N-Glycans on the extracellular domain of the Notch1 receptor control Jagged-1 induced Notch signalling and myogenic differentiation of S100β resident vascular stem cells

Notch signalling, critical for development and postnatal homeostasis of the vascular system, is highly regulated by several mechanisms including glycosylation. While the importance of O-linked glycosylation is widely accepted, the structure and function of N-glycans has yet to be defined. Here, we take advantage of lectin binding assays in combination with pharmacological, molecular, and site-directed mutagenetic approaches to study N-glycosylation of the Notch1 receptor. We find that several key oligosaccharides containing bisecting or core fucosylated structures decorate the receptor, control expression and receptor trafficking, and dictate Jagged-1 activation of Notch target genes and myogenic differentiation of multipotent S100β vascular stem cells. N-glycans at asparagine (N) 1241 and 1587 protect the receptor from accelerated degradation, while the oligosaccharide at N888 directly affects signal transduction. Conversely, N-linked glycans at N959, N1179, N1489 do not impact canonical signalling but inhibit differentiation. Our work highlights a novel functional role for N-glycans in controlling Notch1 signalling and differentiation of vascular stem cells.

The calcium binding protein S100β marks hedgehog-responsive resident vascular stem cells within vascular lesions

A hallmark of subclinical atherosclerosis is the accumulation of vascular smooth muscle cell (SMC)-like cells leading to intimal thickening. While medial SMCs contribute, the participation of hedgehog-responsive resident vascular stem cells (vSCs) to lesion formation remains unclear. Using transgenic eGFP mice and genetic lineage tracing of S100β vSCs in vivo, we identified S100β/Sca1 cells derived from a S100β non-SMC parent population within lesions that co-localise with smooth muscle α-actin (SMA) cells following iatrogenic flow restriction, an effect attenuated following hedgehog inhibition with the smoothened inhibitor, cyclopamine. In vitro, S100β/Sca1 cells isolated from atheroprone regions of the mouse aorta expressed hedgehog signalling components, acquired the di-methylation of histone 3 lysine 4 (H3K4me2) stable SMC epigenetic mark at the Myh11 locus and underwent myogenic differentiation in response to recombinant sonic hedgehog (SHh). Both S100β and PTCH1 cells were present in human vessels while S100β cells were enriched in arteriosclerotic lesions. Recombinant SHh promoted myogenic differentiation of human induced pluripotent stem cell-derived S100β neuroectoderm progenitors in vitro. We conclude that hedgehog-responsive S100β vSCs contribute to lesion formation and support targeting hedgehog signalling to treat subclinical arteriosclerosis.

Label-Free Multi Parameter Optical Interrogation of Endothelial Activation in Single Cells using a Lab on a Disc Platform

Cellular activation and inflammation leading to endothelial dysfunction is associated with cardiovascular disease (CVD). We investigated whether a single cell label-free multi parameter optical interrogation system can detect endothelial cell and endothelial progenitor cell (EPC) activation in vitro and ex vivo, respectively. Cultured human endothelial cells were exposed to increasing concentrations of tumour necrosis factor alpha (TNF-α) or lipopolysaccharide (LPS) before endothelial activation was validated using fluorescence-activated cell sorting (FACS) analysis of inflammatory marker expression (PECAM-1, E-selectin and ICAM-1). A centrifugal microfluidic system and V-cup array was used to capture individual cells before optical measurement of light scattering, immunocytofluorescence, auto-fluorescence (AF) and cell morphology was determined. In vitro, TNF-α promoted specific changes to the refractive index and cell morphology of individual cells concomitant with enhanced photon activity of fluorescently labelled inflammatory markers and increased auto-fluorescence (AF) intensity at three different wavelengths, an effect blocked by inhibition of downstream signalling with Iκβ. Ex vivo, there was a significant increase in EPC number and AF intensity of individual EPCs from CVD patients concomitant with enhanced PECAM-1 expression when compared to normal controls. This novel label-free 'lab on a disc' (LoaD) platform can successfully detect endothelial activation in response to inflammatory stimuli in vitro and ex vivo.

