Roles of Cdk5 in neurodevelopment and neurodegeneration

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In the past year, we have expanded our efforts in this project in two new directions. - Over the previous several years, we had found that transcriptomic profiling of Drosophila offered an exceptionally rich vein for identifying and dissecting processes involved in neurodegeneration, aging, and mortality. However, the transcriptome is several steps removed from the actual physiology of the organism. Transcriptional changes have to be filtered through splicing, RNA stability, translation, protein localization, post-translational modification and other processes before their consequences can be read-out in animal physiology. We therefore felt it was essential to complement our transcriptomic studies with another systems measure that is closer to animal physiology. To that end, we have initiated a collaboration with the NIH Metabolomics Core to query the complete metabolome of Drosophila across the lifespan, both in wild type animals and in animals destined to undergo neurodegeneration due to altered activity of Cdk5/p35, and to do so in both the presence and absence of a bacterial microbiome. These experiments are just beginning, but we are confident that they will provide valuable and unexpected insights into the physiological changes that accompany aging, disease, and mortality. - Consistent with a great deal of evidence from other investigators, our previous transcriptomic studies had targeted mitochondrial function as a key cellular pathway associated with aging and neurodegeneration. Therefore, in the past year we have initiated detailed analysis of mitochondrial localization and activity in the fly brain, both in wild type and in flies with altered Cdk5 /p35 activity, focusing on regions of the brain that we know to be sensitive to Cdk5-associated degeneration. Preliminary experiments suggest differential localization of mitochondria to different portions of the axon in flies destined to undergo degeneration. We have also obtained and expressed bioprobes for different aspects of mitochondrial metabolism and function, including different markers of redox state, ATP/ADP ratio, and NAD+/NADP ratio. Preliminary experiments validate the activity of those bioprobes and suggest that there may indeed be changes in mitochondrial function in degeneration-sensitive areas of the brain. These experiments need to be repeated and extended. If validated, future experiments will be directed toward testing whether mitochondrial effects we observe are pathogenic in nature, or whether they reflect compensatory mechanisms meant to protect the brain from damage.