Bone tissue is known to possess an intrinsic regeneration potential. However, in cases of major injury, trauma, and disease, bone loss is present, and the regeneration potential of the tissue is often impaired. The process of bone regeneration relies on a complex interaction of molecules. MicroRNAs (miRNA) are small, non-coding RNAs that inhibit messenger RNAs (mRNA). One miRNA can inhibit several mRNAs and one mRNA can be inhibited by several miRNAs. Functionally, miRNAs regulate the entire proteome via the local inhibition of translation. In fact, miRNA modulation has been shown to be involved in several musculoskeletal diseases. 1. In those pathologies, they modulate the transcriptional activity of mRNAs important for differentiation, tissue-specific activity, extracellular matrix production, etc. Because of their function in inhibiting translation, miRNAs are being researched in many diseases and are already being used for interventional treatment. 2. Bone tissue and its related conditions have been widely investigated up to this day. 1,3. This talk will focus on the relevancy of miRNAs to bone tissue, its homeostasis, and disease. After, examples will be given of how miRNAs can be used in bone regeneration and diseases such as osteoporosis and osteosarcoma. The use of miRNAs in both, detection and therapy will be discussed

Osteoclasts (OCs) are multinucleated cells that play a pivotal role in skeletal development and bone remodeling. Abnormal activation of OCs contributes to the development of bone-related diseases, such as osteoporosis, bone metastasis and osteoarthritis. Restoring the normal function of OCs is crucial for bone homeostasis. Recently, RNA therapeutics emerged as a new field of research for osteoarticular diseases. The aim of this study is to use non-coding RNAs (ncRNAs) to molecularly engineer OCs and modulate their function. Specifically, we investigated the role of the microRNAs (namely miR-16) and long ncRNAs (namely DLEU1) in OCs differentiation and fusion. DLEU1/DLEU2 region, located at chromosome 13q14, also encodes miR-15 and miR-16. Our results show that levels of these ncRNA transcripts are differently expressed at distinct stages of the OCs differentiation. Specifically, silencing of DLEU1 by small interfering RNAs (siDLEU1) and overexpression of miR-16 by synthetic miRNA mimics (miR-16-mimics) led to a significant reduction in the number of OCs formed per field (OC/field), both at day 5 and 9 of the differentiation stage. Importantly, time-lapse analysis, used to track OCs behavior, revealed a significant decrease in fusion events after transfection with siDLEU1 or miR-16-mimics and an alteration in the fusion mode and partners. Next, we investigated the migration profile of these OCs, and the results show that only miR-16-mimics-OCs, but not siDLEU-OCs, have a lower percentage of immobile cells and an increase in cells with mobile regime, compared with controls. No differences in cell shape were found. Moreover, mass-spectrometry quantitative proteomic analysis revealed independent effects of siDLEU1 and miR-16-mimics at the protein levels. Importantly, DLEU1 and miR-16 act by distinct processes and pathways. Collectively, our findings support the ncRNAs DLEU1 and miR-16 as therapeutic targets to modulate early stages of OCs differentiation and, consequently, to impair OC fusion, advancing ncRNA-therapeutics for bone-related diseases. Acknowledgements: Authors would like to thank to AO CMF / AO Foundation (AOCMFS-21-23A). SRM and MIA are supported by FCT (SFRH/BD/147229/2019 and BiotechHealth Program; CEECINST/00091/2018/CP1500/CT0011, respectively)

