Cruciate ligament healing and injury prevention in the age of regenerative medicine and technostress: homeostasis revisited.

PURPOSE: This clinical concepts paper discusses the essential elements of cruciate ligament recuperation, micro-trauma repair, and remodeling. METHODS: Cruciate ligament mechanobiology and tissue heterogeneity, anatomy and vascularity, and synovial membrane and fluid functions are discussed in relationship to deficiency-induced inflammatory responses, nervous and immune system function, recuperation, repair and remodeling, and modern threats to homeostasis. RESULTS: Cruciate ligament surgical procedures do not appreciate the vital linked functions of the central, peripheral, and autonomic nervous systems and immune system function on knee ligament injury recuperation, micro-trauma repair, and remodeling. Enhanced knowledge of these systems could provide innovative ways to decrease primary non-contact knee injury rates and improve outcomes following reconstruction or primary repair. CONCLUSIONS: Restoration of knee joint homeostasis is essential to cruciate ligament recuperation, micro-trauma repair, and remodeling. The nervous and immune systems are intricately involved in this process. Varying combinations of high-intensity training, under-recovery, technostress, and environmental pollutants (including noise) regularly expose many athletically active individuals to factors that abrogate the environment needed for cruciate ligament recuperation, micro-trauma repair, and remodeling. Current sports training practice, lifestyle psychobehaviors, and environmental factors combine to increase both primary non-contact knee injury risk and the nervous and immune system dysregulation that lead to poor sleep, increased anxiety, and poorly regulated hormone and cytokine levels. These factors may create a worst-case scenario leading to poor ligament recuperation, micro-trauma repair, and remodeling. Early recognition and modification of these factors may decrease knee ligament injury rates and improve cruciate ligament repair or reconstruction outcomes. LEVEL OF EVIDENCE: V.

Identification of Novel Targets of Knee Osteoarthritis Shared by Cartilage and Synovial Tissue.

Arthritis is the leading cause of disability among adults, while osteoarthritis (OA) is the most common form of arthritis that results in cartilage loss. However, accumulating evidence suggests that the protective hyaline cartilage should not be the sole focus of OA treatment. Particularly, synovium also plays essential roles in OA's initiation and progression and warrants serious consideration when battling against OA. Thus, biomarkers with similar OA-responsive expressions in cartilage and synovium should be the potential targets for OA treatment. On the other hand, molecules with a distinguished response during OA in cartilage and synovium should be ruled out as OA therapeutic(s) to avoid controversial effects in different tissues. Here, to pave the path for developing a new generation of OA therapeutics, two published transcriptome datasets of knee articular cartilage and synovium were analyzed in-depth. Genes with statistically significantly different expression in OA and healthy cartilage were compared with those in the synovium. Thirty-five genes with similar OA-responsive expression in both tissues were identified while recognizing three genes with opposite OA-responsive alteration trends in cartilage and synovium. These genes were clustered based on the currently available knowledge, and the potential impacts of these clusters in OA were explored.

Bioinformatics Analysis and Identification of Genes and Molecular Pathways Involved in Synovial Inflammation in Rheumatoid Arthritis.

BACKGROUND Rheumatoid arthritis (RA) has a high prevalence in the elderly population. The genes and pathways in the inflamed synovium in patients with RA are poorly understood. This study aimed to identify differentially expressed genes (DEGs) linked to the progression of synovial inflammation in RA using bioinformatics analysis. MATERIAL AND METHODS Gene expression profiles of datasets GSE55235 and GSE55457 were acquired from the Gene Expression Omnibus (GEO) database. DEGs were identified using Morpheus software, and co-expressed DEGs were identified with Venn diagrams. Protein-protein interaction (PPI) networks were assembled with Cytoscape software and separated into subnetworks using the Molecular Complex Detection (MCODE) algorithm. The functions of the top module were assessed using the Database for Annotation, Visualization, and Integrated Discovery (DAVID). The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were performed. RESULTS DEGs that were upregulated were significantly enhanced in protein binding, the cell cytosol, organization of the extracellular matrix (ECM), regulation of RNA transcription, and cell adhesion. DEGs that were downregulated were associated with control of the immune response, B-cell and T-cell receptor signaling pathway regulation. KEGG pathway analysis showed that upregulated DEGs enhanced pathways associated with the cell adherens junction, osteoclast differentiation, and hereditary cardiomyopathies. Downregulated DEGs were enriched in primary immunodeficiency, cell adhesion molecules (CAMs), cytokine-cytokine receptor interaction, and hematopoietic cell lineages. CONCLUSIONS The findings from this bioinformatics network analysis study identified molecular mechanisms and the key hub genes that may contribute to synovial inflammation in patients with RA.

