CircANKRD12 Is Induced in Endothelial Cell Response to Oxidative Stress.

Redox imbalance of the endothelial cells (ECs) plays a causative role in a variety of cardiovascular diseases. In order to better understand the molecular mechanisms of the endothelial response to oxidative stress, the involvement of circular RNAs (circRNAs) was investigated. CircRNAs are RNA species generated by a "back-splicing" event, which is the covalent linking of the 3'- and 5'-ends of exons. Bioinformatics analysis of the transcriptomic landscape of human ECs exposed to H2O2 allowed us to identify a subset of highly expressed circRNAs compared to their linear RNA counterparts, suggesting a potential biological relevance. Specifically, circular Ankyrin Repeat Domain 12 (circANKRD12), derived from the junction of exon 2 and exon 8 of the ANKRD12 gene (hsa_circ_0000826), was significantly induced in H2O2-treated ECs. Conversely, the linear RNA isoform of ANKRD12 was not modulated. An increased circular-to-linear ratio of ANKRD12 was also observed in cultured ECs exposed to hypoxia and in skeletal muscle biopsies of patients affected by critical limb ischemia (CLI), two conditions associated with redox imbalance and oxidative stress. The functional relevance of circANKRD12 was shown by the inhibition of EC formation of capillary-like structures upon silencing of the circular but not of the linear isoform of ANKRD12. Bioinformatics analysis of the circANKRD12-miRNA-mRNA regulatory network in H2O2-treated ECs identified the enrichment of the p53 and Foxo signaling pathways, both crucial in the cellular response to redox imbalance. In keeping with the antiproliferative action of the p53 pathway, circANKRD12 silencing inhibited EC proliferation. In conclusion, this study indicates circANKRD12 as an important player in ECs exposed to oxidative stress.

Hypoxia-induced miR-210 modulates the inflammatory response and fibrosis upon acute ischemia.

Hypoxia-induced miR-210 is a crucial component of the tissue response to ischemia, stimulating angiogenesis and improving tissue regeneration. Previous analysis of miR-210 impact on the transcriptome in a mouse model of hindlimb ischemia showed that miR-210 regulated not only vascular regeneration functions, but also inflammation. To investigate this event, doxycycline-inducible miR-210 transgenic mice (Tg-210) and anti-miR-210 LNA-oligonucleotides were used. It was found that global miR-210 expression decreased inflammatory cells density and macrophages accumulation in the ischemic tissue. To dissect the underpinning cell mechanisms, Tg-210 mice were used in bone marrow (BM) transplantation experiments and chimeric mice underwent hindlimb ischemia. MiR-210 overexpression in the ischemic tissue was sufficient to increase capillary density and tissue repair, and to reduce inflammation in the presence of Wt-BM infiltrating cells. Conversely, when Tg-210-BM cells migrated in a Wt ischemic tissue, dysfunctional angiogenesis, inflammation, and impaired tissue repair, accompanied by fibrosis were observed. The fibrotic regions were positive for α-SMA, Vimentin, and Collagen V fibrotic markers and for phospho-Smad3, highlighting the activation of TGF-ß1 pathway. Identification of Tg-210 cells by in situ hybridization showed that BM-derived cells contributed directly to fibrotic areas, where macrophages co-expressing fibrotic markers were observed. Cell cultures of Tg-210 BM-derived macrophages exhibited a pro-fibrotic phenotype and were enriched with myofibroblast-like cells, which expressed canonical fibrosis markers. Interestingly, inhibitors of TGF-ß type-1-receptor completely abrogated this pro-fibrotic phenotype. In conclusion, a context-dependent regulation by miR-210 of the inflammatory response was identified. miR-210 expression in infiltrating macrophages is associated to improved angiogenesis and tissue repair when the ischemic recipient tissue also expresses high levels of miR-210. Conversely, when infiltrating an ischemic tissue with mismatched miR-210 levels, macrophages expressing high miR-210 levels display a pro-fibrotic phenotype, leading to impaired tissue repair, fibrosis, and dysfunctional angiogenesis.

Dysregulation of microRNA expression in diabetic skin.

