Study in mice helps explain how exercise protects against heart disease

Researchers have discovered a new biological pathway that promotes chronic inflammation and may help explain why sedentary people have an increased risk for heart disease and strokes. In studies using mice, they showed that regular exercise blocks this pathway, reinforcing the importance of physical activity in preventing heart disease. The study, funded by NHLBI, appeared in Nature Medicine.

Researchers have known for some time that regular exercise protects against heart disease by reducing cholesterol and blood pressure, but certain risk factors are not fully understood. In the study, researchers examined how physical activity affects the activity of bone marrow, specifically hematopoietic stem and progenitor cells (HSPCs). HSPCs can turn into any type of blood cell, including white blood cells called leukocytes, which promote inflammation.

The researchers studied a group of laboratory mice that were housed in cages with treadmills. Some of the mice ran as much as six miles a night on the spinning wheels. Mice in a second group were housed in cages without treadmills. After six weeks, the running mice had significantly reduced HSPC activity and lower levels of inflammatory leukocytes than the sedentary mice. Exercising caused the mice to produce less leptin, a hormone made by fat tissue that helps control appetite, but also signals HSPCs to become more active and increase production of leukocytes, the researchers said.

"This study identifies a new molecular connection between exercise and inflammation that takes place in the bone marrow and highlights a previously unappreciated role of leptin in exercise-mediated cardiovascular protection," said Michelle Olive, Ph.D., Program Officer at NHLBI Division of Cardiovascular Sciences. "This work adds a new piece to the puzzle of how sedentary lifestyles affect cardiovascular health and underscores the importance of following physical activity guidelines."