessive SMS damaged PPDLSCs function, including decreased proliferation, an imbalance between osteogenesis and osteoclastogenesis, and an activated inflammatory response. Our data suggest that PPDLSCs are more sensitive and less tolerant to SMS, and this may explain why mechanical force results in undesirable effects in periodontitis patients.

Effects of Nerve Growth Factor and Basic Fibroblast Growth Factor Promote Human Dental Pulp Stem Cells to Neural Differentiation

Dental pulp stem cells (DPSCs) were the most widely used seed cells in the field of neural regeneration and bone tissue engineering, due to their easily isolation, lack of ethical controversy, low immunogenicity and low rates of transplantation rejection. The purpose of this study was to investigate the role of basic fibroblast growth factor (bFGF) and nerve growth factor (NGF) on neural differentiation of DPSCs in vitro. DPSCs were cultured in neural differentiation medium containing NGF and bFGF alone or combination for 7 days. Then neural genes and protein markers were analyzed using western blot and RT-PCR. Our study revealed that bFGF and NGF increased neural differentiation of DPSCs synergistically, compared with bFGF and NGF alone. The levels of Nestin, MAP-2, βIII-tubulin and GFAP were the most highest in the DPSCs + bFGF + NGF group. Our results suggested that bFGF and NGF signifiantly up-regulated the levels of Sirt1. After treatment with Sirt1 inhibitor, western blot, RT-PCR and immunofluorescence staining showed that neural genes and protein markers had markedly decreased. Additionally, the ERK and AKT signaling pathway played a key role in the neural differentiation of DPSCs stimulated with bFGF + NGF. These results suggested that manipulation of the ERK and AKT signaling pathway may be associated with the differentiation of bFGF and NGF treated DPSCs. Our date provided theoretical basis for DPSCs to treat neurological diseases and repair neuronal damage.

SIRT1 was involved in TNF-α-promoted osteogenic differentiation of human DPSCs through Wnt/β-catenin signal

Dental pulp stem cells (DPSCs), as one type of mesenchymal stem cells (MSCs), have the capability of self-renewal and differentiating along the various directions, including osteogenic, chondrogenic, neurogenic, and adipogenic. We previously study and found that tumor necrosis factor-α (TNF-α) promoted osteogenic differentiation of human DPSCs via the Wnt/β-catenin signaling pathway in low concentration while inhibited that in high concentration. In the abovementioned process, we found that sirtuin-1 (SIRT1) had the same change compared with the characteristic protein of bone formation, such as bone morphogenetic protein 2 (BMP2), runt-related transcription factor 2 (Runx2), and collagen I (COL1). We asked whether SIRT1 could regulate osteogenesis of DPSCs. In inflammation microenvironment constructed by TNF-α, we tested the expression changing of SIRT1 and analyzed the function of SIRT1 on osteogenic differentiation of DPSCs. SIRT1 deacetylated β-catenin, and then promote its accumulation in the nucleus. Accumulated β-catenin can lead to transcription of osteogenic characteristic genes. Using the activator of SIRT1, resveratrol, could promote the above-mentioned process of osteogenic differentiation. SIRT1 could regulate osteogenesis of DPSCs through Wnt/β-catenin signal. SIRT1, as a regulator of differentiation of DPSCs, may be a new target for cell-based therapy in oral diseases and other regenerative medicine.

The effect of calcitriol on high mobility group box 1 expression in periodontal ligament cells during orthodontic tooth movement in rats

High mobility group box 1 (HMGB1) is a late inflammatory cytokine that plays an important role in periodontal tissue remodeling during orthodontic tooth movement. Calcitriol (1,25-dihydroxyvitamin D3 [1α,25 (OH)2D3]) is a systemic calcium-regulating hormone shown to downregulate expression of multiple proinflammatory cytokines in human periodontal ligament cells in response to orthodontic force. The purpose of this study was to investigate the effect of 1α,25(OH)2D3 on the expression of HMGB1 in periodontal ligament (PDL) cells during orthodontic tooth movement. Seven-week-old male Wistar rats were used for experimentation. Tooth movement was assessed using a nickel-titanium coil spring to apply mechanical loading to the tooth for 5 days. This was followed by administration of either 1α,25(OH)2D3 or normal saline by gavage every other day for up to 28 days. Immunohistochemistry was used to analyze the expression of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6 and HMGB1. After discontinuation of orthodontic force, expression of the early inflammatory cytokines IL-6 and TNF-α were time-dependently reduced in the 1α,25(OH)2D3 group compared with the control group at each time point. Similarly, expression of HMGB1 was decreased over time in both the 1α,25(OH)2D3 and normal saline groups, and 1α,25(OH)2D3 administration enhanced this decline. These findings indicate that administration of 1α,25(OH)2D3 might provide a favorable microenvironment for orthodontic tooth movement by downregulating expression of HMGB1 in PDL cells.

