Defective Autophagy, Mitochondrial Clearance and Lipophagy in Niemann-Pick Type B Lymphocytes

PLoS One. 2016 Oct 31;11(10):e0165780. doi: 10.1371/journal.pone.0165780. eCollection 2016.

Abstract

Niemann-Pick disease type A (NP-A) and type B (NP-B) are lysosomal storage diseases (LSDs) caused by sphingomyelin accumulation in lysosomes relying on reduced or absent acid sphingomyelinase. A considerable body of evidence suggests that lysosomal storage in many LSD impairs autophagy, resulting in the accumulation of poly-ubiquitinated proteins and dysfunctional mitochondria, ultimately leading to cell death. Here we test this hypothesis in a cellular model of Niemann-Pick disease type B, in which autophagy has never been studied. The basal autophagic pathway was first examined in order to evaluate its functionality using several autophagy-modulating substances such as rapamycin and nocodazole. We found that human NP-B B lymphocytes display considerable alteration in their autophagic vacuole accumulation and mitochondrial fragmentation, as well as mitophagy induction (for damaged mitochondria clearance). Furthermore, lipid traceability of intra and extra-cellular environments shows lipid accumulation in NP-B B lymphocytes and also reveals their peculiar trafficking/management, culminating in lipid microparticle extrusion (by lysosomal exocytosis mechanisms) or lipophagy. All of these features point to the presence of a deep autophagy/mitophagy alteration revealing autophagic stress and defective mitochondrial clearance. Hence, rapamycin might be used to regulate autophagy/mitophagy (at least in part) and to contribute to the clearance of lysosomal aberrant lipid storage.

MeSH terms

  • Autophagy*
  • B-Lymphocytes / metabolism*
  • B-Lymphocytes / ultrastructure
  • Biomarkers
  • Cell-Derived Microparticles / metabolism
  • Endocytosis
  • Exocytosis
  • Extracellular Space / metabolism
  • Flow Cytometry
  • Humans
  • Intracellular Space / metabolism
  • Lipid Metabolism*
  • Lysosomes / metabolism
  • Mitochondria / metabolism*
  • Mitochondria / ultrastructure
  • Mitophagy
  • Niemann-Pick Diseases / metabolism*
  • Phagosomes

Substances

  • Biomarkers

Grants and funding

This study was supported by the Niemann-Pick ONLUS Italian Association. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.