Increased mitochondrial activity upon CatSper channel activation is required for sperm capacitation

Abstract To fertilize an oocyte, sperm must become hyperactive. However, whether they obtain ATP for hyperactivated motility via glycolysis or mitochondrial respiration is unclear. Here, high-resolution respirometry, flow cytometry, and confocal microscopy experiments revealed that mitochondrial respiration and membrane potential increased during mouse sperm capacitation. Treatment with inhibitors of mitochondrial respiration prevented sperm from hyperactivating and fertilizing an oocyte. Mitochondrial respiration was impaired in sperm from mice lacking the calcium channel CatSper. We developed a method to image mitochondrial calcium in sperm and found that CatSper activation led to increased mitochondrial calcium concentration. Finally, treating sperm with an inhibitor of mitochondrial calcium import impaired mitochondrial function and sperm hyperactivation. Together, our results uncover a new role of sperm mitochondria and reveal a new pathway connecting calcium influx through CatSper to mitochondrial activity and the sperm hyperactivation required to fertilize an oocyte. Summary The source of ATP for sperm hyperactivation is unclear. Ferreira et al. show that mitochondrial activity increases during, and is required for, hyperactivation and fertilization ability. Increased mitochondrial activity depends on calcium influx through the channel CatSper.