FIGURE 1.

Brain vascular cell diversity along the arterial-venous axis. (A) Large arteries (red) and cortical veins (blue) course within the subarachnoid space (gray mesh) inside the dura mater (gray). Cerebral arteries course along the brain’s pial surface and within sulci giving rise to pial and penetrating arterioles which pierce the brain parenchyma. (B) Arterioles progressively branch to form capillaries. Capillaries then converge to form venules which converge further to form veins. Each vessel segment along the arterial-venous axis are comprised of different cell types—including endothelium (shown in red, gray, and blue to denote transcriptional zonations), vascular smooth muscle cells (dark gray, vSMCs), pericytes (green), perivascular fibroblasts (yellow), and perivascular macrophages (light blue). Pericytes further adopt different morphologic configurations along the arteriovenous axis, such as ensheathing pericytes (pre-capillary arterioles) and mesh-like and stellate pericytes in more distal arterioles, capillaries, and venules. vSMCs form concentric rings in arteries but are discrete and stellate shaped in veins. Perivascular fibroblasts and macrophages are found in arteries, arterioles, venules, and veins, but not capillaries. (C–E) Cross section of cellular components of artery (C), capillary (D), and veins (E). Endothelium depicted in artery, capillary, and vein are shown in red, light gray, and blue, respectively, to denote transcriptional differences or molecular zonations defined and validated by independent groups with single cell RNA-sequencing. Dark gray, vascular smooth muscle cells; Navy blue, internal elastic lamina; Green, pericytes; Orange, perivascular fibroblasts; Light blue, perivascular macrophages; Yellow, basement membrane; Purple, astrocyte end feet.