Disruption of p21-activated kinase 1 gene diminishes atherosclerosis in apolipoprotein E-deficient mice

TRIM13 reduces cholesterol efflux and increases oxidized LDL uptake leading to foam cell formation and atherosclerosis

Impaired cholesterol efflux and/or uptake can influence arterial lipid accumulation leading to atherosclerosis. Here, we report that tripartite motif-containing protein 13 (TRIM13), a RING-type E3 ubiquitin ligase, plays a role in arterial lipid accumulation leading to atherosclerosis. Using molecular approaches and KO mouse model, we found that TRIM13 expression was induced both in the aorta and peritoneal macrophages (pMφ) of ApoE-/- mice in response to Western diet (WD) in vivo. Furthermore, proatherogenic cytokine interleukin-1β also induced TRIM13 expression both in pMφ and vascular smooth muscle cells. Furthermore, we found that TRIM13 via ubiquitination and degradation of liver X receptor (LXR)α/β downregulates the expression of their target genes ABCA1/G1 and thereby inhibits cholesterol efflux. In addition, TRIM13 by ubiquitinating and degrading suppressor of cytokine signaling 1/3 (SOCS1/3) mediates signal transducer and activator of transcription 1 (STAT1) activation, CD36 expression, and foam cell formation. In line with these observations, genetic deletion of TRIM13 by rescuing cholesterol efflux and inhibiting foam cell formation protects against diet-induced atherosclerosis. We also found that while TRIM13 and CD36 levels were increased, LXRα/β, ABCA1/G1, and SOCS3 levels were decreased both in Mφ and smooth muscle cells of stenotic human coronary arteries as compared to nonstenotic arteries. More intriguingly, the expression levels of TRIM13 and its downstream signaling molecules were correlated with the severity of stenotic lesions. Together, these observations reveal for the first time that TRIM13 plays a crucial role in diet-induced atherosclerosis, and that it could be a potential drug target against this vascular lesion.

Requirement of Site-Specific Tyrosine Phosphorylation of Cortactin in Retinal Neovascularization and Vascular Leakage

BACKGROUND

Retinal neovascularization is a major cause of vision impairment. Therefore, the purpose of this study is to investigate the mechanisms by which hypoxia triggers the development of abnormal and leaky blood vessels.

METHODS

A variety of cellular and molecular approaches as well as tissue-specific knockout mice were used to investigate the role of Cttn (cortactin) in retinal neovascularization and vascular leakage.

RESULTS

We found that VEGFA (vascular endothelial growth factor A) stimulates Cttn phosphorylation at Y421, Y453, and Y470 residues in human retinal microvascular endothelial cells. In addition, we observed that while blockade of Cttn phosphorylation at Y470 inhibited VEGFA-induced human retinal microvascular endothelial cell angiogenic events, suppression of Y421 phosphorylation protected endothelial barrier integrity from disruption by VEGFA. In line with these observations, while blockade of Cttn phosphorylation at Y470 negated oxygen-induced retinopathy-induced retinal neovascularization, interference with Y421 phosphorylation prevented VEGFA/oxygen-induced retinopathy-induced vascular leakage. Mechanistically, while phosphorylation at Y470 was required for its interaction with Arp2/3 and CDC6 facilitating actin polymerization and DNA synthesis, respectively, Cttn phosphorylation at Y421 leads to its dissociation from VE-cadherin, resulting in adherens junction disruption. Furthermore, whereas Cttn phosphorylation at Y470 residue was dependent on Lyn, its phosphorylation at Y421 residue required Syk activation. Accordingly, lentivirus-mediated expression of shRNA targeting Lyn or Syk levels inhibited oxygen-induced retinopathy-induced retinal neovascularization and vascular leakage, respectively.

CONCLUSIONS

The above observations show for the first time that phosphorylation of Cttn is involved in a site-specific manner in the regulation of retinal neovascularization and vascular leakage. In view of these findings, Cttn could be a novel target for the development of therapeutics against vascular diseases such as retinal neovascularization and vascular leakage.

Inhibition of P21-activated Kinase 1 Promotes Vascular Smooth Muscle Cells Apoptosis Through Reduction of Phosphorylation of Bad

BACKGROUND

P21-activated kinase 1 (Pak1) has an effect on cell apoptosis and has recently been reported to play an important role in various cardiovascular diseases, in which vascular smooth muscle cell (VSMC) apoptosis is a key process. Thus, we hypothesized that Pak1 may be a novel target to regulate VSMC behaviors.

