The effect of growth factor treatment on meniscal chondrocyte proliferation and differentiation on polyglycolic acid scaffolds

Prochondrogenic effect of decellularized extracellular matrix secreted from human induced pluripotent stem cell-derived chondrocytes

Cartilage is mainly composed of chondrocytes and the extracellular matrix (ECM), which exchange important biochemical and biomechanical signals necessary for differentiation and homeostasis. Human articular cartilage has a low ability for regeneration because it lacks blood vessels, nerves, and lymphatic vessels. Currently, cell therapeutics, including stem cells, provide a promising strategy for cartilage regeneration and treatment; however, there are various hurdles to overcome, such as immune rejection and teratoma formation. In this study, we assessed the applicability of the stem cell-derived chondrocyte ECM for cartilage regeneration. Human induced pluripotent stem cell (hiPSC)-derived chondrocytes (iChondrocytes) were differentiated, and decellularized ECM (dECM) was successfully isolated from cultured chondrocytes. Isolated dECM enhanced in vitro chondrogenesis of iPSCs when recellularized. Implanted dECM also restored osteochondral defects in a rat osteoarthritis model. A possible association with the glycogen synthase kinase-3 beta (GSK3β) pathway demonstrated the fate-determining importance of dECM in regulating cell differentiation. Collectively, we suggested the prochondrogenic effect of hiPSC-derived cartilage-like dECM and offered a promising approach as a non-cellular therapeutic for articular cartilage reconstruction without cell transplantation. STATEMENT OF SIGNIFICANCE: Human articular cartilage has low ability for regeneration and cell culture-based therapeutics could aid cartilage regeneration. Yet, the applicability of human induced pluripotent stem cell-derived chondrocyte (iChondrocyte) extracellular matrix (ECM) has not been elucidated. Therefore, we first differentiated iChondrocytes and isolated the secreted ECM by decellularization. Recellularization was performed to confirm the pro-chondrogenic effect of the decellularized ECM (dECM). In addition, we confirmed the possibility of cartilage repair by transplanting the dECM into the cartilage defect in osteochondral defect rat knee joint. We believe that our proof-of-concept study will serve as a basis for investigating the potential of dECM obtained from iPSC-derived differentiated cells as a non-cellular resource for tissue regeneration and other future applications.

Sex-dependent variation in cartilage adaptation: from degeneration to regeneration

Despite acknowledgement in the scientific community of sex-based differences in cartilage biology, the implications for study design remain unclear, with many studies continuing to arbitrarily assign demographics. Clinically, it has been well-established that males and females differ in cartilage degeneration, and accumulating evidence points to the importance of sex differences in the field of cartilage repair. However, a comprehensive review of the mechanisms behind this trend and the influence of sex on cartilage regeneration has not yet been presented. This paper aims to summarize current findings regarding sex-dependent variation in knee anatomy, sex hormones' effect on cartilage, and cartilaginous degeneration and regeneration, with a focus on stem cell therapies. Findings suggest that the stem cells themselves, as well as their surrounding microenvironment, contribute to sex-based differences. Accordingly, this paper underscores the contribution of both stem cell donor and recipient sex to sex-related differences in treatment efficacy. Cartilage regeneration is a field that needs more research to optimize strategies for better clinical results; taking sex into account could be a big factor in developing more effective and personalized treatments. The compilation of this information emphasizes the importance of investing further research in sex differences in cartilage biology.

Treatment strategies for meniscal lesions: from past to prospective therapeutics

Menisci play an important role in the biomechanics of knee joint function, including loading transmission, joint lubrication, prevention of soft tissue impingement during motion and joint stability. Meniscal repair presents a challenge due to a lack of vascularization that limits the healing capacity of meniscal tissue. In this review, the authors aimed to untangle the available treatment options for repairing meniscal tears. Various surgical procedures have been developed to treat meniscal tears; however, clinical outcomes are limited. Consequently, numerous researchers have focused on different treatments such as the application of exogenous and/or autologous growth factors, scaffolds including tissue-derived matrix, cell-based therapy and miRNA-210. The authors present current and prospective treatment strategies for meniscal lesions.

Assessment of joint pharmacokinetics and consequences for the intraarticular delivery of biologics

Intraarticular (IA) injections provide the opportunity to deliver biologics directly to their site of action for a local and efficient treatment of osteoarthritis. However, the synovial joint is a challenging site of administration since the drug is rapidly eliminated across the synovial membrane and has limited distribution into cartilage, resulting in unsatisfactory therapeutic efficacy. In order to rationally develop appropriate drug delivery systems, it is essential to thoroughly understand the unique biopharmaceutical environments and kinetics in the joint to adequately simulate them in relevant experimental models. This review presents a detailed view on articular kinetics and drug-tissue interplay of IA administered drugs and summarizes how these can be translated into reasonable formulation strategies by identification of key factors through which the joint residence time can be prolonged and specific structures can be targeted. In this way, pros and cons of the delivery approaches for biologics will be evaluated and the extent to which biorelevant models are applicable to gain mechanistic insights and ameliorate formulation design is discussed.

Platelet-rich plasma treatment alleviates osteoarthritis-related pain, inflammation, and apoptosis by upregulating the expression levels of microRNA-375 and microRNA-337

OBJECTIVE

The present study was designed to determine the molecular mechanism by which platelet-rich plasma (PRP) acts on Osteoarthritis (OA) -related pain, inflammation, and apoptosis in vivo and in vitro.

MATERIALS AND METHODS

An in vivo OA model was established in rats using anterior cruciate ligament transection, and an in vitro OA model was created by treating chondrocytes with IL-1β. Then, the induced rats and chondrocytes were treated with PRP. Real-time PCR were used to examine the expression of micorRNAs (miRs) and mRNAs of inflammatory cytokines. WB were performed to detect the expression of apoptotic factors and Wnt/β-catenin signals. Structural damage of the cartilage and pain in OA rats were analyzed and represented by Mankin Score, OARSIS score, Tender threshold, and Thermal pain threshold. CCK-8 assay and flow cytometry were used to determine cell viability and apoptosis.

RESULTS

The expression levels of miR-337 and miR-375 were downregulated in the in vivo and vitro OA models; however, PRP treatment elevated their levels. miR-337 and miR-375 inhibition reversed the effects of PRP of reducing tenderness and thermal pain thresholds in OA rats. Moreover, PRP decreased the mRNA expression levels of MMP-13, Bax, and inflammatory factors, such as IL-1β, IL-18, and TNF-α, as well as increased the expression levels of collagen II and antiapoptotic Bcl-2. The decrease in inflammation and apoptosis was reversed by miR-337 and miR-375 inhibition, respectively.

DISCUSSION AND CONCLUSIONS

In conclusion, miR-337 and miR-375 are involved in PRP-delayed OA progression by affecting inflammation and apoptosis.

Meniscus Repair and Regeneration: A Systematic Review from a Basic and Translational Science Perspective

Meniscus injuries are among the most common athletic injuries and result in functional impairment in the knee. Repair is crucial for pain relief and prevention of degenerative joint diseases like osteoarthritis. Current treatments, however, do not produce long-term improvements. Thus, recent research has been investigating new therapeutic options for regenerating injured meniscal tissue. This review comprehensively details the current methodologies being explored in the basic sciences to stimulate better meniscus injury repair. Furthermore, it describes how these preclinical strategies may improve current paradigms of how meniscal injuries are clinically treated through a unique and alternative perspective to traditional clinical methodology.

