Major work stemming from a collaboration between the laboratory of Dr. Nabil G. Seidah – researcher at the Montreal Clinical Research Institute (IRCM) and Full Professor at Université de Montréal’s Faculty of Medicine –, Harvard University and the University of Pennsylvania, and published in Nature Biomedical Engineering, shows a promising first use of CRISPR-Cas-Editing technology in the elimination of the expression of the human PCSK9 gene. The function of the protein encoded by the PCSK9 gene was discovered at the IRCM in 2003. It is a major regulator of LDL-cholesterol that enhances the degradation of the low-density lipoprotein receptor (LDLR) in endosomes/lysosomes, and its inhibition results in a marked decrease in circulating cholesterol.
Overview
Gene editing offers the clinically validated potential to treat a wide variety of genetic disorders for which few therapeutic options are available. Adeno-associated viruses (AAVs) have become a popular in vivo delivery method due to their clinical validation, their ability to target a variety of clinically relevant tissues, and their relatively well-understood and favourable safety profile.
CRISPR-editing has evolved into an efficient technique to silence genes with very minimal off-target effects. However, the viral delivery of CRISPR-base editors has been complicated by the packaging capacity of AAVs to carry a cargo size limited to ~4.7 kilobases.
In the present article authors from Harvard, University of Pennsylvania and the IRCM provided a single minimized AAV construct to silence genes using CRISPR-adenine base editor (AAV-ABE) primarily in liver. As a proof-of-principle the authors selected human PCSK9, a primarily liver-expressed gene discovered at the IRCM. They used mice expressing only human PCSK9 under its own promoter, previously generated in the laboratory of Nabil G. Seidah.
The spectacular data presented revealed a very efficient long-term silencing (>99%) of human PCSK9 expression in liver after a single injection of the engineered AAV-ABE, resulting in a ~25% reduction of total plasma cholesterol (>60% reduction in LDL-cholesterol) equivalent to what was observed in hepatocyte-specific Pcsk9 knockout mice.
The single-AAV-ABE systems described yield robust editing efficiencies in vivo, facilitating therapeutically relevant levels of editing in liver, heart, and muscle tissue at moderate doses of AAV.
‘’The results of ongoing human clinical trials (started in 2022) using similar CRISPR-editing approaches targeting PCSK9 and other genes are eagerly awaited’’, said Dr. Seidah.
Acknowledgment
This work was made possible in part thanks to grants to Dr. Seidah, including a CIHR Foundation grant (# 148363), a Canada Research Chairs in Precursor Proteolysis (# 950-231335) and a Leducq Foundation grant (# 13 CVD 03).
