Background: Fatty infiltration (FI) of the rotator cuff muscles is correlated with shoulder function and retear rates after rotator cuff repair. High-intensity interval training (HIIT) induces beige adipose tissue to express more uncoupling protein 1 (UCP1) to consume lipids. The beta-3 adrenergic receptor (β3AR) is located on adipocyte membrane and induces thermogenesis. Purpose: To test the role of HIIT in improving muscle quality and contractility in a delayed rotator cuff repair mouse model via β3AR. Study Design: Controlled laboratory study. Methods: Three-month-old C57BL/6J mice underwent a unilateral supraspinatus (SS) tendon transection with a 6-week delayed tendon repair. Mice ran on a treadmill with the HIIT program for 6 weeks after tendon transection or after delayed repair. To study the role of β3AR, SR59230A, a selective β3AR antagonist, was administered to mice 10 minutes before each exercise through intraperitoneal injection. The SS, interscapular brown adipose tissue (iBAT), and subcutaneous inguinal white adipose tissue (ingWAT) were harvested at the end of the 12th week after tendon transection and were analyzed by histology and Western blotting. Tests were performed to assess muscle contractility of the SS. Results: Histologic analysis of SS showed that HIIT prevented and reversed muscle atrophy and FI. The contractile tests showed higher contractility of the SS in the HIIT groups than in the no-exercise group. In the HIIT groups, SS, iBAT, and ingWAT all showed increased expression of tyrosine hydroxylase, UCP1, and upregulated β3AR thermogenesis pathway. However, SR59230A inhibited HIIT, suggesting that the effect of HIIT depends on β3AR. Conclusion: HIIT improved SS quality and function after delayed rotator cuff repair through a β3AR-dependent mechanism. Clinical Relevance: HIIT may serve as a new rehabilitation method for patients with rotator cuff muscle atrophy and FI after rotator cuff repair to improve postoperative clinical outcomes.

IntroductionPromoting muscle regeneration through stem cell therapy has potential risks. We investigated the effect of umbilical cord mesenchymal stem cells (UMSCs) Exosomes (Exo) Follistatin on muscle regeneration.Material and methodsThe Exo was derived from UMSCs cells and was utilized to affect the mice muscle injury model and C2C12 cells myotubes atrophy model. The western blot, qRT-PCR and IF were utilized to determine the effects of Exo on the levels of Follistatin, MyHC, MyoD, Myostatin, MuRF1, MAFbx, α-SMA, Collagen I, Smad2, and AKT. In addition, HE and Masson staining were used to assess muscle tissue damage in mice.ResultsThe level of Follistatin in Exo was significantly higher than that in UMSCs. UMSCs-Exo increased the levels of Follistatin, MyHC, MyoD, and p-Smad2 and decreased the levels of Myostatin, MuRF1, MAFbx, α-SMA, Collagen I, p-AKT, and p-mTOR in mice or C2C12 cells. In addition, UMSCs-Exo decreased levels of inflammation and fibrosis in mice. However, UMSCs-Exo-si-Follistatin reversed the effect of UMSCs-Exo. Transfection of oe-Smad2 up-regulated the protein levels of Collagen I, α-SMA, and changed the ratio of p-Smad2/Smad2 expression to 0.33, and 0.34, 0.73. LY294002 decreased the levels of MyHC, MyoD, and the ratio of p-AKT/ AKT and p-mTOR/mTOR expression to 0.12, 0.17, 0.33, and 0.41, increased the levels of MuRF1 and MAFbx to 0.36 and 0.34.ConclusionsThis study demonstrated that Follistatin in UMSCs-Exo inhibits fibrosis and promotes muscle regeneration in mice by regulating Smad and AKT signaling.

BackgroundTraumatic impacts to the articular joint surface are known to lead to degeneration of the cartilage, as in post-traumatic osteoarthritis (PTOA). While animal-based systems have been instrumental in understanding pathogenic progression of PTOA, they have not served to develop effective treatments for the disease. The limited progress in the development of disease-modifying OA drugs (DMOADs) may be due to insufficient mechanistic understanding of human disease onset/progression that can, in part, be attributed to insufficient in vitro models for disease and therapeutic modeling. To overcome this insufficiency, we are testing hydrogel-based models using adult human mesenchymal stromal cells to examine the effects of traumatic impacts on human cell-based engineered cartilage constructs. We hypothesize that cells encapsulated within biomimetic scaffolds will respond to traumatic impacts in a manner congruent with early PTOA pathogenesis in animal models.MethodsEngineered cartilage constructs were fabricated by encapsulating adult human bone marrow-derived mesenchymal stem cells (hBM-MSCs) in a photocrosslinkable, biomimetic hydrogel (15% methacrylated gelatin, GelMA) that were chondrogenically differentiated for 28 days using TGF-b3. Constructs were subjected to traumatic impacts with different strains or 10 ng/ml IL-1b. Cell viability and metabolism, mechanical property, gene expression, matrix protein production and activation of catabolic enzymes were assessed.ResultsLive and dead staining results showed that traumatic impacts of 30% strain caused massive cell death in engineered cartilage constructs. Elastic modulus of engineered cartilage constructs decreased significantly after traumatic impacts. CCK8 assay results also showed significant cell death and metabolism decrease in the constructs. GAG production decreased 1 day after impacts but recovered 7 days after impact, as was also observed in safranin O staining and GAG assay. RT-PCR results and IHC results showed that anabolic activities were depressed and catabolic enzymes (MMP13, ADAMTS4, ADAMTS5) were activated after impact. ConclusionTraumatic impacts delivered to engineered cartilage constructs induced PTOA-like changes in the encapsulated cells. The development of this in vitro PTOA model will contribute to development of DMOADs in the future.