Multiple mesenchymal progenitor cell subtypes with distinct functional potential are present within the intimal layer of the hip synovium.

BACKGROUND: The synovial membrane adjacent to the articular cartilage is home to synovial mesenchymal progenitor cell (sMPC) populations that have the ability to undergo chondrogenesis. While it has been hypothesized that multiple subtypes of stem and progenitor cells exist in vivo, there is little evidence supporting this hypothesis in human tissues. Furthermore, in most of the published literature on this topic, the cells are cultured before derivation of clonal populations. This gap in the literature makes it difficult to determine if there are distinct MPC subtypes in human synovial tissues, and if so, if these sMPCs express any markers in vivo/in situ that provide information in regards to the function of specific MPC subtypes (e.g. cells with increased chondrogenic capacity)? Therefore, the current study was undertaken to determine if any of the classical MPC cell surface markers provide insight into the differentiation capacity of sMPCs. METHODS: Clonal populations of sMPCs were derived from a cohort of patients with hip osteoarthritis (OA) and patients at high risk to develop OA using indexed cell sorting. Tri-differentiation potential and cell surface receptor expression of the resultant clones was determined. RESULTS: A number of clones with distinct differentiation potential were derived from this cohort, yet the most common cell surface marker profile on MPCs (in situ) that demonstrated chondrogenic potential was determined to be CD90+/CD44+/CD73+. A validation cohort was employed to isolate cells with only this cell surface profile. Isolating cells directly from human synovial tissue with these three markers alone, did not enrich for cells with chondrogenic capacity. CONCLUSIONS: Therefore, additional markers are required to further discriminate the heterogeneous subtypes of MPCs and identify sMPCs with functional properties that are believed to be advantageous for clinical application.

Comparison of mesenchymal stem cells obtained by suspended culture of synovium from patients with rheumatoid arthritis and osteoarthritis.

BACKGROUND: Mobilization of mesenchymal stem cells (MSCs) from the synovium was revealed using a "suspended synovium culture model" of osteoarthritis (OA). The pathology of rheumatoid arthritis (RA) differs from that of OA. We investigated whether mobilization of MSCs from the synovium also occurred in RA, and we compared the properties of synovial MSCs collected from suspended synovium culture models of RA and OA. METHODS: Human synovium was harvested during total knee arthroplasty from the knee joints of patients with RA (n = 8) and OA (n = 6). The synovium was suspended in a bottle containing culture medium and a culture dish at the bottom. Cells were harvested from the dish and analyzed. RESULTS: No significant difference was observed between RA and OA in the harvested cell numbers per g of synovium. However, the variation in the number of cells harvested from each donor was greater for RA than for OA. The harvested cells were multipotent and no difference was observed in the cartilage pellet weight between RA and OA. The surface epitopes of the cells in RA and OA were similar to those of MSCs. CONCLUSION: Mobilization of MSCs from the synovium was demonstrated using a suspended synovium culture model for RA. The harvested cell numbers, chondrogenic potentials, and surface epitope profiles were comparable between the RA and OA models.

CD105 promotes chondrogenesis of synovium-derived mesenchymal stem cells through Smad2 signaling.

