Role of epigenetic modifications in normal globin gene regulation and butyrate-mediated induction of fetal hemoglobin

Fetal Hemoglobin Regulation in Beta-Thalassemia

β-thalassemia is caused by mutations that reduce β-globin production, causing globin chain imbalance, ineffective erythropoiesis, and consequent anemia. Increased fetal hemoglobin (HbF) levels can ameliorate the severity of β-thalassemia by compensating for the globin chain imbalance. Careful clinical observations paired with population studies and advances in human genetics have enabled the discovery of major regulators of HbF switching (i.e. BCL11A, ZBTB7A) and led to pharmacological and genetic therapies for treating β-thalassemia patients. Recent functional screens using genome editing and other emerging tools have identified many new HbF regulators, which may improve therapeutic HbF induction in the future.

In Vitro and In Vivo Studies for the Investigation of γ-Globin Gene Induction by Adhatoda vasica: A Pre-Clinical Study of HbF Inducers for β-Thalassemia

Fetal hemoglobin (HbF) is a potent genetic modifier, and the γ-globin gene induction has proven to be a sustainable therapeutic approach for the management of β-thalassemia. In this study, we have evaluated the HbF induction ability of A. vasica in vitro and in vivo, and the identification of potential therapeutic compounds through a bioassay-guided approach. In vitro benzidine-Hb assay demonstrated strong erythroid differentiation of K562 cells by A. vasica extracts. Subsequently, an in vivo study with an aqueous extract of A. vasica (100 mg/kg) showed significant induction of the γ-globin gene and HbF production. While in the acute study, the hematological and biochemical indices were found to be unaltered at the lower dose of A. vasica. Following the bioassay-guided approach, two isolated compounds, vasicinol (1) and vasicine (2) strongly enhanced HbF levels and showed prominent cellular growth kinetics with ample accumulation of total hemoglobin in K562 cultures. High HbF levels were examined by immunofluorescence and flow cytometry analysis, concomitant with the overexpression in the γ-globin gene level. Compound 1 (0.1 µM) and compound 2 (1 µM) resulted in a greater increase in F-cells (90 and 83%) with marked up (8-fold and 5.1-fold) expression of the γ-globin gene, respectively. Molecular docking studies indicated strong binding affinities of (1) and (2) with HDAC2 and KDM1 protein that predict the possible mechanism of compounds in inhibition of these epigenetic regulators in the γ-globin gene reactivation. Altogether, these observations demonstrated the therapeutic usefulness of A. vasica for fostering HbF production in clinical implications for blood disorders.

Exploring epigenetic and microRNA approaches for γ-globin gene regulation

Therapeutic interventions aimed at inducing fetal hemoglobin and reducing the concentration of sickle hemoglobin is an effective approach to ameliorating acute and chronic complications of sickle cell disease, exemplified by the long-term use of hydroxyurea. However, there remains an unmet need for the development of additional safe and effective drugs for single agent or combination therapy for individuals with β-hemoglobinopathies. Regulation of the γ-globin to β-globin switch is achieved by chromatin remodeling at the HBB locus on chromosome 11 and interactions of major DNA binding proteins, such as KLF1 and BCL11A in the proximal promoters of the globin genes. Experimental evidence also supports a role of epigenetic modifications including DNA methylation, histone acetylation/methylation, and microRNA expression in γ-globin gene silencing during development. In this review, we will critically evaluate the role of epigenetic mechanisms in γ-globin gene regulation and discuss data generated in tissue culture, pre-clinical animal models, and clinical trials to support drug development to date. The question remains whether modulation of epigenetic pathways will produce sufficient efficacy and specificity for fetal hemoglobin induction and to what extent targeting these pathways form the basis of prospects for clinical therapy.

Epigenetic activities in erythroid cell gene regulation

Interest in the role of epigenetic mechanisms in human biology has exponentially increased over the past several decades. The multitude of opposing and context-dependent chromatin-modifying enzymes/coregulator complexes is just beginning to be understood at a molecular level. This science has benefitted tremendously from studies of erythropoiesis, in which a series of β-globin genes are in sequence turned "on" and "off," serving as a fascinating model of coordinated gene expression. We, therefore, describe here epigenetic complexes about which we know most, using erythropoiesis as the context. The biochemical insights lay the foundation for proposing and developing novel treatments for diseases of red cells and of erythropoiesis, identifying for example epigenetic enzymes that can be drugged to manipulate β-globin locus regulation, to favor activation of unmutated fetal hemoglobin over mutated adult β-globin genes to treat sickle cell disease and β-thalassemias. Other potential translational applications are in redirecting hematopoietic commitment decisions, as treatment for bone marrow failure syndromes.

Regulating the Regulators: The Role of Histone Deacetylase 1 (HDAC1) in Erythropoiesis

Histone deacetylases (HDACs) play important roles in transcriptional regulation in eukaryotic cells. Class I deacetylase HDAC1/2 often associates with repressor complexes, such as Sin3 (Switch Independent 3), NuRD (Nucleosome remodeling and deacetylase) and CoREST (Corepressor of RE1 silencing transcription factor) complexes. It has been shown that HDAC1 interacts with and modulates all essential transcription factors for erythropoiesis. During erythropoiesis, histone deacetylase activity is dramatically reduced. Consistently, inhibition of HDAC activity promotes erythroid differentiation. The reduction of HDAC activity not only results in the activation of transcription activators such as GATA-1 (GATA-binding factor 1), TAL1 (TAL BHLH Transcription Factor 1) and KLF1 (Krüpple-like factor 1), but also represses transcription repressors such as PU.1 (Putative oncogene Spi-1). The reduction of histone deacetylase activity is mainly through HDAC1 acetylation that attenuates HDAC1 activity and trans-repress HDAC2 activity through dimerization with HDAC1. Therefore, the acetylation of HDAC1 can convert the corepressor complex to an activator complex for gene activation. HDAC1 also can deacetylate non-histone proteins that play a role on erythropoiesis, therefore adds another layer of gene regulation through HDAC1. Clinically, it has been shown HDACi can reactivate fetal globin in adult erythroid cells. This review will cover the up to date research on the role of HDAC1 in modulating key transcription factors for erythropoiesis and its clinical relevance.

