Interleukin-1β Increases Elasticity of Human Bioartificial Tendons

The Therapeutic Effect of iMSC-Derived Small Extracellular Vesicles on Tendinopathy Related Pain Through Alleviating Inflammation: An in vivo and in vitro Study

Background

Tendinopathy is a common cause of tendon pain. However, there is a lack of effective therapies for managing tendinopathy pain, despite the pain being the most common complaint of patients. This study aimed to evaluate the therapeutic effect of small extracellular vesicles released from induced pluripotent stem cell-derived mesenchymal stem cells (iMSC-sEVs) on tendinopathy pain and explore the underlying mechanisms.

Methods

Rat tendinopathy model was established and underwent the injection of iMSC-sEVs to the quadriceps tendon one week after modeling. Pain-related behaviors were measured for the following four weeks. Tendon histology was assessed four weeks after the injection. To further investigate the potential mechanism, tenocytes were stimulated with IL-1β to mimic tendinopathy in vitro. The effect of iMSC-sEVs on tenocyte proliferation and the expression of proinflammatory cytokines were measured by CCK-8, RT-qPCR, and ELISA. RNA-seq was further performed to systematically analyze the related global changes and underlying mechanisms.

Results

Local injection of iMSC-sEVs was effective in alleviating pain in the tendinopathy rats compared with the vehicle group. Tendon histology showed ameliorated tendinopathy characteristics. Upon iMSC-sEVs treatment, significantly increased tenocyte proliferation and less expression of proinflammatory cytokines were observed. Transcriptome analysis revealed that iMSC-sEVs treatment upregulated the expression of genes involved in cell proliferation and downregulated the expression of genes involved in inflammation and collagen degeneration.

Conclusion

Collectively, this study demonstrated iMSC-sEVs protect tenocytes from inflammatory stimulation and promote cell proliferation as well as collagen synthesis, thereby relieving pain derived from tendinopathy. As a cell-free regenerative treatment, iMSC-sEVs might be a promising therapeutic candidate for tendinopathy.

Reparative and Maladaptive Inflammation in Tendon Healing

Tendon injuries are common and debilitating, with non-regenerative healing often resulting in chronic disease. While there has been considerable progress in identifying the cellular and molecular regulators of tendon healing, the role of inflammation in tendon healing is less well understood. While inflammation underlies chronic tendinopathy, it also aids debris clearance and signals tissue repair. Here, we highlight recent findings in this area, focusing on the cells and cytokines involved in reparative inflammation. We also discuss findings from other model systems when research in tendon is minimal, and explore recent studies in the treatment of human tendinopathy to glean further insights into the immunobiology of tendon healing.

Species variations in tenocytes' response to inflammation require careful selection of animal models for tendon research

For research on tendon injury, many different animal models are utilized; however, the extent to which these species simulate the clinical condition and disease pathophysiology has not yet been critically evaluated. Considering the importance of inflammation in tendon disease, this study compared the cellular and molecular features of inflammation in tenocytes of humans and four common model species (mouse, rat, sheep, and horse). While mouse and rat tenocytes most closely equalled human tenocytes’ low proliferation capacity and the negligible effect of inflammation on proliferation, the wound closure speed of humans was best approximated by rats and horses. The overall gene expression of human tenocytes was most similar to mice under healthy, to horses under transient and to sheep under constant inflammatory conditions. Humans were best matched by mice and horses in their tendon marker and collagen expression, by horses in extracellular matrix remodelling genes, and by rats in inflammatory mediators. As no single animal model perfectly replicates the clinical condition and sufficiently emulates human tenocytes, fit-for-purpose selection of the model species for each specific research question and combination of data from multiple species will be essential to optimize translational predictive validity.

