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

Exploring the relationship between pyroptosis and inflammatory bone loss: Evidence from a cigarette smoke-induced osteoporosis mouse model

Smoking is by far one of the greatest public health threats and is recognized as an important predisposing factor for osteoporosis. Exposure to cigarette smoke (CS) has been reported to be associated with inflammation-associated diseases through the induction of pyroptosis. Nevertheless, the correlation between pyroptosis and bone loss induced by CS remains uninvestigated. Here, a mouse model of mainstream smoke exposure-induced osteoporosis was established. μCT, biomechanical testing, and immunohistochemical staining of bone tissue were used to assess the deleterious effects of CS on bone metabolism. In vitro, the effects of cigarette smoke extracts (CSE) on mouse primary bone marrow-derived mesenchymal stem cells (BMSCs) were tested by cell viability assays, gene and protein expression assays, and alizarin red staining. The utilization of the pyroptosis inhibitor MCC950 served to confirm the critical role of BMSCs pyroptosis in CS-induced osteoporosis. Our results indicated that exposure to mainstream smoke led to a notable decrease in the quantity of osteoblasts and hindered the process of osteogenic differentiation in mice. Additionally, there was a significant increase in the expression of pyroptosis-related proteins in the bone marrow. The inhibitory effects of CSE on cell viability and osteogenic differentiation of BMSCs were found to be dose-dependent in vitro. However, the presence of the pyroptosis inhibitor MCC950 significantly improved the impaired osteogenic differentiation and bone mineralization caused by CSE. These results highlight the crucial involvement of BMSCs pyroptosis in the development of bone loss induced by CS. In summary, the findings of this study provide novel evidence that CS exerts a detrimental effect on the process of osteogenesis in BMSCs through the induction of pyroptosis, ultimately leading to bone loss. Inhibition of pyroptosis effectively attenuated the toxicological effects of CS on BMSCs, providing a new target for preventing inflammatory osteoporosis.

Possible role of annexin A1/FPR2 pathway in COX2/NLRP3 inflammasome regulation in alveolar bone cells of estrogen-deficient female rats with diabetes mellitus

BACKGROUND

Annexin A1 (ANXA1) and the NOD-like receptor family pyrin domain-containing protein 3 (NLRP3) inflammasome play important roles in bone remodeling. However, expression profiles of these factors in bone cells under diabetes mellitus (DM) and estrogen-deficient conditions are poorly understood. This study investigated the immunoexpression of ANXA1 and its formyl peptide receptor 2 (FPR2), as well as NLRP3 inflammasome mediators, during remodeling of the alveolar process in diabetic and estrogen-deficient rats.

METHODS

Twenty adult female Wistar rats were divided into four groups (n = 5): Sham-operated (SHAM) and ovariectomized (OVX) rats received a vehicle solution, and SHAM and OVX rats were intraperitoneally administered 60 mg/kg/body weight (BW) of streptozotocin (STZ) to induce DM (SHAM-Di and OVX-Di groups). After 7 weeks, the rats were euthanized and their maxillae were fixed in phosphate-buffered 4% formaldehyde and embedded in paraffin. Sections were stained with hematoxylin/eosin (H&E) and picrosirius red or subjected to immunohistochemical detection of ANXA1, FPR2, NLRP3, interleukin-1β (IL-1β), and cyclooxygenase-2 (COX2).

RESULTS

Estrogen deficiency and DM were associated with deleterious effects in bone tissue, as evidenced by a lower number of osteocytes and higher number of empty lacunae in the SHAM-Di and OVX-Di groups compared to the nondiabetic groups. Both diabetic groups showed a smaller vascular area and weaker collagen fiber birefringence intensity in alveolar bone tissue. A significantly higher number of ANXA1/FPR2-positive osteoblasts, osteocytes, and osteoclasts was accompanied by a significantly higher number of these cells immunolabeled for COX2, NLRP3, and IL-1β in the diabetic and OVX groups, especially in both estrogen-deficient and diabetic rats.

CONCLUSION

These results indicate a possible role for the ANXA1/FPR2 pathway as a fine-tuning/anti-inflammatory regulator to counterbalance exacerbated COX2/NLRP3/IL-1β activation in bone cells during bone remodeling under estrogen deficiency and DM.

Pyroptosis: A spoiler of peaceful coexistence between cells in degenerative bone and joint diseases

BACKGROUND

As people age, degenerative bone and joint diseases (DBJDs) become more prevalent. When middle-aged and elderly people are diagnosed with one or more disorders such as osteoporosis (OP), osteoarthritis (OA), and intervertebral disc degeneration (IVDD), it often signals the onset of prolonged pain and reduced functionality. Chronic inflammation has been identified as the underlying cause of various degenerative diseases, including DBJDs. Recently, excessive activation of pyroptosis, a form of programed cell death (PCD) mediated by inflammasomes, has emerged as a primary driver of harmful chronic inflammation. Consequently, pyroptosis has become a potential target for preventing and treating DBJDs.

AIM OF REVIEW

This review explored the physiological and pathological roles of the pyroptosis pathway in bone and joint development and its relation to DBJDs. Meanwhile, it elaborated the molecular mechanisms of pyroptosis within individual cell types in the bone marrow and joints, as well as the interplay among different cell types in the context of DBJDs. Furthermore, this review presented the latest compelling evidence supporting the idea of regulating the pyroptosis pathway for DBJDs treatment, and discussed the potential, limitations, and challenges of various therapeutic strategies involving pyroptosis regulation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In summary, an interesting identity for the unregulated pyroptosis pathway in the context of DBJDs was proposed in this review, which was undertaken as a spoiler of peaceful coexistence between cells in a degenerative environment. Over the extended course of DBJDs, pyroptosis pathway perpetuated its activity through crosstalk among pyroptosis cascades in different cell types, thus exacerbating the inflammatory environment throughout the entire bone marrow and joint degeneration environment. Correspondingly, pyroptosis regulation therapy emerged as a promising option for clinical treatment of DBJDs.

Luteolin rescues postmenopausal osteoporosis elicited by OVX through alleviating osteoblast pyroptosis via activating PI3K-AKT signaling

BACKGROUND

Recently, osteoblast pyroptosis has been proposed as a potential pathogenic mechanism underlying osteoporosis, although this remains to be confirmed. Luteolin (Lut), a flavonoid phytochemical, plays a critical role in the anti-osteoporosis effects of many traditional Chinese medicine prescriptions. However, its protective impact on osteoblasts in postmenopausal osteoporosis (PMOP) has not been elucidated.

PURPOSE

This research aimed to determine the effect of Lut in ameliorating PMOP by alleviating osteoblast pyroptosis and sustaining osteogenesis.

STUDY DESIGN

This research was designed to investigate the novel mechanism of Lut in alleviating PMOP both in cell and animal models.

METHODS

Ovariectomy-induced PMOP models were established in mice with/without daily gavaged of 10 or 20 mg/kg body weight Lut. The impact of Lut on bone microstructure, metabolism and oxidative stress was evaluated with 0.104 mg/kg body weight Estradiol Valerate Tablets daily gavaged as positive control. Network pharmacological analysis and molecular docking were employed to investigate the mechanisms of Lut in PMOP treatment. Subsequently, the impacts of Lut on the PI3K/AKT axis, oxidative stress, mitochondria, and osteoblast pyroptosis were assessed. In vitro, cultured MC3T3-E1(14) cells were exposed to H2O2 with/without Lut to examine its effects on the PI3K/AKT signaling pathway, osteogenic differentiation, mitochondrial function, and osteoblast pyroptosis.

RESULTS

Our findings demonstrated that 20 mg/kg Lut, similar to the positive control drug, effectively reduced systemic bone loss and oxidative stress, and enhanced bone metabolism induced by ovariectomy. Network pharmacological analysis and molecular docking indicated that the PI3K/AKT axis was a potential target, with oxidative stress response and nuclear membrane function being key mechanisms. Consequently, the effects of Lut on the PI3K/AKT axis and pyroptosis were investigated. In vivo data revealed that the PI3K/AKT axis was deactivated following ovariectomy, and Lut restored the phosphorylation of key proteins, thereby reactivating the axis. Additionally, Lut alleviated osteoblast pyroptosis and mitochondrial abnormalities induced by ovariectomy. In vitro, Lut intervention mitigated the inhibition of the PI3K/AKT axis and osteogenesis, as well as H2O2-induced pyroptosis. Furthermore, Lut attenuated ROS accumulation and mitochondrial dysfunction. The effects of Lut, including osteogenesis restoration, anti-pyroptosis, and mitochondrial maintenance, were all reversed with LY294002 (a PI3K/AKT pathway inhibitor).

CONCLUSION

In summary, Lut could improve mitochondrial dysfunction, alleviate GSDME-mediated pyroptosis and maintain osteogenesis via activating the PI3K/AKT axis, offering a new therapeutic strategy for PMOP.

