Tatiana Gritsaenko1, Valérie Pierrefite-Carle1, Thomas Lorivel2, Véronique Breuil3, Georges F Carle1, Sabine Santucci-Darmanin4. 1. UMR E-4320 TIRO-MATOs CEA/DRF/BIAM, Université Nice Sophia-Antipolis, Faculté de Médecine Nice, 28 avenue de Valombrose, 06107, Nice, France. 2. Institut de Pharmacologie Moléculaire et Cellulaire, UMR7275, CNRS, Université Nice Sophia-Antipolis, 660 route des Lucioles, 06560, Valbonne, France. 3. UMR E-4320 TIRO-MATOs CEA/DRF/BIAM, Université Nice Sophia-Antipolis, Faculté de Médecine Nice, 28 avenue de Valombrose, 06107, Nice, France; Service de Rhumatologie, CHU de Nice, Nice, France. 4. UMR E-4320 TIRO-MATOs CEA/DRF/BIAM, Université Nice Sophia-Antipolis, Faculté de Médecine Nice, 28 avenue de Valombrose, 06107, Nice, France. Electronic address: santucci@unice.fr.
Abstract
BACKGROUND: Uranium is a naturally occurring radionuclide ubiquitously present in the environment. The skeleton is the main site of uranium long-term accumulation. While it has been shown that natural uranium is able to perturb bone metabolism through its chemical toxicity, its impact on bone resorption by osteoclasts has been poorly explored. Here, we examined for the first time in vitro effects of natural uranium on osteoclasts. METHODS: The effects of uranium on the RAW 264.7 monocyte/macrophage mouse cell line and primary murine osteoclastic cells were characterized by biochemical, molecular and functional analyses. RESULTS: We observed a cytotoxicity effect of uranium on osteoclast precursors. Uranium concentrations in the μM range are able to inhibit osteoclast formation, mature osteoclast survival and mineral resorption but don't affect the expression of the osteoclast gene markers Nfatc1, Dc-stamp, Ctsk, Acp5, Atp6v0a3 or Atp6v0d2 in RAW 274.7 cells. Instead, we observed that uranium induces a dose-dependent accumulation of SQSTM1/p62 during osteoclastogenesis. CONCLUSIONS: We show here that uranium impairs osteoclast formation and function in vitro. The decrease in available precursor cells, as well as the reduced viability of mature osteoclasts appears to account for these effects of uranium. The SQSTM1/p62 level increase observed in response to uranium exposure is of particular interest since this protein is a known regulator of osteoclast formation. A tempting hypothesis discussed herein is that SQSTM1/p62 dysregulation contributes to uranium effects on osteoclastogenesis. GENERAL SIGNIFICANCE: We describe cellular and molecular effects of uranium that potentially affect bone homeostasis.
BACKGROUND:Uranium is a naturally occurring radionuclide ubiquitously present in the environment. The skeleton is the main site of uranium long-term accumulation. While it has been shown that natural uranium is able to perturb bone metabolism through its chemical toxicity, its impact on bone resorption by osteoclasts has been poorly explored. Here, we examined for the first time in vitro effects of natural uranium on osteoclasts. METHODS: The effects of uranium on the RAW 264.7 monocyte/macrophage mouse cell line and primary murineosteoclastic cells were characterized by biochemical, molecular and functional analyses. RESULTS: We observed a cytotoxicity effect of uranium on osteoclast precursors. Uranium concentrations in the μM range are able to inhibit osteoclast formation, mature osteoclast survival and mineral resorption but don't affect the expression of the osteoclast gene markers Nfatc1, Dc-stamp, Ctsk, Acp5, Atp6v0a3 or Atp6v0d2 in RAW 274.7 cells. Instead, we observed that uranium induces a dose-dependent accumulation of SQSTM1/p62 during osteoclastogenesis. CONCLUSIONS: We show here that uranium impairs osteoclast formation and function in vitro. The decrease in available precursor cells, as well as the reduced viability of mature osteoclasts appears to account for these effects of uranium. The SQSTM1/p62 level increase observed in response to uranium exposure is of particular interest since this protein is a known regulator of osteoclast formation. A tempting hypothesis discussed herein is that SQSTM1/p62 dysregulation contributes to uranium effects on osteoclastogenesis. GENERAL SIGNIFICANCE: We describe cellular and molecular effects of uranium that potentially affect bone homeostasis.