Secretion of ATP from Schwann cells through lysosomal exocytosis during Wallerian degeneration

The present study demonstrates that adenosine triphosphate (ATP) is released from Schwann cells through lysosomal exocytosis during Wallerian degeneration and in response to stimulation. In primary Schwann cell cultures, ATP was stored in lysosomal vesicles. ATP could then induce Ca2+-dependent lysosomal exocytosis. Among three stimulants of lysosomal exocytosis (glutamate, NH4Cl and zymosan), only NH4Cl was sufficient to induce ATP release from ex vivo sciatic nerve explants at 3 days in vitro. Lysosomal exocytosis inhibitors (metformin, chlorpromazine and vacuolin-1) reversed the effect of NH4Cl-enhanced ATP release, replicating the state of explants treated with NH4Cl in the absence of lysosomal exocytosis inhibitors. Furthermore, we observed ATP release through lysosomal exocytosis during Wallerian degeneration in sciatic explant cultures using the recently identified vesicular nucleotide transporter (VNUT). From these experiments, we conclude that the exocytosis of lysosomes in Schwann cells during Wallerian degeneration is Ca2+-dependent, and that it induces ATP release from Schwann cells.

► ATP is stored in lysosomal vesicles associated with synaptotagmin VII and VAMP7.
► Lysosomal exocytosis inhibitors reverse the effect of NH4Cl-enhanced ATP release.
► A vesicular nucleotide transporter is located in lysosomal vesicles.
► Secretion of ATP is dependent on lysosomal exocytosis during Wallerian degeneration.