Megakaryocytopoiesis in vitro: from the stem cells' perspective

Iron Deficiency is Associated With Platelet Count Elevation in Patients With Dialysis-dependent Chronic Kidney Disease

OBJECTIVE

Iron deficiency is common in patients with end-stage renal disease (ESRD). Platelet count changes may reflect iron status, but the relationship between platelet count and iron indices is unclear in patients with ESRD.

METHODS

We conducted a retrospective study in 1,167 patients with ESRD from 2012 to 2017 in West China Hospital. Baseline data were used to analyze the relationship between the platelet count and iron indices. Patients were followed up for 3 years.

RESULTS

Patients with iron deficiency (both absolute and functional) had a higher platelet count than those without iron deficiency (174 ± 61 × 10⁹/L vs. 153 ± 58 × 10⁹/L, P < .001). Receiver operating characteristic analysis showed a weak predictive power of platelet count on absolute iron deficiency (area under curve 0.620; cutoff value > 137 × 10⁹/L, sensitivity 76%, specificity 43%) and functional iron deficiency (area under curve 0.540; cutoff value > 124 × 10⁹/L, sensitivity 77%, specificity 32%). Platelet count was negatively correlated with ferritin (Spearman's rho [ρ] -0.1547, P < .001), transferrin saturation (ρ = -0.1895, P < .001), and serum iron (ρ = -0.1466, P < .001). The abovementioned correlations remained significant in multivariate regression (β -0.7285, 95% confidence interval [CI] -1.0757 to -0.3814; β -.00347, 95% CI -0.0520 to -0.0174; β -0.0097, 95% CI -0.0159 to -0.0035, respectively). In unadjusted and adjusted Cox regression models, neither baseline platelet count nor relative thrombocytosis was associated with 3-year mortality.

CONCLUSION

There was a weak but significant platelet count elevation in patients with ESRD and with iron deficiency.

KEY WORDS

end-stage renal disease; iron deficiency; iron supplement; mortality; platelet count.

From brain to blood: alternative splicing evidence for the cholinergic basis of Mammalian stress responses

Three principal features of mammalian stress responses are that they span peripheral and CNS changes, modify blood cell composition and activities, and cover inter-related alterations in a large number of gene products. The finely tuned spatiotemporal regulation of these multiple events suggests the hierarchic involvement of modulatory neurotransmitters and modified process(es) in the pathway of gene expression that together would enable widely diverse stress responses. We report evidence supporting the notion that acetylcholine (ACh) acts as a stress-response-regulating transmitter and that altered ACh levels are variously associated with changes in the alternative splicing of pre-mRNA transcripts in brain neurons and peripheral blood cells. We used acetylcholinesterase (AChE) gene expression as a case study and developed distinct probes for its alternative splice variants at the mRNA and protein levels. In laboratory animals and human-derived cells, we found stress-induced changes in the alternative splicing patterns of AChE pre-mRNA, which attributes to this gene and its different protein products diverse stress responsive functions that are associated with the enzymatic and noncatalytic properties of AChE. Together, these approaches provide a conceptually unified view of the studied pathways for controlling stress responses in brain and blood.

Generation and characterization of human hematopoietic cell lines expressing factor VIII

Considering the plasticity of hematopoietic stem cells (HSC), they would be ideal targets for gene therapy of hemophilia A by virtue of their progeny providing immediate access to the bloodstream. However, several attempts to show expression of recombinant factor VIII (rFVIII) by primary hematopoietic cells and cell lines have failed; this failure was attributed to the inability of HSC to secrete rFVIII. Here we describe the generation of stable, FVIII-secreting hematopoietic cell lines representing different blood-cell types using a bicistronic lentiviral vector encoding for a B-domain-deleted FVIII (FVIII Delta B) and enhanced green fluorescence protein (EGFP). Transduced cell lines with erythroid and/or megakaryocytic background, (K562-F8 and TF-1-F8) secrete high levels of FVIII in the order of 76.4 and 41.6 ng FVIII:C/ml, whereas moderate and low levels are observed in B lymphoblastoid Raji-F8 cells and the T leukemia line Jurkat-F8 which secrete 6.73 and 1.83 ng FVIII:C/ml, respectively. The capacity to secrete rFVIII appeared to depend on factors related to the cell lineage rather than on the transduction efficacy. Stimulation of transduced cells with the protein kinase C (PKC)-activator phorbol myristate acetate (PMA) resulted in a marked augmentation of rFVIII secretion and enhanced green fluorescent protein (EGFP). Incubation with 0.1 and 1 ng/ml PMA resulted in up to 2.7-fold (K562-F8, Raji-F8) and 1.8-fold (293T-F8) increased rFVIII secretion. The established cell lines should be helpful in further elucidating mechanisms that are able to improve FVIII secretion in hematopoietic cells on a post-translational level and suggest reanalysis of hematopoietic cells as target for gene therapy of hemophilia.

