Erythropoiesis and red cell function in vertebrate embryos

Toxicity studies of six types of carbon nanoparticles in a chicken-embryo model

In the present study, the toxicity of six different types of carbon nanoparticles (CNPs) was investigated using a chicken-embryo model. Fertilized chicken eggs were divided into the following treatment groups: placebo, diamond NPs, graphite NPs, pristine graphene, small graphene oxide, large graphene oxide, and reduced graphene oxide. Experimental solutions at a concentration of 500 μg/mL were administrated into the egg albumin. Gross pathology and the rate of survival were examined after 5, 10, 15, and 20 days of incubation. After 20 days of incubation, blood samples were collected and the weight of the body and organs measured. The relative ratio of embryo survival decreased after treatment all treatments except diamond NPs. There was no correlation between the rate of survival and the ζ-potential or the surface charge of the CNPs in solution. Body and organ weight, red blood-cell morphology, blood serum biochemical parameters, and oxidative damage in the liver did not differ among the groups. These results indicate that CNPs can remain in blood circulation without any major side effects, suggesting their potential applicability as vehicles for drug delivery or active compounds per se. However, there is a need for further investigation of their properties, which vary depending on production methods and surface functionalization.

A requirement for Lim domain binding protein 1 in erythropoiesis

Lim domain-binding protein 1, a core subunit of complexes containing Scl, Gata1, and Lmo2, is needed continuously throughout erythropoiesis and megakaryopoiesis in adult mice.

During erythrocyte development, the nuclear cofactor Lim domain binding protein 1 (Ldb1) functions as a core subunit of multiprotein DNA binding complexes that include the transcription factors Scl and Gata-1 and the Lim-only adapter Lmo2. Scl, Gata-1, and Lmo2 are each required for erythropoiesis, suggesting that Ldb1-nucleated transcription complexes regulate key steps during erythropoiesis. We documented a requirement for Ldb1 in erythropoiesis in mice. Analysis of ldb1^−/− embryos revealed a critical requirement for Ldb1 during primitive erythropoiesis, and conditional inactivation of ldb1 at later stages of gestation and in adult mice demonstrated that Ldb1 is continuously required for both definitive erythropoiesis and megakaryopoiesis. Down-regulation of Ldb1 in erythroblasts inhibited the expression of multiple erythroid-specific and prosurvival genes. These results represent the first unequivocal demonstration of a role for Ldb1 in erythropoiesis in vivo and establish a critical function for Ldb1-nucleated complexes in regulating the erythroid/megakaryocyte transcriptional program.

The Hox cofactors Meis1 and Pbx act upstream of gata1 to regulate primitive hematopoiesis

During vertebrate development, the initial wave of hematopoiesis produces cells that help to shape the developing circulatory system and oxygenate the early embryo. The differentiation of primitive erythroid and myeloid cells occurs within a short transitory period, and is subject to precise molecular regulation by a hierarchical cascade of transcription factors. The TALE-class homeodomain transcription factors Meis and Pbx function to regulate embryonic hematopoiesis, but it is not known where Meis and Pbx proteins participate in the hematopoietic transcription factor cascade. To address these questions, we have ablated Meis1 and Pbx proteins in zebrafish, and characterized their molecular effects on known markers of primitive hematopoiesis. Embryos lacking Meis1 and Pbx exhibit a severe reduction in the expression of gata1, the earliest marker of erythroid cell fate, and fail to produce visible circulating blood cells. Concomitant with a loss of gata1, Meis1- and Pbx-depleted embryos exhibit downregulated embryonic hemoglobin (hbae3) expression, and possess increased numbers of pu.1-positive myeloid cells. gata1-overexpression rescues hbae3 expression in Pbx-depleted; meis1-morphant embryos, placing Pbx and Meis1 upstream of gata1 in the erythropoietic transcription factor hierarchy. Our study conclusively demonstrates that Meis1 and Pbx act to specify the erythropoietic cell lineage and inhibit myelopoiesis.

