Suppression of the production of extracellular matrix and α-smooth muscle actin induced by transforming growth factor-β1 in fibroblasts of the flexor tendon sheath by hepatocyte growth factor

c-Met Signaling Is Essential for Mouse Adult Liver Progenitor Cells Expansion After Transforming Growth Factor-β-Induced Epithelial-Mesenchymal Transition and Regulates Cell Phenotypic Switch

Adult hepatic progenitor cells (HPCs)/oval cells are bipotential progenitors that participate in liver repair responses upon chronic injury. Recent findings highlight HPCs plasticity and importance of the HPCs niche signals to determine their fate during the regenerative process, favoring either fibrogenesis or damage resolution. Transforming growth factor-β (TGF-β) and hepatocyte growth factor (HGF) are among the key signals involved in liver regeneration and as component of HPCs niche regulates HPCs biology. Here, we characterize the TGF-β-triggered epithelial-mesenchymal transition (EMT) response in oval cells, its effects on cell fate in vivo, and the regulatory effect of the HGF/c-Met signaling. Our data show that chronic treatment with TGF-β triggers a partial EMT in oval cells based on coexpression of epithelial and mesenchymal markers. The phenotypic and functional profiling indicates that TGF-β-induced EMT is not associated with stemness but rather represents a step forward along hepatic lineage. This phenotypic transition confers advantageous traits to HPCs including survival, migratory/invasive and metabolic benefit, overall enhancing the regenerative potential of oval cells upon transplantation into a carbon tetrachloride-damaged liver. We further uncover a key contribution of the HGF/c-Met pathway to modulate the TGF-β-mediated EMT response. It allows oval cells expansion after EMT by controlling oxidative stress and apoptosis, likely via Twist regulation, and it counterbalances EMT by maintaining epithelial properties. Our work provides evidence that a coordinated and balanced action of TGF-β and HGF are critical for achievement of the optimal regenerative potential of HPCs, opening new therapeutic perspectives. Stem Cells 2019;37:1108-1118.

FAK activity is required for HGF to suppress TGF-β1-induced cellular proliferation

Due to the complex nature of the tendon architecture, the regeneration of these tissues results in the formation of scars. As a direct result of scar formation, the ability of the tendon tissues to function is impaired and often results in further damage that has been afflicted to the tendon architecture. The growth and proliferation of tendon fibroblasts involve a complex network of signalling molecules. To understand and aid in the proper repair of this complex tissue network, a more in-depth understanding is required in the events that induce the growth of tendon cells. Several studies have shown the apoptotic mechanisms induced by the mitogen, hepatocyte growth factor, in multiple biological and pathological systems. In our recent research, we have described a mechanism where hepatocyte growth factor (HGF) is able to inhibit the proliferative effects of transforming growth factor-β1 (TGF-β1) and induce apoptosis in rat tendon fibroblasts. Transforming growth factor-β1 is able to induce the proliferation of fibroblast cells by increasing both the gene expression and protein levels of α-smooth muscle actin (α-SMA) and c-MET. We have also shown that inhibition of extracellular signal-regulated kinase 1/2 does not block hepatocyte growth factor-induced growth arrest. However, we have shown that blocking the activity of focal adhesion kinase can prevent the growth inhibition ability of hepatocyte growth factor in tendon fibroblasts. Collectively, our studies show growth inhibitory pathway in tendon fibroblasts induced by hepatocyte growth factor and mediated focal adhesion kinase.

The growth factors involved in flexor tendon repair and adhesion formation

Flexor tendon injuries remain a significant clinical problem, owing to the formation of adhesions or tendon rupture. A number of strategies have been tried to improve outcomes, but as yet none are routinely used in clinical practice. Understanding the role that growth factors play in tendon repair should enable a more targeted approach to be developed to improve the results of flexor tendon repair. This review describes the main growth factors in tendon wound healing, and the role they play in both repair and adhesion formation.

Tendon healing in vivo and in vitro: neutralizing antibody to TGF-β improves range of motion after flexor tendon repair

Adhesion formation between the flexor tendon and its surrounding fibro-osseous sheath results in a decreased postoperative range of motion (ROM) in the hand. Transforming growth factor-beta (TGF-β) is a key cytokine in the pathogenesis of tissue fibrosis. In this study, the effects of TGF-β1 neutralizing antibody were investigated in vitro and in vivo. In the in vitro investigation, primary cell cultures from rabbit flexor tendon sheath, epitenon, and endotenon were established and each was supplemented with TGF-β along with increasing doses of TGF-β1 neutralizing antibody. Collagen I production was measured with enzyme-linked immunosorbent assay. In the in vivo study, rabbit zone-II flexor tendons were transected and then immediately repaired. Transforming growth factor-β1 neutralizing antibody or phosphate-buffered saline solution (control) was added to the repair sites, and the forepaws were tested for ROM and repair strength at 8 weeks postoperatively. Transforming growth factor-β1 neutralizing antibody reduced TGF-β upregulated collagen production. Intraoperative application of TGF-β1 neutralizing antibody significantly improved the ROM of the operatively treated digits. The effect on breaking strength of the tendon repair was inconclusive.

