Cell Mechanics Based Computational Classification of Red Blood Cells Via Machine Intelligence Applied to Morpho-Rheological Markers

Despite fluorescent cell-labelling being widely employed in biomedical studies, some of its drawbacks are inevitable, with unsuitable fluorescent probes or probes inducing a functional change being the main limitations. Consequently, the demand for and development of label-free methodologies to classify cells is strong and its impact on precision medicine is relevant. Towards this end, high-throughput techniques for cell mechanical phenotyping have been proposed to get a multidimensional biophysical characterization of single cells. With this motivation, our goal here is to investigate the extent to which an unsupervised machine learning methodology, which is applied exclusively on morpho-rheological markers obtained by real-time deformability and fluorescence cytometry (RT-FDC), can address the difficult task of providing label-free discrimination of reticulocytes from mature red blood cells. We focused on this problem, since the characterization of reticulocytes (their percentage and cellular features) in the blood is vital in multiple human disease conditions, especially bone-marrow disorders such as anemia and leukemia. Our approach reports promising label-free results in the classification of reticulocytes from mature red blood cells, and it represents a step forward in the development of high-throughput morpho-rheological-based methodologies for the computational categorization of single cells. Besides, our methodology can be an alternative but also a complementary method to integrate with existing cell-labelling techniques.

Genetic manipulation of cell line derived reticulocytes enables dissection of host malaria invasion requirements

Investigating the role that host erythrocyte proteins play in malaria infection is hampered by the genetic intractability of this anucleate cell. Here we report that reticulocytes derived through in vitro differentiation of an enucleation-competent immortalized erythroblast cell line (BEL-A) support both successful invasion and intracellular development of the malaria parasite Plasmodium falciparum. Using CRISPR-mediated gene knockout and subsequent complementation, we validate an essential role for the erythrocyte receptor basigin in P. falciparum invasion and demonstrate rescue of invasive susceptibility by receptor re-expression. Successful invasion of reticulocytes complemented with a truncated mutant excludes a functional role for the basigin cytoplasmic domain during invasion. Contrastingly, knockout of cyclophilin B, reported to participate in invasion and interact with basigin, did not impact invasive susceptibility of reticulocytes. These data establish the use of reticulocytes derived from immortalized erythroblasts as a powerful model system to explore hypotheses regarding host receptor requirements for P. falciparum invasion.

Plasmodium vivax Infection Impairs Regulatory T-Cell Suppressive Function During Acute Malaria

The balance between pro- and antiinflammatory mechanisms is essential to limit immune-mediated pathology, and CD4+ forkhead box P3 (Foxp3+) regulatory T cells (Treg) play an important role in this process. The expression of inhibitory receptors regulates cytokine production by Plasmodium vivax-specific T cells. Our goal was to assess the induction of programmed death-1 (PD-1) and cytotoxic T-lymphocyte antigen (CTLA-4) on Treg during malaria and to evaluate their function. We found that P. vivax infection triggered an increase in circulating Treg and their expression of CTLA-4 and PD-1. Functional analysis demonstrated that Treg from malaria patients had impaired suppressive ability and PD-1+Treg displayed lower levels of Foxp3 and Helios, but had higher frequencies of T-box transcription factor+ and interferon-gamma+ cells than PD-1-Treg. Thus malaria infection alters the function of circulating Treg by triggering increased expression of PD-1 on Treg that is associated with decreased regulatory function and increased proinflammatory characteristics.

A regenerative erythropoietic response does not increase the frequency of Pig-a mutant reticulocytes and erythrocytes in Sprague-Dawley rats