Interleukin-1β Modulation of the Mechanobiology of Primary Human Pulmonary Fibroblasts: Potential Implications in Lung Repair

Pro-inflammatory cytokines like interleukin-1β (IL-1β) are upregulated during early responses to tissue damage and are expected to transiently compromise the mechanical microenvironment. Fibroblasts are key regulators of tissue mechanics in the lungs and other organs. However, the effects of IL-1β on fibroblast mechanics and functions remain unclear. Here we treated human pulmonary fibroblasts from control donors with IL-1β and used Atomic Force Microscopy to unveil that IL-1β significantly reduces the stiffness of fibroblasts concomitantly with a downregulation of filamentous actin (F-actin) and alpha-smooth muscle (α-SMA). Likewise, COL1A1 mRNA was reduced, whereas that of collagenases MMP1 and MMP2 were upregulated, favoring a reduction of type-I collagen. These mechanobiology changes were functionally associated with reduced proliferation and enhanced migration upon IL-1β stimulation, which could facilitate lung repair by drawing fibroblasts to sites of tissue damage. Our observations reveal that IL-1β may reduce local tissue rigidity by acting both intracellularly and extracellularly through the downregulation of fibroblast contractility and type I collagen deposition, respectively. These IL-1β-dependent mechanical effects may enhance lung repair further by locally increasing pulmonary tissue compliance to preserve normal lung distension and function. Moreover, our results support that IL-1β provides innate anti-fibrotic protection that may be relevant during the early stages of lung repair.

A brief history of tendon and ligament bioreactors: Impact and future prospects

Bioreactors are powerful tools with the potential to model tissue development and disease in vitro. For nearly four decades, bioreactors have been used to create tendon and ligament tissue-engineered constructs in order to define basic mechanisms of cell function, extracellular matrix deposition, tissue organization, injury, and tissue remodeling. This review provides a historical perspective of tendon and ligament bioreactors and their contributions to this advancing field. First, we demonstrate the need for bioreactors to improve understanding of tendon and ligament function and dysfunction. Next, we detail the history and evolution of bioreactor development and design from simple stretching of explants to fabrication and stimulation of two- and three-dimensional constructs. Then, we demonstrate how research using tendon and ligament bioreactors has led to pivotal basic science and tissue-engineering discoveries. Finally, we provide guidance for new basic, applied, and clinical research utilizing these valuable systems, recognizing that fundamental knowledge of cell-cell and cell-matrix interactions combined with appropriate mechanical and chemical stimulation of constructs could ultimately lead to functional tendon and ligament repairs in the coming decades.

Different Frequency of Cyclic Tensile Strain Relates to Anabolic/Catabolic Conditions Consistent with Immunohistochemical Staining Intensity in Tenocytes

Tenocytes are mechanosensitive cells intimately adapting their expression profile and hence, their phenotype to their respective mechanomilieu. The immunolocalization and expression intensity of tenogenic, anabolic and catabolic markers in tenocytes in response to in vitro mechanical loading have not been monitored by immunohistochemical staining (IHC). Thus, we investigated the association between IHC intensities, different stimulation frequencies, and tenogenic metabolism using a versatile mechanical stretcher. Primary tenocytes obtained from murine Achilles tendons were transferred to poly(dimethylsiloxane) (PDMS) elastomeric chamber. Chambers were cyclically stretched by 5% in uniaxial direction at a variation of tensile frequency (1 or 2 Hz) for 3 h. After stretching, cell physiology, IHC intensities of tendon-related markers, and protein level of the angiogenesis marker vascular endothelial growth factor (VEGF) were evaluated. Cell proliferation in tenocytes stimulated with 1 Hz stretch was significantly higher than with 2 Hz or without stretch, while 2 Hz stretch induced significantly reduced cell viability and proliferation with microscopically detectable apoptotic cell changes. The amount of scleraxis translocated into the nuclei and tenomodulin immunoreactivity of tenocytes treated with stretch were significantly higher than of non-stretched cells. The collagen type-1 expression level in tenocytes stretched at 1 Hz was significantly higher than in those cultivated with 2 Hz or without stretching, whereas the matrix metalloproteinase (MMP)-1 and MMP-13 immunoreactivities of cells stretched at 2 Hz were significantly higher than in those stimulated with 1 Hz or without stretching. The secreted VEGF-protein level of tenocytes stretched at 2 Hz was significantly higher than without stretching. Our IHC findings consistent with cell physiology suggest that appropriate stretching can reproduce in vitro short-term tenogenic anabolic/catabolic conditions and allow us to identify an anabolic stretching profile.

