Epigenetic regulation of fetal globin gene expression in adult erythroid cells

Protective BCL11A and HBS1L-MYB polymorphisms in a cohort of 102 Congolese patients suffering from sickle cell anemia

BACKGROUND

We aimed to investigate the distribution of selected BCL11A and HMIP polymorphisms (SNP's), and to assess the correlation with HPFH in a cohort of sickle cell patients.

METHODS

A preliminary cross-sectional study was conducted in 102 patients. Group 1 was composed of patients with HPFH and Group 2 consisted of patients without HbF. We assessed 8 SNPs previously associated with HPFH in cohorts genetically close to the Congolese population. Observed frequencies were compared to expected frequencies.

RESULTS

In the group 1, at rs7606173, the observed frequency for the genotype GG was significantly higher and the genotype GC was significantly lower than their respective expected frequencies. At rs9399137, the observed frequency of the genotype TT was significantly lower than expected. Conversely, the observed frequency of the genotype TC was significantly higher than expected. The observed frequency of the genotype TT at rs11886868 was significantly lower than the expected whereas the frequency of the genotype TC was significantly higher than observed. The lowest HbF level was recorded in patients with genotype CC at rs11886868.

CONCLUSION

In this preliminary study, the results demonstrate that alleles of some of the 8 studied SNPs are not randomly distributed among patients with or without HPFH in this cohort.

Heterochromatin Protein 1γ Is a Novel Epigenetic Repressor of Human Embryonic ϵ-Globin Gene Expression

Production of hemoglobin during development is tightly regulated. For example, expression from the human β-globin gene locus, comprising β-, δ-, ϵ-, and γ-globin genes, switches from ϵ-globin to γ-globin during embryonic development and then from γ-globin to β-globin after birth. Expression of human ϵ-globin in mice has been shown to ameliorate anemia caused by β-globin mutations, including those causing β-thalassemia and sickle cell disease, raising the prospect that reactivation of ϵ-globin expression could be used in managing these conditions in humans. Although the human globin genes are known to be regulated by a variety of multiprotein complexes containing enzymes that catalyze epigenetic modifications, the exact mechanisms controlling ϵ-globin gene silencing remain elusive. Here we found that the heterochromatin protein HP1γ, a multifunctional chromatin- and DNA-binding protein with roles in transcriptional activation and elongation, represses ϵ-globin expression by interacting with a histone-modifying enzyme, lysine methyltransferase SUV4-20h2. Silencing of HP1γ expression markedly decreased repressive histone marks and the multimethylation of histone H3 lysine 9 and H4 lysine 20, leading to a significant decrease in DNA methylation at the proximal promoter of the ϵ-globin gene and greatly increased ϵ-globin expression. In addition, using chromatin immunoprecipitation, we showed that SUV4-20h2 facilitates the deposition of HP1γ on the ϵ-globin-proximal promoter. Thus, these data indicate that HP1γ is a novel epigenetic repressor of ϵ-globin gene expression and provide a potential strategy for targeted therapies for β-thalassemia and sickle cell disease.

Correlation of SIN3A genomic variants with β-hemoglobinopathies disease severity and hydroxyurea treatment efficacy

AIMS

Hemoglobinopathies, particularly β-thalassemia and sickle cell disease, are characterized by great phenotypic variability in terms of disease severity, while notable differences have been observed in hydroxyurea treatment efficacy. In both cases, the observed phenotypic diversity is mostly dependent on the elevated fetal hemoglobin levels, resulting from the persistent fetal globin gene expression in the adult erythroid stage orchestrated by intricate mechanisms that still remain only partly understood. We have previously shown that several protein factors act as modifiers of fetal hemoglobin production, exerting their effect via different pathways.

MATERIALS & METHODS

Here, we explored whether SIN3A could act as a modifier of fetal globin gene expression, as it interacts with KLF10, a known modifier of fetal hemoglobin production.

RESULTS

We show that SIN3A genomic variants are associated both with β-thalassemia disease severity (rs11072544) as well as hydroxyurea treatment response (rs7166737) in β-hemoglobinopathies patients.

CONCLUSION

Our findings further underline that fetal hemoglobin production is the result of a complex interplay in which several human globin gene cluster variants interact with protein factors encoded by modifier genes to produce the observed clinical outcome.

O-Linked N-Acetylglucosamine (O-GlcNAc) Transferase and O-GlcNAcase Interact with Mi2β Protein at the Aγ-Globin Promoter

One mode of γ-globin gene silencing involves a GATA-1·FOG-1·Mi2β repressor complex that binds to the -566 GATA site relative to the (A)γ-globin gene cap site. However, the mechanism of how this repressor complex is assembled at the -566 GATA site is unknown. In this study, we demonstrate that the O-linked N-acetylglucosamine (O-GlcNAc) processing enzymes, O-GlcNAc-transferase (OGT) and O-GlcNAcase (OGA), interact with the (A)γ-globin promoter at the -566 GATA repressor site; however, mutation of the GATA site to GAGA significantly reduces OGT and OGA promoter interactions in β-globin locus yeast artificial chromosome (β-YAC) bone marrow cells. When WT β-YAC bone marrow cells are treated with the OGA inhibitor Thiamet-G, the occupancy of OGT, OGA, and Mi2β at the (A)γ-globin promoter is increased. In addition, OGT and Mi2β recruitment is increased at the (A)γ-globin promoter when γ-globin becomes repressed in postconception day E18 human β-YAC transgenic mouse fetal liver. Furthermore, we show that Mi2β is modified with O-GlcNAc, and both OGT and OGA interact with Mi2β, GATA-1, and FOG-1. Taken together, our data suggest that O-GlcNAcylation is a novel mechanism of γ-globin gene regulation mediated by modulating the assembly of the GATA-1·FOG-1·Mi2β repressor complex at the -566 GATA motif within the promoter.

