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. 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!

The DBG welcomes the Orientation and Reach-Back Training class of the U.S. Army May 22nd, 2017

The DBG had the pleasure of hosting the Orientation and Reach-Back Training (ORBT) training class of the U.S. Army Research, Development and Engineering Command (RDECOM) Field Assistance in Science and Technology (FAST) program on May 17, 2017. ORBT is a multi-week mission overview program for senior-level Army officers, non-commissioned officers and Department of the Army civilians on the mechanisms for identifying and resolving technology capability gaps for units in their area of operation. The class visit to Professor (Lieutenant Colonel, Reserves) Parker’s Lab is their only visit to a Lab outside the Department of Defense.

The class met with DBG veterans and attended presentations on Stronger, Tougher, and Lighter Soldier Protection Systems; Nanofiber Scaffolds for Wound Healing/Dressings; Traumatic Brain Injury – Understanding Disease Mechanisms; Fibrous Scaffolds for Tissue Engineered Foods; Cells as Engineering Materials – the Cyborg Ray Project; Cuttlefish Inspired Camouflage; and our unique program for embedding Artists-In- Residence in the Lab.

Guests included members from the U.S. Army Research, Development, and Engineering Command (RDECOM); U.S. Army Engineer Research and Development Center (ERDC); U.S. Army Corps of Engineers; Army Research Laboratory; and RDECOM Research, Development and Engineering Centers.

Pictured below are (clockwise from bottom left): DBG Artist-in- Residence Karaghen Hudson (Harvard Class of 2018); Ms. Valerie Carney (ERDC); Dr. Aimee Poda (ERDC); Dr. (Colonel, Reserves) Steve Hart (RDECOM); Veteran and Program Coordinator John Laursen (Army Retired); Dr. Jerry Ballard (ERDC); Mr. Nathan Frantz (US Army Corps of Engineers); Visiting Scholar and Brigadier General Michael D. Phillips (USA Retired); Dr. Samantha Chambers RDECOM Science Advisor to the XVIII Airborne Corps; and Lieutenant Colonel Jovanna Nelson.

Congratulations to Stephanie Dauth, Ben Maoz, & Sean Sheehy on the cover of the Journal of Neurophysiology May 11th, 2017

Congratulations to our Brain Team for getting the cover of this month’s Journal of Neurophysiology “Neurons derived from different brain regions are inherently different in vitro: A novel multiregional brain-on-a-chip

Close-up image of axons that
have been grown over a 1-mm gap on a microcontact printed PLL/laminin lines connecting the different brain regions

Robotic Stingray wins Gold Medal at Edison Awards! April 25th, 2017

Congratulations to Professor Kit Parker and Sung-Jin Park, Ph.D. who received a gold medal in the engineering category at the Edison Awards for their work on the cyborg stingray.  The Edison Awards honor excellence in new product and service development, marketing, human-centered design and innovation.

 

Photo courtesy of Michael Rosnach