Identification of ARIA regulating endothelial apoptosis and angiogenesis by modulating proteasomal degradation of cIAP-1 and cIAP-2

Unraveling the enigma: housekeeping gene Ugt1a7c as a universal biomarker for microglia

Background

Microglia, brain resident macrophages, play multiple roles in maintaining homeostasis, including immunity, surveillance, and protecting the central nervous system through their distinct activation processes. Identifying all types of microglia-driven populations is crucial due to the presence of various phenotypes that differ based on developmental stages or activation states. During embryonic development, the E8.5 yolk sac contains erythromyeloid progenitors that go through different growth phases, eventually resulting in the formation of microglia. In addition, microglia are present in neurological diseases as a diverse population. So far, no individual biomarker for microglia has been discovered that can accurately identify and monitor their development and attributes.

Summary

Here, we highlight the newly defined biomarker of mouse microglia, UGT1A7C, which exhibits superior stability in expression during microglia development and activation compared to other known microglia biomarkers. The UGT1A7C sensing chemical probe labels all microglia in the 3xTG AD mouse model. The expression of Ugt1a7c is stable during development, with only a 4-fold variation, while other microglia biomarkers, such as Csf1r and Cx3cr1, exhibit at least a 10-fold difference. The UGT1A7C expression remains constant throughout its lifespan. In addition, the expression and activity of UGT1A7C are the same in response to different types of inflammatory activators' treatment in vitro.

Conclusion

We propose employing UGT1A7C as the representative biomarker for microglia, irrespective of their developmental state, age, or activation status. Using UGT1A7C can reduce the requirement for using multiple biomarkers, enhance the precision of microglia analysis, and even be utilized as a standard for gene/protein expression.

GPNMB plays a protective role against obesity-related metabolic disorders by reducing macrophage inflammatory capacity

Obesity is a global health problem that is often related to cardiovascular and metabolic diseases. Chronic low-grade inflammation in white adipose tissue (WAT) is a hallmark of obesity. Previously, during a search for differentially expressed genes in WAT of obese mice, we identified glycoprotein nonmetastatic melanoma protein B (GPNMB), of which expression was robustly induced in pathologically expanded WAT. Here, we investigated the role of GPNMB in obesity-related metabolic disorders utilizing GPNMB-deficient mice. When fed a high-fat diet (HFD), GPNMB-deficient mice showed body weight and adiposity similar to those of wild-type (WT) mice. Nonetheless, insulin and glucose tolerance tests revealed significant obesity-related metabolic disorders in GPNMB-KO mice compared with WT mice fed with HFD. Chronic WAT inflammation was remarkably worsened in HFD-fed GPNMB-KO mice, accompanied by a striking increase in crown-like structures, typical hallmarks for diseased WAT. Macrophages isolated from GPNMB-KO mice were observed to produce more inflammatory cytokines than those of WT mice, a difference abolished by supplementation with recombinant soluble GPNMB extracellular domain. We demonstrated that GPNMB reduced the inflammatory capacity of macrophages by inhibiting NF-κB signaling largely through binding to CD44. Finally, we showed that macrophage depletion by addition of clodronate liposomes abolished the worsened WAT inflammation and abrogated the exacerbation of metabolic disorders in GPNMB-deficient mice fed on HFD. Our data reveal that GPNMB negatively regulates macrophage inflammatory capacities and ameliorates the WAT inflammation in obesity; therefore we conclude that GPNMB is a promising therapeutic target for the treatment of metabolic disorders associated with obesity.

Neuregulin 1 (NRG-1) as a Neuronal Active Substance in the Porcine Intrahepatic Nerve Fibers in Physiological Conditions and Under the Influence of Bisphenol a (BPA )

Bisphenol A (BPA ) is a substance commonly used in the production of plastics. Previous studies have described that it shows multidirectional harmful effects on the living organism. It is known that BPA causes liver damage, but knowledge about the roles of intrahepatic nerves in these mechanisms is extremely scanty. On the other hand, the exact roles of some neuronal substances in the nervous structures located in the liver still remain unknown. One of such substance, which is allocated a role in the stimulation of cell survival is neuregulin 1 (NRG-1). The aim of the present study was to investigate the distribution of NRG-1-like immunoreactive (NRG-1-LI) nerves in the liver in physiological conditions and under the influence of various doses of BPA using routine double immunofluorescence staining. The results (for the first time) show the presence of NRG-1 in the intrahepatic nerves, and co-localization of NGR-1 with neuronal isoform of nitric oxide synthase (nNOS) and vasoactive intestinal polypeptide (VIP). Moreover, it has been observed that high doses of BPA increase the density of NRG-1-LI intrahepatic nerves and the degree of co-localization of NRG-1 with VIP. These observations suggest that NRG-1 located in intrahepatic nerves may play functions in processes connected with liver damage and/or regeneration under the impact of BPA.

The landscape of host genetic factors involved in immune response to common viral infections

BACKGROUND

Humans and viruses have co-evolved for millennia resulting in a complex host genetic architecture. Understanding the genetic mechanisms of immune response to viral infection provides insight into disease etiology and therapeutic opportunities.

