Osteosarcoma (OS) is the most common primary malignant bone tumor mainly affecting children and young adults. Despite current treatments combining polychemotherapy and surgery, survival rates have remained unchanged for decades, highlighting the need to identify novel therapeutic approaches. NXP800, a newly developed orally available molecule, represents a promising therapeutic option. The therapeutic efficacy of NXP800 was evaluated in vitro and in a preclinical murine xenograft model of OS. RNA-seq analysis and functional assays were conducted to investigate the mechanisms of action and molecular target of NXP800. NXP800 decreases the viability of OS cell lines by blocking proliferation and inducing apoptosis. Mechanistically, NXP800 activates the Unfolded Protein Response (UPR), as demonstrated by eIF2α phosphorylation and ATF4 upregulation. This effect is mediated through the engagement of the Integrated Stress Response (ISR) via the activation of GCN2 kinase. Inhibition of GCN2, either through molecular or pharmacological approaches, abolishes NXP800-induced eIF2α phosphorylation and partially restores OS cell viability. Furthermore, NXP800 activates the IRE1α/JNK/c-Jun pathway while increasing the expression of the pro-apoptotic protein Puma. Finally, NXP800 delays tumor growth in preclinical OS model by promoting apoptosis. This study is a preclinical proof-of-principle of therapeutic efficacy of NXP800 both in vitro and in vivo, highlighting the relevance of targeting GCN2, and consequently activating the ISR and UPR, to induce apoptosis and inhibit tumor progression in OS.

Pompe disease is an autosomal recessive metabolic disorder caused by acid alpha-glucosidase deficiency, characterized by progressive skeletal muscle weakness and respiratory insufficiency. Affected muscles exhibit glycogen-filled lysosomes, autophagic build-up, and mitochondrial abnormalities. Despite global myofibrillar disorganization, satellite cells (SCs) fail to activate, due to mechanisms that remain unclear. This study aimed to further characterize the muscle phenotype in Pompe disease, with particular attention to proteins associated with membrane repair processes, as membrane damage is a primary trigger for SC activation. Longitudinal transcriptomic analysis of skeletal muscle from a Pompe disease mouse model, combined with immunohistochemical and biochemical approaches, showed early and sustained overexpression of dysferlin (DYSF), annexin A2 (ANXA2), and AHNAK2. These membrane repair-associated proteins displayed abnormal localization during disease progression, with sarcoplasmic accumulation associated with T-tubules, lysosomes and autophagosomes, respectively. Analysis of muscle biopsies from some patients with late-onset Pompe disease (LOPD) identified similar expression patterns in moderately affected cases, whereas these patterns were less evident or absent in the most severe samples, suggesting stage-dependent redistribution associated with advanced myoarchitectural disorganization. Furthermore, in the mouse model, we observed persistent post-transcriptional accumulation of mature myostatin (MSTN), a key negative regulator of muscle growth, alongside a decrease in the phospho-SMAD3/SMAD3 ratio and reduced SMAD7 expression, which point toward a more complex modulation of its canonical bioactivity rather than a simple increase. Altogether, these findings identify modified distribution proteins linked to membrane repair and dysregulation of MSTN as features of muscle remodeling in Pompe disease.

Pompe disease is an autosomal recessive metabolic disorder caused by acid alpha-glucosidase deficiency, characterized by progressive skeletal muscle weakness and respiratory insufficiency. Affected muscles exhibit glycogen-filled lysosomes, autophagic build-up, and mitochondrial abnormalities. Despite global myofibrillar disorganization, satellite cells (SCs) fail to activate, due to mechanisms that remain unclear. This study sought to comprehensively characterize the phenotypic features of affected muscles in Pompe disease, focusing in particular on membrane repair processes, as membrane damage is a primary trigger for SC activation. Longitudinal transcriptomic analysis of muscle from a Pompe disease mouse model, combined with immunohistochemical and biochemical analyses, showed early and sustained overexpression of dysferlin (DYSF), annexin A2 (ANXA2), and AHNAK2, proteins involved in membrane repair. Abnormal localization of these proteins was observed throughout the disease course, as evidenced by sarcoplasmic accumulation at lysosomes, autophagosomes, and T-tubules, respectively. These alterations suggest a compensatory mechanism to preserve the integrity of intracellular structures. Analysis of muscle biopsies from patients with late-onset Pompe disease (LOPD) suggested sarcoplasmic localization of DYSF, ANXA2 and AHNAK2 that correlated with the severity of the histological phenotype. Moreover, in the mouse model, we observed persistent post-transcriptional accumulation of mature myostatin, a key negative regulator of muscle growth, which may contribute to impaired SC activation and the absence of muscle regeneration despite extensive tissue damage. In conclusion, our findings identified differential expression of proteins associated with intracellular membrane repair and dysregulation of myostatin as key markers in the course of Pompe disease. These insights provide new perspectives on the underlying pathophysiology and point to novel therapeutic avenues for limiting disease-associated damage.

