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Manuscript 2Synapses are often far from the soma and independently cope with proteopathic stress induced by intense neuronal activity. However, how presynaptic compartments turnover proteins is poorly understood. We show that the synapse-enriched protein EndophilinA, thus far studied for its role in endocytosis, induces macroautophagy at presynaptic terminals. We find that EndophilinA executes this unexpected function at least partly independent of its role in synaptic vesicle endocytosis. EndophilinA-induced macroautophagy is activated when the kinase LRRK2 phosphorylates the EndophilinA-BAR domain and is blocked in animals where EndophilinA cannot be phosphorylated. EndophilinA INTRODUCTIONNeurons can be metabolically very active, firing at rates of more than 100 Hz.Synaptic proteins and organelles are used and re-used multiple times and accumulate damage as a result of this stress. Furthermore, synapses are often located far away from the cell body and must therefore in part operate independently. This raises the question how synapses maintain protein quality. Given that neurodegeneration is thought to start with subtle synaptic defects before evolving into blunt neuronal death (Burke and O'Malley, 2013;, the mechanisms of synaptic protein homeostasis are likely relevant for the understanding of neurodegenerative disease.Macroautophagy is well-placed to mediate protein turnover, but how the needs of synapses are served by this process has not been well-studied. Cellular signals like stress and amino acid deprivation induce macroautophagy, where cytoplasm is engulfed by double membrane structures before fusion with degradative lysosomes (Mizushima et al., 2011).Autophagosomes have been visualized using fluorescent markers in yeast, Drosophila and mammalian cells and are often observed as Atg8/LC3 positive puncta (Kabeya et al., 2000;Scott et al., 2004). At the stage of initiation, Atg9-positive vesicles fuse into elongated preautophagosomal structures with growing edges (He et al., 2006). These edges are highly curved and harbor lipid packing defects. These edges serve as protein docking sites, attracting specific autophagic factors such as Atg3, Atg14/Barkor and Atg1 that insert into such zones, recognizing specific lipids (phosphatidylinositol-3-phosphate (PI(3)P)) and lipid packing defects (Fan et al., 2011;Nath et al., 2014;Ragusa et al., 2012). The recruitment of these factors then promotes the further steps of autophagosome formation; in particular the E2-like protein Atg3 itself recruits the autophagic marker LC3/Atg8 (Nath et al., 2014). However, how these highly curved edges are formed and maintained is very poorly understood.While autophagy has been mostly analyzed in the soma of cultured cells and yeast, autophagic markers have also been observed away from the soma at neuronal synapses 4 (Hernandez et al., 2012;Maday and Holzbaur, 2014;Williamson et al., 2010) and these markers were shown to be transported along axons (Maday and Holzbaur, 2014). However, how autophagosomes are formed at synapses an...

Presynaptic terminals are metabolically active and accrue damage through continuous vesicle cycling. How synapses locally regulate protein homeostasis is poorly understood. We show that the presynaptic lipid phosphatase synaptojanin is required for macroautophagy, and this role is inhibited by the Parkinson's disease mutation R258Q. Synaptojanin drives synaptic endocytosis by dephosphorylating PI(4,5)P 2 , but this function appears normal in Synaptojanin RQ knock-in flies. Instead, R258Q affects the synaptojanin SAC1 domain that dephosphorylates PI(3)P and PI(3,5)P 2 , two lipids found in autophagosomal membranes. Using advanced imaging, we show that Synaptojanin RQ mutants accumulate the PI(3)P/PI(3,5)P 2 -binding protein Atg18a on nascent synaptic autophagosomes, blocking autophagosome maturation at fly synapses and in neurites of human patient induced pluripotent stem cell-derived neurons. Additionally, we observe neurodegeneration, including dopaminergic neuron loss, in Synaptojanin RQ flies.Thus, synaptojanin is essential for macroautophagy within presynaptic terminals, coupling protein turnover with synaptic vesicle cycling and linking presynaptic-specific autophagy defects to Parkinson's disease.

SummaryEndophilin-A, a well-characterized endocytic adaptor essential for synaptic vesicle recycling, has recently been linked to neurodegeneration. We report here that endophilin-A deficiency results in impaired movement, age-dependent ataxia, and neurodegeneration in mice. Transcriptional analysis of endophilin-A mutant mice, complemented by proteomics, highlighted ataxia- and protein-homeostasis-related genes and revealed upregulation of the E3-ubiquitin ligase FBXO32/atrogin-1 and its transcription factor FOXO3A. FBXO32 overexpression triggers apoptosis in cultured cells and neurons but, remarkably, coexpression of endophilin-A rescues it. FBXO32 interacts with all three endophilin-A proteins. Similarly to endophilin-A, FBXO32 tubulates membranes and localizes on clathrin-coated structures. Additionally, FBXO32 and endophilin-A are necessary for autophagosome formation, and both colocalize transiently with autophagosomes. Our results point to a role for endophilin-A proteins in autophagy and protein degradation, processes that are impaired in their absence, potentially contributing to neurodegeneration and ataxia.

