CHI 3L1 regulation of inflammation and the effects on osteogenesis in a Staphylococcus aureus ‐induced murine model of osteomyelitis

Naringin exerts antibacterial and anti-inflammatory effects on mice with Staphylococcus aureus-induced osteomyelitis

Osteomyelitis is an invasive bone infection that can lead to severe pain and even disability, posing a challenge for orthopedic surgery. Naringin can reduce bone-related inflammatory conditions. This study aimed to elucidate the function and mechanism of naringin in a Staphylococcus aureus-induced mouse model of osteomyelitis. Femurs of S. aureus-infected mice were collected after naringin administration and subjected to microcomputed tomography to analyze cortical bone destruction and bone loss. Bacterial growth in femurs was also assessed. Proinflammatory cytokine levels in mouse femurs were measured using enzyme-linked immunosorbent assays. Pathological changes and bone resorption were analyzed using hematoxylin and eosin staining and tartrate-resistant acid phosphatase staining, respectively. Quantitative reverse transcription polymerase chain reaction and western blot analysis were used to quantify the messenger RNA and protein expression of osteogenic differentiation-associated genes in the femurs. The viability of human bone marrow-derived stem cells (hBMSCs) was determined using cell counting kit-8. Alizarin Red S staining and alkaline phosphatase staining were performed to assess the formation of mineralization nodules and bone formation in vitro. Notch signaling-related protein levels in femur tissues and hBMSCs were assessed using western blot analysis. Experimental results revealed that naringin alleviated S. aureus-induced cortical bone destruction and bone loss in mice by increasing the bone volume/total volume ratio. Naringin suppressed S. aureus-induced bacterial growth and inflammation in femurs. Moreover, it alleviated histopathological changes, inhibited bone resorption, and increased the expression of osteogenic markers in osteomyelitic mice. It increased the viability of hBMSCs and promoted their differentiation and bone mineralization in vitro. Furthermore, naringin activated Notch signaling by upregulating the protein levels of Notch1, Jagged1, and Hes1 in the femurs of model mice and S. aureus-stimulated hBMSCs. In conclusion, naringin reduces bacterial growth, inflammation, and bone resorption while upregulating the expression of osteogenic markers in S. aureus-infected mice and hBMSCs by activating Notch signaling.

Elevated Serum Levels of YKL-40, YKL-39, and SI-CLP in Patients with Treatment Failure to DMARDs in Patients with Rheumatoid Arthritis

Around 30-60% of patients with rheumatoid arthritis (RA) present treatment failure to conventional synthetic disease-modifying antirheumatic drugs (csDMARDs). Chitinase-like proteins (CLPs) (YKL-40, YKL-39, SI-CLP) might play a role, as they are associated with the inflammatory process. This study aimed to evaluate CLP utility as a biomarker in the treatment failure of csDMARDs. A case-control study included 175 RA patients classified into two groups based on therapeutic response according to DAS28-ESR: responders (DAS28 < 3.2); non-responders (DAS28 ≥ 3.2). CLP serum levels were determined by ELISA. Multivariable logistic regression and receiver operating characteristic (ROC) curves were used to evaluate CLPs' utility as biomarkers of treatment failure. Non-responders presented higher levels of YKL-40, YKL-39, and SI-CLP compared with responders (all: p < 0.001). YKL-40 correlated positively with YKL-39 (rho = 0.39, p < 0.001) and SI-CLP (rho = 0.23, p = 0.011) and YKL-39 with SI-CLP (rho = 0.34, p < 0.001). The addition of CLPs to the regression models improves diagnostic accuracy (AUC 0.918) compared to models including only clinical classical variables (AUC 0.806) p < 0.001. Non-responders were positive for all CLPs in 35.86%. Conclusions: CLPs could be considered as a useful biomarker to assess treatment failure, due to their association with clinical variables and improvement to the performance of regression models.

N6 methyladenosine eraser FTO suppresses Staphylococcus aureus-induced ferroptosis of bone marrow mesenchymal stem cells to ameliorate osteomyelitis through regulating the MDM2/TLR4/SLC7A11 signaling pathway

