Amino acid starvation: Differential response to mGluR5 activation in hippocampal slices from WT and Fmr1 KO mice

Authors

• SK Cooke
• J Russin
• I Louteav
• Z Li
• CB Smith

Abstract

Fragile X syndrome (FXS), the most common inherited form of intellectual disability, results from loss of the protein FMRP. Due to RNA-binding activity of FMRP, impaired protein synthesis (PS) is hypothesized to be a core phenotype. We developed an in vitro method to measure rates of PS in hippocampal slices with [3H]leucine as tracer. Preliminary results show no differences in PS between WT and Fmr1 KO mice, despite previous observations in vivo and in vitro. Our protocol differs from other in vitro methods through inclusion of a full complement of amino acids in the incubation medium (AAR). Amino acid starvation (AAS) has been shown to have widespread effects on activation and translation of proteins involved in regulating protein synthesis. We used Western blotting to examine the effects of genotype, amino acid condition and mGluR5 activation on the ratios of phosphorylated to total proteins (ERK, eIF2α, S6 (Ser235/236), Akt) in the slice. Our preliminary results indicate genotype-specific alterations in some of these signaling molecules with changes in conditions. Additionally, preliminary examination of the effect of AAR on mGluR5-induced long-term depression (LTD) in hippocampal slices reveals that previously reported increased LTD in Fmr1 KO mice may be an amino acid dependent effect. No known defects in whole body amino acid metabolism have been reported in FXS, making AAR the physiologically relevant condition. The response of hippocampal slices to amino acid conditions provides a new domain for understanding the consequences of FMRP loss in cellular signaling pathways.

Scientific Focus Area: Neuroscience

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