The fibroblast expression of RANKL in CoCrMo-particle-induced osteolysis is mediated by ER stress and XBP1s

Particle-induced osteolysis is mediated by endoplasmic reticulum stress-associated osteoblast apoptosis

Osteoblast dysfunction plays a crucial role in periprosthetic osteolysis and aseptic loosening, and endoplasmic reticulum (ER) stress is recognized as an important causal factor of wear particle-induced osteolysis. However, the influence of ER stress on osteoblast activity during osteolysis and its underlying mechanisms remain elusive. This study aims to investigate whether ER stress is involved in the detrimental effects of wear particles on osteoblasts. Through our investigation, we observed elevated expression levels of ER stress and apoptosis markers in particle-stimulated bone specimens and osteoblasts. To probe further, we employed the ER stress inhibitor, 4-PBA, to treat particle-stimulated osteoblasts. The results revealed that 4-PBA effectively alleviated particle-induced osteoblast apoptosis and mitigated osteogenic reduction. Furthermore, our study revealed that wear particle-induced ER stress in osteoblasts coincided with mitochondrial damage, calcium overload, and oxidative stress, all of which were effectively alleviated by 4-PBA treatment. Encouragingly, 4-PBA administration also improved bone formation and attenuated osteolysis in a mouse calvarial model. In conclusion, our results demonstrate that ER stress plays a crucial role in mediating wear particle-induced osteoblast apoptosis and impaired osteogenic function. These findings underscore the critical involvement of ER stress in wear particle-induced osteolysis and highlight ER stress as a potential therapeutic target for ameliorating wear particle-induced osteogenic reduction and bone destruction.

ROS-mediated mitophagy and necroptosis regulate osteocytes death caused by TCP particles in MLO-Y4 cells

Our previous data have revealed TCP particles caused cell death of osteocytes, comprising over 95 % of all bone cells, which contribute to periprosthetic osteolysis, joint loosening and implant failure, but its mechanisms are not fully understood. Here, we reported that TCP particles inhibited cell viability of osteocytes MLO-Y4, and caused cell death. TCP particles caused mitochondrial impairment and increased expressions of LC-3 II, Parkin and PINK 1, accompanied by the elevation of autophagy flux and intracellular acidic components, the accumulation of LC-3II, PINK1 and Parkin in damaged mitochondria, and p62 reduction. The increased LC-3II expression and cell death extent were significantly enhanced by the autophagy inhibitor Baf A1, compared with Baf A1 (or TCP particles) alone, indicating that TCP particles increase autophagic flux and lead to cell even death of MLO-Y4 cells, closely associated with mitophagy. Furthermore, TCP particles induced propidium iodide (PI) uptake and the phosphorylation of RIP1, RIP3 and MLKL, thereby increasing necroptosis in MLO-Y4 cells. The pro-necroptotic effect was alleviated by the RIP1 inhibitor Nec-1 or the MLKL inhibitor NSA. Additionally, TCP particles promoted the production of intracellular reactive oxygen species (ROS) and mitochondrial ROS (mtROS), and increased TXNIP expression, but decreased protein levels of TRX1, Nrf2, HO-1 and NQO1, leading to oxidative stress. The ROS scavenger NAC remarkably reversed mitophagy and necroptosis caused by TCP particles, suggesting that ROS is responsible for mitophagy and necroptosis. Collectively, ROS-mediated mitophagy and necroptosis regulate osteocytes death caused by TCP particles in MLO-Y4 cells, which enhances osteoclastogenesis and periprosthetic osteolysis.

The dual role of autophagy in periprosthetic osteolysis

Periprosthetic osteolysis (PPO) induced by wear particles is an important cause of aseptic loosening after artificial joint replacement, among which the imbalance of osteogenesis and osteoclastic processes occupies a central position. The cells involved in PPO mainly include osteoclasts (macrophages), osteoblasts, osteocytes, and fibroblasts. RANKL/RANK/OGP axis is a typical way for osteolysis. Autophagy, a mode of regulatory cell death and maintenance of cellular homeostasis, has a dual role in PPO. Although autophagy is activated in various periprosthetic cells and regulates the release of inflammatory cytokines, osteoclast activation, and osteoblast differentiation, its beneficial or detrimental role remains controversy. In particular, differences in the temporal control and intensity of autophagy may have different effects. This article focuses on the role of autophagy in PPO, and expects the regulation of autophagy to become a powerful target for clinical treatment of PPO.

