Effects of toll-like receptors 3 and 4 in the osteogenesis of stem cells

Long non-coding RNA LncTUG1 regulates favourable compression force-induced cementocytes mineralization via PU.1/TLR4/SphK1 signalling

Orthodontic tooth movement (OTM) is a highly coordinated biomechanical response to orthodontic forces with active remodelling of alveolar bone but minor root resorption. Such antiresorptive properties of root relate to cementocyte mineralization, the mechanisms of which remain largely unknown. This study used the microarray analysis to explore long non-coding ribonucleic acids involved in stress-induced cementocyte mineralization. Gain- and loss-of-function experiments, including Alkaline phosphatase (ALP) activity and Alizarin Red S staining, quantitative real-time polymerase chain reaction (qRT-PCR), Western blot, and immunofluorescence analyses of mineralization-associated factors, were conducted to verify long non-coding ribonucleic acids taurine-upregulated gene 1 (LncTUG1) regulation in stress-induced cementocyte mineralization, via targeting the Toll-like receptor 4 (TLR4)/SphK1 axis. The luciferase reporter assays, chromatin immunoprecipitation assays, RNA pull-down, RNA immunoprecipitation, and co-localization assays were performed to elucidate the interactions between LncTUG1, PU.1, and TLR4. Our findings indicated that LncTUG1 overexpression attenuated stress-induced cementocyte mineralization, while blocking the TLR4/SphK1 axis reversed the inhibitory effect of LncTUG1 on stress-induced cementocyte mineralization. The in vivo findings also confirmed the involvement of TLR4/SphK1 signalling in cementocyte mineralization during OTM. Mechanistically, LncTUG1 bound with PU.1 subsequently enhanced TLR4 promotor activity and thus transcriptionally elevated the expression of TLR4. In conclusion, our data revealed a critical role of LncTUG1 in regulating stress-induced cementocyte mineralization via PU.1/TLR4/SphK1 signalling, which might provide further insights for developing novel therapeutic strategies that could protect roots from resorption during OTM.

The role of toll-like receptors in orchestrating osteogenic differentiation of mesenchymal stromal cells and osteoimmunology

Osteoimmunology is a concept involving molecular and cellular crosstalk between the skeletal and immune systems. Toll-like receptors (TLRs) are widely expressed both on mesenchymal stromal cells (MSCs), the hematopoietic cells, and immune cells in the osteogenic microenvironment for bone development or repair. TLRs can sense both exogenous pathogen-associated molecular patterns (PAMPs) derived from microorganisms, and damage-associated molecular patterns (DAMPs) derived from normal cells subjected to injury, inflammation, or cell apoptosis under physiological or pathological conditions. Emerging studies reported that TLR signaling plays an important role in bone remodeling by directly impacting MSC osteogenic differentiation or osteoimmunology. However, how to regulate TLR signaling is critical and remains to be elucidated to promote the osteogenic differentiation of MSCs and new bone formation for bone tissue repair. This review outlines distinct TLR variants on MSCs from various tissues, detailing the impact of TLR pathway activation or inhibition on MSC osteogenic differentiation. It also elucidates TLR pathways' interplay with osteoclasts, immune cells, and extracellular vesicles (EVs) derived from MSCs. Furthermore, we explore biomaterial-based activation to guide MSCs' osteogenic differentiation. Therefore, understanding TLRs' role in this context has significant implications for advancing bone regeneration and repair strategies.

Functional role of circRNAs in osteogenesis: A review

The extracellular matrixes (ECM), as well as the microenvironmental signals, play an essential role in osteogenesis by regulating intercellular pathways. Recently, it has been demonstrated that a newly identified RNA, circular RNA, contributes to the osteogenesis process. Circular RNA (circRNA), the most recently identified RNA, is involved in the regulation of gene expression at transcription to translation levels. The dysregulation of circRNAs has been observed in several tumors and diseases. Also, various studies have shown that circRNAs expression is changed during osteogenic differentiation of progenitor cells. Therefore, understanding the role of circRNAs in osteogenesis might help the diagnosis as well as treatment of bone diseases such as bone defects and osteoporosis. In this review, circRNA functions and the related pathways in osteogenesis have been discussed.

