BME MS Defense: Mootaz Eldib

Cyclic Stretch of Alveolar Epithelial Cells alters Cytoskeletal Micromechanics

Supervised by Prof. David Dean

Abstract

Cytoplasmic transport of large molecules such as plasmid DNA (pDNA) has been shown to increase when cells are subjected to mild levels of cyclic stretch for brief periods. In the case of pDNA, this is in part due to the increased active transport of pDNA along stabilized, acetylated microtubules in the cytoplasm, whose levels are increased in response to stretch. It also has been shown that disruption of the dense actin network leads to increased pDNA and macromolecule diffusion as well. We hypothesize that stretch not only increases active transport of pDNA but also, similar to actin disrupting drugs, decreases cytoplasmic stiffness leading to a less restive pathway for macromolecules to diffuse. To test this particle tacking microrheology was used to measure cytoplasmic mechanics. It was concluded that while cyclic stretch transiently decreases cytoplasmic stiffness and increases diffusivity, stretch-independent modulation of the levels of acetylated, stable microtubules has no effect on cytoplasmic stiffness. Furthermore, stretching cells that have maximally acetylated microtubules increases cytoplasmic trafficking of pDNA, without increasing levels of acetylated microtubules. These findings suggest that stretch-enhanced gene transfer may occur by two independent mechanisms: increased levels of acetylated microtubules for directed active transport, and reduced cytoplasmic stiffness for increased diffusion.