Exosomes derived from platelet-rich plasma present a novel potential in alleviating knee osteoarthritis by promoting proliferation and inhibiting apoptosis of chondrocyte via Wnt/β-catenin signaling pathway

Background

Platelet-rich plasma (PRP) provides a nonsurgical approach for treating osteoarthritis (OA). Exosomes that play vital roles in intercellular communication have been studied extensively. Here, we investigated the therapeutic potential and molecular mechanism of exosomes derived from PRP (PRP-Exos) in alleviating OA.

Methods

Exosomes derived from PRP(PRP-Exos) were isolated and purified using the exoEasy Maxi Kit and then identified and analyzed. Primary rabbit chondrocytes were isolated and treated with interleukin 1 beta (IL-1β) to establish the OA model in vitro. Proliferation, migration, and apoptosis assays were measured and compared between PRP-Exos and activated PRP (PRP-As) to evaluate the therapeutic effects on OA. The mechanism involving the Wnt/β-catenin signaling pathway was investigated by Western blot analysis. In vivo, we established animal knee OA model by surgery to compare the therapeutic effect of PRP-Exos and PRP-As.

Results

We successfully isolated and purified exosomes from PRP using the exoEasy Maxi Kit. We also isolated and identified chondrocytes from the New Zealand white rabbit and established the IL-1β-induced OA model; meanwhile, PRP-Exos and PRP-As both inhibited the release of tumor necrosis factor-α(TNF-α) and there was no statistically significant difference between the two. In proliferation, migration, scratch assay, the promoting effect of PRP-Exos was significantly more better than PRP-As. Furthermore, PRP-Exos could significantly decreased apoptotic rate of OA chondrocyte compared with PRP-As. In Western blot analysis, the expression of β-catenin, and RUNX2, Wnt5a were increased in IL-1β-treated chondrocytes, but PRP-Exos and PRP-As could both reverse these changes, and the reversal effect of the former was better than the latter. In vivo, we found that both PRP-Exos and PRP-As displayed the progression of OA, and the effect of PRP-Exos was obviously better than PRP-As by chondrocyte count and Osteoarthritis Research Society International (OARSI) scoring system.

Conclusion

The therapeutic effects of PRP-Exos on OA were similar or better compared with those of PRP-As in vitro or in vivo. PRP-Exos acting as carriers containing growth factors derived from PRP present a novel therapy for OA by activating the Wnt/β-catenin signaling pathway.

Materials and structures used in meniscus repair and regeneration: a review

Meniscus is a vital functional unit in knee joint. It acts as a lubricating structure, a nutrient transporting structure, as well as shock absorber during jumping, twisting and running and offers stability within the knee joint. It helps in load distribution, in bearing the tensile hoop stresses and balancing by providing a cushion effect between hard surfaces of two bones. Meniscus may be injured in sports, dancing, accident or any over stressed condition. Any meniscal lesion can lead to a gradual development of osteoarthritis or erosion of bone contact surface due to disturbed load and contact stress distribution caused by injury/pain. Once injured, the possibilities of self-repair are rare in avascular region of meniscus, due to lack of blood supply in avascular region. Meniscus has vascular and avascular regions in structure. Majority of the meniscus parts turn avascular with increase in age.

Purpose of this review is to highlight advances in meniscus repair with special focus on tissue engineering using textile/fiber based scaffolds, as well as the recent technical advances in scaffolds for meniscus recon- struction/ regeneration treatment.

Postnatal deletion of Alk5 gene in meniscal cartilage accelerates age-dependent meniscal degeneration in mice

Activation of transforming growth factor-β (TGF-β) signaling has been used to enhance healing of meniscal degeneration in several models. However, the exact role and molecular mechanism of TGF-β signaling in meniscus maintenance and degeneration are still not understood due to the absence of in vivo evidence. In this study, we found that the expression of activin receptor-like kinases 5 (ALK5) in the meniscus was decreased with the progression of age and/or osteoarthritis induced meniscal degeneration. Col2α1 positive cells were found to be specifically distributed in the superficial and inner zones of the anterior horn, as well as the inner zone of the posterior horn in mice, indicating that Col2α1-CreER^T2 mice can be a used for studying gene function in menisci. Furthermore, we deleted Alk5 in Col2α1 positive cells in meniscus by administering tamoxifen. Alterations in the menisci structure were evaluated histologically. The expression levels of genes and proteins associated with meniscus homeostasis and TGF-β signaling were analyzed by quantitative real-time PCR analysis (qRT-PCR) and immunohistochemistry (IHC). Our results revealed severe and progressive meniscal degeneration phenotype in 3- and 6-month-old Alk5 cKO mice compared with Cre-negative control, including aberrantly increased hypertrophic meniscal cells, severe fibrillation, and structure disruption of meniscus. qRT-PCR and IHC results showed that disruption of anabolic and catabolic homeostasis of chondrocytes may contribute to the meniscal degeneration phenotype observed in Alk5 cKO mice. Thus, TGF-β/ALK5 signaling plays a chondro-protective role in menisci homeostasis, in part, by inhibiting matrix degradation and maintaining extracellular matrix proteins levels in meniscal tissues.

Biochemical Stimulus-Based Strategies for Meniscus Tissue Engineering and Regeneration

Meniscus injuries are very common and still pose a challenge for the orthopedic surgeon. Meniscus injuries in the inner two-thirds of the meniscus remain incurable. Tissue-engineered meniscus strategies seem to offer a new approach for treating meniscus injuries with a combination of seed cells, scaffolds, and biochemical or biomechanical stimulation. Cell- or scaffold-based strategies play a pivotal role in meniscus regeneration. Similarly, biochemical and biomechanical stimulation are also important. Seed cells and scaffolds can be used to construct a tissue-engineered tissue; however, stimulation to enhance tissue maturation and remodeling is still needed. Such stimulation can be biomechanical or biochemical, but this review focuses only on biochemical stimulation. Growth factors (GFs) are one of the most important forms of biochemical stimulation. Frequently used GFs always play a critical role in normal limb development and growth. Further understanding of the functional mechanism of GFs will help scientists to design the best therapy strategies. In this review, we summarize some of the most important GFs in tissue-engineered menisci, as well as other types of biological stimulation.

Intra-Articular Injections of Autologous Conditioned Serum to Treat Pain from Meniscal Lesions

Routine use of biological therapies is in its early stages. Techniques involve stem cells, platelet preparations, recombinant growth factors and autologous conditioned serum, often combined with surgery. The objective of this case analysis was to document effects of intra-articular autologous conditioned serum injections in outpatients with knee pain associated with meniscal defects. Autologous conditioned serum was prepared from patients’ blood by centrifugal separation from cellular components using a specialized device (EOT ^® II, Orthokine). Outpatients (n=47) with heterogeneous knee meniscus lesions (76.6% traumatic knee injury) were injected once weekly (average 5.2 applications). Average age was 48.6 years (range 21–79). Oxford Knee Score and structural changes with the MRI Boston Leeds Osteoarthritis Knee Score were documented at baseline and 6 months. All analyses were performed retrospectively.

In 83% patients, surgery was avoided during the 6-month observation period. Oxford Knee Score improved significantly from 29.1–44.3 (p<0.001; best possible score=48). Structural findings on MRI, measured by Boston Leeds Osteoarthritis Knee Score, showed significant improvement at 6 months (0.82–0.71, p<0.001). This retrospective study implies that intra-articular autologous conditioned serum injection may be an effective treatment option for knee pain associated with meniscal lesions. Controlled studies of autologous conditioned serum treatment for meniscal lesions are advocated.

