Arterial Lymphatics in Atherosclerosis: Old Questions, New Insights, and Remaining Challenges

The lymphatic network is well known for its role in the maintenance of tissue fluid homeostasis, absorption of dietary lipids, trafficking of immune cells, and adaptive immunity. Aberrant lymphatic function has been linked to lymphedema and immune disorders for a long time. Discovery of lymphatic cell markers, novel insights into developmental and postnatal lymphangiogenesis, development of genetic mouse models, and the introduction of new imaging techniques have improved our understanding of lymphatic function in both health and disease, especially in the last decade. Previous studies linked the lymphatic vasculature to atherosclerosis through regulation of immune responses, reverse cholesterol transport, and inflammation. Despite extensive research, many aspects of the lymphatic circulation in atherosclerosis are still unknown and future studies are required to confirm that arterial lymphangiogenesis truly represents a therapeutic target in patients with cardiovascular disease. In this review article, we provide an overview of factors and mechanisms that regulate lymphangiogenesis, summarize recent findings on the role of lymphatics in macrophage reverse cholesterol transport, immune cell trafficking and pathogenesis of atherosclerosis, and present an overview of pharmacological and genetic strategies to modulate lymphatic vessel density in cardiovascular tissue.

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Vegfr3-tdTomato, a reporter mouse for microscopic visualization of lymphatic vessel by multiple modalities

PLoS ONE ◽

10.1371/journal.pone.0249256 ◽

2021 ◽

Vol 16 (9) ◽

pp. e0249256

Author(s):

Esther Redder ◽

Nils Kirschnick ◽

Stefanie Bobe ◽

René Hägerling ◽

Nils Rouven Hansmeier ◽

...

Keyword(s):

Laser Scanning ◽

Immune Cell ◽

Lymphatic Vessels ◽

Regulatory Elements ◽

Dietary Lipids ◽

Epifluorescence Microscopy ◽

Lymph Vessel ◽

Confocal Laser ◽

Cell Trafficking ◽

Tissue Fluid

Lymphatic vessels are indispensable for tissue fluid homeostasis, transport of solutes and dietary lipids and immune cell trafficking. In contrast to blood vessels, which are easily visible by their erythrocyte cargo, lymphatic vessels are not readily detected in the tissue context. Their invisibility interferes with the analysis of the three-dimensional lymph vessel structure in large tissue volumes and hampers dynamic intravital studies on lymphatic function and pathofunction. An approach to overcome these limitations are mouse models, which express transgenic fluorescent proteins under the control of tissue-specific promotor elements. We introduce here the BAC-transgenic mouse reporter strain Vegfr3-tdTomato that expresses a membrane-tagged version of tdTomato under control of Flt4 regulatory elements. Vegfr3-tdTomato mice inherited the reporter in a mendelian fashion and showed selective and stable fluorescence in the lymphatic vessels of multiple organs tested, including lung, kidney, heart, diaphragm, intestine, mesentery, liver and dermis. In this model, tdTomato expression was sufficient for direct visualisation of lymphatic vessels by epifluorescence microscopy. Furthermore, lymph vessels were readily visualized using a number of microscopic modalities including confocal laser scanning, light sheet fluorescence and two-photon microscopy. Due to the early onset of VEGFR-3 expression in venous embryonic vessels and the short maturation time of tdTomato, this reporter offers an interesting alternative to Prox1-promoter driven lymphatic reporter mice for instance to study the developmental differentiation of venous to lymphatic endothelial cells.

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Hypercholesterolemia and Lymphatic Defects: The Chicken or the Egg?

Frontiers in Cardiovascular Medicine ◽

10.3389/fcvm.2021.701229 ◽

2021 ◽

Vol 8 ◽

Author(s):

Takuro Miyazaki ◽

Akira Miyazaki

Keyword(s):

