Orphan Nuclear Receptors TR2 and TR4 in Erythropoiesis: From Mechanisms to Therapies.

Testicular orphan receptors TR2 and TR4 serve as central regulators of erythropoiesis, orchestrating the entire continuum of erythroid progenitor cell proliferation, differentiation, and maturation. As core components of the direct repeat erythroid determinant (DRED) complex, they activate erythroid-specific transcriptional programs to dynamically control the spatiotemporal expression of globin genes. These nuclear receptors not only engage in functional interactions with key erythroid transcription factors GATA1 and KLF1 to coregulate erythroid differentiation and maturation but also recruit epigenetic modifier complexes such as DNMT1 and LSD1 to modulate chromatin states dynamically. Research has established that dysfunctions in TR2/TR4 are implicated in β-thalassemia and sickle cell disease (SCD): β-thalassemia is associated with the defective silencing of γ-globin genes, while in SCD, TR2/TR4 antagonizes BCL11A to reactivate fetal hemoglobin (HbF) expression. This review systematically dissects the molecular regulatory networks of TR2/TR4 in erythroid cells, interprets their dual regulatory properties across different stages of erythroid differentiation, and explores the therapeutic potential of targeting TR2/TR4 for treating erythroid-related disorders such as β-thalassemia and SCD, thereby providing novel directions for hematological disorder therapy.