Forced enhancer-promoter rewiring to alter gene expression in animal models

Transcriptional enhancers can be in physical proximity with their target genes via chromatin looping. The enhancer at the beta-globin locus (LCR) contacts the fetal (HBG) and adult (HBB) type beta-globin genes during corresponding developmental stages. We previously demonstrated 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 beta-globin locus as a model we provide proof-of-concept at the organismal level that forced enhancer re-wiring might present a strategy to alter gene expression for therapeutic purposes. Hematopoietic stem and progenitor cells (HSPC) from mice bearing human beta-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 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. RNA-Seq analysis of in vitro differentiated erythroid cells at day 13 of culture following lentiviral transduction of CD34+ primary human cells with either GFP control or ZF-Ldb1 constructs