Decrypting linoleic acid metabolism and steatosis-induced effect in differentiated human HepaRG cells

Linoleic acid (LA) is an abundant PUFA in the human diet, with a well-known essential role in human physiology. However, excessive chronic intake of LA is also associated with metabolic disorders, including hepatic steatosis. The mechanisms underlying this association remain poorly understood. In this study, differentiated HepaRG cells were used to investigate the metabolism and effects of chronic LA exposure, compared to other fatty acids, including α-linolenic acid (ALA). The HepaRG model is indeed a human hepatocellular cell line with a high proliferative potential, capable of differentiating into hepatocytes and cholangiocytes. When loaded with incubated fatty acids, it is used as a model of metabolic dysfunction-associated steatotic liver disease (MASLD).  A first interesting result was to detect that differentiated HepaRG cells were partially deficient in D6-desaturase activity. Indeed, mRNA levels of the FADS2 gene were barely detectable and measured D6-desaturase activity showed a sharp decrease compared to primary human hepatocytes. Consequently, differentiated HepaRG cells incubated with LA displayed minimal conversion to arachidonic acid, enabling the distinction of LA-specific effects from its derivative.  Compared to ALA, LA exposure at 150 µM during 1 week led to a marked intracellular triglyceride accumulation, driven by enhanced fatty acid uptake, reduced β-oxidation, and impaired VLDL-mediated triglyceride secretion. Gene expression analyses supported these findings, showing upregulation of lipid uptake and storage markers, and downregulation of VLDL secretion-associated genes. In addition to lipid metabolism alterations, LA induced a rapid pro-inflammatory response, with increased IL-1β and IL-6 expression within hours, contrasting with ALA’s anti-inflammatory effect.  These results highlight the distinct metabolic and inflammatory responses to LA and ALA chronic exposure in HepaRG cells, reinforcing the link between excessive dietary LA and hepatic steatosis. They also underscore the need for further research into LA consumption limits and its broader implications for human health.