Differences in morphology, cytoskeletal architecture and protease production between zone II tendon and synovial fibroblasts in vitro

Prevention of peritendinous adhesions with electrospun poly (lactic acid-co-glycolic acid) (PLGA) bioabsorbable nanofiber: An experimental study

In this study, we investigated the application of poly (lactic acid-co-glycolic acid) in the rat Achilles tendon injury model for the prevention or alleviation of peritendinous adhesion and guidance of Achilles tendon regeneration. In the study, 48 rats were used and the rats were randomized by closed envelope method and divided into 4 mating groups in groups of 12. Left Achilles tendons of the non-PLGA-treated control group (groups 1 and 2) were cut and repaired. In the PLGA-treated groups (groups 3 and 4) the left Achilles tendons were cut and repaired, then PLGA bioabsorbable material was wrapped around the repair line. The rats in the 1st and 3rd groups were sacrificed at the end of the 1st month, and the rats in the 2nd and 4th groups at the end of the 2nd month. The degree of tendon adhesion in the Group 3 was lower in comparison with Group 1. Similarly, compared with Group 2, the degree of tendon adhesion in the Group 4 was lower. Inflammatory density, vascularization and fibrosis were higher in the experimental group. When the Group 3 and Group 1, and Group 2 and Group 4 were compared, adhesion length (p = 0.004, p = 0.041), adhesion characteristics (p = 0.049, p = 0.039) and adhesion severity (p = 0.007, p = 0.025) were found have statistically significant tendon healing in the PLGA-treated group, respectively. Significant difference was observed in inflammatory cell density, vascular density and fibrosis for Group 1 and Group 3, (p = 0.027, p = 0.041, p = 0.002), respectively. Similarly, significant difference was observed in inflammatory cell density, vascular density and fibrosis for Group 2 and Group 4, (p = 0.002, p = 0.027, p = 0.011), respectively. As a result, it was considered that poly (lactic acid-co-glycolic acid) material significantly reduces peritendinous adhesions, and this effect could occur with the vascular density, inflammatory density and fibrosis as indicated in histopathological examination. These data suggest that PLGA membrane has good biocompatibility and alleviates tendon adhesion after injury.

Introduction to cell-hydrogel mechanosensing

The development of hydrogel-based biomaterials represents a promising approach to generating new strategies for tissue engineering and regenerative medicine. In order to develop more sophisticated cell-seeded hydrogel constructs, it is important to understand how cells mechanically interact with hydrogels. In this paper, we review the mechanisms by which cells remodel hydrogels, the influence that the hydrogel mechanical and structural properties have on cell behaviour and the role of mechanical stimulation in cell-seeded hydrogels. Cell-mediated remodelling of hydrogels is directed by several cellular processes, including adhesion, migration, contraction, degradation and extracellular matrix deposition. Variations in hydrogel stiffness, density, composition, orientation and viscoelastic characteristics all affect cell activity and phenotype. The application of mechanical force on cells encapsulated in hydrogels can also instigate changes in cell behaviour. By improving our understanding of cell-material mechano-interactions in hydrogels, this should enable a new generation of regenerative medical therapies to be developed.

Cell migration after synovium graft interposition at tendon repair site

BACKGROUND

We have recently reported that interpositional synovium grafts from tendon sheath have a potential to accelerate tendon healing when implanted at the repair site. The purpose of this study was to investigate the effect of orientation of the synovium after synovium graft transplantation, by comparing the ability of cells from the visceral and parietal surfaces to migrate into the tendon in a canine tissue culture model.

METHODS

The synovium graft was placed within a complete tendon laceration, with either the visceral or parietal surface facing the proximal end of the lacerated tendon. The number of migrating cells was quantified by a cell migration assay. Qualitative immunohistochemistry and confocal laser microscopy were also used at day 10.

RESULTS

Many labeled synovial cells were observed within the tendon to which the visceral surface of the synovium graft was facing. Migrated cells were also observed on the parietal side, but there were fewer cells compared to visceral surface cells. Migrating cells all expressed α-smooth muscle actin.

CONCLUSION

We found that graft orientation affected cell migration. Whether this finding has clinical significance awaits in vivo study.

The attachment of intrinsic and extrinsic, mobilized and immobilized adhesion cells to collagen and fibronectin

This study investigated the attachment of intrinsic and extrinsic, mobilized and immobilized adhesion cells to the extracellular matrix. Five New Zealand White rabbit forepaws were dissected to isolate the flexor tendon core, tendon surface and synovial sheath, which were explanted separately. A further 10 animals were subjected to flexor tendon injuries, randomized to either mobilization or immobilization, and adhesions were explanted at 2 weeks. Cell groups were tested for attachment to collagen type-I or fibronectin and morphometric analysis was made. The attachment of intrinsic tendon cells and adhesion cells from mobilized tendons to both matrix proteins was statistically significantly greater than that of extrinsic tendon cells and adhesion cells from immobilized tendons. Adhesion cells from mobilized tendons were statistically significantly more elongated, which may correlate with the deposition of a more organized matrix. Because the synovial sheath cells were least attached to matrix proteins, selective treatments that reduce cell attachment may be used to exclude them, without inhibiting intrinsic tendon healing.

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.

