Kinase pathway inhibition restores PSD95 induction in neurons lacking fragile X mental retardation protein

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Fragile X syndrome (FXS), the primary genetic cause of autism and intellectual disability, results from the loss of fragile X mental retardation protein (FMRP).
• FMRP, an RNA-binding protein, regulates the translation of mRNAs, particularly at synapses, but its role in the distribution of newly synthesized proteins remains unclear.
• Deficits in local protein synthesis are hypothesized to contribute to FXS etiology.

Purpose of the Study:

• To investigate the role of FMRP in the regulation of new synaptic protein PSD95 synthesis and accumulation at stimulated synapses.
• To explore the molecular pathways involved in FMRP-dependent PSD95 regulation in response to neuronal stimulation.

Main Methods:

• Utilized an in vitro model of synaptic plasticity using cultured neurons.
• Applied brain-derived neurotrophic factor (BDNF) locally to stimulate synapses and observed PSD95 accumulation.
• Investigated the involvement of the PI3K-mTORC1-S6K1 pathway and employed pathway blockade in FMRP-deficient neurons.

Main Results:

• Local BDNF application induced persistent accumulation of newly synthesized PSD95 at stimulated synapses in control neurons, an effect absent in FMRP-deficient neurons.
• PSD95 accumulation was independent of known FMRP-mRNA interaction mechanisms but reliant on the PI3K-mTORC1-S6K1 pathway.
• In FMRP-deficient neurons, inhibiting the mTORC1-S6K1 pathway restored BDNF-induced PSD95 accumulation, indicating constitutive pathway activity can impede regulation.

Conclusions:

• This study provides direct evidence of impaired local protein synthesis and accumulation in response to stimulation in FXS.
• Findings suggest that constitutively active mTORC1-S6K1 signaling in FXS may occlude normal synaptic responses.
• Inhibition of the mTORC1-S6K1 pathway presents a potential therapeutic strategy for FXS.