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Background: Tendon injuries are common problems among athletes. Complete recovery of the mechanical structure and function of ruptured tendons is challenging. It has been demonstrated that upregulation of glycolysis and lactate production occurs in wounds, inflammation sites, and cancerous tumors, and these metabolic changes also control growth and differentiation of stem and progenitor cells. Similar metabolic changes have been reported in human healing tendons. In addition, lactate production has increased in progenitors isolated from injured tendons after treatment with IL-1β. It is thought that the metabolic changes play a role in tendon healing after injury. Hypothesis: Glucose metabolism is altered during tendon injury and healing, and modulation of this altered metabolism improves tendon repair. Study Design: Controlled laboratory study. Methods: The authors used the tendon injury model involving a complete incision of the Achilles tendon in C57BL/6J female mice and studied alterations of glucose metabolism in injured tendons with [U-13C]glucose and metabolomics analysis 1 and 4 weeks after surgery. They also examined the effects of dichloroacetate (DCA; an indirect lactate synthesis inhibitor) treatment on the recovery of structure and mechanical properties of injured tendons 4 weeks after surgery in the same mouse model. Results: Significant changes in glucose metabolism in tendons after injury surgery were detected. 13C enrichment of metabolites and intermediates, flux through glycolysis, and lactate synthesis, as well as tricarboxylic acid cycle activity, were acutely increased 1 week after injury. Increased glycolysis and lactate generation were also found 4 weeks after injury. DCA-treated injured tendons showed decreased cross-sectional area and higher values of modulus, maximum stress, and maximum force when compared with vehicle-treated injured tendons. Improved alignment of the collagen fibers was also observed in the DCA group. Furthermore, DCA treatment reduced mucoid accumulation and ectopic calcification in injured tendons. Conclusion: The findings indicate that injured tendons acutely increase glycolysis and lactate synthesis after injury and that the inhibition of lactate synthesis by DCA is beneficial for tendon healing. Clinical Relevance: Changing metabolism in injured tendons may be a therapeutic target for tendon repair. [ABSTRACT FROM AUTHOR]

Ectopic tendon mineralization can develop following tendon rupture or trauma surgery. The pathogenesis of ectopic tendon mineralization and its clinical impact have not been fully elucidated yet. In this study, we utilized a mouse Achilles tendon injury model to determine whether ectopic tendon mineralization alters the biomechanical properties of the tendon and whether BMP signaling is involved in this condition. A complete transverse incision was made at the midpoint of the right Achilles tendon in 8-week-old CD1 mice and the gap was left open. Ectopic cartilaginous mass formation was found in the injured tendon by 4 weeks post-surgery and ectopic mineralization was detected at 8 to 10 weeks post-surgery. Ectopic mineralization grew over time and volume of the mineralized materials of 25-weeks samples was about 2.5 fold bigger than that of 10-weeks samples, indicating that injury-induced ectopic tendon mineralization is progressive. In vitro mechanical testing showed that max force, max stress and mid-substance modulus in the 25-weeks samples were significantly lower than the 10-weeks samples. We observed substantial increases in expression of bone morphogenetic protein family genes in injured tendons 1 week post-surgery. Immunohistochemical analysis showed that phosphorylation of both Smad1 and Smad3 was highly increased in injured tendons as early as 1 week post-injury and remained high in ectopic chondrogenic lesions 4-weeks post-injury. Treatment with the BMP receptor kinase inhibitor (LDN193189) significantly inhibited injury-induced tendon mineralization. These findings indicate that injury-induced ectopic tendon mineralization is progressive, involves BMP signaling and associated with deterioration of tendon biomechanical properties. [ABSTRACT FROM AUTHOR]

Celecoxib, a selective cox-2 inhibitor, has been shown to prevent the heterotopic ossification following total hip arthroplasty. However, the effects of celecoxib on heterotopic ossification at other locations remain unclear. This study aimed to investigate the effect of celecoxib on heterotopic ossification in the rat model with Achilles tenotomy. Forty male Sprague-Dawley rats, which were randomly divided into 2 groups ( n = 20), underwent midpoint Achilles tenotomy on left legs through a posterior approach under aseptic condition. Experimental group was treated with the saline solution of celecoxib (10 mg/kg) per day, while control group was treated by normal saline (0.9%). At 3, 5 and 10 postoperative weeks, all animals were examined by X-ray to assess new bone formation in the Achilles tendon. At 10 weeks after surgery, all animals were killed and Achilles tendons were taken for hematoxylin-eosin (HE) and immunohistochemical staining. Heterotopic ossification developed in 3 rats (15%) in experimental group and 20 rats (100%) in control group by postoperative 10 weeks. The incidence of heterotopic ossification was significantly lower in experimental group than in control group ( P < 0.05). Our findings suggest that celecoxib inhibits HO development in rat model with Achilles tenotomy. [ABSTRACT FROM AUTHOR]