The cellular biology of flexor tendon adhesion formation: an old problem in a new paradigm

Intrasynovial flexor tendon injuries of the hand can frequently be complicated by tendon adhesions to the surrounding sheath, limiting finger function. We have developed a new tendon injury model in the mouse to investigate the three-dimensional cellular biology of intrasynovial flexor tendon healing and adhesion formation. We investigated the cell biology using markers for inflammation, proliferation, collagen synthesis, apoptosis, and vascularization/myofibroblasts. Quantitative immunohistochemical image analysis and three-dimensional reconstruction with cell mapping was performed on labeled serial sections. Flexor tendon adhesions were also assessed 21 days after wounding using transmission electron microscopy to examine the cell phenotypes in the wound. When the tendon has been immobilized, the mouse can form tendon adhesions in the flexor tendon sheath. The cell biology of tendon healing follows the classic wound healing response of inflammation, proliferation, synthesis, and apoptosis, but the greater activity occurs in the surrounding tissue. Cells that have multiple "fibripositors" and cells with cytoplasmic protrusions that contain multiple large and small diameter fibrils can be found in the wound during collagen synthesis. In conclusion, adhesion formation occurs due to scarring between two damaged surfaces. The mouse model for flexor tendon injury represents a new platform to study adhesion formation that is genetically tractable.

Effects of crystalline glucocorticoid triamcinolone acetonide on cultered human supraspinatus tendon cells

BACKGROUND

Rotator cuff tears are a common cause of shoulder pain and impairment. Subacromial glucocorticoid injections are widely used for treatment of epiphenomenons of chronic impingement syndrome with the possible side effects of tendon rupture and impaired tendon healing.

METHODS

Using qRT-PCR, western blot, immunoflourescence, and measurement of 3H-thymidine uptake we investigated the effects of the crystalline glucocorticoid triamcinolone acetonide (TAA) when added to the culture medium of isolated human rotator cuff tendon cells.

RESULTS

After 2 weeks of incubation, the cells had lost their fibroblastic appearance and parallel orientation, which is characteristic of cellular degeneration in vivo. Moreover, expression and secretion of collagen I was strongly reduced, and there was a decrease in proliferation rate. Cell migration was blocked and the rate of expression of the matrix metalloproteinases MMP2, MMP8, MMP9, and MMP13 was reduced, but expression of TIMP1 (a tissue inhibitor of MMPs) was upregulated, indicating a reduction in the cellular capacity for tendon repair. In addition, changes in cellular differentiation were observed: the number of adipocytes increased and levels of the protein Sox9-a marker of differentiating and mature chondrocytes-were elevated in triamcinolone acetonide treated cells.

INTERPRETATION

These results may indicate that the use of TAA is one reason for weaker mechanical tendon properties and for the high rate of re-rupture after supraspinatus tendon repair.

Roles and regulation of Thy-1, a context-dependent modulator of cell phenotype

Thy-1 or CD90 is a glycophosphatidylinositol-linked glycoprotein expressed on the surface of neurons, thymocytes, subsets of fibroblasts, endothelial cells, mesangial cells and some hematopoietic cells. Thy-1 is evolutionarily conserved, developmentally regulated, and often has dramatic effects on cell phenotype; however, the effects vary between and in some cases within cell types and tissues, and between similar tissues in different species, indicating that the biological role of Thy-1 is context-dependent. Thy-1 exists in soluble form in some body fluids; however, the mechanisms of its shedding are unknown. In addition, Thy-1 expression can be regulated by epigenetic silencing. Because Thy-1 modulates many basic cellular processes and is involved in the pathogenesis of a number of diseases, it is important to better understand its regulation.

Thy-1 is an in vivo and in vitro marker of liver myofibroblasts

Thy-1, a glycophosphatidylinositol-linked glycoprotein of the outer membrane leaflet, has been described in myofibroblasts of several organs. Previous studies have shown that, in fetal liver, Thy-1 is expressed in a subpopulation of ductular/progenitor cells. The aim of this study has been to investigate whether the liver myofibroblasts belong to the Thy-1-positive subpopulation of the adult liver. The expression of Thy-1 has been studied in normal rat liver, in the rat liver regeneration model following 2-acetylaminofluorene treatment and partial hepatectomy (AAF/PH), and in isolated rat liver cells, at the mRNA and protein levels. In normal rat liver, Thy-1 is detected in sparse cells of the periportal area, whereas 7 days after PH in the AAF/PH model, a marked increase of the number of Thy-1-positive cells is detectable by immunohistochemistry. Comparative immunohistochemical analysis has revealed the co-localization of Thy-1 and smooth muscle actin, but not of Thy-1 and cytokeratin-19, both in normal rat liver and in the AAF/PH model. Investigation of isolated rat liver cell populations has confirmed that liver myofibroblasts are Thy-1-positive cells, whereas hepatocytes, hepatic stellate cells, and liver macrophages are not. Thy-1 is the first cell surface marker for identifying liver myofibroblasts in vivo and in vitro.

Tissue repair, contraction, and the myofibroblast

After the first description of the myofibroblast in granulation tissue of an open wound by means of electron microscopy, as an intermediate cell between the fibroblast and the smooth muscle cell, the myofibroblast has been identified both in normal tissues, particularly in locations where there is a necessity of mechanical force development, and in pathological tissues, in relation with hypertrophic scarring, fibromatoses and fibrocontractive diseases as well as in the stroma reaction to epithelial tumors. It is now accepted that fibroblast/myofibroblast transition begins with the appearance of the protomyofibroblast, whose stress fibers contain only beta- and gamma-cytoplasmic actins and evolves, but not necessarily always, into the appearance of the differentiated myofibroblast, the most common variant of this cell, with stress fibers containing alpha-smooth muscle actin. Myofibroblast differentiation is a complex process, regulated by at least a cytokine (the transforming growth factor-beta1), an extracellular matrix component (the ED-A splice variant of cellular fibronectin), as well as the presence of mechanical tension. The myofibroblast is a key cell for the connective tissue remodeling that takes place during wound healing and fibrosis development. On this basis, the myofibroblast may represent a new important target for improving the evolution of such diseases as hypertrophic scars, and liver, kidney or pulmonary fibrosis.