Modeling Phenotypic Heterogeneity of Glycogen Storage Disease Type 1a Liver Disease in Mice by Somatic CRISPR/CRISPR‐associated protein 9–Mediated Gene Editing

Abstract

BaCKgRoUND aND aIMS: Patients with glycogen storage disease type 1a (GSD-1a) primarily present with lifethreatening hypoglycemia and display severe liver disease characterized by hepatomegaly. Despite strict dietary management, long-term complications still occur, such as liver tumor development. Variations in residual glucose-6-phosphatase (G6PC1) activity likely contribute to phenotypic heterogeneity in biochemical symptoms and complications between patients. However, lack of insight into the relationship between G6PC1 activity and symptoms/complications and poor understanding of the underlying disease mechanisms pose major challenges to provide optimal health care and quality of life for GSD-1a patients. Currently available GSD-1a animal models are not suitable to systematically investigate the relationship between hepatic G6PC activity and phenotypic heterogeneity or the contribution of gene-gene interactions (GGIs) in the liver.appRoaCH aND ReSUltS: To meet these needs, we generated and characterized a hepatocyte-specific GSD-1a mouse model using somatic CRISPR/CRISPR-associated protein 9 (Cas9)-mediated gene editing. Hepatic G6pc editing reduced hepatic G6PC activity up to 98% and resulted in failure to thrive, fasting hypoglycemia, hypertriglyceridemia, hepatomegaly, hepatic steatosis (HS), and increased liver tumor incidence. This approach was furthermore successful in simultaneously modulating hepatic G6PC and carbohydrate response element-binding protein, a transcription factor that is activated in GSD-1a and protects against HS under these conditions. Importantly, it also allowed for the modeling of a spectrum of GSD-1a phenotypes in terms of hepatic G6PC activity, fasting hypoglycemia, hypertriglyceridemia, hepatomegaly and HS. CoNClUSIoNS:In conclusion, we show that somatic CRISPR/Cas9-mediated gene editing allows for the modeling of a spectrum of hepatocyte-borne GSD-1a disease symptoms in mice and to efficiently study GGIs in the liver. This approach opens perspectives for translational research and will likely contribute to personalized treatments for GSD-1a and other genetic liver diseases.

Mitochondrial reprogramming in peripheral blood mononuclear cells of patients with glycogen storage disease type Ia

“…We hypothesize that enhanced expression of CPT1A accompanied by the increased VLCAD and CPT2 activity in PBMC may likely represents a mechanism to counter-act malonyl-CoA-induced inhibition of hepatic CPT1 activity in response to high circulating fatty acids [ 25 ]. A possible correlation between (increased) expression of genes involved in FAO and residual G6Pase-α activity has been recently reported in G6pc −/− mice [ 33 ], supporting this hypothesis. Since 8/10 GSDIa patients carried G6PC mutations which completely abolished G6Pase-α activity [ 1 ], a correlation between FAO upregulation and estimated G6Pase-α residual activity could not be assessed in the present study.…”

Glycogen storage disease type I: Genetic etiology, clinical manifestations, and conventional and gene therapies

“…Demonstrated that affected mice with residual G6PC activity <60% showed a markedly increase in hepatomegaly, fasting hypoglycemia, hyperlactatemia, hypertriglyceridemia, glycogen contents, as well as oleate synthesis. These symptoms were more prominent in affected mice with G6PC activity <25% 34 …”

Induced Pluripotent Stem Cells and CRISPR-Cas9 Innovations for Treating Alpha-1 Antitrypsin Deficiency and Glycogen Storage Diseases

“…Post-editing metabolic assays confirmed the normalized metabolic pathways in these cells, alongside their ability to maintain stable blood glucose levels under fasting conditions [ 49 ]. Rutten and colleagues generated a hepatocytic GSDIa mouse model via CRISPR-Cas9 and characterized the effects of G6PC on glucose metabolism and liver functions [ 50 ]. Their study revealed that genome-edited mouse models allow for the modeling of a variety of GSDIa phenotypes [ 50 ].…”