Pyroptosis in Periprosthetic Osteolysis

Periprosthetic osteolysis (PPO) along with aseptic loosening (AL) caused by wear particles after artificial joint replacement is the key factor in surgical failure and subsequent revision surgery, however, the precise molecular mechanism underlying PPO remains unclear. Aseptic inflammation triggered by metal particles, resulting in the imbalance between bone formation by osteoblasts and bone resorption by osteoclasts may be the decisive factor. Pyroptosis is a new pro-inflammatory pattern of regulated cell death (RCD), mainly mediated by gasdermins (GSDMs) family, among which GSDMD is the best characterized. Recent evidence indicates that activation of NLRP3 inflammasomes and pyroptosis play a pivotal role in the pathological process of PPO. Here, we review the pathological process of PPO, the molecular mechanism of pyroptosis and the interventions to inhibit the inflammation and pyroptosis of different cells during the PPO. Conclusively, this review provides theoretical support for the search for new strategies and new targets for the treatment of PPO by inhibiting pyroptosis and inflammation.

Protective effect of zinc supplementation on tricalcium phosphate particles-induced inflammatory osteolysis in mice

Zinc (Zn), an essential trace element, can stimulate bone formation and inhibit osteoclastic bone resorption, which controls the growth and maintenance of bone. However, the effect of Zn supplementation on tricalcium phosphate (TCP) wear particles-induced osteolysis remains unknown. Here, we doped Zn into TCP particles (ZnTCP), and explore the protective effects of Zn on TCP particles-induced osteolysis in vivo. TCP particles and ZnTCP particles were embedded under the periosteum around the middle suture of the mouse calvaria. After 2 weeks, blood, the periosteal tissue, and the calvaria were collected to determine serum levels of Zn and osteocalcin, pro-inflammatory cytokines, bone biochemical markers, osteoclastogenesis and bone resorption area, and to explain its mechanism. Data revealed that Zn significantly prevented TCP particles-induced osteoclastogenesis and bone loss, and increased bone turnover. The Zn supplement remarkably suppressed the release of pro-inflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6. Immunoblotting demonstrated that Zn alleviated expression levels of ER stress-related proteins such as glucose-regulated protein 78 (GRP78), PKR-like ER kinase (PERK), phospho-PERK (p-PERK), eukaryotic initiation factor 2α (eIF2α), phospho-eIF2α (p-eIF2α), activating transcription factor 4 (ATF4), inositol-requiring enzyme 1α (IRE1-α) and transcription factor X-box binding protein spliced (XBP1s), leading to decreasing the ratios of p-PERK/PERK and p-eIF2α/eIF2α. Taken together, Zn supplementation strongly prevents TCP particles-induced periprosthetic osteolysis via inhibition of the ER stress pathway, and it may be a novel therapeutic approach for the treatment of aseptic prosthesis loosening.

Tricalcium phosphate particles promote pyroptotic death of calvaria osteocytes through the ROS/NLRP3/Caspase-1 signaling axis in amouse osteolysis model

Wear particles-induced inflammatory osteolysis, a major factor of aseptic loosening affects the long-term survival of orthopedic prostheses. Increasing observations have demonstrated that osteocytes, making up over 95% of all the bone cells, is involved in wear particle-induced periprosthetic osteolysis, but its mechanism remains unclear. In the present study, we embedded micro-sized tricalcium phosphate (TCP) particles (30 mg) under the periosteum around the middle suture of the mouse calvaria to establish a calvarial osteolysis model and investigated the biological effects of the particles on calvaria osteocytes in vivo. Results showed that TCP particles induced pyroptosis and activated the NLRP3 inflammasome in calvaria osteocytes, which was confirmed by obvious increases in empty lacunae, protein expressions of speck-like protein containing CARD (ASC), NOD-like receptor protein 3 (NLRP3), cleaved caspase-1 (Casp-1 p20) and cleaved gasdermin D (GSDMD-N), and resulted in elevated ratios of Casp-1 p20/Casp-1 and interleukin (IL)-1β/pro-IL-1β. Simultaneously, TCP particles enhanced serum levels of lactate dehydrogenase (LDH) and IL-1β. Furthermore, the pyroptotic effect was reversed by the Casp-1 inhibitor VX765 or the NLRP3 inhibitor MCC950. In addition, TCP particles increased the levels of intracellular reactive oxygen species (ROS) and malonaldehyde (MDA), whereas decreased the antioxidant enzyme nuclear factor E2-related factor 2 (Nrf2) level, leading to oxidative stress in calvaria osteocytes; the ROS scavenger N-acetylcysteine (NAC) attenuated these effects of pyroptotic death and the NLPR3 activation triggered by TCP particles. Collectively, our data suggested that TCP particles promote pyroptotic death of calvaria osteocytes through the ROS/NLRP3/Caspase-1 signaling axis, contributing to osteoclastogenesis and periprosthetic osteolysis.

