Abstract
Mucopolysaccharidosis type II (MPS II) is an X-linked disorder resulting from a deficiency in iduronate 2-sulfatase (IDS), which is reported to be caused by gene mutations in the iduronate 2-sulfatase (IDS) gene. Many IDS mutation sites have not yet had their causal relationship with MPS II characterized. We employed a gain-of-function strategy whereby we microinjected different mutated zebrafish ids (z-ids) mRNAs corresponded to human IDS gene into zebrafish embryos, and then measured their total IDS enzymatic activity and observed the occurrence of defective phenotypes during embryonic development. We examined three known mutation sites for human IDS genes (h-IDS) associated with MPS II symptoms, including h-IDS-P86L, -S333L and -R468W, which corresponded to z-ids-P80L, -S327L and -R454W. When these three mutated z-ids mRNAs were overexpressed in zebrafish embryos, the IDS enzymatic activity of the total proteins extracted from the injected embryos was not increased compared with the endogenous IDS of the untreated embryos, which suggests that the IDS enzymatic activity of these three mutated z-ids was totally lost, as expected. Additionally, we observed defective phenotypes in these injected embryos, resulting from the failed IDS enzyme breakdown, which, in turn, has a dominant negative effect on the endogenous wild-type IDS function. These phenotypes were similar to the clinical symptoms observed in MPS II pathogenesis. We further studied six uncharacterized IDS mutation sites as identified by the Taiwanese MPS newborn screening programs. We propose a novel IDS enzyme activity assay combined with phenotypic observation in zebrafish embryos, as an alternative platform for quickly providing a valuable index for preliminarily assessment of any identified IDS point mutation gene that has not yet been characterized, in the context of its role in MPS II development.
Highlights
Mucopolysaccharidosis type II (MPS II), or Hunter syndrome, is a lysosomal storage disorder, characterized by a lack of the specific enzymes that break down fats or sugars
We compared the z-iduronate 2-sulfatase (IDS) enzymatic activity of the zebrafish embryos injected with z-ids mRNA (300 pg/embryo), and we found it to be significantly increased at 1.71 ± 0.12 (Figure 1)
These findings suggest that injection of z-ids mRNA increased the total amount of z-IDS in the zebrafish embryos, leading to increased z-IDS enzymatic activity
Summary
Mucopolysaccharidosis type II (MPS II), or Hunter syndrome, is a lysosomal storage disorder, characterized by a lack of the specific enzymes that break down fats or sugars. It is an X-linked disorder resulting from a deficiency in iduronate 2-sulfatase (IDS), which catalyzes the hydrolysis of the 2-sulphate group of dermatan sulfate and heparan sulfate. Patients with the mild form of MPS II usually have attenuated somatic complications without mental disability. Patients with the severe form of MPS II show early somatic abnormalities combined with skeletal deformities, hepatosplenomegaly, and progressive cardiopulmonary deterioration. Neurological damage presents progressively and prominently as developmental delay and intellectual disability, often concomitant with neurodegeneration
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