New insights into the biology and pathology of the cutaneous lymphatic system

Application of microscale culture technologies for studying lymphatic vessel biology

Immense progress in microscale engineering technologies has significantly expanded the capabilities of in vitro cell culture systems for reconstituting physiological microenvironments that are mediated by biomolecular gradients, fluid transport, and mechanical forces. Here, we examine the innovative approaches based on microfabricated vessels for studying lymphatic biology. To help understand the necessary design requirements for microfluidic models, we first summarize lymphatic vessel structure and function. Next, we provide an overview of the molecular and biomechanical mediators of lymphatic vessel function. Then we discuss the past achievements and new opportunities for microfluidic culture models to a broad range of applications pertaining to lymphatic vessel physiology. We emphasize the unique attributes of microfluidic systems that enable the recapitulation of multiple physicochemical cues in vitro for studying lymphatic pathophysiology. Current challenges and future outlooks of microscale technology for studying lymphatics are also discussed. Collectively, we make the assertion that further progress in the development of microscale models will continue to enrich our mechanistic understanding of lymphatic biology and physiology to help realize the promise of the lymphatic vasculature as a therapeutic target for a broad spectrum of diseases.

Blockade of MMP-2 and MMP-9 inhibits corneal lymphangiogenesis

PURPOSE

To investigate the roles of a selective MMP-2 and -9 inhibitor (SB-3CT) in corneal inflammatory lymphangiogenesis.

METHODS

The expression of MMP-2 and -9 in the cornea after suture inplacement, treated with SB-3CT or negative control, was detected by real-time polymerase chain reaction (PCR). Inflammatory corneal neovascularization (NV) was induced by corneal suture placement. Mice were treated with SB-3CT eye drops (twice daily for 1 week, 5 μL per drop; 50, 100, or 200 μM). The outgrowth of blood and lymphatic vessels, and macrophage recruitment were analyzed by immunofluorescence assay. The expressions of vascular endothelial growth factor-C (VEGF-C) and its receptor VEGFR-3 were tested by real-time PCR.

RESULTS

MMP-2 and -9 expression were suppressed significantly by treatment with SB-3CT. The data demonstrated, for the first time, that SB-3CT strongly reduced corneal lymphangiogenesis and macrophage infiltration during inflammation. Furthermore, expressions of VEGF-C and its receptor VEGFR-3 were significantly inhibited by SB-3CT during corneal lymphangiogenesis.

CONCLUSIONS

These novel findings indicated that blockade of MMP-2 and -9 could inhibit lymphangiogenesis. Further investigation of this factor may provide novel therapies for transplant rejection and other lymphatic disorders.

Adrenomedullin in lymphangiogenesis: from development to disease

Over the past decade, we have begun to appreciate that the lymphatic vascular system does more than simply return plasma back into the circulatory system and, in fact, contributes to a wide variety of normal and disease states. For this reason, much research has been devoted to understanding how lymphatic vessels form and function, with a particular interest in which molecules contribute to lymphatic vessel growth and maintenance. In the following review, we focus on a potent lymphangiogenic factor, adrenomedullin, and its known roles in lymphangiogenesis, lymphatic function, and human lymphatic disease. As one of the first, pharmacologically tractable G protein-coupled receptor pathways characterized in lymphatic endothelial cells, the continued study of adrenomedullin effects on the lymphatic system may open new avenues for the modulation of lymphatic growth and function in a variety of lymphatic-related diseases that currently have few treatments.

Expression of lymphatic markers and lymphatic growth factors in psoriasis before and after anti-TNF treatment

BACKGROUND

Angiogenesis is an early stage of psoriatic lesion development, but less is known about lymphagiogenesis and its role in the development of psoriasis.

OBJECTIVE

To examine the expression of specific lymphatic markers and lymphatic growth factors in untreated psoriatic skin, in the unaffected skin of patients and skin of healthy volunteers, as well as their alteration after treatment with an anti-TNF agent.