Osteomyelitis is a bone destructive inflammatory disease caused by infection. Ferroptosis is closely related to multiple inflammatory diseases, but the role of ferroptosis in Staphylococcus aureus (SA)-induced osteomyelitis remains unknown. In the present study, we found that SA treatment promoted the accumulation of iron, Fe2+ , lipid peroxide, and malondialdehyde, increased TFRC and reduced FTH1 and GPX4 to trigger ferroptosis in rat bone marrow mesenchymal stem cells (BMSCs). Interestingly, increased level of N6 methyl adenosine (m6A) modification along with decreased expression level of m6A eraser FTO were observed in SA-induced BMSCs, while upregulating FTO alleviated SA-triggered ferroptosis and protected cell viability in BMSCs. Mechanistically, MDM2 was identified as a target of FTO-mediated m6A demethylation, and FTO upregulation promoted MDM2 instability to downregulated TLR4 signal and elevate the expression of SLC7A11 and GPX4 in SA-induced BMSCs. Functional recovery experiments verified that overexpressing MDM2 or TLR4 reversed the inhibiting effect of FTO upregulation on ferroptosis in SA-treated BMSCs. Additionally, FTO upregulation restrained ferroptosis and pathological damage to bone tissue in SA-induced osteomyelitis model rats. Altogether, m6A eraser FTO alleviates SA-induced ferroptosis in osteomyelitis models partly through inhibiting the MDM2-TLR4 axis.

Transcriptomic landscape of human induced pluripotent stem cell-derived osteogenic differentiation identifies a regulatory role of KLF16

Osteogenic differentiation is essential for bone development and metabolism, but the underlying gene regulatory networks have not been well investigated. We differentiated mesenchymal stem cells, derived from 20 human induced pluripotent stem cell lines, into preosteoblasts and osteoblasts, and performed systematic RNA-seq analyses of 60 samples for differential gene expression. We noted a highly significant correlation in expression patterns and genomic proximity among transcription factor (TF) and long noncoding RNA (lncRNA) genes. We identified TF-TF regulatory networks, regulatory roles of lncRNAs on their neighboring coding genes for TFs and splicing factors, and differential splicing of TF, lncRNA, and splicing factor genes. TF-TF regulatory and gene co-expression network analyses suggested an inhibitory role of TF KLF16 in osteogenic differentiation. We demonstrate that in vitro overexpression of human KLF16 inhibits osteogenic differentiation and mineralization, and in vivo Klf16+/- mice exhibit increased bone mineral density, trabecular number, and cortical bone area. Thus, our model system highlights the regulatory complexity of osteogenic differentiation and identifies novel osteogenic genes.

IL13Rα2 as a crucial receptor for Chi3l1 in osteoclast differentiation and bone resorption through the MAPK/AKT pathway

BACKGROUND

Previous research has revealed that the 18 glycoside hydrolase gene family (GH18) member Chitinase 3-like 1 (Chi3l1) can regulate osteoclast differentiation and bone resorption. However, its downstream receptors and molecular mechanisms during osteoclastogenesis have yet to be elucidated.

METHODS

Initially, we conducted a comprehensive investigation to evaluate the effects of recombinant Chi3l1 protein or Chi3l1 siRNA on osteoclast differentiation and the RANKL-induced MAPK/AKT signaling pathways. Moreover, we used immunofluorescence and immunoprecipitation assays to identify IL13Rα2 as the downstream receptor of Chi3l1. Subsequently, we investigated the impact of IL13Rα2 recombinant protein or IL13Rα2-siRNA on osteoclast differentiation and the associated signaling pathways. Finally, we performed in vivo experiments to examine the effect of recombinant IL13Rα2 protein in an LPS-induced mouse model of cranial osteolysis.

RESULTS

Our findings highlight that the administration of recombinant Chi3l1 protein increased the formation of osteoclasts and bolstered the expression of several osteoclast-specific genes (TRAP, NFATC1, CTR, CTSK, V-ATPase d2, and Dc-STAMP). Additionally, Chi3l1 significantly promoted the RANKL-induced MAPK (ERK/P38/JNK) and AKT pathway activation, whereas Chi3l1 silencing inhibited this process. Next, using immunofluorescence and co-immunoprecipitation assays, we identified IL13Rα2 as the binding partner of Chi3l1 during osteoclastogenesis. IL13Rα2 recombinant protein or IL13Rα2-siRNA also inhibited osteoclast differentiation, and IL13Rα2-siRNA attenuated the RANKL-induced activation of the MAPK (ERK/P38/JNK) and AKT pathways, similar to the effects observed upon silencing of Chi3l1. Moreover, the promoting effect of recombinant Chi3l1 protein on osteoclastogenesis and the activation of the MAPK and AKT pathways was reversed by IL13Rα2 siRNA. Finally, recombinant LI13Rα2 protein significantly attenuated the LPS-induced cranial osteolysis and the number of osteoclasts in vivo.

