(806d) Nuclear Structure and Reorganization in Endothelial Cell Responsiveness to VEGF

Mechanical force is found to be increasingly important during development and for proper homeostatic maintenance of cells and tissues. There are many known genome regulators in cells including a myriad of chemical signaling pathways. However, short lived signaling events are not sufficient to explain both the long time responses and permanent changes of cells. We are interested in chromatin organization in endothelial cells and the role of reorganization in enhancing angiogenesis. Our central hypothesis is that chromatin organization is related to gene expression and reorganization is correlated with changes in cellular phenotype.

We image changes in genome structures and quantify movements of the chromatin in live cells. We have decoupled impacts on chromatin movements induced by cellular motors from chromatin decondensation using well-established biological treatments on endothelial cells. We also observe changes in genome organization and movement in the presence of the angiogenic chemical vascular endothelial growth factor (VEGF). We find that early nuclear responses to VEGF appear to be motor induced, followed by chromatin decondensation.

Endothelial cells also respond to extracellular shear stress. The genome within the nucleus is a complex, self-assembled structure which has unique, shear-thinning viscoelastic properties capable of responding proportionally to both the magnitude and duration of applied stress. We observe a statistical change in nuclear rheology at 30 minutes after the application of shear stress. We find that the effects of VEGF and shear stress on the nucleus are additive, suggesting a functionality at the subcellular level.

Combined, these results provide insight into the mechanical regulation of gene expression through altered gene location. We suggest that chemical and mechanical signals are transduced through the cell in multiple ways and cellular structure can enhance chemical responses.