Deficiency of inactive rhomboid protein 2 (iRhom2) attenuates diet-induced hyperlipidaemia and early atherogenesis.

AIMS: Atherosclerosis is a chronic inflammatory disease of the arterial vessel wall and anti-inflammatory treatment strategies are currently pursued to lower cardiovascular disease burden. Modulation of recently discovered inactive rhomboid protein 2 (iRhom2) attenuates shedding of tumour necrosis factor-alpha (TNF-α) selectively from immune cells. The present study aims at investigating the impact of iRhom2 deficiency on the development of atherosclerosis. METHODS AND RESULTS: Low-density lipoprotein receptor (LDLR)-deficient mice with additional deficiency of iRhom2 (LDLR-/-iRhom2-/-) and control (LDLR-/-) mice were fed a Western-type diet (WD) for 8 or 20 weeks to induce early or advanced atherosclerosis. Deficiency of iRhom2 resulted in a significant decrease in the size of early atherosclerotic plaques as determined in aortic root cross-sections. LDLR-/-iRhom2-/- mice exhibited significantly lower serum levels of TNF-α and lower circulating and hepatic levels of cholesterol and triglycerides compared to LDLR-/- mice at 8 weeks of WD. Analyses of hepatic bile acid concentration and gene expression at 8 weeks of WD revealed that iRhom2 deficiency prevented WD-induced repression of hepatic bile acid synthesis in LDLR-/- mice. In contrast, at 20 weeks of WD, plaque size, plaque composition, and serum levels of TNF-α or cholesterol were not different between genotypes. CONCLUSION: Modulation of inflammation by iRhom2 deficiency attenuated diet-induced hyperlipidaemia and early atherogenesis in LDLR-/- mice. iRhom2 deficiency did not affect diet-induced plaque burden and composition in advanced atherosclerosis in LDLR-/- mice.

Biogeography and taxonomy of racket-tail hummingbirds (Aves: Trochilidae: Ocreatus): evidence for species delimitation from morphology and display behavior.

We analyzed geographic variation, biogeography, and intrageneric relationships of racket-tail hummingbirds Ocreatus (Aves, Trochilidae). Presently, the genus is usually considered monospecific, with O. underwoodii including eight subspecies (polystictus, discifer, underwoodii, incommodus, melanantherus, peruanus, annae, addae), although up to three species have been recognized by some authors. In order to evaluate the current taxonomy we studied geographic variation in coloration, mensural characters, and behavioral data of all Ocreatus taxa. We briefly review the taxonomic history of the genus. Applying the Biological Species Concept, species delimitation was based on a qualitative-quantitative criteria analysis including an evaluation of character states. Our results indicate that the genus should be considered a superspecies with four species, the monotypic Ocreatus addae, O. annae, and O. peruanus, and the polytypic O. underwoodii (including the subspecies underwoodii, discifer, incommodus, melanantherus, polystictus). In this taxonomic treatment, O. annae becomes an endemic species to Peru and O. addae is endemic to Bolivia. We recommend additional sampling of distributional, ethological, and molecular data for an improved resolution of the evolutionary history of Ocreatus.

Epigenetic suppression of iNOS expression in human endothelial cells: A potential role of Ezh2-mediated H3K27me3.

OBJECTIVE: Cytokines strongly induce expression of the inducible nitric oxide synthase (iNOS) in rodent but not in human endothelial cells. We recently identified NOS2 as a potential target of the histone methyltransferase enhancer of zeste homolog 2 which mediates trimethylation of histone 3 at lysine 27 (H3K27me3). METHODS AND RESULTS: Compared to an unspecific IgG control, chromatin immunoprecipitation using a H3K27me3-specific antibody followed by DNA quantification by PCR showed a strong DNA enrichment - indicating that NOS2 is associated with H3K27me3 in human umbilical vein endothelial cells (HUVEC). siRNA-mediated knock down of Ezh2 diminished NOS2 DNA enrichment - suggesting that the association of NOS2 with H3K27me3 is mediated by Ezh2. Ezh2 knock down, however, was not sufficient to increase iNOS expression after stimulation of HUVEC. CONCLUSION: NOS2 is associated with Ezh2-mediated H3K27me3 in HUVEC. This might contribute to an epigenetic suppression of iNOS inducibility in human endothelial cells.