The Impact of NLRP3 Inflammasome on Osteoblasts and Osteogenic Differentiation: A Literature Review

Osteoblasts (OBs), which are a crucial type of bone cells, derive from bone marrow mesenchymal stem cells (MSCs). Accumulating evidence suggests inflammatory cytokines can inhibit the differentiation and proliferation of OBs, as well as interfere with their ability to synthesize bone matrix, under inflammatory conditions. NLRP3 inflammasome is closely associated with cellular pyroptosis, which can lead to excessive release of pro-inflammatory cytokines, causing tissue damage and inflammatory responses, however, the comprehensive roles of NLRP3 inflammasome in OBs and their differentiation have not been fully elucidated, making targeting NLRP3 inflammasome approaches to treat diseases related to OBs uncertain. In this review, we provide a summary of NLRP3 inflammasome activation and its impact on OBs. We highlight the significant roles of NLRP3 inflammasome in regulating OBs differentiation and function. Furthermore, current available strategies to affect OBs function and osteogenic differentiation targeting NLRP3 inflammasome are listed and analyzed. Finally, through the prospective discussion, we seek to provide novel insights into the crucial role of NLRP3 inflammasome in diseases related to OBs and offer valuable information for devising treatment strategies.

Identification of PKM2 as a pyroptosis-related key gene aggravates senile osteoporosis via the NLRP3/Caspase-1/GSDMD signaling pathway

BACKGROUNDS

Senile osteoporosis-alternatively labeled as skeletal aging-encompasses age-induced bone deterioration and loss of bone microarchitecture. Recent studies have indicated a potential association between senile osteoporosis and chronic systemic inflammation, and pyroptosis in bone marrow-derived mesenchymal stem cells is speculated to contribute to bone loss and osteoporosis. Therefore, targeting pyroptosis in stem cells may be a potential therapeutic strategy for treating osteoporosis.

METHODS

Initially, we conducted bioinformatics analysis to screen the GEO databases to identify the key gene associated with pyroptosis in senile osteoporosis. Next, we analyzed the relationship between altered proteins and clinical data. In vitro experiments were then performed to explore whether the downregulation of PKM2 expression could inhibit pyroptosis. Additionally, an aging-related mouse model of osteoporosis was established to validate the efficacy of a PKM2 inhibitor in alleviating osteoporosis progression.

RESULTS

We identified PKM2 as a key gene implicated in pyroptosis in senile osteoporosis patients through bioinformatics analysis. Further analyses of bone marrow and stem cells demonstrated significant PKM2 overexpression in senile osteoporosis patients. Silencing PKM2 expression inhibited pyroptosis in senile stem cells, of which the osteogenesis potential and angiogenic function were also primarily promoted. Moreover, the results in vivo demonstrated that administering PKM2 inhibitors suppressed pyroptosis in senile osteoporosis mice and mitigated senile osteoporosis progression.

CONCLUSION

Our study uncovered PKM2, a key pyroptosis marker of bone marrow mesenchymal stem cells in senile osteoporosis. Shikonin, a PKM2 inhibitor, was then identified as a potential drug candidate for the treatment of osteoporosis.

Topology-regulated nanocatalysts for ferroptosis-mediated cancer phototherapy

Ferroptosis-mediated tumor treatment is constrained by the absence of single-component, activatable multifunctional inducers. Given this, a topological synthesis strategy is employed to develop an efficient bismuth-based semiconductor nano-photocatalyst (Bi2O3:S) for tumor ferroptosis therapy. Photo-excited electrons can participate in the reduction reaction to produce harmful reactive oxygen species (ROS) when exposed to near-infrared light. Meanwhile, photo-excited holes can contribute to the oxidation reaction to utilize extra glutathione (GSH) in tumors. In the acidic tumor microenvironment, bismuth ions generated from Bi2O3:S may further cooperate with GSH to amplify oxidative stress damage and achieve biodegradation. Both promote ferroptosis by downregulating glutathione peroxidase 4 (GPX4) expression. Besides, sulfur doping optimizes its near-infrared light-induced photothermal conversion efficiency, benefiting its therapeutic effect. Thus, bismuth ions and holes synergistically drive photo-activable ferroptosis in this nanoplatform, opening up new avenues for tumor therapy.

Serum caspase‑1 levels serve as a predictive biomarker for the prognosis of patients undergoing arthroscopic‑assisted locking plate internal fixation in the treatment of high‑energy pilon fractures

The present study aimed to investigate the serum levels of caspase-1 in patients with high-energy pilon fractures, and its correlation with prognosis and clinical results. In this prospective study, 136 patients with high-energy pilon fractures who were treated with a locking plate combined with ankle arthroscopy from July 2015 to July 2020 were included. The treatment efficacy was evaluated according to the Mazur ankle function score. Serum caspase-1, interleukin (IL)-6, IL-1β and C-reactive protein (CRP) levels were measured using enzyme-linked immunosorbent assay. Reverse transcription-quantitative PCR was used to measure the mRNA expression of caspase-1. Additionally, demographic data and clinical characteristics, such as sex, age, intraoperative blood loss, fracture healing time, fracture classification and complications were collected and analyzed. The study revealed that the intraoperative blood loss, proportion of Ruedi-Allgower III and the serum levels of caspase-1 in the poor prognosis group were significantly higher compared with those in the good prognosis group. Additionally, patients with high-energy pilon fractures in the poor prognosis group exhibited significantly higher levels of caspase-1 and IL-1β serum levels at all time points in contrast to those in the good prognosis group. Spearman's analysis revealed a significant association between caspase-1, IL-1β levels and Mazur scores. Furthermore, caspase-1 could serve as a potential diagnostic biomarker for poor prognosis of patients with high-energy pilon fractures. Caspase-1, IL-1β, intraoperative blood loss and Ruedi-Allgower grade were the risk factors for poor prognosis in patients with high-energy pilon fractures. In summary, this study demonstrated that serum caspase-1 levels were progressively reduced during the treatment of high-energy pilon fractures patients and prominently lowered in those with a favorable prognosis. These findings could provide novel targets and a comprehensive approach to protecting patients with high-energy pilon fractures.

Peptide NCTX15 derived from spider toxin gland effectively relieves hyperuricemia in mice

Hyperuricemia is a clinical disease characterized by a continuous increase in uric acid (UA) due to purine metabolism disorder. As current drug treatments are limited, it is imperative to explore new drugs that offer better safety and efficacy. In this study, Nephila clavata toxin gland homogenates were isolated and purified by exclusion chromatography and high-performance liquid chromatography, resulting in the identification and isolation of a short peptide (NCTX15) with the sequence 'QSGHTFK'. Analysis showed that NCTX15 exhibited no cytotoxicity in mouse macrophages or toxic and hemolytic activity in mice. Notably, NCTX15 inhibited UA production by down-regulating urate transporter 1 and glucose transporter 9 and up-regulating organic anion transporter 1, thus promoting UA excretion. In addition, NCTX15 alleviated the inflammatory response and renal injury by inhibiting the expression of inflammatory factors interleukin-6, interleukin-1β, tumor necrosis factor alpha, NLR family, pyrin domain-containing 3, and pyroptosis-related factor gasdermin D. These results indicate that NCTX15 displayed urate-lowering, anti-inflammatory, and analgesic effects. As the first urate-reducing short peptide isolated from a spider toxin gland homogenate, NCTX15 exhibits considerable potential as a novel drug molecule for anti-gout and hyperuricemia treatment.

Pyroptosis in microbial infectious diseases

Pyroptosis is a gasdermins-mediated programmed cell death that plays an essential role in immune regulation, and its role in autoimmune disease and cancer has been studied extensively. Increasing evidence shows that various microbial infections can lead to pyroptosis, associated with the occurrence and development of microbial infectious diseases. This study reviews the recent advances in pyroptosis in microbial infection, including bacterial, viral, and fungal infections. We also explore potential therapeutic strategies for treating microbial infection-related diseases by targeting pyroptosis.

Pmepa1 knockdown alleviates SpA-induced pyroptosis and osteogenic differentiation inhibition of hBMSCs via p38MAPK/NLRP3 axis

BACKGROUND

Osteomyelitis is a refractory bone infectious disease, which usually results in progressive bone destruction and bone loss. The invasion of pathogens and subsequent inflammatory response could damage bone marrow mesenchymal stem cells (BMSCs) and inhibit osteogenic differentiation, and finally aggravate uncontrolled bone remodeling in osteomyelitis by affecting bone formation. Exploring the mechanisms of BMSCs injury and osteogenic differentiation inhibition may would help us to find potential therapeutic targets.

METHOD

Firstly, staphylococcal protein A (SpA)-treated human bone marrow mesenchymal stem cells (hBMSCs) were used to construct cell models of osteomyelitis. Secondly, transcriptome sequencing was performed to screen differentially expressed genes and then verified the expression of target genes. Next, in vitro experiments were conducted to explore the functions and mechanisms of prostate transmembrane protein androgen induced 1 (Pmepa1) in SpA-treated hBMSCs. Finally, the rat model of osteomyelitis was established to provide an auxiliary validation of the in vitro experimental results.

