Mechanical constrains are both generated at and born by the cell-cell contact. Our line of research is to understand how mechanical forces exerted at different scales (tissue, contact, molecule) organize the cell-cell contact, contribute to the adhesion strength of epithelial tissue and lead to functional consequences such as the development and maintenance of apico-basal polarity.
Building liver cell by cell
We started a bottom up project to understand how hepatocytes develop long secretory tubes between cell doublets (canaliculi) into which bile is secreted. These tube form between 2 cells then elongate to other cell-cell contacts by cord hollowing
On cell liver:
First we studied the minimal parameters that a cell needs to develop an apical pole. If the molecular pathways involved are being unraveled, the role of mechanical organization of the cell cell contact in the initiation of lumen formation is completely unknown. We used our microniches approach to fool a single hepatocytes as if it was in a tissue and force it to polarize and secret bile. This approach allows us to understand precisely how mechanical forces at the contact control apico-basal signaling and lumen development.
Two cell liver:
Then we study a second process: Lumen elongation. We used cell doublets in microwells of controlled biochemical geometry. We showed that the spatial structuration of ECM adhesion lead to the development of anisotropic tension along the cell cell contact. In turn this anisotropy positions the lumen and favors its development in the direction of least tension (Li et al NCB 2016).
In particular we are modeling and exploring the role of osmotic forces and paracellular leaks in lumen development (Gupta et al Jour Hepatology 2017, dasGupta et al PNAS 2018).
Four cell liver:
We then study a third process: the fusion of two adjacent lumens into a single tube. This project is performed by imaging in controlled microniches.
At the larger scale we finally started developing liver organoids to look at the development of lumen during hepatic maturation. The projects involves controlling maturation (Coll SCheik Tamir, Kings College), controlling hepatocytes spatial structures by microfabrication.
Understanding Cell-Cell Adhesion
Modulation of cell-cell adhesion by mechanical forces
In this project we are interested in understanding how mechanical tension and shear lead to the recruitment of adhesion proteins (Cadherin and Tight junctions). In particular we are interested in the coupling of the junctional cortex dynamics with the recruitment of adhesion molecules. Our hypothesis is that the cortex dynamics is highly regulated at the cell cell contact and largely dictates the ability for adhesion molecule to interact.
As a consequence, we explore how cortical dynamics is essential to regulate cell-cell adhesion both as a regulator of the transmembrane interaction as well as a physical way to dissipate energy.
To this end we mostly use suspended S180 doublets to avoid all interaction with extracellular matrix. We developed new methods to image the formation of the junction as well as to measure the adhesive forces.
We show that cortex dynamics slow down when the cortex is under tension leading to the immobilization of E cadherin (Engl et at NCB 2014).
In a mirror fashion the application of mechanical stress on suspended doublet shows an actin mediated reinforcement of both adherens and tight junction proteins under external stimulation. This recruitment occurs only at the stretched part of the junction and result from a modulation of actin dynamics (Gao et al APL, 2018).