In vitro Exposure to Inflammatory Mediators Affects the Differentiation of Mesenchymal Progenitors

The increasing prevalence of joint disease, and in particular osteoarthritis (OA), calls for novel treatment strategies to prevent disease progression in addition to existing approaches focusing mainly on the relief of pain symptoms. The inherent properties of mesenchymal stem cells (MSCs) make them an attractive candidate for novel tissue repair strategies, as these progenitors have the potential to differentiate into chondrocytes needed to replace degraded cartilage and can exert a modulating effect on the inflammatory environment of the diseased joint. However, the inflammatory environment of the joint may affect the ability of these cells to functionally integrate into the host tissue and exert beneficial effects, as hinted by a lack of success seen in clinical trials. Identification of factors and cell signalling pathways that influence MSC function is therefore critical for ensuring their success in the clinic, and here the effects of inflammatory mediators on bone marrow-derived MSCs were evaluated. Human MSCs were cultured in the presence of inflammatory mediators typically associated with OA pathology (IL-1β, IL-8, IL-10). While exposure to these factors did not produce marked effects on MSC proliferation, changes were observed when the mediators were added under differentiating conditions. Results collected over 21 days showed that exposure to IL-1β significantly affected the differentiation response of these cells exposed to chondrogenic and osteogenic conditions, with gene expression analysis indicating changes in MAPK, Wnt and TLR signalling pathways, alongside an increased expression of pro-inflammatory cytokines and cartilage degrading enzymes. These results highlight the value of MSCs as a preclinical model to study OA and provide a basis to define the impact of factors driving OA pathology on the therapeutic potential of MSCs for novel OA treatments.

Human adipose tissue-derived mesenchymal stromal cells and their phagocytic capacity

Mesenchymal stromal cells (MSCs) have evidenced considerable therapeutic potential in numerous clinical fields, especially in tissue regeneration. The immunological characteristics of this cell population include the expression of Toll‐like receptors and mannose receptors, among others. The study objective was to determine whether MSCs have phagocytic capacity against different target particles. We isolated and characterized three human adipose tissue MSC (HAT‐MSC) lines from three patients and analysed their phagocytic capacity by flow cytometry, using fluorescent latex beads, and by transmission electron microscopy, using Escherichia coli, Staphylococcus aureus and Candida albicans as biological materials and latex beads as non‐biological material. The results demonstrate that HAT‐MSCs can phagocyte particles of different nature and size. The percentage of phagocytic cells ranged between 33.8% and 56.2% (mean of 44.37% ± 11.253) according to the cell line, and a high phagocytic index was observed. The high phagocytic capacity observed in MSCs, which have known regenerative potential, may offer an advance in the approach to certain local and systemic infections.

Gut microbiota and bone metabolism

Osteoporosis is the most common metabolic skeletal disease. It is characterized by the deterioration of the skeletal microarchitecture and bone loss, leading to ostealgia, and even bone fractures. Accumulating evidence has indicated that there is an inextricable relationship between the gut microbiota (GM) and bone homeostasis involving host-microbiota crosstalk. Any perturbation of the GM can play an initiating and reinforcing role in disrupting the bone remodeling balance during the development of osteoporosis. Although the GM is known to influence bone metabolism, the mechanisms associated with these effects remain unclear. Herein, we review the current knowledge of how the GM affects bone metabolism in health and disease, summarize the correlation between pathogen-associated molecular patterns of GM structural components and bone metabolism, and discuss the potential mechanisms underlying how GM metabolites regulate bone turnover. Deciphering the complicated relationship between the GM and bone health will provide new insights into the prevention and treatment of osteoporosis.

