Growth/differentiation factor-5 modulates the synthesis and expression of extracellular matrix and cell-adhesion-related molecules of rat Achilles tendon fibroblasts

Therapeutic potential of GDF-5 for enhancing tendon regenerative healing

Tendon injury is a common disorder of the musculoskeletal system, with a higher possibility of occurrence in elderly individuals and athletes. After a tendon injury, the tendon suffers from inadequate and slow healing, resulting in the formation of fibrotic scar tissue, ending up with inferior functional properties. Therapeutic strategies involving the application of growth factors have been advocated to promote tendon healing. Growth and differentiation-5 (GDF-5) represents one such factor that has shown promising effect on tendon healing in animal models and in vitro cultures. Although promising, these studies are limited as the molecular mechanisms by which GDF-5 exerts its effect remain incompletely understood. Starting from broadly introducing essential elements of current understanding about GDF-5, the present review aims to define the effect of GDF-5 and its possible mechanisms of action in tendon healing. Nevertheless, we still need more in vivo studies to explore dosage, application time and delivery strategy of GDF-5, so as to pave the way for future clinical translation.

Scaffold-Mediated Immunoengineering as Innovative Strategy for Tendon Regeneration

Tendon injuries are at the frontier of innovative approaches to public health concerns and sectoral policy objectives. Indeed, these injuries remain difficult to manage due to tendon’s poor healing ability ascribable to a hypo-cellularity and low vascularity, leading to the formation of a fibrotic tissue affecting its functionality. Tissue engineering represents a promising solution for the regeneration of damaged tendons with the aim to stimulate tissue regeneration or to produce functional implantable biomaterials. However, any technological advancement must take into consideration the role of the immune system in tissue regeneration and the potential of biomaterial scaffolds to control the immune signaling, creating a pro-regenerative environment. In this context, immunoengineering has emerged as a new discipline, developing innovative strategies for tendon injuries. It aims at designing scaffolds, in combination with engineered bioactive molecules and/or stem cells, able to modulate the interaction between the transplanted biomaterial-scaffold and the host tissue allowing a pro-regenerative immune response, therefore hindering fibrosis occurrence at the injury site and guiding tendon regeneration. Thus, this review is aimed at giving an overview on the role exerted from different tissue engineering actors in leading immunoregeneration by crosstalking with stem and immune cells to generate new paradigms in designing regenerative medicine approaches for tendon injuries.

Aligned silk fibroin/poly-3-hydroxybutyrate nanofibrous scaffolds seeded with adipose-derived stem cells for tendon tissue engineering

In this work we investigated tenogenic differentiation of adipose-derived mesenchymal stem cells (AdMSCs), which were seeded onto silk fibroin/poly-3-hydroxybutyrate (SF/P3HB) scaffolds with aligned topography, and high mechanical strength. The electrospinning process was optimized by using the response surface method (RSM) and SF/P3HB nanofibrous matrices with a total polymer concentration of 5% (SF: PHB = 3: 1), flow rate 1 mL/h, collector rotation speed 2000 rpm, applied voltage 14 kV, and collector distance 25 cm were obtained. The average fiber diameter was 699 ± 203 nm and 80% of the nanofibers were aligned within the ±15^o range. SF reinforcement reduced the crystallinity of P3HB, and the elastic modulus was found to be 197.0 ± 7.7 MPa. The scaffolds showed bacteriostatic effect. A 21-day of cell culture study was performed with rat rAdMSCs in the absence and presence of tenogenic differentiation factor-5 (GDF-5). The results demonstrated that SF/P3HB scaffolds allow the cells to proliferate and differentiate to the tenocytes. However, no significant effect of GDF-5 on the differentiation of cells was observed. These findings indicated that our aligned SF/P3HB scaffolds have a significant potential to be used for tendon tissue engineering.