PARP1-DNMT1-CTCF complex and the apoptotic-induced factor mRNA expressions in workers occupationally exposed to benzene

Exposure to benzene is a common occupational hazard as well as a hematopoietic system intoxicant, but the entire picture of its molecular pathogenesis is still hazy. Its leukemogenic effect could be attributed to DNA damage, decreased repair capacity, altered methylation patterns, and defective apoptosis. Poly ADP-ribose polymerase1, DNA methyltransferase1, and CCCTC-binding factor (PARP1-DNMT1-CTCF) complex play an essential role in methylation maintenance and DNA damage repair response. This study aimed to assess the expression of PARP1, PAR glycohydrolases (PARG), DNMT1, CTCF, and apoptosis-inducing factor (AIF) in subjects occupationally exposed to benzene. A total of 200 subjects were enrolled in this study: 100 workers occupationally exposed to benzene (painters and decorators) and 100 unexposed office workers. Occupational exposure data were obtained. The biochemical and hematological evaluations were done. Quantitative reverse transcription polymerase chain reaction (RT-PCR) was used to assess mRNA expression of PARP1, PARG, DNMT1, CTCF, and AIF. Both biochemical and hematological parameters were within normal limits; workplace benzene air concentration was significantly higher in exposed workers than the levels among controls (P < 0.001). Significant decrease in mRNA levels of PARP1, DNMT1, CTCF, and AIF was noticed among the exposed group (P = 0.01, P < 0.001, P = 0.004, P < 0.001, respectively) in comparison with the control group, while PARG showed non-significant difference (P = 0.16). There was a significant negative correlation between workplace benzene air concentration and expression levels of PARP1, DNMT1, and AIF. The reduced expression of PARP1, DNMT1, CTCF, and AIF observed in exposed workers may represent one of the first benzene-induced changes that might threaten erythropoiesis.

Genomic variants in members of the Krüppel-like factor gene family are associated with disease severity and hydroxyurea treatment efficacy in β-hemoglobinopathies patients

Aim: β-Type hemoglobinopathies are characterized by vast phenotypic diversity as far as disease severity is concerned, while differences have also been observed in hydroxyurea (HU) treatment efficacy. These differences are partly attributed to the residual expression of fetal hemoglobin (HbF) in adulthood. The Krüppel-like family of transcription factors (KLFs) are a set of zinc finger DNA-binding proteins which play a major role in HbF regulation. Here, we explored the possible association of variants in KLF gene family members with response to HU treatment efficacy and disease severity in β-hemoglobinopathies patients. Materials & methods: Six tag single nucleotide polymorphisms, located in four KLF genes, namely KLF3, KLF4, KLF9 and KLF10, were analyzed in 110 β-thalassemia major patients (TDT), 18 nontransfusion dependent β-thalassemia patients (NTDT), 82 sickle cell disease/β-thalassemia compound heterozygous patients and 85 healthy individuals as controls. Results: Our findings show that a KLF4 genomic variant (rs2236599) is associated with HU treatment efficacy in sickle cell disease/β-thalassemia compound heterozygous patients and two KLF10 genomic variants (rs980112, rs3191333) are associated with persistent HbF levels in NTDT patients. Conclusion: Our findings provide evidence that genomic variants located in KLF10 gene may be considered as potential prognostic biomarkers of β-thalassemia clinical severity and an additional variant in KLF4 gene as a pharmacogenomic biomarker, predicting response to HU treatment.

Benzene metabolite 1,2,4-benzenetriol changes DNA methylation and histone acetylation of erythroid-specific genes in K562 cells

1,2,4-Benzenetriol (BT) is one of the phenolic metabolites of benzene, a general occupational hazard and ubiquitous environmental air pollutant with leukemogenic potential in humans. Previous studies have revealed that the benzene metabolites phenol and hydroquinone can inhibit hemin-induced erythroid differentiation in K562 cells. We investigated the roles of DNA methylation and histone acetylation in BT-inhibited erythroid differentiation in K562 cells. When K562 cells were treated with 0, 5, 10, 15 or 20 µM BT for 72 h, hemin-induced hemoglobin synthesis decreased in a concentration-dependent manner. Both 5-aza-2'-deoxycytidine (5-aza-CdR, DNA methyltransferase inhibitor) and trichostatin A (TSA, histone deacetylases inhibitor) could prevent 20 µM BT from inhibiting hemin-induced hemoglobin synthesis and the mRNA expression of erythroid genes. Exposure to BT changed DNA methylation levels at several CpG sites of erythroid-specific genes, as well as the acetylation of histone H3 and H4, chromatin occupancy of GATA-1 and recruitment of RNA polymerase II at α-globin and β-globin gene clusters after hemin induction. These results demonstrated that BT could inhibit hemin-induced erythroid differentiation, where DNA methylation and histone acetylation also played important roles by down-regulating erythroid-specific genes. This partly explained the mechanisms of benzene hematotoxicity.

Modelling human haemoglobin switching

Genetic lesions of the β-globin gene result in haemoglobinopathies such as β-thalassemia and sickle cell disease. To discover and test new molecular medicines for β-haemoglobinopathies, cell-based and animal models are now being widely utilised. However, multiple in vitro and in vivo models are required due to the complex structure and regulatory mechanisms of the human globin gene locus, subtle species-specific differences in blood cell development, and the influence of epigenetic factors. Advances in genome sequencing, gene editing, and precision medicine have enabled the first generation of molecular therapies aimed at reactivating, repairing, or replacing silenced or damaged globin genes. Here we compare and contrast current animal and cell-based models, highlighting their complementary strengths, reflecting on how they have informed the scope and direction of the field, and describing some of the novel molecular and precision medicines currently under development or in clinical trial.

Pharmacological and molecular approaches for the treatment of β-hemoglobin disorders

β-hemoglobin disorders, such as β-thalassemia and sickle cell anemia are among the most prevalent inherited genetic disorders worldwide. These disorders are caused by mutations in the gene encoding hemoglobin-β (HBB), a vital protein found in red blood cells (RBCs) that carries oxygen from lungs to all parts of the human body. As a consequence, there has been an enduring interest in this field in formulating therapeutic strategies for the treatment of these diseases. Currently, there is no cure available for hemoglobin disorders, although, some patients have been treated with bone marrow transplantation, whose scope is limited because of the difficulty in finding a histocompatible donor and also due to transplant-associated clinical complications that can arise during the treatment. On account of these constraints, reactivation of fetal hemoglobin (HbF) synthesis holds immense promise and is a viable strategy to alleviate the symptoms of β-hemoglobin disorders. Development of new genomic tools has led to the identification of important natural genetic modifiers of hemoglobin switching which include BCL11A, KLF1, HBSIL-MYB, LRF, LSD1, LDB1, histone deacetylases 1 and 2 (HDAC1 and HDAC2). miRNAs are also promising therapeutic targets for development of more effective strategies for the induction of HbF production. Many new small molecule pharmacological inducers of HbF production are already under pre-clinical and clinical development. Furthermore, recent advancements in gene and cell therapy includes targeted genome editing and iPS cell technologies, both of which utilizes a patient's own cells, are emerging as extremely promising approaches for significantly reducing the burden of β-hemoglobin disorders.