RESULTS

We found that SpA treatment induced inflammatory injury and inhibited osteogenic differentiation in hBMSCs, then the transcriptome sequencing and further detection results showed that Pmepa1 was significantly upregulated in this process. Functionally, Pmepa1 knockdown alleviated inflammatory injury and promoted osteogenic differentiation in SpA-treated hBMSCs. Among them, it was demonstrated that Pmepa1 knockdown exerted cytoprotective effects by alleviating pyroptosis of SpA-infected hBMSCs. Furthermore, recovery experiments revealed that Pmepa1 knockdown reversed SpA-mediated adverse effects by downregulating the p38MAPK/NLRP3 axis. Finally, the detection results of rat femoral osteomyelitis showed that the expression of Pmepa1 was up-regulated, and the expression trends of other indicators including p38MAPK, NLRP3, and caspase-1 were also consistent with the in vitro model.

CONCLUSION

Pmepa1 knockdown alleviates SpA-induced pyroptosis and inhibition of osteogenic differentiation in hBMSCs by downregulating p38MAPK/NLRP3 signaling axis. Modulating the expression of Pmepa1 may be a potential strategy to ameliorate osteomyelitis.

The Role of Caspase-11 and Pyroptosis in the Regulation of Inflammation in Peri-Implantitis

Peri-implantitis is an important cause of oral implant failure. In the past, TLR4 and TLR2 in the Toll-like family were generally considered as the key immune recognition receptors regulating peri-implantitis. However, under the guidance of this theory, there are still some unexplainable peri-implantitis symptoms. With the discovery of novel intracellular LPS receptor Caspase-11, a new understanding of inflammatory signaling and immune regulation in the development of peri-implantitis has been gained. However, the regulatory role of Caspase-11 in peri-implantitis and its crosstalk with the TLR4 pathway remain unclear. The therapeutic effect of drugs targeting Caspase-11 on peri-implantitis is still in its early stages. In view of this situation, this paper reviews the possible role of Caspase-11 in peri-implant inflammation, elaborated the entry process of LPS and the activation mechanism of Caspase-11, and analyzes the differences in Caspase-11 between commonly studied animals, mice and humans. The current research hotspots and challenges are also analyzed to provide new insights and ideas for researchers.

Synergistic Photochemo Effects Based on Light-Activatable Dual Prodrug Nanoparticles for Effective Cancer Therapy

Ferroptosis is identified as a novel type of cell death with distinct properties involved in physical conditions and various diseases, including cancers. It is considered that ferroptosis provides a promising therapeutic strategy for optimizing oncotherapy. Although erastin is an effective ferroptosis trigger, the potential of its clinical application is largely restricted by its poor water solubility and concomitant limitations. To address this issue, an innovative nanoplatform (PE@PTGA) that integrated protoporphyrin IX (PpIX) and erastin coated with amphiphilic polymers (PTGA) to evoke ferroptosis and apoptosis is constructed and exemplified using an orthotopic hepatocellular carcinoma (HCC) xenograft mouse model as a paradigm. The self-assembled nanoparticles can enter HCC cells and release PpIX and erastin. With light stimulation, PpIX exerts hyperthermia and reactive oxygen species to inhibit the proliferation of HCC cells. Besides, the accumulated reactive oxygen species (ROS) can further promote erastin-induced ferroptosis in HCC cells. In vitro and in vivo studies reveal that PE@PTGA synergistically inhibits tumor development by stimulating both ferroptosis- and apoptosis-related pathways. Moreover, PE@PTGA has low toxicity and satisfactory biocompatibility, suggesting its promising clinical benefit in cancer treatments.

Artesunate ameliorates ligature-induced periodontitis by attenuating NLRP3 inflammasome-mediated osteoclastogenesis and enhancing osteogenic differentiation

Periodontitis, arguably the greatest common infective chronic inflammatory disease, is characterized by an imbalance of the host immune system and excessive osteoclastogenesis activity with severe alveolar bone loss. Nevertheless, in consideration of the harmful effects of repeated treatment, more sensible intervention drugs for periodontitis need to be developed. Artesunate (ART), derived from Artemisia annua L., has shown remarkable pharmacokinetic and clinical value, as well as anti-inflammatory and immunomodulatory effects in various immune and chronic diseases due to its endoperoxide group. However, the role of ART in mediating periodontitis-induced alveolar bone resorption has not been examined. In this study, ART treatment effectively ameliorated ligature-induced periodontitis via attenuating osteoclast formation in a dose-dependent manner. Mechanistically, RNA-seq revealed that ART dramatically reduced the enrichment of NLRP3 inflammasome-related genes. Concordant with our study, MCC950, a specific inhibitor of NLRP3 inflammasome, also greatly restrained osteoclastogenesis, suggesting that ART suppressed osteoclast formation by blocking NLRP3 inflammasome activation. In addition to regulating osteoclastogenesis, ART significantly enhanced osteogenic differentiation by alleviating the expression of cytokines in inflammatory conditions. Our data shed light on the probably potential mechanism of ART treatment for the intervention of periodontitis.

DNMT1-mediated DNA methylation in toll-like receptor 4 (TLR4) inactivates NF-κB signal pathway-triggered pyroptotic cell death and cellular inflammation to ameliorate lipopolysaccharides (LPS)-induced osteomyelitis

Toll-like receptor 4 (TLR4) plays a critical role in various human diseases, and was associated with pyroptotic cell death and inflammatory responses. DNA methylation, which has stable and reversible properties, has been reported to alter the expression of target genes, including TLR4. However, the role of methylated TLR4 in osteomyelitis (OM) and the underlying molecular mechanisms remain unclear. RNA sequencing was used to identify differentially expressed genes and associated signaling pathways. RT-qPCR, Western blot, emzyme-linked immunosorbent assay (ELISA), cell counting kit-8 (CCK-8) and LDH assay kit were used to detect mRNA and protein expression of relevant genes, cell viability and the LDH activity, respectively. TLR4 methylation was detected by methylation-specific PCR (MSP) and verified by Chromatin immunoprecipitation (ChIP). Here, we found that DNA methyltransferase-1 (DNMT1)-mediated TLR4 demethylation significantly suppressed lipopolysaccharides (LPS)-induced pyroptosis and inflammatory response by inhibiting the TLR4/nuclear transcription factor-kappa B (NF-κB) axis. First, we confirmed TLR4 as the study target by mRNA transcriptome sequencing analysis, and TLR4 was observably high-expressed in both OM patients and LPS-treated osteoblastic MC3T3-E1. Then, we found that downregulation of DNMT1 blocked TLR4 promoter methylation modification, resulting in upregulation of TLR4. Simultaneously, functional experiments indicated that suppression of TLR4 or overexpression of DNMT1 promoted cell proliferation and inhibited cell pyroptosis and inflammation in LPS-induced MC3T3-E1, while upregulation of TLR4 restored the effects of DNMT1 silencing on OM progression. In addition, TLR4 elevated phosphorylation of IκB-α and NF-κB p65 in the NF-κB signal pathway, and inhibition of TLR4 or the NF-κB inhibitor PDTC reversed the influence of inhibition of DNMT1. In conclusion, our study demonstrated that DNMT1-mediated TLR4 DNA methylation alleviated LPS-induced OM by inhibiting the NF-κB signaling pathway.

Iodine-Doped 3D Print Ti Alloy for Antibacterial Therapy on Orthopedic Implants

This study presents a novel approach to mitigating bacterial infections and antibiotic resistance in medical implants through the integration of iodine-doping and 3D printing techniques. Iodine, with its potent antibacterial properties, and titanium alloy (Ti), a popular metal for implants due to its mechanical and biological properties, were combined via electrodeposition on 3D-printed titanium alloy (3D-Ti) implants. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy confirmed the successful creation of iodine-doped titanium implants with improved iodine content due to the rough surface of the 3D-printed material. In vitro studies revealed that these implants significantly inhibited bacterial adhesion and biofilm formation and showed favorable release kinetics for iodine ions. Biocompatibility tests demonstrated no cytotoxic effects and good hemocompatibility. The implants demonstrated enhanced antimicrobial efficacy against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria strains. The findings imply that the integration of iodine-doping and 3D printing technologies is a promising strategy for treating postoperative infections associated with medical implants, consequently bettering the prognosis for patients. Future investigations are encouraged to delve into the long-standing impacts and prospective clinical utility of this groundbreaking methodology.