Mesenchymal stem cells (MSCs) are considered to be suitable for cell-based tissue regeneration. Expressions of different cell surface markers confer distinct differentiation potential to different sub-populations of MSCs. Understanding the effect of cell surface markers on MSC differentiation is essential to their targeted application in different tissues. Although CD105 positive MSCs possess strong chondrogenic capacity, the underlying mechanisms are not clear. In this study, we observed a considerable heterogeneity with respect to CD105 expression among MSCs isolated from synovium. The CD105(+) and CD105(-) synovium-derived MSCs (SMSCs) were sorted to compare their differentiation capacities and relative gene expressions. CD105(+) subpopulation had higher gene expressions of AGG, COL II and Sox9, and showed a stronger affinity for Alcian blue and immunofluorescent staining for aggrecan and collagenase II, as compared to those in CD105(-) cells. However, no significant difference was observed with respect to gene expressions of ALP, Runx2, LPL and PPARγ. CD105(+) SMSCs showed increased levels of Smad2 phosphorylation, while total Smad2 levels were similar between the two groups. There was no difference in activation of Smad1/5. These results were further confirmed by CD105-knockdown in SMSCs. Our findings suggest a stronger chondrogenic potential of CD105(+) SMSCs in comparison to that of CD105(-) SMSCs and that CD105 enhances chondrogenesis of SMSCs by regulating TGF-ß/Smad2 signaling pathway, but not Smad1/5. Our study provides a better understanding of CD105 with respect to chondrogenic differentiation.

Validity and sensitivity to change of the semi-quantitative OMERACT ultrasound scoring system for tenosynovitis in patients with rheumatoid arthritis.

OBJECTIVES: The aim was to evaluate the metric properties of the semi-quantitative OMERACT US scoring system vs a novel quantitative US scoring system for tenosynovitis, by testing its intra- and inter-reader reliability, sensitivity to change and comparison with clinical tenosynovitis scoring in a 6-month follow-up study. METHODS: US and clinical assessments of the tendon sheaths of the clinically most affected hand and foot were performed at baseline, 3 and 6 months in 51 patients with RA. Tenosynovitis was assessed using the semi-quantitative scoring system (0-3) proposed by the OMERACT US group and a new quantitative US evaluation (0-100). A sum for US grey scale (GS), colour Doppler (CD) and pixel index (PI), respectively, was calculated for each patient. In 20 patients, intra- and inter-observer agreement was established between two independent investigators. A binary clinical tenosynovitis score was performed, calculating a sum score per patient. RESULTS: The intra- and inter-observer agreements for US tenosynovitis assessments were very good at baseline and for change for GS and CD, but less good for PI. The smallest detectable change was 0.97 for GS, 0.93 for CD and 30.1 for PI. The sensitivity to change from month 0 to 6 was high for GS and CD, and slightly higher than for clinical tenosynovitis score and PI. CONCLUSION: This study demonstrated an excellent intra- and inter-reader agreement between two investigators for the OMERACT US scoring system for tenosynovitis and a high ability to detect changes over time. Quantitative assessment by PI did not add further information.

Cell-based articular cartilage repair: the link between development and regeneration.

Clinical efforts to repair damaged articular cartilage (AC) currently face major obstacles due to limited intrinsic repair capacity of the tissue and unsuccessful biological interventions. This highlights a need for better therapeutic strategies. This review summarizes the recent advances in the field of cell-based AC repair. In both animals and humans, AC defects that penetrate into the subchondral bone marrow are mainly filled with fibrocartilaginous tissue through the differentiation of bone marrow mesenchymal stem cells (MSCs), followed by degeneration of repaired cartilage and osteoarthritis (OA). Cell therapy and tissue engineering techniques using culture-expanded chondrocytes, bone marrow MSCs, or pluripotent stem cells with chondroinductive growth factors may generate cartilaginous tissue in AC defects but do not form hyaline cartilage-based articular surface because repair cells often lose chondrogenic activity or result in chondrocyte hypertrophy. The new evidence that AC and synovium develop from the same pool of precursors with similar gene profiles and that synovium-derived chondrocytes have stable chondrogenic activity has promoted use of synovium as a new cell source for AC repair. The recent finding that NFAT1 and NFAT2 transcription factors (TFs) inhibit chondrocyte hypertrophy and maintain metabolic balance in AC is a significant advance in the field of AC repair. The use of synovial MSCs and discovery of upstream transcriptional regulators that help maintain the AC phenotype have opened new avenues to improve the outcome of AC regeneration.

ADAMTS-4_v1 is a splice variant of ADAMTS-4 that is expressed as a protein in human synovium and cleaves aggrecan at the interglobular domain.