METHODS

Immunohistochemistry for the lymphatic markers D2-40 and LYVE-1, in addition to the VEGF-C and VEGF-D growth factors, was performed in the skin biopsies of psoriatic lesions and adjacent non-psoriatic skin of 19 patients before and after treatment with etanercept, as well as in the skin biopsies of 10 healthy volunteers.

RESULTS

The expressions of D2-40, VEGF-C and VEGF-D on lymphatic vessels underwent statistically significant increases in untreated psoriatic skin compared with non-lesional skin, in contrast to LYVE-1, which did not involve significant increase in expression in psoriatic skin. VEGF-C expression on lymphatic vessels diminished after treatment with etanercept. Moreover VEGF-C and VEGF-D staining on fibroblasts presented with higher expression in lesional skin than in non-lesional adjacent skin.

CONCLUSION

Remodeling of lymphatic vessels possibly occurs during psoriatic lesion development, parallel to blood vessel formation. The exact role of this alteration is not yet clear and more studies are necessary to confirm these results.

Adrenomedullin delivery in microsphere-scaffold composite for remodeling of the alveolar bone following tooth extraction: an experimental study in the rat

Background

Alveolar ridge resorption, as a significant problem in implant and restorative dentistry, has long been considered as an inevitable outcome following tooth extraction. Recently, adrenomedullin (ADM) is reported to be able to stimulate the proliferation and migration of various cells including osteoblasts. The purpose of this study was to investigate the influence of local ADM application in the tooth extraction socket in vivo.

Methods

Chitosan micropheres were developed by an emulsion-ionic cross-linking method for ADM delivery. Poly (L -lactic-co-glycolic) acid (PLGA) and nano-hydroxyapatite (nHA) were used to prepare scaffolds to contain the micrspheres with ADM. In vivo experiment was evaluated by transplanting the composite into the rat socket right after the incisor extraction. After 4, 8, 12 weeks implantation, radiographic and histological tests were carried out to evaluate the effect of released ADM on the alveolar bone.

Results

The microspheres had a spherical structure and a relative rough and uniform surface, and the particle size was under a normal distribution, with the average diameter of 38.59 μm. The scaffolds had open and interconnected pores. In addition, the high porosity of the composite was 88.93%. Radiographic and histological examination revealed that the PLGA/nHA/CMs/ADM composite could accelerate the alveolar bone remodeling and reduce the residual ridge resorption compared with the PLGA/nHA/CMs scaffold.

Conclusions

The results of this study suggest that local application of ADM has the potential to preserve the residual alveolar ridge and accelerate the alveolar bone remodeling.

Acral pseudolymphomatous angiokeratoma of children: a case report with immunohistochemical study of antipodoplanin antigen

Acral pseudolymphomatous angiokeratoma of children (APACHE) is characterized by multiple angiomatous papules on the hands and feet in children. Here, we report a case of APACHE in a female patient followed up from 13 to 19 years of age with a dark red lesion on the center of the dorsum of the right thigh. Histologically, vacuolar alteration and exocytosis of lymphocytes, and specific dense cellular infiltration beneath the epidermis to the reticular dermis were found. On immunolabeling study, the lesion vessels were found to be positive for both the lymphatic endothelium-specific marker podoplanin and blood vessel-specific marker CD34. These findings suggested that APACHE is a type of vascular malformation.

Development of lymphatic vasculature and morphological characterization in rat kidney

BACKGROUND

The mechanisms and morphological characteristics of lymphatic vascular development in embryonic kidneys remain uncertain.

METHODS

We examined the distribution and characteristics of lymphatic vessels in developing rat kidneys using immunostaining for podoplanin, prox-1, Ki-67, type IV collagen (basement membrane: BM), and α-smooth muscle actin (αSMA: pericytes or mural cells). We also examined the expression of VEGF-C.

