Red Blood Cell Size Research Articles

Effect of in vivo and in vitro exposure to electrostatic field on some hematological parameters in rats.

The aim of this study was to investigate the effect of the external electrostatic field (ESF) on some hematological parameters in rats. Both in vivo and in vitro experiments were carried out. In in vivo investigations, rats were exposed to ESF (200 kV/m) during short (1 h) and long periods (6 days, 6 h daily). For in vitro study, the blood of intact rats was exposed to ESF for 1 h. Blood hematology was measured using validated ABX Micros ESV 60 Veterinary Hematology Analyzer. DNA damage in blood leucocytes was detected by means of comet assay. ESF effect on blood cell count was mainly manifested in white blood cells (WBC) and platelets. Damage of WBC was shown both in vitro and in vivo despite alterations in the count. This means the observed increase in WBC count in some cases might be a result of WBC compensatory mobilization from the bone marrow. Red blood cell (RBC) count and related parameters were slightly affected by ESF. Nevertheless, alterations in the shape and size of RBC were manifested. All ESF effects were extinguished in 14 days after the end of exposure. Bioelectromagnetics. 37:513-526, 2016. © 2016 Wiley Periodicals, Inc.

Ancho de distribución eritrocitaria en apnea obstructiva del sueño

IntroductionRed cell distribution width (RDW) describes heterogeneity in the size of red blood cells. An increase in RDW has been associated with excess mortality in heart failure and other chronic diseases. Since there is an increased risk of cardiovascular morbidity and mortality in obstructive sleep apnea (OSA), it is possible that these patients have a high RDW. MethodWe recruited subjects aged 18 to 60 years referred to the sleep-disordered breathing unit for suspected OSA. Subjects with any comorbidity were excluded. Apnea-hypopnea index (AHI) was calculated from the respiratory polygraphy. The RDW was obtained from the complete blood count. Changes in RDW after one year of treatment with continuous positive airway pressure (CPAP) were determined. ResultsWe included 34 healthy subjects and 138 with OSA, aged 40.5±9.8 and 45.6±9.2 (P=.004) years, respectively. The RDW was higher in subjects with OSA compared to healthy subjects: 13.40 (12.40 to 14.40) vs. 13.15 (12.07 to 14.23) (P=.036). AHI showed a positive independent relationship with RDW in both the whole population (r=0.223; P=.002) and the OSA group (r=0.231; P=.005). No significant changes were found in RDW after one year of CPAP therapy. ConclusionsRDW increase in patients with OSA is directly associated with severity, although levels are not modified by the effective treatment of OSA with CPAP.

The Effects of Blood Flow on Blood Vessel Buckling Embedded in Surrounding Soft Tissues

When blood flows in vessel curved portion, the presence of curvature generates a centrifugal force that acts in the same manner as a compressive load. Therefore, blood flow velocity has an important effect on the stability of vessels. In this study, the blood vessel is simulated as a flexible beam conveying fluid base on Euler–Bernoulli beam theory, and various boundary conditions are represented for the modeled vessels. Then, analytical and numerical methods are deployed to extract desired parameters. The effects of blood flow, hematocrit and stiffness of surrounding tissues on the buckling critical pressure are investigated. The results show that the mentioned parameters have considerable effects on blood vessels stability. Several numerical findings illustrate a reduction in critical buckling pressure with increasing hematocrit and blood flow velocity. In addition, the size of red blood cell has a significant effect on critical buckling pressure in low hematocrits. As increasing red blood cell diameter decreases critical buckling pressure. Furthermore, because of blood viscosity, the non-uniformity effects of the blood flow on blood vessels stability are investigated by considering a modification factor. These results improve our understanding of blood vessels instability.

Biomechanics of red blood cells in human spleen and consequences for physiology and disease

Red blood cells (RBCs) can be cleared from circulation when alterations in their size, shape, and deformability are detected. This function is modulated by the spleen-specific structure of the interendothelial slit (IES). Here, we present a unique physiological framework for development of prognostic markers in RBC diseases by quantifying biophysical limits for RBCs to pass through the IES, using computational simulations based on dissipative particle dynamics. The results show that the spleen selects RBCs for continued circulation based on their geometry, consistent with prior in vivo observations. A companion analysis provides critical bounds relating surface area and volume for healthy RBCs beyond which the RBCs fail the "physical fitness test" to pass through the IES, supporting independent experiments. Our results suggest that the spleen plays an important role in determining distributions of size and shape of healthy RBCs. Because mechanical retention of infected RBC impacts malaria pathogenesis, we studied key biophysical parameters for RBCs infected with Plasmodium falciparum as they cross the IES. In agreement with experimental results, surface area loss of an infected RBC is found to be a more important determinant of splenic retention than its membrane stiffness. The simulations provide insights into the effects of pressure gradient across the IES on RBC retention. By providing quantitative biophysical limits for RBCs to pass through the IES, the narrowest circulatory bottleneck in the spleen, our results offer a broad approach for developing quantitative markers for diseases such as hereditary spherocytosis, thalassemia, and malaria.

