TMBIM6 deficiency leads to bone loss by accelerating osteoclastogenesis

Skeletal and dental tissue mineralization: The potential role of the endoplasmic reticulum/Golgi complex and the endolysosomal and autophagic transport systems

This paper presents a review of the potential role of the endoplasmic reticulum/Golgi complex and intracellular vesicles in mediating events leading to or associated with vertebrate tissue mineralization. The possible importance of these organelles in this process is suggested by observations that calcium ions accumulate in the tubules and lacunae of the endoplasmic reticulum and Golgi. Similar levels of calcium ions (approaching millimolar) are present in vesicles derived from endosomes, lysosomes and autophagosomes. The cellular level of phosphate ions in these organelles is also high (millimolar). While the source of these ions for mineral formation has not been identified, there are sound reasons for considering that they may be liberated from mitochondria during the utilization of ATP for anabolic purposes, perhaps linked to matrix synthesis. Published studies indicate that calcium and phosphate ions or their clusters contained as cargo within the intracellular organelles noted above lead to formation of extracellular mineral. The mineral sequestered in mitochondria has been documented as an amorphous calcium phosphate. The ion-, ion cluster- or mineral-containing vesicles exit the cell in plasma membrane blebs, secretory lysosomes or possibly intraluminal vesicles. Such a cell-regulated process provides a means for the rapid transport of ions or mineral particles to the mineralization front of skeletal and dental tissues. Within the extracellular matrix, the ions or mineral may associate to form larger aggregates and potential mineral nuclei, and they may bind to collagen and other proteins. How cells of hard tissues perform their housekeeping and other biosynthetic functions while transporting the very large volumes of ions required for mineralization of the extracellular matrix is far from clear. Addressing this and related questions raised in this review suggests guidelines for further investigations of the intracellular processes promoting the mineralization of the skeletal and dental tissues.

Denatonium inhibits RANKL-induced osteoclast differentiation and rescues the osteoporotic phenotype by blocking p65 signaling pathway

BACKGROUND

Bone remodeling is a critical process that maintains skeletal integrity, orchestrated by the balanced activities of osteoclasts, which resorb bone, and osteoblasts, which form bone. Osteoclastogenesis, the formation of osteoclasts, is primarily driven by NFATc1, a process activated through c-Fos and NF-κB signaling pathways in response to receptor activator of nuclear factor κB ligand (RANKL). Dysregulation of RANKL signaling is a key contributor to pathological bone loss, as seen in conditions such as osteoporosis.

METHODS

We investigated the effects of denatonium, a known bitter compound, on RANKL-induced osteoclast differentiation. We used RNA sequencing (RNA-seq) to analyze gene expression profiles in osteoclast precursors treated with denatonium. Transcription factor prediction analysis was conducted to identify key targets of denatonium action. Additionally, we performed Western blotting to examine the phosphorylation status of AKT and p65, crucial components of the NF-κB pathway. Chromatin immunoprecipitation (ChIP) assays were employed to assess the binding of p65 to promoter regions of osteoclast-related genes. Finally, we tested the therapeutic potential of denatonium in a mouse model of osteoporosis.

RESULTS

Our findings demonstrated that denatonium significantly inhibited RANKL-induced osteoclastogenesis by targeting the p65 pathway. RNA-seq analysis revealed a downregulation of osteoclast-related genes following denatonium treatment, corroborated by transcription factor prediction analysis, which highlighted p65 as a key target. Denatonium effectively blocked the phosphorylation of AKT and p65, key steps in NF-κB activation. ChIP assays further confirmed that denatonium reduced the enrichment of p65 at promoter regions critical for osteoclast differentiation. In vivo, denatonium treatment in an osteoporosis animal model led to a significant restoration of bone health, demonstrating its potential as a therapeutic agent.

CONCLUSIONS

This study identifies denatonium as an inhibitor of RANKL-induced osteoclast differentiation, potentially acting through suppression of the p65 signaling pathway. The ability of denatonium to downregulate osteoclast-related genes and inhibit key signaling events highlights its potential as a candidate for further investigation in the context of bone loss and osteoporosis.

The CD163/TWEAK/Fn14 axis: A potential therapeutic target for alleviating inflammatory bone loss

Objective

Osteoclast (OC) over-activation is an important cause of bone loss that is strongly correlated with inflammation. Although the CD163/TWEAK/Fn14 axis has been implicated in several inflammatory pathologies, its contributions to inflammatory bone loss remain poorly understood. This study aimed to evaluate the interaction of the CD163/TWEAK/Fn14 axis with OC in inflammatory bone loss.