Effects of Antibacterial Co-Cr-Mo-Cu Alloys on Osteoblast Proliferation, Differentiation, and the Inhibition of Apoptosis

Objectives

To investigate the effects of antibacterial Co‐Cr‐Mo‐Cu alloys with different Cu contents on osteoblast proliferation, differentiation, and the inhibition of apoptosis to optimize the selection of surgical implantation.

Methods

Microstructure, phase structure, and ion release were evaluated using X‐ray diffraction, scanning electron microscopy (SEM), and inductively coupled plasma (ICP) spectrometry. The effects on osteoblast proliferation, differentiation, and apoptosis were characterized by cell proliferation assay, alkaline phosphatase (ALP) activity assay, and western blotting, respectively.

Results

Compared to the original Co‐Cr‐Mo alloys, the released Cu ions from Co‐Cu alloys promoted osteoblast proliferation and differentiation and inhibited apoptosis. It can be noted that the optical density (OD490) and the ALP activity have increased to 1.237 and 1.053, respectively, in Co‐2Cu alloy (0.604 and 0.171 for original Co‐Cr‐Mo alloy). Meanwhile, these effects were evaluated through the upregulation of ROS levels and 4E‐binding protein 1 (4E‐BP1) expression and the downregulation of adenosine 5′‐monophosphate (AMP)‐activated protein kinase (AMPK) and p‐AMPK. Moreover, the antibacterial properties of the Co‐Cu alloys were also enhanced, as demonstrated by the strong antibacterial activity of Cu phases in Co‐Cu alloys incubated with Staphylococcus aureus, in which more than 99.8% of the bacteria has been killed.

Conclusions

The addition of Cu element in the Co‐Cr‐Mo alloys could induce OB proliferation and differentiation and inhibited OB apoptosis. Meanwhile, it can be recognized that the Co‐Cu alloys with 2wt% Cu exhibit the highest performance among all the samples, indicating that the effects of osteoblast differentiation and the inhibition of apoptosis are highly dependent on the adding of Cu elements. Co‐Cr‐Mo‐Cu alloys with an excellent antibacterial property could be used as a tool to improve osteogenic ability and antibacterial properties in orthopaedic implant operations.

Enteropathogenic Escherichia coli Mediates CoCrMo Particle-Induced Peri-Implant Osteolysis by Increasing Peripheral 5-HT

The human gut microbiota has been proven to have great effects on the regulation of bone health. However, the association between gut microbiota and particle-induced osteolysis, which is the primary cause of aseptic loosening, is still unknown. In this study, we used a combination of wide-spectrum antibiotics to eliminate the majority of gut microbiota and found that reduction of gut commensal bacteria significantly alleviated the progression of osteolysis, in which anaerobe was the biggest culprit in the exacerbation of osteolysis. Furthermore, colonization of enteropathogenic Escherichia coli (EPEC), a subspecies of anaerobe, could promote the development of particle-induced osteolysis by increasing the secretion of peripheral 5-hydroxytryptamine (5-HT) from the colon. Elevated 5-HT level decreased the phosphorylation of CREB and inhibited the proliferation of osteoblasts. Collectively, these results indicated EPEC colonization suppressed the bone formation and aggravated particle-induced osteolysis in vivo. Thus, clearance of EPEC is expected to become a potential preventive approach to treat debris-induced osteolysis and aseptic loosening.

