Meniscus tears have been treated using partial meniscectomy to relieve pain in patients, although this leads to the onset of early osteoarthritis (OA). Cell-based therapies can help preserve the meniscus, although the presence of inflammatory cytokines compromises clinical outcomes. Anti-inflammatory drugs (e.g. celecoxib), can help to reduce pain in patients and in vitro studies suggest a beneficial effect on cytokine inhibited matrix content. Previously, we have demonstrated that the inhibitory effects of IL-1β can be countered by culture under low oxygen tension or physioxia. The present study sought to understand whether physioxia, celecoxib or combined application can counter the inhibitory effects IL-1β inhibited meniscus cells. Human avascular and vascular meniscus cells (n =3) were isolated and expanded under 20% (hyperoxia) or 2% (physioxia) oxygen. Cells were seeded into collagen scaffolds (Geistlich, Wolhusen) and cultured for 28 days either in the presence of 0.1ng/mL IL-1β, 5µg/mL celecoxib or both under their expansion oxygen conditions. Histological (DMMB, collagen I and collagen II immunostaining), GAG content and gene expression analysis was evaluated for the scaffolds. Under hyperoxia, meniscus cells showed a significant reduction in GAG content in the presence of IL-1β (*p < 0.05). Celecoxib alone did not significantly increase GAG content in IL-1β treated cultures. In contrast, physioxic culture showed a donor dependent increase in GAG content in control, IL-1β and celecoxib treated cultures with corresponding histological staining correlating with these results. Additionally, gene expression showed an upregulation in COL1A1, COL2A1 and ACAN and a downregulation in MMP13 and ADAMTS5 under physioxia for all experimental groups. Physioxia alone had a stronger effect in countering the inhibitory effects of IL-1β treated meniscus cells than celecoxib under hyperoxia. Preconditioning meniscus cells under physioxia prior to implantation has the potential to improve clinical outcomes for cell-based therapies of the meniscus

Aims

This study aimed to investigate the role and mechanism of meniscal cell lysate (MCL) in fibroblast-like synoviocytes (FLSs) and osteoarthritis (OA).

Introduction and Objective. The meniscus is composed of two distinct regions, a vascular outer zone and an avascular inner zone. Due to vascularization, tears within the vascular zone can be treated by suturing. However, tears in the avascular zone have a poor healing capacity and partial meniscectomy is used to prevent further pain, although this leads to early osteoarthritis. Previous studies have demonstrated that the vascular zone contains a progenitor population with multilineage differentiation potential. Isolation and propagation of these progenitors can be used to develop cell-based therapies for treating meniscal defects. In vivo, the meniscus resides under a low oxygen environment, also known as physioxia (2–7% oxygen) and previous work suggests that it promotes the meniscal phenotype. The objective of the study was to isolate progenitor populations from both meniscus regions and to examine their clonogenecity and differentiation potential under both hyperoxia (20% oxygen) and physioxia (2% oxygen). We hypothesize that physioxia will have a beneficial effect on colony formation and trilineage differentiation of meniscal cells. Materials and Methods. Human meniscus (n =4; mean age: 64 + 6) tissue was split into vascular and avascular regions, finely cut into small pieces and then sequentially digested in pronase (70U/mL) and collagenase (200U/mL) at 37. 0. C. Avascular and vascular meniscus cells were counted and split equally for expansion under hyperoxia and physioxia at a seeding density of 5 × 10. 3. cells/cm. 2. At passage 1, cells were seeded at 2, 5 and 20 cells/cm. 2. in 10cm dishes for observing colony formation using crystal violet assay. At passage 3, vascular and avascular meniscus cells were differentiated towards the chondrogenic, osteogenic and adipogenic lineage. Chondrogenesis was evaluated using DMMB staining for GAG deposition, osteogenesis was assessed using Alizarin Red staining for calcium deposition, whilst adipogenesis was observed using Oil-Red-O staining for fat droplets. Results. Expansion of vascular and avascular meniscus cells showed no difference in doubling time between hyperoxic or physioxic culture. However, physioxia significantly increased the number of colonies compared to hyperoxia for both meniscus cell types (p < 0.05). Both vascular and avascular meniscus cells differentiated towards the chondrogenic, osteogenic and adipogenic lineage under both oxygen tensions. Interestingly, we observed greater DMMB, alizarin red and oil-red-o staining for vascular meniscal cells under physioxia compared to corresponding hyperoxic cultures and avascular meniscal cells. Conclusions. Physioxia enhances the clonogenecity of vascular and avascular meniscus cells. Trilineage differentiation potential was observed from both regions with increased capacity detected under physioxia for vascular meniscal cells. Physioxic isolation of meniscal cells for the propagation of these progenitors can used be for the treatment of meniscal tears/defects

