Cell death in cartilage

Loganin Attenuates Osteoarthritis in Rats by Inhibiting IL-1β-Induced Catabolism and Apoptosis in Chondrocytes Via Regulation of Phosphatidylinositol 3-Kinases (PI3K)/Akt

Background

Chondrocyte apoptosis and catabolism are 2 major factors that contribute to the progression of osteoarthritis (OA). Loganin, an iridoid glycoside present in several herbs, including Flos lonicerae, Cornus mas L, and Strychnos nux vomica, is a valuable medication with anti-inflammatory and anti-apoptotic effects. Our study examines these effects and explores the potential benefits of loganin in the OA treatment.

Material/Methods

To clarify the roles of loganin in OA and its specific signaling pathway, chondrocytes were administrated with IL-1β and supplemented with or without LY294002 (a classic PI3K/Akt inhibitor). The apoptotic level, catabolic factors (MMP-3 and MMP-13 and ADAMTS-4 and ADAMTS-5), extracellular matrix (ECM) degradation, and activation of the PI3K/Akt pathway were evaluated using western blotting, PCR, and an immunofluorescent assay. The degenerative condition of the cartilage was evaluated using the Safranin O assay in vivo. The expression of cleaved-caspase-3 (C-caspase-3) was measured using immunochemistry.

Results

The data suggested that loganin suppressed the apoptotic level, reduced the release of catabolic enzymes, and decreased the ECM degradation of IL-1β-induced chondrocytes. However, suppressing PI3K/Akt signaling using LY294002 alleviated the therapeutic effects of loganin in chondrocytes. Our in vivo experiment showed that loganin partially attenuated cartilage degradation while inhibiting the apoptotic level.

Conclusions

This work revealed that loganin treatment attenuated IL-1β-treated apoptosis and ECM catabolism in rat chondrocytes via regulation of the PI3K/Akt signaling, revealing that loganin is a potentially useful treatment for OA.

miR-21-5p protects IL-1β-induced human chondrocytes from degradation

OBJECTIVE

Osteoarthritis (OA) is a prevalent degenerative disease caused by various factors. MicroRNAs are important regulators in OA. MiR-21-5p expression is decreased in OA cartilage, but the effects of modulating miR-21-5p on cartilage regeneration are unknown. Therefore, our aim was to investigate the effects of miR-21-5p on cartilage metabolism of OA chondrocytes.

DESIGN

We used IL-1β (10 ng/ml) to mimic OA chondrocytes. OA chondrocytes were transfected with miR-21-5p, the gene expression of COL2A1, MMP13, and ADAMTS5 was detected by qPCR. At the same time, COL2A1, MMP13, and ADAMTS5 were analyzed at the protein level by Western blot. CCK8 measured the cell's viability and SA-β-gal detected the cell's senescence.

RESULTS

Upregulation of miR-21-5p had increased COL2A1 expression and decreased MM P13 and ADAMTS5 expression, which were in accord with Western blot data. SA-β-gal activity significantly increased, the viability was decreased in OA chondrocytes, and upregulation of miR-21-5p can decrease the SA-β-gal activity and increase cell viability.

CONCLUSION

MiR-21-5p might be a potential disease-modifying compound in OA, as it promotes hyaline cartilage production. These results provided that novel insights into the important function in OA pathological development.

Adipose derived mesenchymal stem cells alleviated osteoarthritis and chondrocyte apoptosis through autophagy inducing

OBJECTIVE

We aim to explore the effect of adipose derived mesenchymal stem cells (ADMSCs) on a knee osteoarthritis rat model and analyze how ADMSCs affect chondrocyte apoptosis.

MATERIALS AND METHODS

A surgically induced rat knee osteoarthritis (OA) model was constructed. ADMSCs were engrafted into the right knee cavity. Hematoxylin and eosin (H&E), Masson, and Safranin O were used to compare the histopathology of synovial membrane and cartilage. Immunohistochemical (IHC) was used to measure MMP-13, Collagen 2 (Col-2), Caspase-3 (Cas-3), PARP, p62, LC3b, DDR-2, FGFR-1, Wnt, P-AKT/AKT, p-CAMKII/CAMKII, and p-Smad1/Smad1 expression in the articular cartilage. qPCR and Western blot analysis were used to detect mRNA and protein levels of markers in chondrocytes. TUNEL and Annexin-V were used to assess apoptosis.

RESULTS

Histological analysis showed that ADMSCs alleviated the deterioration of cartilage and osteoarthritis. ADMSCs coculture increase the expression of Col2 and Sox-9, while down regulated MMP-13 in IL-1β stimulated chondrocytes. ADMSCs decreased proinflammatory cytokines IL-1β, IL-6, and TNF-α. ADMSCs enhanced the viability of IL-1β stimulated chondrocytes. ADMSC attenuated chondrocyte apoptosis. The pretreatment of 3-methyladenine (3-MA) reversed the reduction of Caspase-3 caused by ADMSCs, showing that the antiapoptotic effect was associated with autophagy inducing. ADMSCs significantly reduced the expression of FGFR-1, DDR-2, and Wnt in IL-1β stimulated chondrocytes. ADMSCs reduced the ratio of p-Smad1/Smad1 and p-CAMK II/CAMKII, and increased the ratio of p-AKT/AKT.

CONCLUSIONS

ADMSCs treatment alleviate osteoarthritis in rat OA models. AMDSCs reduced the secretion of proinflammatory cytokines and protected against apoptosis through autophagy inducing. ADMSCs' function could be related to multiple signaling pathway.

Methylene blue regulates inflammatory response in osteoarthritis by noncoding long chain RNA CILinc02

Long noncoding RNAs serve as novel regulatory molecules involved in various biological processes, but their role in osteoarthritis (OA) remains unknown. Therefore, we aimed to reveal the inflammatory mechanisms regulated by CILinc02 and methylene blue in human osteoarthritic cartilage and to explore the potential functions of CILinc02 and methylene blue in OA. The expression level of CILinc02 in OA cartilage tissues and primary cells was obtained using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). The cytokines, such as interleukin 1 (IL-1), IL-6, IL-17, tissue inhibitor of metalloproteinase-1 (TIMP-1) and matrix metalloproteinase (MMPs), involved in the degradation of chondrocyte in CILinc02 knockdown OA primary cells, which were treated with methylene blue that were determined by enzyme-linked immunosorbent assay, qRT-PCR and Western blot analysis. The results showed that CILinc02 was overexpressed in osteoarthritic cartilage tissues and in OA primary cells, but methylene blue can inhibit the expression of CILinc02. In addition, overexpression of CILinc02 induced the inflammation and apoptosis in primary OA cells, however, the effect of methylene blue was reversed compared to CILinc02. Meanwhile, methylene blue can regulate the expression of TIMP-1, MMP-1, and MMP-13 proteins, thereby suppressing the degradation of chondrocyte in OA. This evidence indicates that methylene blue can act as an inflammatory inhibitor by targeting CILinc02 to regulate the inflammatory response.

Reciprocal inhibition of YAP/TAZ and NF-κB regulates osteoarthritic cartilage degradation

Osteoarthritis is one of the leading causes of pain and disability in the aged population due to articular cartilage damage. This warrants investigation of signaling mechanisms that could protect cartilage from degeneration and degradation. Here we show in a murine model of experimental osteoarthritis that YAP activation by transgenic overexpression or by deletion of its upstream inhibitory kinases Mst1/2 preserves articular cartilage integrity, whereas deletion of YAP in chondrocytes promotes cartilage disruption. Our work shows that YAP is both necessary and sufficient for the maintenance of cartilage homeostasis in osteoarthritis. Mechanistically, inflammatory cytokines, such as TNFα or IL-1β, trigger YAP/TAZ degradation through TAK1-mediated phosphorylation. Furthermore, YAP directly interacts with TAK1 and attenuates NF-κB signaling by inhibiting substrate accessibility of TAK1. Our study establishes a reciprocal antagonism between Hippo-YAP/TAZ and NF-κB signaling in regulating the induction of matrix-degrading enzyme expression and cartilage degradation during osteoarthritis pathogenesis.