OBJECTIVE: We previously described a messenger RNA variant of ADAMTS4 (ADAMTS4_v1) in human synovial cell cocultures obtained from patients with osteoarthritis (OA). This RNA message has been found only in OA synovium and, if translated, would result in a protein identical to ADAMTS-4, except that the C-terminal spacer domain would be different. The purpose of this study was to determine whether ADAMTS4_v1 is translated into a protein, is expressed in vivo, and acts as a functional aggrecanase. METHODS: Polyclonal antibodies were raised against unique C-terminal sequences of ADAMTS-4_v1. An immunohistochemical study of human OA synovium was performed. A mammalian expression vector coding for FLAG-tagged human ADAMTS4 was mutated to contain the different sequences of ADAMTS4_v1, and the resultant plasmid was used to transfect HEK 293 cells. ADAMTS-4_v1 produced by these cells was purified via the FLAG epitope, and the ability of this recombinant protein to cleave aggrecan, biglycan, and decorin was investigated. RESULTS: An antibody specific for ADAMTS-4_v1 was found to bind to the synovial membrane surface on cryosections, and the protein was detected in cell lysates from synovium obtained from OA patients. The recombinant ADAMTS-4_v1 demonstrated enzyme activity toward the target substrate in a commercial aggrecanase 1 enzyme-linked immunosorbent assay and was also found to cleave aggrecan at the pathologically important Glu(373↓374) Ala aggrecanase site. CONCLUSION: ADAMTS-4_v1 is expressed as a protein in vivo in human OA synovium, functions as an aggrecanase, and cleaves other proteoglycan substrates. This splice variant may be a major contributor to loss of aggrecan from the superficial zone of OA cartilage.

Lipopolysaccharide increases the incidence of collagen-induced arthritis in mice through induction of protease HTRA-1 expression.

OBJECTIVE: The protease HTRA-1 is closely associated with rheumatoid arthritis (RA). The molecular mechanisms that control HTRA-1 expression are currently unknown. This study was undertaken to determine the regulatory role of Toll-like receptors (TLRs) on HTRA-1 expression in mice with collagen-induced arthritis (CIA) and in synovial cells from RA patients. METHODS: HTRA-1 messenger RNA and protein production in mouse fibroblasts, mouse macrophages, and freshly isolated RA patient synovial cells treated with TLR ligands were detected by real-time polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Arthritis incidence and severity were determined using clinical scores and histopathologic analysis. Involvement of HTRA-1 in lipopolysaccharide (LPS)-increased arthritis incidence and severity in mice was determined using anti-HTRA-1 monoclonal antibody. The signal pathways involved in HTRA-1 expression were accessed by specific inhibitors, RNA interference, dual-luciferase reporter, and chromatin immunoprecipitation methods. RESULTS: LPS and tenascin-C, but not the other TLR ligands tested, strongly induced HTRA-1 expression. LPS significantly increased HTRA-1 expression in the joint tissue as well as arthritis incidence and severity in mice with CIA. Blocking HTRA-1 by antibody significantly decreased LPS-promoted CIA severity. Inhibiting NF-κB significantly decreased LPS-induced HTRA-1 expression in mouse and human cells. Dual-luciferase reporter assay and ChIP analysis showed that p65 directly binds to HTRA-1 promoter (amino acid 347). CONCLUSION: Our findings indicate that TLR-4 activation increases HTRA-1 expression through the NF-κB pathway in fibroblasts and macrophages. HTRA-1 expression is involved in the enhancing effects of LPS on CIA. This study offers new insights into the regulation of HTRA-1 expression via LPS/TLR-4 and the role of HTRA-1 in RA pathogenesis.

The effect of relaxin on the musculoskeletal system.

Relaxin is a hormone structurally related to insulin and insulin-like growth factor, which exerts its regulatory effect on the musculoskeletal and other systems through binding to its receptor in various tissues, mediated by different signaling pathways. Relaxin alters the properties of cartilage and tendon by activating collagenase. This hormone is also involved in bone remodeling and healing of injured ligaments and skeletal muscle. In this review, we have summarized the literature on the effect of relaxin in musculoskeletal system to provide a broad perspective for future studies in this field.

Toward defining the role of the synovium in mitigating normal articular cartilage wear and tear.

