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KLF1 drives the expression of fetal hemoglobin in British HPFH

Wienert, B., Martyn, G. E., Kurita, R., Nakamura, Y., Quinlan, K. G. R., & Crossley, M.

Key Summary: 

β-hemoglobinopathies are amongst the most common single locus inherited diseases. In this condition high fetal hemoglobin (HbF) levels have been found to be beneficial and boosting fetal hemoglobin expression is seen as an attractive therapy. Naturally occurring mutations in the fetal globin promoter can result in high HbF persisting into adulthood in a benign condition known as Hereditary Persistence of Fetal Hemoglobin (HPFH). Individuals with one form of HPFH, British HPFH, carry a T to C substitution at position -198 of the fetal globin gene promoter. These individuals exhibit HbF levels of up to 20%, enough to ameliorate the symptoms of β hemoglobinopathies. Here we use CRISPR-mediated genome editing to introduce the 198 substitution into human erythroid HUDEP-2 cells and show that this mutation is sufficient to substantially elevate expression of HbF. We also examined the molecular mechanism underlying the increase in fetal globin expression. Through a combination of in vitro and in vivo studies we demonstrate that the mutation creates a de novo binding site for the important erythroid gene activator Krüppel-like Factor 1 (KLF1/EKLF). Our results indicate that introducing this single naturally occurring mutation leads to significantly boosted HbF levels.