ER stress arm XBP1s plays a pivotal role in proteasome inhibition-induced bone formation

Kaempferol attenuates particle-induced osteogenic impairment by regulating ER stress via the IRE1α-XBP1s pathway

Periprosthetic osteolysis and subsequent aseptic loosening are the primary causes of failure following total joint arthroplasty. Wear particle-induced osteogenic impairment is recognized as an important contributing factor in the development of osteolysis, with endoplasmic reticulum (ER) stress emerging as a pivotal underlying mechanism. Hence, searching for potential therapeutic targets and agents capable of modulating ER stress in osteoblasts is crucial for preventing aseptic loosening. Kaempferol (KAE), a natural flavonol compound, has shown promising osteoprotective effects and anti-ER stress properties in diverse diseases. However, the influence of KAE on ER stress-mediated osteogenic impairment induced by wear particles remains unclear. In this study, we observed that KAE effectively relieved TiAl6V4 particles-induced osteolysis by improving osteogenesis in a mouse calvarial model. Furthermore, we demonstrated that KAE could attenuate ER stress-mediated apoptosis in osteoblasts exposed to TiAl6V4 particles, both in vitro and in vivo. Mechanistically, our results revealed that KAE mitigated ER stress-mediated apoptosis by upregulating the IRE1α-XBP1s pathway while concurrently partially inhibiting the IRE1α-regulated RIDD and JNK activation. Collectively, our findings suggest that KAE is a prospective therapeutic agent for treating wear particle-induced osteolysis and highlight the IRE1α-XBP1s pathway as a potential therapeutic target for preventing aseptic loosening.

Pluronic F127 hydrogel-loaded extracellular vesicles from adipose-derived mesenchymal stem cells promote tracheal cartilage regeneration via SCNN1B delivery

Extracellular vesicles (EVs) derived from adipose-derived mesenchymal stem cells (AMSC-EVs) have been highlighted as a cell-free therapy due to their regenerative capability to enhance tissue and organ regeneration. Herein, we aimed to examine the mechanism of PF127-hydrogel@AMSC-EVs in promoting tracheal cartilage defect repair. Based on bioinformatics methods, SCNN1B was identified as a key gene for the osteogenic differentiation of AMSCs induced by AMSC-EVs. EVs were isolated from rat AMSCs and then loaded onto thermo-sensitive PF-127 hydrogel to develop PF127-hydrogel@AMSC-EVs. It was established that PF127-hydrogel@AMSC-EVs could effectively deliver SCNN1B into AMSCs, where SCNN1B promoted AMSC osteogenic differentiation. The promotive effect was evidenced by enhanced ALP activity, extracellular matrix mineralization, and expression of s-glycosaminoglycan, RUNX2, OCN, collagen II, PERK, and ATF4. Furthermore, the in vivo experiments revealed that PF127-hydrogel@AMSC-SCNN1B-EVs stimulated tracheal cartilage regeneration in rats through PERK/ATF4 signaling axis activation. Therefore, PF127-hydrogel@AMSC-SCNN1B-EVs may be a novel cell-free biomaterial to facilitate tracheal cartilage regeneration and cartilage injury repair.

The IRE1α/XBP1 pathway sustains cytokine responses of group 3 innate lymphoid cells in inflammatory bowel disease

Group 3 innate lymphoid cells (ILC3s) are key players in intestinal homeostasis. ER stress is linked to inflammatory bowel disease (IBD). Here, we used cell culture, mouse models, and human specimens to determine whether ER stress in ILC3s affects IBD pathophysiology. We show that mouse intestinal ILC3s exhibited a 24-hour rhythmic expression pattern of the master ER stress response regulator inositol-requiring kinase 1α/X-box-binding protein 1 (IRE1α/XBP1). Proinflammatory cytokine IL-23 selectively stimulated IRE1α/XBP1 in mouse ILC3s through mitochondrial ROS (mtROS). IRE1α/XBP1 was activated in ILC3s from mice exposed to experimental colitis and in inflamed human IBD specimens. Mice with Ire1α deletion in ILC3s (Ire1αΔRorc) showed reduced expression of the ER stress response and cytokine genes including Il22 in ILC3s and were highly vulnerable to infections and colitis. Administration of IL-22 counteracted their colitis susceptibility. In human ILC3s, IRE1 inhibitors suppressed cytokine production, which was upregulated by an IRE1 activator. Moreover, the frequencies of intestinal XBP1s+ ILC3s in patients with Crohn's disease before administration of ustekinumab, an anti-IL-12/IL-23 antibody, positively correlated with the response to treatment. We demonstrate that a noncanonical mtROS-IRE1α/XBP1 pathway augmented cytokine production by ILC3s and identify XBP1s+ ILC3s as a potential biomarker for predicting the response to anti-IL-23 therapies in IBD.

