Activation of TPC2 amplifies lysosome-mitochondria calcium transfer to regulate energetic stress responses.

Mitochondrial Ca2+ uptake governs metabolism and cell fate, yet how signals from other organelles shape this remains incompletely defined. Although lysosomes are relatively small Ca2+ stores, their strategic positioning at organelle contact sites suggests they may amplify Ca2+ transfer within nanodomains. Here, we show that activation of the lysosomal Two-pore channel 2 (TPC2) initiates rapid mitochondrial Ca2+ uptake through an endoplasmic reticulum-dependent relay requiring IP3 receptors and the mitochondrial calcium uniporter channel. The extent of mitochondrial Ca2+ accumulation scales with TPC2 activity without affecting global Ca2+ responses, identifying TPC2 as a specific amplifier of lysosome-mitochondria Ca2+ exchange. Moderate TPC2 activation transiently enhances oxidative phosphorylation, whereas sustained enhancement increases susceptibility to Ca2+-induced mitochondrial permeability transition. In stroke models, hyperactivation of TPC2 exacerbates injury, while acute pharmacological inhibition at reperfusion confers neuroprotection, including in human iPSC-derived neurons. Thus, lysosomal Ca2+ release acts as an upstream regulator of mitochondrial energetic resilience under stress.