Objectives. The purpose of this study was to evaluate chronological changes in the collagen-type composition at tendon–bone interface during tendon–bone healing and to clarify the continuity between Sharpey-like fibres and inner fibres of the tendon. Methods. Male white rabbits were used to create an extra-articular bone–tendon graft model by grafting the extensor digitorum longus into a bone tunnel. Three rabbits were killed at two, four, eight, 12 and 26 weeks post-operatively. Elastica van Gieson staining was used to colour 5 µm coronal sections, which were examined under optical and polarised light microscopy. Immunostaining for type I, II and III collagen was also performed. Results. Sharpey-like fibres comprised of type III collagen in the early phase were gradually replaced by type I collagen from 12 weeks onwards, until continuity between the Sharpey-like fibres and inner fibres of the tendon was achieved by 26 weeks. Conclusions. Even in rabbits, which heal faster than humans, an observation period of at least 12 to 26 weeks is required, because the collagen-type composition of the Sharpey-like fibre bone–tendon connection may have insufficient pullout strength during this period. These results suggest that caution is necessary when permitting post-operative activity in humans who have undergone intra-bone tunnel grafts

Platelet-derived growth factor (PDGF) is known to stimulate osteoblast or osteoprogenitor cell activity. We investigated the effect of locally applied PDGF from poly-d,l-lactide (PDLLA)-coated implants on fracture healing in a rat model. A closed fracture of the right tibia of four-month-old Sprague-Dawley rats (n = 40) was stabilised with implants coated with a biodegradable PDLLA versus implants coated with PDLLA and PDGF. Radiographs were taken throughout the study, and a marker of DNA activity, bromodeoxyuridine (BrdU), was injected before the rats were killed at three, seven and ten days. The radiographs showed consolidation of the callus in the PDGF-treated group compared with the control group at all three time points. In the PDGF-treated group, immunohistochemical staining of BrdU showed that the distribution of proliferating cells in all cellular events was higher after ten days compared with that at three and seven days.

These results indicate that local application of PDGF from biodegradable PDLLA-coated implants significantly accelerates fracture healing in experimental animals. Further development may help fracture healing in the clinical situation.

Tendons display poor intrinsic healing properties and are difficult to treat[1]. Prior in vitro studies[2] have shown that, by targeting the Activin A receptor with magnetic nanoparticles (MNPs), it is possible to remotely induce the tenogenic differentiation of human adipose stem cells (hASCs). In this study, we investigated the tenogenic regenerative potential of remotely-activated MNPs-labelled hASCs in an in vivo rat model. We consider the potential for magnetic controlled nanoparticle mediated tendon repair strategies. hASCs were labelled with 250 nm MNPs functionalized with anti-Activin Receptor IIA antibody. Using a rapid curing fibrin gel as delivery method, the MNPs-labelled cells were delivered into a Ø2 mm rat patellar tendon defect. The receptor was then remotely stimulated by exposing the rats to a variable magnetic gradient (1.28T), using a customised magnetic box. The stimulation was performed 1 hour/day, 3 days/week up to 8 weeks. Tenogenesis, iron deposition and collagen alignment were assessed by histological staining and IHC. Inflammation mediators levels were assessed by ELISA and IHC. The presence of human cells in tendons after 4 and 8 weeks was assessed by FISH analysis. Histological staining showed a more organised collagen arrangement in animals treated with MNPs-labelled cells compared to the controls. IHC showed positive expression of tenomodulin and scleraxis in the experimental groups. Immunostaining for CD45 and CD163 did not detect leukocytes locally, which is consistent with the non-significant levels of the inflammatory cytokines analysis performed on plasma. While no iron deposition was detected in the main organs or in plasma, the FISH analysis showed the presence of human donor cells in rat tendons even after 8 weeks from surgery. Our approach demonstrates in vivo proof of concept for remote control stem cell tendon repair which could ultimately provide injectable solutions for future treatment. We are grateful for ERC Advanced Grant support ERC No.789119, ERC CoG MagTendon No.772817 and FCT grant 2020.01157.CEECIND

