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The neuronal ceroid lipofuscinoses (NCLs) are the most common cause of childhood dementia and are invariably fatal. Early, localised glial activation occurs in all forms of NCL and has been shown to be an accurate predictor of areas in which neuronal loss is most pronounced. Indeed, in a tissue culture model of juvenile NCL, glial cells have been shown to actively contribute to neuronal dysfunction and death. So far the role of glial cells has not been established in other forms of NCL and in order to assess glial function in infantile NCL (INCL, CLN1 disease), a series of different tissue cultures were generated from Ppt1 deficient mice (Ppt1-/- ). These studies revealed that both Ppt1-/-astrocytes and microglia exhibit a more activated phenotype under basal conditions, as well as alterations to their protein expression profile following pharmacological stimulation. Ppt1-/- astrocytes displayed moderately reduced glutamate uptake, as well as changes in lactate release. Perhaps as a consequence of these changes, Ppt1- /-astrocyte survival was severely impaired. In addition the morphological phenotypes of Ppt1-/-neurons were explored, revealing decreased neurite outgrowth, complexity and a reduction in cell body size. Ppt1-/-neuronal cultures contained significantly fewer inhibitory neurons and displayed decreased cell survival after prolonged time in culture. Most importantly, using a co-culture system, the presence of Ppt1-/- glial cells appeared to increase cell death in both WT and Ppt1-/- cultures. Notably, Ppt1-/- microglia appeared to trigger increased Ppt1-/- neuronal death, whereas Ppt1-/- astrocytes also exhibited increased cell death. Ppt1-/- glial cells also affected both wild type and Ppt1-/- neuronal morphology, including further reduced neurite outgrowth. In contrast, wild type glial cells ameliorated some of the morphological defects observed in Ppt1-/- neurons, and this was most apparent when wild type astrocytes where grown in co-cultures with Ppt1-/- neurons. Taken together, these finding present novel evidence for compromised glial function in Cln1 disease, demonstrating that both Ppt1-/- microglia and astrocytes may potentially contribute to the neurodegeneration observed in CLN1 disease. These data highlight the importance of targeting glial cells in the development of therapeutic interventions for CLN1 disease. Furthermore, although sharing some similarities Ppt1-/-glial phenotypes were broadly different from those observed in the tissue culture model of juvenile NCL, suggesting that the role of glia may differ between forms of NCL. |
