Stress granules formation and cell survival in wild type and FMR1 Knockout astrocytes under stress-inducing conditions.

Fragile X syndrome (FXS) is the most common form of inherited mental retardation and autism and is caused by the lack of Fragile X Mental Retardation Protein (FMRP), an RNA binding protein involved in RNA metabolism and protein synthesis. A substantial number of studies suggests that FMRP is associated with the pool of mRNAs that go into stress granules upon cellular stress. Stress granules (SGs) are cytoplasmic aggregates that are formed under stress conditions such as exposure to heat, oxidative agents, UV irradiation; these foci are thought to serve as sites of mRNA storage or triage during the cell stress response. SGs contain translation initiation components and many additional proteins affecting mRNA function. After environmental stress, mRNAs stored in this abortive translation initiation complex can be routed to either translation initiation or degradation. In this study, we tested the appearance of SGs and the cell survival in WT and Fmr1 KO cultured astrocytes after exposure to sodium arsenite (200 uM for 1 hour) and hydrogen peroxide (500 uM for 1 hour). We observed an increased number of cells with granules after exposure to oxidative stress (+ ), as expected; however, we detected a lower number of cells with granules both under basal condition and after exposure to oxidative stress in Fmr1 KO than WT astrocytes. Interestingly, under the same oxidative stress conditions cell survival was lower in Fmr1 KO than WT astrocytes. We also tested the effect of (S)-3,5-Dihydroxyphenylglycine (DHPG, 100 uM for 5 minutes), a selective agonist of group-I metabotropic glutamate receptor subtype 5 on both SG formation and oxidative stress induced damage in both WT and Fmr1 KO astrocytes. We find that the activation of mGlu receptors before oxidative stress reduced SG formation and cell survival in both genotypes. Our data indicate that Fmr1 KO astrocytes are more sensitive to oxidative stress and suggest an interesting correlation between SG formation and cell survival, which support the view that SGs play a protective role under stress conditions.