Supplementary Material for: Association of the Degree of Erythroid Expansion and Maturation Arrest with the Clinical Severity of β⁰-Thalassemia/Hemoglobin E Patients

<b><i>Introduction:</i></b> β-Thalassemia/hemoglobin E represents one-half of all the clinically severe β-thalassemias worldwide. Despite similar genetic backgrounds, patients show clinical heterogeneity ranging from nearly asymptomatic to transfusion-dependent thalassemia. The underlying disease modifying factors remain largely obscure. <b><i>Methods:</i></b> To elucidate the correlation between ineffective erythropoiesis and β⁰-thalassemia/hemoglobin E (HbE) disease severity, in vitro culture of erythroid cells derived from patients with different clinical symptoms was established. Cell proliferation, viability, and differentiation were investigated. To identify potential molecular mechanisms leading to the arrested erythroid maturation, the expression levels of erythropoiesis modifying factors were measured. <b><i>Results:</i></b> The β⁰-thalassemia/HbE cells exhibited enhanced proliferation, limited differentiation, and impaired erythroid terminal maturation but did not show accelerated erythroblast differentiation and increased cell death. Erythroblasts derived from mild patients showed the highest proliferation rate with a faster cell division time, while erythroblasts derived from severe patients displayed extremely delayed erythroid maturation. Downregulation of growth differentiation factor 11 and FOXO3a was observed in mild β⁰-thalassemia/HbE erythroblasts, while upregulation of heat shock protein 70 and activin receptor 2A was revealed in severe erythroblasts. <b><i>Discussion/Conclusion:</i></b> The degree of erythroid expansion and maturation arrest contributes to the severity of β⁰-thalassemia/HbE patients, accounting for the disease heterogeneity. The findings suggest a restoration of erythroid maturation as a promising targeted therapy for severe patients.