Hemoglobin enhances oxygen uptake in larval zebrafish (Danio rerio) but only under conditions of extreme hypoxia

The role of hemoglobin (Hb) in O2 uptake by zebrafish larvae ranging in age from 5 to 42 days postfertilization was assessed under conditions of normoxia, moderate hypoxia and extreme hypoxia. This was achieved by exposing larvae with and without functional Hb to continuously declining oxygen levels (PO2) in closed-system respirometers. Exposure to 5% CO for 2–4 h was used to render Hb effectively non-functional in terms of its ability to transport O2. Routine metabolic rate(rṀO2), critical dissolved oxygen level (Pc) and residual oxygen level(Pr) were determined and used, respectively, as indicators of response in normoxia, moderate hypoxia and extreme hypoxia. rṀO2 was defined as the average rate of O2 uptake before O2 became limiting (i.e. at high PO2s). Pc is the PO2 at which rṀO2 first becomes O2-limited and Pr is the PO2 below which larvae are no longer able to extract O2 from the ambient medium. CO poisoning had no significant impact on rṀO2 or Pc at any age, indicating that the lack of functional Hb does not impair routine O2 usage in normoxia or at moderate levels of hypoxia [down to at least 25–50 torr (1 torr≈0.133 kPa), depending on age]. Pr, however, was significantly lower overall for control larvae (6.7±1.1 torr; mean ± 95%CI) than for CO-poisoned larvae (11.2±2.1 torr). It would appear that the presence of functional Hb allows zebrafish larvae to extract O2 from water down to lower PO2s under conditions of extreme hypoxia. This is the first documented (as opposed to inferred) benefit of Hb in developing zebrafish. However, given the relatively small magnitude of the effect it is unclear if this benefit on its own is sufficient to balance the costs associated with Hb production and maintenance.

In embryonic chicken erythrocytes actively transcribed alpha globin genes are not associated with the nuclear matrix

The spatial organization of a 250 Kb region of chicken chromosome 14, which includes the alpha globin gene cluster, was studied using in situ hybridization of a corresponding BAC probe with nuclear halos. It was found that in non-erythroid cells (DT40) and cultured erythroid cells of definite lineage (HD3) the genomic region under study was partially (DT40 cells) or fully (HD3 cells) associated with the nuclear matrix. In contrast, in embryonic red blood cells (10-day RBC) the same area was located in the crown of DNA loops surrounding the nuclear matrix, although both globin genes and surrounding house-keeping genes were actively transcribed in these cells. This spatial organization was associated with the virtual absence of RNA polymerase II in nuclear matrices prepared from 10-day RBC. In contrast, in HD3 cells a significant portion of RNA polymerase II was present in nuclear matrices. Taken together, these observations suggest that in embryonic erythroid cells transcription does not occur in association with the nuclear matrix.

`Blood-doping' effects on hematocrit regulation and oxygen consumption in late-stage chicken embryos (Gallus gallus)

The extent to which hematocrit (Hct) is regulated and the impact of altered Hct on blood oxygen transport in avian embryos are largely unknown. Consequently, we investigated how acute blood removal or Ringer solution injection modified Hct in day 15 embryos, and how `blood doping' with erythrocyte-enriched whole blood influenced O2 consumption in day 15–17 chicken embryos. Mean Hct (±s.e.m.) at day 15, 16 and 17 was 26.7±0.6%, 28.0±0.4% and 30.7±0.5%, respectively. Blood withdrawal (19 increments of 125 μl each, separated by 30 min) caused a progressive fall in Hct to ∼12% at day 15. Hct decline was strictly proportional to the extent of blood withdrawal. Incremental Ringer solution injection over an 8 h period, transiently increasing blood volume up to 85%over initial values, did not decrease Hct, indicating that injected Ringer solution rapidly left the circulating blood compartment. Blood doping with erythrocyte-enriched whole blood artificially elevated Hct from 27% to 38%,but caused no significant change in routine O2 consumption(0.35–0.39 ml O2 min–1egg–1) at any point over the subsequent 6 h period in day 15–17 embryos. We conclude that Hct is not protected acutely in day 15 chicken embryos, with no evidence of erythrocyte sequestration or release. Additionally, at day 15–17, Hct increases of ∼10% do not enhance embryonic oxygen consumption, suggesting that blood oxygen carrying capacity per se is not limiting to oxygen consumption.

Insulin-like growth factor-II: a novel autocrine growth factor modulating the apoptosis and maturation of umbilical cord blood erythroid progenitors

OBJECTIVE

To search a novel function of erythroid progenitor cells circulating as the major nucleated cell population in umbilical cord blood (CB) cells.

