Year: 2017
Type: dissertation
Abstract: Epithelial migration plays an important role during re-epithelization phase in\n\t\t\t\t wound healing. Several skin diseases, such as chronic ulcers, fail during this\n\t\t\t\t stage. During last years a new insight into this problem has arisen introducing\n\t\t\t\t a mechanical point of view of this process. Kinematics and density distribution\n\t\t\t\t within the epithelium play key role during collective migration. Besides, the\n\t\t\t\t capacity of cells to proliferate and provide the tissue with new cells enhance the\n\t\t\t\t ability of them closing the wound.\n\t\t\t\t The evolution of the leading edge has shown that experiments performed at\n\t\t\t\t starvation stopped at some point whereas those performed at normal condition\n\t\t\t\t kept advancing.\n\t\t\t\t A deeper study of the velocity fields showed that, cells several rows behind\n\t\t\t\t the edge barely moved during the whole experiment. The experiments without\n\t\t\t\t proliferation showed a sudden increase in velocity that rapidly decayed after\n\t\t\t\t some hours while experiments at normal conditions kept a positive velocity\n\t\t\t\t during the whole time.\n\t\t\t\t Although velocity profiles showed a completely different behaviour between\n\t\t\t\t experiments performed at normal conditions and at starvation, the study of\n\t\t\t\t density distribution of cells inside the tissue exhibit almost the same profiles.\n\t\t\t\t This result leads to the idea that cells acquire a well-established profile to move,\n\t\t\t\t ‘advancing formation’, with lower density at the front where cells with greater\n\t\t\t\t velocity are found and many rows behind, confluent cells, which display slower\n\t\t\t\t velocity.\n\t\t\t\t Cell migration results from the interplay of mechanical and chemical interactions\n\t\t\t\t between cells and their extracellular environment. Mathematical in\n\t\t\t\t silico models can reproduce experimental results and can predict different future\n\t\t\t\t behaviours. Due to the complexity and huge amount of data obtained\n\t\t\t\t from in vitro experiments, an emergent need of bioinformatics and mathematical\n\t\t\t\t models have appeared although experiments will always be needed. The\n\t\t\t\t main advantage is their ability to handle multiple interacting variables simultaneously,\n\t\t\t\t which is difficult to deal with in experiments. Here, we introduce the\n\t\t\t\t novelty of density field into Banerjee et al. model with the polarization force\n\t\t\t\t term proposed by Arciero et al. which mimics better our experimental results and is more physiological. The combination of both has provided good results for the starvation case studied. The temporal evolution of the monolayer length\n\t\t\t\t has been fitted to obtain the set of free parameters of the model to be later\n\t\t\t\t used to calculate the main variables governing the problem, displacement, density\n\t\t\t\t and concentration of contractile units. The real size of the cell culture has\n\t\t\t\t shown to be an important factor to be under consideration in regulating the\n\t\t\t\t density distribution in the model. Besides, the study of several parameters\n\t\t\t\t in the model has shown to exert little influence on the solution. Diffusivity or\n\t\t\t\t internal pressure could be then removed from the model without influencing\n\t\t\t\t significantly the results.\n\t\t\t\t Transepithelial potential (TEP) is defined as the voltage across an epithelium\n\t\t\t\t which is the sum of all the voltages of single cell membranes. After epidermis\n\t\t\t\t wounding, this transepithelial potential is disrupted inducing endogeneous\n\t\t\t\t epithelial electric fields (EEF) that might be implicated in wound reepithelization.\n\t\t\t\t In this work we present an epithelial cell monolayer electrical characterization\n\t\t\t\t by means of impedance spectroscopy techniques. We have study a wide\n\t\t\t\t range of frequencies and three different voltages leading to the conclusion that\n\t\t\t\t cell monolayer exhibits a linear impedance behaviour. Given that results, we\n\t\t\t\t proposed an equivalent electric circuit to better understand cell-cell and cell-substrate communication. Besides, 2D wound healing assays were performed\n\t\t\t\t and external electric fields were applied to force different migration rates improving\n\t\t\t\t the ability of cells to migrate towards the wound. Finally, internal calcium\n\t\t\t\t concentration was monitored for the different external voltages showing\n\t\t\t\t higher concentration in those experiments performed with the largest electric\n\t\t\t\t field at the beginning of the experiments. This result suggests that cell-cell communication\n\t\t\t\t is enhanced by electric fields improving ion exhange and therefore\n\t\t\t\t improving migration rates.\n\t\t\t\t This thesis has provided an important knowledge in the physics governing\n\t\t\t\t cell migration to Termeg group. We have started a new research line studying\n\t\t\t\t collective cell migration, mechanical forces or electric fields involved in the\n\t\t\t\t process of wound healing in vitro.
Author: Valencia Blanco, Leticia
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7017717480