Release of Tensile Strain on Engineered Human Tendon Tissue Disturbs Cell Adhesions, Changes Matrix Architecture, and Induces an Inflammatory Phenotype

Abstract

Mechanical loading of tendon cells results in an upregulation of mechanotransduction signaling pathways, cell-matrix adhesion and collagen synthesis, but whether unloading removes these responses is unclear. We investigated the response to tension release, with regard to matrix proteins, pro-inflammatory mediators and tendon phenotypic specific molecules, in an in vitro model where tendon-like tissue was engineered from human tendon cells. Tissue sampling was performed 1, 2, 4 and 6 days after surgical de-tensioning of the tendon construct. When tensile stimulus was removed, integrin type collagen receptors showed a contrasting response with a clear drop in integrin subunit α11 mRNA and protein expression, and an increase in α2 integrin mRNA and protein levels. Further, specific markers for tendon cell differentiation declined and normal tendon architecture was disturbed, whereas pro-inflammatory molecules were upregulated. Stimulation with the cytokine TGF-β1 had distinct effects on some tendon-related genes in both tensioned and de-tensioned tissue. These findings indicate an important role of mechanical loading for cellular and matrix responses in tendon, including that loss of tension leads to a decrease in phenotypical markers for tendon, while expression of pro-inflammatory mediators is induced.

TGFβ and FGF promote tendon progenitor fate and act downstream of muscle contraction to regulate tendon differentiation during chick limb development

“…8) and mouse (Havis et al, 2014) limb explants. This is consistent with previous reports showing TNMD upregulation by TGFβ ligands in 3D-culture systems of human tendon cells (Bayer et al, 2014) and of equine embryo-derived stem cells (Barsby et al, 2014), and in high-density cultures of chick limb cells (Lorda-Diez et al, 2009). It is worth mentioning that TGFβ dramatically decreases Tnmd expression (and activates Scx) in 2D-culture systems of embryonic or adult mouse tendon progenitors and in mouse mesenchymal stem cells (Guerquin et al, 2013;Brown et al, 2014;Liu et al, 2015).…”

The (dys)functional extracellular matrix

“…For example, when tenocytes were subjected to cyclic strain, their gap junctions became disrupted and apoptosis was induced [134]. Cell–matrix adhesions allow tenocytes to sense and respond to their mechanical environment while also allowing them to act on the ECM through actomyosin mediated contractile forces [135]. Altering the tensile forces on tendons can elicit changes in integrin receptors, as well as in downstream ECM proteins [135].…”

“…Cell–matrix adhesions allow tenocytes to sense and respond to their mechanical environment while also allowing them to act on the ECM through actomyosin mediated contractile forces [135]. Altering the tensile forces on tendons can elicit changes in integrin receptors, as well as in downstream ECM proteins [135]. Specifically, de-tensioning tenocytes in vitro caused a decrease in collagen binding integrin α11β 1, which is associated with the organization of collagen in the ECM, and an increase in collagen binding integrin α2β 1 and fibronectin integrin receptor α5β 1, which are associated with the transmission of cytoskeletal forces through collagen fibrils causing contraction and adhesion strength, respectively [135].…”

Three-Dimensional Platelet-Rich Plasma Hydrogel Model to Study Early Tendon Healing

“…Foremost, true tendon regeneration is thought to recapitulate developmental processes, involving cell differentiation and fibrillogenesis, with restoration of native tissue properties. In vitro research in 3D fibrin constructs has proven that mature tendon cells are able to recapitulate fibrillogenesis [Bayer et al, 2014]. These results suggest that regenerative deficits in mature tendons are not associated with tendon capabilities but are related to the hostile molecular environment.…”

“…To address this issue, we devised a 3-dimensional (3D) PRP hydrogel culture technique that allows us to study tendon cell biology in a model halfway between conventional in vitro cultures and tissue engineering constructs in 3D fibrin matrices [Bayer et al, 2014]. Evidently, PRP hydrogels do not intend to emulate the highly organized ECM of native tendons, but the data obtained here can help to better understand the effects of PRP in a more physiological 3D spatial context and in a molecular environment that mimics early healing.…”