Mechanism of Decision Making between Autophagy and Apoptosis Induction upon Endoplasmic Reticulum Stress

Dynamic regulation of the cellular proteome is mainly controlled in the endoplasmic reticulum (ER). Accumulation of misfolded proteins due to ER stress leads to the activation of unfolded protein response (UPR). The primary role of UPR is to reduce the bulk of damages and try to drive back the system to the former or a new homeostatic state by autophagy, while an excessive level of stress results in apoptosis. It has already been proven that the proper order and characteristic features of both surviving and self-killing mechanisms are controlled by negative and positive feedback loops, respectively. The new results suggest that these feedback loops are found not only within but also between branches of the UPR, fine-tuning the response to ER stress. In this review, we summarize the recent knowledge of the dynamical characteristic of endoplasmic reticulum stress response mechanism by using both theoretical and molecular biological techniques. In addition, this review pays special attention to describing the mechanism of action of the dynamical features of the feedback loops controlling cellular life-and-death decision upon ER stress. Since ER stress appears in diseases that are common worldwide, a more detailed understanding of the behaviour of the stress response is of medical importance.

Chronic arsenic exposure suppresses proteasomal and autophagic protein degradation

Ubiquitin Proteasomal System (UPS) and autophagy dysregulation initiate cancer. These pathways are regulated by zinc finger proteins. Trivalent inorganic arsenic (iAs) displaces zinc from zinc finger proteins disrupting functions of important cellular proteins. The effect of chronic environmental iAs exposure (100 nM) on UPS has not been studied. We tested the hypothesis that environmental iAs exposure suppresses UPS, activating autophagy as a compensatory mechanism. We exposed skin (HaCaT and Ker-CT; independent quadruplicates) and lung (BEAS-2B; independent triplicates) cell cultures to 0 or 100 nM iAs for 7 or 8 weeks. We quantified ER stress (XBP1 splicing employing Reverse Transcriptase -Polymerase Chain Reaction), proteasomal degradation (immunoblots), and initiation and completion of autophagy (immunoblots). We demonstrate that chronic iAs exposure suppresses UPS, initiates autophagy, but suppresses autophagic protein degradation in skin and lung cell lines. Our data suggest that chronic iAs exposure inhibits autophagy which subsequently suppresses UPS.

Apoptotic Extracellular Vesicles Induced Endothelial Cell-Mediated Autologous Stem Cell Recruitment Dominates Allogeneic Stem Cell Therapeutic Mechanism for Bone Repair

Although stem cell therapy is proved to be a promising strategy for bone repair and regeneration, transplanted allogeneic stem cells generally suffer from unfavorable apoptosis instead of differentiation into osteocytes. How the apoptotic stem cells promote bone regeneration still needs to be uncovered. In this work, we found that apoptotic extracellular vesicles released by allogeneic stem cells are critical mediators for promoting bone regeneration. Based on the results of in vivo experiments, a mechanism of apoptotic stem cells determined autologous stem cell recruitment and enhance osteogenesis was proposed. The nanoscaled apoptotic extracellular vesicles released from transplanted stem cells were endocytosed by vascular endothelial cells and preferentially distribute at endoplasmic reticular region. The oxidized phosphatidylcholine enriched in the vesicles activated the endoplasmic reticulum stress and triggered the reflective elevation of adhesion molecules, which induced the recruitment of autologous stem cells located in the blood vessels, transported them into the defect region, and promoted osteogenesis and bone repair. These findings not only reveal the mechanism of stem cell therapy of bone defects but also provide a cue for investigation of the biological process of stem cell therapy for other diseases and develop stem cell therapeutic strategies.

Prognostic marker CD27 and its micro-environmental in multiple myeloma

BACKGROUND

The Cluster of Differentiation 27 (CD27) is aberrantly expressed in multiple myeloma (MM) -derived. This expression facilitates the interaction between tumor and immune cells within TME via the CD27-CD70 pathway, resulting in immune evasion and subsequent tumor progression. The objective of this study is to investigate the correlation between CD27 expression and the prognosis of MM, and to elucidate its potential relationship with the immune microenvironment.

METHODS

In this research, CD27 expression in T cells within the 82 newly diagnosed MM microenvironment was assessed via flow cytometry. We then examined the association between CD27 expression levels and patient survival. Subsequent a series of bioinformatics and in vitro experiments were conducted to reveal the role of CD27 in MM.

RESULTS

Clinical evidence suggests that elevated CD27 expression in T cells within the bone marrow serves as a negative prognostic marker for MM survival. Data analysis from the GEO database has demonstrated a strong association between MM-derived CD27 and the immune response, as well as the hematopoietic system. Importantly, patients with elevated levels of CD27 expression were also found to have an increased presence of MDSCs and macrophages in the bone marrow microenvironment. Furthermore, the PERK-ATF4 signaling pathway has been implicated in mediating the effects of CD27 in MM.

CONCLUSIONS

We revealed that CD27 expression levels serve as an indicative marker for the prognosis of MM patients. The CD27- PERK-ATF4 is a promising target for the treatment of MM.

