Short-Term Exposure to Tumor Necrosis Factor-Alpha Enables Human Osteoblasts to Direct Adipose Tissue-Derived Mesenchymal Stem Cells into Osteogenic Differentiation

The role of TNF-α in osteoporosis, bone repair and inflammatory bone diseases: A review

Tumour necrosis factor alpha (TNF-α) is a pleiotropic cytokine synthesised primarily by mononuclear cells; it has a potent pro-inflammatory effect, playing a crucial role in metabolic, immune, and inflammatory diseases. This cytokine has been studied in various biological systems. In bone tissue, TNF-α plays an integral role in skeletal disorders such as osteoporosis, fracture repair and rheumatoid arthritis through its involvement in regulating the balance between osteoblasts and osteoclasts, mediating inflammatory responses, promoting angiogenesis and exacerbating synovial proliferation. The biological effect TNF-α exerts in this context is determined by a combination of the signalling pathway it activates, the type of receptor it binds, and the concentration and duration of exposure. This review summarises the participation and pathophysiological role of TNF-α in osteoporosis, bone damage repair, chronic immunoinflammatory bone disease and spinal cord injury, and discusses its main mechanisms.

Chaperone-mediated autophagy protects the bone formation from excessive inflammation through PI3K/AKT/GSK3β/β-catenin pathway

Multiple regulatory mechanisms are in place to ensure the normal processes of bone metabolism, encompassing both bone formation and absorption. This study has identified chaperone-mediated autophagy (CMA) as a critical regulator that safeguards bone formation from the detrimental effects of excessive inflammation. By silencing LAMP2A or HSCA8, we observed a hindrance in the osteoblast differentiation of human bone marrow mesenchymal stem cells (hBMSCs) in vitro. To further elucidate the role of LAMP2A, we generated LAMP2A gene knockdown and overexpression of mouse BMSCs (mBMSCs) using adenovirus. Our results showed that LAMP2A knockdown led to a decrease in osteogenic-specific proteins, while LAMP2A overexpression favored the osteogenesis of mBMSCs. Notably, active-β-catenin levels were upregulated by LAMP2A overexpression. Furthermore, we found that LAMP2A overexpression effectively protected the osteogenesis of mBMSCs from TNF-α, through the PI3K/AKT/GSK3β/β-catenin pathway. Additionally, LAMP2A overexpression significantly inhibited osteoclast hyperactivity induced by TNF-α. Finally, in a murine bone defect model, we demonstrated that controlled release of LAMP2A overexpression adenovirus by alginate sodium capsule efficiently protected bone healing from inflammation, as confirmed by imaging and histological analyses. Collectively, our findings suggest that enhancing CMA has the potential to safeguard bone formation while mitigating hyperactivity in bone absorption.

ILK inhibition reduces osteophyte formation through suppression of osteogenesis in BMSCs via Akt/GSK-3β/β-catenin pathway

BACKGROUND

Osteophyte development is a common characteristic of inflammatory skeletal diseases. Elevated osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) participates in pathological osteogenesis. Integrin-linked kinase (ILK) positively regulates the osteoblastic differentiation of osteoprogenitors, but whether the ILK blockage prevents osteophytes and its potential mechanism is still unknown. Furthermore, the low-dose tumor necrosis factor-α (TNF-α) promotes osteogenic differentiation, but a lack of study reports on the relationship between this cytokine and ILK. OSU-T315 is a small ILK inhibitor, which was used to determine the effect of ILK inhibition on osteogenesis and osteophyte formation.

METHODS AND RESULTS

The osteogenesis of BMSCs was evaluated using Alizarin red S staining, alkaline phosphatase, collagen type I alpha 2 chain, and bone gamma-carboxyglutamate protein. The expression and phosphorylation of protein were assessed through western blot. Immunofluorescence was employed to display the distribution of β-catenin. microCT, hematoxylin-eosin, and safranin O/fast green staining were utilized to observe the osteophyte formation in collagen antibody-induced arthritis mice. We found that ILK blockage significantly declined calcium deposition and osteoblastic markers in a dose- and time-dependent manner. Furthermore, it lowered osteogenesis in the TNF-α-induced inflammatory microenvironment by diminishing the effect of ILK and inactivating the Akt/ GSK-3β/ β-catenin pathway. Nuclear β-catenin was descended by OSU-T315 as well. Finally, the ILK suppression restrained osteophyte formation but not inflammation in vivo.

CONCLUSIONS

ILK inhibition lowered osteogenesis in TNF-α-related inflammatory conditions by deactivating the Akt/ GSK-3β/ β-catenin pathway. This may be a potential strategy to alleviate osteophyte development in addition to anti-inflammatory treatment.

The effect of alginate scaffolds on bone healing in defects formed with drilling model in rat femur diaphysis

Alginate (ALG) is a biocompatible and biodegradable polymer. Mechanical weakness is one of the main problems for the alginate-based scaffolds. Various plasticizer additives or modifications tested to improve the mechanical properties. In the presented study, ALG plasticized with triacetin (TA), and tributyl citrate (TBC) than tested on bone healing. In the presented study, the alginate modified with triacetin or tributyl citrate. In-vitro, and in-vivo efficiency of the scaffolds tested on bone tissue regeneration. Scaffolds fabricated by solvent casting, and physicochemical characterizations performed. Monocytes (THP-1) cultured with scaffolds, and macrophage-released cytokines was determined. In-vivo efficacy of the scaffolds was tested in the rat drill hole model. Alginate and tributyl citrate-modified scaffolds have no cytotoxic effect on osteoblastic cells (MC-3T3). Tributyl citrate modification increased tumor necrosis factor-alpha (TNF-alpha) level but did not increase interleukin -1 beta (IL-1 beta) level. In vivo studies showed that osteoblastic growth was significant in alginate and triacetin-modified scaffolds. However, the best values for osteoclastic activity and osteoid tissue formation seen in the triacetin modification. The results demonstrated that the modified alginate scaffolds were more successful than non-modified alginate scaffolds and can used as long-term bone repairing treatments.

Regulation of osteogenic differentiation by the pro-inflammatory cytokines IL-1β and TNF-α: current conclusions and controversies

Treatment of complex bone fracture diseases is still a complicated problem that is urged to be solved in orthopedics. In bone tissue engineering, the use of mesenchymal stromal/stem cells (MSCs) for tissue repair brings hope to the medical field of bone diseases. MSCs can differentiate into osteoblasts and promote bone regeneration. An increasing number of studies show that the inflammatory microenvironment affects the osteogenic differentiation of MSCs. It is shown that TNF-α and IL-1β play different roles in the osteogenic differentiation of MSCs via different signal pathways. The main factors that affect the role of TNF-α and IL-1β in osteogenic differentiation of MSCs include concentration and the source of stem cells (different species and different tissues). This review in-depth analyzes the roles of pro-inflammatory cytokines in the osteogenic differentiation of MSCs and reveals some current controversies to provide a reference of comprehensively understanding.

Mesenchymal Stem Cell-Immune Cell Interaction and Related Modulations for Bone Tissue Engineering

Critical bone defects and related delayed union and nonunion are still worldwide problems to be solved. Bone tissue engineering is mainly aimed at achieving satisfactory bone reconstruction. Mesenchymal stem cells (MSCs) are a kind of pluripotent stem cells that can differentiate into bone cells and can be used as one of the key pillars of bone tissue engineering. In recent decades, immune responses play an important role in bone regeneration. Innate immune responses provide a suitable inflammatory microenvironment for bone regeneration and initiate bone regeneration in the early stage of fracture repair. Adaptive immune responses maintain bone regeneration and bone remodeling. MSCs and immune cells regulate each other. All kinds of immune cells and secreted cytokines can regulate the migration, proliferation, and osteogenic differentiation of MSCs, which have a strong immunomodulatory ability to these immune cells. This review mainly introduces the interaction between MSCs and immune cells on bone regeneration and its potential mechanism, and discusses the practical application in bone tissue engineering by modulating this kind of cell-to-cell crosstalk. Thus, an in-depth understanding of these principles of bone immunology can provide a new way for bone tissue engineering.