rhHMGB1 drives osteoblast migration in a TLR2/TLR4- and NF-κB-dependent manner

Osteoblast migration is significant in skeletal development. Recently, high mobility group box 1 protein (HMGB1) has been shown to highly expressed in cartilage to regulate endochondral ossification. Nevertheless, whether HMGB1 can modulate osteoblast proliferation and migration is poorly understood, as well as the intracellular signalling pathways that are involved in this process. Herein, we examined the effects of recombinant human HMGB1 (rhHMGB1) on the proliferation and migration of rat osteoblasts and investigated whether Toll-like receptor 2 (TLR2)- and TLR4-dependent signalling pathways are involved in the regulation of intracellular signalling. A transwell chamber assay was used to evaluate the migration of osteoblasts and the MTT assay was used to assess osteoblast proliferation. rhHMGB1 could significantly promote the migration of osteoblasts without inhibiting their proliferation. Meanwhile, rhHMGB1 can increase the nuclear translocation of nuclear factor-kappa B (NF-κB) p65. Specific siRNA constructs that target TLR2 or TLR4 could markedly inhibit HMGB1-induced migration of osteoblasts and HMGB1-enhanced activation of NF-κB. Collectively, HMGB1 could significantly enhance the migration of osteoblasts in vitro, and TLR2/TLR4-dependent NF-κB pathways are involved in HMGB1-induced osteoblast migration.

Protective effects of SIRT1 in patients with proliferative diabetic retinopathy via the inhibition of IL-17 expression

Diabetic retinopathy (DR) is a chronic microvascular complication of diabetes that may lead to loss of vision. The pathogenesis of DR is complex and elevated expression levels of T helper (Th)17 cells and interleukin (IL)-17 have been suggested to be associated with the development and progression of DR. Sirtuin 1 (SIRT1) is a nicotinamide-adenine dinucleotide⁺-dependent histone deacetylase that is downregulated in patients with DR. Previous studies have demonstrated that SIRT1 is capable of inhibiting the production of IL-17. In the present study, 19 patients with proliferative diabetic retinopathy (PDR) and 20 non-diabetic controls with idiopathic macular epiretinal membranes were recruited and the SIRT1 expression levels of excised specimens were analyzed using immunohistochemistry. IL-17 expression levels in the sera from patients with PDR and controls were determined by enzyme-linked immunosorbent assay (ELISA). Furthermore, SIRT1 mRNA and protein expression levels in peripheral blood mononuclear cells (PBMCs) from the two groups were analyzed following culture with or without a SIRT1 activator, resveratrol. IL-17 expression levels in the supernatants of PBMCs were determined using ELISA and the results demonstrated that IL-17 expression levels were increased in the sera of patients with PDR, as compared with the controls. Furthermore, increased expression levels of SIRT1 and IL-17 were detected in fibrovascular membranes and PBMCs harvested from patients with PDR, respectively. Notably, SIRT1 mRNA and protein expression levels were decreased in the PBMCs of patients with PDR and IL-17 production was inhibited following SIRT1 activation. The results of the present study indicated that imbalanced IL-17 and SIRT1 expression levels may contribute to the pathogenesis of DR, and SIRT1 may have a protective role in PDR by inhibiting the production of IL-17.

DAMPs, ageing, and cancer: The 'DAMP Hypothesis'

Ageing is a complex and multifactorial process characterized by the accumulation of many forms of damage at the molecular, cellular, and tissue level with advancing age. Ageing increases the risk of the onset of chronic inflammation-associated diseases such as cancer, diabetes, stroke, and neurodegenerative disease. In particular, ageing and cancer share some common origins and hallmarks such as genomic instability, epigenetic alteration, aberrant telomeres, inflammation and immune injury, reprogrammed metabolism, and degradation system impairment (including within the ubiquitin-proteasome system and the autophagic machinery). Recent advances indicate that damage-associated molecular pattern molecules (DAMPs) such as high mobility group box 1, histones, S100, and heat shock proteins play location-dependent roles inside and outside the cell. These provide interaction platforms at molecular levels linked to common hallmarks of ageing and cancer. They can act as inducers, sensors, and mediators of stress through individual plasma membrane receptors, intracellular recognition receptors (e.g., advanced glycosylation end product-specific receptors, AIM2-like receptors, RIG-I-like receptors, and NOD1-like receptors, and toll-like receptors), or following endocytic uptake. Thus, the DAMP Hypothesis is novel and complements other theories that explain the features of ageing. DAMPs represent ideal biomarkers of ageing and provide an attractive target for interventions in ageing and age-associated diseases.

