Differential Expression of Mucin in Salivary Gland Tumours.

Background and Objectives: Mucin has been implicated via various mechanisms in the development and growth of tumour cells. However, mucin expression studies in salivary gland tumours are limited, especially with samples from minor salivary glands. This study aims to investigate and compare mucin expression in benign and malignant salivary gland tumours of minor and major salivary gland origins. Materials and Methods: Special stains were used to stain neutral mucin (Periodic acid Schiff), sialomucin (Alcian Blue) and sulfomucin (Aldehyde Fuschin) within tissues from six normal salivary glands and 73 salivary gland tumours including 31 pleomorphic adenomas, 27 mucoepidermoid carcinomas, and 15 adenoid cystic carcinomas. A semi-quantitative approach was used to evaluate mucin expression within ductal lumens. Sialomucin was the most expressed mucin in all salivary gland tumours, regardless of origin. Results: A significant difference was observed in the mucin expression between benign and malignant salivary gland tumours, as pleomorphic adenoma showed three times significantly higher expression of sialomucin compared to mucoepidermoid carcinoma and adenoid cystic carcinoma (p = 0.028). Pleomorphic adenomas of major glands showed 42 times significantly higher expression of sialomucin compared to those of minor glands (p = 0.000). Conclusions: Sialomucin content in pleomorphic adenomas of major glands was vastly increased compared to that in minor glands. Differential sialomucin expression in benign and malignant salivary gland tumours suggests a role in diagnosing of borderline salivary gland tumours.

Endomucin selectively regulates vascular endothelial growth factor receptor-2 endocytosis through its interaction with AP2.

The endothelial glycocalyx, located at the luminal surface of the endothelium, plays an important role in the regulation of leukocyte adhesion, vascular permeability, and vascular homeostasis. Endomucin (EMCN), a component of the endothelial glycocalyx, is a mucin-like transmembrane glycoprotein selectively expressed by venous and capillary endothelium. We have previously shown that knockdown of EMCN impairs retinal vascular development in vivo and vascular endothelial growth factor 165 isoform (VEGF165)-induced cell migration, proliferation, and tube formation by human retinal endothelial cells in vitro and that EMCN is essential for VEGF165-stimulated clathrin-mediated endocytosis and signaling of VEGF receptor 2 (VEGFR2). Clathrin-mediated endocytosis is an essential step in receptor signaling and is of paramount importance for a number of receptors for growth factors involved in angiogenesis. In this study, we further investigated the molecular mechanism underlying EMCN's involvement in the regulation of VEGF-induced endocytosis. In addition, we examined the specificity of EMCN's role in angiogenesis-related cell surface receptor tyrosine kinase endocytosis and signaling. We identified that EMCN interacts with AP2 complex, which is essential for clathrin-mediated endocytosis. Lack of EMCN did not affect clathrin recruitment to the AP2 complex following VEGF stimulation, but it is necessary for the interaction between VEGFR2 and the AP2 complex during endocytosis. EMCN does not inhibit VEGFR1 and FGFR1 internalization or their downstream activities since EMCN interacts with VEGFR2 but not VEGFR1 or FGFR1. Additionally, EMCN also regulates VEGF121-induced VEGFR2 phosphorylation and internalization.

Inflammation-induced sialin mediates nitrate efflux in dysfunctional endothelium affecting NO bioavailability.

