PubMed · 3661504
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R A Savage. 1987. One ambiguity.. https://doi.org/10.1093/ajcp%2F88.4.541
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Erythropoietin (EPO) activates many distinct signal transduction cascades on engagement of its receptor. Deletion of the EPO, EPO receptor (EPO-R), or JAK2 genes in mice results in embryonic lethality due to a fatal anemia. EPO activates signal transducer and activator of transcription 1 (STAT1), STAT3, and STAT5a/b transcription factors in erythroid cell lines. Studies have focused on STAT5 as the primary target of EPO-dependent JAK2 activation. However, STAT5a/b(-/-) mice are viable, displaying a nonfatal anemia during embryogenesis, and delayed differentiation in adult erythropoiesis. Importantly, EPO-R cytoplasmic tyrosines are dispensable for viability in vivo. Interestingly, no cytoplasmic tyrosines are required for phosphorylation of STAT1. This led us to examine whether STAT1-deficient mice have altered erythropoiesis. A shift in erythropoiesis was observed in STAT1(-/-) mice, with reduced bone marrow-derived erythroid colony-forming units (CFU-Es) and a compensatory increase in splenic burst-forming units (BFU-Es) and CFU-Es. Both types of splenic-derived cells displayed EPO hyperresponsiveness. A 1.6-fold reduction in total CFU-Es was observed in STAT1-deficient mice, whereas total BFU-Es were comparable. Flow cytometry of STAT1-deficient erythroid cells revealed a less differentiated phenotype, associated with increased apoptosis of early erythroblasts. STAT1-deficient erythroblasts from phenylhydrazine-primed mice displayed enhanced phosphorylation of STAT5a/b, Erk1/2, and protein kinase B (PKB)/Akt. These results illustrate that STAT1 plays an important role in the regulation of erythropoiesis.
BACKGROUND: Anemia is often observed in patients with chronic heart failure (CHF), but its implications for patient outcomes are not well understood. The goal of this study was to investigate the relationship between anemia, severity of CHF, and clinical outcomes. METHODS AND RESULTS: Hemoglobin concentration (Hb) was measured in 912 subjects with CHF enrolled in the Randomized Etanercept North American Strategy to Study Antagonism of Cytokines (RENAISSANCE) trial. In a subgroup of 69 subjects, cardiac MRI was performed at randomization and 24 weeks later. Anemia (Hb < or =12.0 g/dL) was present in 12% of subjects. Cox regression analysis indicated that for every 1-g/dL-higher baseline Hb, the risk of mortality was 15.8% lower (P=0.0009) and the risk of mortality or hospitalization for heart failure was 14.2% lower (P<0.0001). Greater CHF severity was associated with significantly lower Hb concentrations. An increase in Hb over time was associated with a decrease in left ventricular mass and lower mortality, whereas a decrease in Hb over time was associated with an increase in left ventricular mass and higher mortality. In multivariate analysis, anemia remained a significant, independent predictor of death or hospitalization for heart failure, with both outcomes being significantly higher in all NYHA classes. CONCLUSIONS: Anemia is frequently present in patients with CHF. Lower Hb is associated with greater disease severity, a greater left ventricular mass index, and higher hospitalization and mortality rates.
The formation of red blood cells (RBCs) in the bone marrow is regulated by erythropoietin in response to a cascade of events. Anemia in the intensive care unit can be caused by a host of factors. Patients in the intensive care unit may have decreased RBC production and a blunted response to erythropoietin. Administration of recombinant human erythropoietin may stimulate erythropoiesis, increase hematocrit levels and hemoglobin concentration, and reduce the need for RBC transfusions.