Mechanisms of Globin Regulation and Modeling Fetal Hemoglobin Reactivation

Red blood cell disorders like Sickle Cell Disease (SCD) and β-thalassemias are caused by alterations within the gene for the hemoglobin β (HBβ) subunit. An anti-sickling fetal ortholog of HBβ, hemoglobin γ (HBγ) can reverse disease-related pathophysiology in these disorders by also forming complexes with the required hemoglobin α subunit. Because β-like globin expression is developmentally regulated, with a reduction in the fetal ortholog (γ) occurring shortly after birth concomitantly with an increase in the adult ortholog (β), it has been postulated that maintaining expression of the anti-sickling γ ortholog may be of therapeutic benefit. Previously, inhibitors of a chromatin modifying enzyme G9a/GLP (G9a-i) have been shown to upregulate γ expression relative to β expression and therefore G9a/GLP has been proposed as a reasonable molecular target for maintenance of the anti-sickling γ ortholog. However, we have found that the reactivation of γ occurs in a narrow concentration range of G9a-i with higher concentrations reducing the levels of γ. Moreover, the enhanced γ / β expression ratio occurs simultaneously with a reduction in expression of the critical hemoglobin α subunit. We therefore set out to identify novel modulators and targets of HBγ expression. We have demonstrated that targeting different components of the globin regulatory network can have profoundly different effects on globin expression. Importantly, we are utilizing a newly developed in vitro SCD cellular model to investigate how these globin gene regulators impact SCD pathophysiology.