Low HbF Levels Research Articles

Fetal Hemoglobin In Sickle Cell Anemia: Molecular Characterization of Saudi Patients From the Eastern Province

AbstractAbstract 1627In the Eastern Province of Saudi Arabia, sickle cell anemia (HbSS) is associated with the Saudi Indian (SI) HBB-gene cluster haplotype, high levels of fetal hemoglobin (HbF) and milder disease, when compared with Southwestern Province HbSS patients who have lower HbF levels and different HBB haplotypes. An association between HbF and the Xmn1 restriction site in the HBG2 promoter present in both the SI and African-derived Senegal haplotypes is well known, but the causal elements of this association are unknown. Moreover, among individuals with the SI haplotype, only HbSS patients have high HbF while individuals with sickle cell trait (HbAS) or normal hemoglobin (HbAA) do not. Furthermore, HbF levels are far higher in SI haplotype patients, as shown below, compared with Senegal haplotype homozygotes. For example African patients homozygous for the Senegal haplotype had 12.3±5.3% HbF. To better understand the genetic basis for high HbF in SI haplotype HbSS cases, we compared sequences in the HBB gene cluster in patients with SI and Senegal haplotypes. We hypothesized that the causal elements that modify HbF in Saudi patients are in linkage disequilibrium (LD) with the βS globin gene in this population. Accordingly, we studied 5 Saudi families from the Eastern Province. Seven SI haplotype patients with HbSS (median age 5 yrs, range 2.5–49 yrs) were homozygous for the Xmn I site and had Hb 9.7 ± 1.6 g/dL, MCV 76.5 ± 8.3 fl and median Hb F 30.3 (range 18–41). Seventeen SI haplotype individuals had HbAS (median HbF 1.2, range 0–4.2); and 2 were normal. We first determined the genotypes of 3 known HbF QTLs, BCL11A (rs766432); HBS1L-MYB (rs7775698 and rs9399137); and OR51B5/6 (rs5006884). There were no consistent genotypes among these 7 patients to explain their universal high HbF. Next, we performed homozygosity mapping using Illumina Human610-Quad SNP array and identified runs of homozygosity (RoH) of variable length (from 160 kb to nearly 2 mb) within and surrounding the HBB cluster only in HbSS patients. RoH were absent elsewhere in the genome in HbSS. The RoH that was shared by all HbSS patients was 126.6 kb in chr11:5153026-5279647 (NCBI36/hg18) and contains SNPs from rs11036090 to rs7118113 of the Illumina Human610-Quad SNP array. This region contains: OR51B4, the complete HBB cluster, and OR51V1. Homozygosity mapping in 6 Senegal haplotype homozygotes showed a slightly larger RoH from chr11:4909490-5314457 and SNPs rs840713-rs10837822. Both the Saudi patients and Senegal homozygotes had the same homozygous genotypes for the overlapping region of chr11:5205580-5235931 ranging from rs11036364 to rs5010981.To identify potential genetic modifiers of HbF level in the region detected in the Saudi cases, we sequenced areas within or near the Corfu deletion that is known to cause HPFH, the HBD-HBG1 intergenic region, and core regions of HS- 2, 3, and 4 in the LCR. Core regions of HS-3 and HS-4 were identical to the reference sequences. In the core of HS-2, the 10TA.2CA.2TA.CG.12TA motif was present. This motif is known to be associated with the SI haplotype but not with any other haplotypes. Within the region of the Corfu deletion, many polymorphisms were identified highlighting the complexity of SI haplotype and HBB haplotypes in general. Many of these polymorphisms lead to creation or abolition of transcription factor binding sites when this was examined in silico using the TFBS search program ConSite (consite.genereg.net). Some of these putative sites bind transcription factors presumed to have regulatory roles in globin gene expression. Complete sequencing of the 126.6 kb interval with comparison to other HBB haplotypes associated with high and low HbF might focus attention on areas of interest that can be examined in functional studies. Disclosures:No relevant conflicts of interest to declare.

Differences in BCL11A SUMOylation Are Associated with Differences in γ-Globin Expression in Primary Erythroid Cells.