Aims. Meniscal injuries are common and often induce knee pain requiring surgical intervention. To develop effective strategies for meniscus regeneration, we hypothesized that a minced meniscus embedded in an atelocollagen gel, a firm gel-like material, may enhance meniscus regeneration through cell migration and proliferation in the gel. Hence, the objective of this study was to investigate cell migration and proliferation in atelocollagen gels seeded with autologous meniscus fragments in vitro and examine the therapeutic potential of this combination in an in vivo rabbit model of massive meniscus defect. Methods. A total of 34 Japanese white rabbits (divided into defect and atelocollagen groups) were used to produce the massive meniscus defect model through a medial patellar approach. Cell migration and proliferation were evaluated using immunohistochemistry. Furthermore, histological evaluation of the sections was performed, and a modified Pauli’s scoring system was used for the quantitative evaluation of the regenerated meniscus. Results. In vitro immunohistochemistry revealed that the meniscus cells migrated from the minced meniscus and proliferated in the gel. Furthermore, histological analysis suggested that the minced meniscus embedded in the atelocollagen gel produced tissue resembling the native meniscus in vivo. The minced meniscus group also had a higher Pauli’s score compared to the defect and atelocollagen groups. Conclusion. Our data show that cells in minced meniscus can proliferate, and that implantation of the minced meniscus within atelocollagen induces meniscus regeneration, thus suggesting a novel therapeutic alternative for meniscus tears. Cite this article: Bone Joint Res 2021;10(4):269–276

Objectives

Meniscal injuries are often associated with an active lifestyle. The damage of meniscal tissue puts young patients at higher risk of undergoing meniscal surgery and, therefore, at higher risk of osteoarthritis. In this study, we undertook proof-of-concept research to develop a cellularized human meniscus by using 3D bioprinting technology.

Meniscus is mainly composed of three different cell types; chondrocytes(Ch) situate in the superficial zone, whereas fibroblast-like cells locate in the peripheral region having long cell extensions in contact with different parts of the matrix, fibrochondrocytes(FC), is from the inner part of the meniscus and show a clear cell associated matrix. The aim of this study is to develop meniscus cell population using with mesenchymal stem cells (MSCs). For this purpose, MSCs were isolated from rabbit bone marrow and verified by flow cytometry analyses using cell surface markers (CD73APC, CD90FITC, CD34PE, CD45PE/Cy5.5). The results indicate that CD73 and CD90-positive cells were 92.8%, and CD 45 and CD 34-negative cells were 52.4%. Differentiation potential of MSCs were also evaluated by differentiating into Ch, osteoblasts (Ob), adipocytes (Ad), fibroblasts (Fb). Histology stainings showed that differentiated Ch can produce proteoglycans, Ob have mineralization property, Fb have spindle shape and Ad have oil drops morphology. Afterwards Fb, Ch and undifferentiated MSCs (for formation of the FC) were seeded in same plate in cocktail medium and Fb, Ch, seeded individually, were used as control group. Proliferation activity of the cells was analyzed by XTT assay at 3. th. ,7. th. and14. th. days. In addition, cells were analyzed by flow cytometry with identical surface markers at 3. th. ,7. th. and14. th. days. Results show that cell cocktail have the greatest proliferation ability with a greater speed than the individual Ch or Fb cultures. In addition, FC formation was identified by histological staining. In conclusion, meniscus specific cell population has been successfully generated from the cell cocktail containing rabbit MSCs