Cartilage repair has been studied extensively in the context of injury and disease, but the joint's management of regular sub-injurious damage to cartilage, or 'wear and tear,' which occurs due to normal activity, is poorly understood. We hypothesize that this cartilage maintenance is mediated in part by cells derived from the synovium that migrate to the worn articular surface. Here, we demonstrate in vitro that the early steps required for such a process can occur. First, we show that under physiologic mechanical loads, chondrocyte death occurs in the cartilage superficial zone along with changes to the cartilage surface topography. Second, we show that synoviocytes are released from the synovial lining under physiologic loads and attach to worn cartilage. Third, we show that synoviocytes parachuted onto a simulated or native cartilage surface will modify their behavior. Specifically, we show that synoviocyte interactions with chondrocytes lead to changes in synoviocyte mechanosensitivity, and we demonstrate that cartilage-attached synoviocytes can express COL2A1, a hallmark of the chondrogenic phenotype. Our findings suggest that synoviocyte-mediated repair of cartilage 'wear and tear' as a component of joint homeostasis is feasible and is deserving of future study.

Histological study of the extratympanic portion of the discomallear ligament in adult humans: a functional hypothesis.

This study was carried out on histological aspects of the extratympanic portion of the discomallear ligament (DL) in adult humans. The temporomandibular joint (TMJ) was dissected bilaterally in 20 cadavers; in 15 cases the articular disc (AD) and the retroarticular tissue were extirpated. The extratympanic portion of the DL had the shape of a base-down triangle, in relation to the AD, and an upper vertex, in relation to the petrotympanic fissure. In five cases, the base, measured bilaterally, had an average length of 6.4 mm, while the distance from the base to the upper vertex averaged 9.3 mm in length. The extratypanic portion of the DL is an intrinsic ligament of the TMJ, composed of collagen fibres and abundant elastic fibres. We propose that this ligament could act as a tensor of the synovial membrane in movements of the TMJ.

Chondrogenesis by chemotactic homing of synovium, bone marrow, and adipose stem cells in vitro.

Cell transplantation has been well explored for cartilage regeneration. We recently showed that the entire articular surface of a synovial joint can regenerate by endogenous cell homing and without cell transplantation. However, the sources of endogenous cells that regenerate articular cartilage remain elusive. Here, we studied whether cytokines not only chemotactically recruit adipose stem cells (ASCs), mesenchymal stem cells (MSCs), and synovium stem cells (SSCs) but also induce chondrogenesis of the recruited cells. Recombinant human transforming growth factor-ß3 (TGF-ß3; 100 ng) and/or recombinant human stromal derived factor-1ß (SDF-1ß; 100 ng) was control released into an acellular collagen sponge cube with underlying ASCs, MSCs, or SSCs in monolayer culture. Although all cell types randomly migrated into the acellular collagen sponge cube, TGF-ß3 and/or SDF-1ß recruited significantly more cells than the cytokine-free control group. In 6 wk, TGF-ß3 alone recruited substantial numbers of ASCs (558±65) and MSCs (302±52), whereas codelivery of TGF-ß3 and SDF-1ß was particularly chemotactic to SSCs (400±120). Proliferation of the recruited cells accounted for some, but far from all, of the observed cellularity. TGF-ß3 and SDF-1ß codelivery induced significantly higher aggrecan gene expression than the cytokine-free group for ASCs, MSCs, and SSCs. Type II collagen gene expression was also significantly higher for ASCs and SSCs by SDF-1 and TGF-ß3 codelivery. Remarkably, the expression of aggrecan and type II collagen was detected among all cell types. Thus, homing of multiple stem/progenitor cell populations may potentially serve as an alternative or adjunctive approach to cell transplantation for cartilage regeneration.

Functional mesenchymal stem cell niches in adult mouse knee joint synovium in vivo.

