RNA-Guided Transcriptional Silencing In Vivo with S. aureus CRISPR-Cas9 Repressors

CRISPR-Cas9 transcriptional repressors have emerged as robust tools for disrupting gene regulation in vitro but have not yet been adapted for delivery in adult animal models. Here we created an S. aureus Cas9-based transcriptional repressor (dSaCas9KRAB) compatible with adeno-associated viral (AAV) delivery. To evaluate dSaCas9KRAB efficacy for targeting an endogenous gene in vivo, we silenced transcription of Pcsk9, a regulator of cholesterol levels, in the liver of adult mice. Systemic administration of a dual-vector AAV8 system expressing dSaCas9KRAB and a Pcsk9-targeting guide RNA (gRNA) resulted in significant reductions of serum PCSK9 and cholesterol levels. Despite a moderate host response to dSaCas9KRAB expression, PCSK9 repression was maintained for 24 weeks after a single treatment, demonstrating the potential for long-term gene silencing in post-mitotic tissues with dSaCas9KRAB. In vivo programmable gene silencing enables studies that link gene regulation to complex phenotypes and expands the CRISPR-Cas9 genetic perturbation toolbox for basic research and gene therapy applications. C57Bl/6 wild-type mice were treated with AAVs expressing dSaCas9-KRAB and/or a Pcsk9-targeting gRNA by tail-vein injection. Six weeks after treatment, we harvested the livers of treated mice and performed mRNA-sequencing.