Thoracic lymphatic disorders

Thoracic complications of lymphatic disorders can culminate in respiratory failure and death and should be considered in any patient with a lymphatic disease and clinical or radiographic evidence of chest disease. Congenital lymphatic disorders are being increasingly recognized in the adult population. The spectrum of thoracic manifestations of lymphatic disorders ranges from incidental radiographic findings to diffuse lymphatic disease with respiratory failure. This article serves to review some recent advances that allow improved diagnosis and management of thoracic lymphatic disorders. Herein, we describe their anatomical and physiologic effects, the time course of their progression, and the therapies that are currently available. The management of malignant (cancerous) lymphatic disorders of the thorax is beyond the scope of this paper.     

Causes and consequences of lymphatic disease

The visceral manifestations of lymphatic disorders (lymphangiomatosis and lymphangiectasia) are particularly severe. Any pathology of the lymphatic vasculature, whether superficial or internal, regional, or systemic, is predominated by the appearance of lymphedema, the characteristic form of tissue edema that occurs when lymphatic dysfunction supervenes. Disease manifestations may include dysregulation of body fluid homeostasis, immune traffic impairment, and disturbances of lipid and protein reabsorption from the gut lumen. The appearance of lymphatic edema invokes complex biological alterations. Many of these changes seem to relate uniquely to chronic lymphatic edema, including a profound stimulus to collagen and adipose deposition. Despite the recent advances in our understanding of these disorders, substantial knowledge gaps remain; these gaps inhibit our ability to accurately identify, categorize, treat, and prevent these diseases. Future diagnostic, therapeutic, and reproductive decisions for affected individuals require an accurate knowledge of the clinical and laboratory presentation, mode of inheritance, treatment response, outcomes, and prognosis.     

Lymphatic pump function in the inflamed gut

The role of the lymphatic circulation to actively remove fluid, cells, proteins, and other particles from the interstitium to prevent mounting edema is well appreciated, but whether and how this function is compromised during inflammation has been scarcely investigated. We discuss here the mechanisms of lymphatic pumping and their modulation in inflammatory conditions or by inflammatory mediators in the context of inflammatory bowel disease (IBD), an ensemble of disorders typically described with abnormal or dysfunctional intestinal or mesenteric lymphatic vessels. We report our findings showing impaired mesenteric lymphatic contractile activity in an animal model of intestinal inflammation that recapitulates some features of IBD and suggests a role for prostanoids in this dysfunction. With the knowledge that prostaglandin E(2) and prostacyclin are implicated in IBD pathogenesis and induce a potent inhibition of lymphatic pumping, we established the pharmacological profile for these prostaglandin receptors in mesenteric lymphatic vessels and their respective role in pumping inhibition. Inhibition of mesenteric lymphatic pumping during inflammation may be a cause of edema, compromised immune response, and granuloma associated with IBD.     

Molecular control of lymphangiogenesis

The lymphatic vasculature plays a critical role in the regulation of body fluid volume and immune function. Extensive research into the molecular mechanisms that control blood vessel growth has led to identification of molecules that also regulate development and growth of the lymphatic vessels. This is generating a great deal of interest in the molecular control of the lymphatics in the context of embryogenesis, lymphatic disorders and tumor metastasis. Studies in animal models carried out over the past three years have shown that the soluble protein growth factors, vascular endothelial growth factor (VEGF)-C and VEGF-D, and their cognate receptor tyrosine kinase, VEGF receptor-3 (VEGFR-3), are critical regulators of lymphangiogenesis. Furthermore, disfunction of VEGFR-3 has recently been shown to cause lymphedema. The capacity to induce lymphangiogenesis by manipulation of the VEGF-C/VEGF-D/VEGFR-3 signaling pathway offers new opportunities to understand the function of the lymphatic system and to develop novel treatments for lymphatic disorders.     