Epigenetic regulation of cell adhesion and communication by enhancer of zeste homolog 2 in human endothelial cells.

The histone methyltransferase enhancer of zeste homolog 2 (Ezh2) mediates trimethylation of lysine 27 in histone 3, which acts as a repressive epigenetic mark. Ezh2 is essential for maintaining pluripotency of stem cells, but information on its role in differentiated cells is sparse. Whole-genome mRNA expression arrays identified 964 genes that were regulated by >2-fold 72 hours after small interfering RNA-mediated silencing of Ezh2 in human umbilical vein endothelial cells. Among them, genes associated with the gene ontology terms cell communication and cell adhesion were significantly overrepresented, suggesting a functional role for Ezh2 in the regulation of angiogenesis. Indeed, adhesion, migration, and tube formation assays revealed significantly altered angiogenic properties of human umbilical vein endothelial cells after silencing of Ezh2. To identify direct target genes of Ezh2, we performed chromatin immunoprecipitation experiments followed by whole-genome promoter arrays (chromatin immunoprecipitation-on-chip) and identified 5585 genes associated with trimethylation of lysine 27 in histone 3. Comparative analysis with our mRNA expression data identified 276 genes that met our criteria for putative Ezh2 target genes, upregulation by >2-fold after Ezh2 silencing and association with trimethylation of lysine 27 in histone 3. Notably, we observed a striking overrepresentation of genes involved in wingless-type mouse mammary tumor virus integration site (WNT) signaling pathways. Epigenetic regulation of several of these genes by Ezh2 was specifically confirmed by polymerase chain reaction analysis of DNA enrichment after chromatin immunoprecipitation using an antibody specific for trimethylation of lysine 27 in histone 3. Combining mRNA expression arrays and chromatin immunoprecipitation-on-chip analysis, we identified 276 Ezh2 target genes in endothelial cells. Ezh2-dependent repression of genes involved in cell adhesion and communication contributes to the regulation of angiogenesis.

Human-specific induction of glutathione peroxidase-3 by proteasome inhibition in cardiovascular cells.

Glutathione peroxidase-3 (GPx-3) is a key antioxidant enzyme in the plasma. GPx-3 was previously identified as the major antioxidative enzyme that was induced upon nontoxic proteasome inhibition in endothelial cells. Here, we investigated the determinants of the proteasome inhibitor-induced expression of GPx-3. Nontoxic proteasome inhibition massively upregulates GPx-3 RNA and protein in human umbilical cord vein cells within 24 h. Surprisingly, induction of GPx-3 was species-specific for human cells. The exponential upregulation of GPx-3 is mediated by transcriptional activation of the human GPx-3 promoter and, in addition, stabilization of GPx-3 mRNA: in reporter gene assays with full-length and deleted variants of the human GPx-3 promoter we identified a putative antioxidative response element (ARE) as essential and also sufficient for transcriptional activation of GPx-3 by proteasome inhibition. However, the ARE-specific antioxidative transcription factor Nrf2 is not involved in the activation of GPx-3. UV-crosslinking using the 3'UTR of GPx-3 revealed an altered protein binding pattern in the presence of proteasome inhibitors, thus indicating regulation of mRNA stability of human GPx-3. As GPx-3 is secreted into the plasma, our data point toward a borderline defense mechanism of endothelial cell-derived GPx-3 to protect the vasculature from oxidative stress.

Nrf2-dependent upregulation of antioxidative enzymes: a novel pathway for proteasome inhibitor-mediated cardioprotection.

