APP Causes Hyperexcitability in Fragile X Mice.

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Fragile X syndrome (FXS) is associated with altered Amyloid-beta protein precursor (APP) levels.
• Hyperexcitability is a core neurological phenotype in FXS.
• Normalization of APP levels in Fmr1 mice ameliorates several FXS-related disease characteristics.

Purpose of the Study:

• To investigate the role of APP levels in modulating hyperexcitability within Fmr1 mouse brain slices.
• To explore APP's function as a potential biomarker and therapeutic target for FXS.

Main Methods:

• Electrophysiological recordings from Fmr1 and Fmr1/APP double knockout mouse brain slices.
• Analysis of neocortical UP states and CA3 hippocampal ictal discharge duration.
• Development of a molecular model for APP's role in regulating neural excitability.

Main Results:

• Fmr1/APP slices showed complete rescue of neocortical UP states, a model of hyperexcitability.
• Reduced duration of ictal discharges was observed in the CA3 hippocampal model of epilepsy.
• Both APP over- and under-expression in Fmr1 mice increased seizure propensity, suggesting a critical role for APP homeostasis.

Conclusions:

• APP plays a crucial role in maintaining the excitation-inhibition (E/I) balance in neural circuits.
• A proposed model suggests APP functions as a rheostat, modulating hyperexcitability via mGluR5 and FMRP.
• Restoring APP homeostasis presents a potential therapeutic strategy for FXS by normalizing E/I balance.