Characterization of Subcellular Organelles in Cortical Perisynaptic Astrocytes

Area of Science:

• Neuroscience
• Cell Biology
• Glial Cell Biology

Background:

• Perisynaptic astrocytic processes (PAPs) are vital for synaptic function, yet their intracellular complexity has been underestimated.
• Traditional electron microscopy suggested PAPs lack organelles, posing a question about how they perform diverse functions.

Purpose of the Study:

• To investigate the three-dimensional ultrastructure of PAPs and their organelle content.
• To determine if PAPs contain sufficient intracellular machinery to support their known functions.

Main Methods:

• Serial block-face scanning electron microscopy (SBF-SEM) was used for high-resolution 3D reconstruction.
• PAPs and their organelles were analyzed in two mouse cortical regions: somatosensory and anterior cingulate cortex.

Main Results:

• Five types of organelles were identified in PAPs: endosomes, phagosomes, mitochondria, and endoplasmic reticulum (ER) cisternae.
• PAPs were categorized into branches, branchlets, and leaflets, with leaflets being most common (~60%).
• Organelle distribution varied by PAP category, with branches showing higher densities of mitochondria and ER cisternae.

Conclusions:

• PAPs possess a rich variety of subcellular organelles, including endosomes, phagosomes, mitochondria, and ER.
• This organelle content provides a structural basis for the diverse functions of PAPs at central synapses.
• The findings revise the understanding of PAP intracellular complexity and their role in synaptic regulation.