Meniscus tears in adult patients do not heal spontaneously and represent a risk factor for OA development. PDGF is well known as an enhancer of meniscal cell biosynthetic activity and also has chemotactic activity for mesenchymal cells. PDGF incorporation into scaffolds should be efficient for recruitment of cells to initiate repair in the injured meniscus. We recently developed decellularized meniscus sheet for use in the treatment of meniscus tears. The aim of this study is to examine the potential of PDGF-coated decellularized meniscus scaffold in mediating integrative healing by endogenous cell migration. Fresh bovine meniscus was chemically decellularized. Round sheets were made from the decellularized tissue. Heparin was covalently conjugated with decellularized meniscus scaffold (DMS). PDGF-BB was immobilized by binding to the heparin-conjugated DMS. In vitro, PDGF release kinetics was analyzed by ELISA. DMS was transplanted into the injured meniscus explants and cultured for 2 and 4 weeks. The numbers of migrated cells at the border between DMS and injured explant were counted on DAPI stained sections and PDGFRb expressing cells were counted after immunohistochemical staining. The newly produced ECM and collagen fiber alignment was detected by histology on Safranin-O and picrosirius red stained sections. The explants were also tested for tensile properties. PDGF release kinetics showed sustained slow release in heparin-conjugated DMS, with 11.2% release at day- 16th compared to 26.1% release from the DMS without heparin. Insertion of the PDGF-treated DMS into the meniscus tears in bovine meniscus explants led to the migration of endogenous meniscus cells to the defect zone. The migrated cells expressed PDGFRb and produced new ECM in the defect area. Safranin-O and pircrosirius red staining showed tissue integration between DMS and injured explants. Moreover, the higher concentration of PDGF promoted cell integration into the DMS. Tensile properties of injured explants treated with PDGF coated DMS were significantly higher than in DMS without PDGF. Heparin-conjugated DMS showed strong immobilization of PDGF, which was released slowly. PDGF coated DMS promoted migration of endogenous meniscus cells to the defect area and into the scaffold. New matrix was formed that bridged the space between the native meniscus and the scaffold and this was associated with improved biomechanical properties. The PDGF coated DMS is a novel, feasible and efficient approach for the treatment of meniscus tears

Background. Hyaluronan (HA) promotes extracellular matrix (ECM) production and inhibits the activity of matrix degrading enzymes in chondrocytes. The meniscus is composed of the avascular inner and vascular outer regions. Inner meniscus cells have a chondrocytic phenotype compared with outer meniscus cells. In this study, we examined the effect of HA on chondrocytic gene expression in human meniscus cells. Methods. Human meniscus cells were prepared from macroscopically intact lateral meniscus. Inner and outer meniscus cells were obtained from the inner and outer halves of the meniscus. The proliferative activity of meniscus cells was evaluated by WST-1 assay in the presence or absence of HA (MW = 600–1200 kDa; Seikagaku). Gene expression of SOX9, COL2A1, and COL1A1 was assessed by a quantitative real-time PCR analysis. The effect of HA on the gene expression and cellular proliferation was investigated under the treatment of interleukin (IL)-1α. Meniscal samples perforated by a 2-mm-diameter punch were maintained for 3 weeks in HA-supplemented media. Cultured meniscal samples were evaluated by histological analyses. Results. HA treatments stimulated cellular proliferation in both inner and outer meniscus cells. HA also increased COL2A1 expression in inner meniscus cells. On the other hand, HA did not induce COL2A1 expression in outer meniscus cells. Although IL-1α treatment decreased COL2A1 expression in inner meniscus cells, the decrease of COL2A1 expression was prevented by HA treatments. In addition, HA treatments increased cellular counts along the perforated surface of organ-cultured meniscal samples. Conclusion. The present study demonstrated that HA activated the proliferation and chondrocytic gene expression of inner meniscus cells. In addition, IL-1α-dependent decrease of COL2A1 expression was prevented by HA treatment. Our results suggest that intra-articular HA injection may be useful in the treatment of inner meniscal injury. Level of evidence. in vitro study, level IV. Disclosure. The authors have no conflicts of interest

