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TRP-ML1 regulates lysosomal pH and acidic lysosomal lipid hydrolytic activity

Abigail A Soyombo1, Sandra Tjon-Kon-Sang, Youssef Rbaibi

  • 1Department of Physiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA.

The Journal of Biological Chemistry
|December 20, 2005
PubMed

Insights

Mucolipidosis type IV (MLIV) results from TRP-ML1 mutations, causing over-acidified lysosomes and impaired lipid breakdown. Restoring lysosomal pH reverses MLIV symptoms, revealing a metabolic basis for this lysosomal storage disorder.

Area of Science:

  • Cell Biology
  • Genetics
  • Biochemistry

Background:

  • Mucolipidosis type IV (MLIV) is a genetic disorder linked to mutations in the mucolipin 1 (TRP-ML1) ion channel.
  • MLIV is characterized by the accumulation of lipids and membranous material in cellular organelles.
  • The precise mechanism by which TRP-ML1 mutations cause MLIV pathogenesis, particularly concerning lipolysis, remains unclear.

Purpose of the Study:

  • To investigate the underlying metabolic mechanisms of MLIV.
  • To determine the role of TRP-ML1 in lysosomal function and lipolysis.
  • To explore potential therapeutic strategies by targeting lysosomal pH.

Main Methods:

  • Analysis of lysosomal pH in TRP-ML1 deficient cells.
  • Measurement of lipase activity using various substrates.
  • Assessment of TRP-ML1 expression and its effect on cellular phenotype.
  • Cell fractionation to localize lipase activity.
  • Pharmacological manipulation of lysosomal pH using nigericin and chloroquine.

Main Results:

  • Lysosomes in TRP-ML1(-/-) cells exhibit significant over-acidification, suggesting TRP-ML1 acts as a proton leak channel.
  • A marked reduction in cellular lipase activity, specifically acidic lipase activity, was observed in TRP-ML1(-/-) cells.
  • Re-expression of TRP-ML1 rescued the reduced lipase activity.
  • Correction of lysosomal pH using nigericin or chloroquine ameliorated the lysosomal storage phenotype.

Conclusions:

  • MLIV is a metabolic disorder characterized by lysosomal over-acidification due to loss of TRP-ML1 function.
  • Aberrant lipolysis, rather than altered membrane fusion/fission, is a key pathogenic mechanism in MLIV.
  • Modulating lysosomal pH represents a potential therapeutic avenue for MLIV.

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