Short-term heat pre-treatment modulates the release of HMGB1 and pro-inflammatory cytokines in hPDL cells following mechanical loading and affects monocyte behavior

OBJECTIVE

Heat shock proteins (HSP) act as cell-protective molecules that are upregulated upon thermal insult, hypoxia, and ischemia. Such ischemic conditions can be found during tissue remodeling associated with orthodontic tooth movement or trauma when compression forces lead to cell necrosis and subsequent clearance of cellular debris by immune competent cells. Host immune overreaction can result in undesired side effects such as tooth root resorption. Here, we analyzed whether heat pre-treatment would affect the initially catabolic host immune response induced by mechanical loading of human periodontal ligament (hPDL) cells, which represent major constituents of the tooth supporting apparatus involved in the regulation of periodontal remodeling.

MATERIALS AND METHODS

Fifth passage hPDL cells were exposed to an elevated temperature of 43° for 1 h prior to mechanical loading. Cell morphology, high mobility group box protein 1 (HMGB1), interleukin (IL)-6, and IL-8 expression were analyzed microscopically and by ELISA. The physiological relevance for monocyte behavior was tested in monocyte adhesion and osteoclast differentiation assays.

RESULTS

Short-term heat pre-treatment did not show any visible effect on hPDL cell morphology, but resulted in a significant downregulation of pro-inflammatory cytokines when being additionally loaded mechanically. Supernatants of heat-exposed hPDL cell cultures demonstrated a reduced impact on monocyte adhesion and osteoclastic differentiation.

CONCLUSIONS

Heat pre-treatment of hPDL cells induces cell-protective mechanisms towards mechanical stress and favors the reduction of cell stress associated effects on monocyte/macrophage physiology.

CLINICAL RELEVANCE

These data present the induction of heat shock proteins as a promising treatment option to limit undesired side effects of periodontal remodeling.

SIRT1 protects rat lung tissue against severe burn-induced remote ALI by attenuating the apoptosis of PMVECs via p38 MAPK signaling

Silent information regulator type-1 (SIRT1) has been reported to be involved in the cardiopulmonary protection. However, its role in the pathogenesis of burn-induced remote acute lung injury (ALI) is currently unknown. The present study aims to investigate the role of SIRT1 in burn-induced remote ALI and the involved signaling pathway. We observed that SIRT1 expression in rat lung tissue after burn injury appeared an increasing trend after a short period of suppression. The upregulation of SIRT1 stimulated by resveratrol exhibited remission of histopathologic changes, reduction of cell apoptosis, and downregulation of pro-inflammatory cytokines in rat pulmonary tissues suffering from severe burn. We next used primary pulmonary microvascular endothelial cells (PMVECs) challenged by burn serum (BS) to simulate in vivo rat lung tissue after burn injury, and found that BS significantly suppressed SIRT1 expression, increased cell apoptosis, and activated p38 MAPK signaling. The use of resveratrol reversed these effects, while knockdown of SIRT1 by shRNA further augmented BS-induced increase of cell apoptosis and activation of p38 MAPK. Taken together, these results indicate that SIRT1 might protect lung tissue against burn-induced remote ALI by attenuating PMVEC apoptosis via p38 MAPK signaling, suggesting its potential therapeutic effects on the treatment of ALI.

Altered distribution of HMGB1 in the periodontal ligament of periostin-deficient mice subjected to Waldo's orthodontic tooth movement

Periostin is essential for the integrity and function of the periodontal ligament (PDL), and periostin knockout is related to an enhanced inflammatory status in PDL. High mobility group box 1 (HMGB1), a late inflammatory cytokine, is up-regulated in PDL cells in response to mechanical stress. This study aimed to investigate the effect of periostin deficiency (Pn-/-) on HMGB1 expression in PDL during orthodontic tooth movement. We used 8-week-old male mice homozygous for the disrupted periostin gene and their wild-type (WT) littermates. Tooth movement was performed according to Waldo's method, in which 0.5-mm-thick elastic bands were inserted between the first and second upper molars of anesthetized mice. After 3 days of mechanical loading, mice were fixed by transcardial perfusion of 4% paraformaldehyde in phosphate buffer, and the maxilla was extracted for histochemical analyses. Compared with the WT group, Pn-/- mice showed higher basal expression of HMGB1 in the absence of mechanical loading. Following 3 days of orthodontic tooth movement, the PDL in the compression side of both groups was almost replaced by cell-free hyaline zones, and Pn-/- mice showed a much wider residual PDL than WT mice. In the tension side, the number of HMGB1-positive cells in PDL in both Pn-/- and WT groups increased remarkably without a significant difference between the two groups. Our findings suggest an inhibitory effect of periostin on HMGB1 production by PDL and confirmed the critical role of periostin in integrity of PDL collagen fibrils during orthodontic tooth movement, although mechanical loading is the predominant stimulant of HMGB1 expression relative to periostin deficiency.

