Distinct Mechanistic Pathways in Mouse MASLD Models: High-Sucrose/Starch Versus High-Fat, Methionine- and Choline-Deficient Diets

• Investigated genomic responses in fatty liver disease following a high sucrose or high-fat MCD diet • Both diets induced MASLD and repressed glycolysis, cholesterol and lipid biogenesis • The high sucrose/high starch diet stimulates benign steatosis without inflammation • The high-fat MCD diet causes steatohepatitis with early signs of fibrosis Metabolic dysfunction-associated steatotic liver disease (MASLD) ranges from simple steatosis (MASL) to fibrotic steatohepatitis (MASH). Yet, the molecular mechanisms initiating these divergent outcomes remain unclear. We addressed the question whether MASLD induced by a high-sucrose/ starch diet (MCS) is similar to a high-fat, methionine- and choline-deficient diet (MCD+HFD). To investigate early genomic programming events in these MASLD models, we fed C57BL/6N mice either an MCS or MCD+HFD for 14 days. Histopathology and serum biochemistries confirmed MASLD phenotypes and transcriptomics guided pathway enrichment analysis. Furthermore, ChIP-seq-validated transcription factor targets enabled construction of regulatory gene networks (RGNs) in glucose homeostasis and lipid metabolism. Importantly, the MCS and MCD+HFD caused 692 and 703 differentially expressed genes, and although transcriptomics revealed shared genomic responses, we also observed diet-specific adaptations. Both diets repressed glycolysis, yet MCS showed broader suppression. Furthermore, fatty acid β-oxidation and lipid droplet biogenesis was induced whereas lipogenesis, cholesterol biosynthesis and the kynurenine pathway were repressed. Strikingly, the high-sucrose/high-starch diet suppressed acute-phase, prostaglandin, redox, antigen presentation, and autophagy pathways. Conversely, the high-fat MCD-diet activated cytokine signalling, macrophage networks, and inflammatory programs. Intriguingly, RGNs aided an identification of diet-specific master regulatory networks with MCS stimulating Insig2, Id1 , and Mafb signalling. Conversely, the high-fat MCD-diet silenced Srebf1, Scd1 , and Acly . Together, our findings highlight early genomic reprogramming events in MASLD, and unlike the high-fat MCD-diet which stimulates MASH, we report high-sucrose/high-starch to elicit benign steatosis without inflammation.