USP12 regulates ER stress-associated osteogenesis in human periodontal ligament cells under tension stress

The bone formation (osteogenesis) of human periodontal ligament cells (hPDLCs) under tension stress is essential for alveolar bone remodeling during orthodontic tooth movement (OTM). Deubiquitinating enzymes (DUBs) remove ubiquitin from target proteins, affecting their function and mediating cell survival and differentiation. However, whether and how DUBs regulate hPDLC function under tension force is poorly understood. In this study, we first investigated the expression of DUBs in hPDLCs under cyclic tension stimulation (CTS). Up-regulation of USP12 was observed in hPDLCs and at the tension side of molar teeth in OTM C57BL6 mice models. Knockdown (KD) of USP12 led to enhanced osteogenesis of hPDLCs under CTS. RNA-seq analysis suggested that the unfolded protein response (UPR) was the prevailing biological process in hPDLCs with USP12 KD, indicating that USP12 depletion triggered endoplasmic reticulum (ER) stress. The three major UPR-related signaling branches, namely PERK/eIF2α/ATF4, IRE1α/XBP1s, and ATF6 axis, were activated in hPDLCs with USP12 KD. By utilizing specific inhibitors, we proved that the PERK/eIF2α/ATF4 axis predominantly mediated the enhanced osteogenesis in hPDLCs with USP12 KD under CTS. In summary, our study demonstrates that USP12 serves as a key regulator for CTS-induced osteogenesis in hPDLCs, suggesting that USP12 upregulation serves as an adaptive mechanism for hPDLCs to alleviate ER stress during OTM.

Effects of 625 nm light-emitting diode irradiation on preventing ER stress-induced apoptosis via GSK-3β phosphorylation in MC3T3-E1

Prolonged endoplasmic reticulum (ER) stress contributes to cell apoptosis and interferes with bone homeostasis. Although photobiomodulation (PBM) might be used for ER stress-induced diseases, the role of PBM in relieving cell apoptosis remains unknown. During ER stress, glycogen synthase kinase-3β (GSK-3β) is critical; however, its functions in PBM remain uncertain. Thus, this study aimed to investigate the role of GSK-3β in 625 nm light-emitting diode irradiation (LEDI) relieving tunicamycin (TM)-induced apoptosis. Based on the results, pre-625 nm LEDI (Pre-IR) phosphorylated GSK-3β via ROS production. Compared with the TM group, Pre-IR + TM group reduced the phosphorylation of the α-subunit of eukaryotic translation initiation factor 2 (eIF-2α) and B-cell lymphoma protein 2 (Bcl-2)-associated X (Bax)/Bcl-2 ratio through regulating GSK-3β. Furthermore, a similar tendency was observed between Pre-IR + TM and Pre-LiCl+TM groups in preventing TM-induced early and late apoptosis. In summary, this study suggests that the Pre-IR treatment in TM-induced ER stress is beneficial for preventing cell apoptosis via GSK-3β phosphorylation.

Advances in the roles of ATF4 in osteoporosis

Osteoporosis (OP) is characterized by reduced bone mass, decreased strength, and enhanced bone fragility fracture risk. Activating transcription factor 4 (ATF4) plays a role in cell differentiation, proliferation, apoptosis, redox balance, amino acid uptake, and glycolipid metabolism. ATF4 induces the differentiation of bone marrow mesenchymal stem cells (BM-MSCs) into osteoblasts, increases osteoblast activity, and inhibits osteoclast formation, promoting bone formation and remodeling. In addition, ATF4 mediates the energy metabolism in osteoblasts and promotes angiogenesis. ATF4 is also involved in the mediation of adipogenesis. ATF4 can selectively accumulate in osteoblasts. ATF4 can directly interact with RUNT-related transcription factor 2 (RUNX2) and up-regulate the expression of osteocalcin (OCN) and osterix (Osx). Several upstream factors, such as Wnt/β-catenin and BMP2/Smad signaling pathways, have been involved in ATF4-mediated osteoblast differentiation. ATF4 promotes osteoclastogenesis by mediating the receptor activator of nuclear factor κ-B (NF-κB) ligand (RANKL) signaling. Several agents, such as parathyroid (PTH), melatonin, and natural compounds, have been reported to regulate ATF4 expression and mediate bone metabolism. In this review, we comprehensively discuss the biological activities of ATF4 in maintaining bone homeostasis and inhibiting OP development. ATF4 has become a therapeutic target for OP treatment.

The Role of XBP1 in bone metabolism

Bone is a dynamic organ that, once formed, undergoes a constant remodeling process that includes bone resorption and synthesis. Osteoclasts and osteoblasts are primarily responsible for controlling this process. X-box binding protein 1 (XBP1), a transcription factor, affects the metabolism of bones in various ways. In recent years, numerous studies have revealed that XBP1 plays a vital role in bone metabolism, including osteoclast and osteoblast development, as well as in regulating immune cell differentiation that affects the immune microenvironment of bone remodeling. In this review, we highlight the regulatory mechanisms of XBP1 on osteoclasts and osteoblasts, how XBP1 affects the immune microenvironment of bone remodeling by influencing the differentiation of immune cells, and predict the possible future research directions of XBP1 to provide new insights for the treatment of bone-related metabolic diseases.

