FSCN1-mediated hepatic gluconeogenesis is indispensable for neonatal mice survival

Actin-bundling protein Fascin1 (FSCN1) is encoded by the Fscn1 gene and is crucial for cytoskeletal remodeling and cellular migration. Although a previous study linked Fscn1 deficiency to neonatal lethality in mice, the underlying metabolic mechanism remains unclear. In this study, we report that systemic knockout (KO) of Fscn1 leads to 52.2% mortality within 24 h post-birth, accompanied by severe hypoglycemia in KO pups compared with their littermates. Remarkably, this lethality is fully rescued by oral glucose administration, indicating a glucose supply-dependent survival mechanism. Surviving Fscn1-KO neonates display persistent developmental deficits, including growth retardation and depleted lipid stores, despite intact canonical insulin-regulated hepatic gluconeogenic pathways. Transcriptomic profiling of P0 livers reveals that Fscn1 loss predominantly disrupts metabolic pathways, with the glycerol phosphate shuttle being the most significantly downregulated module. Mechanistically, Fscn1-KO livers exhibit markedly reduced protein levels of glycerol-3-phosphate dehydrogenase isoforms (GPD1/GPD2), key enzymes bridging glycolysis and gluconeogenesis. Consistently, glycerol tolerance tests demonstrate impaired glycerol-to-glucose conversion in Fscn1-KO mice, confirming defective glycerol-driven gluconeogenesis. Our findings establish FSCN1 as a novel cytoskeletal-metabolic integrator essential for neonatal survival by sustaining hepatic glucose production from glycerol, thus revealing an unexpected role of actin dynamics in coordinating metabolic adaptation during early postnatal development.