Previous studies showed that telo-peptides degraded from type II collagen, a type of collagen fragments, could induce cartilage damage in bovine stifle joints. We aim to investigate the role of integrins (ITGs) and matrix metalloproteinases (MMPs) in collagen fragment-induced human cartilage damage that is usually observed in osteoarthritis (OA). We hypothesized that N-telopeptide (NT) derived from type II collagen could up-regulate the expression of β1 integrin (ITGB1) and then MMPs that may lead to osteoarthritic cartilage damage. Human chondrocytes were isolated from femoral head or tibial plateau of patients receiving arthroplasty (N = 24). Primary chondrocyte cultures were either treated with 30 µM NT, or 30 µM scrambled NT (SN), or PBS, or left untreated for 24 hrs. Total proteins and RNAs were extracted for examination of expression of ITGB1 and MMPs-3&13 with Western blotting and quantitative real-time PCR. Compared to untreated or PBS treated chondrocytes, NT-treated chondrocytes expressed significantly higher levels of ITGB1 and MMPs-3&-13. However, SN also up-regulated expression of ITGB1 and MMP-13. ITGB1 and MMPs-3&-13 might mediate the catalytic effect of NT, a type of collagen fragments, on human cartilage damage that is a hallmark of OA

Joint tissues release extracellular vesicles (EVs) that potentially sustain joint homeostasis and contribute to osteoarthritis (OA) pathogenesis. EVs are putative novel therapeutics for OA, and transport biologically active molecules (including small non-coding RNAs (SNCRNAs)) between cells. This study identified altering SNCRNA cargo in EVs in OA which may act as early diagnostic markers and treatment targets. OA was surgically induced in four skeletally mature Standardbred horses using an osteochondral fragment model in the left middle carpal joint. The right joint underwent sham surgery. Synovial fluid (SF) and plasma were obtained weekly throughout the 70-day study. EVs were isolated using size exclusion chromatography and characterised using nanoparticle tracking (Nanosight), and exosome fluorescence detection and tetraspanin phenotyping (Exoview). RNA was extracted from EVs derived from SF (sham and OA joints) and plasma collected at days 10, 35, 42, 49, 56, 63, and subjected to small RNA sequencing on a NovaSeq SP100 flow cell (Illumina). Nanosight-derived EV characteristics of size and concentration were not significantly different following disease induction. The diameter of the temporal population of plasma and SF-derived exosomes changed significantly for CD9 and CD81 following OA induction with significant temporal, and disease-related changes in CD63 and CD81 protein expressin in plasma and SF. In SF and plasma-derived EVs snoRNAs, snRNAs, tRNAs, lncRNA, y-RNA, piRNAs and scRNA were found. Following pairwise analysis of all-time points we identified 27 miRs DE in plasma and 45 DE miRs in SF. Seven were DE in plasma and SF; miR-451, miR-25, miR-215, miR-92a, miR-let-7c, miR-486-5p, miR-23a. In plasma and SF 35 and 21 snoRNAs were DE with four DE in plasma and SF; U3, snord15, snord46, snord58. This work has identified alterations to OA EV sncRNAs in plasma and SF providing a greater understanding of the role of EVs in early OA

When joints sustain injury, the release of inflammation cytokines can cleavage matrix proteins and result in cartilage degradation and the subsequent osteoarthritis. RNA therapeutics emerging recently is a very promising approach to efficiently and specifically inhibit disease gene expression. However, the major challenge is how to deliver therapeutic RNA into joint and cartilage. Janus base nanotubes are self-assembled from synthetic Janus bases inspired from DNA base pairs. Based on the charge interaction, we are able to “sandwich” small RNAs among Janus base nanotubes to form tiny, nano-rod shaped delivery vehicles. Such vehicles can be engineered into different sizes and shapes. We have found that short and slim morphologies can greatly increase their penetration to extracellular matrix and delivery into “difficult-to-reach” tissues, such as cartilage and brain. Moreover, by delivering therapeutic siRNA, we have demonstrated its high-efficacy in inhibiting expression of an inflammatory regulator, Interleukin-1 receptor (IL-1R) in articular cartilage. Moreover, the inhibition effect is long-lasting so that joint inflammation and cartilage degradation caused by meniscus injury are greatly inhibited in a mouse model. Therefore, the Janus base nanotubes present a great potential in engineering into nano-structures for RNA delivery. Such approach may become an effective therapeutic against joint inflammation and arthritis