METHODS

We conducted a comprehensive study including genome-wide and transcriptome-wide association analyses to identify genetic loci associated with immunoglobulin G antibody response to 28 antigens for 16 viruses using serological data from 7924 European ancestry participants in the UK Biobank cohort.

RESULTS

Signals in human leukocyte antigen (HLA) class II region dominated the landscape of viral antibody response, with 40 independent loci and 14 independent classical alleles, 7 of which exhibited pleiotropic effects across viral families. We identified specific amino acid (AA) residues that are associated with seroreactivity, the strongest associations presented in a range of AA positions within DRβ1 at positions 11, 13, 71, and 74 for Epstein-Barr virus (EBV), Varicella zoster virus (VZV), human herpesvirus 7, (HHV7), and Merkel cell polyomavirus (MCV). Genome-wide association analyses discovered 7 novel genetic loci outside the HLA associated with viral antibody response (P < 5.0 × 10-8), including FUT2 (19q13.33) for human polyomavirus BK (BKV), STING1 (5q31.2) for MCV, and CXCR5 (11q23.3) and TBKBP1 (17q21.32) for HHV7. Transcriptome-wide association analyses identified 114 genes associated with response to viral infection, 12 outside of the HLA region, including ECSCR: P = 5.0 × 10-15 (MCV), NTN5: P = 1.1 × 10-9 (BKV), and P2RY13: P = 1.1 × 10-8 EBV nuclear antigen. We also demonstrated pleiotropy between viral response genes and complex diseases, from autoimmune disorders to cancer to neurodegenerative and psychiatric conditions.

CONCLUSIONS

Our study confirms the importance of the HLA region in host response to viral infection and elucidates novel genetic determinants beyond the HLA that contribute to host-virus interaction.

The landscape of host genetic factors involved in immune response to common viral infections

INTRODUCTION

Humans and viruses have co-evolved for millennia resulting in a complex host genetic architecture. Understanding the genetic mechanisms of immune response to viral infection provides insight into disease etiology and therapeutic opportunities.

METHODS

We conducted a comprehensive study including genome-wide and transcriptome-wide association analyses to identify genetic loci associated with immunoglobulin G antibody response to 28 antigens for 16 viruses using serological data from 7924 European ancestry participants in the UK Biobank cohort.

RESULTS

Signals in human leukocyte antigen (HLA) class II region dominated the landscape of viral antibody response, with 40 independent loci and 14 independent classical alleles, 7 of which exhibited pleiotropic effects across viral families. We identified specific amino acid (AA) residues that are associated with seroreactivity, the strongest associations presented in a range of AA positions within DRβ1 at positions 11, 13, 71, and 74 for Epstein-Barr Virus (EBV), Varicella Zoster Virus (VZV), Human Herpes virus 7, (HHV7) and Merkel cell polyomavirus (MCV). Genome-wide association analyses discovered 7 novel genetic loci outside the HLA associated with viral antibody response (P<5.×10-8), including FUT2 (19q13.33) for human polyomavirus BK (BKV), STING1 (5q31.2) for MCV, as well as CXCR5 (11q23.3) and TBKBP1 (17q21.32) for HHV7. Transcriptome-wide association analyses identified 114 genes associated with response to viral infection, 12 outside of the HLA region, including ECSCR: P=5.0×10-15 (MCV), NTN5: P=1.1×10-9 (BKV), and P2RY13: P=1.1×10-8 EBV nuclear antigen. We also demonstrated pleiotropy between viral response genes and complex diseases; from autoimmune disorders to cancer to neurodegenerative and psychiatric conditions.

CONCLUSIONS

Our study confirms the importance of the HLA region in host response to viral infection and elucidates novel genetic determinants beyond the HLA that contribute to host-virus interaction.

Ophiopogonin D', a Natural Product From Radix Ophiopogonis, Induces in Vitro and in Vivo RIPK1-Dependent and Caspase-Independent Apoptotic Death in Androgen-Independent Human Prostate Cancer Cells

Objective: The purpose of this study was to evaluate the anticancer effects of Ophiopogonin D′ (OPD′, a natural product extracted from a traditional Chinese medicine (Radix Ophiopogonis) against androgen-independent prostate cancer cells and to explore the underlying molecular mechanism(s) of action.

Methods: The CCK-8 assay was used to assess the viability of prostate cancer cells. The cell morphology was examined by an ultrastructural analysis via transmission electron microscopy. Cells in apoptosis (early and late stages) were detected using an Annexin V-FITC/propidium iodide kit with a FACSCaliber flow cytometer. JC-1, a cationic lipophilic probe, was employed to measure the mitochondrial membrane potential (MMP) of PC3 cells. Changes in the protein expression of RIPK1, C-RIPK1, caspase 8, cleaved-caspase 8, Bim, Bid, caspase 10, and cleaved-caspase 10 were evaluated by Western blotting. The mRNA expression of Bim was examined by quantitative real-time reverse transcription polymerase chain reaction. Z-VAD-FMK (a caspase inhibitor) and necrostatin-1 (a specific inhibitor of RIPK1) were utilized to determine whether the cell death was mediated by RIPK1 or caspases. PC3 and DU145 xenograft models in BALB/c nude mice were used to evaluate the anticancer activity of OPD′ in vivo.