Hemoglobins emerging roles in mental disorders. Metabolical, genetical and immunological aspects

Hemoglobin (Hb) expression in the central nervous system is recently shown. Cooccurences of mental disorders (mainly bipolar disorder (BD) and tic disorders) with β- or α-thalassemia trait or erythrocytosis were witnessed, which may be due to peripheral or central hypoxia/hyperoxia or haplotypal gene interactions. β-Globin genes reside at 11p15.5 close to tyrosine hydroxylase, dopamine receptor DRD4 and Brain Derived Neurotrophic Factor, which involve in psychiatric diseases. α-Globin genes reside at 16p13.3 which associates with BD, tic disorders, ATR-16 Syndrome and Rubinstein Taybi Syndrome (RTS). CREB-Binding Protein (CEBBP)-gene is mutated in RTS, which commonly associates with mood disorders. 16p13.3 region also contains GRIN2A gene encoding N-methyl-d-aspartate receptor-2A and SSTR5 (Somatostatin Receptor-5), again involving in mental disorders. We demonstrated a protective role of minor HbA2 against post-partum episodes in BD and association of higher minor HbF (fetal hemoglobin) levels with family history of psychosis in a BD-patient cohort. HbA2 increases in cardiac ischemia and in mountain dwellers indicating its likely protection against ischemia/hypoxia. HMGIY, a repressive transcription factor of δ-globin chain of HbA2 is increased in lymphocytes of schizophrenics. In autism, deletional mutations were found in BCL11A gene, which cause persistence of HbF at high levels in adulthood. Also, certain polymorphisms in BCL11A strongly associate with schizophrenia. Further, many drugs from anabolic steroids to antimalarial agents elevate HbF and may cause mania. We ascribe a protective role to HbA2 and a maladaptive detrimental role to HbF in psychopathology. We believe that future studies on hemoglobins may pave to discover novel pathogenesis mechanisms in mental disorders.

Histone deacetylase 1 activates PU.1 gene transcription through regulating TAF9 deacetylation and transcription factor IID assembly

Histone acetyltransferases and histone deacetylases (HDACs) are important epigenetic coregulators. It has been thought that HDACs associate with corepressor complexes and repress gene transcription; however, in this study, we have found that PU.1-a key master regulator for hematopoietic self-renewal and lineage specification-requires HDAC activity for gene activation. Deregulated PU.1 gene expression is linked to dysregulated hematopoiesis and the development of leukemia. In this study, we used erythroid differentiation as a model to analyze how the PU.1 gene is regulated. We found that active HDAC1 is directly recruited to active PU.1 promoter in progenitor cells, whereas acetylated HDAC1, which is inactive, is on the silenced PU.1 promoter in differentiated erythroid cells. We then studied the mechanism of HDAC1-mediated activation. We discovered that HDAC1 activates PU.1 gene transcription via deacetylation of TATA-binding protein-associated factor 9 (TAF9), a component in the transcription factor IID (TFIID) complex. Treatment with HDAC inhibitor results in an increase in TAF9 acetylation. Acetylated TAF9 does not bind to the PU.1 gene promoter and subsequently leads to the disassociation of the TFIID complex and transcription repression. Thus, these results demonstrate a key role for HDAC1 in PU.1 gene transcription and, more importantly, uncover a novel mechanism of TFIID recruitment and gene activation.-Jian, W., Yan, B., Huang, S., Qiu, Y. Histone deacetylase 1 activates PU.1 gene transcription through regulating TAF9 deacetylation and transcription factor IID assembly.

Changes in DNA methylation of erythroid-specific genes in K562 cells exposed to catechol in long term

Catechol is one of phenolic metabolites of benzene that is a general occupational hazard and a ubiquitous environmental air pollutant. Catechol also occurs naturally in fruits, vegetables and cigarettes. Previous studies have revealed that 72h exposure to catechol improved hemin-induced erythroid differentiation of K562 cells accompanied with elevated methylation in erythroid specific genes. In present study, K562 cells were treated with 0, 10 or 20μM catechol for 1-4weeks, hemin-induced hemoglobin synthesis increased in a concentration- and time-dependent manner and the enhanced hemoglobin synthesis was relatively stable. The mRNA expression of α-, β- and γ-globin genes, erythroid heme synthesis enzymes PBGD and ALAS2, transcription factor GATA-1 and NF-E2 showed a significant increase in K562 cells exposed to 20μM catechol for 3w, and catechol enhanced hemin-induced mRNA expression of these genes. Quantitative MassARRAY methylation analysis also confirmed that the exposure to catechol changed DNA methylation levels at several CpG sites in several erythroid-specific genes and their far upstream of regulatory elements. These results demonstrated that long-term exposure to low concentration of catechol enhanced the hemin-induced erythroid differentiation of K562 cells, in which DNA methylation played a role by up-regulating erythroid specific genes.

Gamma reactivation using the spongy effect of KLF1-binding site sequence: an approach in gene therapy for beta-thalassemia

OBJECTIVES

β-thalassemia is one of the most common genetic disorders in the world. As one of the promising treatment strategies, fetal hemoglobin (Hb F) can be induced. The present study was an attempt to reactivate the γ-globin gene by introducing a gene construct containing KLF1 binding sites to the K562 cell line.

MATERIALS AND METHODS

A plasmid containing a 192 bp sequence with two repeats of KLF1 binding sites on β-globin and BCL11A promoters was constructed and used to transfect the K562 cell line. Positive selection was performed under treatment with 150 μg/ml hygromycin B. The remaining cells were expanded and harvested on day 28, and genomic DNA was extracted. The PCR was carried out to verify insertion of DNA fragment to the genome of K562 cells. The cells were differentiated with 15 μg/ml cisplatin. Flowcytometry was performed to identify erythroid differentiation by detection of CD235a+ cells. Real-time RT-PCR was performed to evaluate γ-globin expression in the transfected cells.

RESULTS

A 1700 bp fragment was observed on agarose gel as expected and insertion of DNA fragment to the genome of K562 cells was verified. Totally, 84% of cells were differentiated. The transfected cells significantly increased γ-globin expression after differentiation compared to untransfected ones.

CONCLUSION

The findings demonstrate that the spongy effect of KLF1-binding site on BCL11A and β-globin promoters can induce γ-globin expression in K562 cells. This novel strategy can be promising for the treatment of β-thalassemia and sickle cell disease.

Long-term exposure of K562 cells to benzene metabolites inhibited erythroid differentiation and elevated methylation in erythroid specific genes

Benzene is a common occupational hazard and a widespread environmental pollutant. Previous studies have revealed that 72 h exposure to benzene metabolites inhibited hemin-induced erythroid differentiation of K562 cells accompanied with elevated methylation in erythroid specific genes. However, little is known about the effects of long-term and low-dose benzene metabolite exposure. In this study, to elucidate the effects of long-term benzene metabolite exposure on erythroid differentiation, K562 cells were treated with low-concentration phenol, hydroquinone and 1,2,4-benzenetriol for at least 3 weeks. After exposure of K562 cells to benzene metabolites, hemin-induced hemoglobin synthesis declined in a concentration- and time-dependent manner, and the hemin-induced expressions of α-, β- and γ-globin genes and heme synthesis enzyme porphobilinogen deaminase were significantly suppressed. Furthermore, when K562 cells were continuously cultured without benzene metabolites for another 20 days after exposure to benzene metabolites for 4 weeks, the decreased erythroid differentiation capabilities still remained stable in hydroquinone- and 1,2,4-benzenetriol-exposed cells, but showed a slow increase in phenol-exposed K562 cells. In addition, methyltransferase inhibitor 5-aza-2'-deoxycytidine significantly blocked benzene metabolites inhibiting hemoglobin synthesis and expression of erythroid genes. Quantitative MassARRAY methylation analysis also confirmed that the exposure to benzene metabolites increased DNA methylation levels at several CpG sites in several erythroid-specific genes and their far-upstream regulatory elements. These results demonstrated that long-term and low-dose exposure to benzene metabolites inhibited the hemin-induced erythroid differentiation of K562 cells, in which DNA methylation played a role through the suppression of erythroid specific genes.

