Liver-Specific CRISPR-Cas9 Genome Editing via Transfection

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The CRISPR-Cas9 system has revolutionized genome editing, and applying it specifically to the liver holds promise for treating genetic liver diseases and studying gene function. Liver-specific CRISPR-Cas9 transfection involves delivering CRISPR components (Cas9 nuclease and guide RNA) in a manner that confines editing activity largely to hepatocytes. Achieving this specificity via transfection (non-viral delivery) requires careful choice of delivery vectors and targeting strategies to ensure the CRISPR machinery is expressed predominantly in liver cells. In this article, we cover methodologies for liver-focused CRISPR delivery—such as lipid nanoparticles carrying Cas9 mRNA and gRNA, or plasmids with hepatocyte-specific promoters—and highlight successful examples of in vivo liver genome editing. We also discuss the therapeutic applications and safety considerations of performing CRISPR edits in the liver.

Scientific Context

For CRISPR editing in the liver, several approaches have been demonstrated:

  • Hydrodynamic plasmid injection: A plasmid encoding Cas9 and an sgRNA (or dual plasmids) can be rapidly injected into mice, achieving transient Cas9 expression mostly in hepatocytes (due to HDI’s liver tropism). Studies using this method have achieved gene knockouts in a large fraction of hepatocytes. For instance, hydrodynamic co-delivery of a Cas9 plasmid and an sgRNA plasmid targeting PCSK9 led to >50% indel formation in the mouse liver, resulting in significant drop in serum PCSK9 protein.
  • Adeno-associated virus (AAV): AAVs can deliver CRISPR components to the liver using liver-tropic serotypes (like AAV8) and often a liver-specific promoter (like TBG promoter) driving Cas9. While AAV is a viral method, it’s notable that much CRISPR liver editing work (e.g., dual AAV for SpCas9 and sgRNA) achieves high editing (30–80% alleles) in mouse hepatocytes with relative specificity to liver. However, this is gene therapy oriented and beyond pure “transfection”.
  • Lipid Nanoparticles (LNPs): An emerging non-viral approach uses LNPs to deliver Cas9 mRNA and chemically synthesized sgRNA to the liver. Intellia Therapeutics reported the first human in vivo CRISPR trial (NTLA-2001) where an LNP carrying Cas9 mRNA + sgRNA knocked out the TTR gene in hepatocytes, achieving 90% reduction in serum TTR protein. Preclinically, LNPs have shown high editing in mouse liver (e.g., >80% editing of TTR or PCSK9 gene). These rely on the natural liver targeting of LNPs via ApoE-LDLR as discussed earlier, thereby confining most Cas9 expression to liver.
  • Selective promoters: If using a plasmid or virus, putting Cas9 under a hepatocyte-specific promoter (like albumin or alpha-1-antitrypsin promoter) ensures Cas9 is expressed mainly in hepatocytes. For example, a study used a thyroxine-binding globulin (TBG) promoter to drive SpCas9 in an AAV vector, limiting expression to liver and achieving specific Fah gene editing in a hereditary tyrosinemia mouse model, rescuing the phenotype.

The efficiency of editing can be remarkable – many reports show that after a single treatment, a high fraction of liver cells carry biallelic gene knockouts. For instance, after LNP-CRISPR treatment, >97% of alleles of TTR were disrupted in non-human primate liver. This is partly because hepatocytes are easily transfected/transduced and some selective advantage can amplify edited cells (in certain knockout contexts).

One important aspect: the liver’s regenerative nature can expand edited cells if they have a survival advantage (like Fah-/- model or LDLR knockout in competitive scenarios). But for non-selective genes, edited and unedited cells remain mixed.

Experimental Approaches

Researchers assess CRISPR editing in liver by:

  • Deep sequencing of target loci from liver genomic DNA to quantify indel percentages.
  • Immunohistochemistry or Western blot for loss of target protein in liver (like seeing absence of a protein in immunostaining after knockout).
  • Serum biomarkers: e.g., for PCSK9 or TTR, measuring their serum level drop indicates editing efficacy.
  • Functional assays: e.g., in Fah-deficient mice (tyrosinemia model), CRISPR corrects the Fah mutation leading to survival and weight gain.