RESULTS

At embryonic day 17 (E17), podoplanin-positive lymphatic vessels were observed mainly in the kidney hilus. At E20, lymphatic vessels extended further into the developing kidneys along the interlobar vasculature. In 1-day-old pups (P1) to P20, lymphatic vessels appeared around the arcuate arteries and veins of the kidneys, with some reaching the developing cortex via interlobular vessels. In 8-week-old adult rats, lymphatic vessels were extensively distributed around the blood vasculature from the renal hilus to cortex. Only lymphatic capillaries lacking continuous BM and αSMA-positive cells were present within adult kidneys, with none observed in renal medulla. VEGF-C was upregulated in the developing kidneys and expressed mainly in tubules. Importantly, the developing lymphatic vessels were characterized by endothelial cells immunopositive for podoplanin, prox-1, and Ki-67, with no surrounding BM or αSMA-positive cells.

CONCLUSION

During nephrogenesis, lymphatic vessels extend from the renal hilus into the renal cortex along the renal blood vasculature. Podoplanin, prox-1, Ki-67, type IV collagen, and αSMA immunostaining can detect lymphatic vessels during lymphangiogenesis.

Targeted overexpression of Angptl6/angiopoietin-related growth factor in the skin promotes angiogenesis and lymphatic vessel enlargement in response to ultraviolet B

Angiogenesis is required for physiological tissue repair processes, such as cutaneous wound healing. However, recent studies indicate that endogenous angiogenic factors may enhance photo-induced skin alterations in response to experimental ultraviolet (UV)-B exposure. Angiopoietin-related growth factor (AGF), also known as angiopoietin-like protein 6 (Angptl6), is known to promote new blood vessel formation and vascular hyperpermeability. Importantly, epidermal overexpression of Angptl6/AGF in mice promotes wound healing in the skin. However, it remains unclear whether overexpression of Angptl6/AGF facilitates tissue repair processes in response to UV-B irradiation. To test this hypothesis, we subjected Angptl6/AGF transgenic mice to acute or chronic UV-B exposure. Surprisingly, transgenic mice showed enhanced photosensitivity to subthreshold doses of UV-B that did not induce skin alterations in wild-type littermates. Marked enlargement of blood vessels was observed after a single exposure to UV-B in Angptl6/AGF transgenic mice, although no epidermal changes were observed. Chronic UV-B exposure over 14 weeks promoted cutaneous skin damage in Angptl6/AGF transgenic mice, whereas wild-type mice showed little or no macroscopic skin alteration. In addition to pronounced angiogenesis and epidermal hyperplasia, marked enlargement of dermal lymphatic vessels was observed in UV-B-exposed Angptl6/AGF transgenic mice. Electron microscopy analysis further revealed that the number and size of collagen bundles in the dermis was markedly reduced after chronic UV-B exposure in Angptl6/AGF transgenic mice. Taken together, these results indicate that ectopic expression of Angptl6/AGF in mice likely promotes UV-B-induced skin alterations, and that angiogenesis could be a therapeutic target in prevention of skin photo-aging.

Expression of lymphatic endothelium-specific hyaluronan receptor LYVE-1 in the developing mouse kidney

Our knowledge of the embryonic development of the lymphatic vessels within the kidney is limited. The aim of this study was to establish the time of appearance and the distribution of intra-renal lymphatic vessels in the developing mouse kidney by using the lymphatic marker, LYVE-1. Kidneys from embryonic day 12 (E12) to E18, from neonates at post-natal day 1 (P1) to P21, and from adults were studied. In the adult mouse kidney, LYVE-1 was expressed mainly in the lymphatic endothelial cells (LECs) and in a subset of endothelial cells in the glomerular capillaries. However, in the developing mouse kidney, LYVE-1 was also expressed transiently in F4/80(+)/CD11b(-) immature macrophages/dendritic cells and in the developing renal vein. LYVE-1(+) lymphatic vessels connected with extra-renal lymphatics were detected in the kidney at E13. F4/80(+)/CD11b(-)/LYVE-1(+) immature macrophages/dendritic cells appeared prior to the appearance of LYVE-1(+) renal lymphatic vessels and were closely intermingled or even formed part of the lymphatic vascular wall. Prox1 was expressed only in the LYVE-1(+) LECs from fetus to adult-hood, but not in LYVE-1(+) endothelial cells of the developing renal vein and macrophages/dendritic cells. Thus, lymphatic vessels of the kidney might originate by extension of extra-renal lymphatics through an active branching process possibly associated with F4/80(+)/CD11b(-)/LYVE-1(+) macrophages/dendritic cells.

