The Pnpla3 Variant I148M Reveals Protective Effects Towards Hepatocellular Carcinoma in Mice via Restoration of Omega-3 Polyunsaturated Fats

The Patatin-Like Phospholipase Domain-Containing 3 148M Variant Exacerbates Alcohol-Induced Liver Injury and Tumorigenesis in Mice

Patatin-like phospholipase domain-containing 3 (PNPLA3) protein 148M variant is strongly associated with cirrhosis and hepatocellular carcinoma (HCC); however, the underlying mechanisms remain elusive. This study aimed to elucidate the role of the PNPLA3148M variant in alcohol-related HCC development. Control and humanized PNPLA3148M transgenic mice were fed with an ethanol-containing diet for 12 weeks. The animals were examined for liver tumors. After the alcohol feeding, the PNPLA3148M mice had twofold higher liver cancer incidence rates and larger tumor sizes than those in the control mice. Cancer stem cell markers in the PNPLA3148M mouse livers were elevated relative to those in the control mouse livers. Alcohol detoxification was impaired in the PNPLA3148M mouse livers. Hepatic oxidative stress and DNA damage were elevated in the PNPLA3148M mice. Wnt/β-catenin and Yes-associated protein (YAP) and WW domain-containing transcription regulator 1 (TAZ) were activated in the PNPLA3148M mouse livers. The data suggest that the PNPLA3148M variant has a strong interaction with alcohol in HCC development through attenuation of alcohol detoxification and promotion of oncogenic pathways. Targeting the PNPLA3148M variant might be useful for the prevention or treatment of alcohol-associated HCC in patients carrying this variant.

Experimental Models to Investigate PNPLA3 in Liver Steatosis

Patatin-like phospholipase domain-containing 3 (PNPLA3) was the first gene identified through genome-wide association studies to be linked to hepatic fat accumulation. A missense variant, encoding the PNPLA3-148M allele, has since been shown to increase the risk for the full spectrum of steatotic liver disease (SLD), from simple steatosis to steatohepatitis, cirrhosis, and hepatocellular carcinoma. Despite extensive validation of this association and ongoing research into its pathogenic role, the precise mechanisms by which PNPLA3-148M contributes to the progression of SLD remain poorly understood. In this review, we evaluate preclinical in vitro and in vivo models used to investigate PNPLA3 and its involvement in SLD, with particular emphasis on metabolic dysfunction-associated steatotic liver disease. We assess the strengths and limitations of these models, as well as the challenges arising from species differences in PNPLA3 expression and function between human and murine systems.

Genetics of Metabolic Dysfunction-associated Steatotic Liver Disease: The State of the Art Update

Recent advances in the genetics of metabolic dysfunction-associated steatotic liver disease (MASLD) are gradually revealing the mechanisms underlying the heterogeneity of the disease and have shown promising results in patient stratification. Genetic characterization of the disease has been rapidly developed using genome-wide association studies, exome-wide association studies, phenome-wide association studies, and whole exome sequencing. These advances have been powered by the increase in computational power, the development of new analytical algorithms, including some based on artificial intelligence, and the recruitment of large and well-phenotyped cohorts. This review presents an update on genetic studies that emphasize new biological insights from next-generation sequencing approaches. Additionally, we discuss innovative methods for discovering new genetic loci for MASLD, including rare variants. To comprehensively manage MASLD, it is important to stratify risks. Therefore, we present an update on phenome-wide association study associations, including extreme phenotypes. Additionally, we discuss whether polygenic risk scores and targeted sequencing are ready for clinical use. With particular focus on precision medicine, we introduce concepts such as the interplay between genetics and the environment in modulating genetic risk with lifestyle or standard therapies. A special chapter is dedicated to gene-based therapeutics. The limitations of approved pharmacological approaches are discussed, and the potential of gene-related mechanisms in therapeutic development is reviewed, including the decision to perform genetic testing in patients with MASLD.

Impact of PNPLA3 I148M on alpha-1 antitrypsin deficiency-dependent liver disease progression

BACKGROUND AND AIMS

Genetic risk factors are major determinants of chronic liver disease (CLD) progression. Patatin-like phospholipase domain-containing protein 3 (PNPLA3) I148M polymorphism and alpha-1 antitrypsin (AAT) E342K variant, termed PiZ, are major modifiers of metabolic CLD. Both variants are known to affect metabolic CLD through increased endoplasmic reticulum stress, but their combined effect on CLD progression remains largely unknown. Here, we aimed to test our working hypothesis that their combined incidence triggers CLD disease progression.

APPROACH AND RESULTS

We showed that patients with PiZZ/PNPLA3 I148M from the European alpha-1-antitrypsin deficiency (AATD) liver consortium and the UK Biobank had a trend towards higher liver enzymes, but no increased liver fat accumulation was evident between subgroups. After generating transgenic mice that overexpress the PiZ variant and simultaneously harbor the PNPLA3 I148M knockin (designated as PiZ/PNPLA3 I148M ), we observed that animals with PiZ and PiZ/PNPLA3 I148M showed increased liver enzymes compared to controls during aging. However, no significant difference between PiZ and PiZ/PNPLA3 I148M groups was observed, with no increased liver fat accumulation over time. To further study the impact on CLD progression, a Western-styled diet was administered, which resulted in increased fat accumulation and fibrosis in PiZ and PiZ/PNPLA3 I148M livers compared to controls, but the additional presence of PNPLA3 I148M had no impact on liver phenotype. Notably, the PiZ variant protected PNPLA3 I148M mice from liver damage and obesity after Western-styled diet feeding.

CONCLUSION

Our results demonstrate that the PNPLA3 polymorphism in the absence of additional metabolic risk factors is insufficient to drive the development of advanced liver disease in severe AATD.