Suppression of Spleen Tyrosine Kinase (Syk) by Histone Deacetylation Promotes, Whereas BAY61-3606, a Synthetic Syk Inhibitor Abrogates Colonocyte Apoptosis by ERK Activation

Spleen tyrosine kinase (Syk), a non-receptor tyrosine kinase, regulates tumor progression, either negatively or positively, depending on the tissue lineage. Information about the role of Syk in colorectal cancers (CRC) is limited, and conflicting reports have been published. We studied Syk expression and its role in differentiation and apoptosis of the colonocytes. Here, we reported for the first time that expression of two transcript variants of Syk is suppressed in colonocytes during butyrate-induced differentiation, which mediates apoptosis of HT-29 cells. Despite being a known HDAC inhibitor, butyrate deacetylates histone3/4 around the transcription start site (TSS) of Syk. Histone deacetylation precludes the binding of RNA Polymerase II to the promoter and inhibits transcription. Since butyrate is a colonic metabolite derived from undigested fibers, our study offers a plausible explanation of the underlying mechanisms of the protective role of butyrate as well as the dietary fibers against CRC through the regulation of Syk. We also report that combined use of butyrate and highly specific Syk inhibitor BAY61-3606 does not enhance differentiation and apoptosis of colonocytes. Instead, BAY completely abolishes butyrate-induced differentiation and apoptosis in a Syk- and ERK1/2-dependent manner. While butyrate dephosphorylates ERK1/2 in HT-29 cells, BAY re-phosphorylates it, leading to its activation. This study describes a novel mechanism of butyrate action in CRC and explores the role of Syk in butyrate-induced differentiation and apoptosis. In addition, our study highlights those commercial small molecule inhibitors, although attractive drug candidates should be used with concern because of their frequent off-target effects. J. Cell. Biochem. 118: 191-203, 2017. © 2016 Wiley Periodicals, Inc.

Thalidomide is more efficient than sodium butyrate in enhancing GATA-1 and EKLF gene expression in erythroid progenitors derived from HSCs with β-globin gene mutation

BACKGROUND

Efficient induction of fetal hemoglobin (HbF) is considered as an effective therapeutic approach in beta thalassemia. HbF inducer agents can induce the expression of γ-globin gene and produce high levels of HbF via different epigenetic and molecular mechanisms. Thalidomide and sodium butyrate are known as HbF inducer drugs.

MATERIAL AND METHODS

CD133(+) stem cells were isolated from umbilical cord blood of a newborn with minor β-thalassemia in order to evaluate the effects of these two drugs on the in vitro expression of GATA-1 and EKLF genes as erythroid transcription factors. CD133(+) stem cells were expanded and differentiated into erythroid lineage and then treated with thalidomide and sodium butyrate and finally analyzed by quantitative real-time PCR. Statistical analysis was performed using student's t-test by SPSS software.

RESULTS

Thalidomide and sodium butyrate increased GATA-1 and EKLF gene expression, compared to the non-treated control (P<0.05).

CONCLUSION

Thalidomide was more efficient than sodium butyrate in augmenting expression of GATA-1 and EKLF genes. It seems that GATA-1 and EKLF have crucial roles in the efficient induction of HbF by thalidomide.

Gum Arabic as fetal hemoglobin inducing agent in sickle cell anemia; in vivo study

Background

High levels of fetal haemoglobin (HbF) decrease sickle cell anaemia (SCA) severity and leads to improved survival. According to in vivo and in vitro studies, butyrate increases HbF production. Its utilization in clinical practice is hampered, however, by its short half-life. Serum butyrate concentrations could be enhanced by colonic bacterial fermentation of Gum Arabic (GA), edible, dried, gummy exudates from Acacia Senegal tree. We hypothesized that regular intake of GA increases serum butyrate levels, thus inducing HbF production and ameliorating symptoms of sickle cell anemia.

Methods

Fourty seven patients (5–42 years) carrying hemoglobin SS were recruited from April 2014 to January 2015. Patients received 30 g/day GA for 12 weeks. HbF, blood count and erythropoietin level were measured. The main outcome of interest was the level of HbF after 12 weeks. The secondary outcomes were improvement in clinical and laboratory results. The study was ethically approved by Alneelain University IRB.

Results

The study revealed significant increase in HbF level P.V0.000 [95 % CI, 0.43–1.02], MCV P.V:000 [95 % CI, 2.312–6.058] and Hematocrit level P.V:0.026 [95 % CI, 0.124–1.902]. No significant difference was encountered in platelets count P.V: 0.346 [95 % CI,−25.76–71.94], and WBCs count P.V:0.194 [95 % CI,−8.035–1.68]. Thirty seven percent of patients experienced minor side effects which resolved within a week.

Conclusion

These findings reveal a novel effect of GA, which may be used to foster fetal hemoglobin production.

Trial registration

ClinicalTrials.gov Identifier: NCT02467257. Registered 3rd June 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s12878-015-0040-6) contains supplementary material, which is available to authorized users.

Epigenetic regulation of fetal globin gene expression in adult erythroid cells

The developmental regulation of globin gene expression has served as an important model for understanding higher eukaryotic transcriptional control mechanisms. During human erythroid development, there is a sequential switch from expression of the embryonic ε-globin gene to the fetal ɣ-globin gene in utero, and postpartum the ɣ-globin gene is silenced, as the β-globin gene becomes the predominantly expressed locus. Because the expression of normally silenced fetal ɣ-type globin genes and resultant production of fetal hemoglobin (HbF) in adult erythroid cells can ameliorate the pathophysiological consequences of both abnormal β-globin chains in sickle cell anemia and deficient β-globin chain production in β-thalassemia, understanding the complex mechanisms of this developmental switch has direct translational clinical relevance. Of particular interest for translational research are the factors that mediate silencing of the ɣ-globin gene in adult stage erythroid cells. In addition to the regulatory roles of transcription factors and their cognate DNA sequence motifs, there has been a growing appreciation of the role of epigenetic signals and their cognate factors in gene regulation, and in particular in gene silencing through chromatin. Much of the information about epigenetic silencing stems from studies of globin gene regulation. As discussed here, the term epigenetics refers to postsynthetic modifications of DNA and chromosomal histone proteins that affect gene expression and can be inherited through somatic cell replication. A full understanding of the molecular mechanisms of epigenetic silencing of HbF expression should facilitate the development of more effective treatment of β-globin chain hemoglobinopathies.

