Integrin α9ß1 deficiency does not impact the development of atherosclerosis in mice.

Sushi, von Willebrand factor type A, EGF and pentraxin domain containing 1 (SVEP1) is an extracellular matrix protein that causally promotes cardiovascular disease in humans and mice. However, the receptor mediating the effect of SVEP1 on the development of disease remains unclear. We previously demonstrated that depleting either vascular smooth muscle cell (VSMC)- or myeloid cell-derived integrin α9ß1, the first receptor that was identified to interact with SVEP1, did not phenocopy the disease-abrogating effect of depleting SVEP1. Due to its wide expression in tissues and cell types, here we extend this line of investigation to definitively determine if integrin α9ß1 impacts the development of atherosclerosis. In a mouse model of atherosclerosis, we found that depleting integrin α9ß1 in all cells did not alter plaque size or characteristics of plaque complexity when compared to wild type mice. Further, the significant SVEP1-mediated effects on increase in macrophage content and VSMC proliferation within the atherosclerotic plaque were not altered in animals lacking integrin α9ß1. Together, these findings strongly suggest that integrin α9ß1 is not responsible for mediating the SVEP1-induced promotion of atherosclerosis and support further studies aimed at characterizing other receptors whose interaction with SVEP1 may represent a therapeutically targetable interaction.

EGR1 transcriptionally regulates SVEP1 to promote proliferation and migration in human coronary artery smooth muscle cells.

A low-frequency variant of sushi, von Willebrand factor type A, EGF, and pentraxin domain-containing protein 1 (SVEP1) is associated with the risk of coronary artery disease, as determined by a genome-wide association study. SVEP1 induces vascular smooth muscle cell proliferation and an inflammatory phenotype to promote atherosclerosis. In the present study, qRT‒PCR demonstrated that the mRNA expression of SVEP1 was significantly increased in atherosclerotic plaques compared to normal tissues. Bioinformatics revealed that EGR1 was a transcription factor for SVEP1. The results of the luciferase reporter assay, siRNA interference or overexpression assay, mutational analysis and ChIP confirmed that EGR1 positively regulated the transcriptional activity of SVEP1 by directly binding to its promoter. EGR1 promoted human coronary artery smooth muscle cell (HCASMC) proliferation and migration via SVEP1 in response to oxidized low-density lipoprotein (ox-LDL) treatment. Moreover, the expression level of EGR1 was increased in atherosclerotic plaques and showed a strong linear correlation with the expression of SVEP1. Our findings indicated that EGR1 binding to the promoter region drive SVEP1 transcription to promote HCASMC proliferation and migration.

BVES-AS1 suppresses the colorectal cancer progression via the miR-1269a/b-SVEP1-PI3K/AKT axis.

BACKGROUND: Numerous studies have indicated the engagement of long non-coding RNA (lncRNA) in various cancer types, including colorectal cancer (CRC). However, the functional and mechanistic roles of lncRNAs in CRC remain largely elusive. OBJECTIVES: The aim of this study was to explore the function and mechanism of lncRNA BVES-AS1 in CRC. MATERIAL AND METHODS: The expression levels of BVES-AS1 were validated in CRC tissues and paired normal samples using quantitative real-time polymerase chain reaction (qPCR) Subsequently, the biological functions of BVES-AS1 in CRC cells were investigated both in vitro and in vivo. Various experimental techniques such as western blot, fluorescence in situ hybridization, RNA-sequencing (RNA-seq), biotin-labeled miRNA pulldown assay, dual-luciferase reporter gene assay, and RNA-protein immunoprecipitation (RIP) assay were employed to elucidate the potential mechanism of BVES-AS1. RESULTS: The findings of this study demonstrated that BVES-AS1 expression was downregulated in CRC tissues compared to normal tissues, and its expression level was associated with tumor infiltration and tumor-nodule-metastasis (TNM) stage. Furthermore, BVES-AS1 was found to suppress CRC cell proliferation, migration and metastasis both in vitro and in vivo. Mechanistically, BVES-AS1 acted as a sponge for miR-1269a and miR-1269b, thereby regulating SVEP1. Additionally, the silencing of SVEP1 activated the PI3K/AKT pathway. CONCLUSIONS: These results suggest that BVES-AS1 plays a crucial role in the progression of CRC through the miR-1269a/b-SVEP1-PI3K/AKT axis, providing new insights into the therapeutic strategies for CRC.