Clinically used JAK inhibitor blunts dsRNA-induced inflammation and calcification in aortic valve interstitial cells

Calcific aortic valve disease (CAVD) is the most prevalent valvulopathy worldwide. Growing evidence supports a role for viral and cell-derived double-stranded (ds)-RNA in cardiovascular pathophysiology. Poly(I:C), a dsRNA surrogate, has been shown to induce inflammation, type I interferon (IFN) responses, and osteogenesis through Toll-like receptor 3 in aortic valve interstitial cells (VIC). Here, we aimed to determine whether IFN signaling via Janus kinase (JAK)/Signal transducers and activators of transcription (STAT) mediates dsRNA-induced responses in primary human VIC. Western blot, ELISA, qPCR, calcification, flow cytometry, and enzymatic assays were performed to evaluate the mechanisms of dsRNA-induced inflammation and calcification. Poly(I:C) triggered a type I IFN response characterized by IFN-regulatory factors gene upregulation, IFN-β secretion, and STAT1 activation. Additionally, Poly(I:C) promoted VIC inflammation via NF-κB and subsequent adhesion molecule expression, and cytokine secretion. Pretreatment with ruxolitinib, a clinically used JAK inhibitor, abrogated these responses. Moreover, Poly(I:C) promoted a pro-osteogenic phenotype and increased VIC calcification to a higher extent in cells from males. Inhibition of JAK with ruxolitinib or a type I IFN receptor blocking antibody blunted Poly(I:C)-induced calcification. Mechanistically, Poly(I:C) promoted VIC apoptosis in calcification medium, which was inhibited by ruxolitinib. Moreover, Poly(I:C) co-operated with IFN-γ to increase VIC calcification by synergistically activating extracellular signal-regulated kinases and hypoxia-inducible factor-1α pathways. In conclusion, JAK/STAT signaling mediates dsRNA-triggered inflammation, apoptosis, and calcification and may contribute to a positive autocrine loop in human VIC in the presence of IFN-γ. Blockade of dsRNA responses with JAK inhibitors may be a promising therapeutic avenue for CAVD.

Use of Therapeutic Pathogen Recognition Receptor Ligands for Osteo-Immunomodulation

Therapeutic pathogen recognition receptor (PRR) ligands are reaching clinical practice following their ability to skew the immune response in a specific direction. We investigated the effects of various therapeutic PRR ligands on bone cell differentiation and inflammation. Following stimulation, alkaline phosphatase (ALP) activity (Day 10), osteocalcin, osteonectin expression (Day 14), and calcium deposition (Day 21) were quantified in bone marrow-derived human mesenchymal stem cells (hMSCs). The osteoclastogenic response was determined by measuring tartrate-resistant acid phosphate (TRAP) activity in human monocytes. TNF-α, IL-6, IL-8, and IL-10 expressions were measured by enzyme-linked immunosorbent assay as an indicator of the ligands’ inflammatory properties. We found that nucleic acid-based ligands Poly(I:C) and CpG ODN C increased early ALP activity in hMSCs by 4-fold without affecting osteoclast formation. These ligands did not enhance expression of the other, late osteogenic markers. MPLA, Curdlan, and Pam3CSK4 did not affect osteogenic differentiation, but inhibited TRAP activity in monocytes, which was associated with increased expression of all measured cytokines. Nucleic acid-based ligands are identified as the most promising osteo-immunomodulators, as they favor early osteogenic differentiation without inducing an exaggerated immune-cell mediated response or interfering in osteoclastogenesis and thus can be potentially harnessed for multifunctional coatings for bone biomaterials.

TLR2 and TLR4 Differentially Regulate the Osteogenic Capacity of Human Periodontal Ligament Fibroblasts

AIMS

To test that the osteogenic capacity of periodontal ligament (PDL) fibroblasts can be mediated by TLR2 and TLR4 activation.

MATERIALS AND METHODS

Human PDL fibroblasts were cultured in osteogenic medium and treated with TLR2 and TLR4 agonists (Pam3CSK4 and monophosphoryl Lipid A (MPLA), respectively). Cell proliferation was measured by MTT and BrdU incorporation. Osteogenic differentiation was measured by alkaline phosphatase (ALP) activity. Nodule formation was measured for osteoblast function. The expression of markers of potential signaling pathways (RUNX2, OCN, BSP and Osterix) was evaluated by quantitative PCR.

