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S. El Hoss et al.
Our findings show that in vitro induction of HbF by pomalidomide rescues SCD erythroblasts from cell death and improves their differentiation, in accordance with improved efficiency of erythropoiesis in vivo in treated SCD mice.39 Furthermore, results using genetically modi- fied CD34+ cells strongly imply that overexpression of HbF and concomitant down-regulation of HbS12 in a spe- cific and selective manner corrects the apoptosis observed during erythroid differentiation, which is therefore presumably a feature of HbS.
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Figure 5. Analysis of human terminal erythroid differentiation in vivo. (A) A contour plot representing the distribution of glycophorin A (GPA)-positive cells with respect to Band 3 (x-axis) and CD49d (y-axis) from a bone marrow sample of a sickle cell disease (SCD) patient. (B) Images obtained using imaging flow cytometry from the gating of polychromatic (Poly) and orthochromatic (Ortho) erythroblasts. Nucleus was stained with Hoechst. (C) Percentage of cells at the early basophilic (EB), late basophilic (LB), polychromatic (Poly) and orthochromatic (Ortho) stages in five bone marrow samples of controls (green) and SCD patients (orange) (means ± stan- dard error of the mean [SEM]). (D) The fold increase of cells between the EB and LB (LB/EB), LB and Poly (Poly/LB), Poly and Ortho (Ortho/Poly) stages in five controls and five SCD patients (means ± SEM). (E) Percentage of cells expressing fetal hemoglobin (F-cells) in vivo in the polychromatic (Poly) and orthochromatic (Ortho) sub- populations of the patient bone marrow samples (n=5) (means ± SEM). (F) Imaging flow cytometry images of early basophilic (EB), late basophilic (LB), polychromatic (Poly) and orthochromatic (Ortho) precursors. Upper images are a merge of brightfield and nucleus, lower images are for fetal hemoglobin (HbF) staining (red). *P<0.05, **P<0.01; Mann-Whitney test (D and E).
HSP70 is a chaperone protein that plays an important role during erythropoiesis by protecting GATA-1 from cleavage by caspase-3 in the presence of Epo,40 thus pro- moting normal terminal differentiation. From a mechanis- tic perspective, sequestration of HSP70 in the cytoplasm through interaction with HbS polymers is therefore a possible mechanism for ineffective erythropoiesis in SCD. Co-immunoprecipitation of HSP70 and HbS under hypoxia is indeed highly suggestive of such interactions between these proteins. Furthermore, specific HSP70
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haematologica | 2021; 106(10)