Development and differentiation of the erythroid lineage in mammals

The red blood cell (RBC) is responsible for performing the highly specialized function of oxygen transport, making it essential for survival during gestation and postnatal life. Establishment of sufficient RBC numbers, therefore, has evolved to be a major priority of the postimplantation embryo. The "primitive" erythroid lineage is the first to be specified in the developing embryo proper. Significant resources are dedicated to producing RBCs throughout gestation. Two transient and morphologically distinct waves of hematopoietic progenitor-derived erythropoiesis are observed in development before hematopoietic stem cells (HSCs) take over to produce "definitive" RBCs in the fetal liver. Toward the end of gestation, HSCs migrate to the bone marrow, which becomes the primary site of RBC production in the adult. Erythropoiesis is regulated at various stages of erythroid cell maturation to ensure sufficient production of RBCs in response to physiological demands. Here, we highlight key aspects of mammalian erythroid development and maturation as well as differences among the primitive and definitive erythroid cell lineages.

Leukemia cell infiltration causes defective erythropoiesis partially through MIP-1α/CCL3

Leukemia often results in severe anemia, which may significantly contribute to patient mortality and morbidity. However, the mechanisms underlying defective erythropoiesis in leukemia have not been fully elucidated. In this study, we demonstrated that insufficient erythropoiesis in an immunocompetent acute myeloid leukemia (AML) murine model was due to reduced proliferation of megakaryocyte erythroid progenitors and increased apoptosis of erythroblasts. Colony-forming cell assays indicated that the leukemic bone marrow (BM) plasma inhibited erythroid colony formation, whereas they had no inhibitory effect on other types of colonies. Cytokine array analysis demonstrated that the chemokine CCL3 was elevated in the plasma of AML mice and patients. CCL3 inhibited erythroid differentiation of hematopoietic stem cells, common myeloid progenitors and especially megakaryocytic-erythroid progenitors. Administration of the CCR1 antagonist partially recovered the yield of erythroid colonies in the presence of CCL3 or leukemic BM plasma. Mechanistically, we observed an increase of p38 phosphorylation and subsequent downregulation of GATA1 after CCL3 treatment. Furthermore, knockdown of CCL3 attenuated leukemic progression and alleviated anemia. Therefore, our results demonstrate that elevated CCL3 in the leukemic environment suppresses erythropoiesis via CCR1-p38 activation, suggesting a novel mechanism for the erythroid defects observed in leukemia.

Activated Neutrophils Are Associated with Pediatric Cerebral Malaria Vasculopathy in Malawian Children

Most patients with cerebral malaria (CM) sustain cerebral microvascular sequestration of Plasmodium falciparum-infected red blood cells (iRBCs). Although many young children are infected with P. falciparum, CM remains a rare outcome; thus, we hypothesized that specific host conditions facilitate iRBC cerebral sequestration. To identify these host factors, we compared the peripheral whole-blood transcriptomes of Malawian children with iRBC cerebral sequestration, identified as malarial-retinopathy-positive CM (Ret+CM), to the transcriptomes of children with CM and no cerebral iRBC sequestration, defined as malarial-retinopathy-negative CM (Ret-CM). Ret+CM was associated with upregulation of 103 gene set pathways, including cytokine, blood coagulation, and extracellular matrix (ECM) pathways (P < 0.01; false-discovery rate [FDR] of <0.05). Neutrophil transcripts were the most highly upregulated individual transcripts in Ret+CM patients. Activated neutrophils can modulate diverse host processes, including the ECM, inflammation, and platelet biology to potentially facilitate parasite sequestration. Therefore, we compared plasma neutrophil proteins and neutrophil chemotaxis between Ret+CM and Ret-CM patients. Plasma levels of human neutrophil elastase, myeloperoxidase, and proteinase 3, but not lactoferrin or lipocalin, were elevated in Ret+CM patients, and neutrophil chemotaxis was impaired, possibly related to increased plasma heme. Neutrophils were rarely seen in CM brain microvasculature autopsy samples, and no neutrophil extracellular traps were found, suggesting that a putative neutrophil effect on endothelial cell biology results from neutrophil soluble factors rather than direct neutrophil cellular tissue effects. Meanwhile, children with Ret-CM had lower levels of inflammation, higher levels of alpha interferon, and upregulation of Toll-like receptor pathways and other host transcriptional pathways, which may represent responses that do not favor cerebral iRBC sequestration.