AIM: The mechanism of NO bioavailability in endothelial dysfunction, the trigger for atherogenesis is still unclear as exogenous nitrate therapy fails to alleviate endothelial dysfunction. Recently, sialin, a nitrate transporter, has been linked to affect tissue nitrate/nitrite levels. Hence, we investigated the role of sialin in NO bioavailability in endothelial dysfunction. METHODS: Serum-starved HUVECs were stimulated with either TNFα or AT-2 for 24 h either alone or in the presence of autophagy inducer or autophagy inhibitor alone. Nitric oxide, nitrite, and nitrate levels were measured in cell supernatant and cell lysate. Quantitative real-time PCR, Annexin V-PI, and monocyte adhesion assays were performed. Immunofluorescence staining for sialin, vWF, and LC3 was performed. STRING database was used to create protein interacting partners for sialin. RESULTS: Sialin is strongly expressed in activated EC in vitro and atherosclerotic plaque as well as tumor neo-vessel ECs. Sialin mediates nitrate ion efflux and is negatively regulated by autophagy via mTOR pathway. Blocking sialin enhances NO bioavailability, autophagy, cell survival, and eNOS expression while decreasing monocyte adhesion. PPI shows LGALS8 to directly interact with sialin and regulate autophagy, cell-cell adhesion, and apoptosis. CONCLUSION: Sialin is a potential novel therapeutic target for treating endothelial dysfunction in atherosclerosis and cancer.

Mucin levels in glands of the colonic mucosa of rats with diversion colitis subjected to enemas containing sucralfate and n-acetylcysteine alone or in combination.

PURPOSE: To evaluate the tissue content of neutral and acidic mucins, sulfomucins and sialomucins in colonic glands devoid of intestinal transit after enemas containing sucralfate and n-acetylcysteine alone or in combination. METHODS: Sixty-four rats underwent intestinal transit bypass. A colonic segment was collected to compose the white group (without intervention). After derivation, the animals were divided into two groups according to whether enemas were performed daily for two or four weeks. Each group was subdivided into four subgroups according to the substance used: control group: saline 0.9%; sucralfate group (SCF): SCF 2 g/kg/day; n-acetylcysteine group (NAC): NAC 100 mg/kg/day; and SCF+NAC group: SCF 2 g/kg/day + NAC 100 mg/kg/day.Neutral and acidic mucins were stained by periodic acid-Schiff and alcian-blue techniques, respectively. The distinction between sulfomucins and sialomucin was made by the high alcian-blue iron diamine technique. The content of mucins in the colonic glands was measured by computerized morphometry. The inflammatory score was assessed using a validated scale. The results between the groups were compared by the Mann-Whitney's test, while the variation according to time by the Kruskal-Wallis' test (Dunn's post-test). A significance level of 5% was adopted. RESULTS: There was reduction in the inflammatory score regardless of the application of isolated or associated substances. Intervention with SCF+NAC increased the content of all mucin subtypes regardless of intervention time. CONCLUSIONS: The application of SCF+NAC reduced the inflammatory process of the colonic mucosa and increased the content of different types of mucins in the colonic glands of segments excluded from fecal transit.

Tumor-derived endomucin promotes colorectal cancer proliferation and metastasis.

BACKGROUND: Endomucin (EMCN) is a type I transmembrane glycoprotein and a mucin-like component of the endothelial cell glycocalyx. The mechanism of EMCN action in colorectal cancer (CRC) remains unclear. AIMS: Our aim was to explore the role of EMCN in the progression of CRC. MATERIALS & METHODS: We examined EMCN expression in CRC tissues and normal para-carcinoma tissues. The function and mechanisms of EMCN were checked in CRC cell lines and in mouse xenograft. Additionally, we used co-immunoprecipitation and mass spectrometry to identify the potential EMCN-binding proteins. Functional annotation analysis showed where these genes were enriched. RESULTS: We found that EMCN was overexpressed in tumor tissues compared with that in normal para-carcinoma tissues. We also found that overexpression of EMCN induced CRC proliferation and metastasis both in vitro and in vivo. EMCN knockdown prevents epithelial-mesenchymal transition in vitro. We identified 178 potential EMCN-binding partners. Furthermore, functional annotation analysis indicated that these genes were considerably enriched in carcinogenic-related functions and pathways. Collectively, the identification of EMCN-binding partners enhanced our understanding of the mechanism of EMCN-mediated malignant phenotypes, and this research may provide valuable insights into the molecular mechanisms underlying CRC. CONCLUSION: Tumor-derived endomucin promotes colorectal cancer proliferation and metastasis. We identified 178 EMCN-binding proteins and initially screened three potential EMCN-interacting proteins: NALCN, and TPM2, ANKK1. Our study provides valuable insights into the molecular mechanisms underlying CRC development.

miR-210-3p protects against osteoarthritis through inhibiting subchondral angiogenesis by targeting the expression of TGFBR1 and ID4.

