SNAPIN is critical for lysosomal acidification and autophagosome maturation in macrophages

Bo Shi, Qi Quan Huang, Robert Birkett, Renee Doyle, Andrea Dorfleutner, Christian Stehlik, Congcong He, Richard M. Pope

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

We previously observed that SNAPIN, which is an adaptor protein in the SNARE core complex, was highly expressed in rheumatoid arthritis synovial tissue macrophages, but its role in macrophages and autoimmunity is unknown. To identify SNAPIN's role in these cells, we employed siRNA to silence the expression of SNAPIN in primary human macrophages. Silencing SNAPIN resulted in swollen lysosomes with impaired CTSD (cathepsin D) activation, although total CTSD was not reduced. Neither endosome cargo delivery nor lysosomal fusion with endosomes or autophagosomes was inhibited following the forced silencing of SNAPIN. The acidification of lysosomes and accumulation of autolysosomes in SNAPIN-silenced cells was inhibited, resulting in incomplete lysosomal hydrolysis and impaired macroautophagy/autophagy flux. Mechanistic studies employing ratiometric color fluorescence on living cells demonstrated that the reduction of SNAPIN resulted in a modest reduction of H+ pump activity; however, the more critical mechanism was a lysosomal proton leak. Overall, our results demonstrate that SNAPIN is critical in the maintenance of healthy lysosomes and autophagy through its role in lysosome acidification and autophagosome maturation in macrophages largely through preventing proton leak. These observations suggest an important role for SNAPIN and autophagy in the homeostasis of macrophages, particularly long-lived tissue resident macrophages.

Original languageEnglish (US)
Pages (from-to)285-301
Number of pages17
JournalAutophagy
Volume13
Issue number2
DOIs
StatePublished - Feb 1 2017

Keywords

  • acidification
  • autophagy
  • CTSD
  • endosome
  • LC3
  • lysosome
  • macrophage
  • proton leak
  • SNAPIN
  • vacuolar-type H-ATPase

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology

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    Shi, B., Huang, Q. Q., Birkett, R., Doyle, R., Dorfleutner, A., Stehlik, C., He, C., & Pope, R. M. (2017). SNAPIN is critical for lysosomal acidification and autophagosome maturation in macrophages. Autophagy, 13(2), 285-301. https://doi.org/10.1080/15548627.2016.1261238