Purpose. The biomechanical role of the meniscus in the knee joint is a function of its extracellular matrix which consists of type I collagen throughout, type II collagen in the inner meniscus region and glycosaminoglynated (GAG) proteins of which aggrecan is the most prevaleet. Meniscus reparative capacity is limited, particularly when a defect is located in the inner avascular portion, and menisectomy predisposes the joint to osteoarthritis. Using meniscus cells in tissue engineering strategies has been advocated to generate functional meniscus substitutes. However, meniscus cells, like chondrocytes of cartilage, lose their matrix-forming phenotype during culture expansion. Co-culture of chondrocytes with stem cells has been shown to result in enhanced matrix formation. We hypothesized that meniscus cells in co-culture with stem cells will result in increased matrix formation. Method. Tissue specimens were obtained after approval of the local ethical committee and informed consent. Menisci were obtained from 3 patients undergoing total knee arthroplasty; (53–84; mean age 66.6). Meniscus cells were isolated after digestion of menisci with collagenase II. Isolated meniscus cells were plated for 24–48 hr before use. Bone marrow aspirates were obtained from the iliac crest of 3 donors: 1 female (46) and 2 males (15 and 21) undergoing routine orthopaedic procedures. Plastic adherent bone marrow stromal cell populations were isolated and expanded under normal oxygen tension of 21%O2 in a-MEM growth media plus FGF-2 until passage 2. Cells were mixed at a variety of meniscus cells (Men): BMSC ratio including 5/95, 10/90 and 25/75, respectively. Mixed cells were centrifuged to form spherical pellets followed by culture in a defined serum free chondrogenic differentiation medium. Control groups were pure Men and pure BMSCs. Total cell number per pellet was 25×104. Pellets were cultured for 3 weeks under normal oxygen tension. Thereafter, pellets were processed: biochemically for GAG and DNA content, and histologically for Safranin-O staining of sulphated GAG and immunohistochemical analyses for collagen types I and II. Analysis was performed on a minimum of 2 independent pellets. Results. Relative to pure cell control pellets, co-cultured cell pellets of expanded human BMSCs and meniscus cells had more GAG matrix per DNA content. The amplitude of GAG enhancement in all co-cultures varied with donor and with the Men:BMSC ratio. However, the mean GAG enhancement was 1.8–6 fold. The GAG contents of pellets correlated with Safranin-O staining. Positive staining for collagens types I and II was increased in co-cultured cell pellets. Conclusion. Co-seeding of meniscus cells and stem cells on a suitable scaffold may aid the generation of functional grafts with improved biomechanical properties relative to those generated via expanded meniscus cells alone or stem cells alone

Introduction and Objectives: Cryopreservation as a meniscus conservation method affects cellularity to a lesser degree than simple freezing. Recent studies have shown that freezing alters meniscus ultrastructure. The effects of cryopreservatioin on the meniscus collagen net has not been so extensively studied. The aim of this study was to determine if cryopreservation alters meniscus ultrastructure and cellularity. Materials and Methods: We obtained 10 external menisci for the purpose of studying their cellularity and collagen structure before and after cryoprservation at −180°C. We analyzed the architecture of the meniscus collagen using transmission electronic microscopy and assessed the degree to which this was altered according to a previously determined scale. We measured collagen fibers in transverse and longitudinal sections, and also calculated the percentage of cells that survived cryopreservation. Results: Cryopreserved menisci averaged 4.8 points and the control menisci 4.1 (p< 0.17). In the cryopreserved menisci the collagen fibers in longitudinal section had a mean length of 12.61 nm and in the control menisci 13.38 nm (p=0.34), whereas in transverse sections the average was 15.48 nm and 16.7 nm respectively (p=0.41). The percentage of cells that survived cryopreservation went from 3.99 to 53.57%. Discussion and Conclusions: Cryopreservation does not alter meniscus ultrastructure. Cell survival is highly variable. Results suggest that cryopreservation would be a more appropriate method than freezing at −80°C for the preservation of meniscal allografts