Tendon diseases are prevalent health concerns for which current therapies present limited success, in part due to the intrinsically low regenerative ability of tendons. Therefore, tissue engineering presents a potential to improve this outcome. Here, we hypothesize that a concurrent control over both biophysical and biochemical stimuli will boost the tenogenic commitment of stem cells, thus promoting regeneration. To achieve this, we combine molecularly imprinted nanoparticles (MINPs), which act as artificial amplifiers for endogenous growth factor (GF) activity, with bioinspired anisotropic hydrogels. 2. to manufacture 3D tenogenic constructs. MINPs were solid phase-imprinted using a TGF-β3 epitope as template and their affinity for the target was assessed by SPR and dot blot. Magnetically-responsive microfibers were produced by cryosectioning electrospun meshes containing iron oxide nanoparticles. The constructs were prepared by encapsulating adipose tissue-derived stem cells (ASCs), microfibers, and MINPs within gelatin hydrogels, while aligning the microfibers with an external magnetostatic field during gelation. This allows an effective modulation of hydrogel fibrillar topography, mimicking the native tissue's anisotropic architecture. Cell responses were analyzed by multiplex immunoassay, quantitative polymerase chain reaction, and immunocytochemistry. MINPs showed an affinity for the template comparable to monoclonal antibodies. Encapsulated ASCs acquired an elongated shape and predominant orientation along the alignment direction. Cellular studies revealed that combining MINPs with aligned microfibers increased TGF-β signaling via non-canonical Akt/ERK pathways and upregulated tendon-associated gene expression, contrasting with randomly oriented gels. Immunostaining of tendon-related proteins presented analogous outcomes, corroborating our hypothesis. Our results thus demonstrate that microstructural cues and biological signals synergistically direct stem cell fate commitment, suggesting that this strategy holds potential for improving tendon healing and might be adaptable for other biological tissues. The proposed concept highlights the GF-sequestering ability of MINPs which allows a cost-effective alternative to recombinant GF supplementation, potentially decreasing the translational costs of tissue engineering strategies. Acknowledgements: The authors acknowledge the funding from the European Union's Horizon 2020 under grant No. 772817; from FCT/MCTES for scholarships PD/BD/143039/2018 & COVID/BD/153025/2022 (S.P.B.T.), and PD/BD/129403/2017 (S.M.B.), co-financed by POCH and NORTE 2020, under the Portugal 2020 partnership agreement through the European Social Fund, for contract 2020.03410.CEECIND (R.M.A.D.) and project 2022.05526.PTDC; and from Xunta de Galicia for grant ED481B2019/025 (A.P.)