3D Biomimetic Scaffold for Growth Factor Controlled Delivery: An In-Vitro Study of Tenogenic Events on Wharton's Jelly Mesenchymal Stem Cells

The present work described a bio-functionalized 3D fibrous construct, as an interactive teno-inductive graft model to study tenogenic potential events of human mesenchymal stem cells collected from Wharton’s Jelly (hWJ-MSCs). The 3D-biomimetic and bioresorbable scaffold was functionalized with nanocarriers for the local controlled delivery of a teno-inductive factor, i.e., the human Growth Differentiation factor 5 (hGDF-5). Significant results in terms of gene expression were obtained. Namely, the up-regulation of Scleraxis (350-fold, p ≤ 0.05), type I Collagen (8-fold), Decorin (2.5-fold), and Tenascin-C (1.3-fold) was detected at day 14; on the other hand, when hGDF-5 was supplemented in the external medium only (in absence of nanocarriers), a limited effect on gene expression was evident. Teno-inductive environment also induced pro-inflammatory, (IL-6 (1.6-fold), TNF (45-fold, p ≤ 0.001), and IL-12A (1.4-fold)), and anti-inflammatory (IL-10 (120-fold) and TGF-β1 (1.8-fold)) cytokine expression upregulation at day 14. The presented 3D construct opens perspectives for the study of drug controlled delivery devices to promote teno-regenerative events.

GDF-5 induces epidermal stem cell migration via RhoA-MMP9 signalling

The migration of epidermal stem cells (EpSCs) is critical for wound re-epithelization and wound healing. Recently, growth/differentiation factor-5 (GDF-5) was discovered to have multiple biological effects on wound healing; however, its role in EpSCs remains unclear. In this work, recombinant mouse GDF-5 (rmGDF-5) was found via live imaging in vitro to facilitate the migration of mouse EpSCs in a wound-scratch model. Western blot and real-time PCR assays demonstrated that the expression levels of RhoA and matrix metalloproteinase-9 (MMP9) were correlated with rmGDF-5 concentration. Furthermore, we found that rmGDF-5 stimulated mouse EpSC migration in vitro by regulating MMP9 expression at the mRNA and protein levels through the RhoA signalling pathway. Moreover, in a deep partial-thickness scald mouse model in vivo, GDF-5 was confirmed to promote EpSC migration and MMP9 expression via RhoA, as evidenced by the tracking of cells labelled with 5-bromo-2-deoxyuridine (BrdU). The current study showed that rmGDF-5 can promote mouse EpSC migration in vitro and in vivo and that GDF-5 can trigger the migration of EpSCs via RhoA-MMP9 signalling.

Stem Cells for the Regeneration of Tendon and Ligament: A Perspective

Tendons are structures that connect muscles to the bones in our body and transmit the force generated by contraction of the muscles to the bones. Ligaments are structures that connect bones to bones, with histological properties similar to tendons. In tendon and ligament tissue, there are very small amounts of cells similar to mesenchymal stem cells (MSCs) called tendon stem/progenitor cells (TSPCs), or tenogenic stem cells. While the role of specific growth factors and transcription factors is well established in the osteogenic and chondrogenic differentiation of stem cells, a consensus has not been established for tenogenic differentiation. Injuries to tendons and ligaments are very common, but natural healing is very slow and inefficient due to limited vascularization. Currently, there is no adequate method for restoring extensive tendon or ligament defects. Procedures addressing the unmet need for regeneration of these tissues are needed. In this review, the current knowledge, as well as the authors’ ideas and perspective on stem cell and regenerative medicine for tendon and ligament defects are presented.