LncRNA-CIR promotes articular cartilage degeneration in osteoarthritis by regulating autophagy

Osteoarthritis (OA) is a common joint disease that is regarded as a local inflammatory response caused by joint instability and accompanied by the progressive degeneration of articular cartilage. However, the molecular mechanisms involved in the maintenance of articular cartilage remain a subject of debate and research. This study aims to analyze the roles of long noncoding RNA (lncRNA)CIR and autophagy in cartilages and determine their overall contribution to the degradation of extracellular matrix. Patients with OA possessed high levels of lncRNA-CIR and MMP3 and low level of COL2A1. The levels of autophagy-related proteins, including LC3BI/II and beclin-1, increased from 12 h to 48 h. The use of si-lncRNA-CIR reversed the trend compared with that in the OA group. The negative effect of lncRNA-CIR was assessed in vivo by establishing a model of surgically induced OA. Moreover, si-lncRNA-CIR-treated joints exhibited fewer OA changes than saline-treated joints. Results were confirmed by histopathological grading of the models by using the Osteoarthritis Research Society International Scoring System and the outcomes of immunohistochemistry for LC3B-II and MMP-3. Overall, lncRNA-CIR played a negative role in the OA process by activating autophagy.

Menisci protect chondrocytes from load-induced injury

Menisci in the knee joint are thought to provide stability, increased contact area, decreased contact pressures, and offer protection to the underlying articular cartilage and bone during joint loading. Meniscal loss or injury is typically accompanied by degenerative changes in the knee, leading to an increased risk for osteoarthritis in animals including humans. However, the detailed mechanisms underlying joint degeneration and the development of osteoarthritis remain largely unknown, and the acute effects of meniscal loss have not been studied systematically. We developed a microscopy-based system to study microscale joint mechanics in living mice loaded by controlled muscular contractions. Here, we show how meniscal loss is associated with rapid chondrocyte death (necrosis) in articular cartilage within hours of injury, and how intact menisci protect chondrocytes in vivo in the presence of intense muscle-based joint loading and/or injury to the articular cartilage. Our findings suggest that loading the knee after meniscal loss is associated with extensive cell death in intact and injured knees, and that early treatment interventions should be aimed at preventing chondrocyte death.

Activation of NF-κB in Synovium versus Cartilage from Patients with Advanced Knee Osteoarthritis: A Potential Contributor to Inflammatory Aspects of Disease Progression

The aim was to assess the activation and association of the NF-κB system across synovial membrane (SM) and articular cartilage (AC) in patients with knee osteoarthritis (OA) and ascertain its potential effects on catabolic mediator expression in advanced OA. SM and AC were obtained from 40 OA patients undergoing total knee arthroplasty and from 19 postmortem control subjects. NF-κB subunit RelA in nuclear and cytosolic fractions and NF-κB1-DNA binding in nuclear extracts was assessed by ELISA, whereas NFKB1, RELA, IL-8, IL-6, and MMP3 gene expression were analyzed by reverse transcriptase-quantitative PCR in tissues. We observed higher SM nuclear RelA protein levels and upregulated NF-κB1-DNA binding in OA patients compared with postmortem controls. However, in AC, lower nuclear RelA levels were observed compared with cytosolic extracts in patients. Nuclear RelA levels correlated positively with NF-κB1-DNA binding in SM and AC in patients. SM RELA and MMP3 mRNA levels were upregulated, whereas IL-8 and IL-6 as well as AC RELA were downregulated in patients compared with controls. In SM, nuclear RelA levels correlated positively with MMP3 gene expression in patients. A negative correlation was observed between SM nuclear RelA levels and AC NF-κB1-DNA binding, and SM nuclear NF-κB1-DNA binding correlated negatively with AC MMP3 and NFKB1 mRNA levels in patients. These findings highlight NF-κB-triggered cross-talk and feedback mechanisms between SM and AC in OA. Further, our findings strongly support a role for an activated NF-κB system in the transcriptional mechanism of inflammatory processes, especially in SM of patients with advanced OA.

Long non-coding RNA reprogramming (lncRNA-ROR) regulates cell apoptosis and autophagy in chondrocytes

Long Non-Coding RNA Reprogramming (lncRNA-ROR) plays an important role in regulating various biologic processes, whereas the effect of lncRNA-ROR in osteoarthritis (OA) is little studied. This study aimed to explore lncRNA-ROR expression in articular cartilage and identify the functional mechanism of lncRNA-ROR in OA. OA cartilage tissues were obtained from 15 OA patients, and 6 normal cartilage tissues were set as controls. Chondrocytes were isolated from the collected cartilage tissues. lncRNA-ROR was knockdown in normal cells and overexpressed in OA cells. Cell viability was determined with Cell Counting Kit-8 assay, and apoptosis was measured using flow cytometric analysis. Moreover, proteins and mRNAs involved in this study were also measured using Western blotting and quantitative real-time PCR (qPCR). Level of lncRNA-ROR was decreased in OA compared with normal chondrocytes, and overexpression of lncRNA-ROR dramatically promoted cell viability of OA chondrocytes. In addition, knockdown lncRNA-ROR inhibited apoptosis and promoted autophagy of normal chondrocytes. Moreover, lncRNA-ROR inhibited the expression of p53 in both mRNA and protein levels. Furthermore, we revealed that lncRNA-ROR regulated apoptosis and autophagy of chondrocytes via HIF1α and p53. The results indicated that lncRNA-ROR played a critical role in the pathogenesis of OA, suggesting that lncRNA-ROR could serve as a new potential therapeutic target for OA.

The ghrelin paradox in the control of equine chondrocyte function: The good and the bad

Increasing evidence suggests a role for ghrelin in the control of articular inflammatory diseases like osteoarthritis (OA). In the present study we examined the ability of ghrelin to counteract LPS-induced necrosis and apoptosis of chondrocytes and the involvement of GH secretagogue receptor (GHS-R)1a in the protective action of ghrelin. The effects of ghrelin (10^-7-10^-11 mol/L) on equine primary cultured chondrocytes viability and necrosis in basal conditions and under LPS treatment (100 ng/ml) were detected by using both acridine orange/propidium iodide staining and annexin-5/propidium iodide staining. The presence of GHS-R1a on chondrocytes was detected by Western Blot. The involvement of the GHS-R1a in the ghrelin effect against LPS-induced cytotoxicity was examined by pretreating chondrocytes with D-Lys3-GHRP-6, a specific GHS-R1a antagonist, and by using des-acyl ghrelin (DAG, 10^-7 and 10^-9 mol/L) which did not recognize the GHS-R 1a. Low ghrelin concentrations reduced chondrocyte viability whereas 10^-7 mol/L ghrelin protects against LPS-induced cellular damage. The protective effect of ghrelin depends on the interaction with the GHS-R1a since it is significantly reduced by D-Lys3-GHRP-6. The negative action of ghrelin involves caspase activation and could be due to an interaction with a GHS-R type different from the GHS-R1a recognized by both low ghrelin concentrations and DAG. DAG, in fact, induces a dose-dependent decrease in chondrocyte viability and exacerbates LPS-induced damage. These data indicate that ghrelin protects chondrocytes against LPS-induced damage via interaction with GHS-R1a and suggest the potential utility of local GHS-R1a agonist administration to treat articular inflammatory diseases such as OA.

Articular Cartilage Aging-Potential Regenerative Capacities of Cell Manipulation and Stem Cell Therapy

Changes in articular cartilage during the aging process are a stage of natural changes in the human body. Old age is the major risk factor for osteoarthritis but the disease does not have to be an inevitable consequence of aging. Chondrocytes are particularly prone to developing age-related changes. Changes in articular cartilage that take place in the course of aging include the acquisition of the senescence-associated secretory phenotype by chondrocytes, a decrease in the sensitivity of chondrocytes to growth factors, a destructive effect of chronic production of reactive oxygen species and the accumulation of the glycation end products. All of these factors affect the mechanical properties of articular cartilage. A better understanding of the underlying mechanisms in the process of articular cartilage aging may help to create new therapies aimed at slowing or inhibiting age-related modifications of articular cartilage. This paper presents the causes and consequences of cellular aging of chondrocytes and the biological therapeutic outlook for the regeneration of age-related changes of articular cartilage.

