Hong-Yuan Luo

Development of primitive and definitive hematopoiesis from nonhuman primate embryonic stem cells in vitro

Although information about the development of primitive and definitive hematopoiesis has been elucidated in murine embryos and embryonic stem (ES) cells, there have been few in vitro studies of these processes in primates. In this study, we investigated hematopoietic differentiation from cynomolgus monkey ES cells grown on OP9, a stromal cell line deficient in macrophage colony-stimulating factor. Primitive erythrocytes (EryP) and definitive erythrocytes (EryD) developed sequentially from ES cells in the culture system; this was confirmed by immunostaining and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of embryonic, fetal and adult globin genes. EryP were detected on day 8 without exogenous erythropoietin (EPO), whereas EryD appeared on day 16 and had an indispensable requirement for exogenous EPO. RT-PCR analysis of the cultures revealed a sequential expression of genes associated with primitive and definitive hematopoietic development that was equivalent to that seen during primate ontogeny in vivo. Vascular endothelial growth factor (VEGF) increased, in a dose-dependent manner, not only the number of floating hematopoietic cells, but also the number of adherent hematopoietic cell clusters containing CD34-positive immature progenitors. In colony assays, exogenous VEGF also had a dose-dependent stimulatory effect on the generation of primitive erythroid colonies. More efficient primitive and definitive erythropoiesis was induced by re-plating sorted CD34-positive cells. Thus, this system reproduces early hematopoietic development in vitro and can serve as a model for analyzing the mechanisms of hematopoietic development in primates.

A 3-bp deletion in the HBS1L-MYB intergenic region on chromosome 6q23 is associated with HbF expression

Fetal hemoglobin (HbF) is regulated as a multigenic trait. By genome-wide association study, we confirmed that HBS1L-MYB intergenic polymorphisms (HMIP) and BCL11A polymorphisms are highly associated with HbF in Chinese β-thalassemia heterozygotes. In this population, the variance in HbF resulting from the HMIP is 13.5%; that resulting from the BCL11A polymorphism is 6.4%. To identify the functional variant in HMIP, we used 1000 Genomes Project data, single nucleotide polymorphism imputation, comparisons of association results across populations, potential transcription factor binding sites, and analysis of phylogenetic conservation. Based on these studies, a hitherto unreported association between HbF expression and a 3-bp deletion, between 135 460 326 and 135 460 328 bp on chromosome 6q23 was found. This 3-bp deletion is in complete linkage disequilibrium with rs9399137, which is the single nucleotide polymorphism in HMIP most significantly associated with HbF among Chinese, Europeans, and Africans. Chromatin immunoprecipitation assays confirmed erythropoiesis-related transcription factors binding to this region in K562 cells. Based on transient expression of a luciferase reporter plasmid, the DNA fragment encompassing the 3-bp deletion polymorphism has enhancer-like activity that is further augmented by the introduction of the 3-bp deletion. This 3-bp deletion polymorphism is probably the most significant functional motif accounting for HMIP modulation of HbF in all 3 populations.

BCL11A represses HBG transcription in K562 cells.

BCL11A on chromosome 2p16 was recently shown to be a major quantitative trait locus for Hb F level and F-cell number in several populations with or without beta-hemoglobinopathy. We now show that BCL11A isoforms are expressed in K562 cells. Butyrate induction of HBG globin production in K562 is associated with reduced BCL11A. Conversely, augmented expression of BCL11A in K562 cells through transfection of BCL11A expression vector results in more than 50% reduction of HBG promoter transcription activity. This transcription repression can be abrogated by sodium butyrate. BCL11A binds to GGCCGG motif in nucleotide -56 to -51 on the HBG proximal promoter. Together, these data are consistent with BCL11A being able to bind to a core motif in the HBG proximal promoter, recruit and interact with partners to form a repression complex, leading to deacetylation of histones and down-regulation of the HBG transcription.