CONCLUSIONS

Our findings suggested that IL13Rα2 served as a crucial receptor for Chi3l1, enhancing RANKL-induced MAPK and AKT activation to promote osteoclast differentiation. These findings provide valuable insights into the molecular mechanisms of Chi3l1 in osteoclastogenesis, with potential therapeutic implications for osteoclast-related diseases. Video Abstract.

Chronic osteomyelitis risk is associated with NLRP3 gene rs10754558 polymorphism in a Chinese Han Population

BACKGROUND

Single nucleotide polymorphisms (SNPs) in the nucleotide-binding domain leucine-rich repeat protein-3 (NLRP3) gene are reported to be linked to many inflammatory disorders. However, uncertainty persists over the associations between these SNPs and susceptibilities to chronic osteomyelitis (COM). This study aimed to investigate potential relationships between NLRP3 gene SNPs and the risks of developing COM in a Chinese Han cohort.

METHODS

The four tag SNPs of the NLRP3 gene were genotyped in a total of 428 COM patients and 368 healthy controlsusing the SNapShot technique. The genotype distribution, mutant allele frequency, and the four genetic models (dominant, recessive, homozygous, and heterozygous) of the four SNPs were compared between the two groups.

RESULTS

A significant association was found between rs10754558 polymorphism and the probability of COM occurence by the heterozygous model (P = 0.037, odds ratio [OR] = 1.541, 95% confidence interval [CI] = 1.025-2.319), indicating that rs10754558 may be associated with a higher risk of developing COM.In addition, possible relationship was found between rs7525979 polymorphism and the risk of COM development by the outcomes of homozygous (P = 0.073, OR = 0.453, 95% CI = 0.187-1.097) and recessive (P = 0.093, OR = 0.478, 95% CI = 0.198-1.151) models, though no statistical differences were obtained.

CONCLUSIONS

Outcomes of the present study showed, for the first time, that rs10754558 polymorphism of the NLRP3 gene may increase the risk of COM development in this Chinese Han population, with genotype CG as a risk factor. Nonetheless, this conclusion requires verification from further studies with a larger sample size.

[YKL-40 Promotes the Expression of Inflammatory Factors in Type Ⅱ Alveolar Epithelial Cell Model of A549 Cell Line]

Objective

YKL-40, also known as chitinase-3-like-1 (CHI3L1), is a human cartilage glycoprotein-39, with its N-terminus consisting of tyrosine (Y), lysine (K), and leucine (L), hence the name YKL-40. In this study, we explored whether YKL-40 could promote the expression of inflammatory factors in type Ⅱ alveolar epithelial cells.

Methods

A549 cells were cultured in vitro with interleukin (IL)-1β (20 ng/mL), IL-6 (20 ng/mL), tumor necrosis factor-alpha (TNF-α) (20 ng/mL), and interferon-gamma (IFN-γ) (20 ng/mL). The expression of YKL-40 transcription was determined by RT-qPCR. A549 cells were cultured with IL-1β at 5, 10, and 20 ng/mL and the expression of YKL-40 protein was determined by Western blot. A549 cells were cultured with recombinant YKL-40 protein at 0, 100, 500, and 1 000 ng/mL and the expression levels of IL-6 and IL-8 were measured by RT-qPCR. Three pairs of small interfering RNAs targeting YKL-40 (si- YKL-40-1/2/3) and the negative control (NC) were designed and used to transfect A549 cells, respectively, and the expression of YKL-40 was determined by RT-qPCR and Western blot. si- YKL-40-3 was screened out for subsequent experiments. In A549 cells, si- YKL-40-3 and si-NC were transfected and, then, IL-1β (20 ng/mL) was added in for culturing. The expression of YKL-40, IL-6, and IL-8 was determined by RT-qPCR and the expression of multiple factors in the supernatant was measured with the QAH-INF-1 kit.

Results

RT-qPCR results showed that IL-1β could up-regulate YKL-40 protein transcription level compared with that of the control group and the difference was statistically significant ( P<0.01), but IL-6, TNF-α, and IFN-γ could not up-regulate YKL-40 protein transcription level. Western blot results showed that IL-1β (20 ng/mL) could significantly promote the expression of YKL-40 and, compared with that of the control group, the differences showed by groups treated with different concentrations of IL-1β were all statistical significant ( P<0.01). After adding human recombinant YKL-40 protein to A549 cells, the results showed that the expression of inflammatory factors IL-6 and IL-8 was significantly increased and the difference was statistically significant compared with that of the control group ( P<0.05). After the expression of YKL-40 was decreased by si- YKL-40-3 transfection, the expression of IL-6 ( P<0.05), IL-8 ( P<0.05), and other inflammatory factors was inhibited compared with that of the control group.

