One Shock, Not One Cure: Electroporation Reveals Disease-Specific Constraints in Hepatocyte Gene Editing Therapy

We previously demonstrated lipid nanoparticle-mediated CRISPR-Cas9 gene editing to disrupt the gene encoding cytochrome P450 oxidoreductase (Cypor), combined with transient administration of acetaminophen (APAP), to repopulate the liver with healthy hepatocytes and rescue a phenylketonuria mouse model. This study aimed to investigate electroporation-mediated delivery of <i>Cypor</i>-targeting CRISPR-Cas9 ribonucleoproteins into wild-type hepatocytes, combined with liver engraftment under APAP treatment, as an in vivo selection approach in a mouse model of homozygous familial hypercholesterolemia (<i>Ldlr</i>^-/-). Electroporation provides higher delivery efficiency compared to lipid nanoparticles. We observed engraftment levels up to 13% engraftment of electroporated Cypor-deficient hepatocytes with indels in the liver of <i>Ldlr</i>^-/- mice after transient APAP administration, while negligible engraftment was observed in no-APAP controls (mean 9% and 2%, respectively, <i>p</i> = 0.0121). The engraftment of Cypor-deficient <i>Ldlr</i>^+/+ hepatocytes was associated with reductions in LDL-cholesterol (18%) and triglycerides (52%) compared to the untransplanted control <i>Ldlr</i>^-/- mice fed a Western diet for 5 weeks, but offered no protection from the development of diet-induced aortic root atherosclerosis or liver steatosis. While biochemical markers for liver damage normalized after discontinuation of APAP, we observed persistent lipid accumulation in the liver of <i>Ldlr</i>^-/- mice grafted with Cypor-deficient <i>Ldlr</i>^+/+ hepatocytes, likely stemming from the impact of Cypor deficiency on cholesterol clearance. Therefore, the combination of CRISPR-Cas9-mediated Cypor knockdown to induce clonal expansion of gene-edited hepatocytes using transient APAP administration is not a viable therapeutic strategy for familial hypercholesterolemia due to the essential role of Cypor in cholesterol metabolism. Unlike findings from phenylketonuria mouse model studies, the loss of Cypor function could not be compensated by unedited native hepatocytes in <i>Ldlr</i>^-/- mice. Collectively, our results demonstrate that electroporation is a viable and informative approach for evaluating gene editing strategies for the treatment of inherited metabolic diseases that affect the liver. Our electroporation procedure revealed that a one-size-fits-all gene editing strategy may not be universally applicable for treating inherited metabolic liver disorders. Tailored gene editing and selection strategies may be needed for different liver disorders.