Unexpectedly low pulse oximetry measurements associated with variant hemoglobins: A systematic review

Pulse oximetry estimates arterial blood oxygen saturation based on light absorbance of oxy‐ and deoxy‐hemoglobin at 660 and 940 nm wavelengths. Patients with unexpectedly low SpO2 often undergo cardio‐pulmonary testing to ascertain the cause of their hypoxemia. However, in a subset of patients, a variant hemoglobin is responsible for low SpO2 measurements. The extent of this problem is unclear. We performed a systematic literature review for reports of low SpO2 associated with variant hemoglobins. We also reviewed unpublished cases from an academic hemoglobin diagnostic reference laboratory. Twenty‐five publications and four unpublished cases were identified, representing 45 patients with low SpO2 and confirmed variant hemoglobin. Fifty‐seven family members of patients had confirmed or suspected variant hemoglobin. Three low oxygen affinity variant hemoglobins had concordantly low SpO2 and SaO2. Eleven variant hemoglobins were associated with unexpectedly low SpO2 measurements but normal SaO2. Hemoglobin light absorbance testing was reported in three cases, all of which showed abnormal absorption spectra between 600 and 900 nm. Seven other variant hemoglobins had decreased SpO2, with unreported or uncertain SaO2. Twenty‐one variant hemoglobins were found to be associated with low SpO2. Most variant hemoglobins were associated with spuriously low SpO2. Abnormal absorption spectra explain the discrepancy between SpO2 and SaO2 for some variants. The differential diagnosis of possible variant hemoglobin ought to be considered in asymptomatic patients found to have unexpectedly low SpO2. The correct diagnosis will help to spare patients from unnecessary investigations and anxiety. Am. J. Hematol., 2010.

Identification and characterization of hemoangiogenic progenitors during cynomolgus monkey embryonic stem cell differentiation

We identified intermediate‐stage progenitor cells that have the potential to differentiate into hematopoietic and endothelial lineages from nonhuman primate embryonic stem (ES) cells. Sequential fluorescence‐activated cell sorting and immunostaining analyses showed that when ES cells were cultured in an OP9 coculture system, both lineages developed after the emergence of two hemoangiogenic progenitor‐bearing cell fractions, namely, vascular endothelial growth factor receptor (VEGFR)‐2high CD34− and VEGFR‐2high CD34+ cells. Exogenous vascular endothelial growth factor increased the proportion of VEGFR‐2high cells, particularly that of VEGFR‐2high CD34+ cells, in a dose‐dependent manner. Although either population of VEGFR‐2high cells could differentiate into primitive and definitive hematopoietic cells (HCs), as well as endothelial cells (ECs), the VEGFR‐2high CD34+ cells had greater hemoangiogenic potential. Both lineages developed from VEGFR‐2high CD34−or VEGFR‐2high CD34+ precursor at the single‐cell level, which strongly supports the existence of hemangioblasts in these cell fractions. Thus, this culture system allows differentiation into the HC and EC lineages to be defined by surface markers. These observations should facilitate further studies both on early developmental processes and on regeneration therapies in human.

Mutations in the paralogous human α-globin genes yielding identical hemoglobin variants

The human α-globin genes are paralogues, sharing a high degree of DNA sequence similarity and producing an identical α-globin chain. Over half of the α-globin structural variants reported to date are only characterized at the amino acid level. It is likely that a fraction of these variants, with phenotypes differing from one observation to another, may be due to the same mutation but on a different α-globin gene. There have been very few previous examples of hemoglobin variants that can be found at both HBA1 and HBA2 genes. Here, we report the results of a systematic multicenter study in a large multiethnic population to identify such variants and to analyze their differences from a functional and evolutionary perspective. We identified 14 different Hb variants resulting from identical mutations on either one of the two human α-globin paralogue genes. We also showed that the average percentage of hemoglobin variants due to a HBA2 gene mutation (α2) is higher than the percentage of hemoglobin variants due to the same HBA1 gene mutation (α1) and that the α2/α1 ratio varied between variants. These α-globin chain variants have most likely occurred via recurrent mutations, gene conversion events, or both. Based on these data, we propose a nomenclature for hemoglobin variants that fall into this category.

Fetal hemoglobin in sickle cell anemia: genetic studies of the Arab-Indian haplotype.

Sickle cell anemia is common in the Middle East and India where the HbS gene is sometimes associated with the Arab-Indian (AI) β-globin gene (HBB) cluster haplotype. In this haplotype of sickle cell anemia, fetal hemoglobin (HbF) levels are 3-4 fold higher than those found in patients with HbS haplotypes of African origin. Little is known about the genetic elements that modulate HbF in AI haplotype patients. We therefore studied Saudi HbS homozygotes with the AI haplotype (mean HbF 19.2±7.0%, range 3.6 to 39.6%) and employed targeted genotyping of polymorphic sites to explore cis- and trans- acting elements associated with high HbF expression. We also described sequences which appear to be unique to the AI haplotype for which future functional studies are needed to further define their role in HbF modulation. All cases, regardless of HbF concentration, were homozygous for AI haplotype-specific elements cis to HBB. SNPs in BCL11A and HBS1L-MYB that were associated with HbF in other populations explained only 8.8% of the variation in HbF. KLF1 polymorphisms associated previously with high HbF were not present in the 44 patients tested. More than 90% of the HbF variance in sickle cell patients with the AI haplotype remains unexplained by the genetic loci that we studied. The dispersion of HbF levels among AI haplotype patients suggests that other genetic elements modulate the effects of the known cis- and trans-acting regulators. These regulatory elements, which remain to be discovered, might be specific in the Saudi and some other populations where HbF levels are especially high.

