b'Carnegie Science|Spring/Summer 2020 11Revolutionizing Tendon Recovery?Recovery from torn rotator cuffs, jumpers knee, and other tendon injuries is painful and challenging because of scar tissue buildup,Quadriceps Tendonwhich can lead to secondary tendon ruptures. Research led byFemur Jumpers kneeChen-Ming Fan, published in Nature Cell Biology, shows that tendon stem cellsnot found until nowpotentially could be harnessed to improve tendon healing. Patella. . . it was thought that tendonStart of Patellar Tendonstem cells might not exist.Middle of Patellar TendonTendons are connective tissue that tether our muscles to our bones, Fan explained. They improve our stability andTibiafacilitate the transfer of force that allows us to move. But they areInsertion of Patellar Tendonalso particularly susceptible to injury and damage.FibulaUnfortunately, once tendons are injured, they rarely fully recover, which can result in limited mobility and require long-Recovery from tendon injuries is painful and challenging, because scar tissue buildup term pain management or surgery. The culprit is fibrous scars,can lead to secondary tendon ruptures. Chen-Ming Fans team studied the cell types which disrupt the tendon tissue structure.in the patellar tendon, below the kneecap, including previously undefined tendon Working with Carnegies Tyler Harvey and Sara Flamenco,stem cellscells that have not yet specialized. The team believes that these cells potentially could be harnessed to improve tendon healing. Fan revealed all of the cell types present in the patellar tendon,Image courtesy Harry Gouvas, WikiCommonslocated below the kneecap, including previously undefined tendon stem cells.Because tendon injuries rarely heal completely, it wastendon stem cells are part of a competitive system with thought that tendon stem cells might not exist, said lead authorprecursors of fibrous scars, which explains why tendon healing Harvey. Many searched for them to no avail, but our workis such a challenge.defined them for the first time. The team demonstrated that both tendon stem cells and Stem cells are undifferentiated cells associated with nearlyprecursor cells to scar tissue are activated by a protein called every type of tissue. They have not specialized into a specific tissueplatelet-derived growth factor-A. When tendon stem cells are type, and they can self-renew, creating a pool from which newlyaltered so that they dont respond to this growth factor, then only differentiated cell types can form to support a specific tissue.scar tissueno new tendon cellsform after an injury.Muscle stem cells, for instance, can differentiate into muscle cells.Tendon stem cells exist, but they must outcompete the scar But until now, stem cells for the tendon were unknown. tissue precursors to prevent the formation of difficult, fibrous Surprisingly, the team showed that both fibrous scar tissuescars, Fan explained. Finding a therapeutic way to block the cells and tendon stem cells originate in the same spacethescar-forming cells and enhance the tendon stem cells could be a protective cells that surround a tendon. Whats more, thesegame changer when it comes to treating tendon injuries.Graduate student Tyler Harvey was lead author on the study. Image courtesy Tyler HarveySUPPORT:The U.S. National Institutes of Health This image shows the patellar tendon 30 days after an injury. Red marks newly discovered tendon stem cells that have self-renewed andsupported this work.are layered over green, original tendon cells. During regeneration, some tendon stem cells differentiate to make newly regenerated tendon cellsa process during which they transition into a yellow-orange color. Blue indicates cellular nuclei. Image courtesy Tyler Harvey'