MATERIALS AND METHODS

Human CB-derived CD36(+) erythroid progenitors were subjected to cDNA microarray. Gene expression and biological property of CB-erythroid progenitors and adult peripheral blood (PB)-erythroid progenitors were compared by using real-time polymerase chain reaction (PCR) and serum-free culture system with erythropoietin (EPO).

RESULTS

The microarray revealed 124-fold higher levels of insulin-like growth factor-II (IGF-II) gene expression in CB-CD36(+) erythroid progenitors than in stimulated lymphocytes of adult PB. Real-time PCR verified that IGF-II mRNA levels were highest in CB-CD36(+) erythroid progenitors compared to other CB- or adult PB-fractionated cells. When CB-CD36(+) erythroid progenitors were cultured with EPO in serum-free medium, anti-IGF-II-antibody (Ab) reduced the number of erythroid colonies. When CB- and adult PB-derived erythroid colony-forming cells (ECFCs) were cultured with interleukin-3, stem cell factor, and EPO, mRNA levels per cells of IGF-II peaked on day 12, but those of type 1 and type 2 receptors did not increase with ECFCs maturation. The maturation rate by IGF-II was higher in CB-ECFCs than in adult PB-ECFCs. The majority of CB-ECFCs expressed IGF-II protein. Anti-IGF-II-Ab, but not anti-IGF-I-Ab, reduced the number of CB-ECFCs in liquid culture with EPO. Anti-IGF-II-Ab accelerated apoptosis of ECFCs, assessed by dimethylthiazole tetrazolium bromide, bromodeoxyuridine, and flow cytometric analyses. ECFCs failed to attain full maturity in the presence of anti-IGF-II-Ab.

CONCLUSIONS

These results suggest that IGF-II is produced by erythroid progenitors themselves, and has a crucial role in fetal erythropoiesis by modulating apoptosis and maturation in an autocrine fashion.

Erythropoietin modulation of podocalyxin and a proposed erythroblast niche

Epo's erythropoietic capacity is ascribed largely to its antiapoptotic actions. In part via gene profiling of bone marrow erythroblasts, Epo is now shown to selectively down-modulate the adhesion/migration factors chemokine receptor-4 (Cxcr4) and integrin alpha-4 (Itga4) and to up-modulate growth differentiation factor-3 (Gdf3), oncostatin-M (OncoM), and podocalyxin like-1 (PODXL). For PODXL, Epo dose-dependent expression of this CD34-related sialomucin was discovered in Kit(+)CD71(high) proerythroblasts and was sustained at subsequent Kit(-)CD71(high) and Ter119(+) stages. In vivo, Epo markedly induced PODXL expression in these progenitors and in marrow-resident reticulocytes. This was further associated with a rapid release of PODXL(+) reticulocytes to blood. As studied in erythroblasts expressing minimal Epo receptor (EpoR) alleles, efficient PODXL induction proved dependence on an EpoR-PY343 Stat5 binding site. Moreover, in mice expressing an EpoR-HM F343 allele, compromised Epo-induced PODXL expression correlated with abnormal anucleated red cell representation in marrow. By modulating this select set of cell-surface adhesion molecules and chemokines, Epo is proposed to mobilize erythroblasts from a hypothesized stromal niche and possibly promote reticulocyte egress to blood.

Inhibition of rats extramedullary liver erytropoiesis by hyperbaric oxygen therapy

PURPOSE: To research the hyperbaric oxygen therapy effects on rats' livers and spleens. METHODS: 30 adult male Hotzman rats were used, being randomly distributed, by raffle, into 2 groups of 15 animals each: group 1 - control; group 2 - hyperbaric oxygen therapy. Group-2 animals underwent hyperbaric oxygen therapy for 120 minutes daily, 90 minutes of which were under pressure of 2.5 atmospheres. The first and last 15 minutes were used for gradual compression and decompression, respectively, for 20 days in a row. The livers and spleens of the animals from the two groups were taken out for histologic examination, on the day after the end of hyperbaric oxygen therapy in group 2 animals. Liver and spleen histologic changes of the animals from the two groups were compared by using Fisher exact test. P < 0.05 was regarded as a significant difference. RESULTS: The only change in liver and spleen histology was the significant reduction in hepatic extramedullary erythropoiesis in the animals that underwent hyperbaric oxygen therapy (p < 0.05). CONCLUSION: Hyperbaric oxygen therapy reduces hepatic extramedullary erythropoiesis in rats and doesn't jeopardize the other liver and spleen structures.