METHODS AND RESULTS

In the present study, we found that the expression of Pak1 was dramatically upregulated in vascular smooth muscle cells (VSMCs) on H2O2 administration and was dependent on stimulation time. Through a loss-of-function approach, Pak1 knockdown increased apoptosis of VSMCs, as tested by TUNEL (TdT-mediated dUTP Nick-End Labeling) immunofluorescence staining, whereas it inhibited the proliferation of VSMCs examined by EdU staining. Moreover, we also noticed that Pak1 silencing promoted the mRNA and protein levels of pro-apoptosis genes but decreased anti-apoptosis marker expression. Importantly, we showed that Pak1 knockdown reduced the phosphorylation of Bad. Moreover, increased Pak1 expression was also noticed in carotid arteries on the wire jury.

CONCLUSIONS

Our study identified that Pak1 acted as a novel regulator of apoptosis of VSMCs partially through phosphorylation of Bad.

cSTAR analysis identifies endothelial cell cycle as a key regulator of flow-dependent artery remodeling

Fluid shear stress (FSS) from blood flow is sensed by vascular endothelial cells (ECs) to determine vessel stability, remodeling and susceptibility to atherosclerosis and other inflammatory diseases but the regulatory networks that govern these behaviors are only partially understood. We used cSTAR, a powerful new computational method, to define EC transcriptomic states under low shear stress (LSS) that triggers vessel inward remodeling, physiological shear stress (PSS) that stabilizes vessels, high shear stress (HSS) that triggers outward remodeling, and oscillatory shear stress (OSS) that confers disease susceptibility, all in comparison to cells under static conditions (STAT). We combined these results with the LINCS database where EC transcriptomic responses to drug treatments to define a preliminary regulatory network in which the cyclin-dependent kinases CDK1/2 play a central role in promoting vessel stability. Experimental analysis showed that PSS induced a strong late G1 cell cycle arrest in which CDK2 was activated. EC deletion of CDK2 in mice resulted in inward artery remodeling and both pulmonary and systemic hypertension. These results validate use of cSTAR to determine EC state and in vivo vessel behavior, reveal unexpected features of EC phenotype under different FSS conditions, and identify CDK2 as a key element within the EC regulatory network that governs artery remodeling.

Genome-wide association study of 17 serum biochemical indicators in a chicken F2 resource population

BACKGROUND

Serum biochemical indicators are often regarded as direct reflections of animal metabolism and health. The molecular mechanisms underlying serum biochemical indicators metabolism of chicken (Gallus Gallus) have not been elucidated. Herein, we performed a genome-wide association study (GWAS) to identify the variation associated with serum biochemical indicators. The aim of this research was to broaden the understanding of the serum biochemical indicators in chickens.

RESULTS

A GWAS of serum biochemical indicators was carried out on 734 samples from an F2 Gushi× Anka chicken population. All chickens were genotyped by sequencing, 734 chickens and 321,314 variants were obtained after quality control. Based on these variants, a total of 236 single-nucleotide polymorphisms (SNPs) on 9 chicken chromosomes (GGAs) were identified to be significantly (-log₁₀(P) > 5.72) associated with eight of seventeen serum biochemical indicators. Ten novel quantitative trait locis (QTLs) were identified for the 8 serum biochemical indicator traits of the F2 population. Literature mining revealed that the ALPL, BCHE, GGT2/GGT5 genes at loci GGA24, GGA9 and GGA15 might affect the alkaline phosphatase (AKP), cholinesterase (CHE) and γ-glutamyl transpeptidase (GGT) traits, respectively.

CONCLUSION

The findings of the present study may contribute to a better understanding of the molecular mechanisms of chicken serum biochemical indicator regulation and provide a theoretical basis for chicken breeding programs.

Novel Role of Prereplication Complex Component Cell Division Cycle 6 in Retinal Neovascularization

BACKGROUND

The major aim of this study is to investigate whether CDC6 (cell division cycle 6), a replication origin recognition complex component, plays a role in retinal neovascularization, and if so, to explore the underlying mechanisms.

METHODS

In this study, we used a variety of approaches including cellular and moleculer biological methodologies as well as global and tissue-specific knockout mice in combination with an oxygen-induced retinopathy model to study the role of CDC6 in retinal neovascularization.