Mitoprotective therapy preserves chondrocyte viability and prevents cartilage degeneration in an ex vivo model of posttraumatic osteoarthritis

No disease-modifying osteoarthritis (OA) drugs are available to prevent posttraumatic osteoarthritis (PTOA). Mitochondria (MT) mediate the pathogenesis of many degenerative diseases, and recent evidence indicates that MT dysfunction is a peracute (within minutes to hours) response of cartilage to mechanical injury. The goal of this study was to investigate cardiolipin-targeted mitoprotection as a new strategy to prevent chondrocyte death and cartilage degeneration after injury. Cartilage was harvested from bovine knee joints and subjected to a single, rapid impact injury (24.0 ±1.4 MPa, 53.8 ± 5.3 GPa/s). Explants were then treated with a mitoprotective peptide, SS-31 (1µM), immediately post-impact, or at 1, 6, or 12 h after injury, and then cultured for up to 7 days. Chondrocyte viability and apoptosis were quantified in situ using confocal microscopy. Cell membrane damage (lactate dehydrogenase activity) and cartilage matrix degradation (glycosaminoglycan loss) were quantified in cartilage-conditioned media. SS-31 treatment at all time points after impact resulted in chondrocyte viability similar to that of un-injured controls. This effect was sustained for up to a week in culture. Further, SS-31 prevented impact-induced chondrocyte apoptosis, cell membrane damage, and cartilage matrix degeneration.

CLINICAL SIGNIFICANCE

This study is the first investigation of cardiolipin-targeted mitoprotective therapy in cartilage. These results suggest that even when treatment is delayed by up to 12 h after injury, mitoprotection may be a useful strategy in the prevention of PTOA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 9999:1-10, 2018.

Activation of the cannabinoid receptor 1 by ACEA suppresses senescence in human primary chondrocytes through sirt1 activation

Senescence of chondrocytes and cartilage degeneration induced by the proinflammatory cytokine interleukin-1β is associated with the pathogenesis of osteoarthritis. The cannabinoid receptor 1 has been involved in the pathological development of various diseases. Here, we evaluated whether activation of cannabinoid receptor 1 using its selective agonist arachidonyl-2-chloroethylamide had an influence on cellular senescence induced by interleukin-1βin human chondrocytes. Our findings demonstrate that agonist arachidonyl-2-chloroethylamidedecreased senescence-associated β-galactosidase activity and cell cycle arrest in the G0/G1 phase induced by interleukin-1β. Importantly, our results display interleukin-1βtreatment significantly increased the expressions of senescence genes (caveolin-1, PAI-1 and p21), which were prevented by agonist arachidonyl-2-chloroethylamide treatment. However, it was noticed that these functions of agonist arachidonyl-2-chloroethylamide were abolished by the cannabinoid receptor 1 selective antagonist AM251, suggesting the involvement of cannabinoid receptor 1. Also, our results indicate that agonist arachidonyl-2-chloroethylamide enhanced the expression of sirt1. These findings suggest that activation of cannabinoid receptor 1 by agonist arachidonyl-2-chloroethylamide might have a protective effect against pro-inflammatory cytokines such as interleukin-1β-induced chondrocytes senescence in osteoarthritis patients. Impact statement Senescence of chondrocytes and cartilage degeneration induced by the proinflammatory cytokine interleukin-1β (IL-1β) are associated with the pathogenesis of osteoarthritis (OA). Here we found that: (a) the CB1 agonist ACEA abolished IL-1β-induced senescence and cell arrest in chondrocytes; (b) the CB1 agonist ACEA also abolished IL-1β-induced expression of caveolin-1, PAI-1, and p21;

Significant Chondrocyte Viability Is Present in Acetabular Chondral Flaps Associated With Femoroacetabular Impingement

BACKGROUND

Patients presenting with cam deformity of the femoral head and neck sustain repeated trauma to the articular cartilage of the superior acetabulum, with chondral delamination injuries found during hip arthroscopy. Two previous studies reveal conflicting chondrocyte viability data in these traumatic cartilage injuries. The full-thickness nature of flaps may suggest that chondrocytes residing in the cartilage flap matrix in the joint environment would remain viable despite shear trauma. Hypothesis/Purpose: The purpose of this study is to determine the in vivo tissue viability of acetabular chondral flaps in patients with femoroacetabular impingement (FAI) when samples are analyzed immediately after biopsy. We hypothesize that the majority of the tissue in acetabular chondral flaps is viable in the joint microenvironment.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Partially detached cartilage flaps from 10 patients undergoing arthroscopic hip surgery for FAI were biopsied in a minimally traumatic manner before chondroplasty and microfracture. Samples were placed in cold Hank's Balanced Salt Solution without phenol red solution and immediately transported on ice to our laboratory. The edge of the samples was trimmed and further cut into 3 separate, 1-mm-thick sections. Sections were stained using a live/dead staining kit. Images were obtained with confocal microscopy, and the percentage of live cells was quantified.

RESULTS

Patients averaged 36 ± 11 years (range, 18-48 years), and 2 patients were female. The mean body mass index was 28.9 ± 5.6 kg/m². The total proportion of live cells from all sections analyzed was 85.8%. The proportion of live cells per patient was 87% ± 10%.

CONCLUSION

We determined that acetabular chondral flaps are approximately 87% live cells when analyzed immediately after biopsy, with 6 of 10 patients having greater than 90% live cells. These data point to the importance of laboratory techniques in making viability judgments in biologic systems.

CLINICAL RELEVANCE

Full-thickness cartilage loss is a difficult problem for all active people but particularly in the young population in whom joint preservation is key. We describe the viability of chondrocytes present in full-thickness acetabular-based chondral flaps encountered during hip arthroscopy. Identification of greater than 85% chondrocyte viability supports a foundation for evaluation and creation of novel clinical innovations for repair and replacement techniques using the flap as donor tissue, as alternatives to chondroplasty and microfracture.

Oxidized low density lipoprotein facilitates tumor necrosis factor‑α mediated chondrocyte death via autophagy pathway

We aimed to investigate the role of oxidized low density lipoprotein (ox-LDL) in tumor necrosis factor-α (TNF-α) mediated chondrocyte death and explore the mechanisms. Ten osteoarthritis (OA) and normal control cartilage tissue and synovial fluid (SF) samples were collected, and the expression of lectin-like ox-LDL receptor-1 (LOX-1) and ox-LDL level was examined by real time quantitative PCR and enzyme-linked immunosorbent assay (ELISA). An in vitro chondrocyte model was established by the introduction of TNF-α and ox-LDL, cell death was analyzed by trypan blue assay and the mechanisms were explored based on the apoptosis related pathway and autophagy pathway. Significantly increased ox-LDL level (70.30±17.83 vs. 37.22±19.97, P<0.05) in SF sample and LOX-1 expression level (0.51±0.10 vs. 0.32±0.04, P<0.05) in cartilage tissue was found in OA patients compared to those corresponding samples from control subjects. Ox-LDL could facilitate TNF-α mediated chondrocyte death and this effect could be blocked by LOX-1 antibody neutralization. Autophagy inhibition by 3-MA and Atg-5 siRNA could reverse the cell death effect mediated by TNF-α and ox-LDL co-treatment on chondrocytes. Oxidized low density lipoprotein facilitates tumor necrosis factor-α mediated chondrocyte death via its interaction with LOX-1, and autophagy is involved in the mechanisms.

