Mechanical stimulation improves rotator cuff tendon-bone healing via activating IL-4/JAK/STAT signaling pathway mediated macrophage M2 polarization

Yuqian Liu; Linfeng Wang; Shengcan Li; Tao Zhang; Can Chen; Jianzhong Hu; Deyi Sun; Hongbin Lu

doi:10.1016/j.jot.2022.08.008

Mechanical stimulation improves rotator cuff tendon-bone healing via activating IL-4/JAK/STAT signaling pathway mediated macrophage M2 polarization

J Orthop Translat. 2022 Oct 6:37:78-88. doi: 10.1016/j.jot.2022.08.008. eCollection 2022 Nov.

Authors

Yuqian Liu^{1

2

3}, Linfeng Wang^{1

2

3}, Shengcan Li^{1

2

3}, Tao Zhang^{1

2

3}, Can Chen^{2

3}, Jianzhong Hu^{2

3

4}, Deyi Sun^{1

2

3}, Hongbin Lu^{1

2

3}

Affiliations

¹ Department of Sports Medicine, Xiangya Hospital, Central South University, Changsha, China.
² Key Laboratory of Organ Injury, Aging and Regenerative Medicine of Hunan Province, Changsha, China.
³ National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, Changsha, China.
⁴ Department of Spine Surgery and Orthopedics, Xiangya Hospital, Central South University, Changsha, China.

Abstract

Background: It is well known that appropriate mechanical stimulation benefits tendon-bone (T-B) healing, however, the mechanisms behind this are still uncovered completely. Here, we aimed to explore whether the IL-4/JAK/STAT signaling pathway mediated macrophage polarization was involved in mechanical stimulation induced T-B healing.

Method: C57BL/6 mice rotator cuff (RC) repair model was established, and the mice were randomly allocated to the following group. 1. Mice were allowed for free cage activities after surgery (FC group); 2. Mice received treadmill running initiated on postoperative day 7 (TR group); 3. Mice only received a local injection of hydrogel containing IL-4 neutralizing antibody without postoperative intervention (FC + AF-404-SP group); 4. Mice received a local injection of hydrogel containing IL-4 neutralizing antibody and postoperative treadmill running (TR + AF-404-SP group). The expression of IL-4 within supraspinatus tendon (SST) enthesis was measured by Enzyme-linked immunosorbent assay (ELISA). In addition, the activation of JAK/STAT signaling pathway in macrophages and identification of macrophage phenotype at the RC insertion site was detected by Flow cytometry and qRT-PCR. T-B healing quality in this RC repair model was evaluated by histological staining, Micro-computed tomography (Micro-CT) scanning, and biomechanical testing.

Result: In this study, using the RC repair model, we confirmed that generation of IL-4, activation of the JAK/STAT signaling pathway in macrophages, the ability of macrophages to polarize towards M2 subtype, and T-B healing quality were significantly enhanced in TR group compared to FC group. When comparing FC + AF-404-SP group with TR + AF-404-SP group, it was found that the mechanical stimulation induced this effect was depleted following the blockade of the IL-4/JAK/STAT signaling pathway.

Conclusion: Our finding suggested that mechanical stimulation could accelerate T-B healing via activating the IL-4/JAK/STAT signaling pathway that modulates macrophages to polarize towards M2 subtype.

The translational potential of this article: This is the first study to reveal a significant role of mechanical stimulation in the IL-4/JAK/STAT signaling pathway activation and macrophage polarization during RC T-B healing, which highlights the IL-4/JAK/STAT signaling pathway as a potential target to mediate macrophage M2 polarization and improves T-B healing for RC repair.

Keywords: IL-4/JAK/STAT signaling Pathway; Macrophage polarization; Mechanical stimulation; Rotator cuff repair; Tendon-bone healing.