Conclusion

YKL-40 can promote the expression and secretion of IL-6, IL-8, and other acute inflammatory factors in A549 cell line, a type Ⅱ alveolar epithelial cell model, thus aggravating the inflammatory response. Targeted inhibition of YKL-40 expression may effectively inhibit inflammatory response.

EGR1 mediates METTL3/m6A/CHI3L1 to promote osteoclastogenesis in osteoporosis

OBJECTIVE

To investigate EGR1-mediated METTL3/m6A/CHI3L1 axis in osteoporosis.

METHODS

Ovariectomy (OVX) was performed on mice to induce osteoporosis, followed by μ-CT scanning of femurs, histological staining, immunohistochemistry analysis of MMP9 and NFATc1, and ELISA of serum BGP, ALP, Ca, and CTXI. The isolated mouse bone marrow mononuclear macrophages (BMMs) were differentiated into osteoclasts under cytokine stimulation. TRAP staining was performed to quantify osteoclasts. The levels of Nfatc1, c-Fos, Acp5, and Ctsk in osteoclasts, m6A level, and the relationships among EGR1, METTL3, and CHI3L1 were analyzed.

RESULTS

The EGR1/METTL3/CHI3L1 levels and m6A level were upregulated in osteoporotic mice and the derived BMMs. EGR1 was a transcription factor of METTL3. METTL3 promoted the post-transcriptional regulation of CHI3L1 by increasing m6A methylation. EGR1 downregulation reduced BMMs-differentiated osteoclasts and alleviated OVX-induced osteoporosis by regulating the METTL3/m6A/CHI3L1 axis.

CONCLUSION

EGR1 promotes METTL3 transcription and increases m6A-modified CHI3L1 level, thereby stimulating osteoclast differentiation and osteoporosis development.

Single-cell sequencing analysis reveals development and differentiation trajectory of Schwann cells manipulated by M. leprae

BACKGROUND

M. leprae preferentially infects Schwann cells (SCs) in the peripheral nerves leading to nerve damage and irreversible disability. Knowledge of how M. leprae infects and interacts with host SCs is essential for understanding mechanisms of nerve damage and revealing potential new therapeutic strategies.

METHODOLOGY/PRINCIPAL FINDINGS

We performed a time-course single-cell sequencing analysis of SCs infected with M. leprae at different time points, further analyzed the heterogeneity of SCs, subpopulations associated with M. leprae infection, developmental trajectory of SCs and validated by Western blot or flow cytometry. Different subpopulations of SCs exhibiting distinct genetic features and functional enrichments were present. We observed two subpopulations associated with M. leprae infection, a stem cell-like cell subpopulation increased significantly at 24 h but declined by 72 h after M. leprae infection, and an adipocyte-like cell subpopulation, emerged at 72 h post-infection. The results were validated and confirmed that a stem cell-like cell subpopulation was in the early stage of differentiation and could differentiate into an adipocyte-like cell subpopulation.

CONCLUSIONS/SIGNIFICANCE

Our results present a systematic time-course analysis of SC heterogeneity after infection by M. leprae at single-cell resolution, provide valuable information to understand the critical biological processes underlying reprogramming and lipid metabolism during M. leprae infection of SCs, and increase understanding of the disease-causing mechanisms at play in leprosy patients as well as revealing potential new therapeutic strategies.

Role of Chitinase-3-like Protein 1 in Cardioprotection and Angiogenesis by Post-Infarction Exercise Training

Chitinase-3-like protein 1 (CHI3L1) is a myokine involving tissue remodeling and inflammatory processes. CHI3L1 and its receptor protease-activated receptor 2 (PAR2) are induced by exercise in skeletal muscles. However, it remains unknown if CHI3L1/PAR2 signaling also mediates exercise-induced cardioprotection after myocardial infarction. Twenty-four adult male rats were divided into three groups (n = 8/group), receiving: (1) a sham operation; (2) permanent ligation of left anterior descending coronary artery; and (3) post-MI exercise training with one-week adaptive treadmill exercise for seven days followed by four weeks of aerobic exercise. Left ventricular systolic and end-diastolic pressure indices were measured and cardiac fibrosis, and angiogenesis were examined. Furthermore, HUVEC cells were treated in vitro with AMPK agonist—AICAR (a putative pharmacological memetic of exercise), recombinant human CHI3L1, PAR2 receptor blocker (AZ3451), and PI3K inhibitor (LY294002), respectively. We found that post-MI exercise significantly upregulated CHI3L1, PAR2, pPI3K/PI3K, pAKT/AKT, pERK/ERK, improved cardiac function, and diminished fibrosis. AICAR increased HUVEC tubules formation and upregulated CHI3L1 and PAR2 and these changes were attenuated by PAR2 blocker. In conclusion, post-MI exercise training can effectively activate CHI3L1/PAR2 signaling, which led to the improved myocardial function and enhanced cardiac angiogenesis in the infarcted heart.

