# LDB1 represses fetal hemoglobin expression by enhancing BCL11A transcription

## TL;DR

LDB1 helps switch from fetal to adult hemoglobin by boosting BCL11A, which prevents cell death in blood cell development.

## Contribution

LDB1 is newly identified as a key enhancer of BCL11A transcription, crucial for fetal globin silencing in erythropoiesis.

## Key findings

- LDB1 deficiency causes ROS-mediated apoptosis due to excessive heme in proerythroblasts.
- LDB1 activates BCL11A transcription by binding to its enhancer regions.
- BCL11A overexpression rescues LDB1-deficient cells from apoptosis.

## Abstract

Deciphering the mechanism governing the temporal switch from fetal to adult hemoglobin during erythropoiesis has significant clinical relevance. Here, we identify LDB1 as a pivotal regulator of β-globin switching in erythroid progenitors. The absence of LDB1 in proerythroblasts from mouse fetal liver leads to cell cycle arrest and apoptosis due to the accumulation of reactive oxygen species (ROS), resulting from excessive heme content caused by significant overexpression of embryonic β-globin genes such as Hbb-y and Hbb-bh1. Mechanistically, LDB1 directly enhances the mRNA expression of fetal globin gene repressors, including Bcl11a, Cbfa2t3, and Sox6. Moreover, the LDB1 complex, which includes LMO2 and GATA1, binds directly to enhancer regions of Bcl11a, promoting its transcription. CRISPR/Cas9-mediated LDB1 knockout in human erythroleukemia cells confirmed LDB1 as a key enhancer of BCL11A transcription, reducing its mRNA expression while upregulating transcription of the fetal globin gene HBG. Following chromatin immunoprecipitation (ChIP) assays revealed LDB1 binding to intron 2 enhancers within the BCL11A locus, reinforcing its indispensable role in BCL11A transcription in humans. Consequently, ectopic expression of BCL11A in LDB1-deficient proerythroblasts promotes their proliferation by rescuing them from ROS-mediated apoptosis. These findings highlight the essential role of LDB1 in fetal globin silencing during erythropoiesis.

Image 1

•LDB1 deficiency in proerythroblasts causes ROS-mediated apoptosis by excessive heme.•LDB1 regulates fetal globin to prevent ROS-mediated apoptosis in erythroblasts.•LDB1 transcriptionally activates BCL11A, fetal β-globin repressor.•The LDB1 complex binds BCL11A enhancers to promote its transcription.

LDB1 deficiency in proerythroblasts causes ROS-mediated apoptosis by excessive heme.

LDB1 regulates fetal globin to prevent ROS-mediated apoptosis in erythroblasts.

LDB1 transcriptionally activates BCL11A, fetal β-globin repressor.

The LDB1 complex binds BCL11A enhancers to promote its transcription.