Fetal globin gene repressors as drug targets for molecular therapies to treat the β-globinopathies

The human β-globin locus is comprised of embryonic, fetal, and adult globin genes that are expressed in a developmental stage-specific manner. Mutations in the globin locus give rise to the β-globinopathies, β-thalassemia and sickle cell disease, which begin to manifest symptoms around the time of birth. Although the fetal globin genes are autonomously silenced in adult-stage erythroid cells, mutations lying both within and outside the locus lead to natural variations in the level of fetal globin gene expression, and some of these significantly ameliorate the clinical symptoms of the β-globinopathies. Multiple reports have now identified several transcription factors that are involved in fetal globin gene repression in definitive (adult)-stage erythroid cells (the TR2/TR4 heterodimer, MYB, KLFs, BCL11A, and SOX6). To carry out their repression functions, chromatin-modifying enzymes (such as DNA methyltransferase, histone deacetylases, and lysine-specific histone demethylase 1) are additionally involved as a consequence of forming large macromolecular complexes with the DNA-binding subunits of these cellular machines. This review focuses on the molecular mechanisms underlying fetal globin gene silencing and possible near-future molecularly targeted therapies for treating the β-globinopathies.

The role of epigenetics in the induction of fetal hemoglobin: a combination therapy approach

BACKGROUND

β-thalassemia considers worldwide public health disorders. Novel fetal hemoglobin inducer agents such as thalidomide and sodium butyrate have been attended for ameliorating clinical complications of such disorders.

MATERIAL AND METHODS

We used thalidomide and sodium butyrate for increasing the level of fetal hemoglobin in erythroid progenitors. Briefly, after isolation of CD133+ stem cells from umbilical cord blood and differentiation into erythroid lineage, erythroid progenitors were treated with thalidomide and sodium butyraye as single and combination. H3K4 histone methylation was evaluated following fetal hemoglobin induction using chromatin immuno percipitation (ChIP) technique.

RESULTS

The results of this study showed that the effect of thalidomide on increasing of H3K4 methylation was highest compared to sodium butyrate and combination of both agents (p < 0.05).

CONCLUSION

Consequently, our study of the epigenetic modification of the γ-globin suggests that histone H3K4 dimethylation are significant for the regulation of developmental stage-specific expression of the γ-globin genes.

Evaluation of H3 histone methylation and colony formation in erythroid progenitors treated with thalidomide and sodium butyrate

OBJECTIVES

β-thalassemia and sickle cell disease are hemoglobinopathies with reduced/absent β chains in the former and dysfunctional β chains in the latter. In both conditions, up-regulation of hemoglobin F through demethylation can alleviate the symptoms. This can be attained with drugs such as thalidomide and sodium butyrate.

MATERIALS AND METHODS

This study was performed on erythroid progenitors derived from CD133+ cord blood stem cells. Erythroid progenitors were treated with thalidomide and sodium butyrate in single and combined groups. Colony-formation potential in each group was evaluated by the colony assay. Real-time polymerase chain reaction (RT-PCR) was used to evaluate the effect of these drugs on histone H3 lysine 27 (H3K27) methylation patterns.

FINDINGS

Compared to other treatment groups, CD133+ cells treated with thalidomide alone produced more hematopoietic colonies. Thalidomide alone was also more effective in decreasing H3K27 methylation.

CONCLUSIONS

Thalidomide shows superiority to sodium butyrate as a hypomethylating agent in this cell culture study, and it has the potential to become conventional treatment for sickle cell disease and β-thalassemia.

Changes in NAD content induced by nicotinic acid-related compounds in K562 cells during differentiation

Two nicotinic acid-related compounds were found to induce erythroid differentiation in K562 cells. We investigated the changes in nicotinamide adenine dinucleotide (NAD) content induced by nicotinic acid-related compounds during differentiation. The NAD content was reduced by a treatment with nicotinic acid and isonicotinic acid. These results provide important clues toward elucidating the erythroid differentiation mechanism.

Plastrum testudinis induces γ-globin gene expression through epigenetic histone modifications within the γ-globin gene promoter via activation of the p38 MAPK signaling pathway

The pharmacologically-induced expression of the γ-globin gene, to increase fetal hemoglobin (HbF) production, is a therapeutic strategy used for the treatment of β-thalassemia and sickle cell anemia (SCA). The aim of this study was to investigate the effects of Plastrum testudinis (PT) on differentiation, proliferation, γ-globin gene expression and HbF synthesis in human erythroid cells. For this purpose, we used the K562 human leukemia cell line and human erythroid progenitor cells from normal donors and patients with β-thalassemia cultured using the two-phase liquid culture system. The effects of PT on erythroid differentiation, proliferation, γ-globin gene expression and HbF synthesis, as well as the involvement of epigenetic histone modifications within the γ-globin gene promoter via activation of the p38 mitogen-activated protein kinase (MAPK) signaling pathway, were assessed by benzidine staining, trypan-blue dye exclusion, quantitative real-time RT-PCR (qRT-PCR), western blot analysis and chromatin immunoprecipitation (ChIP). PT promoted the erythroid differentiation of K562 cells, and increased γ-globin mRNA accumulation and HbF synthesis without inhibiting cell proliferation in K562 cells and human erythroid progenitors. PT exerted no effect on α- and β-globin gene expression. In human erythroid cells, PT activated the p38 MAPK signaling pathway, and enhanced the acetylation of histone H3 and H4, the phosphorylation of histone H3 within the Gγ- and Aγ-globin gene promoter regions, γ-globin mRNA accumulation and HbF synthesis. These effects were suppressed by pre-treatment with the p38 MAPK inhibitor, SB203580. Epigenetic histone modifications within γ-globin gene promoter regions, via activation of the p38 MAPK signaling pathway, are important for the induction of γ-globin gene expression in human erythroid cells by PT. PT may be a novel potential therapeutic agent for β-hemoglobinopathies, including β-thalassemia and SCA.

Induction of human fetal hemoglobin expression by adenosine-2',3'-dialdehyde

Background

Pharmacologic reactivation of fetal hemoglobin expression is a promising strategy for treatment of sickle cell disease and β-thalassemia. The objective of this study was to investigate the effect of the methyl transferase inhibitor adenosine-2’,3’-dialdehyde (Adox) on induction of human fetal hemoglobin (HbF) in K562 cells and human hematopoietic progenitor cells.

Methods

Expression levels of human fetal hemoglobin were assessed by northern blot analysis and Real-time PCR. HbF and adult hemoglobin (HbA) content were analyzed using high-performance liquid chromatography (HPLC). DNA methylation levels on human gamma-globin gene promoters were determined using Bisulfite sequence analysis. Enrichment of histone marks on genes was assessed by chromosome immunoprecipitation (ChIP).

Results

Adox induced γ-globin gene expression in both K562 cells and in human bone marrow erythroid progenitor cells through a mechanism potentially involving inhibition of protein arginine methyltransferase 5 (PRMT5).

Conclusions

The ability of methyl transferase inhibitors such as Adox to efficiently reactivate fetal hemoglobin expression suggests that these agents may provide a means of reactivating fetal globin expression as a therapeutic option for treating sickle cell disease and β-thalassemia.