Expression of HMGB1 in the periodontal tissue subjected to orthodontic force application by Waldo's method in mice

Recent studies indicate that high mobility group box protein 1 (HMGB1) originating from periodontal ligament (PDL) cells can be a potential regulator in the process of orthodontic tooth movement and periodontal tissue remodeling. The aim of this study is to investigate HMGB1 expression in periodontal tissue during orthodontic tooth movement in mice according to Waldo's method. Six 7-week-old C57BL6 mice were used in these experiments. The elastic band was inserted into the teeth space between the right first and second maxillary molars. After 3 days of mechanical loading, mice were fixed with transcardial perfusion of 4 % paraformaldehyde in 0.1 M phosphate buffer (pH 7.4), and the maxillary was extracted for histochemical analyses. The histological examination revealed local PDL tear at the tension side and the formation of extensive cell-free hyaline zones at the compression side. The immunolocalization of HMGB1 was significantly presented at tension side of PDL, apical area and dental pulp, whereas at the compression side of PDL, the labeling of HMGB1 was almost undetectable as the presence of hyaline zone. Taken together, we concluded that the orthodontic tooth movement by Waldo's method leads to histological changes and HMGB1 expression pattern that differ from those of coil spring method, including PDL tear and extensive hyaline zone which may severely destroy periodontal tissue and in turn impede tooth movement.

PIN1 inhibition suppresses osteoclast differentiation and inflammatory responses

Inflammatory responses and osteoclast differentiation play pivotal roles in the pathogenesis of osteolytic bone diseases such as periodontitis. Although overexpression or inhibition of peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 (PIN1) offers a possible therapeutic strategy for chronic inflammatory diseases, the role of PIN1 in periodontal disease is unclear. The aim of the present study was to evaluate PIN1 expression in periodontitis patients as well as the effects of PIN1 inhibition by juglone or PIN1 small-interfering RNA (siRNA) and of PIN1 overexpression using a recombinant adenovirus encoding PIN1 (Ad-PIN1) on the inflammatory response and osteoclastic differentiation in lipopolysaccharide (LPS)- and nicotine-stimulated human periodontal ligament cells (PDLCs). PIN1 was up-regulated in chronically inflamed PDLCs from periodontitis patients and in LPS- and nicotine-exposed PDLCs. Inhibition of PIN1 by juglone or knockdown of PIN1 gene expression by siRNA markedly attenuated LPS- and nicotine-stimulated prostaglandin E2 (PGE2) and nitric oxide (NO) production, as well as cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) expression, whereas PIN1 overexpression by Ad-PIN1 increased it. LPS- and nicotine-induced nuclear factor (NF)-κB activation was blocked by juglone and PIN1 siRNA but increased by Ad-PIN1. Conditioned medium prepared from LPS- and nicotine-treated PDLCs increased the number of tartrate-resistant acid phosphatase-stained osteoclasts and osteoclast-specific gene expression. These responses were blocked by PIN1 inhibition and silencing but stimulated by Ad-PIN1. Furthermore, juglone and PIN1 siRNA inhibited LPS- and nicotine-induced osteoclastogenic cytokine expression in PDLCs. This study is the first to demonstrate that PIN1 inhibition exhibits anti-inflammatory effects and blocks osteoclastic differentiation in LPS- and nicotine-treated PDLCs. PIN1 inhibition may be a therapeutic strategy for inflammatory osteolysis in periodontal disease.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

Anabolic properties of high mobility group box protein-1 in human periodontal ligament cells in vitro

High mobility group box protein-1 (HMGB1) is mainly recognized as a chemoattractant for macrophages in the initial phase of host response to pathogenic stimuli. However, recent findings provide evidence for anabolic properties in terms of enhanced proliferation, migration, and support of wound healing capacity of mesenchymal cells suggesting a dual role of the cytokine in the regulation of immune response and subsequent regenerative processes. Here, we examined potential anabolic effects of HMGB1 on human periodontal ligament (PDL) cells in the regulation of periodontal remodelling, for example, during orthodontic tooth movement. Preconfluent human PDL cells (hPDL) were exposed to HMGB1 protein and the influence on proliferation, migration, osteogenic differentiation, and biomineralization was determined by MTS assay, real time PCR, immunofluorescence cytochemistry, ELISA, and von Kossa staining. HMGB1 protein increased hPDL cell proliferation, migration, osteoblastic marker gene expression, and protein production as well as mineralized nodule formation significantly. The present findings support the dual character of HMGB1 with anabolic therapeutic potential that might support the reestablishment of the structural and functional integrity of the periodontium following periodontal trauma such as orthodontic tooth movement.

TNF-α and LPS activate angiogenesis via VEGF and SIRT1 signalling in human dental pulp cells

AIM

To assess whether SIRT1 and VEGF are responsible for tumour necrosis factor-α (TNF-α) and lipopolysaccharide (LPS)-induced angiogenesis and to examine the molecular mechanism(s) of action in human dental pulp cells (HDPCs).

