Validating BRD9’s Role as an HBD/HBG Activator Through Acute Degradation
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hemoglobin
hemoglobin-switching
HBG
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Hemoglobinopathies, including sickle cell disease and β-thalassemia are a class of genetic disorders characterized by abnormal hemoglobin production. Reversing the switch from fetal (HBG, γ-globin) to adult hemoglobin (HBB, β-globin) production has proved an invaluable method for treating such disorders. However, treatments either come with harsh side effects or are prohibitively expensive and inaccessible in the parts of the world where hemoglobinopathies are most prevalent. A better understanding of the complex pathways controlling the switch from fetal to adult hemoglobin can help aid the development of more accessible treatments. While most research focuses on repressors of HBG, such as BCL11A, our lab has found the non-canonical BAF (ncBAF) complex to be a potential activator of HBG expression. Genetic and pharmacological depletion of the essential ncBAF component BRD9 preferentially leads to decreased expression of HBG and HBD (δ-globin). However, a possible limitation with these studies is that the observed decrease in globin expression may be a result of non-specific effects of the CFT-8634 degrader, rather than BRD9 loss itself. Here we address this concern by optimizing and analyzing the effects of a different PROTAC drug in primary human erythroid progenitors. The drug, FHD-609, functions via a different binding domain specific to BRD9. It was found to induce degradation best at a concentration of 10 nM, although similar levels of globin reduction were observed across different doses. Subsequent testing showed stronger degradation during earlier stages of erythroid maturation. Results were confirmed across multiple biological replicates to ensure reproducibility. The observed decreases in HBD and HBG expression confirmed BRD9’s influence on globin regulation.