The meniscus of the human knee joint has an outstanding function for stability, shock absorption and power transmission of the thigh on the shank. After a meniscus trauma so far often only the partial or complete removal of the meniscus has to be performed. Only with injuries in the outside third a primary suture of a tear leads to the healing due to the existing vascularisation in a high number of cases in younger patients. After partial or total meniscektomie cartilage degeneration and resulting osteoarthrosis of the knee joint often is the consequence. A goal of our investigations was the establishment of meniscus cell cultures as well as their characterisation regarding the expression of different growth factors, cytokines and proteins and the influence by adding different recombinant growth factors. We are able to cultivate human fibrochondrocytes, which originate from menisci of the knee from patient undergoing total knee replacement. Investigations were performed by immune-histochemistry and RT PCR. We could show the expression of collagen I, II, III and VI, the matrix-metalloproteinases 1, -2, -3 and -8 in the human meniscus. In Addition the expression of TGFβ1, BMP II, AS.02, Thy 1, TGFβ1, iNOS and interleukin (IL) -1, -6 and -18, ECGF and VEGF was proved. PDGF-1 and collagen X could not be found in the meniscus investigated. Same expression analysis was performed in same patients’ synovial cells and chondrocytes from knee joint. Differences were found in the collagen expression. Synovial cells do not synthesise collagen II but collagen I. Investigated chon-drocytes show a high level of collagen I an II expression, but fibrochondrocytes a low level of collagen II and high of collagen I, too. After stimulation of meniscus cells with IL-1, TGFβ1 and TNF-α no difference was found in the expression of TGFβ1, BMP II and IL-18, but a total inhibition of IL-6. TGFβ1 suppressed IL-1 expression totally compared to not stimulated fibrochondrocytes. We were able to cultivate, characterize and stimulate human fibrochondrocytes from meniscus of the knee. We could show that meniscus cells express a huge amount of different growth factors, cytokines and proteins and can be distinguished from synovial cells and joint chondrocytes by the low level expression of collagen II. We also investigated first time the reaction of human meniscus cells after stimulation by recombinant growth factors. These results are a basis for the tissue engineering of meniscus tissue

Introduction: After a meniscus trauma, preservation of the meniscus is the most important surgical goal. The use of scaffolds colonized with meniscus cells (fibrochondrocytes) to reconstruct meniscal defects seem to be a promising way for the treatment of a meniscus trauma. The goal of our investigations was the analysis of expression of different anabolic and catabolic factors in human fibrochondrocytes after seeding these cells onto a collagen I scaffold to investigate the regenerative potential of such a construct for the treatment of meniscus tears. Material and Methods: Human meniscus tissue was digested in collagenase and dispase and cells were characterized by immunohistochemistry. To test scaffolds, we used a commercially available bovine collagen I matrix approved for surgical purposes. The scaffold was colonized with human fibrochondrocytes in a density of 106 cells per cm2. Cells expanded at the same ínoculation density w/o scaffold served as mock-controls. After 14 and 28 days in culture, the cells were extracted from the scaffold by aid of collagenase (Sigma, Deisenhofen, FGR) and analyzed for the expression of different factors, including IL-1β, IL-6, TGF-β, TIMP-1, TIMP-3, MMP-1, and MMP-3 using a quantitative RT-PCR-technology. Results: Bovine collagen I matrices could be colonized with human fibrochondrocytes. After 14 and 28 days of incubation on the scaffolds, the cells show the same mRNA expression levels of IL-1β, TIMP-1, TIMP-3, and TGF-β when compared to controls. In contrast, after 14 days IL-6 (12.7-fold ± 4.4, p< 0.001), MMP-1 (11.3-fold ± 2.4, p< 0.001), and MMP-3 (13.7-fold ± 6.8, p< 0.031) were upregulated on transcription levels in the scaffold when compared to controls after the same period of culture. After 28 days of culture in scaffold the expression of MMP-3 was upregulated 78.2-fold (± 7.4, p< 0.0001), MMP-1 (71.3-fold ± 5.9, p< 0.0001) and IL-6 was elevated 98.9-fold (± 9.1, p< 0.0001) compared to controls. Discussion/Conclusion: We were able to cultivate and characterize human fibrochondrocytes from menisci of the knee joint colonized onto a bovine collagen I matrix. We could show that meniscus cells revealed a significantly increased expression of MMP-1 and MMP-3, and also a significant elevation of IL-6 mRNA after 14 and 28 days of culture. No changes were found in the expression levels of IL-1β, TGF-β, and the TIMPs. This suggests that the meniscus cells colonized onto a bovine collagen I scaffold produce a considerable amount of catabolic or inflammatory factors. This may lead to a destruction of the scaffold-matrix itself and the extracellular matrix of the meniscus. Secondly, IL-6 could induce a global inflammation around the scaffold by activating the IL-6 inflammation cascade

