Cell migration and invasion

Cell contractility fulfills essential physiological functions such as muscle contraction and cell migration and plays a role in several human diseases, including fibrosis, scarring, and cancer. Besides muscle cells, myofibroblasts are another type of professional contractile cell. In most cases, myofibroblasts are transient entities believed to arise from normal fibroblasts following stress and whose function is to remodel the connective tissue by contracting and pulling on the extracellular matrix (ECM). Such a process is, for example, required to repair a wounded epithelium. Once the wound is repaired, myofibroblasts typically die.

If they persist longer, the excessive contraction and the resulting over-remodeling of the ECM lead to scars' formation. These highly contractile cells are always present where substantial matrix remodeling is happening. However, myofibroblasts are also present in many tissues under physiological conditions, including the gut. There is no dramatic remodeling of the ECM in gut homeostasis, and the role of myofibroblasts in this context is unclear. We are investigating the role of myofibroblasts' contractility in epithelial homeostasis and wound repair. 

The gut epithelium acts as a barrier between the outside world and the body while at the same time ensuring nutrient absorption. The small intestine epithelium is composed of a single layer of columnar cells that line the villi that project into the gut's lumen and the crypts that descend into the connective tissue. The constant epithelium renewal is achieved by stem cell proliferation in the crypts giving rise to specialized epithelial cell types. Upon exiting the crypt, most cell types migrate towards the villus tip, where they die and are shed into the lumen. The basal surface of the epithelium is underlined by the basement membrane (BM), a thin and dense sheet-like structure composed of a network of collagen IV and laminin on which cells adhere and migrate. It was believed that cell migration on the BM is a passive process, driven by mitotic pressure generated at the crypts. However, recently we showed that mitotic pressure has a short-range effect restricted to the crypts and that active migration is required to reach the villus tip (Krndija et al., Science, 2019). While cells migrate collectively, maintaining their apicobasal polarity, they also display a second polarity axis (front-back), characterized by actin-rich basal protrusions oriented in the direction of migration. How this front-back polarity is established and what is the guidance cue for directional migration towards the tip of villi remains unknown. Currently, we are investigating how the BM provides cues for the directional migration of epithelial cells, what are the roles of adhesive structures in reading those cues and how front-back polarity is built to allow directional cell migration. Finally, we are addressing the role of the actomyosin cytoskeleton in the maintenance of intestinal epithelium integrity and cell migration.

In collaboration with Stephanie Descroix (UMR168, IPGG), we have developed a device - reconstituted Gut-on-Chip - that will allow us to test the impact of individual parameters such as physical constraints peristalsis and the extracellular matrix (ECM) on epithelium homeostasis.

During tumor progression, CAFs and ECM accumulate in tumors forming a capsule that enwraps cancer cells. This capsule is a barrier that restricts tumor growth leading to the buildup of intratumoral pressure. Combining genetic and physical manipulations in vivo with microfabrication and force measurements in vitro, we found that the CAFs capsule is not a passive barrier but instead actively compresses cancer cells using actomyosin contractility. Cancer cells mechanosense CAF compression. Abrogation of CAFs contractility in vivo leads to the dissipation of compressive forces and impairment of capsule formation. By mapping CAF force patterns, we show that compression is a CAF-intrinsic property independent of cancer cell growth. Supracellular coordination of CAFs is achieved through fibronectin cables that serve as scaffolds allowing force transmission. This study unveils that the contractile capsule actively compresses cancer cells, modulates their mechanical signaling, and reorganizes tumor morphology (Barbazan et al, BioRxiv, 2021).

In carcinoma in situ, the basement membrane represents a physical barrier that prevents the tumor from spreading to the adjacent stroma. Cancer cells perforate the basement membrane using proteases-rich protrusions. We have questioned whether stromal cells such as cancer-associated fibroblasts (CAFs) cooperate with cancer cells to breach the basement membrane. We found that in the presence of CAFs, cancer cells invade the basement membrane in a protease-independent manner. Using live imaging and atomic force microscopy we show that CAFs use mechanical forces to remodel the basement membrane, leading to the formation of gaps through which cancer cells can migrate (Glentis et al, Nature Commun, 2017, Atieh et al, J Cell Biol, 2017).

We are currently investigating if the specific organization of CAFs and the matrix they produce can stimulate invasion of cancer cells and their resistance to therapy.

The colon is primarily responsible for absorbing fluids. It contains many microorganisms including fungi, which are particularly enriched in its distal segment. Therefore, the colonic mucosa must tightly regulate fluid influx to avoid absorption of potentially dangerous fungal metabolites, which can be toxic to epithelial cells and reach the blood circulation, ultimately leading to barrier dysfunction and sepsis. How this is achieved remains unknown. In collaboration with Ana-Maria Lennon (U932) we found that the innate immune system allows rapid quality-check of fluids absorbed through epithelial cells to avoid intoxication of colonocytes by fungi products. This mechanism relies on a peculiar population of colon macrophages equipped with "balloon-like" protrusions (BLPs) inserted at the base of epithelial cells. BLPs sample the absorbed fluids and stop absorption when fluids are poisoned with the fungal toxin. In the absence of macrophages or BLPs, epithelial cells keep absorbing fungal toxin-containing fluids, leading to their death and subsequent loss of epithelial barrier integrity. These results reveal an unexpected and essential role of macrophages in maintaining colonic homeostasis (Chikina et al, Cell, 2020).

Currently we are investigating how BLP control fluid absorption by epithelial cells and how does this function of macrophages regulate colon inflammation and immune activation at steady-state or in pathological conditions.