RESULTS

VEGFA (vascular endothelial growth factor A)-induced CDC6 expression in a time-dependent manner in human retinal microvascular endothelial cells. In addition, VEGFA-induced CDC6 expression was dependent on PLCβ3 (phospholipase Cβ3)-mediated NFATc1 (nuclear factor of activated T cells c1) activation. Furthermore, while siRNA-mediated depletion of PLCβ3, NFATc1, or CDC6 levels blunted VEGFA-induced human retinal microvascular endothelial cell angiogenic events such as proliferation, migration, sprouting, and tube formation, CDC6 overexpression rescued these effects in NFATc1-deficient mouse retinal microvascular endothelial cells. In accordance with these observations, global knockdown of PLCβ3 or endothelial cell-specific deletion of NFATc1 or siRNA-mediated depletion of CDC6 levels substantially inhibited oxygen-induced retinopathy-induced retinal sprouting and neovascularization. In addition, retroviral-mediated overexpression of CDC6 rescued oxygen-induced retinopathy-induced retinal neovascularization from inhibition in PLCβ3 knockout mice and in endothelial cell-specific NFATc1-deficient mice.

CONCLUSIONS

The above observations clearly reveal that PLCβ3-mediated NFATc1 activation-dependent CDC6 expression plays a crucial role in VEGFA/oxygen-induced retinopathy-induced retinal neovascularization.

p21-Activated kinase 1 (PAK1) in aging and longevity: An overview

The p21-activated kinases (PAKs) belong to serine/threonine kinases family, regulated by ∼21 kDa small signaling G proteins RAC1 and CDC42. The mammalian PAK family comprises six members (PAK1-6) that are classified into two groups (I and II) based on their domain architecture and regulatory mechanisms. PAKs are implicated in a wide range of cellular functions. PAK1 has recently attracted increasing attention owing to its involvement in oncogenesis, tumor progression, and metastasis as well as several life-limiting diseases and pathological conditions. In Caenorhabditis elegans, PAK1 functions limit the lifespan under basal conditions by inhibiting forkhead transcription factor DAF-16. Interestingly, PAK depletion extended longevity and attenuated the onset of age-related phenotypes in a premature-aging mouse model and delayed senescence in mammalian fibroblasts. These observations implicate PAKs as not only oncogenic but also aging kinases. Therefore, PAK-targeting genetic and/or pharmacological interventions, particularly PAK1-targeting, could be a viable strategy for developing cancer therapies with relatively no side effects and promoting healthy longevity. This review describes PAK family proteins, their biological functions, and their role in regulating aging and longevity using C. elegans. Moreover, we discuss the effect of small-molecule PAK1 inhibitors on the lifespan and healthspan of C. elegans.

P21 activated kinase-1 (PAK1) in macrophages is required for promotion of Th17 cell response during helminth infection

CD4⁺T cells differentiate into distinct functional effector and inhibitory subsets are facilitated by distinct cytokine cues present at the time of antigen recognition. Maintaining a balance between T helper 17 (Th17) and regulatory T (Treg) cells are critical for the control of the immunopathogenesis of liver diseases. Here, by using the mouse model of helminth Schistosoma japonicum (Sjaponicum) infection, we show that the hepatic mRNA levels of P21‐activated kinase 1 (PAK1), a key regulator of the actin cytoskeleton, adhesion and cell motility, are significantly increased and associated with the development of liver pathology during Sjaponicum infection. In addition, PAK1‐deficient mice are prone to suppression of Th17 cell responses but increased Treg cells. Furthermore, PAK1 enhances macrophage activation through promoting IRF1 nuclear translocation in an NF‐κB‐dependent pathway, resulting in promoting Th17 cell differentiation through inducing IL‐6 production. These findings highlight the importance of PAK1 in macrophages fate determination and suggest that PAK1/IRF1 axis‐dependent immunomodulation can ameliorate certain T cell–based immune pathologies.