High-pressure hydrocephalus: a novel analytical modeling approach

Hydrocephalus is an abnormal accumulation of cerebrospinal fluid (CSF) within ventricles and subarachnoid space (SAS) as a result of disturbances in secretion or absorption procedures. It is believed that arachnoid villi cells, which are microscopic projections of pia-arachnoid mater that extend into venous channels in sagittal sinus, are the main sites for CSF absorption, but it is tempting to speculate that a significant portion of CSF is removed from the SAS by nasal lymphatic vessels around olfactory nerve. Thus, in this paper, we propose an analytical model of CSF-lymphatic-blood circulation, in which these two output pathways for CSF absorption have been considered. Mathematical relations governing the pressures in different interacting compartments of the brain are considered. In addition, for increasing the similarity of our model to the physiological conditions, the bulk flow mechanism, which is supposed to occur during CSF absorption, has been considered in our model. We used our model to simulate hydrocephalus. The results indicate that the lymphatic disorders have more considerable effect in decreasing CSF absorption, compared to the disturbances in arachnoid villi cells. Based on our modeling, we believe that disorders in lymphatic pathway may be a cause of high-pressure hydrocephalus. Surely experimental studies are required to validate our hypothesis.     

Lymphatic Tissue Engineering and Regeneration

The lymphatic system is a major circulatory system within the body, responsible for the transport of interstitial fluid, waste products, immune cells, and proteins. Compared to other physiological systems, the molecular mechanisms and underlying disease pathology largely remain to be understood which has hindered advancements in therapeutic options for lymphatic disorders. Dysfunction of the lymphatic system is associated with a wide range of disease phenotypes and has also been speculated as a route to rescue healthy phenotypes in areas including cardiovascular disease, metabolic syndrome, and neurological conditions. This review will discuss lymphatic system functions and structure, cell sources for regenerating lymphatic vessels, current approaches for engineering lymphatic vessels, and specific therapeutic areas that would benefit from advances in lymphatic tissue engineering and regeneration.     

Choose your fate: artery, vein or lymphatic vessel?

The specification of cell fate is integral to embryonic development. Recent research has identified several molecules that are involved in the development of the embryonic vasculature. Their combined actions are required for the specification and development of the arteries, veins and lymphatic vessels; vascular networks that are vital for embryonic and adult survival, and whose malfunction causes major pathological disorders. Recent discoveries have impacted our understanding of the embryonic origins of arterial, venous and lymphatic endothelial cells and the signals that mediate their navigation into mature, functional circulatory systems.     

Mechanics of interstitial-lymphatic fluid transport: theoretical foundation and experimental validation

Interstitial fluid movement is intrinsically linked to lymphatic drainage. However, their relationship is poorly understood, and associated pathologies are mostly untreatable. In this work we test the hypothesis that bulk tissue fluid movement can be evaluated in situ and described by a linear biphasic theory which integrates the regulatory function of the lymphatics with the mechanical stresses of the tissue. To accomplish this, we develop a novel experimental and theoretical model using the skin of the mouse tail. We then use the model to demonstrate how interstitial–lymphatic fluid movement depends on a balance between the elasticity, hydraulic conductivity, and lymphatic conductance as well as to demonstrate how chronic swelling (edema) alters the equipoise between tissue fluid balance parameters. Specifically, tissue fluid equilibrium is perturbed with a continuous interstitial infusion of saline into the tip of the tail. The resulting gradients in tissue stress are measured in terms of interstitial fluid pressure using a servo-null system. These measurements are then fit to the theory to provide in vivo estimates of the tissue hydraulic conductivity, elastic modulus, and overall resistance to lymphatic drainage. Additional experiments are performed on edematous tails to show that although chronic swelling causes an increase in the hydraulic conductivity, its greatly increased distensibility (due to matrix remodeling) dampens the driving forces for fluid movement and leads to fluid stagnation. This model is useful for examining potential treatments for edema and lymphatic disorders as well as substances which may alter tissue fluid balance and/or lymphatic drainage.     

