Abstract Mitochondrial Ca 2+ uptake is crucial for coupling receptor stimulation to cellular bioenergetics. Further, Ca 2+ uptake by respiring mitochondria prevents Ca 2+ -dependent inactivation (CDI) of store-operated Ca 2+ release-activated Ca 2+ (CRAC) channels and inhibits Ca 2+ extrusion to sustain cytosolic Ca 2+ signaling. However, how Ca 2+ uptake by the mitochondrial Ca 2+ uniporter (MCU) shapes receptor-evoked interorganellar Ca 2+ signaling is unknown. Here, we generated several cell lines with MCU-knockout (MCU-KO) as well as tissue-specific MCU-knockdown mice. We show that mitochondrial depolarization, but not MCU-KO, inhibits store-operated Ca 2+ entry (SOCE). Paradoxically, despite enhancing Ca 2+ extrusion and promoting CRAC channel CDI, MCU-KO increased cytosolic Ca 2+ in response to store depletion. Further, physiological agonist stimulation in MCU-KO cells led to enhanced frequency of cytosolic Ca 2+ oscillations, endoplasmic reticulum Ca 2+ refilling, NFAT nuclear translocation and proliferation. However, MCU-KO did not affect inositol-1,4,5-trisphosphate receptor activity. Mathematical modeling supports that MCU-KO enhances cytosolic Ca 2+ , despite limiting CRAC channel activity.

Regulation of Interorganellar Ca2+ Transfer and NFAT Activation by the Mitochondrial Ca2+ Uniporter