The emerging Janus face of SVEP1 in development and disease.

Sushi, von Willebrand factor type A, EGF, and pentraxin domain containing 1 (SVEP1) is a large extracellular matrix protein that is also detected in circulation. Recent plasma proteomic and genomic studies have revealed a large number of associations between SVEP1 and human traits, particularly chronic disease. These include associations with cardiac death and disease, diabetes, platelet traits, glaucoma, dementia, and aging; many of these are causal. Animal models demonstrate that SVEP1 is critical in vascular development and disease, but its molecular and cellular mechanisms remain poorly defined. Future studies should aim to characterize these mechanisms and determine the diagnostic, prognostic, and therapeutic value of measuring or intervening on this enigmatic protein.

SVEP1 influences monocyte to macrophage differentiation via integrin α4ß1/α9ß1 and Rho/Rac signalling.

BACKGROUND: The large extracellular matrix protein SVEP1 mediates cell adhesion via integrin α9ß1. Recent studies have identified an association between a missense variant in SVEP1 and increased risk of coronary artery disease (CAD) in humans and in mice Svep1 deficiency alters the development of atherosclerotic plaques. However how SVEP1 functionally contributes to CAD pathogenesis is not fully understood. Monocyte recruitment and differentiation to macrophages is a key step in the development of atherosclerosis. Here, we investigated the requirement for SVEP1 in this process. METHODS: SVEP1 expression was measured during monocyte-macrophage differentiation in primary monocytes and THP-1 human monocytic cells. SVEP1 knockout THP-1 cell lines and the dual integrin α4ß1/α9ß1 inhibitor, BOP, were utilised to investigate the effect of these proteins in THP-1 cell adhesion, migration and cell spreading assays. Subsequent activation of downstream integrin signalling intermediaries was quantified by western blotting. RESULTS: SVEP1 gene expression increases in monocyte to macrophage differentiation in human primary monocytes and THP-1 cells. Using two SVEP1 knockout THP-1 cells we observed reduction in monocyte adhesion, migration, and cell spreading compared to control cells. Similar results were found with integrin α4ß1/α9ß1 inhibition. We demonstrate reduced activity of Rho and Rac1 in SVEP1 knockout THP-1 cells. CONCLUSIONS: SVEP1 regulates monocyte recruitment and differentiation phenotypes through an integrin α4ß1/α9ß1 dependent mechanism. GENERAL SIGNIFICANCE: These results describe a novel role for SVEP1 in monocyte behaviour relevant to CAD pathophysiology.

Effects of SVEP1 on Lung Squamous Cell Carcinoma and its Association with Tumor Mutation Burden, Prognosis, and Immune Regulation.

BACKGROUND: The mutated genes in lung squamous cell carcinoma were investigated for their possible association with tumor mutation burden, microsatellite instability, and cancer prognosis. OBJECTIVE: Our study aims to evaluate the value of the candidate genes as a potential biomarker of lung squamous cell carcinoma and pan-cancer analysis. METHODS: The landscape of the tumor microenvironment and infiltrating lymphocytes in lung squamous cell carcinoma was calculated using ESTIMATE and CIBERSORT algorithm. Weighed gene co-expression network analysis was used to screen key modules related to immune cell infiltration. Somatic mutations were found by data analysis from the TCGA and ICGC databases. Mann-Whitney U test was used to evaluate the tumor mutation burden difference between patients with mutant and wild-type SVEP1 genes. The Kaplan-Meier method was used to examine the prognosis of the patients with mutations. The effects of SVEP1 expression on tumor mutation burden and immunity in different cancers were determined by pan-cancer analysis. RESULTS: SVEP1 mutation was found to be associated with a higher tumor mutation burden and prognosis. SVEP1 mutation might be involved in the possible biological process of the anti-tumor immune response. SVEP1 is related to different degrees of immune infiltration in cancer. Moreover, the miRNA-SVEP1 targeting network was used to illuminate the possible mechanisms. CONCLUSION: SVEP1 mutation and its mRNA expression are related to tumor mutation burden and cancer immunity in lung squamous cell carcinoma. Our findings reveal the underlying mechanisms, indicating that SVEP1 may be a prognostic marker of lung squamous cell carcinoma.

