Promoter or enhancer activation by CRISPRa rescues haploinsufficiency caused obesity

Haploinsufficiency, having only one functional copy of a gene, leads to a wide-range of human diseases. Using obesity as a disease model, we tested whether haploinsufficiency can be rescued by CRISPR-mediated activation (CRISPRa) of the normal allele. Haploinsufficiency of either SIM1 or MC4R, results in severe obesity in humans and mice. In transgenic mice, CRISPRa targeting of the Sim1 promoter or its ~270kb distant hypothalamic enhancer, rescued the obesity phenotype in Sim1 heterozygous mice. Interestingly, despite using a ubiquitous promoter for CRISPRa, Sim1 was upregulated only in tissues where the promoter or enhancer are active, suggesting that cis-regulatory elements can determine CRISPRa tissue-specificity. To evaluate the potential therapeutic use of CRISPRa, we injected CRISPRa-rAAV into the hypothalamus, leading to reversal of the obesity phenotype in Sim1 and Mc4r heterozygous mice. Our results show that CRISPRa can be developed as a gene regulation therapy (GRT) to treat altered gene dosage diseases. RNA-seq and ChIP-seq experiments to confirm on-target CRISPRa binding and activation as well as to identify potential off-target sites.