| Summary: | Gaucher disease (GD) results from mutations in the <i>GBA1</i> gene, which encodes lysosomal glucocerebrosidase (GCase). The large number of mutations known to date in the gene lead to a heterogeneous disorder, which is divided into a non-neuronopathic, type 1 GD, and two neurological, type 2 and type 3, forms. We studied the two fly <i>GBA1</i> orthologs, <i>GBA1a</i> and <i>GBA1b</i>. Each contains a Minos element insertion, which truncates its coding sequence. In the <i>GBA1a<sup>m/m</sup></i> flies, which express a mutant protein, missing 33 C-terminal amino acids, there was no decrease in GCase activity or substrate accumulation. However, <i>GBA1b<sup>m/m</sup></i> mutant flies presented a significant decrease in GCase activity with concomitant substrate accumulation, which included C14:1 glucosylceramide and C14:0 glucosylsphingosine. <i>GBA1b<sup>m/m</sup></i> mutant flies showed activation of the Unfolded Protein Response (UPR) and presented inflammation and neuroinflammation that culminated in development of a neuronopathic disease. Treatment with ambroxol did not rescue GCase activity or reduce substrate accumulation; however, it ameliorated UPR, inflammation and neuroinflammation, and increased life span. Our results highlight the resemblance between the phenotype of the <i>GBA1b<sup>m/m</sup></i> mutant fly and neuronopathic GD and underlie its relevance in further GD studies as well as a model to test possible therapeutic modalities.
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