Mechanoresponsive Characterization of the Nucleus with Implication in Aging

Extracellular forces alter gene expression through chemical signaling and transduction of force. This thesis studied how cells respond to mechanical stimuli within their environments, specifically the subnuclear response to shear and compressive stress, and cell motility through nuclear deforming 3D matrices. Subnuclear response to shear stress was measured by single particle tracking of fluorescently tagged nucleolar proteins under shear and compressive stress. In cells under stress for short periods of time, there was an initial intranuclear response followed by an increase in movement at 30 minutes. The subnuclear temporal response correlates along the same times scales as intracellular signaling for transcription and reorganization of the surrounding cytoskeleton. The increase in intranuclear movement may alter chromatin organization leading to altered gene expression.;Cells show a decrease in mechanoresponsivness during the aging process. A potential contributor to this decline is expression and accumulation of a mutant lamin A protein, progerin. Lamins are located at the inner nuclear membrane where they self assemble into the nuclear lamina which provides the majority of the mechanical structure and support for the cell. Progerin is dominantly expressed in people with Hutchinson Gilford Progeria Syndrome (HGPS) and is sporadically expressed and accumulates during healthy adult lifetimes. The incorporation of progerin into the nuclear lamina stiffens the nucleus, decreases nuclear to cytoskeletal connectivity, and damages the underlying chromatin. The inclusion of progerin in cells under shear and compressive stress show attenuated cell response to stress at the chromatin level potentially affecting gene expression. Inclusion of progerin further effects cellular processes such as migration through 3D substrates. Progeriod cells show decreased movement and nuclear deformation when migrating through 3D substrates. Decreased cell motility through tight interstitia has the potential to impact development, wound healing, cancer metastasis and many other cellular functions. In this thesis we demonstrate that nuclei are mechanoresponsive at the subnuclear level and that the aging process can attenuate this response. Additionally, cell functionality from nuclear stiffness during the aging process should be considered during cell migration through 3D substrates.