A method for isolating and cryopreserving intact mitochondria with improved integrity and functionality

Mitochondria isolated from cells are essential tools in biological research. However, many mitochondria are often damaged during the isolation process. Although cryopreservation can greatly improve the usability of isolated mitochondria, it typically leads to significant loss of activity following freezing and thawing. In this study, we present our own techniques for mitochondrial isolation and cryopreservation to overcome these challenges. Our isolation method begins by selectively weakening the plasma membrane through the incorporation of digitonin, under conditions that do not increase membrane permeability. The plasma membrane is then selectively ruptured to release mitochondria. Notably, mitochondria contract within the cell before the plasma membrane ruptures, a process that facilitates their extraction. The isolated mitochondria showed polarized inner membranes in approximately 90% of the population. Compared to mitochondria isolated by homogenization, they retained more intermembrane space proteins and exhibited greater outer membrane integrity. For cryopreservation, rapid thawing was critical to maintaining mitochondrial activity after freeze-thaw cycles. When thawing was completed in under 1.5 minutes, the proportion of polarized mitochondria decreased by only about 10%. These findings suggest that our isolation and cryopreservation protocols are promising for applications requiring intact, functional mitochondria.