Abstract 480: Injury-Activated Vascular Cells Share a Common Photonic Fingerprint with Stem Cell-Derived Myogenic Progeny Following Interrogation Using a Lab-on-a-Disc (Load) Platform

The accumulation of vascular smooth muscle (SMC)-like cells within the intima contributes significantly to intimal medial thickening (IMT) and vascular remodeling typical of arteriosclerotic disease. Light has emerged as a powerful tool to interrogate cells label-free and facilitates discriminant observations both in vitro and in vivo . The auto-fluorescence (AF) profile of individual cells isolated from arteriosclerotic vessels, captured on V-cup array and interrogated across five wavelengths using a novel Lab-on-a-Disc platform, was significantly increased at the 565 ± 20nm wavelength concomitant with a reduction in Myh11 expression, when compared to differentiated vascular smooth muscle (SMC) cells from control vessels. In vitro, TGF-β1 promoted myogenic differentiation of murine bone-marrow derived Sca1 + /CD44 + mesenchymal stem cells (MSC) and murine Sca1 + C3H 10T1/2 cells concomitant with enrichment of the specific SMC epigenetic histone mark, H3K4me2 at the Myh11 promoter, Myh11 promoter transactivation and increased SMC differentiation marker mRNA and protein expression. Myogenic differentiation resulted in a significant increase in the AF intensity across 565 ± 20nm wavelength, an effect not observed for TGF-β1 treated RAMOS human B lymphocytes but mimicked by Notch activation of resident Sca1 + multipotent vascular stem cells (MVSCs) with Jagged1 and inhibited following elastin and collagen III depletion, respectively. Moreover, the temporal increase in the AF intensity at 565 ± 20nm wavelength during myogenic differentiation was similar to the AF profile of dissociated cells from arteriosclerotic vessels at this same wavelength. These data suggest that an AF photonic fingerprint of stem cell-derived myogenic progeny in vitro mimics that of vascular cells ex vivo following injury.

Abstract 716: Generation of γ-secretase Inhibitor-loaded PLGA-Fe 3 O 4 - Magnetic Nanoparticles

Cardiovascular disease (CVD) is the number one killer in Ireland and the wider EU. A hallmark of the disease is the obstruction to blood flow due to the build-up of vascular smooth muscle (SMCs)-like cells within the vessel wall. While polymer-coated DES have significantly reduced the incident of in-stent restenosis, current DESs lack the fundamental capacity for (i) adjustment of the drug dose and release kinetics and the (ii) ability to replenish the stent with a new drug on depletion. This limitation can be overcome by a strategy combining magnetic targeting via a uniform field-induced magnetization effect and a biocompatible magnetic nanoparticle (MNP) formulation designed for efficient entrapment and delivery of specific drugs that target the resident vascular stem cell source of the SMC. Magnetic nanoparticles (MNP’s) containing magnetite (Fe3O4) were fabricated, polymer coated with poly (DL-lactide-co-glycolide) polyvinyl alcohol [PLGA-PVA] and loaded with a γ-secretase inhibitor (GSI) of Notch signalling, DAPT using an oil in water emulsification technique. The free GSI’s and GSI-loaded MNP’s were assessed for drug release, the efficacy at controlling mesenchymal stem cell (MSC) growth (proliferation and apoptosis) and inhibiting myogenic differentiation under magnetic and non-magnetic conditions. The DAPT-loaded MNPs had an average hydrodynamic diameter of 351 d.nm Up to 40% of drug was released from MNPs within 48 h rising to 65% after 1 week under magnetic conditions. The Notch ligand, Jagged1 increased Hey1 mRNA levels and promoted myogenic differentiation of MSCs in vitro by increasing SMC differentiation markers, myosin heavy chain 11 (Myh11) and calponin1 (CNN1) expression, respectively. This effect was significantly attenuated following treatment of cells with MNP’s loaded with DAPT when compared to unloaded MNP’s. Notch GSI -loaded magnetic nanoparticles are functional at targeting vascular stem cells in vitro.