Autophagy inhibitors 3-MA and LY294002 repress osteoclastogenesis and titanium particle-stimulated osteolysis

Aseptic loosening caused by peri-implant osteolysis (PIO) is a common complication after joint replacement, and there is still no better treatment than revision surgery. The wear particle-induced inflammation response, especially subsequent osteoclastic bone resorption, is responsible for PIO. As the importance of wear particles in inducing autophagy in cells around the prosthesis in PIO has been discovered, this might be a central process underlying aseptic loosening. However, the role of autophagy induced by wear particles in osteoclastogenesis during PIO remains unclear. In this study, we investigated the role of autophagy in osteoclastogenesis and verified it in a mouse calvarial osteolysis model. We found that osteoclasts were increased in the interface membranes of patients with aseptic loosening. In vitro, knocking down the Atg5 gene or using autophagy inhibitors (3-MA, LY294002) to inhibit autophagy was found to repress osteoclastogenesis and decrease expression of the osteoclast-related genes TRAP, cathepsin K, and matrix metalloprotein 9 (MMP-9) with or without titanium (Ti) particles. In vivo, 3-MA and LY294002 repressed Ti particle-stimulated osteolysis and osteoclastogenesis and reduced expression of the pro-inflammatory factors TNF-α, IL-1β, and IL-6. Our results suggest that 3-MA and LY294002 might be the potential medicines to prevent and treat PIO and aseptic loosening.

Melatonin Rescues the Ti Particle-Impaired Osteogenic Potential of Bone Marrow Mesenchymal Stem Cells via the SIRT1/SOD2 Signaling Pathway

Wear particles released by joint implants are a major cause of osteolysis around the prosthesis by negatively affecting bone reconstruction. Bone marrow mesenchymal stem cells (BMMSCs) stimulated by wear particles showed an impaired osteogenic potential. Melatonin has been shown beneficial effects on intracellular antioxidant functions and bone formation; however, whether it could restore the osteogenic potential of BMMSCs inhibited by wear particles was unknown. This study aimed to evaluate the protective effect of melatonin on the osteogenic capacity of BMMSCs exposed to titanium (Ti) wear particles and to investigated the underlying mechanisms involving intracellular antioxidant properties. When BMMSCs were exposed to Ti particles in vitro, melatonin treatment successfully improved the matrix mineralization and expression of osteogenic markers in BMMSCs, while decreasing the levels of intracellular reactive oxygen species (ROS) and mitochondrial superoxide. The protective effect of melatonin on osteolysis was validated in a Ti particle-exposed murine calvarial model. Meanwhile, silent information regulator type 1 (SIRT1) and intracellular antioxidant enzymes were significantly up-regulated, particularly superoxide dismutase 2 (SOD2), in melatonin-treated BMMSCs. Furthermore, inhibition of SIRT1 by EX527 completely counteracted the protective effect of melatonin on Ti particle-treated BMMSCs, evidenced by the reduced expression of SOD2, increased ROS and superoxide, and decreased osteogenic differentiation. These results demonstrated that melatonin restored the osteogenic potential and improved the antioxidant properties of BMMSCs through the SIRT1 signaling pathway. Our findings suggest that melatonin is a promising candidate for treating osteolysis induced by wear particles.

Endoplasmic reticulum stress remodels alveolar bone formation after tooth extraction

Bone healing in tooth extraction sockets occurs in a complex environment containing saliva and many microorganisms and is affected by many factors. Endoplasmic reticulum (ER) stress affects bone metabolism, but the role of ER stress in bone healing after tooth extraction remains unclear. We utilized a rat tooth extraction model, in which we promoted wound healing by using salubrinal to regulate the ER stress response. Western blot analysis showed increased expression of p‐eIF2α/eIF2α, Runx2 and alkaline phosphatase (ALP) in bone tissue, and histological assays showed irregularly arranged and new bone with more collagen fibres 14 days after tooth extraction and after modulating the degree of ER stress. Micro‐CT showed that modulating ER stress to an appropriate degree increases bone filling in regards to the density in the bottom and the surrounding bone wall of the tooth extraction wounds. Transmission electron microscopy showed rough ER expansion and newly formed collagen fibrils in osteoblasts after modulating ER stress to an appropriate degree. We also used different concentrations of salubrinal to evaluate the resistance to tunicamycin‐induced ER stress in an osteogenic induction environment. Salubrinal restored the tunicamycin‐induced decrease in the viability of primary calvarial osteoblasts and increased the expression of Runx2 and ALP, and decreased p‐eIF2α/eIF2α in a dose‐dependent manner. Taken together, the results demonstrate that ER stress occurred after tooth extraction, and regulating the degree of ER stress can promote bone healing in tooth extraction sockets, providing clinical evidence for bone healing.