Osteoinductive and antimicrobial mechanisms of graphene-based materials for enhancing bone tissue engineering

Graphene-based materials (GMs) have great application prospects in bone tissue engineering due to their osteoinductive ability and antimicrobial activity. GMs induce osteogenic differentiation through several mechanisms and pathways in bone tissue engineering. First of all, the surface and high hardness of the porous folds of graphene or graphene oxide (GO) can generate mechanical stimulation to initiate a cascade of reactions that promote osteogenic differentiation without any chemical inducers. In addition, change of the extracellular matrix (ECM), regulation of macrophage polarization, the oncostatin M (OSM) signaling pathway, the MAPK signaling pathway, the BMP signaling pathway, the Wnt/β-catenin signaling pathway, and other pathways are involved in GMs' regulation of osteogenesis. In bone tissue engineering, GMs prevent the formation of microbial biofilms mainly through preventing microbial adhesion and killing them. The former is mainly achieved by reducing surface free energy (SFE) and increasing hydrophobicity. The latter mainly includes oxidative stress and photothermal/photodynamic effects. Graphene and its derivatives (GDs) are mainly combined with bioactive ceramic materials, metal materials and macromolecular polymers to play an antimicrobial effect in bone tissue engineering. Concentration, number of layers, and type of GDs often affect the antimicrobial activity of GMs. In this paper, we reviewed relevant osteoinductive and antimicrobial mechanisms of GMs and their applications in bone tissue engineering.

The Transcription Factor NF-κB in Stem Cells and Development

NF-κB (nuclear factor kappa B) belongs to a family of transcription factors known to regulate a broad range of processes such as immune cell function, proliferation and cancer, neuroprotection, and long-term memory. Upcoming fields of NF-κB research include its role in stem cells and developmental processes. In the present review, we discuss one role of NF-κB in development in Drosophila, Xenopus, mice, and humans in accordance with the concept of evo-devo (evolutionary developmental biology). REL domain-containing proteins of the NF-κB family are evolutionarily conserved among these species. In addition, we summarize cellular phenotypes such as defective B- and T-cell compartments related to genetic NF-κB defects detected among different species. While NF-κB proteins are present in nearly all differentiated cell types, mouse and human embryonic stem cells do not contain NF-κB proteins, potentially due to miRNA-dependent inhibition. However, the mesodermal and neuroectodermal differentiation of mouse and human embryonic stem cells is hampered upon the repression of NF-κB. We further discuss NF-κB as a crucial regulator of differentiation in adult stem cells such as neural crest-derived and mesenchymal stem cells. In particular, c-REL seems to be important for neuronal differentiation and the neuroprotection of human adult stem cells, while RELA plays a crucial role in osteogenic and mesodermal differentiation.

Bone physiological microenvironment and healing mechanism: Basis for future bone-tissue engineering scaffolds

Bone-tissue defects affect millions of people worldwide. Despite being common treatment approaches, autologous and allogeneic bone grafting have not achieved the ideal therapeutic effect. This has prompted researchers to explore novel bone-regeneration methods. In recent decades, the development of bone tissue engineering (BTE) scaffolds has been leading the forefront of this field. As researchers have provided deep insights into bone physiology and the bone-healing mechanism, various biomimicking and bioinspired BTE scaffolds have been reported. Now it is necessary to review the progress of natural bone physiology and bone healing mechanism, which will provide more valuable enlightenments for researchers in this field. This work details the physiological microenvironment of the natural bone tissue, bone-healing process, and various biomolecules involved therein. Next, according to the bone physiological microenvironment and the delivery of bioactive factors based on the bone-healing mechanism, it elaborates the biomimetic design of a scaffold, highlighting the designing of BTE scaffolds according to bone biology and providing the rationale for designing next-generation BTE scaffolds that conform to natural bone healing and regeneration.

Associations of Tumor Necrosis Factor Alpha Gene Polymorphisms and Ankylosing Spondylitis Susceptibility: A Meta-analysis Based on 35 Case-control Studies

Background: Scores of studies on tumor necrosis factor alpha (TNF-α) gene polymorphisms and AS have been performed with inconsistent results. The purpose of this study was to provide some more convincing evidence on the associations of TNF-a polymorphisms and AS by using a meta-analysis approach.Methods: Potentially relevant studies were identified from Web of Science, PubMed, EMBASE, Wanfang, and CNKI from inception to March 5, 2020. Newcastle-Ottawa Scale (NOS) was utilized to appraise the quality of included studies. Odds ratios (ORs) with 95% confidence intervals (95%CIs) were calculated to assess the strength of the associations under five genetic models.Results: Thirty-five studies with 37 independent cohorts in total were included in the meta-analysis. Based upon NOS, eligible studies were in moderate- to high quality. The merged data suggested rs1799724 polymorphisms were significantly correlated with a reduced risk of AS (C vs. T, OR = 0.55, 95%CI 0.38-0.79, P < .001, P_Bon = 0.005, P_FDR = 0.003). Subgroup analysis by ethnicity indicated that rs1800629 polymorphism significantly increased the risk of AS in Caucasians and decreased the risk of AS in mixed populations. Besides, rs361525 and rs1800630 polymorphisms conferred to an elevated risk of AS, and rs1799724 conferred to a reduced risk of AS in Asians.Conclusions: This study suggests that rs1800629 polymorphism is associated with an increased AS risk in Caucasians, rs361525 and rs1800630 polymorphisms are linked to an elevated AS susceptibility in Asians.

Osteocalcin and osteoprotegerin levels and their relationship with adipokines and proinflammatory cytokines in children with nonalcoholic fatty liver disease

OBJECTIVES

To investigate the relationship between osteocalcin and osteoprotegerin as bone markers and inflammatory biomarkers such as adiponectin, leptin, tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6) in children with nonalcoholic fatty liver disease (NAFLD).

METHODS

This study included 40 obese children with NAFLD as the patient group and 40 healthy obese children of matched age, sex and BMI as the control group. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), fasting blood glucose, fasting insulin, Homeostatic model assessment method of insulin resistance (HOMA-IR), lipid profile, osteocalcin, osteoprotegerin, adiponectin, leptin, TNF-α, and IL-6 were measured in all participants.

RESULTS

Children with NAFLD had a significant decrease in osteocalcin, osteoprotegerin and adiponectin level with a significant increase in TNF-α and IL-6 levels. We also found a significant positive correlation between osteocalcin level and adiponectin levels but a significant negative correlation of osteocalcin with each of leptin and TNF-α. However, there was a significant negative correlation between osteoprotegerin levels and both TNF-α and IL-6 levels. Moreover, adiponectin and TNF-α were significant predictors for osteocalcin, and IL-6 was a significant predictor for osteoprotegerin.

CONCLUSION

Adiponectin, leptin, TNF-α, and IL-6 have potential association with the changes of osteocalcin and osteoprotegerin levels in children with NAFLD.

Clinical plasma concentration of vinpocetine does not affect osteogenic differentiation of mesenchymal stem cells

AIM

Vinpocetine (Vin) has long been used as a medicine to treat cerebrovascular disorders and as a dietary supplement to improve cognitive functions. Previous studies have revealed that the transcription factor nuclear factor kappa B (NF-κB) activity plays an important role in osteogenic differentiation of mesenchymal stem cells (MSC). Vin inhibits NF-κB-dependent inflammatory responses; however, the effect of Vin on the osteogenic differentiation of MSCs has not been reported. In this study, we aimed to the investigate effect of Vin on the osteogenic differentiation of rat bone marrow-derived MSCs (BMSCs).

METHODS

We treated BMSCs with clinical plasma (0.17 µM) or higher concentrations (5 and 20 µM) of Vin with no significant effect on the cell viability. Alizarin Red S and alkaline phosphatase (ALP) stainings were used to evaluate mineralizations on days 14 and 21. Moreover, expressions of target genes were detected using qRT-PCR analysis.