Excessive subchondral angiogenesis is a key pathological feature of osteoarthritis (OA), as it alters the balance of subchondral bone remodeling and causes progressive cartilage degradation. We previously found that miR-210-3p correlates negatively with angiogenesis, though the specific mechanism of miR-210-3p-related angiogenesis in subchondral bone during OA progression remains unclear. This study was conducted to identify the miR-210-3p-modulating subchondral angiogenesis mechanism in OA and investigate its therapeutic effect. We found that miR-210-3p expression correlated negatively with subchondral endomucin positive (Emcn+) vasculature in the knee joints of OA mice. miR-210-3p overexpression regulated the angiogenic ability of endothelial cells (ECs) under hypoxic conditions in vitro. Mechanistically, miR-210-3p inhibited ECs angiogenesis by suppressing transforming growth factor beta receptor 1 (TGFBR1) mRNA translation and degrading DNA-binding inhibitor 4 (ID4) mRNA. In addition, TGFBR1 downregulated the expression of ID4. Reduced ID4 levels led to a negative feedback regulation of TGFBR1, enhancing the inhibitory effect of miR-210-3p on angiogenesis. In OA mice, miR-210-3p overexpression in ECs via adeno-associated virus (AAV) alleviated cartilage degradation, suppressed the type 17 immune response and relieved symptoms by attenuating subchondral Emcn+ vasculature and subchondral bone remodeling. In conclusion, we identified a miR-210-3p/TGFBR1/ID4 axis in subchondral ECs that modulates OA progression via subchondral angiogenesis, representing a potential OA therapy target.

Gli1+-PDL Cells Contribute to Alveolar Bone Homeostasis and Regeneration.

The periodontal ligament (PDL) contains mesenchymal stem cells (MSCs) that can differentiate into osteoblasts, cementoblasts, and fibroblasts. Nevertheless, the distribution and characteristics of these cells remain uncertain. Gli1, an essential hedgehog signaling transcription factor, functions in undifferentiated cells during embryogenesis. Therefore, in the present study, the differentiation ability of Gli1+ cells was examined using Gli1-CreERT2/ROSA26-loxP-stop-loxP-tdTomato (iGli1/Tomato) mice. In 4-wk-old iGli1/Tomato mice, Gli1/Tomato+ cells were only slightly detected in the PDL, around endomucin-expressing blood vessels. These cells had proliferated over time, localizing in the PDL as well as on the bone and cementum surfaces at day 28. However, in 8-wk-old iGli1/Tomato mice, Gli1/Tomato+ cells were quiescent, as most cells were not immunoreactive for Ki-67. These cells in 8-wk-old mice exhibited high colony-forming unit fibroblast activity and were capable of osteogenic, chondrogenic, and adipogenic differentiation in vitro. In addition, after transplantation of teeth of iGli1/Tomato mice into the hypodermis of wild-type mice, Tomato fluorescence indicating the progeny of Gli1+ cells was detected in the osteoblasts and osteocytes of the regenerated bone. These results demonstrate that Gli1+ cells in the PDL were MSCs and could contribute to the alveolar bone regeneration.

Total flavonoids of Rhizoma Drynariae enhances CD31hiEmcnhi vessel formation and subsequent bone regeneration in rat models of distraction osteogenesis by activating PDGF­BB/VEGF/RUNX2/OSX signaling axis.

