Origin, fate and dynamics of macrophages at central nervous system interfaces

Area of Science:

• Neuroimmunology
• Developmental Neuroscience
• Hematopoiesis

Background:

• Non-parenchymal macrophages, including perivascular, subdural meningeal, and choroid plexus macrophages, are crucial for immune responses at the brain's boundaries.
• While the origin of parenchymal microglia is understood, the precursors and dynamics of other CNS macrophages remain largely unknown.
• Previous assumptions suggested high turnover from blood-borne monocytes for these macrophages.

Purpose of the Study:

• To investigate the developmental origins and population dynamics of non-parenchymal macrophages in the central nervous system (CNS).
• To identify the key transcriptional regulators involved in the generation of CNS macrophages.
• To differentiate the origins and lifespans of various CNS macrophage populations.

Main Methods:

• Parabiosis experiments in mice to assess cell contribution and stability.
• Fate-mapping techniques to trace the developmental origins of macrophage populations.
• Analysis of transcription factor requirements for CNS macrophage generation.

Main Results:

• CNS macrophages originate from hematopoietic precursors during embryonic development and establish stable populations.
• Choroid plexus macrophages exhibit dual origins and a shorter lifespan compared to other CNS macrophages.
• The transcription factor PU.1 is essential for CNS macrophage generation, while MYB, BATF3, and NR4A1 are not required.

Conclusions:

• Non-parenchymal CNS macrophages are primarily derived from embryonic hematopoietic precursors, not blood monocytes.
• Choroid plexus macrophages represent a distinct population with unique developmental origins and turnover dynamics.
• PU.1 is a critical regulator for the development of CNS macrophages.