Astrocytic phagocytosis is a compensatory mechanism for microglial dysfunction

Area of Science:

• Neuroscience
• Immunology
• Cell Biology

Background:

• Microglia are the primary phagocytic cells in the central nervous system (CNS), responsible for clearing cellular debris.
• Impaired microglial function can compromise CNS homeostasis, necessitating alternative debris clearance mechanisms.

Purpose of the Study:

• To identify the cells responsible for clearing microglial debris when microglial phagocytic activity is compromised.
• To investigate the mechanisms and implications of alternative phagocytosis in the CNS.

Main Methods:

• Utilized Siglech^dtr mice for targeted ablation of microglia.
• Analyzed CNS-associated macrophages, inflammatory monocytes, and astrocytes for phagocytic activity.
• Performed RNA sequencing (RNA-seq) to identify expressed phagocytic receptors in astrocytes.

Main Results:

• Non-microglial mononuclear phagocytes did not clear microglial debris.
• Activated astrocytes extended processes to engulf microglial debris, exhibiting a pro-inflammatory gene profile.
• Astrocytic phagocytosis was also observed in Irf8-deficient mice with dysfunctional microglia.
• Astrocytes express TAM phagocytic receptors, indicating a latent phagocytic capacity.

Conclusions:

• Astrocytes act as a compensatory phagocytic mechanism in the CNS when microglia are impaired.
• This astrocytic phagocytosis, mediated by TAM receptors, is vital for maintaining CNS health during microglial dysfunction.