The switch from fetal to adult hemoglobin

The fetal-to-adult hemoglobin switch and silencing of fetal hemoglobin (HbF) have been areas of long-standing interest among hematologists, given the fact that clinical induction of HbF production holds tremendous promise to ameliorate the clinical symptoms of sickle cell disease (SCD) and β-thalassemia. In this article, we discuss historic attempts to induce HbF that have resulted in some therapeutic approaches to manage SCD and β-thalassemia. We then go on to discuss how more recent molecular studies that have identified regulators, including BCL11A, MYB, and KLF1, hold great promise to develop targeted and more effective approaches for HbF induction. We go on to discuss strategies by which such approaches may be developed. Older studies in this field can provide important lessons for future studies aimed at developing more effective strategies for HbF induction, and we therefore chronologically cover the work accomplished as this field has evolved over the course of the past four decades.

Novel approaches to the treatment of sickle cell disease: the potential of histone deacetylase inhibitors

Sickle cell disease (SCD) is a severe genetic disorder of hemoglobin causing vaso-occlusion. Patients suffer severe anemia, strokes, renal failure, pulmonary compromise and shortened life expectancy. Over 90,000 people in the USA have SCD, and the options for therapy are limited and only partially effective. With the available therapies - hydroxyurea, blood transfusion, hydration and pain medicines - patients continue to suffer the long-term complications of the disease. This review focuses on the pathogenesis of SCD and the role of fetal hemoglobin in disrupting the polymerization of sickle hemoglobin. The authors review the compounds that induce fetal hemoglobin: hydroxyurea, which is currently US FDA approved, and the histone deacetylase inhibitors and discuss their role in the treatment of SCD and other β-hemoglobinopathies.

Can nutritional modulation of maternal intestinal microbiota influence the development of the infant gastrointestinal tract?

The gastrointestinal microbiota plays an important role in maintaining host health by preventing the colonization of pathogens, fermenting dietary compounds, and maintaining normal mucosal immunity. Particularly in early life, the composition of the microbiota profoundly influences the development and maturation of the gastrointestinal tract (GIT) mucosa, which may affect health in later life. Therefore, strategies to manipulate the microbiota during infancy may prevent the development of some diseases later in adult life. Earlier research suggested that term fetuses are sterile and that the initial bacterial colonization of the newborn GIT occurs only after the baby transits through the birth canal. However, recent studies have demonstrated that the colonization and/or contact of the fetus with the maternal GIT microbiota may start in utero. After vaginal birth, the colonization of the neonate GIT continues through contact with maternal feces and vaginal bacteria, leading to a relatively simple microbial community that is influenced by feeding type (breast vs. formula feeding). Maternal GIT microbiota, vaginal microbiota, and breast milk composition are influenced by maternal diet. Alterations of the maternal GIT microbiota composition via supplementation with probiotics and prebiotics have been shown; however, transfer of these benefits to the offspring remains to be demonstrated. This review focuses on the influence of maternal GIT microbiota during the pre- and postpartum periods on the colonization of the infant GIT. In particular, it examines the manipulation of the maternal GIT microbiota composition through the use of probiotics and/or prebiotics and subsequent consequences for the health of the offspring.

FK228 Analogues Induce Fetal Hemoglobin in Human Erythroid Progenitors

Fetal hemoglobin (HbF) improves the clinical severity of sickle cell disease (SCD), therefore, research to identify HbF-inducing agents for treatment purposes is desirable. The focus of our study is to investigate the ability of FK228 analogues to induce HbF using a novel KU812 dual-luciferase reporter system. Molecular modeling studies showed that the structure of twenty FK228 analogues with isosteric substitutions did not disturb the global structure of the molecule. Using the dual-luciferase system, a subgroup of FK228 analogues was shown to be inducers of HbF at nanomolar concentrations. To determine the physiological relevance of these compounds, studies in primary erythroid progenitors confirmed that JMA26 and JMA33 activated HbF synthesis at levels comparable to FK228 with low cellular toxicity. These data support our lead compounds as potential therapeutic agents for further development in the treatment of SCD.

Nuclear receptors TR2 and TR4 recruit multiple epigenetic transcriptional corepressors that associate specifically with the embryonic β-type globin promoters in differentiated adult erythroid cells

Nuclear receptors TR2 and TR4 (TR2/TR4) were previously shown to bind in vitro to direct repeat elements in the mouse and human embryonic and fetal β-type globin gene promoters and to play critical roles in the silencing of these genes. By chromatin immunoprecipitation (ChIP) we show that, in adult erythroid cells, TR2/TR4 bind to the embryonic β-type globin promoters but not to the adult β-globin promoter. We purified protein complexes containing biotin-tagged TR2/TR4 from adult erythroid cells and identified DNMT1, NuRD, and LSD1/CoREST repressor complexes, as well as HDAC3 and TIF1β, all known to confer epigenetic gene silencing, as potential corepressors of TR2/TR4. Coimmunoprecipitation assays of endogenous abundance proteins indicated that TR2/TR4 complexes consist of at least four distinct molecular species. In ChIP assays we found that, in undifferentiated murine adult erythroid cells, many of these corepressors associate with both the embryonic and the adult β-type globin promoters but, upon terminal differentiation, they specifically dissociate only from the adult β-globin promoter concomitant with its activation but remain bound to the silenced embryonic globin gene promoters. These data suggest that TR2/TR4 recruit an array of transcriptional corepressors to elicit adult stage-specific silencing of the embryonic β-type globin genes through coordinated epigenetic chromatin modifications.

Thalassemia: an overview of 50 years of clinical research

The thalassemias are attributable to the defective production of the α- and β-globin polypeptides of hemoglobin. Significant discoveries have illuminated the pathophysiology and enhanced the prevention and treatment of the thalassemias, and this article reviews many of the advances that have occurred in the past 50 years. However, the application of new approaches to the treatment of these disorders has been slow, particularly in the developing world where the diseases are common, but there is definite progress. This article emphasizes how the increasing knowledge of cellular and molecular biology are facilitating the development of more effective therapies for these patients.

Genetic predisposition to β-thalassemia and sickle cell anemia in Turkey: a molecular diagnostic approach

The thalassemia syndromes are a diverse group of inherited disorders that can be characterized according to their insufficient synthesis or absent production of one or more of the globin chains. They are classified in to α, β, γ, δβ, δ, and εγδβ thalassemias depending on the globin chain(s) affected. The β-thalassemias refer to that group of inherited hemoglobin disorders, which are characterized by a reduced synthesis (β(+)-thalassemia) or absence (β(0)-thalassemia) of beta globin (β-globin) chain production (1). Though known as single-gene disorders, hemoglobinopathies such as β-thalassemia and sickle cell anemia are far from being fully resolved in terms of cure, considering the less complex nature of the beta globin (β-globin) gene family compared to more complex multifactorial genetic disorders such as cancer. Currently, there are no definitive therapeutic options for patients with β-thalassemia and sickle cell anemia, and new insights into the pathogenesis of these devastating diseases are urgently needed. Here we address in detail the overall picture utilizing molecular diagnostic approaches that contribute to unraveling the population-specific mutational analysis of β-globin gene. We also present approaches for molecular diagnostic strategies that are applicable to β-thalassemia, sickle cell anemia, and other genetic disorders.