The in vivo rodent Pig-a mutation assay is a sensitive test to identify exposure to mutagenic substances, and has been proposed as an assay for the identification of impurities for pharmaceuticals. Red blood cells (RBCs) and reticulocytes (RETs) are analyzed by flow cytometry after exposure to potentially mutagenic chemicals for cells deficient in the cell surface anchored protein CD59, representing mutation in the X-linked Pig-a gene. The full potential of the assay as well as its limitations are currently being explored. The current study investigated the effects of regenerative erythropoietic bone marrow responses on the frequency of Pig-a mutated reticulocytes (RET^CD59- ) and erythrocytes (RBC^CD59- ). We hypothesized that a robust regenerative erythropoietic response would not increase the basal frequency of RET^CD59- or RBC^CD59- cells. Two groups of six male Sprague-Dawley rats either had 2 mL of blood sampled each day via an indwelling catheter over a period of 5 days or were minimally sampled for hematology and used as controls. Blood was also then collected and evaluated 5, 18, and 49 days after the initial bleed period for the number of Pig-a mutant cells in either the RET or RBC population. Despite the expected decrease in hematocrit and the correlative increase in reticulocytes after bleeding, no increase in the number of Pig-a mutant cells was observed in male Sprague-Dawley rats that were bled for five consecutive days. These results indicate that changes in erythropoiesis and hematology parameters in rats appear to have no effect on the background levels of Pig-a mutated RETs and RBCs. Environ. Mol. Mutagen. 59:91-95, 2018. © 2017 Wiley Periodicals, Inc.

Antagonists of the system L neutral amino acid transporter (LAT) promote endothelial adhesivity of human red blood cells

The system L neutral amino acid transporter (LAT; LAT1, LAT2, LAT3, or LAT4) has multiple functions in human biology, including the cellular import of S-nitrosothiols (SNOs), biologically active derivatives of nitric oxide (NO). SNO formation by haemoglobin within red blood cells (RBC) has been studied, but the conduit whereby a SNO leaves the RBC remains unidentified. Here we hypothesised that SNO export by RBCs may also depend on LAT activity, and investigated the role of RBC LAT in modulating SNO-sensitive RBC-endothelial cell (EC) adhesion. We used multiple pharmacologic inhibitors of LAT in vitro and in vivo to test the role of LAT in SNO export from RBCs and in thereby modulating RBC-EC adhesion. Inhibition of human RBC LAT by type-1-specific or nonspecific LAT antagonists increased RBC-endothelial adhesivity in vitro, and LAT inhibitors tended to increase post-transfusion RBC sequestration in the lung and decreased oxygenation in vivo. A LAT1-specific inhibitor attenuated SNO export from RBCs, and we demonstrated LAT1 in RBC membranes and LAT1 mRNA in reticulocytes. The proadhesive effects of inhibiting LAT1 could be overcome by supplemental L-CSNO (S-nitroso-L-cysteine), but not D-CSNO or L-Cys, and suggest a basal anti-adhesive role for stereospecific intercellular SNO transport. This study reveals for the first time a novel role of LAT1 in the export of SNOs from RBCs to prevent their adhesion to ECs. The findings have implications for the mechanisms of intercellular SNO signalling, and for thrombosis, sickle cell disease, and post-storage RBC transfusion, when RBC adhesivity is increased.

Monoclonal gammopathy-associated pure red cell aplasia

Pure red cell aplasia (PRCA) is a rare disorder characterized by inhibition of erythroid precursors in the bone marrow and normochromic, normocytic anaemia with reticulocytopenia. Among 51 PRCA patients, we identified 12 (24%) patients having monoclonal gammopathy, monoclonal gammopathy of undetermined significance or smouldering multiple myeloma, with presence of monoclonal protein or abnormal serum free light chains and atypical bone marrow features of clonal plasmacytosis, hypercellularity and fibrosis. Thus far, three patients treated with anti-myeloma based therapeutics have responded with reticulocyte recovery and clinical transfusion independence, suggesting plasma cells play a key role in the pathogenesis of this specific monoclonal gammopathy-associated PRCA.

A Chemical Screening Approach to Identify Novel Key Mediators of Erythroid Enucleation

Erythroid enucleation is critical for terminal differentiation of red blood cells, and involves extrusion of the nucleus by orthochromatic erythroblasts to produce reticulocytes. Due to the difficulty of synchronizing erythroblasts, the molecular mechanisms underlying the enucleation process remain poorly understood. To elucidate the cellular program governing enucleation, we utilized a novel chemical screening approach whereby orthochromatic cells primed for enucleation were enriched ex vivo and subjected to a functional drug screen using a 324 compound library consisting of structurally diverse, medicinally active and cell permeable drugs. Using this approach, we have confirmed the role of HDACs, proteasomal regulators and MAPK in erythroid enucleation and introduce a new role for Cyclin-dependent kinases, in particular CDK9, in this process. Importantly, we demonstrate that when coupled with imaging analysis, this approach provides a powerful means to identify and characterize rate limiting steps involved in the erythroid enucleation process.