Total flavonoids of Rhizoma Drynariae (TFRD), extracted from the kidney­tonifying Traditional Chinese medicine Rhizoma Drynariae, can be effective in treating osteoporosis, bone fractures and defects. However, the pharmacological effects of TFRD on the specific vessel subtype CD31hiEmcnhi during distraction osteogenesis (DO) remains unclear. The present study aimed to investigate the effects of TFRD on CD31hiEmcnhi vessels in a rat model of DO. In the present study, tibial DO models were established using 60 rats with a distraction rate of 0.2 mm per day for 20 days. Co­immunofluorescence staining of CD31 and endomucin (Emcn) was conducted to determine CD31hiEmcnhi vessels. Radiographic, angiographic and histological analyses were performed to assess bone and vessel formation. Tube formation, alkaline phosphatase (ALP) and Von Kossa staining assays were performed to test angiogenesis of endothelial precursor cells (EPCs) and osteogenesis of bone marrow­derived mesenchymal stem cells (BMSCs). Additionally, expression levels of platelet­derived growth factor (PDGF)­BB, VEGF, runt­related transcription factor 2 (RUNX2) and Osterix (OSX) were determined by western blotting and reverse transcription­quantitative PCR. The in vivo assays demonstrated that TFRD markedly promoted CD31hiEmcnhi vessel formation during DO, whereas PDGF­BB neutralizing antibody suppressed vessel formation. Furthermore, the ALP, Von Kossa staining and tube formation assays indicated that TFRD notably elevated the angiogenic capacity of EPCs and osteogenic capacity of BMSCs under stress conditions, which was significantly suppressed by blocking PDGF­BB. The protein and mRNA levels of PDGF­BB, VEGF, RUNX2 and OSX were upregulated by TFRD, but downregulated by blocking PDGF­BB. Thus, TFRD could facilitate CD31hiEmcnhi vessel formation and subsequently enhance angiogenic­osteogenic coupling to regenerate bone defects during DO via the PDGF­BB/VEGF/RUNX2/OSX signaling axis, which indicated that CD31hiEmcnhi vessels could be a potential novel therapeutic target for DO, and TFRD may represent a promising drug for promoting bone regeneration in DO by increasing CD31hiEmcnhi vessels.

Immunolocalization of endomucin-reactive blood vessels and α-smooth muscle actin-positive cells in murine nasal conchae.

OBJECTIVES: Recently, the biological functions of endomucin-positive blood vessels and closely associated αSMA-positive cells in long bones have been highlighted. The surrounding tissues of the flat bones, such as nasal bones covered with mucosa and lamina propria, are different from those of the long bones, indicating the different distributions of endomucin-positive blood vessels and αSMA-reactive cells in nasal bones. This study demonstrates the immunolocalization of endomucin-reactive blood vessels and αSMA-positive cells in the nasal conchae of 3- and 7-week-old mice. METHODS: The nasal conchae of 3-week-old and 7-week-old male C57BL/6J mice were used for immunoreaction of endomucin, CD34, PDGFbb, TRAP, and c-kit. RESULTS: While we identified abundant endomucin-reactive blood vessels in the lamina propria neighboring the bone, not all were positive for endomucin. More CD34-reactive cells and small blood vessels were observed in the nasal conchae of 3-week-old mice than in those of 7-week-old mice. Some αSMA-positive cells in the nasal conchae surrounded the blood vessels, indicating vascular smooth muscle cells, while other αSMA-immunopositive fibroblastic cells were detected throughout the lamina propria. αSMA-positive cells did not co-localize with c-kit-immunoreactivity, thereby indicating that the αSMA-positive cells may be myofibroblasts rather than undifferentiated mesenchymal cells. CONCLUSIONS: Unlike long bones, nasal conchae contain endomucin-positive as well as endomucin-negative blood vessels and exhibit numerous αSMA-positive fibroblastic cells throughout the lamina propria neighboring the bone. Apparently, the distribution patterns of endomucin-positive blood vessels and αSMA-positive cells in nasal conchae are different from those in long bones.

Histochemical examination of blood vessels in murine femora with intermittent PTH administration.