AIMS: We have shown previously that non-toxic inhibition of the ubiquitin-proteasome system upregulates antioxidative defence mechanisms and protects endothelial cells from oxidative stress. Here, we have addressed the question whether the induction of antioxidative enzymes contributes to cardioprotection by non-toxic proteasome inhibition. METHODS AND RESULTS: Treatment with 0.5 micromol/L MG132 for 48 h proved to be non-toxic and protected neonatal rat cardiac myocytes against H(2)O(2)-mediated oxidative stress in lactate dehydrogenase assays. This correlated with reduced levels of intracellular reactive oxygen species as determined by loading myocytes with dichlorofluorescein. Immunoblots showed significant upregulation of superoxide dismutase 1 (SOD1), haem oxygenase 1, and catalase upon proteasome inhibition. Luciferase assays using a reporter driven by the SOD1 promoter revealed proteasome inhibitor-mediated induction of luciferase activity. Deletion and mutation analyses identified an antioxidant response element (ARE) in the SOD1 promoter to be not only essential but also sufficient for transcriptional upregulation by proteasome inhibition. An essential role for the antioxidative transcription factor NF-E2-related factor 2 (Nrf2)-which was stabilized by proteasome inhibition-in ARE-mediated transcriptional activation was revealed in cardiac myocytes from Nrf2 wild-type and knockout mice: proteasome inhibition upregulated antioxidative enzymes and conferred protection against H(2)O(2)-mediated oxidative stress in Nrf2 wild-type cells. In contrast, the induction of antioxidative enzymes and cytoprotection were completely abolished in cardiac myocytes from Nrf2 knockout mice. CONCLUSION: Non-toxic proteasome inhibition upregulates antioxidative enzymes via an Nrf2-dependent transcriptional activation of AREs and confers cardioprotection.

Downregulation of matrix metalloproteinases and collagens and suppression of cardiac fibrosis by inhibition of the proteasome.

Myocardial remodeling is an adaptive response of the myocardium to several forms of stress culminating in cardiac fibrosis, left ventricular dilation, and loss of contractility. The remodeling processes of the extracellular matrix are controlled by matrix metalloproteinases, which are in turn regulated by growth factors and inflammatory cytokines. The inflammatory transcription factor nuclear factor kappaB has been implicated in the transcriptional regulation of several matrix metalloproteinases. Because activation of nuclear factor kappaB in turn is essentially controlled by the ubiquitin-proteasome system, we investigated the hypothesis that inhibition of the proteasome may prevent activation of matrix metalloproteinases. We demonstrate here that inhibition of the proteasome in rat cardiac fibroblasts suppressed not only expression of matrix metalloproteinases 2 and 9, but also expression of collagen Ialpha1, Ialpha2, and IIIalpha1 as determined by in-gel zymography and real-time reverse transcription-polymerase chain reaction. Moreover, myocardial expression of matrix metalloproteinases and collagens was effectively suppressed by systemic treatment of spontaneously hypertensive rats over 12 weeks with the proteasome inhibitor MG132, which resulted in a marked reduction of cardiac fibrosis (-38%) compared with control animals. We conclude that inhibition of the ubiquitin-proteasome system may provide a new and attractive tool to interfere with collagen and matrix metalloproteinase expression, and therefore might be of possible use in the therapy of myocardial remodeling.

Inhibition of proteasome activity induces concerted expression of proteasome genes and de novo formation of Mammalian proteasomes.

The 26 S proteasome is a high molecular mass proteinase complex that is built by at least 32 different protein subunits. Such protease complexes in bacteria and yeast are systems that undergo a highly sophisticated network of gene expression regulation. However, regulation of mammalian proteasome gene expression has been neglected so far as a possible control mechanism for the amount of proteasomes in the cell. Here, we show that treatment of cells with proteasome inhibitors and the concomitant impairment of proteasomal enzyme activity induce a transient and concerted up-regulation of all mammalian 26 S proteasome subunit mRNAs. Proteasome inhibition in combination with inhibition of transcription revealed that the observed up-regulation is mediated by coordinated transcriptional activation of the proteasome genes and not by post-transcriptional events. Our experiments also demonstrate that inhibitor-induced proteasome gene activation results in enhanced de novo protein synthesis of all subunits and in increased de novo formation of proteasomes. This phenomenon is accompanied by enhanced expression of the proteasome maturation factor POMP. Thus, our experiments present the first evidence that the amount of proteasomes in mammalia is regulated at the transcriptional level and that there exists an autoregulatory feedback mechanism that allows the compensation of reduced proteasome activity.