Increased longevity and metabolic correction following syngeneic BMT in a murine model of mucopolysaccharidosis type I

Abstract

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive inherited disease caused by deficiency of the glycosidase α-L-iduronidase (IDUA). Deficiency of IDUA leads to lysosomal accumulation of glycosaminoglycans (GAG) heparan and dermatan sulfate and associated multi-systemic disease, the most severe form of which is known as Hurler syndrome. Since 1981, the treatment of Hurler patients has often included allogeneic BMT from a matched donor. However, mouse models of the disease were not developed until 1997. To further characterize the MPS-I mouse model and to study the effectiveness of BMT in these animals, we engrafted a cohort (n=33) of 4-8-week-old Idua(-/-) animals with high levels (88.4±10.3%) of wild-type donor marrow. Engrafted animals displayed an increased lifespan, preserved cardiac function, partially restored IDUA activity in peripheral organs and decreased GAG accumulation in both peripheral organs and in the brain. However, levels of GAG and GM3 ganglioside in the brain remained elevated in comparison to unaffected animals. As these results are similar to those observed in Hurler patients following BMT, this murine-transplantation model can be used to evaluate the effects of novel, more effective methods of delivering IDUA to the brain as an adjunct to BMT.

Figure 1. Survival of MPS I mice engrafted with syngeneic marrow compared to untreated MPS I animals

The Kaplan-Meier plot shows the percentage of animals surviving to the indicated age in weeks depicted on the x-axis. Lines on the graph represent untreated Idua^−/− animals (thin grey) and Idua^−/− animals treated by BMT at 4–6 weeks of age (thick black).

Figure 2. IDUA activity levels in peripheral organs and brain

(a) Mean (± S.D.) IDUA activity detected in peripheral organs of BMT recipient MPS I mice (MPS I + BMT) and heterozygous control animals (Het). (b) Mean percentage of heterozygous IDUA levels detected in the peripheral organs of BMT recipient animals. (c) Mean (± S.D.) IDUA activity in microdissected brain samples from unaffected heterozygous animals. IDUA activity was undetectable in peripheral organ and brain samples from untreated MPS I animals and in brain samples from BMT recipient mice.

Figure 3. GAG storage in peripheral organs following BMT

Levels of GAG storage material detected in the peripheral organs of MPS I (MPS I, circles), heterozygous (Het, squares) and BMT recipient mice (MPS I + BMT, triangles). The mean is indicated by a solid line. ***P < 0.001, **P < 0.01, *P < 0.05 by one-way ANOVA as compared to untreated MPS I mice; Δ = no statistical significance compared to heterozygous animals by one-way ANOVA.

Figure 4. Relationship between GAG reduction and IDUA activity level in peripheral organs of BMT recipients

The mean percent reduction of GAG storage material detected in each peripheral organ (BMT-treated mice compared to untreated MPS I mice) was plotted vs. the mean percentage of heterozygous IDUA activity (BMT-treated mice compared to heterozygous mice) detected in the same organ The correlative relationship between GAG storage and IDUA activity corresponded to a hyperbolic model with coefficient of determination (R²) value = 0.95.

Figure 5. GAG levels in the brain

(a) Levels of GAG storage material detected in microdissected regions of brain tissue collected from MPS I (MPS I, circles), heterozygous (Het, squares) and BMT recipient mice (MPS I + BMT, triangles). The mean is indicated by a solid line. (b) Mean (± S.D.) GAG content detected in the brains of MPS I (MPS I, white bar), heterozygous (Het, black bar) and BMT recipient mice (MPS I + BMT, grey bar) upon compiling all data points in part (a). *P < 0.05 (MPS I vs. MPS I + BMT), ***P < 0.001 (MPS I vs. Het) by one-way ANOVA.

Figure 6. GM3 ganglioside accumulation in the brain

GM3 ganglioside, a substrate that accumulates in neurons and glia of MPS I animals (27, 38), was visualized by immunofluorescence microscopy as punctate aggregates (white arrows) within grey matter throughout the brains of untreated MPS I mice. Representative images demonstrate focal accumulation of GM3 ganglioside in the dentate gyrus region of the hippocampus and within the septal nucleus, both parts of the limbic system. These GM3 ganglioside aggregates were absent from the grey matter of Idua^+/− mice, but persisted in the brains of BMT recipient mice.