Compartmentalized VEGF receptor expression in hypothalamic tanycytes reveals a novel non-endothelial axis of VEGF signaling : Tanycytes as a novel non-endothelial target of VEGF signaling.

BACKGROUND: Vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) are critical regulators of angiogenesis and vascular homeostasis. While VEGF signaling has been extensively studied in endothelial cells, emerging evidence suggests it also plays roles in non-endothelial brain cells. However, its spatial and cell-type-specific function within the hypothalamus, and more specifically at the level of the blood/CSF barrier, remains poorly defined. In particular, little is known about VEGF receptor expression in tanycytes, a specialized glial population that lines the third ventricle and regulates body-brain communication within the median eminence (ME), a key neurovascular interface located at the tuberal region of the hypothalamus. METHODS: We used a multi-modal approach including single-cell RNA sequencing (scRNA-seq) reanalysis, RNAscope in situ hybridization, immunohistochemistry, FACS-isolated qPCR in male and female mice, and human spatial transcriptomics to map the expression of VEGFR1 (Flt1), VEGFR2 (Kdr), and VEGF ligands in hypothalamic tanycytes across gender, development, and aging. RESULTS: Our data reveal a striking spatial compartmentalization of VEGFR expression in tanycytes within the ME and the arcuate (ARH), ventromedial (VMH) and dorsomedial (DMH) hypothalamus. VEGFR2 is preferentially expressed in ARH-tanycytes, while VEGFR1 is confined to VMH/DMH-tanycytes; and none of these receptors are expressed in ME-tanycytes. This pattern is unique to the ME and not observed in other circumventricular organs. VEGFR1 expression is established neonatally in mice (P0) and remains stable throughout life, whereas VEGFR2 expression becomes progressively refined postnatally, localizing to ARH-tanycytes in adulthood and showing a significant decline with aging. VEGFA is broadly expressed in all hypothalamic tanycytes, including ME-tanycytes, supporting a paracrine model of signaling. Importantly, despite species-specific differences in the spatial organization of VEGF receptors in tanycytes, the presence of VEGF ligands (Vegfa and Vegfb) and receptors in tanycytes of both mice and humans supports partial evolutionary conservation of VEGF signaling at the brain-blood interface. CONCLUSION: Our findings unveil, for the first time a non-endothelial VEGF signaling system in hypothalamic tanycytes that is spatially compartmentalized, developmentally programmed and age-dependent. These insights reveal new roles for VEGF signaling in neurovascular and neuroendocrine function, raising important considerations for central effects of VEGF-targeted therapies in aging and disease.