Pericyte and Endothelial Primary Cilia and Centrioles have Disparate Organization Across the Brain Microvasculature

The brain microvascular functions are strongly influenced by the local microenvironment and cellular organization. Intracellular organelles, including primary cilia and centrioles, play critical roles in sensing and transmitting environmental cues and maintaining vascular integrity. However, their distribution across the brain vasculature remains poorly understood. In this study, we utilized publicly available large-volume electron microscopy datasets encompassing the cerebral vasculature from pial arterioles through parenchymal capillaries to pial venules. We systematically analyzed the cellular organization and characterized the distribution of primary cilia and centrioles in the mouse and human brain microvasculature. We found primary cilia exclusively on human cortical endothelial cells (ECs), indicating inter-species differences between mouse and human. Primary cilia were frequently present on mural cells (MCs, smooth muscle cells or pericytes) surrounding venules and capillaries but rarely observed on arterioles in both mouse and human brains. These MC primary cilia exhibited heterogeneity in ciliogenesis, including cells with ciliary pockets, surface cilia, and a hybrid configuration we refer as a partial pocket. In the mouse brain, many MC primary cilia were closely ensheathed by astrocytic endfeet and occasionally extended between them to establish proximity to synapses, whereas all primary cilia in the human brain were confined within the basal lamina. Our analysis of cellular density revealed similar EC densities between arterioles and venules in mice, but not in human. EC centrioles were consistently positioned against the direction of blood flow relative to the nuclei, suggesting that they may serve as a structural marker for flow direction. Collectively, these findings provide a comprehensive characterization of primary cilia and centrioles, highlighting distinct interspecies differences between mouse and human brain microvasculature. The proximity to neural cells and gradient distribution of these subcellular structures suggest that they may act as antennae for sensing mechanical and chemical signals within the brain microvascular environment.