Comparative evaluation of the effects of platelet‑rich plasma formulations on extracellular matrix formation and the NF‑κB signaling pathway in human articular chondrocytes

Concentrated leukocytes in leukocyte and platelet-rich plasma (L-PRP) may deliver increased levels of pro-inflammatory cytokines to activate the nuclear factor (NF)-κB signaling pathway, to counter or overwhelm the beneficial effects of growth factors on cartilage regeneration. However, to date, no relevant studies have substantiated this. In the present study, L-PRP and pure platelet-rich plasma (P-PRP) were prepared, and leukocytes, platelets, pro-inflammatory cytokines and growth factor concentrations were quantified; they were then used to treat human articular chondrocytes (HACs). Pyrrolidine dithiocarbamate (PDTC; 50 µM) was used to inhibit the activation of NF-κB. The nuclear translocation of NF-κB p65 and the protein expression of cartilaginous markers (collagen II, aggrecan and sex-determining region Y-box 9) were determined using western blot analysis. The mRNA expression of NF-κB-dependent inflammatory mediators, including inducible nitric oxide synthase and cyclooxygenase-2, and cartilaginous markers were determined using reverse transcription-quantitative polymerase chain reaction analysis. The production of prostaglandin E2, nitric oxide and glycosaminoglycan (GAG) were quantified using enzyme-linked immunosorbent assays, the Griess reaction and a 1,9-dimethylmethylene blue assay, respectively. The results demonstrated that L-PRP induced the nuclear translocation of NF-κB p65, upregulated the mRNA expression of NF-κB-dependent inflammatory mediators and upregulated the production of their products, whereas P-PRP, which had similar growth factor concentrations but significantly lower pro-inflammatory cytokine concentrations than L-PRP, did not. P-PRP promoted the mRNA and protein expression levels of cartilaginous markers and the production of GAG more effectively, compared with L-PRP. Furthermore, inhibition of the activation of NF-κB by PDTC enhanced the effects of L-PRP on extracellular matrix formation in the HACs to a level similar to that of P-PRP. These findings suggested that leukocytes in L-PRP activated the NF-κB signaling pathway via the delivery of interleukin-1β and tumor necrosis factor-α to counter the beneficial effects of growth factors on extracellular matrix formation in HACs. Therefore, P-PRP may be more suitable for the treatment of osteoarthritis.

Identification and characterization of adult mouse meniscus stem/progenitor cells

Meniscal damage is a common problem that accelerates the onset of knee osteoarthritis. Stem cell-based tissue engineering treatment approaches have shown promise in preserving meniscal tissue and restoring meniscal function. The purpose of our study was to identify meniscus-derived stem/progenitor cells (MSPCs) from mouse, a model system that allows for in vivo analysis of the mechanisms underlying meniscal injury and healing. MSPCs were isolated from murine menisci grown in explant culture and characterized for stem cell properties. Flow cytometry was used to detect the presence of surface antigens related to stem cells, and qRT-PCR was used to examine the gene expression profile of MSPCs. Major proteins associated with MSPCs were localized in the adult mouse knee using immunohistochemistry. Our data show that MSPCs have universal stem cell-like properties including clonogenicity and multi-potentiality. MSPCs expressed the mesenchymal stem cell markers CD44, Sca-1, CD90, and CD73 and when cultured had elevated levels of biglycan and collagen type I, important extracellular matrix components of adult meniscus. MSPC also expressed significant levels of Lox and Igf-1, genes associated with the embryonic meniscus. Localization studies showed staining for these same proteins in the superficial and outer zones of the adult mouse meniscus, regions thought to harbor endogenous repair cells. MSPCs represent a novel resident stem cell population in the murine meniscus. Analysis of MSPCs in mice will allow for a greater understanding of the cell biology of the meniscus, essential information for enhancing therapeutic strategies for treating knee joint injury and disease.

In vitro effects of platelet-rich gel supernatants on histology and chondrocyte apoptosis scores, hyaluronan release and gene expression of equine cartilage explants challenged with lipopolysaccharide

Background

Platelet-rich plasma (PRP) preparations are a common treatment in equine osteoarthritis (OA). However, there are controversies regarding the ideal concentration of platelets and leukocytes in these biological substances necessary to induce an adequate anti-inflammatory and anabolic response in articular cartilage. The aims were to study the influence of leukocyte- and platelet-rich gel (L-PRG) and pure platelet-rich gel (P-PRG) supernatants on the histological changes of cartilage, the degree of chondrocyte apoptosis, the production of hyaluronan (HA) and the gene expression of nuclear factor kappa beta (NFkβ), matrix metalloproteinase 13 (MMP-13), a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS-4), collagen type I alpha 1 (COL1A1), collagen type II alpha 1 (COL2A1) and cartilage oligomeric matrix protein (COMP) in normal cartilage explants (CEs) challenged with lipopolysaccharide (LPS).

Results

Overall, 25 % L-PRG supernatant (followed in order of importance by, 50 % P-PRG, 25 % P-PRG and 50 % L-PRG) represented the substance with the most important anti-inflammatory and anabolic effect. 25 % P-PRG supernatant presented important anabolic effects, but it induced a more severe chondrocyte apoptosis than the other evaluated substances.

Conclusions

25 % L-PRG supernatant presented the best therapeutic profile. Our results demonstrate that the biological variability of PRP preparations makes their application rather challenging. Additional in vivo research is necessary to know the effect of PRP preparations at different concentrations.

Advantages of Pure Platelet-Rich Plasma Compared with Leukocyte- and Platelet-Rich Plasma in Treating Rabbit Knee Osteoarthritis

Background

Concentrated leukocytes in leukocyte- and platelet-rich plasma (L-PRP) may deliver increased levels of pro-inflammatory cytokines to activate the NF-κB signaling pathway, to counter the beneficial effects of growth factors on osteoarthritic cartilage. However, to date no relevant studies have substantiated that in vivo.

Material/Methods

Autologous L-PRP and pure platelet-rich plasma (P-PRP) were prepared, measured for componential composition, and injected intra-articularly after 4, 5, and 6 weeks post-anterior cruciate ligament transection. Caffeic acid phenethyl ester (CAPE) was injected intraperitoneally to inhibit NF-κB activation. All rabbits were sacrificed after 8 weeks postoperative. Enzyme-linked immunosorbent assays were performed to determine interleukin 1β (IL-1β) and prostaglandin E2 (PGE2) concentrations in the synovial fluid, Indian ink staining was performed for gross morphological assessment, and hematoxylin and eosin staining and toluidine blue staining were performed for histological assessment.

Results

Compared with L-PRP, P-PRP injections achieved better outcomes regarding the prevention of cartilage destruction, preservation of cartilaginous matrix, and reduction of IL-1β and PGE2 concentrations. CAPE injections reversed the increased IL-1β and PGE2 concentrations in the synovial fluid after L-PRP injections and improved the outcome of L-PRP injections to a level similar to P-PRP injections, while they had no influence on the therapeutic efficacy of P-PRP injections.

Conclusions

Concentrated leukocytes in L-PRP may release increased levels of pro-inflammatory cytokines to activate the NF-κB signaling pathway, to counter the beneficial effects of growth factors on osteoarthritic cartilage, and finally, result in a inferior efficacy of L-PRP to P-PRP for the treatment of osteoarthritis.

Biological augmentation and tissue engineering approaches in meniscus surgery

PURPOSE

The purpose of this review was to evaluate the role of biological augmentation and tissue engineering strategies in meniscus surgery. Although clinical (human), preclinical (animal), and in vitro tissue engineering studies are included here, we have placed additional focus on addressing preclinical and clinical studies reported during the 5-year period used in this review in a systematic fashion while also providing a summary review of some important in vitro tissue engineering findings in the field over the past decade.