Abstract 458Increased fetal hemoglobin (HbF) levels associated with acute erythropoietic stress in man and experimental baboons have been proposed to result from increased commitment of early progenitors that preferentially express γ-globin to the terminal erythroid differentiation pathway. The increased propensity of early progenitors to preferentially express γ-globin has been hypothesized to be due to the presence of trans-acting factors favoring γ-globin expression. Because increased HbF in response to acute erythropoietic stress does not occur in transgenic human β-globin gene locus mouse models, investigation of the mechanism responsible for this phenomenon requires the use of a primate model system. We investigated the role of DNA methylation and the trans-acting factor BCL11A in the mechanism responsible for increased HbF in a primary cell culture system designed to mimic conditions associated with acute erythropoietic stress. Erythroid progenitor cells (EPC) derived from CD34+ baboon bone marrow (BM) cells cultured in Iscove's medium containing 30% fetal bovine serum supplemented with 2 U/ml Epo, 200ng/ml SCF, and 1uM dexamethasone express high levels of γ-globin (0.47+ 0.09 γ/γ+β; n=6). Bisulfite sequence analysis performed to determine whether changes in DNA methylation of 5 CpG residues within the 5' γ-globin promoter regions were associated with increased γ-globin expression showed that DNA methylation levels were similar in BM erythroid cells from normal baboons expressing very low levels of HbF (<1%), bled baboons expressing moderately elevated levels of HbF (5-10%), and cultured erythroid progenitor cells expressing highly elevated levels of HbF (30-50%). Changes in γ-globin promoter DNA methylation were thus not associated with increased γ-globin expression in EPC cultures. Further experiments were therefore performed to investigate whether differences in BCL11A expression were associated with increased γ-globin in EPC cultures. Western blot assays performed using three different anti-BCL11A monoclonal antibodies recognizing epitopes present in the N terminus, core, and C terminus detected different BCL11A isoforms in cultured EPC and normal BM erythroid cells. The size of the predominant protein band detected in cultured EPC was 125kDa, corresponding to the reported size of the in vitro transcription/translation product encoded by the BCL11A-XL transcript (Liu et al, Mol Cancer 16:18, 2006). In contrast, the size of the predominant band observed in BM erythroid cells was 220kDa. The 220kDa isoform was not observed in cultured EPC. Higher molecular weight forms of BCL11A have been observed following co-transfection of vectors encoding BCL11A and SUMO-1 (Kuwata and Nakamura, Genes Cells 13:931, 2008). Therefore we investigated whether the post-translational modification SUMOylation was responsible for the difference in the size of the 125 and 220kDa isoforms. Immunoprecipitation experiments performed using either SUMO-1 or SUMO 2/3 antibodies followed by Western blot with anti-BCL11A antibody showed that the 220 kDa isoform, but not the 125kDa isoform, was immunoprecipitated by either anti-SUMO-1 or anti-SUMO-2/3 antibody, confirming that the 220 kDA isoform, but not the 125 kDa isoform, was SUMOylated. Western blot assays performed to investigate the relative levels of these isoforms in BM erythroid cells of normal baboons, phlebotomized baboons, and early gestational age (53d) baboon fetal liver showed that expression of the 125kDa isoform was increased in bled compared to normal unbled baboons, suggesting that the deSUMOylated BCL11A isoform was increased by erythropoietic stress. The relative levels of the 125 and 220 kDa isoforms were similar in bled BM and fetal liver, indicating that SUMOylation of BCL11A was not developmentally regulated. The absolute level of BCL11A was reduced in fetal liver erythroid cells compared to BM erythroid cells consistent with observations showing that the level of BCL11A expression is developmentally regulated in man (Sankaran et al, Nature epub 2009). We conclude that BCL11A is post-translationally modified by SUMOylation in primary BM erythroid cells, but not in cultured EPC expressing high levels of HbF and suggest that modulation of the level of BCL11A SUMOylation is important in the mechanism responsible for increased HbF levels during recovery from acute erythropoietic stress. Disclosures:No relevant conflicts of interest to declare.

The -566 Aγ-Globin HPFH Mutation Disrupts Temporal Repression of Fetal Hemoglobin Synthesis During Fetal Liver Definitive Erythropoiesis.

Abstract 2019Poster Board I-1041Hereditary persistence of fetal hemoglobin (HPFH) is a condition associated with continued fetal hemoglobin (HbF) production in adults, where normally only very low levels of HbF are found. Sickle cell disease (SCD) patients are phenotypically normal if they carry a compensatory HPFH mutation due to the high levels of HbF. Understanding the molecular mechanisms leading to reactivation or derepression of γ-globin gene expression will lead to the development of new or better therapies to treat SCD patients. In our long-established and highly-characterized model system, transgenic mice carrying wild-type human β-globin locus yeast artificial chromosomes (β-YACs) express predominantly γ-globin and a lesser amount of γ-globin in the primitive erythroid cells of the yolk sac, mostly β-globin and some γ-globin in the definitive erythroid cells of the fetal liver and nearly exclusively β-globin in the adult definitive red blood cells, as measured both at the transcript and protein levels. We recently identified a novel Aγ-globin gene silencer motif located at -566 relative to the mRNA CAP site in a GATA motif. Repression is mediated by binding a GATA-1-FOG-1-Mi2 protein complex. Since our initial studies of this GATA-1 repressor complex were performed using β-YAC transgenic mice in which a second copy of the Aγ-globin gene was introduced between the locus control region (LCR) and the γ-globin gene, our first goal was to test if this mutation was functional at the normally-located Aγ-globin globin gene. β-YAC transgenic mice were produced with the T>G HPFH point mutation at the -566 GATA site of this gene. These mice display a mild HPFH phenotype during adult definitive erythropoiesis; γ-globin gene expression levels were increased approximately 3% compared to wild-type β-YAC mice. Expression of γ-globin is also elevated relative to wild-type β-YAC controls during primitive erythropoiesis in the embryonic yolk sac and definitive erythropoiesis in the fetal liver. Chromatin immunoprecipitation (ChIP) experiments using day E12 to E18 post-conception fetal liver samples from wild type β-YAC transgenic mice demonstrate that GATA-1 is recruited to this GATA silencer first at day E16, followed by recruitment of FOG-1 and Mi2 at day E17. In addition, ChIP experiments performed with day E18 samples from the -566 HPFH mice demonstrate that this point mutation disrupts the recruitment of GATA-1 to this site at a developmental stage when it normally binds as a repressor in wild-type β-YAC transgenic samples. GATA-2 does not bind at the -566 GATA motif when γ-globin is actively transcribed. Thus, GATA-2/GATA-1 competition does not play a role in the function of this silencer or the mechanism of HPFH at this site. In addition, BCL11A does not appear to be a component of this GATA-1 repressor complex. Taken together our data indicate that a temporal repression mechanism is operative in the silencing of γ-globin gene expression and that the presence of the -566 Aγ-globin HPFH mutation disrupts establishment of repression, resulting in continued γ-globin gene transcription during adult definitive erythropoiesis. Disclosures:No relevant conflicts of interest to declare.

A Zinc-Finger Transcriptional Activator Designed to Interact with the Gamma-Globin Gene Promoters Enhances Fetal Hemoglobin Production in Erythroid Cells Derived From Normal and Beta-Thalassemic CD34+ Cells.

