The generation and detection of mechanical force is a central aspect of cell and developmental biology. Cells sense their physical surroundings by pulling on each other and the extracellular matrix (ECM). The resulting physical cues allow cells to communicate with each other, to coordinate complex collective movements, and to make critical decisions about cell growth and differentiation. Despite this central importance, the mechanisms by which cells exert and detect force remain poorly understood both in single cells and in whole organisms.
Our goal is to understand how cells generate, detect, and respond to tension at the molecular level. To do so, we are using new microscopy techniques that allow us to measure mechanical forces inside living cells, and even in whole organisms. The results from this endeavor will be highly relevant to many aspects of basic research and human health, including heart disease, cancer metastasis, and the development of stem cell therapies, all of which are governed in part by the mechanical interactions of cells with their surroundings.
In life, as in love, one must know when to hold on and when to let go. Complex, multi-cellular life is only possible because cells build adhesions, sophisticated molecular complexes that assemble when needed and disassemble when it's time to move on. Our lab uses single-molecule force spectroscopy to study how the building blocks of cellular adhesions might be regulated by the pulling forces between neighboring cells. One of the key findings of our approach was that the minimal cadherin-catenin complex strengthens its connection to the actin cytoskeleton under load. Current work aims to extend our understanding to other proteins that might associate with the cadherin-catenin complex in a force-dependent manner. We hope to build up, molecule by molecule, a picture of cellular adhesions as self-assembled mechanical sensors and actuators within multicellular structures.
People in this line of research: Derek, Leannna and Nick
Key publications:1. Buckley CD et al., SCIENCE 346, (2014). 2. Huang, D., Bax, N. et al., SCIENCE 357, (2017)
Living cells are extremely responsive to mechanical cues, yet how cells produce and detect force remains poorly understood due to a lack of methods that visualize cell-generated forces at the molecular scale. We have developed molecular tension sensors that allow us to directly visualize cell-generated forces with single-molecule sensitivity. We apply these sensors to determine the distribution of forces generated by integrins, a class of cell adhesion molecules with prominent roles throughout cell and developmental biology. The experimental setup and results of our studies can be seen in our published paper here.
People in this line of research: Steven, Cayla and Sarang
Key publications:1. Chang AC, Mekhdjian AH, Morimatsu M, et al., ACS Nano. October 2016.
Cells in tissues use mechanical forces to transmit information between each other in a poorly understood process called mechanotransduction. At the heart of mechanotransduction lies the cadherin-catenin complex, a force-responsive machinery that integrates its kinetics to transduce extracellular mechanical forces into intracellular biochemical information. Thus far, it is unclear how temporal and spatial mechanical cues integrate into the mechanotransduction process.
To fill this gap of knowledge our lab aims to combine single molecule lattice light sheet microscopy together with single molecule magnetic force spectroscopy directly in cells to study the force-depend kinetics of the cadherin-catenin complex. This study will help us to understand how intracellular macromolecular complexes integrate forces to accomplish cellular function..
People in this line of research: Carlos and Elgin
Key publications:1. Price, AJ et al., Nat. Commun. 9, 5284 (2018).
Endothelial cells (ECs) line the inner surface of blood and lymphatic vessels and are highly sensitive to fluid flow as part of their physiological function. EC migration and vessel development are profoundly influenced by hydrodynamic stresses but how ECs sense fluid flow to coordinate their migration is a central and unanswered question in cardiovascular research with important implications in vessel structure formation. In the lymphatic system, fluid flow is particularly important in coordinating sites of endothelial valve formation, which prevent fluid retention and tissue swelling (lymphedema) and promote the unidirectional flow of lymph to reentry in the blood circulatory system.
We have developed high-throughput flow devices which apply physiologically relevant flow profiles to a monolayer of adherent ECs. These flow devices model the regions surrounding a lymphatic valve such as a straight vessel, a constricting vessel and vessel bifurcations, whereby the wall shear stress (WSS) experienced by the EC monolayer is either uniform, or spatially varying, respectively. Using these devices we aim to elucidate the role of WSS in controlling lymphatic endothelial cell migration, alignment and mechanotransduction during vascular development.
People in this line of research: Vinay and Eleftheria
Key publications:1. M. A. Ostrowski et al., 106, 366-374 (2014).
In a seminal Cell paper in 2006, Engler et al. showed that mesenchymal stem cells can adopt different lineages (differentiate to various cell types) based on the stiffness of the underlying substrate. This work highlighted the notion that mechanobiology has a profound impact in stem cell differentiation.
We are poised to investigate how mechanical forces influence the differentiation of embryonic stem cells (ESCs); we would like to identify how mechanical forces translate into chemical signals and downstream signaling. We can utilize tools that we have developed to measure intracellular forces at the molecular scale and also have the breadth of stem cell expertise in the Stanford Hospital to aid us in our endeavors.
People in this line of research: Andrew and Eva
Key publications:1. Price AJ, Huang EY, Sebastiano V, Dunn AR. Biomaterials. 2016;121:179-192.
The formation of three-dimensional tissue structures such as organs and organisms requires exquisite control of chemical signal transduction and mechanical shape change. One of the common building blocks of organs are cysts and tubules. These building blocks are defined by a monolayer of epithelial cells that surround a central cavity, or lumen. The components of the signaling network required for lumen formation are well studied; however, the physical processes that drive lumen formation are not well understood. Using high-resolution 4D imaging, our goal is to develop a quantitative, physical model for lumen formation, a morphological process that underlies much of morphogenesis.
People in line of research: Claudia and Vipul
Implantation is a critical step in early human fetal development, in which the embryo physically attaches to the maternal uterine lining. Many pregnancy diseases arise from improper implantation and subsequent trophoblast outgrowth and placentation within maternal tissue. However, we cannot visualize this process as it occurs internally in mammals and therefore have an incomplete understanding of the mechanisms driving it. We are interested in the physical, mechanical, and biochemical cues involved in implantation, and thus our goal is to engineer a model that allows us to systematically investigate the effect of ECM/matrix cues, dynamic soluble signaling, and active nutrient exchange on implantation success.
Funding: Stanford ChEM-H CBI Training Program Fellowship, Stanford EDGE-STEM Fellowship, Stanford Bio-X Bowes Fellowship, NIH T32 Training Grant, Stanford MCHRI TIP Grant
People in this line of research: Kiara and Eva
California Institute for Regenerative Medicine (2012)
National Institutes of Health (2010)
Stanford Cardiovascular Institute (2010-2011)
Stanford Graduate Fellowship (2010)
NSF Graduate Research Fellowship Program (2009, 2010, 2011)
Digestive Disease Center, Stanford University (2010)
Burroughs Wellcome Career Award At the Scientific Interface (2008)