Enhanced lysosomal glycogen breakdown is associated with liver tumorigenesis in glycogen storage disease type III

Glycogen storage disease type III (GSDIII) is a rare metabolic disorder caused by mutations in the glycogen debranching enzyme (AGL), leading to hepatic glycogen accumulation, fibrosis and increased hepatocellular carcinoma (HCC) risk. This study investigates the metabolic mechanisms driving liver tumorigenesis in an Agl ^-/- model of GSDIII.

Liver and tumor samples from 14-month-old Agl ^-/- and Agl ^+/+ mice, and liver biopsies from patients with GSDIII (n = 4), were analyzed using histological, biochemical and molecular approaches.

Agl ^-/- mice recapitulated key features of GSDIII, including a 3.5-fold hepatic glycogen overload (p <0.001), and chronic liver disease. More than 30% of the animals developed liver tumors, associated with a 2.5-fold increase in alpha-fetoprotein levels (p <0.005). Despite marked reductions in glucose (7.5-fold, p <0.0001), glucose-6 phosphate (266-fold, p <0.0001), lactate (8-fold, p <0.005), cholesterol (1.9-fold, p <0.001) and triglyceride levels (6.2-fold, p <0.001) in the liver, glycaemia was maintained at around 87.0 ± 9.6 mg/dl after 6 h of fasting, through activated extrahepatic, but not hepatic, gluconeogenesis. Intriguingly, most tumors exhibited lower glycogen content than surrounding tissue (3.3-fold decrease, p <0.0001), which was associated with increased lysosomal alpha-acid glucosidase activity (19.5 ± 5.5 in tumor vs. 9.9 ± 2.0 mmol/h/mg in Agl ^-/- liver; p <0.0005) and the presence of glycophagosomes. PAS-negative staining in HCCs from patients with GSDIII supported these observations. Although YAP nuclear staining varied among tumors, the overall increase in YAP nuclear localization and CTGF expression suggests that inhibition of the Hippo/YAP pathway may contribute to tumorigenesis in GSDIII hepatocytes.

In GSDIII, liver metabolism is characterized by the accumulation of structurally abnormal glycogen and a significant reduction of key energy substrates. In this metabolic context, enhanced lysosomal glycogen degradation may support tumor growth, highlighting a mechanistic link between glycogen metabolism and the development of liver cancer.

This study provides novel insights into the metabolic dysregulations driving liver tumorigenesis in glycogen storage disease type III (GSDIII). Our findings reveal a potential link between abnormal glycogen accumulation and liver cancer, highlighting the pivotal role of lysosomal glycogen degradation in supporting tumor growth. These results are particularly important for researchers and clinicians working on metabolic liver diseases, as they suggest potential glycogen-targeting therapeutic strategies for GSDIII and other related liver disorders. Practically, they could guide future interventions aimed at modulating glycogen metabolism, offering new treatment avenues for patients with GSDIII at risk of hepatocellular carcinoma, while contributing to the broader understanding of metabolic dysregulation in cancer biology.