Abstract 3567Poster Board III-504Fetal hemoglobin (α2γ2; HbF) is a potent genetic modifier of the severity of beta-thalassemia and sickle cell anemia. Clinical studies indicate that moderate elevation in production of HbF achieved through heritable persistence of HbF or administration of hydroxyurea, effectively reduce the severity of beta-chain defects. Accordingly, we are exploring strategies to maintain expression of the endogenous gamma-globin genes following lentiviral vector-mediated gene transfer. The artificial zinc-finger transcription factor (GG1-VP64) was designed to interact with sequences in the proximal gamma-globin gene promoters and has been shown to enhance gamma-globin expression in human erythroleukemia cells and mouse marrow cells which are transgenic for the human beta-globin locus. Here, we describe studies designed to evaluate the impact of expression of GG1-VP64 on gamma-globin expression by maturing adult erythroblasts derived from CD34+ cells of normal and thalassemic donors. We utilized an in vitro culture model of human erythropoiesis in which late stage erythroblasts are derived from human CD34+ hematopoietic cells. In this system, cytokine-mobilized peripheral blood or steady state bone marrow CD34+ cells from adults yielded erythroblasts containing 2% or less HbF. The lentiviral vector encodes for bicistronic expression of the GG1-VP64 transactivator and GFP under transcriptional control of the beta-spectrin or ankyrin-1 promoter which give low but progressive increase in expression during erythroid development. Three normal donor CD34+ cells were transduced 48 hours after initiation of culture by overnight exposure to the GG1-VP64 vector or GFP control vector. Approximately 50-60% of the cells were successfully transduced with the control and GG1-VP64 vectors as monitored by flow cytometry analysis for GFP expression. Control vector transduction had no effect on cell proliferation or differentiation monitored by consistent increases in cell numbers and the appearance of CD71 (transferrin receptor) and CD235 (glycophorin A) on most cells (>98% and >80%, respectively) whereas GG1-VP64 gene transfer reduced cell proliferation slightly without affecting erythroid differentiation. Erythroblasts derived from GFP transduced cells expressed low levels of HbF (1.7+/−0.6%) whereas those derived from cells transduced with GG1-VP64 demonstrated induction of HbF ranging from 12-21% with an average vector copy number of 0.8 to 1.0. When cells from a normal donor were sorted into GFP- and GFP+ populations, significant levels of HbF were present only in the GFP+ fraction. We next tested the GG1-VP64 transactivator in three independent studies using bone marrow CD34+ cells from two patients with beta-thalassemia major. Gene transfer was effective as reflected by 74+/−6% (control) and 47+/− 2% (GG1-VP64) GFP marking in bulk cultures. Again, GG1-VP64 gene transfer in beta-thalassemia CD34+ cells reduced cell growth somewhat but did not perturb erythroid differentiation as monitored by the appearance of transferrin receptor (>98%) and Glycophorin A (>80%) as well as cell morphology. Erythroblasts derived from GFP transduced cells expressed levels of HbF in the range of 26+/−5% whereas those derived from cells transduced with GG1-VP64 demonstrated a 2-fold induction of HbF to 52+/−9% with an average vector copy number of 0.5-0.9. Our data show that lentiviral-mediated, enforced expression of GG1-VP64 under the control of erythroid-specific promoters induced significant amounts of HbF in normal and thalassemic erythroblasts derived from adult CD34+ cells without altering their capacity for erythroid maturation following transduction. These observations demonstrate the potential for sequence specific enhancement of HbF in patients with beta-thalassemia or sickle cell anemia. Disclosures:No relevant conflicts of interest to declare.

Lentiviral Vector-Mediated Transfer of the Gamma-Globin Gene Into Normal and Beta-Thalassemic Human CD34+ Cells Results in Potentially Therapeutic Levels of Fetal Hemoglobin in Erythroid Progeny.

Abstract 3579Poster Board III-516Beta-thalassemia results from severely reduced or absent expression of the beta-globin chain of hemoglobin, leading to severe anemia which is dependent upon transfusion for survival. The pathophysiology centers on the alpha- to beta-globin chain imbalance, which results in precipitation of excess alpha chains. These precipitates caused oxidative stress, membrane damage, and apoptosis of erythroid precursors in the bone marrow (BM). Allogeneic stem cell transplant can be curative but is only available to individuals with a matched donor. It is well known that increased levels of fetal hemoglobin (α2γ2;HbF), such as in the case of hereditary persistence of fetal hemoglobin, ameliorate the clinical severity of beta-thalassemia. We therefore developed a self-inactivating (SIN), erythroid-specific, gamma-globin lentiviral vector with the goal of reducing the chain imbalance through the production of HbF in red blood cells following transduction and transplantation of autologous HSCs. The vector, termed V5m3, contains 3.1-kb of transcriptional regulatory sequences from the β-globin locus control region, a 130-bp beta-globin promoter regulating transcription of the gamma-globin gene, and 3′ untranslated sequences from the native beta-globin gene. We previously showed that this vector was effective in correcting mouse models of beta-thalassemia and sickle cell disease (SCD). We further modified V5m3 to include a 400-bp chicken HS4 insulator element. Mobilized peripheral blood (PB)- or steady state bone marrow (BM)-derived CD34+ cells from normal or thalassemic human donors were used to evaluate vector performance. A two-phase in vitro model of human erythropoiesis was used in which a seed population of CD34+ cells is first expanded and then differentiated into late stage erythroblasts over a two week period. Gene transfer is performed 48 hours after initiation of culture. In this model, we routinely observe a 1000-fold expansion in total cell numbers where the vast majority of maturing erythroid cells are late stage erythroblasts reflected by nearly complete enrichment for expression of transferrin receptor (CD71; ≥98%) and glycophorin A (CD235; ≥80%) and loss or reduced expression of CD34 and CD45. Erythroid cells generated from normal adult PB and BM CD34+ cells demonstrate an adult pattern of hemoglobin production (HbA>96%;HbF<2%), as measured by acetate gel electrophoresis and HPLC, making this model ideal to evaluate enhancement of HbF levels by gene transfer. Normal PB CD34+ cells from four independent donors were transduced with the gamma-globin vector (MOI=20) or a GFP control vector (MOI=5). Vector transduction had no effect on cell growth or differentiation as monitored by consistent increases in total cell numbers and the appearance of CD71 (transferrin receptor) and glycophorin A on most cells (≥98% and '80%, respectively). The GFP vector achieved an average transduction rate of 87+/−6% and erythroblasts expressed low levels of HbF (1.7+/−0.6). Gamma globin gene transfer with the V5m3 (N=2) and V5m3-400 (N=4) vectors resulted in HbF levels ranging from 6 to 25%, with an average vector copy number of 0.8 to 1.1. We next tested the V5m3-400 vector using BM CD34+ cells from two patients with beta-thalassemia major. High levels of gene transfer were obtained with both the GFP and the globin vector, as evidenced by bulk marking (74+/−6% GFP+) or PCR analysis of CFU for presence of the V5m3-400 vector (12/12 positive Exp 1); (18/20 Exp 2); (18/24 Exp 3). Again, gene transfer did not perturb erythroid differentiation as monitored by the appearance glycophorin A (88+/−9%; GFP control and 86+/−6%; V5m3-400) as well as cell morphology. Erythroblasts derived from GFP transduced cells had a mean HbF level of 26+/−5% whereas those derived from cells transduced with V5m3-400 demonstrated a 100% increase of HbF to 58+/−2% with an average vector copy number of 0.6-0.8. Importantly, cultures of cells transduced with the globin vector demonstrated an average of 30% reduction in apoptotic cells (10% tunnel+) cells compared to GFP transduced control cells (15% tunnel+), suggesting rescue of erythroblasts through correction of the globin chain imbalance. Our data show that potentially therapeutic levels of HbF in thalassemic erythroblasts can be obtained following gene transfer using a gamma-globin lentiviral vector. Disclosures:No relevant conflicts of interest to declare.