Abstract 651: Hedgehog Responsive S100β + /Stem Cell Antigen-1 + Vascular Stem Cells Contribute to Neointimal Formation

Intimal medial thickening (IMT) and vascular remodeling are hallmarks of arteriosclerotic disease. However, the origin of neointimal cells and the signaling molecules that dictate their fate and function remains controversial. Herein, we examined whether Hedgehog (Hh) responsive S100β + /Sca1 + stem cells contribute to IMT within carotid arteries of transgenic mice following ligation-induced injury in vivo and myogenic differentiation of undifferentiated multipotent S100β + /Sca1 + stem cells in vitro . Using Sca1-eGFP and S100β-eGFP transgenic mice, we demonstrated a significant accumulation in the number of eGFP + cells within the intima and medial layers of injured arteries following ligation concomitant with enhanced expression of Hh signaling components (ptch1 and Gli). Genetic lineage tracing analysis using S100β-eGFP/Cre/ERT2–dTomato transgenic mice to mark S100β + resident vascular stem cells before injury confirmed that S100β + progeny that are Sca1 + significantly contribute to IMT, an effect significantly attenuated following treatment with the Hh smoothened inhibitor, cylopamine. In vitro, recombinant SHh (rSHh) treatment of multipotent S100β + /Sca1 + resident stem cells increased Hh target gene Gli expression, decreased telomerase activity and promoted myogenic differentiation and cell growth; effects significantly attenuated following Hh inhibition. In human arteriosclerotic lesions, Hh components were upregulated concomitant with enhanced expression of S100β. Together, these findings suggest that S100β + /Sca1 + stem cells are a major source of neointimal cells contributing to IMT and suggest that this cohort may be a relevant therapeutic target to prevent arteriosclerosis.

Abstract 143: Enrichment of Dimethylation of Lysine 4 on Histone 3 and Resident Vascular Stem Cell Transition to Vascular Smooth Muscle Cells

Data support a role for stem cell-derived vascular smooth muscle cells (SMC) in arteriosclerosis. Epigenetics play a critical role in SMC differentiation where histone proteins associated with the myosin heavy chain (Myh11) promoter are post-translationally modified by dimethylation of lysine 4 on histone 3 (H3K4me2). Studies report that ‘de-differentiated’ SMC do not exhibit loss of H3K4me2 at the Myh11 promoter even when mRNA levels decrease thereby allowing this modification to be used to track differentiated SMC.

Our aim was to determine the level of H3K4me2 and H3K27me3 methylation of differentiated SMCs and compare to resident vascular stem cells and stem cell-derived SMC.

Murine adventitial Sca1 + stem cells (APCs), rat medial Sox10 + multipotent vascular stem cells (MVSCs) and CD44 + bone-marrow derived mesenchymal stem cells (MSCs) were all examined for methylation of lysine 4 (H3K4me2) and lysine 27 (H3K27me3) on histone 3 associated with the Myh11 promoter, before and after SMC differentiation and compared to fresh aortic differentiated SMC and sub-cultured de-differentiated SMC in vitro by Chromatin Immunoprecipitation (ChIP) assay. Cells were also examined for Myh11 expression, stemness (telomerase activity) and multipotentcy.

Differentiated rat and murine SMC were enriched for H3K4Me2 at the Myh11 promoter, compared to H3K27me3. Phenotypically de-differentiated sub-cutured rat and murine SMC were enriched for H3K4Me2 when compared to H3K27me3, but to a much lesser extent when compared to differentiated aortic SMC. In contrast, resident APCs and MVSCs, and bone-marrow derived MSCs, were all enriched for H3K27me3, concomitant with significant telomerase activity and multipotent differentiation capacity. The levels of enrichment of H3K27me3 dropped significantly after SMC differentiation with TGF-βeta1 concomitant with a significant enrichment of H3K4me2 to levels that mimicked the level of enrichment in de-differentiated SMC when compared to aortic differentiated SMC.

De-differentiated SMC exhibit reduced enrichment of H3K4me2 at the Myh11 promoter region when compared to differentiated aortic SMCs, but mimic the level of enrichment of H3K4me2 observed following resident vascular stem cell differentiation to SMCs.

