Histone demethylase Lsd1 represses hematopoietic stem and progenitor cell signatures during blood cell maturation.

Here, we describe that lysine-specific demethylase 1 (Lsd1/KDM1a), which demethylates histone H3 on Lys4 or Lys9 (H3K4/K9), is an indispensible epigenetic governor of hematopoietic differentiation. Integrative genomic analysis, combining global occupancy of Lsd1, genome-wide analysis of its substrates H3K4 monomethylation and dimethylation, and gene expression profiling, reveals that Lsd1 represses hematopoietic stem and progenitor cell (HSPC) gene expression programs during hematopoietic differentiation. We found that Lsd1 acts at transcription start sites, as well as enhancer regions. Loss of Lsd1 was associated with increased H3K4me1 and H3K4me2 methylation on HSPC genes and gene derepression. Failure to fully silence HSPC genes compromised differentiation of hematopoietic stem cells as well as mature blood cell lineages. Collectively, our data indicate that Lsd1-mediated concurrent repression of enhancer and promoter activity of stem and progenitor cell genes is a pivotal epigenetic mechanism required for proper hematopoietic maturation. DOI:http://dx.doi.org/10.7554/eLife.00633.001.

Corepressor-dependent silencing of fetal hemoglobin expression by BCL11A.

Reactivation of fetal hemoglobin (HbF) in adults ameliorates the severity of the common ß-globin disorders. The transcription factor BCL11A is a critical modulator of hemoglobin switching and HbF silencing, yet the molecular mechanism through which BCL11A coordinates the developmental switch is incompletely understood. Particularly, the identities of BCL11A cooperating protein complexes and their roles in HbF expression and erythroid development remain largely unknown. Here we determine the interacting partner proteins of BCL11A in erythroid cells by a proteomic screen. BCL11A is found within multiprotein complexes consisting of erythroid transcription factors, transcriptional corepressors, and chromatin-modifying enzymes. We show that the lysine-specific demethylase 1 and repressor element-1 silencing transcription factor corepressor 1 (LSD1/CoREST) histone demethylase complex interacts with BCL11A and is required for full developmental silencing of mouse embryonic ß-like globin genes and human γ-globin genes in adult erythroid cells in vivo. In addition, LSD1 is essential for normal erythroid development. Furthermore, the DNA methyltransferase 1 (DNMT1) is identified as a BCL11A-associated protein in the proteomic screen. DNMT1 is required to maintain HbF silencing in primary human adult erythroid cells. DNMT1 haploinsufficiency combined with BCL11A deficiency further enhances γ-globin expression in adult animals. Our findings provide important insights into the mechanistic roles of BCL11A in HbF silencing and clues for therapeutic targeting of BCL11A in ß-hemoglobinopathies.

Bending effects of ZnO nanorod metal-semiconductor-metal photodetectors on flexible polyimide substrate.

The authors report the fabrication and I-V characteristics of ZnO nanorod metal-semiconductor-metal photodetectors on flexible polyimide substrate. From field-emission scanning electron microscopy and X-ray diffraction spectrum, ZnO nanorods had a (0002) crystal orientation and a wurtzite hexagonal structure. During the I-V and response measurement, the flexible substrates were measured with (i.e., the radius of curvatures was 0.2 cm) and without bending. From I-V results, the dark current decreased, and the UV-to-visible rejection ratio increased slightly in bending situation. The decreasing tendency of the dark current under bending condition may be attributed to the increase of the Schottky barrier height.

Impact of elevated uric acid on ventricular remodeling in infarcted rats with experimental hyperuricemia.

Hyperuricemia is associated with cardiovascular disease, but it is usually considered a marker rather than a risk factor. Previous studies using uric acid-lowering drugs in normouricemic animals are not suitable to answer the effect of hyperuricemia on ventricular remodeling after myocardial infarction. The purpose of this study was to determine whether hyperuricemia adversely affects ventricular remodeling in infarcted rats with elevated uric acid. Male Wistar rats aged 8 wk were randomly assigned into either vehicle, oxonic acid, oxonic acid + allopurinol, oxonic acid + benzbromarone, oxonic acid + ABT-627, or oxonic acid + tempol for 4 wk starting 24 h after ligation. Postinfarction was associated with increased oxidant production, as measured by myocardial superoxide, isoprostane, xanthine oxidase activity, and dihydroethidium staining. Compared with normouricemic infarcted rats, hyperuricemic infarcted rats had a significant increase of superoxide production (1.7×) and endothelin-1 protein (1.2×) and mRNA (1.4×) expression, which was associated with increased left ventricular dysfunction and enhanced myocardial hypertrophy and fibrosis. These changes were all prevented by treatment with allopurinol. For similar levels of urate lowering, the uricosuric agent benzbromarone had no effect on ventricular remodeling. In spite of equivalent hyperuricemia, the ability of both ABT-627 and tempol to attenuate ventricular remodeling suggested involvement of endothelin-1 and redox pathways. Hyperuricemia is associated with unfavorable ventricular remodeling probably through a superoxide and endothelin-1-dependent pathway. Uric acid lowering without inhibition of superoxide and endothelin-1 may not have an effect on remodeling. Chronic administration of allopurinol, ABT-627, and tempol is associated with attenuated ventricular remodeling.

