Protecting cells by protecting their vulnerable lysosomes: Identification of a new mechanism for preserving lysosomal functional integrity upon oxidative stress

PLoS Genet. 2017 Feb 9;13(2):e1006603. doi: 10.1371/journal.pgen.1006603. eCollection 2017 Feb.


Environmental insults such as oxidative stress can damage cell membranes. Lysosomes are particularly sensitive to membrane permeabilization since their function depends on intraluminal acidic pH and requires stable membrane-dependent proton gradients. Among the catalog of oxidative stress-responsive genes is the Lipocalin Apolipoprotein D (ApoD), an extracellular lipid binding protein endowed with antioxidant capacity. Within the nervous system, cell types in the defense frontline, such as astrocytes, secrete ApoD to help neurons cope with the challenge. The protecting role of ApoD is known from cellular to organism level, and many of its downstream effects, including optimization of autophagy upon neurodegeneration, have been described. However, we still cannot assign a cellular mechanism to ApoD gene that explains how this protection is accomplished. Here we perform a comprehensive analysis of ApoD intracellular traffic and demonstrate its role in lysosomal pH homeostasis upon paraquat-induced oxidative stress. By combining single-lysosome in vivo pH measurements with immunodetection, we demonstrate that ApoD is endocytosed and targeted to a subset of vulnerable lysosomes in a stress-dependent manner. ApoD is functionally stable in this acidic environment, and its presence is sufficient and necessary for lysosomes to recover from oxidation-induced alkalinization, both in astrocytes and neurons. This function is accomplished by preventing lysosomal membrane permeabilization. Two lysosomal-dependent biological processes, myelin phagocytosis by astrocytes and optimization of neurodegeneration-triggered autophagy in a Drosophila in vivo model, require ApoD-related Lipocalins. Our results uncover a previously unknown biological function of ApoD, member of the finely regulated and evolutionary conserved gene family of extracellular Lipocalins. They set a lipoprotein-mediated regulation of lysosomal membrane integrity as a new mechanism at the hub of many cellular functions, critical for the outcome of a wide variety of neurodegenerative diseases. These results open therapeutic opportunities by providing a route of entry and a repair mechanism for lysosomes in pathological situations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Animals, Genetically Modified
  • Animals, Newborn
  • Apolipoproteins D / genetics
  • Apolipoproteins D / metabolism
  • Apolipoproteins D / pharmacology
  • Astrocytes / drug effects
  • Astrocytes / metabolism*
  • Astrocytes / ultrastructure
  • Autophagy / drug effects
  • Autophagy / genetics
  • Cell Line, Tumor
  • Cells, Cultured
  • Drosophila
  • HEK293 Cells
  • Herbicides / pharmacology
  • Humans
  • Hydrogen-Ion Concentration
  • Immunoblotting
  • Lipocalins / pharmacology
  • Lysosomes / chemistry
  • Lysosomes / metabolism*
  • Mice, Knockout
  • Microscopy, Confocal
  • Microscopy, Electron
  • Models, Biological
  • Neurodegenerative Diseases / genetics
  • Neurodegenerative Diseases / metabolism
  • Neurodegenerative Diseases / prevention & control
  • Neurons / drug effects
  • Neurons / metabolism*
  • Oxidative Stress*
  • Paraquat / pharmacology
  • Phagosomes / metabolism


  • Apolipoproteins D
  • Herbicides
  • Lipocalins
  • Paraquat

Grants and funding

This work was supported by grants to MDG and DS (Ministerio de Ciencia e Innovación (MICINN) grants BFU2011-23978 and BFU2015-68149-R, co-financed by European Regional Development Fund). RPM was supported by a Junta de Castilla y León (JCyL) fellowship to young researchers (call#EDU/1883/2013), financed by the European Social Fund, Operational Programme for Castilla y León and managed by Consejería de Educación (JCyL). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.