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

The lymphatic system controls fluid homeostasis and the clearance of macromolecules from interstitial compartments. In mammals brain lymphatics were only recently discovered, with significant implications for physiology and disease. We examined zebrafish for the presence of brain lymphatics and found loosely connected endothelial cells with lymphatic molecular signature covering parts of the brain without forming endothelial tubular structures. These brain lymphatic endothelial cells (BLECs) derive from venous endothelium, are distinct from macrophages, and are sensitive to loss of Vegfc. BLECs endocytose macromolecules in a selective manner, which can be blocked by injection of mannose receptor ligands. This first report on brain lymphatic endothelial cells in a vertebrate embryo identifies cells with unique features, including the uptake of macromolecules at a single cell level. Future studies will address whether this represents an uptake mechanism that is conserved in mammals and how these cells affect functions of the embryonic and adult brain.

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Differential Clearance of Aβ Species from the Brain by Brain Lymphatic Endothelial Cells in Zebrafish

International Journal of Molecular Sciences ◽

10.3390/ijms222111883 ◽

2021 ◽

Vol 22 (21) ◽

pp. 11883

Author(s):

Yun-Mi Jeong ◽

Jae-Geun Lee ◽

Hyun-Ju Cho ◽

Wang Sik Lee ◽

Jinyoung Jeong ◽

...

Keyword(s):

Endothelial Cells ◽

Mannose Receptor ◽

Lymphatic Endothelial Cells ◽

Zebrafish Model ◽

Vertebrate Brain ◽

Aβ Clearance ◽

The Brain ◽

Defective Clearance

The failure of amyloid beta (Aβ) clearance is a major cause of Alzheimer’s disease, and the brain lymphatic systems play a crucial role in clearing toxic proteins. Recently, brain lymphatic endothelial cells (BLECs), a non-lumenized lymphatic cell in the vertebrate brain, was identified, but Aβ clearance via this novel cell is not fully understood. We established an in vivo zebrafish model using fluorescently labeled Aβ42 to investigate the role of BLECs in Aβ clearance. We discovered the efficient clearance of monomeric Aβ42 (mAβ42) compared to oligomeric Aβ42 (oAβ42), which was illustrated by the selective uptake of mAβ42 by BLECs and peripheral transport. The genetic depletion, pharmacological inhibition via the blocking of the mannose receptor, or the laser ablation of BLECs resulted in the defective clearance of mAβ42. The treatment with an Aβ disaggregating agent facilitated the internalization of oAβ42 into BLECs and improved the peripheral transport. Our findings reveal a new role of BLECs in the differential clearance of mAβ42 from the brain and provide a novel therapeutic strategy based on promoting Aβ clearance.

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Meningeal lymphatic endothelial cells fulfill scavenger endothelial cell function and employ Mrc1a for cargo uptake

10.1101/691477 ◽

2019 ◽

Author(s):

Yvonne Padberg ◽

Andreas van Impel ◽

Max van Lessen ◽

Jeroen Bussmann ◽

Stefan Schulte-Merker

Keyword(s):

Endothelial Cells ◽

Cell Function ◽

Molecular Level ◽

Physiological Role ◽

Specific Substrate ◽

Lymphatic Endothelial Cells ◽

Cardinal Vein ◽

Endothelial Cell Function ◽

Surface Receptors ◽

The Brain

AbstractBrain lymphatic endothelial cells (BLECs) constitute a group of loosely connected endothelial cells within the meningeal layer of the zebrafish brain. We previously reported that BLECs efficiently endocytose extracellular cargo molecules (van Lessen et al., 2017), but how this is accomplished and controlled on the molecular level remains unclear. We here compare BLECs to scavenging endothelial cells (SECs) in the embryonic cardinal vein and find them to accept an identical set of substrate molecules. While there is redundancy in the type of scavenger receptors being used, the two cell populations rely for specific substrate molecules on different cell surface receptors to mediate their physiological role: Stab2 appears more critical within SECs in the cardinal vein, while BLECs depend more on the Mrc1a receptor for internalization of cargo. Given the striking similarities to the substrate specificity of cardinal vein SECs, we postulate that BLECs qualify functionally as SECs of the brain.

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Structural and functional conservation of non-lumenized lymphatic endothelial cells in the mammalian leptomeninges

Acta Neuropathologica ◽

10.1007/s00401-019-02091-z ◽

2019 ◽

Vol 139 (2) ◽

pp. 383-401 ◽

Cited By ~ 5

Author(s):

Shannon Shibata-Germanos ◽

James R. Goodman ◽

Alan Grieg ◽

Chintan A. Trivedi ◽

Bridget C. Benson ◽

...