Parkinson's disease, the second most common neurodegenerative disorder, affects millions of people globally. There is no cure, and its prevalence will double by 2030. In recent years, numerous causative genes and risk factors for Parkinson's disease have been identified and more than half appear to function at the synapse. Subtle synaptic defects are thought to precede blunt neuronal death, but the mechanisms that are dysfunctional at synapses are only now being unraveled. Here, we review recent work and propose a model where different Parkinson proteins interact in a cell compartment-specific manner at the synapse where these proteins regulate endocytosis and autophagy. While this field is only recently emerging, the work suggests that the loss of synaptic homeostasis may contribute to neurodegeneration and is a key player in Parkinson's disease.

The humoral response to fungal and Gram-positive infections is regulated by the serpin-family inhibitor, Necrotic. Following immune-challenge, a proteolytic cascade is activated which signals through the Toll receptor. Toll activation results in a range of antibiotic peptides being synthesised in the fat-body and exported to the haemolymph. As with mammalian serpins, Necrotic turnover in Drosophila is rapid. This serpin is synthesised in the fat-body, but its site of degradation has been unclear. By “freezing” endocytosis with a temperature sensitive Dynamin mutation, we demonstrate that Necrotic is removed from the haemolymph in two groups of giant cells: the garland and pericardial athrocytes. Necrotic uptake responds rapidly to infection, being visibly increased after 30 mins and peaking at 6–8 hours. Co-localisation of anti-Nec with anti-AP50, Rab5, and Rab7 antibodies establishes that the serpin is processed through multi-vesicular bodies and delivered to the lysosome, where it co-localises with the ubiquitin-binding protein, HRS. Nec does not co-localise with Rab11, indicating that the serpin is not re-exported from athrocytes. Instead, mutations which block late endosome/lysosome fusion (dor, hk, and car) cause accumulation of Necrotic-positive endosomes, even in the absence of infection. Knockdown of the 6 Drosophila orthologues of the mammalian LDL receptor family with dsRNA identifies LpR1 as an enhancer of the immune response. Uptake of Necrotic from the haemolymph is blocked by a chromosomal deletion of LpR1. In conclusion, we identify the cells and the receptor molecule responsible for the uptake and degradation of the Necrotic serpin in Drosophila melanogaster. The scavenging of serpin/proteinase complexes may be a critical step in the regulation of proteolytic cascades.

Synapses are very specialized compartments with high metabolic demand to maintain neurotransmission, an essential step for basic brain function. Neurons are post-mitotic and synapses need to stay functional over time-sometimes over decades. Given that synapses are often at a long distance from the cell body, they must use local mechanisms to regulate protein quality control. We show that macroautophagy/autophagy is one of these local processes and found that it is under strict control of the synapse-enriched protein EndoA/Endophilin-A, previously only implicated in endocytosis. Metabolic and neuronal stimulation induce synaptic autophagy and phosphorylation of EndoA by the Parkinson disease kinase Lrrk/LRRK2 is essential to promote the process. EndoA induces membrane curvature in vitro, and, mechanistically, phosphorylated EndoA creates curved membrane-protein docking sites that are capable of recruiting Atg3. Our work reveals a synapse-enriched branch of autophagy under the control of EndoA that may be deregulated in Parkinson disease.

Neurodegenerative diseases are, at present, major socioeconomic burdens without effective treatments and their increasing prevalence means that these diseases will be a challenge for future generations. Neurodegenerative diseases may differ in etiology and pathology but are often caused by the accumulation of dysfunctional and aggregation-prone proteins. Autophagy, a conserved cellular mechanism, deals with cellular stress and waste product build-up and has been shown to reduce the accumulation of dysfunctional proteins in animal models of neurodegenerative diseases. Historically, progress in understanding the precise function of lipids has traditionally been far behind other biological molecules (like proteins) but emerging works demonstrate the importance of lipids in the autophagy pathway and how the disturbance of lipid metabolism is connected to neurodegeneration. Here we review how altered autophagy and the disturbance of lipid metabolism, particularly of phosphoinositols and sphingolipids, feature in neurodegenerative diseases and address work from the field that suggests that these potentially offer an opportunity of therapeutic intervention.