Online Ph.D. Defense: “Tunable Collagen I Matrices for Cellular Migration Assay and Mechanical Properties of Mitotic Mammary Cells” — April 22, 2021 at 1 PM
Ms. Melissa Pashayan
Mentor: Professor Jed Macosko
Department of Physics
Wake Forest University
Thursday, April 22, 2021 at 1:00 pm
(Private defense will follow public presentation)
Via Video Conference (contact wfuphys@wfu.edu for link information)
ABSTRACT
The mechanical properties of cells influence their function in the way they differentiate, proliferate, migrate, adhere, and sense their local microenvironment. In disease, these properties are significantly altered and are hallmarks of disease onset and progression. Cancer cells, particularly, have been shown to be softer than normal tissue, and the changes in mechanical properties are linked to tumor formation and metastatic potential. The study of mechanical properties of different cells and their diseased counterparts can therefore provide insight into both the normal development of tissue and the pathophysiology of disease and may aid in the development of novel diagnostic techniques and treatments.
Cancer metastasis is one of the deadliest aspects of the disease. Metastatic cells break away from their primary tumor and invade the surrounding tissue, traveling though the stroma into the vasculature or lymph before settling onto a secondary site and forming new tumors. Along this journey, cancer cells must migrate though vastly different tissues with varied properties, namely stiffness, which can change by factors up to 20 for breast cancer; observing how cells migrate through diverse stiffness matrices is crucial to understanding the process of metastasis. Though there are many different matrices used for in vitro studies of cell migration, stiffness variation is often achieved though the change of other material properties, such as ligand density. This makes it difficult to separate the effect of stiffness from the effect of these other properties. In this work, a novel method for the functionalization of collagen I gels with glycidyl methacrylate (GMA), using lithium acylphosphinate as a photoinitiator of GMA cross-linking, is tested in migration assay. This method allows for matrix stiffness to be tuned via timed exposure to UV light independent of ligand density. Metastatic breast cells embedded in the gels survived and migrated, proving these matrices viable for migration study.
Cell division, which is often deregulated in cancer, involves the complete remodeling and restructuring of the cell, from its interior components to the cytoskeleton, in addition to the morphological changes as the divides into two daughter cells. During mitosis, cells round up as microtubules form the mitotic spindle responsible for chromosomal segregation, elongate as the chromosomes separate along the spindle, and furrow, or pinch off, into two new cells via constriction of a contractile actin ring along the equator. Morphology and cytoskeletal structure often determine cellular mechanical properties, which would therefore be expected to change throughout the process of cell division. In this work, the Young’s modulus, a measure of stiffness, is measured with an atomic force microscope for synchronized normal human mammary epithelial cells, HMECs, as they divide. The stiffness is found to increase 4-fold, peaking shortly after the onset of furrowing, before softening as the cell finishes dividing. This work provides a baseline for comparison to different grades of breast cancer, which could provide insight into the altered mechanisms of cancer cell growth and proliferation.
PUBLICATIONS
- Smelser A.M., Gomez M.M., Smyre S., Fender Pashayan M.L., Macosko J.C. (2018) Stiffness-Tuned Matrices for Tumor Cell Studies. In: Soker S., Skardal A. (eds) Tumor Organoids. Cancer Drug Discovery and Development. Humana Press, Cham. https://doi.org/10.1007/978-3-319-60511-1_9