Results: OPD′ was shown to exert potent anti-tumor activity against PC3 cells. It induced apoptosis via a RIPK1-related pathway, increased the protein expression levels of RIPK1 and Bim, and decreased the levels of cleaved-RIPK1, caspase 8, cleaved-caspase 8, Bid, caspase 10, and cleaved-caspase 10. OPD′ also increased the mRNA expression of Bim. The protein expression of Bim was decreased when cells were pre-treated with necrostatin-1. Treatment with OPD′ inhibited the growth of PC3 and DU145 xenograft tumors in BALB/c nude mice.

Conclusion: OPD′ significantly inhibited the in vitro and in vivo growth of prostate cells via RIPK1, suggesting that OPD′ may be developed as a potential anti-prostate cancer agent.

ECSM2, an endothelial specific VE-cadherin binding protein, has a tyrosine phosphorylation site essential to cell migration

Endothelial cell-specific molecule 2 (ECSM2) is a transmembrane protein located in cell-cell junction of endothelial cells (EC). ECSM2 was determined to play an important role in vascular development, EC migration, apoptosis and proliferation, however, no functional domains were determined in intracellular and extracellular region of ECSM2. In current work, functional domains of ECSM2, the relationship of ECSM2 with other endothelial specific protein such as VE-cadherin and the role of ECSM2 in neovascular diseases were determined. It was shown that the 54th amino acid residue of ECSM2 extracellular domain was a tyrosine phosphorylation site, whose mutation led to the loss of EGF-induced tyrosine phosphorylation and inhibition of cell migration. In primary human umbilical vein endothelial cells, ECSM2 bound with VE-cadherin and VEGF stimulation enhanced their binding. In hepatocellular carcinoma, ECSM2 expression was increased, as compared with para-cancerous tissue. This data firstly revealed the functional sites of ECSM2, the crosstalk between ECSM2 and other endothelial cell specific molecules, the expression of ECSM2 in tissues of angiogenesis diseases, thus providing understanding about ECSM2 in depth.

Anti-angiogenic nanotherapy via active targeting systems to tumors and adipose tissue vasculature

Sophisticated drug delivery systems (DDS) are required for delivering drugs, especially macromolecules such as nucleic acids or proteins, to their sites of action. Therefore it is a prerequisite that future DDS are designed to selectively target a tissue. In this review, we focus on systems that actively target the vasculature in tumors or adipose tissues. For targeting tumor vasculatur, a new strategy referred to as dual-targeting is proposed that uses a combination of a receptor specific ligand and a cell penetrating peptide, which can induce the synergistic enhancement of tissue selectivity under in vivo conditions. A novel pH-sensitive cationic lipid was designed to enhance the endosomal release of encapsulated compounds such as siRNA as well as to improve the stability in blood circulation after intravenous administration. A cyclic RGD peptide is used as an active targeting ligand. For targeting adipose vasculature, prohibitin, which is expressed on the surface of adipose endothelial cells, was targeted with KGGRAKD peptides on the surface of PEGylated nanoparticles. Prohibitin targeted nanoparticles (PTNP) encapsulating Cytochrome c (CytC) can selectively target adipose vasculature by optimizing the lengths of the PEG linkers and can deliver CytC to adipose endothelial cells. PTNP can successfully induce anti-obese effects as well as apoptosis by delivering CytC to the cytosol in endothelial cells. Unexpectedly, the EPR (enhanced permeability and retention) effect, which is usually observed in tumor tissue, was also observed in the adipose vasculature, especially in obese mice, where PEGylated nanoparticles can pass through the endothelial barriers in adipose tissue. We believe that these achievements in active targeting will allow a greatly expanded use of DDS for nanomedicines.

Loss of apoptosis regulator through modulating IAP expression (ARIA) protects blood vessels from atherosclerosis

Atherosclerosis is the primary cause for cardiovascular disease. Here we identified a novel mechanism underlying atherosclerosis, which is provided by ARIA (apoptosis regulator through modulating IAP expression), the transmembrane protein that we recently identified. ARIA is expressed in macrophages present in human atherosclerotic plaque as well as in mouse peritoneal macrophages. When challenged with acetylated LDL, peritoneal macrophages isolated from ARIA-deficient mice showed substantially reduced foam cell formation, whereas the uptake did not differ from that in wild-type macrophages. Mechanistically, loss of ARIA enhanced PI3K/Akt signaling and consequently reduced the expression of acyl coenzyme A:cholesterol acyltransferase-1 (ACAT-1), an enzyme that esterifies cholesterol and promotes its storage, in macrophages. Inhibition of PI3K abolished the reduction in ACAT-1 expression and foam cell formation in ARIA-deficient macrophages. In contrast, overexpression of ARIA reduced Akt activity and enhanced foam cell formation in RAW264.7 macrophages, which was abrogated by treatment with ACAT inhibitor. Of note, genetic deletion of ARIA significantly reduced the atherosclerosis in ApoE-deficient mice. Oil red-O-positive lipid-rich lesion was reduced, which was accompanied by an increase of collagen fiber and decrease of necrotic core lesion in atherosclerotic plaque in ARIA/ApoE double-deficient mice. Analysis of bone marrow chimeric mice revealed that loss of ARIA in bone marrow cells was sufficient to reduce the atherosclerogenesis in ApoE-deficient mice. Together, we identified a unique role of ARIA in the pathogenesis of atherosclerosis at least partly by modulating macrophage foam cell formation. Our results indicate that ARIA could serve as a novel pharmacotherapeutic target for the treatment of atherosclerotic diseases.

