Deciphering Intracellular Forces: Mechanical Interactions Shaping Mitochondrial Transport and Morphology

Mitochondria are dynamic organelles that continually undergo changes in size and morphology due to processes such as fusion and fission, active transport, mechanical stress, and cellular signaling cascades—all of which influence their functionality. The cytoskeleton, consisting of microtubules, F-actin, and intermediate filaments, interacts with mitochondria and plays a crucial role in determining their structure, organization, and function. These interactions are mediated by molecular motors like kinesin, dynein, and myosin, which drive mitochondrial transport and shape changes.

In this study, we employed high-resolution live-cell imaging and quantitative analyses to investigate mitochondrial behavior in Xenopus laevis melanophore cells. We tracked individual mitochondria with nanometer precision, examining their transport dynamics, shape fluctuations, and responses to mechanical forces. Our findings indicate that microtubules act as the primary scaffold for mitochondrial organization and transport, promoting elongation and influencing cellular distribution. Conversely, actin and microtubules have distinct roles in shaping mitochondrial morphology, with actin restricting organelle mobility and microtubules transmitting movement-induced jittering.

Also, we present an innovative quantitative approach to study the forces affecting mitochondria in living cells with minimal invasiveness. This tool enables the detection of localized mechanical impulses acting on these organelles, differentiating them from the background of cytoplasmic thermal fluctuations. Additionally, a numerical worm-like chain model incorporating thermal noise and external forces demonstrated that active force application is necessary for reproducing mitochondrial behaviors observed in living cells.

Overall, our findings highlight the complex mechanical interplay between mitochondria and the cytoskeleton and its importance in shaping mitochondrial behavior, impacting cellular homeostasis and function.