PKCθ-JunB axis via upregulation of VEGFR3 expression mediates hypoxia-induced pathological retinal neovascularization

Pathological retinal neovascularization is the most common cause of vision loss. PKCθ has been shown to play a role in type 2 diabetes, which is linked to retinal neovascularization. Based on these clues, we have studied the role of PKCθ and its downstream target genes JunB and VEGFR3 in retinal neovascularization using global and tissue-specific knockout mouse models along with molecular biological approaches. Here, we show that vascular endothelial growth factor A (VEGFA) induces PKCθ phosphorylation in human retinal microvascular endothelial cells (HRMVECs) and downregulation of its levels attenuates VEGFA-induced HRMVECs migration, sprouting and tube formation. Furthermore, the whole body deletion of PKCθ or EC-specific deletion of its target gene JunB inhibited hypoxia-induced retinal EC proliferation, tip cell formation and neovascularization. VEGFA also induced VEGFR3 expression via JunB downstream to PKCθ in the regulation of HRMVEC migration, sprouting, and tube formation in vitro and OIR-induced retinal EC proliferation, tip cell formation and neovascularization in vivo. In addition, VEGFA-induced VEGFR3 expression requires VEGFR2 activation upstream to PKCθ-JunB axis both in vitro and in vivo. Depletion of VEGFR2 or VEGFR3 levels attenuated VEGFA-induced HRMVEC migration, sprouting and tube formation in vitro and retinal neovascularization in vivo and it appears that these events were dependent on STAT3 activation. Furthermore, the observations using soluble VEGFR3 indicate that VEGFR3 mediates its effects on retinal neovascularization in a ligand dependent and independent manner downstream to VEGFR2. Together, these observations suggest that PKCθ-dependent JunB-mediated VEGFR3 expression targeting STAT3 activation is required for VEGFA/VEGFR2-induced retinal neovascularization.

Identification of Biological Pathways Contributing to Marbling in Skeletal Muscle to Improve Beef Cattle Breeding

Red meat is an important dietary source that provides part of the nutritional requirements. Intramuscular fat, known as marbling, is located throughout skeletal muscle. Marbling is a trait of major economic relevance that positively influences sensory quality aspects. The aim of the present study was to identify and better understand biological pathways defining marbling in beef cattle. Pathway analysis was performed in PathVisio with publicly available transcriptomic data from semitendinosus muscle of well-marbled and lean-marbled beef. Moreover, for Bos taurus we created a gene identifier mapping database with bridgeDb and a pathway collection in WikiPathways. The regulation of marbling is possibly the result of the interplay between signaling pathways in muscle, fat, and intramuscular connective tissue. Pathway analysis revealed 17 pathways that were significantly different between well-marbled and lean-marbled beef. The MAPK signaling pathway was enriched, and the signaling pathways that play a role in tissue development were also affected. Interestingly, pathways related to immune response and insulin signaling were enriched.

The anti-inflammatory vasostatin-2 attenuates atherosclerosis in ApoE-/- mice and inhibits monocyte/macrophage recruitment

We showed previously that reduced level of vasostatin-2 (VS-2) correlates to the presence and severity of coronary artery disease. In this study, we aimed to figure out the role of chromogranin A (CGA) derived VS-2 in the development of atherosclerosis and monocyte/macrophage recruitment. Apolipoprotein E-deficient (ApoE-/-) mice fed a high-fat diet exhibited attenuated lesion size by 65 % and 41 % in En face and aortic root Oil red O staining, MOMA-2 positive area by 64 %, respectively, in VS-2 treatment group compared with PBS group. Proinflammatory cytokines tumour necrosis factor-alpha (TNF-α), monocyte chemoattractant protein-1 (MCP-1) and vascular cell adhesion molecule-1 (VCAM-1) were all remarkably reduced in aortic tissues after VS-2 treatment. Mechanistically, in adhesion assay using intravital microscopy in vivo, VS-2 suppressed the number of leukocytes adhering to the wall of apoE-/- mice mesenteric arteries. In chemotactic assay, flow cytometry analysis of peritoneal lavage exudate from C57BL/6 mice showed VS-2 significantly decreased the recruiment number of inflammatory monocytes/macrophages in a thioglycollate-induced peritonitis model. Furthermore, fewer fluorescent latex beads labelled Ly-6Chi monocytes accumulated in aortic sinus lesions of apoE-/- mice after VS-2 treatment. In addition, according to the microarray of human monocyte/macrophage, we found VS-2 stimulation caused a dose-dependent decrease of Rac1 expression and inactivation of Pak1 in mice primary monocytes as well as THP-1 cells and inhibited MCP-1/CCL-5 induced transmigration in vitro. In conclusion, the Chromogranin A-derived VS-2 attenuates atherosclerosis in apoE-/- mice and, in addition to its anti-inflammatory property, also acts as an inhibitor in monocyte/macrophage recruitment.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Quantitative and qualitative estimation of atherosclerotic plaque burden in vivo at 7T MRI using Gadospin F in comparison to en face preparation evaluated in ApoE KO mice

Background

The aim of the study was to quantify atherosclerotic plaque burden by volumetric assessment and T1 relaxivity measurement at 7T MRI using Gadospin F (GDF) in comparison to en face based measurements.

