Final Project: Nazila Daneshjou- Rac1 and VE-cadherin dynamic

 Rac1, a monomeric RhoGTPase plays a critical role in regulating endothelial junctional permeability; however, the causal relationship between Rac1 activity at adherens junctions (AJs) and stability of Vascular Endothelial (VE)-cadherin adhesion, the main protein of AJ complex, is not well understood. My research interest is to determine the underlying molecular and signaling mechanism involved in Rac1-mediated VE-cadherin adhesion. I utilized photo-activatable and photo-switchable proteins, which allowed me to control the spatial and temporal activity of Rac1 and determine the effect of its activity at the level of cell-cell junction on the dynamic of VE-cadherin adhesion. My experimental data suggests that activation of Rac1 at AJs promotes VE-cadherin accumulation by reducing the rate at which VE-cadherin molecules leave the junction (ie. dissociation). Using mathematical modeling, I asked whether the observed decrease in the rate of VE-cadherin dissociation is sufficient to explain the Rac1-induced VE-cadherin accumulation. I generated 11 ODE questions to explain VE-cadherin association and dissociation (including dimerization and complex formation) and by using parameter estimation (COPASI) I showed that VE-cadherin dissociation at the rate of 1.348±0.015 1/sec is sufficient to promote VE-cadherin accumulation as seen in my experimental data. Interestingly, this rate is much faster than what I measured experimentally (0.0018±0.002 1/sec). However, it is important to note that the experimental measurement is the total amount of signal; hence the dimerization and complex formation influence the rate. Another Interesting observation was that the model suggests that the dimerization of VE-cadherin happens at much higher affinity compared to the complex formation, which is both unexpected and interesting since the complex formation has shown to be critical for stability of the junctions. For future studies, I’d like to design and perform experiments that can explain this phenomenon.

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