Unravelling how mechanical forces build breast tissue to help tackle cancer

Disrupted tissue architecture is a central hallmark of cancer. For example, breast cancer is characterized by an abnormal growth of cells filling the hollow spaces of the tissue. Defective interactions between cells and their microenvironment play a key role in disrupting tissue organization and potentially augmenting cancer. Increasing data indicate that reinforcing tissue organisation prevents the manifestation of neoplastic features, ultimately suppressing tumour development. The female breast is structured as an epithelial tree made up of hollow ducts connected to lobular alveoli and each structure is compartmentalised into a bi-layer of inner luminal epithelia and outer myoepithelia. Extreme cell proliferation is perfectly natural within the breast, for example in pregnancy, but when tightly regulated this rarely augments cancer. A key problem is that we do not understand the developmental mechanisms that sort tissues into the correct architecture. There is a pressing need to unravel the mechanisms as these tightly regulated processes act as powerful tumour suppressors.
It is now recognized that physical forces both from within the cells and outside of the cells contribute to tissue development. Epithelial tissues adhere to a supporting extracellular matrix (ECM) that acts like a glue holding the tissues together. Cellular mechanoreceptors called beta1-integrin provide the link between external forces exerted by the ECM to internal force-generating actin-myosin networks. Using gene deletion in mice we previously showed that beta1-integrin is crucial for lobular alveolar development and formation of the lumen space. We hypothesise that beta1-integrin has a multifaceted mechanical role in breast tissue morphogenesis. To test this, we will use genetic deletion in vivo and in primary 3D organoid cultures that mimic breast tissue structures combined with computational modelling. We will address three specific objectives:

1) Determine how lobular shaped alveoli are engineered from the ends of ducts. We will test two hypotheses that explain how the tissue bends to create a ball shape and then uncover the mechanism of cleft formation to create lobules within lobes.

2) Determine the mechanism of beta1-integrin in single lumen formation. We will test the hypothesis that beta1-integrin regulates polarized fluid secretion, which generates a hydrostatic pressure that pushes open the lumen spaces. Rescue studies to restore lumen spaces in integrin-defective organoids will be employed through forced activation of fluid secretion.

3) Determine how the two cell types spatially assemble to form breast tissue. Myoepithelia express higher levels of integrins compared to luminal cells, which might act as a driving force to position these cells towards the outside. We will test the hypothesis that integrin-mediated affinity of the cell to the ECM facilitates self-organization within tissues either through cell sorting or cell division axis orientation.

This timely project will use cutting-edge primary 3D co-culture organoids that recapitulate breast tissue structures in vivo. 3D rendered imaging data will provide a framework to build novel 3D computational models of alveolar morphogenesis. This combined approach will provide a biological blueprint for the fundamental processes that become deregulated in cancer and may expose new biomarkers for detecting the disease at its early stages.
Identifying the factors that govern tissue morphogenesis has wider implications for stem cell biology and regenerative medicine. Use of computational modelling to test hypotheses and design new experiments will reduce the time and expense, associated with genetic testing in transgenic animals and accelerate research within these particular fields. The project will involve an integration of both biological and mathematical disciplines, which align strongly with the overall UKRI strategic vision.