Mechanobiology

National Institute Of Biomedical Imaging And Bioengineering, Bethesda

Investigators

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Abstract

The NIBIB's Section on Mechanobiology mainly focuses on developing advanced atomic force microscopy (AFM) approaches to determine the micro- and nano-scale mechanical properties of cells and tissues. AFM is a versatile biophysical technique where a sample is probed with a micron sized cantilever with or without an indenter to measure, in a minimally invasive way, the physical material properties of complex biological systems (from molecules to tissues) at physiologically relevant conditions. A major advantage of this experimental approach is that it does not require any chemical manipulation (neither labelling or fixation). This is the main reason why AFM is the main biophysical approach used in our lab. Project #1: Ovarian and pancreatic cancer cells and solid tumor mechanics: role of cellular actomyosin cytoskeleton, glycocalyx, and microenvironment architectures promoting mechanical heterogeneity, anisotropy, and regulation. Cancer is one of the leading causes of death in the world, and currently the major concern with cancer mortality is metastasis. Cancer is a broad term applying to diseases having the common characteristic traits that can lead to abnormal cellular development with a rapid and uncontrollable burst of growth and proliferation, resulting in solid tumor formation and metastatic dissemination. Different cell types and mediators in the tumor microenvironment aid in disease progression, whereby tumor cell adaptability is key for their motility and invasiveness. Besides many abnormalities in structural architecture and composition, cellular and ECM mechanics are directly implicated in disease progression. Changes in the actomyosin cytoskeleton and glycocalyx, for example, play a critical role in metastasis of ovarian and pancreatic cancers, among others. To successfully metastasize to a distal site, cells must migrate through physical constraints, including regions of high confinement, requiring the cell body and its nucleus (the largest and stiffest organelle) to deform, generally at timescales considered slow in the nanomechanics community. Thus, understanding the ways in which the solid tumor microenvironment and cancer cell aberrations are related to changes in mechanical properties at timescales of biological relevance may reveal new therapeutic strategies to stop or at least slow down cancer progression and metastasis. My laboratory's Postdoctoral fellow Dr. Andrew Massey together with my previous lab Post-Baccalaureate IRTA fellow Ms. Chynna Smith, performed a wide survey of the mechanical properties (actomyosin cortical tension, Young's modulus, and hydrostatic intracellular pressure) of ovarian and pancreatic cancer cell lines at different stages of malignancy. It should be noted that cellular cortical mechanics could be a great candidate for cancer detection, monitoring, and prognosis. We used a biophysical methodology developed during my postdoctoral training based on quasi-static AFM force spectroscopy that utilizes tipless cantilevers to determine relevant mechanical properties of single loosely adhered cells including actomyosin tension, Young's modulus, and intracellular hydrostatic pressure. Additionally, we performed high spatiotemporal nanomechanical mapping to determine the nanoscale viscoelastic properties (elastic storage and loss viscous modulus). We observed that ovarian and pancreatic cancer cells show are softer and less viscous than healthy ones and that they become much softer and fluid with increased levels of malignancy. These observations are critical for establishing novel strategies for cancer treatment. Project #2: Understanding the mechanobiology of T lymphocytes. The immunological synapse formed between a T lymphocyte and its target is a physical and dynamic cellular structure capable of exerting mechanical force. Recently, it has been shown that force generation by the actin and microtubule cytoskeletons enable the formation and maintenance of the immune synapse in T lymphocytes and can vary in the presence of different antigens. However, T lymphocytes ability to promote and sustain changes in force generation within the immune synapse by modulating their mechanical properties remains unknown. My laboratorys Post-Baccalaureate fellow Mr. Kun Do is spearheading this research project. We quantified biomechanical properties on both the dorsal and basal side of activated T lymphocytes by coating the surface of well-characterized soft polymer gels with antibodies against the CD3 region of the TCR-complex, the lymphocyte integrin LFA-1, and costimulatory molecule CD28 to mimic interactions between T lymphocytes and antigen presenting cells (APCs). To do this, we combined high spatiotemporal nanomechanical AFM mapping and traction force microscopy to measure dorsal biomechanics, including surface tension and viscoelasticity, as well as basal side mechanics that present themselves through traction stresses at the immune synapse. We are also currently exploring the role of key filamentous actin cytoskeletal regulatory proteins known to play an important role in immune cell activation and in the formation and maintenance of the immune synapse, including non-muscle myosin II, formin, and septins.