Introduction. Osteoarthritis (OA) of the knee, a prevalently degenerative joint disorder provoked by articular cartilage loss, accounts for the leading cause of total knee arthroplasty. Autophagy is an indispensable intracellular event that maintains chondrocyte survival and metabolism. MicroRNAs are non-coding small RNAs participating in tissue morphogenesis, remodeling, and homeostasis. This study was undertaken to investigate the effect of microRNA-128 (miR-128) knockdown on the development of OA knees. Materials/Methods. Knee joints in rats were subjected to anterior cruciate ligament transection (ACLT) for inducing OA. Articular cartilage, synovium, and subchondral bone microarchitecture were assessed by OARSI scoring system, histomorphometry, and μCT imaging. Chondrocyte autophagy in terms of the expression of autophagic markers Atg4, Atg12, microtubule-associated protein 1 light chain 3 (LC3), and autophagosome formation was verified. Expression of microRNA, mRNA and signaling transduction were quantified with in situ hybridization, RT- quantitative PCR, and immunoblotting. Results. Chondrocytes in the affected knees showed weak expression of autophagic markers Atg4, Atg12, and LC3-II abundances in conjunction with significant increases in OARSI scores and a 2.5-fold elevation in miR-128 expression. The gain of miR-128 signaling in intact joints through intra-articular injection of miR-128 precursor resulted in 1.8–2.1-fold elevations in serum cartilage breakdown products CTX-II and COMP concentrations. miR-128 overexpression caused the joints to show evident chondrocyte apoptosis as evidenced by TUNEL staining concomitant with severe cartilage damage. Of note, antisense oligonucleotide knockdown of miR-128 (miR-128-AS) enabled the affected knee joints to show minor responses to the ACLT escalation of autophagy dysfunction in chondrocytes, cartilage breakdown histopathology, and OARSI scores. Administration with miR-128-AS also attenuated the ACLT-induced synovial membrane thickening, hyper-angiogenesis, and hypercellularity, which subsequently alleviated osteophyte accumulation, subchondral plate destruction, and trabecular microstructure loss. Conclusion. miR-128 signaling impairs chondrocyte autophagy, which ramps up chondrocyte apoptosis and OA knee development. This study highlights an emerging miR-128 knockdown strategy that sustains cartilage microarchitecture integrity and thereby delays OA knee pathogenesis

Introduction. During osteoarthritis (OA) progression the articular chondrocyte undergoes a phenotypic switch in which the chondrocyte acquires a catabolic and hypertrophy-like state. Bone morphogenetic protein (BMP)-7 is known for its anti-catabolic and pro-anabolic properties in cartilage repair and in OA chondrocytes. In its anabolic state the chondrocyte”s metabolism and protein synthesis are up-regulated. In order to meet a higher demand of protein synthesis, it is expected that the translational capacity of the chondrocyte is increased after exposure to BMP-7. The cellular availability of maturated ribosomal RNAs (rRNA) is rate-limiting in the assembly of ribosomes and previously it has been shown that BMP-7 treatment resulted in increased expression levels of bagpipe homeobox homolog 1 (BAPX-1/NKX3.2). We therefore hypothesize that BMP-7 enhances the translational capacity of articular chondrocytes via BAPX-1/NKX3.2-dependent synthesis of rRNAs. Methods. OA human articular chondrocytes (HACs) were isolated from OA cartilage from total knee arthroplasty. SW1353 cells and OA HACs were exposed to BMP-7 (1 nM) and expression levels of rRNAs (18S, 5.8S, 28S) rRNA processing snoRNAs (RMRP and U3), a crucial co-factor in rRNA transcription (UBF-1) and BAPX-1/NKX3.2 were determined by RT-qPCR (and immunoblotting for BAPX-1/NKX3.2). BAPX-1/NKX3.2 overexpression and knockdown were achieved via transfection of FLAG-BAPX-1/NKX3.2 or a BAPX-1/NKX3.2 siRNA. For ex vivo confirmation, human OA cartilage explants from total knee arthroplasty were exposed to BMP-7 (1 nM) and gene expression levels of rRNAs were measured via qPCR. Results. BMP-7 treatment resulted in increased 18S and 5.8S rRNA levels, increased UBF-1, RMRP and U3 expression. This correlated with increased BAPX-1/NKX3.2 mRNA and protein expression. Overexpression of BAPX-1/NKX3.2 resulted in increased rRNA expression levels and the reciprocal knockdown of BAPX-1/NKX3.2 resulted in decreased rRNA expression levels. Besides these in vitro data, exposure of OA cartilage explants to BMP-7 confirmed our in vitro data (increase of 18S, 5.8S, UBF-1, RMRP, U3 and BAPX-1 expression levels). Discussion/Conclusion. Here we show that BMP-7 induces increased cellular levels of maturated rRNAs, with concomitant induction of factors involved in the transcription and maturation of rRNAs. This process is directly influenced by BAPX-1/NKX3.2 in similar ways as BMP-7. In future research the transcriptional activity of the 47S pre-rRNA gene will be determined via a luciferase promoter reporter approach and increased translation will be directly determined via puromycilation assays. Our data provide important novel insights into the mechanism behind the anabolic properties of BMP-7 and may even provide a new molecular cue to target the chondrocyte phenotype in OA