Role and Mechanism of Endoplasmic Reticulum Stress in Mice Pancreatic Islet Dysfunction After Severe Burns

This study attempted to investigate the role and mechanism of endoplasmic reticulum (ER) stress in the islet dysfunction in mice after severe burns. C57BL/6 mice were randomly divided into the sham group, burn group, and burn+4-phenylbutyric acid (4-PBA) group. Mice were burned with full thickness of 30% total surface area (TBSA), and 4-PBA solution was intraperitoneally injected into mice in burn+4-PBA group. Glucose-stimulated insulin secretion (GSIS), Fasting blood glucose (FBG) and glucose tolerance were detected 24 hours post severe burns. The ER stress-related pathway markers immunoglobulin binding protein (BIP), X-box binding protein 1 (XBP1), phosphorylation-PKR-like ER kinase (p-PERK), phosphorylation-eukaryotic translation initiation factor 2α (p-eIF2α), CHOP, activating transcription factor 6 (ATF6), apoptosis-related protein Cleaved-Caspase 3, and islet cell apoptosis were measured. Mice were characterized with elevated FBG, decreased glucose tolerance and GSIS levels post severe burns. The expression of BIP, XBP1, p-PERK, p-eIF2α, CHOP, ATF6, Cleaved-Caspase 3, and islet cell apoptosis were increased significantly after severe burns. 4-PBA treatment contributed to decreased FBG, improved glucose tolerance, increased GSIS, inhibited islet ER stress, and reduced pancreatic islet cell apoptosis in mice post severe burns. ER stress occurs in islets of severely burned mice, which leads to increased apoptosis of islet cells, thus resulting in islet dysfunction.

Advances in the interaction between endoplasmic reticulum stress and osteoporosis

The endoplasmic reticulum (ER) is the main site for protein synthesis, folding, and secretion, and accumulation of the unfolded/misfolded proteins in the ER may induce ER stress. ER stress is an important participant in various intracellular signaling pathways. Prolonged- or high-intensity ER stress may induce cell apoptosis. Osteoporosis, characterized by imbalanced bone remodeling, is a global disease caused by many factors, such as ER stress. ER stress stimulates osteoblast apoptosis, increases bone loss, and promotes osteoporosis development. Many factors, such as the drug's adverse effects, metabolic disorders, calcium ion imbalance, bad habits, and aging, have been reported to activate ER stress, resulting in the pathological development of osteoporosis. Increasing evidence shows that ER stress regulates osteogenic differentiation, osteoblast activity, and osteoclast formation and function. Various therapeutic agents have been developed to counteract ER stress and thereby suppress osteoporosis development. Thus, inhibition of ER stress has become a potential target for the therapeutic management of osteoporosis. However, the in-depth understanding of ER stress in the pathogenesis of osteoporosis still needs more effort.

Endoplasmic reticulum stress: a novel targeted approach to repair bone defects by regulating osteogenesis and angiogenesis

Bone regeneration therapy is clinically important, and targeted regulation of endoplasmic reticulum (ER) stress is important in regenerative medicine. The processing of proteins in the ER controls cell fate. The accumulation of misfolded and unfolded proteins occurs in pathological states, triggering ER stress. ER stress restores homeostasis through three main mechanisms, including protein kinase-R-like ER kinase (PERK), inositol-requiring enzyme 1ɑ (IRE1ɑ) and activating transcription factor 6 (ATF6), collectively known as the unfolded protein response (UPR). However, the UPR has both adaptive and apoptotic effects. Modulation of ER stress has therapeutic potential for numerous diseases. Repair of bone defects involves both angiogenesis and bone regeneration. Here, we review the effects of ER stress on osteogenesis and angiogenesis, with emphasis on ER stress under high glucose (HG) and inflammatory conditions, and the use of ER stress inducers or inhibitors to regulate osteogenesis and angiogenesis. In addition, we highlight the ability for exosomes to regulate ER stress. Recent advances in the regulation of ER stress mediated osteogenesis and angiogenesis suggest novel therapeutic options for bone defects.

Jintiange proteins promote osteogenesis and inhibit apoptosis of osteoblasts by enhancing autophagy via PI3K/AKT and ER stress pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Tiger bone, which had long been used in traditional Chinese medicine, had the action of removing wind and alleviating pain, strengthening the sinews and bones, and often used to treat bone impediment, and atrophic debility of bones in TCM clinical practice. As a substitute of natural bone tiger, artificial tiger bone Jintiange (JTG), has been approved by the State Food and Drug Administration of China for relief the symptom of osteoporosis, such as lumbago and back pain, lassitude in loin and legs, flaccidity and weakness legs, and walk with difficulty based on TCM theory. JTG has similar chemical profile to natural tiger bone, and contains mineral substance, peptides and proteins, and has been shown to protect bone loss in ovariectomized mice and exert the regulatory effects on osteoblast and osteoclast activities. But how the peptides and proteins in JTG modulate bone formation remains unclear.

