Hematopoietic Growth Factors Regulate the Entry of Monocytes into the Adult Brain via Chemokine Receptor CCR5

Area of Science:

• Neuroimmunology
• Hematology
• Cellular Biology

Background:

• Monocytes are crucial for replenishing brain macrophages under physiological conditions.
• While pathological monocyte brain infiltration is studied, physiological entry mechanisms remain unclear.
• Understanding monocyte brain entry is vital for neuroinflammatory and neurodegenerative diseases.

Purpose of the Study:

• To elucidate the mechanisms of monocyte entry into the adult brain under physiological conditions.
• To investigate the role of hematopoietic growth factors and specific receptors in monocyte-brain endothelial cell interactions.
• To identify factors regulating monocyte recruitment for perivascular macrophage renewal.

Main Methods:

• In vitro and in vivo studies using monocyte-endothelial cell co-cultures and knockout mouse models.
• Dose-dependent analysis of stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF) effects on monocyte adhesion.
• Assessment of cysteine-cysteine chemokine receptor 5 (CCR5) involvement in monocyte recruitment.

Main Results:

• SCF and G-CSF synergistically enhance monocyte adhesion to cerebral endothelial cells in a dose-dependent manner.
• Cysteine-cysteine chemokine receptor 5 (CCR5) on brain endothelial cells mediates this SCF+G-CSF-induced adhesion.
• Blocking or deleting CCR5 significantly reduces monocyte-endothelial cell adhesion and brain perivascular space recruitment.

Conclusions:

• SCF and G-CSF play a key role in regulating physiological monocyte entry into the adult brain.
• CCR5 is a critical mediator of SCF+G-CSF-enhanced monocyte recruitment to the brain.
• These findings provide insights into maintaining brain homeostasis and potential therapeutic targets.