Periodic Reporting for period 1 - MiMEtiC (Molecular mechanisms of the mechanical interaction between the cell nucleus and the actin cytoskeleton)
Reporting period: 2017-03-01 to 2019-02-28
Epithelial tissues such as the skin epidermis are critical load-bearing elements of the body. They undergo large-scale, force-driven deformations during morphogenesis and in the adult organism. Strikingly, in contrast to cancer cells where mechanical deformations have been shown to induce nuclear rupture and DNA damage, such effects have not been observed in untransformed epithelial cells. On the contrary, epithelial cells have been shown to be capable of undergoing extreme deformation without damage, and to withstand long-term mechanical strain without signs of genomic damage or loss of viability. This project aimed to understand how nuclei respond to mechanical stress and how the genome is protected under extreme nuclear deformations
EPCs were chosen because they can be maintained in a stem cell state as well as differentiated in vitro to obtain epidermal lineages, and thus represent excellent model to identify and study mechanically controlled genetic programs that drive cell fate decisions.
To identify nuclear mechanotransduction pathways, I exposed EPCs to diverse regimes of cyclic uniaxial mechanical strain (5%, 20%, 40%, frequency 0.1 Hz). By using a large panel of experimental tools, including super resolution and regular confocal imaging, electron microscopy, quantitative phosphoproteomics, atomic force microscopy and a number of biochemical techniques, I observed that uniaxial strain, even at low strain levels, triggers nuclear deformation that catalyzes remodeling of the nuclear lamina and the lamina-associated heterochromatin. This remodeling facilitated an increase in nuclear elasticity. Intriguingly, blocking this response induced DNA damage upon strain, demonstrating that the remodeling of the lamina-associated heterochromatin is required for genome protection in the presence of strain. I further observed that high levels of strain induced a slower response where cells aligned their long axis and cytoskeletal fibers perpendicular to the direction of strain. This allowed the cells to dissipate the mechanical force before it reached the nucleus, allowing the cells to restore their steady state nuclear architecture. This project highlighted a novel, active role for chromatin as an element that can dynamically adapt to exogenous mechanical stresses by altering its own state to protect the genetic material