Background: Although muscle injuries tend to heal uneventfully in most cases, incomplete functional recovery commonly occurs as a result of scar tissue formation at the site of injury, even after treatment with muscle-derived stem cells (MDSCs).
Hypothesis: The transplantation of MDSCs in the presence of a transforming growth factor β1 (TGF-β1) antagonist (losartan) would result in decreased scar tissue formation and enhance muscle regeneration after contusion injuries in a mouse model.
Study design: Controlled laboratory study.
Methods: An animal model of muscle contusion was developed using the tibialis anterior muscle in 48 healthy mice at 8 to 10 weeks of age. After sustaining muscle contusion injuries, the mice were divided into 4 groups: (1) saline injection group (control group; n = 15), (2) MDSC transplantation group (MDSC group; n = 15), (3) MDSC transplantation plus oral losartan group (MDSC/losartan group; n = 15), and (4) healthy uninjured group (healthy group; n = 3). Losartan was administrated systemically beginning 3 days after injury and continued until the designated endpoint (1, 2, or 4 weeks after injury). MDSCs were transplanted 4 days after injury. Muscle regeneration and fibrotic scar formation were evaluated by histology, and the expression of follistatin, MyoD, Smad7, and Smad2/3 were analyzed by immunohistochemistry and reverse transcription polymerase chain reaction analysis. Functional recovery was measured via electrical stimulation of the peroneal nerve.
Results: When compared with MDSC transplantation alone, MDSC/losartan treatment resulted in significantly decreased scar formation, an increase in the number of regenerating myofibers, and improved functional recovery after muscle contusions. In support of these findings, the expression levels of Smad7 and MyoD were significantly increased in the group treated with both MDSCs and losartan.
Conclusion: When compared with MDSCs alone, the simultaneous treatment of muscle contusions with MDSCs and losartan significantly reduced scar formation, increased the number of regenerating myofibers, and improved the functional recovery of muscle; these effects were caused, at least in part, by the losartan-mediated upregulation of Smad7 and MyoD. Increased levels of Smad7 and MyoD together reduced the deposition of scar tissue (via the inhibition of TGF-β1 by Smad7) and committed the transplanted MDSCs toward a myogenic lineage (via Smad7-regulated MyoD expression).
Clinical relevance: The study findings contribute to the development of biological treatments to accelerate and improve the quality of muscle healing after injury.
Keywords: Smad7; fibrosis; losartan; muscle contusion; muscle injury; scar tissue; stem cells.
© 2016 The Author(s).