Giant scrotal elephantiasis: an idiopathic case

Scrotal elephantiasis is very rare disease in industrialized countries, where it is mainly due to surgery, irradiation or malignancies. It can be defined as idiopathic only when the possible congenital, infectious and compressive causes are excluded. We report a case of massive scrotal lymphoedema in an adult Caucasian patient, in Italy. He presented an extremely voluminous scrotal mass measuring 50 x 47 x 13 cm (weight 18 kg), which extended below his knees, invalidating all his daily activities. The patient was hospitalized in order to undergo to surgical treatment. Although genetic causes were searched and the possible role of infectious agents and compressive factors was evaluated, no etiology was ascertained. Histopathologic examination showed non-specific chronic inflammation, confirming the diagnosis of idiopathic elephantiasis. One year after surgical treatment, the patient is healthy without recurrence signs.

Laminin-421 produced by lymphatic endothelial cells induces chemotaxis for human melanoma cells

Melanoma has a high tendency to metastasize to lymph nodes, which is one of the clinicopathological factors to indicate poor prognosis. Recent investigations have shown the importance of lymphangiogenesis in lymph node metastasis in a variety of human tumors including melanoma. However, molecular mechanism of lymphatic metastasis is still poorly defined. We examined influence of interactions between normal lymphatic endothelial cells (LECs) and melanoma cells on cell migration. Medium conditioned with LEC (LEC-CM) contained chemotactic and chemokinetic activities for human melanoma cell lines. The chemotactic activity was fractionated in more than 100 kDa, and inactivated by heat-treatment. The chemotactic activity of LEC-CM was abolished by immunodepletion with anti-laminin-1 antibody. And immunoprecipitation and Western blot analyses revealed that LEC-CM contained laminin-421. When melanoma C8161 cells were treated with function-blocking antibodies to integrin alpha3 or alpha6, their chemotactic responses to LEC-CM were markedly reduced. Furthermore, the knock-down of tetraspanin CD151 weakened the chemotactic responses of C8161 and MeWo cells to LEC-CM. These data suggest that laminin-421 secreted by LEC possibly facilitates lymphatic metastasis through the induction of chemotaxis of melanoma cells.

Role of macrophages in inflammatory lymphangiogenesis: Enhanced production of vascular endothelial growth factor C and D through NF-kappaB activation

The close association of inflammation, angiogenesis and cancer progression is now highlighted, and in this study we especially focused on a close association of inflammation and lymphangiogenesis. We found that proinflammatory cytokine, interleukin-1beta (IL-1beta), could induce lymphangiogenesis in mouse cornea through enhanced production of potent lymphangiogenic factors, VEGF-A, VEGF-C and VEGF-D. IL-1beta-induced lymphangiogenesis, but not angiogenesis, was inhibited by administration of a selective anti-VEGF receptor-3 (VEGFR-3) neutralizing antibody. And in mouse cornea we observed recruitment of monocyte/macrophages and neutrophils by IL-1beta implanted cornea. Depletion of macrophages by a bisphosphonate encapsulated in liposomes inhibited this IL-1beta-induced lymphangiogenesis and also up-regulation of VEGF-A, VEGF-C, and VEGF-D. Furthermore, IL-1beta-induced lymphangiogenesis and angiogenesis were suppressed by NF-kappaB inhibition with marked suppression of VEGF-A, VEGF-C, and VEGF-D expression.

Adrenomedullin induces lymphangiogenesis and ameliorates secondary lymphoedema

AIMS

Adrenomedullin (AM) is a multifunctional peptide hormone that plays a significant role in vasodilation and angiogenesis. Lymphoedema is a common but refractory disorder that is difficult to be treated with conventional therapy. We therefore investigated whether AM promotes lymphangiogenesis and improves lymphoedema.