Abstract 61: Hedgehog-Responsive Stem Cell Antigen 1 Positive Cells Contribute To Vascular Smooth Muscle Cell Accumulation Following Vascular Injury

Background: Cardiovascular disease such as atherosclerosis is associated with the formation of an neointimal layer and medial hyperplasia as a result of the accumulation of vascular smooth muscle cells (vSMC) in the artery wall (i.e., intimal medial thickening, IMT). There is strong, albeit controversial, evidence indicating a putative role for stem cell antigen 1 positive (Sca1 + ) progenitor cell-derived vSMC in contributing to IMT. Interestingly, the Hedgehog (Hh) signaling receptor Patched 1 is present in the adventitial boundary and co-localizes with both Sca1 and Patched 1, the ligand for sonic hedgehog (SHh). The aim of our study was to determine the effect of Hh signaling on Sca1+ stem cells and their contribution to vSMC accumulation and IMT following vascular injury.

Methods: Sca1 + stem cells were treated with differentiation inductive stimuli in the absence or presence of recombinant SHh (rSHh), with or without the Hh inhibitor cyclopamine, before the cells were examined for their stemness (telomerase activity), differentiation capacity (SMC differentiation) and epigenetic profile. In parallel, Sca1-eGFP transgenic mice were subjected to carotid injury (i.e., partial ligation), with or without cyclopamine, before IMT, Sca1 expression and SMC phenotype was assessed.

Results: Sonic Hedgehog stimulated Sca1 + stem cell differentiation capacity, as demonstrated by enhanced expression of SMC differentiation markers in addition to their altered stemness, epigenetic profile (H3K4me2:H3K27me3) and proliferative status. In parallel studies, Hh signaling components were elevated in ligated carotids when compared to sham-operated controls, concomitant with increased Sca1 expression and SMC accumulation. Moreover, there was a significant attenuation of SMC accumulation and intimal medial thickening of injured carotids following Hh inhibition with cyclopamine.

Conclusion: Sca1 + stem cells are Hh-responsive and they contribute to vSMC accumulation in the carotid following ligation injury.

Abstract 352: Adventitial Stem Cell Progenitors Express Neural Stem Cell Markers

Many forms of cardiovascular disease (CVD) are charaterised by intimal medial thickening (IMT) due to the formation of a neointimal layer as a result of the accumulation of vascular smooth muscle cells (vSMC) within the vessel wall. There is strong evidence, albeit controversial, that indicates a putative role for both adventitial (Sca1 + , CD34 + and Lin - ) and medial multipotent vascular progenitor stem cell-derived [Sox10, Sox17 and S100β] vSMC in contributing to IMT.

The objective of this study was to characterise adventitial progenitor stem cells (APCs) from aortic explants and compare them to medial MVSCs. APC and MVSC phenotype was determined by immunocytochemistry using antisera specific for adventitial stem cell marker Sca1 and stem cell markers Sox10, Sox 17 and S100β respectively. Differentiated vSMC markers, α-actin, calponin 1 and smooth muscle myosin hevy chain II (Myh11) were used to detect SMCs. Discrete APC populations were positive for neural stem cell markers [Sox 10, Sox17 and S100β] as well as marker α-actin. Notably a significant number of intial cells migrating from the adventitial explant were Sox 10, Sox 17 and S100β positive respectively. Similarly, MVSC from medial explants were positive for neural stem cell markers [Sox 10, Sox17 and S100β] and Sca1 (when grown in maintenance media). There was a distinct absence of smooth muscle myosin heavy chain II filaments (differentiated vSMC markers) in both the APC and MVSC cell populations.

We conclude that APCs and MVSCs may be derived from a similar source.