METHODOLOGY

Immortalized HDPCs obtained from Prof. Takashi Takata (Hiroshima University, Japan) were treated with LPS (1 μg mL(-1) ) and TNF-α (10 ng mL(-1) ) for 24 h. mRNA and protein levels were examined by RT-PCR and Western blotting, respectively. Migration and tube formation were examined in human umbilical vein endothelial cells (HUVECs). The data were analysed by one-way anova. Statistical analysis was performed at α = 0.05.

RESULTS

LPS and TNF-α upregulated VEGF and SIRT1 mRNA and protein levels. Inhibition of SIRT1 activity by sirtinol and SIRT1 siRNA or inhibition of the VEGF receptor by CBO-P11 significantly attenuated LPS + TNF-α-stimulated MMPs production in HDPCs, as well as migration and tube formation in HUVECs (P < 0.05). Furthermore, sirtinol, SIRT1 siRNA and CBO-P11 attenuated phosphorylation of Akt, extracellular signal-regulated kinase (ERK), p38 and c-Jun N-terminal kinase (JNK) and the nuclear translocation of NF-κB p65. Pre-treatment with inhibitors of p38, ERK, JNK, PI3K and NF-κB decreased LPS + TNF-α-induced VEGF and SIRT1 expression, MMPs activity in HDPCs and angiogenesis (P < 0.05) in HUVECs.

CONCLUSIONS

TNF-α and LPS led to upregulation of VEGF and SIRT1, and subsequent upregulation of MMP-2 and MMP-9 production, and promote angiogenesis via pathways involving PI3K, p38, ERK, JNK and NF-κB. The results suggest that inhibition of SIRT1 and VEGF might attenuate pro-inflammatory mediator-induced pulpal disease.

Protective effect of saponins extract from Panax japonicus on myocardial infarction: involvement of NF-κB, Sirt1 and mitogen-activated protein kinase signalling pathways and inhibition of inflammation

Objective

Inflammation is widely acknowledged to increase morbidity and mortality in myocardial infarction (MI), and the ideal therapeutic methods should be aimed at the inflammation reaction triggers. The aim was to evaluate the protective effect of saponins extracted from Panax japonicus (SPJ) on MI, and based on these results investigate the possible involvement mechanism of the nuclear factor-kappa B (NF-κB), sirtuin1 (SIRT1) and mitogen-activated protein kinases (MAPKs) signalling pathways.

Methods

Sprague-Dawley rats were randomly divided into sham, MI, MI + SPJ 50 and SPJ 100 mg/kg groups. After administration for 3 days, MI rats were created by ligaturing coronary artery, and then underwent the same administration for 7 days as before. Cardiac function and the expressions of pro-apoptosis protein Bax, anti-apoptosis protein Bcl-2, NF-κB, SIRT1, MAPKs signal pathway-related proteins and inflammatory factor, such as tumour necrosis factor alpha (TNF-α) and monocyte chemoattractant protein 1 (MCP-1), were assessed.

Key findings

SPJ might significantly improve cardiac function, decrease the serum MCP-1 and TNF-α levels, ameliorate the increased Bax protein expression and decrease Bcl-2 protein expression, and suppress the protein expressions of NF-κBp65 subunit, extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 MAPK, but have no effect on c-Jun NH2-terminal kinase, and increase the expression of SIRT1. Histopathological observations provided supportive evidence for aforementioned results, and with the dose of SPJ increasing, the aforesaid improvement became more and more strong.

Conclusion

The studies demonstrated that SPJ exerted beneficially cardioprotective effects on MI rats, mainly inhibiting NF-κB, ERK1/2 and p38 MAPK activation, but increased the expression of SIRT1, alleviating MI injury and cardiac cell death.

HMGB1 localization during experimental periodontitis

AIM

This study sought to investigate the in vitro expression profile of high mobility group box 1 (HMGB1) in murine periodontal ligament fibroblasts (mPDL) stimulated with LPS or IL-1β and in vivo during ligature- or LPS-induced periodontitis in rats.

MATERIAL AND METHODS

For the in vivo study, 36 rats were divided into experimental and control groups, and biopsies were harvested at 7-30 d following disease induction. Bone loss and inflammation were evaluated. HMGB1 expression was assessed by immunohistochemistry, qPCR, and Western blot.

RESULTS

Significant increases in mPDL HMGB1 mRNA occurred at 4, 8, and 12 h with protein expression elevated by 24 h. HMGB1 mRNA expression in gingival tissues was significantly increased at 15 d in the LPS-PD model and at 7 and 15 d in the ligature model. Immunohistochemical staining revealed a significant increase in the number of HMGB1-positive cells during the experimental periods.