Dose-Response Tendon-Specific Markers Induction by Growth Differentiation Factor-5 in Human Bone Marrow and Umbilical Cord Mesenchymal Stem Cells

Mesenchymal stem cells derived from human bone marrow (hBM-MSCs) are utilized in tendon tissue-engineering protocols while extra-embryonic cord-derived, including from Wharton's Jelly (hWJ-MSCs), are emerging as useful alternatives. To explore the tenogenic responsiveness of hBM-MSCs and hWJ-MSCs to human Growth Differentiation Factor 5 (hGDF-5) we supplemented each at doses of 1, 10, and 100 ng/mL of hGDF-5 and determined proliferation, morphology and time-dependent expression of tenogenic markers. We evaluated the expression of collagen types 1 (COL1A1) and 3 (COL3A1), Decorin (DCN), Scleraxis-A (SCX-A), Tenascin-C (TNC) and Tenomodulin (TNMD) noting the earliest and largest increase with 100 ng/mL. With 100 ng/mL, hBM-MSCs showed up-regulation of SCX-A (1.7-fold) at Day 1, TNC (1.3-fold) and TNMD (12-fold) at Day 8. hWJ-MSCs, at the same dose, showed up-regulation of COL1A1 (3-fold), DCN (2.7-fold), SCX-A (3.8-fold) and TNC (2.3-fold) after three days of culture. hWJ-MSCs also showed larger proliferation rate and marked aggregation into a tubular-shaped system at Day 7 (with 100 ng/mL of hGDF-5). Simultaneous to this, we explored the expression of pro-inflammatory (IL-6, TNF, IL-12A, IL-1β) and anti-inflammatory (IL-10, TGF-β1) cytokines across for both cell types. hBM-MSCs exhibited a better balance of pro-inflammatory and anti-inflammatory cytokines up-regulating IL-1β (11-fold) and IL-10 (10-fold) at Day 8; hWJ-MSCs, had a slight expression of IL-12A (1.5-fold), but a greater up-regulation of IL-10 (2.5-fold). Type 1 collagen and tenomodulin proteins, detected by immunofluorescence, confirming the greater protein expression when 100 ng/mL were supplemented. In the same conditions, both cell types showed specific alignment and shape modification with a length/width ratio increase, suggesting their response in activating tenogenic commitment events, and they both potential use in 3D in vitro tissue-engineering protocols.

Treatment of adhesions after Achilles tendon injury using focused ultrasound with targeted bFGF plasmid-loaded cationic microbubbles

Nonviral targeting technology has become promising as a form of gene therapy for diseases and injuries, such as Achilles tendon injuries. In this study, we used avidin–biotin bridge and positive–negative charge attractions to load the intercellular adhesion molecule-1 (ICAM-1) antibody and the basic fibroblast growth factor (bFGF) plasmid onto the surface of the microbubbles. The saturated loading capacity for 1.1 × 108 microbubble was 6.55 ± 0.53 µg. We established the ICAM-1 antigen microenvironment using tumor necrosis factor-alpha-stimulated human umbilical vein endothelial cells and found the targeting ability of the prepared microbubbles in vitro. In vivo, we also found that the injected targeted bFGF gene microbubbles expressed the bFGF gene better when compared with that of the control group. Furthermore, we evaluated adhesions after Achilles tendon injuries in rabbits using hematoxylin and eosin and immunohistochemical (IHC) staining methods. The collagen fibers were properly arranged in the tendon, and there was greater cellularity inside the tendon sheath and a clearer boundary between the internal and external tendon sheath than that of the control group. IHC staining showed greater ICAM-1 expression inside the tendon sheath when compared with outside the tendon sheath. In conclusion, targeted microbubbles can be a useful carrier of genes to provide gene therapy for the prevention of adhesions after tendon injury.

Tendon and Cytokine Marker Expression by Human Bone Marrow Mesenchymal Stem Cells in a Hyaluronate/Poly-Lactic-Co-Glycolic Acid (PLGA)/Fibrin Three-Dimensional (3D) Scaffold

