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.

What's New

DBG Lab is Operational! March 15th, 2021

After 17 years of outstanding science in Cambridge, the DBG has moved to the Engineering School’s new campus in Allston. As of March 2, the lab is fully operational and has resumed experiments. Thank you to all alumni and current personnel for constantly raising the bar. Stand by for the next chapter of DBG science!

Congratulations to Dr. Megan McCain! March 10th, 2021

Our congratulations go out to DBG alumna, Dr. Megan McCain, who has recently received tenure at University of Southern California!

Farewell to Dr. Suhwan Kim! January 13th, 2021

Congratulations to Dr. Suhwan Kim, who has accepted a position as an Assistant Professor in the Department of Chemical Engineering at Dong-A University in Basun, South Korea! Dr. Kim was an integral part of our brain team for over a year as a postdoctoral fellow. We wish him the best on this next step in his career!

Inaugural Issue — Biophysics Reviews! January 4th, 2021

Dr. Kevin Kit Parker launched Biophysics Reviews, a new peer-reviewed journal for the biophysics research community on December 14. Produced by scientific publisher AIP Publishing, the aims to expand “on the tradition of excellence set by Applied Physics Reviews (APR) by publishing high impact, cutting edge research and reviews that are valuable for both emerging and experienced researchers”.

1. KK Parker, L Longobardi, A Sulicz. “Welcome to Biophysics Reviews, a big tent for the biophysics community”. Biophysics Reviews. 14 Dec 2020; 1(1); 010401.

A Belated Farewell and Congratulations to Dr. Ardoña! October 14th, 2020

Congratulations to Dr. Herdeline Ardoña, who has accepted a position as an Assistant Professor in the University of California Irvine Department of Chemical and Biomolecular Engineering. She joined the Disease Biophysics Group as a postdoctoral fellow in 2017 and was an essential part of our research and mentoring team. Best of luck to you as you settle in and get your research group up and running!