Summary Statement. Differential expression of canonical and noncanonical Wnt signalling along cartilage canals and osteochondral junctions is dependent on age. Increased gene expression of PTHrP along cartilage canals and Ihh along osteochondral junctions suggests paracrine feedback in articular-epiphyseal cartilage. Introduction. Wnt signaling has been shown to regulate chondrocyte differentiation during pre-/post-natal cartilage development. In addition, parathyroid-related peptide(PTHrP) and Indian hedgehog(Ihh) create a negative feedback loop in growth cartilage, but less is known in articular cartilage. The objective of this study was to elucidate expression of regulatory molecules in chondrocytes surrounding cartilage canals and osteochondral junctions during neonatal and pre-adolescent development. We hypothesised there would be increased expression of canonical Wnt signalling molecules and Ihh in osteochondral junction chondrocytes compared to cartilage canal chondrocytes. In addition, we hypothesised that Wnt signaling and PTHrP expression would be greater in neonates than pre-adolescents. Patients & Methods. Osteochondral samples were obtained(IACUC-approved) from normal femoropatellar joints of 14 euthanised immature horses(6 neonates, 8 pre-adolescents). Samples were frozen in OCT for laser capture microdissection(LCM) or fixed in 4% paraformaldehyde and paraffin-embedded for immunohistochemistry. Chondrocytes surrounding cartilage canals and osteochondral junctions were captured using LCM. Following RNA isolation, equine-specific β-catenin, Wnt-4, Wnt-5b, Wnt-11, Dickkopf-1(Dkk-1), low-density lipoprotein receptor-related protein-4,-6(Lrp4, Lrp6), Axin1, Wnt inhibitory factor-1(WIF)-1, secreted Frizzled-related protein-1,-3,-5(sFRP), retinoic acid receptor gamma(RARG), RAR-inducible serine carboxypeptidase(SC-PEP), Ihh, PTHrP, VEGF, PDGF, MMP-13, and 18S mRNA expression levels were evaluated by two-step real-time qPCR. Following immunohistochemistry using rabbit polyclonal or mouse monoclonal primary antibodies (confirmed by Western blot), spatial tissue protein expression was scored (0–3). Statistical analysis included Wilcoxon signed rank test(paired samples) or rank sum test(unpaired samples)(P<0.05). Results. Gene expression in chondrocytes along cartilage canals was significantly higher for PTHrP, β-catenin, Lrp6, Axin1, sFRP5, RARgamma, and SC-PEP than osteochondral junctions. Conversely, gene expression of Ihh, Wnt4, Wnt11, sFRP3, and VEGF were higher in osteochondral junction chondrocytes than cartilage canals. There was higher protein expression of β-catenin, PDGF, VEGF, and MMP-13 along osteochondral junctions than cartilage canals of pre-adolescents. Neonates had higher gene expression of PTHrP, Wnt-5b, sFRP3, Lrp6, and RARG in cartilage canal chondrocytes than pre-adolescents, while Ihh, Wnt-11, Lrp4, and Dkk1 were significantly higher in pre-adolescents. Immunostaining was higher for β-catenin and Wnt-11 in pre-adolescent osteochondral junction cartilage than neonates. No differences were found between age groups for Wnt-4 immunostaining. Dkk1 protein expression was significantly higher in the middle cartilage layer of pre-adolescents than neonates. Immunostaining was greater for Ihh and PTHrP in the deep cartilage layer of pre-adolescents than neonates. PDGF, VEGF, and MMP13 protein expression was higher in the superficial cartilage layer of pre-adolescents than neonates. Discussion. Wnt/β-catenin and Ihh/PTHrP signaling regulate cartilage differentiation during development and are important in endochondral ossification. This study revealed cell-specific, age-related differences in gene/protein expression of both regulatory pathways. Cells surrounding cartilage canals typically appeared small/rounded compared to larger chondrocytes along osteochondral junctions, likely due to different developmental stages. Higher PTHrP gene expression along cartilage canals and Ihh expression along osteochondral junctions may reflect these stages, suggesting paracrine feedback in articular-epiphyseal cartilage. β-catenin signaling may induce chondrocyte hypertrophy, potentially by enhancing Ihh and MMP-13 expression. Differential expression of canonical(β-catenin, Wnt-4, Lrp4, Lrp6) and noncanonical Wnt signalling(Wnt-5b, Wnt-11) and Wnt inhibitors (Dkk1, Axin1, sFRP3, sFRP5, Wif-1) surrounding cartilage canals and osteochondral junctions provides evidence of age-related interactions during postnatal development

Mesenchymal stem cells (MSC) have a well recognised potential for tissue repair. This potential is two pronged: they can differentiate into the functional cell types of the damaged tissues and they can support tissue recovery by secreting trophic factors, depositing an extracellular matrix (ECM) and dampening inflammation. Three-dimensional microscopy recently shown that MSCs in the bone marrow create an intricate proteo-cellular scaffold with the ECM forming an interconnected cellular continuum whose structure is guided by the deposited ECM. This proteo-cellular scaffold controls bone marrow functions from hematopoiesis to osteogenesis. In the current study we aimed to optimise ECM production under in vitro conditions by immortalised MSCs with the view that the generated ECM can be utilised for tissue repair. With immunocytochemistry we determined the deposition of bone marrow-characteristic ECM proteins: collagen I, III, IV, V, VI, laminin and fibronectin. While primary MSCs produced slightly higher amount ECM proteins than immortalised MSCs, the relative abundancy of the ECM proteins was very similar. In order to isolate the ECM, we optimised a decellularisation method based on gentle lysis with sodium-deoxycholate and DNase digestion. Immunostaining for collagen I, III, VI and fibronectin and labelling the nuclei with Hoechst-33342 confirmed removal of all cells while retaining the ECM in its original architecture. Ideally, the decellularised ECM retains associated cytokines and chemokines, such as CXCL12, important for attracting MSCs. To test this, we seeded Molm-13 leukemia cells on decellularised ECM as MSC-produced CXCL12- and other cytokines protect leukemia cells against chemotherapeutics. We found that the decellularisation process however removed these factors and thus for therapeutic purposes, the decellularised ECM would need to be re-loaded with the essential chemo/cytokines. Overall, we developed a system for decellularised ECM production by immortalised MSCs and the results warrant further exploration of this avenue

Aims

Pigment epithelium-derived factor (PEDF) is known to induce several types of tissue regeneration by activating tissue-specific stem cells. Here, we investigated the therapeutic potential of PEDF 29-mer peptide in the damaged articular cartilage (AC) in rat osteoarthritis (OA).

