Experimental Models to Investigate PNPLA3 in Liver Steatosis

Abstract

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.

Keywords: MASH; MASLD; NAFLD; fatty liver; mouse.

Figure 1:

Alphafold ribbon structure overlay of human (blue) and mouse (green) PNPLA3. The isoleucine at position 148 (orange) and serine at position 47 (pink) are part of a region highly conserved between the two species. Human PNPLA3 contains two alpha helices as part of unstructured regions that are absent from the mouse ortholog.

Figure 2:

In PNPLA3-148I hepatocytes, phosphorylation of perilipins (PLIN) releases the cofactor ABHD5 to bind ATGL and, with higher affinity, PNPLA3. Binding by ABHD5 enhances triglyceride hydrolysis of both lipases, with ATGL being more enzymatically effective than PNPLA3. This contrasts with PNPLA3-148M hepatocytes, where enzymatically impaired PNPLA3 accumulates on lipid droplets. ABHD5 that is released from PLIN preferentially binds to PNPLA3, preventing enzymatic enhancement of ATGL while its own triglyceride hydrolysis activity remains low even when bound to ABHD5. TAG: triacylglycerol, DAG: diacyl glycerol.