We developed a (three-dimensional) 3D scaffold, we named HY-FIB, incorporating a force-transmission band of braided hyaluronate embedded in a cell localizing fibrin hydrogel and poly-lactic-co-glycolic acid (PLGA) nanocarriers as transient components for growth factor controlled delivery. The tenogenic supporting capacity of HY-FIB on human-Bone Marrow Mesenchymal Stem Cells (hBM-MSCs) was explored under static conditions and under bioreactor-induced cyclic strain conditions. HY-FIB elasticity enabled to deliver a mean shear stress of 0.09 Pa for 4 h/day. Tendon and cytokine marker expression by hBM-MSCs were studied. Results: hBM-MSCs embedded in HY-FIB and subjected to mechanical stimulation, resulted in a typical tenogenic phenotype, as indicated by type 1 Collagen fiber immunofluorescence. RT-qPCR showed an increase of type 1 Collagen, scleraxis, and decorin gene expression (3-fold, 1600-fold, and 3-fold, respectively, at day 11) in dynamic conditions. Cells also showed pro-inflammatory (IL-6, TNF, IL-12A, IL-1β) and anti-inflammatory (IL-10, TGF-β1) cytokine gene expressions, with a significant increase of anti-inflammatory cytokines in dynamic conditions (IL-10 and TGF-β1 300-fold and 4-fold, respectively, at day 11). Mechanical signaling, conveyed by HY-FIB to hBM-MSCs, promoted tenogenic gene markers expression and a pro-repair cytokine balance. The results provide strong evidence in support of the HY-FIB system and its interaction with cells and its potential for use as a predictive in vitro model.

Cell-cell junctions in developing and adult tendons

Tendons connect muscles to bones to transfer the forces necessary for movement. Cell-cell junction proteins, cadherins and connexins, may play a role in tendon development and injury. In this review, we begin by highlighting current understanding of how cell-cell junctions may regulate embryonic tendon development and differentiation. We then examine cell-cell junctions in postnatal tendon, before summarizing the role of cadherins and connexins in adult tendons. More information exists regarding the role of cell-cell junctions in the formation and homeostasis of other musculoskeletal tissues, namely cartilage and bone. Therefore, to inform future tendon studies, we include a brief survey of cadherins and connexins in chondrogenesis and osteogenesis, and summarize how cell-cell junctions are involved in some musculoskeletal tissue pathologies. An enhanced understanding of how cell-cell junctions participate in tendon development, maintenance, and disease will benefit future regenerative strategies.

Tendon stem progenitor cells: Understanding the biology to inform therapeutic strategies for tendon repair

Tendon and ligament injuries are a leading cause of healthcare visits with significant impact in terms of economic cost and reduced quality of life. To date, reparative strategies remain largely restricted to conservative treatment or surgical repair. However, these therapies fail to restore native tendon structure and function; thus, the tissue may re-rupture or degenerate with time. To improve tendon healing, one promising strategy may be harnessing the innate potential of resident tendon stem/progenitor cells (TSPCs) to guide tenogenic regeneration. In this review, we outline recent advances in the identification and characterization of putative TSPC populations, and discuss biochemical, biomechanical, and biomaterial methods employed for their culture and differentiation. Finally, we identify limitations in our current understanding of TSPC biology, key challenges for their use, and potential therapeutic strategies to inform cell-based tendon repair. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1270-1280, 2019.

Regenerative Engineering of the Rotator Cuff of the Shoulder

Rotator cuff tears often heal poorly, leading to re-tears after repair. This is in part attributed to the low proliferative ability of the resident cells (tendon fibroblasts and tendon-stem cells) upon injury to the rotator cuff tissue and the low vascularity of the tendon insertion. In addition, surgical outcomes of current techniques used in clinical settings are often suboptimal, leading to the formation of neo-tissue with poor biomechanics and structural characteristics, which results in re-tears. This has prompted interest in a new approach, which we term as "Regenerative Engineering", for regenerating rotator cuff tendons. In the Regenerative Engineering paradigm, roles played by stem cells, scaffolds, growth factors/small molecules, the use of local physical forces, and morphogenesis interplayed with clinical surgery techniques may synchronously act, leading to synergistic effects and resulting in successful tissue regeneration. In this regard, various cell sources such as tendon fibroblasts and adult tissue-derived stem cells have been isolated, characterized, and investigated for regenerating rotator cuff tendons. Likewise, numerous scaffolds with varying architecture, geometry, and mechanical characteristics of biologic and synthetic origin have been developed. Furthermore, these scaffolds have been also fabricated with biochemical cues (growth factors and small molecules), facilitating tissue regeneration. In this Review, various strategies to regenerate rotator cuff tendons using stem cells, advanced materials, and factors in the setting of physical forces under the Regenerative Engineering paradigm are described.