METHODS AND RESULTS

The effects of AM on lymphatic endothelial cells (LEC) were investigated. AM promoted proliferation, migration, and network formation of cultured human lymphatic microvascular endothelial cells (HLMVEC). AM increased intracellular cyclic adenosine monophosphate (cAMP) level in HLMVEC. The cell proliferation induced by AM was inhibited by a cAMP antagonist and mitogen-activated protein kinase kinase (MEK) inhibitors. Phosphorylated extracellular signal-regulated kinase (ERK) in HLMVEC was increased by AM. Continuous administration of AM (0.05 microg/kg/min) to BALB/c mice with tail lymphoedema resulted in a decrease in lymphoedema thickness. AM treatment increased the number of lymphatic vessels and blood vessels in the injury site.

CONCLUSION

AM promoted LEC proliferation at least in part through the cAMP/MEK/ERK pathway, and infusion of AM induced lymphangiogenesis and improved lymphoedema in mice.

Neostatin-7 regulates bFGF-induced corneal lymphangiogenesis

Neostatin-7, with an anti-angiogenic potential, is generated from the proteolytic action of matrix metalloproteinase-7 on collagen XVIII. We previously reported that neostatin-7 inhibited angiogenesis in vitro and in vivo. Here we demonstrate that neostatin-7/collagen XVIII may possess anti-lymphangiogenic activities by: (1) corneal micropellet implantation of neostatin-7 reduced bFGF-induced corneal lymphangiogenesis; (2) neostatin-7 bound to VEGF receptor-3 in vitro; and (3) enhanced corneal lymphangiogenesis and VEGF-C expression in collagen XVIII knockout mice in a corneal wounding model. Understanding the mechanism of neostatin-7/collagen XVIII on corneal lymphangiogenesis may provide therapeutic interventions to treat lymphangiogenesis-related disorders, such as lymphedema, transplantation rejection and cancers.

Schlemm??s Canal Endothelia, Lymphatic, or Blood Vasculature?

In the human eye, the final barrier for aqueous humor to cross before returning to systemic circulation is the inner wall of Schlemm's canal. Unfortunately, the specific contribution of the inner wall to total outflow resistance in the conventional pathway is unknown in both normal and glaucomatous eyes. To better understand inner wall physiology, we contrasted it with 2 specialized continuous endothelia, initial lymphatic, and blood capillary endothelia. Specifically, we compare their developmental origin, morphology, junctional complexes, microenvironment, and physiologic responses to different biomechanical factors. Our evaluation concludes that the inner wall of Schlemm's canal is unique, sharing extraordinary characteristics with both types of specialized endothelia in addition to having distinctive features of its own.

A failure of mucocutaneous lymphangiogenesis may underlie the clinical features of lipoid proteinosis

Lipoid proteinosis (LiP) (OMIM 247100) is a rare autosomal recessive disease caused by loss of function mutations in the extracellular matrix protein 1 gene, ECM1, on chromosome 1q21. LiP is characterized clinically by hoarseness in early infancy, followed by waxy papules and plaques on the face and body along with pox-like and acneiform scars. We studied a 20-year-old Japanese woman with LiP. She was born of consanguineous parents. Biopsy specimens obtained from a nodule on the elbow were used for histopathology, immunohistology and electron microscopy. Exons 6 and 7 of ECM1 were amplified by polymerase chain reaction (PCR) from genomic DNA from the proband, her parents, her brother and an unrelated person. PCR products were sequenced to detect the mutation. Histopathological examination revealed an irregular mass of calcium beneath deposits of a hyaline material in the dermis. Immunofluorescence double staining showed that the CD31-positive microvascular density was increased but that staining for the lymphatic-specific hyaluronan receptor LYVE-1 was drastically diminished in lesional compared with nonlesional skin of the patient and with normal skin. Electron microscopy revealed marked concentric reduplication of basal laminae not only around blood vessels but also around solitary dermal cells positive for Weibel-Palade bodies scattered in the hyaline material. Sequencing of the PCR products revealed a homozygous frameshift mutation, 507delT, in exon 6. This led to a premature stop codon 23 bp downstream. The results of immunopathological and ultrastructural characterization suggest that a failure of mucocutaneous lymphangiogenesis may underlie the clinical features of LiP. Identification of mutation 507delT in a Japanese patient with LiP further supports the thesis that this mutation represents a recurrent mutation in ECM1 in patients with LiP. To our knowledge, this case represents the first report of calcinosis cutis occurring in LiP.