Vascular smooth muscle- and myeloid cell-derived integrin α9ß1 does not directly mediate the development of atherosclerosis in mice.

BACKGROUND AND AIMS: Sushi, von Willebrand factor type A, EGF pentraxin domain-containing 1 (SVEP1), an extracellular matrix protein, is a human coronary artery disease locus that promotes atherosclerosis. We previously demonstrated that SVEP1 induces vascular smooth muscle cell (VSMC) proliferation and an inflammatory phenotype in the arterial wall to enhance the development of atherosclerotic plaque. The only receptor known to interact with SVEP1 is integrin α9ß1, a cell surface receptor that is expressed by VSMCs and myeloid lineage-derived monocytes and macrophages. Our previous in vitro studies suggested that integrin α9ß1 was necessary for SVEP1-induced VSMC proliferation and inflammation; however, the underlying mechanisms mediated by integrin α9ß1 in these cell types during the development of atherosclerosis remain poorly understood. METHODS AND RESULTS: Here, using cell-specific gene targeting, we investigated the effects of the integrin α9ß1 receptor on VSMCs and myeloid cells in mouse models of atherosclerosis. Interestingly, we found that depleting integrin α9ß1 in either VSMCs or myeloid cells did not affect the formation or complexity of atherosclerotic plaque in vessels after either 8 or 16 weeks of high fat diet feeding. CONCLUSIONS: Our results indicate that integrin α9ß1 in these two cell types does not mediate the in vivo effect of SVEP1 in the development of atherosclerosis. Instead, our results suggest either the presence of other potential receptor(s) or alternative integrin α9ß1-expressing cell types responsible for SVEP1 induced signaling in the development of atherosclerosis.

The integrin ligand SVEP1 regulates GPCR-mediated vasoconstriction via integrins α9ß1 and α4ß1.

BACKGROUND AND PURPOSE: Vascular tone is regulated by the relative contractile state of vascular smooth muscle cells (VSMCs). Several integrins directly modulate VSMC contraction by regulating calcium influx through L-type voltage-gated Ca2+ channels (VGCCs). Genetic variants in ITGA9, which encodes the α9 subunit of integrin α9ß1, and SVEP1, a ligand for integrin α9ß1, associate with elevated blood pressure; however, neither SVEP1 nor integrin α9ß1 has reported roles in vasoregulation. We determined whether SVEP1 and integrin α9ß1 can regulate VSMC contraction. EXPERIMENTAL APPROACH: SVEP1 and integrin binding were confirmed by immunoprecipitation and cell binding assays. Human induced pluripotent stem cell-derived VSMCs were used in in vitro [Ca2+ ]i studies, and aortas from a Svep1+/- knockout mouse model were used in wire myography to measure vessel contraction. KEY RESULTS: We confirmed the ligation of SVEP1 to integrin α9ß1 and additionally found SVEP1 to directly bind to integrin α4ß1. Inhibition of SVEP1, integrin α4ß1 or α9ß1 significantly enhanced [Ca2+ ]i levels in isolated VSMCs to Gαq/11 -vasoconstrictors. This response was confirmed in whole vessels where a greater contraction to U46619 was seen in vessels from Svep1+/- mice compared to littermate controls or when integrin α4ß1 or α9ß1 was inhibited. Inhibition studies suggested that this effect was mediated via VGCCs, PKC and Rho A/Rho kinase dependent mechanisms. CONCLUSIONS AND IMPLICATIONS: Our studies reveal a novel role for SVEP1 and the integrins α4ß1 and α9ß1 in reducing VSMC contractility. This could provide an explanation for the genetic associations with blood pressure risk at the SVEP1 and ITGA9 loci.

The impact of decreased expression of SVEP1 on abnormal neovascularization and poor prognosis in patients with intrahepatic cholangiocarcinoma.