AIM

To investigate the stimulating effects of JTG proteins on osteogenesis and explore the possible underlying mechanisms.

MATERIALS AND METHODS

JTG proteins were prepared from JTG Capsules by extracting calcium, phosphorus and other inorganic elements using SEP-PaktC18 desalting column. MC3T3-E1 cells were treated with JTG proteins to evaluate their effects and explore the underlying mechanisms. Osteoblast proliferation was detected by CCK-8 method. ALP activity was detected using a relevant assay kit, and bone mineralized nodules were stained with alizarin red-Tris-HCl solution. Cell apoptosis was analyzed by flow cytometry. Autophagy was observed by MDC staining, and autophagosomes were observed by TEM. Nuclear translocations of LC3 and CHOP were detected by immunofluorescence and observed under a laser confocal microscope. The expression of key proteins related to osteogenesis, apoptosis, autophagy and PI3K/AKT and ER stress pathways was analyzed by Western Blot analysis.

RESULTS

JTG proteins improved osteogenesis as evidenced by the alteration of proliferation, differentiation and mineralization of MC3T3-E1 osteoblasts, inhibited their apoptosis, and enhanced autophagosome formation and autophagy. They also regulated the expression of key proteins of PI3K/AKT and ER stress pathways. In addition, PI3K/AKT and ER stress pathway inhibitors could reverse the regulatory effects of JTG proteins on osteogenesis, apoptosis, autophagy and PI3K/AKT and ER stress pathways.

CONCLUSION

JTG proteins increased the osteogenesis and inhibited osteoblast apoptosis by enhancing autophagy via PI3K/AKT and ER stress signaling pathways.

Pancreatic islet protection at the expense of secretory function involves serine-linked mitochondrial one-carbon metabolism

Type 2 diabetes is characterized by insulin hypersecretion followed by reduced glucose-stimulated insulin secretion (GSIS). Here we show that acute stimulation of pancreatic islets with the insulin secretagogue dextrorphan (DXO) or glibenclamide enhances GSIS, whereas chronic treatment with high concentrations of these drugs reduce GSIS but protect islets from cell death. Bulk RNA sequencing of islets shows increased expression of genes for serine-linked mitochondrial one-carbon metabolism (OCM) after chronic, but not acute, stimulation. In chronically stimulated islets, more glucose is metabolized to serine than to citrate, and the mitochondrial ATP/ADP ratio decreases, whereas the NADPH/NADP+ ratio increases. Activating transcription factor-4 (Atf4) is required and sufficient to activate serine-linked mitochondrial OCM genes in islets, with gain- and loss-of-function experiments showing that Atf4 reduces GSIS and is required, but not sufficient, for full DXO-mediated islet protection. In sum, we identify a reversible metabolic pathway that provides islet protection at the expense of secretory function.

XBP1s gene of endoplasmic reticulum stress enhances proliferation and osteogenesis of human periodontal ligament cells

BACKGROUND

The endoplasmic reticulum stress (ERS) pathway, inositol-requiring enzyme-1 alpha-X-box binding protein-1 (IRE1α-XBP1), has been considered as a critical factor of human periodontal ligament cells (hPDLCs) in proliferation and osteogenesis. This study aimed to explore the effect and mechanism of XBP1s, which was cleaved by IRE1α on the proliferation and osteogenesis of hPDLCs.

METHODS

ERS model was induced by tunicamycin (TM); cell proliferation was assessed by CCK-8 assay; pLVX-XBP1s-hPDLCs cell line was established by lentivirus infaction; expression of ERS-related protein including eIF2α, GRP78, ATF4 and XBP1s, autophagy-related P62 and LC3, and apoptosis-related Bcl-2 and Caspase-3 were detected by Western Blot; expression of osteogenic genes was detected by RT-qPCR, and senescence of hPDLCs was explored by β-galactosidase staining. Furthermore, the interaction between XBP1s and human bone morphogenetic protein 2 (BMP2) was examined by immunofluorescence antibody test (IFAT).

RESULTS

The results showed an increase in proliferation of hPDLCs from 0 to 24 h when ERS was induced by TM treatment (P < 0.05). XBP1s overexpression induced hPDLCs proliferation, upgraded autophagy and degraded apoptosis significantly (P < 0.05). In pLVX-XBP1s-hPDLCs, the ratio of senescent cells was markedly decreased after several passages (P < 0.05); After infection with pLVX-BMP2 lentiviral supernatant, IFAT result showed that XBP1s and BMP2 well co-located in the cytoplasm of pLVX-XBP1s-hPDLCs and PERK-ATF4 ERS branch was activated, meanwhile, there were obviously more mineralized nodules and mRNA expression of osteogenesis-related genes was continually up-regulated (P < 0.05).

CONCLUSIONS

XBP1s promotes the proliferation via regulating the autophagy and apoptosis, and enhances expression of osteogenic genes in hPDLCs. The mechanisms in this regard need exploring further for periodontal tissue regeneration, functionalization and clinical applications.

