New Atg9 Phosphorylation Sites Regulate Autophagic Trafficking in Glia

We previously identified a role for dAuxilin (dAux), the fly homolog of Cyclin G-associated kinase, in glial autophagy contributing to Parkinson's disease (PD). To further dissect the mechanism, we present evidence here that lack of glial dAux enhanced the phosphorylation of the autophagy-related protein Atg9 at two newly identified threonine residues, T62 and T69. The enhanced Atg9 phosphorylation in the absence of dAux promotes autophagosome formation and Atg9 trafficking to the autophagosomes in glia. Whereas the expression of the non-phosphorylatable Atg9 variants suppresses the lack of dAux-induced increase in both autophagosome formation and Atg9 trafficking to autophagosome, the expression of the phosphomimetic Atg9 variants restores the lack of Atg1-induced decrease in both events. In relation to pathophysiology, Atg9 phosphorylation at T62 and T69 contributes to dopaminergic neurodegeneration and locomotor dysfunction in a Drosophila PD model. Notably, increased expression of the master autophagy regulator Atg1 promotes dAux-Atg9 interaction. Thus, we have identified a dAux-Atg1-Atg9 axis relaying signals through the Atg9 phosphorylation at T62 and T69; these findings further elaborate the mechanism of dAux regulating glial autophagy and highlight the significance of protein degradation pathway in glia contributing to PD.