Role of estrogen in angiogenesis in cardiovascular diseases

The formation of new blood vessels from existing ones is a major process of angiogenesis and it is most effective in the vascular systems. The physiological process like hypoxia inducible factors involved in the regeneration of damaged tissues varies within the vascular systems in the endothelium and could be limited due to some major angiogenic growth factors like vascular endothelial growth factor, fibroblast growth factors and epidermal growth factor among others which bring about this cellular vascular regrowth. These physiological processes leading to cellular vascular regrowth could be a major function for the treatment of cardiovascular diseases such as ischemia and atherosclerosis. Estrogens are one of the known factors within the cellular mechanisms that could initiate repairs to the damaged vascular tissues, since estrogens are known inducers of angiogenesis leading to this cellular regrowth. Research has also shown that this cellular regrowth is induced by vascular angiogenic growth factors via the estrogen receptors. In this review we will attempt to summarize the main angiogenic growth factors involved in these physiological processes leading to angiogenesis and possible new mechanisms that could lead to this vascular regrowth. And also we will try to summarize some reports on the effect of estrogen on these physiological processes leading to angiogenesis in cardiovascular diseases.

Manipulation of cardiac phosphatidylinositol 3-kinase (PI3K)/Akt signaling by apoptosis regulator through modulating IAP expression (ARIA) regulates cardiomyocyte death during doxorubicin-induced cardiomyopathy

PI3K/Akt signaling plays an important role in the regulation of cardiomyocyte death machinery, which can cause stress-induced cardiac dysfunction. Here, we report that apoptosis regulator through modulating IAP expression (ARIA), a recently identified transmembrane protein, regulates the cardiac PI3K/Akt signaling and thus modifies the progression of doxorubicin (DOX)-induced cardiomyopathy. ARIA is highly expressed in the mouse heart relative to other tissues, and it is also expressed in isolated rat cardiomyocytes. The stable expression of ARIA in H9c2 cardiac muscle cells increased the levels of membrane-associated PTEN and subsequently reduced the PI3K/Akt signaling and the downstream phosphorylation of Bad, a proapoptotic BH3-only protein. When challenged with DOX, ARIA-expressing H9c2 cells exhibited enhanced apoptosis, which was reversed by the siRNA-mediated silencing of Bad. ARIA-deficient mice exhibited normal heart morphology and function. However, DOX-induced cardiac dysfunction was significantly ameliorated in conjunction with reduced cardiomyocyte death and cardiac fibrosis in ARIA-deficient mice. Phosphorylation of Akt and Bad was substantially enhanced in the heart of ARIA-deficient mice even after treatment with DOX. Moreover, repressing the PI3K by cardiomyocyte-specific expression of dominant-negative PI3K (p110α) abolished the cardioprotective effects of ARIA deletion. Notably, targeted activation of ARIA in cardiomyocytes but not in endothelial cells reduced the cardiac PI3K/Akt signaling and exacerbated the DOX-induced cardiac dysfunction. These studies, therefore, revealed a previously undescribed mode of manipulating cardiac PI3K/Akt signaling by ARIA, thus identifying ARIA as an attractive new target for the prevention of stress-induced myocardial dysfunction.

Endothelial cell-specific chemotaxis receptor (ECSCR) enhances vascular endothelial growth factor (VEGF) receptor-2/kinase insert domain receptor (KDR) activation and promotes proteolysis of internalized KDR

The endothelial cell-specific chemotaxis receptor (ECSCR) is a cell-surface protein selectively expressed by endothelial cells (ECs), with roles in EC migration, apoptosis and proliferation. Our previous study (Verma, A., Bhattacharya, R., Remadevi, I., Li, K., Pramanik, K., Samant, G. V., Horswill, M., Chun, C. Z., Zhao, B., Wang, E., Miao, R. Q., Mukhopadhyay, D., Ramchandran, R., and Wilkinson, G. A. (2010) Blood 115, 4614-4622) showed that loss of ECSCR in primary ECs reduced tyrosine phosphorylation of vascular endothelial growth factor (VEGF) receptor 2/kinase insert domain receptor (KDR) but not VEGF receptor 1/FLT1. Here, we show that ECSCR biochemically associates with KDR but not FLT1 and that the predicted ECSCR cytoplasmic and transmembrane regions can each confer association with KDR. Stimulation with VEGF165 rapidly and transiently increases ECSCR-KDR complex formation, a process blocked by the KDR tyrosine kinase inhibitor compound SU5416 or inhibitors of endosomal acidification. Triple labeling experiments show VEGF-stimulated KDR(+)/ECSCR(+) intracellular co-localization. Silencing of ECSCR disrupts VEGF-induced KDR activation and AKT and ERK phosphorylation and impairs VEGF-stimulated KDR degradation. In zebrafish, ecscr interacts with kdrl during intersomitic vessel sprouting. Human placenta and infantile hemangioma samples highly express ECSCR protein, suggesting a role for ECSCR-KDR interaction in these tissues.