Hematopoietic stem cells (HSCs) reside within a specialised niche area in the bone marrow (BM). They have tremendous clinical relevance, although HSC expansion and culture ex vivo is not currently possible, reducing BM transplant success. This project expands a novel 3D MSC niche model developed in our lab to include HSCs. MSCs were loaded with green fluorescent magnetic iron oxide (FeO. 3. ) nanoparticles (200 nm diameter) at a concentration of 0.1 mg ml. −1. , and incubated for 30 min over a magnet to enhance cellular uptake. The cells were washed, detached and resuspended, then transferred to a plate with magnets above. Spheroids formed within hours and were implanted into 2 mg ml. −1. collagen gel. HSCs were loaded with nanoparticles via incubation with suspension, and then introduced to the gel containing the spheroid. Immunostaining, BrdU and Calcein/ ethidium homodimer viability assays were performed to characterise the cells. Cells in both monolayers and spheroids remain viable up to 7 days in culture. MSCs in monolayers and spheroids were stained with antibodies for: STRO-1, an MSC marker; SDF-1 (CXCL-12), a secreted HSC homing factor; and nestin, a marker for HSC-supportive MSCs in vitro. MSCs in spheroids retain a higher level of expression of all three for 7 days compared to MSCs in monolayers. BrdU assay results show that the MSCs are more quiescent in spheroids compared to monolayers. Proof of principle studies are promising for the success of the proposed niche model. MSCs express a higher level of MSC markers and retain quiescence when they are in spheroids as compared to monolayers. They also express a higher level of HSC niche factor SDF-1α, which facilitates HSC migration and retention

For unrepairable nerve defects, to date autogenous nerves are considered the golden standard, but donor site morbidity, limited availability and operation time prolongation are relevant problem. Acellular nerves from cadaveric donor, introduced since more than one decade ago, represent a novel promising alternative to bridge unrepairable nerve gaps. Aim of this study is to provide a new tool to ameliorate the assistance of the numerous patients suffering from traumatic, oncological and jatrogenic nerve lesions. For this purpose, our project is promoting a progress beyond the state of the art of nerve gaps bridging surgery by developing a new technique to obtain acellular nerve allografts (ANAs). Several methods to examine the effect of detergents on nerve tissue morphology and protein composition have been previously reported. Most of them are too expensive and time consuming. The presented novel decellularization technique is a modification of the Michigan detergent-based organic material removal, to speed up myelin and cellular debris detachment. The previously published Hudson's method. 1. has been chosen as control of the decellularization process). To validate the new nerve decellularization method, in terms of histological characteristics, outcomes were estimated through morphological and immunohistochemical studies in vitro and in vivo. The in vivo study consisted of a 1 cm defect in the tibial nerve of 3 new Zealand rabbits. This nerve defect was microsurgically replaced with a “Rizzoli” acellular nerve allograft. Rabbits were sacrificed 12 weeks after surgery. Endpoints were nerve conduction studies and histology. Histological analysis of processed acellular nerve have been performed to evaluate the preservation of the structure and almost complete clearance of donor cells and cellular debris. Immunostaining analysis confirmed absence of Schwann cells and the maintenance of basal lamina. In vivo studies showed an effective and abundant nerve regeneration through the microsurgically reconstructed nerve defects. This was histologically proven. However no electophysiological return of function was showed. The novel method will allow the storing of acellular nerve allografts. First results obtained by morphological analysis and immunofluorescence experiments and in vivo studies indicate that the internal structure of native nerve is maintained. It is then possible to decellularize nerves with the novel technique reducing both manufacturing times and costs. The relatively inexpensive method of decellularization will facilitate the number of patients that will benefit from reconstruction of nerve defects with ANAs

Aims

To explore the efficacy of extracorporeal shockwave therapy (ESWT) in the treatment of osteochondral defect (OCD), and its effects on the levels of transforming growth factor (TGF)-β, bone morphogenetic protein (BMP)-2, -3, -4, -5, and -7 in terms of cartilage and bone regeneration.