Introduction: Intrahepatic cholangiocarcinoma (ICC) is one of the most highly heterogeneous malignant solid tumors; it is generally insensitive to clinical treatment and has a poor prognosis. Evidence suggests that abnormal neovascularization in the tumor microenvironment is an important cause of treatment resistance as well as recurrence and metastasis, but the key regulatory molecules are still largely unknown and should be identified. Method: We assessed the novel extracellular matrix protein (ECM) Sushi, von Willebrand factor type A, EGF and pentraxin containing 1 (SVEP1) expression pattern in the ICC by using immunohistochemistry. Multiplex immunofluorescence and Kaplan-Meier analysis were applied to explore the correlation between the low expression of SVEP1 and abnormal blood vessels and the clinical prognosis of ICC. Results: Our study showed that the expression of SVEP1 in most ICC samples was relatively lower than in the adjacent tissues. Statistical analysis suggested that patients with decreased SVEP1 expression always had shorter overall survival (OS) and disease-free survival (DFS). Moreover, the expression of SVEP1 was negatively correlated with the proportion of abnormal neovascularization in the tumor microenvironment of the ICC. Consistently, the key molecule of promoting vascular normalization, Ang-1, is positively correlated with the SVEP1 expression and prognosis in the ICC. In addition, the proportion of high Ki-67 expression was higher in the ICC samples with low SVEP1 expression, suggesting that the SVEP1 low expressed sample is in a malignant phenotype with high proliferation. Conclusion: This study reveals that SVEP1 is a promising prognostic biomarker for ICC and provides fresh insight into the role and potential new mechanism of abnormal neovascularization in ICC progression.

SVEP1 is important for morphogenesis of lymphatic system: Possible implications in lymphedema.

SVEP1, also known as Polydom, is a large extracellular mosaic protein with functions in protein interactions and adhesion. Since Svep1 knockout animals show severe edema and lymphatic system malformations, the aim of this study is to evaluate the presence of SVEP1 variants in patients with lymphedema. We analyzed DNA from 246 lymphedema patients for variants in known lymphedema genes, 235 of whom tested negative and underwent a second testing for new candidate genes, including SVEP1, as reported here. We found three samples with rare heterozygous missense single-nucleotide variants in the SVEP1 gene. In one family, healthy members were found to carry the same variants and reported some subclinical edema. Based on our findings and a review of the literature, we propose SVEP1 as a candidate gene that should be sequenced in patients with lymphatic malformations, with or without lymphedema, in order to investigate and add evidence on its possible involvement in the development of lymphedema.

Identification of the RP11-21C4.1/SVEP1 gene pair associated with FAT2 mutations as a potential biomarker in gastric cancer.

Gastric cancer (GC) is one of the most common malignancies worldwide. Despite rapid advances in systemic therapy, GC remains the third leading cause of cancer-related deaths. We aimed to identify a novel prognostic signature associated with FAT2 mutations in GC. We analyzed the expression levels of FAT2-mutant and FAT2-wildtype GC samples obtained from The Cancer Genome Atlas (TCGA). The Kaplan-Meier survival curve showed that patients with FAT2 mutations showed better prognosis than those without the mutation. Sixteen long non-coding RNAs (lncRNAs) and 62 messenger RNAs (mRNAs) associated with FAT2 mutations were correlated with the prognosis of GC. We then constructed a 4-mRNA signature and a 5-lncRNA signature for GC. Finally, we identified the most relevant RP11-21 C4.1/SVEP1 gene pair as a prognostic signature of GC that exhibited superior predictive performance in comparison with the 4-mRNA or 5-lncRNA signature by weighted gene correlation network analysis (WGCNA) and Cox proportional hazards regression analysis. In this study, we constructed a prognostic signature of GC by integrative genomics analysis, which also provided insights into the molecular mechanisms linked to FAT2 mutations in GC.

Role of SVEP1 in Stroma-Dependent Hematopoiesis In vitro.

