Treadmill exercise facilitated rotator cuff healing is coupled with regulating periphery neuropeptides expression in a murine model

Abstract

Postoperative exercise has been found able to accelerate bone‐tendon (B‐T) healing. In this study, we systematically compared tendon‐to‐bone healing in mice subjected to postoperative treadmill exercise and free cage recovery in a murine rotator cuff repair model. Specifically, C57BL/6 mice underwent unilateral supraspinatus tendon (SST) detachment and repair were randomly allocated into treadmill group and control group. Treadmill group received daily treadmill running initiated from postoperative day 7 while the control group was allowed free cage activity. Mice were euthanized at postoperative 4 and 8 weeks for synchrotron radiation micro‐computed tomography (SR‐μCT), histology and biomechanical tests to investigate the effect of treadmill running on B‐T healing. The results indicated that treadmill running initiated at day 7 postoperatively was able to accelerate B‐T healing, as evidenced by better tendon‐to‐bone maturation and increased mechanical property. Recent studies show that peripheral neuropeptides are closely associated with musculoskeletal tissue repair. We furtherly conducted quantitative reverse transcription‐polymerase chain reaction and immunofluorescence staining to investigate the temporal‐spatial expression of calcitonin gene‐related peptide (CGRP), substance P (SP), and peripheral neuropeptide Y (NPY) to verify whether they are related to rotator cuff healing. Our results show increased expression of CGRP, SP, and NPY at the healing site under the effect of mechanical stimulation. In conclusion, delayed postoperative exercise with moderate strength appears to accelerate the early phase of B‐T healing, a process that may prove to be linked to increased expression of periphery neuropeptides known to play a role in tissue healing.

Effect of Exercise Intensity on the Healing of the Bone-Tendon Interface: A Mouse Rotator Cuff Injury Model Study

“…48 Previous studies have established a method for evaluating subchondral bone at the BTI during the healing process by SR-mCT in the X-ray Imaging and Biomedical Application Beamline of the SSRF. 27,42,51 In this study, various postoperative treadmill rehabilitation programs demonstrated different qualities of subchondral bone at the BTI by SR-mCT. We observed that the morphological features of the healing interface at the SST enthesis and the subchondral bone quality continued improving with increasing intensity of the treadmill exercise.…”

“…38 Rabbits are popular 6,42 because they are mild tempered and relatively easy to handle, but they are not able to tolerate the stress of surgery and infectious diseases as well as rodents can. 31 In particular, mouse models are useful for studying a wide range of RC pathologies 3,51 because their cellular and tissue physiology is close to that of humans; further, mouse models are more advantageous than rat models in terms of the availability of genetically altered strains to test the effects of specific signaling pathways and molecule changes on BTI development and repair. 3 Many strategies are used to evaluate the BTI healing process.…”

“…The scanning method was previously reported. 27,29,51 Briefly, after being fixed in 4% neutral buffered formalin for 24 hours, the specimens were dehydrated via a series of graded ethanol (75%, 85%, 95%, and 100% twice for 4 h each) before scanning. The beam energy was set to 18.0 keV with an exposure time of 0.2 seconds to obtain optimal imaging results.…”

“…A biomechanical materials testing system (model 5942; Instron) was used to detect the failure load and ultimate strength of these samples, as per a previously reported method. 51 In brief, before the test, the humerus was firmly clamped with a vise grip, while the SST was secured in a clamp using sandpaper. The specimen was placed into the biomechanical materials testing machine for uniaxial tensile testing at a 60°a bduction angle 22 to approximate the anatomic positioning of the SST.…”

“…The samples were preconditioned with a load of 0.1 N. Meanwhile, the width and thickness of the footprint were measured with a caliper under the same tensile load (0.1 N), and the cross-sectional area (mm 2 = width [mm] 3 thickness [mm]) was calculated. 51 The samples were loaded to failure at a rate of 0.03 mm/s, and the failure load, ultimate strength, stiffness, and distance at maximum load were recorded. The specimens were tested at room temperature, and a consistent gauge length was used throughout the test.…”