A rat model of lumbar root constriction with an additional sympathectomy in some animals was used to assess whether the sympathetic nerves influenced radicular pain. Behavioural tests were undertaken before and after the operation. On the 28th post-operative day, both dorsal root ganglia and the spinal roots of L4 and L5 were removed, frozen and sectioned on a cryostat (8 μm to 10 μm). Immunostaining was then performed with antibodies to tyrosine hydroxylase (TH) according to the Avidin Biotin Complex method. In order to quantify the presence of sympathetic nerve fibres, we counted TH-immunoreactive fibres in the dorsal root ganglia using a light microscope equipped with a micrometer graticule (10 x 10 squares, 500 mm x 500 mm). We counted the squares of the graticule which contained TH-immunoreactive fibres for each of five randomly-selected sections of the dorsal root ganglia. The root constriction group showed mechanical allodynia and thermal hyperalgesia. In this group, TH-immunoreactive fibres were abundant in the ipsilateral dorsal root ganglia at L5 and L4 compared with the opposite side. In the sympathectomy group, mechanical hypersensitivity was attenuated significantly. We consider that the sympathetic nervous system plays an important role in the generation of radicular pain

Introduction. Mesenchymal stem cells (MSCs) are identified by having the ability to differentiate into various tissues and typically used to generate bone tissue by a process of resembling intramembranous ossification, namely by direct osteoblastic differentiation. However, most bones develop by endochondral ossification, namely via remodeling of hypertrophic cartilaginous templates. To date, reconstruction of bone defects by endochondral ossification using mesenchymal stem cell-derived chondrocytes (MSC-DCs) have not been reported. The purpose of this study was to evaluate the effects of the transplantation of MSC-DCs on bone healing in segmental defects in rat femurs. Methods. Segmental bone defects (5, 10, 15-millimeter) were produced in the mid-shaft of the femur of the Fisher 344 rats and stabilised with an external fixator. Bone marrow was aspirated from the rat's femur and tibia at 4 weeks before operation. MSCs were isolated and grown in culture and seeded on a Poly dl-lactic-co glycolic acid (PLGA) scaffold. Subsequently, the scaffold was cultured using chondrogenic inducing medium for 21 days. The characteristics of the PLGA scaffold are radiolucent and to be absorbed in about 4 months. The Treatment Group received MSC-DCs, seeded on a PLGA scaffold, locally at the site of the bone defect, and Control Group received scaffold only. The healing processes were monitored radiographically and studied biomechanically and histologically. Results. 5-millimeter defect model: The bone defects in the Treatment Group healed radiographically with a bridging callus formation at 4 weeks after the procedure. Micro-CT scans showed that newly formed bone volume in the Treatment Group at 16 weeks was 1.5 times larger than that of the unaffected side. Biomechanical testing revealed that the Treatment Group showed more than 100% higher bending strength compared to the unaffected side at 8 weeks after the procedure. Histological examination showed that the implanted scaffold of the Treatment Group were covered with recipient periosteum-derived bridging callus and filled with cancellous bone-like tissues derived from endochondral ossification. Bone marrow was reconstituted at about 16 weeks after the procedure. Immunostaining examination revealed that the Type 2 collagen, that is the main component of cartilage (MSC-DCs) gradually disappeared and the Type 1 collagen became to be stained better by degrees, i.e. bone was formed clearly. 10, 15-millimeter defect model: Morphological changes were equivalent to 5-millimeter defect model, and the speed of bone regeneration did not depend on the size of the defect length. On the other hand, none of the Control Group achieved bone union. Conclusion. The results of this study suggested that ossification mechanism of MSC-DCs was very close to endochondral ossification. The quality, quantity, and speed of ossification overwhelm those of past similar models, and further development to new bone regeneration can be expected using this method. Summary. Transplantation of mesenchymal stem cell-derived chondrocytes (MSC-DCs) surprisingly enhances bone healing in segmental bone defects in rats significantly better than the previously reported similar therapy using MSCs

Mesenchymal stem cells (MSC) are promising for the treatment of articular cartilage defects; however, common protocols for in vitro chondrogenesis induce typical features of hypertrophic chondrocytes reminiscent of endochondral bone formation. This may implicate a risk for graft stability. We here analysed the early healing response in experimental full-thickness cartilage defects, asking whether and how MSC can differentiate to chondrocytes in an orthotopic environment. Cartilage defects in knees of minipigs were covered with a collagen-type I/III membrane, and half of them received transplantation of expanded autologous MSC. Integration into surrounding cartilage tissue was poor to moderate after 1 and 3 weeks and no sign of cartilaginous matrix production as indicated by negative safranin-O staining was visible for both groups. At 8 weeks regenerative tissue was integrated into the surrounding tissue and a safranin-O positively stained neocartilage was detectable in 4 tissue regenerates out of 6 in the MSC group compared to 2 out of 6 in the MSC-free group. At 1 and 3 weeks after surgery only marginal Col2A1 and no AGC expression were detectable in both groups. At 8 weeks Col2A1 and AGC levels had significantly increased. Hypertrophic maker induction (Col10A1 and MMP13) was similar in both groups 8 weeks after surgery. Immunostaining for collagen type X, however, was restricted to the regenerative tissue close to the subchondral bone in both groups, while collagen type II staining was detected from below the superficial to the deep zone. Our data provide molecular evidence for spontaneous differentiation of MSC in cartilage and the development of a collagen type II positive, collagen type X negative neocartilage. Whether by remodelling of defect filling tissue collagen type X positive areas will further diminish or even disappear from repair cartilage at later stages has to be evaluated in a longer follow-up study