Study on the mechanism of NLRP3 effect on the skeleton of de-ovalized mice

Postmenopausal osteoporosis caused by estrogen deficiency affects millions of women worldwide. By influencing both osteoblast and osteoclast development, NOD-like receptor thermoprotein structural domain-associated protein 3 (NLRP3) is a key player in the etiology of osteoporosis (OP). The purpose of this research was to look into the mechanism of action of NLRP3 in osteoporosis caused by a lack of estrogen, highlighting that NLRP3 induces osteoblast pyroptosis and thus inflammatory responses in de-ovulated mice, thereby inhibiting osteogenic differentiation and participating in the development of osteoporosis. In de-ovulated mice, we found an enhanced inflammatory response and suppression of osteogenic activity. In vitro experiments, we found a significant increase in markers of cell pyroptosis and inflammatory responses and a significant decrease in markers of osteogenic differentiation in osteoblasts from de-ovulated mice. However, knockdown of the NLRP3 gene inhibited this cell pyroptosis and improved osteogenic differentiation of osteoblasts. Our findings indicate a potential therapeutic potential for the treatment of estrogen deficiency-induced osteoporosis by demonstrating the critical role that NLRP3 inflammatory vesicles and their downstream-mediated cellular pyroptosis play in bone differentiation.

Pyroptosis -related potential diagnostic biomarkers in steroid-induced osteonecrosis of the femoral head

PURPOSE

Steroid-induced necrosis of the femoral head (SONFH) is a refractory orthopedic hip disease occurring in young and middle-aged people, with glucocorticoids being the most common cause. Previous experimental studies have shown that cell pyroptosis may be involved in the pathological process of SONFH, but its pathogenesis in SONFH is still unclear. This study aims to screen and validate potential pyroptosis-related genes in SONFH diagnosis by bioinformatics analysis to further elucidate the mechanism of pyroptosis in SONFH.

METHODS

There were 33 pyroptosis-related genes obtained from the prior reviews. The mRNA expression was downloaded from GSE123568 dataset in the Gene Expression Omnibus (GEO) database, including 10 non-SONFH (following steroid administration) samples and 30 SONFH samples. The pyroptosis-related differentially expressed genes involved in SONFH were identified with "affy" and "limma" R package by intersecting the GSE123568 dataset with pyroptosis genes. In addition, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of the pyroptosis-related differentially expressed genes involved in SONFH were conducted by "clusterProfiler" R package and visualized by "GOplot" R package. Then, the correlations between the expression levels of the pyroptosis-related differentially expressed genes involved in SONFH were confirmed with "corrplot" R package. Moreover, the protein-protein interaction (PPI) network was analysed by using GeneMANIA database. Next, The ROC curve of pyroptosis-related differentially expressed genes were analyzed by "pROC" R package.

RESULTS

A total of 10 pyroptosis-related differentially expressed genes were identified between the peripheral blood samples of SONFH patients and non-SONFH patients based on the defined criteria, including 20 upregulated genes and 10 downregulated genes. The GO and KEGG pathway enrichment analyses revealed that these 10 pyroptosis-related differentially expressed genes involved in SONFH were particularly enriched in cysteine-type endopeptidase activity involved in apoptotic process, positive regulation of interleukin-1 beta secretion and NOD-like receptor signaling pathway. Correlation analysis revealed significant correlations among the 10 differentially expressed pyroptosis-related genes involved in SONFH. The PPI results demonstrated that the 10 pyroptosis-related differentially expressed genes interacted with each other. Compared to non-SONFH samples, these pyroptosis-related differentially expressed genes had good predictive diagnostic efficacy (AUC = 1.000, CI = 1.000-1.000) in the SONFH samples, and NLRP1 had the highest diagnostic value (AUC: 0.953) in the SONFH samples.

CONCLUSIONS

There were 10 potential pyroptosis-related differentially expressed genes involved in SONFH were identified via bioinformatics analysis, which might serve as potential diagnostic biomarkers because they regulated pyroptosis. These results expand the understanding of SONFH associated with pyroptosis and provide new insights to further explore the mechanism of action and diagnosis of pyroptosis associated in SONFH.

Pyroptosis in bone loss

Pyroptosis could be responsible for the bone loss from bone metabolic diseases, leading to the negative impact on people's health and life. It has been shown that osteoclasts, osteoblasts, macrophages, chondrocytes, periodontal and gingival cells may be involved in bone loss linked with pyroptosis. So far, the involved mechanisms have not been fully elucidated. In this review, we introduced the related cells involved in the pyroptosis associated with bone loss and summarized the role of these cells in the bone metabolism during the process of pyroptosis. We also discuss the clinical potential of targeting mechanisms in the osteoclasts, osteoblasts, macrophages, chondrocytes, periodontal and gingival cells touched upon pyroptosis to treat bone loss from bone metabolic diseases as well as the challenges of avoiding potential side effects and producing efficient treatment methods.

Cell death regulation: A new way for natural products to treat osteoporosis

Osteoporosis is a common metabolic bone disease that results from the imbalance of homeostasis within the bone. Intra-bone homeostasis is dependent on a precise dynamic balance between bone resorption by osteoclasts and bone formation by mesenchymal lineage osteoblasts, which comprises a series of complex and highly standardized steps. Programmed cell death (PCD) (e.g., apoptosis, autophagy, ferroptosis, pyroptosis, and necroptosis) is a cell death process that involves a cascade of gene expression events with tight structures. These events play a certain role in regulating bone metabolism by determining the fate of bone cells. Moreover, existing research has suggested that natural products derived from a wide variety of dietary components and medicinal plants modulate the PCDs based on different mechanisms, which show great potential for the prevention and treatment of osteoporosis, thus revealing the emergence of more acceptable complementary and alternative drugs with lower costs, fewer side effects and more long-term application. Accordingly, this review summarizes the common types of PCDs in the field of osteoporosis. Moreover, from the perspective of targeting PCDs, this review also discussed the roles of currently reported natural products in the treatment of osteoporosis and the involved mechanisms. Based on this, this review provides more insights into new molecular mechanisms of osteoporosis and provides a reference for developing more natural anti-osteoporosis drugs in the future.

Exercise-Linked Skeletal Irisin Ameliorates Diabetes-Associated Osteoporosis by Inhibiting the Oxidative Damage-Dependent miR-150-FNDC5/Pyroptosis Axis

Recent evidence suggests that physical exercise (EX) promotes skeletal development. However, the impact of EX on the progression of bone loss and deterioration of mechanical strength in mice with type 2 diabetic mellitus (T2DM) remains unexplored. In the current study, we investigated the effect of EX on bone mass and mechanical quality using a diabetic mouse model. The T2DM mouse model was established with a high-fat diet with two streptozotocin injections (50 mg/kg/body wt) in C57BL/6 female mice. The diabetic mice underwent treadmill exercises (5 days/week at 7-11 m/min for 60 min/day) for 8 weeks. The data showed that diabetes upregulated miR-150 expression through oxidative stress and suppressed FNDC5/Irisin by binding to its 3'-untranslated region. The decreased level of irisin further triggers the pyroptosis response in diabetic bone tissue. EX or N-acetyl cysteine or anti-miRNA-150 transfection in T2DM mice restored FNDC5/Irisin expression and bone formation. Furthermore, EX or recombinant irisin administration prevented T2DM-Induced hyperglycemia and improved glucose intolerance in diabetic mice. Furthermore, osteoblastic knockdown of Nlrp3 silencing (si-Nlrp3) or pyroptosis inhibitor (Ac-YVADCMK [AYC]) treatment restores bone mineralization in diabetic mice. Micro-computed tomography scans and mechanical testing revealed that trabecular bone microarchitecture and bone mechanical properties were improved after EX in diabetic mice. Irisin, either induced by skeleton or daily EX or directly administered, prevents bone loss by mitigating inflammasome-associated pyroptosis signaling in diabetic mice. This study demonstrates that EX-induced skeletal irisin ameliorates diabetes-associated glucose intolerance and bone loss and possibly provides a mechanism of its effects on metabolic osteoporosis.

Pyroptosis in inflammatory bone diseases: Molecular insights and targeting strategies

Inflammatory bone diseases include osteoarthritis (OA) and rheumatoid arthritis (RA), which can cause severe bone damage in a chronic inflammation state, putting tremendous pressure on the patients' families and government agencies regarding medical costs. In addition, the complexity of osteoimmunology makes research on these diseases difficult. Hence, it is urgent to determine the potential mechanisms and find effective drugs to target inflammatory bone diseases to reduce the negative effects of these diseases. Recently, pyroptosis, a gasdermin-induced necrotic cell death featuring secretion of pro-inflammatory cytokines and lysis, has become widely known. Based on the effect of pyroptosis on immunity, this process has gradually emerged as a vital component in the etiopathogenesis of inflammatory bone diseases. Herein, we review the characteristics and mechanisms of pyroptosis and then focus on its clinical significance in inflammatory bone diseases. In addition, we summarize the current research progress of drugs targeting pyroptosis to enhance the therapeutic efficacy of inflammatory bone diseases and provide new insights for future directions.

Screening of crosstalk and pyroptosis-related genes linking periodontitis and osteoporosis based on bioinformatics and machine learning

Background and objective

This study aimed to identify crosstalk genes between periodontitis (PD) and osteoporosis (OP) and potential relationships between crosstalk and pyroptosis-related genes.