BACKGROUND: Clinical skin manifestations are common in diabetes; however, molecular mechanisms underlying such defects are largely unknown. Several findings indicate a role for microRNAs (miRNAs) in skin homeostasis. OBJECTIVE: To investigate whether miRNA expression is altered in diabetic skin. METHODS: Type 1 and 2 mouse models of diabetes were used. MiRNA profiling was performed on RNA extracted from the skin of type 1 diabetic mice and non-diabetic controls. Expression levels of pri-miRNAs and of miRNA-biogenesis genes were also analyzed. Biogenesis gene expression analysis was performed in human dermal fibroblasts cultured in hyperglycemic, hypoxic or oxidative stress conditions. RESULTS: Several miRNAs were differentially expressed in diabetic skin with a general down-modulation as compared to controls. Bioinformatics analysis of signature-miRNA target genes showed the enrichment in pathways involved in skin homeostasis, such as TGF-ß and Wnt. MiRNA alteration in diabetic skin associated with reduced expression levels of DROSHA, DGCR8, XPO5, DICER1, AGO2, both as mRNA and protein. Reduced biogenesis gene expression did not correlate with accumulation of pri-miRNAs, which displayed differences in expression levels similar to those found for their mature miRNAs. Experiments with cultured fibroblasts showed that hypoxia and oxidative stress induced the down-regulation of miRNA-biogenesis genes in this skin cell type. CONCLUSION: A general down-regulation of differentially expressed miRNAs was found in diabetic skin. This alteration is part of and is dependent from a wider transcriptional defect also affecting the expression of pri-miRNAs and of genes responsible for miRNA biogenesis. Such an alteration is likely contributing to diabetic skin manifestations.

Central role of the p53 pathway in the noncoding-RNA response to oxidative stress.

Oxidative stress plays a fundamental role in many conditions. Specifically, redox imbalance inhibits endothelial cell (EC) growth, inducing cell death and senescence. We used global transcriptome profiling to investigate the involvement of noncoding-RNAs in these phenotypes. By RNA-sequencing, transcriptome changes were analyzed in human ECs exposed to H2O2, highlighting a pivotal role of p53-signaling. Bioinformatic analysis and validation in p53-silenced ECs, identified several p53-targets among both mRNAs and long noncoding-RNAs (lncRNAs), including MALAT1 and NEAT1. Among microRNAs (miRNAs), miR-192-5p was the most induced by H2O2 treatment, in a p53-dependent manner. Down-modulated mRNA-targets of miR-192-5p were involved in cell cycle, DNA repair and stress response. Accordingly, miR-192-5p overexpression significantly decreased EC proliferation, inducing cell death. A central role of the p53-pathway was also confirmed by the analysis of differential exon usage: Upon H2O2 treatment, the expression of p53-dependent 5'-isoforms of MDM2 and PVT1 increased selectively. The transcriptomic alterations identified in H2O2-treated ECs were also observed in other physiological and pathological conditions where redox control plays a fundamental role, such as ECs undergoing replicative senescence, skeletal muscles of critical limb-ischemia patients and the peripheral-blood mononuclear cells of long-living individuals. Collectively, these findings indicate a prominent role of noncoding-RNAs in oxidative stress response.

The expression of the BPIFB4 and CXCR4 associates with sustained health in long-living individuals from Cilento-Italy.

The study of the health status in long-living individuals (LLIs) may help identifying health-span and life-span determinants. BPI-Fold-Containing-Family-B-Member-4 (BPIFB4) protein is higher in healthy vs. non-healthy (frail) LLIs serum and its longevity-associated variant forced expression improves cardiovascular outcomes in ischemia mice models. Thus, we tested the association of BPIFB4 and ischemia-responding HIF-1α pathway components (i.e. CXCR4, AK3, ALDO-C, ADM, VEGF-A, GLUT-1 and miR-210) with human life-span and health-span by analyzing mRNA expression in circulating mononuclear cells (MNCs) of LLIs (N=14 healthy; N=31 frail) and young controls (N=63).ALDO-C, ADM, VEGF-A and GLUT-1 significantly decreased and miR-210 increased in LLIs vs. CONTROLS: Only VEGF-A and GLUT-1 showed further significant reduction in healthy-LLIs vs. frail-LLIs comparison. While BPIFB4 and CXCR4 were similar between LLIs and controls, BPIFB4 was significantly higher and CXCR4 lower in healthy- versus frail-LLIs. On a new set of LLIs (N=7 healthy and N=5 non-healthy) we assessed a potentially correlated function with low CXCR4 expression. Healthy donors' MNCs showed efficient migration ability toward CXCR4 ligand SDF-1α/CXCL12 and high percentage of migrated CXCR4pos cells which inversely correlated with CXCR4 RNA expression. In conclusion, BPIFB4 and CXCR4 expression classify LLIs health status that correlates with maintained MNCs migration.

p75(NTR)-dependent activation of NF-κB regulates microRNA-503 transcription and pericyte-endothelial crosstalk in diabetes after limb ischaemia.