A T-to-G Transversion at Nucleotide −567 Upstream of HBG2 in a GATA-1 Binding Motif Is Associated with Elevated Hemoglobin F

ABSTRACT Increased fetal hemoglobin (Hb F; α2γ2) production in adults can ameliorate the clinical severity of sickle cell disease and β-thalassemia major. Thus, understanding the regulation of γ-globin gene expression and its silencing in adults has potential therapeutic implications. We studied a father and son in an Iranian-American family who had elevated Hb F levels and found a novel T-to-G transversion at nucleotide (nt) −567 of the HBG2 promoter. This mutation alters a GATA-1 binding motif to a GAGA sequence located within a previously identified silencing element. DNA-protein binding assays showed that the GATA motif of interest is capable of binding GATA-1 transcription factor in vitro and in vivo. Truncation analyses of the HBG2 promoter linked to a luciferase reporter gene revealed a negative regulatory activity present between nt −675 and −526. In addition, the T-to-G mutation at the GATA motif increased the promoter activity by two- to threefold in transiently transfected erythroid cell lines. The binding motif is uniquely conserved in simian primates with a fetal pattern of γ-globin gene expression. These results suggest that the GATA motif under study has a functional role in silencing γ-globin gene expression in adults. The T-to-G mutation in this motif disrupts GATA-1 binding and the associated repressor complex, abolishing its silencing effect and resulting in the up-regulation of γ-globin gene expression in adults.

Sickle cell disease caused by heterozygosity for Hb S and novel LCR deletion: Report of two patients

The b-globin gene LCR is located approximately 6 kb upstream of the embryonic epsilon-globin gene, and is made up of five DNase I hypersensitive sites (HSs), HS 1-5. LCR plays a pivotal role in regulating the expression of downstream epsilon-, (G)gamma-, (A)gamma-, delta-, and beta-globin genes in cis [1]. Deletions removing the LCR and parts of the downstream beta-globin gene cluster in patients have been described [2]. These individuals present with a (gammadeltabeta)0-thalassemia carrier phenotype. We now report two patients with severe sickle cell disease who were compound heterozygous for Hb S mutation and novel LCR deletion. In one case, HS 1-3 were deleted; in the other, HS 1-5 were deleted. In both cases, the b-like globin genes in cis to the LCR deletions were intact. Genotypically, both patients appeared to have sickle cell trait. Coinherited with either LCR deletion, these individuals presented as sickle cell disease patients. The breakpoints of these LCR deletions were defined. These results affirm that HS 2 and 3 are primarily responsible for conferring erythroid specific high-level expression of cis-linked beta-like globin genes. Furthermore, LCR deletions might cause hemolytic disease of newborns.

Hb A2 Hong Kong - A novel δ-globin variant in a chinese family masks the diagnosis of β-thalassemia trait

A 42-year-old Chinese woman (FP) was the mother of a patient with β-thalassemia major (β-TM) due to a compound heterozygosity for β0-thalassemia (β0-thal) mutations. She was also found to have a low Hb A2 level of 1.6% by high performance liquid chromatography (HPLC) despite being a heterozygous carrier of the codons 41/42 (–TCTT) (HBB:c.126_129delCTTT) β0-thal mutation. Doubling the amount of hemolysate loaded for chromatography revealed a widened Hb A2 peak and raised the level to 4.1%, consistent with β-thal trait. Direct nucleotide sequencing detected a novel δ-globin gene mutation at codon 29 (HBD:c.89G>A), which leads to a glycine to aspartic acid substitution. A homologous mutation at codon 29 in the β-globin gene [Hb Lufkin or β29(B11)Gly→Asp] has been reported in Black families. This report highlights the importance of genotype-phenotype correlation and the potential pitfall of relying on Hb A2 level for phenotypic diagnosis of β0-thal trait.