In the pubertal growth plate, sex hormones play important roles for the regulation of the proliferation, differentiation, maturation and programmed death of chondrocytes. Many studies have been reported on the regulation of oestrogen in long bone growth, however, some of the mechanisms have remained unclarified to date including its role for cell kinetics in the growth plate chondrocytes. The aim of this study was to clarify the effect of the deficiency of oestrogen on growth plate chondrocytes. We obtained the growth plates of femoral head from the normal and ovariectomized Japanese white rabbits at 10, 15, 20 and 25 weeks. Ovariectomy was performed at 8 weeks. The cell kinetics of chondrocytes as defined by the numbers of proliferating and programmed dying cells was investigated using immunohistological methods. The lengths of the femur were almost same both in the ovariectomised and normal rabbits. The height of the growth plate was larger in the former. The total number of chondrocytes in the ovariectomised rabbits was less than that of normal rabbits of the same age. Immunostaining of proliferating cell nucleous antigen (PCNA) showed a decrease number of proliferating chondrocytes and that of caspase-3 indicated a little increased number of apoptotic chondrocytes. Oestrogen regulates endochondral bone formation through several pathways. It directly binds oestrogen receptor alpha and beta, and the former accelerates longitudinal bone growth whereas the latter represses it. Another pathway is through the GH-IGF-I axis: it closely interacts with GH and IGF-I for the control of longitudinal bone growth. In addition, there might be other mediators including transforming growth factor-beta, other IGFs and still unknown paracrine or auto-crine factors as IHH PTHrP. Our study suggests that in the rabbit growth plate during puberty, oestrogen mainly acts through the GH-IGF-I axis since its defi-ciency declined the proliferating ability of chondrocytes, which led the decrease of the number of chondrocytes

Aim: Previous investigations have shown the vital role of chondrocyte CD44 in cartilage homeostasis and matrix attachment and indicated a participation of CD44v5 in the development of osteoarthritis. However, all reports dealt with late stage human osteoarthritis, as human specimens are only available at the time of surgery. Thus, little is known about the expression of CD44v5 in the time course of osteoarthritis. The current study was designed to evaluate the expression of CD44v5 on chondrocytes of hyaline cartilage in the time course of osteoarthritis. Methods: In twelve white new-zealand-rabbits the anterior cruciate ligament was resected to create an anterior instability of the knee. In twelve control rabbits only a sham operation without resection of the ACL was done. Four animals of each group were sacrificed at three, six and twelve weeks each. After opening of the knee joint, osteoarthritis was macroscopically graded and hyaline cartilage of the load bearing area was evaluated histologically according to Mankin and by immunostaining for CD44v5. Results: In the trial group, macroscopic and histological grades of OA showed a positive linear correlation to the time after surgery. Immunostaining showed an increased expression of CD44v5 in the control group after 3 and 6 weeks, which dropped to normal after twelve weeks. There was no difference between control and trial groups after 3 and 6 weeks, but after 12 weeks. We found a significant positive correlation between CD44v5-expression and macroscopic (r=0.294) and histological (r=0.314) grades of OA. Conclusion: The current study shows in-vivo an increase of expression of the hyaluronan receptor CD44v5 in the time course of osteoarthritis. Further studies are needed to evaluate whether this pattern applies to human beings and whether new treatment approaches could evolve from this knowledge