Differential effects of NADPH oxidase and xanthine oxidase inhibition on sympathetic reinnervation in postinfarct rat hearts.

Superoxide has been shown to play a major role in ventricular remodeling and arrhythmias after myocardial infarction. However, the source of increased myocardial superoxide production and the role of superoxide in sympathetic innervation remain to be further characterized. Male Wistar rats, after coronary artery ligation, were randomized to vehicle, allopurinol, or apocynin for 4weeks. To determine the role of peroxynitrite in sympathetic reinnervation, we also used 3-morpholinosydnonimine (a peroxynitrite generator). The postinfarction period was associated with increased oxidative stress, as measured by myocardial superoxide, nitrotyrosine, xanthine oxidase activity, NADPH oxidase activity, and dihydroethidium fluorescent staining. Measurement of myocardial norepinephrine levels revealed a significant elevation in vehicle-treated infarcted rats compared with sham. Sympathetic hyperinnervation was blunted after administration of allopurinol. Arrhythmic scores in the allopurinol-treated infarcted rats were significantly lower than those in vehicle. For similar levels of ventricular remodeling, apocynin had no beneficial effects on oxidative stress, sympathetic hyperinnervation, or arrhythmia vulnerability. Allopurinol-treated hearts had significantly decreased nerve growth factor expression, which was substantially increased after coadministration of 3-morpholinosydnonimine. These results indicate that xanthine oxidase but not NADPH oxidase largely mediates superoxide production after myocardial infarction. Xanthine oxidase inhibition ameliorates sympathetic innervation and arrhythmias possibly via inhibition of the peroxynitrite-mediated nerve growth factor pathway.

Effect of pravastatin on ventricular arrhythmias in infarcted rats: role of connexin43.

Epidemiologic studies showed that men treated with statins appear to have a lower incidence of sudden death than men without statins. However, the specific factor for this remained disappointingly elusive. We assessed whether pravastatin enhanced connexin43 expression after myocardial infarction through attenuation of endothelin-1. Twenty-four hours after ligation of the anterior descending artery, male Wistar rats were randomized to vehicle, pravastatin, mevalonate, bosentan, or a combination of pravastatin and mevalonate or pravastatin and bosentan for 4 wk. Myocardial endothelin-1 levels were significantly elevated in vehicle-treated rats at the border zone compared with sham-operated rats. Myocardial connexin43 expression at the border zone was significantly decreased in vehicle-treated infarcted rats compared with sham-operated rats. Attenuated connexin43 expression was blunted after administration of pravastatin, as assessed by immunofluorescence analysis, Western blotting, and real-time quantitative RT-PCR of connexin43. Bosentan enhanced connexin43 amount in infarcted rats and did not have additional beneficial effects on pravastatin-treated rats. Arrhythmic scores during programmed stimulation in vehicle-treated rats were significantly higher than scores in those treated with pravastatin. In contrast, the beneficial effects of pravastatin-induced connexin43 were abolished by the addition of mevalonate and a protein kinase C inducer. In addition, the amount of connexin43 showed significant increase after addition of bisindolylmaleimide, implicating that protein kinase C is a relevant target in endothelin-1-mediated connexin43 expression. Thus chronic use of pravastatin after infarction, resulting in enhanced connexin43 amount by attenuation of mevalonate-dependent endothelin-1 through a protein kinase C-dependent pathway, may attenuate the arrhythmogenic response to programmed electrical stimulation.

EZH1 mediates methylation on histone H3 lysine 27 and complements EZH2 in maintaining stem cell identity and executing pluripotency.

Trimethylation on H3K27 (H3K27me3) mediated by Polycomb repressive complex 2 (PRC2) has been linked to embryonic stem cell (ESC) identity and pluripotency. EZH2, the catalytic subunit of PRC2, has been reported as the sole histone methyltransferase that methylates H3K27 and mediates transcriptional silencing. Analysis of Ezh2(-/-) ESCs suggests existence of an additional enzyme(s) catalyzing H3K27 methylation. We have identified EZH1, a homolog of EZH2 that is physically present in a noncanonical PRC2 complex, as an H3K27 methyltransferase in vivo and in vitro. EZH1 colocalizes with the H3K27me3 mark on chromatin and preferentially preserves this mark on development-related genes in Ezh2(-/-) ESCs. Depletion of Ezh1 in cells lacking Ezh2 abolishes residual methylation on H3K27 and derepresses H3K27me3 target genes, demonstrating a role of EZH1 in safeguarding ESC identity. Ezh1 partially complements Ezh2 in executing pluripotency during ESC differentiation, suggesting that cell-fate transitions require epigenetic specificity.