Developmental NMDA receptor dysregulation in the infantile neuronal ceroid lipofuscinosis mouse model

Area of Science:

• Neuroscience
• Molecular Biology
• Developmental Biology

Background:

• Protein palmitoylation, a reversible post-translational modification, regulates protein function and is vital for synaptic transmission and plasticity.
• Mutations in palmitoyl-protein thioesterase 1 (PPT1) lead to infantile neuronal ceroid lipofuscinosis (CLN1), a severe pediatric neurodegenerative disorder.
• The specific role of protein depalmitoylation in synaptic maturation remains largely unexplored.

Purpose of the Study:

• To investigate the function of protein depalmitoylation in synaptic maturation.
• To elucidate the role of the depalmitoylating enzyme PPT1 in the development of the postsynaptic structure.
• To understand the molecular mechanisms underlying synaptic deficits in PPT1-deficient conditions.

Main Methods:

• Comparative analysis of synapse development in wild-type and Ppt1-deficient mouse visual cortex.
• Electrophysiological recordings to assess N-methyl-D-aspartate receptor (NMDAR) currents in vivo and in cultured neurons.
• Analysis of dendritic spine morphology and calcium influx patterns.
• Biochemical assays to examine protein palmitoylation levels of key synaptic proteins, including GluN2B and Fyn kinase.

Main Results:

• The developmental switch of NMDAR subunits from GluN2B to GluN2A is arrested in Ppt1-deficient mice.
• Ppt1 neurons exhibit immature evoked NMDAR currents and abnormal dendritic spine morphology.
• Cultured Ppt1 neurons display altered calcium signaling and increased susceptibility to excitotoxicity, indicative of predominant GluN2B-containing receptors.
• Hyperpalmitoylation of GluN2B and Fyn kinase was observed in Ppt1 neurons, suggesting impaired proteostasis of palmitoylated proteins.

Conclusions:

• PPT1 is essential for postsynaptic maturation, particularly for the critical NMDAR subunit switch during development.
• Impaired depalmitoylation by PPT1 disrupts the proteostasis of key synaptic proteins like GluN2B and Fyn kinase.
• These findings highlight PPT1's critical role in synaptic development and offer insights into the pathogenesis of CLN1 disease.