OBJECTIVE: We previously reported that human synovium contains cells that, after culture expansion, display properties of mesenchymal stem cells (MSCs). The objective of this study was to identify MSCs in native synovium in vivo. METHODS: To identify stem cells in the synovium in vivo, a double nucleoside analog cell-labeling scheme was used in a mouse model of joint-surface injury. For labeling of slow-cycling cells, mice received iododeoxyuridine (IdU) for 30 days, followed by a 40-day washout period. For labeling of cells that proliferate after injury, mice underwent knee surgery to produce an articular cartilage defect and received chlorodeoxyuridine (CIdU) for 4 days, starting at multiple time points after surgery. Unoperated and sham-operated joints served as controls. Knee joint paraffin sections were analyzed by double and triple immunostaining to detect nucleoside analogs, conventional MSC markers, and chondrocyte-lineage markers. RESULTS: Long-term-retaining, slow-cycling IdU-positive cells were detected in the synovium. At 4 days and 8 days after injury, there was marked proliferation of IdU-positive cells, which costained for CIdU. IdU-positive cells were nonhematopoietic, nonendothelial stromal cells, were distinct from pericytes, and stained positive for MSC markers. MSCs were phenotypically heterogeneous and located in topographically distinct niches in the lining layer and the subsynovial tissue. Twelve days after injury, double nucleoside-labeled cells within synovium were embedded in cartilage-specific metachromatic extracellular matrix and costained positive for the chondrocyte-lineage markers Sox9 and type II collagen. CONCLUSION: Our findings provide the first evidence of the existence of resident MSCs in the knee joint synovium that undergo proliferation and chondrogenic differentiation following injury in vivo.

[Structure and function of lymphatic capillaries in synovial joint]. / K struktúre a funkcii lymfatických kapilár v synoviálnom klbe.

The review article focuses on the structure and function of lymphatic capillaries in connective tissues of skin, muscles and synovial membrane. Lymphatic capillaries (initial lymphatics) are formed from endothelial cells mutually arranged so that their intercellular junctions have different structure. In one of the different types of intercellular junctions the distal ends of endothelial cells overlap one another in the form of projections. Desmosomes are missing between the cell membranes of the internal and external projection without presence of any other junctional complexes. The external projection of the endothelial cell is tightly attached to the surrounding connective tissue with the help of anchoring filaments. The internal projection of the neighbouring endothelial cell may tilt over to the lumen of the lymphatic capillary and this may result in a several micrometers wide communication between the interstitium and the lumen with efflux of tissue fluid and leukocytes from the interstitium in to the lumen of the capillary. Lymphologists call the above mentioned openable intercellular junctions in their works also endothelial microvalves or primary valves. These primary valves in cooperation with classical (secondary) intralymphatic valves enable one way lymph flow during spontaneous contractions of the initial lymphatics. It is supposed that primary valves in lymphatic capillaries have an important role in the drainage of the connective tissues affected by inflammation also in the synovial joint.

Induction of the p16INK4a senescence gene as a new therapeutic strategy for the treatment of rheumatoid arthritis.

Synovial tissue affected by rheumatoid arthritis is characterized by proliferation, which leads to irreversible cartilage and bone destruction. Current and experimental treatments have been aimed mainly at correcting the underlying immune abnormalities, but these treatments often prove ineffective in preventing the invasive destruction. We studied the expression of cyclin-dependent kinase inhibitors in rheumatoid synovial cells as a means of suppressing synovial cell proliferation. Synovial cells derived from hypertrophic synovial tissue readily expressed p16INK4a when they were growth-inhibited. This was not seen in other fibroblasts, including those derived from normal and osteoarthritis-affected synovial tissues. In vivo adenoviral gene therapy with the p16INK4a gene efficiently inhibited the pathology in an animal model of rheumatoid arthritis. Thus, the induction of p16INK4a may provide a new approach to the effective treatment of rheumatoid arthritis.

The effects of the synovium on chondrocyte growth: an experimental study.

PURPOSE: The objective of this study was to evaluate the effects of synovium on the proliferation of the cartilage tissue and chondrocytes using a rabbit knee model as an in vivo synovial culture medium. METHODS: Twelve New Zealand rabbits were used as the animal model in this investigation. Standard size chondral and osteochondral cartilage grafts were taken from, respectively, the left and right knees of all the animals. Two groups of 6 animals were formed: in Group I (synovium group), grafts were placed into the synovial tissue and in group II (patellar tendon group) behind the patellar tendon of the corresponding knees. After 4 months, samples were collected and evaluated macroscopically by measuring their dimensions (vertical = D1, horizontal = D2, and depth = D3) and volumes, and histologically by counting the chondrocyte number using camera lucida method. RESULTS: Macroscopically, the increase in average D1, D2, and D3 measurements and volume in the osteochondral specimens were significantly higher compared to the chondral specimens in both groups (P < 0.05). However, no significant difference was observed between the two groups in terms of macroscopic values. Histologically, the mean chondrocyte counts in osteochondral and chondral specimens for Group I (synovium) were 20.2 and 18.1, and for Group II (patellar tendon) were 18.7 and 15.6, respectively. The mean number of chondrocytes was found to be significantly higher in osteochondral specimens than that of chondral specimens in either group (P < 0.05). Overall average chondrocyte count was significantly higher for Group I compared to Group II (P < 0.05). CONCLUSION: Transplantation of the cartilage grafts into the synovial tissue in rabbit knees significantly enhanced the chondrocyte production compared with the group where the grafts were transplanted into intra-articular patellar tendon. The results of this study indicate that native synovial tissue may have the potential to be used as an in vivo culture medium for osteochondral tissue growth.