Keyword(s):

Endothelial Cells ◽

Dura Mater ◽

Lymphatic Vessels ◽

Amyloid Β ◽

Lymphatic Endothelial Cells ◽

Cell Type ◽

Functional Conservation ◽

Spherical Inclusions ◽

Lymphatic Markers ◽

The Brain

Abstract The vertebrate CNS is surrounded by the meninges, a protective barrier comprised of the outer dura mater and the inner leptomeninges, which includes the arachnoid and pial layers. While the dura mater contains lymphatic vessels, no conventional lymphatics have been found within the brain or leptomeninges. However, non-lumenized cells called Brain/Mural Lymphatic Endothelial Cells or Fluorescent Granule Perithelial cells (muLECs/BLECs/FGPs) that share a developmental program and gene expression with peripheral lymphatic vessels have been described in the meninges of zebrafish. Here we identify a structurally and functionally similar cell type in the mammalian leptomeninges that we name Leptomeningeal Lymphatic Endothelial Cells (LLEC). As in zebrafish, LLECs express multiple lymphatic markers, containing very large, spherical inclusions, and develop independently from the meningeal macrophage lineage. Mouse LLECs also internalize macromolecules from the cerebrospinal fluid, including Amyloid-β, the toxic driver of Alzheimer’s disease progression. Finally, we identify morphologically similar cells co-expressing LLEC markers in human post-mortem leptomeninges. Given that LLECs share molecular, morphological, and functional characteristics with both lymphatics and macrophages, we propose they represent a novel, evolutionary conserved cell type with potential roles in homeostasis and immune organization of the meninges.

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Cells with Many Talents: Lymphatic Endothelial Cells in the Brain Meninges

Cells ◽

10.3390/cells10040799 ◽

2021 ◽

Vol 10 (4) ◽

pp. 799

Author(s):

Irina Suárez ◽

Stefan Schulte-Merker

Keyword(s):

Endothelial Cells ◽

Single Cells ◽

Lymphatic Vessels ◽

Gene Expression Signature ◽

Brain Parenchyma ◽

Dietary Fats ◽

Lymphatic Endothelial Cells ◽

Edema Formation ◽

Peripheral Tissues ◽

The Brain

The lymphatic system serves key functions in maintaining fluid homeostasis, the uptake of dietary fats in the small intestine, and the trafficking of immune cells. Almost all vascularized peripheral tissues and organs contain lymphatic vessels. The brain parenchyma, however, is considered immune privileged and devoid of lymphatic structures. This contrasts with the notion that the brain is metabolically extremely active, produces large amounts of waste and metabolites that need to be cleared, and is especially sensitive to edema formation. Recently, meningeal lymphatic vessels in mammals and zebrafish have been (re-)discovered, but how they contribute to fluid drainage is still not fully understood. Here, we discuss these meningeal vessel systems as well as a newly described cell population in the zebrafish and mouse meninges. These cells, termed brain lymphatic endothelial cells/Fluorescent Granular Perithelial cells/meningeal mural lymphatic endothelial cells in fish, and Leptomeningeal Lymphatic Endothelial Cells in mice, exhibit remarkable features. They have a typical lymphatic endothelial gene expression signature but do not form vessels and rather constitute a meshwork of single cells, covering the brain surface.

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Fc receptor mediated endocytosis of small soluble immunoglobulin G immune complexes in Kupffer and endothelial cells from rat liver

Journal of Cell Science ◽

10.1242/jcs.113.18.3255 ◽

2000 ◽

Vol 113 (18) ◽

pp. 3255-3266

Author(s):

T. Lovdal ◽

E. Andersen ◽

A. Brech ◽

T. Berg

Keyword(s):

