Tissue-specific regulation of PNPLA3 promotes lipid remodeling in response to dietary and environmental challenges

PNPLA3(I148M) is the strongest genetic risk factor for steatotic liver disease (SLD), but its functional role and tissue-specific regulation remain unclear. Pnpla3 mRNA levels are significantly higher in mouse adipose tissue than in liver tissue, yet its role in adipose tissue is not known. Here, we characterize the molecular mechanisms underlying tissue-specific differences in PNPLA3 expression in mice to clarify its functional role and link to SLD risk.

Pnpla3 mRNA and PNPLA3 protein levels were quantified in liver tissue and adipose depots of fasted and refed mice at 30 °C and 6 °C. Signaling pathways regulating PNPLA3 expression in adipocytes were examined using adrenergic agonists and pathway-specific modulators. Translation and proteasomal inhibitors were used during adrenergic stimulation to investigate the discordance between Pnpla3 mRNA and protein levels. The relationship between PNPLA3 levels and triglyceride (TG) fatty acid composition was also assessed.

At thermoneutrality, feeding strongly increased PNPLA3 levels in the liver, but it remained undetectable in adipose tissue. Conversely, cold exposure or β3-adrenergic stimulation had no effect on hepatic PNPLA3 but increased PNPLA3 >19-fold in brown adipose tissue (BAT), despite causing a >75% reduction in Pnpla3 mRNA, indicating robust post-translational regulation. In BAT, adrenergic signaling via cAMP/PKA and PI3K/AKT elevated PNPLA3 by reducing proteasomal degradation. PNPLA3 expression correlated with depletion of TG-long-chain polyunsaturated fatty acids (TG-LCPUFAs) in both the liver and BAT, consistent with a role in lipid remodeling.

These findings reveal striking tissue- and context-specific regulation of PNPLA3, but a conserved association between its expression and TG-LCPUFAs levels, suggesting that PNPLA3 modulates lipid remodeling in response to metabolic stress and that disrupting this function may contribute to SLD susceptibility.

Despite being the strongest genetic risk factor for steatotic liver disease, PNPLA3's physiological role remains unclear. Using mouse models, this study reveals that PNPLA3 is regulated in a tissue-specific manner in response to feeding and cold exposure, thereby promoting remodeling of cellular lipids to adapt to dietary and environmental challenges. The localization of PNPLA3 action and its tissue-specific regulation are directly relevant to hepatologists and metabolic researchers aiming to understand its influence on intracellular lipid composition and its effects on disease susceptibility. Moreover, modulation of PNPLA3 turnover - and its impact on long-chain polyunsaturated fatty acid remodeling - emerges as a potential therapeutic strategy for regulating lipid homeostasis in steatotic liver disease.