α2δ-2 Protein Controls Structure and Function at the Cerebellar Climbing Fiber Synapse

Area of Science:

• Neuroscience
• Molecular Biology
• Synaptic Plasticity

Background:

• Alpha-2/delta (α2δ) proteins are auxiliary subunits of voltage-dependent calcium channels involved in synaptogenesis.
• Multiple α2δ isoforms (Cacna2d1-4) complicate understanding their specific synaptic roles.
• Cerebellar Purkinje cells (PCs) predominantly express α2δ-2 (Cacna2d2), making them a model for studying its function.

Purpose of the Study:

• To investigate the role of α2δ-2 in excitatory synaptic function using α2δ-2 knock-out (KO) mice.
• To elucidate the impact of α2δ-2 deletion on climbing fiber (CF) synaptic transmission onto PCs.
• To explain the mechanistic basis for altered cerebellar output and associated phenotypes in Cacna2d2 KO mice.

Main Methods:

• Whole-cell electrophysiological recordings from Purkinje cells in acute cerebellar slices.
• Immunohistochemical analysis using VGLUT2+ to assess CF terminal localization.
• Computational modeling to evaluate the impact of terminal location on EPSC amplitude.
• Electron microscopy to examine vesicle release site morphology.
• Analysis of synaptic transmission during repetitive stimulation.

Main Results:

• α2δ-2 KO mice exhibited altered CF-evoked complex spike generation and increased EPSC amplitude with faster decay.
• CF terminals were located more proximally on PC dendrites in KO mice.
• KO CFs showed increased multivesicular release and more vesicle release sites, despite reduced release probability.
• Enhanced glutamate reuptake in KO mice led to faster EPSC decay, maintaining charge transfer despite larger amplitude.

Conclusions:

• Loss of α2δ-2 results in larger, faster excitatory postsynaptic currents (EPSCs) due to altered presynaptic terminal morphology and function.
• These synaptic changes disrupt information transfer in Purkinje cells, contributing to ataxia observed in Cacna2d2 KO mice.
• The study highlights the critical and multidimensional role of α2δ-2 in regulating excitatory synaptic transmission and cerebellar function.