MAPK15 PROTECTS AGAINST THE DEVELOPMENT OF METABOLIC DYSFUNCTION-ASSOCIATED STEATOTIC LIVER DISEASE

Accumulation of lipids in the liver characterizes metabolic dysfunction-associated steatotic liver disease (MASLD), the most prevalent chronic liver disease worldwide. As liver injury progresses to metabolic dysfunction-associated steatohepatitis (MASH), MASLD can predispose individuals to cirrhosis and hepatocellular carcinoma. Here, we characterized the first knockout mouse model for mitogen-activated protein kinase 15 (MAPK15) and revealed its critical role in controlling lipid homeostasis in the liver. Indeed, Mapk15 ^-/- mice exhibited a MASLD-like phenotype, and hepatocellular models allowed us to demonstrate that dysregulated accumulation of lipids was due to increased expression and membrane localization of the CD36 fatty acid translocase. Consistently, Mapk15 ^-/- mice exhibited elevated hepatic levels of CD36 and feeding them with a western-type diet significantly accelerated their progression to a MASH-like phenotype. Ultimately, transcriptomic analysis of human cohorts revealed increased liver expression of MAPK15 in MASLD patients, compared to unaffected individuals, ultimately supporting a protective role for MAPK15 against this disease. Overall, our data highlight a critical role for MAPK15 in liver physiopathology, by contributing to maintain physiological intracellular levels of lipids in this tissue.