RESULTS

PDL fibroblasts grew at the same rate during the first 5 days in response to both Pam3CSK5 and MPLA. On day 7, cells cultured in the presence of Pam3CSK4 had a significantly higher rate of DNA replication, while cells in MPLA group had a significantly lower DNA replication rate (one-third) compared to the control (p less than 0.05). Pam3CSK4 induced significantly higher ALP activity and larger calcified nodules. TLR4 activation significantly reduced the expression of RUNX2 and osterix and enhanced OCN. Neither TLR2 nor TLR4 affected BSP expression.

CONCLUSIONS

These data suggest that the activation of TLR2 and TLR4 differentially and perhaps antagonistically modulate osteogenesis by human PDL fibroblasts and have a direct role of TLR-mediated PDL function during periodontal regeneration as a potential target for therapeutics.

Chronic Exposure of Gingival Fibroblasts to TLR2 or TLR4 Agonist Inhibits Osteoclastogenesis but Does Not Affect Osteogenesis

Chronic exposure to periodontopathogenic bacteria such as Porphyromonas gingivalis and the products of these bacteria that interact with the cells of the tooth surrounding tissues can ultimately result in periodontitis. This is a disease that is characterized by inflammation-related alveolar bone degradation by the bone-resorbing cells, the osteoclasts. Interactions of bacterial products with Toll-like receptors (TLRs), in particular TLR2 and TLR4, play a significant role in this chronic inflammatory reaction, which possibly affects osteoclastic activity and osteogenic capacity. Little is known about how chronic exposure to specific TLR activators affects these two antagonistic activities. Here, we studied the effect of TLR activation on gingival fibroblasts (GF), cells that are anatomically close to infiltrating bacterial products in the mouth. These were co-cultured with naive osteoclast precursor cells (i.e., monocytes), as part of the peripheral blood mononuclear cells (PBMCs). Activation of GF co-cultures (GF + PBMCs) with TLR2 or TLR4 agonists resulted in a weak reduction of the osteoclastogenic potential of these cultures, predominantly due to TLR2. Interestingly, chronic exposure, especially to TLR2 agonist, resulted in increased release of TNF-α at early time points. This effect, was reversed at later time points, thus suggesting an adaptation to chronic exposure. Monocyte cultures primed with M-CSF + RANKL, led to the formation of bone-resorbing osteoclasts, irrespective of being activated with TLR agonists. Late activation of these co-cultures with TLR2 and with TLR4 agonists led to a slight decrease in bone resorption. Activation of GF with TLR2 and TLR4 agonists did not affect the osteogenic capacity of the GF cells. In conclusion, chronic exposure leads to diverse reactions; inhibitory with naive osteoclast precursors, not effecting already formed (pre-)osteoclasts. We suggest that early encounter of naive monocytes with TLR agonists may result in differentiation toward the macrophage lineage, desirable for clearing bacterial products. Once (pre-)osteoclasts are formed, these cells may be relatively insensitive for direct TLR stimulation. Possibly, TLR activation of periodontal cells indirectly stimulates osteoclasts, by secreting osteoclastogenesis stimulating inflammatory cytokines.

Preconditioning of Rat Bone Marrow-Derived Mesenchymal Stromal Cells with Toll-Like Receptor Agonists