Human erythrocyte PIG-A assay: an easily monitored index of gene mutation requiring low volume blood samples

This laboratory has previously described a method for scoring the incidence of rodent blood Pig-a mutant phenotype erythrocytes using immunomagnetic separation in conjunction with flow cytometric analysis (In Vivo MutaFlow®). The current work extends this approach to human blood. The frequencies of CD59- and CD55-negative reticulocytes (RET(CD59-/CD55-)) and erythrocytes (RBC(CD59-/CD55-)) serve as phenotypic reporters of PIG-A gene mutation. Immunomagnetic separation was found to provide an effective means of increasing the number of reticulocytes and erythrocytes evaluated. Technical replicates were utilized to provide a sufficient number of cells for precise scoring while at the same time controlling for procedural accuracy by allowing comparison of replicate values. Cold whole blood samples could be held for at least one week without affecting reticulocyte, RET(CD59-/CD55-) or RBC(CD59-/CD55-) frequencies. Specimens from a total of 52 nonsmoking, self-reported healthy adult subjects were evaluated. The mean frequency of RET(CD59-/CD55-) and RBC(CD59-/CD55-) were 6.0 × 10(-6) and 2.9 × 10(-6), respectively. The difference is consistent with a modest selective pressure against mutant phenotype erythrocytes in the circulation, and suggests advantages of studying both populations of erythrocytes. Whereas intra-subject variability was low, inter-subject variability was relatively high, with RET(CD59-/CD55-) frequencies differing by more than 30-fold. There was an apparent correlation between age and mutant cell frequencies. Taken together, the results indicate that the frequency of human PIG-A mutant phenotype cells can be efficiently and reliably estimated using a labeling and analysis protocol that is well established for rodent-based studies. The applicability of the assay across species, its simplicity and statistical power, and the relatively non-invasive nature of the assay should benefit myriad research areas involving DNA damage, including studies of environmental factors that modify "spontaneous" mutation frequencies.

Supplemental dietary folic acid has no effect on chromosome damage in erythrocyte progenitor cells of mice

Folate deficiency can cause chromosome damage, which could result from reduced de novo thymidylate synthesis or DNA hypomethylation. High folic acid intake has been hypothesized to inhibit folate-dependent one-carbon metabolism, which could also lead to DNA damage. A large proportion of the general population may have high folic acid intakes. In this study, 2 experiments were conducted to examine the effects of folate on chromosome damage. First, male mice were fed folic acid-deficient (D) (0 mg folic acid/kg diet), control (C) (2 mg/kg), or folic acid-supplemented (S) (6 mg folic acid/kg diet) diets from weaning to maturity. Second, female mice were fed the D, C, or S diet throughout pregnancy, lactation, and breeding for 3 generations; male mice from the F3 generation were fed the same diet as their mothers from weaning, producing D, C, and S F3 male mice. RBC micronucleus frequencies, a measure of chromosome damage or aneuploidy, were determined for both experimental groups. In mice fed diets from weaning to maturity, erythrocyte micronucleus frequency was 24% greater in D compared with C mice. F3 mice fed diet D had 260% and 174% greater reticulocyte and erythrocyte micronucleus frequencies compared with F3 C mice, respectively. The S diets did not affect micronucleus frequency, suggesting that excess folic acid at this level does not promote or protect against chromosome damage. The results suggest that chronic exposure to folic acid at the levels similar to those achieved through fortification is unlikely to be clastogenic or aneugenic.