Injured tendons do not regain their native structure except at fetal or very young ages. Healing tendons often show mucoid degeneration involving accumulation of sulfated glycosaminoglycans (GAGs), but its etiology and molecular base have not been studied substantially. We hypothesized that quality and quantity of gene expression involving the synthesis of proteoglycans having sulfated GAGs are altered in injured tendons and that a reduction in synthesis of sulfated GAGs improves structural and functional recovery of injured tendons. C57BL6/j mice were subjected to Achilles tendon tenotomy surgery. The injured tendons accumulated sulfate proteoglycans as early as 1‐week postsurgery and continued so by 4‐week postsurgery. Transcriptome analysis revealed upregulation of a wide range of proteoglycan genes that have sulfated GAGs in the injured tendons 1 and 3 weeks postsurgery. Genes critical for enzymatic reaction of initiation and elongation of chondroitin sulfate GAG chains were also upregulated. After the surgery, mice were treated with the 2‐deoxy‐d‐glucose (2DG) that inhibits conversion of glucose to glucose‐6‐phosphate, an initial step of glucose metabolism as an energy source and precursors of monosaccharides of GAGs. The 2DG treatment reduced accumulation of sulfated proteoglycans, improved collagen fiber alignment, and reduced the cross‐sectional area of the injured tendons. The modulus of the 2DG‐treated groups was higher than that in the vehicle group, but not of statistical significance. Our findings suggest that mucoid degeneration in injured tendons may result from the upregulated expression of genes involved the synthesis of sulfate proteoglycans and can be inhibited by reduction of glucose utilization. [ABSTRACT FROM AUTHOR]

Background: Hypercholesterolemia increases the risk of tendon pain and tendon rupture. Tendon-derived stem cells (TDSCs) play a vital role in the development of tendinopathy. Our previous research found that high cholesterol inhibits tendon-related gene expression in TDSCs. Whether high cholesterol has other biological effects on TDSCs remains unknown. Methods: TDSCs isolated from female SD rats were exposed to 10 mg/dL cholesterol for 24 h. Then, cell apoptosis was assessed using flow cytometry and fluorescence microscope. RFP-GFP-LC3 adenovirus transfection was used for measuring autophagy. Signaling transduction was measured by immunofluorescence and immunoblotting. In addition, Achilles tendons from ApoE −/− mice fed with a high-fat diet were histologically assessed using HE staining and immunohistochemistry. Results: In this work, we verified that 10 mg/dL cholesterol suppressed cell proliferation and migration and induced G0/G1 phase arrest. Additionally, cholesterol induced apoptosis and autophagy simultaneously in TDSCs. Apoptosis induction was related to increased expression of cleaved caspase-3 and BAX and decreased expression of Bcl-xL. The occurrence of autophagic flux and accumulation of LC3-II demonstrated the induction of autophagy by cholesterol. Compared with the effects of cholesterol treatment alone, the autophagy inhibitor 3-methyladenine (3-MA) enhanced apoptosis, while the apoptosis inhibitor Z-VAD-FMK diminished cholesterol-induced autophagy. Moreover, cholesterol triggered reactive oxygen species (ROS) generation and activated the AKT/FOXO1 pathway, while the ROS scavenger NAC blocked cholesterol-induced activation of the AKT/FOXO1 pathway. NAC and the FOXO1 inhibitor AS1842856 rescued the apoptosis and autophagy induced by cholesterol. Finally, high cholesterol elevated the expression of cleaved caspase-3, Bax, LC3-II, and FOXO1 in vivo. Conclusion: The present study indicated that high cholesterol induced apoptosis and autophagy through ROS-activated AKT/FOXO1 signaling in TDSCs, providing new insights into the mechanism of hypercholesterolemia-induced tendinopathy. High cholesterol induces apoptosis and autophagy through the ROS-activated AKT/FOXO1 pathway in tendon-derived stem cells. [ABSTRACT FROM AUTHOR]