Upregulation of HSP72 attenuates tendon adhesion by regulating fibroblast proliferation and collagen production via blockade of the STAT3 signaling pathway
Introduction
The tendons consist of a special collagen-rich connective tissue that links muscle to bone, thus transmitting mechanical force to the joint and enabling joint movement in the musculoskeletal system [1]. Tendon adhesion commonly occurs between the surgical tendon and the synovial sheath, and it contributes to tendon dysfunction following operation [2] and incurs common complications including peritendinous adhesion [3]. Various types of collagen in the extracellular matrix (ECM) of tendons exert important functions on the repair and regeneration of injured tissues, whereby fibroblasts, the main cells in the tendon are responsible for the maintenance and modification for the ECM in response to tendon injury [4]. However, functional problems may arise because of immoderate ECM production and tissue contraction following injury, and the persistent (myo) fibroblast proliferation and their excessive ECM production contribute to the pathology of scarring [5]. Elucidating cellular mechanisms that inhibit the proliferation of fibroblast is therefore critical to attenuating tendon adhesion.
The stress-inducible 70-kDa heat shock protein (HSP70) exerts multiple functions intracellularly and extracellularly, and elevation of its expression helps maintain muscle fiber integrity after injury, thereby accelerating the regeneration and recovery of muscle [6]. Heat shock protein 72 (HSP72), a member of the HSP70 family, is a stress-inducible ATPase molecular chaperone, which can stabilize and refold substrate proteins to maintain cellular homeostasis [7]. HSP72 can be synthesized as a cytoprotective response to cellular stress, and its upregulation in human fibroblasts by heat and mechanical stress is a response that involves its nuclear translocation [8]. Interestingly, HSP72 can induce antagonistic actions depending on its location; specifically, intracellular HSP72 exerts an anti-inflammatory function while extracellular HSP72 has the potency to activate pro-inflammatory-related pathways [9,10]. A previous study showed that repressed expression of HSP72 is related to the chronic inflammation in type 2 diabetes [11]. Interestingly, the overexpression of HSP72 induced by thermal preconditioning has the capacity to alleviate tendon adhesion [8]. The regulatory mechanism of HSP70 on signal transducer and activator of transcription (STAT3), a member of the STAT family, has been previously investigated in myeloid-derived suppressor cells [12]. STAT3 exerts effects on the transcription of genes mediating cell proliferation and conversion in phenotype [13]. The STAT3 signaling pathway modulated by aspirin is associated with attenuated inflammation and scar formation during tendon healing [14]. In addition, STAT3 phosphorylation is promoted mainly by proliferating blood vessels in ruptured rotator cuff tendon [15]. Inhibition of STAT3 signaling pathway decreases ECM production and fibroblast proliferation from hypertrophic scars [16]. The aforementioned findings present a possible mechanism by which HSP72 and the STAT3 signaling pathway interact in fibroblast proliferation and tendon adhesion. Thus, we established a mouse tendon injury model to explore the contribution of this pathway to tendon adhesion pathology.
Section snippets
Ethical approval
The study was approved by the Institutional Animal Care and Use Committee of Zhongnan Hospital of Wuhan University. Animal experiments were conducted in compliance with the recommendations in the Guide for the Care and Use of Laboratory Animals published by the US National Institutes of Health. All efforts were made to minimize the number and discomfort of the included animals.
Establishment of a rat model of tendon injury
A total of 120 male Sprague-Dawley rats (aged 9 weeks; weighing 250–300 g) were obtained from the Hubei Provincial
HSP72 elevation contributed to inhibited fibroblast proliferation and attenuated tendon adhesion in vivo
To verify the regulatory role of HSP72 in tendon adhesion, we initially established a rat model of tendon injury. As shown in Fig. 2A, markedly higher scores were observed in the rat model of tendon injury (4.54 + CI 2.03–2.803) than that in normal rats (2.32) (p = .001), while sham-operated rats (2.46 + CI - 0.06 - 0.723) exhibited no obvious disparity (p = .09). HE staining results (Fig. 2B) revealed that compared to normal rats, the rat tendon injury model exhibited disorder of collagen
Discussion
Tendon injuries commonly promote the formation of scar-like tissues with a poor biochemical structure and mechanical properties [23], and the resultant tendon adhesion is a leading cause of gliding dysfunction pain, or even the complex re-operative surgery [24]. Patients suffering from tendon rupture or tendinopathy would experience matrix degeneration and tendon healing [25]. The emerging field of epigenetics has the potential for revealing new molecular biomarkers to prevent or alleviate
Authors contributions
Zhengqi Pan, Qinfen Wu, Zhe Xie and Qiang Wu designed the study. Xinti Tan collated the data, designed and developed the database, carried out data analyses and produced the initial draft of the manuscript. Xin Wang, Zhengqi Pan and Qinfen Wu contributed to drafting the manuscript. All authors have read and approved the final submitted manuscript.
Data availability statement
The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.
Funding
This study was supported by Science and Technology Innovation and Cultivation Fund of Zhongnan Hospital of Wuhan University (No. znpy2018018).
Declaration of Competing Interest
The authors declare that they have no competing interests.
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These authors contributed equally to this work.