CONCLUSION

The results show that PDL cells produce HMGB1, which is increased and secreted extracellularly after inflammatory stimuli. In conclusion, this study demonstrates that HMGB1 may be associated with the onset and progression of periodontitis, suggesting that further studies should investigate the potential role of HMGB1 on periodontal tissue destruction.

High-mobility group box protein-1 released by human-periodontal ligament cells modulates macrophage migration and activity in vitro

Recent studies have demonstrated the interplay of human periodontal ligament cells (hPDLs) with immune cells, such as macrophages, during tissue repair. High-mobility group box protein-1 (HMGB1) is released into the extracellular milieu by damaged cells and functions as an alarmin to mediate the inflammatory host response. The present study addressed the role of HMGB1 released by hPDLs in the regulation of macrophage differentiation, migration and activity. The aim was to examine the inflammatory potential of HMGB1 itself and in combination with other mediators. The induction of sterile necrosis by thermal insult of hPDLs resulted in HMGB1 translocation from the nucleus to the cytoplasm and on to the extracellular space, as determined by immunocytochemistry/ELISA. Exposure of human macrophages to the conditioned PDL cell medium increased the expression of macrophage differentiation/activation markers CD14, CD23, CD64 and CD163. Chemotactic migration and osteoclastic differentiation of macrophages were also enhanced. Supplementation of the conditioned medium with a saturating concentration of HMGB1-Ab reduced these effects. Challenge with recombinant HMGB1 protein induced less migration and osteoclast differentiation than thermal insult. These data point to the immune modulatory capacity of hPDLs by the release of mediators, including HMGB1, which modify macrophage differentiation, migration and activity during periodontal repair, and indicate an enhanced HMGB1 activity when acting in concert with other mediators.

Regulation of macrophage migration and activity by high-mobility group box 1 protein released from periodontal ligament cells during orthodontically induced periodontal repair: an in vitro and in vivo experimental study

OBJECTIVE

Recent studies have shown that periodontal ligament (PDL) cells interact with macrophages from the immune system during orthodontically induced repair of periodontal tissue. Hypothesizing that high-mobility group box 1 (HMGB1) protein is released by mechanically stressed PDL cells into the extracellular space and has a role in mediating the local immune response by acting as an "alarmin", this study was performed to further elucidate these cellular interactions, with a special focus on the impact of proinflammatory mediators secreted by PDL cells on macrophage physiology.

MATERIALS AND METHODS

The study included an in vivo part in which orthodontic stress was induced in rats and their PDL analyzed for expression of HMGB1 by immunohistochemistry after 5 days of tooth movement. In the in vitro part, human PDL cells were subjected to compressive loading, followed by stimulating human macrophages with conditioned supernatants of these stressed PDL cells and analyzing how mediators that had been released by these cells into the medium would impact macrophage physiology. Assays for macrophage migration and osteoclast differentiation were used in addition to immunohistochemistry, enzyme-linked immunosorbent assays, and western blotting.

RESULTS

Induction of mechanical stress was found to upregulate HMGB1 expression both in vivo and in vitro. At the same time, translocation HMGB1 from nuclei into cytoplasm was observed. Culturing macrophages in conditioned PDL cell medium was associated with enhanced chemotactic migration and osteoclast differentiation. Addition of anti-HMGB1 antibodies to inhibit HMGB1 in the conditioned medium was found to significantly attenuate these effects. A less marked increase of migration and osteoclast differentiation by macrophages was observed after isolated addition of HMGB1, at its observed pathological concentration, to nonconditioned medium.

CONCLUSION

This study clearly indicates an immunomodulatory potential of human PDL cells via release of mediators, including HMGB1 protein. Our finding that these mediators modify the migration and differentiation of macrophages as a function of periodontal repair during orthodontic treatment broadens the theoretical basis toward developing interventional strategies to avoid orthodontically induced root resorption.

Effects of sirtuin 1 activation on nicotine and lipopolysaccharide-induced cytotoxicity and inflammatory cytokine production in human gingival fibroblasts

BACKGROUND AND OBJECTIVE

Although sirtuin 1 (SIRT1) over-expression and resveratrol exert anti-inflammatory and proinflammatory effects, their effects and the mechanism of action on human gingival fibroblast (HGF)-mediated inflammation are unknown. The aim of this study was to demonstrate the effects of activating SIRT1 using resveratrol and recombinant adenovirus encoding SIRT1 (Ad-SIRT1) on the expression of proinflammatory cytokines and to elucidate its mechanism of action of lipopolysaccharide (LPS) and nicotine stimulated-HGF.

MATERIAL AND METHODS

Cytotoxicity and the production of reactive oxygen species (ROS) were measured using the 3-(4,5-dimethylthiazolyl-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry, respectively. The amount of prostaglandin E2 (PGE2 ) released into the culture medium was measured by radioimmunoassay. mRNA and protein levels were analyzed using RT-PCR and western blotting, respectively.