Background. MicroRNAs are non-coding small RNAs that reportedly regulate mRNA targets or protein translation of various tissues in physiological and pathological contexts. This study was undertaken to characterise the contributions of microRNA-29a (miR-29a) to the progression of estrogen deficiency-mediated excessive osteoclast resorption and bone loss. Methods. Osteoblast-specific transgenic mice overexpressing miR-29a driven by osteocalcin promoter (C57BL/6JNarl-TgOCN-mir29a) or wild-type mice were subjected to bilateral ovariectomy. Bone mineral density, trabecular microarchitecture and osteoclast distribution was quantified by μCT and histomorphometry. Primary CD11b+CSF-1R+ preosteoclasts were isolated for detecting ex vivo osteoclast differentiation. Gene expression and transcription factor-promoter interaction were quantified by RT-PCR and chromatin immunoprecipitation. Results. Estrogen depletion deteriorated bone integrity in concomitant with decrement of miR-29a expression. Transgenic mice had increased bone mass and skeletal microstructure and mitigated responses to the deleterious effects of estrogen deficiency on bone mineral density, B.Ar/T.Ar, Tb.Th and Tb.No. miR-29a overexpression attenuated the estrogen loss-mediated histopathology of osteoclast number, surface and erosion surface. Ex vivo, miR-29a transgenic mice had decreased osteoclast differentiation, osteoclastogenic marker expression (osteoclastogenic transcription factor NFATc1, TRAP, MMP-9, cathepsin K, and V-ATPase), F-actin ring and pit formation of primary preosteoclast cells. miR-29a alleviated the estrogen deficiency-induced promotion of interleukin-17 (IL-17) expression and enrichment of suppressor of cytokine signaling 2 (SOCS2) and signal transducer and activator of transcription 4 (STAT4) on IL-17 proximal promoter regions. Conclusions. Estrogen deficiency-mediated interruption of miR-29a expression exacerbates bone tissue resorption. miR-29a signalling via suppression of proinflammatory cytokine IL-17 action counteracts osteoclast differentiation and resorption reactions, thereby attenuates the deleterious effect of estrogen loss on bone integrity. This study highlights the skeletal-protective actions of miR-29a against excessive bone remodelling. Sustained miR-29a in bone tissue is beneficial for ameliorating osteoporosis. Level of evidence. II

