Background and aim <p>Liver regeneration is impaired in end-stage liver disease characterized by advanced fibrosis and cirrhosis, where metabolic reprogramming is considered as a therapeutic target. The shift in glutaminolysis from liver-type Glutaminase 2 (GLS2) to kidney-type Glutaminase 1 (GLS1) is crucial in different liver diseases, though its role in liver progenitor cell-mediated regeneration remains unclear. This study aimed to analyze the expression of glutamine-metabolizing enzymes in fibrotic human livers and investigate the role of GLS1 in LGR5⁺-progenitor cell expansion in liver regeneration.</p> Methods <p>Healthy and chronically diseased human liver tissue from patients with alcoholic liver disease, viral hepatitis, biliary atresia, primary biliary cholangitis or non-alcoholic steatohepatitis were immunostained for GLS1, GLS2 and glutamine synthetase (GS), and co-stained for LGR5. GLS1 was inhibited in adult progenitor cell-rived human liver organoids to evaluate its role in stemness and cell proliferation pathways.</p> Results <p>GLS1 expression was enhanced and GLS2 decreased in chronic liver diseases compared to healthy liver. GLS1 was expressed in parenchymal, including hepatocytes, and non-parenchymal cells. In cirrhotic livers, GLS1⁺ hepatocytes showed a spatial distribution comparable to the progenitor cell marker LGR5. The GLS1 inhibitor CB839 suppressed progenitor cell markers (LGR5 and AXIN2) via the ROS-Wnt/β-Catenin pathway, which was rescued by glutathione (GSH). The CB839-mediated decrease in cell proliferation in human liver organoids was rescued by non-essential amino acids.</p> Conclusions <p>This study identifies GLS1 as a metabolic regulator of progenitor cell expansion aiding liver regeneration in various etiologies of human liver cirrhosis.</p>