Fetal and embryonic haemoglobins

Epigenetic Regulation of β-Globin Genes and the Potential to Treat Hemoglobinopathies through Epigenome Editing

Beta-like globin gene expression is developmentally regulated during life by transcription factors, chromatin looping and epigenome modifications of the β-globin locus. Epigenome modifications, such as histone methylation/demethylation and acetylation/deacetylation and DNA methylation, are associated with up- or down-regulation of gene expression. The understanding of these mechanisms and their outcome in gene expression has paved the way to the development of new therapeutic strategies for treating various diseases, such as β-hemoglobinopathies. Histone deacetylase and DNA methyl-transferase inhibitors are currently being tested in clinical trials for hemoglobinopathies patients. However, these approaches are often uncertain, non-specific and their global effect poses serious safety concerns. Epigenome editing is a recently developed and promising tool that consists of a DNA recognition domain (zinc finger, transcription activator-like effector or dead clustered regularly interspaced short palindromic repeats Cas9) fused to the catalytic domain of a chromatin-modifying enzyme. It offers a more specific targeting of disease-related genes (e.g., the ability to reactivate the fetal γ-globin genes and improve the hemoglobinopathy phenotype) and it facilitates the development of scarless gene therapy approaches. Here, we summarize the mechanisms of epigenome regulation of the β-globin locus, and we discuss the application of epigenome editing for the treatment of hemoglobinopathies.

Insight of fetal to adult hemoglobin switch: Genetic modulators and therapeutic targets

The clinical heterogeneity of β-hemoglobinopathies is so variable that it prompted the researchers to identify the genetic modulators of these diseases. Though the primary modulator is the type of β-globin mutation which affects the degree of β-globin chain synthesis, the co-inheritance of α-thalassemia and the fetal hemoglobin (HbF) levels also act as potent secondary genetic modifiers. As elevated HbF levels ameliorate the severity of hemoglobinopathies, in this review, the genetic modulators lying within and outside the β-globin gene cluster with their plausible role in governing the HbF levels have been summarised, which in future may act as potential therapeutic targets.

Near-Newtonian Blood Behavior - Is It Good to Be a Camel?

From a certain level of exercise-intensity onward, hematocrit increases in horses, which brings more oxygen carriers into the bloodstream. Camels, however, when used in competitive racing could be even in need of iron supplementation and blood transfusions due to a severe reduction of their available hematocrit compared to their resting hematocrit. Since the extrinsic and intrinsic mechanical properties of camel erythrocytes (RBC) are so different compared to RBCs of other mammals, the question arises whether this observation might be a response to endurance exercise aiming at keeping the RBC count low. Rheometry indicated dromedary camel blood to behave almost Newtonian, which is unique amongst mammals. Shear thinning did increase with the hematocrit, but remained marginal compared to horses. As a result, camel whole blood viscosity (WBV) exceeded horse WBV at high shear rates, an effect, which was significantly augmented when the packed cell volume (PCV) was increased. Therefore, in camels any infusion of RBCs into the bloodstream can increase the cardiac work and the energy input into the endothelium more effectively, which should generate vascular remodeling in the long term. Yielding, however, was completely absent in camel blood, confirming low cohesion between its components at quasi-static flow. Camel blood remained a viscous liquid without a threshold even at unphysiologically high PCVs. This can help to washout lactate when camels start to dehydrate and might contribute to the sustained working ability of these animals. The subtle pseudoplastic behavior and the high viscosity contrast across the RBC membrane point to weak coupling between blood flow and red cell behavior. We predict that RBCs flow as separate entities and can show various types of motion, which can lead to friction instead of being collectively aligned to the flow direction. In comparison to horses, this behavior will become relevant at higher RBC counts in front of flow obstacles and possibly cause vascular remodeling if the PCV rises during strenuous exercise, a matter that should be avoided.

Discrimination Between Infant and Adult Bloodstains Using Micro-Raman Spectroscopy: A Preliminary Study

In the present study, we used micro-Raman spectroscopy with high-resolution analysis to discriminate between bloodstains from infants and bloodstains from adults. Raman peaks were detected at 674, 754, 976, 1002, 1105, 1127, 1176, 1248, 1340, 1368, 1390, 1560, and 1611 cm^-1 ; these peaks were derived from hemoglobin, albumin, and glucose. However, a peak was obtained at 1105 cm^-1 , which was assigned to histidine; this peak was observed only for bloodstains from adults. Human adult hemoglobin (HbA) is composed of an α₂ β₂ tetramer structure, whereas human fetal hemoglobin (HbF) is composed of an α₂ γ₂ . Therefore, the lack of a Raman peak at 1105 cm^-1 in bloodstains from infants indicates the possibility of two histidine substitutions (His116Ile and His143Ser) in the γ chain of HbF. This study discriminates between bloodstains from infants and bloodstains from adults using micro-Raman spectroscopy, with beneficial implications in forensic science.

Epsilon haemoglobin specific antibodies with applications in noninvasive prenatal diagnosis

Invasive procedures for prenatal diagnosis are associated with increased risk of abortion; thus, development of noninvasive procedures would be beneficial. Based on the observation that embryonic nucleated red blood cell (NRBC) crosses the placenta and enters the circulation of pregnant women, the ability to identify such cell would allow development of such procedures. Identification of NRBCs in blood samples would be possible provided that specific antibodies are available. Here we have isolated recombinant antibodies using phage display. From the panel of antibody fragments specifically recognising epsilon-Hb, one was chosen for further characterization, DAb1. DAb1 binds to epsilon-Hb both in Western blots and immunocytochemistry. Several epsilon-Hb positive cells were detected in a blood sample taken as postchorionic villus sampling (CVS). To evaluate the sensitivity of the method, K562 cells (which express epsilon-Hb) were spiked in a blood sample followed by staining in solution and FACS analysis.