Causal Relationship ◽

Immune Cell ◽

Lymphatic Vessels ◽

Lymphatic Drainage ◽

Lymphatic Invasion ◽

Dietary Lipids ◽

Cell Trafficking ◽

Tissue Fluid ◽

Lipoprotein Composition ◽

Factor C

Lymphatic vessels are necessary for maintaining tissue fluid balance, trafficking of immune cells, and transport of dietary lipids. Growing evidence suggest that lymphatic functions are limited under hypercholesterolemic conditions, which is closely related to atherosclerotic development involving the coronary and other large arteries. Indeed, ablation of lymphatic systems by Chy-mutation as well as depletion of lymphangiogenic factors, including vascular endothelial growth factor-C and -D, in mice perturbs lipoprotein composition to augment hypercholesterolemia. Several investigations have reported that periarterial microlymphatics were attracted by atheroma-derived lymphangiogenic factors, which facilitated lymphatic invasion into the intima of atherosclerotic lesions, thereby modifying immune cell trafficking. In contrast to the lipomodulatory and immunomodulatory roles of the lymphatic systems, the critical drivers of lymphangiogenesis and the details of lymphatic insults under hypercholesterolemic conditions have not been fully elucidated. Interestingly, cholesterol-lowering trials enable hypercholesterolemic prevention of lymphatic drainage in mice; however, a causal relationship between hypercholesterolemia and lymphatic defects remains elusive. In this review, the contribution of aberrant lymphangiogenesis and lymphatic cholesterol transport to hypercholesterolemic atherosclerosis was highlighted. The causal relationship between hypercholesterolemia and lymphatic insults as well as the current achievements in the field were discussed.

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When form meets function: the cells and signals that shape the lymphatic vasculature during development

Development ◽

10.1242/dev.167098 ◽

2021 ◽

Vol 148 (11) ◽

Author(s):

Mathias Francois ◽

Anna Oszmiana ◽

Natasha L. Harvey

Keyword(s):

Network Formation ◽

Immune Cell ◽

Lymphatic Endothelial Cell ◽

Dietary Lipids ◽

Cell Trafficking ◽

Tissue Fluid ◽

Cellular Events ◽

Formation Function ◽

Lymphatic Vasculature ◽

Lymphatic Network

ABSTRACT The lymphatic vasculature is an integral component of the cardiovascular system. It is essential to maintain tissue fluid homeostasis, direct immune cell trafficking and absorb dietary lipids from the digestive tract. Major advances in our understanding of the genetic and cellular events important for constructing the lymphatic vasculature during development have recently been made. These include the identification of novel sources of lymphatic endothelial progenitor cells, the recognition of lymphatic endothelial cell specialisation and heterogeneity, and discovery of novel genes and signalling pathways underpinning developmental lymphangiogenesis. Here, we review these advances and discuss how they inform our understanding of lymphatic network formation, function and dysfunction.

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Vegfr3-tdTomato, a reporter mouse for microscopic visualization of lymphatic vessel by multiple modalities

10.1101/2021.03.16.435629 ◽

2021 ◽

Author(s):

Esther Redder ◽

Nils Kirschnick ◽

René Hägerling ◽

Nils Hansmeier ◽

Friedemann Kiefer

Keyword(s):

Laser Scanning ◽

Immune Cell ◽

Lymphatic Vessels ◽

Regulatory Elements ◽

Dietary Lipids ◽

Epifluorescence Microscopy ◽

Lymph Vessel ◽

Confocal Laser ◽

Cell Trafficking ◽

Tissue Fluid

AbstractLymphatic vessels are indispensable for tissue fluid homeostasis, transport of solutes and dietary lipids and immune cell trafficking. In contrast to blood vessels, which are easily visible by their erythrocyte cargo, lymphatic vessels are not readily detected in the tissue context. Their invisibility interferes with the analysis of the three-dimensional lymph vessel structure in large tissue volumes and hampers dynamic intravital studies on lymphatic function and pathofunction. An approach to overcome these limitations are mouse models, which express transgenic fluorescent proteins under the control of tissue-specific promotor elements.We introduce here the BAC-transgenic mouse reporter strain Vegfr3-tdTomato that expresses a membrane-tagged version of tdTomato under control of Flt4 regulatory elements. Vegfr3-tdTomato mice inherited the reporter in a mendelian fashion and showed selective and stable fluorescence in the lymphatic vessels of multiple organs tested, including lung, kidney, heart, diaphragm, intestine, mesentery and dermis. In this model, tdTomato expression was sufficient for direct visualisation of lymphatic vessels by epifluorescence microscopy. Furthermore, lymph vessels were readily visualized using a number of microscopic modalities including confocal laser scanning, light sheet fluorescence and two-photon microscopy. Due to the early onset of VEGFR-3 expression in venous embryonic vessels and the short maturation time of tdTomato, this reporter offers an interesting alternative to Prox1-promoter driven lymphatic reporter mice for instance to study the developmental differentiation of venous to lymphatic endothelial cells.

