Reactivation of Lysosomal Ca2+ Efflux Rescues Abnormal Lysosomal Storage in FIG4-Deficient Cells.
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.
Department of Histology and Embryology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou 510085, China, Department of Neurology, Center for Human Genetics Research, Vanderbilt Brain Institute, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Jianlong
J
Zou
Department of Neurology, Center for Human Genetics Research, Vanderbilt Brain Institute, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Bo
B
Hu
Department of Neurology, Center for Human Genetics Research, Vanderbilt Brain Institute, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Sezgi
http://orcid.org/0000-0002-6449-4164
S
Arpag
Department of Neurology, Center for Human Genetics Research, Vanderbilt Brain Institute, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Qing
Q
Yan
Department of Neurology, Center for Human Genetics Research, Vanderbilt Brain Institute, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Audra
A
Hamilton
Department of Histology and Embryology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou 510085, China.
Yuan-Shan
YS
Zeng
Department of Pharmacology, Northwestern University, Evanston, Illinois 60208, and.
Carlos G
CG
Vanoye
Department of Neurology, Center for Human Genetics Research, Vanderbilt Brain Institute, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, Tennessee Valley Healthcare System-Nashville Veterans Administration, Nashville, Tennessee 37212 jun.li.2@vanderbilt.edu.
Jun
J
Li
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D005347:Fibroblasts / Q000187:drug effects / Q000648:ultrastructure; D005420:Flavoproteins / Q000235:genetics / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism; D005727:Ganglia, Spinal / Q000166:cytology; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D052118:Lysosomal-Associated Membrane Protein 1 / Q000235:genetics / Q000378:metabolism; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D009046:Motor Neurons / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D000072180:Phosphoinositide Phosphatases; D012583:Schwann Cells / Q000378:metabolism / Q000648:ultrastructure*; D012584:Sciatic Nerve / Q000166:cytology; D013116:Spinal Cord / Q000166:cytology
D005420:Flavoproteins; D006576:Heterocyclic Compounds, 4 or More Rings; D052118:Lysosomal-Associated Membrane Protein 1; C503870:vacuolin-1; C522216:Fig4 protein, mouse; D000072180:Phosphoinositide Phosphatases; D020558:GTP Phosphohydrolases; D002118:Calcium
Charcot-Marie-Tooth disease; ML-SA1; TRPML1; lysosomal storage; membrane trafficking; neurodegeneration