Effect of natural uranium on the UMR-106 osteoblastic cell line: impairment of the autophagic process as an underlying mechanism of uranium toxicity

Abstract

Natural uranium (U), which is present in our environment, exerts a chemical toxicity, particularly in bone where it accumulates. Generally, U is found at oxidation state +VI in its oxocationic form [Formula: see text] in aqueous media. Although U(VI) has been reported to induce cell death in osteoblasts, the cells in charge of bone formation, the molecular mechanism for U(VI) effects in these cells remains poorly understood. The objective of our study was to explore U(VI) effect at doses ranging from 5 to 600 µM, on mineralization and autophagy induction in the UMR-106 model osteoblastic cell line and to determine U(VI) speciation after cellular uptake. Our results indicate that U(VI) affects mineralization function, even at subtoxic concentrations (<100 µM). The combination of thermodynamic modeling of U with EXAFS data in the culture medium and in the cells clearly indicates the biotransformation of U(VI) carbonate species into a meta-autunite phase upon uptake by osteoblasts. We next assessed U(VI) effect at 100 and 300 µM on autophagy, a survival process triggered by various stresses such as metal exposure. We observed that U(VI) was able to rapidly activate autophagy but an inhibition of the autophagic flux was observed after 24 h. Thus, our results indicate that U(VI) perturbs osteoblastic functions by reducing mineralization capacity. Our study identifies for the first time U(VI) in the form of meta-autunite in mammalian cells. In addition, U(VI)-mediated inhibition of the autophagic flux may be one of the underlying mechanisms leading to the decreased mineralization and the toxicity observed in osteoblasts.

Advances in element speciation analysis of biomedical samples using synchrotron-based techniques

“…A remarkable and very recent example of toxicological study supported by XAS is offered by Pierrefite-Carle and collaborators [54]. The primary sites of uranyl ions {U(VI)O 2 } 2+ (U(VI) for simplicity) accumulation are bones, where a permanent storage takes place potentially leading to a long term toxicity.…”

Mimicking bone–metal exchanges with synthetic nanocrystalline apatites

“…Furthermore, it is very likely also mediated by bone cells. 53,54 An instantaneous fixation by bone mineral such as what is observed with NCA-ref-young sample would lead to a much higher fraction in the skeleton.…”

Cytoplasmic aggregation of uranium in human dopaminergic cells after continuous exposure to soluble uranyl at non-cytotoxic concentrations

“…We performed a cellular correlative microscopy approach by coupling SXRF imaging to epifluorescence microscopy for the identification of organelles and/or proteins fluorescently labeled (Roudeau et al, 2014;Carmona et al, 2019;Das et al, 2019). Previous studies using transmission electron microscopy (TEM) indicated that after acute exposure to high uranium concentrations (> 300 µM) of alveolar macrophages, renal, or bone cells, uranium precipitates forming large needle-shape structures within cytoplasmic vesicles such as lysosomes (Hengé-Napoli et al, 1996;Mirto et al, 1999;Carrière et al, 2008;Pierrefite-Carle et al, 2017). We thus designed our study in order to evaluate, at lower non-cytotoxic concentration, the possible uranium co-localization with the cellular vesicular pathway (early endosomes, late endosomes, and lysosomes).…”