Targeted therapeutic strategies for fetal hemoglobin induction

Increased levels of fetal hemoglobin (HbF) can ameliorate the severity of the β-hemoglobin disorders, sickle cell disease (SCD) and β-thalassemia, which are major sources of morbidity and mortality worldwide. As a result, there has been a longstanding interest in developing therapeutic approaches for inducing HbF. For more than 3 decades, the majority of HbF inducers developed were based on empiric observations and have had limited success. Recently, human genetic approaches have provided insight into previously unappreciated regulators of the fetal-to-adult hemoglobin switch and HbF silencing, revealing molecular targets to induce HbF. This article reviews these developments and discusses how molecules including BCL11A, KLF1, MYB, SOX6, miRNAs 15a and 16-1, and histone deacetylase 1 and 2 (HDAC1/2) could be important targets for HbF induction in humans. The current understanding of how these molecules function and the benefits and drawbacks of each of these potential therapeutic targets are also examined. The identification of these regulators of HbF expression is extremely promising and suggests that rationally designed approaches targeting the very mechanisms mediating this switching process could lead to better, less toxic, and more effective strategies for HbF induction.

siDNMT1 increases γ-globin expression in chemical inducer of dimerization (CID)-dependent mouse βYAC bone marrow cells and in baboon erythroid progenitor cell cultures

OBJECTIVE

These studies were performed to test the hypothesis that DNMT1 is required for maintenance of DNA methylation and repression of the γ-globin gene in adult-stage erythroid cells.

MATERIALS AND METHODS

DNMT1 levels were reduced by nucleofection of small interfering RNA targeting DNMT1 in chemical inducer of dimerization-dependent multipotential mouse bone marrow cells containing the human β-globin gene locus in the context of a yeast artificial chromosome and in primary cultures of erythroid progenitor cells derived from CD34(+) baboon bone marrow cells. The effect of reduced DNMT1 levels on globin gene expression was measured by real-time polymerase chain reaction and the effect on globin chain synthesis in primary erythroid progenitor cell cultures was determined by biosynthetic radiolabeling of globin chains followed by high-performance liquid chromatography analysis. The effect on DNA methylation was determined by bisulfite sequence analysis.

RESULTS

Reduced DNMT1 levels in cells treated with siDNMT1 were associated with increased expression of γ-globin messenger RNA, an increased γ/γ+β chain ratio in cultured erythroid progenitors, and decreased DNA methylation of the γ-globin promoter. Similar effects were observed in cells treated with decitabine, a pharmacological inhibitor of DNA methyltransferase inhibitor.

CONCLUSIONS

DNMT1 is required to maintain DNA methylation of the γ-globin gene promoter and repress γ-globin gene expression in adult-stage erythroid cells.

Pharmacologic induction of fetal hemoglobin production

Reactivation of fetal hemoglobin (HbF) expression is an important therapeutic option in adult patients with hemoglobin disorders. The understanding of the developmental regulation of γ-globin gene expression was followed by the identification of a number of chemical compounds that can reactivate HbF synthesis in vitro and in vivo in patients with hemoglobin disorders. These HbF inducers can be grouped in several classes based on their mechanisms of action. This article focuses on pharmacologic agents that were tested in humans and discusses current knowledge about the mechanisms by which they induce HbF.

Investigational drugs in sickle cell anemia

Sickle cell anemia is one of the most common autosomal recessive diseases in the world. Patients with sickle cell anemia have variable penetrance and it is hard to predict the risk and timing of complications. It is characterized by a point mutation in the beta-globin gene (GAG --> GTG) and the production of hemoglobin S. The latter leads to decreased deformability of the red blood cells (RBCs) that adhere to endothelia cells culminating in vascular occlusion and its sequelae of tissue ischemia and organ damage. Moreover, sickled RBCs undergo intravascular hemolysis and accelerated erythropoesis. The hallmarks of this disease are shortened RBC survival and vaso-occlusive crises. For the past ten years, the pathophysiology of this disease has been better elucidated and has led to significant improvements in the standard of care. Vaso-occlusion is now understood to be a complex event that involves abnormal interactions between RBCs, leukocytes, endothelial cells and the coagulation pathways. The field of translational research in sickle cell anemia has expanded greatly and has led to new clinical trials with new therapeutic agents and strategies. In this paper, we review the drugs that are now being investigated in the treatment of sickle cell anemia.

Functional food for pregnant, lactating women and in perinatal nutrition: a role for dietary fibres?

PURPOSE OF REVIEW

If the benefits of dietary fibre in healthy adults have extensively been studied, little information is available on the specific needs of pregnant, lactating women or foetus. As far as infants are concerned, milk oligosaccharides are supposed to be the optimal 'dietary fibre'. The supplementation of infant formula with prebiotic oligosaccharides is still discussed. However, recent studies provide a large amount of information, allowing a new discussion on this topic.

RECENT FINDINGS

Most recent findings are linked to the involvement of dietary fibre in occurrence or prevention of obesity. The multiple mechanisms appear more clearly than earlier. This finding will soon allow appropriate counselling for young mothers at risk of obesity and/or postpartum retention weight, gestational diabetes and preeclampsia. Another area which benefits from recent research is the use of prebiotics in formula.

SUMMARY

Pregnancy is a critical period during which many physiologic changes occurred and is associated with several gut disorders and metabolic diseases. Dietary fibre may be helpful in the prevention and management of these diseases. Lactation and pregnancy are two phases during which food consumption of the mother can interact with the physiology of the baby. Moreover, the use of formula supplemented in oligosaccharides is able to compensate for the lack of some of the complex molecules naturally present in human milk.

Transcriptional activation of the gamma-globin gene in baboons treated with decitabine and in cultured erythroid progenitor cells involves different mechanisms

OBJECTIVE

To investigate the mechanism(s) responsible for increased gamma-globin expression in vivo in decitabine-treated baboons and in vitro in cultured erythroid progenitor cells (EPC) from adult baboon bone marrow (BM).

MATERIALS AND METHODS

Fetal liver, adult BM erythroid cells pre- and post-decitabine, and cultured EPCs were analyzed for distribution of RNA polymerase II, histone acetylation, and histone H3 (lys4) trimethyl throughout the gamma-globin gene complex by chromatin immunoprecipitation. DNA methylation of the gamma-globin promoter was determined by bisulfite sequencing. Expression of the baboon Igamma- and Vgamma-globin chains was determined by high performance liquid chromatography (HPLC). Expression of BCL11A, a recently identified repressor of gamma-globin expression, was analyzed by Western blot.