Nrf2 Regulates CHI3L1 to Suppress Inflammation and Improve Post-Traumatic Osteoarthritis

Introduction

Post-traumatic osteoarthritis (PTOA) is an inflammatory condition that occurs following mechanical joint trauma and that results in joint degeneration. This study sought to evaluate the regulatory function of nuclear factor erythroid 2-related factor 2 (Nrf2) in a murine model of anterior cruciate ligament transection (ACLT)-induced PTOA and in an in vitro model of synoviocyte inflammation induced by LPS treatment with the goal of exploring the role of chitinase 3-like-1 (CHI3L1) in this pathogenic context.

Methods

PTOA model mice were intra-articularly injected with Nrf2 overexpression lentiviral vector, and safranin O-fast green staining as well as the Osteoarthritis Research Society International (OARSI) Scoring System were used to evaluate the severity of cartilage damage. Protein expression in the synovial tissue was evaluated by Western blotting, immunohistochemical staining, and ELISA. Additionally, murine synoviocytes were infected with Nrf2 overexpression lentivirus and stimulated with LPS. The levels of inflammatory cytokines were detected by ELISA. ROS levels were measured using dihydroethidium (DHE) dye.

Results

We determined that the overexpression of Nrf2 was sufficient to reduce cartilage degradation in the context of PTOA in vivo, and we observed a significant decrease in the expression of matrix metalloproteinase 13 (MMP13) in the articular cartilage of samples from mice overexpressing Nrf2 relative to control mice. Synovial CHI3L1 expression and serum TNF-α, IL-1β, and IL-6 levels were reduced in animals overexpressing this transcription factor relative to PTOA model controls. Consistent with these findings, murine synoviocytes treated with LPS exhibited dose-dependent increases in ROS, TNF-α, IL-1β, IL-6, Nrf2, and CHI3L1 levels, whereas Nrf2 overexpression was sufficient to suppress these increases.

Conclusion

Our data indicated that Nrf2 negatively regulates CHI3L1, suggesting that this signaling axis may regulate PTOA progression and may thus be a viable therapeutic target in individuals affected by this condition.

Merlin functions as a critical regulator in Staphylococcus aureus-induced osteomyelitis

Merlin is known as a tumor suppressor, while its role in osteomyelitis remains unclear. This study aimed to investigate the role of Merlin in Staphylococcus aureus-induced osteomyelitis and its underlying mechanisms. S. aureus-induced osteomyelitis mouse model was established in Merlin^fl/fl Lyz2^cre/+ and Merlin^fl/fl Lyz2^+/+ mice. Bone marrow-derived macrophages (BMDMs) were isolated and stimulated by lipopolysaccharide (LPS). Bioassays, including quantitative reverse transcription polymerase chain reaction (qRT-PCR), Western blot analysis, and enzyme-linked immunosorbent assays, were conducted to determine the levels of target genes or proteins. Immunoprecipitation was applied to determine the interactions between proteins. DCAF1^fl/fl mice were further crossed with Lyz2-Cre mice to establish myeloid cell conditional knockout mice (DCAF1^fl/fl Lyz2^cre/+ ). It was found that the level of Merlin was elevated in patients with osteomyelitis and S. aureus-infected BMDMs. Merlin deficiency in macrophages suppressed the production of inflammatory cytokines and ameliorated the symptoms of osteomyelitis induced by S. aureus. Merlin deficiency in macrophages also suppressed the production of proinflammatory cytokines in BMDMs induced by LPS. The inhibitory effects of Merlin deficiency on the inflammatory response were associated with DDB1-Cul4-associated factor 1 (DCAF1). In summary, Merlin deficiency ameliorates S. aureus-induced osteomyelitis through the regulation of DCAF1.

Genetic Determinants for Bacterial Osteomyelitis: A Focused Systematic Review of Published Literature

Background: Osteomyelitis is an inflammatory process characterized by progressive bone destruction. Moreover, chronic bacterial osteomyelitis is regarded as a difficult-to-treat clinical entity due to its long-standing course and frequent infection recurrence. However, the role of genetic factors in the occurrence and development of bacterial osteomyelitis is poorly understood.