The G9A Histone Methyltransferase BIX-01294 Reactivates ε-Globin Expression and Blocks Erythroid Differentiation in Primary Baboon Erythroid Progenitor Cell Cultures

The development of new therapies to increase fetal hemoglobin (HbF) levels in patients with sickle cell disease and β-thalassemia depends on an increased understanding of the mechanism responsible for the developmental regulation of globin gene expression. A role for epigenetic modifications in the mechanism of of globin gene regulation is suggested by the presence of high levels of DNA methylation near the 5' regions of developmentally silenced ε- and γ-globin genes and the ability of pharmacological inhibitors of DNA methyltransferase (DNMTase) to reactivate ε- and γ-globin expression in adults. Whether additional epigenetic modifications associated with gene silencing and DNA methylation, such as histone H3 (lys9) dimethylation, are also involved is unknown. To investigate the hypothesis that histone H3 (lys9) dimethylation may function in the mechanism of developmental globin gene silencing, chromatin immunopreciptation assays were performed to determine the distribution of histone H3 (lys9) dimethyl and histone H3 (lys9) acetyl throughout the β-globin gene complex in purified primary baboon bone marrow (BM) erythroid cells from phlebotomized baboons expressing low levels (5–10%) of HbF and purified erythroid cells from erythroid progenitor cell cultures expressing high levels of HbF (30–50%). In BM erythroid cells, the level of histone H3 (lys9) acetyl associated with the β-globin gene was 10–20 fold higher than with the ε- and γ-globin genes, while the level of histone H3 (lys9) dimethyl associated with the ε- and γ-globin genes was 2–4 fold higher than with the β-globin gene. In erythroid cells from day 12 erythroid progenitor cell cultures, the level of histone H3 (lys9) acetyl associated with the highly expressed γ- and β-globin genes was 10–20 fold higher than with the silent ε-globin gene, while the level of histone H3 (lys9) dimethyl associated with the ε-globin gene was 2–4 fold higher than with the γ- and β-globin genes. Therefore a reciprocal relationship was observed between levels of histone H3 (lys9) acetylation and dimethylation associated with active and inactive globin genes. Experiments were performed to further investigate the role of histone H3 (lys9) dimethyl in ε-globin gene silencing by determining the effect of the G9A histone methyltransferase inhibitor BIX-01294 on ε-globin expression. Erythroid progenitor cell cultures derived from CD34+ BM cells of three individual baboons were treated with the varying doses of the DNMTase inhibitor decitabine (0.125–1.0μM), and BIX-01294 (1.25–5μM), alone and in combination. Changes in ε- globin were assessed by real time PCR using the ΔΔCT method with α-globin as the standard. Decitabine (0.5μM) increased ε-globin 25.8±7.7 fold while BIX-01294 (2.5μM) increased ε-globin 3.09±1.16 fold. Decitabine (1μM) and BIX-01294 (2.5μM) in combination increased ε-globin 55.7±24.9 fold. BIX-01294 enhanced ε-globin expression approximately twofold at all decitabine doses ranging from 0.125–1.0μM (mean increase=103± 44.7%). BIX-01294 also blocked terminal erythroid differentiation and allowed expansion of more primitive cells as evidenced by the presence of a large population of basophilic erythroblasts at late stages of culture (day 14). These results demonstrate that BIX-01294 reactivates expression of the silenced ε-globin gene and that synergistic reactivation can be achieved using combinations of BIX-01294 and decitabine. While these results are consistent with the hypothesis that epigenetic modifications are important in the mechanism of developmental globin gene silencing, the observation that BIX-01294 blocks erythroid differentiation suggests the possible involvement of a reprogramming mechanism.

Expression of γ-Globin Is Reactivated by a Novel Mechanism in Baboon CD34+ Erythroid Progenitor Cell Cultures.

