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Skeletal muscle fibrosis and stiffness increase after rotator cuff tendon injury and neuromuscular compromise in a rat model.

ABSTRACT: Rotator cuff tears can cause irreversible changes (e.g., fibrosis) to the structure and function of the injured muscle(s). Fibrosis leads to increased muscle stiffness resulting in increased tension at the rotator cuff repair site. This tension influences repairability and healing potential in the clinical setting. However, the micro- and meso-scale structural and molecular sources of these whole-muscle mechanical changes are poorly understood. Here, single muscle fiber and fiber bundle passive mechanical testing was performed on rat supraspinatus and infraspinatus muscles with experimentally induced massive rotator cuff tears (Tenotomy) as well as massive tears with chemical denervation (Tenotomy + BTX) at 8 and 16 weeks post-injury. Titin molecular weight, collagen content, and myosin heavy chain profiles were measured and correlated with mechanical variables. Single fiber stiffness was not different between controls and experimental groups. However, fiber bundle stiffness was significantly increased at 8 weeks in the Tenotomy + BTX group compared to Tenotomy or control groups. Many of the changes were resolved by 16 weeks. Only fiber bundle passive mechanics was weakly correlated with collagen content. These data suggest that tendon injury with concomitant neuromuscular compromise results in extra-cellular matrix production and increases in stiffness of the muscle, potentially complicating subsequent attempts for surgical repair.

SUBMITTER: Sato EJ

PROVIDER: S-EPMC4415493 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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Skeletal muscle fibrosis and stiffness increase after rotator cuff tendon injury and neuromuscular compromise in a rat model.

Sato Eugene J EJ Killian Megan L ML Choi Anthony J AJ Lin Evie E Esparza Mary C MC Galatz Leesa M LM Thomopoulos Stavros S Ward Samuel R SR

Journal of orthopaedic research : official publication of the Orthopaedic Research Society 20140519 9

Rotator cuff tears can cause irreversible changes (e.g., fibrosis) to the structure and function of the injured muscle(s). Fibrosis leads to increased muscle stiffness resulting in increased tension at the rotator cuff repair site. This tension influences repairability and healing potential in the clinical setting. However, the micro- and meso-scale structural and molecular sources of these whole-muscle mechanical changes are poorly understood. Here, single muscle fiber and fiber bundle passive ...[more]

PMID: 24838823

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Project description:Myosteatosis is the pathological accumulation of lipid that occurs in conjunction with atrophy and fibrosis following skeletal muscle injury or disease. Little is known about the mechanisms by which lipid accumulates in myosteatosis, but many studies have demonstrated the degree of lipid infiltration negatively correlates with muscle function and regeneration. Our goal was to identify biochemical pathways that lead to muscle dysfunction and lipid accumulation in injured rotator cuff muscles, a model that demonstrates severe myosteatosis. Adult rats were subjected to a massive tear to the rotator cuff musculature. After a period of either 0 (healthy control), 10, 30, or 60 days, muscles were prepared for RNA sequencing, shotgun lipidomics, metabolomics, biochemical measures, electron microscopy, and muscle fiber contractility. Following rotator cuff injury, there was a decrease in muscle fiber specific force production that was lowest at 30d. There was a dramatic time dependent increase in triacylglyceride content. Interestingly, genes related to not only triacylglyceride synthesis, but also lipid oxidation were largely downregulated over time. Using bioinformatics techniques, we identified that biochemical pathways related to mitochondrial dysfunction and reactive oxygen species were considerably increased in muscles with myosteatosis. Long chain acyl-carnitines and L-carnitine, precursors to beta-oxidation, were depleted following rotator cuff tear. Electron micrographs showed injured muscles displayed large lipid droplets within mitochondria at early time points, and an accumulation of peripheral segment mitochondria at all time points. Several markers of oxidative stress were elevated following rotator cuff tear. The results from this study suggest that the accumulation of lipid in myosteatosis is not a result of canonical lipid synthesis, but occurs due to decreased lipid oxidation in mitochondria. A failure in lipid utilization by mitochondria would ultimately cause an accumulation of lipid even in the absence of increased synthesis. Further study will identify whether this process is required for the onset of myosteatosis.

