BDE-47 and 6-OH-BDE-47 modulate calcium homeostasis in primary fetal human neural progenitor cells via ryanodine receptor-independent mechanisms
Polybrominated diphenyl ethers (PBDEs) are bioaccumulating flame retardants found in rising concentrations in human tissue. Epidemiological and animal studies have raised concern for their potential to induce developmental neurotoxicity (DNT). Considering the essential role of calcium homeostasis in neurodevelopment, PBDE-induced disturbance of intracellular calcium concentration ([Ca2+]i) may underlie PBDE-induced DNT. To test this hypothesis, we investigated acute effects of BDE-47 and 6-OH-BDE-47 on [Ca2+]i in human neural progenitor cells (hNPCs) and unraveled involved signaling pathways. Short-time differentiated hNPCs were exposed to BDE-47, 6-OH-BDE-47, and multiple inhibitors/stimulators of presumably involved signaling pathways to determine possible effects on [Ca2+]i by single-cell microscopy with the fluorescent dye Fura-2. Initial characterization of calcium signaling pathways confirmed the early developmental stage of hNPCs. In these cells, BDE-47 (2 μM) and 6-OH-BDE-47 (0.2 μM) induce [Ca2+]i transients. This increase in [Ca2+]i is due to extracellular Ca2+ influx and intracellular release of Ca2+, mainly from the endoplasmic reticulum (ER). While extracellular Ca2+ seems to enter the cytoplasm upon 6-OH-BDE-47 by interfering with the cell membrane and independent of Ca2+ ion channels, ER-derived Ca2+ is released following activation of protein lipase C and inositol 1,4,5-trisphosphate receptor, but independently of ryanodine receptors. These findings illustrate that immature developing hNPCs respond to low concentrations of 6-OH-BDE-47 by an increase in [Ca2+]i and provide new mechanistic explanations for such BDE-induced calcium disruption. Thus, these data support the possibility of a critical window of PBDE exposure, i.e., early human brain development, which has to be acknowledged in risk assessment.
KeywordsBrominated flame retardant Calcium Human neural progenitor cell Neurotoxicity Polybrominated diphenyl ether Ryanodine receptor
We acknowledge the expert technical help of Ulrike Huebenthal and thank Marta Barenys for critical reading of the manuscript. Parts of this project were funded by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU), by the German Research Foundation (DFG GRK1427), by the Research Commission of the Department of Medicine, Heinrich-Heine University Duesseldorf and the Faculty of Veterinary Medicine, Utrecht University. The authors declare no actual or potential competing financial interests.
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