Elevated levels of fetal hemoglobin (HbF) reduce the symptoms of sickle cell disease and increase the life span of patients. Future pharmacologic therapies to increase HbF will depend on increased knowledge of the mechanism(s) regulating γ-globin gene expression. To investigate the relationship between DNA methylation, chromatin structure, and γ-globin gene regulation, DNA methylation of 5 CpG sites within γ-globin gene promoter, levels of acetyl-histone H3 and H4 and histone H3 lys4 trimethyl throughout the β-globin gene complex, and the pattern of γ-globin polypeptide chain synthesis were analyzed in1.primary baboon fetal liver (FL) erythroid cells,2.primary baboon bone marrow (ABM) erythroid cells from phlebotomized adults expressing low levels of HbF,3.ABM erythroid cells from adults expressing high levels of HbF following treatment in vivo with the DNA demethylating drug decitabine, and4.erythroid cells expressing high levels of HbF generated from CD34+ baboon BM erythroid progenitors in a liquid culture system.High levels of histone acetylation were associated with the ε- and γ-globin genes and low levels with the β-globin gene in FL erythroid cells while in ABM erythroid cells expressing low levels of HbF (6.69±1.93%) high levels were associated with the β-globin gene and low levels with the γ-globin gene. Histone H3 lys 4 trimethyl was enriched near the γ-globin gene in FL and the β-globin gene in ABM. The γ-globin gene was not methylated in FL. The level of methylation was similar in bled (75.1±8.26%) and normal (82.1±7.51%) ABM erythroid cells. The ratio of expression of 5′ Iγ- and 3′ Vγ-globin genes in the fetus (1.85) differed from bled adults (0.65). Expression of γ-globin was reactivated to similar levels in decitabine-treated baboons (51.5±4.50%) and in erythroid progenitor cell cultures (45.3±12.1%; d14). The Iγ- and Vγ-globin chains were expressed at the characteristic fetal ratio in erythroid progenitor cell cultures (1.76±0.21), but not in decitabine-treated baboons (0.76±0.32). Distribution of histone acetylation and histone H3 lys4 trimethyl was nearly identical in erythroid cells expressing high levels of HbF from decitabine-treated animals and from erythroid progenitor cultures and was characterized by high levels of histone H3 lys4 trimethyl associated with both the active γ- and β-globin genes and enrichment of histone H3 and H4 acetylation near the ε-, γ-, and β-globin genes. HbF reactivation in decitabine-treated baboons was associated with a reduction in the level of γ-globin gene methylation (33.5±9.43% dmC). Surprisingly, the level of γ-globin gene methylation in erythroid cells purified from erythroid progenitor cell cultures (79.5±9.80% dmC; d11) synthesizing high levels of γ-globin was not significantly different than in ABM erythroid cells expressing <2% HbF. These results demonstrate that reactivation of γ-globin expression in erythroid progenitor cell cultures is uniquely characterized by the Iγ/Vγ-globin chain ratio of fetal development. In contrast to the absence of γ-globin gene methylation in FL and reduced levels associated with reactivation of HbF following decitabine treatment, the level of γ-globin gene methylation in erythroid progenitor cell cultures was the same as in ABM. Our data strongly suggests that reactivation of γ-globin gene expression in erythroid progenitor cell cultures is achieved through a novel mechanism not dependent on loss of DNA methylation.

Aminophospholipid Translocase Activity and Phosphatidylserine Externalization in Sickle Red Blood Cell Subpopulations.

Red blood cell (RBC) membrane phosphatidylserine (PS) is normally confined to the inner leaflet. In sickle RBC, however, PS externalization has been observed and may contribute to thrombogenesis, endothelial adhesion, and shortened RBC lifespan. Increased calcium leads to PS externalization through inhibition of aminophospholipid translocase (APLT), which normally returns external PS to the inner leaflet, and activation of phospholipid scramblase, which allows nonspecific phospholipid equilibration between the leaflets. Sickle RBC in the light and dense (dehydrated) fractions exhibit increased PS externalization compared to sickle RBC in the normal density fractions. Sickle RBC with modest PS exposure (Type I PS+) occur in both light and dense fractions and, especially in the light fractions, include many reticulocytes. Sickle Cells with high levels of PS exposure (Type II PS+) occur predominantly in the dense fraction. Type II PS+ sickle cells have low levels of HbF, are more adherent than Type I PS+ cells, and tend to increase in number as sickle cells age in the circulation. Dense sickle cells have decreased APLT activity and this has been considered necessary (but probably not sufficient) for PS externalization. In the current studies we have examined the relationship between PS externalization and translocase activity in sickle cell density fractions. APLT activity and PS externalization were determined flow cytometrically using NBD-PS internalization and annexin V-phycoerythrin binding respectively. Sickle RBC density fractions were isolated using a discontinuous Optiprep® gradient, and two fractions were selected for further study, Fx 4 with essentially normal hydration (1.093< g/cc <1.100) and the dehydrated Fx 6 (> 1.120 g/cc). As expected, Fx 6 sickle RBC had a decreased percentage of APLT positive cells (29.9±10.8, N=4) compared to normal RBC (94.5±3.6, N=3) and Fx 4 sickle RBC (92.9±2.3, N=4). Fx 4 contained 5.7±2.8% Type I and 0.3±0.2% Type II PS+ cells. Fx 6 had 9.1±2.5% Type I and 3.2±2.3% Type II PS+ cells. Figure 1 shows the percentage of APLT positive cells in the PS negative (PS-), Type I PS+, and Type II PS+ groups for Fx 4 and Fx 6. Type I PS+ cells in Fx 4 are positive for APLT, whereas those in Fx 6 are mostly negative. In Fx 4, the Type I PS+ group most likely contains many reticulocytes, and in a separate experiment TfR+ reticulocytes had a uniform, slightly elevated APLT activity. The Type II PS+ cells in both Fx 4 and Fx 6 had decreased percentages of APLT positive cells. It thus appears that high levels of PS externalization, regardless of hydration state, are associated with low APLT activity. We therefore conclude:In normally hydrated sickle cells, Type II PS+ cells, but not Type I PS+ cells, are associated with decreased APLT;In dense sickle RBC, both Type I and Type II PS+ cells are associated with decreased APLT. These results further emphasize the pathologic nature of the Type II PS+ sickle cells. [Display omitted]

A New Sequence Change in the Hs2-Lcr (G→A − 10.677) and Gg-Globin Gene Promoter Region (T→C − 157 and a 4 Bp Deletion − 222 to − 225) in Sickle Cell Anemia Patients with Fetal Hemoglobin Level and bS-Globin Gene Haplotypes Diversity.