OBJECTIVE: To verify the biological effects of parathyroid hormone (PTH) on the blood vessels in the bone, this study aimed to investigate histological alterations in endomucin-positive blood vessels and perivascular cells in murine femora after intermittent PTH administration. For comparison with blood vessels in the bone, we examined the distribution of endomucin-positive blood vessels and surrounding αSMA-immunoreactive perivascular cells in the liver, kidney, and aorta with or without PTH administration. METHODS: Six-week-old male C57BL/6J mice received hPTH [1-34] or vehicle for two weeks. All mice were fixed with a paraformaldehyde solution after euthanasia, and the right femora, kidney, liver, and aorta were extracted for immunohistochemical analysis of endomucin, αSMA, ephrinB2, EphB4, and HIF1α. Light microscopic observations of semi-thin sections and transmission electron microscopic (TEM) observations of ultra-thin sections were performed on the left femora. RESULTS: After intermittent PTH administration, αSMA-reactive/ephrinB2-positive stromal cells appeared around endomucin-positive/EphB4-immunoreactive blood vessels in the bone. In addition, intense immunoreactivities of EphB4 and HIF1α were seen in vascular endothelial cells after the PTH treatment. Several stromal cells surrounding PTH-treated blood vessels exhibited well-developed rough endoplasmic reticulum under TEM observations. In contrast to bone tissues, αSMA-positive stromal cells did not increase around the endomucin-positive blood vessels in the kidney, liver, or aorta, even after PTH administration. CONCLUSION: These findings show that intermittent PTH administration increases αSMA-reactive/ephrinB2-positive perivascular stromal cells in bone tissue but not in the kidney, liver, or aorta, suggesting that PTH preferentially affects blood vessels in the bone.

Genome-Wide Knockout Screen Identifies Human Sialomucin CD164 as an Essential Entry Factor for Lymphocytic Choriomeningitis Virus.

Lymphocytic choriomeningitis virus (LCMV) is a well-studied mammarenavirus that can be fatal in congenital infections. However, our understanding of LCMV and its interactions with human host factors remains incomplete. Here, host determinants affecting LCMV infection were investigated through a genome-wide CRISPR knockout screen in A549 cells, a human lung adenocarcinoma line. We identified and validated a variety of novel host factors that play a functional role in LCMV infection. Among these, knockout of the sialomucin CD164, a heavily glycosylated transmembrane protein, was found to ablate infection with multiple LCMV strains but not other hemorrhagic mammarenaviruses in several cell types. Further characterization revealed a dependency of LCMV entry on the cysteine-rich domain of CD164, including an N-linked glycosylation site at residue 104 in that region. Given the documented role of LCMV with respect to transplacental human infections, CD164 expression was investigated in human placental tissue and placental cell lines. CD164 was found to be highly expressed in the cytotrophoblast cells, an initial contact site for pathogens within the placenta, and LCMV infection in placental cells was effectively blocked using a monoclonal antibody specific to the cysteine-rich domain of CD164. Together, this study identifies novel factors associated with LCMV infection of human tissues and highlights the importance of CD164, a sialomucin that previously had not been associated with viral infection. IMPORTANCE Lymphocytic choriomeningitis virus (LCMV) is a human-pathogenic mammarenavirus that can be fatal in congenital infections. Although frequently used in the study of persistent infections in the field of immunology, aspects of this virus's life cycle remain incomplete. For example, while viral entry has been shown to depend on a cell adhesion molecule, DAG1, genetic knockout of this gene allows for residual viral infection, implying that additional receptors can mediate cell entry. The significance of our study is the identification of host factors important for successful infection, including the sialomucin CD164, which had not been previously associated with viral infection. We demonstrated that CD164 is essential for LCMV entry into human cells and can serve as a possible therapeutic target for treatment of congenital infection.

Optimization of Alcian blue pH 1.0 histo-staining protocols to match mass spectrometric quantification of sulfomucins and circumvent false positive results due to sialomucins.

Sulfomucins are in some body locations and species a normal occurrence, whereas in other situations, are a sign of pathology. Sulfomucin content on histological sections and isolated material is frequently analyzed with Alcian blue staining at pH 1.0. However, since the stain detects the charge, a high density of other charged molecules, such as sialic acids, has potential to impede specificity. Here, we compared the outcome from four staining protocols with the level of sulfation determined by liquid chromatography-tandem mass spectrometric analysis on samples from various tissues with variable sulfation and sialylation levels. We found that a protocol we designed, including rinsing with MetOH and 0.5 M NaCl buffer at pH 1.0, eliminates the false positive staining of tissues outperforming commonly recommended solutions. In tissues with low-to-moderately sulfated mucins (e.g. human stomach and salmonid epithelia), this method enables accurate relative quantification (e.g. sulfate scoring comparisons between healthy and diseased tissues), whereas the range of the method is not suitable for comparisons between tissues with high sulfomucin content (e.g. pig stomach and colon).