RESULTS

Osteogenic differentiation of BMSCs did not significantly change with Vin's clinical plasma concentration, but significantly decreased with higher concentrations. Calcium mineralization, ALP staining and mRNA gene expressions of Runx2 and ALP were decreased significantly with high concentrations of Vin, paticularly on day 21.

CONCLUSION

Our in vitro findings suggest that clinically relevant concentration of Vin seems safe to use in elderly patients with respect to osteoporosis. On the other hand, Vin at high concentrations appears to be harmful to bone homeostasis.

Parthenolide Has Negative Effects on In Vitro Enhanced Osteogenic Phenotypes by Inflammatory Cytokine TNF-α via Inhibiting JNK Signaling

Nuclear factor kappa B (NF-κB) regulates inflammatory gene expression and represents a likely target for novel disease treatment approaches, including skeletal disorders. Several plant-derived sesquiterpene lactones can inhibit the activation of NF-κB. Parthenolide (PTL) is an abundant sesquiterpene lactone, found in Mexican Indian Asteraceae family plants, with reported anti-inflammatory activity, through the inhibition of a common step in the NF-κB activation pathway. This study examined the effects of PTL on the enhanced, in vitro, osteogenic phenotypes of human periosteum-derived cells (hPDCs), mediated by the inflammatory cytokine tumor necrosis factor (TNF)-α. PTL had no significant effects on hPDC viability or osteoblastic activities, whereas TNF-α had positive effects on the in vitro osteoblastic differentiation of hPDCs. c-Jun N-terminal kinase (JNK) signaling played an important role in the enhanced osteoblastic differentiation of TNF-α-treated hPDCs. Treatment with 1 µM PTL did not affect TNF-α-treated hPDCs; however, 5 and 10 µM PTL treatment decreased the histochemical detection and activity of alkaline phosphatase (ALP), alizarin red-positive mineralization, and the expression of ALP and osteocalcin mRNA. JNK phosphorylation decreased significantly in TNF-α-treated hPDCs pretreated with PTL. These results suggested that PTL exerts negative effects on the increased osteoblastic differentiation of TNF-α-treated hPDCs by inhibiting JNK signaling.

Burst, Short, and Sustained Vitamin D3 Applications Differentially Affect Osteogenic Differentiation of Human Adipose Stem Cells

Incorporation of 1,25(OH)₂ vitamin D₃ (vitD₃) into tissue-engineered scaffolds could aid the healing of critical-sized bone defects. We hypothesize that shorter applications of vitD₃ lead to more osteogenic differentiation of mesenchymal stem cells (MSCs) than a sustained application. To test this, release from a scaffold was mimicked by exposing MSCs to exactly controlled vitD₃ regimens. Human adipose stem cells (hASCs) were seeded onto calcium phosphate particles, cultured for 20 days, and treated with 124 ng vitD₃, either provided during 30 min before seeding ([200 nM]), during the first two days ([100 nM]), or during 20 days ([10 nM]). Alternatively, hASCs were treated for two days with 6.2 ng vitD₃ ([10 nM]). hASCs attached to the calcium phosphate particles and were viable (~75%). Cell number was not affected by the various vitD₃ applications. VitD₃ (124 ng) applied over 20 days increased cellular alkaline phosphatase activity at Days 7 and 20, reduced expression of the early osteogenic marker RUNX2 at Day 20, and strongly upregulated expression of the vitD₃ inactivating enzyme CYP24. VitD₃ (124 ng) also reduced RUNX2 and increased CYP24 applied at [100 nM] for two days, but not at [200 nM] for 30 min. These results show that 20-day application of vitD₃ has more effect on hASCs than the same total amount applied in a shorter time span.

Inhibition of the epigenetic suppressor EZH2 primes osteogenic differentiation mediated by BMP2

Bone-stimulatory therapeutics include bone morphogenetic proteins (e.g. BMP2), parathyroid hormone, and antibody-based suppression of WNT antagonists. Inhibition of the epigenetic enzyme enhancer of zeste homolog 2 (EZH2) is both bone anabolic and osteoprotective. EZH2 inhibition stimulates key components of bone-stimulatory signaling pathways, including the BMP2 signaling cascade. Because of high costs and adverse effects associated with BMP2 use, here we investigated whether BMP2 dosing can be reduced by co-treatment with EZH2 inhibitors. Co-administration of BMP2 with the EZH2 inhibitor GSK126 enhanced differentiation of murine (MC3T3) osteoblasts, reflected by increased alkaline phosphatase activity, Alizarin Red staining, and expression of bone-related marker genes (e.g. Bglap and Phospho1). Strikingly, co-treatment with BMP2 (10 ng/ml) and GSK126 (5 μm) was synergistic and was as effective as 50 ng/ml BMP2 at inducing MC3T3 osteoblastogenesis. Similarly, the BMP2-GSK126 co-treatment stimulated osteogenic differentiation of human bone marrow-derived mesenchymal stem/stromal cells, reflected by induction of key osteogenic markers (e.g. Osterix/SP7 and IBSP). A combination of BMP2 (300 ng local) and GSK126 (5 μg local and 5 days of 50 mg/kg systemic) yielded more consistent bone healing than single treatments with either compound in a mouse calvarial critical-sized defect model according to results from μCT, histomorphometry, and surgical grading of qualitative X-rays. We conclude that EZH2 inhibition facilitates BMP2-mediated induction of osteogenic differentiation of progenitor cells and maturation of committed osteoblasts. We propose that epigenetic priming, coupled with bone anabolic agents, enhances osteogenesis and could be leveraged in therapeutic strategies to improve bone mass.

EphB4/ TNFR2/ERK/MAPK signaling pathway comprises a signaling axis to mediate the positive effect of TNF-α on osteogenic differentiation

BACKGROUND

Low concentrations of tumor necrosis factor-alpha (TNF-α) and its receptor TNFR2 are both reported to promote osteogenic differentiation of osteoblast precursor cells. Moreover, low concentrations of TNF-α up-regulate the expression of EphB4. However, the molecular mechanisms underlying TNF-α-induced osteogenic differentiation and the roles of TNFR2 and EphB4 have not been fully elucidated.

RESULTS

The ALP activity, as well as the mRNA and protein levels of RUNX2, BSP, EphB4 and TNFR2, was significantly elevated in MC3T3-E1 murine osteoblast precursor cells when stimulated with 0.5 ng/ml TNF-α. After TNFR2 was inhibited by gene knockdown with lentivirus-mediated shRNA interference or by a neutralizing antibody against TNFR2, the pro-osteogenic effect of TNF-α was partly reversed, while the up-regulation of EphB4 by TNF-α remained unchanged. With EphB4 forward signaling suppressed by a potent inhibitor of EphB4 auto-phosphorylation, NVP-BHG712, TNF-α-enhanced expressions of TNFR2, BSP and Runx2 were significantly decreased. Further investigation into the signaling pathways revealed that TNF-α significantly increased levels of p-JNK, p-ERK and p-p38. However, only the p-ERK level was significantly inhibited in TNFR2-knockdown cells. In addition, the ERK pathway inhibitor, U0126 (10 μM), significantly reversed the positive effect of TNF-α on the protein levels of RUNX2 and BSP.

CONCLUSIONS

The EphB4, TNFR2 and ERK/MAPK signaling pathway comprises a signaling axis to mediate the positive effect of TNF-α on osteogenic differentiation.