The sickle cell anemia has a very high prevalence in Bahia, a state of Brazil. The HbF levels and bS-globin gene haplotypes of 125 sickle cell anemia patients were investigated and the Gγ and Aγ gene promoter and HS2-LCR regions of ten patients were selected for DNA sequence. The study was approved by the Oswaldo Cruz Research Foundation's human research ethics committee. The bS- globin gene haplotypes were investigated using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) techniques; the HbF levels were estimated by high performance liquid chromatography (HPLC). The Gg and Ag-globin gene promoter and HS2-LCR regions were sequenced in an automatic sequencer. The distribution of bS- globin gene haplotypes showed 64 (51.2%) patients with genotype CAR/Ben; 36 (28.8%) Ben/Ben; 18 (14.4%) CAR/CAR; two (1.6%) CAR/Aty; two (1.6%) Ben/Cam; one (0.8%) Car/Cam; one (0.8%) CAR/Arab-India and one (0.8%) Sen/Aty. Among these patients, four CAR/CAR had HbF ≥10.0%; three Ben/Ben had HbF ≤ 5.0%; 11 CAR/Ben had HbF ≥15.0% and 18 had HbF ≤ 5.0%; two Cam/Ben patients had HbF levels ≥15.0%. Ten individuals presenting HbF and bS-globin gene haplotypes diversity were selected to sequence the Gg and Ag-globin gene promoter and HS2-LCR regions. The HS2-LCR sequence analyses demonstrated a G→A change (−10.677) (GeneBank DQ873522) in five sickle cell anemia patients with Ben haplotype and high HbF levels (Table 1); the CAR/Ben and Ben/Ben patients with low HbF levels did not have this sequence variation; among the small patient group investigated, there were two CAR/CAR patients with high HbF levels without this substitution. The Gg gene promoter sequence analyses showed a T→C substitution (−157) (GeneBank DQ873521) among all patients and a 4 bp deletion (−222 to −225) (GeneBank DQ873519) related to Cam haplotype (Figure 1). The HS2-LCR sequence change reported here is located in the proximity to a binding site of the GATA-1 and a ubiquitous trans-acting factor and can constitute a motif associated to the Ben chromosome and may play an important role in g-globin gene transcription regulation. The polymorphic site on Gg-globin gene promoter region can be a common sequence characteristic among the Brazilian sickle cell anemia patients. The results described here suggest new polymorphisms in the HS2-LCR and Gg gene promoter and confirms the genotypic heterogeneity among Brazilian sickle cell anemia patients, justifying further studies to investigate its correlation with HbF synthesis and clinical profile in sickle cell anemia patients. [Display omitted]

Hydroxyurea in thalassemia intermedia—a promising therapy

Pharmacological agents such as hydroxyurea (HU) have been known to cause induction of fetal hemoglobin and possibly may alleviate the symptoms in thalassemia intermedia patients. Thirty-seven patients with beta-thalassemia intermedia were enrolled to assess response to HU therapy. Major response was defined as transfusion independence or hemoglobin rise of more than 20 g/l and minor response as rise in hemoglobin of 10-20 g/l or reduction in transfusion frequency by 50%. The median age was 10 years (range: 4-50 years) and median follow-up was 12 months (range: 4-36 months). Twenty-six patients (70.2%) showed response to HU therapy. Seventeen patients (45.9%) were major responders, and nine patients (24.3%) showed minor response. There was no correlation of response with beta-thalassemia mutation or XmnI polymorphism; however, the presence of alpha(3.7) deletion was associated with major response in three patients. Mean fetal hemoglobin (HbF) levels rose on HU therapy. Older age, low baseline F cell percent, and low baseline HbF levels (below 10%) were predictors of poor response. Response was evident within 1 month of starting HU therapy in the majority of responders. Thus, a short trial of HU therapy can predict durable response.

Foetal haemoglobin in homozygous sickle cell disease: a study of patients with low HBF levels.

High foetal haemoglobin (HbF) levels are believed to ameliorate the manifestations of homozygous sickle cell (SS) disease. The corollary implies that patients with low HbF levels should have more severe clinical courses. We investigated this in a retrospective study of 50 Jamaican patients with steady-state HbF levels below 1% compared with a control group (A) of 54 subjects with steady-state HbF levels between 2.5 and 3.4% (around the 25th centile for our population), and a second control group (B) of 60 patients with steady-state HbF levels between 4.6 and 5.2% (around the 50th centile). Comparisons across the groups indicated significantly fewer females in the study group (16, 50 and 57%, respectively). Examination for haematological trends across the groups showed positive linear trends for haemoglobin (Hb) (P=0.004), packed cell volume (PCV) (P=0.01), mean cell volume (MCV) (P= < 0.001), mean cell haemoglobin (MCH) (P= < 0.001) and a negative trend for haemoglobin A2 (P=0.03). Clinically, there were no differences in the incidence of painful crises, abdominal crises and the acute chest syndrome, but leg ulcers were significantly less frequent in the study group (P=0.04). Therefore low HbF levels do not appear to increase the clinical severity of SS disease and may be protective against leg ulceration.

Detection of fetal red cells in fetomaternal hemorrhage using a fetal hemoglobin monoclonal antibody by flow cytometry.

The laboratory determination of the level of fetal cells in maternal circulation remains an important support in the obstetrical management of women with suspected uterine trauma and in the proper dose administration of anti-D for prevention of Rh hemolytic disease of the newborn. Limitations in the sensitivity and precision of the widely used manual Kleihauer-Betke test have prompted an increased utilization of flow cytometric methods for fetal cell detection in maternal blood samples. Murine monoclonal antibodies directed against fetal hemoglobin (HbF) were developed, conjugated to fluorescein isothiocyanate, and used in a multiparametric flow cytometric assay developed for the quantitation of fetal red cells. A rapid intracellular staining method using brief glutaraldehyde fixation and Triton X-100 permeabilization prior to monoclonal antibody incubation was developed, along with optimization of the flow cytometric analysis protocol for the analysis of 50,000 cells. The performance of the assay was assessed for linearity and precision and correlated with the Kleihauer-Betke acid elution method. The anti-HbF flow cytometric method showed good correlation with the Kleihauer-Betke method (r2 = 0.86) and superior precision with a CV < 15 percent for blood samples with > 0.1 percent fetal cells. Analysis of 150 blood samples from nonpregnant adults, including individuals with elevated HbF due to hemoglobinopathies and hereditary persistence of HbF, gave a mean value of 0.02 percent fetal cells, and all results were less than 0.1 percent. The anti-HbF flow cytometric method for detection of fetal cells offers a simple, reliable, and more precise alternative to the Kleihauer-Betke manual technique for the assessment of fetomaternal hemorrhage. The method has additional potential applications for the study of HbF levels or frequency of adult red cells with low levels of HbF (F cells) in individuals with hemoglobinopathies.