High Endothelial Venules: A Vascular Perspective on Tertiary Lymphoid Structures in Cancer.

High endothelial venules (HEVs) are specialized postcapillary venules composed of cuboidal blood endothelial cells that express high levels of sulfated sialomucins to bind L-Selectin/CD62L on lymphocytes, thereby facilitating their transmigration from the blood into the lymph nodes (LN) and other secondary lymphoid organs (SLO). HEVs have also been identified in human and murine tumors in predominantly CD3+T cell-enriched areas with fewer CD20+B-cell aggregates that are reminiscent of tertiary lymphoid-like structures (TLS). While HEV/TLS areas in human tumors are predominantly associated with increased survival, tumoral HEVs (TU-HEV) in mice have shown to foster lymphocyte-enriched immune centers and boost an immune response combined with different immunotherapies. Here, we discuss the current insight into TU-HEV formation, function, and regulation in tumors and elaborate on the functional implication, opportunities, and challenges of TU-HEV formation for cancer immunotherapy.

Role of MUC1 in lubrication of pleural mesothelial cells cultured on fibrine gel.

To elucidate the role of sialomucin in friction reduction, we investigated the sliding friction of pleural mesothelial cells monolayers cultured on fibrine gel. These measurements were performed on normal (4/4 RM-4) and on tumor (CARM-L1 TG3) cell lines. The effect of treatment with neuraminidase, which removes sialic acid from sialomucin, and of dexamethasone, which has shown to increase sialomucin expression, were also assessed. Furthermore, the expression of the main form of cell-surface-associated mucin (MUC1) present in the mesothelium, was assessed by western blot and immunofluorescence, under different experimental conditions. Expression of MUC1 was not significantly different in the two cell lines. Moreover, dexamethasone did not increase the expression of MUC1. Coefficient of kinetic friction (µ) was significantly higher in tumor cells than in normal cells. Neuraminidase increased µ in both cell lines. These results suggest that sialomucin may play a role in reducing the friction of pleural mesothelial cells.

Elements of the Endomucin Extracellular Domain Essential for VEGF-Induced VEGFR2 Activity.

Endomucin (EMCN) is the type I transmembrane glycoprotein, mucin-like component of the endothelial cell glycocalyx. We have previously shown that EMCN is necessary for vascular endothelial growth factor (VEGF)-induced VEGF receptor 2 (VEGFR2) internalization and downstream signaling. To explore the structural components of EMCN that are necessary for its function and the molecular mechanism of EMCN in VEGF-induced endothelial functions, we generated a series of mouse EMCN truncation mutants and examined their ability to rescue VEGF-induced endothelial functions in human primary endothelial cells (EC) in which endogenous EMCN had been knocked down using siRNA. Expression of the mouse full-length EMCN (FL EMCN) and the extracellular domain truncation mutants ∆21-81 EMCN and ∆21-121 EMCN, but not the shortest mutant ∆21-161 EMCN, successfully rescued the VEGF-induced EC migration, tube formation, and proliferation. ∆21-161 EMCN failed to interact with VEGFR2 and did not facilitate VEGFR2 internalization. Deletion of COSMC (C1GalT1C1) revealed that the abundant mucin-type O-glycans were not required for its VEGFR2-related functions. Mutation of the two N-glycosylation sites on ∆21-121 EMCN abolished its interaction with VEGFR2 and its function in VEGFR2 internalization. These results reveal ∆21-121 EMCN as the minimal extracellular domain sufficient for VEGFR2-mediated endothelial function and demonstrate an important role for N-glycosylation in VEGFR2 interaction, internalization, and angiogenic activity.

