Description
Alzheimer’s Disease (AD) is a neurodegenerative disease characterized by amyloid plaques, which are composed of insoluble Aβ42. Plaques accumulate despite the fact that neurons have systems to degrade them. In the endolysosomal system, proteins are trafficked to lysosomes where they are degraded by enzymes, such as Cathepsins. In models of AD, this system appears to be malfunctioning. Accumulations of Aβ42 reduce the functionality of the endolysosomal system to some degree. We and others have chosen Drosophila photoreceptors to model AD, yet our study system has consequences. Light can induce photoreceptors to endocytose the receptor protein Rhodopsin. If photoreceptors contain lysosome-impairing mutations, Rhodopsin aggregates and causes degeneration. Furthermore, we have shown that light increases the amount of degeneration seen in Aβ42-expressing photoreceptors. If we predict that Aβ42 dramatically impairs lysosomal function, we must account for the effect that light-dependent Rhodopsin endocytosis may have on degeneration. To test this, we developed an assay that tracks Cathepsin through the endolysosomal system. Cathepsin becomes functional when its pro-region is cleaved in a lysosome, and thus we can see a molecular weight difference between pro and mature Cathepsin. Using this assay, we can compare lysosomal function of Aβ42 mutants to that of wildtype flies and determine how severely endolysosomal function is impaired. If the endocytosis of Rhodopsin exacerbates the lysosomal defects caused by Aβ42, we will see a greater level of degeneration in light-reared flies. Through experimentation with other AD models, we can determine if this characteristic of Drosophila photoreceptors applies to all AD models.
Lysosomal function in a Drosophila model of Alzheimer's Disease
Alzheimer’s Disease (AD) is a neurodegenerative disease characterized by amyloid plaques, which are composed of insoluble Aβ42. Plaques accumulate despite the fact that neurons have systems to degrade them. In the endolysosomal system, proteins are trafficked to lysosomes where they are degraded by enzymes, such as Cathepsins. In models of AD, this system appears to be malfunctioning. Accumulations of Aβ42 reduce the functionality of the endolysosomal system to some degree. We and others have chosen Drosophila photoreceptors to model AD, yet our study system has consequences. Light can induce photoreceptors to endocytose the receptor protein Rhodopsin. If photoreceptors contain lysosome-impairing mutations, Rhodopsin aggregates and causes degeneration. Furthermore, we have shown that light increases the amount of degeneration seen in Aβ42-expressing photoreceptors. If we predict that Aβ42 dramatically impairs lysosomal function, we must account for the effect that light-dependent Rhodopsin endocytosis may have on degeneration. To test this, we developed an assay that tracks Cathepsin through the endolysosomal system. Cathepsin becomes functional when its pro-region is cleaved in a lysosome, and thus we can see a molecular weight difference between pro and mature Cathepsin. Using this assay, we can compare lysosomal function of Aβ42 mutants to that of wildtype flies and determine how severely endolysosomal function is impaired. If the endocytosis of Rhodopsin exacerbates the lysosomal defects caused by Aβ42, we will see a greater level of degeneration in light-reared flies. Through experimentation with other AD models, we can determine if this characteristic of Drosophila photoreceptors applies to all AD models.