A novel mechanism for the protection of embryonic stem cell derived tenocytes from inflammatory cytokine interleukin 1 beta

Interleukin 1β (IL-1β) is upregulated following tendon injury. Here we demonstrate that in adult and fetal tenocytes IL-1β increases the expression of matrix metalloproteinases, tenascin-C and Sox9 and decreases the expression of scleraxis and cartilage oligomeric matrix protein. When cultured in 3-dimensional collagen gels adult and fetal tenocytes exposed to IL-1β have reduced contraction ability and generate tendon-like constructs with a lower storage modulus. In contrast, equine embryonic stem cell (ESC) derived tenocytes exposed to IL-1β exhibit no changes in gene expression and generate identical tendon-like constructs. We propose that ESC-derived tenocytes do not respond to IL-1β due to their low expression of interleukin 1 (IL-1) receptor 1 and high expression of the decoy receptor IL-1 receptor 2 and IL-1 receptor antagonist protein (IL1Ra). This may make ESC-derived tenocytes an advantageous source of cells for tissue regeneration and allow the development of novel pharmaceutical interventions to protect endogenous cells from inflammation.

Chemically Modified Messenger RNA: Modified RNA Application for Treatment of Achilles Tendon Defects

Different regenerative medicine approaches for tendon healing exist. Recently, especially gene therapy gained popularity. However, potential mutagenic and immunologic effects might prevent its translation to clinical research. Chemically modified mRNA (cmRNA) might bypass these limitations of gene therapy. Therefore, the purpose of this study was to evaluate the early healing properties of Achilles tendon defects in rats treated with basic fibroblast growth factor (bFGF) cmRNA. Forty male Lewis rats were used for the study and randomly assigned to two study groups: (1) treatment with cmRNA coding for bFGF and (2) noncoding cmRNA control. Protein expression was measured using in vivo bioluminescence imaging at 24, 48, and 72 h, as well as 14 days. Animals were euthanized 2 weeks following surgery. Biomechanical, histological, and immunohistological analyses were performed with the significance level set at p < 0.05. Protein expression was evident for 3 days. At 14 days, bioluminescence imaging revealed only little protein expression. Biomechanically, tendons treated with bFGF cmRNA showed a construct stiffness closer to the healthy contralateral side when compared with the control group (p = 0.034), without any significant differences in terms of load to failure. Hematoxylin and eosin staining detected no side effects of the treatment, as signs of inflammation, or necrosis. Furthermore, it revealed the shape of the nuclei to be more oval in the bFGF group in the tendon midsubstance (p = 0.043) with a reduced cell count (p = 0.035). Immunohistological staining for type I, II, III, and IV collagen did not differ significantly between the two groups. In conclusion, this pilot study demonstrates the feasibility of a novel messenger RNA (mRNA)-based therapy for Achilles tendon defects using chemically modified mRNA coding for bFGF.

The roles of inflammatory mediators and immunocytes in tendinopathy

Tendinopathy is a common disease of the musculoskeletal system, particularly in athletes and sports amateurs. In this review, we will present evidence for the critical role of inflammatory mediators and immunocytes in the pathogenesis of tendinopathy and the efficacy of current antiinflammatory therapy and regenerative medicine in the clinic. We hereby propose a hypothesis that in addition to pulling force there may be compressive forces being exerted on the tendon during physical activities, which may initiate the onset of tendinopathy. We performed literature searches on MEDLINE from the inception of this review to February 2018. No language restrictions were imposed. The search terms were as follows: ("Tendinopathy"[Mesh] OR "Tendon Injuries"[Mesh] OR "Tendinitis"[Mesh] OR "Tendon"[Mesh]) AND (Inflammation OR "Inflammatory mediator*" OR Immunocyte*) OR ("anti inflammatory*" OR "regenerative medicine"). Inclusion criteria included articles that were original and reliable, with the main contents being highly relevant to our review. Exclusion criteria included articles that were not available online or have not been published. We scanned the abstract of these articles first. This was then followed by a careful screening of the articles which might be suitable for our review. Finally, 84 articles were selected as references. This review article is written in the narrative form. The translational potential of this article: Understanding the mechanisms of inflammation and existing antiinflammatory and regenerative therapies is key to the development of therapeutic strategies in tendinopathy.