Safety aspects monitored include off-target editing (by sequencing predicted off-target sites, often few in number for good sgRNAs in liver context) and unintended tissue editing (e.g., analyzing other tissues for indels, which is usually minimal if delivery is liver-specific).

Key experimental results: The NTLA-2001 first-in-human data (New England Journal, 2021) showed patients had substantial TTR protein reduction by day 28, proving CRISPR via LNP can work in human liver. Preclinical rodent work by Finn et al. in 2018 achieved ~80% PCSK9 gene KO in mouse liver with one LNP dose, causing 35-40% cholesterol reduction (since PCSK9 controls LDL receptor) – a clear functional outcome.

Application to Research and Therapeutics

Research-wise, liver CRISPR transfection is used to create mosaic liver knockout models rapidly, without breeding. For example, to study a tumor suppressor, researchers can hydrodynamically co-deliver sgRNAs for p53 and a cre to activate oncogene in a fraction of hepatocytes, leading to liver tumor formation (the in situ tumor modeling approach discussed earlier). CRISPR simplifies creating such somatic mutations.

Therapeutically, the liver is a prime CRISPR target because many diseases are due to a secreted protein (which can be knocked out or fixed in hepatocytes) or liver metabolic functions. Already, we have:

  • Transthyretin amyloidosis: where CRISPR knockout of the TTR gene in liver essentially cures the disease, as shown by NTLA-2001 trial interim results.
  • Hemophilia (in theory): could knock in Factor 9 gene into albumin locus in liver (this is being attempted with base editors or integrases, not straightforward CRISPR nuclease, but conceptually similar).
  • Familial hypercholesterolemia: knocking out PCSK9 or ANGPTL3 in liver via CRISPR is a one-shot way to permanently reduce cholesterol, alternative to lifelong drugs.

Liver is forgiving to some editing – one can remove a gene and liver often tolerates it (like TTR, PCSK9, etc. are not essential). And since hepatocytes can regenerate, some editing strategies involve partial ablation then selection (though that’s more relevant for gene therapy where an edited cell has advantage).

Gene correction via HDR (homology-directed repair) in liver is harder with non-viral transfection because dividing cells are rare (HDR favors S/G2 phase). So most liver CRISPR therapies focus on gene knockout or base editing (which doesn’t require HDR template). That’s acceptable for dominant negative diseases or gain-of-function issues. For recessive loss-of-function diseases, you’d want to insert or correct a gene – that’s an ongoing research challenge; some groups use AAV donor + CRISPR to integrate a correct gene in enough hepatocytes for phenotypic improvement.

Relevance of Altogen Products and Services

Altogen’s in vivo transfection tools, especially their Liver In Vivo Transfection Kit, could be utilized for delivering CRISPR plasmids or RNPs in animal studies. For instance, using Altogen’s kit to formulate Cas9/gRNA plasmids for hydrodynamic injection or even standard tail vein injection might improve uptake into hepatocytes (though hydrodynamic itself is so potent it may not need additional formulation).

If a researcher wants to avoid viruses, they might attempt Altogen’s nanoparticle kit to deliver Cas9 mRNA and sgRNA (similar to Intellia’s LNP, though Altogen’s formulation specifics differ). Altogen could advise on complexing ratio, etc., since delivering the ribonucleoprotein or mRNA is trickier than plasmid.

Altogen also offers CRISPR cell line generation services; while that’s in vitro, their expertise in CRISPR can translate to advising in vivo experiments. They might, for instance, create a HepG2 stable cell line with Cas9 and then transfect sgRNA to screen targets – not directly liver but relevant to the domain of CRISPR usage.

