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Joshua Newberg

November 20 @ 11:00 am - 12:00 pm MST

Thesis Information

Title: Isolated Nucleus Stiffens in Response to Low Intensity Vibration

Program: Master of Science in Mechanical Engineering

Advisor: Dr. Gunes Uzer, Mechanical and Biomedical Engineering

Committee Members: Dr. Clare Fitzpatrick, Mechanical and Biomedical Engineering, Dr. Trevor Lujan, Mechanical and Biomedical Engineering, and Dr. Paul Davis, Materials Science and Engineering

Abstract

The nucleus, central to all cellular activity, relies on both direct mechanical input and its molecular transducers to sense and respond to external stimuli. This occurs by regulating intra-nuclear organization that ultimately determines gene expression to control cell function and fate. It is long studied that signals propagate from an extracellular environment to the cytoskeleton and into nucleus (outside-in signaling) to regulate cell behavior. Emerging evidence, however, shows that both the cytoskeleton and nucleus have inherent abilities to sense and adapt to mechanical force, independent of each other. While it has shown that isolated nuclei can adapt to force directly ex vivo, the role of nuclear mechanoadaptation in response to physiologic forces in vivo remains unclear. To gain more knowledge on nuclear mechanoadaptation in cells, we have developed an atomic force microscopy based experimental procedure to isolate live nuclei and specifically test whether nuclear stiffness increases in mesenchymal stem cells (MSCs) following the application of low intensity vibration (LIV). Results indicated that isolated nuclei, on average, were 36% softer than nuclei of intact MSCs. In intact MSCs, depletion of nuclear structural proteins LaminA/C and Sun-1&2 led to both decreases in nuclear elastic moduli and chromatin condensation. In isolated nuclei, identical depletions led to stiffness decreases but not in chromatin dynamics. When LIV was applied in series (0.7g, 90Hz, 20min) either twice (2x) or four times (4x), increased nuclear stiffness of intact MSCs showed dose dependency while stiffness changes in isolated nuclei was only detectable at the 4x LIV dose. Changes in isolated nuclear stiffness was not accompanied by changes in LaminA/C or Sun1&2 protein levels. Overall, our findings show that nuclear stiffness measurements on intact cells were heavily influenced by changes in the cell cytoskeleton and that acute application of LIV increases the isolated nuclear stiffness at the levels detectable by atomic force microscopy.