Mitochondrial Ca2+ uniporter b (MCUb) regulates neuronal Ca2+ dynamics and resistance to ischemic stroke.

Mitochondrial Ca2+ transport regulates many neuronal functions including synaptic transmission, ATP production, gene expression and neuronal survival. The mitochondrial Ca2+ uniporter (MCU) is the core molecular component of the mitochondrial Ca2+ uptake complex in the inner mitochondrial membrane. MCUb is a paralog of MCU that negatively regulates mitochondrial Ca2+ uptake in the heart and the cells of the immune system. However, the function of MCUb in the brain is largely unknown. Here, we report that MCUb knockout (KO) led to enhanced mitochondrial Ca2+ uptake in cortical neurons. By simultaneously monitoring changes in cytosolic and mitochondrial Ca2+ concentrations, [Ca2+]cyt and [Ca2+]mt, respectively, we also found that MCUb KO reduced the [Ca2+]cyt threshold required to induce mitochondrial uptake in cortical neurons during electrical stimulation. Exposure of cortical neurons to toxic concentrations of glutamate led to a collapse of mitochondrial membrane potential (ΔΨmt) and [Ca2+]cyt deregulation, and MCUb deletion accelerated the development of both events. Furthermore, using the middle cerebral artery occlusion (MCAO) as a model of transient ischemic stroke in mice, we found that MCUb KO significantly increased MCAO-induced brain damage in male, but not female mice. These results suggest that MCUb regulates neuronal Ca2+ dynamics and excitotoxicity and reveal a sex-dependent role of MCUb in controlling resistance to brain damage following ischemic stroke.