Degeneration of Photoreceptor Cells in Arylsulfatase G-Deficient Mice

PURPOSE: Retinal degeneration is a common feature of several lysosomal storage disorders, including the mucopolysaccharidoses, a group of metabolic disorders that is characterized by widespread accumulation of glycosaminoglycans due to lysosomal enzyme dysfunction. We used a new mouse model of mucopolysaccharidosis IIIE to study the effect of Arylsulfatase G (ARSG) deficiency on retina integrity.

METHODS: The retina of Arsg knockout mice aged 1 to 24 months was studied by immunohistochemistry and Western blot analysis. Electron microscopic analyses were performed on retinas from 15- and 22-month-old animals. Photoreceptor and microglia cell numbers and retina thickness were determined to quantitatively characterize retinal degeneration in ARSG-deficient mice.

RESULTS: Arsg knockout mice showed a progressive degeneration of photoreceptor cells starting between 1 and 6 months of age, resulting in the loss of more than 50% of photoreceptor cells in 24-month-old mice. Photoreceptor loss was accompanied by reactive astrogliosis, reactive microgliosis that was evident in the outer but not inner retina, and elevated expression levels of some lysosomal proteins. Electron microscopic analyses of retinas revealed no evidence for the presence of storage vacuoles. Of note, expression of ARSG protein in wild-type mice was detectable only in the RPE which, however, appeared morphologically unaffected in knockout mice at the electron microscopic level.

CONCLUSIONS: To our knowledge, this is the first study demonstrating that ARSG deficiency results in progressive photoreceptor degeneration and dysregulation of various lysosomal proteins.