PCSK9 gene: first promising use of CRISPR-Cas-Editing technology

Major work resulting from a collaboration between the laboratory of Dr Nabil G. Seidah (of the Clinical Research Institute of Montreal [IRCM] and full professor at the Faculty of Medicine of the University of Montreal), Harvard University and the University of Pennsylvania and published in Nature Biomedical Engineering show a promising first use of CRISPR-Cas-Editing technology in knocking out the expression of the human PCSK9 gene.

Recall that 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 which enhances the degradation of the low-density lipoprotein (LDL) receptor in endosomes/lysosomes , and its inhibition leads to 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 (AAV) have become a popular in vivo delivery method due to their clinical validation, ability to target different clinically relevant tissues, and relatively well understood and favorable safety profile.

CRISPR editing is an efficient technique for knocking out genes with minimal off-target effects. However, viral delivery of CRISPR base editors has been complicated by the ability of AAVs to carry cargo limited to ~4.7 kilobases.

In the present paper, authors from Harvard University, University of Pennsylvania and IRCM provided a single minimized AAV construct to inactivate genes using the CRISPR-adenine base editor (AAV-ABE) mainly in the liver. As proof of concept, the authors chose human PCSK9, a gene mainly expressed in the liver, discovered at the IRCM. They used mice expressing only the human PCSK9 gene under its own promoter, previously created in the laboratory of Nabil G. Seidah.

The dramatic data presented revealed a highly effective (>99%) long-term silencing of human PCSK9 expression in the liver following a single injection of the modified AAV-ABE, resulting in a ~25% reduction total plasma cholesterol (> 60% LDL cholesterol) equivalent to what has been observed in mice knockout Hepatocyte-specific PCSK9.

The disclosed AAV-ABE systems exhibit robust editing efficiencies in vivo, facilitating therapeutically relevant levels of editing in liver, heart, and muscle tissues at moderate doses of AAV.

“We eagerly await the results of the ongoing human clinical trials [commencés en 2022] using similar CRISPR editing approaches targeting PCSK9 and other genes,” said Dr.r Seidah in the wake of this work.

About this work

This work was made possible in part by funds awarded to the Dr Nabil G. Seidah, including a grant from the Canadian Institutes of Health Research Foundation, the Canada Research Chair in Precursor Proteolysis and a grant from the Leducq Foundation.

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