HMGB proteins and arthritis

The high-mobility group box (HMGB) family includes four members: HMGB1, 2, 3 and 4. HMGB proteins have two functions. In the nucleus, HMGB proteins bind to DNA in a DNA structure-dependent but nucleotide sequence-independent manner to function in chromatin remodeling. Extracellularly, HMGB proteins function as alarmins, which are endogenous molecules released upon tissue damage to activate the immune system. HMGB1 acts as a late mediator of inflammation and contributes to prolonged and sustained systemic inflammation in subjects with rheumatoid arthritis. By contrast, Hmgb2 ^-/- mice represent a relevant model of aging-related osteoarthritis (OA), which is associated with the suppression of HMGB2 expression in cartilage. Hmgb2 mutant mice not only develop early-onset OA but also exhibit a specific phenotype in the superficial zone (SZ) of articular cartilage. Given the similar expression and activation patterns of HMGB2 and β-catenin in articular cartilage, the loss of these pathways in the SZ of articular cartilage may lead to altered gene expression, cell death and OA-like pathogenesis. Moreover, HMGB2 regulates chondrocyte hypertrophy by mediating Runt-related transcription factor 2 expression and Wnt signaling. Therefore, one possible mechanism explaining the modulation of lymphoid enhancer binding factor 1 (LEF1)-dependent transactivation by HMGB2 is that a differential interaction between HMGB2 and nuclear factors affects the transcription of genes containing LEF1-responsive elements. The multiple functions of HMGB proteins reveal the complex roles of these proteins as innate and endogenous regulators of inflammation in joints and their cooperative roles in cartilage hypertrophy as well as in the maintenance of joint tissue homeostasis.

Reduced Osteoarthritis Severity in Aged Mice With Deletion of Macrophage Migration Inhibitory Factor

OBJECTIVE

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that is elevated in the serum and synovial fluid of patients with osteoarthritis (OA). This study was undertaken to investigate the potential role of MIF in OA in human joint tissues and in vivo in mice with age-related and surgically induced OA.

METHODS

MIF in conditioned media from human chondrocytes and meniscal cells and from cartilage explants was measured by enzyme-linked immunosorbent assay. The severity of OA was analyzed histologically in male wild-type and MIF^-/- mice at 12 and 22 months of age and following destabilization of the medial meniscus (DMM) surgery in 12-week-old MIF^-/- mice as well as in wild-type mice treated with a neutralizing MIF antibody. Synovial hyperplasia was graded in S100A8-immunostained histologic sections. Bone morphometric parameters were measured by micro-computed tomography.

RESULTS

Human OA chondrocytes secreted 3-fold higher levels of MIF than normal chondrocytes, while normal and OA meniscal cells produced equivalent amounts. Compared to age- and strain-matched controls, the cartilage, bone, and synovium in older adult mice with MIF deletion were protected against changes of naturally occurring age-related OA. No protection against DMM-induced OA was seen in young adult MIF^-/- mice or in wild-type mice treated with anti-MIF. Increased bone density in 8-week-old mice with MIF deletion was not maintained at 12 months.

CONCLUSION

These results demonstrate a differential mechanism in the pathogenesis of naturally occurring age-related OA compared to injury-induced OA. The inhibition of MIF may represent a novel therapeutic target in the reduction of the severity of age-related OA.

Different doses of strontium ranelate and mechanical vibration modulate distinct responses in the articular cartilage of ovariectomized rats

OBJECTIVE

To investigate the effects of different strontium ranelate (SrR) doses alone or in combination with low-intensity and high-frequency mechanical vibration (MV) on articular cartilage in ovariectomized rats.

DESIGN

Fifty 6-month-old female Wistar rats underwent ovariectomy (OVX) and after 3 months were divided into: control group (Control); SrR 300 mg/kg/day (SrR300); SrR 625 mg/kg/day (SrR625); MV; SrR 625 mg/kg/day plus MV (SrR625 + MV). The vehicle and the SrR were administered by gavage 7 days/week and vibration (0.6 g/60 Hz) was performed for 20 min/day, 5 days/week. Bone mineral density (BMD) and body composition were evaluated by densitometry. Changes in cartilage were assessed 90 days after treatment by histomorphometry; immunohistochemistry analysis evaluating cell death (caspase-3), tumor necrosis factor-α (TNF-α), metalloproteinase 9 (MMP-9) and type II collagen; Osteoarthritis Research Society International (OARSI) grading system and glycosaminoglycans (GAGs) analyses.

RESULTS

SrR-treated groups exhibited a lower OARSI grade, a smaller number of chondrocyte clusters, increased levels of chondroitin sulfate (CS) and decreased expression of caspase-3. Additionally, compared to all the groups, SrR300 exhibited increased levels of hyaluronic acid (HA). Vibration applied alone or in combination accelerated cartilage degradation, as demonstrated by increased OARSI grade, reduced number of chondrocytes, increased number of clusters, elevated expression of type II collagen and cell death, and was accompanied by decreased amounts of CS and HA; however, MV alone was able to reduce MMP-9.

CONCLUSIONS

SrR and vibration modulate distinct responses in cartilage. Combined treatment accelerates degeneration. In contrast, SrR treatment at 300 mg/kg/day attenuates osteoarthritis (OA) progression, improving cartilage matrix quality and preserving cell viability in ovariectomized rats.

Emerging Roles of circRNA Related to the Mechanical Stress in Human Cartilage Degradation of Osteoarthritis

Circular RNAs (circRNAs) are involved in the development of various diseases; however, knowledge on circRNAs in osteoarthritis (OA) is limited. This study aims to identify circRNA expression in different regions affected by OA and to explore the function of mechanical stress-related circRNAs (circRNAs-MSR) in cartilage. Bioinformatics was employed to predict the interaction of circRNAs and mRNAs in the cartilage. Loss-of-function experiments for circRNAs-MSR were performed in vitro. A total of 104 circRNAs were differentially expressed in damaged versus intact cartilage. Of these circRNAs, 44 and 60 were upregulated and downregulated, respectively, in the damaged tissue. circRNA-MSR expression increased under mechanical stress in chondrocytes. circRNAs-MSR were silenced using small interfering RNA, and knockdown of circRNAs-MSR could suppress tumor necrosis factor alpha (TNF-α) expression and increase extracellular matrix (ECM) formation. Our results demonstrated that circRNAs-MSR regulated TNF-α expression and participated in the chondrocyte ECM degradation process. We propose that the inhibition of circRNAs-MSR could inhibit the degradation of chondrocyte ECM and knockdown of circRNAs-MSR could be a potential therapeutic target for OA.

On mechanical mechanism of damage evolution in articular cartilage

Superficial lesions of cartilage are the direct indication of osteoarthritis. To investigate the mechanical mechanism of cartilage with micro-defect under external loading, a new plain strain numerical model with micro-defect was proposed and damage evolution progression in cartilage over time has been simulated, the parameter were studied including load style, velocity of load and degree of damage. The new model consists of the hierarchical structure of cartilage and depth-dependent arched fibers. The numerical results have shown that not only damage of the cartilage altered the distribution of the stress but also matrix and fiber had distinct roles in affecting cartilage damage, and damage in either matrix or fiber could promote each other. It has been found that the superficial cracks in cartilage spread preferentially along the tangent direction of the fibers. It is the arched distribution form of fibers that affects the crack spread of cartilage, which has been verified by experiment. During the process of damage evolution, its extension direction and velocity varied constantly with the damage degree. The rolling load could cause larger stress and strain than sliding load. Strain values of the matrix initially increased and then decreased gradually with the increase of velocity, and velocity had a greater effect on matrix than fibers. Damage increased steadily before reaching 50%, sharply within 50 to 85%, and smoothly and slowly after 85%. The finding of the paper may help to understand the mechanical mechanism why the cracks in cartilage spread preferentially along the tangent direction of the fibers.