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Intravenous apoA-I/lecithin discs increase pre-β-HDL concentration in tissue fluid and stimulate reverse cholesterol transport in humans

The Journal of Lipid Research ◽

10.1016/s0022-2275(20)32212-4 ◽

2001 ◽

Vol 42 (10) ◽

pp. 1586-1593 ◽

Cited By ~ 14

Author(s):

M.N. Nanjee ◽

C.J. Cooke ◽

R. Garvin ◽

F. Semeria ◽

G. Lewis ◽

...

Keyword(s):

Reverse Cholesterol Transport ◽

Cholesterol Transport ◽

Tissue Fluid

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Impact of Dietary Lipids on the Reverse Cholesterol Transport: What We Learned from Animal Studies

Nutrients ◽

10.3390/nu13082643 ◽

2021 ◽

Vol 13 (8) ◽

pp. 2643

Author(s):

Bianca Papotti ◽

Joan Carles Escolà-Gil ◽

Josep Julve ◽

Francesco Potì ◽

Ilaria Zanotti

Keyword(s):

Reverse Cholesterol Transport ◽

Animal Studies ◽

Cardiovascular Health ◽

Current Knowledge ◽

Physiological Mechanism ◽

Experimental Models ◽

Dietary Lipids ◽

Cholesterol Transport ◽

Biological Functions ◽

Excessive Accumulation

Reverse cholesterol transport (RCT) is a physiological mechanism protecting cells from an excessive accumulation of cholesterol. When this process begins in vascular macrophages, it acquires antiatherogenic properties, as has been widely demonstrated in animal models. Dietary lipids, despite representing a fundamental source of energy and exerting multiple biological functions, may induce detrimental effects on cardiovascular health. In the present review we summarize the current knowledge on the mechanisms of action of the most relevant classes of dietary lipids, such as fatty acids, sterols and liposoluble vitamins, with effects on different steps of RCT. We also provide a critical analysis of data obtained from experimental models which can serve as a valuable tool to clarify the effects of dietary lipids on cardiovascular disease.

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Lymphatic Clearance of Immune Cells in Cardiovascular Disease

Cells ◽

10.3390/cells10102594 ◽

2021 ◽

Vol 10 (10) ◽

pp. 2594

Author(s):

Christophe Ravaud ◽

Nikita Ved ◽

David G. Jackson ◽

Joaquim Miguel Vieira ◽

Paul R. Riley

Keyword(s):

Immune Cells ◽

Lymphatic System ◽

Immune Cell ◽

Heart Function ◽

Cell Trafficking ◽

Tissue Fluid ◽

Lymphatic Endothelium ◽

Cell Clearance ◽

Cardiac Outcome ◽

And Function

Recent advances in our understanding of the lymphatic system, its function, development, and role in pathophysiology have changed our views on its importance. Historically thought to be solely involved in the transport of tissue fluid, lipids, and immune cells, the lymphatic system displays great heterogeneity and plasticity and is actively involved in immune cell regulation. Interference in any of these processes can be deleterious, both at the developmental and adult level. Preclinical studies into the cardiac lymphatic system have shown that invoking lymphangiogenesis and enhancing immune cell trafficking in ischaemic hearts can reduce myocardial oedema, reduce inflammation, and improve cardiac outcome. Understanding how immune cells and the lymphatic endothelium interact is also vital to understanding how the lymphatic vascular network can be manipulated to improve immune cell clearance. In this Review, we examine the different types of immune cells involved in fibrotic repair following myocardial infarction. We also discuss the development and function of the cardiac lymphatic vasculature and how some immune cells interact with the lymphatic endothelium in the heart. Finally, we establish how promoting lymphangiogenesis is now a prime therapeutic target for reducing immune cell persistence, inflammation, and oedema to restore heart function in ischaemic heart disease.

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