Methods: We performed a systematic review to assess the frequency of individual alleles and genotypes of single-nucleotide polymorphisms (SNPs) among patients with bacterial osteomyelitis and healthy people to identify whether the SNPs are associated with the risk of developing bacterial osteomyelitis. Then, gene ontology and Kyoto Encyclopedia of Gene and Genomes analyses were performed to identify the potential biological effects of these genes on the pathogenesis of bacterial osteomyelitis.

Result: Fourteen eligible studies containing 25 genes were analyzed. In this review, we discovered that the SNPs in IL1B, IL6, IL4, IL10, IL12B, IL1A, IFNG, TNF, PTGS2, CTSG, vitamin D receptor (VDR), MMP1, PLAT, and BAX increased the risk of bacterial osteomyelitis, whereas those in IL1RN and TLR2 could protect against osteomyelitis. The bioinformatic analysis indicated that these osteomyelitis-related genes were mainly enriched in inflammatory reaction pathways, suggesting that inflammation plays a vital role in the development of bacterial osteomyelitis. Furthermore, functional notation for 25 SNPs in 17 significant genes was performed using the RegulomeDB and NCBI databases. Four SNPs (rs1143627, rs16944, rs2430561, and rs2070874) had smaller scores from regulome analysis, implying significant biological function.

Conclusion: We systematically summarized several SNPs linked to bacterial osteomyelitis and discovered that these gene polymorphisms could be a genetic factor for bacterial osteomyelitis. Moreover, further large-scale cohort studies are needed to enhance our comprehensive understanding of the development of osteomyelitis to provide earlier individualized preventions and interventions for patients with osteomyelitis in clinical practice.

CHI3L1 promotes Staphylococcus aureus-induced osteomyelitis by activating p38/MAPK and Smad signaling pathways

AIMS

Staphylococcus aureus (S. aureus) is the most common causative bacterial pathogen involved in promoting infection-induced osteomyelitis, a disease resulting in severe bone degradation. In this study, we aimed to identify the mechanism behind inhibition of osteoclast survival and differentiation by CHI3L1, a lectin previously reported to regulate S. aureus-induced osteomyelitis.

MAIN METHODS

The role of CHI3L1 in osteoclast survival, proliferation, and differentiation was studied ex vivo using primary human bone marrow derived stem cells (HBMSCs) and transducing them with lentiviral expression vectors or shRNA knockdown constructs. Cell apoptosis was analyzed by flow cytometry using annexin V-fluorescein isothiocyanate/propidium iodide staining. Cell proliferation was assessed using alkaline phosphatase, Alcian Blue, and TRAP staining. The qRT-PCR was used to measure mRNA levels of osteoclast maturation markers, and western blotting was used to analyze protein expression. An in vivo murine model for osteomyelitis and microcomputed tomography analyses of infected femurs were used to study the effects of CHI3L1 on bone erosion.

KEY FINDINGS

Overexpression of CHI3L1 significantly reduced HBMSC cell viability, proliferation, and differentiation, and knockdown improved these effects in the presence of S. aureus infection. More specifically, CHI3L1 constitutively activated the p38/MAPK pathway to promote apoptosis. Furthermore, CHI3L1 induced activation of the Smad pathway by promoting phosphorylation of Smad-1/5 proteins. Finally, overexpression of CHI3L1 significantly induced bone erosion upon S. aureus infection in a murine osteomyelitis model, and knockdown of CHI3L1 significantly alleviated this effect.

SIGNIFICANCE

CHI3L1 played a vital role in osteoblast differentiation and proliferation by regulating the p38/MAPK and Smad signaling pathways to promote S. aureus-induced osteomyelitis.

Efficacy of chitinase-3-like protein 1 as an in vivo bone formation predictable marker of maxillary/mandibular bone marrow stromal cells

Introduction

Maxillary/mandibular bone marrow stromal cells (MBMSCs) are a useful cell source for bone regeneration in the oral and maxillofacial region. To further ensure the clinical application of MBMSCs in bone regenerative therapy, it is important to determine the bone formation capacity of MBMSCs before transplantation. The aim of this study is to identify the molecular marker that determines the in vivo bone formation capacity of MBMSCs.

Methods

The cell growth, cell surface antigens, in vitro and in vivo bone formation capacity of MBMSCs were examined. The amount of chitinase-3-like protein 1 (CHI3L1) secreted into the conditioned medium was quantified. The effects of CHI3L1 on the cell growth and osteogenic differentiation potential of MBMSCs and on the cell growth and migration of vascular endothelial cells and fibroblasts were examined.