Titanium dioxide nanoparticles affect osteoblast-derived exosome cargos and impair osteogenic differentiation of human mesenchymal stem cells

Titanium (Ti) and its alloys are the most widely used metallic biomaterials in total joint replacement; however, increasing evidence supports the degradation of its surface due to corrosion and wear processes releasing debris (ions, and micro and nanoparticles) and contribute to particle-induced osteolysis and implant loosening. Cell-to-cell communication involving several cell types is one of the major biological processes occurring during bone healing and regeneration at the implant-bone interface. In addition to the internal response of cells to the uptake and intracellular localization of wear debris, a red flag is the ability of titanium dioxide nanoparticles (mimicking wear debris) to alter cellular communication with the tissue background, disturbing the balance between osseous tissue integrity and bone regenerative processes. This study aims to understand whether titanium dioxide nanoparticles (TiO₂ NPs) alter osteoblast-derived exosome (Exo) biogenesis and whether exosomal protein cargos affect the communication of osteoblasts with human mesenchymal stem/stromal cells (HMSCs). Osteoblasts are derived from mesenchymal stem cells coexisting in the bone microenvironment during development and remodelling. We observed that TiO₂ NPs stimulate immature osteoblast- and mature osteoblast-derived Exo secretion that present a distinct proteomic cargo. Functional tests confirmed that Exos derived from both osteoblasts decrease the osteogenic differentiation of HMSCs. These findings are clinically relevant since wear debris alter extracellular communication in the bone periprosthetic niche, contributing to particle-induced osteolysis and consequent prosthetic joint failure.

Spliced X-Box binding protein 1 predicts satisfying responsiveness and survival benefit toward bortezomib-based therapy in multiple myeloma patients

OBJECTIVE

Spliced X-Box binding protein 1 (sXBP1) modulates malignant cell activities and enhances the bortezomib sensitivity in multiple myeloma (MM) cells, while its clinical value in MM patients remains elusive. Hence, the current study aimed to explore this issue, particularly the correlation of sXBP1 with treatment outcomes of bortezomib-based therapy in MM patients.

METHODS

Totally, 97 newly-diagnosed MM patients undergoing bortezomib-based therapy, 20 disease controls (DCs), and 20 health controls (HCs) were enrolled. Bone marrow plasma cell samples were acquired to determine sXBP1 by RT-qPCR.

RESULTS

sXBP1 was lowest in MM patients, followed by DCs, and highest in HCs (P < 0.001). Beyond that, sXBP1 discriminated MM patients from DCs with area under curve (AUC) of 0.728 (95% confidence interval (CI): 0.610-0.847) and HCs with AUC of 0.855 (95% CI: 0.771-0.939). sXBP1 was negatively associated with t (4; 14) (P = 0.047), Revised International Staging System stage (P = 0.008). There was a trend that sXBP1 was negatively correlated with β₂-MG, LDH, and t (14; 16) (without statistical significance). sXBP1 was higher in patients with complete response (CR) compared to those with non-CR (P = 0.017) and higher in patients with objective response rate (ORR) compared to those with non-ORR (P = 0.006). sXBP1 (high vs. low) was linked with longer progression-free survival (PFS) (P = 0.011) and overall survival (P = 0.045) in MM patients. Additionally, sXBP1 (high vs. low) (P = 0.025) independently estimated a longer PFS.

CONCLUSION

sXBP1 forecasts a favorable treatment response and survival benefit toward bortezomib-based therapy in multiple myeloma patients.

Hepatocyte Growth Factor Promotes Differentiation Potential and Stress Response of Human Stem Cells from Apical Papilla

Harsh local microenvironment, such as hypoxia and lack of instructive clues for transplanted stem cells, presents the serious obstacle for stem cell therapies' efficacy. Therefore, continued efforts have been taken to improve stem cells' viability and plasticity. Hepatocyte growth factor (HGF) has previously been reported to mitigate the complications of various human diseases in animal model studies and in some clinical trials. Besides, human stem cells from the root apical papilla (SCAP) are deemed a better resource of mesenchymal stem cells due to derived stem cells holding greater amplification ability in vitro compared with those from other dental resources. To move forward, evaluating effects and understanding underlying molecular mechanisms of HGF on SCAP for periodontal regeneration are needed. In this study, HGF was transgenically expressed in SCAP, and it was found that HGF enhanced osteo/dentinogenic differentiation capacity of SCAP compared with those of non-treated control in an ectopic mineralization model. Moreover, HGF reduced the apoptosis of SCAP under both normoxic and hypoxic conditions, whereas the combination of HGF and hypoxia exposure had inhibitory effects on cell proliferation during an 8-day in vitro culture period. Transcriptome analysis further revealed that suppressed cell cycle progression and activated BMP/TGFβ, Hedgehog, WNT, FGF, HOX, and other morphogen family members result upon HGF overexpression, which may render SCAP recapitulate part of neural crest stem cell characteristics. Moreover, strengthened stress response modulation such as unfolded protein response, macroautophagy, and anti-apoptotic molecules might explain the increased viability of SCAP. In all, our results imply that these potential mechanisms underlying HGF-promoting SCAP differentiation could be further elucidated and harnessed to improve periodontal tissue regeneration.

