The liver plays a central role in regulating the transition between fasting and feeding states, coordinating glycogen breakdown, gluconeogenesis, fatty acid catabolism, and lipid storage. Disruptions in this balance contribute to metabolic disorders, including Metabolic dysfunction Associated Steatotic Liver Disease (MASLD). Here, we identify a novel biological pathway downstream of glucagon that promotes the hepatic lipid accumulation associated with fasting. Using gain- and loss-of-function in vivo and in vitro models, we found that glucagon induces sustained expression of PGC-1α4, promoting lipid uptake and storage in hepatocytes by increasing PPARγ activity. Increased PPARγ/PGC-1α4 promotes hepatic Fsp27/Cidec expression, leading to lipid droplet expansion and triglyceride trapping in liver. Activity of the PPARGC1A alternative promoter and PGC-1α4 expression were higher in livers of patients with MASLD, and PGC-1α4 expression correlated with macrosteatosis. Consistently, persistent expression of hepatic PGC-1α4 in mice fed a western diet promoted macrosteatosis, exacerbated oxidative stress and altered hepatic lipid composition to resemble worsening Metabolic dysfunction Associated Steatohepatitis (MASH) in humans. Our findings demonstrate that glucagon-induced hepatic PGC-1α4/PPARγ activity facilitates efficient uptake and storage of lipids during fasting, but over-activation of this coordinated metabolic pathway leads to lipid accumulation and worsening of steatosis in MASLD.
Güneş et al. (Mon,) studied this question.