A possible case of spontaneous Loa loa encephalopathy associated with a glomerulopathy

Background

There is a danger that mass drug administration campaigns may fail to maintain adequate treatment coverage to achieve lymphatic filariasis elimination. Hence, additional measures to suppress transmission might be needed to ensure the success of the Global Program for the Elimination of Lymphatic Filariasis.

Discussion

Vector control successfully eliminated lymphatic filariasis when implemented alone or with mass drug administration. Challenges to lymphatic filariasis elimination include uncertainty of the exact level and duration of microfilarial suppression required for elimination, the mobility of infected individuals, consistent non-participation of some infected individuals with mass drug administration, the possible development of anti-filarial drug resistance and treatment strategies in areas co-endemic with loasis. Integration of vector control with mass drug administration can address some of these challenges. The potential benefits of vector control would include: (1) the ability to suppress filariasis transmission without the need to identify all individual 'foci of infection'; (2) minimizing the risk of reestablishment of transmission from imported microfilaria positive individuals; and (3) decreasing the risk of dengue or malaria transmission where, respectively, Aedes or Anopheles are lymphatic filariasis vectors.

Summary

With adequate sustained treatment coverage, mass drug administration should meet the criteria for elimination of lymphatic filariasis. However, it may be difficult to sustain sufficiently high mass drug administration coverage to achieve lymphatic filariasis elimination in some areas, particularly, where Aedes species are the vectors. Since vector control was effective in controlling and even eliminating lymphatic filariasis transmission, integration of vector control with mass drug administration will ensure the sustainability of transmission suppression and thereby better ensure the success of national filariasis elimination programs. Although trials of some vector control interventions are needed, proven vector control strategies are ready for immediate integration with mass drug administration for many important vectors. Vector control is the only presently available additional lymphatic filariasis control measure with the potential for immediate implementation.     

Evidence for SH2 Domain-Containing 5′-Inositol Phosphatase-2 (SHIP2) Contributing to a Lymphatic Dysfunction

The lymphatic vasculature plays a critical role in a number of disease conditions of increasing prevalence, such as autoimmune disorders, obesity, blood vascular diseases, and cancer metastases. Yet, unlike the blood vasculature, the tools available to interrogate the molecular basis of lymphatic dysfunction/disease have been lacking. More recently, investigators have reported that dysregulation of the PI3K pathway is involved in syndromic human diseases that involve abnormal lymphatic vasculatures, but there have been few compelling results that show the direct association of this molecular pathway with lymphatic dysfunction in humans. Using near-infrared fluorescence lymphatic imaging (NIRFLI) to phenotype and next generation sequencing (NGS) for unbiased genetic discovery in a family with non-syndromic lymphatic disease, we discovered a rare, novel mutation in INPPL1 that encodes the protein SHIP2, which is a negative regulator of the PI3K pathway, to be associated with lymphatic dysfunction in the family. In vitro interrogation shows that SHIP2 is directly associated with impairment of normal lymphatic endothelial cell (LEC) behavior and that SHIP2 associates with receptors that are associated in lymphedema, implicating its direct involvement in the lymphatic vasculature.     

The ultrastructure of lymphatic valves in the adult rabbit lung

Summary An electron microscopic investigation has revealed that the pulmonary lymphatic valves of adult rabbits are not simple duplicatures of the lymphatic vessel wall. They consist of an uninterrupted central connective tissue core, covered on both sides with a single layer of flattened endothelial cells. Near their insertion in the lymphatic vessel wall, the connective tissue core reveals a distinct thickening being composed mainly of collagen bundles. In the other parts it contains mainly elastic fibers and fine filaments, enclosing also some rather peculiar connective tissue cells. Nervous and muscular elements were not observed. The endothelium is continuous and exhibits no open junctions. The valvular basement membrane is better developed than in lymphatic capillaries. The endothelial cells contain numerous cytoplasmic filaments which might be endowed with contractile properties. The nuclei of the endothelial and the connective tissue cells are irregularly spaced and frequently clustered near the free edge of the valve.These ultrastructural features suggest that the function of the lymphatic valves is mainly passive. They are firmly inserted in the lymphatic vessel wall by collagen fibers and their moving parts are slender and elastic. Their endothelium appears relatively impermeable and is firmly attached to the subjacent connective tissue.This study has been supported by a grant from The Council for Tobacco Research—U.S.A.. We thank Professor Robert C. Rosan (Saint Louis University—U.S.A.) for expert advice, R. Janssens for technical, G. Pison and St. Ons for photographic and N. Tyberghien for secretarial assistance.     