Unfolding of membrane ruffles of in situ chondrocytes under compressive loads

Impact loading results in chondrocyte death. Previous studies implicated high tensile strain rates in chondrocyte membranes as the cause of impact-induced cell deaths. However, this hypothesis relies on the untested assumption that chondrocyte membranes unfold in vivo during physiological tissue compression, but do not unfold during impact loading. Although membrane unfolding has been observed in isolated chondrocytes during osmotically induced swelling and mechanical compression, it is not known if membrane unfolding also occurs in chondrocytes embedded in their natural extracellular matrix. This study was aimed at quantifying changes in membrane morphology of in situ superficial zone chondrocytes during slow physiological cartilage compression. Bovine cartilage-bone explants were loaded at 5 μm/s to nominal compressive strains ranging from 0% to 50%. After holding the final strains for 45 min, the loaded cartilage was chemically pre-fixed for 12 h. The cartilage layer was post-processed for visualization of cell ultrastructure using electron microscopy. The changes in membrane morphology in superficial zone cells were quantified from planar electron micrographs by measuring the roughness and the complexity of the cell surfaces. Qualitatively, the cell surface ruffles that existed before loading disappeared when cartilage was loaded. Quantitatively, the roughness and complexity of cell surfaces decreased with increasing load magnitudes, suggesting a load-dependent use of membrane reservoirs. Chondrocyte membranes unfold in a load-dependent manner when cartilage is compressed. Under physiologically meaningful loading conditions, the cells likely expand their surface through unfolding of the membrane ruffles, and therefore avoid direct stretch of the cell membrane. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:304-310, 2017.

Controlling joint instability delays the degeneration of articular cartilage in a rat model

OBJECTIVE

Joint instability induced by anterior cruciate ligament (ACL) transection is commonly considered as a predisposing factor for osteoarthritis (OA) of the knee; however, the influence of re-stabilization on the protection of articular cartilage is unclear. The aim of this study was to evaluate the effect of joint re-stabilization on articular cartilage using an instability and re-stabilization ACL transection model.

DESIGN

To induce different models of joint instability, our laboratory created a controlled abnormal joint movement (CAJM) group and an anterior cruciate ligament transection group (ACL-T). Seventy-five Wistar male rats were randomly assigned to the CAJM (n = 30), ACL-T (n = 30), or no treatment (INTACT) group (n = 15). Cartilage changes were assessed with soft X-ray analysis, histological and immunohistochemistry analysis, and real-time polymerase chain reaction (PCR) analysis at 2, 4, and 12 weeks.

RESULTS

Joint instability, as indicated by the difference in anterior displacement between the CAJM and ACL-T groups (P < 0.001), and cartilage degeneration, as evaluated according to the Osteoarthritis Research Society International (OARSI) score, were significantly higher in the ACL-T group than the CAJM group at 12 weeks (P < 0.001). Moreover, joint re-stabilization maintained cartilage structure (thickness [P < 0.001], surface roughness [P < 0.001], and glycosaminoglycan stainability [P < 0.001]) and suppressed tumor necrosis factor-alpha (TNF-α) and caspase-3 at 4 weeks after surgery.

CONCLUSION

Re-stabilization of joint instability may suppress inflammatory cytokines, thereby delaying the progression of OA. Joint instability is a substantial contributor to cartilage degeneration.

Ginsenoside‑Rg5 treatment inhibits apoptosis of chondrocytes and degradation of cartilage matrix in a rat model of osteoarthritis

This study investigated the effect of ginsenoside‑Rg5 on the degradation of articular cartilage in osteoarthritis rat model and on induction of chondrocyte apoptosis. Osteoarthritis rat model was prepared by ligament transection and medial meniscus resection. The rats were then treated with different doses (1, 2, 5, 10 and 15 µM) of ginsenoside‑Rg5 for 48 h. The results from histopathological analysis revealed a significant (P=0.005) prevention of cartilage degradation in OA rat model by ginsenoside‑Rg5 treatment at 15 µM. Ginsenoside‑Rg5 treatment prevented the disintegration of synovial membrane to a significant (P=0.005) extent. The proportion of apoptotic cells in the knee joints was reduced to 7% by ginsenoside‑Rg5 treatment after one month compared to the control. Treatment of the rats with ginsenoside‑Rg5 caused increase in the levels of proteoglycan, collagen and type II collagen by 5-, 3- and 4-fold compared to the control group. Immunohistochemistry revealed that the level of MMP-13 was reduced to 45% and that of TIMP‑1 was increased by 67% on treatment with ginsenoside‑Rg5. The levels of interleukin-1β, tumor necrosis factor-α, nitric oxide and inducible nitric oxide synthetase were reduced by 67, 54, 32 ad 49%, respectively after one month of treatment with 15 mg/kg dose of ginsenoside‑Rg5. The expression was increased to 67 and 52% for BMP-2 and TGF-β1, respectively on treatment with ginsenoside‑Rg5. Thus ginsenoside‑Rg5 prevents cartilage degradation in the OA rats and inhibits cartilage apoptosis, therefore it can be used for osteoarthritis treatment.

Hydrogen sulfide protects against endoplasmic reticulum stress and mitochondrial injury in nucleus pulposus cells and ameliorates intervertebral disc degeneration

It has been suggested that excessive apoptosis in intervertebral disc cells induced by inflammatory cytokines, such as interleukin (IL)-1β, is related to the process of intervertebral disc degeneration (IVDD). Hydrogen sulfide (H₂S), a gaseous signaling molecule, has drawn attention for its anti-apoptosis role in various pathophysiological processes in degenerative diseases. To date, there has been no investigation of the correlation of H₂S production and IVDD or of the effects of H₂S on IL-1β-induced apoptosis in nucleus pulposus (NP) cells. Here, we found that the expression levels of cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE), two key enzymes in the generation of H₂S, were significantly decreased in human degenerate NP tissues as well as in IL-1β-treated NP cells. NaHS (H₂S donor) administration showed a protective effect by inhibiting the endoplasmic reticulum (ER) stress response and mitochondrial dysfunction induced by IL-1β stimulation in vitro, the effect was related to activation of the PI3K/Akt and ERK1/2 signaling pathways. Suppression of these pathways by specific inhibitors, LY294002 and PD98059, partially reduced the protective effect of NaHS. Moreover, in the percutaneous needle puncture disc degeneration rat tail model, disc degeneration was partially reversed by NaHS administration. Taken together, our results suggest that H₂S plays a protective role in IVDD and the underlying mechanism involves PI3K/Akt and ERK1/2 signaling pathways-mediated suppression of ER stress and mitochondrial dysfunction in IL-1β-induced NP cells.

Cell Death in Chondrocytes, Osteoblasts, and Osteocytes

Cell death in skeletal component cells, including chondrocytes, osteoblasts, and osteocytes, plays roles in skeletal development, maintenance, and repair as well as in the pathogenesis of osteoarthritis and osteoporosis. Chondrocyte proliferation, differentiation, and apoptosis are important steps for endochondral ossification. Although the inactivation of P53 and RB is involved in the pathogenesis of osteosarcomas, the deletion of p53 and inactivation of Rb are insufficient to enhance chondrocyte proliferation, indicating the presence of multiple inhibitory mechanisms against sarcomagenesis in chondrocytes. The inflammatory processes induced by mechanical injury and chondrocyte death through the release of danger-associated molecular patterns (DAMPs) are involved in the pathogenesis of posttraumatic osteoarthritis. The overexpression of BCLXL increases bone volume with a normal structure and maintains bone during aging by inhibiting osteoblast apoptosis. p53 inhibits osteoblast proliferation and enhances osteoblast apoptosis, thereby reducing bone formation, but also exerts positive effects on osteoblast differentiation through the Akt–FoxOs pathway. Apoptotic osteocytes release ATP, which induces the receptor activator of nuclear factor κ-B ligand (Rankl) expression and osteoclastogenesis, from pannexin 1 channels. Osteocyte death ultimately results in necrosis; DAMPs are released to the bone surface and promote the production of proinflammatory cytokines, which induce Rankl expression, and osteoclastogenesis is further enhanced.

Effects of mechanical stress on chondrocyte phenotype and chondrocyte extracellular matrix expression

Mechanical factors play a key role in regulating the development of cartilage degradation in osteoarthritis. This study aimed to identify the influence of mechanical stress in cartilage and chondrocytes. To explore the effects of mechanical stress on cartilage morphology, we observed cartilages in different regions by histological and microscopic examination. Nanoindentation was performed to assess cartilage biomechanics. To investigate the effects of mechanical stress on chondrocytes, cyclic tensile strain (CTS, 0.5 Hz, 10%) was applied to monolayer cultures of human articular chondrocytes by using Flexcell-5000. We quantified the mechanical properties of chondrocytes by atomic force microscopy. Chondrocytes were stained with Toluidine blue and Alcian blue after exposure to CTS. The expression of extracellular matrix (ECM) molecules was detected by qPCR and immunofluorescence analyses in chondrocytes after CTS. Our results demonstrated distinct morphologies and mechanical properties in different cartilage regions. In conclusion, mechanical stress can affect the chondrocyte phenotype, thereby altering the expression of chondrocyte ECM.

