mTORC1 controls lysosomal Ca²⁺ release through the two-pore channel TPC2

Area of Science:

• Cell Biology
• Ion Channel Physiology
• Autophagy Regulation

Background:

• Two-pore segment channel 2 (TPC2) is a lysosomal ion channel involved in autophagy termination.
• Its precise role in lysosomal Ca²⁺ or Na⁺ flux and regulation by NAADP or PI(3,5)P₂ remains debated.

Purpose of the Study:

• To investigate the role of TPC2 in intracellular Ca²⁺ signaling.
• To determine if TPC2 mediates lysosomal Ca²⁺ release in response to NAADP or mTOR inhibition.

Main Methods:

• Utilized pulmonary arterial myocytes and HEK293 cells.
• Employed rapamycin and NAADP treatments.
• Used Tpcn2 knockout mice and shRNA-mediated knockdown of mTOR.
• Applied confocal imaging with a genetically encoded Ca²⁺ indicator fused to TPC2.

Main Results:

• TPC2 is essential for Ca²⁺ signaling induced by NAADP or rapamycin-mediated mTOR inhibition.
• Rapamycin and NAADP evoked lysosomal Ca²⁺ transients in wild-type cells, but not in Tpcn2 knockout cells.
• Knockdown of mTOR abolished rapamycin- and NAADP-evoked Ca²⁺ signals.
• Ca²⁺ signals localized to lysosomes near TPC2.

Conclusions:

• TPC2 mediates lysosomal Ca²⁺ release.
• mTOR inactivation activates TPC2, leading to lysosomal Ca²⁺ release and influencing intracellular Ca²⁺ signaling.