Morphological arrangement of the coronary vasculature in a shark (Squalus sucklei) and a teleost (Oncorhynchus mykiss).

The coronary circulation is of great importance in maintaining cardiovascular function and consequently it has been extensively studied in many mammalian species. However, much less attention has been paid to the coronary circulation in other vertebrates. For example, while elasmobranch fishes are of special interest as they are the most ancient lineage of vertebrates to possess a coronary circulation, only qualitative studies exist on their coronary circulation and most concern the architecture of the large arteries. Our study tested the prediction that the coronary circulation of sharks is better developed than previously thought. However, to test this idea, a methodology was needed to quantify vascularity, vessel morphology and oxygen diffusion distances in a heart with predominantly spongy myocardium. Here, we describe this methodology using dogfish and rainbow trout and suggest that the dogfish spongy myocardium appears to rely predominantly on the coronary circulation for its oxygen supply, an arrangement that contrasts with the spongy myocardial tissue of rainbow trout. In support of this suggestion, the density of the microvasculature of the spongy myocardial tissue of dogfish exceeded that of their compact tissue. Although vascularity in the compact myocardium of dogfish was significantly lower than trout, intervascular distances were similar on account of a significantly larger vessel diameter in dogfish, which corresponds to a larger red blood cell size of the dogfish when compared to trout. J. Morphol. 277:896-905, 2016. © 2016 Wiley Periodicals, Inc.

The fertile physics of chemical gardens

Many a child has enjoyed watching the gardens grow; many a physicist has puzzled over the transformation of self-organized, nonequilibrium patterns into permanent structures.

Differential diagnosis of anemia in true and functional iron deficiency in patients with chronic diseases (malignant tumors)

To make a differential diagnosis of true and functional iron deficiency (ID) in anemia of chronic diseases (ACD). A total of 540 patients (785 investigations) and 311 healthy individuals (a control group) were examined. Among them, there were 118 cancer patients admitted for surgical treatment and 226 for chemotherapy (CT), 56 blood cancer patients, 86 with breast diseases without anemia, and 54 workers of the institute with the signs of ID. An enzyme immunoassay was used to determine the plasma levels of ferritin (FR), soluble transferrin receptor (sTFR), and endogenous erythropoietin (EPO). 183 cancer patients did not receive specific treatment, 161 had different cycles of CT. In true ID, anemia was microcytic (average red blood cell size, <80.0 fl) and hypochromic (mean corpuscular hemoglobin concentration, <27.0 pg) with low FR levels (less than 20 ng/ml) and high sTFR concentrations (more than 4.0 µg/ml). The EPO level corresponded to the degree of anemia and was 4-5-fold the normal values. In ACDs, 292 (55%) patients had normocytic normochromic anemia with high FR levels (more than 100 ng/ml), the level of sTFR was low and that of EPO did not correspond to the degree of anemia in 74% of the patients. Functional ID was detected in 108 (37%) cancer patients in the presence of ACD. Despite high FR levels and low sTFR, anemia in Hodgkin's and non-Hodgkin's lymphomas was hypochromic microcytic, which may be considered as severe functional ID in ACD. In addition to a clinical blood test, the pharmacokinetic parameters (FR, sRFR, and EPO) should be determined for the differential diagnosis of true and functional ID.

Enhancing cell-free layer thickness by bypass channels in a wall

When blood flows near a wall, red blood cells (RBCs) drift away from the wall and a cell-free layer (CFL) is formed adjacent to the wall. Controlling the CFL thickness is important for preventing adhesion of cells in the design of biomedical devices. In this study, a novel wall configuration with stenoses and bypass channels is proposed to increase the CFL thickness. We found that the presence of bypass channels modified the spatial distribution of cells and substantially increased the CFL downstream of the stenosis. A single-bypass geometry with 5% hematocrit (Hct) blood flow showed a 1.7μm increase in CFL thickness compared to without the bypass. In the case of three bypass channels, a 3μm increase in CFL thickness was observed. The CFL enhancement was observed up to 10% Hct, but no significant enhancement of CFL was indicated for 20% Hct blood flow. The mechanism of the CFL enhancement was investigated using a numerical simulation of the flow field. The results showed that the distance between each streamline and the corner of the stenosis compared with size of RBC was important parameter in regulating CFL thickness. These results show the potential of the proposed mechanism to prevent adhesion of cells to biomedical devices.

