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

DBG Nanofibers Merge with Art by Carla Ciuffo August 23rd, 2017

The Disease Biophysics Group would like to congratulate and thank Tennessee based artist Carla Ciuffo in her efforts to integrate our nanofibers into her art exhibit “Cosmic Garden” at Tinney Contemporary, opening this Saturday.

“Tundra,” 2017, polished acrylic with floating museum back frame, 48×48 on display at Tinney Contemporary. (Photo: Photo courtesy of the gallery)

Thank you to our Summer Students! August 16th, 2017

Thank you to all the undergraduate students who spent time working in the lab over the summer. We wish you all the best this school year!

 

Jenny Wang, United States Military Academy at West Point
Daniel Gray, United States Military Academy at West Point
Nikita Pereverzin, United States Military Academy at West Point
Kathryn Dula, United States Military Academy at West Point
Daniel Drennan, Nicholls State University
Michael Ferris, James Madison University
Karla Rivera, Barry University
John Doyle, University of Massachusetts at Lowell
Madeleine Dahl, Salem State University
Nikita Budnik, McGill University
Karaghen Hudson, Harvard University
Sayo Eweje, Harvard University
Michael Peters, Harvard University
Gabriela Berner, Harvard University

Welcome Dr. Ardoña! August 15th, 2017

The DBG would like to extend a warm welcome to our newest postdoctoral fellow, Dr. Herdeline Ardoña. Herdeline recently completed her Ph.D. in Chemistry at Johns Hopkins University,  where she was a part of Prof. Tovar’s lab.  Welcome, Herdeline!

Welcome Dr. Liu! June 23rd, 2017

The DBG would like to extend a warm welcome to our newest postdoctoral fellow, Dr. Qihan Liu. Qihan completed his Ph.D. in Prof. Zhigang Suo’s lab here at Harvard University, where he focused on the mechanics and physics of soft materials.  Welcome, Qihan!

Farewell Jack! June 16th, 2017

The DBG would like to wish Jack Zhou all the best as he leaves us for his next adventure – Medical School. Congratulations Jack!