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 (ΔΨ_mt) 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.