Titanium particles induce apoptosis by promoting autophagy in macrophages via the PI3K/Akt signaling pathway

Chronic inflammation and infection in the tissue surrounding implants after total joint replacement is closely associated with the innate immune response to surgical implants. Wear particles are known to increase apoptosis and impair the innate immunity in macrophages, which can cause immunosuppression around the implants. Excessive autophagy can induce apoptosis. However, the link between autophagy and apoptosis in macrophages during chronic inflammation and infection remains unknown. In this study, we investigated the autophagy and apoptosis induced by titanium particles in RAW264.7 macrophages, and in the interface membrane of patients with late-onset periprosthetic joint infection (PJI). We found that titanium particles stimulated autophagy and apoptosis in macrophages. Inhibition of autophagy significantly reduced titanium particle-induced apoptosis in macrophages, which may be related to the PI3K/Akt signaling pathway. The secretion of inflammatory factors, such as IL-1β, IL-6, and TNF-α, decreased after inhibition of autophagy in titanium particle-stimulated macrophages, which may be caused by immune dysfunction due to titanium particle-induced autophagy and apoptosis in macrophages. Furthermore, our in vivo mouse calvarial model also showed that autophagy inhibitors lowered the rate of cell apoptosis. Our findings indicate that wear particle-induced apoptosis may be caused by enhanced autophagy in macrophages, which could potentially impair the local innate immunity in periprosthetic tissues and could be a risk factor for PJI. Based on these results, autophagy modulators may act as a new therapeutic option for PJI.

The Effects of Biomaterial Implant Wear Debris on Osteoblasts

Aseptic loosening subsequent to periprosthetic osteolysis is the leading cause for the revision of arthroplasty failure. The biological response of macrophages to wear debris has been well established, however, the equilibrium of bone remodeling is not only dictated by osteoclastic bone resorption but also by osteoblast-mediated bone formation. Increasing evidence shows that wear debris significantly impair osteoblastic physiology and subsequent bone formation. In the present review, we update the current state of knowledge regarding the effect of biomaterial implant wear debris on osteoblasts. The interaction of osteoblasts with osteoclasts and macrophages under wear debris challenge, and potential treatment options targeting osteoblasts are also presented.

Nano-sized Al2O3 particle-induced autophagy reduces osteolysis in aseptic loosening of total hip arthroplasty by negative feedback regulation of RANKL expression in fibroblasts

Aseptic loosening is mainly caused by wear debris generated by friction that can increase the expression of receptor activation of nuclear factor (NF)-κB (RANKL). RANKL has been shown to support the differentiation and maturation of osteoclasts. Although autophagy is a key metabolic pathway for maintaining the metabolic homeostasis of cells, no study has determined whether autophagy induced by Al₂O₃ particles is involved in the pathogenesis of aseptic loosening. The aim of this study was to evaluate RANKL levels in patients experiencing aseptic loosening after total hip arthroplasty (THA) and hip osteoarthritis (hOA) and to consequently clarify the relationship between RANKL and LC3II expression. We determined the levels of RANKL and autophagy in fibroblasts treated with Al₂O₃ particles in vitro while using shBECN-1 interference lentivirus vectors to block the autophagy pathway and BECN-1 overexpression lentivirus vectors to promote autophagy. We established a novel rat model of femoral head replacement and analyzed the effects of Al₂O₃ particles on autophagy levels and RANKL expression in synovial tissues in vivo. The RANKL levels in the revision total hip arthroplasty (rTHA) group were higher than those in the hOA group. In patients with rTHA with a ceramic interface, LC3II expression was high, whereas RANKL expression was low. The in vitro results showed that Al₂O₃ particles promoted fibroblast autophagy in a time- and dose-dependent manner and that RANKL expression was negatively correlated with autophagy. The in vivo results further confirmed these findings. Al₂O₃ particles induced fibroblast autophagy, which reduced RANKL expression. Decreasing the autophagy level promoted osteolysis and aseptic prosthetic loosening, whereas increasing the autophagy level reversed this trend.

