Alex X. Cartagena-Rivera
Laboratory of Cellular Biology, Section on Auditory Mechanics
National Institute on Deafness and Other Communication Disorders
NIH, Bethesda MD
Thursday March 24, 2016
2:00pm
800 22nd Street NW, SEH B1220
Washington, DC 20052
Hosted by: Dr. Santiago Solares ([email protected])
Abstract
In recent times, more evidence indicates that the determination of critical physical parameters of complex biological systems is key for understanding the relationships between the molecular structure, biophysicochemical properties, and biological function/processes. Recently our lab developed novel atomic force microscopy (AFM) methods for the quantitative determination of relevant mechanical properties of (i) nonadherent cells actomyosin cortex and (ii) outer hair cell (OHC) stereocilia bundle.
The cortical actin cytoskeleton lies just beneath the cell plasma membrane to define cell shape and mechanical properties, and thus plays a key role in cellular processes such as migration and morphogenesis, and contributes to the macroscale mechanics of tissues. We developed a new minimally invasive method for using an AFM to determine actomyosin cortical tension, elastic modulus, and intracellular pressure of fibroblasts nonadherent cells before and after pharmacological drug perturbations. Our results show that myosin II activity, actin polymerization, and actin branching contribute to cortex tension and intracellular pressure, whereas cortical elastic modulus is more dependent on myosin II activity.
Deflection of the mature OHC stereocilia bundle results in mechanical opening or closing of mechanoelectrical transduction (MET) channels at the tip of the stereocilia from the middle and short rows and also alters elastic energy in horizontal top connectors, the lateral links that connect adjacent stereocilia both within and between the three rows. Previous studies showed that the stereocilin-null mice, that lack horizontal top connectors in OHC stereocilia bundles, become progressively deaf from postnatal day 15 (P15). However, at P14, the cochlea sensitivity and frequency tuning are intact, but interestingly suppressive masking and both acoustic and electrical waveform distortions are absent. This unique phenotype suggest that the main source of cochlear waveform distortions may be a top connector-mediated MET channel cooperativity or a mechanical deflection-dependent hair bundle stiffness resulting from constraints imposed by the presence of horizontal top connectors, not only from canonical MET nonlinear behavior. Here we propose a noninvasive, acoustic, and quantitative method to investigate the mechanical stiffness and coherence of stereocilia hair bundles. Interestingly, a significant decrease in bundle stiffness was measured when horizontal top connectors were absent.
Taken together, we predict that these novel AFM methods will help to unveil further evidence of differences in mechanical properties that underlay cellular processes and disease progression, therefore reinforcing the importance of AFM in cellular mechanobiology.
Biography:
Alexander X. Cartagena-Rivera has been an IRTA postdoctoral fellow in the research lab of Dr. Richard S. Chadwick at NIDCD/NIH since April 2014. He is originally from Bayamón, Puerto Rico. He received a B.S. in Mechanical Engineering from the University of Puerto Rico at Mayagüez in 2010. Then he was a graduate student and research assistant in the lab of Prof. Arvind Raman at Purdue University. He received a Ph.D. in Mechanical Engineering from Purdue University in 2014. He has received numerous awards including the prestigious Purdue Univ. College of Engineering David M. Knox Fellowship and NSF REACH. He has held visiting scientist appointments at the Universidad Autónoma de Madrid, Spain and the University of Oxford, U.K. His research interest lies in fluid mechanics, soft matter, micro/nanofluidics, micro/nanomechanics, hearing mechanics, cellular biology, and living cell and viruses’ biomechanics studied using the atomic force microscope in physiological conditions.