Roles of hypoxia inducible factor-1α in the temporomandibular joint

OBJECTIVE

Temporomandibular joint osteoarthritis (TMJ-OA) is a degenerative disease characterized by permanent cartilage loss. Articular cartilage is maintained in a low-oxygen environment. The chondrocyte response to hypoxic conditions involves expression of hypoxia inducible factor 1α (HIF-1α), which induces chondrocytes to increase expression of vascular endothelial growth factor (VEGF). Here, we investigated the role of HIF-1α in mechanical load effects on condylar cartilage and subchondral bone in heterozygous HIF-1α-deficient mice (HIF-1α^+/-).

DESIGN

Mechanical stress was applied to the TMJ of C57BL/6NCr wild-type (WT) and HIF-1α^+/- mice with a sliding plate for 10 days. Histological analysis was performed by HE staining, Safranin-O/Fast green staining, and immunostaining specific for articular cartilage homeostasis.

RESULTS

HIF-1α^+/- mice had thinner cartilage and smaller areas of proteoglycan than WT controls, without and with mechanical stress. Mechanical stress resulted in prominent degenerative changes with increased expression of HIF-1α, VEGF, and the apoptosis factor cleaved Caspase-3 in condylar cartilage.

CONCLUSION

Our results indicate that HIF-1α may be important for articular cartilage homeostasis and protective against articular cartilage degradation in the TMJ under mechanical stress condition, therefore HIF-1α could be an important new therapeutic target in TMJ-OA.

Phosphorylation of osteopontin has proapoptotic and proinflammatory effects on human knee osteoarthritis chondrocytes

The aim of the present study was to investigate the effects of phosphorylated osteopontin (p-OPN) on apoptosis and pro-inflammatory cytokine expression in human knee osteoarthritis (OA) chondrocytes. Human knee OA chondrocytes obtained from patients who underwent total knee arthroplasty were treated with p-OPN, OPN or buffer. Reverse transcription quantitative-polymerase chain reaction (RT-qPCR) and western blot analysis were used to assess the expression levels of proinflammatory factors, including interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6 and nuclear factor (NF)-κB. Apoptosis of human knee OA chondrocytes was detected by Annexin V-fluorescein isothiocyanate/propidium iodide flow cytometry. Compared with the controls, chondrocytes treated with OPN exhibited higher mRNA and protein expression levels of proinflammatory factors (IL-1β, TNF-α, IL-6 and NF-κB), and a higher percentage of apoptotic chondrocytes. Furthermore, chondrocytes treated with p-OPN exhibited the highest mRNA and protein expression levels of proinflammatory factors (IL-1β, TNF-α, IL-6, NF-κB) and the highest percentage of apoptotic chondrocytes. p-OPN induces chondrocyte apoptosis and proinflammatory factor release, which suggests that p-OPN may contribute to OA pathogenesis, and inhibition of p-OPN may provide a novel effective strategy to slow or halt OA progression.

A novel rat model for subchondral microdamage in acute knee injury: a potential mechanism in post-traumatic osteoarthritis

OBJECTIVE

Subchondral microdamage may play an important role in post-traumatic osteoarthritis (PTOA) development following anterior cruciate ligament (ACL) rupture. It remains unknown whether this injury mechanism causes subchondral microdamage, or whether its repair occurs by targeted osteoclast-mediated remodeling. If so these events may represent a mechanism by which subchondral bone is involved in PTOA. Our objective was to test the hypothesis that subchondral microdamage occurs, and is co-localized with remodeling, in a novel rat model of ACL rupture.

DESIGN

We developed a novel non-invasive rat animal model for ACL rupture and subchondral microdamage generation. By inducing ACL rupture noninvasively rather than surgically, this more closely mimics the clinical injury. MicroCT, MRI and histological methods were used to measure microstructural changes, ligament damage, and cellular/matrix degeneration, respectively.

RESULTS

We reproducibly generated ACL rupture without damage to other soft joint tissues. Immediately after injury, increased microdamage was found in the postero-medial aspect of the tibia. Microstructural parameters showed increased resorption at 2 weeks, which returned to baseline. Dynamic histomorphometry showed increased calcein label uptake in the same region at 4 and 8 weeks. Chondrocyte death and protease activity in cartilage was also noted, however whether this was directly linked to subchondral changes is not yet known. Similarly, cartilage scoring showed degradation at 4 and 8 weeks post-injury.

CONCLUSIONS

This study shows that our novel model can be used to study subchondral microdamage after ACL-rupture, and its association with localized remodeling. Cartilage degeneration, on a similar time-scale to other models, is also a feature of this system.

Protection of carboxymethylated chitosan on chondrocytes from nitric oxide-induced apoptosis by regulating phosphatidylinositol 3-kinase/Akt signaling pathway

Chondrocyte apoptosis is the most important element of development and progression of osteoarthritis (OA). Nitric oxide (NO) was used as the agent to induce chondrocyte apoptosis. Carboxymethylated chitosan (CMCS) has anti-apoptosis effect on many cell types in vitro. This study was designed to investigate the protective effect of CMCS on NO-induced chondrocyte apoptosis and the probable molecular mechanisms. The newborn Sprague-Dawley (SD) rats were used in this study for isolation of chondrocytes. The cell viability was determined by cell counting kit (CCK-8), cell apoptosis was detected by Annexin-V/PI double staining assay kit. The levels of phosphorylated-PI3K (p-PI3K), phosphorylated-Akt (p-Akt), Bcl-2 and Bax were determined by Western blot analysis. The caspase-3 activity was determined by a quantitative colorimetric assay. Results showed that pretreatment with CMCS could inhibit the apoptosis induced by NO. CMCS could decrease the activity of NO and decrease the expression of Bcl-2, p-PI3K and p-Akt, increase the expression of Bax, cytochrome c and caspase-3. CMCS also could reverse the effect of NO that prompted matrix metalloproteinase-13 (MMP-13) and inhibited tissue inhibitor of metalloproteinase-1 (TIMP-1) activity. All the present results indicated that CMCS can protect NO induced chondrocytes apoptosis by activate PI3K/Akt signaling pathway.

Post-traumatic arthritis: overview on pathogenic mechanisms and role of inflammation

Post-traumatic arthritis (PTA) develops after an acute direct trauma to the joints. PTA causes about 12% of all osteoarthritis cases, and a history of physical trauma may also be found in patients with chronic inflammatory arthritis. Symptoms include swelling, synovial effusion, pain and sometimes intra-articular bleeding. Usually, PTA recoveries spontaneously, but the persistence of symptoms after 6 months may be considered pathological and so-called chronic PTA. A variety of molecular, mechanobiological and cellular events involved in the pathogenesis and the progression of PTA have been identified. The activation of inflammatory mechanisms during the PTA acute phase appears to play a critical role in the chronic disease onset. Human studies and experimental models have revealed that a series of inflammatory mediators are released in synovial fluid immediately after the joint trauma. These molecules have been proposed as markers of disease and as a potential target for the development of specific and preventative interventions. Currently, chronic PTA cannot be prevented, although a large number of agents have been tested in preclinical studies. Given the relevance of inflammatory reaction, anticytokines therapy, in particular the inhibition of interleukin 1 (IL-1), seems to be the most promising strategy. At the present time, intra-articular injection of IL-1 receptor antagonist is the only anticytokine approach that has been used in a human study of PTA. Despite the fact that knowledge in this area has increased in the past years, the identification of more specific disease markers and new therapeutic opportunities are needed.

