Designer high-density lipoprotein particles enhance endothelial barrier function and suppress inflammation.

High-density lipoprotein (HDL) nanoparticles promote endothelial cell (EC) function and suppress inflammation, but their utility in treating EC dysfunction has not been fully explored. Here, we describe a fusion protein named ApoA1-ApoM (A1M) consisting of apolipoprotein A1 (ApoA1), the principal structural protein of HDL that forms lipid nanoparticles, and ApoM, a chaperone for the bioactive lipid sphingosine 1-phosphate (S1P). A1M forms HDL-like particles, binds to S1P, and is signaling competent. Molecular dynamics simulations showed that the S1P-bound ApoM moiety in A1M efficiently activated EC surface receptors. Treatment of human umbilical vein ECs with A1M-S1P stimulated barrier function either alone or cooperatively with other barrier-enhancing molecules, including the stable prostacyclin analog iloprost, and suppressed cytokine-induced inflammation. A1M-S1P injection into mice during sterile inflammation suppressed neutrophil influx and inflammatory mediator secretion. Moreover, systemic A1M administration led to a sustained increase in circulating HDL-bound S1P and suppressed inflammation in a murine model of LPS-induced endotoxemia. We propose that A1M administration may enhance vascular endothelial barrier function, suppress cytokine storm, and promote resilience of the vascular endothelium.

Signal Transduction and Gene Regulation in the Endothelium.

Extracellular signals act on G-protein-coupled receptors (GPCRs) to regulate homeostasis and adapt to stress. This involves rapid intracellular post-translational responses and long-lasting gene-expression changes that ultimately determine cellular phenotype and fate changes. The lipid mediator sphingosine 1-phosphate (S1P) and its receptors (S1PRs) are examples of well-studied GPCR signaling axis essential for vascular development, homeostasis, and diseases. The biochemical cascades involved in rapid S1P signaling are well understood. However, gene-expression regulation by S1PRs are less understood. In this review, we focus our attention to how S1PRs regulate nuclear chromatin changes and gene transcription to modulate vascular and lymphatic endothelial phenotypic changes during embryonic development and adult homeostasis. Because S1PR-targeted drugs approved for use in the treatment of autoimmune diseases cause substantial vascular-related adverse events, these findings are critical not only for general understanding of stimulus-evoked gene regulation in the vascular endothelium, but also for therapeutic development of drugs for autoimmune and perhaps vascular diseases.

Sphingosine 1-Phosphate Receptor Signaling Establishes AP-1 Gradients to Allow for Retinal Endothelial Cell Specialization.

Transcriptional mechanisms that drive angiogenesis and organotypic vascular endothelial cell specialization are poorly understood. Here, we show that retinal endothelial sphingosine 1-phosphate receptors (S1PRs), which restrain vascular endothelial growth factor (VEGF)-induced angiogenesis, spatially restrict expression of JunB, a member of the activator protein 1 (AP-1) family of transcription factors (TFs). Mechanistically, VEGF induces JunB expression at the sprouting vascular front while S1PR-dependent vascular endothelial (VE)-cadherin assembly suppresses JunB expression in the nascent vascular network, thus creating a gradient of this TF. Endothelial-specific JunB knockout mice showed diminished expression of neurovascular guidance genes and attenuated retinal vascular network progression. In addition, endothelial S1PR signaling is required for normal expression of ß-catenin-dependent genes such as TCF/LEF1 and ZIC3 TFs, transporters, and junctional proteins. These results show that S1PR signaling restricts JunB function to the expanding vascular front, thus creating an AP-1 gradient and enabling organotypic endothelial cell specialization of the vascular network.

Sphingosine 1-phosphate-regulated transcriptomes in heterogenous arterial and lymphatic endothelium of the aorta.

Despite the medical importance of G protein-coupled receptors (GPCRs), in vivo cellular heterogeneity of GPCR signaling and downstream transcriptional responses are not understood. We report the comprehensive characterization of transcriptomes (bulk and single-cell) and chromatin domains regulated by sphingosine 1-phosphate receptor-1 (S1PR1) in adult mouse aortic endothelial cells. First, S1PR1 regulates NFκB and nuclear glucocorticoid receptor pathways to suppress inflammation-related mRNAs. Second, S1PR1 signaling in the heterogenous endothelial cell (EC) subtypes occurs at spatially-distinct areas of the aorta. For example, a transcriptomically distinct arterial EC population at vascular branch points (aEC1) exhibits ligand-independent S1PR1/ß-arrestin coupling. In contrast, circulatory S1P-dependent S1PR1/ß-arrestin coupling was observed in non-branch point aEC2 cells that exhibit an inflammatory gene expression signature. Moreover, S1P/S1PR1 signaling regulates the expression of lymphangiogenic and inflammation-related transcripts in an adventitial lymphatic EC (LEC) population in a ligand-dependent manner. These insights add resolution to existing concepts of endothelial heterogeneity, GPCR signaling and S1P biology.

A Conserved Target Site in HIV-1 Gag RNA is Accessible to Inhibition by Both an HDV Ribozyme and a Short Hairpin RNA.