Construction and Evaluation of a Murine Calvarial Osteolysis Model by Exposure to CoCrMo Particles in Aseptic Loosening

Wear particle-induced osteolysis is a major cause of aseptic loosening in arthroplasty failure, but the underlying mechanism remains unclear. Due to long follow-ups necessary for detection and sporadic occurrence, it is challenging to assess the pathogenesis ofparticle-induced osteolysis in clinical cases. Hence, optimal animal models are required for further studies. The murine model of calvarial osteolysis established by exposure to CoCrMo particles is an effective and valid tool for assessing the interactions between particles and various cells in aseptic loosening. In this model, CoCrMo particles were first obtained by high-vacuum three-electrode direct current and resuspended in phosphate-buffered saline at a concentration of 50 mg/mL. Then, 50 µL of the resulting suspension was applied to the middle of the murine calvaria after separation of the cranial periosteum by sharp dissection. After two weeks, the mice were sacrificed, and calvaria specimens were harvested; qualitative and quantitative evaluations were performed by hematoxylin and eosin staining and micro computed tomography. The strengths of this model include procedure simplicity, quantitative evaluation of bone loss, rapidity of osteolysis development, potential use transgenic or knockout models, and a relatively low cost. However, this model cannot to be used to assess the mechanical force and chronic effects of particles in aseptic loosening. Murine calvarial osteolysis model generated by exposure to CoCrMo particles is an ideal tool for assessing the interactions between wear particles and various cells, e.g., macrophages, fibroblasts, osteoblasts and osteoclasts, in aseptic loosening.

The metal nanoparticle-induced inflammatory response is regulated by SIRT1 through NF-κB deacetylation in aseptic loosening

Aseptic loosening is the most common cause of total hip arthroplasty (THA) failure, and osteolysis induced by wear particles plays a major role in aseptic loosening. Various pathways in multiple cell types contribute to the pathogenesis of osteolysis, but the role of Sirtuin 1 (SIRT1), which can regulate inflammatory responses through its deacetylation, has never been investigated. We hypothesized that the downregulation of SIRT1 in macrophages induced by metal nanoparticles was one of the reasons for osteolysis in THA failure. In this study, the expression of SIRT1 was examined in macrophages stimulated with metal nanoparticles from materials used in prosthetics and in specimens from patients suffering from aseptic loosening. To address whether SIRT1 downregulation triggers these inflammatory responses, the effects of the SIRT1 activator resveratrol on the expression of inflammatory cytokines in metal nanoparticle-stimulated macrophages were tested. The results demonstrated that SIRT1 expression was significantly downregulated in metal nanoparticle-stimulated macrophages and clinical specimens of prosthesis loosening. Pharmacological activation of SIRT1 dramatically reduced the particle-induced expression of inflammatory cytokines in vitro and osteolysis in vivo. Furthermore, SIRT1 regulated particle-induced inflammatory responses through nuclear factor kappa B (NF-κB) acetylation. Thus, the results of this study suggest that SIRT1 plays a key role in metal nanoparticle-induced inflammatory responses and that targeting the SIRT1 pathway may lead to novel therapeutic approaches for the treatment of aseptic prosthesis loosening.

SIRT1 protects osteoblasts against particle-induced inflammatory responses and apoptosis in aseptic prosthesis loosening

We hypothesized that SIRT1 downregulation in osteoblasts induced by wear particles was one of the reasons for particle-induced osteolysis (PIO) in total joint arthroplasty failure. In the present study, the expression of SIRT1 was examined in osteoblasts treated with TiAl6V4 particles (TiPs) and CoCrMo particles (CoPs) from materials used in prosthetics and specimens from PIO animal models. To address whether SIRT1 downregulation triggers inflammatory responses and apoptosis in osteoblasts, the effect of a SIRT1 activator, resveratrol on the expression of inflammatory cytokines and apoptosis in particle-treated osteoblasts was tested. The results demonstrated that SIRT1 expression was significantly downregulated in particle-treated osteoblasts and PIO animal models. Both pharmacological activation and overexpression of SIRT1 dramatically reduced the particle-induced expression of inflammatory cytokines and osteoblast apoptosis through NF-κB and p53 signaling, respectively. Furthermore, in PIO animal models, resveratrol significantly reduced the severity of osteolysis. Collectively, the results of the present study indicated that SIRT1 plays a vital role in the pathogenesis of aseptic loosening, and further treatment targeted at SIRT1 possibly lead to novel approaches for prevention of aseptic prosthesis loosening.

