Developing novel injury and repair models
Stem cells found within rotator cuff muscle can be stimulated into fibrotic tissue (red) or fat tissue (green) depending on the stimulus. Researchers are evaluating tools to improve the function of these cells to improve outcomes after rotator cuff repair.

Transplantation of muscle stem cells (FAPs) stimulates rotator cuff muscle to regenerate more quickly with increased muscle quality and better muscle function. (Photo Credit:  Feeley-Liu Lab at UCSF)

Dr. Brian Feeley and Dr. Xuhui Liu's lab performs research on muscle tissue quality and its impact on common problems, including rotator cuff tears, knee pain, limb immobilization, joint contractures, and low back pain. They collaborate with Hubert Kim, MD and other researchers at the UCSF/VA Mission Bay campus to develop models for studying the molecular and cellular mechanisms responsible for muscle degeneration—and regeneration. This stem cell research is funded by the NIH, the VA, UCSF, and private donations. Members of the lab have won awards from the American Academy of Orthopaedic Surgeons (AAOS), the American Orthopaedic Society for Sports Medicine (AOSSM), and the Orthopaedic Research Society (ORS).  

What we study

Cells within muscle can look like muscle or they can be fibrotic or fat. We see more fibrotic and fatty cells after injury and muscle breakdown (atrophy). As a result, for a long time doctors assumed that many of the non-muscle cells in muscle were a result of injury and were not helpful to the muscle. They also thought all fat cells in muscle were the same. In rotator cuff tissue, it was thought that the fat ‘infiltrated’ or ‘walked in’ from the surrounding tissue. Once any of these cells “infiltrated” the muscle, doctors believed, they stayed the same and didn’t have anything positive to give back to muscle. We now know that cells can change over time (cellular plasticity). Some stem cells act like little blank slates that become different based on what’s going on around them. Certain cells (called fibroadipoprogenitors or FAPs), can turn into white fat, which may be energy stores for the muscle. They can also become brown fat or beige fat. As it turns out, beige fat plays an important role in energy balance, and it may produce local growth factors, such as IGF-1, that promote a regenerative environment for muscle. In other words, with the right stimulus, these cells might be available to help muscle get healthy again. Please click on the Research tab above to learn more about how we’re investigating this.