The erythroid niche: molecular processes occurring within erythroblastic islands

Erythroblasts terminally differentiate within specialized niches composed of erythroblast islands nesting in extracellular matrix proteins. A number of adhesion molecules active in erythroid island attachments have been identified. We have recently observed a receptor/counter receptor interaction that appears to maintain island integrity: erythroid ICAM-4 interacting with macrophage alphaV integrin. When ICAM-4/alphaV binding is blocked, a 70% decrease in islands is observed. Moreover, erythroblastic islands are markedly decreased in ICAM-4 null mice. Using erythropoietin to examine whether ICAM-4/alphaV binding plays a role in stress erythropoiesis, we found that the reticulocyte response is different in ICAM-4 null mice compared to control mice. We speculate that this may be a reflection of the baseline decrease in island number in the ICAM-4 null mice. Erythroblast enucleation also occurs within the erythroid niche. Earlier, we examined whether abnormal protein sorting during nuclear extrusion creates the deficiencies of membrane proteins that are well described in hereditary spherocytosis (HS) and hereditary elliptocytosis (HE). We observed that whereas glycophorin C partitions to reticulocytes in normal mouse cells, it sorts to extruding nuclei in murine hereditary elliptocytosis cells. Additionally, in a murine model of hereditary spherocytosis, band 3, glycophorin A and RhAG partition to both nuclei and reticulocytes, while in normal cells these three proteins distribute predominantly to reticulocytes. Hence, it appears that abnormal protein sorting generates specific protein deficiencies in hereditary elliptocytosis and hereditary spherocytosis.

Modular domains of the Dicistroviridae intergenic internal ribosome entry site

The intergenic region internal ribosome entry site (IGR IRES) of the Dicistroviridae viral family can directly assemble 80S ribosomes and initiate translation at a non-AUG codon from the ribosomal A-site. These functions are directed by two independently folded domains of the IGR IRES. One domain, composed of overlapping pseudoknots II and III (PKII/III), mediates ribosome recruitment. The second domain, composed of PKI, mimics a tRNA anticodon-codon interaction to position the ribosome at the ribosomal A-site. Although adopting a common secondary structure, the dicistrovirus IGR IRESs can be grouped into two classes based on distinct features within each domain. In this study, we report on the modularity of the IGR IRESs and show that the ribosome-binding domain and the tRNA anticodon mimicry domain are functionally interchangeable between the Type I and the Type II IGR IRESs. Using structural probing, ribosome-binding assays, and ribosome positioning analysis by toeprinting assays, we show that the chimeric IRESs fold properly, assemble 80S ribosomes, and can mediate IRES translation in rabbit reticulocyte lysates. We also demonstrate that the chimeric IRESs can stimulate the ribosome-dependent GTPase activity of eEF2, which suggests that the ribosome is primed for a step downstream from IRES binding. Overall, the results demonstrate that the dicistrovirus IGR IRESs are composed of two modular domains that work in concert to manipulate the ribosome and direct translation initiation.

Extrusion of Na,K-ATPase and transferrin receptor with lipid raft-associated proteins in different populations of exosomes during reticulocyte maturation in dogs

The present study characterizes canine reticulocyte exosomes. Exosomes are small membrane vesicles involved in membrane remodeling that are released from reticulocytes during the final maturation step of red blood cells. The vesicles collected from reticulocyte culture supernatants by differential centrifugation contained major exosomal proteins including heat shock protein cognate 70 (Hsc70) and transferrin receptors (TfR), consistent with the definition of the exosome. In addition, the Na,K-ATPase alpha-subunit and stomatin, a lipid raft-associated protein, were extruded by the exosome pathway, possibly leading to the absence of these proteins in erythrocytes, while the major protein constituents of erythrocyte membranes, spectrin and band 3 were retained in reticulocytes and not expelled into exosomes. The Na,K-ATPase alpha-subunit, as well as TfR and about half of the stomatin contained in exosomes, was obtained in a detergent-soluble fraction that was distinct from the lipid raft microdomain. Moreover, Na,K-ATPase and a portion of stomatin were distributed differently to Hsc70, TfR, stomatin, and ganglioside GM1 in vesicles separated with sucrose density gradient centrifugation. These results demonstrate that a heterogeneous group of exosomes participates in the loss of Na,K-ATPase and membrane remodeling during reticulocyte maturation in dogs.

