The equilibrative nucleoside transporter ENT1 is critical for nucleotide homeostasis and optimal erythropoiesis

Abstract

The tight regulation of intracellular nucleotides is critical for the self-renewal and lineage specification of hematopoietic stem cells (HSCs). Nucleosides are major metabolite precursors for nucleotide biosynthesis and their availability in HSCs is dependent on their transport through specific membrane transporters. However, the role of nucleoside transporters in the differentiation of HSCs to the erythroid lineage and in red cell biology remains to be fully defined. Here, we show that the absence of the equilibrative nucleoside transporter (ENT1) in human red blood cells (RBCs) with a rare Augustine-null blood type (AUG:-1) is associated with macrocytosis, anisopoikilocytosis, an abnormal nucleotide metabolome, and deregulated protein phosphorylation. A specific role for ENT1 in human erythropoiesis was demonstrated by a defective erythropoiesis of human CD34+ progenitors following shRNA-mediated knockdown of ENT1. Furthermore, genetic deletion of ENT1 in mice was associated with reduced erythroid progenitors in the bone marrow, anemia and macrocytosis. Mechanistically, we found that ENT1-mediated adenosine transport is critical for cAMP homeostasis and the regulation of erythroid transcription factors. Notably, genetic investigation of two ENT1null individuals demonstrated a compensation by a loss-of-function variant in the ABCC4 cyclic nucleotide exporter. Indeed, pharmacological inhibition of ABCC4 in Ent1-/- mice rescued erythropoiesis. Overall, our results highlight the importance of ENT1-mediated nucleotide metabolism in erythropoiesis.

Augustine Blood Group System and Equilibrative Nucleoside Transporter 1

“…Absence of ENT1 in individuals with the AUG null phenotype is associated with misshapen red cells (macrocytosis, anisopoikilocytosis) and with deregulated protein phosphorylation, but no shortening of red cell lifespan. In addition, defective in vitro erythropoiesis of human CD34 + progenitors derived from individuals with normal ENT1 expression occurred following shRNA-mediated knockdown of ENT1, confirming that reduction of ENT1 in human erythroid progenitors impedes erythropoiesis [33].…”

“…GATA transcription factors, which actuate genetic networks in HSCs, erythroid precursor cells, and other erythroid cells [31], regulate many membrane transporters, including ENT1 during erythropoiesis [32]. Slc29a1−/− mice had macrocytosis, anaemia, and reduced numbers of erythroid progenitors in the bone marrow [33]. In an acute anaemia mouse model, an Slc29a1dependent mechanism promoted erythroblast survival and differentiation and reduced anaemia [32].…”

“…Analysis of AUG null individuals has revealed that ENT1 deficiency results in defective human erythropoiesis, although anaemia was not apparent [33]. Absence of ENT1 in individuals with the AUG null phenotype is associated with misshapen red cells (macrocytosis, anisopoikilocytosis) and with deregulated protein phosphorylation, but no shortening of red cell lifespan.…”

Ticagrelor-Pretreated Cardiomyocyte Derived Exosomes Provide Cardioprotection Under Hyperglycemia Through Alleviation In Oxidative Stress, Apoptosis, And ER-Stress

“…Superoxide production is also associated with ENT1, while ENT1 plays a central role in the determination of the extracellular content of adenosine, which is generated extracellularly by the degradation of ATP 37 .…”

Nucleoside ENTry modulates erythropoiesis

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In this issue of Blood, Mikdar et al show that deficiency of ENT1, a nucleoside transporter, leads to defects in erythropoiesis and morphological changes in erythrocytes. 1

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