Modeling endophilin-mediated A beta disposal in glioma cells

Autophagy dysregulation has emerged in age-related neurological diseases (Ulland et al.; Matheoud et al.; Ashkenazi et al.). Alzheimer Disease (AD), the most common progressive neurodegenerative disorder, is characterized by the accumulation of amyloid-beta (A beta) plaques caused by aberrant A beta metabolism (Qiang et al.; Sevigny et al.; Ittner et al.). Glia constitute the brain immune system and ingest extracellular A beta for degradation via the autophagy-lysosome machinery (Ries and Sastre; Cho et al.). Here, we model the molecular rationale for this clearance process in glioma cells by showing that miR34a inhibits autophagy-mediated disposal of A beta fibrils and identifying two novel direct targets of miR34a, endophilin-3 and cathepsin B (CTSB, a previously reported enzyme for A beta degrading (Sun et al.)). Bioinformatics analyses revealed that endophilin-3 expresses at a significantly lower level in neurodegenerative diseases. Its gain-of-function substantially promotes both uptake and degradation of A beta while small interfering RNA (siRNA)-mediated endophilin-3 knockdown slowed down A beta clearance and blocked autolysosome formation. Mechanistically, gene ontology (GO) analysis of the endophilin-3 interactome identified by mass spectrometry uncovered enriched components involved in actin binding (with the highest score). Importantly, we validated that the actin-binding protein phostensin interacted with endophilin-3. Phostensin knockdown restored endophilin-3-mediated up-regulation of A beta clearance. Thus, our findings indicate that miR34a inhibits A beta clearance by targeting endophilin-3 and CTSB at multiple steps including uptake and autophagy-mediated degradation.