Two mutations in the locus control region hypersensitivity site-2 (5′HS-2) of haplotype 19 βs chromosomes alter binding oftrans-acting factors

There are five major haplotypes associated with sickle cell anemia (SS). Individuals homozygous for haplotypes 3 (Senegal) and 31 (Saudi Arabian) have high fetal hemoglobin (HbF) levels (15 to 30% of total hemoglobin) whereas individuals homozygous for haplotypes 17 (Cameroon), 19 (Benin), and 20 (Bantu) have low HbF levels (1 to 10%). We previously identified several point mutations in the LCR 5'HS-2 that were specific for haplotype 19 beta s chromosomes (compared to the GenBank HUMHBB reference sequence, T-->G at position 8580, A-->G at position 8598, and A-->T at position 9114). We postulated that one or more of these mutations may alter the binding of specific trans-acting factors and ultimately affect the expression of HbF in these sickle cell patients. We performed gel mobility shift assays using 32P-end-labeled double-stranded 19mers corresponding to each of the LCR 5'HS-2 normal (GenBank) and mutant sequences. Nuclear extracts prepared from HeLa and HEL cells were used in our experiments and neither the normal nor mutant sequence at position 8580 bound trans-acting factors in either nuclear extract. The 8598 mutant increased binding of Sp1; using purified protein and both nuclear extracts. HEL extracts were used to quantify the increase in Sp1 binding to the 8598 mutation and we found an increase in binding of 66 and 47%, respectively, in two shifted bands. The 9114 mutation sharply decreased binding of an unknown trans-acting factor by 74%. This factor was present in both HeLa and HEL nuclear extracts.

Fetal hemoglobin and potassium in isolated transferrin receptor- positive dense sickle reticulocytes

A subset of sickle cells have an increased density at the reticulocyte stage of development, indicating that they are either abnormally dense upon release from the bone marrow or become dense quickly in the circulation. These cells are of interest because they most likely have severely disrupted cation regulation and a short lifespan. Based on the distribution of fetal hemoglobin (HbF) in the density fractions of sickle red blood cells (RBCs) and in vitro studies of cellular K+ loss, it seems likely that HbF content is an important in vivo determinant of dense cell formation. In this study, we tested the hypothesis that young, dense cells have low HbF content. Sickle RBCs were first separated into light and dense fractions. Reticulocytes were isolated from unfractionated cells and from each density fraction with an immunomagnetic technique directed against transferrin receptors (TfR) and assayed for the percentage of HbF and K+/Hb ratio. TfR+ reticulocytes isolated from unfractionated cells had a much lower HbF content when compared with all the unfractionated RBCs. This is most likely caused by enrichment of F cells because of a longer circulation life span. Heavy TfR+ reticulocytes had a K+/Hb ratio similar to that measured in the entire dense population and contained very low levels of HbF, averaging 2.5% of the level in all RBCs, 11.7% of the level in all TfR+ reticulocytes, and 4.0% of the level in all dense RBCs. These findings suggest that TfR+ dense cells derive predominantly from non-F cells. Furthermore, the amount of HbF in the circulating dense cells suggests that many of these cells do not derive from the TfR+ dense cells.

Fetal Hemoglobin and Potassium in Isolated Transferrin Receptor-Positive Dense Sickle Reticulocytes

A subset of sickle cells have an increased density at the reticulocyte stage of development, indicating that they are either abnormally dense upon release from the bone marrow or become dense quickly in the circulation. These cells are of interest because they most likely have severely disrupted cation regulation and a short lifespan. Based on the distribution of fetal hemoglobin (HbF) in the density fractions of sickle red blood cells (RBCs) and in vitro studies of cellular K+ loss, it seems likely that HbF content is an important in vivo determinant of dense cell formation. In this study, we tested the hypothesis that young, dense cells have low HbF content. Sickle RBCs were first separated into light and dense fractions. Reticulocytes were isolated from unfractionated cells and from each density fraction with an immunomagnetic technique directed against transferrin receptors (TfR) and assayed for the percentage of HbF and K+/Hb ratio. TfR+ reticulocytes isolated from unfractionated cells had a much lower HbF content when compared with all the unfractionated RBCs. This is most likely caused by enrichment of F cells because of a longer circulation life span. Heavy TfR+ reticulocytes had a K+/Hb ratio similar to that measured in the entire dense population and contained very low levels of HbF, averaging 2.5% of the level in all RBCs, 11.7% of the level in all TfR+ reticulocytes, and 4.0% of the level in all dense RBCs. These findings suggest that TfR+ dense cells derive predominantly from non-F cells. Furthermore, the amount of HbF in the circulating dense cells suggests that many of these cells do not derive from the TfR+ dense cells.

Circulating cytokines in sickle cell patients during steady state.

Plasma levels of GM-CSF, IL-3, IL-6 and IL-1 (alpha,beta) were investigated in steady-state sickle cell patients. We find that SS patients with low levels of HbF (< 9% [LFSS]) are characterized by elevated plasma GM-CSF, whereas in patients with high levels of HbF (HFSS), GM-CSF is not detectable. In contrast, HFSS patients exhibited increased plasma IL-3 (m = 84.8 +/- 57 pg/ml), whereas LFSS patients had lower or no detectable plasma IL-3, IL-1(alpha,beta) and IL-6 were also detected in plasma from some SS patients, but there was no correlation with HbF levels. Normal controls tested negative for all cytokines, except for one individual positive for IL-3. These results are compatible with a model in which the level of haemopoietic stress determines the level of participation of GM-CSF or IL-3 in the regulation of SS circulating BFU-E.

