Reactivation of Lysosomal Ca2+ Efflux Rescues Abnormal Lysosomal Storage in FIG4-Deficient Cells.

Abstract

Loss of function of FIG4 leads to Charcot-Marie-Tooth disease Type 4J, Yunis-Varon syndrome, or an epilepsy syndrome. FIG4 is a phosphatase with its catalytic specificity toward 5'-phosphate of phosphatidylinositol-3,5-diphosphate (PI3,5P2). However, the loss of FIG4 decreases PI3,5P2 levels likely due to FIG4's dominant effect in scaffolding a PI3,5P2 synthetic protein complex. At the cellular level, all these diseases share similar pathology with abnormal lysosomal storage and neuronal degeneration. Mice with no FIG4 expression (Fig4(-/-)) recapitulate the pathology in humans with FIG4 deficiency. Using a flow cytometry technique that rapidly quantifies lysosome sizes, we detected an impaired lysosomal fission, but normal fusion, in Fig4(-/-) cells. The fission defect was associated with a robust increase of intralysosomal Ca(2+) in Fig4(-/-) cells, including FIG4-deficient neurons. This finding was consistent with a suppressed Ca(2+) efflux of lysosomes because the endogenous ligand of lysosomal Ca(2+) channel TRPML1 is PI3,5P2 that is deficient in Fig4(-/-) cells. We reactivated the TRPML1 channels by application of TRPML1 synthetic ligand, ML-SA1. This treatment reduced the intralysosomal Ca(2+) level and rescued abnormal lysosomal storage in Fig4(-/-) culture cells and ex vivo DRGs. Furthermore, we found that the suppressed Ca(2+) efflux in Fig4(-/-) culture cells and Fig4(-/-) mouse brains profoundly downregulated the expression/activity of dynamin-1, a GTPase known to scissor organelle membranes during fission. This downregulation made dynamin-1 unavailable for lysosomal fission. Together, our study revealed a novel mechanism explaining abnormal lysosomal storage in FIG4 deficiency. Synthetic ligands of the TRPML1 may become a potential therapy against diseases with FIG4 deficiency.

• Authors: Jianlong Zou, Bo Hu, Sezgi Arpag, Qing Yan, Audra Hamilton, Yuan-Shan Zeng, Carlos G Vanoye, Jun Li
• Journal: The Journal of neuroscience : the official journal of the Society for Neuroscience (J Neurosci) Vol. 35 Issue 17 Pg. 6801-12 (Apr 29 2015) ISSN: 1529-2401 [Electronic] United States
• PMID: 25926456 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)
• Copyright: Copyright © 2015 the authors 0270-6474/15/356801-12$15.00/0.

Chemical References

• Flavoproteins
• Heterocyclic Compounds, 4 or More Rings
• Lysosomal-Associated Membrane Protein 1
• vacuolin-1
• Fig4 protein, mouse
• Phosphoinositide Phosphatases
• GTP Phosphohydrolases
• Calcium

Topics

• Animals
• Animals, Newborn
• Calcium (metabolism)
• Cells, Cultured
• Down-Regulation (drug effects, genetics)
• Fibroblasts (drug effects, ultrastructure)
• Flavoproteins (genetics, metabolism)
• GTP Phosphohydrolases (metabolism)
• Ganglia, Spinal (cytology)
• Heterocyclic Compounds, 4 or More Rings (pharmacology)
• Humans
• In Vitro Techniques
• Lysosomal-Associated Membrane Protein 1 (genetics, metabolism)
• Lysosomes (drug effects, metabolism, pathology)
• Membrane Potentials (drug effects, genetics, physiology)
• Mice
• Mice, Transgenic
• Motor Neurons (drug effects, metabolism, ultrastructure)
• Neurons (drug effects, metabolism, ultrastructure)
• Phosphoinositide Phosphatases
• Schwann Cells (metabolism, ultrastructure)
• Sciatic Nerve (cytology)
• Spinal Cord (cytology)