This chapter is a revised version of the first Edition which aims to describe a method used to evaluate gene expression and microRNAs (miRNAs) in bone cells or bone tissue using Reverse transcription and quantitative Polymerase Chain Reaction (RT-qPCR), and methods to assess chromogenic in situ hybridization (CISH) on Formalin Fixed Paraffin Embedded (FFPE) mouse bone tissue to detect both DNA and mRNA transcripts using the double digoxigenin (DIG) locked nucleic acid (LNA™) probes or using RNAscope technology.

Osteosarcoma is medically defined as a bone-forming tumor with associated bone-degrading activity. There is a lack of knowledge about the network that generates the overproduction of bone. We studied the early stage of osteosarcoma development with mice enduring a periosteum injection of osteosarcoma cells at the proximal third of the tibia. On day 7 (D7), tumor cells activate the over-synthesis of bone-like material inside the medulla. This overproduction of bone is quickly (D13) followed by degradation. Samples were characterized by microfocus small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), optical and electron microscopies, and micro-indentation. This intramedullary apatite-collagen composite synthesis highlights an unknown network of bone synthesis stimulation by extramedullary osteosarcoma cells. This synthesis activation mechanism, coupled with the well-known bone induced osteosarcoma growth activation, produces a rare synergy that may enlighten the final osteosarcoma morphology. With this aim, a 3D cellular automaton was developed that only included two rules. Simulations can accurately reproduce the bi-continuous sponge macroscopic structure that was analyzed from mice tumor micro-tomography. This unknown tumor activation pathway of bone synthesis, combined with the known bone activation of tumor growth, generates a positive feedback synergy explaining the unusual sponge-like morphology of this bone cancer. From a biomaterials point of view, how nature controls self-assembly processes remains an open question. Here, we show how the synergy between two biological growth processes is responsible for the complex morphology of a bone tumor. This highlights how hierarchical morphologies, accurately defined from the nanometer to the centimeter scale, can be controlled by positive feedback between the self-assembly of a scaffold and the deposition of solid material.

Rationale: During development, the contribution of IL34, a ligand of macrophage colony stimulating factor receptor (MCSFR), has not been fully defined. Together with its twin cytokine MCSF, they display an essential role in macrophage differentiation and activation, including tissue specialized macrophages. The mechanism of action of each molecule involves the phosphorylation of MCSFR in varying intensity and kinetics. Furthermore, IL34 can interact with other receptors and cofactors, opening a wide range of modulations during development. The aim of this work was to investigate these effects through the suppression of IL34 in different animal models and study molecular interactions, with a particular focus on osteoclast / osteoblast regulation. Methods: Two different and unique models of IL34-/- were generated in zebrafish and mouse. The skeleton of both species was analyzed and compared by histological and morphometric (Micro-CT) approaches. The role of IL34 and new partners in osteoclast and osteoblast differentiation was analyzed by multiple techniques including mineralization assays, tartrate resistant acid phosphatase (TRAP) staining, receptor phosphorylation and activation assays, and gene expression (real-time quantitative PCR) studies. Furthermore, protein interactions were studied by surface plasmon resonance approach and protein-protein docking ClusPro analysis. Results: Significant growth delay and hypo-mineralization of skeletal elements were observed in both IL34-/- models, as well as craniofacial dysmorphoses in mice. With regard to bone cells, an unexpected increase in the number of osteoclasts and an accumulation of pre-osteoblasts were observed in mice lacking IL34. For the first time, in vitro analyses complemented by protein binding and molecular docking studies established that IL34 interacts directly with certain Bone Morphogenetic Proteins (BMPs), modulating their various activities such as the stimulation of osteoblast differentiation. Conclusions: A new mechanism of action for IL34 through BMPs has been characterized. IL34 interactions with MCSFR and BMPs appear crucial for both osteoclastogenesis and osteoblastogenesis, impacting bone tissue homeostasis and development. The potential interaction of IL34 with different members of the BMP family and their functional impact, including pathological situations such as cancer, should be further explored, opening new therapeutic perspectives.