Mitochondrial clearance is regulated by Atg7-dependent and -independent mechanisms during reticulocyte maturation

Mitochondrial clearance is a well recognized but poorly understood biologic process, and reticulocytes, which undergo programmed mitochondrial clearance, provide a useful model to study this phenomenon. At the ultrastructural level, mitochondrial clearance resembles an autophagy-related process; however, the role of autophagy in mitochondrial clearance has not been established. Here we provide genetic evidence that autophagy pathways, initially identified in yeast, are involved in mitochondrial clearance from reticulocytes. Atg7 is an autophagy protein and an E1-like enzyme, which is required for the activity of dual ubiquitin-like conjugation pathways. Atg7 is required for the conjugation of Atg12 to Atg5, and Atg8 to phosphatidylethanolamine (PE), and is essential for autophagosome formation. In the absence of Atg7, mitochondrial clearance from reticulocytes is diminished but not completely blocked. Mammalian homologs of Atg8 are unmodified in Atg7(-/-) erythroid cells, indicating that canonical autophagy pathways are inactive. Thus, mitochondrial clearance is regulated by both autophagy-dependent and -independent mechanisms. In addition, mitochondria, which depolarize in wild-type cells before elimination, remain polarized in Atg7(-/-) reticulocytes in culture. This suggests that mitochondrial depolarization is a consequence rather than a cause of autophagosome formation in reticulocytes.

Use of Nramp2-transfected Chinese hamster ovary cells and reticulocytes from mk/mk mice to study iron transport mechanisms

OBJECTIVE

We investigated mechanisms involved in iron (Fe) transport by DMT1 (endosomal Fe(II) exporter, encoded by the Nramp2 gene) using wild-type Chinese hamster ovary (CHO) cells and Nramp2-transfected CHO cells, as well as reticulocytes from normal and mk/mk mice that have a defect in DMT1.

MATERIALS AND METHODS

CHO cells and reticulocytes were incubated with 59Fe bound to various ligands. The radioiron was present in its Fe(II) or Fe(III) forms or bound to transferrin (Tf), and the internalized 59Fe measured under varying experimental conditions. Additionally, 125I-Tf interaction with reticulocytes was investigated and 59Fe incorporation into their heme was determined.

RESULTS

Hyperexpression of DMT1 in CHO cells greatly increases their capacity to acquire ferrous iron. Although CHO-Nramp2 cells showed an increase in Fe(III) uptake as compared to CHO cells, they transported Fe(III) with much lower efficacy than Fe(II). In addition to their defect in Fe uptake, mk/mk reticulocytes also showed a decrease in Tf receptor levels.

CONCLUSIONS

Given that CHO cells acquire iron from Fe(II)-ascorbate with much higher rates than from Fe(III)-Tf, Tf-receptor levels represent the rate-limiting step in their iron uptake. As Fe(III) transport by CHO-Nramp2 cells can be inhibited by the impermeable oxidant K3Fe(CN)6, a membrane ferric reductase is probably needed for reduction of Fe(III) to Fe(II), which is then transported by DMT1. DMT1 is not a limiting factor in Fe acquisition by normal reticulocytes and their heme synthesis.

Modeling time variant distributions of cellular lifespans: increases in circulating reticulocyte lifespans following double phlebotomies in sheep

Many pharmacodynamic (PD) models of cellular response assume a single and time invariant lifespan of all cells, despite the existence of a true underlying distribution of cellular lifespans and known changes in the lifespan distributions with time. To account for these features of cellular populations, a time variant cellular lifespan distribution PD model was formulated and theoretical aspects of modeling cellular populations presented. The model extends prior work assuming time variant "point distributions" of cellular lifespans (Freise et al. J Pharmacokinet Pharmacodyn 34:519-547, 2007) and models assuming a time invariant lifespan distribution (Krzyzanski et al. J Pharmacokinet Pharmacodyn 33:125-166, 2006). The formulated time variant lifespan distribution model was fitted to endogenous plasma erythropoietin (EPO), reticulocyte, and red blood cell (RBC) concentrations in sheep phlebotomized on two occasions, 8 days apart. The time variant circulating reticulocyte lifespan was modeled as a truncated and scaled Weibull distribution, with the location parameter of the distribution non-parametrically represented by an end constrained quadratic spline function. The formulated time variant lifespan distribution model was compared to the identical time invariant distribution, time variant "point distribution", and time invariant "point distribution" cellular lifespan models. Parameters of the time variant lifespan distribution model were well estimated with low standard errors. The mean circulating reticulocyte lifespan was estimated at 0.304 days, which rapidly increased over 3-fold following the first phlebotomy to a maximum of 1.03 days (P = 0.009). On average, the percentage of erythrocytes being released as reticulocytes maximally increased an estimated two-fold following the phlebotomies. The primary features of immature RBC physiology were captured by the model and gave results consistent with other estimates in sheep and humans. The comparison of the four lifespan models gave similar parameter estimates of the stimulation function and fits to the RBC data. However, the time invariant models fit the reticulocyte data poorly, while the time variant "point distribution" cellular lifespan model gave physiologically unrealistic estimates of the changes in the circulating reticulocyte lifespan under stress erythropoiesis. Thus the underlying physiology must be considered when selecting the most appropriate cellular lifespan model and not just the goodness-of-fit criteria. The proposed PD model and the numerical implementation allows for a flexible framework to incorporate time variant lifespan distributions when modeling populations of cells whose production or stimulation depends on endogenous growth factors and/or exogenous drugs.