RESULTS

Nicotine and LPS up-regulated the expression of SIRT1 mRNA and SIRT1 protein in a time- and concentration-dependent manner. Resveratrol and Ad-SIRT1 decreased LPS and nicotine-induced cytotoxicity, ROS and PGE2 production, and expression of cyclooxygenase-2 in HGFs. Resveratrol and Ad-SIRT1 inhibited nicotine and LPS-mediated protein kinase C (PKC), phosphatidylinositol 3-kinase (PI3K), p38, ERK, JNK, MAPK and nuclear factor-kappa B (NF-κB) activation.

CONCLUSION

This study is the first to show that the anti-inflammatory and cytoprotective effects of SIRT1 activation in HGFs occur through the PKC, PI3K, MAPK and NF-κB pathways.

Cytoprotective and anti-inflammatory effects of melatonin in hydrogen peroxide-stimulated CHON-001 human chondrocyte cell line and rabbit model of osteoarthritis via the SIRT1 pathway

Melatonin has potent antioxidant, analgesic, and antinociceptive properties. However, the effects of melatonin against oxidative stress-induced cytotoxicity and inflammatory mediators in human chondrocytes remain poorly understood. This study examined the effects and underlying mechanism of melatonin in hydrogen peroxide (H(2) O(2) )-stimulated human chondrocytes and rabbit osteoarthritis (OA) model. Melatonin markedly inhibited hydrogen peroxide (H(2) O(2) )-stimulated cytotoxicity, iNOS, and COX-2 protein and mRNA expression, as well as the downstream products, NO and PGE(2) . Incubation of cells with melatonin decreased H(2) O(2) -induced Sirtuin 1 (SIRT1) mRNA and protein expression. SIRT1 inhibition by sirtinol or Sirt1 siRNA reversed the effects of melatonin on H(2) O(2) -mediated induction of pro-inflammatory cytokines (NO, PGE(2) , TNF-α, IL-1β, and IL-8) and the expression of iNOS, COX-2, and cartilage destruction molecules. Melatonin blocked H(2) O(2) -induced phosphorylation of PI3K/Akt, p38, ERK, JNK, and MAPK, as well as activation of NF-κB, which was reversed by sirtinol and SIRT1 siRNA. In rabbit with OA, intra-articular injection of melatonin significantly reduced cartilage degradation, which was reversed by sirtinol. Taken together, this study shows that melatonin exerts cytoprotective and anti-inflammatory effects in an oxidative stress-stimulated chondrocyte model and rabbit OA model, and that the SIRT1 pathway is strongly involved in this effect.

Potential role of high mobility group box protein 1 and intermittent PTH (1-34) in periodontal tissue repair following orthodontic tooth movement in rats

OBJECTIVES

Recent studies indicate that high mobility group box protein 1 (HMGB1) can be released by necrotic and damaged cells and functions as an alarmin that is recognized by the innate immune system. Little is known about the role of HMGB1 within the periodontal ligament (PDL). Therefore, we examined HMGB1 expression by PDL cells in vitro and compared the findings to an in vivo model of orthodontically induced tooth root resorption. In addition, we addressed the question of whether a potentially anabolic intermittent administration of parathyroid hormone (iPTH) would modulate the expression of HMGB1.

MATERIALS AND METHODS

In confluent PDL cell cultures, HMGB1 messenger RNA (mRNA) expression was quantified by real-time polymerase chain reaction. In a rat model comprising 25 animals, mechanical loading for 5 days was followed by administration of either iPTH (1-34) systemically or sham injections for up to 56 days. HMGB1 expression was determined by means of immunohistochemistry and histomorphometry.

RESULTS

The in vitro experiments revealed an inhibitory effect of iPTH on basal HMGB1 mRNA expression in confluent PDL cells. In vivo, the mechanical force-induced enhanced HMGB1 protein expression declined time dependently. Intermittent PTH further inhibited HMGB1 expression. The significantly higher basal HMGB1 protein expression in the former compression side was followed by a more pronounced time- and iPTH-dependent decline in the same area.

CONCLUSIONS

These data indicate a major role for HMGB1 in the regulation of PDL wound healing following mechanical load-induced tissue injury.

CLINICAL RELEVANCE

The findings point to the potential benefit of iPTH in the attempt to support these immune-associated reparative processes.

