Fig. 1: Microglia positioning in the neurovascular unit.
a Schematic of the neurovascular unit, which is comprised of neurons, vascular cells (endothelial cells, pericytes, smooth muscle cells) and glia (astrocytes, microglia). Endothelial cells (gray) are separated from pericytes (light blue) by the basement membrane (red). Astrocytes make contacts with both pericytes and endothelial cells at the capillary wall with their astrocytic endfeet (dark blue). Neurons (gold) innervate contractile cells of the vessel walls—smooth muscle cells in arterioles, and pericytes in brain capillaries. Capillary-associated microglia (CAMs; pink) make close contacts with brain capillary wall especially in areas not covered by astrocyte endfeet. Bisht et al.9 identified three types of CAMs with lined, wrapped or junctional morphologies in relation to brain capillaries. b Inset shows brain capillary with P2RY12 (green)-positive microglia that are activated by purines (yellow circles) released from PANX1 channels (purple) from the brain capillary wall likely expressed in endothelial cells, and/or pericytes or astrocyte endfeet. Bisht et al.9 have identified a signaling mechanism that attracts and maintains CAMs at the capillary wall.