Resveratrol rescues TNF‑α‑induced inhibition of osteogenesis in human periodontal ligament stem cells via the ERK1/2 pathway

Periodontitis is a common inflammatory disorder affecting the tissues surrounding the teeth, which can lead to the destruction of periodontal tissue and tooth loss. Resveratrol, a natural phytoalexin, exerts multiple biological effects. For example, its anti-inflammatory activity has been widely studied for the treatment of inflammatory bowel disease for a number of years. However, its effect on bone repair and new bone formation in an inflammatory microenvironment is not well understood. Accordingly, the effect of resveratrol on inflammation-affected human periodontal ligament stem cells (hPDLSCs) requires further investigation. In the present study, the effect of tumor necrosis factor-α (TNF-α), resveratrol, or the combination of both on the osteogenic differentiation of hPDLSCs, as well as the underlying mechanisms involved, were investigated. Cell Counting Kit-8 assay, alkaline phosphatase staining, Alizarin red staining, Oil Red O staining, reverse transcription-quantitative PCR and western blotting were used in the present study. It was demonstrated that resveratrol enhanced hPDLSC osteogenesis and reversed the inhibitory effects of TNF-α on this process. Further mechanistic studies indicated that resveratrol exerted anti-inflammatory activity by activating the ERK1/2 pathway, decreasing the secretion of interleukin (IL)-6 and IL-8 induced by TNF-α, and enhancing hPDLSCs osteogenesis. The present study suggested that resveratrol may be a novel and promising therapeutic choice for periodontitis.

miR-21 may Act as a Potential Mediator Between Inflammation and Abnormal Bone Formation in Ankylosing Spondylitis Based on TNF-α Concentration-Dependent Manner Through the JAK2/STAT3 Pathway

Objective:

To explore the role of microRNA (miR-21) in new bone formation in ankylosing spondylitis (AS) as mediated by different concentration of tumor necrosis factor-α (TNF-α).

Methods:

Fibroblasts isolated from the hips of patients with AS were induced to osteogenesis. These cells were then stimulated with varying concentrations of TNF-α. MicroRNA-21 expressions were evaluated using reverse transcription–polymerase chain reaction (RT-PCR) and osteogenesis was detected via Alizarin Red S (ARS) staining and measurement of alkaline phosphatase (ALP) activity. Relative expressions of p-STAT3, Nuclear STAT3, cytoplasm STAT3, Runx2, BMP2, osteopontin, osteocalcin, and LC3B in AS fibroblasts were measured after exposure to different concentrations of TNF-α. The STAT3-inhibiting small interfering RNA allowed further exploration on its impact on miR-21 and primary miR-21 expressions. A proteoglycan-induced arthritis (PGIA) Balb/c mouse model was established in order to monitor sacroiliac joint (SIJ) inflammation and subsequent damage through magnetic resonance image. Serum miR-21 and TNF-α expressions were evaluated using RT-PCR and enzyme-linked immunosorbent assay. At week 16, mice models were transfected intravenously with miR-21 overexpressing agomir and miR-21 inhibiting antagomir for 7 successive days. The rate of abnormal bone formation at SIJ was evaluated using microcomputed tomography and hematoxylin and eosin staining at week 24. Western blot analysis enabled quantification of STAT-3, JAK-2, and interleukin (IL)-17A expressions present in the SIJ.

Results:

The in vitro miR-21 expression and osteogenesis activity were noted to be augmented in the setting of low TNF-α concentrations (0.01-0.1 ng/mL) while they were depressed in settings with higher TNF-α concentrations (1-10 ng/mL). Samples with the most distinct ARS manifestation and ALP activity as well as the highest miR-21 expressions were those who received 0.1 ng/mL of TNF-α. Primary miR-21 was found to be notable raised by Si-STAT3, while the converse effect was seen in mature miR-21 expressions. Intravenous injection of exogenous miR-21 contributed to new bone formation and significantly elevated expressions of STAT3, JAK2, and IL-17 in PGIA mice.

Conclusions:

The results revealed that miR-21 may act as a potential mediator between new bone formation and inflammation in AS.

Review of the Pathways Involved in the Osteogenic Differentiation of Adipose-Derived Stem Cells

Grafts and prosthetic materials used for the repair of bone defects are often accompanied by comorbidity and rejection. Therefore, there is an immense need for novel approaches to combating the issues surrounding such defects. Because of their accessibility, substantial proportion, and osteogenic differentiation potential, adipose-derived stem cells (ASCs) make for an ideal source of bone tissue in regenerative medicine. However, efficient induction of ASCs toward an osteoblastic lineage in vivo is met with challenges, and many signaling pathways must come together to secure osteoblastogenesis. Among them are bone morphogenic protein, wingless-related integration site protein, Notch, Hedgehog, fibroblast growth factor, vascular endothelial growth factor, and extracellular regulated-signal kinase. The goal of this literature review is to conglomerate the present research on these pathways to formulate a better understanding of how ASCs are most effectively transformed into bone in the context of tissue engineering.

An update on pathogenesis of psoriatic arthritis and potential therapeutic targets

Introduction: Innate immune response and bone remodeling are key factors contributing to the pathogenesis of psoriatic arthritis (PsA). Moreover, the evidence of autoantibodies in patients' sera suggests an autoimmune side in PsA. Besides the immune pathways, studies strongly support the role of genetic risk alleles in affecting the clinical heterogeneity of PsA as well as the response to therapy. A good clinical response to treatment, indeed, represents a challenge in PsA patients and the identification of patient-targeted therapies is still a critical issue. Areas covered: We performed a systematic review aiming at describing new evidence on PsA pathogenesis and treatments. Reported items for systematic reviews (PRISMA checklist) were analyzed. Studies included from the PubMed database addressed the following items: innate immunity, autoimmunity, bone remodeling, and therapeutic targets in PsA; time frame of research 1970-2019. Specifically, we reviewed data on IL-17 inhibitors, abatacept, JAK inhibitors, ABT 122, and A (3) adenosine receptors agonist, CF101. Expert opinion: In PsA an intriguing pathogenetic network has been documented. Several biological and synthetic drugs are promising in terms of efficacy and safety profile.

ELP2 negatively regulates osteoblastic differentiation impaired by tumor necrosis factor α in MC3T3-E1 cells through STAT3 activation

Tumor necrosis factor‐α (TNF‐α) is a pluripotent signaling molecule. The biological effect of TNF‐α includes slowing down osteogenic differentiation, which can lead to bone dysplasia in long‐term inflammatory microenvironments. Signal transducer and activator of transcription 3 (STAT3)‐interacting protein 1 (StIP1, also known as elongator complex protein 2, ELP2) play a role in inhibiting TNF‐α‐induced osteoblast differentiation. In the present study, we investigated whether and how ELP2 activation mediates the effects of TNF‐α on osteoblastic differentiation. Using in vitro cell cultures of preosteoblastic MC3T3‐E1 cells, we found that TNF‐α inhibited osteoblastic differentiation accompanied by an increase in ELP2 expression and STAT3 activation. Forced ELP2 expression inhibited osteogenic differentiation of MC3T3‐E1 cells, with a decrease in the expression of osteoblast marker genes, alkaline phosphatase activity, and matrix mineralization capacity. In contrast, ELP2 silencing ameliorated osteogenic differentiation in MC3T3‐E1 cells, even after TNF‐α stimulation. The TNF‐α‐induced inhibitory effect on osteoblastic differentiation was therefore mediated by ELP2, which was associated with Janus kinase 2 (JAK2)/STAT3 activation. These results suggest that ELP2 is upregulated at the differentiation of MC3T3‐E1 cells into osteoblasts and inhibits osteogenic differentiation in response to TNF‐α through STAT3 activation.

Targeting tumor necrosis factor receptors in ankylosing spondylitis

Over the past two decades, considerable advances in our understanding of inflammatory and immune pathways have allowed for the growing use of targeted biologic therapy. Most notably, the introduction of tumor necrosis factor (TNF) inhibitors has dramatically changed the management of autoimmune inflammatory disorders, including ankylosing spondylitis (AS). Despite the efficacy of TNF inhibitors documented in multiple clinical trials, anti-TNF therapy in AS is far from foolproof; it is associated with serious adverse effects and limited response to therapy in some patients. Moreover, specific questions regarding the role of TNF as a mediator of AS remain unanswered. Therefore, additional efforts are needed in order to better understand the role of TNF in the pathogenesis of AS and to develop safer and more effective treatment strategies. The purpose of this review is to better the understanding of the physiologic and pathogenic roles of TNF signaling in the course of AS. Relevant TNF biology and novel approaches to TNF blockade in AS are discussed.