Silk fibroin and hydroxyapatite segmented coating enhances graft ligamentization and osseointegration processes of the polyethylene terephthalate artificial ligament in vitro and in vivo

A silk fibroin and hydroxyapatite segmented coating ligament is fabricated to enhances graft ligamentization and osseointegration processes successfully.

* An Engineered Multiphase Three-Dimensional Microenvironment to Ensure the Controlled Delivery of Cyclic Strain and Human Growth Differentiation Factor 5 for the Tenogenic Commitment of Human Bone Marrow Mesenchymal Stem Cells

At present, injuries or rupture of tendons are treated by surgical repair or conservative approaches with unpredictable clinical outcome. Alternative strategies to repair tendon defects without the undesirable side effects associated with the current options are needed. With this in mind, a tissue engineering approach has gained considerable attention as a promising strategy. Here we investigated a synthetic three-dimensional (3D) microenvironment able to interact with stem cells and inducing, via coupled biochemical and physical signals, their early commitment toward the tenogenic lineage. This multiphase 3D construct consisted of a braided hyaluronate elastic band merged with human bone marrow mesenchymal stem cells (hBMSCs) and poly-lactic-co-glycolic acid microcarriers loaded with human growth differentiation factor 5 (hGDF-5) by means of fibrin hydrogel. The multiphase structure allowed hBMSC culture under cyclic strain within a microenvironment where a controlled amount of hGDF-5 was regularly delivered. The cooperative biochemical and physical stimuli induced significantly increased expression of tenogenic markers, such as collagen type I and III, decorin, scleraxis, and tenascin-C, within only 3 days of dynamic hBMSC culture. This approach opens exciting perspectives for future development of engineered tendon tissue substitutes.

A Clinical, Biological, and Biomaterials Perspective into Tendon Injuries and Regeneration

Tendon injury is common and debilitating, and it is associated with long-term pain and ineffective healing. It is estimated to afflict 25% of the adult population and is often a career-ending disease in athletes and racehorses. Tendon injury is associated with high morbidity, pain, and long-term suffering for the patient. Due to the low cellularity and vascularity of tendon tissue, once damage has occurred, the repair process is slow and inefficient, resulting in mechanically, structurally, and functionally inferior tissue. Current treatment options focus on pain management, often being palliative and temporary and ending in reduced function. Most treatments available do not address the underlying cause of the disease and, as such, are often ineffective with variable results. The need for an advanced therapeutic that addresses the underlying pathology is evident. Tissue engineering and regenerative medicine is an emerging field that is aimed at stimulating the body's own repair system to produce de novo tissue through the use of factors such as cells, proteins, and genes that are delivered by a biomaterial scaffold. Successful tissue engineering strategies for tendon regeneration should be built on a foundation of understanding of the molecular and cellular composition of healthy compared with damaged tendon, and the inherent differences seen in the tissue after disease. This article presents a comprehensive clinical, biological, and biomaterials insight into tendon tissue engineering and regeneration toward more advanced therapeutics.

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.