Bone marrow-derived mesenchymal stromal cells (BM-MSCs) are dynamic cells that can sense the environment, adapting their regulatory functions to different conditions. Accordingly, the therapeutic potential of BM-MSCs can be modulated by preconditioning strategies aimed at modifying their paracrine action. Although rat BM-MSCs (rBM-MSCs) have been widely tested in preclinical research, most preconditioning studies have employed human and mouse BM-MSCs. Herein, we investigated whether rBM-MSCs modify their phenotype and paracrine functions in response to Toll-like receptor (TLR) agonists. The data showed that rBM-MSCs expressed TLR3, TLR4, and MDA5 mRNA and were able to internalize polyinosinic-polycytidylic acid (Poly(I:C)), a TLR3/MDA5 agonist. rBM-MSCs were then stimulated with Poly(I:C) or with lipopolysaccharide (LPS, a TLR4 agonist) for 1 h and were grown under normal culture conditions. LPS or Poly(I:C) stimulation did not affect the viability or the morphology of rBM-MSCs and did not modify the expression pattern of key cell surface markers. Poly(I:C) did not induce statistically significant changes in the release of several inflammatory mediators and VEGF by rBM-MSCs, although it tended to increase IL-6 and MCP-1 secretion, whereas LPS increased the release of IL-6, MCP-1, and VEGF, three factors that were constitutively secreted by unstimulated cells. The neurotrophic activity of the conditioned medium from unstimulated and LPS-preconditioned rBM-MSCs was investigated using dorsal root ganglion explants, showing that soluble factors produced by unstimulated and LPS-preconditioned rBM-MSCs can stimulate neurite outgrowth similarly, in a VEGF-dependent manner. LPS-preconditioned cells, however, were slightly more efficient in increasing the number of regrowing axons in a model of sciatic nerve transection in rats. In conclusion, LPS preconditioning boosted the production of constitutively secreted factors by rBM-MSCs, without changing their mesenchymal identity, an effect that requires further investigation in exploratory preclinical studies.

Nomenclature and heterogeneity: consequences for the use of mesenchymal stem cells in regenerative medicine

Mesenchymal stem cells (MSCs) are in development for many clinical indications, based both on ‘stem’ properties (tissue repair or regeneration) and on signaling repertoire (immunomodulatory and anti-inflammatory effects). Potential conflation of MSC properties with those of tissue-derived stromal cells presents difficulties in comparing study outcomes and represents a source of confusion in cell therapy development. Cultured MSCs demonstrate significant heterogeneity in clonogenicity and multi-lineage differentiation potential. However in vivo biology of MSCs includes native functions unrelated to regenerative medicine applications, so do nomenclature and heterogeneity matter? In this perspective we examine some consequences of the nomenclature debate and heterogeneity of MSCs. Regulatory expectations are considered, emphasizing that product development should prioritize detailed characterization of therapeutic cell populations for specific indications.

TLR activation inhibits the osteogenic potential of human periodontal ligament stem cells through Akt signaling in a Myd88- or TRIF-dependent manner

BACKGROUND

This study investigated the effects of Toll-like receptors (TLRs) on human periodontal ligament stem cells (hPDLSCs) osteogenic differentiation and the associated mechanisms.

METHODS

TLR1, TLR3, TLR4, and TLR6 expression in hPDLSCs was evaluated by real-time reverse transcriptase polymerase chain reaction (RT-PCR) and flow cytometry, whereas their functional roles were assessed based on nuclear factor (NF)-κB activation and proinflammatory cytokine expression. The osteogenic effects of these TLRs were analyzed by alkaline phosphatase (ALP) staining, ALP activity, and alizarin red staining. The roles of Myd88, TRIF, and downstream molecules mitogen-activated protein kinases (MAPKs) and protein kinase B (Akt) in TLR-mediated impaired osteogenic differentiation were examined by real-time RT-PCR and western blotting using specific small interfering RNA siRNA and pharmacologic inhibitors. The involvement of Akt activation in restoring TLR1-, 4-, and 6-mediated osteogenic suppression was verified using the Akt activator SC-79.

RESULTS

TLR1, TLR3, TLR4, and TLR6 were highly expressed functionally in hPDLSCs and high doses of TLR ligands inhibited osteogenic potential. Furthermore, blocking Myd88 partly rescued the decrease in osteogenesis mediated by TLR1, TLR4, and TLR6 activation by enhancing Akt phosphorylation; likewise, TRIF suppression partially rescued lipopolysaccharide (LPS)-mediated osteogenic inhibition through ERK and Akt activation. Moreover, Akt activation restored the TLR-mediated inhibition of hPDLSC osteogenic differentiation.