Altered Bone Remodeling in Psoriatic Disease: New Insights and Future Directions

Psoriatic arthritis (PsA) is an inflammatory rheumatic disorder that occurs in patients with psoriasis and predominantly affects musculoskeletal structures, skin, and nails. The etiology of PsA is not well understood but evidence supports an interplay of genetic, immunologic, and environmental factors which promote pathological bone remodeling and joint damage in PsA. Localized and systemic bone loss due to increased activity of osteoclasts is well established in PsA based on animal models and translational studies. In contrast, the mechanisms responsible for pathological bone remodeling in PsA remain enigmatic although new candidate molecules and pathways have been identified. Recent reports have revealed novel findings related to bone erosion and pathologic bone formation in PsA. Many associated risk factors and contributing molecular mechanisms have also been identified. In this review, we discuss new developments in the field, point out unresolved questions regarding the pathogenetic origins of the wide array of bone phenotypes in PsA, and discuss new directions for investigation.

Current Approaches to Bone Tissue Engineering: The Interface between Biology and Engineering

The successful regeneration of bone tissue to replace areas of bone loss in large defects or at load-bearing sites remains a significant clinical challenge. Over the past few decades, major progress is achieved in the field of bone tissue engineering to provide alternative therapies, particularly through approaches that are at the interface of biology and engineering. To satisfy the diverse regenerative requirements of bone tissue, the field moves toward highly integrated approaches incorporating the knowledge and techniques from multiple disciplines, and typically involves the use of biomaterials as an essential element for supporting or inducing bone regeneration. This review summarizes the types of approaches currently used in bone tissue engineering, beginning with those primarily based on biology or engineering, and moving into integrated approaches in the areas of biomaterial developments, biomimetic design, and scalable methods for treating large or load-bearing bone defects, while highlighting potential areas for collaboration and providing an outlook on future developments.

Preconditioning of murine mesenchymal stem cells synergistically enhanced immunomodulation and osteogenesis

Background

Mesenchymal stem cells (MSCs) are capable of immunomodulation and tissue regeneration, highlighting their potential translational application for treating inflammatory bone disorders. MSC-mediated immunomodulation is regulated by proinflammatory cytokines and pathogen-associated molecular patterns such as lipopolysaccharide (LPS). Previous studies showed that MSCs exposed to interferon gamma (IFN-γ) and the proinflammatory cytokine tumor necrosis factor alpha (TNF-α) synergistically suppressed T-cell activation.

Methods

In the current study, we developed a novel preconditioning strategy for MSCs using LPS plus TNF-α to optimize the immunomodulating ability of MSCs on macrophage polarization.

Results

Preconditioned MSCs enhanced anti-inflammatory M2 macrophage marker expression (Arginase 1 and CD206) and decreased inflammatory M1 macrophage marker (TNF-α/IL-1Ra) expression using an in-vitro coculture model. Immunomodulation of MSCs on macrophages was significantly increased compared to the combination of IFN-γ plus TNF-α or single treatment controls. Increased osteogenic differentiation including alkaline phosphate activity and matrix mineralization was only observed in the LPS plus TNF-α preconditioned MSCs. Mechanistic studies showed that increased prostaglandin E2 (PGE2) production was associated with enhanced Arginase 1 expression. Selective cyclooxygenase-2 inhibition by Celecoxib decreased PGE2 production and Arginase 1 expression in cocultured macrophages.

Conclusions

The novel preconditioned MSCs have increased immunomodulation and bone regeneration potential and could be applied to the treatment of inflammatory bone disorders including periprosthetic osteolysis, fracture healing/nonunions, and osteonecrosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0730-z) contains supplementary material, which is available to authorized users.

Strategies for MSC expansion and MSC-based microtissue for bone regeneration

Mesenchymal stem cells (MSCs) have gained increasing attention as a potential approach for the treatment of bone injuries due to their multi-lineage differentiation potential and also their ability to recognize and home to damaged tissue sites, secreting bioactive factors that can modulate the immune system and enhance tissue repair. However, a wide gap between the number of MSCs obtainable from the donor site and the number required for implantation, as well as the lack of understanding of MSC functions under different in vitro and in vivo microenvironment, hinders the progression of MSCs toward clinical settings. The clinical translation of MSCs pre-requisites a scalable expansion process for the biomanufacturing of therapeutically qualified cells. This review briefly introduces the features of implanted MSCs to determine the best strategies to optimize their regenerative capacity, as well as the current MSC implantation for bone diseases. Current achievements for expansion of MSCs using various culturing methods, bioreactor technologies, biomaterial platforms, as well as microtissue-based expansion strategies are also discussed, providing new insights into future large-scale MSC expansion and clinical applications.

TNF and Bone Remodeling

PURPOSE OF REVIEW

The mechanisms involved in the TNF-mediated deregulated bone remodeling are little appreciated. This review will discuss and summarize the impact of TNF, Notch, and RBP-J signaling on bone remodeling.

RECENT FINDINGS

The integrity of the adult skeleton undergoes constant and dynamic remodeling throughout life to maintain a proper bone homeostasis, which is achieved by the essential tight control of coupling between osteoclast-mediated bone resorption and osteoblast-mediated bone formation. The studies in this field include not only the differentiation and function of osteoblasts and osteoclasts, but also the mechanisms that simultaneously control both cell types during bone remodeling. Chronic inflammation is one of the most evident and common pathological settings that often leads to deregulated bone remodeling. The resounding success of TNF blockade therapy has demonstrated a key role for TNF in inflammation and the pathogenesis of inflammatory bone resorption associated with diseases such as rheumatoid arthritis and periodontitis. Recent studies have highlighted the function of Notch and RBP-J signaling in both physiological and TNF-mediated inflammatory bone remodeling.

Mesenchymal stem cells in the aseptic loosening of total joint replacements

Peri-prosthetic osteolysis remains as the main long-term complication of total joint replacement surgery. Research over four decades has established implant wear as the main culprit for chronic inflammation in the peri-implant tissues and macrophages as the key cells mediating the host reaction to implant-derived wear particles. Wear debris activated macrophages secrete inflammatory mediators that stimulate bone resorbing osteoclasts; thus bone loss in the peri-implant tissues is increased. However, the balance of bone turnover is not only dictated by osteoclast-mediated bone resorption but also by the formation of new bone by osteoblasts; under physiological conditions these two processes are tightly coupled. Increasing interest has been placed on the effects of wear debris on the cells of the bone-forming lineage. These cells are derived primarily from multipotent mesenchymal stem cells (MSCs) residing in bone marrow and the walls of the microvasculature. Accumulating evidence indicates that wear debris significantly impairs MSC-to-osteoblast differentiation and subsequent bone formation. In this review, we summarize the current understanding of the effects of biomaterial implant wear debris on MSCs. Emerging treatment options to improve initial implant integration and treat developing osteolytic lesions by utilizing or targeting MSCs are also discussed. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1195-1207, 2017.

Inducing Temporal and Reversible Autophagy by Nanotopography for Potential Control of Cell Differentiation

Tuning autophagy has become a new strategy to control cell differentiation in tissue engineering. The nanosized surface is well-known for its ability to interfere with intracellular procedures, while its role in autophagy regulation is unclear. In this study, we found that a nanotube (NT) structure was able to induce enhanced mTOR-independent autophagy in osteoblasts compared to a flat surface. Further analysis revealed that autophagy was temporally promoted by NTs in the initial day contact and it was also reversible by exchanging the substrate nanotopographies. Actin filaments were significantly dispersed and there were numerous filopodia on the leading edge of cells grown on the NT surface. Intracellular Ca²⁺ was significantly increased on the NT surface. Moreover, the phenomenon was also found on different nanotopographies as well as in different cell lines. These indicated that cell membrane stretching might be the central regulation factor. Finally, we found that the NT surface exhibited enhanced autophagy-dependent osteogenic differentiation efficacy. In addition, the enhancement on NT surface could be remembered. In conclusion, the nanotopographic surface is able to induce temporal, reversible, and memorable autophagy via cell membrane stretching, which may be used as a versatile method to control cell differentiation.