Segmental territories along the cardinal veins generate lymph sacs via a ballooning mechanism during embryonic lymphangiogenesis in mice

During lymphangiogenesis in the mammalian embryo, a subset of vascular endothelial cells in the cardinal veins is reprogrammed to adopt a lymphatic endothelial fate. The prevailing model of lymphangiogenesis contends that these lymphatic precursor cells migrate away from the cardinal veins and reassemble peripherally as lymph sacs from which a lymphatic vasculature is generated. However, this model fails to account for a number of observations that, as a result, have remained anecdotal. Here, we use optical projection tomography, confocal microscopy and in vivo live imaging to uncover three key stages of lymphatic vascular morphogenesis in the mouse embryo at high resolution. First, we define territories or "pre-lymphatic clusters" of Prox1-positive lymphatic endothelial progenitor cells along the antero-posterior axis of the cardinal veins. Second, these pre-lymphatic clusters undergo progressive extrusion ("ballooning") to generate primitive lymph sacs. Third, lymphatic vessels emerge by a combination of mechanisms including sprouting from the lymph sacs and direct delamination of streams of cells from the cardinal veins. Our data support a new model for lymphatic vascular patterning and morphogenesis, as a basis for identifying the molecular cues governing these processes.     

Lymphatic vasculature development

Although the process of blood vasculature formation has been well documented, little is known about lymphatic vasculature development, despite its importance in normal and pathological conditions. The lack of specific lymphatic markers has hampered progress in this field. However, the recent identification of genes that participate in the formation of the lymphatic vasculature denotes the beginning of a new era in which better diagnoses and therapeutic treatment(s) of lymphatic disorders could become a reachable goal.     

Structure of the venous and lymphatic beds of the heart and their alteration in experimental pathology

The investigation performed has demonstrated that under a great deal of coronary, pulmonary and other organs' disorders, in the venous and lymphatic beds of the heart compensatory-adaptive and pathological changes occur. The earliest and deepest changes are noted in the microcirculatory bed. Most of morphological signs on vascular reconstruction are not specific and are observed at different kinds of clinical and experimental pathology. Changes in venous and lymphatic vessels of pathological conditions& do not only result from damage in the organ's wall or hemodynamical changes in the cavities of the cardiac vessels but they themselves can cause some disturbances in the miocardial microcirculation intensifying its hypoxia, congestive symptoms and enhancing the development of decompensation in the organ.     

Spatio-Temporal Changes of Lymphatic Contractility and Drainage Patterns following Lymphadenectomy in Mice

Objective

To investigate the redirection of lymphatic drainage post-lymphadenectomy using non-invasive near-infrared fluorescence (NIRF) imaging, and to subsequently assess impact on metastasis.

Background

Cancer-acquired lymphedema arises from dysfunctional fluid transport after lymphadenectomy performed for staging and to disrupt drainage pathways for regional control of disease. However, little is known about the normal regenerative processes of the lymphatics in response to lymphadenectomy and how these responses can be accelerated, delayed, or can impact metastasis.

Methods

Changes in lymphatic “pumping” function and drainage patterns were non-invasively and longitudinally imaged using NIRF lymphatic imaging after popliteal lymphadenectomy in mice. In a cohort of mice, B16F10 melanoma was inoculated on the dorsal aspect of the paw 27 days after lymphadenectomy to assess how drainage patterns affect metastasis.