CONCLUSIONS

High doses of TLR1, TLR4, and TLR6 ligands suppress hPDLSC osteogenic differentiation by inhibiting Akt activation through Myd88- or TRIF-dependent signaling pathways. Blocking these adaptors or reactivating Akt could restore the TLR-mediated decrease in hPDLSC osteogenesis, and might be an ideal strategy for periodontitis treatment.

Mesenchymal Stem Cell Functionalization for Enhanced Therapeutic Applications

IMPACT STATEMENT

Culture expansion of MSCs has detrimental effects on various cell characteristics and attributes (e.g., phenotypic changes and senescence), which, in addition to inherent interdonor variability, negatively impact the standardization and reproducibility of their therapeutic potential. The identification of innate distinct functional MSC subpopulations, as well as the description of ex vivo protocols aimed at maintaining phenotypes and enhancing specific functions have the potential to overcome these limitations. The incorporation of those approaches into cell-based therapy would significantly impact the field, as more reproducible clinical outcomes may be achieved.

Concise Review: TLR Pathway-miRNA Interplay in Mesenchymal Stromal Cells: Regulatory Roles and Therapeutic Directions

Mesenchymal stromal cells (MSCs) deploy Toll-like receptors (TLRs) to respond to exogenous and endogenous signals. Activation of TLR pathways in MSCs alters their inflammatory profile and immunomodulatory effects on cells from both the innate and adaptive immune systems. Micro-RNAs (miRNAs), whose expression is modulated by TLR activation, can regulate inflammatory responses by targeting components of the TLR signaling pathways either in MSCs or in the cells with which they interact. Here, we review how the miRNA-TLR pathway axis can regulate the immunomodulatory functions of MSCs, including their interactions with monocytes/macrophages and natural killer cells, and discuss the therapeutic implications for MSC-based therapies. Stem Cells 2018;36:1655-1662.

Mesenchymal stem cells internalize Mycobacterium tuberculosis through scavenger receptors and restrict bacterial growth through autophagy

Human mesenchymal stem cells (MSCs) express scavenger receptors that internalize lipids, including oxidized low-density lipoprotein (oxLDL). We report that MSCs phagocytose Mycobacterium tuberculosis (Mtb) through two types of scavenger receptors (SRs; MARCO and SR-B1), as blockade of the receptors with antibodies or siRNA knockdown decreased the uptake of Mtb. MSCs also expressed mannose receptor (MR) that was found to endocytose rhodamine-labeled mannosylated BSA (rMBSA), though the receptor was not involved in the uptake of Mtb. Dil-oxLDL and rMBSA taken up into MSC endosomes colocalized with Mtb phagosomes, thus suggesting that the latter were fusion competent. Phagocytosed Mtb did not replicate within MSCs, thus suggesting an intrinsic control of bacterial growth. Indeed, MSCs exhibited intrinsic autophagy, which was up-regulated after activation with rapamycin. SiRNA knockdown of autophagy initiator beclin-1 enhanced Mtb survival, whereas rapamycin-induced autophagy increased intracellular killing of Mtb. In addition, MSCs secreted nitric oxide after Mtb infection, and inhibition of NO by N(G)-monomethyl-L-arginine enhanced intracellular survival of Mtb. MSCs can be grown in large numbers in vitro, and autologous MSCs transfused into tuberculosis patients have been found to be safe and improve lung immunity. Thus, MSCs are novel phagocytic cells with a potential for immunotherapy in treating multidrug-resistant tuberculosis.

Mesenchymal Stromal Cells and Toll-Like Receptor Priming: A Critical Review

Mesenchymal Stromal Cells (MSCs) are potential cellular candidates for several immunotherapy purposes. Their multilineage potential and immunomodulatory properties make them interesting tools for the treatment of various immunological diseases. However, depending on the local microenvironment, diverse biological functions of MSCs can be modulated. Indeed, during infections such as obtained following TLR-agonist engagement (called as TLR priming), the phenotype, multilineage potential, hematopoietic support and immunomodulatory capacity of MSCs can present critical changes, which could further affect their therapeutic potential. Thus, for appropriate clinical application of MSCs, it is important to well know and understand these effects in particular during infectious episodes and to find the suitable experimental settings to study that. Pre-stimulation of MSCs with a specific TLR ligand may serve as an effective priming step to modulate one of its function to achieve a desired therapeutic issue.