Results

The cell growth, and in vitro and in vivo bone formation capacity of the cells treated with different conditions were observed. MBMSCs that secreted a large amount of CHI3L1 into the conditioned medium tended to have low in vivo bone formation capacity, whereas MBMSCs that secreted a small amount of CHI3L1 had greater in vivo bone formation capacity. CHI3L1 promoted the migration of vascular endothelial cells, and the cell growth and migration of fibroblasts.

Conclusion

Our study indicates that the in vitro osteogenic differentiation capacity of MBMSCs and the in vivo bone formation capacities of MBMSCs were not necessarily correlated. The transplantation of high CHI3L1 secretory MBMSCs may suppress bone formation by inducing fibrosis at the site. These results suggest that the CHI3L1 secretion levels from MBMSCs may be used as a predictable marker of bone formation capacity in vivo.

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In vitro and in vivo bone formation capacities of MBMSCs were not correlated.

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MBMSCs with high CHI3L1 secretion tended to have low in vivo bone formation.

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MBMSCs with low CHI3L1 secretion tended to have high in vivo bone formation.

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CHI3L1 can be in vivo bone formation capacity predictable marker of MBMSCs.

RETRACTED: Upregulated microRNA-381-5p strengthens the effect of dexmedetomidine preconditioning to protect against myocardial ischemia-reperfusion injury in mouse models by inhibiting CHI3L1

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. Concern was raised about the reliability of the Western blot results in Figs. 1F, 2F, 3F, 4F and 5F, which appear to have the same eyebrow shaped phenotype as many other publications tabulated here (https://docs.google.com/spreadsheets/d/149EjFXVxpwkBXYJOnOHb6RhAqT4a2llhj9LM60MBffM/edit#gid=0 [docs.google.com]). The journal requested the corresponding author comment on these concerns and provide the raw data. However, the authors were not responsive to the request for comment. Since original data could not be provided, the overall validity of the results could not be confirmed. Therefore, the Editor-in-Chief decided to retract the article.

Detailed Functional Characterization of a Waist-Hip Ratio Locus in 7p15.2 Defines an Enhancer Controlling Adipocyte Differentiation

We combined CAGE sequencing in human adipocytes during differentiation with data from genome-wide association studies to identify an enhancer in the SNX10 locus on chromosome 7, presumably involved in body fat distribution. Using reporter assays and CRISPR-Cas9 gene editing in human cell lines, we characterized the role of the enhancer in adipogenesis. The enhancer was active during adipogenesis and responded strongly to insulin and isoprenaline. The allele associated with increased waist-hip ratio in human genetic studies was associated with higher enhancer activity. Mutations of the enhancer resulted in less adipocyte differentiation. RNA sequencing of cells with disrupted enhancer showed reduced expression of established adipocyte markers, such as ADIPOQ and LPL, and identified CHI3L1 on chromosome 1 as a potential gene involved in adipocyte differentiation. In conclusion, we identified and characterized an enhancer in the SNX10 locus and outlined its plausible mechanisms of action and downstream targets.

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An enhancer active during adipogenesis is located in an obesity GWAS locus

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The enhancer responded strongly to insulin and isoprenaline

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Mutation of the enhancer by CRISPR-Cas9 decreased adipocyte differentiation

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Knockout of CHI3L1 decreased adipocyte differentiation

Contextual Regulation of Skeletal Physiology by Notch Signaling

PURPOSE OF REVIEW

This article reviews the past 2 years of research on Notch signaling as it relates to bone physiology, with the goal of reconciling seemingly discrepant findings and identifying fruitful areas of potential future research.

RECENT FINDINGS

Conditional animal models and high-throughput omics have contributed to a greater understanding of the context-dependent role of Notch signaling in bone. However, significant gaps remain in our understanding of how spatiotemporal context and epigenetic state dictate downstream Notch phenotypes. Biphasic activation of Notch signaling orchestrates progression of mesenchymal progenitor cells through the osteoblast lineage, but there is a limited understanding of ligand- and receptor-specific functions. Paracrine Notch signaling through non-osteoblastic cell types contributes additional layers of complexity, and we anticipate impactful future work related to the integration of these cell types and signaling mechanisms.