During growth, the contribution of IL34, a ligand of MCSFR, have not been established. The aim of this work was therefore to establish these implications using two models of IL34 invalidation generated in zebrafish and mouse. Significant growth delay and hypo-mineralization of skeletal elements were observed in both models, as well as craniofacial dysmorphoses in mice. With regard to bone cells, an unexpected increase in the number of osteoclasts and an accumulation of pre-osteoblasts were observed. In vitro analyses complemented by protein binding and molecular docking studies established that IL34 interacts directly with certain Bone Morphogenetic Proteins, modulating their various activities such as the stimulation of osteoblast differentiation. A new mechanism of action for IL34 has thus been characterized, opening up new therapeutic perspectives.

ObjectivesInvestigation of the therapeutic effect of zoledronic acid (ZA) in a preclinical model of jaw osteosarcoma (JO).Materials and MethodsThe effect of 100 mu g/kg ZA administered twice a week was assessed in a xenogenic mouse model of JO. The clinical (tumor growth, development of lung metastasis), radiological (bone microarchitecture by micro-CT analysis), and molecular and immunohistochemical (TRAP, RANK/RANKL, VEGF, and CD146) parameters were investigated.ResultsAnimals receiving ZA exhibited an increased tumor volume compared with nontreated animals (71.3 +/- 14.3 mm3 vs. 51.9 +/- 19.9 mm3 at D14, respectively; p = 0.06) as well as increased numbers of lung metastases (mean 4.88 +/- 4.45 vs. 0.50 +/- 1.07 metastases, respectively; p = 0.02). ZA protected mandibular bone against tumor osteolysis (mean bone volume of 12.81 +/- 0.53 mm3 in the ZA group vs. 11.55 +/- 1.18 mm3 in the control group; p = 0.01). ZA induced a nonsignificant decrease in mRNA expression of the osteoclastic marker TRAP and an increase in RANK/RANKL bone remodeling markers.ConclusionThe use of bisphosphonates in the therapeutic strategy for JO should be further explored, as should the role of bone resorption in the pathophysiology of the disease.

Ewing sarcoma (ES) is characterized by EWS::FLI1 or EWS::ERG fusion proteins. Knowing that ion channels are involved in tumorigenesis, this work aimed to study the involvement of the KCNN1 gene, which encodes the SK1 potassium channel, in ES development. Bioinformatics analyses from databases were used to study KCNN1 expression in patients and cell lines. Molecular approaches and in vitro assays were used to study the transcriptional regulation of KCNN1 and its involvement in the regulation of ES cell proliferation. KCNN1 is overexpressed in ES patient biopsies, and its expression is inversely correlated with patient survival. EWS::FLI1, like EWS::ERG, promotes KCNN1 and SK1 expression, binding to GGAA microsatellites near the promoter of KCNN1 isoforms. KCNN1 is involved in the regulation of ES cell proliferation, with its silencing being associated with a slowing of the cell cycle, and its expression modulates membrane potential and therefore calcium flux. These results highlight that KCNN1 is a direct target of EWS::FLI1 and EWS::ERG and demonstrate that KCNN1 is involved in the regulation of intracellular calcium activity and ES cell proliferation, making it a promising therapeutic target in ES.

We describe the case report of an Osteosarcoma patient, with a Li-Fraumeni Syndrome, presenting with a pathological femoral fracture. The patient was treated with a multidisciplinary approach associating neoadjuvant and adjuvant chemotherapy with excisional surgery. The femoral reconstruction consisted of a ``Capasquelet'' reconstruction combining an induced membrane and a vascularized fibula allograft allowing a good functional result with an early weight-bearing. We managed to complete our histological analysis in this patient, in order to evaluate the tumor vascularization. Indeed, using the syngeneic osteosarcoma MOS-J mouse model, we highlighted previously that CD31+/\ensuremath{\alpha }-SMA+ vessels may be indicators of vasculature normalization and therefore may be used as specific markers of a good therapeutic response. Thus, we search for its interest in this specific case as preliminary work. The aim was to assess the feasibility and technical validity of the vascularization analysis of a human osteosarcoma tumor specimen. Therefore, we propose an immunohistochemistry methodology with multiplexed immunofluorescence to assess the vascularization as a promising marker in human osteosarcoma tissue.

p63 and p73 regulate SMAD4 and TβRII.

miR-527 and miR-665 regulate metastasis dissemination in vivo.

Supp. Figure 3. Tumors were collected after 42 days and HSP70, MET; FAK and MMP9 were evaluated by immunohistochemical analysis. Specimens were scored and estimated in percentage of positive cells.