Methods

PD and OP datasets were downloaded from the GEO database and were performed differential expression analysis to obtain DEGs. Overlapping DEGs got crosstalk genes linking PD and OP. Pyroptosis-related genes were obtained from literature reviews. Pearson coefficients were used to calculate crosstalk and pyroptosis-related gene correlations in the PD and OP datasets. Paired genes were obtained from the intersection of correlated genes in PD and OP. PINA and STRING databases were used to conduct the crosstalk-bridge-pyroptosis genes PPI network. The clusters in which crosstalk and pyroptosis-related genes were mainly concentrated were defined as key clusters. The key clusters' hub genes and the included paired genes were identified as key crosstalk-pyroptosis genes. Using ROC curve analysis and XGBoost screened key genes. PPI subnetwork, gene-biological process and gene-pathway networks were constructed based on key genes. In addition, immune infiltration was analyzed on the PD dataset using the CIBERSORT algorithm.

Results

A total of 69 crosstalk genes were obtained. 13 paired genes and hub genes TNF and EGFR in the key clusters (cluster2, cluster8) were identified as key crosstalk-pyroptosis genes. ROC and XGBoost showed that PRKCB, GSDMD, ARMCX3, and CASP3 were more accurate in predicting disease than other key crosstalk-pyroptosis genes while better classifying properties as a whole. KEGG analysis showed that PRKCB, GSDMD, ARMCX3, and CASP3 were involved in neutrophil extracellular trap formation and MAPK signaling pathway pathways. Immune infiltration results showed that all four key genes positively correlated with plasma cells and negatively correlated with T cells follicular helper, macrophages M2, and DCs.

Conclusion

This study shows a joint mechanism between PD and OP through crosstalk and pyroptosis-related genes. The key genes PRKCB, GSDMD, ARMCX3, and CASP3 are involved in the neutrophil extracellular trap formation and MAPK signaling pathway, affecting both diseases. These findings may point the way to future research.

Effect of Enterococcus faecalis OG1RF on human calvarial osteoblast apoptosis

Background

Enterococcus faecalis is a dominant pathogen in the root canals of teeth with persistent apical periodontitis (PAP), and osteoblast apoptosis contributes to imbalanced bone remodelling in PAP. Here, we investigated the effect of E. faecalis OG1RF on apoptosis in primary human calvarial osteoblasts. Specifically, the expression of apoptosis-related genes and the role of anti-apoptotic and pro-apoptotic members of the BCL-2 family were examined.

Methods

Primary human calvarial osteoblasts were incubated with E. faecalis OG1RF at multiplicities of infection corresponding to infection time points. Flow cytometry, terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay, caspase-3/-8/-9 activity assay, polymerase chain reaction (PCR) array, and quantitative real-time PCR were used to assess osteoblast apoptosis.

Results

E. faecalis infection increased the number of early- and late-phase apoptotic cells and TUNEL-positive cells, decreased the mitochondrial membrane potential (ΔΨm), and activated the caspase-3/-8/-9 pathway. Moreover, of all 84 apoptosis-related genes in the PCR array, the expression of 16 genes was upregulated and that of four genes was downregulated in the infected osteoblasts. Notably, the mRNA expression of anti-apoptotic BCL2 was downregulated, whereas that of the pro-apoptotic BCL2L11, HRK, BIK, BMF, NOXA, and BECN1 and anti-apoptotic BCL2A1 was upregulated.

Conclusions

E. faecalis OG1RF infection triggered apoptosis in human calvarial osteoblasts, and BCL-2 family members acted as regulators of osteoblast apoptosis. Therefore, BCL-2 family members may act as potential therapeutic targets for persistent apical periodontitis.

Staphylococcus aureus Induces Goat Endometrial Epithelial Cells Apoptosis via the Autophagy and Endoplasmic Reticulum Stress Pathway

Simple Summary

The toxicity mechanism of Staphylococcus aureus on goat endometrial epithelial cells (gEECs) is still unelucidated. The purpose of this experiment was to investigate the molecular mechanism of gEECs death caused by S. aureus in terms of autophagy and endoplasmic reticulum (ER) stress. We found that the accumulation of autophagosomes exacerbated S. aureus-induced gEECs apoptosis, and that ER stress was involved in the regulation of the autophagy. These findings may provide new insight into the therapeutic target of endometrial cell injury.

Abstract

Increasing evidence indicates that autophagy and endoplasmic reticulum (ER) stress are involved in the regulation of cell death; however, the role of autophagy and ER stress in Staphylococcus aureus-induced endometrial epithelial cell damage is still unelucidated. In the present study, our results showed that infection with S. aureus increased the cytotoxicity and the protein expression of Bax, caspase-3, and cleaved-PARP-1 in goat endometrial epithelial cells (gEECs). Moreover, after infection, the expression of LC3II and autophagosomes were markedly increased. The autophagosome inhibitor 3-methyladenine (3-MA) significantly decreased the cytotoxicity and the expression of caspase-3, and cleaved-PARP-1; however, the autophagosome–lysosome fusion inhibitor chloroquine (CQ) increased their expression. Additionally, the protein expression of GRP78, EIF2α, and ATF4 were also markedly increased after infection. The ER stress inhibitor 4-PBA decreased the cytotoxicity and the expression of LC3II and apoptosis-related proteins in S. aureus-infected gEECs. Collectively, our findings prove that the accumulation of autophagosomes exacerbated S. aureus-induced gEECs apoptosis, and that ER stress was involved in the regulation of the autophagy and apoptosis.

Interleukin-13 Affects the Recovery Processes in a Mouse Model of Hemorrhagic Stroke with Bilateral Tibial Fracture

As one form of stroke, intracerebral hemorrhage (ICH) is a fatal cerebrovascular disease, which has high morbidity and mortality and lacks effective medical treatment. Increased infiltration of inflammatory cytokines coupled with pyroptotic cell death is involved in the pathophysiological process of ICH. However, little is known about whether concomitant fracture patients have the same progression of inflammation and pyroptosis. Hence, we respectively established the mouse ICH model and ICH with bilateral tibial fracture model (MI) to explore the potential cross-talk between the above two injuries. We found that MI obviously reversed the expressions of pyroptosis-associated proteins, which were remarkably up-regulated at the acute phase after ICH. Similar results were observed in neuronal expressions via double immunostaining. Furthermore, brain edema was also significantly alleviated in mice who suffered MI, when compared with ICH alone. To better clarify the potential mechanisms that mediated this cross-talk, recombinant mouse interleukin-13 (IL-13) was used to investigate its effect on pyroptosis in the mouse MI model, in which a lower level of IL-13 was observed. Remarkably, IL-13 administration re-awakened cell death, which was mirrored by the re-upregulation of pyroptosis-associated proteins and PI-positive cell counts. The results of hemorrhage volume and behavioral tests further confirmed its critical role in regulating neurological functions. Besides, the IL-13-treated MI group showed poor outcomes of fracture healing. To sum up, our research indicates that controlling the IL-13 content in the acute phase would be a promising target in influencing the outcomes of brain injury and fracture, and meanwhile, provides new evidence in repairing compound injuries in clinics.

Urolithin A suppresses RANKL-induced osteoclastogenesis and postmenopausal osteoporosis by, suppresses inflammation and downstream NF-κB activated pyroptosis pathways

Osteoporosis (OP) is characterized by decreased trabecular bone volume and microarchitectural deterioration in the medullary cavity. Urolithin A (UA) is a biologically active metabolite generated by the gut microbiota. UA is the measurable product considered the most relevant urolithin as the final metabolic product of polyphenolic compounds. Considering that catabolic effects mediated by the intestinal microbiota are highly involved in pathological bone disorders, exploring the biological influence and molecular mechanisms by which UA alleviates OP is crucial. Our study aimed to investigate the effect of UA administration on OP progression in the context of estrogen deficiency-induced bone loss. The in vivo results indicated that UA effectively reduced ovariectomy-induced systemic bone loss. In vitro, UA suppressed Receptor Activator for Nuclear Factor-κB Ligand (RANKL)-triggered osteoclastogenesis in a concentration-dependent manner. Signal transduction studies and sequencing analysis showed that UA significantly decreased the expression of inflammatory cytokines (e.g., IL-6 and TNF-α) in osteoclasts. Additionally, attenuation of inflammatory signaling cascades inhibited the NF-κB-activated NOD-like receptor signaling pathway, which eventually led to decreased cytoplasmic secretion of IL-1β and IL-18 and reduced expression of pyroptosis markers (NLRP3, GSDMD, and caspase-1). Consistent with this finding, an NLRP3 inflammasome inhibitor (MCC950) was employed to treat OP, and modulation of pyroptosis was found to ameliorate osteoclastogenesis and bone loss in ovariectomized (OVX) mice, suggesting that UA suppressed osteoclast formation by regulating the inflammatory signal-dependent pyroptosis pathway. Conceivably, UA administration may be a safe and promising therapeutic strategy for osteoclast-related bone diseases such as OP.