Expression and function of NJ-1 surface antigen in megakaryopoiesis

Immunostaining with NJ-1 monoclonal antibody (MoAb) revealed that NJ-1 is expressed on megakaryocytes (MKs). NJ-1-positive and lineage-negative progenitor cells have a higher potency to proliferate and differentiate into MKs. MKs were divided into NJ-1(+)MKs and NJ-1(-)MKs. NJ-1(+)MKs are immature MKs because of their low potential to generate pro-platelets. When cultured CD41-positive MK cells were analyzed with RT-PCR, we found that the expression of NJ-1 is down-regulated. NJ-1(+)MKs have a high adherent potential to endothelial cells comparing with NJ-1(-)MKs, and this binding ability could be inhibited by the NJ-1-Fc fusion protein. We hypothesize that NJ-1(+)MKs are immature MKs and the NJ-1 molecule is involved in MK adhesion to endothelial cells.

Targeted approaches for the treatment of thrombocytopenia

Molecular targeting of novel therapies has the promise of inducing very specific biologic effects. In clinical hematology and oncology, molecular targeting of specific cell surface receptors with erythropoietin, G-CSF, or GM-CSF has been used to stimulate erythropoiesis and granulopoiesis, respectively. Although anemia and neutropenia can be corrected with targeted therapy, safe and effective treatment of thrombocytopenia remains an unmet medical need. While platelet transfusions still represent the standard of care for severe thrombocytopenia, there are several negative aspects associated with their use, including issues of availability, transient effectiveness, costs, adverse effects, negative perception by patients, and infection considerations. Despite extensive investigations of cytokines which act primarily on primitive levels of hematopoiesis, pharmacologic interventions to date have failed to elevate platelet counts in a reliable, highly effective, and well-tolerated fashion. Recombinant human interleukin-11 has been approved by the U.S. Food and Drug Administration for the treatment of chemotherapy-induced thrombocytopenia but has only modest efficacy and significant side effects. The identification of c-Mpl as the thrombopoietin receptor has opened new avenues for the therapeutic manipulation of thrombopoiesis. The development of specific c-Mpl ligands, including recombinant human thrombopoietin (rHuTPO), has allowed investigators to target this receptor for the treatment of chemotherapy-induced thrombocytopenia and other medical disorders characterized by extremely low platelet counts. As a potent stimulator of platelet production, rHuTPO has the potential to reduce the need for platelet transfusions and their attendant complications.

Promegapoietin-1a, an engineered chimeric IL-3 and Mpl-L receptor agonist, stimulates hematopoietic recovery in conventional and abbreviated schedules following radiation-induced myelosuppression in nonhuman primates

Promegapoietin-1a (PMP-1a), a multifunctional agonist for the human interleukin 3 and Mpl receptors, was evaluated for its ability to stimulate hematopoietic reconstitution in nonhuman primates following severe radiation-induced myelosuppression. Animals were total body x-irradiated (250 kVp) to 600 cGy total midline tissue dose. PMP-1a was administered s.c. in several protocols: A) daily (50 microg/kg) for 18 days; B) nine doses (5 microg/kg) every other day for 3 weeks; C) a single high dose (100 microg/kg) at 20 hours, or D) a single high dose (100 microg/kg) at 1 hour following TBI. The irradiation controls received 0.1% autologous serum for 18 consecutive days. Hematopoietic recovery was assessed by bone marrow clonogenic activity, peripheral blood cell nadirs, duration of cytopenias, time to recovery to cellular thresholds, and requirements for clinical support. PMP-1a, irrespective of administration schedule, significantly improved all platelet-related parameters: thrombocytopenia was eliminated, the severity of platelet nadirs was significantly improved, and recovery of platelet counts to > or =20,000/miccrol was significantly reduced in all PMP-1a-treated cohorts. As a consequence, all PMP-1a-treated cohorts were transfusion-independent. Neutrophil regeneration was augmented in all treatment schedules. Additionally, all PMP-1a-treated cohorts showed an improvement in red blood cell nadir and recovery. PMP-1a in conventional or abbreviated schedules induced significant thrombopoietic regeneration relative to the control cohort, whereas significant improvement in neutrophil recovery was schedule-dependent in radiation-myelosuppressed nonhuman primates.

Effects of megakaryocyte growth and development factor (thrombopoietin) on liver endothelial cells in vitro

Thrombopoietin (TPO) is the major regulator of growth and differentiation of megakaryocytes. Recent studies have shown that TPO also has activity on hematopoietic lineages other than megakaryocytes. However, little is known about the effects of TPO on nonhematopoietic cells expressing the TPO receptor, such as endothelial cells (EC). We have previously shown that specific murine liver EC (LEC-1) located in the hepatic sinusoids coexpress TPO and its receptor, c-mpl. Likewise, we showed that TPO has a proliferative effect on LEC-1. In this study, we have further examined the effects of TPO on other biological functions of LEC-1. Stimulation with TPO induced secretion of proinflammatory cytokines (i.e., IL-1beta, IL-6, TNF-alpha) from LEC-1. TPO-induced proliferation of LEC-1 was synergistically enhanced with the addition of TNF-alpha. TPO also induced the proliferation of LEC-1 in the presence of IFN-gamma, which alone inhibited the growth of these cells. TPO has no effect on other endothelial cell functions such as nitric oxide production and adhesion molecule expression. These observations establish a novel activity of TPO on murine liver endothelial cells in terms of inducing cytokine production by these cells. Our results suggest that this cytokine may act synergistically with other cytokines to induce LEC-1 proliferation.