Formation Of Lymphatic Capillaries Research Articles

Lymphatic Vessels in the Inner Ear of Patients With Meniere Disease: A Novel Pathological Finding.

Meniere disease, characterized by intermittent episodes of vertigo, fluctuating sensorineural hearing loss, tinnitus, and aural pressure, is a common cause of vertigo in humans. The pathogenesis of Meniere disease remains unknown. The current study aimed to describe a novel pathological change discovered in the inner ears of patients with Meniere disease who underwent labyrinthectomy. This retrospective case-control study was conducted with 21 patients with MD who underwent labyrinthectomy. A total of 15 patients diagnosed with acoustic neuroma or glomus jugular tumor were review over the same period of time as control. The clinical information of the patients and the pathological features of the membrane are described. The new pathological tissue was a morbid membrane structure sealing the round window, characterized by the formation of lymphatic capillaries. Histochemical and immunofluorescent staining was positive for D2-40, LYVE-1, podoplanin, and PROX1, which are the classical markers of the lymphatic vessels. Transmission electron microscopy revealed that the lymph capillaries lacked a typical basement membrane and that their ends were blind, composed of a single layer of endothelial cells with valval connection structures between adjacent capillary epithelial cells. This is the first report of lymphatic vessels in the human inner ear, and this pathological structure is a completely new discovery. The lymphatic vessels may develop due to inflammation or decompensation of pressure in the inner ear, suggesting that the inner ear can reactively form lymphatic vessels in some inflammation and fluid flow-dependent pathological conditions. The current findings help in improving our understanding of the pathogenesis of Meniere disease.

The Role of Methionine Aminopeptidase 2 in Lymphangiogenesis.

During the metastasis process, tumor cells invade the blood circulatory system directly from venous capillaries or indirectly via lymphatic vessels. Understanding the relative contribution of each pathway and identifying the molecular targets that affect both processes is critical for reducing cancer spread. Methionine aminopeptidase 2 (MetAp2) is an intracellular enzyme known to modulate angiogenesis. In this study, we investigated the additional role of MetAp2 in lymphangiogenesis. A histological staining of tumors from human breast-cancer donors was performed in order to detect the level and the localization of MetAp2 and lymphatic capillaries. The basal enzymatic level and activity in vascular and lymphatic endothelial cells were compared, followed by loss of function studies determining the role of MetAp2 in lymphangiogenesis in vitro and in vivo. The results from the histological analyses of the tumor tissues revealed a high MetAp2 expression, with detectable sites of co-localization with lymphatic capillaries. We showed slightly reduced levels of the MetAp2 enzyme and MetAp2 mRNA expression and activity in primary lymphatic cells when compared to the vascular endothelial cells. The genetic and biochemical manipulation of MetAp2 confirmed the dual activity of the enzyme in both vascular and lymphatic remodulation in cell function assays and in a zebrafish model. We found that cancer-related lymphangiogenesis is inhibited in murine models following MetAp2 inhibition treatment. Taken together, our study provides an indication that MetAp2 is a significant contributor to lymphangiogenesis and carries a dual role in both vascular and lymphatic capillary formation. Our data suggests that MetAp2 inhibitors can be effectively used as anti-metastatic broad-spectrum drugs.

Orbital Angiogenesis and Lymphangiogenesis in Thyroid Eye Disease: An Analysis of Vascular Growth Factors with Clinical Correlation

The human orbit is an environment that is vulnerable to inflammation and edema in the setting of autoimmune thyroid disease. Our study investigated the tenet that orbital adipose tissue lacks lymphatic vessels and analyzed the clinicopathologic differences between patients with acute and chronic thyroid eye disease (TED). The underlying molecular mediators of blood and lymphatic vessel formation within the orbital fat also were evaluated. Retrospective cohort study. The study included fat specimens from 26 orbits of 15 patients with TED undergoing orbital decompression. Orbital fat specimens from patients without TED as well as cadaveric orbital fat served as controls. Tissue specimens were processed as formalin-fixed, paraffin-embedded sections or frozen cryosections for immunohistochemistry. Total RNA was extracted and analyzed via quantitative (real-time) reverse-transcription polymerase chain reaction. Clinicopathologic correlation was made by determining the clinical activity score (CAS) of each patient with TED. Samples were examined for vascular and lymphatic markers including podoplanin, lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), and cluster of differentiation 31 (CD31) by immunohistochemistry, as well as for mRNA levels of vascular endothelial growth factor (VEGF), VEGF receptors, semaphorin 3F, neuropilin 1, neuropilin 2, podoplanin, and LYVE-1 by quantitative (real-time) reverse-transcription polymerase chain reaction. Clinicopathologic correlation revealed increased staining of CD31-positive blood vessels in patients with acute TED with a CAS more than 4, as well as rare staining of podoplanin-positive lymphatic vessels within acutely inflamed orbital fat tissue. Additionally, quantitative (real-time) reverse-transcription polymerase chain reaction analysis demonstrated increased expression of VEGF receptor (VEGFR) 2 as well as VEGF signaling molecules VEGF-A, VEGF-C, and VEGF-D. In acute TED, compared with chronic TED and control orbital fat, there is increased blood vessel density, suggesting neovascularization and rare lymphatic vessels suggestive of limited lymphangiogenesis. This proangiogenic and prolymphangiogenic microenvironment is likely the result of the increased expression of VEGFR-2, VEGF-A, VEGF-C, and VEGF-D. These findings imply that orbital edema in acute TED may be mediated, in part, by both the formation of new, immature blood vessels and the formation of lymphatic capillaries that are functionally incapable of draining interstitial fluid.

Src contributes to IL6-induced vascular endothelial growth factor-C expression in lymphatic endothelial cells

Formation of lymphatic capillaries by lymphatic endothelial cells (LECs) occurs both in normal tissues as well as in pathological processes including tumor metastasis. Interleukin-6 (IL-6), a potent pro-inflammatory cytokine, has been shown to be highly elevated in various cancers. IL-6 has also been shown to increase tumor lymphangiogenesis through vascular endothelial growth factor-C (VEGF-C) induction in tumor cells. Although lymphangiogenesis is associated with lymph node metastasis and also resistance to conventional therapy in various cancers, the precise mechanisms of lymphangiogenesis in LECs remain unclear. This study aimed to investigate the signaling cascade involved in IL-6-induced VEGF-C expression in murine LECs (SV-LEC). The VEGF-C mRNA and protein levels were increased in SV-LECs exposed to IL-6. IL-6 time-dependently induced Src phosphorylation and downstream phosphorylation of ERK1/2 and p38MAPK. In contrast, PP2, an inhibitor of Src signaling, abrogated IL-6's effects on ERK1/2 and p38MAPK phosphorylation. IL-6 exposure also led to increase in VEGF-C promoter-luciferase activity as well as C/EBPβ- and κB-luciferase activities. VEGF-C promoter-, C/EBPβ- and κB-luciferase activities were all suppressed by Src, ERK1/2 or p38MAPK signaling blockades despite presence of IL-6. Finally, C/EBPβ and p65 binding to the VEGF-C promoter region were increased after IL-6 exposure in SV-LECs. Taken together, we report a Src-mediated ERK1/2 and p38MAPK activation resulting in C/EBPβ and p65 binding to the promoter region of VEGF-C, leading to VEGF-C expression in IL-6-exposed SV-LECs.