In Vivo Actions of Angiopoietins on Quiescent and Remodeling Blood and Lymphatic Vessels in Mouse Airways and Skin

Objective— We investigated and compared the in vivo effects of all four angiopoietins (COMP-Ang1, Ang2, Ang3, and Ang4) on blood and lymphatic vascular remodeling in adult mice. We analyzed the microvasculature of trachea and ear skin, and compared quiescent skin microvasculature with that during wound healing.

Methods and Results— We were able to achieve similar levels of relatively long-term and sustained circulating expression of each angiopoietin using an adenoviral delivery system. Two weeks after treatment, we observed tracheal blood and lymphatic vascular enlargement, and lymphatic filopodia formation, with the following order of potency: COMP-Ang1>Ang3=Ang4>Ang2. Co-treatment with Ang2 attenuated Ang1-induced tracheal blood and lymphatic remodeling. In the normal ear skin, all angiopoietins induced blood vessel enlargement, whereas none induced lymphatic vascular remodeling. However, in the healing margin of ear skin wounds, all angiopoietins strongly induced lymphatic vascular enlargement and formation of lymphatic sprouts and filopodia, while they potentiated blood vascular enlargement. Co-treatment of Ang2 with Ang1 produced an additive effect on these changes.

Conclusion— This study, one of the first to our knowledge to characterize the in vivo actions of all 4 angiopoietins, may expand the current concepts for use of angiopoietins for therapeutic angiogenesis and lymphangiogenesis.

Distributional characteristics of lymphatic vessels in normal human nasal mucosa and sinus mucosa

An immunohistochemical staining technique with the D2-40 antibody was undertaken to examine the functional and morphological features of lymphatic networks in tissue sections and whole-mount preparations of normal nasal mucosa and ethmoid sinus mucosa. In normal nasal mucosa, most lymphatic vessels were found in the superficial mucosa beneath the epithelial layer. Some of these vessels were dilated, whereas others were compressed and had a slit-like lumen. Whole-mount preparations revealed the extent of lymphatic vessels in normal ethmoid sinus mucosa. A network of lymphatic vessels was mainly found in the subepithelial layer, where lymphatic vessels represented rich networks, possessing antler-like branches and typical blind ends. However, these lymphatic networks were not arranged in the form of lymphangion chains, with each lymphangion consisting of a contractile compartment and valve. Thus, recognition of the distinctive features of the lymphatic network in normal nasal and sinus mucosa might aid investigations of lymphatic involvement in sinonasal diseases, such as rhinitis, sinusitis, and malignancy.

New Insights into the Molecular Control of the Lymphatic Vascular System and its Role in Disease

The cutaneous lymphatic system plays an important role in the maintenance of tissue fluid homeostasis, in the afferent phase of the immune response, and in the metastatic spread of skin cancers. However, the lymphatic system has not received as much scientific attention as the blood vascular system, largely due to a lack of lymphatic-specific markers and to the dearth of knowledge about the molecular regulation of its development and function. The recent identification of genes that specifically control lymphatic development and the growth of lymphatic vessels (lymphangiogenesis), together with the discovery of new lymphatic endothelium-specific markers, have now provided new insights into the molecular mechanisms that control lymphatic growth and function. Moreover, studies of several genetic mouse models have set the framework for a new molecular model for embryonic lymphatic vascular development, and have identified molecular pathways whose mutational inactivation leads to human diseases associated with lymphedema. These scientific advances have also provided surprising evidence that malignant tumors can directly promote lymphangiogenesis and lymphatic metastasis, and that lymphatic vessels play a major role in cutaneous inflammation and in the cutaneous response to UVB irradiation.

