Biophysical control of cell migration by mechanical gradients in cell microenvironment

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Cell migration is a fundamental biological phenomenon that is critical for life of unicellular and multicellular organisms. Simple organisms, such as amebae, have to migrate to find food and to mate. Complexity of multicellular organisms, such as vertebrates, brings the necessity for individual cells and groups of cells to position themselves during developmental morphogenesis that is largely achieved through directed cell migration. In the adult, directed migration plays an important role in a wide range of physiological and pathological processes, including renewal of skin and intestinal epithelium, immune system function, and wound healing, as well as cancer metastasis and cardiovascular diseases. In tissue environment, cell migration is tightly regulated by numerous guidance cues that modulate activity of signaling networks, which in turn control intracellular machineries, e.g. actin cytoskeleton and focal adhesions, driving cell migration. In the last few decades, much attention has focused on understanding how chemical signals, such as soluble growth factors, guide cell migration. However, more recent studies have highlighted the importance of the mechanical signals in cell microenvironment, including density and stiffness of the extracellular matrix (ECM) in regulating cell migration. By using synthetic ECMs it has been shown that many cell types show a strong propensity to migrate toward areas of stiffer ECM - a process known as durotaxis. Durotaxis is thought to be critical to epithelial--to--mesenchymal transition and developmental morphogenesis, but its abnormal regulation is associated with the malignant nature of cancer cells. Despite the apparent biological and clinical significance of durotaxis, the exact mechanisms by which the cells sense mechanical cues and transduce them into cellular responses, such as migration,  are largely unknown. Here, we propose to reveal these mechanisms by using a combination of state--of--the--art biophysical techniques: synthetic hydrogels with tunable mechanical properties to mimic stiffness landscape of the biological tissues and genetically encoded FRET biosensors to visualize signaling activity across migrating cells. By coupling these approaches with quantitative image analysis and genetic/pharmacological perturbations of intracellular signaling pathways we will reveal specific molecular players that transduce mechanical guidance cues into directed cell migration. The specific aims of this proposal include: (1) To unravel the spatiotemporal dynamics of signaling molecules in the cells guided by a gradient of ECM stiffness; (2) To determine how mechanosensing by integrin-based focal adhesions modulates signaling activities in the cells guided by a gradient of ECM stiffness. The proposed study will uncover fundamental biological mechanisms that underpin how cells sense mechanical properties of the microenvironment and convert this information into a specific cellular response - directed migration.