Effectiveness of an aquatic exercise program and low-level laser therapy on articular cartilage in an experimental model of osteoarthritis in rats

OBJECTIVE

The aim of this study was to evaluate the effects of an aquatic exercise program and low-level laser therapy (LLLT) (associated or not) on degenerative modifications and inflammatory mediators on the articular cartilage using an experimental model of knee OA.

METHOD

Forty male Wistar rats were divided into 4 groups: knee OA - without treatment (OA); OA plus exercise program group (OAE); OA plus LLLT (OAL); OA plus exercise program associated with LLLT (OAEL). Trained rats performed a water-jumping program carrying a load equivalent to 50-80 % of their body mass strapped to their chest. The laser irradiation was used either as the only method or after the exercise training had been performed, at 2 points contact mode (medial and lateral side of the left joint). The treatments started 4 weeks after the surgery, 3 days/week for 8 weeks.

RESULTS

The results revealed that all treated groups (irradiated or not) exhibited a better pattern of tissue organization, with less fibrillation and irregularities along the articular surface and improved chondrocytes organization. Also, a lower cellular density and structural damage (OARSI score) and higher thickness values were observed in all treated groups. Additionally, OAE and OAEL showed a reduced expression in IL-1β and caspase-3 as compared with OA. Furthermore, a statistically lower MMP-13 expression was only observed in OAEL as compared with OA.

CONCLUSION

These results suggest that aquatic exercise program and LLLT were effective in preventing cartilage degeneration. Also, physical exercise program presented anti-inflammatory effects in the knees in OA rats.

Pollutants make rheumatic diseases worse: Facts on polychlorinated biphenyls (PCBs) exposure and rheumatic diseases

BACKGROUND

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that bioaccumulate in adipose tissue, disturbing its metabolism and the balance of adipokines, related to obesity. The altering secretion pattern of adipokines from the adipose tissue and the increasing mechanical load in weight-bearing joints presented in obesity condition, are risk factors for osteoarthritis development. The most prevalent rheumatic diseases, osteoarthritis and rheumatoid arthritis, are chronic conditions that target the whole joints, leading to increasing disability and health care cost. The goal of this focused review is to summarize the current knowledge on the role of PCBs in osteoarthritis and rheumatoid arthritis pathogenesis.

SEARCH STRATEGY

A PubMed search was managed using keywords as "rheumatic diseases", "polychlorinated biphenyls", "obesity" and "endocrine disruption".

MAIN RESULTS OF THE REVIEW

The incidence of rheumatoid arthritis has been reported to be increased especially in urban areas in industrialized countries, emphasizing the importance of environment in the pathogenesis of rheumatic diseases. Analysis of two cohorts exposed to PCBs food contamination showed high incidence of arthritis. In addition, PCBs in serum correlated positively with the prevalence of self-reported arthritis. Few studies support the hypothesis that osteoarthritis development could be related to PCBs induction of chondrocytes apoptosis.

CONCLUSION

Evidences have emerged for a relationship between PCBs and development of several types of arthritis. Further research is encouraged to determine the correlation between PCBs exposure and the development of rheumatic diseases.

Forced exercise-induced osteoarthritis is attenuated in mice lacking the small leucine-rich proteoglycan decorin

OBJECTIVE

Interterritorial regions of articular cartilage matrix are rich in decorin, a small leucine-rich proteoglycan and important structural protein, also involved in many signalling events. Decorin sequesters transforming growth factor β (TGFβ), thereby regulating its activity. Here, we analysed whether increased bioavailability of TGFβ in decorin-deficient (Dcn^-/-) cartilage leads to changes in biomechanical properties and resistance to osteoarthritis (OA).

METHODS

Unchallenged knee cartilage was analysed by atomic force microscopy (AFM) and immunohistochemistry. Active transforming growth factor β-1 (TGFβ1) content within cultured chondrocyte supernatants was measured by ELISA. Quantitative real-time (RT)-PCR was used to analyse mRNA expression of glycosaminoglycan (GAG)-modifying enzymes in C28/I2 cells following TGFβ1 treatment. In addition, OA was induced in Dcn^-/- and wild-type (WT) mice via forced exercise on a treadmill.

RESULTS

AFM analysis revealed a strikingly higher compressive stiffness in Dcn^-/- than in WT cartilage. This was accompanied by increased negative charge and enhanced sulfation of GAG chains, but not by alterations in the levels of collagens or proteoglycan core proteins. In addition, decorin-deficient chondrocytes were shown to release more active TGFβ1. Increased TGFβ signalling led to enhanced Chst11 sulfotransferase expression inducing an increased negative charge density of cartilage matrix. These negative charges might attract more water resulting in augmented compressive stiffness of the tissue. Therefore, decorin-deficient mice developed significantly less OA after forced exercise than WT mice.

CONCLUSIONS

Our study demonstrates that the disruption of decorin-restricted TGFβ signalling leads to higher stiffness of articular cartilage matrix, rendering joints more resistant to OA. Therefore, the loss of an important structural component can improve cartilage homeostasis.

Drying of open animal joints in vivo subsequently causes cartilage degeneration

Objectives

During open orthopaedic surgery, joints may be exposed to air, potentially leading to cartilage drying and chondrocyte death, however, the long-term effects of joint drying in vivo are poorly understood. We used an animal model to investigate the subsequent effects of joint drying on cartilage and chondrocytes.

Methods

The patellar groove of anaesthetised rats was exposed (sham-operated), or exposed and then subjected to laminar airflow (0.25m/s; 60 minutes) before wounds were sutured and animals recovered. Animals were monitored for up to eight weeks and then sacrificed. Cartilage and chondrocyte properties were studied by histology and confocal microscopy, respectively.

Results

Joint drying caused extensive chondrocyte death within the superficial regions of cartilage. Histology of dried cartilage demonstrated a loss of surface integrity at four weeks, fibrillations at eight weeks, and an increased modified Mankin score (p < 0.001). Cartilage thickness increased (p < 0.001), whereas chondrocyte density decreased at four weeks (p < 0.001), but then increased towards sham-operated levels (p < 0.01) at eight weeks. By week eight, chondrocyte pairing/clustering and cell volume increased (p < 0.05; p < 0.001, respectively).

Conclusions

These in vivo results demonstrated for the first time that as a result of laminar airflow, cartilage degeneration occurred which has characteristics similar to those seen in early osteoarthritis. Maintenance of adequate cartilage hydration during open orthopaedic surgery is therefore of paramount importance.

Cite this article: Dr A. Hall. Drying of open animal joints in vivo subsequently causes cartilage degeneration. Bone Joint Res 2016;5:137–144. DOI: 10.1302/2046-3758.54.2000594.

MicroRNA-30a promotes extracellular matrix degradation in articular cartilage via downregulation of Sox9

OBJECTIVES

Sox9 has recently been reported to be a key mediator during cartilage degradation in osteoarthritis (OA). Our aim was to clarify the role of microRNA-30a (miR-30a) and its target gene Sox9 in regulation of extracellular matrix (ECM) degradation in OA.

MATERIALS AND METHODS

Expression of miR-30a in cartilage tissues and in primary chondrocytes from healthy and OA donors, was determined by real-time PCR, and levels of Sox9 mRNA and protein were analyzed by real-time PCR and western blotting, respectively. Subsequently, the target of miR-30a was predicted by bioinformatics and confirmed using a luciferase assay. Expression of ECM-related genes was determined by tissue-specific staining, immunofluorescence, real-time PCR, and western blotting. The role of miR-30a in OA was examined in vivo using a collagenase-induced OA rat model.

RESULTS

miR-30a was significantly upregulated and Sox9 was downregulated in primary chondrocytes from cartilage taken from OA donors compared to healthy controls. We showed that miR-30a specifically bound to the 3' UTR of Sox9, and overexpression of miR-30a downregulated expression levels of Sox9, proteoglycan aggrecan, and Col II compared to those induced by small interfering RNA transfection to knockdown Sox9. miR-30a inhibition reversed the effects of ECM degradation in vitro and in vivo.

CONCLUSIONS

miR-30a acts as a virulence MRA in OA, promoting ECM degradation by targeting Sox9 and by modulating activity of its downstream effectors Col II and proteoglycan aggrecan.