Summary Statement. In articular cartilage defects, chemokines are upregulated and potentially induce the migration of bone marrow cells to accelerate the healing processes. Introduction. The treatment of damaged articular cartilages is one of the most challenging issues in sports medicine and in aging societies. In the microfracture technique for the treatment of articular cartilage defects, bone marrow cells are assumed to migrate from the bone marrow. Bone marrow cells are well-known for playing crucial roles in the healing processes, but how they can migrate from underlying bone marrow remains to be investigated. We have previously shown that SDF-1, one of chemokines, play crucial roles in the recruitment of mesenchymal stem cells in bone healing processes, and the induction of SDF-1 can induce a successful bone repair. If the migration can be stimulated by any means in the cartilage defects, a better result can be expected. The aim of this study was to elucidate the mechanisms of the migration of bone marrow cells and which factors contribute to the processes. Materials & Methods. Articular cartilage defects of 2 mm of diameter were created by drilling the cartilage with a wire to just the subchondral bone in 5-week-old SD rats. The width and depth of the created defects were confirmed by HE staining in histology. The healing tissues were harvested at days 2, 6, and 14 after the operation, and total RNAs were entracted. PCR array was conducted according to the manufacturer's instruction. Quantitative PCR (qPCR) was performed using cDNA of the healing tissues. Bone marrow cells were harvested from 5-week-old SD rat, and a standard migration assay was performed using chemokines. Results. CCL2, CCL3, CCL7 and CCL12 were upregulated in the healing tissues of cartilage defects shown by PCR array. The expression pattterns were confirmed by an expression analysis by qPCR. Both CCL2 and CCL3 induced the migration of bone marrow cells in the in vitro migration assay. Discussion/Conclusion. This study showed for the first time that CCL chemokines are upregulated in the articular cartilage defects and induce the migration of bone marrow cells. These results lead to an innovative measures along with an appropriate delivery method in induction the migration of bone marrow cells from the underlying bone marrow to stimulate articular cartilage healing processes

Summary. PCA-III, a phosphocitrate analog, acts not only as a potent calcification inhibitor but also as a protective agent for extracellular matrices. PCA-III has potential as a disease-modifying drug in the treatment of primary osteoarthritis and posttraumatic osteoarthritis in humans. Introduction. Phosphocitrate (PC) inhibits the development of primary osteoarthritis (OA) in Hartley guineas pigs but not menisectomy-induced OA in rabbits (1). We sought to examine the molecular mechanisms underlying the disease-modifying activity of PC, and evaluate the effect of PCA-III, a PC analog (PCA), on the development of primary and secondary OA. Patients & Methods. Meniscal explant and microarray. OA menisci were obtained from OA patients undergoing joint replacement surgery. OA meniscal explants were cultured in medium containing PC (three wells) and medium without PC (three wells). Total RNA was extracted from the explant, and subjected to microarray analysis. RT-PCR. OA fibroblast-like synoviocytes were treated with basic calcium phosphate (BCP) crystals in the absence or presence of PCA-III. RNAs were extracted, and subjected to semi-quantitative RT-PCR to examine the expression of MMP1 and IL-1b. Micromass culture. A droplet of OA chondrocyte suspension was placed in each well of a 24-well plate. After placing all droplets, the wells were fed with chondrogenesis medium with PCA-III (five wells) and without PCA-III (five wells). The production of proteoglycans was examined by alcian blue staining. Animal treatment. The first group of Hartley guinea pigs (n=5) received injections of PCA-III and the second group received injections of saline as control. Two months later, partial-menisectomy surgery was performed on the right knee of all guinea pigs. After the surgery, injections of PCA-III and saline were resumed. All animal were euthanatised four months later, and both knees were examined. Results. PC inhibited the expression of many genes classified into the molecular function group of MMP activity. Of the 23 genes classified into MMP activity, the expression of 16 genes, including CPM, ADAM28, MMP7, MMP10, MMP1, MMP3, ADAMTS5, ADAMTS1, and ADAMTS9, was inhibited. In contrast, the expression of many genes classified into the molecular function group of extracellular matrix structural constituents, was induced by PC, including COL2A1, COL11A1, COL1A1 and ACAN. PC also inhibited the expression of numerous genes classified into the biological process of inflammatory response (data not shown). PCA-III, similar to PC, inhibited BCP crystals-induced expression of MMP1 and IL-1b). In addition, PC-III strongly stimulated the production of proteoglycans by OA chondrocytes while inhibiting calcium deposition (not shown). Microscopic examination of the Indian ink stained medial tibia plateau of the left knees (non-surgery knee) of the guinea pigs indicated that PCA-III inhibited the development of primary OA in the Hartley guinea pigs. Microscopic examination also indicated that PCA-III inhibited the development of partial-menisectomy-induced OA or posttraumatic OA in the post-operative knees. Discussion/Conclusion. PC is thought to act as a potential structural disease-modifying drug for crystal-associated OA by inhibiting crystal deposition within the OA joints. However, PC and its analogs are not only potent calcification inhibitors, but also protective agents for extracellular matrices. Our findings indicate that PCA-III has potential as a disease-modifying drug for both human crystal-associated OA and posttraumatic OA