Legend for Supplementary Figures S1-S6

p63-regulated microRNAs target the TGFβ pathway.

Classically, particle-induced periprosthetic osteolysis at the implant–bone interface has explained the aseptic loosening of joint replacement. This response is preceded by triggering both the innate and acquired immune response with subsequent activation of osteoclasts, the bone-resorbing cells. Although particle-induced periprosthetic osteolysis has been considered a foreign body chronic inflammation mediated by myelomonocytic-derived cells, current reports describe wide heterogeneous inflammatory cells infiltrating the periprosthetic tissues. This review aims to discuss the role of those non-myelomonocytic cells in periprosthetic tissues exposed to wear particles by showing original data. Specifically, we discuss the role of T cells (CD3+, CD4+, and CD8+) and B cells (CD20+) coexisting with CD68+/TRAP− multinucleated giant cells associated with both polyethylene and metallic particles infiltrating retrieved periprosthetic membranes. This review contributes valuable insight to support the complex cell and molecular mechanisms behind the aseptic loosening theories of orthopedic implants.

AbstractEwing sarcoma (ES) is characterized by chimeric fusion proteins, which act as oncogenes. Over the last decade, patient survival has not increased, especially for high risk patients. Knowing that ion channels are studied for their implication in tumorigenesis, the aim of this work is to study the involvement of the SK1 potassium channels in ES. RNA-Seq analyses showed a high restricted expression ofKCNN1, the gene encoding SK1, only in ES patients, and its expression is inversely correlated with patient survival. EWS-FLI1 silencing demonstrated the regulation ofKCNN1by these fusion proteins, which bind at GGAA microsatellites nearKCNN1promoter. In addition,KCNN1has been shown to be involved in the regulation of ES cell proliferation, its silencing being associated with a slowing of the cell cycle. Finally,KCNN1expression modulates membrane potential and calcium flux suggesting the role of calcium inKCNN1driving cell proliferation. These results highlight thatKCNN1is a direct EWS-FLI1 and EWS-ERG target, and is involved in the regulation of ES cell proliferation, making it an interesting therapeutic target in ES.

<p>The p63 and p73-controlled miR network regulates TGFβ induced migration.</p>

Bone destruction is a hallmark of chronic inflammation, and bone-resorbing osteoclasts arising under such a condition differ from steady-state ones. However, osteoclast diversity remains poorly explored. Here, we combined transcriptomic profiling, differentiation assays and in vivo analysis in mouse to decipher specific traits for inflammatory and steady-state osteoclasts. We identified and validated the pattern-recognition receptors (PRR) Tlr2, Dectin-1, and Mincle, all involved in yeast recognition as major regulators of inflammatory osteoclasts. We showed that administration of the yeast probiotic Saccharomyces boulardii CNCM I-745 (Sb) in vivo reduced bone loss in ovariectomized but not sham mice by reducing inflammatory osteoclastogenesis. This beneficial impact of Sb is mediated by the regulation of the inflammatory environment required for the generation of inflammatory osteoclasts. We also showed that Sb derivatives as well as agonists of Tlr2, Dectin-1, and Mincle specifically inhibited directly the differentiation of inflammatory but not steady-state osteoclasts in vitro. These findings demonstrate a preferential use of the PRR-associated costimulatory differentiation pathway by inflammatory osteoclasts, thus enabling their specific inhibition, which opens new therapeutic perspectives for inflammatory bone loss.

Background-The purpose of this study was to investigate the bone resorption, as well as the vascular and immune microenvironment, of jaw osteosarcomas (JO) and to correlate these features with patient clinical outcomes. Methods-We studied 50 JO biopsy samples by immunohistochemical analysis of tissue microarrays (TMAs). We investigated the bone remodeling markers RANK/RANKL/OPG, the endothelial glycoprotein CD146, and biomarkers of the immune environment (CD163 and CD68 of macrophages, CD4+ and CD8+ of tumor-infiltrating lymphocytes (TILs), and an immune checkpoint PD-1/PD-L1). The biomarkers were analyzed for their influence on progression (recurrence and metastasis), overall survival (OS), and disease-free survival (DFS). Results-A strong and significant correlation has been found between CD163 staining and lower OS and DFS. The level of CD4+ and CD8+ staining was low and non-significantly associated with survival outcomes. High levels of RANK and RANKL were found in the tumor samples and correlated with lower DFS. Conclusion-Our findings suggest that CD163+ TAMs represent markers of poor prognosis in JO. Targeting TAMs could represent a valuable therapeutic strategy in JO.