Our aim was to investigate whether nitric oxide synthase (NOS) isoforms, responsible for the generation of NO, are expressed during the healing of fractures. To localise the sites of expression compared with those in normal bone we made standardised, stabilised, unilateral tibial fractures in male Wistar rats. Immunostaining was used to determine the precise tissue localisation of the different NOS isoforms. Western blotting was used to assess expression of NOS isoform protein and L-citrulline assays for studies on NOS activity. Control tissue was obtained from both the contralateral uninjured limb and limbs of normal rats. Immunohistochemistry showed increased expression of endothelial NOS (eNOS) to be strongest in the cortical blood vessels and in osteocytes in the early phase of fracture repair. Western blot and image analysis confirmed this initial increase. Significantly elevated calcium-dependent NOS activity was observed at day 1 after fracture. Inducible NOS (iNOS) was localised principally in endosteal osteoblasts and was also seen in chondroblasts especially in the second week of fracture healing. Western blotting showed a reduction in iNOS during the early healing period. Significantly reduced calcium-independent NOS activity was also seen. No neuronal NOS was seen in either fracture or normal tissue. Increased eNOS in bone blood vessels is likely to mediate the increased blood flow recognised during fracture healing. eNOS expression in osteocytes may occur in response to changes in either mechanical or local fluid shear stress. The finding that eNOS is increased and iNOS reduced in early healing of fractures may be important in their successful repair

Animal studies examining tendon-bone healing have demonstrated that the overall structure, composition, and organization of direct type entheses are not regenerated following repair. We examined the effect of Low-Intensity Pulsed Ultrasound (LIPUS) on tendon-bone healing. LIPUS may accelerate and augment the tendon-bone healing process through alteration of critical molecular expressions. Eight skeletally mature wethers, randomly allocated to either control group (n=4) or LIPUS group (n=4), underwent rotator cuff surgery following injury to the infraspinatus tendon. All animals were sacrificed 28 days post surgery to allow examination of early effects of LIPUS. Humeral head – infraspinatus tendon constructs were harvested and processed for histology and immunohistochemical staining for BMP2, Smad4, VEGF and RUNX2. All the growth factors were semiquantitative evaluated. T-tests were used to examine differences which were considered significant at p < 0.05. Levene's Test (p < 0.05) was used to confirm variance homogeneity of the populations. The surgery and LIPUS treatment were well tolerated by all animals. Placement of LIPUS sensor did not unsettle the animals. Histologic appearance at the tendon-bone interface in LIPUS treated group demonstrated general improvement in appearance compared to controls. Generally a thicker region of newly formed woven bone, morphologically resembling trabecular bone, was noted at the tendon-bone interface in the LIPUS-treated group compared to the controls. Structurally, treatment group also showed evidence of a mature interface between tendon and bone as indicated by alignment of collagen fibres as visualized under polarized light. Immunohistochemistry revealed an increase in the protein expression patterns of VEGF (p = 0.038), RUNX2 (p = 0.02) and Smad4 (p = 0.05) in the treatment group. There was no statistical difference found in the expression patterns of BMP2. VEGF was positively stained within osteoblasts in newly formed bone, endothelial cells and some fibroblasts at the interface and focally within fibroblasts around the newly formed vessels. Expression patterns of RUNX2 were similar to that of BMP-2; the staining was noted in active fibroblasts found at the interface as well as in osteoblast-like cells and osteoprogenitor cells. Immunostaining of Smad4 was present in all cell types at the healing interface. The results of this study indicate that LIPUS may aid in tendon to bone healing process in patients who have undergone rotator cuff repair. This treatment may also be beneficial following other types of reconstructive surgeries involving the tendon-bone interface

Mechanical load is crucial to maintaining skeletal homeostasis, but the pathways involved in mecha-notransduction are still unclear. The OPG/RANK/ RANKL triumvirate has recently been implicated in bone homeostasis. These molecules, which are produced by the osteoblast (OPG and RANKL) and the macrophage/osteoclast (RANK), modulate osteoclastogenesis. We have previously shown that cyclical hydrostatic pressure influenced synthesis of various molecules by cultured human macrophages. These factors are important in osteoclastogenesis and bone resorption and have been linked to the development of aseptic loosening. We have also demonstrated that 1,25-dihydroxyvitamin D3 (1,25D3) influences macrophage response to pressure. For this study human macrophages were co-cultured with osteoblasts and subjected to cyclical hydrostatic pressure (34.5x10–3MPa [5.0 psi]) for up to five days, with or without 1,25D3 supplementation. Cells were immunostained for RANK and culture media were assayed for sRANKL and OPG using specific ELISAs. Immunostaining for RANK showed that macrophages subjected to pressure or 1,25D3 supplementation synthesised more RANK than controls. In addition, when exogenous 1,25D3 and hydrostatic pressure were administered simultaneously, immunostaining for RANK was more intense. There was a reciprocal relationship between OPG and sRANKL in co-cultures subjected to pressure. If pressure increased synthesis of sRANKL, OPG was decreased. In cultures where pressure decreased sRANKL, a corresponding increase in OPG was seen. In addition, samples from different individuals responded differently to pressure. The majority of cell populations responded to pressure by increasing OPG synthesis, compared to non-pressurised controls. These results demonstrate for the first time that the OPG/RANK/RANKL complex is sensitive to hydrostatic pressure and that 1,25-dihydroxyvitamin D3 might be involved in this response. These findings suggest a possible transduction mechanism for mechanical load in the skeleton, which has implications for future therapies for aseptic loosening and for skeletal abnormalities such as osteoporosis

