The Ultrastructural Properties of the Endoplasmic Reticulum Govern Microdomain Signaling in Perisynaptic Astrocytic...

Area of Science:

• Neuroscience
• Cell Biology
• Astrocyte Biology

Background:

• Astrocytes are crucial for brain function and behavior.
• Perisynaptic astrocytic processes (PAPs) regulate neurotransmission via calcium (Ca²⁺) signals.
• The role of calcium stores within PAPs remains unclear due to their small size.

Purpose of the Study:

• To investigate the ultrastructural basis of astrocytic calcium signals.
• To determine the contribution of endoplasmic reticulum (ER) in PAPs to astrocytic calcium activity.
• To elucidate the relationship between ER geometry and calcium signal characteristics.

Main Methods:

• 3D reconstruction of hippocampal tripartite synapses using high-resolution electron microscopy (EM).
• Development of an algorithm to generate 3D PAP meshes with varied ER distribution.
• Reaction-diffusion simulations to model calcium dynamics within these meshes.

Main Results:

• 75% of PAPs contain endoplasmic reticulum (ER), a significant calcium store.
• ER in PAPs exhibits diverse shapes and spatial distributions.
• ER location, ER surface-volume ratio, and calcium channel distribution critically influence astrocytic activity.
• ER-plasma membrane contact sites amplify or attenuate calcium signals based on IP₃R clustering.

Conclusions:

• The diverse ultrastructure of ER within PAPs underlies varied astrocytic calcium microdomain signals.
• ER geometry and its interaction with plasma membrane channels are key regulators of neuron-astrocyte communication.
• This study provides novel insights into the mechanisms governing astrocytic calcium signaling and synaptic transmission.