Identification and Characterization of Cyprinid Herpesvirus-3 (CyHV-3) Encoded MicroRNAs

MicroRNAs (miRNAs) are a class of small non-coding RNAs involved in post-transcriptional gene regulation. Some viruses encode their own miRNAs and these are increasingly being recognized as important modulators of viral and host gene expression. Cyprinid herpesvirus 3 (CyHV-3) is a highly pathogenic agent that causes acute mass mortalities in carp (Cyprinus carpio carpio) and koi (Cyprinus carpio koi) worldwide. Here, bioinformatic analyses of the CyHV-3 genome suggested the presence of non-conserved precursor miRNA (pre-miRNA) genes. Deep sequencing of small RNA fractions prepared from in vitro CyHV-3 infections led to the identification of potential miRNAs and miRNA–offset RNAs (moRNAs) derived from some bioinformatically predicted pre-miRNAs. DNA microarray hybridization analysis, Northern blotting and stem-loop RT-qPCR were then used to definitively confirm that CyHV-3 expresses two pre-miRNAs during infection in vitro. The evidence also suggested the presence of an additional four high-probability and two putative viral pre-miRNAs. MiRNAs from the two confirmed pre-miRNAs were also detected in gill tissue from CyHV-3-infected carp. We also present evidence that one confirmed miRNA can regulate the expression of a putative CyHV-3-encoded dUTPase. Candidate homologues of some CyHV-3 pre-miRNAs were identified in CyHV-1 and CyHV-2. This is the first report of miRNA and moRNA genes encoded by members of the Alloherpesviridae family, a group distantly related to the Herpesviridae family. The discovery of these novel CyHV-3 genes may help further our understanding of the biology of this economically important virus and their encoded miRNAs may have potential as biomarkers for the diagnosis of latent CyHV-3.

Repression of the proapoptotic cellular BIK/NBK gene by Epstein-Barr virus antagonizes transforming growth factor β1-induced B-cell apoptosis

The Epstein-Barr virus (EBV) establishes a lifelong latent infection in humans. EBV infection of primary B cells causes cell activation and proliferation, a process driven by the viral latency III gene expression program, which includes EBV nuclear proteins (EBNAs), latent membrane proteins, and untranslated RNAs, including microRNAs. Some latently infected cells enter the long-lived memory B-cell compartment and express only EBNA1 transiently (Lat I) or no EBV protein at all (Lat 0). Targeting the molecular machinery that controls B-cell fate decisions, including the Bcl-2 family of apoptosis-regulating proteins, is crucial to the EBV cycle of infection. Here, we show that BIK (also known as NBK), which encodes a proapoptotic "sensitizer" protein, is repressed by the EBNA2-driven Lat III program but not the Lat I program. BIK repression occurred soon after infection of primary B cells by EBV but not by a recombinant EBV in which the EBNA2 gene had been knocked out. Ectopic BIK induced apoptosis in Lat III cells by a mechanism dependent on its BH3 domain and the activation of caspases. We show that EBNA2 represses BIK in EBV-negative B-cell lymphoma-derived cell lines and that this host-virus interaction can inhibit the proapoptotic effect of transforming growth factor β1 (TGF-β1), a key physiological mediator of B-cell homeostasis. Reduced levels of TGF-β1-associated regulatory SMAD proteins were bound to the BIK promoter in response to EBV Lat III or ectopic EBNA2. These data are evidence of an additional mechanism used by EBV to promote B-cell survival, namely, the transcriptional repression of the BH3-only sensitizer BIK.

IMPORTANCE

Over 90% of adult humans are infected with the Epstein-Barr virus (EBV). EBV establishes a lifelong silent infection, with its DNA residing in small numbers of blood B cells that are a reservoir from which low-level virus reactivation and shedding in saliva intermittently occur. Importantly, EBV DNA is found in some B-cell-derived tumors in which viral genes play a key role in tumor cell emergence and progression. Here, we report for the first time that EBV can shut off a B-cell gene called BIK. When activated by a molecular signal called transforming growth factor β1 (TGF-β1), BIK plays an important role in killing unwanted B cells, including those infected by viruses. We describe the key EBV-B-cell molecular interactions that lead to BIK shutoff. These findings further our knowledge of how EBV prevents the death of its host cell during infection. They are also relevant to certain posttransplant lymphomas where unregulated cell growth is caused by EBV genes.