Reduced Levels of the Synaptic Functional Regulator FMRP in Dentate Gyrus of the Aging Sprague-Dawley Rat.

Roman Smidak,Daniel D Feyissa,Jovana Malikovic,Harald Hoeger,Judit Wackerlig,Fernando J Sialana,Gert Lubec,Tamara Stojanovic,Martina Kristofova,Diana Mechtcheriakova,Volker Korz,Dragana Rajcic

doi:10.3389/fnagi.2017.00384

Abstract

Fragile X mental retardation protein (FMRP) encoded by Fragile X mental retardation 1 (FMR1) gene is a RNA-binding regulator of mRNA translation, transport and stability with multiple targets responsible for proper synaptic function. Epigenetic silencing of FMR1 gene expression leads to the development of Fragile X syndrome (FXS) that is characterized by intellectual disability and other behavioral problems including autism. In the rat FXS model, the lack of FMRP caused a deficit in hippocampal-dependent memory. However, the hippocampal changes of FMRP in aging rats are not fully elucidated. The current study addresses the changes in FMRP levels in dentate gyrus (DG) from young (17 weeks) and aging (22 months) Sprague – Dawley rats. The aging animal group showed significant decline in spatial reference memory. Protein samples from five rats per each group were analyzed by quantitative proteomic analysis resulting in 153 significantly changed proteins. FMRP showed significant reduction in aging animals which was confirmed by immunoblotting and immunofluorescence microscopy. Furthermore, bioinformatic analysis of the differential protein dataset revealed several functionally related protein groups with individual interactions with FMRP. These include high representation of the RNA translation and processing machinery connected to FMRP and other RNA-binding regulators including CAPRIN1, the members of Pumilio (PUM) and CUG-BP, Elav-like (CELF) family, and YTH N(6)-methyladenosine RNA-binding proteins (YTHDF). The results of the current study point to the important role of FMRP and regulation of RNA processing in the rat DG and memory decline during the aging process.

Highlights

The Fragile X mental retardation protein (FMRP) is a RNA-binding regulator encoded by Fragile X mental retardation 1 (FMR1) gene
It was shown that the activation of metabotropic glutamate receptors affects FMRP localization in dendrites and synapses (Antar et al, 2004), FMRP deficiency leads to excessive mGluR5- and local protein synthesis-dependent internalization of AMPA receptors (Nakamoto et al, 2007) and that the expression of the NMDA receptor subunit NR2A is regulated by FMRP-associated microRNAs (Edbauer et al, 2010)
The cell body layer of dentate gyrus (DG) granule cells and hilus were separately outlined as regions of interest (ROI) according to the DAPI signal in each slice

Summary

Introduction

The Fragile X mental retardation protein (FMRP) is a RNA-binding regulator encoded by Fragile X mental retardation 1 (FMR1) gene. Reduction of FMRP in Hippocampus of Aging Rats (KH1 and KH2) and a C-terminal RGG box, involved in RNAbinding, together with nuclear localization and nuclear export signal (Adinolfi et al, 1999; Valverde et al, 2007) These structural features suggest the molecular functions of FMRP which have been associated with mRNA stability (Zalfa et al, 2007), nuclear – cytoplasmic shuttling of mRNA (Eberhart et al, 1996) and repression of mRNA translation (Jin and Warren, 2000; Li et al, 2001; Kalidas and Smith, 2003). It was shown that the activation of metabotropic glutamate receptors (mGluR) affects FMRP localization in dendrites and synapses (Antar et al, 2004), FMRP deficiency leads to excessive mGluR5- and local protein synthesis-dependent internalization of AMPA receptors (Nakamoto et al, 2007) and that the expression of the NMDA receptor subunit NR2A is regulated by FMRP-associated microRNAs (Edbauer et al, 2010)

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Results

Discussion

Conclusion