IRE1α Inhibitors as a Promising Therapeutic Strategy in Blood Malignancies

Synthesis, folding, and structural maturation of proteins occur in the endoplasmic reticulum (ER). Accumulation of misfolded or unfolded proteins in the ER lumen contributes to the induction of ER stress and activation of the unfolded protein response (UPR) signaling pathway. Under ER stress, the UPR tries to maintain cellular homeostasis through different pathways, including the inositol-requiring enzyme 1 alpha (IRE1α)-dependent ones. IRE1α is located in an ER membrane, and it is evolutionarily the oldest UPR sensor. Activation of IRE1α via ER stress triggers the formation of the spliced form of XBP1 (XBP1s), which has been linked to a pro-survival effect in cancer cells. The role of IRE1α is critical for blood cancer cells, and it was found that the levels of IRE1α and XBP1s are elevated in various hematological malignancies. This review paper is focused on summarizing the latest knowledge about the role of IRE1α and on the assessment of the potential utility of IRE1α inhibitors in blood cancers.

Potential Load-Bearing Bone Substitution Material: Carbon-Fiber-Reinforced Magnesium-Doped Hydroxyapatite Composites with Excellent Mechanical Performance and Tailored Biological Properties

A potential load-bearing bone substitution and repair material, that is, carbon fiber (CF)-reinforced magnesium-doped hydroxyapatite (CF/Mg-HAs) composites with excellent mechanical performance and tailored biological properties, was constructed via the hydrothermal method and spark plasma sintering. A high-resolution transmission electron microscopy (TEM) was employed to characterize the nanostructure of magnesium-doped hydroxyapatite (Mg-HA). TEM images showed that the doping of Mg-induced distortions and dislocations in the hydroxyapatite lattice, resulting in decreased crystallinity and enhanced dissolution. Compressive strengths of 10% magnesium-doped hydroxyapatite (1Mg-HAs) and CF-reinforced 1Mg-HAs (CF/1Mg-HAs) were within the range of that of cortical bone. Compared with 1Mg-HAs, the fracture toughness of CF/1Mg-HAs increased by approximately 38%. The bioactivity, biocompatibility, and osteogenic induction properties of Mg-HAs and CF/Mg-HAs composites were evaluated in vitro using simulated body fluid (SBF) immersion, cell culture, osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), and expression of genes associated with osteogenesis. When Mg-HAs were immersed in SBF, Mg²⁺ continued to release for up to 21 days. Mg-HAs demonstrated a satisfactory ability to induce apatite formation in comparison with HAs. The cell proliferation and morphology on CF/1Mg-HAs were similar to those of 1Mg-HAs, suggesting that adding CF had no adverse effect on cellular activity. The expression levels of osteogenesis-related genes [osteocalcin (OPN), osteopontin (OCN), and runt-related transcription factor 2 (Runx2)] on 1Mg-HAs were significantly higher at days 3 and 7 than those on HAs and 0.5Mg-HAs groups. This finding suggests that a certain amount of Mg doping had beneficial influences in the different stages of osteogenic differentiation and could induce osteogenic differentiation of BMSCs. The new bone volume to total volume ratio of implanted 1Mg-HAs (30.9% ± 4.1%) and CF/1Mg-HAs (25.4% ± 5.4%) was remarkably higher than that of HAs (21.6% ± 3.9%). 1Mg-HAs and CF/1Mg-HAs tailored an ideal effect of new bone information and implant osseointegration. The excellent mechanical performance and tailored biological properties of CF/Mg-HAs were attributed to nano Mg-doped HA, CF reinforcing, refined microstructure, and controlled composition.

Mechanisms, Diagnosis and Treatment of Bone Metastases

Bone and bone marrow are among the most frequent metastatic sites of cancer. The occurrence of bone metastasis is frequently associated with a dismal disease outcome. The prevention and therapy of bone metastases is a priority in the treatment of cancer patients. However, current therapeutic options for patients with bone metastatic disease are limited in efficacy and associated with increased morbidity. Therefore, most current therapies are mainly palliative in nature. A better understanding of the underlying molecular pathways of the bone metastatic process is warranted to develop novel, well-tolerated and more successful treatments for a significant improvement of patients' quality of life and disease outcome. In this review, we provide comparative mechanistic insights into the bone metastatic process of various solid tumors, including pediatric cancers. We also highlight current and innovative approaches to biologically targeted therapy and immunotherapy. In particular, we discuss the role of the bone marrow microenvironment in the attraction, homing, dormancy and outgrowth of metastatic tumor cells and the ensuing therapeutic implications. Multiple signaling pathways have been described to contribute to metastatic spread to the bone of specific cancer entities, with most knowledge derived from the study of breast and prostate cancer. However, it is likely that similar mechanisms are involved in different types of cancer, including multiple myeloma, primary bone sarcomas and neuroblastoma. The metastatic rate-limiting interaction of tumor cells with the various cellular and noncellular components of the bone-marrow niche provides attractive therapeutic targets, which are already partially exploited by novel promising immunotherapies.

