Mural lymphatic endothelial cells regulate meningeal angiogenesis in the zebrafish

Abstract

Mural cells of the vertebrate brain maintain vascular integrity and function, play roles in stroke and are involved in maintenance of neural stem cells. However, the origins, diversity and roles of mural cells remain to be fully understood. Using transgenic zebrafish, we identified a population of isolated mural lymphatic endothelial cells surrounding meningeal blood vessels. These meningeal mural lymphatic endothelial cells (muLECs) express lymphatic endothelial cell markers and form by sprouting from blood vessels. In larvae, muLECs develop from a lymphatic endothelial loop in the midbrain into a dispersed, nonlumenized mural lineage. muLEC development requires normal signaling through the Vegfc-Vegfd-Ccbe1-Vegfr3 pathway. Mature muLECs produce vascular growth factors and accumulate low-density lipoproteins from the bloodstream. We find that muLECs are essential for normal meningeal vascularization. Together, these data identify an unexpected lymphatic lineage and developmental mechanism necessary for establishing normal meningeal blood vasculature.

Postnatal development of lymphatic vasculature in the brain meninges

“…Interestingly, LYVE-1-positive perivascular cells with macrophage-like morphology have also been reported on the surface of the zebrafish brain (Bower et al, 2017; Venero Galanternik et al, 2017). These cells express Prox1, but no other macrophage markers, and are not of hematopoietic origin.…”

“…We have observed that Prox1-GFP-negative/LYVE-1-positive individual cells are distributed in close proximity to meningeal vasculature and express the macrophage markers CD206 and F4/ 80, indicative of tissue-localized macrophages. Of interest, LYVE-1-positive perivascular cells with macrophage-like morphology have also been reported on the surface of the zebrafish brain (Bower et al, 2017;Venero Galanternik et al, 2017). These cells express Prox1, but no other macrophage markers, and are not of hematopoietic origin.…”

Intracellular uptake of macromolecules by brain lymphatic endothelial cells during zebrafish embryonic development

“…BLECs often are in close proximity to blood vessels, possibly also suggesting a functional interconnectivity. Indeed, BLECs were recently found to express pro-angiogenic factors such as vegfab and egfl7 (Bower et al, 2017; Venero Galanternik et al, 2017) required by blood vessels in the brain. Furthermore, genetic and laser-ablation mediated depletion of BLECs results in a concomitant reduction of blood vessels, and recovery of BLECs precedes regeneration of blood vessels in the affected areas during larval stages (Bower et al, 2017).…”

“…Indeed, BLECs were recently found to express pro-angiogenic factors such as vegfab and egfl7 (Bower et al, 2017; Venero Galanternik et al, 2017) required by blood vessels in the brain. Furthermore, genetic and laser-ablation mediated depletion of BLECs results in a concomitant reduction of blood vessels, and recovery of BLECs precedes regeneration of blood vessels in the affected areas during larval stages (Bower et al, 2017). Anatomically, BLECs cover many, but not all, surfaces of the brain, and display distinct morphological characteristics depending on which region of the brain they occupy.…”

Cerebrovascular Injuries Induce Lymphatic Invasion into Brain Parenchyma to Guide Vascular Regeneration in Zebrafish

“…They interact with blood vessels to remove toxic waste (Da Mesquita et al, 2018). In zebrafish, meningeal mural lymphatic ECs (muLECs), also called brain lymphatic endothelial cells (BLECs) or fluorescent granular perithelial (FGP) cells, are able to regulate meningeal angiogensis during development and endocytose macromolecules (Bower et al, 2017;Venero Galanternik et al, 2017;van Lessen et al, 2017). Although muLECs/BLECs/FGPs do not form tubes, they express all lymphatic markers and are sensitive to loss of Ccbe1/Vegfc/Vegfr3, thus believed as zebrafish meningeal lymphatics.…”