NF-κB as a Therapeutic Target in Inflammatory-Associated Bone Diseases

Inflammation is a defensive mechanism for pathogen clearance and maintaining tissue homeostasis. In the skeletal system, inflammation is closely associated with many bone disorders including fractures, nonunions, periprosthetic osteolysis (bone loss around orthopedic implants), and osteoporosis. Acute inflammation is a critical step for proper bone-healing and bone-remodeling processes. On the other hand, chronic inflammation with excessive proinflammatory cytokines disrupts the balance of skeletal homeostasis involving osteoblastic (bone formation) and osteoclastic (bone resorption) activities. NF-κB is a transcriptional factor that regulates the inflammatory response and bone-remodeling processes in both bone-forming and bone-resorption cells. In vitro and in vivo evidences suggest that NF-κB is an important potential therapeutic target for inflammation-associated bone disorders by modulating inflammation and bone-remodeling process simultaneously. The challenges of NF-κB-targeting therapy in bone disorders include: (1) the complexity of canonical and noncanonical NF-κB pathways; (2) the fundamental roles of NF-κB-mediated signaling for bone regeneration at earlier phases of tissue damage and acute inflammation; and (3) the potential toxic effects on nontargeted cells such as lymphocytes. Recent developments of novel inhibitors with differential approaches to modulate NF-κB activity, and the controlled release (local) or bone-targeting drug delivery (systemic) strategies, have largely increased the translational application of NF-κB therapy in bone disorders. Taken together, temporal modulation of NF-κB pathways with the combination of recent advanced bone-targeting drug delivery techniques is a highly translational strategy to reestablish homeostasis in the skeletal system.

Low concentrations of TNF-α promote osteogenic differentiation via activation of the ephrinB2-EphB4 signalling pathway

OBJECTIVES

Low concentrations of tumour necrosis factor-alpha (TNF-α) have been reported to promote osteogenic differentiation. In this study, a series of in vitro experiments was performed to investigate underlying molecular mechanisms involved.

MATERIALS AND METHODS

MC3T3-E1 murine preosteoblasts were treated with TNF-α at doses of 0, 0.1 or 1 ng/mL. The ephrinB2-EphB4 signalling pathway was activated using ephrinB2-fc, or inhibited using lentiviruses encoding siRNAs specifically targeting EphB4. Cell proliferation/survival was evaluated using the Cell Counting Kit-8 (CCK-8) assay, and expression levels of Runx2, BSP, ephrinB2 and EphB4 were determined using RT-PCR and Western blotting. ALP activity in these cells was also determined, and mineral nodule formation was evaluated with alizarin red S staining.

RESULTS

Low concentrations of TNF-α had no influence on cell proliferation/survival. However, expression levels of Runx2, BSP, ephrinB2 and EphB4, as well as ALP activity and mineral nodule formation, were significantly enhanced in MC3T3-E1 cells treated with low concentrations of TNF-α. Moreover, activation of the ephrinB2-EphB4 signalling pathway by ephrinB2-fc enhanced TNF-α-induced osteogenic differentiation, while down-regulation of EphB4 level reversed the positive effect of TNF-α.

CONCLUSIONS

Low concentrations of TNF-α promoted osteogenic differentiation via activation of the ephrinB2-EphB4 signalling pathway.

Cytokines TNF-α, IL-6, IL-17F, and IL-4 Differentially Affect Osteogenic Differentiation of Human Adipose Stem Cells

During the initial stages of bone repair, proinflammatory cytokines are released within the injury site, quickly followed by a shift to anti-inflammatory cytokines. The effect of pro- and anti-inflammatory cytokines on osteogenic differentiation of mesenchymal stem cells is controversial. Here, we investigated the effect of the proinflammatory cytokines TNF-α, IL-6, IL-8, and IL-17F and the anti-inflammatory cytokine IL-4 on proliferation and osteogenic differentiation of human adipose stem cells (hASCs). hASCs were treated with TNF-α, IL-6, IL-8, IL-17F, or IL-4 (10 ng/mL) for 72 h mimicking bone repair. TNF-α reduced collagen type I gene expression but increased hASC proliferation and ALP activity. IL-6 also strongly enhanced ALP activity (18-fold), as well as bone nodule formation by hASCs. IL-8 did not affect proliferation or osteogenic gene expression but reduced bone nodule formation. IL-17F decreased hASC proliferation but enhanced ALP activity. IL-4 enhanced osteocalcin gene expression and ALP activity but reduced RUNX2 gene expression and bone nodule formation. In conclusion, all cytokines studied have both enhancing and reducing effects on osteogenic differentiation of hASCs, even when applied for 72 h only. Some cytokines, specifically IL-6, may be suitable to induce osteogenic differentiation of mesenchymal stem cells as a strategy for enhancing bone repair.

Increased sensitivity of rheumatoid synoviocytes to Schnurri-3 expression in TNF-α and IL-17A induced osteoblastic differentiation

OBJECTIVE

To compare the effects of TNF-α and IL-17A on osteogenic differentiation of isolated fibroblast-like synoviocytes (FLS) from healthy donors, osteoarthritis (OA) and rheumatoid arthritis (RA) patients.

METHODS

FLS were cultured in osteogenic medium, with and without TNF-α and/or IL-17A. Extracellular matrix mineralization was evaluated by alizarin red staining and alkaline phosphatase activity (ALP) measurement. mRNA expression was analyzed by qRT-PCR for Wnt5a, BMP2 and Runx2, genes associated with osteogenesis, for DKK1 and RANKL, genes associated with osteogenesis inhibition and Schnurri-3, a new critical gene in the cross talk with osteoclasts. IL-6 and IL-8 production was measured by ELISA.

RESULTS

In osteogenic medium, matrix mineralization and increased ALP activity indicated that FLS can undergo osteogenic differentiation, which was increased with TNF-α and IL-17A. The expression of osteogenesis activators (BMP2 and Wnt5a) was increased with cytokines and that of the osteogenesis inhibitor DKK1 was decreased. There was no difference between all three cell types. In contrast, RA FLS were particularly sensitive to the synergistic increase of Shn3 with TNF-α and IL-17A. Levels of IL-6 and IL-8 were also higher for RA-FLS, compared to healthy and OA FLS.

CONCLUSION

IL-17A and/or TNF-α treatment favor an osteogenesis induction in isolated FLS, independent of their origin. RA-FLS were more sensitive to the synergistic increase of Schnurri-3 expression. Combined with the higher levels of inflammation, this may in turn activate osteoclastogenesis, leading to increased bone destruction seen in destructive arthritis.

Serum of patients with active rheumatoid arthritis inhibits differentiation of osteochondrogenic precursor cells

Delayed fracture healing is frequently experienced in patients with systemic inflammation such as during rheumatoid arthritis (RA). The reasons for this are diverse, but could also be caused by inflammatory cytokines and/or growth factors in serum from patients with active disease. We hypothesized that serum from patients with active RA contains circulating inflammatory factors that inhibit differentiation of osteochondrogenic precursors. Serum was obtained from 15 patients with active RA (active RA-sera) and from the same patients in clinical remission 1 year later (remission RA-sera; controls). The effect of active RA-sera on osteochondrogenic differentiation of chondrogenic ATDC5 cells and primary human periosteum-derived progenitor cells (HPDC) was determined in micromass culture. In ATDC5 cells, active RA-sera reduced Ki67 transcription levels by 40% and cartilage matrix accumulation by 14% at day 14, and Alp transcription levels by 16%, and matrix mineralization by 17% at day 21 compared with remission RA-sera. In HPDCs, active RA-sera inhibited metabolic activity by 8%, SOX9 transcription levels by 14%, and cartilage matrix accumulation by 7% at day 7 compared with remission RA-sera. In conclusion, sera from patients with active RA negatively affect differentiation of osteochondrogenic precursors, and as a consequence may contribute to delayed fracture healing in these patients.