Identification of novel splice variants and exons of human endothelial cell-specific chemotaxic regulator (ECSCR) by bioinformatics analysis

Recent discovery of biological function of endothelial cell-specific chemotaxic regulator (ECSCR), previously known as endothelial cell-specific molecule 2 (ECSM2), in modulating endothelial cell migration, apoptosis, and angiogenesis, has made it an attractive molecule in vascular research. Thus, identification of splice variants of ECSCR could provide new strategies for better understanding its roles in health and disease. In this study, we performed a series of blast searches on the human EST database with known ECSCR cDNA sequence (Variant 1), and identified additional three splice variants (Variants 2-4). When examining the ECSCR gene in the human genome assemblies, we found a large unknown region between Exons 9 and 11. By PCR amplification and sequencing, we partially mapped Exon 10 within this previously unknown region of the ECSCR gene. Taken together, in addition to previously reported human ECSCR, we identified three novel full-length splice variants potentially encoding different protein isoforms. We further defined a total of twelve exons and nearly all exon-intron boundaries of the gene, of which only eight are annotated in current public databases. Our work provides new information on gene structure and alternative splicing of the human ECSCR, which may imply its functional complexity. This undoubtedly opens new opportunities for future investigation of the biological and pathological significance of these ECSCR splice variants.

Temporal genome expression profile analysis during t-cell-mediated colitis: identification of novel targets and pathways

BACKGROUND

T cells critically regulate inflammatory bowel disease (IBD), with T-cell-dependent experimental colitis models gaining favor in identifying potential pathogenic mechanisms; yet limited understanding of specific pathogenic molecules or pathways still exists.

METHODS

In this study we sought to identify changes in whole genome expression profiles using the CD4CD45Rbhi T-cell transfer colitis model compared to genome expression differences from Crohn's disease (CD) tissue specimens. Colon tissue was used for histopathological and genome expression profiling analysis at 0, 2, 4, or 6 weeks after adoptive T-cell transfer.

RESULTS

We identified 1775 genes that were significantly altered during disease progression, with 361 being progressively downregulated and 341 progressively upregulated. Gene expression changes were validated by quantitative real-time polymerase chain reaction (qRT-PCR), confirming genome expression analysis data. Differentially expressed genes were clearly related to inflammation/immune responses but also strongly associated with metabolic, chemokine signaling, Jak-STAT signaling, and angiogenesis pathways. Ingenuity network analysis revealed 25 unique network associations that were associated with functions such as antigen presentation, cell morphology, cell-to-cell signaling and interaction, as well as nervous system development and function. Moreover, many of these genes and pathways were similarly identified in CD specimens.

CONCLUSIONS

These findings reveal novel, complex, and dynamic changes in gene expression that may provide useful targets for future therapeutic approaches.

Structural and functional characterization of two alternative splicing variants of mouse Endothelial Cell-Specific Chemotaxis Regulator (ECSCR)

Endothelial cells (ECs) that line the lumen of blood vessels are important players in blood vessel formation, and EC migration is a key component of the angiogenic process. Thus, identification of genes that are specifically or preferentially expressed in vascular ECs and in-depth understanding of their biological functions may lead to discovery of new therapeutic targets. We have previously reported molecular characterization of human endothelial cell-specific molecule 2 (ECSM2)/endothelial cell-specific chemotaxis regulator (ECSCR). In the present study, we cloned two mouse full-length cDNAs by RT-PCR, which encode two putative ECSCR isoform precursors with considerable homology to the human ECSCR. Nucleotide sequence and exon-intron junction analyses suggested that they are alternative splicing variants (ECSCR isoform-1 and -2), differing from each other in the first and second exons. Quantitative RT-PCR results revealed that isoform-2 is the predominant form, which was most abundant in heart, lung, and muscles, and moderately abundant in uterus and testis. In contrast, the expression of isoform-1 seemed to be more enriched in testis. To further explore their potential cellular functions, we expressed GFP- and FLAG-tagged ECSCR isoforms, respectively, in an ECSCR deficient cell line (HEK293). Interestingly, the actual sizes of either ECSCR-GFP or -FLAG fusion proteins detected by immunoblotting are much larger than their predicted sizes, suggesting that both isoforms are glycoproteins. Fluorescence microscopy revealed that both ECSCR isoforms are localized at the cell surface, which is consistent with the structural prediction. Finally, we performed cell migration assays using mouse endothelial MS1 cells overexpressing GFP alone, isoform-1-GFP, and isoform-2-GFP, respectively. Our results showed that both isoforms significantly inhibited vascular epidermal growth factor (VEGF)-induced cell migration. Taken together, we have provided several lines of experimental evidence that two mouse ECSCR splicing variants/isoform precursors exist. They are differentially expressed in a variety of tissue types and likely involved in modulation of vascular EC migration. We have also defined the gene structure of mouse ECSCR using bioinformatics tools, which provides new information towards a better understanding of alternative splicing of ECSCR.

