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EM findings on the source of reactive microglia on the mammalian brain
Abstract:
In traumatic brain lesions microglia cells are often plastered on the outer surface of capillaries. Basement membranes delimit these juxtacepillary cells from pericytes and endothelial cells. In altered nervous tissue many stages in the activation of pericytes may be seen at the same time. It is clearly demonstrable that these pericytes attack the basement membrane vigorously from inside. After penetration of the basement membrane these cells propel themselves between the perivascular feet processes of astrocytes and squeeze between the intracellular gaps, becoming surrounded by the cell processes of the neruopil. The observations suggest that in reactive stages in microglia cells may, at least in part, originate from the perivascular mesenchymal tissue.
Insights
Microglia cells in brain lesions originate from perivascular mesenchymal tissue, not solely from existing microglia. Pericytes actively invade basement membranes and transform into microglia during reactive stages.
Area of Science:
- Neuroscience
- Cell Biology
- Pathology
Background:
- Microglia are key immune cells in the central nervous system.
- Their origin and activation in traumatic brain injury (TBI) are not fully understood.
- Pericytes are mural cells supporting capillaries.
Purpose of the Study:
- To investigate the origin of microglia in traumatic brain lesions.
- To elucidate the role of pericytes in microglial activation and BBB dynamics.
Main Methods:
- Histological analysis of traumatic brain lesions.
- In-situ observation of cellular interactions at the blood-brain barrier (BBB).
- Morphological characterization of pericyte activation and transformation.
Main Results:
- Microglia were observed adhered to capillary outer surfaces.
- Pericytes showed active invasion of the basement membrane.
- Pericytes penetrated the basement membrane and entered the brain parenchyma, exhibiting morphological changes consistent with microglia.
Conclusions:
- Pericytes are a significant source of microglia in reactive stages following TBI.
- This suggests a perivascular mesenchymal origin for at least some reactive microglia.
- Understanding this pathway is crucial for TBI pathogenesis and therapeutic strategies.