Iodine Immobilized Metal-Organic Framework for NIR-Triggered Antibacterial Therapy on Orthopedic Implants

Iodine has been known as an effective disinfectant with broad-spectrum antimicrobial potency yet without drug resistance risk when used in clinic. However, the exploration of iodine for antibacterial therapy in orthopedics remains sparse due to its volatile nature and poor solubility. Herein, leveraging the superior absorption capability of metal-organic frameworks (MOFs) and their inherent photocatalytic properties, iodine-loaded MOF surface is presented to realize responsive iodine release along with intracellular reactive oxygen species(ROS) oxidation under near-infrared (NIR) exposure to achieve synergistic antibacterial effect. Iodine is successfully loaded using vapor deposition process onto zeolitic imidazolate framework-8(ZIF-8), which is immobilized onto micro arc oxidized titanium via a hydrothermal approach. The combination of NIR-triggered iodine release and ZIF-8 mediated ROS oxidative stress substantially augments the antibacterial efficacy of this approach both in vitro and in vivo. Furthermore, this composite coating also supported osteogenic differentiation of bone marrow stromal cells, as well as improved osseointegration of coated implants using an intramedullary rat model, suggesting improvement of antibacterial efficacy does not impair osteogenic potential of the implants. Altogether, immobilization of iodine via MOF on orthopedic implants with synergistic antibacterial effect can be a promising strategy to combat bacterial infections.

Enterococcus faecalis OG1RF induces apoptosis in MG63 cells via caspase-3/-8/-9 without activation of caspase-1/GSDMD

OBJECTIVE

Regulated cell death is key in the pathogenesis of persistent apical periodontitis. Here, we investigated the mechanisms of regulated cell death in osteoblast-like MG63 cells infected with Enterococcus faecalis OG1RF.

MATERIALS AND METHODS

MG63 cells were infected with live E. faecalis OG1RF at the indicated multiplicity of infection for the indicated infection time. We evaluated the cells by flow cytometry, terminal deoxynucleotidyl transferase dUTP nick end labelling assay and lactate dehydrogenase release analysis; measured the activity of caspase-1/-3/-8/-9 and the release of interleukin-1β; and determined the expression of apoptosis-associated proteins and gasdermin D by apoptosis antibody array and Western blotting.

RESULTS

Enterococcus faecalis OG1RF reduced the mitochondrial membrane potential of the infected cells, increased the percentage of apoptotic and terminal deoxynucleotidyl transferase dUTP nick end labelling-positive cells, and enhanced lactate dehydrogenase release. The expression of caspase-3 and survivin and the activity of caspase-3/-8/-9 were upregulated, while the expression of death receptor 6 was downregulated. The activity of caspase-1/gasdermin D and the release of interleukin-1β remained unaltered.

CONCLUSION

Enterococcus faecalis OG1RF induced both intrinsic and extrinsic MG63 cell apoptosis via caspase-3/-8/-9 activation but did not activate the pyroptotic pathway regulated by caspase-1/gasdermin D.

Necrosulfonamide reverses pyroptosis-induced inhibition of proliferation and differentiation of osteoblasts through the NLRP3/caspase-1/GSDMD pathway

The acute inflammatory stimulation occurring after a bone fracture regulates the repair and healing of local bone injury; however, under certain conditions, pyroptosis may occur in osteoblasts, which affects osteoblast proliferation and differentiation, thereby affecting the growth, development and morphological changes of bone tissue. The aim of the present study was to examine the effect of the pyroptosis inhibitor necrosulfonamide (NSA) on the proliferation and differentiation of osteoblasts and elucidate the underlying mechanism. The results revealed that NSA reversed the effects of ATP/lipopolysaccharide (LPS) on cell viability and pyroptosis, and on the mRNA and protein expression of pyroptosis-related genes. It also suppressed the secretion of IL-6, TNF-α and IL-1β and reversed the effects of ATP/LPS on the activity of ALP and the mRNA expression of differentiation-related genes in osteoblasts. The fact that overexpression of caspase-1, gasdermin D (GSDMD) and NLRP3 abolished the effects of NSA on the viability and pyroptosis of osteoblasts, as well as the mRNA expression of differentiation-related genes and the activity of ALP in osteoblasts, indicated that NSA promoted the proliferation and differentiation of osteoblasts by inhibiting the NLRP3/caspase-1/GSDMD pyroptosis pathway. The present study provides proof supporting the potential application of NSA for improving the function of osteoblasts in fracture repair and indicates the value of the NLRP3/caspase-1/GSDMD pyroptosis pathway as a pharmaceutical target.

Inflammasomes in Alveolar Bone Loss

Bone remodeling is tightly controlled by osteoclast-mediated bone resorption and osteoblast-mediated bone formation. Fine tuning of the osteoclast-osteoblast balance results in strict synchronization of bone resorption and formation, which maintains structural integrity and bone tissue homeostasis; in contrast, dysregulated bone remodeling may cause pathological osteolysis, in which inflammation plays a vital role in promoting bone destruction. The alveolar bone presents high turnover rate, complex associations with the tooth and periodontium, and susceptibility to oral pathogenic insults and mechanical stress, which enhance its complexity in host defense and bone remodeling. Alveolar bone loss is also involved in systemic bone destruction and is affected by medication or systemic pathological factors. Therefore, it is essential to investigate the osteoimmunological mechanisms involved in the dysregulation of alveolar bone remodeling. The inflammasome is a supramolecular protein complex assembled in response to pattern recognition receptors and damage-associated molecular patterns, leading to the maturation and secretion of pro-inflammatory cytokines and activation of inflammatory responses. Pyroptosis downstream of inflammasome activation also facilitates the clearance of intracellular pathogens and irritants. However, inadequate or excessive activity of the inflammasome may allow for persistent infection and infection spreading or uncontrolled destruction of the alveolar bone, as commonly observed in periodontitis, periapical periodontitis, peri-implantitis, orthodontic tooth movement, medication-related osteonecrosis of the jaw, nonsterile or sterile osteomyelitis of the jaw, and osteoporosis. In this review, we present a framework for understanding the role and mechanism of canonical and noncanonical inflammasomes in the pathogenesis and development of etiologically diverse diseases associated with alveolar bone loss. Inappropriate inflammasome activation may drive alveolar osteolysis by regulating cellular players, including osteoclasts, osteoblasts, osteocytes, periodontal ligament cells, macrophages, monocytes, neutrophils, and adaptive immune cells, such as T helper 17 cells, causing increased osteoclast activity, decreased osteoblast activity, and enhanced periodontium inflammation by creating a pro-inflammatory milieu in a context- and cell type-dependent manner. We also discuss promising therapeutic strategies targeting inappropriate inflammasome activity in the treatment of alveolar bone loss. Novel strategies for inhibiting inflammasome signaling may facilitate the development of versatile drugs that carefully balance the beneficial contributions of inflammasomes to host defense.

Interleukin-17 induces pyroptosis in osteoblasts through the NLRP3 inflammasome pathway in vitro

OBJECTIVE

Interleukin-17 (lL-17), a pro-inflammatory cytokine produced by Th17 cells, is also considered to play an important role in bone metabolism, but the exact mechanism of bone destruction remains unclear. In this study, we explored whether IL-17 could induce osteoblasts pyroptosis in vitro.

METHODS

The murine primary osteoblasts were isolated from the calvarial bones of mice. The proliferation of osteoblasts was evaluated by cell counting kit-8 (CCK-8) assay. The mRNA levels of NOD-like receptor family pyrin domain containing 3 (NLRP3), apoptosis associated speck like protein containing a card (ASC), caspase-1, gasdermin-D (GSDMD), IL-1β and receptor activator of nuclear factor-kappa B ligand (RANKL) were measured by real-time quantitative PCR. Pyroptosis after IL-17 treatment was evaluated by lactate dehydrogenase (LDH) Release Assay Kit and the morphological characteristics of osteoblasts were observed via Scanning Electron Microscopy (SEM). Pyroptosis associated proteins, cleaved IL-1β and RANKL were evaluated through western blot. The release of IL-1β and RANKL was measured by ELISA. In addition, calcium nodule was tested by alizarin red staining.

RESULTS

High concentration IL-17 (100 ng/mL) could affect the proliferation of osteoblasts, promote the gene expression of NLRP3, caspase-1, GSDMD, IL-1β and RANKL. In contrast to control group, osteoblasts treated with IL-17 had the appearance of numerous pores, swelling and rupture. Also, the release of LDH, IL-1β and RANKL increased in the presence of IL-17. However, inhibition of NLRP3 prevented activation of the NLRP3 inflammasome, thereby restoring osteoblasts morphology and function.

CONCLUSION

IL-17 induced osteoblasts pyroptosis, and the pyroptosis of osteoblasts may prompt the release of IL-1β and RANKL,which may further contribute to disruption of bone metabolism. Besides, the NLRP3 inflammasome pathway was involved in the pyroptosis of osteoblasts.

