The endoplasmic reticulum, not the pH gradient, drives calcium refilling of lysosomes

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Abstract

Impaired homeostasis of lysosomal Ca²⁺ causes lysosome dysfunction and lysosomal storage diseases (LSDs), but the mechanisms by which lysosomes acquire and refill Ca²⁺ are not known. We developed a physiological assay to monitor lysosomal Ca²⁺ store refilling using specific activators of lysosomal Ca²⁺ channels to repeatedly induce lysosomal Ca²⁺ release. In contrast to the prevailing view that lysosomal acidification drives Ca²⁺ into the lysosome, inhibiting the V-ATPase H+ pump did not prevent Ca²⁺ refilling. Instead, pharmacological depletion or chelation of Endoplasmic Reticulum (ER) Ca²⁺ prevented lysosomal Ca²⁺ stores from refilling. More specifically, antagonists of ER IP3 receptors (IP3Rs) rapidly and completely blocked Ca²⁺ refilling to lysosomes, but not in cells lacking IP3Rs. Furthermore, reducing ER Ca²⁺ or blocking IP3Rs caused a dramatic LSD-like lysosome storage phenotype. By closely apposing each other, the ER may serve as a direct and primary source of Ca²⁺ to the lysosome.

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Abigail G Garrity

Neuroscience Program, University of Michigan, Ann Arbor, United States

Competing interests
The authors declare that no competing interests exist.
Wuyang Wang

Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, United States

Competing interests
The authors declare that no competing interests exist.
Crystal MD Collier

Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, United States

Competing interests
The authors declare that no competing interests exist.
Sara A Levey

Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, United States

Competing interests
The authors declare that no competing interests exist.
Qiong Gao

Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, United States

Competing interests
The authors declare that no competing interests exist.
Haoxing Xu

Neuroscience Program, University of Michigan, Ann Arbor, United States

For correspondence
haoxingx@umich.edu

Competing interests
The authors declare that no competing interests exist.

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