Effects of Tumor Necrosis Factor Inhibitor on Stress-Shielded Tendons

Mechanical stress plays an important role in preserving the integrity of bone and ligament. Stress shielding reduces mechanical load on bone or tendons, resulting in tissue degradation. Previous studies showed that deterioration of the tendon structure during stress shielding is associated with elevated expression of tumor necrosis factor (TNF)-α. This study examined the therapeutic potential of the TNF inhibitor etanercept in preventing morphologic deterioration of the Achilles tendon after stress shielding. Rats (N=48) were exposed to stress shielding of the left Achilles tendon and treated with etanercept or phosphate-buffered saline for 2 or 4 weeks. The right Achilles tendons were used as controls. After 2 or 4 weeks, stress-shielded tendons appeared less smooth than control tendons, and the stress-shielded tendons formed adhesions with surrounding tissues. Transmission electron microscopy also showed disarray of the collagen fibrils and a significant increase in the number of small-diameter collagen fibrils. These changes were associated with increased expression of TNF-α, matrix metalloproteinase (MMP)-13, MMP-3, collagen I, and collagen III. Treatment with 2 weeks of etanercept injection reduced morphologic changes in collagen organization and structure induced by stress shielding. Etanercept treatment also attenuated upregulation of MMP-13, MMP-3, and collagen III levels. However, no significant difference was observed between the etanercept group and the phosphate-buffered saline group after 4 weeks of treatment. The current findings show that TNF-α inhibition can protect against the early stages of tendon tissue remodeling induced by stress shielding, but additional interventions may be necessary to prevent tendon degeneration with long-term stress shielding. [Orthopedics. 2017; 40(1):49-55.].

Impact of mechanical stretch on the cell behaviors of bone and surrounding tissues

Mechanical loading is recognized to play an important role in regulating the behaviors of cells in bone and surrounding tissues in vivo. Many in vitro studies have been conducted to determine the effects of mechanical loading on individual cell types of the tissues. In this review, we focus specifically on the use of the Flexercell system as a tool for studying cellular responses to mechanical stretch. We assess the literature describing the impact of mechanical stretch on different cell types from bone, muscle, tendon, ligament, and cartilage, describing individual cell phenotype responses. In addition, we review evidence regarding the mechanotransduction pathways that are activated to potentiate these phenotype responses in different cell populations.

Tendon mechanobiology: Current knowledge and future research opportunities

Tendons mainly function as load-bearing tissues in the muscloskeletal system; transmitting loads from muscle to bone. Tendons are dynamic structures that respond to the magnitude, direction, frequency, and duration of physiologic as well as pathologic mechanical loads via complex interactions between cellular pathways and the highly specialized extracellular matrix. This paper reviews the evolution and current knowledge of mechanobiology in tendon development, homeostasis, disease, and repair. In addition, we review several novel mechanotransduction pathways that have been identified recently in other tissues and cell types, providing potential research opportunities in the field of tendon mechanobiology. We also highlight current methods, models, and technologies being used in a wide variety of mechanobiology research that could be investigated in the context of their potential applicability for answering some of the fundamental unanswered questions in this field. The article concludes with a review of the major questions and future goals discussed during the recent ORS/ISMMS New Frontiers in Tendon Research Conference held on September 10 and 11, 2014 in New York City.

Progress in cell-based therapies for tendon repair

The last decade has seen significant developments in cell therapies, based on permanently differentiated, reprogrammed or engineered stem cells, for tendon injuries and degenerative conditions. In vitro studies assess the influence of biophysical, biochemical and biological signals on tenogenic phenotype maintenance and/or differentiation towards tenogenic lineage. However, the ideal culture environment has yet to be identified due to the lack of standardised experimental setup and readout system. Bone marrow mesenchymal stem cells and tenocytes/dermal fibroblasts appear to be the cell populations of choice for clinical translation in equine and human patients respectively based on circumstantial, rather than on hard evidence. Collaborative, inter- and multi-disciplinary efforts are expected to provide clinically relevant and commercially viable cell-based therapies for tendon repair and regeneration in the years to come.