Study of the microenvironment that supports hematopoietic stem cell (HSC) development in vivo is very difficult involving small numbers of interacting cells which are usually not well defined. While much is known about HSC niches located within the bone marrow in terms of contributing cell types and signalling molecules, very little is known about equivalent niches within spleen. Extramedullary hematopoiesis in spleen contributes myeloid cells important in the mobilisation of an immune response. As a result, it is important to develop in vitro models to identify the cells which constitute HSC niches in spleen and to identify the regulatory molecules supporting myeloid cell development. Studies described here document a model system to study the maintenance and differentiation of HSC by splenic stromal cells in vitro. The splenic stromal lines 5G3 and 3B5 differ in hematopoietic support capacity. SVEP1 and IGF2 are molecules of interest specifically expressed by 5G3 stroma. Gene knockdown technology using shRNA plasmids has been used to reduce gene expression in 5G3 and to determine specific effects on myeloid cell development following co-culture with overlaid hematopoietic progenitors in vitro. Knockdown of Svep1 gave specific inhibition of a dendritic cell (DC) population described previously in spleen (L-DC). Knockdown of Igf2 resulted in loss of production of a minor subset of conventional (c) DC. SVEP1 is now considered a marker of mesenchymal stromal cells with osteogenic differentiative capacity reflective of perivascular stromal cells. The power of this in vitro model is evidenced by the fact that it has been used to define SVEP1 as a specific adhesion molecule that regulates the hematopoietic process dependent on stromal niche interaction. The identification of stromal cells and molecules that contribute to the hematopoietic process in spleen, brings us closer to the realm of therapeutically regulating hematopoiesis in vivo, and to inhibiting niches which support cancer stem cells.

Functional investigation of the coronary artery disease gene SVEP1.

A missense variant of the sushi, von Willebrand factor type A, EGF and pentraxin domain containing protein 1 (SVEP1) is genome-wide significantly associated with coronary artery disease. The mechanisms how SVEP1 impacts atherosclerosis are not known. We found endothelial cells (EC) and vascular smooth muscle cells to represent the major cellular source of SVEP1 in plaques. Plaques were larger in atherosclerosis-prone Svep1 haploinsufficient (ApoE-/-Svep1+/-) compared to Svep1 wild-type mice (ApoE-/-Svep1+/+) and ApoE-/-Svep1+/- mice displayed elevated plaque neutrophil, Ly6Chigh monocyte, and macrophage numbers. We assessed how leukocytes accumulated more inside plaques in ApoE-/-Svep1+/- mice and found enhanced leukocyte recruitment from blood into plaques. In vitro, we examined how SVEP1 deficiency promotes leukocyte recruitment and found elevated expression of the leukocyte attractant chemokine (C-X-C motif) ligand 1 (CXCL1) in EC after incubation with missense compared to wild-type SVEP1. Increasing wild-type SVEP1 levels silenced endothelial CXCL1 release. In line, plasma Cxcl1 levels were elevated in ApoE-/-Svep1+/- mice. Our studies reveal an atheroprotective role of SVEP1. Deficiency of wild-type Svep1 increased endothelial CXCL1 expression leading to enhanced recruitment of proinflammatory leukocytes from blood to plaque. Consequently, elevated vascular inflammation resulted in enhanced plaque progression in Svep1 deficiency.

SVEP1, PKHD1, and P53 expression in primary liver cancer and its clinical significance / 中国肿瘤临床

