The Role of IMP1 in Erythropoiesis and the Globin Switch

Abstract

During human development, the globin subunits of haemoglobin undergo two switches: first from embryonic to fetal subunits, and then from fetal to adult subunits. Reactivating fetal globin expression has been proposed as a treatment for patients with sickle cell disease or β-thalassemia.

In this thesis, the proteomes of erythroid cells differentiated from umbilical cord blood and adult peripheral blood CD34+ cells were compared and identified RNA-binding proteins IMP1 and IMP3 as among the most differentially expressed proteins. A previous report showed that overexpression of IMP1 in adult erythroid cells could increase fetal globin expression1. However, the role of IMP1 had not previously been investigated in fetal erythroid cells where it is natively expressed.
shRNA-mediated IMP1 knockdown in the fetal-like HUDEP-1 erythroid cell line increased haemoglobinisation; increased adult β-globin and reduced embryonic ε-globin expression; increased expression of adult marker carbonic anhydrase 1 (CA1) and iron transporter transferrin receptor 2 (TFR2); and reduced expression of fetal marker Arid3A. CRISPR-mediated knockout of IMP1 in the same cell line similarly affected globin, CA1 and TFR2 expression. RNA immunoprecipitation showed that IMP1 could bind to CA1, TFR2 and fetal globin suppressor BCL11A mRNA. This implicates IMP1 in translational regulation of these transcripts.

This thesis also presented the discovery of two populations of IMP1-expressing cells in CB-derived erythroid cells, suggesting these are a mix of fetal- and adult-like cells. Cells were sourced from different stages of human development to determine how fetal or adult CB-derived erythroid cells are, as these are commonly used as a fetal model. Erythroid cells differentiated from 10-17 post-conception week (PCW), 35 PCW, 42 PCW and adult CD34+ cells were compared and developmental differences in terms of expansion, differentiation, globin expression profile and other erythroid cell markers evaluated.

Overall IMP1 has a role in fetal erythropoiesis, particularly in altering TFR2 and CA1 abundance, and maintaining the fetal erythroid cell phenotype.

Date of Award	2 Dec 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Jan Frayne (Supervisor) & Ash M Toye (Supervisor)