Methods and results

9-weeks old ApoE^-/- (n = 5 for each group) and wildtype mice (n = 5) were set on high fat diet (HFD). Progression group received MRI at 9, 13, 17 and 21 weeks after HFD initiation. Regression group was reswitched to chow diet (CD) after 13 weeks HFD and monitored with MRI for 12 weeks. MRI was performed before and two hours after iv injection of GDF (100 μmol/kg) at 7T (Clinscan, Bruker) acquiring a 3D inversion recovery gradient echo sequence and T1 Mapping using Saturation Recovery sequences. Subsequently, aortas were prepared for en face analysis using confocal microscopy. Total plaque volume (TPV) and T1 relaxivity were estimated using ImageJ (V. 1.44p, NIH, USA).

2D and 3D en face analysis showed a strong and exponential increase of plaque burden over time, while plaque burden in regression group was less pronounced. Correspondent in vivo MRI measurements revealed a more linear increase of TPV and T1 relaxivity for regression group. A significant correlation was observed between 2D and 3D en face analysis (r = 0.79; p<0.001) as well as between 2D / 3D en face analysis and MRI (r = 0.79; p<0.001; r = 0.85; p<0.001) and delta R1 (r = 0.79; p<0.001; r = 0.69; p<0.01).

Conclusion

GDF-enhanced in vivo MRI is a powerful non-invasive imaging technique in mice allowing for reliable estimation of atherosclerotic plaque burden, monitoring of disease progression and regression in preclinical studies.

p115 RhoGEF activates the Rac1 GTPase signaling cascade in MCP1 chemokine-induced vascular smooth muscle cell migration and proliferation

Although the involvement of Rho proteins in the pathogenesis of vascular diseases is well studied, little is known about the role of their upstream regulators, the Rho guanine nucleotide exchange factors (RhoGEFs). Here, we sought to identify the RhoGEFs involved in monocyte chemotactic protein 1 (MCP1)-induced vascular wall remodeling. We found that, among the RhoGEFs tested, MCP1 induced tyrosine phosphorylation of p115 RhoGEF but not of PDZ RhoGEF or leukemia-associated RhoGEF in human aortic smooth muscle cells (HASMCs). Moreover, p115 RhoGEF inhibition suppressed MCP1-induced HASMC migration and proliferation. Consistent with these observations, balloon injury (BI) induced p115 RhoGEF tyrosine phosphorylation in rat common carotid arteries, and siRNA-mediated down-regulation of its levels substantially attenuated BI-induced smooth muscle cell migration and proliferation, resulting in reduced neointima formation. Furthermore, depletion of p115 RhoGEF levels also abrogated MCP1- or BI-induced Rac1-NFATc1-cyclin D1-CDK6-PKN1-CDK4-PAK1 signaling, which, as we reported previously, is involved in vascular wall remodeling. Our findings also show that protein kinase N1 (PKN1) downstream of Rac1-cyclin D1/CDK6 and upstream of CDK4-PAK1 in the p115 RhoGEF-Rac1-NFATc1-cyclin D1-CDK6-PKN1-CDK4-PAK1 signaling axis is involved in the modulation of vascular wall remodeling. Of note, we also observed that CCR2-G_i/o-Fyn signaling mediates MCP1-induced p115 RhoGEF and Rac1 GTPase activation. These findings suggest that p115 RhoGEF is critical for MCP1-induced HASMC migration and proliferation in vitro and for injury-induced neointima formation in vivo by modulating Rac1-NFATc1-cyclin D1-CDK6-PKN1-CDK4-PAK1 signaling.