Rosavin suppresses osteoclastogenesis in vivo and in vitro by blocking the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways

Background

Bone homeostasis is mediated by osteoblast-related bone formation and osteoclast-related resorption. The imbalance of bone homeostasis due to excessive osteoclastogenesis or reduced osteogenesis can result in various disorders, such as postmenopausal osteoporosis (PMOP). The receptor activator of nuclear factor-κB ligand (RANKL)-induced nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and mitogen-activated protein kinase (MAPK) pathways are essential in osteoclastogenesis. In this study, we aimed to investigate the effects of rosavin, an alkylbenzene diglycoside compound from the traditional Chinese medicine Rhodiola Rosea L, on RANKL-induced osteoclastogenesis in vitro and in vivo.

Methods

The effects of rosavin on osteoclastogenesis were assessed by TRAP staining of bone marrow monocyte cells (BMMCs) and RAW 264.7 cells. The effects of rosavin on osteogenesis were determined using alkaline phosphatase (ALP) and alizarin red staining, as well as real-time quantitative reverse transcription polymerase chain reaction. Actin ring formation and bone formation experiments were performed to evaluate osteoclast function. Western blotting was carried out to determine the expression of osteoclastogenesis-related genes, and the activation of the NF-κB and MAPK pathways was evaluated by performing western blotting and immunofluorescence staining. Ovariectomized mice were used to explore the effect of rosavin on bone loss.

Results

Rosavin could inhibit osteoclastogenesis, suppress the function of osteoclasts, and decrease the expression of osteoclast differentiation-related genes, including tartrate-resistant acid phosphatase (TRAP), cathepsin K, matrix metalloproteinase-9 (MMP-9), calcitonin receptor (CTR), TNF receptor-associated factor 6 (TRAF-6), receptor activator of nuclear factor-κB (RANK), and colony-stimulating factor-1 receptor (c-fms). Rosavin inhibited RANKL-induced phosphorylation of p65 and inhibitory subunit of NF-κB alpha (IκBα), and suppressed p65 nuclear translocation. Rosavin was also found to inhibit the phosphorylation of extracellular-signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK). Furthermore, rosavin promoted osteogenesis in bone marrow mesenchymal stem cells (BMSCs). In vivo experiments showed that treatment with rosavin could alleviate ovariectomy-induced osteoporosis in mice.

Conclusions

Our results indicated that rosavin suppressed RANKL-induced osteoclastogenesis in vivo and in vitro by blocking the NF-κB and MAPK pathways. Rosavin treatment is a potential therapy for the clinical treatment of osteoclastogenesis-related disorders.

Staphylococcus aureus Internalization in Osteoblast Cells: Mechanisms, Interactions and Biochemical Processes. What Did We Learn from Experimental Models?

Bacterial internalization is a strategy that non-intracellular microorganisms use to escape the host immune system and survive inside the human body. Among bacterial species, Staphylococcus aureus showed the ability to interact with and infect osteoblasts, causing osteomyelitis as well as bone and joint infection, while also becoming increasingly resistant to antibiotic therapy and a reservoir of bacteria that can make the infection difficult to cure. Despite being a serious issue in orthopedic surgery, little is known about the mechanisms that allow bacteria to enter and survive inside the osteoblasts, due to the lack of consistent experimental models. In this review, we describe the current knowledge about S. aureus internalization mechanisms and various aspects of the interaction between bacteria and osteoblasts (e.g., best experimental conditions, bacteria-induced damages and immune system response), focusing on studies performed using the MG-63 osteoblastic cell line, the best traditional (2D) model for the study of this phenomenon to date. At the same time, as it has been widely demonstrated that 2D culture systems are not completely indicative of the dynamic environment in vivo, and more recent 3D models—representative of bone infection—have also been investigated.

Selective Host Cell Death by Staphylococcus aureus: A Strategy for Bacterial Persistence

Host cell death programs are fundamental processes that shape cellular homeostasis, embryonic development, and tissue regeneration. Death signaling and downstream host cell responses are not only critical to guide mammalian development, they often act as terminal responses to invading pathogens. Here, we briefly review and contrast how invading pathogens and specifically Staphylococcus aureus manipulate apoptotic, necroptotic, and pyroptotic cell death modes to establish infection. Rather than invading host cells, S. aureus subverts these cells to produce diffusible molecules that cause death of neighboring hematopoietic cells and thus shapes an immune environment conducive to persistence. The exploitation of cell death pathways by S. aureus is yet another virulence strategy that must be juxtaposed to mechanisms of immune evasion, autophagy escape, and tolerance to intracellular killing, and brings us closer to the true portrait of this pathogen for the design of effective therapeutics and intervention strategies.

NLRP3 Inflammasome: A New Target for Prevention and Control of Osteoporosis?

Osteoporosis is a systemic bone metabolism disease that often causes complications, such as fractures, and increases the risk of death. The nucleotide-binding oligomerization domain-like-receptor family pyrin domain-containing 3 (NLRP3) inflammasome is an intracellular multiprotein complex that regulates the maturation and secretion of Caspase-1 dependent proinflammatory cytokines interleukin (IL)-1β and IL-18, mediates inflammation, and induces pyroptosis. The chronic inflammatory microenvironment induced by aging or estrogen deficiency activates the NLRP3 inflammasome, promotes inflammatory factor production, and enhances the inflammatory response. We summarize the related research and demonstrate that the NLRP3 inflammasome plays a vital role in the pathogenesis of osteoporosis by affecting the differentiation of osteoblasts and osteoclasts. IL-1β and IL-18 can accelerate osteoclast differentiation by expanding inflammatory response, and can also inhibit the expression of osteogenic related proteins or transcription factors. In vivo and in vitro experiments showed that the overexpression of NLRP3 protein was closely related to aggravated bone resorption and osteogenesis deficiency. In addition, abnormal activation of NLRP3 inflammasome can not only produce inflammation, but also lead to pyroptosis and dysfunction of osteoblasts by upregulating the expression of Caspase-1 and gasdermin D (GSDMD). In conclusion, NLRP3 inflammasome overall not only accelerates bone resorption, but also inhibits bone formation, thus increasing the risk of osteoporosis. Thus, this review highlights the recent studies on the function of NLRP3 inflammasome in osteoporosis, provides information on new strategies for managing osteoporosis, and investigates the ideal therapeutic target to treat osteoporosis.

Re-appraising the potential of naringin for natural, novel orthopedic biotherapies

Naringin is a naturally occurring flavonoid found in plants of the Citrus genus that has historically been used in traditional Chinese medical regimens for the treatment of osteoporosis. Naringin modulates signaling through numerous molecular pathways critical to musculoskeletal development, cellular differentiation, and inflammation. Administration of naringin increases in vitro expression of bone morphogenetic proteins (BMPs) and activation of the Wnt/β-catenin and extracellular signal-related kinase (Erk) pathways, thereby promoting osteoblastic proliferation and differentiation from stem cell precursors for bone formation. Naringin also inhibits osteoclastogenesis by both modifying RANK/RANKL interactions and inducing apoptosis in osteoclasts in vitro. In addition, naringin acts on the estrogen receptor in bone to mimic the native bone-preserving effects of estrogen, with few systemic side effects on other estrogen-sensitive tissues. The efficacy of naringin therapy in reducing the osteolysis characteristic of common musculoskeletal pathologies such as osteoporosis, degenerative joint disease, and osteomyelitis, as well as inflammatory conditions affecting bone such as diabetes mellitus, has been extensively demonstrated in vitro and in animal models. Naringin thus represents a naturally abundant, cost-efficient agent whose potential for use in novel musculoskeletal biotherapies warrants re-visiting and further exploration through human studies. Here, we review the cellular mechanisms of action that have been elucidated regarding the action of naringin on bone resident cells and the bone microenvironment, in vivo evidence of naringin’s osteostimulative and chondroprotective properties in the setting of osteolytic bone disease, and current limitations in the development of naringin-containing translational therapies for common musculoskeletal conditions.

The Role of NLRP3 Inflammasome Activities in Bone Diseases and Vascular Calcification

Continuous stimulation of inflammation is harmful to tissues of an organism. Inflammatory mediators not only have an effect on metabolic and inflammatory bone diseases but also have an adverse effect on certain genetic and periodontal diseases associated with bone destruction. Inflammatory factors promote vascular calcification in various diseases. Vascular calcification is a pathological process similar to bone development, and vascular diseases play an important role in the loss of bone homeostasis. The NLRP3 inflammasome is an essential component of the natural immune system. It can recognize pathogen-related molecular patterns or host-derived dangerous signaling molecules, recruit, and activate the pro-inflammatory protease caspase-1. Activated caspase-1 cleaves the precursors of IL-1β and IL-18 to produce corresponding mature cytokines or recognizes and cleaves GSDMD to mediate cell pyroptosis. In this review, we discuss the role of NLRP3 inflammasome in bone diseases and vascular calcification caused by sterile or non-sterile inflammation and explore potential treatments to prevent bone loss.

