Interference Traction Force Microscopy (iTFM) for Bioimaging of Cellular Forces

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The human body consists of over 100,000 billion individual cells, with each cell being on some level an independent entity. Coordination of this hugely complex system relies on an intricate network of signalling, many aspects of which are still poorly understood. While the involvement of chemical signals (e.g. hormones) in this challenging coordination is widely accepted, there is now rapidly increasing interest in how cells interact with each other and with their environment on the mechanical level, for example by pushing and pulling or by sensing the stiffness or mechanical stress in their local environment. This is motivated by strong evidence that mechanical signalling (known as mechanotransduction) plays a critical role in a number of important processes, ranging from controlling how stem cells differentiate in the growing human embryo to affecting the progression of important diseases. However, while mechanotransduction is therefore obviously both fascinating and important for improving human health, our ability to study mechanics on a cellular level remains limited due to a lack of suitable methods to 'image' the forces that cells or components of cells apply. (Several microscopy methods to investigate cell force have been developed but their application requires special expertise that is often not available in a biology lab and even if this expertise is available it remains very challenging to follow the mechanical behaviour of cells over the extended time periods over which many relevant processes in cell biology occur. In addition, existing methods are not sensitive enough to study the activity of weaker cells.) In this project, light is used as an optical ruler to accurately and robustly image the force pattern applied by cells. Using an effect known as optical interference, the short wavelength of visible light will facilitate an increase in the sensitivity of force imaging by 5 to 10-fold over existing techniques. In addition, light-waves will provide an internal reference for the new method which means that it will be able to track force patterns over long periods of time (up to several weeks) without a need for disruptive reference measurements which many of the existing methods currently require. There are many areas of cell biology where the new technique may prove to be highly useful. Due to the short-term nature of this project, it will initially be applied to one specific example: a study of the forces involved in the adhesion of cells normally found in the kidney where they are responsible for blood filtration and thus for removal of waste products from the body. These cells are under constant mechanical pressure and their failure is associated with kidney malfunction. Studying the involved forces therefore promises to improve our functional understanding of the kidney and may in the long-run lead to methods for early detection and treatment of kidney failure, a condition often associated with obesity and diabetes.