Shear stress, tip cells and regulators of endothelial migration

We have in recent years described several endothelial-specific genes that mediate cell migration. These include Robo4 (roundabout 4), CLEC14A (C-type lectin 14A) and ECSCR (endothelial cell-specific chemotaxis regulator) [formerly known as ECSM2 (endothelial cell-specific molecule 2)]. Loss of laminar shear stress induces Robo4 and CLEC14A expression and an endothelial 'tip cell' phenotype. Low shear stress is found not only at sites of vascular occlusion such as thrombosis and embolism, but also in the poorly structured vessels that populate solid tumours. The latter probably accounts for strong expression of Robo4 and CLEC14A on tumour vessels. The function of Robo4 has, in the past, aroused controversy. However, the recent identification of Unc5B as a Robo4 ligand has increased our understanding and we hypothesize that Robo4 function is context-dependent. ECSCR is another endothelial-specific protein that promotes filopodia formation and migration, but, in this case, expression is independent of shear stress. We discuss recent papers describing ECSCR, including intracellular signalling pathways, and briefly contrast these with signalling by Robo4.

Loss of bcl-2 during the senescence exacerbates the impaired angiogenic functions in endothelial cells by deteriorating the mitochondrial redox state

Ageing is an important risk factor for ischemic cardiovascular diseases, although its underlying molecular mechanisms remain to be elucidated. Here, we report a crucial role of Bcl-2 in the impaired angiogenic functions in senescent endothelial cells (ECs) by modulating the mitochondrial redox state. Cellular senescence impaired angiogenic functions in ECs without attenuating the mitogen-activated protein kinase or Akt signaling, and vascular endothelial growth factor receptor 2 or Tie-2 expressions. We identified that Bcl-2 expression was markedly reduced in 3 independent models for senescent ECs, and pharmacological inhibition, as well as small interfering RNA-mediated gene silencing of Bcl-2, significantly impaired the angiogenic functions in young ECs. Bcl-2 has an antioxidative role by locating the glutathione at mitochondria, and we found that mitochondrial oxidative stress was significantly augmented in senescent ECs, in association with reduced mitochondria-associated glutathione. Transfection of Bcl-2 in senescent ECs significantly reduced the mitochondrial oxidative stress, restored the mitochondrial membrane potential, and improved the angiogenic capacity. Furthermore, gene transfer of Bcl-2 using adenovirus significantly improved the in vivo angiogenesis in the Matrigel plugs implanted into aged mice, whereas the Bcl-2 inhibitor reduced the angiogenesis in the Matrigel plugs implanted into young mice. Together, Bcl-2 plays a crucial role in the regulation of the mitochondrial redox state in ECs, and, thus, loss of Bcl-2 during the senescence exacerbates the impaired angiogenesis by augmenting the mitochondrial oxidative stress.

Endothelial cell-specific molecule 2 (ECSM2) localizes to cell-cell junctions and modulates bFGF-directed cell migration via the ERK-FAK pathway

Background

Despite its first discovery by in silico cloning of novel endothelial cell-specific genes a decade ago, the biological functions of endothelial cell-specific molecule 2 (ECSM2) have only recently begun to be understood. Limited data suggest its involvement in cell migration and apoptosis. However, the underlying signaling mechanisms and novel functions of ECSM2 remain to be explored.

Methodology/Principal Findings

A rabbit anti-ECSM2 monoclonal antibody (RabMAb) was generated and used to characterize the endogenous ECSM2 protein. Immunoblotting, immunoprecipitation, deglycosylation, immunostaining and confocal microscopy validated that endogenous ECSM2 is a plasma membrane glycoprotein preferentially expressed in vascular endothelial cells (ECs). Expression patterns of heterologously expressed and endogenous ECSM2 identified that ECSM2 was particularly concentrated at cell-cell contacts. Cell aggregation and transwell assays showed that ECSM2 promoted cell-cell adhesion and attenuated basic fibroblast growth factor (bFGF)-driven EC migration. Gain or loss of function assays by overexpression or knockdown of ECSM2 in ECs demonstrated that ECSM2 modulated bFGF-directed EC motility via the FGF receptor (FGFR)-extracellular regulated kinase (ERK)-focal adhesion kinase (FAK) pathway. The counterbalance between FAK tyrosine phosphorylation (activation) and ERK-dependent serine phosphorylation of FAK was critically involved. A model of how ECSM2 signals to impact bFGF/FGFR-driven EC migration was proposed.

