The broad objective of our research is to understand how epithelial cells interact with their microenvironment during migration in gut homeostasis and cancer invasion (Figure 1). We use a gut as a model system, and our strategy is to combine different models such as 3D cell cultures, tissue explants, mouse models and human samples coupled with different microscopy techniques and biophysical modeling.
Epithelial cell migration in gut homeostasis
The entire intestinal epithelium is renewed every week due to cell division in the crypts coupled with cell migration towards the villi and loss of cells by apoptosis at the tip of villi. What is the mechanism responsible for the movement of intestinal cells? In the crypts, epithelial cells move passively as a consequence of the pushing force generated by dividing cells. However, we found that along the villi, cells move actively using Arp2/3-dependent actin cytoskeleton (Krndija et al., Science, 2019) (Movie 1). We also found that cells migrate collectively with minimal rearrangements; and exhibit dual-polarity – apicobasal, and front-back, characterized by actin-rich basal protrusions oriented in the direction of migration. We are currently investigating the cue for directional cell migration towards the villus top and what role the actomyosin and cell-matrix adhesions play in this process. In collaboration with Stephanie Descroix (UMR168, IPGG) we are developing 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.
Movie 1: Epithelial migration along the villus (Denis Krndija)
Gut explants derived from Villin: CreERT2/mTmG mouse. Mosaic expression of GFP (green) in epithelial cells in the villus, other epithelial cells, and stroma (red).
Role of stromal cells in gut homeostasis
Fibroblasts are one of the major components of the stroma. There has been tremendous progress in understanding the importance of the chemical signals that fibroblasts produce for homeostasis of stem cell niche in the intestine. However, the way fibroblasts use mechanical forces to shape the extracellular matrix and consequently dictate the response of epithelial cells remains unexplored. We aim to understand how fibroblast contractility impacts epithelial cell proliferation, differentiation, and migration in homeostasis. In collaboration with Ana-Maria Lennon’s lab (Institut Curie, U932) we are also investigating the role of other stromal cells, such as dendritic cells and macrophages, in intestinal physiology.
Cancer cell invasion
The long-lasting interest of our team is the mechanism of cancer cell migration during the first steps of cancer metastasis. Until now, cancer cell migration has been described at the so-called “invasive front”, the region where cancer cells reach stromal tissue. The core of tumors has been considered as a relatively immobile tissue. However, using tumor explants and long-term 3D imaging we found that cancer cells in the tumor core are remarkably motile and that a collective behavior of neighboring cells is giving rise to large-scale tissue dynamics (Staneva et al., J Cell Science, 2019). After escaping the primary tumor, cancer cells migrate through the stroma either as single cells or in groups. We are investigating biomechanical advantages for cancer cells to migrate collectively. Cells migrate through the stroma by extending membrane protrusions which are stabilized by focal adhesions that link the actin cytoskeleton to the underlying extracellular matrix (Movie 2). We are interested in how focal adhesions are formed (Geraldo et al., EJCB, 2012; Elkhatib et al, Curr Biology, 2014) and we showed that cancer cells use focal adhesions to attach to endothelial fibronectin deposits, which allow them to extravasate and form metastasis in the liver (Barbazan et al., Cancer Research, 2017).
Movie 2: Cancer cell invasion (Sara Geraldo)
Cancer cells (green) invade the extracellular matrix (pink) in the living mouse observed by intravital two-photon microscopy.
Cancer-associated fibroblasts (CAFs) in cancer invasion
The tumor microenvironment plays an essential role in tumor progression. The basement membrane represents a first physical barrier that prevents spreading of the primary tumor to adjacent tissues. We found that in the presence of primary human colon CAFs, cancer cells invade the basement membrane in a protease-independent manner. Using live imaging showed 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., 2017) (Movie 3). Besides secreting growth factors that can stimulate invasive migration of cancer cells, CAFs can also actively excavate passageways in the ECM and lead cancer cell invasion. We found that CAFs assemble fibronectin fibrils via integrin β3 that triggers invasion of cancer cells through the stroma (Atieh et al., 2017) (Movie 4). Currently, we are investigating if the specific organization of CAFs, their contractile capacity, and the matrix they produce can stimulate invasion of cancer cells, resistance to therapy, and tumor relapse.