Biologics in Achilles tendon healing and repair: a review

Injuries of the Achilles tendon are relatively common with potentially devastating outcomes. Healing Achilles tendons form a fibrovascular scar resulting in a tendon which may be mechanically weaker than the native tendon. The resulting strength deficit causes a high risk for reinjury and other complications. Treatments using biologics aim to restore the normal properties of the native tendon and reduce the risk of rerupture and maximize tendon function. The purpose of this review was to summarize the current findings of various therapies using biologics in an attempt to improve the prognosis of Achilles tendon ruptures and tendinopathies. A PubMed search was performed using specific search terms. The search was open for original manuscripts and review papers limited to publication within the last 10 years. From these searches, papers were included in the review if they investigated the effects of biological augmentation on Achilles tendon repair or healing. Platelet-rich plasma may assist in the healing process of Achilles tendon ruptures, while the evidence to support its use in the treatment of chronic Achilles tendinopathies remains insufficient. The use of growth factors such as hepatocyte growth factor, recombinant human platelet-derived growth factor-BB, interleukin-6, and transforming growth factor beta as well as several bone morphogenetic proteins have shown promising results for Achilles tendon repair. In vitro and preclinical studies have indicated the potential effectiveness of bone marrow aspirate as well. Stem cells also have positive effects on Achilles tendon healing, particularly during the early phases. Polyhydroxyalkanoates (PHA), decellularized tendon tissue, and porcine small intestinal submucosa (SIS) are biomaterials which have shown promising results as scaffolds used in Achilles tendon repair. The application of biological augmentation techniques in Achilles tendon repair appears promising; however, several techniques require further investigation to evaluate their clinical application.

Preferential tendon stem cell response to growth factor supplementation

Tendon injuries are increasingly prevalent around the world, accounting for more than 100 000 new clinical cases/year in the USA alone. Cell-based therapies have been proposed as a therapeutic strategy, with recent data advocating the use of tendon stem cells (TSCs) as a potential cell source with clinical relevance for tendon regeneration. However, their in vitro expansion is problematic, as they lose their multipotency and change their protein expression profile in culture. Herein, we ventured to assess the influence of insulin-like growth factor 1 (IGF-1), growth and differentiation factor-5 (GDF-5) and transforming growth factor-β1 (TGFβ1) supplementation in TSC culture. IGF-1 preserved multipotency for up to 28 days. Upregulation of decorin and scleraxis expression was observed as compared to freshly isolated cells. GDF-5 treated cells exhibited reduced differentiation along adipogenic and chondrogenic pathways after 28 days, and decorin, scleraxis and collagen type I expression was increased. After 28 days, TGFβ1 supplementation led to increased scleraxis, osteonectin and collagen type II expression. The varied responses to each growth factor may reflect their role in tendon repair, suggesting that: GDF-5 promotes the transition of tendon stem cells towards tenocytes; TGFβ1 induces differentiation along several pathways, including a phenotype indicative of fibrocartilage or calcified tendon, common problems in tendon healing; and IGF-1 promotes proliferation and maintenance of TSC phenotypes, thereby creating a population sufficient to have a beneficial effect. Copyright © 2014 John Wiley & Sons, Ltd.

A modified aggregate culture for chondrogenesis of human adipose-derived stem cells genetically modified with growth and differentiation factor 5

Adipose-derived stem cells (ADSCs) are an attractive cell source for tissue engineering, and recently a modified aggregate culture of human ADSCs (hADSCs) was established based on preparation of three-dimensional (3D) cell aggregates in growth factor–enriched low serum medium using the hanging droplet method. Growth and differentiation factor 5 (GDF5) plays a critical role in chondrogenesis and cartilage development. In the present study, we examine (1) whether the modified aggregate culture is feasible for chondrogenic induction of hADSCs, (2) whether overexpressed GDF5 can promote chondrogenesis, and (3) the gene expression profile during chondrogenesis in this aggregate culture. hADSCs were infected with an adenovirus carrying the GDF5 gene (Ad-GDF5). Cells were cultured with chondrogenic media either in a modified aggregate culture or in an attached micromass culture that served as a control. The chondrogenic phenotype was assessed by morphology (n=8), biochemistry (n=3), and histology (n=2). Expression of 12 genes was determined by quantitative real-time polymerase chain reaction (n=3). We found that ADSCs cultured in the modified aggregates exhibited denser pellets and higher content of sulfated glycosaminoglycan (sGAG) compared with those cultured in the micromass. Infection of cells with Ad-GDF5 increased the aggregate size and sGAG content. It also up-regulated expression of GDF5, aggrecan, and leptin and down-regulated expression of COL I, while expression of COL II and COL 10 remained unchanged. We concluded that the modified aggregate culture is feasible for chondrogenic induction of human ADSCs. Infection with Ad-GDF5 appears to promote the chondrogenesis. These findings suggest that genetic modification of ADSCs with GDF5 in the modified aggregate culture could be useful for treating diseases with cartilage defects.