Project description:BackgroundMore than 450,000 rotator cuff repairs are performed annually, yet healing of tendon to bone often fails. This failure is rooted in the fibrovascular healing response, which does not regenerate the native attachment site. Better healing outcomes may be achieved by targeting inflammation during the early period after repair. Rather than broad inhibition of inflammation, which may impair healing, the current study utilized a molecularly targeted approach to suppress IKKβ, shutting down only the inflammatory arm of the nuclear factor κB (NF-κB) signaling pathway.PurposeTo evaluate the therapeutic potential of IKKβ inhibition in a clinically relevant model of rat rotator cuff repair.Study designControlled laboratory study.MethodsAfter validating the efficacy of the IKKβ inhibitor in vitro, it was administered orally once a day for 7 days after surgery in a rat rotator cuff repair model. The effect of treatment on reducing inflammation and improving repair quality was evaluated after 3 days and 2, 4, and 8 weeks of healing, using gene expression, biomechanics, bone morphometry, and histology.ResultsInhibition of IKKβ attenuated cytokine and chemokine production in vitro, demonstrating the potential for this inhibitor to reduce inflammation in vivo. Oral treatment with IKKβ inhibitor reduced NF-κB target gene expression by up to 80% compared with a nontreated group at day 3, with a subset of these genes suppressed through 14 days. Furthermore, the IKKβ inhibitor led to enhanced tenogenesis and extracellular matrix production, as demonstrated by gene expression and histological analyses. At 4 weeks, inhibitor treatment led to increased toughness, no effects on failure load and strength, and decreases in stiffness and modulus when compared with vehicle control. At 8 weeks, IKKβ inhibitor treatment led to increased toughness, failure load, and strength compared with control animals. IKKβ inhibitor treatment prevented the bone loss near the tendon attachment that occurred in repairs in control.ConclusionPharmacological inhibition of IKKβ successfully suppressed excessive inflammation and enhanced tendon-to-bone healing after rotator cuff repair in a rat model.Clinical relevanceThe NF-κB pathway is a promising target for enhancing outcomes after rotator cuff repair.

Project description:Purpose To compare patient-reported and surgical outcome measures in patients with and without secondary shoulder stiffness (SSS) undergoing rotator cuff repair (RCR). Methods Patients undergoing rotator cuff repair from 2014 to 2020 with complete patient-reported outcome measures (PROMs) by the short-form 12 survey (SF-12) were retrospectively reviewed to identify if operative intervention for SSS was performed alongside the RCR. Those patients with operative intervention for SSS were propensity matched to a group without prior intervention for stiffness by age, sex, laterality, body mass index, diabetes mellitus status, and the presence of a thyroid disorder. The groups were compared by rotator cuff tear (RCT) size, surgical outcomes, further surgical intervention, rotator cuff retear rate, postoperative range of motion (ROM), and SF-12 results at 1 year after surgery. Delta values were calculated for component scores of the SF-12 and ROM values by subtracting the preoperative result from the postoperative result. Results A total of 89 patients with SSS were compared to 156 patients in the control group at final analysis. The patients in the SSS group experienced a significant improvement in the delta mental health component score (MCS-12) of the SF-12 survey that was not seen in the control group (P = .005 to P = .539). Both groups experienced significant improvement by the delta physical health component score (PCS-12) of the SF-12 survey (SSS: 7.68; P < .001; control: 6.95; P < .001). The SSS group also experienced greater improvement of their forward flexion (25.8° vs 12.9°; P = .005) and external rotation (7.13° vs 1.65°; P = .031) ROM than the control group. Conclusions Operative intervention of SSS at the time of RCR has equivalent postoperative SF-12 survey outcome scores when compared to patients undergoing RCR without preoperative stiffness despite those patients having lower preoperative scores. Level of Evidence Level III retrospective comparative study.

Dataset Information

Skeletal muscle fibrosis and stiffness increase after rotator cuff tendon injury and neuromuscular compromise in a rat model.

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Skeletal muscle fibrosis and stiffness increase after rotator cuff tendon injury and neuromuscular compromise in a rat model.

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