Neuronal health depends on quality control functions of autophagy, but mechanisms regulating neuronal autophagy are poorly understood. Previously, we showed that in Drosophila starvation-independent quality control autophagy is regulated by Acinus and the Cdk5-dependent phosphorylation of its serine437 (Nandi et al., 2017). Here, we identify the phosphatase that counterbalances this activity and provides for the dynamic nature of Acinus-S437 phosphorylation. A genetic screen identified six phosphatases that genetically interacted with an Acinus gain-of-function model. Among these, loss of function of only one, the PPM-type phosphatase Nil (CG6036), enhanced pS437-Acinus levels. Cdk5-dependent phosphorylation of Acinus serine437 in nil1 animals elevates neuronal autophagy and reduces the accumulation of polyQ proteins in a Drosophila Huntington's disease model. Consistent with previous findings that Cd2+ inhibits PPM-type phosphatases, Cd2+-exposure elevated Acinus-serine437 phosphorylation which was necessary for increased neuronal autophagy and protection against Cd2+-induced cytotoxicity. Together, our data establish the Acinus-S437 phospho-switch as critical integrator of multiple stress signals regulating neuronal autophagy.

Neuronal health depends on quality control functions of autophagy, but mechanisms regulating neuronal autophagy are poorly understood. Previously, we showed that in Drosophila starvation-independent quality control autophagy is regulated by Acinus and the Cdk5-dependent phosphorylation of its serine437 (Nandi et al., 2017). Here, we identify the phosphatase that counterbalances this activity and provides for the dynamic nature of Acinus-S437 phosphorylation. A genetic screen identified six phosphatases that genetically interacted with an Acinus gain-of-function model. Among these, loss of function of only one, the PPM-type phosphatase Nil (CG6036), enhanced pS437-Acinus levels. Cdk5-dependent phosphorylation of Acinus serine437 in nil1 animals elevates neuronal autophagy and reduces the accumulation of polyQ proteins in a Drosophila Huntington's disease model. Consistent with previous findings that Cd2+ inhibits PPM-type phosphatases, Cd2+-exposure elevated Acinus-serine437 phosphorylation which was necessary for increased neuronal autophagy and protection against Cd2+-induced cytotoxicity. Together, our data establish the Acinus-S437 phospho-switch as critical integrator of multiple stress signals regulating neuronal autophagy.

Neurodegenerative diseases affect millions of people worldwide and will soon become the most expensive diseases to treat ahead of cancer and diabetes in the next 20–30 years. Most neurodegenerative diseases such as Alzheimer’s, Parkinson’s and Huntington’s are caused by the failure of neurons and glial cells to clear out cellular debris. Autophagy is the process that cells both in the central nervous system as well as in the periphery use to clear out misfolded proteins and damaged organelles from the cytoplasm. This process is incredibly important as it is through this very mechanism that our bodies combat the development of neurodegeneration. This process has been found to be controlled by a protein named Acinus in the Drosophila Melanogaster. Acinus’s role in this process is still not fully understood, but my project has been to elucidate some of its mechanisms through the use of the Drosophila Melanogaster animal model. Before entering the lab, the Kramer Lab at UT Southwestern had just recently published a paper characterizing the kinase of Acinus. A kinase is a protein that phosphorylates another protein to activate/deactivate the receiving protein’s function. The kinase is the first step in understanding the regulatory pathway that triggers the phosphorylation or activation of Acinus. However, since the autophagy process is tightly regulated, meaning the fluctuation of its function can be detrimental to the animal’s well‐being, there must be an inhibitory protein that controls Acinus and prevents Acinus’s fatal overactivity. With this, the dephosphorylation event of Acinus is an equally important phenomenon to understand due to its incredible scope of influence in autophagy. The approach to study the phosphatase was bipartite. The first would be to screen for a phosphatase using the sensitized Drosophila eye‐system. Through use of an RNAi‐mediated knockdown, flies were engineered using the UAS‐GAL4 system to test which phosphatase would be in some way interacting with Acinus. Acinus over‐expression produced a rough eye as a phenotype so a hit would present as a very rough eye. As a result, 6 possible hits were found possibly interacting and a qPCR found 1 robust candidate. The second experiment was to understand the triggers that cause Acinus to become phosphorylated and trigger autophagy. This would be done by treating flies with a toxic metal ion that is known to be conducive to Acinus phosphorylation to save the cell from toxicological death. As a result, flies that survived longer would show decreased levels of phosphatase inhibition and would live longer. The experiment showed that flies that had a mutant phosphatase and were subjected to toxicological stress had increased phosphorylation which lead to increased survivability on the order of 3–7 days. This research has shown that increased Acinus phosphorylation led to increased survivability and guides us to research more about what mechanisms the cell employs to combat disease‐specific stresses. This data is exciting because it offers a glimpse into...

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