Inhibition of BET proteins and epigenetic signaling as a potential treatment for osteoporosis

International audienceHistone modifications are important for maintaining the transcription program. BET proteins, an important class of " histone reading proteins " , have recently been described as essential in bone biology. This study presents the therapeutic opportunity of BET protein inhibition in osteoporosis. We find that the pharmacological BET protein inhibitor JQ1 rescues pathologic bone loss in a post-ovariectomy osteoporosis model by increasing the trabecular bone volume and restoring mechanical properties. The BET protein inhibition suppresses osteoclast differentiation and activity as well as the osteoblastogenesis in vitro. Moreover, we show that treated non-resorbing osteoclasts could still activate osteoblast differentiation. In addition, specific inhibition of BRD4 using RNA interference inhibits osteoclast differentiation but strongly activates osteoblast mineralization activity. Mechanistically, JQ1 inhibits expression of the master osteoclast transcription factor NFATc1 and the transcription factor of osteoblast Runx2. These findings strongly support that targeting epigenetic chromatin regulators such as BET proteins may offer a promising alternative for the treatment of bone-related disorders such as osteoporosis

Hypoxia exerts differential effects on the chondrogenic and osteogenic differentiation of human adipose-derived mesenchymal stem cells

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The Intrinsic and Extrinsic Implications of RANKL/RANK Signaling in Osteosarcoma: From Tumor Initiation to Lung Metastases

Background: Osteosarcoma is the most frequent form of malignant pediatric bone tumor. Despite the current therapeutic arsenal, patient life-expectancy remains low if metastases are detected at the time of diagnosis, justifying research into better knowledge at all stages of osteosarcoma ontogenesis and identification of new therapeutic targets. Receptor Activator of Nuclear factor κB (RANK)expression has been reported in osteosarcoma cells, raising the question of Receptor Activator of Nuclear factor κB Ligand (RANKL)/RANK signaling implications in these tumor cells (intrinsic), in addition to previously reported implications through osteoclast activation in the tumor microenvironment (extrinsic). Methods: Based on in vitro and in vivo experimentations using human and mouse osteosarcoma cell lines, the consequences on the main cellular processes of RANK expression in osteosarcoma cells were analyzed. Results: The results revealed that RANK expression had no impact on cell proliferation and tumor growth, but stimulated cellular differentiation and, in an immune-compromised environment, increased the number of lung metastases. The analysis of RANKL, RANK and osteoprotegerin (OPG) expressions in biopsies of a cohort of patients revealed that while RANK expression in osteosarcoma cells was not significantly different between patients with or without metastases at the time of diagnosis, the OPG/RANK ratio decreased significantly. Conclusion: Altogether, these results are in favor of RANKL-RANK signaling inhibition as an adjuvant for the treatment of osteosarcoma

Sonic Hedgehog Signature in Pediatric Primary Bone Tumors: Effects of the GLI Antagonist GANT61 on Ewing’s Sarcoma Tumor Growth

International audienceOsteosarcoma (OS) and Ewing’s sarcoma (ES) are the most common malignant bone tumors in children and adolescents. In many cases, the prognosis remains very poor. The Sonic hedgehog (SHH) signaling pathway, strongly involved in the development of many cancers, regulate transcription via the transcriptional factors Gli1-3. In this context, RNAseq analysis of OS and ES cell lines reveals an increase of some major compounds of the SHH signaling cascade in ES cells, such as the transcriptional factor Gli1. This increase leads to an augmentation of the transcriptional response of Gli1 in ES cell lines, demonstrating a dysregulation of Gli1 signaling in ES cells and thus the rationale for targeting Gli1 in ES. The use of a preclinical model of ES demonstrates that GANT61, an inhibitor of the transcriptional factor Gli1, reduces ES primary tumor growth. In vitro experiments show that GANT61 decreases the viability of ES cell, mainly through its ability to induce caspase-3/7-dependent cell apoptosis. Taken together, these results demonstrates that GANT61 may be a promising therapeutic strategy for inhibiting the progression of primary ES tumors

Sonic Hedgehog Signature in Pediatric Primary Bone Tumors: Effects of the GLI Antagonist GANT61 on Ewing’s Sarcoma Tumor Growth

Osteosarcoma (OS) and Ewing’s sarcoma (ES) are the most common malignant bone tumors in children and adolescents. In many cases, the prognosis remains very poor. The Sonic hedgehog (SHH) signaling pathway, strongly involved in the development of many cancers, regulate transcription via the transcriptional factors Gli1-3. In this context, RNAseq analysis of OS and ES cell lines reveals an increase of some major compounds of the SHH signaling cascade in ES cells, such as the transcriptional factor Gli1. This increase leads to an augmentation of the transcriptional response of Gli1 in ES cell lines, demonstrating a dysregulation of Gli1 signaling in ES cells and thus the rationale for targeting Gli1 in ES. The use of a preclinical model of ES demonstrates that GANT61, an inhibitor of the transcriptional factor Gli1, reduces ES primary tumor growth. In vitro experiments show that GANT61 decreases the viability of ES cell, mainly through its ability to induce caspase-3/7-dependent cell apoptosis. Taken together, these results demonstrates that GANT61 may be a promising therapeutic strategy for inhibiting the progression of primary ES tumors

Loss of connexin43 expression in Ewing's sarcoma cells favors the development of the primary tumor and the associated bone osteolysis

AbstractEwing's sarcoma (ES) is a primary bone tumor characterized by a chromosomic translocation between the EWS gene and a member of the ETS gene family, mainly FLI1, which leads to an aberrant transcription factor EWS–FLI1 that promotes tumorigenicity. Gap junctions are intercellular channels composed of transmembrane proteins (connexin: Cx), that allow direct intercellular communication between adjacent cells. Numerous studies have shown that tumorigenesis may be associated with a loss of gap junctional intercellular communication (GJIC).Loss of Cx43 expression was observed at the protein and mRNA levels in ES cell lines compared to those measured in human mesenchymal stem cells. A673 ES cells stably transfected with an shRNA targeting EWS–FLI1 showed an increase in Cx43 expression (at the mRNA, protein and transcriptional levels) and GJIC. In an osteolytic murine model of ES, the overexpression of Cx43 in ES cells dramatically reduced tumor growth, leading to a significant increase in animal survival. In vitro assays showed that Cx43 overexpression increases the p27 level with an associated marked decrease of Rb phosphorylation, consistent with the observed blockade of the cell cycle in G0/G1 phase. In addition, the bone microarchitectural parameters, assessed by micro-CT analysis, showed an increased bone volume when Cx43 expression was enhanced. Histological analysis demonstrated that the overexpression of Cx43 in ES tumor cells inhibits osteoclast activity and therefore bone resorption.Our study demonstrated that the loss of Cx43 expression in ES cells plays a crucial role in the development of the primary tumor and the associated bone osteolysis