Mechanobiology

National Institute Of Biomedical Imaging And Bioengineering, Bethesda

Investigators

Linked publications & trials

Abstract

The NIBIB's Section on Mechanobiology mainly focuses in developing advanced atomic force microscopy (AFM) approaches to determine the nanoscale and global mechanical properties of cells and tissues. AFM is a versatile biomedical technique whereby a sample is probed with a microcantilever with or without an indenter to measure minimally invasively the physical material properties of complex biological systems (from molecules to tissues) in a physiologically relevant environment. A major advantage of this experimental approach is that 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: 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, with cancer metastasis being the dominant driver of deaths. Cancer is a generic word for diseases having the common characteristic of leading to abnormal cell development with a rapid and uncontrollable burst of growth and proliferation, resulting in solid tumor formation. Different cell types and mediators in the tumor microenvironment aid to disease progression, whereby tumor cell adaptability is key for their motility and invasiveness, which leads to tumor growth and metastasis, with the latter being generally considered as the major cause of cancer-associated deaths. Besides many abnormalities in structural architecture and composition, cell mechanics are directly implicated in disease progression. Changes in the actomyosin cytoskeleton and glycocalyx, for example, plays a critical role in metastasis of breast cancer and melanoma, among others. In melanoma, cytoskeleton abnormalities due to increased contractility lead to a switch in cell migration patterns from mesenchymal to a highly motile migration modality called fast-ameboid leader-bleb migration. 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. This actomyosin-based aggression is not unique to melanoma and seems to be common to almost all cancers. 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 Post-Baccalaureate IRTA fellows (Jamie Neal and Chynna Smith) together with my lab Postdoctoral fellow Andrew Massey, are currently performing a wide survey of the mechanical properties (actomyosin cortical tension, Young's modulus, and hydrostatic intracellular pressure) of melanoma, breast, ovarian, pancreatic cancer cell lines at different stages. It should be noted that cellular cortical mechanics could be a great candidate for cancer detection, monitoring, and prognosis. We use a new biophysical methodology developed during my postdoctoral training, based on quasi-static AFM force spectroscopy that utilizes tipless cantilevers to determine global physical relevant mechanical properties including actomyosin tension, Young's modulus, and intracellular hydrostatic pressure. We have preliminary data suggesting that contrary to current knowledge, transformed cancerous melanoma cells have increased cortical tension and intracellular pressure than normal/healthy counterparts, whereas breast, ovarian, and pancreatic cancer cells shows a canonical mechanical behavior in which cancer cells are softer than healthy ones. Moreover, we observed apparent complex biphasic mechanical behavior in melanoma and breast cancer cells, while pancreatic and ovarian cancer cells followed a monotonic decrease in mechanical properties. These observations are critical for establishing novel strategies for cancer treatment. Towards that goal, we are also investigating the role of the actomyosin cytoskeleton and mechanical properties to chemotherapy resistance in ovarian and pancreatic cancer cells that has been identified to be Paclitaxel sensitive or resistant. Project #2: Advanced atomic force microscopy for multiparametric, multiscale, and anisotropic tissue mechanical properties determination. The apical surface mechanical properties of polarized tissues are another new field of study because of the implications of force transmission to the maintenance of tissue integrity. New evidence suggests that epithelial mechanics are essential for important tissue level biological processes including growth, elongation, shape, morphogenesis, cell extrusion, and homeostasis. In many tissues including the inner ear hearing and balance organs, kidney, and gut, the apical surface epithelial mechanics by observing their complex shapes suggest that they are not isotropic as typically assumed. Often tissues possess highly complex shapes and patterns to fulfill their unique biological function, thus I find it unlikely that the surface mechanical properties are strictly isotropic. Therefore, in my lab we use high spatiotemporal resolution quantitative nanomechanical AFM mapping and a novel noninvasive AFM method developed during my postdoctoral training to measure the apical surface anisotropic mechanics of polarized epithelia. The recently developed noninvasive AFM method utilizes acoustic frequency modulation curves acquired using cantilevers with an attached microsphere to determine the supracellular apical surface tension, effective viscosity, and intercellular adhesive forces in polarized epithelial tissues. These approaches will provide more physiological relevant 3-dimensional characterization of polarized epithelia and will unveil currently un-addressable molecular and mechanical regulation aspects of tissue mechanics critical to understating development and disease. In this project we wanted to investigate the role of a novel filamentous actin bundling protein TRIOBP-4 and -5 isoforms to modify the cochlear reticular lamina anisotropic mechanical properties. Recently, we reported key roles of TRIOBP-4 and TRIOBP-5 isoforms on the mechanical properties of the cochlear stereocilia hair bundles and supporting cell apical phalangeal processes; however, the modulation of the mechanical properties of the supracellular reticular lamina has not been carefully investigated. We performed high spatio-temporal resolution AFM nanomechanical mapping on inner ear cochlear sensorial epithelial tissues and measured the Young's modulus (stiffness) of two mouse models with loss of TRIOBP-4 and TRIOBP-5 isoforms. We observed that the absence of both isoforms TRIOBP -4 & -5 significantly reduced the stiffness of the entire reticular lamina. Moreover, consistent with previous observation, absence of the TRIOBP isoforms significantly reduces the stereociliary hair bundle stiffness. Interestingly, due to the significant increase in spatial resolution (sub-100nm) of the AFM modality used in this project, this allowed us to discover an unrecognized bidirectional radial stiffness gradients in the cochlear sensory epithelium. These radial stiffness gradients are unique since it depicts intriguing behaviors with opposite directions, differential magnitudes, and is unbalanced (anisotropic). These observations have direct implications in better understanding the reticular laminar sensitivity, frequency mapping, and sound amplification. This is a collaborative research project with Dr. Thomas B. Friedman's lab at the NIDCD. One manuscript has been submitted and is currently under review.