HA15 alleviates bone loss in ovariectomy-induced osteoporosis by targeting HSPA5

The imbalance between osteogenesis and adipogenesis in the bone marrow is the main characteristic of osteoporosis (OP). Thus, exploring regulation of the differentiation of bone marrow stromal cells (BMSCs) into osteoblasts and adipocytes is important to identify novel targets for the treatment of OP. In the present study, the master regulator of endoplasmic reticulum (ER) stress, heat shock protein family A (Hsp70) member 5 (HSPA5) was shown to significantly accumulate in osteoblasts and adipocytes, but not in osteoclasts in bone sections from aged and postmenopausal OP mice. In vitro study revealed that HSPA5 negatively modulated osteogenic differentiation and positively promoted adipogenic differentiation, and that targeting HSPA5 with its inhibitor HA15 enhanced osteogenic differentiation and inhibited adipogenic differentiation. Also, HA15 treatment induces ER stress and autophagy, and decreases apoptosis in cells. We constructed a postmenopausal OP model in mice with ovariectomy surgery, and treated the mice with HA15. The results showed that HA15 treatment induced appropriate ER stress, activated autophagy and decreased apoptosis in osteoblasts, thereby alleviating bone loss in vivo. Our results indicated that HSPA5 participated in OP pathogenesis by regulating the differentiation of BMSCs. HSPA5 may serve as a new target for the treatment of OP, and targeting HSPA5 with HA15 prevents the progression of OP and provides a candidate therapeutic molecule for postmenopausal OP.

Expression and Role of Ubiquitin-Specific Peptidases in Osteoblasts

The ubiquitin-proteasome system regulates biological processes in normal and diseased states. Recent investigations have focused on ubiquitin-dependent modifications and their impacts on cellular function, commitment, and differentiation. Ubiquitination is reversed by deubiquitinases, including ubiquitin-specific peptidases (USPs), whose roles have been widely investigated. In this review, we explore recent findings highlighting the regulatory functions of USPs in osteoblasts and providing insight into the molecular mechanisms governing their actions during bone formation. We also give a brief overview of our work on USP53, a target of PTH in osteoblasts and a regulator of mesenchymal cell lineage fate decisions. Emerging evidence addresses questions pertaining to the complex layers of regulation exerted by USPs on osteoblast signaling. We provide a short overview of our and others' understanding of how USPs modulate osteoblastogenesis. However, further studies using knockout mouse models are needed to fully understand the mechanisms underpinning USPs actions.

Carfilzomib Improves Bone Metabolism in Patients with Advanced Relapsed/Refractory Multiple Myeloma: Results of the CarMMa Study

Simple Summary

Carfilzomib with dexamethasone is an important therapeutic option for patients with relapsed/refractory multiple myeloma. We sought to evaluate the effect of this regimen on the bone-related outcomes, which are associated with both quality of life and survival. Among 25 patients, less than one third experienced a new skeletal-related event during treatment, even in the absence of any bone-targeted agent. Interestingly, there was a significant decrease in serum biomarkers of bone resorption, which was at least partially due to the sRANKL/OPG ratio reduction. Furthermore, Kd produced an increase in markers of bone formation. Importantly, these changes were independent of myeloma response to treatment. Therefore, the combination of carfilzomib and dexamethasone improves bone metabolism and bone health in patients with advanced multiple myeloma.

Abstract

Carfilzomib with dexamethasone (Kd) is a well-established regimen for the treatment of relapsed/refractory multiple myeloma (RRMM). There is limited information for the effects of Kd on myeloma-related bone disease. This non-interventional study aimed to assess skeletal-related events (SREs) and bone metabolism in patients with RRMM receiving Kd, in the absence of any bone-targeted agent. Twenty-five patients were enrolled with a median of three prior lines of therapy; 72% of them had evidence of osteolytic bone disease at study entry. During Kd treatment, the rate of new SREs was 28%. Kd produced a clinically relevant (≥30%) decrease in C-telopeptide of collagen type-1 (p = 0.048) and of tartrate-resistant acid phosphatase-5b (p = 0.002) at 2 months. This reduction was at least partially due to the reduction in the osteoclast regulator RANKL/osteoprotegerin ratio, at 2 months (p = 0.026). Regarding bone formation, there was a clinically relevant increase in osteocalcin at 6 months (p = 0.03) and in procollagen type I N-propeptide at 8 months post-Kd initiation. Importantly, these bone metabolism changes were independent of myeloma response to treatment. In conclusion, Kd resulted in a low rate of SREs among RRMM patients, along with an early, sustained and clinically relevant decrease in bone resorption, which was accompanied by an increase in bone formation, independently of myeloma response and in the absence of any bone-targeted agent use.