VAMP associated proteins are required for autophagic and lysosomal degradation by promoting a PtdIns4P-mediated endosomal pathway

Autophagy. 2019 Jul;15(7):1214-1233. doi: 10.1080/15548627.2019.1580103. Epub 2019 Feb 20.

Abstract

Mutations in the ER-associated VAPB/ALS8 protein cause amyotrophic lateral sclerosis and spinal muscular atrophy. Previous studies have argued that ER stress may underlie the demise of neurons. We find that loss of VAP proteins (VAPs) leads to an accumulation of aberrant lysosomes and impairs lysosomal degradation. VAPs mediate ER to Golgi tethering and their loss may affect phosphatidylinositol-4-phosphate (PtdIns4P) transfer between these organelles. We found that loss of VAPs elevates PtdIns4P levels in the Golgi, leading to an expansion of the endosomal pool derived from the Golgi. Fusion of these endosomes with lysosomes leads to an increase in lysosomes with aberrant acidity, contents, and shape. Importantly, reducing PtdIns4P levels with a PtdIns4-kinase (PtdIns4K) inhibitor, or removing a single copy of Rab7, suppress macroautophagic/autophagic degradation defects as well as behavioral defects observed in Drosophila Vap33 mutant larvae. We propose that a failure to tether the ER to the Golgi when VAPs are lost leads to an increase in Golgi PtdIns4P levels, and an expansion of endosomes resulting in an accumulation of dysfunctional lysosomes and a failure in proper autophagic lysosomal degradation. Abbreviations: ALS: amyotrophic lateral sclerosis; CSF: cerebrospinal fluid; CERT: ceramide transfer protein; FFAT: two phenylalanines in an acidic tract; MSP: major sperm proteins; OSBP: oxysterol binding protein; PH: pleckstrin homology; PtdIns4P: phosphatidylinositol-4-phosphate; PtdIns4K: phosphatidylinositol 4-kinase; UPR: unfolded protein response; VAMP: vesicle-associated membrane protein; VAPA/B: mammalian VAPA and VAPB proteins; VAPs: VAMP-associated proteins (referring to Drosophila Vap33, and human VAPA and VAPB).

Keywords: ALS8; PI4KB; VAPA/VAPB; autophagy.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Autophagosomes / drug effects
  • Autophagosomes / metabolism
  • Autophagosomes / ultrastructure
  • Autophagy / drug effects
  • Autophagy / genetics*
  • Carrier Proteins / chemistry
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Drosophila / genetics
  • Drosophila / metabolism
  • Drosophila Proteins / chemistry
  • Drosophila Proteins / genetics
  • Drosophila Proteins / metabolism*
  • Endoplasmic Reticulum / genetics
  • Endoplasmic Reticulum / metabolism
  • Endoplasmic Reticulum / ultrastructure
  • Endosomes / drug effects
  • Endosomes / genetics
  • Endosomes / metabolism*
  • Golgi Apparatus / genetics
  • Golgi Apparatus / metabolism
  • HEK293 Cells
  • HeLa Cells
  • Humans
  • Lysosomal-Associated Membrane Protein 2 / metabolism
  • Lysosomes / drug effects
  • Lysosomes / genetics
  • Lysosomes / metabolism*
  • Lysosomes / ultrastructure
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mice
  • Mice, Inbred C57BL
  • Mutation
  • Phosphatidylinositol Phosphates / metabolism*
  • R-SNARE Proteins / genetics
  • R-SNARE Proteins / metabolism*
  • Vesicular Transport Proteins / metabolism*
  • eIF-2 Kinase / chemistry
  • eIF-2 Kinase / genetics
  • eIF-2 Kinase / metabolism
  • rab GTP-Binding Proteins / genetics
  • rab GTP-Binding Proteins / metabolism

Substances

  • Carrier Proteins
  • Drosophila Proteins
  • Lysosomal-Associated Membrane Protein 2
  • Membrane Proteins
  • Phosphatidylinositol Phosphates
  • R-SNARE Proteins
  • VAPA protein, human
  • VAPB protein, human
  • Vap33 protein, Drosophila
  • Vesicular Transport Proteins
  • phosphatidylinositol 4-phosphate
  • rab7 protein
  • PERK kinase
  • eIF-2 Kinase
  • rab GTP-Binding Proteins