Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Researchers learn how blood vessel cells cope with their pressure-packed job


UCSD scientists have gained a better understanding of how repetitive stretching of endothelial cells that line arteries can make them healthy and resistant to vascular diseases.

Top: When aortic endothelial cells were stretched in the up-and-down orientation shown here, they grew "stress fibers" (red) in a "healty" alignment perpendicular to the axis of stretch. Bottom: When researchers inhibited a protein called Rho in aortic endothelial cells, stress fibers grew in an "unhealthy" direction parallel to the axis of stretch.

Each of these bovine aorta endothelial cells were stretched along an axis that runs up and down in these photographs. An unstretched cell, top, produced "stress fiber" filaments in random directions, but as the stretching increased from 3 percent of a cell length, middle, to 10 percent of a cell length, stress fibers were increasingly likely to be aligned perpendiculat to the stretching force.

UCSD researchers stretched cells in a workout chamber the size of a credit card to gain a better understanding of how repetitive stretching of endothelial cells that line arteries can make them healthy and resistant to vascular diseases.

Bioengineering researchers at UCSD’s Jacobs School of Engineering will report in the Nov. 1 issue of Proceedings of the National Academy of Sciences (PNAS) that arterial endothelial cells subjected to repeated stretching (10 percent of their length, 60 times per minute) produced intracellular arrays of parallel "stress fibers" in a few hours.

The tests were performed on endothelial cells lining the aorta of a cow, but the endothelial cells of the human aorta are expected to react similarly. The stress fibers were made of actin, a fibrous protein that is part of the machinery that gives muscle its ability to contract. Actin also gives virtually all cells their ability to make an internal "cytoskeleton." The stress fibers of endothelial cells in arteries are aligned parallel to the long axis of blood vessels, and this alignment is perpendicular to the direction of rhythmic stretching caused by a beating heart. Such an orientation of stress fibers is a hallmark of healthy blood vessels, but scientists currently understand few of the factors responsible for generating that configuration.

Rubber bands and most other flexible materials react to stretching by forming stress wrinkles parallel to the direction in which they are being pulled. However, the healthy bovine aorta endothelial cells did not behave that way in tests performed in the laboratory of Shu Chien, a coauthor of the PNAS paper and a professor of bioengineering and medicine and director of the Whitaker Institute of Biomedical Engineering at UCSD. When Chien and his collaborators stretched the cells back and forth along one axis in the miniature workout chambers, the cells formed stress fibers perpendicular to the direction of stretch. "This orientation of actin fibers can be thought of as a feedback control in which the external stresses imposed on the cell are felt internally to a much reduced degree," said Chien.

Post-doctoral fellow Roland Kaunas, now an assistant professor of biomedical engineering at Texas A&M University, with the help of UCSD laboratory assistant Phu Nguyen, found that unstretched cells or cells that were stretched only 1 percent of their length contained actin fibers with no directional orientation. However, as they increased the rhythmic stretching from 3 percent of a cell’s length to 10 percent, stretch fibers became increasingly oriented perpendicular to the stretching direction.

In the most significant finding in the PNAS article, which was made available online Oct. 24, Chien’s group reported that when an intracellular protein called Rho was chemically inhibited, stress fibers grew in the "wrong" direction; they grew parallel rather than perpendicular to the direction of cell stretching. Without Rho, the cells lost their ability to orient stress fibers properly. "Rho is a very important molecule," said Chien. "It works in response to, and in concert with, physical stretching to generate the healthy alignment of stress fibers." Indeed, when Chien’s group used a genetic technique to increase the activity of Rho, those cells grew stress fibers in the healthy direction at a lower threshold of stretching.

"Until now, it has not been shown that there is an equivalence and cooperation between mechanical and biochemical stimuli to regulate the proper orientation of these stress fibers," said Kaunas. "Indeed, we found that the stress fibers oriented in such a way to control their level of stress – not too little and not too much."

Chien and Kaunas collaborated with UCSD research scientist Shunichi Usami, who contributed to the design of the miniature workout chambers. Silicone rubber membranes inside the chambers were coated with a protein that allowed the endothelial cells to adhere to the membranes in a manner similar to how they attach to underlying blood vessel tissue in the body. The researchers isolated endothelial cells from the bovine aorta, grew the cells in culture flasks, and seeded them onto the silicone membranes. After the cells grew into confluent layers, a piston-like "indenter" was programmed to repeatedly push into the underside of the membranes and retract. The 60-cycle-per-minute motion of the indenter simulated the stretching movements of a blood vessel in response to the rising-and-falling blood pressure produced by a beating heart.

The researchers also demonstrated that inhibition of either Rho or a related protein called Rho kinase resulted in loss of the healthy alignment of stress fibers as well as alignment of adhesion sites where those stress fibers would attach to the cell membrane. These new results clearly show that Rho and physical stresses cooperate to produce healthy alignments of stress fibers," said Chien. "We need to understand how cells can sense the mechanical force and achieve this beneficial effect through the activation of Rho, and we also need to identify other proteins that may be involved in this feedback control mechanism."

Rex Graham | EurekAlert!
Further information:

More articles from Life Sciences:

nachricht Signaling Pathways to the Nucleus
19.03.2018 | Albert-Ludwigs-Universität Freiburg im Breisgau

nachricht In monogamous species, a compatible partner is more important than an ornamented one
19.03.2018 | Max-Planck-Institut für Ornithologie

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Tiny implants for cells are functional in vivo

For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.

In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

Im Focus: Surveying the Arctic: Tracking down carbon particles

Researchers embark on aerial campaign over Northeast Greenland

On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...

Im Focus: Unique Insights into the Antarctic Ice Shelf System

Data collected on ocean-ice interactions in the little-researched regions of the far south

The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...

Im Focus: ILA 2018: Laser alternative to hexavalent chromium coating

At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.

When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

Latest News

A new kind of quantum bits in two dimensions

19.03.2018 | Physics and Astronomy

Scientists have a new way to gauge the growth of nanowires

19.03.2018 | Materials Sciences

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Science & Research
Overview of more VideoLinks >>>