Duke researchers have previously shown that introducing bone marrow stem cells to a bone injury can expedite healing, but the exact process was unclear.

Now, the same Duke-led team believes it has pinpointed the “youth factor” inside bone marrow stem cells that enables the macrophage and the proteins it secretes to have a rejuvenating effect on tissue. The study was published in Nature Communications on December 5, 2018.

“Delayed fracture healing is a major health issue in aging, and strategies to improve the pace of repair and prevent the need for additional surgeries to achieve healing substantially improve patient outcomes,” says senior author Benjamin Alman, MD, chair of the Department of Orthopaedic Surgery.

After tissue injury, the body dispatches macrophages to areas of trauma, where they undergo functional changes to coordinate tissue repair. During fracture healing, macrophages are found at the fracture site. But when they’re depleted, fractures will not heal effectively. Macrophage populations and characteristics can change with aging.

“We show that young macrophage cells produce factors that lead to bone formation, and when introduced in older mice, improves fracture healing,” says Gurpreet Baht, PhD, assistant professor of orthopaedic surgery and a lead author of the study.

“While macrophages are known to play a role in repair and regeneration, prior studies do not identify secreted factors responsible for the effect,” says Alman. “Here we show that young macrophage cells play a role in the rejuvenation process, and injection of one of the factors produced by the young cells into a fracture in old mice rejuvenates the pace of repair. This suggests a new therapeutic approach to fracture rejuvenation.”