METHODS

A search was performed on PubMed for original works published from 2009 to March 31, 2014 using the term "meniscus" with all the following terms: "scaffolds," "constructs," "cells," "growth factors," "implant," "tissue engineering," and "regenerative medicine." Inclusion criteria were the following: English-language articles and original clinical, preclinical (in vivo), and in vitro studies of tissue engineering and regenerative medicine application in knee meniscus lesions published from 2009 to March 31, 2014.

RESULTS

Three clinical studies and 18 preclinical studies were identified along with 68 tissue engineering in vitro studies. These reports show the increasing promise of biological augmentation and tissue engineering strategies in meniscus surgery. The role of stem cell and growth factor therapy appears to be particularly useful. A review of in vitro tissue engineering studies found a large number of scaffold types to be of promise for meniscus replacement. Limitations include a relatively low number of clinical or preclinical in vivo studies, in addition to the fact there is as yet no report in the literature of a tissue-engineered meniscus construct used clinically. Neither does the literature provide clarity on the optimal meniscus scaffold type or biological augmentation with which meniscus repair or replacement would be best addressed in the future. There is increasing focus on the role of mechanobiology and biomechanical and biochemical cues in this process, however, and it is hoped that this may lead to improvements in this strategy.

CONCLUSIONS

There appears to be significant potential for biological augmentation and tissue engineering strategies in meniscus surgery to enhance options for repair and replacement. However, there are still relatively few clinical studies being reported in this regard. There is a strong need for improved translational activities and infrastructure to link the large amounts of in vitro and preclinical biological and tissue engineering data to clinical application.

LEVEL OF EVIDENCE

Level IV, systematic review of Level I-IV studies.

Why menisci show higher healing rate when repaired during ACL reconstruction? Growth factors release can be the explanation

PURPOSE

Healing rate of meniscus repair is higher when the suture is associated with anterior cruciate ligament reconstruction. A possible explanation can be a different pattern of release of growth factors between anterior cruciate ligament reconstruction and isolated meniscus surgery. Hypothesis of this study is that the concentrations of bFGF, TGF-β and platelet-derived growth factor (PDGF) in joint fluid, immediately after single-bundle anterior cruciate ligament reconstruction and arthroscopic partial meniscectomy, can be different.

METHODS

Twenty consecutive patients underwent partial medial meniscectomy and twenty consecutive patients underwent single-bundle anterior cruciate ligament reconstruction with hamstring grafts were enrolled in the study. Thirty minutes after the end of the surgical procedure, a sample of joint fluid, as well of venous blood, was collected from all the patients. Concentrations of growth factors were determined by enzyme-linked immunosorbent assay.

RESULTS

The peripheral blood concentration of TGF-β, bFGF and PDGF was comparable between partial meniscectomy and anterior cruciate ligament reconstruction groups. No differences between the two surgical techniques were also found in term of TGF-β and bFGF joint fluid concentration, whereas joint PDGF concentration of anterior cruciate ligament reconstruction patients was significantly higher than the one found in partial meniscectomy patients.

CONCLUSIONS

A significant growth factors release was detected in the knee joint during arthroscopic surgery. PDGF concentration was significantly higher in anterior cruciate ligament reconstructed knee than in the meniscectomy group. PDGF can play an important role enhancing the healing response of meniscus suture and can be one of the biological reasons of the higher meniscal healing rate in anterior cruciate ligament reconstructed knee.

Meniscal repair possibilities using bone morphogenetic protein-7

This study analysed the influence of bone morphogenetic protein-7 (BMP-7) on cells and meniscal structure. The effect of treatment with BMP-7 was assessed in vitro and in vivo in lesions in the avascular area of the meniscus. Cells were extracted from the outer and inner part of eight menisci of four 2-year-old merino sheep. The menisci were digested with a collagenase mix, and meniscus cells of the synovium, vascular area and avascular area were extracted. The expression of genes for collagen (Col1 and Col2A), matrix metalloproteinases (MMP-2 and MMP-13) and aggrecan was analysed by real time quantitative polymerase chain reaction (qPCR) at baseline and after incubation with BMP-7. Eight sheep aged 2 years and weighing 35-40 kg were used for the in vivo study. Surgery was performed in both knees of every animal. Two holes were made in the avascular area of the medial meniscus of both knees and filled using Putty(®) (control groups) or OP-1 Putty(®), which comprises BMP-7 mixed with a cellulose putty carrier (experimental groups). Animals were sacrificed at 6, 12 and 25 weeks. Adding BMP-7 to vascular cells of the meniscus was associated with a 15-fold increase in Col2A expression and a 78-fold increase in BMP-7 expression. BMP-7 inhibited MMP-2 and MMP-13 expression. Adding BMP-7 to synovial cells inhibited the expression of Col1, doubled the expression of Col2A and reduced the expression of BMP-7; the expression of MMP-2 was inhibited, while that of MMP-13 was increased three-fold. Incubation of cells from the avascular region with BMP-7 was associated with a 2.4-fold increase in Col1 expression, and a 4.4-fold increase in Col2A expression compared with the control. The expression of MMP-2 and BMP-7 was inhibited. In the in vivo study, treatment of the holes in the avascular area of the meniscus with BMP-7 was associated with an important cell presence inside the holes and the appearance of fibrous tissue after 12 weeks; these features were not seen in the control groups. BMP-7 may be a suitable growth factor for stimulation of meniscal cell and collagen formation.

Signaling pathways in cartilage repair

In adult healthy cartilage, chondrocytes are in a quiescent phase characterized by a fine balance between anabolic and catabolic activities. In ageing, degenerative joint diseases and traumatic injuries of cartilage, a loss of homeostatic conditions and an up-regulation of catabolic pathways occur. Since cartilage differentiation and maintenance of homeostasis are finely tuned by a complex network of signaling molecules and biophysical factors, shedding light on these mechanisms appears to be extremely relevant for both the identification of pathogenic key factors, as specific therapeutic targets, and the development of biological approaches for cartilage regeneration. This review will focus on the main signaling pathways that can activate cellular and molecular processes, regulating the functional behavior of cartilage in both physiological and pathological conditions. These networks may be relevant in the crosstalk among joint compartments and increased knowledge in this field may lead to the development of more effective strategies for inducing cartilage repair.

Comparison of growth factor treatments on the fibrochondrogenic potential of canine fibroblast-like synoviocytes for meniscal tissue engineering

OBJECTIVE

To determine the in vitro effects of differing growth factor treatments on the fibrochondrogenic potential of fibroblast-like synoviocytes from cruciate ligament deficient femorotibial joints of dogs.

STUDY DESIGN

In vitro study.

SAMPLE POPULATION

Synoviocytes from dogs (n = 8) with naturally occurring cruciate ligament insufficiency.

METHODS

Synoviocytes were cultured in monolayer and synthesized into tensioned synoviocyte bioscaffolds (TSB) suspended in media containing TGF-β3, or FGF-2, TGF-β1, and IGF-I. The 1,9-dimethylmethylene blue (DMMB) assay and toluidine blue stain assessed glycosaminoglycan content; hydroxyproline assay, and collagen I and II immunohistochemistry assessed collagen content. Biomechanical properties were determined by materials testing/force-deformation curves.

RESULTS

All tissue cultures formed tensioned fibrous tissue-like constructs. Mean tissue cellularity and cellular viability was significantly greater in the triple growth factor-treated TSB by 0.09% and 44%, respectively. Percentage collagen content, and relative gene expression for collagen I, II, and aggrecan was not significantly different between groups. Median percentage of GAG content was significantly greater in triple growth factor-treated TSB by 1.6%. Biomechanical properties were not different in compression. Triple growth factor-treated TSB were significantly stronger in toughness, peak load to failure, and stiffness in tension.

