CRISPR-edited hepatic organoids as drug screening platform for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD), is a chronic liver disease caused by a build-up of intrahepatic fat. Metabolic comorbidities associated with NAFLD included obesity, type 2 diabetes, hyperlipidemia, hypertension, and metabolic syndrome (1-3). With changes in diet and lifestyle, the incidence of NAFLD is rapidly increasing to an estimated 30% of global population (4). Histologic manifestations of NAFLD range from the mild stage of simple steatosis, to the advanced stage of steatosis accompanied with necroinflammation or fibrosis, so called nonalcoholic non-alcoholic steatohepatitis (NASH). NASH has a global prevalence of 5.27% (4), and more than 20% of patients with NASH will develop cirrhosis (5), which could further progress into hepatocellular carcinoma (HCC). NASH is predicted to be the first leading cause of HCC by 2030 (6).

Potential therapeutic agents of NASH/NAFLD mainly target glucose and lipid metabolisms, including de novo lipogenesis inhibitor, antidiabetic agents and bile acid therapeutics (7-9). Despite huge efforts, there are currently no approved therapies for NASH. Even the most promising agent, obeticholic acid, steroidal agonist of farnesoid X receptor evidenced by the REGENERATE study to significantly improved fibrosis in NASH (10), has been rejected by Food and Drug Administration (FDA) due to the uncertain predicted benefit balanced with potential risks.

A recent article published in Nature Biotechnology titled “Engineered human hepatocyte organoids enable CRISPR-based target discovery and drug screening for steatosis” has provided a new insight on this topic (11). The authors built a steatosis organoid model using 3 different triggers, including free fatty acids (FFA) loading, interindividual genetic variability (PNPLA3 I148M) and monogenic lipid disorders (APOB and MTTP mutations), to study their interplay and further identify steatosis modulators and putative targets. The study demonstrated that addition of FFA exacerbated steatosis in hepatic organoids carrying PNPLA3 I148M variants. However, for APOB- and MTTP-mutant organoids, the majority of intrahepatic lipids accumulation originates from de novo lipogenesis (DNL) rather than lipid sources in the culture medium. APOB- and MTTP-mutant organoids show high similarity in candidate drug response to FFA-induced steatosis organoids, and therefore, could be used as long-term expandable steatosis models and CRISPR genetic screening platform of potential steatosis modulators. Loss-of-function editing of candidate genes, which are identified in treatment-based transcriptome cluster analysis of APOB- and MTTP-mutant organoids, reveals that FADS2 serves a critical target for resolving steatosis.

This study by Hendriks et al. (11) has made a ground-breaking contribution to the field. Most of the previous organoid researches focused on normal tissue or tumor model construction. This study fully demonstrates the advantages of organoids for building in vitro models of genetic metabolic diseases for drug screening and potential mechanism exploration.

We are, however, concerned about different proliferation capacities displayed in FFA-induced and DNL-induced organoids. Addition of FFA greatly impairs hepatic proliferation, while APOB- and MTTP-mutant organoids could undergo long-term culture and expansion. Effect of high-fat diet on liver regenerative capacity and related mechanisms are worth exploring. In addition to fat deposition in liver cells, focal inflammation and/or secondary fibrosis are more important factors pathological features in NAFLD/NASH that significantly affect clinical prognosis, which involves multi-cellular crosstalk. Other liver-resident cells should be incorporated into the system to study the interaction between hepatocytes and other cells in lipid metabolism, as well as reproduce the in vitro NAFLD/NASH model with similar molecular and pathological characteristics to that in vivo.

Acknowledgments

Funding: This paper was supported by the National High Level Hospital Clinical Research Funding (No. 2022-PUMCH-B-034).

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, Hepatobiliary Surgery and Nutrition. The article did not undergo external peer review.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://hbsn.amegroups.com/article/view/10.21037/hbsn-23-247/coif). The authors have no conflicts of interest to declare.

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