Composite growth factor supplementation strategies to enhance tenocyte bioactivity in aligned collagen-GAG scaffolds

Biomolecular environments encountered in vivo are complex and dynamic, with combinations of biomolecules presented in both freely diffusible (liquid-phase) and sequestered (bound to the extracellular matrix) states. Strategies for integrating multiple biomolecular signals into a biomimetic scaffold provide a platform to simultaneously control multiple cell activities, such as motility, proliferation, phenotype, and regenerative potential. Here we describe an investigation elucidating the influence of the dose and mode of presentation (soluble, sequestered) of five biomolecules (stromal cell-derived factor 1α [SDF-1α], platelet-derived growth factor BB [PDGF-BB], insulin-like growth factor 1 [IGF-1], basic fibroblast growth factor [bFGF], and growth/differentiation factor 5 [GDF-5]) on the recruitment, proliferation, collagen synthesis, and genomic stability of equine tenocytes within an anisotropic collagen-GAG scaffold for tendon regeneration applications. Critically, we found that single factors led to a dose-dependent trade-off between driving tenocyte proliferation (PDGF-BB, IGF-1) versus maintenance of a tenocyte phenotype (GDF-5, bFGF). We identified supplementation schemes using factor pairs (IGF-1, GDF-5) to rescue the tenocyte phenotype and gene expression profiles while simultaneously driving proliferation. These results suggest coincident application of multi-biomolecule cocktails has a significant value in regenerative medicine applications where control of cell proliferation and phenotype are required. Finally, we demonstrated an immobilization strategy that allows efficient sequestration of bioactive levels of these factors within the scaffold network. We showed sequestration can lead to a greater sustained bioactivity than soluble supplementation, making this approach particularly amenable to in vivo translation where diffusive loss is a concern and continuous biomolecule supplementation is not feasible.

The effect of platelet-rich plasma on patterns of gene expression in a dog model of anterior cruciate ligament reconstruction

BACKGROUND

Autologous platelet-rich plasma (PRP) has been investigated as a potential promoter of tendon healing and has an enhancing effect on the anterior cruciate ligament (ACL) graft maturation process. However, the influence of PRP on the synthesis and degradation of the extracellular matrix during the ACL graft remodeling process has never been investigated.

MATERIALS AND METHODS

Healthy and mature beagle dogs were randomly assigned to one of four groups: in group I (PRP group), ACL grafts were treated with PRP; in group II (control group), ACL grafts were treated with saline; in group III (sham group), only the knee joints were exposed; in group IV (normal control group), no surgery was performed to the knees. Ligament tissue was dissected at 2, 6, and 12 wk after surgery, and real-time PCR was performed using primers for growth factor-β1 (TGF-β1), collagen type1A1 (COL1Al), collagen type3A1 (COL3A1), decorin, biglycan, matrix metalloproteinase-1 (MMP-1), matrix metalloproteinase-13 (MMP-13), and tissue inhibitor of metalloproteinase-1 (TIMP-1).

RESULT

In group I, the messenger RNA (mRNA) levels of collagen type 1A1, biglycan, and MMP-1 all increased 2, 6, and 12 wk after surgery, compared with group II (P < 0.05). At 2 and 6 wk after surgery, increased levels of COL3A1, MMP-1, and MMP-13 mRNA were also detected in group I (P < 0.05). Increased levels of TGF-β1 mRNA was observed at 6 and 12 wk in group I after surgery (P < 0.05).

CONCLUSIONS

During the graft remodeling process, we observed a time-dependent change of gene expression following ACL reconstruction surgery. Furthermore, our results demonstrate that PRP alters the expression of some target genes at certain time points, especially during the early stages of graft remodeling, which might explain the enhancing effect of PRP on the ACL graft maturation process.