CONCLUSIONS

TGF-β3 cultured bioscaffolds failed to outperform triple growth factor-treated TSB. Architectural extracellular matrix (ECM) organization and cellularity likely explained the differences between groups. TGF-β3 alone cannot be recommended at this time for in vitro formation of autologous fibrocartilage bioscaffolds for meniscal deficiency.

Release of growth factors from a reinforced collagen GAG matrix supplemented with platelet rich plasma: Influence on cultured human meniscal cells

Damage to meniscal cartilage has been strongly linked to accelerated articular wear and consequently to osteoarthritis. Damage might be ameliorated by delivery of growth factors from platelet rich plasma (PRP) via a fiber reinforced collagen matrix designed for meniscal repair. PRP composition, release of growth factors, and influence on meniscal cell growth and gene expression were investigated. PRP was prepared using Harvest Smartprep (HS-PRP), Cascade Fibrinet (CF-PRP), and a simple centrifuge protocol (DC-PRP) from four donors each. CF-PRP had the highest ratio of platelets, with very few other blood cell types. HS-PRP had the highest total number of platelets but also contained high levels of red and white blood cells. Absorbed to collagen matrices HS-PRP released the highest levels of TGF-β1 and PDGF-AB with DC-PRP the most IGF-1. Cumulative release from collagen matrix was 48 ng/cm(3) IGF-1, 96 ng/cm(3) TGF-β1, and 9.6 ng/cm(3) PDGF-AB. Collagen matrix with PRP was able to increase meniscal cell number above peripheral whole blood and up-regulated gene expression of Aggrecan, Collagen type I (α1), and Elastin (3.3 ± 0.8-fold, 2.9 ± 0.6-fold, 4.0 ± 1.4-fold, respectively). Demonstrating that PRP combined with fiber reinforced collagen matrix could influence meniscal cells and might be of use for treating meniscal defects.

Intraarticular injection of synovial stem cells promotes meniscal regeneration in a rabbit massive meniscal defect model

We investigated whether single intraarticular injection of synovial MSCs enhanced meniscal regeneration in a rabbit massive meniscal defect model. Synovium were harvested from the knee joint of rabbits, and the colony-forming cells were collected. Two weeks after the anterior half of the medial menisci were excised in both knees, 1 × 10(7) MSCs in 100 μl PBS were injected into the right knee. The MSC and control groups were compared macroscopically and histologically at 1, 3, 4, and 6 months (n = 4). Articular cartilage of the medial femoral condyle was also evaluated histologically at 6 months. Multipotentiality of the colony-forming cells was confirmed. Injected MSCs labeled with DiI were detected and remained in the meniscal defect at 14 days. The size of meniscus in the MSC group was larger than that in the control group at 1 and 3 months. The difference of the size between the two groups was indistinct at 4 and 6 months. However, histological score was better in the MSC group than in the control group at 1, 3, 4, and 6 months. Macroscopically, the surface of the medial femoral condyle in the control group was fibrillated at 6 months, while looked close to intact in the MSC group. Histologically, defect or thinning of the articular cartilage with sclerosis of the subchondral bone was observed in the control group, contrarily articular cartilage and subchondral bone were better preserved in the MSC group. Synovial MSCs injected into the knee adhered around the meniscal defect, and promoted meniscal regeneration in rabbits.

The effect of IGF-I on anatomically shaped tissue-engineered menisci

This study investigates the effect of insulin-like growth factor (IGF)-I on the development of anatomically-shaped alginate menisci seeded with meniscal fibrochondrocytes. To accomplish this, bovine meniscal fibrochondrocytes were seeded into 2% w/v alginate, crosslinked with calcium sulfate, and injected into anatomical molds derived from microcomputed tomography scans. The meniscal constructs were then cultured for up to 4 weeks with or without 100 ng/mL IGF-I supplemented in the media. Histological, immunohistological, biochemical, and mechanical analyses were performed to characterize tissue development, accumulation and localization of extracellular matrix, and mechanical properties. After 4 weeks of culture, IGF-I treatment significantly improved mechanical and biochemical properties, while maintaining DNA content, with a 26-fold increase in glycosaminoglycan (GAG) content and 10-fold increase in collagen content compared to 0-week controls, and a 3-fold increase in the equilibrium modulus at 2 weeks compared to controls. IGF-I-treated menisci had ∼60% of the GAG content of native tissue and the compressive equilibrium modulus matched native properties by 2 weeks of culture. Further, IGF-I-treated menisci developed a distinct surface layer similar to native tissue with elongated cells and collagen fibers aligned parallel to the surface, the presence of types I and II collagen, and accumulation of lubricin. This study demonstrates that IGF-I treatment can greatly increase the mechanical and biochemical properties of engineered tissues and aid in the development of a distinct surface zone similar to the superficial zone of native menisci.

Biologic agents in osteoarthritis: hopes and disappointments

New treatment options are needed for osteoarthritis (OA) to slow down the structural progression of the disease; current therapies mostly target pain and function with minimal effectiveness. OA results from an imbalance between catabolic and anabolic factors, and biologic agents either target specific catabolic proinflammatory mediators, such as cytokines, nitric oxide synthesis, or affect anabolism more generally. Biologic agents have dramatic effects in other rheumatic inflammatory diseases such as rheumatoid arthritis; they were hoped to have similar effects in the treatment of OA. In this Review, we will discuss the three main types of cytokine blockers used in knee and hand OA, which target β-nerve growth factor (β-NGF), IL-1β or TNF. We will also discuss inhibitors of nitrogen oxide production and the use of growth factors to treat OA. Among the targeted agents, anti-β-NGF therapy has shown promising results, although cases of rapid destructive arthropathy caution against its widespread use. The future of therapies targeting cytokines, nitrogen oxide synthesis and growth factors in OA is questionable, as results from clinical trials have been repeatedly negative. Strategies in OA therapy need to be reconsidered. New molecules emerging from preclinical data should focus on treating the early phase of the disease where damage may be reversible, and treatment should be modified to fit each patient.

New findings in osteoarthritis pathogenesis: therapeutic implications

This review focuses on the new perspectives which can provide insight into the crucial pathways that drive cartilage-bone physiopathology. In particular, we discuss the critical signaling and effector molecules that can activate cellular and molecular processes in both cartilage and bone cells and which may be relevant in cross talk among joint compartments: growth factors (bone morphogenetic proteins and transforming growth factor), hypoxia-related factors, cell-matrix interactions [discoidin domain receptor 2 (DDR2) and syndecan 4], signaling molecules [WNT, Hedgehog (Hh)]. With the continuous progression of our knowledge on the molecular pathways involved in cartilage and bone changes in osteoarthritis (OA), an increasing number of potentially effective candidates for OA therapy are already under scrutiny in clinical trials to ascertain their possible safe use in an attempt to identify molecules active in slowing or halting OA progression and reducing joint pain. We then review the principal molecules currently under clinical investigation.

Meniscus reconstruction: today's achievements and premises for the future

Injuries of the meniscus remain a burden for the development of premature cartilage degeneration and osteoarthritis. This review surveys all treatment options and focuses on the recent development of tissue engineering. Tissue engineering of the meniscus means a successful combination of cells, scaffolds and specific stimuli. Each element of the combination can be subject to variation. Studies investigating the optimum meniscus implant and previous steps in producing these implants are presented in this article. A comprehensive search of the English and German literature was performed in PubMed to retrieve appropriate manuscripts for review. Based on the literatures, autografts and allografts can delay the progress of osteoarthritis for a restricted time period, but several concerns persist. The biomechanical properties of the native meniscus are not copied entirely by the current existing autografts. Congruence, fixation, biocompatibility and potential infection will always remain as limitations for the users of allografts. Long-term results are still not available for meniscus prosthesis and even though it permits fast recovery, several aspects are questionable: bioincompatibility and a lack of cellular adhesion are likely to compromise their long-term fate. Currently, there is no ideal implant generated by means of tissue engineering. However, meniscus tissue engineering is a fast developing field, which promises to develop an implant that mimics histological and biomechanical properties of the native meniscus. At present several cell sources and scaffolds have been used successfully to grow 3-dimensional constructs. In future, optimal implants have to be developed using growth factors, modified scaffolds and stimuli that support cellular proliferation and differentiation to regenerate the native meniscus more closely.