RESULTS

Increased gamma-globin expression in decitabine-treated baboons and cultured EPC correlated with increased levels of RNA polymerase II, histone acetylation, and histone H3 (lys4) trimethyl associated with the gamma-globin gene consistent with a transcriptional activation mechanism. Cultured EPC expressed the Igamma- and Vgamma-globin chains in a pattern characteristic of fetal development. The level of DNA methylation of the gamma-globin gene promoter in EPC cultures was similar to BM erythroid cells from normal adult baboons. Different BCL11A isoforms were observed in BM erythroid cells and cultured EPC.

CONCLUSION

The mechanism responsible for increased gamma-globin expression in cultured EPC was unexpectedly not associated with increased DNA hypomethylation of the gamma-globin gene promoter compared to normal BM erythroid cells, in contrast to BM erythroid cells of decitabine-treated baboons. Rather, increased fetal hemoglobin in EPC cultures was associated with a fetal Igamma/Vgamma chain ratio and a difference in the size of the BCL11A protein compared to normal BM erythroid cells.

Differential requirement of a distal regulatory region for pre-initiation complex formation at globin gene promoters

Although distal regulatory regions are frequent throughout the genome, the molecular mechanisms by which they act in a promoter-specific manner remain to be elucidated. The human β-globin locus constitutes an extremely well-established multigenic model to investigate this issue. In erythroid cells, the β-globin locus control region (LCR) exerts distal regulatory function by influencing local chromatin organization and inducing high-level expression of individual β-like globin genes. Moreover, in transgenic mice expressing the entire human β-globin locus, deletion of LCR-hypersensitive site 2 (HS2) can alter β-like globin gene expression. Here, we show that abnormal expression of human β-like globin genes in the absence of HS2 is associated with decreased efficacy of pre-initiation complex formation at the human ɛ- and γ-promoters, but not at the β-promoter. This promoter-specific phenomenon is associated with reduced long-range interactions between the HS2-deleted LCR and human γ-promoters. We also find that HS2 is dispensable for high-level human β-gene transcription, whereas deletion of this hypersensitive site can alter locus chromatin organization; therefore the functions exerted by HS2 in transcriptional enhancement and locus chromatin organization are distinct. Overall, our data delineate one mechanism whereby a distal regulatory region provides promoter-specific transcriptional enhancement.

Developmentally regulated extended domains of DNA hypomethylation encompass highly transcribed genes of the human beta-globin locus

OBJECTIVE

DNA methylation has long been implicated in developmental beta-globin gene regulation. However, the mechanism underlying this regulation is unclear, especially because these genes do not contain CpG islands. This has led us to propose and test the hypothesis that, just as for histone modifications, developmentally specific changes in human beta-like globin gene expression are associated with long-range changes in DNA methylation.

MATERIALS AND METHODS

Bisulfite sequencing was used to determine the methylation state of individual CpG dinucleotides across the beta-globin locus in uncultured primary human erythroblasts from fetal liver and bone marrow, and in primitive-like erythroid cells derived from human embryonic stem cells.

RESULTS

beta-globin locus CpGs are generally highly methylated, but domains of DNA hypomethylation spanning thousands of base pairs are established around the most highly expressed genes during each developmental stage. These large domains of DNA hypomethylation are found within domains of histone modifications associated with gene expression. We also find hypomethylation of a small proportion of gamma-globin promoters in adult erythroid cells, suggesting a mechanism by which adult erythroid cells produce fetal hemoglobin.

CONCLUSION

This is one of the first reports to show that changes in DNA methylation patterns across large domains around non-CpG island genes correspond with changes in developmentally regulated histone modifications and gene expression. These data support a new model in which extended domains of DNA hypomethylation and active histone marks are coordinately established to achieve developmentally specific gene expression of non-CpG island genes.

Differences in response to fetal hemoglobin induction therapy in beta-thalassemia and sickle cell disease

Inducers of fetal hemoglobin (HbF) have shown considerable promise in the treatment of sickle cell disease (SCD). However, the same agents have shown less clinical activity in beta-thalassemia (beta-Thal). To understand the basis of these differences in clinical effectiveness, we compared the effects of butyrate and hemin on the expression of the different globin genes in progenitors-derived erythroid cells from patients with beta-Thal intermedia and SCD. Exposure to butyrate resulted in an augmentation of gamma-globin mRNA levels in both SCD and beta-Thal. Interestingly, butyrate exposure increased alpha-globin expression in beta-Thal, while alpha-globin mRNA levels decreased in SCD in response to butyrate. As a result, the favorable effects of the butyrate-induced increase in gamma-globin expression on alpha:beta-like globin mRNA imbalance in beta-Thal were reduced as a result of the associated increase in alpha-globin expression. Hemin had similar but less profound effects on all three globin genes in both categories of patients. Although the majority of patients with beta-Thal did not correct their globin imbalance in response to butyrate or hemin induction of HbF in a minority of patients resulted in marked reduction in globin imbalance. Thus, we believe that the poor clinical response in a majority of patients with beta-Thal to inducers of gamma-globin expression may be a reflection of unfavorable effects of these agents on the other globin genes.

Haemoglobin F modulation in childhood sickle cell disease

While supportive care remains the best option for most well children with sickle cell disease (SCD), increasing awareness of early signs of chronic organ damage in childhood has focused attention on therapy which modulates the natural history of the disease. Since cure by stem cell transplantation is only feasible for a minority and gene therapy remains developmental, pharmacological modification by Haemoglobin F (HbF)-inducers, is the most widely used approach in SCD. Currently, the only HbF modulator with a clear place in the management of childhood SCD is hydroxycarbamide for which the main indications are frequent painful crises and recurrent acute chest syndrome. In the majority of SCD children treated with hydroxycarbamide there is clear evidence of clinical benefit and the drug is well tolerated. The main disadvantages are the need for frequent monitoring and uncertainity about long-term risks of carcinogenicity and impaired fertility, although these risks appear to be very low. The role of hydroxycarbamide in sickle-associated central nervous system disease remains to be established. Decitabine and butyrate derivatives show some promise although robust data in children with SCD are lacking. A number of other drugs are currently under investigation for their effects on HbF production including thalidomide and lenolidamide.

Fetal hemoglobin chemical inducers for treatment of hemoglobinopathies

The switch from fetal ((G)gamma and (A)gamma) to adult (beta and delta) globin gene expression occurs at birth, leading to the gradual replacement of HbF with HbA. Genetic regulation of this switch has been studied for decades, and the molecular mechanisms underlying this developmental change in gene expression have been in part elucidated. The understanding of the developmental regulation of gamma-globin gene expression was paralleled by the identification of a series of chemical compounds able to reactivate HbF synthesis in vitro and in vivo in adult erythroid cells. Reactivation of HbF expression is an important therapeutic option in patients with hemoglobin disorders, such as sickle cell anemia and beta-thalassemia. These HbF inducers can be grouped in several classes based on their chemical structures and mechanisms of action. Clinical studies with some of these agents have shown that they were effective, in a part of patients, in ameliorating the clinical condition. The increase in HbF in response to these drugs varies among patients with beta-thalassemia and sickle cell disease due to individual genetic determinants.