Evaluation of reticulocyte parameters in iron deficiency, vitamin B(12) deficiency and beta-thalassemia minor patients

The aim of this study was to test the clinical utility of reticulocyte parameters in differential diagnosis in iron deficiency anemia (IDA), vitamin B(12) deficiency (B12) and beta-thalassemia minor (TM). We analyzed the percentage of reticulocyte, absolute reticulocyte count, mean content hemoglobin of reticulocyte (CHr), mean corpuscular volume of reticulocyte (MCVr), corpuscular hemoglobin concentration mean of reticulocyte (CHCMr), MCVr/MCV ratio, CHr/CH ratio and CHCMr/CHCM ratio in healthy donors (n = 34), iron deficiency (IDA) (n = 41), vitamin B(12) deficiency (B12) (n = 22), and TM (n = 34). This study demonstrates that the cutoff value of CHr was 25.7 as indicative of IDA (85.4% sensitivity, 97.1% specificity). CHr and MCVr may be useful for TM (cutoff value < or = 24.8 for CHr) and B12 (>102.1, cutoff value for MCVr), respectively. Sensitivity and specificity of these parameters were 90.9, 86.4% and 97.1, 82.4%, respectively. CHCMr is useful to differentiate IDA and TM from B12. While CHr was low value in microcytic groups (mean 21.8 +/- 3.3 for IDA, 21.0 +/- 2.9 for TM), it was high in B12 (mean 32.1 +/- 5.7). However, that of CHr/CH ratio was only significantly in IDA group compared with the control (P < 0.05, mean 0.98). Therefore, there are limitations regarding CHr and CHr/CH ratio differential diagnosis in microcytic and macrocytic groups. CHr, MCVr, and CHCMr are not sufficiently sensitive and specific to differentiate TM from IDA. We conclude that measurement of reticulocyte count and parameters may be a very useful implement in the diagnosis of IDA and TM.

Reticulocyte haemoglobin content vs. soluble transferrin receptor and ferritin index in iron deficiency anaemia accompanied with inflammation

Ferritin concentration, as a parameter of iron status that is commonly used in the diagnosis of iron deficiency anaemia (IDA), often has limited values if the iron deficiency is accompanied by inflammatory disease. This study evaluated the value of reticulocyte haemoglobin content (CHr) and soluble transferrin receptor-ferritin index (sTfR/F) in the diagnosis of IDA and differential diagnosis of IDA and anaemia of chronic disease. The study included 66 nonanaemic individuals as controls, 86 patients with IDA divided into noninflammatory and inflammatory subgroups, and 32 patients with anaemia of chronic disease. Blood count, iron, transferrin saturation, total iron binding capacity, ferritin, C-reactive protein, sTfR and CHr were determined. Receiver operator characteristic curve analysis showed very high discriminating power for CHr, soluble transferrin receptor (sTfR) and sTfR/F in the diagnosis of IDA. In patients with anaemia of chronic disease these parameters showed no significant difference from the control. CHr and sTfR enabled recognition of iron deficiency and were not affected by acute phase reaction. They are sensitive markers of body iron status with additional value to conventional tests for the detection of iron deficiency.