Aim: To investigate the directed chondrogenic differentiation of human embryonic and adult stem cells in 3D alginate bead culture. Introduction: Cartilage possesses limited self-renewal potential and current repair of damage due to trauma or disease involves removal of non-load bearing chon-drocytes from a healthy part of the joint, expansion of chondrocytes and subsequent surgery to replace damaged, load-bearing cartilage. We investigated the potential of human embryonic and adult stem cells as an alternative cell source for cartilage repair. Experimental design: Human embryonic stem cells (hESC) and human adult marrow stromal cells (hMSCs) cells were cultured in alginate in a 3D bead format in control or chondrogenic media over a 21day period. Cells were subsequently released from their matrix for gene expression analysis or fixed within alginate beads and crytostat sections prepared for immunostaining and histology. Cell types used: H9 human embryonic stem cells, bone-marrow derived hMSCs and HEK293 (human embryonic kidney epithelium cell line, used as a negative control). Data: H9 and hMSC cells cultured in alginate beads bathed in control media have a denser matrix with no lacunae-like structures compared to those cultured in the presence of chondrogenic media. The presence of chondrogenic media results in a matrix containing cells within lacunae-like structures very similar to those seen in human cartilage. In contrast, HEK293 cells formed large highly cellular clusters which had clearly undergone significant proliferation. As both H9 and HEK293 cells are highly proliferative the reduction in the proliferative potential of the chondrogenic H9 derived cells is consistent with entry into a stable terminally differentiated state. Immunostaining demonstrated that hMSCs and H9 cells express cartilage specific Collagen II and Collagen X. Conclusion: 3D culture of adult hMSCs and hESC (H9) in alginate beads has resulted in stable directed differentiation down the chondrogenic lineage. These data point towards the future use of these human cell sources in cartilage repair

Purpose: The objective of this project is to determine the suitability of modified fibrin hydrogels as scaffolds for articular cartilage tissue engineering. The attractive feature of the fibrin system is that the gel precursors are available in autologous form. We have previously demonstrated that genipin, a naturally occurring cross-linking agent, stabilizes the fibrin gel. Methods: Human articular chondrocytes were isolated from articular cartilage harvested from consenting patients undergoing total knee arthroplasty. The human cells were encapsulated into fibrin gels where gelation was induced by combining fibrinogen, thrombin, and genipin. The resulting gels were evaluated for extracellular matrix (ECM) production, mechanical properties, cell viability, and biodegradation. Results: No breakdown of the gels was detected during 5 weeks of cell culture. After several weeks in culture, histology indicates significant proteoglycan production by encapsulated cells, and collagen II and aggrecan were detected in this ECM by immunostaining. There was a greater accumulation of cartilage-like ECM in the gels cross-linked with genipin. Dynamic compression tests performed at 0.1 Hz for 10 cycles using an MTS machine indicate that accumulation of ECM was associated with increased stiffness of the material. Cell viability was assessed using live/dead staining, and was found to be > 50% after 24 hours and at 1 week in culture. The presence of genipin cross-linking did not significantly affect cell viability. Real-Time RT-PCR indicated that encapsulated chondrocytes show an increase in Sox9, collagen II and aggrecan expression over 5 weeks and that this is further increased in the presence of genipin. The gene expression results agreed with the enhanced ECM seen under these conditions by histology and immunostaining. The fibrin material was also implanted subcutaneously into rats and after 30 days the material was removed, sectioned and evaluated. Immunostaining indicated that while there was evidence of biodegradation, the material did not appear to cause an inflammatory response. Conclusions: Modified fibrin hydrogels show potential as cellular scaffolds for articular cartilage tissue engineering. An in vivo orthopaedic model must now be developed to fully evaluate the potential of the fibrin gel. Funding: Other Education Grant