Interleukin-1β and tumor necrosis factor-α increase stiffness and impair contractile function of articular chondrocytes

Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) are major proinflammatory cytokines involved in osteoarthritis (OA). These cytokines disturb chondrocyte metabolism by suppressing the synthesis of extracellular matrix proteins and stimulating the release of catabolic proteases, but little is known about their role in chondrocyte mechanics. Thus, the aim of this study was to measure the effects of IL-1β and TNF-α on the mechanical properties of the chondrocytes. Chondrocytes from goat knee joints were cultured in 96-well plates. The cellular stiffness and contractile function were probed using optical magnetic twisting cytometry, the cytoskeleton and the expression of extracellular matrix proteins were visualized using immunofluorescent staining, and chondrocyte phenotypical expression was measured by western blot analysis. Results showed that chondrocyte stiffness was dramatically decreased by disruption of F-actin but was unaffected by disruption of the intermediate filament vimentin. Treatment with 10 ng/ml IL-1β or 40 ng/ml TNF-α for 24 h substantially increased the expression level of F-actin and cellular stiffness, and impaired cell stiffening in response to the contractile agonist histamine, but these effects were blocked by the Rho-associated protein kinase inhibitor Y27632. In conclusion, IL-1β and TNF-α substantially change the mechanical properties of the chondrocytes in vitro. While changes of chondrocyte mechanics in vivo during OA progression remain unclear, this finding reveals a prominent role of these cytokines in cellular mechanics and provides insight for anti-cytokine therapies of OA.

Tenocyte activation and regulation of complement factors in response to in vitro cell injury

Inferior tendon healing can lead to scarring and tendinopathy. The role of complement in tendon healing is still unclear. The aim of this study was to understand tenocytes response to mechanical injury and whether complement is regulated by injury. Tenocytes were injured using an optimized automated scratch assay model. Using a self-assembled plotter system, 50 parallel lines of injury were created in a 6 cm diameter tenocyte cell layer. Tenocytes mitotic activity and survival post injury was assessed using FDA/ethidiumbromide assay. Furthermore, this injury model was combined with stimulation of the tenocytes with the complement split fragment C3a. Gene expression of C3aR, C5aR (CD88), CD46, CD55, tumor necrosis factor (TNF)α, interleukin (IL)-1β, matrix metalloproteinase (MMP)-1 was analyzed. Immunolabeling for C5aR and CD55 was performed. An enhanced mitotic activity and some dead cells were detected in the vicinity of the scratches. Gene expression of the C3aR was suppressed after 4 h but induced after 24 h post injury. C5aR was down-regulated at 24 h, CD46 and CD55 were induced at 24 h in response to injury and CD55 was also elevated at 4 h. MMP-1 was upregulated by injury but both proinflammatory cytokines remained mainly unaffected. Combination of injury with C3a stimulation led to an enhanced C3aR, CD55 and TNFα gene expression. According to the gene expression data, the protein expression of C5aR was reduced and that of CD55 induced. In summary, a specific response of complement regulation was found in mechanically injured tenocytes which may be involved in healing responses.

Fiber-aligned polymer scaffolds for rotator cuff repair in a rat model

BACKGROUND

Repair techniques of rotator cuff tendon tears have improved in recent years; nonetheless, the failure rate remains high. Despite the availability of various graft materials for repair augmentation, there has yet to be a biomechanical study using fiber-aligned scaffolds in vivo. The objective of this study was to evaluate the efficacy of fiber-aligned nanofibrous polymer scaffolds as a potential treatment-delivery vehicle in a rat rotator cuff injury model.

MATERIALS AND METHODS

Scaffolds with and without sacrificial fibers were fabricated via electrospinning and implanted to augment supraspinatus repair in rats. Repairs without scaffold augmentation were also performed to serve as controls. Rats were sacrificed at 4 and 8 weeks postoperatively, and repairs were evaluated histologically and biomechanically.

RESULTS

Both scaffold formulations remained in place, with more noticeable cellular infiltration and colonization at 4 and 8 weeks after injury and repair for scaffolds lacking sacrificial fibers. Specimens with scaffolds were larger in cross-sectional area compared with controls. Biomechanical testing revealed no significant differences in structural properties between the groups. Some apparent material properties were significantly reduced in the scaffold groups. These reductions were due to increases in cross-sectional area, most likely caused by the extra thickness of the implanted scaffold material. No differences were observed between the 2 scaffold groups.

