Neurodegenerative diseases have become an increasing problem in our aging society. Many studies have addressed these complex diseases in the recent years.Scientists have learned a lot about specific proteins, their regulation and roles in diseases, yet there are still many unanswered questions in this area. As the knowledge increases, it has become apparent that these diseases affect more than one protein and that entire processes are dysregulated or dysfunctional, leading to similar but often non-identical symptoms in patients of different neurodegenerative diseases. Emerging evidence is accumulating that while the proteins involved in these diseases are diverse, many of them ultimately disrupt basic cellular processes in neurons. It is therefore not surprising that recent reports have shown that impairments of endocytosis or autophagy, two processes involved in maintaining proteostasis in synapses, can lead to neurodegeneration. This thesis was designed to shed light on questions of if and how the family of endophilin-As, key proteins in synaptic endocytosis, is involved in neurodegeneration.Taking advantage of the complex endophilin mouse model, this thesis shows that endophilin mutants have progressive motor impairments depending on the number of deleted endophilin alleles and the animal age. The motor deficits are prominently detected in the Rotarod test which requires motor coordination and in the overall running ability on a motorized treadmill and subtly found in gait analysis or general muscle strength.Furthermore, data presented here also reveal signs of neurodegeneration in mouse models for endophilin deficiency. The evidence points to a mild form of neurodegeneration that is found in the hippocampus, cortex and cerebellum. These findings include an increase in apoptotic and necrotic cells in brain sections from different endophilin mutants and a strong gliosis in endophilin 1,2-DKO mice.Unexpectedly, data reported in this thesis, complemented by additional data produced in the laboratory, indicate that endophilin has a previously unknown role in autophagy in addition to its well-described role in endocytosis. Most prominently, an E3 ubiquitin ligase, Fbxo32, is robustly up-regulated in various endophilin mutants. complex that causes actin branching (Hotulainen, et al., 2009). The increased size is important to create space for more receptors which then stabilize and strengthen the synapse. Head size also correlates with the number of SVs in the pre-synapse (Harris & Stevens, 1988;Harris & Stevens, 1989;Schikorski & Stevens, 1997). Because of that, mushroom spines, which have a large head, are regarded as mature spines while thin and stubby spines are classifies as young or dormant spines (Matsuzaki, et al., 2001; reviewed in Woolfrey & Srivastava, 2016).(PI(4,5)P2). AP2 is also responsible to recruit transmembrane proteins (cargo) to the SVs: it binds to PI(4,5)P2, cargo and one arm of a clathrin triskelion, thereby initiating the formation of the clathrin coat.Upon assembly of several clathrin triske...