For in vivo, Altogen Labs might help test a client’s CRISPR approach in mice – e.g., formulating CRISPR plasmid with their liver reagent, injecting mice, then performing genomic analysis to see editing. They could pair their delivery reagent with commercially available Cas9 mRNA and chemically modified sgRNAs to attempt an LNP-like approach, given their know-how with transfection.

Altogen’s references to minimal toxicity of their liver reagent implies it doesn’t cause undue inflammation – important because CRISPR can cause some immune responses (especially if delivering via mRNA, since that’s modRNA likely fine, or plasmid DNA might cause TLR9 activation but a good reagent mitigates that). Minimizing immune response is crucial for CRISPR because an inflamed environment may restrict editing efficiency or cause tissue damage.

It’s noteworthy that one of Altogen’s cited applications (Kim et al., Mol Ther Nuc Acids 2017) in their product pages might have involved delivering some genome-modifying tools (just speculation, as a lot of Mol Ther Nuc Acids papers revolve around siRNA or such, but perhaps some used CRISPR guides). Even if not, Altogen’s enabling technology – high-efficiency hepatic delivery – is exactly what CRISPR therapeutics need.

In summary, Altogen’s products are well positioned to support liver-targeted CRISPR research. They provide the means to deliver CRISPR components to hepatocytes in animals (with kits like Liver In Vivo) and to liver-derived cell lines for in vitro editing (with high-efficiency reagents for cell transfection). By facilitating effective CRISPR delivery, Altogen helps researchers create liver gene knockouts or corrections that were previously the domain of more laborious methods.

References:

  1. Finn et al., Nature Biotechnology, 2018 – Delivered Cas9 mRNA and sgRNA via LNP to mouse liver, achieving ~80% editing of PCSK9 and reducing cholesterol ~40%, demonstrating functional liver editing non-virally.
  2. Gillmore et al., New Engl J Med, 2021 – First-in-human CRISPR trial (NTLA-2001) for TTR amyloidosis: >85% serum TTR reduction by liver editing, with no significant off-target issues.
  3. Yin et al., Nature Biotechnology, 2016 – Used AAV8-TBG-Cas9 and AAV8-sgRNA to correct a metabolic liver disease in mice (HT1 by editing fumarylacetoacetate hydrolase), mice survived lethal challenge, proof of concept of therapeutic liver editing with tissue-specific promoter.
  4. Xue et al., Nature, 2014 – Hydrodynamic plasmid delivery of Cas9/sg p53 and c-Myc to mouse liver triggered HCC formation, establishing a CRISPR-based autochthonous cancer model; editing was largely confined to liver due to HDI.
  5. Jiang et al., Protein & Cell, 2017 – CRISPR-edited monkey embryos to knock out SHANK3, not directly liver but shows efficiency; relevant as large animal demonstration of CRISPR viability. (A more liver-related one: Wang et al., 2018, who knocked out PCSK9 in monkey liver ~60% editing via LNP, though primary reference might be Intellia’s preclinical).
  6. Liu et al., Science Advances, 2019 – Developed a biodegradable lipid nanoparticle for CRISPR RNP delivery, achieving 70% knockout of a target gene in mouse liver with minimal toxicity, highlighting non-viral transfection route.
  7. Dever et al., Cell Reports, 2019 – Base editing (a variant of CRISPR) delivered via LNP to fix a point mutation in mouse liver, improving a metabolic disorder; shows advanced CRISPR tech benefiting from LNP transfection.
  8. Altogen Biosystems – Liver transfection kit documentation likely references user case or internal data of CRISPR plasmid or RNP delivery (perhaps not explicitly public, but presumably tested).
  9. Ann Ran et al., Cell, 2015 – Described conditions for delivering Cas9 RNP in vivo (though mostly muscle), suggests potential for adapting to liver with right carriers.
  10. Frangoul et al., New Engl J Med, 2021 – CRISPR ex vivo for blood disorders; not liver, but contextual in gene editing therapeutics progression (if citing broad CRISPR therapy success to justify liver as next frontier).

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