CONCLUSIONS

No adverse effect of surgical implantation of overlaid fiber-aligned scaffolds on structural properties of supraspinatus tendons in rat rotator cuff repair was demonstrated, validating this model as a platform for targeted delivery.

Biological factors in the pathogenesis of rotator cuff tears

Rotator cuff tears are common, and lead to shoulder pain and functional impairment. Despite their frequency and related disability, etiology and pathogenesis are still debated. Multiple factors contribute to tears of the rotator cuff. Extrinsic factors are anatomic variables, such as acromial morphologic characteristics, os acromiale, and acromial spurs that compress the rotator cuff by bony impingement or direct pressure from the surrounding soft tissue. Intrinsic factors arise from the tendon itself, because of tensile overload, aging, microvascular supply, traumatisms, or degeneration. Little information is available from a cellular and molecular point of view. We reviewed the biological factors involved in the pathogenesis of rotator cuff tears. Understanding the mechanism of rotator cuff pathology would facilitate the rationale for therapeutic interventions, by guiding the design, selection, and implementation of treatment strategies such as biologic modulation and preventive measures.

The role of pro-inflammatory and immunoregulatory cytokines in tendon healing and rupture: new insights

Owing to limited self-healing capacity, tendon ruptures and healing remain major orthopedic challenges. Increasing evidence suggests that post-traumatic inflammatory responses, and hence, cytokines are involved in both cases, and also in tendon exercise and homeostasis. This review summarizes interrelations known between the cytokines interleukin (IL)-1β, tumor necrosis factor (TNF)α, IL-6 and vascular endothelial growth factor (VEGF) in tendon to assess their role in tendon damage and healing. Exogenic cytokine sources are blood-derived leukocytes that immigrate in damaged tendon. Endogenous expression of IL-1β, TNFα, IL-6, IL-10 and VEGF was demonstrated in tendon-derived cells. As tendon is a highly mechanosensitive tissue, cytokine homeostasis and cell survival underlie an intimate balance between adequate biomechanical stimuli and disturbance through load deprivation and overload. Multiple interrelations between cytokines and tendon extracellular matrix (ECM) synthesis, catabolic mediators e.g. matrix-degrading enzymes, inflammatory and angiogenic factors (COX-2, PGE2, VEGF, NO) and cytoskeleton assembly are evident. Pro-inflammatory cytokines affect ECM homeostasis, accelerate remodeling, amplify biomechanical adaptiveness and promote tenocyte apoptosis. This multifaceted interplay might both contribute to and interfere with healing. Much work must be undertaken to understand the particular interrelation of these inflammatory and regulatory mediators in ruptured tendon and healing, which has relevance for the development of novel immunoregulatory therapeutic strategies.

Effect of pro-inflammatory and immunoregulatory cytokines on human tenocytes

Tendon injury induces a local inflammatory response, characterized by the induction of pro-inflammatory cytokines. The aim of the present study was to analyze the effects of TNFalpha, IL-6 and IL-10 on key parameters of tendon homeostasis. Cultured primary human tenocytes were treated with the recombinant cytokines IL-6, IL-10, TNFalpha, or combinations of TNFalpha with IL-6 and IL-10 (10 ng/mL, 6, 24 h). Expression of type I collagen, elastin, MMP-1, TNFalpha, IL-1beta, IL-6, IL-10, and suppressors of cytokine signaling (SOCS1, 3) was analyzed with the use of RTD-PCR, immunocytochemistry, and Western blot analysis. In response to TNFalpha, tenocytes reduced their type I collagen deposition but increased their elastin gene expression and highly upregulated their expression for MMP-1, pro-inflammatory (TNFalpha, IL-1beta) and immunoregulatory (IL-6, IL-10) cytokines. TNFalpha stimulation augmented SOCS1, whereas SOCS3 expression in tenocytes was also induced by IL-6. The treatment of tenocytes with IL-6 and IL-10 had no effect on cytokine expression. Neither IL-6 nor IL-10 modulated the observed effects of TNFalpha significantly. These results indicate that TNFalpha strongly activates the tenocytes to amplify their own TNFalpha expression and, subsequently, that of other regulatory cytokines and matrix degrading enzymes. However, the impact of IL-6 and IL-10 on tenocytes remains unclear.

