Forced enhancer-promoter rewiring to alter in animal models

Transcriptional enhancers can be in physical proximity of their target genes via chromatin looping. The enhancer at the 0-globin locus (locus control region [LCR]) contacts the fetal-type (HBG) and adult-type (HBB) 0-globin genes during corresponding developmental stages. We have demonstrated previously that forcing proximity between the LCR and HBG genes in cultured adult-stage erythroid cells can activate HBG transcription. Activation of HBG expression in erythroid cells is of benefit to patients with sickle cell disease. Here, using the 0-globin locus as a model, we provide proof of concept at the organismal level that forced enhancer rewiring might present a strategy to alter gene expression for therapeutic purposes. Hematopoietic stem and progenitor cells (HSPCs) from mice bearing human 0-globin genes were transduced with lentiviral vectors expressing a synthetic transcription factor (ZF-Ldb1) that fosters LCR-HBG contacts. When engrafted into host animals, HSPCs gave rise to adult-type erythroid cells with elevated HBG expression. Vectors containing ZF-Ldb1 were optimized for activity in cultured human and rhesus macaque erythroid cells. Upon transplantation into rhesus macaques, erythroid cells from HSPCs expressing ZF-Ldb1 displayed elevated HBG production. These findings in two animal models suggest that forced redirection of gene-regulatory elements may be used to alter gene expression to treat disease.

Automated summary

This study demonstrates that forced enhancer rewiring can alter gene expression and presents a potential strategy for therapeutic purposes. By transducing hematopoietic stem and progenitor cells (HSPCs) with lentiviral vectors expressing a synthetic transcription factor (ZF-Ldb1) and forcing contact between the enhancer and the target gene, elevated expression of the target gene was achieved in adult-type erythroid cells. This proof of concept was demonstrated in both mice and rhesus macaque models.