Influence of Mechanical Stress on Biological Processes of Human Cells

Abstract

With an increasing number of spaceflights, it is crucial that we understand the changes that occur to our cells in space. I was interested in testing the effects of real (r-) and simulated (s-) microgravity (μg) on human breast cancer cells with the objective of investigating cytoskeletal alterations, focal adhesion molecules, extracellular matrix proteins, inflammatory cytokines and the potential mechanism of spheroid formation during microgravity. Besides microgravity, astronauts are subjected to other factors during space travel, including vibration, hypergravity and cosmic radiation. Moreover, vibrations occur during parabolic flights. To evaluate whether vibration has any beneficial impact on chondrocytes, I examined the effect of low-frequency vibration on human chondrocytes. Microgravity is known to exert a negative impact on chondrocytes and vibration could be the countermeasure to prevent such a negative impact. This thesis evaluated the impact of a 14-day-exposure of MCF-7 breast cancer cells to a random positioning machine (RPM). The cells exposed to the RPM divided into adherent and multicellular spheroids. A proteomics analysis examined the difference between adherent, spheroid and 1g control cells. The analysis revealed a reduction in E-cadherin in spheroids. This finding was confirmed by measuring the messenger RNA (mRNA) expression and protein content. There is a relation between E-cadherin regulation and spheroid formation. Furthermore, I performed live-cell imaging of transfected MCF-7 cells with a spinning-disc fluorescence microscopy analysis system (FLUMIAS) microscope during a sounding rocket mission. The cells exhibited a rearrangement of F-actin and tubulin. Moreover, I detected filopodia- and lamellipodia-like structures in the F-actin cytoskeleton shortly after the beginning of the microgravity phase. I also investigated the effect of microgravity on MCF-7 cells during a parabolic flight campaign (PFC). The cells manifested elevated KRT8, RDX, TIMP1 and CXCL8 mRNA, while VCL was downregulated. Furthermore, E-cadherin protein was significantly downregulated. These changes indicate a transformation of the MCF-7 cells into a more invasive cell type. In another study, I evaluated the effect of microgravity on the triple negative breast cancer cell line MDA-MB-231 during a PFC. The parabolic flight induced alterations in cell adhesion molecules, findings that are in agreement with previous data from other cell lines. Finally, I evaluated the impact of low-frequency vibration on human chondrocytes. There were no morphological changes, cytoskeletal alterations or apoptotic cells. Moreover, there was an upregulation of ANXA1, PXN and VCL mRNA and downregulation of ANXA2. Thus, I concluded that there is a beneficial effect of low-frequency vibration on human chondrocytes.