COMP-angiopoietin-1 promotes wound healing through enhanced angiogenesis, lymphangiogenesis, and blood flow in a diabetic mouse model

Microvascular dysfunction is a major cause of impaired wound healing seen in diabetic patients. Therefore, reestablishment of structural and functional microvasculature could be beneficial to promote wound healing in these patients. Angiopoietin-1 (Ang1) is a specific growth factor functioning to generate a stable and functional vasculature through the Tie2 and Tie1 receptors. Here we determined the effectiveness of cartilage oligomeric matrix protein (COMP)-Ang1, a soluble, stable, and potent form of Ang1, on promotion of healing in cutaneous wounds of diabetic mice. An excisional full-thickness wound was made in the dorsal side of the tail of diabetic (db/db) mice, and mice were then treated systemically with adenovirus (Ade) encoding COMP-Ang1 or with control virus encoding beta-gal (Ade-beta-gal) or treated topically with recombinant COMP-Ang1 protein or BSA. Time course observations revealed that mice treated with Ade-COMP-Ang1 or COMP-Ang1 protein showed accelerated wound closure and epidermal and dermal regeneration, enhanced angiogenesis and lymphangiogenesis, and higher blood flow in the wound region compared with mice treated with control virus or BSA. COMP-Ang1 promotion of wound closure and angiogenesis was not dependent on endothelial nitric oxide synthase or inducible nitric oxide synthase alone. Taken together, these findings indicate that COMP-Ang1 can promote wound healing in diabetes through enhanced angiogenesis, lymphangiogenesis, and blood flow.

Lymphangiogenesis in development and human disease

The lymphatic vasculature forms a vessel network that drains interstitial fluid from tissues and returns it to the blood. Lymphatic vessels are also an essential part of the body's immune defence. They have an important role in the pathogenesis of several diseases, such as cancer, lymphoedema and various inflammatory conditions. Recent biological and technological developments in lymphatic vascular biology will lead to a better understanding and treatment of these diseases.

Lymphgef��system und Haut

Dermatology offers many clinical examples of abnormalities in the production, absorption and transport of lymph. Lymphatic thromboses also occur. Many diseases are not named in accordance with their underlying pathogenesis. Malignant lymphedema must be recognized immediately. The differential diagnosis of regional lymphedema is also part of dermatology. Stemmer sign is a clue to chronic lymphedema. Lymphoedema is first divided into primary and secondary forms, depending on the cause, and then subdivided into stages depending on severity. Complications of chronic lymphedema include recurrent erysipelas, superficial lymphangiectases, verrucous lymphedema (papillomatosis lymphostatica) and angiosarcoma, which is often multifocal. Established diagnostic approaches are available to correctly diagnose lymphatic disease. The treatment of chronic lymphedema centers around reducing the edema which then influences all of the other problems. The physical therapeutic approach to reducing blockage is the best way to achieve these goals.

Angiopoietin-1 promotes LYVE-1-positive lymphatic vessel formation

Angiopoietin (Ang) signaling plays a role in angiogenesis and remodeling of blood vessels through the receptor tyrosine kinase Tie2, which is expressed on blood vessel endothelial cells (BECs). Recently it has been shown that Ang-2 is crucial for the formation of lymphatic vasculature and that defects in lymphangiogenesis seen in Ang-2 mutant mice are rescued by Ang-1. These findings suggest important roles for Ang signaling in the lymphatic vessel system; however, Ang function in lymphangiogenesis has not been characterized. In this study, we reveal that lymphatic vascular endothelial hyaluronan receptor 1-positive (LYVE-1(+)) lymphatic endothelial cells (LECs) express Tie2 in both embryonic and adult settings, indicating that Ang signaling occurs in lymphatic vessels. Therefore, we examined whether Ang-1 acts on in vivo lymphatic angiogenesis and in vitro growth of LECs. A chimeric form of Ang-1, cartilage oligomeric matrix protein (COMP)-Ang-1, promotes in vivo lymphatic angiogenesis in mouse cornea. Moreover, we found that COMP-Ang-1 stimulates in vitro colony formation of LECs. These Ang-1-induced in vivo and in vitro effects on LECs were suppressed by soluble Tie2-Fc fusion protein, which acts as an inhibitor by sequestering Ang-1. On the basis of these observations, we propose that Ang signaling regulates lymphatic vessel formation through Tie2.