Down-regulation of polycystin in lymphatic malformations: possible role in the proliferation of lymphatic endothelial cells.

Lymphatic malformations (LMs) are composed of aberrant lymphatic vessels and regarded as benign growths of the lymphatic system. Recent studies have demonstrated that the mutant embryos of PKD1 and PKD2, encoding polycystin-1 (PC-1) and polycystin-2 (PC-2), respectively, result in aberrant lymphatic vessels similar to those observed in LMs. In this study, for the first time, we investigated PC-1 and PC-2 expression and assessed their roles in the development of LMs. Our results demonstrated that PC-1 and PC-2 gene and protein expressions were obviously decreased in LMs compared with normal skin tissues. In addition, the expression of phosphorylated ERK but not total ERK was up-regulated in LMs and negatively correlated with the expression of PC-1 and PC-2. Moreover, up-regulation of Ki67 was detected in LMs and positively correlated with ERK phosphorylation levels. Furthermore, cluster analysis better reflected close correlation between these signals. All of the above results provided strong evidence suggesting that the hyperactivation of the ERK pathway may be caused by down-regulation of PC-1 and PC-2 in LMs, contributing to increased proliferation of lymphatic endothelial cells in LMs. Our present study sheds light on novel potential mechanisms involved in LMs and may help to explore novel treatments for LMs.

Polydom Is an Extracellular Matrix Protein Involved in Lymphatic Vessel Remodeling.

RATIONALE: Lymphatic vasculature constitutes a second vascular system essential for immune surveillance and tissue fluid homeostasis. Maturation of the hierarchical vascular structure, with a highly branched network of capillaries and ducts, is crucial for its function. Environmental cues mediate the remodeling process, but the mechanism that underlies this process is largely unknown. OBJECTIVE: Polydom (also called Svep1) is an extracellular matrix protein identified as a high-affinity ligand for integrin α9ß1. However, its physiological function is unclear. Here, we investigated the role of Polydom in lymphatic development. METHODS AND RESULTS: We generated Polydom-deficient mice. Polydom-/- mice showed severe edema and died immediately after birth because of respiratory failure. We found that although a primitive lymphatic plexus was formed, it failed to undergo remodeling in Polydom-/- embryos, including sprouting of new capillaries and formation of collecting lymphatic vessels. Impaired lymphatic development was also observed after knockdown/knockout of polydom in zebrafish. Polydom was deposited around lymphatic vessels, but secreted from surrounding mesenchymal cells. Expression of Foxc2 (forkhead box protein c2), a transcription factor involved in lymphatic remodeling, was decreased in Polydom-/- mice. Polydom bound to the lymphangiogenic factor Ang-2 (angiopoietin-2), which was found to upregulate Foxc2 expression in cultured lymphatic endothelial cells. Expressions of Tie1/Tie2 receptors for angiopoietins were also decreased in Polydom-/- mice. CONCLUSIONS: Polydom affects remodeling of lymphatic vessels in both mouse and zebrafish. Polydom deposited around lymphatic vessels seems to ensure Foxc2 upregulation in lymphatic endothelial cells, possibly via the Ang-2 and Tie1/Tie2 receptor system.

An Evolutionarily Conserved Role for Polydom/Svep1 During Lymphatic Vessel Formation.

RATIONALE: Lymphatic vessel formation and function constitutes a physiologically and pathophysiologically important process, but its genetic control is not well understood. OBJECTIVE: Here, we identify the secreted Polydom/Svep1 protein as essential for the formation of the lymphatic vasculature. We analyzed mutants in mice and zebrafish to gain insight into the role of Polydom/Svep1 in the lymphangiogenic process. METHODS AND RESULTS: Phenotypic analysis of zebrafish polydom/svep1 mutants showed a decrease in venous and lymphovenous sprouting, which leads to an increased number of intersegmental arteries. A reduced number of primordial lymphatic cells populated the horizontal myoseptum region but failed to migrate dorsally or ventrally, resulting in severe reduction of the lymphatic trunk vasculature. Corresponding mutants in the mouse Polydom/Svep1 gene showed normal egression of Prox-1+ cells from the cardinal vein at E10.5, but at E12.5, the tight association between the cardinal vein and lymphatic endothelial cells at the first lymphovenous contact site was abnormal. Furthermore, mesenteric lymphatic structures at E18.5 failed to undergo remodeling events in mutants and lacked lymphatic valves. In both fish and mouse embryos, the expression of the gene suggests a nonendothelial and noncell autonomous mechanism. CONCLUSIONS: Our data identify zebrafish and mouse Polydom/Svep1 as essential extracellular factors for lymphangiogenesis. Expression of the respective genes by mesenchymal cells in intimate proximity with venous and lymphatic endothelial cells is required for sprouting and migratory events in zebrafish and for remodeling events of the lymphatic intraluminal valves in mouse embryos.

