Science and Technology
Study: Adult Stem Cells Can Become Muscle

UC Berkeley bioengineering researchers have found that stretching an adult stem cell taken from bone marrow could cause it to become muscle tissue, bringing new hope for treating diseased or damaged body parts.

The adult stem cell can quickly replicate into a broad range of specialized cell types.

“Mechanical forces like compression or tension on cells will simulate tension-bearing tissues like cartilage,” said Song Li, UC Berkeley assistant professor of bioengineering and principal investigator of the study.

The stem cells the researchers are working with are typically extracted from human bone marrow. They can transform into different types of tissues including bone, cartilage and connective tissues.

The scientists placed stem cells onto a silicone membrane with microgrooves to replicate the environment found in the walls of blood vessels. The membrane was then stretched longitudinally once every second.

“We chose that pace because it mimics the beating of a heart because the heart beats 60 times (a minute), and we didn’t want to do too much because we’re trying to mimic the body as best as we can,” said Kyle Kurpinski, a UC Berkeley graduate student in bioengineering and the lead author of the study.

The researchers observed that when the mechanical stress placed upon a cell changed direction, some effects disappeared or became weaker.

“Mechanical force can direct cell transformation and how you apply the mechanical force is important,” Li said.

After two days of continuous stretching of the cells, researchers observed a significant increase in the expression of a group of genes in the cell, demonstrating the beginnings of stem cell transformation into muscle tissue.

According to Kurpinski, previous studies on the effects of mechanical strain on cells had cells pulled in all directions. This study is the first to examine the effects of a single directional strain on stem cell regeneration.

“The new thing is that there’s micropatterning involved,” Kurpinski said. “People have done uniaxial cell studies before, but cells have aligned themselves perpendicularly to the axis.”

The researchers have also recently been working on another similar project using the same adult stem cells and nanofibers to create small-diameter blood vessels. They said they hope that it will be a much-needed treatment for people with small-diameter blood vessels and blood clots.

The smallest vascular graft on the market is five to six millimeters, but the graft the UC Berkeley scientists are working on is 0.7 millimeters.

“The goal of this product is to make it into a coronary artery bypass graft for humans,” said Craig Hashi, UC Berkeley graduate student in bioengineering. “There’s a very distinct subpopulation of people who have small-diameter arteries that are clogged.”

Li’s lab has successfully tested the vascular graft on rats thus far.

“We placed a one-millimeter blood vessel graft in a rat bypass surgery and after a month we retrieved it and found it had formed into a native vessel,” Li said.

The scientists’ future work includes looking for the chemical factors, such as enzymes and hormones, in addition to the mechanical forces that work on transforming the stem cells.

“In the body, there’s both chemical and mechanical forces combined,” Kurpinski said. “The next step will be to stretch (the cell) and add specific hormones and growth chemicals.”

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