Needle-like ion-doped hydroxyapatite crystals influence osteogenic properties of PCL composite scaffolds

Surface topography and chemistry both play a crucial role on influencing cell response in 3D porous scaffolds in terms of osteogenesis. Inorganic materials with peculiar morphology and chemical functionalities may be proficiently used to improve scaffold properties-in the bulk and along pore surface-promoting in vitro and in vivo osseous tissue in-growth. The present study is aimed at investigating how bone regenerative properties of composite scaffolds made of poly(Ɛ-caprolactone) (PCL) can be augmented by the peculiar properties of Mg(2+) ion doped hydroxyapatite (dHA) crystals, mainly emphasizing the role of crystal shape on cell activities mediated by microstructural properties. At the first stage, the study of mechanical response by crossing experimental compression tests and theoretical simulation via empirical models, allow recognizing a significant contribution of dHA shape factor on scaffold elastic moduli variation as a function of the relative volume fraction. Secondly, the peculiar needle-like shape of dHA crystals also influences microscopic (i.e. crystallinity, adhesion forces) and macroscopic (i.e. roughness) properties with relevant effects on biological response of the composite scaffold: differential scanning calorimetry (DSC) analyses clearly indicate a reduction of crystallization heat-from 66.75 to 43.05 J g(-1)-while atomic force microscopy (AFM) ones show a significant increase of roughness-from (78.15  ±  32.71) to (136.13  ±  63.21) nm-and of pull-off forces-from 33.7% to 48.7%. Accordingly, experimental studies with MG-63 osteoblast-like cells show a more efficient in vitro secretion of alkaline phosphatase (ALP) and collagen I and a more copious in vivo formation of new bone trabeculae, thus suggesting a relevant role of dHA to support the main mechanisms involved in bone regeneration.

Low-dose TNF augments fracture healing in normal and osteoporotic bone by up-regulating the innate immune response

The mechanism by which trauma initiates healing remains unclear. Precise understanding of these events may define interventions for accelerating healing that could be translated to the clinical arena. We previously reported that addition of low-dose recombinant human TNF (rhTNF) at the fracture site augmented fracture repair in a murine tibial fracture model. Here, we show that local rhTNF treatment is only effective when administered within 24 h of injury, when neutrophils are the major inflammatory cell infiltrate. Systemic administration of anti-TNF impaired fracture healing. Addition of rhTNF enhanced neutrophil recruitment and promoted recruitment of monocytes through CCL2 production. Conversely, depletion of neutrophils or inhibition of the chemokine receptor CCR2 resulted in significantly impaired fracture healing. Fragility, or osteoporotic, fractures represent a major medical problem as they are associated with permanent disability and premature death. Using a murine model of fragility fractures, we found that local rhTNF treatment improved fracture healing during the early phase of repair. If translated clinically, this promotion of fracture healing would reduce the morbidity and mortality associated with delayed patient mobilization.

In vitro evaluation of the risk of inflammatory response after chitosan/HA and chitosan/β-1,3-glucan/HA bone scaffold implantation

The aim of the study was to evaluate in vitro the risk of inflammatory response induced by chitosan/hydroxyapatite (chit/HA) and novel chitosan/β-1,3-glucan/hydroxyapatite (chit/glu/HA) bone scaffolds. The inflammatory response was assessed via measurement of proinflammatory cytokine and ROI production by human monocytes, macrophages, and osteoblasts stimulated with investigated scaffolds. Moreover, adsorption of human serum/plasma proteins to the tested materials was determined. Both biomaterials did not induce intracellular ROI generation by monocytes, macrophages, and osteoblasts and did not stimulate proinflammatory cytokine (IL-6 and TNF-α) production by inflammatory cells. Moreover, the chit/glu/HA material induced increased TNF-α production by osteoblasts that is believed to enhance osteogenic differentiation. Thus, it was demonstrated that chit/HA and chit/glu/HA scaffolds carry a low risk of biomaterial-induced inflammatory response and are promising materials as bone scaffolds for bone tissue engineering and regenerative medicine applications.

Multiple roles of tumor necrosis factor-alpha in fracture healing

This review presents a summary of basic science evidence examining the influence of tumor necrosis factor-alpha (TNF-α) on secondary fracture healing. Multiple studies suggest that TNF-α, in combination with the host reservoir of peri-fracture mesenchymal stem cells, is a main determinant in the success of bone healing. Disease states associated with poor bone healing commonly have inappropriate TNF-α responses, which likely contributes to the higher incidence of delayed and nonunions in these patient populations. Appreciation of TNF-α in fracture healing may lead to new therapies to augment recovery and reduce the incidence of complications.

Paracrine effect of inflammatory cytokine-activated bone marrow mesenchymal stem cells and its role in osteoblast function

Mesenchymal stem cells (MSCs) have a crucial function in bone regeneration. Inflammation is a well-documented component of the osteogenic microenvironment. In the present study, we investigated whether stimulation of MSCs with inflammatory cytokines promotes osteogenesis through a paracrine mediator. MSCs were pre-stimulated with the inflammatory factors IFN-γ and TNF-α. After pre-stimulation, the MSC secretion levels of IL-6, HGF, VEGF, and TGF-β were significantly elevated (p < 0.01); however, the production of IL-2, IL-4, and IL-10 was not changed (p > 0.05). MG63, an osteoblast-like cell line, was cultured in different MSC-conditioned media. After treatment with conditioned media collected from MSCs pre-treated with cytokines, the proliferation and migration of MG63 cells were significantly improved, and the expression levels of the osteoblast differentiation markers ALP, COLI, OCN and OPN were significantly increased as revealed by a quantitative PCR analysis (p < 0.05). Furthermore, an immunofluorescence staining assay showed that more MG63 cells were OPN-positive, while an Alizarin red staining indicated the increased formation of calcium nodules in the IFN-γ and TNF-α combined pretreatment group. The results indicated that conditioned medium from inflammatory cytokine-activated MSCs can significantly promote osteoblast proliferation, migration, differentiation, and mineralization and ultimately enhance osteogenesis through paracrine mechanisms. These findings present a new direction for the clinical application of MSCs in the repair of bone defects.

Skeletal tissue engineering using mesenchymal or embryonic stem cells: clinical and experimental data

INTRODUCTION

Mesenchymal stem cells (MSCs) can be obtained from a wide variety of tissues for bone tissue engineering such as bone marrow, adipose, birth-associated, peripheral blood, periosteum, dental and muscle. MSCs from human fetal bone marrow and embryonic stem cells (ESCs) are also promising cell sources.

AREAS COVERED

In vitro, in vivo and clinical evidence was collected using MEDLINE® (1950 to January 2014), EMBASE (1980 to January 2014) and Google Scholar (1980 to January 2014) databases.

EXPERT OPINION

Enhanced results have been found when combining bone marrow-derived mesenchymal stem cells (BMMSCs) with recently developed scaffolds such as glass ceramics and starch-based polymeric scaffolds. Preclinical studies investigating adipose tissue-derived stem cells and umbilical cord tissue-derived stem cells suggest that they are likely to become promising alternatives. Stem cells derived from periosteum and dental tissues such as the periodontal ligament have an osteogenic potential similar to BMMSCs. Stem cells from human fetal bone marrow have demonstrated superior proliferation and osteogenic differentiation than perinatal and postnatal tissues. Despite ethical concerns and potential for teratoma formation, developments have also been made for the use of ESCs in terms of culture and ideal scaffold.