Methods

To assess the role of CD163 in bone homeostasis, we characterized the bone phenotypes of CD163-deficient mice and their wild-type littermates. CD163 and TWEAK levels were evaluated in the bone marrow of mice with LPS-induced bone loss and individuals with rheumatoid arthritis (RA). Bone mass changes were assessed using uCT and histology following supplementation with recombinant mouse CD163 protein (rCD163) or blockade of TWEAK/Fn14 signaling in CD163-deficient mice and mice with LPS-induced bone loss. The impact of CD163/TWEAK on OC differentiation and bone resorption capacity was analyzed in vitro.

Results

CD163 deficiency caused decreased bone mass and increased OC abundance. Lower CD163 expression and higher TWEAK expression were observed in the bone marrow of mice with LPS-induced bone loss and individuals with RA. TWEAK, mainly derived from CD68+ macrophages, was responsible for bone loss, and supplementing rCD163 or blocking TWEAK/Fn14 signaling contributed to rescue bone loss. TWEAK/Fn14 synergistically promoted RANKL-dependent OC differentiation and bone resorption capability through downstream mitogen-activated protein kinases (MAPK) signaling, while the pro-osteoclastic effect of TWEAK was suppressed by CD163.

Conclusion

Our findings suggest that the CD163/TWEAK/Fn14 axis is a potential therapeutic target for inflammatory bone loss by regulating osteoclastogenesis.

Inhibition of insulin degrading enzyme suppresses osteoclast hyperactivity via enhancing Nrf2-dependent antioxidant response in glucocorticoid-induced osteonecrosis of the femoral head

BACKGROUND

Osteoclast hyperactivation due to the pathological overproduction of reactive oxygen species (ROS) stimulated by glucocorticoids (GCs) is one of the key drivers behind glucocorticoid-induced osteonecrosis of the femoral head (GIONFH). The insulin degrading enzyme (IDE), a conserved Zn2+ metallo-endopeptidase, facilitates the DNA binding of glucocorticoid receptor and plays a substantial role in steroid hormone-related signaling pathways. However, the potential role of IDE in the pathogenesis of GIONFH is yet undefined.

METHODS

In this study, we employed network pharmacology and bioinformatics analysis to explore the impact of IDE inhibition on GIONFH with 6bK as an inhibitory agent. Further evidence was collected through in vitro osteoclastogenesis experiments and in vivo evaluations involving methylprednisolone (MPS)-induced GIONFH mouse model.

RESULTS

Enrichment analysis indicated a potential role of 6bK in redox regulation amid GIONFH development. In vitro findings revealed that 6bK could attenuate GCs-stimulated overactivation of osteoclast differentiation by interfering with the transcription and expression of key osteoclastic genes (Traf6, Nfatc1, and Ctsk). The use of an H2DCFDA probe and subsequent WB assays introduced the inhibitory effects of 6bK on osteoclastogenesis, linked with the activation of the nuclear factor erythroid-derived 2-like 2 (Nrf2)-mediated antioxidant system. Furthermore, Micro-CT scans validated that 6bK could alleviate GIONFH in MPS-induced mouse models.

CONCLUSIONS

Our findings suggest that 6bK suppresses osteoclast hyperactivity in GCs-rich environment. This is achieved by reducing the accumulation of intracellular ROS via promoting the Nrf2-mediated antioxidant system, thus implying that IDE could be a promising therapeutic target for GIONFH.

Engineered Niobium Carbide MXenzyme-Integrated Self-Adaptive Coatings Inhibiting Periprosthetic Osteolysis by Orchestrating Osteogenesis-Osteoclastogenesis Balance