Visualization of endothelial barrier damage prior to formation of atherosclerotic plaques

En-face fat staining is frequently used to visualize atherosclerotic lesions. This method, however, is not suitable to visualize endothelial barrier damage prior to microscopically detectable morphological alterations of the arterial wall such as sub-endothelial lipid deposition. To enable the investigation of early endothelial barrier damage and in particular the initial steps of atherosclerosis, a new method has to fulfill three requirements: (i) easy and fast to perform, (ii) low cost of applicability without requirement for highly sophisticated technical equipment, and (iii) reliable reproducibility of valid results. To this end, we used intracardial Evans blue dye injection after washout of blood and measured dye deposition within the aortic wall as a parameter of endothelial barrier leakiness, which is recognized as one of the earliest signs of atherosclerotic plaque formation. These analyses were performed in ApoE ^-/-, LDL receptor ^-/- and Cc1 ^-/- mouse models which have been reported to develop aortic plaques with or without high cholesterol diet. Our data show that sub-endothelial dye deposition is a reliable and reproducible readout parameter to assess endothelial barrier damage. Along these lines, measurements of aortic intima areas with Evans blue deposition in relation to total intima circumference enabled quantitative assessments of the results. Our technique enables the imaging of endothelial barrier damage prior to detectable aortic lipid deposition and plaque development. Thus, it will facilitate the detection of the initial vascular pathogenetic processes that lead to cardiovascular diseases. It will also enable the testing of new drugs and therapeutic procedures to prevent these disorders.

PLCβ3 mediates cortactin interaction with WAVE2 in MCP1-induced actin polymerization and cell migration

Monocyte chemotactic protein 1 (MCP1) stimulates vascular smooth muscle cell (VSMC) migration in vascular wall remodeling. However, the mechanisms underlying MCP1-induced VSMC migration have not been understood. Here we identify the signaling pathway associated with MCP1-induced human aortic smooth muscle cell (HASMC) migration. MCP1, a G protein-coupled receptor agonist, activates phosphorylation of cortactin on S405 and S418 residues in a time-dependent manner, and inhibition of its phosphorylation attenuates MCP1-induced HASMC G-actin polymerization, F-actin stress fiber formation, and migration. Cortactin phosphorylation on S405/S418 is found to be critical for its interaction with WAVE2, a member of the WASP family of cytoskeletal regulatory proteins required for cell migration. In addition, the MCP1-induced cortactin phosphorylation is dependent on PLCβ3-mediated PKCδ activation, and siRNA-mediated down-regulation of either of these molecules prevents cortactin interaction with WAVE2, affecting G-actin polymerization, F-actin stress fiber formation, and HASMC migration. Upstream, MCP1 activates CCR2 and Gαq/11 in a time-dependent manner, and down-regulation of their levels attenuates MCP1-induced PLCβ3 and PKCδ activation, cortactin phosphorylation, cortactin-WAVE2 interaction, G-actin polymerization, F-actin stress fiber formation, and HASMC migration. Together these findings demonstrate that phosphorylation of cortactin on S405 and S418 residues is required for its interaction with WAVE2 in MCP1-induced cytoskeleton remodeling, facilitating HASMC migration.

Cyclic AMP Response Element Binding Protein Mediates Pathological Retinal Neovascularization via Modulating DLL4-NOTCH1 Signaling

Retinal neovascularization is the most common cause of moderate to severe vision loss in all age groups. Despite the use of anti-VEGFA therapies, this complication continues to cause blindness, suggesting a role for additional molecules in retinal neovascularization. Besides VEGFA and VEGFB, hypoxia induced VEGFC expression robustly. Based on this finding, we tested the role of VEGFC in pathological retinal angiogenesis. VEGFC induced proliferation, migration, sprouting and tube formation of human retinal microvascular endothelial cells (HRMVECs) and these responses require CREB-mediated DLL4 expression and NOTCH1 activation. Furthermore, down regulation of VEGFC levels substantially reduced tip cell formation and retinal neovascularization in vivo. In addition, we observed that CREB via modulating the DLL4-NOTCH1 signaling mediates VEGFC-induced tip cell formation and retinal neovascularization. In regard to upstream mechanism, we found that down regulation of p38β levels inhibited hypoxia-induced CREB-DLL4-NOTCH1 activation, tip cell formation, sprouting and retinal neovascularization. Based on these findings, it may be suggested that VEGFC besides its role in the regulation of lymphangiogenesis also plays a role in pathological retinal angiogenesis and this effect depends on p38β and CREB-mediated activation of DLL4-NOTCH1 signaling.