Reduction of TMEM97 increases NPC1 protein levels and restores cholesterol trafficking in Niemann-pick type C1 disease cells

Hum Mol Genet. 2016 Aug 15;25(16):3588-3599. doi: 10.1093/hmg/ddw204. Epub 2016 Jul 4.


Niemann-Pick type C disease (NP-C) is a progressive lysosomal lipid storage disease caused by mutations in the NPC1 and NPC2 genes. NPC1 is essential for transporting cholesterol and other lipids out of lysosomes, but little is known about the mechanisms that control its cellular abundance and localization. Here we show that a reduction of TMEM97, a cholesterol-responsive NPC1-binding protein, increases NPC1 levels in cells through a post-transcriptional mechanism. Reducing TMEM97 through RNA-interference reduces lysosomal lipid storage and restores cholesterol trafficking to the endoplasmic reticulum in cell models of NP-C. In TMEM97 knockdown cells, NPC1 levels can be reinstated with wild type TMEM97, but not TMEM97 missing an ER-retention signal suggesting that TMEM97 contributes to controlling the availability of NPC1 to the cell. Importantly, knockdown of TMEM97 also increases levels of residual NPC1 in NPC1-mutant patient fibroblasts and reduces cholesterol storage in an NPC1-dependent manner. Our findings propose TMEM97 inhibition as a novel strategy to increase residual NPC1 levels in cells and a potential therapeutic target for NP-C.

MeSH terms

  • Animals
  • CHO Cells
  • Carrier Proteins / biosynthesis
  • Carrier Proteins / genetics*
  • Cholesterol / genetics*
  • Cholesterol / metabolism
  • Cricetulus
  • Endoplasmic Reticulum / genetics
  • Fibroblasts / metabolism
  • Fibroblasts / physiology
  • Gene Knockdown Techniques
  • Glycoproteins / genetics
  • Humans
  • Intracellular Signaling Peptides and Proteins
  • Lysosomes / metabolism
  • Lysosomes / pathology
  • Membrane Glycoproteins / biosynthesis
  • Membrane Glycoproteins / genetics*
  • Membrane Proteins / genetics*
  • Mutation
  • Niemann-Pick C1 Protein
  • Niemann-Pick Disease, Type C / genetics*
  • Niemann-Pick Disease, Type C / metabolism
  • Niemann-Pick Disease, Type C / pathology
  • Vesicular Transport Proteins


  • Carrier Proteins
  • Glycoproteins
  • Intracellular Signaling Peptides and Proteins
  • Membrane Glycoproteins
  • Membrane Proteins
  • NPC1 protein, human
  • NPC2 protein, human
  • Niemann-Pick C1 Protein
  • TMEM97 protein, human
  • Vesicular Transport Proteins
  • Cholesterol