Neuronal lysosomal dysfunction releases exosomes harboring APP C-terminal fragments and unique lipid signatures

André M Miranda,Zofia M Lasiecka,Scott A Small,Robin B Chan,Tiago Gil Oliveira,Sabrina Simoes,Sanjid Shahriar,Jessi Neufeld,Yimeng Xu,Gilbert Di Paolo

doi:10.1038/s41467-017-02533-w

Abstract

Defects in endolysosomal and autophagic functions are increasingly viewed as key pathological features of neurodegenerative disorders. A master regulator of these functions is phosphatidylinositol-3-phosphate (PI3P), a phospholipid synthesized primarily by class III PI 3-kinase Vps34. Here we report that disruption of neuronal Vps34 function in vitro and in vivo impairs autophagy, lysosomal degradation as well as lipid metabolism, causing endolysosomal membrane damage. PI3P deficiency also promotes secretion of unique exosomes enriched for undigested lysosomal substrates, including amyloid precursor protein C-terminal fragments (APP-CTFs), specific sphingolipids, and the phospholipid bis(monoacylglycero)phosphate (BMP), which normally resides in the internal vesicles of endolysosomes. Secretion of these exosomes requires neutral sphingomyelinase 2 and sphingolipid synthesis. Our results reveal a homeostatic response counteracting lysosomal dysfunction via secretion of atypical exosomes eliminating lysosomal waste and define exosomal APP-CTFs and BMP as candidate biomarkers for endolysosomal dysfunction associated with neurodegenerative disorders.

Highlights

Defects in endolysosomal and autophagic functions are increasingly viewed as key pathological features of neurodegenerative disorders
Based on our previous work showing a deficiency of PI3P in AD brain[15], we have investigated the impact of neuronal Vps[34] kinase inhibition and genetic ablation on endolysosomal function, autophagy, and amyloid precursor protein (APP) metabolism
We found that blocking Vps[34] leads to a profound dysregulation of lipid metabolism and endolysosomal membrane disruption, accumulation, and secretion of APP-CTFs on a subpopulation of exosomes enriched for ubiquitinated proteins and atypical lipids such as BMP, demonstrating that neurons have the capacity to eliminate undigested, potentially toxic endolysosomal cargoes via exosomes

Summary

Introduction

Defects in endolysosomal and autophagic functions are increasingly viewed as key pathological features of neurodegenerative disorders. PI3P serves as a substrate for the synthesis of PI(3,5)P2 by the PI3P 5-kinase PIKfyve on late endosomes, controlling additional aspects of endolysosomal function[10,11] This pathway mediates a variety of critical processes, such as endosomal fusion, intraluminal vesicle (ILV) budding, endosomal motility as well as the biogenesis and maturation of autophagosomes during macroautophagy ( referred as autophagy)[9,10]. Silencing Vps[34] in primary neurons was shown to cause endosomal anomalies and altered amyloidogenic processing of amyloid precursor protein (APP), which are important pathological features of AD1,2 Overall, these studies implicate dysregulation of the PI3P pathway and associated endolysosomal perturbation in neurodegeneration

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Conclusion