Monocytes, Macrophages, and Their Potential Niches in Synovial Joints - Therapeutic Targets in Post-Traumatic Osteoarthritis?

Synovial joints are complex structures that enable normal locomotion. Following injury, they undergo a series of changes, including a prevalent inflammatory response. This increases the risk for development of osteoarthritis (OA), the most common joint disorder. In healthy joints, macrophages are the predominant immune cells. They regulate bone turnover, constantly scavenge debris from the joint cavity and, together with synovial fibroblasts, form a protective barrier. Macrophages thus work in concert with the non-hematopoietic stroma. In turn, the stroma provides a scaffold as well as molecular signals for macrophage survival and functional imprinting: "a macrophage niche". These intricate cellular interactions are susceptible to perturbations like those induced by joint injury. With this review, we explore how the concepts of local tissue niches apply to synovial joints. We introduce the joint micro-anatomy and cellular players, and discuss their potential interactions in healthy joints, with an emphasis on molecular cues underlying their crosstalk and relevance to joint functionality. We then consider how these interactions are perturbed by joint injury and how they may contribute to OA pathogenesis. We conclude by discussing how understanding these changes might help identify novel therapeutic avenues with the potential of restoring joint function and reducing post-traumatic OA risk.

Efficacy of Combination Therapy with Apigenin and Synovial Membrane-Derived Mesenchymal Stem Cells on Knee Joint Osteoarthritis in a Rat Model.

Background: Osteoarthritis (OA) is a degenerative joint disease that causes a variety of adverse health effects. Considering the need to identify additional effective therapeutic options for OA therapy, we investigated the effect of co-injection of apigenin and synovial membrane-derived mesenchymal stem cells (SMMSCs) on OA in male rats' knee joints. Methods: The study was performed in 2019 at the Department of Pharmacology, Shiraz University of Medical Sciences, Shiraz, Iran. Anterior cruciate ligament transection (ACLT) was used to induce OA. For three weeks, male Sprague-Dawley rats (eight groups, n=6 each) were treated once-weekly with intra-articular injections of apigenin alone or in combination with SMMSC (three million cells), phosphate-buffered saline, or hyaluronic acid. After three months, the interleukin 1 beta (IL-1ß), tumor necrosis factor-alpha (TNF-α), superoxide dismutase (SOD), and malondialdehyde (MDA) levels were measured in the cartilage homogenate. The expression of extracellular matrix (ECM) components including collagen 2a1, aggrecan, IL-1ß, TNF-α, inducible nitric oxide synthase (iNOS), transcription factor SOX-9, and matrix metalloproteinases 3 and 13 were assessed using real-time polymerase chain reaction (RT-PCR) analysis. Radiological evaluation and histopathological assessment were used to evaluate the knees. Results: Levels of TNF-α (P=0.009), MDA (P>0.001), and IL-1ß (P<0.001) decreased and the level of SOD increased (P=0.004) in the apigenin 0.3 µM with SMMSCs group. RT-PCR analysis indicated that IL-1ß in the apigenin 0.3 µM with SMMSCs group reduced significantly (P<0.001). This group also exhibited increased expression levels of SOX-9, collagen 2a1, and aggrecan (P<0.001). Conclusion: Apigenin may have supplementary beneficial effects on cell therapy in a rat model of OA due to its possible effect on the reduction of oxidative stress, suppression of inflammation, and promotion of production of ECM components.