Antisense-based molecules targeting HIV-1 RNA have the potential to be used as part of gene or drug therapy to treat HIV-1 infection. In this study, HIV-1 RNA was screened to identify more conserved and accessible target sites for ribozymes based on the hepatitis delta virus motif. Using a quantitative screen for effects on HIV-1 production, we identified a ribozyme targeting a highly conserved site in the Gag coding sequence with improved inhibitory potential compared to our previously described candidates targeting the overlapping Tat/Rev coding sequence. We also demonstrate that this target site is highly accessible to short hairpin directed RNA interference, suggesting that it may be available for the binding of antisense RNAs with different modes of action. We provide evidence that this target site is structurally conserved in diverse viral strains and that it is sufficiently different from the human transcriptome to limit off-target effects from antisense therapies. We also show that the modified hepatitis delta virus ribozyme is more sensitive to a mismatch in its target site compared to the short hairpin RNA. Overall, our results validate the potential of a new target site in HIV-1 RNA to be used for the development of antisense therapies.

Design and evaluation of clinically relevant SOFA-HDV ribozymes targeting HIV RNA.

Nucleic acid therapies targeting HIV replication have the potential to be used in conjunction with or in place of the standard small-molecule therapies. Among the different classes of nucleic acid therapies, several ribozymes (Rzs, RNA enzymes) have been developed to target HIV RNA. The design of Rzs targeting HIV RNA is complicated by the sequence diversity of viral strains and the structural diversity of their target sites. Using the SOFA-HDV Rz as an example, this chapter describes methods that can be used to design Rzs for controlling HIV replication. We describe how to (1) identify highly conserved Rz target sites in HIV RNA; (2) generate a set of Rzs with the potential to be used as therapeutics; and (3) screen these Rzs for activity against HIV production.

Target-induced SOFA-HDV ribozyme.

Small cis-acting ribozymes have been converted into trans-acting ribozymes possessing the ability to cleave RNA substrates. The Hepatitis Delta Virus (HDV) ribozyme is one of the rare examples of these that is derived from an RNA species that is found in human cells. Consequently, it possesses the natural ability to function in the presence of human proteins in addition to an outstanding stability in human cells, two significant advantages in its use. The development of an additional specific on/off adaptor (SOFA) has led to the production of a new generation of HDV ribozymes with improved specificities that provide a tool with significant potential for future development in the fields of both functional genomics and gene -therapy. SOFA-HDV ribozyme-based gene inactivation systems have been reported in both prokaryotic and eukaryotic cells. Here, a step-by-step approach for the efficient design of highly specific SOFA-HDV ribozymes with a minimum investment of time and effort is described.

Selection of the most potent specific on/off adaptor-hepatitis delta virus ribozymes for use in gene targeting.

The Hepatitis Delta Virus (HDV) ribozyme, which is well adapted to the environment of the human cell, is an excellent candidate for the future development of gene-inactivation systems. On top of this, a new generation of HDV ribozymes now exists that benefits from the addition of a specific on/off adaptor (specifically the SOFA-HDV ribozymes) which greatly increases both the ribozyme's specificity and its cleavage activity. Unlike RNAi and hammerhead ribozymes, the designing of SOFA-HDV ribozymes to cleave, in trans, given RNA species has never been the object of a systematic optimization study, even with their recent use for the gene knockdown of various targets. This report aims at both improving and clarifying the design process of SOFA-HDV ribozymes. Both the ribozyme and the targeted RNA substrate were analyzed in order to provide new criteria that are useful in the selection of the most potent SOFA-HDV ribozymes. The crucial features present in both the ribozyme's biosensor and blocker, as well as at the target site, were identified and characterized. Simple rules were derived and tested using hepatitis C virus NS5B RNA as a model target. Overall, this method should promote the use of the SOFA-HDV ribozymes in a plethora of applications in both functional genomics and gene therapy.

Investigating a new generation of ribozymes in order to target HCV.

For a long time nucleic acid-based approaches directed towards controlling the propagation of Hepatitis C Virus (HCV) have been considered to possess high potential. Towards this end, ribozymes (i.e. RNA enzymes) that specifically recognize and subsequently catalyze the cleavage of their RNA substrate present an attractive molecular tool. Here, the unique properties of a new generation of ribozymes are taken advantage of in order to develop an efficient and durable ribozyme-based technology with which to target HCV (+) RNA strands. These ribozymes resulted from the coupling of a specific on/off adaptor (SOFA) to the ribozyme domain derived from the Hepatitis Delta Virus (HDV). The former switches cleavage activity "on" solely in the presence of the desired RNA substrate, while the latter was the first catalytic RNA reported to function naturally in human cells, specifically in hepatocytes. In order to maximize the chances for success, a step-by-step approach was used for both the design and the selection of the ribozymes. This approach included the use of both bioinformatics and biochemical methods for the identification of the sites possessing the greatest potential for targeting, and the subsequent in vitro testing of the cleavage activities of the corresponding SOFA-HDV ribozymes. These efforts led to a significant improvement in the ribozymes' designs. The ability of the resulting SOFA-HDV ribozymes to inhibit HCV replication was further examined using a luciferase-based replicon. Although some of the ribozymes exhibited high levels of cleavage activity in vitro, none appears to be a potential long term inhibitor in cellulo. Analysis of recent discoveries in the cellular biology of HCV might explain this failure, as well as provide some ideas on the potential limits of using nucleic acid-based drugs to control the propagation of HCV. Finally, the above conclusions received support from experiments performed using a collection of SOFA-HDV ribozymes directed against HCV (-) strands.