Characterisation of Novel Hypomorphic and Null Mutations in Klf1 Derived from a Genetic Screen for Modifiers of a-Globin Transgene Variegation

Position-effect variegation of transgene expression is sensitive to the chromatin state. We previously reported a forward genetic screen in mice carrying a variegated a-globin GFP transgene to find novel genes encoding epigenetic regulators. We named the phenovariant strains "Mommes" for Modifiers of murine metastable epi-alleles. Here we report positional cloning of mutations in two Momme strains which result in suppression of variegation; i.e. an increased percentage of GFP+ circulating red blood cells. Both strains harbour point mutations in the erythroid specific transcription factor, Klf1. One (D11) generates a stop codon in the zinc finger domain. D11 homozygous mice die in utero of anaemia at 14.5DPC. The other (D45) generates an amino acid transversion (H350R) within a conserved linker between zinc fingers two and three. Homozygous MommeD45 mice have mild compensated microcytic anaemia which models the phenotype in a recently described human family. Mice Carrying the H350R mutation were interbred with Klf1+/- mice. Klf1H350R/- mice have severe perinatal haemolytic anaemia and marked splenomegaly. Furthermore blood haemoglobin content, haematocrit and red blood cell size (MCV) were significantly reduced in Klf1H350R/- mice compared to wildtype and D45 homozygous offspring of the same age. Analysis of Klf1H350R/- by flow cytometry showed an increase in circulating immature red blood cells. In the bone marrow, a lack of mature red blood cells was observed. Flow cytometric analysis of the spleen from Klf1H350R/- animals revealed an expansion of erythroid cells and a relative reduction in B and T Cells. Gel shifts assays of a recombinant Klf1 zinc finger protein with the H350R mutation showed normal binding to the b -globin promoter sequence but weak binding to the Alas2 intronic enhancer site. Furthermore b -globin gene expression was near normal whereas expression of other known Klf1 target genes was decreased. We will discuss how H350R disrupts function from ChIP-seq and RNA-seq in primary fetal liver tissue. Previous studies of the linkers in C2H2 zinc finger transcription factors have revealed their necessity as structural and regulatory components for the C2H2 class of transcription factors. Our results thus far show that the second linker of Klf1 has a role in maintaining the integrity of Klf1 function (at a subset of Klf1-occupied sites,) and does not act just as a spacer for the zinc fingers. DisclosuresPerkins:Novartis Oncology: Honoraria.

Validating the measurement of red blood cell diameter in fresh capillary blood by darkfield microscopy: A pilot study

ObjectivesAnalysis of fresh capillary blood using darkfield microscopy involves measuring red blood cell (RBC) diameter to assess for microcytosis or macrocytosis. The reference range for normal RBC diameter currently used in fresh capillary blood analysis by darkfield microscopy (FCB-DM) is the same as that used in haematology, i.e. 6.2–8.2μm. However, the haematology reference range for RBC diameter refers to stained and dried blood specimens. Evidence from early research suggests that fresh RBCs are larger than stained and dried RBCs. The following article presents methodology and findings for the objective measurement of RBC diameter using the FCB-DM technique. MethodsFCB-DM screenings of 14 consenting participants were photographed to permit a quantitative analysis of RBC size and morphology. Participants also provided a venous blood sample for pathology testing, which included markers for RBC size. The researcher was blinded to the pathology results until all FCB-DM data analysis was complete. ResultsAll participants had a normal reference range for all pathology markers tested. The mean RBC diameter, determined by FCB-DM, was 8.51μm (s=0.161, s2=0.026, range=±0.656) and the mode was 8.55μm. ConclusionThese findings support evidence from early studies of RBC diameter, that fresh blood cells observed with darkfield microscopy are approximately 1.3μm larger than dried and stained RBCs. Further research using a larger sample size is recommended.

Red blood cell distribution width and cardiovascular diseases.

