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.
Grp_photo_Jan 2014_305W_230H

What's New

Congratulations Grant Gonzalez and Michael Rosnach on the cover of Macromolecular Materials and Engineering! January 23rd, 2017

Parker Lab Artist Michael Rosnach’s illustration accompanying PhD Student Grant Gonzalez’s paper “Production of synthetic, para-aramid and biopolymer nanofibers by immersion rotary jet-spinning” was chosen for the January 2017 cover of Macromolecular Materials and Engineering.

“Utilizing a precipitant vortex, a novel nanofiber platform produces Kevlar, nylon, DNA, and alginate nanofibers for high-performance composites and tissue engineering applications.”

mame201600365_Cover Art Submission

Congratulations to Ian Perkins & Alex Cho! January 5th, 2017

The DBG would like to congratulate Ian Perkins and Alex Cho who both graduated from Northeastern University in December. Ian received his B.S. in Mechanical Engineering and Alex his B.S. in Biology. We would like to thank you both for your significant contributions to the DBG over the past several years, and we are grateful that you are both continuing with us in the lab this semester!

Congratulations Dr. Capulli! December 15th, 2016

Congratulations to Dr. Andrew Capulli who successfully defended his dissertation in December, and will continue in the DBG as a Postdoctoral Fellow.

Congratulations Dr. Nesmith! December 15th, 2016

Congratulations to Dr. Peyton Nesmith who successfully defended his dissertation last month.  We wish him the best of luck as he returns to the University of Alabama to complete his M.D.

Congratulations to Parker Lab Post-doc Johan Lind, Ph.D., on the publication of his Heart-on-a-Chip paper in Nature Materials on October 24! October 25th, 2016