Periprosthetic osteolysis induced by the ultrahigh-molecular-weight polyethylene (UHMWPE) wear particles is a major complication associated with the sustained service of artificial joint prostheses and often necessitates revision surgery. Therefore, a smart implant with direct prevention and repair abilities is urgently developed to avoid painful revision surgery. Herein, we fabricate a phosphatidylserine- and polyethylenimine-engineered niobium carbide (Nb2C) MXenzyme-coated micro/nanostructured titanium implant (PPN@MNTi) that inhibits UHMWPE particle-induced periprosthetic osteolysis. The specific mechanism by which PPN@MNTi operates involves the bioresponsive release of nanosheets from the MNTi substrate within an osteolysis microenvironment, initiated by the cleavage of a thioketal-dopamine molecule sensitive to reactive oxygen species (ROS). Subsequently, functionalized Nb2C MXenzyme could target macrophages and escape from lysosomes, effectively scavenging intracellular ROS through its antioxidant nanozyme-mimicking activities. This further achieves the suppression of osteoclastogenesis by inhibiting NF-κB/MAPK and autophagy signaling pathways. Simultaneously, based on the synergistic effect of MXenzyme-integrated coatings and micro/nanostructured topography, the designed implant promotes the osteogenic differentiation of bone mesenchymal stem cells to regulate bone homeostasis, further achieving advanced osseointegration and alleviable periprosthetic osteolysis in vivo. This study provides a precise prevention and repair strategy of periprosthetic osteolysis, offering a paradigm for the development of smart orthopedic implants.

Redox signaling and antioxidant defense in osteoclasts

Bone remodeling is essential for the repair and replacement of damaged or aging bones. Continuous remodeling is necessary to prevent the accumulation of bone damage and to maintain bone strength and calcium balance. As bones age, the coupling mechanism between bone formation and absorption becomes dysregulated, and bone loss becomes dominant. Bone development and repair rely on interaction and communication between osteoclasts and surrounding cells. Osteoclasts are specialized cells that are accountable for bone resorption and degradation, and any abnormalities in their activity can result in notable alterations in bone structure and worsen disease symptoms. Recent findings from transgenic mouse models and bone analysis have greatly enhanced our understanding of the origin, differentiation pathway, and activation stages of osteoclasts. In this review, we explore osteoclasts and discuss the cellular and molecular events that drive their generation, focusing on intracellular oxidative and antioxidant signaling. This knowledge can help develop targeted therapies for diseases associated with osteoclast activation.

Molecular landscapes of glioblastoma cell lines revealed a group of patients that do not benefit from WWOX tumor suppressor expression

Introduction

Glioblastoma (GBM) is notorious for its clinical and molecular heterogeneity, contributing to therapeutic failure and a grim prognosis. WWOX is one of the tumor suppressor genes important in nervous tissue or related pathologies, which was scarcely investigated in GBM for reliable associations with prognosis or disease progression despite known alterations. Recently, we observed a phenotypic heterogeneity between GBM cell lines (U87MG, T98G, U251MG, DBTRG-05MG), among which the anti-GBM activity of WWOX was generally corresponding, but colony growth and formation were inconsistent in DBTRG-05MG. This prompted us to investigate the molecular landscapes of these cell lines, intending to translate them into the clinical context.

Methods

U87MG/T98G/U251MG/DBTRG-05MG were subjected to high-throughput sequencing, and obtained data were explored via weighted gene co-expression network analysis, differential expression analysis, functional annotation, and network building. Following the identification of the most relevant DBTRG-distinguishing driver genes, data from GBM patients were employed for, e.g., differential expression analysis, survival analysis, and principal component analysis.

Results

Although most driver genes were unique for each cell line, some were inversely regulated in DBTRG-05MG. Alongside driver genes, the differentially-expressed genes were used to build a WWOX-related network depicting protein-protein interactions in U87MG/T98G/U251MG/DBTRG-05MG. This network revealed processes distinctly regulated in DBTRG-05MG, e.g., microglia proliferation or neurofibrillary tangle assembly. POLE4 and HSF2BP were selected as DBTRG-discriminating driver genes based on the gene significance, module membership, and fold-change. Alongside WWOX, POLE4 and HSF2BP expression was used to stratify patients into cell lines-resembling groups that differed in, e.g., prognosis and treatment response. Some differences from a WWOX-related network were certified in patients, revealing genes that clarify clinical outcomes. Presumably, WWOX overexpression in DBTRG-05MG resulted in expression profile change resembling that of patients with inferior prognosis and drug response. Among these patients, WWOX may be inaccessible for its partners and does not manifest its anti-cancer activity, which was proposed in the literature but not regarding glioblastoma or concerning POLE4 and HSF2BP.

Conclusion

Cell lines data enabled the identification of patients among which, despite high expression of WWOX tumor suppressor, no advantageous outcomes were noted due to the cancer-promoting profile ensured by other genes.