The red blood cell distribution width (RDW) is a rather simple measure of red blood cell (RBC) size heterogeneity (i.e., anisocytosis), which is easily calculated by dividing the standard deviation (SD) of erythrocyte volumes for the mean corpuscular volume (MCV). Emerging evidence suggests that, besides RBC abnormalities, many human disorders may be frequently associated with a high degree of anisocytosis. In this narrative review, we analyzed the current scientific literature about the putative role and the potential epidemiologic association between RDW and cardiovascular diseases. The findings of the most representative epidemiological studies were summarized and discussed. Overall, considerable and convincing evidence has been brought that an increased RDW value is associated with acute coronary syndrome (ACS) [including acute myocardial infarction (AMI)], ischemic cerebrovascular disease (including stroke), peripheral artery disease (PAD), as well as with atrial fibrillation (AF), heart failure (HF) and hypertension. Higher anisocytosis also significantly and independently predicts adverse outcomes in patients with these conditions. Although the role of anisocytosis in the pathogenesis of cardiovascular diseases remains uncertain, the considerable evidence available so far suggests that the clinical use of RDW may be broadened beyond the conventional boundaries of erythrocyte disorders, in particular for assisting the diagnosis and prognostication of patients with ACS, ischemic cerebrovascular disease, PAD, HF and AF.

Development of a 3D circular microfluidic centrifuge for the separation of mixed particles by using their different centrifuge times

This paper presents a circular microfluidic centrifuge with two inlets and two outlets to separate mixed microparticles with a specially designed sample injection hole. To separate the mixed particles, it uses a rotational flow, generated in a chamber by counter primary flows in the microchannels. The shape and sizes of the circular microfluidic centrifuge have been designed through numerical evaluation to have a large relative centrifugal force. The difference of centrifuge times of the mixed particles of 1 μm and 6 μm was determined to be 8.2 s at an inlet Reynolds number of 500 and a sample Reynolds number of 20. In the experiment, this was measured to be about 10 s. From the separation of the two polymer particles analogous to the representative sizes of platelets and red blood cells, the circular microfluidic centrifuge shows a potential to separate human blood cells size-selectively by using the difference of centrifuge times.

Red blood cells open promising avenues for longitudinal studies of ageing in laboratory, non-model and wild animals

Ageing is characterized by a progressive deterioration of multiple physiological and molecular pathways, which impair organismal performance and increase risks of death with advancing age. Hence, ageing studies must identify physiological and molecular pathways that show signs of age-related deterioration, and test their association with the risk of death and longevity. This approach necessitates longitudinal sampling of the same individuals, and therefore requires a minimally invasive sampling technique that provides access to the larger spectrum of physiological and molecular pathways that are putatively associated with ageing. The present paper underlines the interest in using red blood cells (RBCs) as a promising target for longitudinal studies of ageing in vertebrates. RBCs provide valuable information on the following six pathways: cell maintenance and turnover (RBC number, size, and heterogeneity), glucose homeostasis (RBC glycated haemoglobin), oxidative stress parameters, membrane composition and integrity, mitochondrial functioning, and telomere dynamics. The last two pathways are specific to RBCs of non-mammalian species, which possess a nucleus and functional mitochondria. We present the current knowledge about RBCs and age-dependent changes in these pathways in non-model and wild species that are especially suitable to address questions related to ageing using longitudinal studies. We discuss how the different pathways relate with survival and lifespan and give information on their genetic and environmental determinants to appraise their evolutionary potential.

Dynamics of biconcave vesicles in a confined shear flow

To study the dynamics of red blood cells (RBCs) in confined shear flows is essential to understand the flow behavior of RBCs in capillaries and in microfluidics, especially when the length scale of the flow is comparable to the RBC size. However, previous studies are focused on RBC dynamics in unbounded shear flows, and only a limited number of cases concern RBC dynamics in confined shear flows by using two-dimensional (2D) vesicle model. Here, we develop a more native-mimicking three-dimensional (3D) model to investigate RBC dynamics in confined shear flows. The present model can reproduce experimental data of the deformation of healthy RBCs under the stretching of optical tweezers. Using the validated model, we find that RBCs in a 3D confined shear flow can exhibit breathing, swinging and tumbling motion. Particularly, breathing and swinging motion were observed in previous 3D simulations of unbounded shear flows, but in previous 2D simulations of confined shear flows only tumbling and tank-treading motion were observed. In confined shear flows, the deformation of RBCs is significantly promoted by increasing the confinement (i.e., the ratio of the RBC size to the channel size), thus breathing motion is preferable over tumbling motion. By increasing confinement alone, the dynamical state of RBCs can transit from the tumbling to the breathing via an intermittent state (i.e., breathing with a weak tumbling). These results provide new insights into the dynamics of RBCs suspended in confined shear flows, and can be helpful for further studies on the dynamics of RBC suspensions in capillaries and in microfluidics.