Circular RNA Related to the Chondrocyte ECM Regulates MMP13 Expression by Functioning as a MiR-136 'Sponge' in Human Cartilage Degradation

Circular RNAs (circRNAs) are involved in the development of various diseases, but there is little knowledge of circRNAs in osteoarthritis (OA). The aim of study was to identify circRNA expression in articular cartilage and to explore the function of chondrocyte extracellular matrix (ECM)-related circRNAs (circRNA-CER) in cartilage. To identify circRNAs that are specifically expressed in cartilage, we compared the expression of circRNAs in OA cartilage with that in normal cartilage. Bioinformatics was employed to predict the interaction of circRNAs and mRNAs in cartilage. Loss-of-function and rescue experiments for circRNA-CER were performed in vitro. A total of 71 circRNAs were differentially expressed in OA and normal cartilage. CircRNA-CER expression increased with interleukin-1 and tumor necrosis factor levels in chondrocytes. Silencing of circRNA-CER using small interfering RNA suppressed MMP13 expression and increased ECM formation. CircRNA-CER could compete for miR-136 with MMP13. Our results demonstrated that circRNA-CER regulated MMP13 expression by functioning as a competing endogenous RNA (ceRNA) and participated in the process of chondrocyte ECM degradation. We propose that circRNA-CER could be used as a potential target in OA therapy.

Molecular changes indicative of cartilage degeneration and osteoarthritis development in patients with anterior cruciate ligament injury

BACKGROUND

Anterior cruciate ligament (ACL) tear is considered a risk factor for osteoarthritis development. The purpose of our study was to investigate the expression levels of the apoptotic enzyme caspase 3, pro-inflammatory cytokines interleukin-1β (IL-1β) and interleukin-6 (IL-6) and degrading enzyme matrix metalloproteinase 13 (MMP-13), all indicative of cartilage degeneration and osteoarthritis development in patients' chondrocytes after ACL rupture.

METHODS

We investigated the correlation between grade of cartilage degradation and time from injury or patients' age. IL-1β, IL-6 and MMP-13 mRNA expression levels were investigated in normal (n = 4) and chondrocytes from patients with ACL rupture (n = 33) using real-time polymerase chain reaction (PCR). Moreover, MMP-13 and caspase-3 protein expression levels were evaluated by western blot analysis. Trend analysis and correlation coefficient were performed to derive the relations between gene expression (MMP13, IL-6, IL-1β) and grading of cartilage defects and between gene expression (MMP13, IL-6, IL-1β) and patients' age, respectively.

RESULTS

Correlations were established between grade of cartilage degradation and time from injury. MMP-13, IL-6, IL-1β and caspase 3 expression levels were significantly upregulated in chondrocytes from ACL-deficient knee compared to normal. Among the patients with ACL-deficient knees, a significant upregulation of MMP-13 was observed in patients with ACL-rupture > 18 months from the time of injury to arthroscopy compared to patients with ACL-injury up to 18 months, whereas IL-6 and IL-1β expression was higher in chondrocytes from patients with more than 10 months ACL injury compared to those that underwent surgery within the first 10 months after injury. Νο association was observed between IL-1β, IL-6 and MMP-13 expression levels and cartilage defects or patients' age.

CONCLUSION

Our results showed that increased levels of apoptotic, inflammatory and catabolic factors in chondrocytes are associated with time from injury and could contribute to cartilage degradation and osteoarthritis development after ACL rupture.

Messenger RNA delivery of a cartilage-anabolic transcription factor as a disease-modifying strategy for osteoarthritis treatment

Osteoarthritis (OA) is a chronic degenerative joint disease and a major health problem in the elderly population. No disease-modifying osteoarthritis drug (DMOAD) has been made available for clinical use. Here we present a disease-modifying strategy for OA, focusing on messenger RNA (mRNA) delivery of a therapeutic transcription factor using polyethylene glycol (PEG)-polyamino acid block copolymer-based polyplex nanomicelles. When polyplex nanomicelles carrying the cartilage-anabolic, runt-related transcription factor (RUNX) 1 mRNA were injected into mouse OA knee joints, OA progression was significantly suppressed compared with the non-treatment control. Expressions of cartilage-anabolic markers and proliferation were augmented in articular chondrocytes of the RUNX1-injected knees. Thus, this study provides a proof of concept of the treatment of degenerative diseases such as OA by the in situ mRNA delivery of therapeutic transcription factors; the presented approach will directly connect basic findings on disease-protective or tissue-regenerating factors to disease treatment.

Chondrocyte Apoptosis in the Pathogenesis of Osteoarthritis

Apoptosis is a highly-regulated, active process of cell death involved in development, homeostasis and aging. Dysregulation of apoptosis leads to pathological states, such as cancer, developmental anomalies and degenerative diseases. Osteoarthritis (OA), the most common chronic joint disease in the elderly population, is characterized by progressive destruction of articular cartilage, resulting in significant disability. Because articular cartilage depends solely on its resident cells, the chondrocytes, for the maintenance of extracellular matrix, the compromising of chondrocyte function and survival would lead to the failure of the articular cartilage. The role of subchondral bone in the maintenance of proper cartilage matrix has been suggested as well, and it has been proposed that both articular cartilage and subchondral bone interact with each other in the maintenance of articular integrity and physiology. Some investigators include both articular cartilage and subchondral bone as targets for repairing joint degeneration. In late-stage OA, the cartilage becomes hypocellular, often accompanied by lacunar emptying, which has been considered as evidence that chondrocyte death is a central feature in OA progression. Apoptosis clearly occurs in osteoarthritic cartilage; however, the relative contribution of chondrocyte apoptosis in the pathogenesis of OA is difficult to evaluate, and contradictory reports exist on the rate of apoptotic chondrocytes in osteoarthritic cartilage. It is not clear whether chondrocyte apoptosis is the inducer of cartilage degeneration or a byproduct of cartilage destruction. Chondrocyte death and matrix loss may form a vicious cycle, with the progression of one aggravating the other, and the literature reveals that there is a definite correlation between the degree of cartilage damage and chondrocyte apoptosis. Because current treatments for OA act only on symptoms and do not prevent or cure OA, chondrocyte apoptosis would be a valid target to modulate cartilage degeneration.

Tauroursodeoxycholic acid suppresses endoplasmic reticulum stress in the chondrocytes of patients with osteoarthritis

The main pathogenic events in osteoarthritis (OA) include loss and abnormal remodeling of cartilage extracellular matrix. The present study aimed to evaluate the protective effect of tauroursodeoxycholic acid on chondrocyte apoptosis induced by endoplasmic reticulum (ER) stress. Articular cartilage tissues were collected from 18 patients who underwent total knee arthroplasty and were analyzed histologically. Subsequently, chondrocyte apoptosis was assessed by TUNEL. Quantitative polymerase chain reaction and western blot analysis were employed to evaluate gene and protein expression, respectively, of ER stress markers, including glucose‑regulated protein 78 (GRP78), growth arrest and DNA‑damage‑inducible gene 153 (GADD153) and caspase‑12 along with type II collagen. Chondrocytes obtained from osteoarthritis patients at different stages were cultured in three conditions including: No treatment (CON group), tunicamycin treatment to induce ER stress (ERS group) and tauroursodeoxycholic acid treatment after 4 h of tunicamycin (TDA group); and cell proliferation, apoptosis, function and ER stress level were assessed. Degradation of cartilage resulted in histological damage with more apoptotic cartilage cells observed. Of note, GRP78, GADD153 and caspase‑12 mRNA and protein expression increased gradually from grade I to III cartilage tissue, while type II collagen expression decreased. Tunicamycin induced ER stress, as shown by a high expression of ER stress markers, reduced cell proliferation, increased apoptosis and decreased synthesis of type II collagen. Notably, tauroursodeoxycholic acid treatment resulted in the improvement of tunicamycin‑induced ER stress. These results indicated that ER stress is highly involved in the tunicamycin‑induced apoptosis in chondrocytes, which can be prevented by tauroursodeoxycholic acid.