High-Throughput Identification of Proteins and Unanticipated Sequence Modifications Using a Mass-Based Alignment Algorithm for MS/MS de Novo Sequencing Results

With the increasing availability of de novo sequencing algorithms for interpreting high-mass accuracy tandem mass spectrometry (MS/MS) data, there is a growing need for programs that accurately identify proteins from de novo sequencing results. De novo sequences derived from tandem mass spectra of peptides often contain ambiguous regions where the exact amino acid order cannot be determined. One problem this poses for sequence alignment algorithms is the difficulty in distinguishing discrepancies due to de novo sequencing errors from actual genomic sequence variation and posttranslational modifications. We present a novel, mass-based approach to sequence alignment, implemented as a program called OpenSea, to resolve these problems. In this approach, de novo and database sequences are interpreted as masses of residues, and the masses, rather than the amino acid codes, are compared. To provide further flexibility, the masses can be aligned in groups, which can resolve many de novo sequencing errors. The performance of OpenSea was tested with three types of data: a mixture of known proteins, a mixture of unknown proteins that commonly contain sequence variations, and a mixture of posttranslationally modified known proteins. In all three cases, we demonstrate that OpenSea can identify more peptides and proteins than commonly used database-searching programs (SEQUEST and ProteinLynx) while accurately locating sequence variation sites and unanticipated posttranslational modifications in a high-throughput environment.

The laboratory evaluation of microcytic red blood cells

Microcytic red blood cell states are common clinical problems in both adult and pediatric age groups. The recent widespread availability of electronic blood cell counters for performing routine blood counts has increased the detection of microcytic red blood cells. Physicians must workup both symptomatic and asymptomatic patients with microcytic red blood cells before they can initiate proper therapy and/or counseling. The purpose of this review is threefold: (1) to discuss the causes of microcytic red blood cells in terms of disorders of decreased heme production vs. disorders of decreased globin production, (2) to review the clinical laboratory tests useful in differentiating microcytic red blood cell states, and (3) to present a practical approach for the laboratory workup of microcytic red blood cells.

The switch from haemoglobin F to A: the time course of qualitative and quantitative variations of haemoglobins after birth

The time course of the transition from HbF to HbA production in the postnatal period has been studied. The description is based on the time-dependent pattern of total haemoglobin and of HbF observed in an 8 months follow-up of 25 premature newborns. The absolute amount of HbF decreases exponentially from birth to approximately 25 weeks (from 15.56 +/- 0.48 g/dl to 0.66 +/- 0.08 g/dl), at a weekly rate of approximately 16%. On the other hand, HbA shows a biphasic pattern: first it decreases slightly from birth to 6 weeks (from 4.09 +/- 0.32 g/dl to 2. 63 +/- 0.33 g/dl); afterwards it increases exponentially at a weekly rate of 5% up to a plateau value, until HbF is almost completely replaced by HbA. Therefore the total haemoglobin decreases exponentially from birth to approximately constant for the next 6 weeks, and thereafter it increases very slowly. From these data, two distinct phases of postnatal erythropoiesis can be identified: the first (from birth to 6 weeks) is characterized by a decrease in the total amount of haemoglobin produced whereas in the second there is an alteration in the relative proportions of HbF and HbA being synthesized.

Gamma chain variants in Jamaican newborns

15,661 cord bloods from Jamaican infants were examined for abnormal hemoglobins using alkaline cellulose acetate electrophoresis for the initial screening, supplemented by acid agar gel electrophoresis for samples exhibiting abnormal hemoglobin bands. Of the 16 electrophoretic variants which were detected, six were fully characterized and found to be: four Hb F Port Royal (alpha2 Ggamma2 125 Glu replaced by Ala) and two Hb F Victoria Jubilee (alpha2Agamma2 80 Asp replaced by Tyr). The Hb F Port Royal samples each constituted about one eighth of the total Hb F as did seven additional samples presumed to be Hb F Port Royal. The infants with this variant exhibited no special hematological characteristics or other consistent associations. Both Hb F Victoria Jubilee samples occurred in somewhat lower proportions of the total Hb F compared with Hb F Port Royal and exhibited an apparent increase of free alpha chains in the whole hemolysate. The data available on detectable gamma chain variants suggest that a specific point mutation may occur in either a HbGgamma or a HbAgamma locus.

The genetic control of protein synthesis: The haemoglobin model

The major steps in haemoglobin synthesis in red cell precursors are now worked out and only details of specific mechanisms remain to be filled in. Thus the major steps in the production of a globin chain are the transcription of large-molecular-weight precursor mRNA (Hn RNA) from the appropriate gene, the cleavage of Hn RNA to produce definitive template mRNA which diffuses into the cell cytoplasm, the processes of chain initiation, translation, and termination, and finally the association of subunits to form a stable tetramer. From what little information there is it appears that this complex series of events is controlled at several levels but that the major control mechanisms are mediated in the processes of transcription rather than translation. There is increasing evidence that the chromatin proteins, particularly the acidic proteins, have specific functions in maintaining areas of DNA repressed and the activation of the haemoglobin loci results from complex interactions with external inducers, the nature of which is not yet known. Virtually nothing is known about the factors involved in the switch from the intrauterine to adult haemoglobins although this appears to be a coordinated event throughout the erythropoietic tissue of the fetus. The isolation and characterization of human mRNA has made possible both the study of the function of thalassaemic mRNA in heterologous systems and , more recently, its quantitation in abnormal red-cell precursors. Furthermore the ability to make cDNA using viral re verse transcriptase has made possible the estimation of the number of haemoglobin genes, both in normal human subjects and in those with different forms of thalassaemia and other genetic disorders of haemoglobin production.