Summary Statement. Using the latest Next Generation Sequencing technologies, we have investigated miRNA expression profiles in human trabecular bone from total hip replacement (THR) revision surgery where wear particle associated osteolysis was evident. Introduction. A major problem in orthopaedic surgery is aseptic loosening of prosthetic implants caused by wear particle associated osteolysis. Wear debris is known to impact on a variety of cellular responses and genes in multiple pathways associated with the development of the periprosthetic osteolysis. MicroRNAs (miRNAs) act as negative regulators of gene expression and the importance of miRNAs in joint pathologies has only recently been addressed. However, miRNA profiles in osteolytic bone are largely unknown. Using the latest Next Generation Sequencing technologies, we have investigated miRNA expression profiles in human trabecular bone sourced from bone discarded during total hip replacement (THR) revision surgery where wear particle associated osteolysis was evident. Patients and Methods. Three groups of gender and age-matched patients (n=9 per group) were recruited for this study including patients undergoing revision surgery, primary THR patients and healthy subjects. Total RNAs were prepared from trabecular bone specimens. The cDNA libraries were constructed using a TruSeq Small RNA Sample Preparation kit, and then sequenced on an Illumina HiSeq2000 sequencer. All good quality tags were aligned against the reference sequences containing human chromosomal sequences and 18s and 28s rRNA sequences were analysed using Bowtie software. We used miRBase v19 to identify the start positions of all mature miRNA and the edgeR package to analyse differential expression. Osteogenesis pathway-related gene expression was also investigated using RT-qPCR Array assay. Results. We observed a significant difference in expressed miRNAs between revision and primary THR groups, including upexpressed miR127, miR-409, miR-211 and miR-146a. Importantly, the miR-127 (3.1 fold, p=0.005) and miR-146a (3.5 fold, p=0.001) were not only upexpressed in the revision group vs primary group, but also upexpressed in the revision group vs the healthy group. Thus, miR-127 and miR-146a may have potential as both biomarkers to predict osteolysis and as therapeutic targets. The miR-127 and miR-146a are critical in bone diseases because some of their target genes play an important role in osteogenesis. We have thus studied osteogenic genes and confirmed that SMAD4, RUNX2, FGFR1, TGFβ1, COL1A1 and WNT4 were downregulated. Our data also revealed that miR-93 and miR-204a were downexpressed (−3.7 fold, p=0.023; −2.5, p=0.003 respectively) and t IL-6 and IL-6R, which had been reported as miR-204 target genes, were upexpressed. Discussion and Conclusion. Our results showed that upexpressed miR-127, miR-146a, miR-204a and miR-93 in trabecular bone from revision THR may be the key negative regulators in either osteogenic genes involved in osteogenic differentiation of bone formation or inflammatory genes involved in osteoclastogenesis. Aberrant miRNA expressions identified in the revision THR group may also suggest the existence of genetic risk factors favouring the development of osteolysis in certain specific subgroups of patients. An in-depth understanding of the roles of these regulatory miRNAs in the skeleton warrants further investigation

