Stress Granules formation and cell survival are reduced in Fmr1 knockout astrocytes after exposure to oxidative stress

Fragile X syndrome (FXS) is the most frequent form of inherited intellectual disability and a leading monogenic cause of autism. FXS is caused by the silencing of the fragile X mental retardation 1 (FMR1) gene expression and ensuing lack of the fragile X mental retardation protein (FMRP), an RNA binding protein involved in several aspect of RNA metabolism, including mRNA transport and translation. Consequently, abnormal expression of proteins at synapses may underlie brain dysfunction in FXS. FMRP is also implicated in DNA damage response (DDR) and is a component of stress granules (SGs), cytoplasmic aggregates containing translation initiation components and many additional proteins affecting mRNA function. Upon cellular stress, global protein synthesis is blocked, and mRNAs are temporarily recruited into SGs, which are thought to serve as sites of mRNA storage or triage. Evidence in the Fmr1 knockout mouse model of FXS suggests increased oxidative stress in the brain and higher susceptibility to apoptosis. In this study we tested the appearance of SGs and the cell survival in wild-type (WT) and Fmr1 knockout (KO) cultured astrocytes after exposure to sodium arsenite and hydrogen peroxide, by using immunocytochemistry with an anti-G3DP1 antibody recognizing SGs and MTT assay. We observed an increased number of cells with SGs after exposure to oxidative stress, as expected; however, we detected a lower number of cells with SGs in Fmr1 KO than WT astrocytes both under basal condition and after exposure to oxidative stress. Interestingly, we also detected a lower cell survival in Fmr1 KO than WT astrocytes upon exposure to oxidative stress. These results indicate that the lack of FMRP impairs the formation of SGs and sensitizes to oxidative stress induced damage in astrocytes, disclosing a contribution of this cell type to brain dysfunction in FXS.