Results

NIRF imaging demonstrates that, although lymphatic function and drainage patterns change significantly in early response to popliteal lymph node (PLN) removal in mice, these changes are transient and regress dramatically due to a high regenerative capacity of the lymphatics and co-opting of collateral lymphatic pathways around the site of obstruction. Metastases followed the pattern of collateral pathways and could be detected proximal to the site of lymphadenectomy.

Conclusions

Both lymphatic vessel regeneration and co-opting of contralateral vessels occur following lymphadenectomy, with contractile function restored within 13 days, providing a basis for preclinical and clinical investigations to hasten lymphatic repair and restore contractile lymphatic function after surgery to prevent cancer-acquired lymphedema. Patterns of cancer metastasis after lymphadenectomy were altered, consistent with patterns of re-directed lymphatic drainage.     

Novel characterization of lymphatic valve formation during corneal inflammation

Lymphatic research has progressed rapidly in recent years. Though lymphatic dysfunction has been found in a wide array of disorders from transplant rejection to cancer metastasis, to date, there is still little effective treatment for lymphatic diseases. The cornea offers an optimal site for lymphatic research due to its accessible location, transparent nature, and lymphatic-free but inducible features. However, it still remains unknown whether lymphatic valves exist in newly formed lymphatic vessels in the cornea, and how this relates to an inflammatory response. In this study, we provide the first evidence showing that lymphatic valves were formed in mouse cornea during suture-induced inflammation with the up-regulation of integrin alpha 9. The number of corneal valves increased with the progression of inflammatory lymphangiogenesis. Moreover, we have detected lymphatic valves at various developmental stages, from incomplete to more developed ones. In addition to defining the average diameter of lymphatic vessels equipped with lymphatic valves, we also report that lymphatic valves were more often located near the branching points. Taken together, these novel findings not only provide new insights into corneal lymphatic formation and maturation, but also identify a new model for future investigation on lymphatic valve formation and possibly therapeutic intervention.     

Mechanisms of lymphatic regeneration after tissue transfer

Introduction

Lymphedema is the chronic swelling of an extremity that occurs commonly after lymph node resection for cancer treatment. Recent studies have demonstrated that transfer of healthy tissues can be used as a means of bypassing damaged lymphatics and ameliorating lymphedema. The purpose of these studies was to investigate the mechanisms that regulate lymphatic regeneration after tissue transfer.

Methods

Nude mice (recipients) underwent 2-mm tail skin excisions that were either left open or repaired with full-thickness skin grafts harvested from donor transgenic mice that expressed green fluorescent protein in all tissues or from LYVE-1 knockout mice. Lymphatic regeneration, expression of VEGF-C, macrophage infiltration, and potential for skin grafting to bypass damaged lymphatics were assessed.

Results

Skin grafts healed rapidly and restored lymphatic flow. Lymphatic regeneration occurred beginning at the peripheral edges of the graft, primarily from ingrowth of new lymphatic vessels originating from the recipient mouse. In addition, donor lymphatic vessels appeared to spontaneously re-anastomose with recipient vessels. Patterns of VEGF-C expression and macrophage infiltration were temporally and spatially associated with lymphatic regeneration. When compared to mice treated with excision only, there was a 4-fold decrease in tail volumes, 2.5-fold increase in lymphatic transport by lymphoscintigraphy, 40% decrease in dermal thickness, and 54% decrease in scar index in skin-grafted animals, indicating that tissue transfer could bypass damaged lymphatics and promote rapid lymphatic regeneration.

Conclusions

Our studies suggest that lymphatic regeneration after tissue transfer occurs by ingrowth of lymphatic vessels and spontaneous re-connection of existing lymphatics. This process is temporally and spatially associated with VEGF-C expression and macrophage infiltration. Finally, tissue transfer can be used to bypass damaged lymphatics and promote rapid lymphatic regeneration.