STATEMENT OF SIGNIFICANCE

Aseptic loosening is the most common cause of total hip arthroplasty (THA) and total knee arthroplasty (TKA) failure and revision surgery. However, there is still no effective therapeutic target in the clinical treatment. Besides, the underlying mechanism of aseptic loosening is largely unknown. The result of our study indicated that SIRT1 has the ability to effectively regulate the wear particle-induced inflammatory responses, apoptosis, osteolysis in particle-stimulated osteoblasts and particle-induced osteolysis animal models. Our study provides a potential target for the prevention and treatment of aseptic loosening and further investigated the underlying mechanism of aseptic loosening, which may make contribution to decrease the incidence of THA and TKA failure in the clinical practice.

TiAl6V4 particles promote osteoclast formation via autophagy-mediated downregulation of interferon-beta in osteocytes

Wear debris-induced osteolysis is the leading cause of aseptic loosening, which is the most common reason for total hip arthroplasty (THA) failure in the medium and long term. Although osteocytes are the most abundant cells in bone and make direct contact with implants, the interaction between osteocytes and wear debris remains largely unknown. In the present study, we investigated the effect of TiAl₆V₄ alloy particles (TiPs) on osteocytes and the subsequent effects on osteoclast formation. Our study demonstrated that osteocyte-conditioned medium (CM) inhibited osteoclast differentiation from bone marrow monocytes (BMMs) to osteoclasts. However, TiPs attenuated this inhibitory effect. The expression of several osteoclastogenesis-associated factors, including receptor activator of nuclear factor-kappaB ligand (RANKL), osteoprotegerin (OPG), nitric oxide (NO) and interferon-beta (IFN-β), was examined, and we found that TiPs markedly decreased the expression of IFN-β, but not the other factors. In an osteoclastogenesis assay, our results suggested that the downregulation of IFN-β mediated the stimulatory effect of TiPs on osteoclastogenesis. Additional evidence suggested that TiPs decreased the expression of IFN-β in osteocytes via macroautophagy (hereinafter referred to as "autophagy"). Moreover, inhibiting autophagy with Atg5 siRNA prevented the increase in osteoclastogenesis induced by TiPs. Collectively, these results suggested a possible mechanism underlying wear debris-induced osteolysis.

STATEMENT OF SIGNIFICANCE

For the first time, our study demonstrated that Ti-alloy particles attenuated the inhibitory effect of osteocytes-conditioned medium on osteoclast formation. With an osteoclastogenesis assay, we found that the downregulation of IFN-β in osteocytes mediated the promoting effect of TiPs on osteoclast formation. Furthermore, our results suggested that TiPs-induced autophagy mediated the downregulation of IFN-β in osteocytes. Inhibition of autophagy recovered the expression of IFN-β and ameliorated the promoting effect of TiPs on osteoclast formation. Collectively, these findings suggest a possible mechanism underlying wear debris-induced osteolysis and identified autophagy inhibition in osteocytes as a potential therapeutic approach for wear debris induced osteolysis.

Adverse Biological Effect of TiO₂ and Hydroxyapatite Nanoparticles Used in Bone Repair and Replacement

The adverse biological effect of nanoparticles is an unavoidable scientific problem because of their small size and high surface activity. In this review, we focus on nano-hydroxyapatite and TiO₂ nanoparticles (NPs) to clarify the potential systemic toxicological effect and cytotoxic response of wear nanoparticles because they are attractive materials for bone implants and are widely investigated to promote the repair and reconstruction of bone. The wear nanoparticles would be prone to binding with proteins to form protein-particle complexes, to interacting with visible components in the blood including erythrocytes, leukocytes, and platelets, and to being phagocytosed by macrophages or fibroblasts to deposit in the local tissue, leading to the formation of fibrous local pseudocapsules. These particles would also be translocated to and disseminated into the main organs such as the lung, liver and spleen via blood circulation. The inflammatory response, oxidative stress, and signaling pathway are elaborated to analyze the potential toxicological mechanism. Inhibition of the oxidative stress response and signaling transduction may be a new therapeutic strategy for wear debris-mediated osteolysis. Developing biomimetic materials with better biocompatibility is our goal for orthopedic implants.