Neuropeptide, mast cell, and myofibroblast expression after rabbit deep flexor tendon repair

PURPOSE

Increased numbers of myofibroblasts, mast cells, and neuropeptide-containing nerve fibers have been found in a number of fibrotic processes in connective tissues. The purpose of the present study was to investigate the occurrence of factors implicated in a hypothesized profibrotic neuropeptide-mast cell-myofibroblast pathway in deep flexor tendon healing.

METHODS

In a rabbit model of flexor tendon injury, with repair of the sharply transected deep flexor tendon using a modified Kessler and a running circumferential peripheral suture, segments of flexor tendons and sheaths were analyzed. The time points chosen-3, 6, 21, and 42 days after tendon repair-represent different stages in tendon healing. The messenger RNA levels of transforming growth factor-β1 and α-smooth muscle actin were measured with conventional reverse transcription-polymerase chain reaction, and the numbers of myofibroblasts, mast cells, and neuropeptide-containing nerve fibers were determined with immunohistochemistry.

RESULTS

The messenger RNA levels for transforming growth factor-β1 and the myofibroblast marker α-smooth muscle actin were significantly increased in deep flexor tendons after injury and repair, at all studied time points, but remained unchanged or even down-regulated in the sheaths. Myofibroblasts, mast cells, and neuropeptide-containing nerve fibers all increased significantly in the healing tendons, exhibiting similar patterns of change in percentages of total cell number over time, reaching levels resembling that of the tendon sheaths with 33% to 50% of the total cell population.

CONCLUSIONS

After injury to the deep flexor tendon in a rabbit model, the proportion of myofibroblasts, mast cells, and neuropeptide-containing nerve fibers increases significantly. These findings support the hypothesis that the profibrotic neuropeptide-mast cell-myofibroblast pathway is activated in deep flexor tendon healing.

Modulation of wound contracture alpha-smooth muscle actin and multispecific vitronectin receptor integrin alphavbeta3 in the rabbit's experimental model

The myofibroblast, a major component of granulation tissue, is a key cell during wound healing, tissue repair and connective tissue remodelling. Persistence of myofibroblasts within a fibrotic lesion leads to excessive scarring impairing function and aesthetics. Various wound-healing cytokines can be modulated by topical application of active agents to promote optimal wound healing and improve scar quality. Thus, the myofibroblast may represent an important target for wound-healing modulation to improve the evolution of conditions such as hypertrophic scars. The purpose of this work is to study the modulation of myofibroblasts and integrin alphavbeta3 in a full thickness wound performed on rabbits treated with different topical agents using: (1) saline, (2) Tegaderm occlusive dressing (3) silver sulfadiazine and (4) moist exposed burn ointment (MEBO). The reepithelialisation was 4 days faster in the MEBO group compared with the other therapies with less oedema formation, delayed contraction, less inflammatory cells and the lowest transepidermal water loss (TEWL) resulting in a soft scar. Although alpha-smooth muscle actin (alpha-SMA) was the highest around day 12 in the MEBO group, wound contraction and myofibroblast's activity were the least for the same period probably because of a downregulation of the integrin alphavbeta3. It seems that the effect of MEBO could be more pronounced on force transmission rather then on force generation. Greater insight into the pathology of scars may translate into non surgical treatments in the future and further work in myofibroblast biology will eventually result in efficient pharmacological tools, improving the evolution of healing and scar formation.

Profiling of anti-fibrotic signaling by hepatocyte growth factor in renal fibroblasts

Hepatocyte growth factor (HGF) is a multifunctional growth factor affecting cell proliferation and differentiation. Due to its mitogenic potential, HGF plays an important role in tubular repair and regeneration after acute renal injury. However, recent reports have shown that HGF also acts as an anti-inflammatory and anti-fibrotic factor, affecting various cell types such as renal fibroblasts and triggering tubulointerstitial fibrosis of the kidney. The present study provides evidence that HGF stimulation of renal fibroblasts results in the activation of both the Erk1/2 and the Akt pathways. As previously shown, Erk1/2 phosphorylation results in Smad-linker phosphorylation, thereby antagonizing cellular signals induced by TGFbeta. By siRNA mediated silencing of the Erk1/2-Smad linkage, however, we now demonstrate that Akt signaling acts as an auxiliary pathway responsible for the anti-fibrotic effects of HGF. In order to define the anti-fibrotic function of HGF we performed comprehensive expression profiling of HGF-stimulated renal fibroblasts by microarray hybridization. Functional cluster analyses and quantitative PCR assays indicate that the HGF-stimulated pathways transfer the anti-fibrotic effects in renal interstitial fibroblasts by reducing expression of extracellular matrix proteins, various chemokines, and members of the CCN family.