Heart disease has its own clock

Broken timers in organs may cause disease

Broken biological clocks in blood vessels may contribute to hardened arteries, even if the main timer in the brain works fine. The finding, from transplant experiments with mice, suggests that throwing off the daily rhythms of the body’s organs can have serious health consequences.

A wealth of evidence shows that skimping on sleep and working against the body’s natural daily, or circadian, rhythms can raise the risk of developing illnesses such as heart disease and diabetes. Scientists assumed that the diseases resulted from malfunctions in a master clock in the brain, which synchronizes sleeping, waking and other body functions with the rising and setting of the sun.

But recently, scientists have discovered that the liver and other organs have their own internal clocks that may work independently of the brain clock and are set by meal times or other cues (SN: 4/10/10, p. 22). It wasn’t clear until now whether disrupting these body clocks could also contribute to disease, says Satchidananda Panda, a circadian rhythm researcher at the Salk Institute for Biological Studies in La Jolla, Calif.

The finding may help explain why shift workers, people with sleep disorders and others who disrupt their circadian rhythms by staying up late or eating meals at the wrong time tend to be more vulnerable to heart disease.“If you want to prevent people from getting heart attacks, you have to know whether to treat the clock in the brain or the clock in the heart,” Panda says.

To determine whether it is the brain or body clocks that malfunction when arteries harden, vascular biologist R. Daniel Rudic, of the Georgia Health Sciences University in Augusta and colleagues transplanted blood vessels in mice. Inserting vessels from normal mice into mice with broken brain clocks didn’t lead to problems, the team reports online October 3 in the Proceedings of the National Academy of Sciences . “The blood vessels were pretty normal,” Rudic says. “They didn’t seem to be impacted by the surrounding mess of circadian rhythms.”

But putting arteries from mice with broken clocks into normal mice resulted in the walls of the transplanted arteries becoming thick and less flexible, indicating that diseases may result from timing defects in the vessels, not the brain or the rest of the body. The researchers don’t yet know if blood vessels are more susceptible to circadian defects than other tissues, or whether people with heart disease have timing defects in their blood vessels.

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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