Mechanotransduction

Overview

Mechanical Stress, Cell Shape, and Cell Architecture In Mechanotransduction

Primary Investigator: Nicholas Geisse, Ph.D

We are investigating the role of the cytoskeleton in the organization and regulation of cellular physiology. We are using several enabling technologies to assist this investigation, including microcontact printing, epifluorescence and confocal microscopy, electrophysiological conduction mapping, electron microscopy, and atomic force microscopy.

Adult myocytes have a characteristic rectangular structure that does not change even when extracted from the whole heart. This structure enhances contractile function of the heart, as the cell generates contractile force along the axis of the sarcomeric actin and perpendicular to the axis of the sarcomere Z-line, which together compose the myofibril. In contrast, neonatal rat cardiac myocytes have a malleable myofibrillar architecture after extraction. Our hypothesis is that structure and organization of the cardiac myocyte cytoskeleton can be influenced by geometrical cues in the extracellular environment. We have cultured neonatal rat myocytes onto geometrically controlled islands of extracellular matrix (see Parker et al. FASEB J 2002). Our results show that in the absence of defined geometrical cues, myofibrils in the neonatal cell assemble in a seemingly random manner. However, in geometries with defined boundary conditions myofibrils assemble based on the edges and corners of their environment. In circular patterns, where edges and corners are absent, these cells lack a regular myofibrillar pattern based on imposed cell geometry.

Immunofluorescence Staining of Micropatterned Cardiac Myocytes

FIGURE: Microcontact Printing used to control Cardiomyocyte geometry and cellular architecture. For all Images: Sarcomeric actin labeled in green, sarcomeric alpha-actinin (Z-lines) marked in red, nucleus marked in blue.
A: Adult Rat Cardiac Myocyte without structural modification (nucleus not shown).
B: Neonatal Rat Cardiac Myocyte without structural modification, cultured on a monolayer of extracellular matrix protein.
C: Neonatal Rat Cardiac Myocyte cultured on a rectangular island of extracellular matrix protein.
D: Neonatal Rat Cardiac Myocyte cultured on a triangular island of extracellular matrix protein.
E: Neonatal Rat Cardiac Myocyte cultured on a square island of extracellular matrix protein.
F: Neonatal Rat Cardiac Myocyte cultured on a circular island of extracellular matrix protein.

Detection, Characterization and Visualization of Calcium Sparks In Micropatterned Cardiac Myocytes

Primary Investigator: Mark Bray, Ph.D.

The cytoarchitecture of the myocyte has been determined to be critical in understanding not only mechanical contraction of the cell but also electrical propagation. Knowledge of this mechanotransduction mechanism has implications in the treatment of stretch-activated arrhythmias, as well as understanding the role of the extracellular environment on intracellular signaling pathways. Our objective is to micropattern myocytes into various shapes and examine spark occurrence as a function of cell shape. The expectation is that cell shapes which incorporate regions of high mechanical cellular stress will modulate calcium spark characteristics as the cytoskeleton reconfigures itself accordingly. A critical and novel component of this project is the development of software able to detect and visualize sparks in two-dimensions.

Visualization of Calcium Sparks in Cardiac Myocytes

FIGURE: Fluorescence map of square cell (top left) and with background fluorescence subtracted (bottom left). Visualization of spark boundaries with respect to (x,y,t), shown in red (right).

Estimation of Contractile Stress on Cardiac Myocytes

Primary Investigator: Poling Kuo, M.D.

We hypothesize that mechanical coupling between cells plays a critical role both in the normal and pathological development of cardiac tissues. We are using traction force microscopy to map the contractile stresses of micropatterned neonatal rat cardiomyocytes.

Analysis of Traction Forces In Contractile Cardiac Myocytes
FIGURE: Relative stress field of cardiac myocytes exhibited by red vectors. The bottom black scale bar represents 10 um.
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What's New

Welcome, Dr. Suji Choi and Dr. Sarah Motta! October 5th, 2018

The DBG would like to extend a warm welcome to our new postdoctoral fellows, Suji Choi and Sarah Motta. Suji joins us from Seoul National University, where she completed her Ph.D. in Chemical and Biological Engineering in Prof. Dae-hyeong Kim’s Flextronics group. Sarah recently completed her Ph.D. at the Institute for Regenerative Medicine in Zurich in Tissue Engineering and Regenerative Medicine. We are excited for both of them to join us!

Welcome, Huibin! September 5th, 2018

The DBG welcomes Post-Doctoral Fellow Huibin Chang, who joined the group September 1. Huibin joins us from Georgia Tech, where he recently completed his Ph.D. in Materials Science and Engineering. Welcome, Huibin!

Congressional Staffers Visit the DBG August 31st, 2018

The DBG welcomed several opportunities so far in 2018 to discuss Federal budget appropriations to the National Institutes of Health and the Department of Defense. After discussions with staffers from Senator Elizabeth Warren (D-MA), Congresswoman Katherine Clark (D-MA), and the Senate Armed Services Committee regarding our experiences with the various offices of the DoD and NIH, we showed our work and introduced the professional staff and trainees within the laboratory. Over the years we have enjoyed interactions with a variety of elected officials and Congressional staffers who have requested to hear about our work and the challenges with funding research at the cutting edge.

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Farewell John August 20th, 2018

Congratulations to John P. Ferrier Jr., who was accepted into the Northeastern University Physics Ph.D. program in Boston. He moves to Northeastern in September 2018. Congratulations, John!

Farewell Sung Jin August 20th, 2018

Congratulations to Dr. Sung Jin Park, who accepted a position as an Assistant Professor of Biomedical Engineering at Georgia Tech and Emory University. He arrived in Atlanta in August 2018. Congratulations, Professor Park!