MCU Interacts with Miro1 to Modulate Mitochondrial Functions in Neurons.

Mitochondrial Ca2+ uptake is gated by the mitochondrial calcium uniplex, which is comprised of mitochondrial calcium uniporter (MCU), the Ca2+ pore-forming subunit of the complex, and its regulators. Ca2+ influx through MCU affects both mitochondrial function and movement in neurons, but its direct role in mitochondrial movement has not been explored. In this report, we show a link between MCU and Miro1, a membrane protein known to regulate mitochondrial movement. We find that MCU interacts with Miro1 through MCU's N-terminal domain, previously thought to be the mitochondrial targeting sequence. Our results show that the N-terminus of MCU has a transmembrane domain that traverses the outer mitochondrial membrane, which is dispensable for MCU localization into mitochondria. However, this domain is required for Miro1 interaction and is critical for Miro1 directed movement. Together, our findings reveal Miro1 as a new component of the MCU complex, and that MCU is an important regulator of mitochondrial transport.SIGNIFICANCE STATEMENT Mitochondrial calcium level is critical for mitochondrial metabolic activity and mitochondrial transport in neurons. While it has been established that calcium influx into mitochondria is modulated by mitochondrial calcium uniporter (MCU) complex, how MCU regulates mitochondrial movement still remains unclear. Here, we discover that the N-terminus of MCU plays a different role than previously thought; it is not required for mitochondrial targeting but is essential for interaction with Miro1, an outer mitochondrial membrane protein important for mitochondrial movement. Furthermore, we show that MCU-Miro1 interaction is required to maintain mitochondrial transport. Our data identify that Miro1 is a novel component of the mitochondrial calcium uniplex and demonstrate that coupling between MCU and Miro1 as a novel mechanism modulating both mitochondrial Ca2+ uptake and mitochondrial transport.