Quality Saving Mechanisms of Mitochondria during Aging in a Fully Time-Dependent Computational Biophysical Model

Mitochondrial Morphologies Driven by Energy-Consuming Cell Sites in a Spatially and Time-Resolved Quality Model

Mitochondria are the energy plants of eukaryotic cells. Mitochondrial network morphologies are essential for the energy supply of eukaryotic cells. However, the associated dynamics are not yet fully understood. They behave as a dynamic network that adapts to the cell's environment and its energetic needs. Various processes such as mitochondrial fission and fusion, mitochondrial recycling, repair mechanisms, and oxidative stress influence the state of the mitochondrial network. Here, we introduce a novel time-dependent and spatially resolved quality model on mitochondrial morphology. The interplay between the mitochondrial network and energy-consuming cell sites is modeled by biophysical interactions of quality-dependent mitochondrial clusters in the presence of adenosine triphosphate (ATP) consumers represented by Mie potentials. Mitochondria are modeled as simplified ballistic particles that move within the cytoplasm of a virtual cell, and connect and divide by inelastic collisions. With this model, we investigate the coupling of mitochondrial dynamics with oscillating cell functions, representing diverse global states of the energetic architecture in the cell. Our simulations based on a generalized cell reveal a perinuclear condensation of mitochondria during phases of high-energy demand. Furthermore, quality-increasing mechanisms disclose the benefits of high mitochondrial masses. Simulations reveal that varying energy demands modeled by oscillations of ATP consumers alter the morphology of the network. Phases of high-energy consumption lead to interconnected network structures and perinuclear condensation of mitochondria. The model explains quality-increasing benefits of high mitochondrial masses.

Fragmentation of the mitochondrial network in skin in vivo

Mitochondria form dynamic networks which adapt to the environmental requirements of the cell. We investigated the aging process of these networks in human skin cells in vivo by multiphoton microscopy. A study on the age-dependency of the mitochondrial network in young and old volunteers revealed that keratinocytes in old skin establish a significantly more fragmented network with smaller and more compact mitochondrial clusters than keratinocytes in young skin. Furthermore, we investigated the mitochondrial network during differentiation processes of keratinocytes within the epidermis of volunteers. We observe a fragmentation similar to the age-dependent study in almost all parameters. These parallels raise questions about the dynamics of biophysical network structures during aging processes.