Batten disease is a common progressive neurodegenerative disease in children, with an incidence as high as one in 12,500 live births. The first major consequence of Batten disease is the onset of blindness due to retinal degeneration, followed by deteriorating psychomotor and mental function and premature death. Although the gene responsible for this disease, CLN3, was positionally cloned in 1995, little has been determined about the function of CLN3 in mammalian cell models. The major goal of the proposed research is to develop and utilize a neuronal cell model for the study of Cln3-mediated neurodegeneration. The investigator will use intact retinue and a retinal cell culture model, derived from the Cln3 knockout mouse for this purpose. They propose to examine the survival of retinal cells, and whether Cln3 mice undergo photoreceptor-specific apoptosis, using DNA laddering, DNA fragmentation and ssDNA analysis. Furthermore they will examine by electron microscopy the ultrastructure of retinal cells, in particular for the occurrence of lysosomal curvilinear or fingerprint-like deposits of membrane structures characteristic of Batten disease. The most promising studies into the function of CLN3 have come from the yeast homolog, Btn1p. It has been established that deletion of Btn1p results in a more acidic vacuole (lysosomal), and that this altered pH is corrected by manipulating proton pumping at the plasma membrane through increased expression of HSP30, and through increased expression of BTN2, which is implicated in a novel endocytic pathway. The investigator intends to measure lysosomal pH in primary retinal culture from Cln2 and control normal mice and to determine whether pH homeostasis is disturbed in Cln3 cells. Endocytosis will be monitored by confocal microscopy through the uptake of fluorescent dyes that associate to acidified compartments, and the recycling of tagged transferrin conjugates in both Cln3 and control normal primary culture. Furthermore, for the first time this model system will allow the test of a potential therapeutic agent, chloroquine, which has been shown in the yeast model to reverse the phenotypic effects of deleting Btn1p. Overall this proposal will provide for the first time a retinal cell based model-system for the study of neurodegeneration, morphological and biochemical abnormalities characteristic of Batten disease and to test the efficacy of chloroquine as a potential therapy.
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