We developed a rat model of limb lengthening to study the basic mechanism of distraction osteogenesis, using a small monolateral external fixator. In 11-week-old male rats we performed a subperiosteal osteotomy in the midshaft of the femur with distraction at 0.25 mm every 12 hours from seven days after operation. Radiological and histological examinations showed a growth zone of constant thickness in the middle of the lengthened segment, with formation of new bone at its proximal and distal ends. Osteogenic cells were arranged longitudinally along the tension vector showing the origin and the fate of individual cells in a single section. Typical endochondral bone formation was prominent in the early stage of distraction, but intramembraneous bone formation became the predominant mechanism of ossification at later stages. We also showed a third mechanism of ossification, ‘transchondroid bone formation’. Chondroid bone, a tissue intermediate between bone and cartilage, was formed directly by chondrocyte-like cells, with transition from fibrous tissue to bone occurring gradually and consecutively without capillary invasion. In situ hybridisation using digoxigenin-11-UTP-labelled complementary RNAs showed that the chondroid bone cells temporarily expressed type-II collagen mRNA. They did not show the classical morphological characteristics of chondrocytes, but were assumed to be young chondrocytes undergoing further differentiation into bone-forming cells. We found at least three different modes of ossification during bone lengthening by distraction osteogenesis. We believe that this is the first report of such a rat model, and have shown the validity of in situ hybridisation techniques for the study of the cellular and molecular mechanisms involved in distraction osteogenesis

Objectives

Osteoarthritis (OA) is characterised by articular cartilage degradation. MicroRNAs (miRNAs) have been identified in the development of OA. The purpose of our study was to explore the functional role and underlying mechanism of miR-138-5p in interleukin-1 beta (IL-1β)-induced extracellular matrix (ECM) degradation of OA cartilage.

Objectives

This study aimed to investigate the functional effects of microRNA (miR)-214-5p on osteoblastic cells, which might provide a potential role of miR-214-5p in bone fracture healing.

Objectives

This study aimed to explore the role of miR-320a in the pathogenesis of osteoarthritis (OA).

Objective

Excessive mechanical stress on synovial joints causes osteoarthritis (OA) and results in the production of prostaglandin E2 (PGE2), a key molecule in arthritis, by synovial fibroblasts. However, the relationship between arthritis-related molecules and mechanical stress is still unclear. The purpose of this study was to examine the synovial fibroblast response to cyclic mechanical stress using an in vitro osteoarthritis model.

The patellofemoral joint is an important source of symptoms in osteoarthritis of the knee. We have used a newly designed surgical model of patellar strengthening to induce osteoarthritis in BALB/c mice and to establish markers by investigating the relationship between osteoarthritis and synovial levels of matrix metalloproteinases (MMPs). Osteoarthritis was induced by using this microsurgical technique under direct vision without involving the cavity of the knee. Degeneration of cartilage was assessed by the Mankin score and synovial tissue was used to determine the mRNA expression levels of MMPs. Irrigation fluid from the knee was used to measure the concentrations of MMP-3 and MMP-9. Analysis of cartilage degeneration was correlated with the levels of expression of MMP.

After operation the patellofemoral joint showed evidence of mild osteoarthritis at eight weeks and further degenerative changes by 12 weeks. The level of synovial MMP-9 mRNA correlated with the Mankin score at eight weeks, but not at 12 weeks. The levels of MMP-2, MMP-3 and MMP-14 mRNA correlated with the Mankin score at 12 weeks. An increase in MMP-3 was observed from four weeks up to 16 weeks. MMP-9 was notably increased at eight weeks, but the concentration at 16 weeks had decreased to the level observed at four weeks.

Our observations suggest that MMP-2, MMP-3 and MMP-14 could be used as markers of the progression of osteoarthritic change.