Defining the molecular mechanism that leads to cellular aging and neural degeneration has proven to be difficult. Many types of damage are thought to contribute to senescence and neural degeneration and include mitochondrial and nuclear DNA mutations, protein misfolding, aggregate formation, reactive oxygen species (ROS), and stem cell senescence. However, a consensus has not yet developed as to which mechanism plays a causal role in aging. Indeed, each tissue may have a select set of processes, or "Achilles'heel" that further exacerbated cellular decline. In the nervous system there is an agreement that mitochondrial senescence, the accumulation of ROS-dependent damage and the formation of protein aggregates or inclusion containing ubiquitin are involved with the most human neurological disorders, such as Alzheimer's and Parkinson's disease. There is a growing understanding that the autophagy pathway is involved with maintaining the mature nervous system by facilitating the removal of cellular damage and protein aggregates. The pathway is highly conserved and we found that expression profiles of autophagy genes show a significant decrease in the aging Drosophila CNS. At the same time, markers of cellular damage and aggregates, such as insoluble ubiquitinated aggregates (IUP), show a dramatic increase. Genetic analysis also shows that mutations in key genes significantly shorten adult lifespans (35 to 60%) and cause progressive neural defects that share striking similarities to those seen with Alzheimer's and other neurodegenerative disorders. Of greater significance is our observation that enhancing autophagy in the aging nervous system suppresses the accumulation of cellular damage (IUP) and significantly extends adult life spans. This work shows that examining factors that promote healthy neuronal aging can be done using Drosophila as a model system. In this proposal we take advantage of the conserved regulation of autophagy to identify neural protective compounds that enhance the pathway, promote longevity and neural function. This project involves several validated and optimized assays proposed in our original Phase-I application that were designed to identify compounds that enhanced autophagy, suppressed aggregate formation and extend life spans.
In Specific Aim 1 an additional assay, which assesses the ability of different treatments to suppress oxidative stress was included.
Specific Aim 2 represents an expansion of our drug-testing platform to assess the effectiveness of different compounds to promote neuronal health and function by examining their effect on several adult behaviors that show an age-dependent decline.
Specific Aim 3 takes advantage of the conserved regulation of autophgy and other key protective pathways to identify those neural protective compounds that alter gene expression profiles in the aging nervous system. The goal of this proposal is to better understand the role of clearance pathways on aging and to develop in vivo assays that identify drugs that could be used for the treatment of human neurological disorders.
Presently there is no effective treatment for Alzheimer's disease and other age-related disorders that affect millions worldwide. Developing an effective method for validating neural protective compounds would streamline the development of life saving therapies. The research outlined in this proposal used Drosophila to develop several medium-throughput in vivo screening techniques that can identify novel therapeutic compounds for the treatment of aging disorders.