Altered surface mGluR5 dynamics provoke synaptic NMDAR dysfunction and cognitive defects in Fmr1 knockout mice

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Fragile X Syndrome (FXS) pathophysiology is linked to metabotropic glutamate receptor subtype 5 (mGluR5).
• Sub-cellular dysfunction, synaptic, and cognitive phenotypes associated with mGluR5 in FXS remain largely unexplored.
• The role of mGluR5/Homer scaffold disruption in FXS pathogenesis requires detailed investigation.

Purpose of the Study:

• To investigate the consequences of mGluR5/Homer scaffold disruption on mGluR5 cell-surface mobility.
• To examine the impact on synaptic N-methyl-D-aspartate receptor (NMDAR) function and cognitive phenotypes in a mouse model of FXS.
• To elucidate the mechanistic link between mGluR5 dynamics and FXS-related pathological phenotypes.

Main Methods:

• Utilized single-molecule tracking to assess mGluR5 cell-surface mobility in hippocampal neurons of second-generation Fmr1 knockout (KO) mice.
• Measured synaptic NMDAR currents and mGluR5-activated long-term depression.
• Investigated behavioral and cognitive deficits, and the effect of Homer1a knockdown in Fmr1 KO mice.

Main Results:

• mGluR5 exhibited significantly increased mobility at synapses in Fmr1 KO neurons.
• This correlated with enhanced synaptic co-clustering of mGluR5 and NMDAR, reduced synaptic NMDAR current amplitude, and impaired mGluR5-activated long-term depression.
• Cognitive deficits dependent on NMDAR and hippocampus were observed, and these were reversed by Homer1a knockdown.

Conclusions:

• Disrupted mGluR5 dynamics and Homer scaffold interactions mechanistically link to FXS pathological phenotypes.
• Increased mGluR5 mobility at synapses contributes to synaptic and cognitive deficits in FXS.
• Targeting mGluR5 dynamics and Homer1a presents a potential therapeutic strategy for FXS.