Fetal dermal fibroblasts exhibit enhanced growth and collagen production in two- and three-dimensional culture in comparison to adult fibroblasts

The high morbidity of tendon injuries and the poor outcomes observed following repair or replacement have stimulated interest in regenerative approaches to treatment and, in particular, the use of cell-based analogues as alternatives to autologous and allogeneic graft repair. Given the known regenerative properties of fetal tissues, the objective of this study was to assess the biological and mechanical properties of tissue-engineered three-dimensional (3D) composites seeded with fetal skin cells. Dermal fibroblasts were isolated from pregnant rats and their fetuses and characterized in monolayer culture and on 3D resorbable polyester scaffolds. To determine the differences between fetal and adult fibroblasts, DNA, total protein and types I and III collagen production were measured. In addition, morphology and mechanical properties of the 3D constructs were examined. In monolayer culture, fetal fibroblasts produced significantly more types I and III collagen and displayed serum-independent growth, while adult fibroblasts elaborated less collagen and exhibited reduced cell spreading and attachment under low-serum conditions. In 3D culture, fetal constructs appeared more developed based on gross examination, with significantly more total DNA, total protein and normalized type I collagen production compared to adult specimens. Finally, after 35 days, fetal fibroblast-seeded constructs possessed superior mechanical properties compared to adult samples. Taken together, these findings indicate that fetal dermal fibroblasts may be an effective source of cells for fabricating tissue equivalents to regenerate injured tendons.

Cytokines and apoptosis in supraspinatus tendinopathy

The role of inflammatory cells and their products in tendinopathy is not completely understood. Pro-inflammatory cytokines are upregulated after oxidative and other forms of stress. Based on observations that increased cytokine expression has been demonstrated in cyclically-loaded tendon cells we hypothesised that because of their role in oxidative stress and apoptosis, pro-inflammatory cytokines may be present in rodent and human models of tendinopathy. A rat supraspinatus tendinopathy model produced by running overuse was investigated at the genetic level by custom micro-arrays. Additionally, samples of torn supraspinatus tendon and matched intact subscapularis tendon were collected from patients undergoing arthroscopic shoulder surgery for rotator-cuff tears and control samples of subscapularis tendon from ten patients with normal rotator cuffs undergoing arthroscopic stabilisation of the shoulder were also obtained. These were all evaluated using semiquantitative reverse transcription polymerase chain-reaction and immunohistochemistry.

We identified significant upregulation of pro-inflammatory cytokines and apoptotic genes in the rodent model (p = 0.005). We further confirmed significantly increased levels of cytokine and apoptotic genes in human supraspinatus and subscapularis tendon harvested from patients with rotator cuff tears (p = 0.0008).

These findings suggest that pro-inflammatory cytokines may play a role in tendinopathy and may provide a target for preventing tendinopathies.

A new microrheometric approach reveals individual and cooperative roles for TGF-beta1 and IL-1beta in fibroblast-mediated stiffening of collagen gels

The stiffness of the extracellular matrix can profoundly influence cell and tissue behaviors. Thus there is an emerging emphasis on understanding how matrix mechanical environments are established, regulated, and modified. Here we develop a microrheometric assay to measure the mechanical properties of a model extracellular matrix (type I collagen gel) and use it to explore cytokine-induced, cell-mediated changes in matrix mechanical properties. The microrheometric assay uses micron-scale ferrimagnetic beads embedded within collagen gels during fibrillogenesis. The beads are magnetized, then subjected to a twisting field, with the aggregate rotation of the beads measured by a magnetometer. The degree of bead rotation reflects the stiffness of the surrounding matrix. We show that the microscale assay provides stiffness measures for collagen gels comparable to those obtained with standard macroscale rheometry. To demonstrate the utility of the assay for biological discovery, we measure stiffness changes in fibroblast-populated collagen gels exposed to three concentrations of six cytokines over 2 to 14 days. Among the cytokines tested, transforming growth factor-beta1 and interleukin-1beta enhanced matrix stiffness, and together exerted cooperative effects on cellular modulation of matrix mechanics. The microrheometry approach developed here should accelerate the discovery of biological pathways orchestrating cellular modulation of matrix mechanics.