Method of determination of the reticulocyte age distribution from flow cytometry count by a structured-population model

BACKGROUND

A flow cytometry count of reticulocytes (RET) provides information about distribution of signal emitted by reticulocyte RNA. A new method of determination of the RNA degradation rate in RET is provided. This technique allows one to determinate the age distribution of RET.

METHODS

The method is based on a series of flow cytometry counts of cultured RET. From those counts, the changes of signal distribution of RET over time are obtained. The RNA degradation rate of individual RET is then resolved based on changes in the signal distribution of the whole population of cells. The obtained relation between signal and age allows obtaining a RET age density that can be used to characterize RET age distribution and age dependence of processes that control the population dynamics.

RESULTS

The total maturation time of RET in rats is 3 days. The median time that a homeostatic RET spends in blood or before it becomes a mature RBC is about 0.6 days, whereas a stress RET needs 0.8 days.

CONCLUSIONS

The proposed method provides means for studies in vivo RET dynamics using age-structured models.

Enhanced susceptibility to suicidal death of erythrocytes from transgenic mice overexpressing erythropoietin

Eryptosis, a suicidal death of mature erythrocytes, is characterized by decrease of cell volume, cell membrane blebbing, and breakdown of cell membrane asymmetry with phosphatidylserine exposure at the cell surface. Triggers of eryptosis include increased cytosolic Ca(2+) activity, which could result from activation of Ca(2+)-permeable cation channels. Ca(2+) triggers phosphatidylserine exposure and activates Ca(2+)-sensitive K(+) channels, leading to cellular K(+) loss and cell shrinkage. The cation channels and thus eryptosis are stimulated by Cl(-) removal and inhibited by erythropoietin. The present experiments explored eryptosis in transgenic mice overexpressing erythropoietin (tg6). Erythrocytes were drawn from tg6 mice and their wild-type littermates (WT). Phosphatidylserine exposure was estimated from annexin binding and cell volume from forward scatter in fluorescence-activated cell sorting (FACS) analysis. The percentage of annexin binding was significantly larger and forward scatter significantly smaller in tg6 than in WT erythrocytes. Transgenic erythrocytes were significantly more resistant to osmotic lysis than WT erythrocytes. Cl(-) removal and exposure to the Ca(2+) ionophore ionomycin (1 microM) increased annexin binding and decreased forward scatter, effects larger in tg6 than in WT erythrocytes. The K(+) ionophore valinomycin (10 nM) triggered eryptosis in both tg6 and WT erythrocytes and abrogated differences between genotypes. An increase of extracellular K(+) concentration to 125 mM blunted the difference between tg6 and WT erythrocytes. Fluo-3 fluorescence reflecting cytosolic Ca(2+) activity was larger in tg6 than in WT erythrocytes. In conclusion, circulating erythrocytes from tg6 mice are sensitized to triggers of eryptosis but more resistant to osmotic lysis, properties at least partially due to enhanced Ca(2+) entry and increased K(+) channel activity.

Reticulocyte Maturation Parameters Are Reliable Early Predictors of Hematopoietic Engraftment after Allogeneic Stem Cell Transplantation

Early detection of donor-derived hematopoietic restoration after allogeneic stem cell transplantation (allo-SCT) is a crucial issue in the management of heavily immunocompromised patients. The aim of this prospective study was to validate our previously defined cutoff values for reticulocyte maturation parameters as early predictors of hematopoietic engraftment. Importantly, the effect of clinical variables in reticulocyte engraftment was also sought. For this purpose, we prospectively studied 136 consecutive patients undergoing allo-SCT from related (n = 89) or unrelated (n = 47) donors. High fluorescence reticulocytes (RETH), immature reticulocyte fraction (IRF), mean fluorescence index (MFI), and mean reticulocyte volume (MRV) were automatically measured in peripheral blood samples drawn on a daily basis. We previously defined reticulocyte engraftment when MFI > or =10, RETH > or =3%, IRF > or =10%, and MRV > or =110 fL. Median neutrophil engraftment was 18 days (range, 10-35 days); for reticulocyte parameters, the values were 14 days for IRF (range, 7-45 days), 14 days for MFI (range, 7-43 days), 15 days for RETH (range, 7-43 days), and 21 days for MRV (range, 9-74 days). These differences reached statistical significance for MFI and IRF when compared with standard neutrophil recovery, even when analyzing siblings or unrelated donors separately. In univariate analysis, donor-recipient ABO disparity adversely influenced erythroid engraftment (P = .04 for IRF, P = .03 for MFI), but the infusion of >2.9 x 10(6)/kg of CD34+ cells was associated with a shorter time to reach erythroid engraftment (P = .02 for IRF and MFI). In Cox regression analysis, > or =100/microL neutrophils and IRF > or =10% were predictive parameters for standard neutrophil engraftment. Based on these findings, we suggest that serial measurement of IRF or MFI should be routinely used to trace hematopoietic restoration after allo-SCT because these preceded standard neutrophil recovery by a median of 4 days and are therefore very useful to make clinical decisions.