The communication between vascular endothelial cells (ECs) and pericytes in the microvasculature is fundamental for vascular growth and homeostasis; however, these processes are disrupted by diabetes. Here we show that modulation of p75(NTR) expression in ECs exposed to high glucose activates transcription of miR-503, which negatively affects pericyte function. p75(NTR) activates NF-κB to bind the miR-503 promoter and upregulate miR-503 expression in ECs. NF-κB further induces activation of Rho kinase and shedding of endothelial microparticles carrying miR-503, which transfer miR-503 from ECs to vascular pericytes. The integrin-mediated uptake of miR-503 in the recipient pericytes reduces expression of EFNB2 and VEGFA, resulting in impaired migration and proliferation. We confirm operation of the above mechanisms in mouse models of diabetes, in which EC-derived miR-503 reduces pericyte coverage of capillaries, increased permeability and impaired post-ischaemic angiogenesis in limb muscles. Collectively, our data demonstrate that miR-503 regulates pericyte-endothelial crosstalk in microvascular diabetic complications.

ROD1 is a seedless target gene of hypoxia-induced miR-210.

Most metazoan microRNA (miRNA) target sites have perfect pairing to the "seed" sequence, a highly conserved region centering on miRNA nucleotides 2-7. Thus, complementarity to this region is a necessary requirement for target prediction algorithms. However, also non-canonical miRNA binding can confer target regulation. Here, we identified a seedless target of miR-210, a master miRNA of the hypoxic response. We analyzed 20 genes that were inversely correlated to miR-210 expression and did not display any complementarity with miR-210 seed sequence. We validated ROD1 (Regulator of Differentiation 1, also named PTBP3, Polypyrimidine Tract Binding protein 3) as a miR-210 seedless transcript enriched in miR-210-containing RNA-induced silencing complexes. ROD1 was not indirectly targeted by a miR-210-induced miRNA. Conversely, we identified a "centered" miR-210 binding site in ROD1 involving 10 consecutive bases in the central portion of miR-210. Reporter assays showed that miR-210 inhibited ROD1 by the direct binding to this sequence, demonstrating that ROD1 is a bona fide seedless target of miR-210. As expected, both ROD1 mRNA and protein were down-modulated upon hypoxia in a miR-210 dependent manner. ROD1 targeting by miR-210 was biologically significant: the rescue of ROD1 inhibition significantly increased hypoxia-induced cell death. These data highlight the importance of ROD1 regulation by miR-210 for cell homeostasis.

Deep-sequencing of endothelial cells exposed to hypoxia reveals the complexity of known and novel microRNAs.

In order to understand the role of microRNAs (miRNAs) in vascular physiopathology, we took advantage of deep-sequencing techniques to accurately and comprehensively profile the entire miRNA population expressed by endothelial cells exposed to hypoxia. SOLiD sequencing of small RNAs derived from human umbilical vein endothelial cells (HUVECs) exposed to 1% O2 or normoxia for 24 h yielded more than 22 million reads per library. A customized bioinformatic pipeline identified more than 400 annotated microRNA/microRNA* species with a broad abundance range: miR-21 and miR-126 totaled almost 40% of all miRNAs. A complex repertoire of isomiRs was found, displaying also 5' variations, potentially affecting target recognition. High-stringency bioinformatic analysis identified microRNA candidates, whose predicted pre-miRNAs folded into a stable hairpin. Validation of a subset by qPCR identified 18 high-confidence novel miRNAs as detectable in independent HUVEC cultures and associated to the RISC complex. The expression of two novel miRNAs was significantly down-modulated by hypoxia, while miR-210 was significantly induced. Gene ontology analysis of their predicted targets revealed a significant association to hypoxia-inducible factor signaling, cardiovascular diseases, and cancer. Overexpression of the novel miRNAs in hypoxic endothelial cells affected cell growth and confirmed the biological relevance of their down-modulation. In conclusion, deep-sequencing accurately profiled known, variant, and novel microRNAs expressed by endothelial cells in normoxia and hypoxia.

ChIP-on-chip analysis of in vivo mutant p53 binding to selected gene promoters.

Growing evidence shows that mutant p53 proteins, which are present in many human tumors, gain oncogenic activities that can actively contribute to tumorigenesis. Mutant p53 proteins have been extensively shown to affect the expression of several genes involved in various aspects of cancer biology. We show here the ChIP-on-chip analysis of mutant p53 binding to a set of 154 promoters, composed of both validated and putative mutant p53 target genes. By using the chromatin obtained from mutant p53R175H-immunoprecipitation in proliferating SKBr3 breast cancer cells, we found that mutant p53 binds to 40 of the 154 promoters analyzed. siRNA-mediated mutant p53 knock-down modulates the transcript abundance of some of these target genes. Two-thirds of the mutant p53-bound promoters were also engaged by either p300 or PCAF acetyl-transferases, strongly indicating the presence of transcriptionally active complexes. We also found that NF-kB binding sites are overrepresented among the mutant p53-bound promoters; a ChIP-on-chip analysis confirmed that NF-kB p65 binds to 27 of the mutant p53-bound promoters, indicating that mutant p53 could influence the transcriptional output of these NF-kB target genes.