There were approximately 198 million cases of malaria worldwide in 2013, with an estimated 584,000 deaths occurring mostly in sub-Saharan African children. CM is a severe and rare form of Plasmodium falciparum infection and is associated with high rates of mortality and neurological morbidity, despite antimalarial treatment. A greater understanding of the pathophysiology of CM would allow the development of adjunctive therapies to improve clinical outcomes. A hallmark of CM is cerebral microvasculature sequestration of P. falciparum-infected red blood cells (iRBCs), which results in vasculopathy in some patients. Our data provide a global analysis of the host pathways associated with CM and newly identify an association of activated neutrophils with brain iRBC sequestration. Products of activated neutrophils could alter endothelial cell receptors and coagulation to facilitate iRBC adherence. Future studies can now examine the role of neutrophils in CM pathogenesis to improve health outcomes.

Hydroxymethylcytosine and demethylation of the γ-globin gene promoter during erythroid differentiation

The mechanism responsible for developmental stage-specific regulation of γ-globin gene expression involves DNA methylation. Previous results have shown that the γ-globin promoter is nearly fully demethylated during fetal liver erythroid differentiation and partially demethylated during adult bone marrow erythroid differentiation. The hypothesis that 5-hydroxymethylcytosine (5hmC), a known intermediate in DNA demethylation pathways, is involved in demethylation of the γ-globin gene promoter during erythroid differentiation was investigated by analyzing levels of 5-methylcytosine (5mC) and 5hmC at a CCGG site within the 5′ γ-globin gene promoter region in FACS-purified cells from baboon bone marrow and fetal liver enriched for different stages of erythroid differentiation. Our results show that 5mC and 5hmC levels at the γ-globin promoter are dynamically modulated during erythroid differentiation with peak levels of 5hmC preceding and/or coinciding with demethylation. The Tet2 and Tet3 dioxygenases that catalyze formation of 5hmC are expressed during early stages of erythroid differentiation and Tet3 expression increases as differentiation proceeds. In baboon CD34+ bone marrow-derived erythroid progenitor cell cultures, γ-globin expression was positively correlated with 5hmC and negatively correlated with 5mC at the γ-globin promoter. Supplementation of culture media with Vitamin C, a cofactor of the Tet dioxygenases, reduced γ-globin promoter DNA methylation and increased γ-globin expression when added alone and in an additive manner in combination with either DNA methyltransferase or LSD1 inhibitors. These results strongly support the hypothesis that the Tet-mediated 5hmC pathway is involved in developmental stage-specific regulation of γ-globin expression by mediating demethylation of the γ-globin promoter.

MicroRNA Expression in β-Thalassemia and Sickle Cell Disease: A Role in The Induction of Fetal Hemoglobin

Today the regulatory role of microRNAs (miRs) is well characterized in many diverse cel- lular processes. MiR-based regulation is categorized under epigenetic regulatory mecha- nisms. These small non-coding RNAs participate in producing and maturing erythrocytes, expressing hematopoietic factors and regulating expression of globin genes by post-tran- scriptional gene silencing. The changes in expression of miRs (miR-144/-320/-451/-503) in thalassemic/sickle cells compared with normal erythrocytes may cause clinical severity. According to the suppressive effects of certain miRs (miR-15a/-16-1/-23a/-26b/-27a/-451) on a number of transcription factors [myeloblastosis oncogene (MYB), B-cell lymphoma 11A (BCL11A), GATA1, Krüppel-like factor 3 (KLF3) and specificity protein 1 (Sp1)] during β globin gene expression, It has been possible to increasing γ globin gene expression and fetal hemoglobin (HbF) production. Therefore, this strategy can be used as a novel therapy in infusing HbF and improving clinical complications of patients with hemoglobi- nopathies.

3,5-Diamino-1,2,4-triazoles as a novel scaffold for potent, reversible LSD1 (KDM1A) inhibitors

The chromatin remodeling amine oxidase lysine-specific demethylase 1 (LSD1) has become an attractive target for the design of specific inhibitors with therapeutic potential. We, and others, have described LSD1 inhibitors that have potential as antitumor agents. Many of the currently known LSD1 inhibitors are poor drug candidates, or are structurally based on the tranylcypromine backbone, thus increasing the potential for off-target effects mediated by other amine oxidases. We now describe a series of potent LSD1 inhibitors based on a novel 1,2,4-triazole scaffold; these inhibitors show a high degree of specificity for LSD1 in vitro, and cause increases in cellular histone 3 dimethyllysine 4 (H3K4me2), a gene transcription activating mark. Importantly, these inhibitors are not toxic to mammalian cells in vitro, and thus they may show utility in the treatment of epigenetically-based diseases where cell death is not a desired endpoint Figure 1. Structures of LSD1 inhibitors 1, verlindamycin 2, (bis)thioureas 3, amidoxime 4, cyclic peptide 5, N3-(2-chloro-6-phenoxybenzyl)-4H-1,2,4-triazole-3,5-diamine 6 and N3,N5-bis(2-methoxybenzyl)-1H-1,2,4-triazole-3,5-diamine 7.