Dissecting polycomb complexes for enhanced fetal hemoglobin production

Area of Science:

• Epigenetics and Gene Regulation
• Hematology
• Molecular Biology

Background:

• Polycomb repressive complexes (PRC1 and PRC2) are crucial regulators of gene expression during development.
• Reversing the fetal-to-adult hemoglobin switch is a therapeutic target for sickle cell disease and b-thalassemia.
• Current PRC inhibitors have limited use due to broad cellular effects.

Purpose of the Study:

• To investigate selective perturbations of PRC components for targeted fetal hemoglobin (HbF) reactivation.
• To assess if HbF can be reactivated without complete loss of PRC function.
• To identify specific PRC modifications with therapeutic potential.

Main Methods:

• High-density CRISPR-Cas9 mutagenesis screen on PRC components.
• Generation and characterization of a modified EZH2 subunit (EZH2D14) lacking part of the CXC domain.
• Functional assays in erythroid cells and a mouse model of hemoglobin switching.

Main Results:

• A CRISPR screen identified EZH2 exon 14 skipping (EZH2D14) as a key modification.
• EZH2D14 selectively relieves HbF repression while maintaining cellular fitness.
• EZH2D14 retains H3K27 methylation and repression of a subset of PRC target genes.
• The identified pathway for EZH2 control of HbF functions in a relevant mouse model.

Conclusions:

• Partial disruption of PRC components, specifically targeting non-enzymatic domains, can yield selective phenotypes.
• EZH2D14 demonstrates therapeutic potential for reactivating HbF in hemoglobinopathies.
• Selective targeting of chromatin-modifying complexes offers a promising therapeutic strategy.