Objective: To detect the expression of SVEP1, PKHD1 and P53 in primary liver cancer tissues by immunohistochemistry for predicting the recurrence of liver cancer. Methods: The clinical data of 103 patients with primary liver cancer who underwent surgical resection at Tianjin Medical University Cancer Institute and Hospital were gathered from January 2013 to January 2014 and analyzed retrospectively. Expression values of three different proteins were used to develop separate immunohistochemical scores for the prog-nosis of recurrence in patients. The patients were classified into either a high-risk or a low-risk group based on their immunohisto-chemical scores through ROC curve analysis. The difference in recurrence ratio between the two groups was then compared using the common research index of disease-free survival (DFS). Results: The median age of the total patients was 55 years (range 21-88 years), the median AFP level was 70.6 (range 1.03-718840.0) μg/L, the median CA19-9 level was 22.89 (range 0.6-1000.0) kU/L, and the medi-an tumor size was 4.5 (1.0-27.0) cm. The expression levels of SVEP1, PKHD1, and P53 in primary liver tumors were detected by immu-nohistochemistry and assigned separate immunohistochemical scores. The areas under the ROC curves of the immunohistochemical scores of SVEP1, PKHD1, and P53 were 0.861, 0.829, and 0.716, respectively. The critical values of SVEP1, PKHD1, and P53 were 4, 4, and 1 point, respectively (P<0.001). The three-year DFS rates among the SVEP1 high-risk (expression≤4 points) and low-risk groups (expression>4 points) were 4.1% and 51.7%, respectively. Similarly, the three-year survival rates among the PKHD1 high-risk (expres-sion≤4 points) and low-risk groups (expression>4 points) were 5.3% and 51.9%, respectively. The three-year DFS rates among the P53 high-risk (expression>1 point) and the low-risk group (expression≤1 point) were 6.3% and 27.3%, respectively. The survival differenc-es between all the pairs were statistically significant (P<0.001,<0.001, and 0.003 respectively). When PKHD1 was used in combination with SVEP1, the ROC curve had an area of 0.897 (P<0.001) with a sensitivity of 76.5% and a specificity of 94.4%. Conclusions: The accu-racy of P53 data for predicting primary liver cancer recurrence is insufficient and therefore it is not recommended for use. SVEP1 and PKHD1 data achieve sufficient accuracy for predicting the recurrence of primary liver cancer. Since SVEP1 data impart a higher specifici-ty and PKHD1 data impart a higher sensitivity to the prognosis scores, the combined use of the two markers is better than being used individually.

Investigating human placentation and pregnancy using first trimester chorionic villi.

Chorionic villus sampling (CVS), routinely used for prenatal diagnosis of cytogenetic disorders, also possesses great potential for the study of placentation. To better understand villus biology, human placentation, and how these relate to pregnancy outcomes, we examined the morphology and transcriptomes of villi obtained via CVS from 10 to 14 weeks of pregnancy and correlated these with pregnancy attributes and clinical outcomes. First, we established a morphological scoring system based on three main villus features: branching, budding and vascularization. We then tested whether morphology scores were predictive of pregnancy attributes and clinical outcomes. Finally, we used RNA sequencing to assess the transcriptional basis of villus morphology and tested the hypothesis that gene expression may predict pregnancy outcomes. We demonstrate that villus morphology varies tremendously between patients, irrespective of gestational age, and that transcriptional differences are highly predictive of villus morphology. We show that pre-eclampsia markers are associated with villi with low morphology scores. Additionally, we identify SVEP1 as a possible biomarker for defining gestational age. Overall, chorionic villi in the first trimester remain one of the few means to correlate placental function with pregnancy outcome and these samples are a valuable and increasingly rare resource.

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.

SVEP1 plays a crucial role in epidermal differentiation.

SVEP1 is a recently identified multidomain cell adhesion protein, homologous to the mouse polydom protein, which has been shown to mediate cell-cell adhesion in an integrin-dependent manner in osteogenic cells. In this study, we characterized SVEP1 function in the epidermis. SVEP1 was found by qRT-PCR to be ubiquitously expressed in human tissues, including the skin. Confocal microscopy revealed that SVEP1 is normally mostly expressed in the cytoplasm of basal and suprabasal epidermal cells. Downregulation of SVEP1 expression in primary keratinocytes resulted in decreased expression of major epidermal differentiation markers. Similarly, SVEP1 downregulation was associated with disturbed differentiation and marked epidermal acanthosis in three-dimensional skin equivalents. In contrast, the dispase assay failed to demonstrate significant differences in adhesion between keratinocytes expressing normal vs low levels of SVEP1. Homozygous Svep1 knockout mice were embryonic lethal. Thus, to assess the importance of SVEP1 for normal skin homoeostasis in vivo, we downregulated SVEP1 in zebrafish embryos with a Svep1-specific splice morpholino. Scanning electron microscopy revealed a rugged epidermis with perturbed microridge formation in the centre of the keratinocytes of morphant larvae. Transmission electron microscopy analysis demonstrated abnormal epidermal cell-cell adhesion with disadhesion between cells in Svep1-deficient morphant larvae compared to controls. In summary, our results indicate that SVEP1 plays a critical role during epidermal differentiation.