Marrow stimulation improves meniscal healing at early endpoints in a rabbit meniscal injury model

PURPOSE

To critically evaluate the effect of marrow stimulation (MS) on the extent of healing and the local biological environment after meniscal injury in ligamentously stable knees in a rabbit model.

METHODS

A reproducible 1.5-mm cylindrical defect was created in the avascular portion of the anterior horn of the medial meniscus bilaterally in 18 New Zealand White rabbits (36 knees). In right knees (MS knees), a 2.4-mm Steinman pin was drilled into the apex of the femoral intercondylar notch and marrow contents were observed spilling into the joint. Left knees served as controls. Rabbits were killed in 3 groups (n = 6 rabbits each) at 1, 4, and 12 weeks with meniscal harvest and blinded histomorphometric and histologic evaluation using an established 3-component tissue quality score (range, 0 to 6). One-week specimens were also evaluated for the presence of proregenerative cytokines using immunohistochemistry.

RESULTS

The mean proportion of the avascular zone defect bridged by reparative tissue was greater in MS knees than in controls at each endpoint (1 week, 55% v 30%, P = .02; 4 weeks, 71% v 53%, P = .047; 12 weeks, 96% v 77%, P = .16). Similarly, there was a consistent trend toward superior tissue quality scores in knees treated with MS compared with controls (1 week, 1.8 v 0.3, P = .03; 4 weeks, 4.3 v 2.8, P = .08; 12 weeks, 5.9 v 4.5, P = .21). No statistically significant differences, however, were observed at the 12-week endpoint. Increased staining for insulin-like growth factor I, transforming growth factor-β, and platelet-derived growth factor was observed in regenerated tissue, compared with native meniscal tissue, in all specimens at 1 week. Staining density for all growth factors was similar, however, in reparative tissue of MS and control knees.

CONCLUSIONS

The results of this study suggest that marrow stimulation leads to modest improvements in quality and quantity of reparative tissue bridging a meniscal defect, particularly during the early recovery period.

CLINICAL RELEVANCE

Clinical evaluation of marrow stimulation techniques designed to enhance healing in isolated meniscus repair surgery may be indicated.

Species-specific biological effects of FGF-2 in articular cartilage: implication for distinct roles within the FGF receptor family

Existing literature demonstrates that fibroblast growth factor-2 (FGF-2) exerts opposing, contradictory biological effects on cartilage homeostasis in different species. In human articular cartilage, FGF-2 plays a catabolic and anti-anabolic role in cartilage homeostasis, driving homeostasis toward degeneration and osteoarthritis (OA). In murine joints, however, FGF-2 has been identified as an anabolic mediator as ablation of the FGF-2 gene demonstrated increased susceptibility to OA. There have been no previous studies specifically addressing species-specific differences in FGF-2-mediated biological effects. In this study, we provide a mechanistic understanding by which FGF-2 exerts contradictory biological effects in human versus murine tissues. Using human articular cartilage (ex vivo) and a medial meniscal destabilization (DMM) animal model (in vivo), species-specific expression patterns of FGFR receptors (FGFRs) are elucidated between human and murine articular cartilage. In the murine OA model followed by intra-articular injection of FGF-2, we further correlate FGFR profiles to changes in behavioral pain perception, proteoglycan content in articular cartilage, and production of inflammatory (CD11b) and angiogenic (VEGF) mediators in synovium lining cells. Our results suggest that the fundamental differences in cellular responses between human and murine tissues may be secondary to distinctive expression patterns of FGFRs that eventually determine biological outcomes in the presence of FGF-2. The complex interplay of FGFRs and the downstream signaling cascades induced by FGF-2 in human cartilage should add caution to the use of this particular growth factor for biological therapy in the future.

The role of platelet rich plasma in musculoskeletal science

The idea of using platelet rich plasma (PRP) in medicine has been around since the 1970s. It is only more recently that its use has been employed in the area of musculoskeletal science. Platelet rich plasma in this area has received much media attention being used by many celebrity sports athletes for musculoskeletal injuries. Therefore it is important for the musculoskeletal practitioner to be aware of the concepts surrounding its use and application. In this article we cover what platelet rich plasma is, how it is prepared and administered, its potential clinical application, and what the current literature discusses in the various areas of musculoskeletal science.

Implantation of allogenic synovial stem cells promotes meniscal regeneration in a rabbit meniscal defect model

BACKGROUND

Indications for surgical meniscal repair are limited, and failure rates remain high. Thus, new ways to augment repair and stimulate meniscal regeneration are needed. Mesenchymal stem cells are multipotent cells present in mature individuals and accessible from peripheral connective tissue sites, including synovium. The purpose of this study was to quantitatively evaluate the effect of implantation of synovial tissue-derived mesenchymal stem cells on meniscal regeneration in a rabbit model of partial meniscectomy.

METHODS

Synovial mesenchymal stem cells were harvested from the knee of one New Zealand White rabbit, expanded in culture, and labeled with a fluorescent marker. A reproducible 1.5-mm cylindrical defect was created in the avascular portion of the anterior horn of the medial meniscus bilaterally in fifteen additional rabbits. Allogenic synovial mesenchymal stem cells suspended in phosphate-buffered saline solution were implanted into the right knees, and phosphate-buffered saline solution alone was placed in the left knees. Meniscal regeneration was evaluated histologically at four, twelve, and twenty-four weeks for (1) quantity and (2) quality (with use of an established three-component scoring system). A similar procedure was performed in four additional rabbits with use of green fluorescent protein-positive synovial mesenchymal stem cells for the purpose of tracking progeny following implantation.

RESULTS

The quantity of regenerated tissue in the group that had implantation of synovial mesenchymal stem cells was greater at all end points, reaching significance at four and twelve weeks (p < 0.05). Tissue quality scores were also superior in knees treated with mesenchymal stem cells compared with controls at all end points, achieving significance at twelve and twenty-four weeks (3.8 versus 2.8 at four weeks [p = 0.29], 5.7 versus 1.7 at twelve weeks [p = 0.008], and 6.0 versus 3.9 at twenty-four weeks [p = 0.021]). Implanted cells adhered to meniscal defects and were observed in the regenerated tissue, where they differentiated into type-I and II collagen-expressing cells, at up to twenty-four weeks.

CONCLUSIONS

Synovial mesenchymal stem cells adhere to sites of meniscal injury, differentiate into cells resembling meniscal fibrochondrocytes, and enhance both quality and quantity of meniscal regeneration.

Interleukin-1, tumor necrosis factor-alpha, and transforming growth factor-beta 1 and integrative meniscal repair: influences on meniscal cell proliferation and migration

Introduction

Interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α) are up-regulated in injured and osteoarthritic knee joints. IL-1 and TNF-α inhibit integrative meniscal repair; however, the mechanisms by which this inhibition occurs are not fully understood. Transforming growth factor-β1 (TGF-β1) increases meniscal cell proliferation and accumulation, and enhances integrative meniscal repair. An improved understanding of the mechanisms modulating meniscal cell proliferation and migration will help to improve approaches for enhancing intrinsic or tissue-engineered repair of the meniscus. The goal of this study was to examine the hypothesis that IL-1 and TNF-α suppress, while TGF-β1 enhances, cellular proliferation and migration in cell and tissue models of meniscal repair.

