Fig. 5.

CD71⁺Mito⁻ reticulocytes are presented in a majority of MDS patients. a Relative levels of IEX-1 mRNA in human peripheral blood cells in patients and healthy donors. MDS patients with at least a twofold decrease of IEX-1 mRNA compared with the median of healthy controls were defined as MDS patients with low IEX-1. b Reticulocytosis in MDS patients. Peripheral blood cells of healthy donors and MDS patients were stained with CD235a and CD71, followed by flow cytometric analysis. MDS patients exhibited a significantly increased proportion of CD235a⁺CD71⁺ reticulocytes compared to healthy controls independent of IEX-1. c Increased CD71⁺Mito⁻ reticulocytes in MDS patients with a highest level in MDS patients with low IEX-1. d, e Reduced mitochondrial membrane potential Δψ_m in reticulocytes of MDS patients. Mitochondrial membrane potential Δψ_m of CD235a⁺CD71⁺ reticulocytes was analyzed by flow cytometry using JC1 as Fig. 3a (d). Inverse correlations between mitochondrial membrane potential Δψ_m and the percentages of CD71⁺Mito⁻ reticulocytes are analyzed in all healthy donors and MDS patients by coefficient of determination (e). Data represent mean ± SEM, *P < 0.05, **P < 0.01, and ***P < 0.001 compared between indicated groups. (f) A model for CD71 shedding in couple with mitochondrial clearance. Fe³⁺ released from the CD71/Tf complex by a low pH in the endosomes after endocytosis of CD71/Tf-bounded Fe³⁺ is converted to Fe²⁺ by a metalloreductase Steap3 before transported to the cytoplasm by DMT1. An increasing ROS modulates Steap3 activity resulting in a shift of the reductive reaction toward Fe³⁺. A rise of ROS/Fe³⁺ would trigger fusion of the endosomes with MVBs followed by exosome excretion. An increase of ROS would also trigger mitophagy to limit ROS production. Altogether, a couple of CD71 shedding with mitochondrial clearance can effectively minimize the toxicity of Fe³⁺ and ROS during reticulocyte maturation