Conclusions/Significance

ECSM2 is likely a novel EC junctional protein. It can promote cell-cell adhesion and inhibit bFGF-mediated cell migration. Mechanistically, ECSM2 attenuates EC motility through the FGFR-ERK-FAK pathway. The findings suggest that ECSM2 could be a key player in coordinating receptor tyrosine kinase (RTK)-, integrin-, and EC junctional component-mediated signaling and may have important implications in disorders related to endothelial dysfunction and impaired EC junction signaling.

Apoptosis regulator through modulating IAP expression (ARIA) controls the PI3K/Akt pathway in endothelial and endothelial progenitor cells

Endothelial and endothelial progenitor cells (ECs and EPCs) play a fundamental role in angiogenesis that is essential for numerous physiological and pathological processes. The phosphatase and tensin homolog (PTEN)/ phosphoinositide 3-kinase (PI3K) pathway has been implicated in angiogenesis, but the mechanism in the regulation of this pathway in ECs and EPCs is poorly understood. Here we show that ARIA (apoptosis regulator through modulating IAP expression), a transmembrane protein that we recently identified, regulates the PTEN/PI3K pathway in ECs and EPCs and controls developmental and postnatal angiogenesis in vivo. We found that ARIA is abundantly expressed in EPCs and regulates their angiogenic functions by modulating PI3K/Akt/endothelial nitric oxide synthase (eNOS) signaling. Genetic deletion of ARIA caused nonfatal bleeding during embryogenesis, in association with increased small vessel density and altered expression of various vascular growth factors including angiopoietins and VEGF receptors. Postnatal neovascularization induced by critical limb ischemia was substantially enhanced in ARIA-null mice, in conjunction with more bone marrow (BM)-derived ECs detected in ischemic muscles. Administration of PI3K or NO synthase inhibitor completely abolished the enhanced neovascularization in ARIA(-/-) mice. Mechanistically, we identified that ARIA interacts with PTEN at the intracellular domain independently of the PTEN phosphorylation in its C-terminal tail. Overexpressed ARIA increased PTEN in the membrane fraction, whereas ARIA-silencing reduced the membrane-associated PTEN, resulting in modified PI3K/Akt signaling. Taken together, our findings establish a previously undescribed mode of regulation of the PTEN/PI3K/Akt pathway by ARIA, and reveal a unique mechanism in the control of angiogenesis. These functions of ARIA might offer a unique therapeutic potential.

PC3 prostate tumor-initiating cells with molecular profile FAM65Bhigh/MFI2low/LEF1low increase tumor angiogenesis

BACKGROUND

Cancer stem-like cells are proposed to sustain solid tumors by virtue of their capacity for self-renewal and differentiation to cells that comprise the bulk of the tumor, and have been identified for a variety of cancers based on characteristic clonal morphologies and patterns of marker gene expression.

METHODS

Single cell cloning and spheroid culture studies were used to identify a population of cancer stem-like cells in the androgen-independent human prostate cancer cell line PC3.

RESULTS

We demonstrate that, under standard culture conditions, ~10% of PC3 cells form holoclones with cancer stem cell characteristics. These holoclones display high self-renewal capability in spheroid formation assays under low attachment and serum-free culture conditions, retain their holoclone morphology when passaged at high cell density, exhibit moderate drug resistance, and show high tumorigenicity in scid immunodeficient mice. PC3 holoclones readily form spheres, and PC3-derived spheres yield a high percentage of holoclones, further supporting their cancer stem cell-like nature. We identified one gene, FAM65B, whose expression is consistently up regulated in PC3 holoclones compared to paraclones, the major cell morphology in the parental PC3 cell population, and two genes, MFI2 and LEF1, that are consistently down regulated. This molecular profile, FAM65Bhigh/MFI2low/LEF1low, also characterizes spheres generated from parental PC3 cells. The PC3 holoclones did not show significant enriched expression of the putative prostate cancer stem cell markers CD44 and integrin α2β1. PC3 tumors seeded with holoclones showed dramatic down regulation of FAM65B and dramatic up regulation of MFI2 and LEF1, and unexpectedly, a marked increase in tumor vascularity compared to parental PC3 tumors, suggesting a role of cancer stem cells in tumor angiogenesis.

CONCLUSIONS

These findings support the proposal that PC3 tumors are sustained by a small number of tumor-initiating cells with stem-like characteristics, including strong self-renewal and pro-angiogenic capability and marked by the expression pattern FAM65Bhigh/MFI2low/LEF1low. These markers may serve as targets for therapies designed to eliminate cancer stem cell populations associated with aggressive, androgen-independent prostate tumors such as PC3.

Quantitative proteome analysis of the 20S proteasome of apoptotic Jurkat T cells

Regulated proteolysis plays important roles in cell biology and pathological conditions. A crosstalk exists between apoptosis and the ubiquitin-proteasome system, two pathways responsible for regulated proteolysis executed by different proteases. To investigate whether the apoptotic process also affects the 20S proteasome, we performed three independent SILAC-based quantitative proteome approaches: 1-DE/MALDI-MS, small 2-DE/MALDI-MS and large 2-DE/nano-LC-ESI-MS. Taking the results of all experiments together, no quantitative changes were observed for the α- and β-subunits of the 20S proteasome except for subunit α7. This protein was identified in two protein spots with a down-regulation of the more acidic protein species (α7a) and up-regulation of the more basic protein species (α7b) during apoptosis. The difference in these two α7 protein species could be attributed to oxidation of cysteine-41 to cysteine sulfonic acid and phosphorylation at serine-250 near the C terminus in α7a, whereas these modifications were missing in α7b. These results pointed to the biological significance of posttranslational modifications of proteasome subunit α7 after induction of apoptosis.