A detailed study of time-dependent changes in human red blood cells: from reticulocyte maturation to erythrocyte senescence

The use of microfabrication technology in the study of biological systems continues to grow rapidly in both prevalence and ascendancy. Customised microdevices that provide superior results than traditional macroscopic methods can be designed in order to investigate specific cell types and cellular processes. This study showed the benefit of this approach in precisely characterising the progressive losses of surface area and haemoglobin (Hb) content by the human red blood cell (RBC), from newborn reticulocyte to senescent erythrocyte. The high-throughput, multiparametric measurements made on individual cells with a specialised microdevice enabled, for the first time, delineation and quantification of the losses that occur during the two stages of the human RBC lifespan. Data acquired on tens of thousands of red cells showed that nearly as much membrane area is lost during the 1-2 d of reticulocyte maturation (c. 10-14%) as in the subsequent 4 months of erythrocyte ageing (c. 16-17%). The total decrease in Hb over the red cell lifespan is also estimated (c. 15%) and a model describing the complete time-course of diminishing mean RBC area and Hb is proposed. The relationship between the losses of Hb and area, and their possible influence on red cell lifespan, are discussed.

Exosomes: a common pathway for a specialized function

Exosomes are membrane vesicles that are released by cells upon fusion of multivesicular bodies with the plasma membrane. Their molecular composition reflects their origin in endosomes as intraluminal vesicles. In addition to a common set of membrane and cytosolic molecules, exosomes harbor unique subsets of proteins linked to cell type-associated functions. Exosome secretion participates in the eradication of obsolete proteins but several findings, essentially in the immune system, indicate that exosomes constitute a potential mode of intercellular communication. Release of exosomes by tumor cells and their implication in the propagation of unconventional pathogens such as prions suggests their participation in pathological situations. These findings open up new therapeutic and diagnostic strategies.

Assessment of survival of aging erythrocyte in circulation and attendant changes in size and CD147 expression by a novel two step biotinylation method

Three intravenous injections (1mg each) of biotin-X-NHS (BXN) given at 24h intervals labeled all circulating erythrocytes with biotin in C57Bl/6 mice. After 5 days, administration of another i.v. injection of BXN (0.6mg) resulted in the labeling of erythrocytes released in blood circulation after the first biotinylation step, with a lower intensity of biotin. The older erythrocyte population with high intensity of biotin (biotin(high) population) and the later population of newly formed erythrocytes with lower intensity of biotin (biotin(low) population) could be stained with streptavidin-APC (SAv) and identified by flow cytometry. Using the double biotinylation technique, we could examine the survival and age related changes in biotin(low) population of erythrocytes that was released in circulation during a defined time period (5 days). Our results indicate that the percentage of Biotin(low) erythrocytes in circulation remained static for 10 days after the second biotinylation step and than started to decline steadily with time. Mean fluorescence intensity of biotin label on surviving biotin(low) population of erythrocytes however remained stable. These results suggest that after 15 days of release in blood, erythrocytes may undergo random destruction. Furthermore, forward scatter as well as CD147 expression of Biotin(low) population also declined with age. Double biotinylation technique described in this communication offers an easy method for tracking age related changes in populations of erythrocytes released in circulation during a defined period of time.