PFOS-induced excitotoxicity is dependent on Ca2+ influx via NMDA receptors in rat cerebellar granule neurons.

Perfluoroalkyl acids (PFAAs) are persistent compounds used in many industrial as well as consumer products. Despite restrictions, these compounds are found at measurable concentrations in samples of human and animal origin. In the present study we examined whether the effects on cell viability of two sulfonated and four carboxylated PFAAs in cultures of cerebellar granule neurons (CGNs), could be associated with deleterious activation of the N-methyl-d-aspartate receptor (NMDA-R). PFAA-induced effects on viability in rat CGNs and unstimulated PC12 cells were examined using the MTT assay. Cells from the PC12 rat pheochromocytoma cell line lack the expression of functional NMDA-Rs and were used to verify lower toxicity of perfluorooctanesulfonic acid (PFOS) in cells not expressing NMDA-Rs. Protective effects of NMDA-R antagonists, and extracellular as well as intracellular Ca2+ chelators were investigated. Cytosolic Ca2+ ([Ca2+]i) was measured using Fura-2. In rat CGNs the effects of the NMDA-R antagonists MK-801, memantine and CPP indicated involvement of the NMDA-R in the decreased viability induced by PFOS and perfluorohexanesulfonic acid (PFHxS). No effects were associated with the four carboxylated PFAAs studied. Further, EGTA and CPP protected against PFOS-induced decreases in cell viability, whereas no protection was afforded by BAPTA-AM. [Ca2+]i significantly increased after exposure to PFOS, and this increase was completely blocked by MK-801. In PC12 cells a higher concentration of PFOS was required to induce equivalent levels of toxicity as compared to in rat CGNs. PFOS-induced toxicity in PC12 cells was not affected by CPP. In conclusion, PFOS at the tested concentrations induces excitotoxicity in rat CGNs, which likely involves influx of extracellular Ca2+ via the NMDA-R. This effect can be blocked by specific NMDA-R antagonists.

ATR is required to complete meiotic recombination in mice.

Precise execution of recombination during meiosis is essential for forming chromosomally-balanced gametes. Meiotic recombination initiates with the formation and resection of DNA double-strand breaks (DSBs). Cellular responses to meiotic DSBs are critical for efficient repair and quality control, but molecular features of these remain poorly understood, particularly in mammals. Here we report that the DNA damage response protein kinase ATR is crucial for meiotic recombination and completion of meiotic prophase in mice. Using a hypomorphic Atr mutation and pharmacological inhibition of ATR in vivo and in cultured spermatocytes, we show that ATR, through its effector kinase CHK1, promotes efficient RAD51 and DMC1 assembly at RPA-coated resected DSB sites and establishment of interhomolog connections during meiosis. Furthermore, our findings suggest that ATR promotes local accumulation of recombination markers on unsynapsed axes during meiotic prophase to favor homologous chromosome synapsis. These data reveal that ATR plays multiple roles in mammalian meiotic recombination.