Effect of variation in hemorheology between human and animal blood on the binding efficacy of vascular-targeted carriers.

Animal models are extensively used to evaluate the in vivo functionality of novel drug delivery systems (DDS). However, many variations likely exist in vivo between the animals and human physiological environment that significantly alter results obtained with animal models relative to human system. To date, it is not clear if the variation in hemorheology and hemodynamics between common animal and human models affect the functionality of DDS. This study investigates the role of hemorheology of humans and various animal models in dictating the binding efficiency of model vascular-targeted carriers (VTCs) to the wall in physiological blood flows. Specifically, the adhesion of sLeA-coated nano- and micro-spheres to inflamed endothelial cells monolayers were conducted via a parallel plate flow chamber assay with steady and disturbed red blood cells (RBCs)-in-buffer and whole blood flows of common animal models. Our results suggest that the ratio of carrier size to RBC size dictate particle binding in blood flow. Additionally, the presence of white blood cells affects the trend of particle adhesion depending on the animal species. Overall, this work sheds light on some deviation in VTC vascular wall interaction results obtained with in vivo animal experimentation from expected outcome and efficiency in vivo in human.

Persistent increase in red cell size distribution width after acute diseases: A biomarker of hypoxemia?

BackgroundA biomarker of hypoxic exposure would be useful in clinical diagnosis and prognosis. Acute hypoxia stimulates large increases in serum erythropoietin (EPO), and EPO induces formation of characteristic enlarged red blood cells (RBCs). The presence of large RBCs perturbs red cell distribution width (RDW). MethodsUsing a >2M patient medical claims database, the human pathome was scanned for diseases where RDW rose 0–50days following a new diagnosis. The course of RDW after selected diagnoses was visualized by registering RDW measurements by diagnosis date. ResultsAcute hemorrhage, which provokes EPO-driven erythropoiesis, is followed by increases in RDW but not mean cell volume (MCV). Similar RDW increases follow many acute diseases with risk of hypoxia, including heart failure, pneumonia, atelectasis, pulmonary embolism, pneumothorax, and sepsis. Elevations reach maximum within 1month after onset and subside to pre-disease levels about 6months later. Unlike the case with iron-deficiency anemia (IDA), RDW elevations after hypoxia-associated diseases are unaccompanied by discernible change in average RBC size. ConclusionsAs predicted by a model risk pathway linking hypoxia to formation of enlarged RBCs via EPO, acute hypoxemia-related disease episodes induce change in RBC size distribution. Further study is needed to explore whether a more sensitive and specific signal can be extracted from the fine structure of the RBC size distribution routinely measured in automated hemocytometers.

Diving Related Changes in the Blood Oxygen Stores of Rehabilitating Harbor Seal Pups (Phoca vitulina).

Harbor seal (Phoca vitulina) pups begin diving within hours of birth, stimulating the development of the blood oxygen (O2) stores necessary to sustain underwater aerobic metabolism. Since harbor seals experience a brief nursing period, the early-life development of these blood O2 stores is necessary for successful post-weaning foraging. If mothers and pups become prematurely separated, the pup may be transported to a wildlife rehabilitation center for care. Previous studies suggest that the shallow pools and lack of diving in rehabilitation facilities may lead to under-developed blood O2 stores, but diving behavior during rehabilitation has not been investigated. This study aimed to simultaneously study the diving behaviors and blood O2 store development of rehabilitating harbor seal pups. Standard hematology measurements (Hct, Hb, RBC, MCV, MCH, MCHC) were taken to investigate O2 storage capacity and pups were equipped with time-depth recorders to investigate natural diving behavior while in rehabilitation. Linear mixed models of the data indicate that all measured blood parameters changed with age; however, when compared to literature values for wild harbor seal pups, rehabilitating pups have smaller red blood cells (RBCs) that can store less hemoglobin (Hb) and subsequently, less O2, potentially limiting their diving capabilities. Wild pups completed longer dives at younger ages (maximum reported <25 days of age: 9 min) in previous studies than the captive pups in this study (maximum <25 days of age: 2.86 min). However, captivity may only affect the rate of development, as long duration dives were observed (maximum during rehabilitation: 13.6 min at 89 days of age). Further, this study suggests that there may be a positive relationship between RBC size and the frequency of long duration dives. Thus, rehabilitating harbor seal pups should be encouraged to make frequent, long duration dives to prepare themselves for post-release foraging.