Endothelial Notch activation promotes neutrophil transmigration via downregulating endomucin to aggravate hepatic ischemia/reperfusion injury.

Inflammatory leukocytes infiltration is orchestrated by mechanisms involving chemokines, selectins, addressins and other adhesion molecules derived from endothelial cells (ECs), but how they respond to inflammatory cues and coordinate leukocyte transmigration remain elusive. In this study, using hepatic ischemia/reperfusion injury (HIRI) as a model, we identified that endothelial Notch activation was rapidly and dynamically induced in liver sinusoidal endothelial cells (LSECs) in acute inflammation. In mice with EC-specific Notch activation (NICeCA), HIRI induced exacerbated liver damage. Consistently, endothelial Notch activation enhanced neutrophil infiltration and tumor necrosis factor (TNF)-α expression in HIRI. Transcriptome analysis and further qRT-PCR as well as immunofluorescence indicated that endomucin (EMCN), a negative regulator of leukocyte adhesion, was downregulated in LSECs from NICeCA mice. EMCN was downregulated during HIRI in wild-type mice and in vitro cultured ECs insulted by hypoxia/re-oxygenation injury. Notch activation in ECs led to increased neutrophil adhesion and transendothelial migration, which was abrogated by EMCN overexpression in vitro. In mice deficient of RBPj, the integrative transcription factor of canonical Notch signaling, although overwhelming sinusoidal malformation aggravated HIRI, the expression of EMCN was upregulated; and pharmaceutical Notch blockade in vitro also upregulated EMCN and inhibited transendothelial migration of neutrophils. The Notch activation-exaggerated HIRI was compromised by blocking LFA-1, which mediated leukocyte adherence by associating with EMCN. Therefore, endothelial Notch signaling controls neutrophil transmigration via EMCN to modulate acute inflammation in HIRI.

GCNT1-Mediated O-Glycosylation of the Sialomucin CD43 Is a Sensitive Indicator of Notch Signaling in Activated T Cells.

Notch signaling is emerging as a critical regulator of T cell activation and function. However, there is no reliable cell surface indicator of Notch signaling across activated T cell subsets. In this study, we show that Notch signals induce upregulated expression of the Gcnt1 glycosyltransferase gene in T cells mediating graft-versus-host disease after allogeneic bone marrow transplantation in mice. To determine if Gcnt1-mediated O-glycosylation could be used as a Notch signaling reporter, we quantified the core-2 O-glycoform of CD43 in multiple T cell subsets during graft-versus-host disease. Pharmacological blockade of Delta-like Notch ligands abrogated core-2 O-glycosylation in a dose-dependent manner after allogeneic bone marrow transplantation, both in donor-derived CD4+ and CD8+ effector T cells and in Foxp3+ regulatory T cells. CD43 core-2 O-glycosylation depended on cell-intrinsic canonical Notch signals and identified CD4+ and CD8+ T cells with high cytokine-producing ability. Gcnt1-deficient T cells still drove lethal alloreactivity, showing that core-2 O-glycosylation predicted, but did not cause, Notch-dependent T cell pathogenicity. Using core-2 O-glycosylation as a marker of Notch signaling, we identified Ccl19-Cre+ fibroblastic stromal cells as critical sources of Delta-like ligands in graft-versus-host responses irrespective of conditioning intensity. Core-2 O-glycosylation also reported Notch signaling in CD8+ T cell responses to dendritic cell immunization, Listeria infection, and viral infection. Thus, we uncovered a role for Notch in controlling core-2 O-glycosylation and identified a cell surface marker to quantify Notch signals in multiple immunological contexts. Our findings will help refine our understanding of the regulation, cellular source, and timing of Notch signals in T cell immunity.

Sialomucin and phosphorylated-ERM are inhibitors for cadherin-mediated aggregate formation.