Endothelial cell-specific chemotaxis receptor (ecscr) promotes angioblast migration during vasculogenesis and enhances VEGF receptor sensitivity

Endothelial cell-specific chemotaxis receptor (ECSCR) is a cell surface protein expressed by blood endothelial cells with roles in endothelial cell migration and signal transduction. We investigated the function of ecscr in the development of the zebrafish vasculature. Zebrafish ecscr is expressed in angioblasts and in axial vessels during angioblast migration and vasculogenesis. Morpholino-directed ecscr knockdown resulted in defective angioblast migration in the posterior lateral plate mesoderm, a process known to depend on vascular endothelial-derived growth factor (VEGF). In cultured cells, transfected ECSCR localized to actin-rich membrane protrusions, colocalizing with kinase insert domain protein receptor (KDR)/VEGF receptor 2 in these regions. ECSCR-silenced cells show reduced VEGF-induced phosphorylation of KDR but not of FMS-like tyrosine kinase 1 (FLT1)/VEGF receptor 1. Finally, chemical inhibition of VEGF receptor activity in zebrafish resulted in angioblast deficiencies that partially overlap with those seen in ecscr morphants. We propose that ecscr promotes migration of zebrafish angioblasts by enhancing endothelial kdr sensitivity to VEGF.

Functionally defining the endothelial transcriptome, from Robo4 to ECSCR

We have applied search algorithms to expression databases to identify genes whose expression is restricted to the endothelial cell. Such genes frequently play a critical role in endothelial biology and angiogenesis. Two such genes are the roundabout receptor Robo4 and the ECSCR (endothelial-cell-specific chemotaxis regulator). Endothelial cells express both Robo1 and Robo4, which we have knocked down using siRNA (small interfering RNA) and then studied the effect in a variety of in vitro assays. Both Robo4 and Robo1 knockdown inhibited in vitro tube formation on Matrigel. Transfection of Robo4 into endothelial cells increased the number of filopodial extensions from the cell, but failed to do so in Robo1-knockdown cells. Separate immunoprecipitation studies showed that Robo1 and Robo4 heterodimerize. We conclude from this and other work that a heteroduplex of Robo1 and Robo4 signals through WASP (Wiskott-Aldrich syndrome protein) and other actin nucleation-promoting factors to increase the number of filopodia and cell migration. Knockdown of the transmembrane ECSCR protein in endothelial cells also reduced chemotaxis and impaired tube formation on Matrigel. Yeast two-hybrid analysis and immunoprecipitation studies showed that, in contrast with the roundabouts, ECSCR binds to the actin-modulatory filamin A. We conclude that all three of these genes are critical for effective endothelial cell migration and, in turn, angiogenesis.

Replicative senescence of vascular smooth muscle cells enhances the calcification through initiating the osteoblastic transition

Medial artery calcification, which does not accompany lipid or cholesterol deposit, preferentially occurs in elderly population, but its underlying mechanisms remain unclear. In the present study, we investigated the potential role of senescent vascular smooth muscle cells (VSMCs) in the formation of senescence-associated medial calcification. Replicative senescence was induced by the extended passages (until passages 11-13) in human primary VSMCs, and cells in early passage (passage 6) were used as control young cells. VSMC calcification was markedly enhanced in the senescent cells compared with that in the control young cells. We identified that genes highly expressed in osteoblasts, such as alkaline phosphatase (ALP) and type I collagen, were significantly upregulated in the senescent VSMCs, suggesting their osteoblastic transition during the senescence. Knockdown of either ALP or type I collagen significantly reduced the calcification in the senescent VSMCs. Of note, runt-related transcription factor-2 (RUNX-2), a core transcriptional factor that initiates the osteoblastic differentiation, was also upregulated in the senescent VSMCs. Knockdown of RUNX-2 significantly reduced the ALP expression and calcification in the senescent VSMCs, suggesting that RUNX-2 is involved in the senescence-mediated osteoblastic transition. Furthermore, immunohistochemistry of aorta from the klotho(-/-) aging mouse model demonstrated in vivo emergence of osteoblast-like cells expressing RUNX-2 exclusively in the calcified media. We also found that statin and Rho-kinase inhibitor effectively reduced the VSMC calcification by inhibiting P(i)-induced apoptosis and potentially enhancing matrix Gla protein expression in the senescent VSMCs. These findings strongly suggest an important role of senescent VSMCs in the pathophysiology of senescence-associated medial calcification, and the inhibition of osteoblastic transition could be a new therapeutic approach for the prevention of senescence-associated medial calcification.