Aberrant lymphatic development in euploid fetuses with increased nuchal translucency including Noonan syndrome.

OBJECTIVE: Increased nuchal translucency in the human fetus is associated with aneuploidy, structural malformations and several syndromes such as Noonan syndrome. In 60­70% of the Noonan syndrome cases, a gene mutation can be demonstrated. Previous research showed that aneuploid fetuses with increased nuchal translucency (NT) demonstrate an aberrant lymphatic endothelial differentiation. METHOD: Fetuses with increased NT and normal karyotype (n = 7) were compared with euploid controls having normal NT (n = 5). A Noonan syndrome gene mutation was found in three out of seven fetuses with increased NT. Endothelial differentiation was evaluated by immunohistochemistry using lymphatic markers (PROX-1, Podoplanin, LYVE-1) and blood vessel markers vascular endothelial growth factor-A (VEGF-A), Neuropilin-1 (NP-1), Sonic hedgehog, von Willebrand factor, and the smooth muscle cell marker, smooth muscle actin. RESULTS: Nuchal edema and enlarged jugular lymphatic sacs (JLSs) were observed in fetuses with increased NT, together with abnormal lymphatic endothelial differentiation i.e. the presence of blood vessel characteristics, including high levels of VEGF-A and NP-1 expression. The enlarged JLSs contained erythrocytes and were surrounded by smooth muscle cells. CONCLUSION: This study shows an aberrant lymphatic endothelial differentiation in fetuses with increased NT and a normal karyotype (including Noonan syndrome fetuses), as was previously reported before in aneuploid fetuses.

Prox-1 and VEGFR3 antibodies are superior to D2-40 in identifying endothelial cells of lymphatic malformations--a proposal of a new immunohistochemical panel to differentiate lymphatic from other vascular malformations.

We previously reported that D2-40 antibody identifies lymphatic endothelial cells (LECs) of lymphatic malformations (LM) with high specificity but only moderate sensitivity. The aim of this study was to compare the sensitivity and specificity of the markers Prospero-related homeobox gene-1 (Prox-1) and VEGFR3 to those of D2-40 for LECs in LM. Seventeen LM and 6 other vascular malformations with venous component (VM) were stained with D2-40, Prox-1, VEGFR3, CD31, and CD34 antibodies. The staining characteristics of vessels by each marker were assessed. Prox-1 and VEGFR3 specificity for LECs was examined by endothelial staining of VMs. Prox-1 and VEGFR3 stained substantially more large vessels than did D2-40 (15 of 17 cases). Small vessel staining was uniformly positive with all vascular markers except CD34, which did not stain lymphatic vessels. Eight cases had no or minimal D2-40 staining of large vessels, but the selected D2-40-vessels stained positive with VEGFR3, and 7 of 8 vessels were Prox-1 positive. Nine cases had variable D2-40 staining of large vessels; the selected D2-40 channels were all Prox-1 positive, and 8 of 9 were VEGFR3 positive. Two had rare vascular channels with no lymphatic marker stain but were positive for CD31 and CD34. Endothelial cells of VM had no Prox-1 but were VEGFR3/CD31/CD34 positive. VEGFR3 and Prox-1 antibodies have greater sensitivity for large lymphatic vessels than does D2-40. All lymphatic markers have high sensitivity for LECs of small lymphatic channels. Prox-1 has superior sensitivity and specificity to LECs. We recommend utilizing an immunohistochemical panel consisting of Prox-1, VEGFR3, CD31, and CD34 antibodies to differentiate lymphatic from venous malformations in pathologic practice.

Jugular lymphatic maldevelopment in Turner syndrome and trisomy 21: different anomalies leading to nuchal edema.

Increased nuchal translucency (NT), morphologically known as nuchal edema, is an ultrasound marker for aneuploidy. Turner syndrome presents with massive NT, called cystic hygroma. Conflicting data exist as to whether cystic hygroma and increased NT are different entities. Both are associated with jugular lymphatic distension. The authors investigated jugular lymphatics of trisomy 21, Turner syndrome, and normal karyotype fetuses. Fetuses were investigated using immunohistochemistry for blood vascular, lymphatic, and smooth muscle cell markers. Trisomy 21 fetuses showed nuchal cavities within the mesenchymal edema negative for endothelial markers. These were extremely large in Turner fetuses, showing similar characteristics. The skin showed numerous dilated lymphatics in the case of trisomy 21 and scanty small lymphatics in Turner fetuses. A jugular lymphatic sac was present in control and trisomy 21 fetuses and was enlarged in trisomy 21 cases. In Turner fetuses, no jugular lymphatic sac was observed. Nuchal edema in trisomy 21 and Turner syndrome appears to be a similar entity caused by different lymphatic abnormalities.