StemCell Therapy

UC Berkeley scientists have discovered a type of stem cell that appears to lie dormant in blood vessel walls for decades before waking up and causing the arterial hardening and clogging that are associated with deadly strokes and heart attacks.

The findings, published Wednesday in the journal Nature Communications, go against the prevailing theory on the cause of heart disease - that the smooth muscle cells that line blood vessels become damaged over time and are triggered to proliferate. Those smooth muscle cells were thought to build up like scar tissue and cause the blood vessels to become narrow or brittle.

The new theory suggests that the smooth muscle cells found in the blood vessel walls aren't to blame, but rather a small cluster of stem cells is. It's those stem cells that proliferate and cause damage, and they should be the target of drug therapies to treat, and potentially cure, heart disease, the UC Berkeley scientists say.

"We call them sleeping beauty or sleeping evil cells, because they don't do anything when they're dormant. The stem cells stay quiescent for decades before they start to grow and they make the blood vessels harden," said senior author Song Li, a bioengineering professor at UC Berkeley and a researcher at the Berkeley Stem Cell Center.

"These stem cells are probably less than 5 percent of the cells in the blood vessel when they're dormant," Li said. "But they can dominate. They can become the major cell."

Li and his team still believe that smooth muscle cells are to blame for much of the damage in the blood vessels. What's changed is where those cells come from.

Scientists have known for decades that the blood vessel damage associated with heart disease is caused by a buildup of smooth muscle cells. Those clumps of cells cause the blood vessel to become dangerously narrow, hindering the flow of blood, or they become brittle clots that break off and block vessels entirely.

When the blood flow is slowed or stopped completely, it can cause strokes or heart attacks, depending on the location of the blockage. Strokes and heart attacks are among the most common causes of death in the United States.

The stem cells, which Li and his team have named multipotent vascular stem cells, remained undiscovered because so few of them exist when they're dormant. It didn't help that after they become activated, they look very similar to the smooth muscle cells that scientists have long thought were the culprit in heart disease.

The prevailing theory has been that damage to the blood vessel caused the smooth muscle cells in the vessel walls to "de-differentiate," or revert to an earlier stage of development that allows them to reproduce and build the scar-like tissue. But there was no proof of it, Li and others noted.

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Type of stem cell may contribute to heart disease

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