Differential long noncoding RNA/mRNA expression profiling and functional network analysis during osteogenic differentiation of human bone marrow mesenchymal stem cells

BACKGROUND

Mesenchymal stem cells (MSCs) are the most promising cell types for bone regeneration and repair due to their osteogenic potential. MSC differentiation is precisely regulated and orchestrated by the mechanical and molecular signals from the extracellular environment, involving complex pathways regulated at both the transcriptional and post-transcriptional levels. However, the potential role of long noncoding RNA (lncRNA) in the osteogenic differentiation of human MSCs remains largely unclear.

METHODS

Here, we undertook the survey of differential coding and noncoding transcript expression profiling and functional network analysis during osteogenic differentiation of human bone marrow mesenchymal stem cells (BMSCs) using human whole transcriptome microarray. The key pathways, mRNAs, and lncRNAs controlling osteogenic differentiation of BMSCs were identified by further bioinformatic analysis. The role of lncRNA in the osteogenic differentiation of MSCs was verified by lncRNA overexpression or knockdown methods.

RESULTS

A total of 1269 coding transcripts with 648 genes significantly upregulated and 621 genes downregulated, and 1408 lncRNAs with 785 lncRNAs significantly upregulated and 623 lncRNAs downregulated were detected along with osteogenic differentiation. Bioinformatic analysis identified that several pathways may be associated with osteogenic differentiation potentials of BMSCs, such as the MAPK signaling pathway, the Jak-STAT signaling pathway, the Toll-like receptor signaling pathway, and the TGF-beta signaling pathway, etc. Bioinformatic analysis also revealed 13 core regulatory genes including seven mRNAs (GPX3, TLR2, BDKRB1, FBXO5, BRCA1, MAP3K8, and SCARB1), and six lncRNAs (XR_111050, NR_024031, FR374455, FR401275, FR406817, and FR148647). Based on the analysis, we identified one lncRNA, XR_111050, that could enhance the osteogenic differentiation potentials of MSCs.

CONCLUSIONS

The potential regulatory mechanisms were identified using bioinformatic analyses. We further predicted the interactions of differentially expressed coding and noncoding genes, and identified core regulatory factors by co-expression networks during osteogenic differentiation of BMSCs. Our results could lead to a better understanding of the molecular mechanisms of genes and lncRNAs, and their cooperation underlying MSC osteogenic differentiation and bone formation. We identified that one lncRNA, XR_111050, could be a potential target for bone tissue engineering.

Transcriptome Analysis of Long Noncoding RNAs in Toll-Like Receptor 3-Activated Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) possess great immunomodulatory capacity which lays the foundation for their therapeutic effects in a variety of diseases. Recently, toll-like receptors (TLR) have been shown to modulate MSC functions; however, the underlying molecular mechanisms are poorly understood. Emerging evidence suggests that long noncoding RNAs (lncRNAs) are an important class of regulators involved in a wide range of biological processes. To explore the potential involvement of lncRNAs in TLR stimulated MSCs, we performed a comprehensive lncRNA and mRNA profiling through microarray. 10.2% of lncRNAs (1733 out of 16967) and 15.1% of mRNA transcripts (1760 out of 11632) were significantly differentially expressed (absolute fold-change ≥5 , P value ≤0.05) in TLR3 stimulated MSCs. Furthermore, we characterized the differentially expressed lncRNAs through their classes and length distribution and correlated them with differentially expressed mRNA. Here, we are the first to determine genome-wide lncRNAs expression patterns in TLR3 stimulated MSCs by microarray and this work could provide a comprehensive framework of the transcriptome landscapes of TLR3 stimulated MSCs.