Introduction: The highest goal after meniscus damage is the preservation of the meniscus, which is often not possible due to the bad healing of meniscus lesions in the avascular zone. Therefore, the goal of our investigations was the analysis of expression of different angiogenic factors, growth hormones and cytokines in human meniscus cells (fibrochondrocytes). The mutual influence of the fibrochondrocytes by endothelial cell cocultures was analyzed, in order to examine the molecular bases of the healing of meniscus tears in vascularized zones more exactly. For this purpose, commercially available HUVEC [human umbilical vein endothelial cells] were used as well established and stable endothelial cell model. Material and Methods: Meniscal fibrochondrocytes were expanded in DMEM medium enriched with antibiotics and 10 % FCS. Cocultures of mensical cells and HUVEC were incubated in transwells over four and twelve days, separated by a semipermeable membrane. The expression of Angiopoietin-1, Angiopoietin-2, End-ostatin, VEGF, SMAD-4, Thrombospondin-1, Aggrecan, Biglycan, Fibronectin, Vimentin, Connexin-43, IL-1β, iNOS, MMP-1, MMP-3, MMP-13, collagen-I, -II, -III, -VI, X, and -XVIII were examined by RT-PCR and immunhistochemistry in fibrochondrocytes in the comparison to cultures without endothelial coculture. A proliferation assay was used to investigate the mitotic activity in the coculture compared to the control culture after 4 and 12 days. Results: In presence of HUVEC, meniscal fibrochon-drocytes expressed the following factors at rates comparable to cells w/o HUVECS: Angiopoietin-1, Angiopoietin-2, VEGF, SMAD-4, Aggrecan, Biglycan, Fibronectin, Vimentin, Connexin-43, iNOS, MMP-1, MMP-3, MMP-13, Thrombostatin-1, collagen-I, -II, -III, -VI, X, and -XVIII. In contrast, expression of end-ostatin (5.1-fold ± 1.2, p< 0.01) and IL-1β (10.3-fold ± 2.3, p< 0.003) were expressed significantly higher in the coculture when compared to the individual cell cultures. The proliferation rate of HUVEC was significantly decreased in coculture when compared to controls: 22 % after 7 days and 35 % after 14 days (p< 0.001). Discussion/ Conclusion: We were able to cultivate and characterize human fibrochondrocytes from menisci of the knee joint. We could show that coculture of meniscus cells with endothelial cells revealed an increased expression of the anti-angiogenetic factor endostatin and the pro-inflammatory IL-1β. This suggests that meniscus cells are trying to inhibit proliferation of endothelial cells in their neigbourhood, which implicates huge problems in the research field of neoangiogenisis and tissue engineering in meniscus tissue for new healing methods after meniscus trauma