Proinflammatory Mediators Enhance the Osteogenesis of Human Mesenchymal Stem Cells after Lineage Commitment

Several inflammatory processes underlie excessive bone formation, including chronic inflammation of the spine, acute infections, or periarticular ossifications after trauma. This suggests that local factors in these conditions have osteogenic properties. Mesenchymal stem cells (MSCs) and their differentiated progeny contribute to bone healing by synthesizing extracellular matrix and inducing mineralization. Due to the variation in experimental designs used in vitro, there is controversy about the osteogenic potential of proinflammatory factors on MSCs. Our goal was to determine the specific conditions allowing the pro-osteogenic effects of distinct inflammatory stimuli. Human bone marrow MSCs were exposed to tumor necrosis factor alpha (TNF-α) and lipopolysaccharide (LPS). Cells were cultured in growth medium or osteogenic differentiation medium. Alternatively, bone morphogenetic protein 2 (BMP-2) was used as osteogenic supplement to simulate the conditions in vivo. Alkaline phosphatase activity and calcium deposition were indicators of osteogenicity. To elucidate lineage commitment-dependent effects, MSCs were pre-differentiated prior treatment. Our results show that TNF-α and LPS do not affect the expression of osteogenic markers by MSCs in the absence of an osteogenic supplement. In osteogenic differentiation medium or together with BMP-2 however, these mediators highly stimulated their alkaline phosphatase activity and subsequent matrix mineralization. In pre-osteoblasts, matrix mineralization was significantly increased by these mediators, but irrespective of the culture conditions. Our study shows that inflammatory factors potently enhance the osteogenic capacity of MSCs. These properties may be harnessed in bone regenerative strategies. Importantly, the commitment of MSCs to the osteogenic lineage greatly enhances their responsiveness to inflammatory signals.

High dose of TNF-α suppressed osteogenic differentiation of human dental pulp stem cells by activating the Wnt/β-catenin signaling

Dental pulp stem cells (DPSCs) were a clonogenic, highly proliferative cells capable of self-renewal and multi-lineage differentiation including chondrocytes, adipocytes, neural cells and osteoblasts, which make it an attractive choice for bone regeneration and repair of craniofacial defects. Recent studies showed that tumor necrosis factor α (TNF-α) may affect osteoclastogenesis and bone formation. However, the effect and mechanism of TNF-α on DPSCs is not clear. In this study, we found that low dose TNF-α promoted mineralization and high dose TNF-α suppressed osteogenic differentiation of DPSCs. Levels of ALP, Osteopontin, Osteocalcin, Osterix and Runx2 were up-regulated in DPSCs treated with TNF-α at low concentration, while down-regulated in DPSCs treated with TNF-α at high concentration. Blockade of Wnt/β-catenin signaling reversed the inhibitory effect observed on osteogenic differentiation of DPSCs treated with TNF-α at high concentration. In addition, we did not detect any proliferative effect of TNF-α on DPSCs by cell cycle and cell counts analysis. In summary, our data suggested that high concentration TNF-α suppressed mineralization and mineralization-related gene expressions through the Wnt/β-catenin signaling in DPSCs. Our findings may provide a foundation for autologous transplantation of DPSCs.

Role of transforming growth factor-activated kinase-1 on tumor necrosis factor-α actions in human adipose tissue-derived stromal cells

Tumor necrosis factor-α (TNF-α) has multiple effects on proliferation and differentiation of human mesenchymal stem cells. Transforming growth factor-activated kinase-1 (TAK1) mediates the activation of nuclear factor-kappa B (NF-κB), c-Jun N-terminal kinase (JNK), and p38 pathways in response to TNF-α. However, the role of TAK1 in TNF-α-induced effects in human adipose-derived stem cells (hADSCs) and its signaling pathway has not been clearly defined. Therefore, this study was designated to clarify the role of TAK1 in TNF-α-induced actions on proliferation and differentiation of hADSCs and its downstream signaling pathway. Inhibiting TAK1 expression inhibited the TNF-α-induced increase in osteogenic differentiation and basal osteogenic differentiation without affecting the TNF-α-induced effect on proliferation and adipogenic differentiation of hADSCs. A western blot analysis showed that TNF-α treatment induced degradation of IκB, but that TAK1 small interfering RNA (siRNA) transfection did not protect against TNF-α-induced IκB degradation. The transfection of TAK1 siRNA also did not affect TNF-α-induced IκB phosphorylation or ERK1/2 phosphorylation. However, downregulating TAK1 inhibited this TNF-α-induced S536 phosphorylation of the p65 subunit. TNF-α treatment induced p38 phosphorylation, which was inhibited by the transfection of TAK1 siRNA. Adding p38 inhibitor inhibited TNF-α-induced p65 phosphorylation, NF-κB promoter activity, and TNF-α-induced increase in hADSC osteogenic differentiation. These data indicate that TAK1 is involved in the TNF-α-induced activation of p38 kinase, which subsequently phosphorylates the NF-κB p65 subunit, and increases the transactivation potential of p65 and osteogenic differentiation in hADSCs.

Tumor necrosis factor improves vascularization in osteogenic grafts engineered with human adipose-derived stem/stromal cells

The innate immune response following bone injury plays an important role in promoting cellular recruitment, revascularization, and other repair mechanisms. Tumor necrosis factor-α (TNF) is a prominent pro-inflammatory cytokine in this cascade, and has been previously shown to improve bone formation and angiogenesis in a dose- and timing-dependent manner. This ability to positively impact both osteogenesis and vascular growth may benefit bone tissue engineering, as vasculature is essential to maintaining cell viability in large grafts after implantation. Here, we investigated the effects of exogenous TNF on the induction of adipose-derived stem/stromal cells (ASCs) to engineer pre-vascularized osteogenic tissue in vitro with respect to dose, timing, and co-stimulation with other inflammatory mediators. We found that acute (2-day), low-dose exposure to TNF promoted vascularization, whereas higher doses and continuous exposure inhibited vascular growth. Co-stimulation with platelet-derived growth factor (PDGF), another key factor released following bone injury, increased vascular network formation synergistically with TNF. ASC-seeded grafts were then cultured within polycaprolactone-fibrin composite scaffolds and implanted in nude rats for 2 weeks, resulting in further tissue maturation and increased angiogenic ingrowth in TNF-treated grafts. VEGF-A expression levels were significantly higher in TNF-treated grafts immediately prior to implantation, indicating a long-term pro-angiogenic effect. These findings demonstrate that TNF has the potential to promote vasculogenesis in engineered osteogenic grafts both in vitro and in vivo. Thus, modulation and/or recapitulation of the immune response following bone injury may be a beneficial strategy for bone tissue engineering.

Effects of Interleukin-17A on Osteogenic Differentiation of Isolated Human Mesenchymal Stem Cells

OBJECTIVES

Rheumatoid arthritis (RA) is characterized by defective bone repair and excessive destruction and ankylosing spondylitis (AS) by increased ectopic bone formation with syndesmophytes. Since TNF-α and IL-17A are involved in both diseases, this study investigated their effects on the osteogenic differentiation of isolated human bone marrow-derived mesenchymal stem cells (hMSCs).

METHODS

Differentiation of hMSCs into osteoblasts was induced in the presence or absence of IL-17A and/or TNF-α. Matrix mineralization (MM) was evaluated by alizarin red staining and alkaline phosphatase (ALP) activity. mRNA expression was measured by qRT-PCR for bone morphogenetic protein (BMP)-2 and Runx2, genes associated with osteogenesis, DKK-1, a negative regulator of osteogenesis, Schnurri-3 and receptor activator of nuclear factor kappa B ligand (RANKL), associated with the cross talk with osteoclasts, and TNF-α receptor type I and TNF-α receptor type II (TNFRII).

RESULTS

TNF-α alone increased both MM and ALP activity. IL-17A alone increased ALP but not MM. Their combination was more potent. TNF-α alone increased BMP2 mRNA expression at 6 and 12 h. These levels decreased in combination with IL-17A at 6 h only. DKK-1 mRNA expression was inhibited by TNF-α and IL-17A either alone or combined. Supporting an imbalance toward osteoblastogenesis, RANKL expression was inhibited by TNF-α and IL-17A. However, TNF-α but not IL-17 alone decreased Runx2 mRNA expression at 6 h. In parallel, TNF-α but not IL-17 alone increased Schnurri-3 expression with a synergistic effect with their combination. This may be related to an increase of TNFRII overexpression.

CONCLUSION

IL-17 increased the effects of TNF-α on bone matrix formation by hMSCs. However, IL-17 decreased the TNF-α-induced BMP2 inhibition. Synergistic interactions between TNF-α and IL-17 were seen for RANKL inhibition and Schnurri-3 induction. Such increase of Schnurri-3 may in turn activate osteoclasts leading to bone destruction as in RA. Conversely, in the absence of osteoclasts, this could promote ectopic bone formation as in AS.