The impact of acute brucellosis on mean platelet volume and red blood cell distribution.

Background:Brucellosis is an inflammatory disease which may infect any organs or systems in the body. Mean Platelet Volume (MPV) is one of the most frequently used surrogate markers of platelet function. It reveals the presence of disease activity in many inflammatory diseases. Red blood cell distribution width (RDW) is a parameter that measures variation in red blood cell size or red blood cell volume. Its predictive value approves inflammatory and infectious diseases.Objectives:The current study aimed to determine the assessment levels of red blood cell distribution in cases with acute brucellosis.Patients and Methods:The current study investigated whether MPV and RDW played any roles in acute brucellosis diagnosis. The study was conducted from 2008 to 2014 through prospective examination of the inflammatory markers found in adult patients with acute brucellosis.Results:The follow-up within the year after treatment was examined. The values of age, gender, leukocyte count, C-reactive protein, RDW and MPV were recorded. The study included 351 subjects, 250 of them in the acute brucellosis group and 101 in the control group. The mean MPV levels were 7.64 ± 1.30 fL, and 7.67 ± 1.29 fL in the acute brucellosis and control groups, respectively (P > 0.05). The mean CRP levels were 32.57 ± 53.20 mg/dL, and 4.81 ± 4.89 mg/dL in the acute brucellosis and control groups, respectively (P < 0.05). There was no statistically significant difference between the two groups regarding the RDW level and the mean leukocyte count (P > 0.05).Conclusions:While the CRP value was in patients with acute brucellosis in the current study, the MPV, RDW and leukocyte counts were within the normal range. CRP value remains the most valuable inflammatory marker in cases of acute brucellosis.

Heme oxygenase-1 deficiency alters erythroblastic island formation, steady-state erythropoiesis and red blood cell lifespan in mice

Heme oxygenase-1 is critical for iron recycling during red blood cell turnover, whereas its impact on steady-state erythropoiesis and red blood cell lifespan is not known. We show here that in 8- to 14-week old mice, heme oxygenase-1 deficiency adversely affects steady-state erythropoiesis in the bone marrow. This is manifested by a decrease in Ter-119(+)-erythroid cells, abnormal adhesion molecule expression on macrophages and erythroid cells, and a greatly diminished ability to form erythroblastic islands. Compared with wild-type animals, red blood cell size and hemoglobin content are decreased, while the number of circulating red blood cells is increased in heme oxygenase-1 deficient mice, overall leading to microcytic anemia. Heme oxygenase-1 deficiency increases oxidative stress in circulating red blood cells and greatly decreases the frequency of macrophages expressing the phosphatidylserine receptor Tim4 in bone marrow, spleen and liver. Heme oxygenase-1 deficiency increases spleen weight and Ter119(+)-erythroid cells in the spleen, although α4β1-integrin expression by these cells and splenic macrophages positive for vascular cell adhesion molecule 1 are both decreased. Red blood cell lifespan is prolonged in heme oxygenase-1 deficient mice compared with wild-type mice. Our findings suggest that while macrophages and relevant receptors required for red blood cell formation and removal are substantially depleted in heme oxygenase-1 deficient mice, the extent of anemia in these mice may be ameliorated by the prolonged lifespan of their oxidatively stressed erythrocytes.

Genome-wide association study follow-up identifies cyclin A2 as a regulator of the transition through cytokinesis during terminal erythropoiesis.

Genome-wide association studies (GWAS) hold tremendous promise to improve our understanding of human biology. Recent GWAS have revealed over 75 loci associated with erythroid traits, including the 4q27 locus that is associated with red blood cell size (mean corpuscular volume). The close linkage disequilibrium block at this locus harbors the CCNA2 gene that encodes cyclin A2. CCNA2 mRNA is highly expressed in human and murine erythroid progenitor cells and regulated by the essential erythroid transcription factor GATA1. To understand the role of cyclin A2 in erythropoiesis, we have reduced expression of this gene using short hairpin RNAs in a primary murine erythroid culture system. We demonstrate that cyclin A2 levels affect erythroid cell size by regulating the passage through cytokinesis during the final cell division of terminal erythropoiesis. Our study provides new insight into cell cycle regulation during terminal erythropoiesis and more generally illustrates the value of functional GWAS follow-up to gain mechanistic insight into hematopoiesis.