Mechanotransduction
Overview
- Mechanical Stress, Cell Shape, and Cell Architecture in Mechanotransduction
- Detection, Characterization and Visualization of Calcium Sparks In Micropatterned Cardiac Myocytes
- Estimation of Contractile Stress on Cardiac Myocytes
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.
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.
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.
What's New
Picture of the Month – April 2012 April 6th, 2012
Isotropic cardiac myocyte monolayer stained for actin (red), beta-catenin (white), and nuclear DNA (blue). Image by Megan McCain, Parker lab.
Congrats to Kartik Balachandran! March 14th, 2012
Kartik Balachandran has been awarded the Postdoctoral Fellow Best Abstract Award by the Association of Scientists of Indian Origin Special Interest Group of the Society of Toxicology (SOT) at the SOT Annual Meeting in San Francisco, CA. This competitive award was based on a submitted abstract and a cover letter outlining the significance of his research. The award includes a plaque and monetary award of $500. Congratulations, Kartik!!
Congrats to Josh Goss!! March 5th, 2012
Josh Goss is one of the winners of the first Harvard School of Engineering and Applied Sciences Dean’s Excellence Award. Josh is the senior instrumentation engineer and staff scientists in the Disease Biophysics Group, designing and prototyping all of our experimental systems from microfluidic systems for organs on chips to blast bioreactors for brain injury research. Congratulations, Josh!! Thanks for all of your hard work!!
Picture of the Month – February 2012 February 24th, 2012
Micropatterned mouse ventricular muscle cells assembled into an anisotropic tissue showing nuclei (pink) and organized sarcomeres (orange). This organization recapitulates features of the native architecture of cardiac tissue. Image by Anna Grosberg, Parker lab.
Postdoctoral Positions in the DBG February 19th, 2012
We have several postdoctoral positions opening now and in the coming months. We are especially interested in candidates with backgrounds in theoretical biomechanics who are interested in conducting bench experiments. These positions will focus on our efforts to recapitulate organ-level function on chips for drug discovery and safety pharmacology.
All of these positions require a doctoral degree in an appropriate field and a demonstrated publication record. Applications in the form of a single PDF file containing a cover letter, resume, and up to three examples of first author papers should be forwarded to Prof Parker (kkparker@seas.harvard.edu). A list of references should be submitted with the resume with contact information.