Endocrine Abstracts

Glycogen storage disease 1A (GSD1A) is an inherited metabolic disorder caused by glucose-6-phosphatase (G6PC) deficiency. Patients with GSD1A present disturbed glucose homeostasis and exhibit glycogen accumulation accompanied by hepatomegaly, hypoglycemia, lactic acidosis and hyperlipidemia. However, there are currently no licensed treatments for GSD1A, and human in vitro systems for disease modelling and drug screening are lacking. We aimed to develop a human hepatocyte model recapitulating the GSD1A phenotype in-a-dish. Healthy and GSD1A patient-derived (R83C) induced pluripotent stem cells (iPSCs), alongside isogenic controls, were differentiated towards hepatocyte-like cells (HLCs). Successful differentiation was confirmed by expression of the hepatocyte markers Albumin, Alpha-1-antitrypsin, Alpha-fetoprotein and HNF4alpha using qPCR and immunocytochemistry. Mutation correction (C83R) in G6PC was performed by CRISPR/Cas9 mediated gene editing, and iPSC genotyping was confirmed by Sanger sequencing. Media glucose secretion and intracellular glycogen levels were measured by colorimetric assays. Intracellular glycogen levels were significantly reduced in healthy HLCs following 1h glucagon stimulation under starvation. However, no differences in GSD1A-derived HLCs were observed. In line with this, media glucose levels were elevated in healthy glucagon-stimulated HLCs compared to vehicle-treated ones, but not in GSD1A-HLCs, suggesting impaired glycogen breakdown towards glucose formation. In contrast, correction of disease mutation in GSD1A-HLCs reduced glycogen levels in a time dependent manner, alongside enhanced glucagon-stimulated glycogen breakdown. Finally, to confirm that the observed effects were the result of corrected G6Pase activity, transient over-expression of G6PC in unedited GSD1A-HLCs similarly resulted in increased glucose secretion, suggestive of restored glycogen mobilization. We have developed an iPSC-derived hepatocyte model that recapitulates human GSD1A phenotype in vitro. This technology provides a framework for the development of human liver disease models from patients of varied genetic disease backgrounds. Crucially, it highlights the advantage of iPSCs as an effective platform for liver disease modelling and hit-lead drug screening.