Osteocyte apoptosis: the roles and key molecular mechanisms in resorption-related bone diseases

Vital osteocytes have been well known to function as an important orchestrator in the preservation of robustness and fidelity of the bone remodeling process. Nevertheless, some key pathological factors, such as sex steroid deficiency and excess glucocorticoids, and so on, are implicated in inducing a bulk of apoptotic osteocytes, subsequently resulting in resorption-related bone loss. As much, osteocyte apoptosis, under homeostatic conditions, is in an optimal state of balance tightly controlled by pro- and anti-apoptotic mechanism pathways. Importantly, there exist many essential signaling proteins in the process of osteocyte apoptosis, which has a crucial role in maintaining a homeostatic environment. While increasing in vitro and in vivo studies have established, in part, key signaling pathways and cross-talk mechanism on osteocyte apoptosis, intrinsic and complex mechanism underlying osteocyte apoptosis occurs in various states of pathologies remains ill-defined. In this review, we discuss not only essential pro- and anti-apoptotic signaling pathways and key biomarkers involved in these key mechanisms under different pathological agents, but also the pivotal role of apoptotic osteocytes in osteoclastogenesis-triggered bone loss, hopefully shedding new light on the attractive and proper actions of pharmacotherapeutics of targeting apoptosis and ensuing resorption-related bone diseases such as osteoporosis and fragility fractures.

Pyroptosis executioner gasdermin D contributes to host defense and promotes Th 1 immune response during Neospora caninum infection

Neospora caninum (N. caninum) is an intracellular parasite and is the causative agent of neosporosis, which leads to reproductive failure in cattle. Pyroptosis is a recently discovered form of programmed cell death executed by gasdermin D (GSDMD). This cell death mechanism is an important host defense against intracellular pathogens. However, pyroptosis induced by N. caninum is poorly understood. The aim of this study was to explore the roles of GSDMD-mediated pyroptosis during N. caninum infection in vivo. N. caninum-infected wild type mice and GSDMD-deficient mice were used to evaluate host resistance and its ability to affect immune response against this parasite. The results showed that GSDMD deficiency significantly reduced survival and impaired the host's abilities to clear parasite loads in tissues, monocytes/macrophages and neutrophils. Additionally, GSDMD was essential for circulating IL-18 and IFN-γ production induced by N. caninum infection, indicating that GSDMD can mediate the Th 1 immune response against N. caninum infection. Additional data revealed that treatment with exogenous recombinant IL-18 in N. caninum-infected Gsdmd^-/- mice rescues the reduction of circulating IFN-γ production to help eliminate the parasite. Taken together, our data indicate that GSDMD-mediated pyroptosis plays a vital role in maintaining host resistance to N. caninum and is essential for clearing the parasite. This form of programmed cell death promotes the Th 1 immune response by controlling IL-18 release and is considered a host defense against N. caninum. This study expands our understanding of interactions between host immune response/defense and N. caninum infection.

A comprehensive review of bacterial osteomyelitis with emphasis on Staphylococcus aureus

Osteomyelitis, a significant infection of bone tissue, gives rise to two main groups of infection: acute and chronic. These groups are further categorized in terms of the duration of infection. Usually, children and adults are more susceptible to acute and chronic infections, respectively. The aforementioned groups of osteomyelitis share almost 80% of the corresponding bacterial pathogens. Among all bacteria, Staphylococcus aureus (S. aureus) is a significant pathogen and is associated with a high range of osteomyelitis symptoms. S. aureus has many strategies for interacting with host cells including Small Colony Variant (SCV), biofilm formation, and toxin secretion. In addition, it induces an inflammatory response and causes host cell death by apoptosis and necrosis. However, any possible step to take in this respect is dependent on the conditions and host responses. In the absence of any immune responses and antibiotics, bacteria actively duplicate themselves; however, in the presence of phagocytic cell and harassing conditions, they turn into a SCV, remaining sustainable for a long time. SCV is characterized by notable advantages such as (a) intracellular life that mediates a dam against immune cells and (b) low ATP production that mediates resistance against antibiotics.

Involvement of caspase-1 in inflammasomes activation and bacterial clearance in S. aureus-infected osteoblast-like MG-63 cells

Staphylococcus aureus, a versatile Gram-positive bacterium, is the main cause of bone and joint infections (BJI), which are prone to recurrence. The inflammasome is an immune signaling platform that assembles after pathogen recognition. It activates proteases, most notably caspase-1 that proteolytically matures and promotes the secretion of mature IL-1β and IL-18. The role of inflammasomes and caspase-1 in the secretion of mature IL-1β and in the defence of S. aureus-infected osteoblasts has not yet been fully investigated. We show here that S. aureus-infected osteoblast-like MG-63 but not caspase-1 knock-out CASP1 -/- MG-63 cells, which were generated using CRISPR-Cas9 technology, activate the inflammasome as monitored by the release of mature IL-1β. The effect was strain-dependent. The use of S. aureus deletion and complemented phenole soluble modulins (PSMs) mutants demonstrated a key role of PSMs in inflammasomes-related IL-1β production. Furthermore, we found that the lack of caspase-1 in CASP1 -/- MG-63 cells impairs their defense functions, as bacterial clearance was drastically decreased in CASP1 -/- MG-63 compared to wild-type cells. Our results demonstrate that osteoblast-like MG-63 cells play an important role in the immune response against S. aureus infection through inflammasomes activation and establish a crucial role of caspase-1 in bacterial clearance.

EGFR/FAK and c-Src signalling pathways mediate the internalisation of Staphylococcus aureus by osteoblasts

Internalisation of Staphylococcus aureus in osteoblasts plays a critical role in the persistence and recurrence of osteomyelitis, the mechanisms involved in this process remain largely unknown. In the present study, evidence of internalised S. aureus in osteoblasts was found in long bone of haematogenous osteomyelitis in mice after 2 weeks of infection. Meanwhile, eliminating extracellular S. aureus by gentamicin can partially rescue bone loss, whereas the remaining intracellular S. aureus in osteoblasts may be associated with continuous bone destruction. In osteoblastic MC3T3 cells, intracellular S. aureus was detectable as early as 15 min after infection, and the internalisation rates increased with the extension of infection time. Additionally, S. aureus invasion stimulated the expression of phosphor-focal adhesion kinase (FAK), phosphor-epidermal growth factor receptor (EGFR) and phosphor-c-Src in a time-dependent way, and blocking EGFR/FAK or c-Src signalling significantly reduced the internalisation rate of S. aureus in osteoblasts. Our findings provide new insights into the mechanism of S. aureus internalisation in osteoblast and raise the potential of targeting EGFR/FAK and c-Src as adjunctive therapeutics for treating chronic S. aureus osteomyelitis.

Staphylococcus aureus Osteomyelitis: Bone, Bugs, and Surgery

Osteomyelitis, or inflammation of bone, is most commonly caused by invasion of bacterial pathogens into the skeleton. Bacterial osteomyelitis is notoriously difficult to treat, in part because of the widespread antimicrobial resistance in the preeminent etiologic agent, the Gram-positive bacterium Staphylococcus aureus Bacterial osteomyelitis triggers pathological bone remodeling, which in turn leads to sequestration of infectious foci from innate immune effectors and systemically delivered antimicrobials. Treatment of osteomyelitis therefore typically consists of long courses of antibiotics in conjunction with surgical debridement of necrotic infected tissues. Even with these extreme measures, many patients go on to develop chronic infection or sustain disease comorbidities. A better mechanistic understanding of how bacteria invade, survive within, and trigger pathological remodeling of bone could therefore lead to new therapies aimed at prevention or treatment of osteomyelitis as well as amelioration of disease morbidity. In this minireview, we highlight recent developments in our understanding of how pathogens invade and survive within bone, how bacterial infection or resulting innate immune responses trigger changes in bone remodeling, and how model systems can be leveraged to identify new therapeutic targets. We review the current state of osteomyelitis epidemiology, diagnostics, and therapeutic guidelines to help direct future research in bacterial pathogenesis.

Pyroptosis in Osteoblasts: A Novel Hypothesis Underlying the Pathogenesis of Osteoporosis

Osteoporosis has become a worldwide disease characterized by a reduction in bone mineral density and the alteration of bone architecture leading to an increased risk of fragility fractures. And an increasing number of studies have indicated that osteoblasts undergo a large number of programmed death events by many different causes in osteoporosis and release NLRP3 and interleukin (e.g., inflammatory factors), which play pivotal roles in contributing to excessive differentiation of osteoclasts and result in exaggerated bone resorption. NLRP3 is activated during pyroptosis and processes the precursors of IL-1β and IL-18 into mature forms, which are released into the extracellular milieu accompanied by cell rupture. All of these compounds are the classical factors of pyroptosis. The cellular effects of pyroptosis are commonly observed in osteoporosis. Although many previous studies have focused on the pathogenesis of these inflammatory factors in osteoporosis, pyroptosis has not been previously evaluated. In this review, pyroptosis is proposed as a novel hypothesis of osteoporosis pathogenesis for the first time, thus providing a new direction for the treatment of osteoporosis in the future.