Methods

A micro-wound assay was used to assess meniscal cell migration and proliferation in response to the following treatments for 0, 24, or 48 hours: 0 to 10 ng/mL IL-1, TNF-α, or TGF-β1, in the presence or absence of 10% serum. Proliferated and total cells were fluorescently labeled and imaged using confocal laser scanning microscopy and the number of proliferated, migrated, and total cells was determined in the micro-wound and edges of each image. Meniscal cell proliferation was also assessed throughout meniscal repair model explants treated with 0 or 10 ng/mL IL-1, TNF-α, or TGF-β1 for 14 days. At the end of the culture period, biomechanical testing and histological analyses were also performed. Statistical differences were assessed using an ANOVA and Newman-Keuls post hoc test.

Results

IL-1 and TNF-α decreased cell proliferation in both cell and tissue models of meniscal repair. In the presence of serum, TGF-β1 increased outer zone cell proliferation in the micro-wound and in the cross section of meniscal repair model explants. Both IL-1 and TNF-α decreased the integrative shear strength of repair and extracellular matrix deposition in the meniscal repair model system, while TGF-β1 had no effect on either measure.

Conclusions

Meniscal cell proliferation in vivo may be diminished following joint injury due to the up-regulation of inflammatory cytokines, thereby limiting native cellular repair of meniscal lesions. Therefore, therapies that can promote meniscal cell proliferation have promise to enhance meniscal repair and improve tissue engineering strategies.

Advances in meniscal tissue engineering

Meniscal tears are the most common knee injuries and have a poor ability of healing. In the last few decades, several techniques have been increasingly used to optimize meniscal healing. Current research efforts of tissue engineering try to combine cell-based therapy, growth factors, gene therapy, and reabsorbable scaffolds to promote healing of meniscal defects. Preliminary studies did not allow to draw definitive conclusions on the use of these techniques for routine management of meniscal lesions. We performed a review of the available literature on current techniques of tissue engineering for the management of meniscal tears.

Fibroblast growth factor receptor 1 is principally responsible for fibroblast growth factor 2-induced catabolic activities in human articular chondrocytes

INTRODUCTION

Cartilage degeneration driven by catabolic stimuli is a critical pathophysiological process in osteoarthritis (OA). We have defined fibroblast growth factor 2 (FGF-2) as a degenerative mediator in adult human articular chondrocytes. Biological effects mediated by FGF-2 include inhibition of proteoglycan production, up-regulation of matrix metalloproteinase-13 (MMP-13), and stimulation of other catabolic factors. In this study, we identified the specific receptor responsible for the catabolic functions of FGF-2, and established a pathophysiological connection between the FGF-2 receptor and OA.

METHODS

Primary human articular chondrocytes were cultured in monolayer (24 hours) or alginate beads (21 days), and stimulated with FGF-2 or FGF18, in the presence or absence of FGFR1 (FGF receptor 1) inhibitor. Proteoglycan accumulation and chondrocyte proliferation were assessed by dimethylmethylene blue (DMMB) assay and DNA assay, respectively. Expression of FGFRs (FGFR1 to FGFR4) was assessed by flow cytometry, immunoblotting, and quantitative real-time PCR (qPCR). The distinctive roles of FGFR1 and FGFR3 after stimulation with FGF-2 were evaluated using either pharmacological inhibitors or FGFR small interfering RNA (siRNA). Luciferase reporter gene assays were used to quantify the effects of FGF-2 and FGFR1 inhibitor on MMP-13 promoter activity.

RESULTS

Chondrocyte proliferation was significantly enhanced in the presence of FGF-2 stimulation, which was inhibited by the pharmacological inhibitor of FGFR1. Proteoglycan accumulation was reduced by 50% in the presence of FGF-2, and this reduction was successfully rescued by FGFR1 inhibitor. FGFR1 inhibitors also fully reversed the up-regulation of MMP-13 expression and promoter activity stimulated by FGF-2. Blockade of FGFR1 signaling by either chemical inhibitors or siRNA targeting FGFR1 rather than FGFR3 abrogated the up-regulation of matrix metalloproteinases 13 (MMP-13) and a disintegrin and metalloproteinase with a thrombospondin type 1 motif 5 (ADAMTS5), as well as down-regulation of aggrecan after FGF-2 stimulation. Flow cytometry, qPCR and immunoblotting analyses suggested that FGFR1 and FGFR3 were the major FGFR isoforms expressed in human articular chondrocytes. FGFR1 was activated more potently than FGFR3 upon FGF-2 stimulation. In osteoarthritic chondrocytes, FGFR3 was significantly down regulated (P < 0.05) with a concomitant increase in the FGFR1 to FGFR3 expression ratio (P < 0.05), compared to normal chondrocytes. Our results also demonstrate that FGFR3 was negatively regulated by FGF-2 at the transcriptional level through the FGFR1-ERK (extracellular signal-regulated kinase) signaling pathway in human articular chondrocytes.

CONCLUSIONS

FGFR1 is the major mediator with the degenerative potential in the presence of FGF-2 in human adult articular chondrocytes. FGFR1 activation by FGF-2 promotes catabolism and impedes anabolism. Disruption of the balance between FGFR1 and FGFR3 signaling ratio may contribute to the pathophysiology of OA.

The knee meniscus: structure-function, pathophysiology, current repair techniques, and prospects for regeneration

Extensive scientific investigations in recent decades have established the anatomical, biomechanical, and functional importance that the meniscus holds within the knee joint. As a vital part of the joint, it acts to prevent the deterioration and degeneration of articular cartilage, and the onset and development of osteoarthritis. For this reason, research into meniscus repair has been the recipient of particular interest from the orthopedic and bioengineering communities. Current repair techniques are only effective in treating lesions located in the peripheral vascularized region of the meniscus. Healing lesions found in the inner avascular region, which functions under a highly demanding mechanical environment, is considered to be a significant challenge. An adequate treatment approach has yet to be established, though many attempts have been undertaken. The current primary method for treatment is partial meniscectomy, which commonly results in the progressive development of osteoarthritis. This drawback has shifted research interest toward the fields of biomaterials and bioengineering, where it is hoped that meniscal deterioration can be tackled with the help of tissue engineering. So far, different approaches and strategies have contributed to the in vitro generation of meniscus constructs, which are capable of restoring meniscal lesions to some extent, both functionally as well as anatomically. The selection of the appropriate cell source (autologous, allogeneic, or xenogeneic cells, or stem cells) is undoubtedly regarded as key to successful meniscal tissue engineering. Furthermore, a large variation of scaffolds for tissue engineering have been proposed and produced in experimental and clinical studies, although a few problems with these (e.g., byproducts of degradation, stress shielding) have shifted research interest toward new strategies (e.g., scaffoldless approaches, self-assembly). A large number of different chemical (e.g., TGF-β1, C-ABC) and mechanical stimuli (e.g., direct compression, hydrostatic pressure) have also been investigated, both in terms of encouraging functional tissue formation, as well as in differentiating stem cells. Even though the problems accompanying meniscus tissue engineering research are considerable, we are undoubtedly in the dawn of a new era, whereby recent advances in biology, engineering, and medicine are leading to the successful treatment of meniscal lesions.

