Nucleostemin- and Oct 3/4-positive stem/progenitor cells exhibit disparate anatomical and temporal expression during rat Achilles tendon healing.
BACKGROUND
The recent discovery of residing tendon stem/progenitor cells has triggered a growing interest in stem cells as a useful tool in tendon repair. Our knowledge of their involvement in naturally healing tendons is, however, sparse. The aim of this study was to identify and determine stem/progenitor cells in relation to different healing phases and regions in a rat model of Achilles tendon rupture.


METHODS
Surgery was performed to create a mid-tendon rupture on the right Achilles tendon of 24 rats, whereas the left tendon was used as a control. Tendons were harvested at one, two, eight and 17 weeks post-rupture and stained with antibodies specific to stem/progenitor cells (Octamer-binding transcription factor 3/4 (Oct 3/4) and nucleostemin), migrating cells (Dynamin 2 (Dyn 2)) and leukocytes (CD45). A histological examination was performed on sections stained with Alcian blue.


RESULTS
At one and two weeks post-rupture, a large number of stem/progenitor cells were discovered throughout the tendon. Most of these cells were nucleostemin positive, whereas only a few Oct 3/4-positive cells were found, mainly situated inside the injury region (I region). At eight and 17 weeks, the increment in stem/progenitor cells had diminished to equal that in the control tendons. At all time points, Oct 3/4-positive cells were also found in the connective tissue surrounding the tendon and at the muscle-tendon junction in both ruptured and control tendons and were often seen at the same location as the migration marker, Dyn 2.


CONCLUSIONS
The whole length of the Achilles tendon is infiltrated by stem/progenitor cells at early time points after a mid-tendon rupture. However, different stem/progenitor cell populations exhibit varying anatomical and temporal expressions during Achilles tendon healing, suggesting distinct reparative implications. Oct 3/4 may thus act as a more local, migrating stem/progenitor cell involved in injury-site-specific regenerative effects, as compared to the more general proliferative role of nucleostemin-positive stem/progenitor cells.
Department of Orthopaedics, Lundberg Laboratory for Orthopaedic Research, Institute of Clinical Sciences, University of Gothenburg, Gröna Stråket 12, Sahlgrenska University Hospital, SE-413 45, Gothenburg, Sweden. eva.runesson@gu.se.
Eva
E
Runesson
Integrative Orthopaedic Laboratory, Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden. paul.ackermann@karolinska.se.
Paul
P
Ackermann
Department of Orthopaedics, Lundberg Laboratory for Orthopaedic Research, Institute of Clinical Sciences, University of Gothenburg, Gröna Stråket 12, Sahlgrenska University Hospital, SE-413 45, Gothenburg, Sweden. jon.karlsson@telia.com.
Jón
J
Karlsson
Department of Orthopaedics, Lundberg Laboratory for Orthopaedic Research, Institute of Clinical Sciences, University of Gothenburg, Gröna Stråket 12, Sahlgrenska University Hospital, SE-413 45, Gothenburg, Sweden. bengt.eriksson@gu.se.
Bengt I
BI
Eriksson
D000125:Achilles Tendon / Q000293:injuries* / Q000473:pathology; D000818:Animals; D002352:Carrier Proteins / Q000032:analysis*; D002452:Cell Count; D019070:Cell Lineage; D034285:Dynamin II / Q000032:analysis; D005260:Female; D019204:GTP-Binding Proteins; D017493:Leukocyte Common Antigens / Q000032:analysis; D007962:Leukocytes / Q000473:pathology; D009687:Nuclear Proteins / Q000032:analysis*; D050814:Octamer Transcription Factor-3 / Q000032:analysis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012421:Rupture / Q000473:pathology; D013234:Stem Cells / Q000145:classification / Q000502:physiology*; D013997:Time Factors; D014945:Wound Healing / Q000502:physiology*
D002352:Carrier Proteins; C470310:Gnl3 protein, rat; D009687:Nuclear Proteins; D050814:Octamer Transcription Factor-3; D017493:Leukocyte Common Antigens; C516771:Ptprc protein, rat; D019204:GTP-Binding Proteins; D034285:Dynamin II