Activation of γ-globin expression by hypoxia-inducible factor 1α

Area of Science:

• Hematology
• Molecular Biology
• Genetics

Background:

• Human red blood cells (RBCs) normally switch from fetal hemoglobin (HbF) to adult hemoglobin (HbA) after birth.
• This developmental shift is a key target for treating genetic blood disorders like sickle cell disease and β-thalassemia.

Purpose of the Study:

• To identify novel regulators of globin gene switching and fetal hemoglobin (HbF) expression using a CRISPR-Cas9 screen.
• To elucidate the molecular mechanisms underlying HbF induction in erythroid precursors.

Main Methods:

• Conducted a CRISPR-Cas9 screen targeting ubiquitin-proteasome components to identify regulators of HbF.
• Investigated the role of the von Hippel-Lindau (VHL) E3 ubiquitin ligase and hypoxia-inducible factor 1α (HIF1α) in γ-globin gene expression.
• Analyzed gene regulation, chromatin interactions, and transcriptional activation in response to VHL depletion or hypoxia.

Main Results:

• Depletion of VHL stabilized HIF1α, leading to increased γ-globin gene transcription and HbF production in RBC precursors.
• HIF1α-HIF1β heterodimers were found to bind regulatory elements of the BGLT3 long noncoding RNA gene, influencing γ-globin gene expression.
• HbF induction was also observed under hypoxic conditions or upon inhibition of prolyl hydroxylase domain enzymes, mimicking VHL-mediated stabilization of HIF1α.

Conclusions:

• The study links globin gene regulation to canonical hypoxia adaptation pathways.
• A novel mechanism for HbF induction during stress erythropoiesis involving the VHL-HIF1α axis was identified.
• These findings suggest a promising new therapeutic avenue for β-hemoglobinopathies by modulating HbF levels.