News Release
March 20, 2013

Differences in Bone Healing in Young Vs. Old Mice May Hold Answers to Better Bone Healing for Seniors

Poster P480/P480: Notch Signaling in Mesenchymal Stem Cells (MSCs) and Tibial Fracture Callus Harvested from Geriatric Mice

PHILADELPHIA — By studying the underlying differences in gene expression during healing after a bone break in young versus aged mice, Jaimo Ahn, MD, PhD, assistant professor of Orthopaedic Surgery at the Perelman School of Medicine, University of Pennsylvania, and his colleagues aim to find specific pathways of fracture healing in humans. The team of researchers will present their findings in a poster presentation beginning Tuesday, March 19, 2013 at the 2013 American Academy of Orthopedic Surgeons annual meeting in Chicago.

Problems with healing after bone fractures in elderly patients can be attributed, in part, to the compromised function of certain stem cells, called MSCs, that participate in the mending of the fracture. MSCs (Mesenchymal stem cells), can differentiate into a variety of cell types: cartilage, fat and – most notably in fractures – bone cells.

An important pathway — called Notch, for the name of the receptor that is critical in relaying the “signal” — has been identified as a critical event in the healing of non-skeletal tissues in an age-dependent manner. In the new study, the Penn team suspected that Notch would play a vital role in healing aged broken bones.

The team characterized fracture healing as a function of age and time post fracture in laboratory mice. Five-month-old laboratory mice are reproductively and skeletally mature. At 25-months-old, mice of the same strain are considered “geriatric.” The researchers looked for progression of tissue and healing and the expression of Notch pathway genes including the ligands (small molecules that bind Notch to spur it into action), as well as Notch receptors and their down-stream effects.  They examined both the healing fracture itself as well as the MSCs from the two age groups.

The team found that young mice produce a more robust healing response (timing, quantity and quality) than geriatric mice which persisted throughout healing.  Interestingly, base line levels of Notch signaling are reduced in MSCs from geriatric mice.  However, MSCs from young and old mice are both able to be stimulated by Jagged1 (one of the main ligands of Notch).

“The Notch signaling pathway’s importance in skeletogenesis combined with our data showing reduced baseline Notch activity in geriatric MSCs and the ability of the MSCs to respond to Jagged1 provides a rational basis for delivery of Jagged1 as a potential therapeutic option for aged fractures” says Dr Ahn.

Importantly, this model provides a validated system for further study of the age-dependent differences in fracture healing—and to test alterations that will enhance that healing for years to come.

Additional Penn authors include Kurt Hankenson, DVM, PhD, Nicole Belkin, MD, Luke Lopas, Lorraine Mutyaba, and Lee McDaniel.

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Penn Medicine is one of the world's leading academic medical centers, dedicated to the related missions of medical education, biomedical research, and excellence in patient care. Penn Medicine consists of the Raymond and Ruth Perelman School of Medicine at the University of Pennsylvania (founded in 1765 as the nation's first medical school) and the University of Pennsylvania Health System, which together form a $4.3 billion enterprise.

The Perelman School of Medicine has been ranked among the top five medical schools in the United States for the past 17 years, according to U.S. News & World Report's survey of research-oriented medical schools. The School is consistently among the nation's top recipients of funding from the National Institutes of Health, with $392 million awarded in the 2013 fiscal year.

The University of Pennsylvania Health System's patient care facilities include: The Hospital of the University of Pennsylvania -- recognized as one of the nation's top "Honor Roll" hospitals by U.S. News & World Report; Penn Presbyterian Medical Center; Chester County Hospital; Penn Wissahickon Hospice; and Pennsylvania Hospital -- the nation's first hospital, founded in 1751. Additional affiliated inpatient care facilities and services throughout the Philadelphia region include Chestnut Hill Hospital and Good Shepherd Penn Partners, a partnership between Good Shepherd Rehabilitation Network and Penn Medicine.

Penn Medicine is committed to improving lives and health through a variety of community-based programs and activities. In fiscal year 2013, Penn Medicine provided $814 million to benefit our community.

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