Inhomogeneity of the circulating BFU-E regulation in sickle cell anaemia: accessory cells properties and BFU-E growth factor response pattern.

Sickle cell anaemia (SS) patients with low (< 9%) HbF levels (LFSS) are characterized by an increased number of circulating BFU-E in active DNA synthesis, and release of burst promoting activity (BPA) by unstimulated low density (LD) adherent cells. In contrast, circulating BFU-E from SS patients with high (> 9%) HbF levels (HFSS) are normal in number, largely in resting phase, and their LD cells do not release BPA-like activity. We report now that in LFSS patients, adherent cell depletion decreases BFU-E growth in culture and apparent BFU-E cycling. Furthermore, addition of conditioned media (CM) from LD cells of LFSS patients restored cycling BFU-E expression in culture. Neutralization analysis with anti-GM-CSF antibody demonstrated that GM-CSF is, at least, one factor responsible for BPA activity present in this CM. Thus, GM-CSF is constitutively produced by unstimulated monocytes in LFSS patients. In contrast, HFSS patients' adherent cell depletion increases cycling of BFU-E in culture. CM from HFSS patients inhibits BFU-E expression in culture. Hence, LD adherent cells from HFSS patients may release a yet unknown inhibitor factor(s). In addition, we report a distinct response pattern in SS patients' BFU-E to growth factor (GM-CSF, IL-3): (a) LFSS patients have a BFU-E population, equally responsive to GM-CSF and IL-3; (b) HFSS patients, have a subset of BFU-E exclusively dependent on IL-3 (20-40% of the circulating BFU-E). This pattern is very similar to that of normal BFU-E. In conclusion, BFU-E from LFSS patients represent an actively proliferating population, equally responsive to GM-CSF and IL-3, controlled by constitutively produced GM-CSF, suggesting a unique BFU-E behaviour in SS patients with low HbF levels and high haemopoietic stress. The heterogeneous regulation of BFU-E in SS disease seems to be the epiphenomenon of HbF levels, and not vice versa.

Early circulating erythroid progenitors (BFU-E) in sickle cell anemia.

Sickle cell anemia (SS) patients can be divided into two sub-populations according to peripheral HbF levels. Patients with low (< 9%) HbF levels (LFSS) are characterized by an increased number of circulating BFU-E in active DNA synthesis, and release of burst promoting activity (BPA) by unstimulated low density (LD) adherent cells. In contrast, circulating BFU-E from SS patients with high (> 9%) HbF levels (HFSS) are normal in number, largely in resting phase, and their LD cells do not release BPA-like activity. More recently further heterogeneity has been found among these two groups. In LFSS patients GM-CSF is constitutively produced by unstimulated monocytes. In contrast, HFSS patients' adherent cell depletion increases cycling of BFU-E in culture. CM from HFSS patients inhibits BFU-E expression in culture. Hence, LD adherent cells from HFSS patients may release an inhibitory factor(s). The nature of this factor has to be determined. In addition, there are distinct subpopulations of BFU-E responsiveness to growth factor (GM-CSF, IL-3): a) LFSS patients have a homogeneous BFU-E population, equally responsive to GM-CSF and IL-3; b) HFSS patients, in addition to this subpopulation, have a subset of BFU-E dependent exclusively on IL-3 which is 20 to 40% of the total number of circulating BFU-E. This is similar to BFU-E from normal individuals. Hence, LFSS BFU-E represent an actively proliferating population, equally responsive to GM-CSF and IL-3, controlled by at least constitutively produced GM-CSF and possibly other factors. These observations suggest a significant modification in BFU-E behavior in the subset of SS patients with low HbF levels and high hemopoietic stress. The heterogenous regulation of BFU-E in SS disease seems to be an epiphenomenon of HbF levels, and not vice-versa.

A beta-thalassaemia phenotype not linked to the beta-globin cluster in an Italian family.

This paper describes a family of Central Italian origin in which three patients in two generations had either thalassaemia intermedia or a late presenting form of thalassaemia major. Sequence analysis of the patients' DNA revealed that only one of the beta-globin genes was affected by a beta-thalassaemia mutation (the codon 39 nonsense mutation), the other being completely normal, apart from the complex rearrangement (-T +ATA) at position -530 5' to the CAP site of the beta-globin gene, which has uncertain clinical significance. Haematologically, all these patients were characterized by unusually low HbF levels (1.8-7.3%) for a beta-thalassaemia major or intermedia phenotype. The mother of the two patients with thalassaemia intermedia was heterozygous for beta-thalassaemia (codon 39 nonsense mutation), while the father had thalassaemia-like red cell indices, an increased alpha/non alpha chain synthesis ratio, a slight increase of HbF and a low HbA2 level, but showed entirely normal beta-globin gene sequences, apart from the complex rearrangement (-T +ATA) at position -530 5' to the CAP site. One of the thalassaemia intermedia patients married a normal woman and they had a child with thalassaemia major who inherited only the codon 39 nonsense mutation but not the complex rearrangement at position -530. The clinical phenotype of thalassaemia-intermedia or major in the patients from this family may be explained by postulating the inheritance of the double heterozygous state for beta-thalassaemia and for a mutation in a gene coding for an erythroid-specific DNA binding protein which may impair the function of the normal beta-globin gene. Heterozygosity for this postulated mutation (father of the patients with thalassaemia intermedia) may result in the production of a beta-thalassaemia carrier state with normal HbA2 level.

Regional Variations in Sickle Cell Anemia in Saudi Arabia

ABSTRACT We examined mean corpuscular volume (MCV), fetal hemoglobin (HbF) levels, and severity of clinical disease in 81 patients with sickle cell anemia from various regions of Saudi Arabia. We f...