Roles of chitinase 3-like 1 in the development of cancer, neurodegenerative diseases, and inflammatory diseases

Chitinase 3-like 1 (CHI3L1) is a secreted glycoprotein that mediates inflammation, macrophage polarization, apoptosis, and carcinogenesis. The expression of CHI3L1 is strongly increased by various inflammatory and immunological conditions, including rheumatoid arthritis, multiple sclerosis, Alzheimer's disease, and several cancers. However, its physiological and pathophysiological roles in the development of cancer and neurodegenerative and inflammatory diseases remain unclear. Several studies have reported that CHI3L1 promotes cancer proliferation, inflammatory cytokine production, and microglial activation, and that multiple receptors, such as advanced glycation end product, syndecan-1/αVβ3, and IL-13Rα2, are involved. In addition, the pro-inflammatory action of CHI3L1 may be mediated via the protein kinase B and phosphoinositide-3 signaling pathways and responses to various pro-inflammatory cytokines, including tumor necrosis factor-α, interleukin-1β, interleukin-6, and interferon-γ. Therefore, CHI3L1 could contribute to a vast array of inflammatory diseases. In this article, we review recent findings regarding the roles of CHI3L1 and suggest therapeutic approaches targeting CHI3L1 in the development of cancers, neurodegenerative diseases, and inflammatory diseases.

Lysophosphatidic acid: Its role in bone cell biology and potential for use in bone regeneration

Lysophosphatidic acid (LPA) is a simple phospholipid that exerts pleiotropic effects on numerous cell types by activating its family of cognate G protein-coupled receptors (GPCRs) and participates in many biological processes, including organismal development, wound healing, and carcinogenesis. Bone cells, such as bone marrow mesenchymal stromal (stem) cells (BMSCs), osteoblasts, osteocytes and osteoclasts play essential roles in bone homeostasis and repair. Previous studies have identified the presence of specific LPA receptors in these bone cells. In recent years, an increasing number of cellular effects of LPA, such as the induction of cell proliferation, survival, migration, differentiation and cytokine secretion, have been found in different bone cells. Moreover, some biomaterials containing LPA have shown the ability to enhance osteogenesis. This review will focus on findings associated with LPA functions in these bone cells and present current studies related to the application of LPA in bone regenerative medicine. Further understanding this information will help us develop better strategies for bone healing.

Inhibition of pyroptosis attenuates Staphylococcus aureus-induced bone injury in traumatic osteomyelitis

Background

Osteomyelitis is a severe bone infection and typically leads to progressive bone resorption, destruction and dysfunction. Pyroptosis is a form of programmed cell death involved in various infectious diseases. However, the identification of pyroptosis and the role it plays in osteomyelitis remains to be clarified. In this study, we investigated the expression of pyroptosis-associated proteins in osteomyelitis and the effects of inhibiting pyroptosis on S. aureus-induced osteomyelitis both in vitro and in vivo.

Methods

The expression of pyroptosis-associated protein-NLRP3 (NLR Family Pyrin Domain Containing 3), Caspase1 and GSDMD (GasderminD) were examined in murine and human infectious bone fragments by western blot. Bone destruction was evaluated by microcomputed tomography (µCT). The concentration of inflammatory factors was tested by Enzyme linked Immunosorbent Assay (ELISA). The expression of pyroptosis-associated gene was detected by real-time quantitative polymerase chain reaction (RT-qPCR).

Results

The expression of pyroptosis-associated proteins in infectious bone fragments from patients with osteomyelitis was significantly higher than uninfected bone. Additionally, in S. aureus-induced murine osteomyelitis model, higher expression of pyroptosis-associated proteins was noticed. Furthermore, the inhibitors of pyroptosis-associated proteins alleviated S. aureus-induced pyroptosis both in vivo and in vitro. More importantly, the inhibition of pyroptosis restored the bone formative property, attenuated the aberrant activation of osteoclast in vitro and reversed bone injury in vivo.

Conclusions

Our study identified pyroptosis as a key pathway in osteomyelitis and elaborated that the inhibition of pyroptosis could attenuate S. aureus-induced bone destruction in osteomyelitis, providing a potential treatment target to osteomyelitis.

Chitinase-like proteins as regulators of innate immunity and tissue repair: helpful lessons for asthma?

Chitinases and chitinase-like proteins (CLPs) belong to the glycoside hydrolase family 18 of proteins. Chitinases are expressed in mammals and lower organisms, facilitate chitin degradation, and hence act as host-defence enzymes. Gene duplication and loss-of-function mutations of enzymatically active chitinases have resulted in the expression of a diverse range of CLPs across different species. CLPs are genes that are increasingly associated with inflammation and tissue remodelling not only in mammals but also across distant species. While the focus has remained on understanding the functions and expression patterns of CLPs during disease in humans, studies in mouse and lower organisms have revealed important and overlapping roles of the CLP family during physiology, host defence and pathology. This review will summarise recent insights into the regulatory functions of CLPs on innate immune pathways and discuss how these effects are not only important for host defence and tissue injury/repair after pathogen invasion, but also how they have extensive implications for pathological processes involved in diseases such as asthma.