In vitro ovine articular chondrocyte proliferation: experiments and modelling

This study focuses on analysis of in vitro cultures of chondrocytes from ovine articular cartilage. Isolated cells were seeded in Petri dishes, then expanded to confluence and phenotypically characterized by flow cytometry. The sigmoidal temporal profile of total counts was obtained by classic haemocytometry and corresponding cell size distributions were measured electronically using a Coulter Counter. A mathematical model recently proposed (1) was adopted for quantitative interpretation of these experimental data. The model is based on a 1-D (that is, mass-structured), single-staged population balance approach capable of taking into account contact inhibition at confluence. The model's parameters were determined by fitting measured total cell counts and size distributions. Model reliability was verified by predicting cell proliferation counts and corresponding size distributions at culture times longer than those used when tuning the model's parameters. It was found that adoption of cell mass as the intrinsic characteristic of a growing chondrocyte population enables sigmoidal temporal profiles of total counts in the Petri dish, as well as cell size distributions at 'balanced growth', to be adequately predicted.

Three-dimensional culture of human meniscal cells: extracellular matrix and proteoglycan production

Background

The meniscus is a complex tissue whose cell biology has only recently begun to be explored. Published models rely upon initial culture in the presence of added growth factors. The aim of this study was to test a three-dimensional (3D) collagen sponge microenvironment (without added growth factors) for its ability to provide a microenvironment supportive for meniscal cell extracellular matrix (ECM) production, and to test the responsiveness of cells cultured in this manner to transforming growth factor-β (TGF-β).

Methods

Experimental studies were approved prospectively by the authors' Human Subjects Institutional Review Board. Human meniscal cells were isolated from surgical specimens, established in monolayer culture, seeded into a 3D scaffold, and cell morphology and extracellular matrix components (ECM) evaluated either under control condition or with addition of TGF-β. Outcome variables were evaluation of cultured cell morphology, quantitative measurement of total sulfated proteoglycan production, and immunohistochemical study of the ECM components chondroitin sulfate, keratan sulfate, and types I and II collagen.

Result and Conclusion

Meniscal cells attached well within the 3D microenvironment and expanded with culture time. The 3D microenvironment was permissive for production of chondroitin sulfate, types I and II collagen, and to a lesser degree keratan sulfate. This microenvironment was also permissive for growth factor responsiveness, as indicated by a significant increase in proteoglycan production when cells were exposed to TGF-β (2.48 μg/ml ± 1.00, mean ± S.D., vs control levels of 1.58 ± 0.79, p < 0.0001). Knowledge of how culture microenvironments influence meniscal cell ECM production is important; the collagen sponge culture methodology provides a useful in vitro tool for study of meniscal cell biology.

Biological impact of the fibroblast growth factor family on articular cartilage and intervertebral disc homeostasis

Two members of the fibroblast growth factor (FGF) family, basic FGF (bFGF) and FGF-18, have been implicated in the regulation of articular and intervertebral disc (IVD) cartilage homeostasis. Studies on bFGF from a variety of species have yielded contradictory results with regards to its precise role in cartilage matrix synthesis and degradation. In contrast, FGF-18 is a well-known anabolic growth factor involved in chondrogenesis and articular cartilage repair. In this review, we examined the biological actions of bFGF and FGF-18 in articular and IVD cartilage, the specific cell surface receptors bound by each factor, and the unique signaling cascades and molecular pathways utilized to exert their biological effects. Evidence suggests that bFGF selectively activates FGF receptor 1 (FGFR1) to exert degradative effects in both human articular chondrocytes and IVD tissue via upregulation of matrix-degrading enzyme activity, inhibition of matrix production, and increased cell proliferation resulting in clustering of cells seen in arthritic states. FGF-18, on the other hand, most likely exerts anabolic effects in human articular chondrocytes by activating FGFR3, increasing matrix formation and cell differentiation while inhibiting cell proliferation, leading to dispersed cells surrounded by abundant matrix. The results from in vitro and in vivo studies suggest the potential usefulness of bFGF and FGFR1 antagonists, as well as FGF-18 and FGFR3 agonists, as potential therapies to prevent cartilage degeneration and/or promote cartilage regeneration and repair in the future.

Action of fibroblast growth factor-2 on the intervertebral disc

Introduction

Fibroblast growth factor 2 (FGF2) is a growth factor that is immediately released after cartilage injury and plays a pivotal role in cartilage homeostasis. In human adult articular cartilage, FGF2 mediates anti-anabolic and potentially catabolic effects via the suppression of proteoglycan (PG) production along with the upregulation of matrix-degrading enzyme activity. The aim of the present study was to determine the biological effects of FGF2 in spine disc cells and to elucidate the complex biochemical pathways utilized by FGF2 in bovine intervertebral disc (IVD) cells in an attempt to further understand the pathophysiologic processes involved in disc degeneration.

Methods

We studied the effect of FGF2 on IVD tissue homeostasis by assessing MMP-13 expression (potent matrix-degrading enzyme), PG accumulation, and PG synthesis in the bovine spine IVD, as well as evaluating whether FGF2 counteracts known anabolic factors such as BMP7. To understand the molecular mechanisms by which FGF2 antagonizes BMP7 activity, we also investigated the signaling pathways utilized by FGF2 in bovine disc tissue.

Results

The primary receptor expressed in bovine nucleus pulposus cartilage is FGFR1, and this receptor is upregulated in degenerative human IVD tissue compared with normal IVD tissue. Stimulation of bovine nucleus pulposus cells cultured in monolayer with FGF2 augmented the production of MMP-13 at the transcriptional and translational level in a dose-dependent manner. Stimulation of bovine nucleus pulposus cells cultured in alginate beads for 21 days with FGF2 resulted in a dose-dependent decrease in PG accumulation, due at least in part to the inhibition of PG synthesis. Further studies demonstrate that FGF2 (10 ng/ml) antagonizes BMP7-mediated acceleration of PG production in bovine nucleus pulposus cells via the upregulation of noggin, an inhibitor of the transforming growth factor beta/bone morphogenetic protein signaling pathway. Chemical inhibitor studies showed that FGF2 utilizes the mitogen-activated protein kinase and NF-κB pathways to upregulate noggin, serving as one potential mechanism for its anti-anabolic effects.

Conclusion

FGF2 is anti-anabolic in bovine spine disc cells, revealing the potential of FGF2 antagonists as unique biologic treatments for both prevention and reversal of IVD degeneration.

Fibrochondrogenesis in two embryonic stem cell lines: effects of differentiation timelines

Human embryonic stem cells (hESCs) are an exciting cell source for fibrocartilage engineering. In this study, the effects of differentiation time and cell line, H9 versus BG01V, were examined. Embryoid bodies (EBs) were fibrochondrogenically differentiated for 1, 3, or 6 weeks and then used to engineer tissue constructs that were grown for an additional 4 weeks. Construct matrix was fibrocartilaginous, containing glycosaminoglycans (GAGs) and collagens I, II, and VI. A differentiation time of 3 or 6 weeks produced homogeneous constructs, with matrix composition varying greatly with cell line and differentiation time: from 2.6 to 17.4 microg of GAG per 10(6) cells and from 22.3 to 238.4 microg of collagen per 10(6) cells. Differentiation for 1 week resulted in small constructs with poor structural integrity that could not be mechanically tested. The compressive stiffness of the constructs obtained from EBs differentiated for 3 or 6 weeks did not vary significantly as a function of either differentiation time or cell line. In contrast, the tensile properties were markedly greater with the H9 cell line, 1,562-1,940 versus 32-80 kPa in the BG01V constructs. These results demonstrate the dramatic effects of hESC line and differentiation time on the biochemical and functional properties of tissue-engineered constructs and show progress in fibrocartilage tissue engineering with an exciting new cell source.