Identification of a Novel Enhancer/Chromatin Opening Element Associated with High-Level γ-Globin Gene Expression

Proteomics screening uncovers HMGA1 as a promising negative regulator for γ-globin expression in response to decreased β-globin levels

Reactivation of fetal hemoglobin (HbF) is a critical goal for the treatment of patients with hemoglobinopathies. β-globin disorders can trigger stress erythropoiesis in red blood cells (RBCs). Cell-intrinsic erythroid stress signals promote erythroid precursors to express high levels of fetal hemoglobin, which is also known as γ-globin. However, the molecular mechanism underlying γ-globin production during cell-intrinsic erythroid stress remains to be elucidated. Here, we utilized CRISPR-Cas9 to model a stressed state caused by reduced levels of adult β-globin in HUDEP2 human erythroid progenitor cells. We found that a decrease in β-globin expression correlates with the upregulation of γ-globin expression. We also identified transcription factor high-mobility group A1 (HMGA1; formerly HMG-I/Y) as a potential γ-globin regulator that responds to reduced β-globin levels. Upon erythroid stress, there is a downregulation of HMGA1, which normally binds -626 to -610 base pairs upstream from the STAT3 promoter, to downregulate STAT3 expression. STAT3 is a known γ-globin repressor, so the downregulation of HMGA1 ultimately upregulates γ-globin expression. SIGNIFICANCE: This study demonstrated HMGA1 as a potential regulator in the poorly understood phenomenon of stress-induced globin compensation, and after further validation these results might inform new strategies to treat patients with sickle cell disease and β-thalassemia.

Short and long-term effect of dexamethasone on the transcriptome profile of primary human trabecular meshwork cells in vitro

In the quest of identifying newer molecular targets for the management of glucocorticoid-induced ocular hypertension (GC-OHT) and glaucoma (GCG), several microarray studies have attempted to investigate the genome-wide transcriptome profiling of primary human trabecular meshwork (TM) cells in response to dexamethasone (DEX). However, no studies are reported so far to demonstrate the temporal changes in the expression of genes in the cultured human TM cells in response to DEX treatment. Therefore, in the present study, the time-dependent changes in the genome-wide expression of genes in primary human TM cells after short (16 hours: 16 h) and long exposure (7 days: 7 d) of DEX was investigated using RNA sequencing. There were 199 (118 up-regulated; 81 down-regulated) and 525 (119 up-regulated; 406 down-regulated) DEGs in 16 h and 7 d treatment groups respectively. The unique genes identified in 16 h and 7 d treatment groups were 152 and 478 respectively. This study found a distinct gene signature and pathways between two treatment regimes. Longer exposure of DEX treatment showed a dys-regulation of Wnt and Rap1 signaling and so highlighted potential therapeutic targets for pharmacological management of GC-OHT/glaucoma.

The HBG2 rs7482144 (C > T) Polymorphism is Linked to HbF Levels but not to the Severity of Sickle Cell Anemia

Sickle cell anemia (SCA) is a severe disease characterized by anemia, acute clinical complications, and a relatively short life span. In this disease, abnormal hemoglobin makes the red blood cells deformed, rigid, and sticky. Fetal hemoglobin (HbF) is one of the key modulators of SCA morbidity and mortality. Interindividual HbF variation is a heritable trait that is controlled by polymorphism in genes linked and unlinked to the hemoglobin β gene (HBB). The genetic polymorphisms that determine HbF levels are known to ameliorate acute clinical events. About 190 well-characterized homozygous SCA patients were included in this study. Complete blood count (CBC), high-performance liquid chromatography (HPLC), and clinical investigations were obtained from patient's records. Severity scores were determined by using the combination of anemia, complications, total leucocyte count, and transfusion scores. HBG2 rs7482144 polymorphism was genotyped by using the polymerase chain reaction and restriction fragment length polymorphism. The association between HBG2 rs7482144 polymorphism and HbF levels as well as the disease severity of SCA were assessed. SCA patients carrying TT genotype were found to have higher HbF levels. In addition, SCA patients with increased severity showed significantly lower levels of hemoglobin, HbF, and hematocrit values. However, the genotypes of HBG2 rs7482144 polymorphism were not found to be associated with the risk of disease severity. In summary, this study demonstrated that HBG2 rs7482144 polymorphism is linked with HbF levels, but it does not affect disease severity. The sample sizes used and the pattern of association deduced from our small sample size prevents us from extrapolating our findings further.

'Enhancing' red cell fate through epigenetic mechanisms

PURPOSE OF REVIEW

Transcription of erythroid-specific genes is regulated by the three-dimensional (3D) structure and composition of chromatin, which dynamically changes during erythroid differentiation. Chromatin organization and dynamics are regulated by several epigenetic mechanisms involving DNA (de-)methylation, posttranslational modifications (PTMs) of histones, chromatin-associated structural proteins, and higher-order structural changes and interactions. This review addresses examples of recent developments in several areas delineating the interface of chromatin regulation and erythroid-specific lineage transcription.

RECENT FINDINGS

We survey and discuss recent studies that focus on the erythroid chromatin landscape, erythroid enhancer-promotor interactions, super-enhancer functionality, the role of chromatin modifiers and epigenetic crosstalk, as well as the progress in mapping red blood cell (RBC) trait-associated genetic variants within cis-regulatory elements (CREs) identified in genome-wide association study (GWAS) efforts as a step toward determining their impact on erythroid-specific gene expression.

SUMMARY

As one of the best characterized and accessible cell differentiation systems, erythropoiesis has been at the forefront of studies aiming to conceptualize how chromatin dynamics regulate transcription. New emerging technologies that bring a significantly enhanced spatial and temporal resolution of chromatin structure, and allow investigation of small cell numbers, have advanced our understanding of chromatin dynamics during erythroid differentiation in vivo.

Surface plasmon resonance based analysis of the binding of LYAR protein to the rs368698783 (G>A) polymorphic Aγ-globin gene sequences mutated in β-thalassemia

Recent studies have identified and characterized a novel putative transcriptional repressor site in a 5' untranslated region of the Aγ-globin gene that interacts with the Ly-1 antibody reactive clone (LYAR) protein. LYAR binds the 5'-GGTTAT-3' site of the Aγ-globin gene, and this molecular interaction causes repression of gene transcription. In β-thalassemia patients, a polymorphism has been demonstrated (the rs368698783 G>A polymorphism) within the 5'-GGTTAT-3' LYAR-binding site of the Aγ-globin gene. The major results gathered from surface plasmon resonance based biospecific interaction analysis (SPR-BIA) studies (using crude nuclear extracts, LYAR-enriched lysates, and recombinant LYAR) support the concept that the rs368698783 G>A polymorphism of the Aγ-globin gene attenuates the efficiency of LYAR binding to the LYAR-binding site. This conclusion was fully confirmed by a molecular docking analysis. This might lead to a very important difference in erythroid cells from β-thalassemia patients in respect to basal and induced levels of production of fetal hemoglobin. The novelty of the reported SPR-BIA method is that it allows the characterization and validation of the altered binding of a key nuclear factor (LYAR) to mutated LYAR-binding sites. These results, in addition to theoretical implications, should be considered of interest in applied pharmacology studies as a basis for the screening of drugs able to inhibit LYAR-DNA interactions. This might lead to the identification of molecules facilitating induced increase of γ-globin gene expression and fetal hemoglobin production in erythroid cells, which is associated with possible reduction of the clinical severity of the β-thalassemia phenotype. Graphical abstract.