Disruption of the gaa Gene in Zebrafish Fails to Generate the Phenotype of Classical Pompe Disease.

The underlying pathogenic lesions of glycogen storage disease type II (GSD II) and the diversity of this disease among different species are still under exploration. Thus, we created an acid alpha-glucosidase (gaa) gene-mutated zebrafish model of GSD II and examined the sequential pathogenic changes. gaa mRNA and protein expression, enzymatic activity, and lysosomal glycogen accumulation were assessed, and the phenotypic changes were compared between wild-type (WT) and gaa-mutated zebrafish. The presence of a Δ13 frameshift mutation in the gaa gene was confirmed at both the DNA and transcribed mRNA levels by Sanger sequencing. The relative amount of gaa mRNA was decreased before 2 days postfertilization (dpf), after which it unexpectedly increased in the mutant compared with the WT zebrafish. Consistent with the mRNA expression, the Gaa enzymatic activity in the mutant was downregulated before 3 dpf, while the Gaa protein level was slightly decreased at 4 dpf and was maintained at a consistent level in the adult gaa mutant muscle tissue. However, more than half of the adult mutant zebrafish exhibited excessive glycogen accumulation in the liver and muscles, along with the presence of autophagosomes, as determined by transmission electron microscopy. Thus, we have successfully generated a frameshift mutation in the gaa gene in zebrafish. The unique gaa gene expression changes and mild GSD II features during the adult stage strongly indicate the existence of species-specific differences, as well as an underlying compensatory network, which may warrant further examination.