Uptake of alpha-(L)-iduronidase produced by retrovirally transduced fibroblasts into neuronal and glial cells in vitro

The uptake of recombinant alpha-(L)-iduronidase into glial and neuronal cells, produced by retrovirally transduced NIH3T3 fibroblasts, was studied. We demonstrate that: (1) neuronal and glial cells take up alpha-(L)-iduronidase released into the medium by retrovirally transduced fibroblasts expressing high levels of alpha-(L)-iduronidase; (2) both glial and neuronal cells express the cation independent mannose-6-phosphate receptor responsible for lysosomal enzyme uptake; and (3) uptake of the lysosomal enzyme can be blocked by excess free mannose-6-phosphate, but not glucose-6-phosphate. Thus, various brain cells take up alpha-(L)-iduronidase, possibly through a cation independent mannose-6-phosphate receptor mediated pathway, and this uptake is higher in actively dividing or immature brain cells. Consequently, (1) neuronal metabolism ought to be capable of cross correction by enzyme provided by genetically engineered and transplanted cells provided by bone marrow transplantation (BMT); (2) that BMT could have a more beneficial effect on neurological function if performed as early as possible; and (3) given that the uptake mechanism of glial cells has a higher capacity, it might be easier to target diseases like the leukodystrophies in which lysosomal enzymes are needed in glial cells, compared to diseases where lysosomal enzymes ought to be delivered into neurons.