Cell adhesion is mediated by adhesion molecules, but also regulated by adhesion inhibitory molecules. Molecules such as leukocyte sialomucin and phosphorylated-Ezrin/Radixin/Moesin (ERM) inhibit cell-substratum adhesion. Here we show that these adhesion inhibitory molecules also inhibit aggregate formation of adherent cells in suspension culture. Expression of sialomucin, CD43 or CD34, inhibited formation of packed aggregates in HEK293T cells. Deletion mutant analysis and enzymatic cleavage indicated the significance of the extracellular sialomucin domain for this inhibition. Meanwhile, phosphorylated-ERM were decreased coincidently with aggregate formation. Combined with the inhibition of aggregate formation by the expression of phospho-mimetic Moesin mutant (Moesin-T558D), phosphorylated-ERM are inhibitors for aggregate formation. Increase of phosphorylated-ERM by CD43 and sialomucin-dependence of Moesin-T558D's inhibition indicate that sialomucin and phosphorylated-ERM collaborate to inhibit aggregate formation. Because aggregate formation of HEK293T cells is mediated by N-cadherin, sialomucin and phosphorylated-ERM inhibit cadherin-mediated cell-cell adhesion. Thus, sialomucin and phosphorylated-ERM are inhibitors for both cell-cell adhesion and cell-substratum adhesion, and regulation of these inhibitory molecules is essential for cell adhesion.

Endomucin restores depleted endothelial glycocalyx in the retinas of streptozotocin-induced diabetic rats.

Endothelial glycocalyx plays a significant role in the development and progression of diabetic complications. Endomucin (EMCN) is an anti-inflammatory membrane glycoprotein that is mainly expressed in venous and capillary endothelial cells. However, the function of EMCN in diabetic retinopathy (DR) progression is still completely unknown. We first investigated the change of EMCN expression in the retina and human retinal microvascular endothelial cells. We then overexpressed EMCN in the retina with adeno-associated virus and induced DR with streptozotocin (STZ). We analyzed EMCN's effect on the integrity of endothelial glycocalyx under conditions of DR. Furthermore, we investigated EMCN's protective effect against inflammation and blood-retinal barrier (BRB) destruction. We found that EMCN is specifically expressed in retinal endothelial cells and that its levels are decreased during hyperglycemia in vitro and in vivo. Overexpression of EMCN can restore the retinal endothelial glycocalyx of STZ-induced diabetic rats. Furthermore, EMCN overexpression can decrease leukocyte-endothelial adhesion to ameliorate inflammation and stabilize the BRB to inhibit vessel leakage in rats with DR. EMCN may protect patients with diabetes from retinal vascular degeneration by restoring the endothelial glycocalyx. EMCN may thus represent a novel therapeutic strategy for DR because it targets endothelial glycocalyx degradation associated with this disease.-Niu, T., Zhao, M., Jiang, Y., Xing, X., Shi, X., Cheng, L., Jin, H., Liu, K. Endomucin restores depleted endothelial glycocalyx in the retinas of streptozotocin-induced diabetic rats.

Glycocalyx regulation of vascular endothelial growth factor receptor 2 activity.

We have previously shown that knockdown of endomucin (EMCN), an integral membrane glycocalyx glycoprotein, prevents VEGF-induced proliferation, migration, and tube formation in vitro and angiogenesis in vivo. In the endothelium, VEGF mediates most of its angiogenic effects through VEGF receptor 2 (VEGFR2). To understand the role of EMCN, we examined the effect of EMCN depletion on VEGFR2 endocytosis and activation. Results showed that although VEGF stimulation promoted VEGFR2 internalization in control endothelial cells (ECs), loss of EMCN prevented VEGFR2 endocytosis. Cell surface analysis revealed a decrease in VEGFR2 following VEGF stimulation in control but not siRNA directed against EMCN-transfected ECs. EMCN depletion resulted in heightened phosphorylation following VEGF stimulation with an increase in total VEGFR2 protein. These results indicate that EMCN modulates VEGFR2 endocytosis and activity and point to EMCN as a potential therapeutic target.-LeBlanc, M. E., Saez-Torres, K. L., Cano, I., Hu, Z., Saint-Geniez, M., Ng, Y.-S., D'Amore, P. A. Glycocalyx regulation of vascular endothelial growth factor receptor 2 activity.