OREF grant recipient investigates promising perivascular stem cell therapy

Rotator cuff tears (RCTs) are common shoulder injuries that often result in disability, pain, and diminished quality of life. More than 75,000 rotator cuff repairs are performed every year in the United States, and massive RCTs have a high rate of failure following repair, resulting in additional physical and emotional distress and costly revision surgery. Moreover, as the active population ages, orthopaedic surgeons expect to see an increasing number of degenerative rotator cuff tears.

To date, most research has focused on improving rotator cuff repair by addressing tendon-to-bone healing, but this effort has not resulted in improved patient outcomes. Conversely, little research has been done on how regenerative approaches could be used to treat the atrophy and fatty degeneration associated with massive RCTs.

To explore the potential of stem cell therapy for treating massive RCTs, Frank A. Petrigliano, MD, an assistant professor in residence at the University of California, Los Angeles department of orthopaedic surgery, was awarded an OREF/Zimmer Young Investigator Grant in 2012.

"Currently, we have no good treatment option for massive rotator cuff tears,” said Dr. Petrigliano, who is also a member of the UCLA Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research. “We want to see how perivascular stem cells can be used to treat the muscle atrophy and fatty degeneration associated with these tears. These cells reside along with endothelial cells in the vasculature of many soft tissues and have the potential to differentiate down a variety of pathways, including muscle. We are using an animal model to determine whether delivering the cells to muscle that has undergone fatty degeneration can reverse that atrophy."

Approach and methodology
To study rotator cuff injury and massive RCTs, Dr. Petrigliano selected a rodent model that is based on the work of Brian T. Feeley, MD, an associate professor of orthopaedic surgery at the University of California, San Francisco. This model has been effective in demonstrating significant and consistent muscle atrophy and fat degeneration following transection of the rotator cuff—similar to changes seen in human RCT pathology. The model shows muscle atrophy with associated progressive gross loss of muscle mass and histologic evidence of fibrosis at both the 2- and 6-week time points. Further histologic evidence of fatty degeneration is seen at the 6-week time point.

In the OREF-funded study, Dr. Petrigliano and his research team delivered purified human perivascular cells to the rodent rotator cuff muscle either at the time of tendon transection and denervation or at 6 weeks after the index surgery in the setting of established atrophy. Using in vivo imaging and histology/immunohistochemistry, the researchers assessed cellular proliferation and engraftment over time. They also used histology and immunohistochemistry to assess local angiogenesis and growth factor expression.

The study had the following key objectives:

• to describe the fate of perivascular cells applied in a small animal model of massive RCTs
• to describe the effects of local perivascular cell delivery on muscle atrophy and fatty degeneration

"We hope to characterize the behavior of perivascular cells in the rodent RCT model in the presence and absence of atrophy," said Dr. Petrigliano. "Our global hypothesis is that perivascular stem cells can diminish muscle atrophy and fatty degeneration in a rodent model of massive RCTs."

Promising results
Dr. Petrigliano has completed all of the in vivo surgeries and gathered data on muscle atrophy, fibrosis, and fatty degeneration following the induction of full-thickness rotator cuff tears. Results show that treatment with either human pericytes or human adventitial cells—both are perivascular mesenchymal stem cells found in close association with blood vessels—reduce muscle atrophy following rotator cuff tears. The treatment also results in diminished fibrosis and fatty degeneration.

"Another exciting finding is that the cells do persist up to 4 to 6 weeks following implantation, with a proportion of these cells actively contributing to muscle regeneration—suggesting both a trophic and regenerative role in diminishing muscle atrophy," stated Dr. Petrigliano.

Dr. Petrigliano's next steps will be to identify and characterize certain subpopulations of perivascular stem cells that are particularly well-suited for muscle regeneration. He plans to use a novel reporter mouse and induce full-thickness rotator cuff tears in this model.

"Our goal is to identify specific perivascular stem cells that are uniquely programmed to regenerate muscle, rather than depend on a heterogenous population of progenitors typically used in most approaches to stem cell therapy," he said. "Ultimately we hope that this type of therapy will be available to patients not only with large rotator cuff tears, but who have other varieties of muscle-wasting disease as well."

Instrumental funding
Dr. Petrigliano hopes to publish his current findings shortly. He noted that research is critical to drive potential new treatments like the regenerative therapies for RCTs that he's investigating, but it requires financial support.

"Research has significantly changed the way we practice orthopaedics over the last 25 years, and we don't want to see that diminished by a lack of innovation and funding," he said. "Clinicians benefit every day from the work of clinician scientists and basic science researchers—from the implants they use, the biologics that they employ, the imaging studies that they utilize—and all of that cannot be done without funding."

He said that the grant he received from OREF was instrumental in moving his project forward and believes that the data he gathered will help him obtain funding from larger sources.

"Few research-funding resources are available for orthopaedists in their early careers, but OREF has a long track record of jumpstarting clinician scientist careers. Funding from OREF enables researchers to build from young investigator to career development grants and then on to independent external funding," he said. "National Institutes of Health (NIH) funding is increasingly more difficult to garner because of the economic environment. OREF grants make us much more competitive for larger NIH, Department of Defense, and Veterans Administration grants. OREF provides initial funding to look at innovative ideas and give us the ability to generate meaningful preliminary data."

Mark Crawford is a contributing writer for OREF. He can be reached at communications@oref.org
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