Endothelial Cells ◽

Kupffer Cells ◽

Immune Complexes ◽

Scavenger Receptor ◽

Mannose Receptor ◽

Endocytic Pathway ◽

Scavenger Receptors ◽

Receptor Ligands ◽

Receptor Ligand ◽

Liver Endothelial Cells

Soluble circulating immunoglobulin G immune complexes are mainly eliminated by the liver, predominantly by uptake in the Kupffer cells, but also the liver endothelial cells seem to be of importance. In the present study we have followed the intracellular turnover of immune complexes after Fc(gamma) receptor mediated endocytosis in cultured rat liver endothelial cells and Kupffer cells by means of isopycnic centrifugation, DAB cross-linking and morphological techniques. For the biochemical experiments the antigen, dinitrophenylated bovine serum albumin (BSA), was labeled with radioiodinated tyramine cellobiose that cannot cross biological membranes and therefore traps labeled degradation products at the site of formation. The endocytic pathway followed by immune complexes was compared with that followed by scavenger receptor ligands, such as formaldehyde treated BSA and dinitrophenylated BSA, and the mannose receptor ligand ovalbumin. Both Kupffer cells and liver endothelial cells took up and degraded the immune complexes, but there was a clear delay in the degradation of immune complexes as compared to degradation of ligands taken up via scavenger receptors. The kinetics of the endocytosis of scavenger receptor ligand was unaffected by simultaneous uptake of immune complexes. Experiments using both biochemical and morphological techniques indicated that the delayed degradation was due to a late arrival of the immune complexes at the lysosomes, which partly was explained by retroendocytosis of immune complexes. Electron microscopy studies revealed that the immune complexes were retained in the early endosomes that remained accessible to other endocytic markers such as ovalbumin. In addition, the immune complexes were seen in multivesicular compartments apparently devoid of other endocytic markers. Finally, the immune complexes were degraded in the same lysosomes as the ligands of scavenger receptors. Thus, immune complexes seem to follow an endocytic pathway that is kinetically or maybe morphologically different from that followed by scavenger and mannose receptor ligands.

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Meningeal lymphatic endothelial cells fulfill scavenger endothelial cell function and cooperate with microglia in waste removal from the brain

Glia ◽

10.1002/glia.24081 ◽

2021 ◽

Cited By ~ 1

Author(s):

Yvonne Huisman ◽

Katharina Uphoff ◽

Michael Berger ◽

Ulrich Dobrindt ◽

Mario Schelhaas ◽

...

Keyword(s):

Endothelial Cells ◽

Endothelial Cell ◽

Cell Function ◽

Lymphatic Endothelial Cells ◽

Endothelial Cell Function ◽

Waste Removal ◽

The Brain

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Endotoxin Alteration of the Mucopolysaccharide Blood Vessel Coating in Rats

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100050755 ◽

1974 ◽

Vol 32 ◽

pp. 148-149

Author(s):

D. E. Philpott ◽

A. Takahashi

Keyword(s):

Skeletal Muscle ◽

Endothelial Cells ◽

Salivary Gland ◽

Carotid Artery ◽

Basement Membrane ◽

Coronary Vessels ◽

Ruthenium Red ◽

E Coli ◽

Old Rats ◽

The Brain

Two month, eight month and two year old rats were treated with 10 or 20 mg/kg of E. Coli endotoxin I. P. The eight month old rats proved most resistant to the endotoxin. During fixation the aorta, carotid artery, basil arartery of the brain, coronary vessels of the heart, inner surfaces of the heart chambers, heart and skeletal muscle, lung, liver, kidney, spleen, brain, retina, trachae, intestine, salivary gland, adrenal gland and gingiva were treated with ruthenium red or alcian blue to preserve the mucopolysaccharide (MPS) coating. Five, 8 and 24 hrs of endotoxin treatment produced increasingly marked capillary damage, disappearance of the MPS coating, edema, destruction of endothelial cells and damage to the basement membrane in the liver, kidney and lung.

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Complex Vesicles, Microtubules, and Cytoplasmic Filaments in the Endothelial Cells of Normal Dog Aorta

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100100603 ◽

1968 ◽

Vol 26 ◽

pp. 172-173

Author(s):

C. N. Sun ◽

J. J. Ghidoni

Keyword(s):

Electron Microscopy ◽

Endothelial Cells ◽

Cross Sections ◽

Functional Significance ◽

Tubular Structures ◽

Aldehyde Fixation ◽

Cytoplasmic Filaments

Endothelial cells in longitudinal and cross sections of aortas from 3 randomly selected “normal” mongrel dogs were studied by electron microscopy. Segments of aorta were distended with cold cacodylate buffered 5% glutaraldehyde for 10 minutes prior to being cut into small, well oriented tissue blocks. After an additional 1-1/2 hour period in glutaraldehyde, the tissue blocks were well rinsed in buffer and post-fixed in OsO4. After dehydration they were embedded in a mixture of Maraglas, D.E.R. 732, and DDSA.Aldehyde fixation preserves the filamentous and tubular structures (300 Å and less) for adequate demonstration and study. The functional significance of filaments and microtubules has been recently discussed by Buckley and Porter; the precise roles of these cytoplasmic components remains problematic. Endothelial cells in canine aortas contained an abundance of both types of structures.

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