Porphyromonas gingivalis lipopolysaccharide regulates interleukin (IL)-17 and IL-23 expression via SIRT1 modulation in human periodontal ligament cells

Increased interleukin (IL)-17 and IL-23 levels exist in the gingival tissue of periodontitis patients, but the precise molecular mechanisms that regulate IL-17 and IL-23 production remain unknown. The aim of this study was to explore the role of SIRT1 signaling on Porphyromonas gingivalis lipopolysaccharide (LPS)-induced IL-17 and IL-23 production in human periodontal ligament cells (hPDLCs). IL-17 and IL-23 production was significantly increased in LPS-treated cells. LPS treatment also led to the upregulation of SIRT1 mRNA and protein expression. LPS-induced IL-17 and IL-23 upregulation was attenuated by pretreatment with inhibitors of phosphoinositide 3-kinase (PI3K), p38, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), mitogen-activated protein kinase (MAPK), and NF-κB, as well as neutralizing antibodies against Toll-like receptors (TLRs) 2 and 4. Sirtinol treatment (a known SIRT1 inhibitor) or SIRT1 knockdown by small interfering RNA blocked LPS-stimulated IL-17 and IL-23 expression. Further investigation showed that LPS decreased osteoblast markers (i.e., ALP, OPN, and BSP) and concomitantly increased osteoclast markers (i.e., RANKL and M-CSF). This response was attenuated by inhibitors of the PI3K, p38, ERK, JNK, NF-κB, and SIRT1 pathways. These findings, for the first time, suggest that human periodontopathogen P. gingivalis LPS is implicated in periodontal disease bone destruction and may mediate IL-17 and IL-23 release from hPDLCs. This process is dependent, at least in part, on SIRT1-Akt/PI3K-MAPK-NF-κB signaling.

Mechanical stress-activated immune response genes via Sirtuin 1 expression in human periodontal ligament cells

Recently, Sirtuin 1 (SIRT1) has been implicated in the molecular control of ageing and immune response. Although the remodelling of periodontal ligament (PDL) in response to mechanical stress (MS) is mediated by several host factors, including cytokines and chemokines, the transmission of mechanical stimuli into specific cellular activity is still not understood fully. This study aimed to investigate the effects of MS, particularly cyclic strain, on immune response genes, as well as SIRT1 and its signal transduction pathways, in human PDL cells. MS up-regulated the expression of SIRT1 and immune response genes encoding cytokines [tumour necrosis factor (TNF)-α, interleukin (IL)-1β], chemokines [IL-8, monocyte cheoattractant protein (CCL)-20], defensins [human β-defensin (hBD)-2, hBD-3] and Toll-like receptors (TLR-2 and TLR-4) in a force- and time-dependent manner. The SIRT1 inducers resveratrol and isonicotinamide attenuated MS-induced cytokine and chemokine expression, but enhanced the expression of defensins and TLRs. Blockade of SIRT1 activity by the SIRT1 inhibitors sirtinol and nicotinamide and down-regulation of SIRT1 expression by SIRT1 siRNA reduced the stimulatory effects of MS on defensins and TLRs, but increased its effects on cytokines and chemokines. MS induced activation of protein kinase B (Akt), protein kinase C (PKC), nuclear factor (NF)-κB and p38 mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). Treatment with the anti-oxidants N-acetylcysteine and glutathione inhibited MS-induced reactive oxygen species production and expression of cytokines, chemokines, defensins and TLRs. These results suggest that MS activates human PDL cells to express immune/defence genes encoding cytokines, chemokines, defensins and TLRs via a SIRT1 pathway.

Activation of Sirt1 by resveratrol inhibits TNF-α induced inflammation in fibroblasts

Inflammation is one of main mechanisms of autoimmune disorders and a common feature of most diseases. Appropriate suppression of inflammation is a key resolution to treat the diseases. Sirtuin1 (Sirt1) has been shown to play a role in regulation of inflammation. Resveratrol, a potent Sirt1 activator, has anti-inflammation property. However, the detailed mechanism is not fully understood. In this study, we investigated the anti-inflammation role of Sirt1 in NIH/3T3 fibroblast cell line. Upregulation of matrix metalloproteinases 9 (MMP-9), interleukin-1beta (IL-1β), IL-6 and inducible nitric oxide synthase (iNOS) were induced by tumor necrosis factor alpha (TNF-α) in 3T3 cells and resveratrol suppressed overexpression of these pro-inflammatory molecules in a dose-dependent manner. Knockdown of Sirt1 by RNA interference caused 3T3 cells susceptible to TNF-α stimulation and diminished anti-inflammatory effect of resveratrol. We also explored potential anti-inflammatory mechanisms of resveratrol. Resveratrol reduced NF-κB subunit RelA/p65 acetylation, which is notably Sirt1 dependent. Resveratrol also attenuated phosphorylation of mammalian target of rapamycin (mTOR) and S6 ribosomal protein (S6RP) while ameliorating inflammation. Our data demonstrate that resveratrol inhibits TNF-α-induced inflammation via Sirt1. It suggests that Sirt1 is an efficient target for regulation of inflammation. This study provides insight on treatment of inflammation-related diseases.