Microarray analysis reveals age-related differences in gene expression during the development of osteoarthritis in mice

Mouse Models of Osteoarthritis: Surgical Model of Post-traumatic Osteoarthritis Induced by Destabilization of the Medial Meniscus

The surgical model of destabilization of the medial meniscus (DMM) has become a gold standard for studying the onset and progression of post-traumatic osteoarthritis (OA). The DMM model mimics clinical meniscal injury, a known predisposing factor for the development of human OA, and permits the study of structural and biological changes over the course of the disease. In addition, when applied to genetically modified or engineered mouse models, this surgical procedure permits dissection of the relative contribution of a given gene to OA initiation and/or progression. This chapter describes the requirements for the surgical induction of OA in mouse models, and provides guidelines and tools for the subsequent histological, immunohistochemical, and molecular analyses. Methods for the assessment of the contributions of selected genes in genetically modified strains are also provided.

Sex- and injury-based differences in knee biomechanics in mouse models of post-traumatic osteoarthritis

Sex and joint injury are risk factors implicated in the onset and progression of osteoarthritis (OA). In mouse models of post-traumatic OA (ptOA), the pathogenesis of disease is notably impacted by sex (often worse in males) and injury model (e.g. meniscal versus ligament injury). Increasing ptOA progression and severity is often associated with greater relative instability of the joint but few studies have directly quantified changes in joint mechanics after injury and compared outcomes across multiple models in both male and female mice. Passive anterior-posterior knee biomechanics were evaluated in 10-week-old, male and female C57BL/6J mice. PtOA injury models included destabilisation of the medial meniscus (DMM), anterior cruciate ligament transection (ACLT) or mechanical rupture (ACLR), and combined DMM and ACLT (DMM + ACLT). Sham operated and non-operated controls (NOC) were included for baseline comparisons. The test apparatus loaded hindlimbs at 60° flexion between ± 1 N at 0.5 mm/s (build specifications available for download: https://doi.org/10.17632/z754455x3c.1). Measures of joint laxity (range of motion, neutral zone) and stiffness were calculated. Joint laxity was comparable between male and female mice while joint stiffness was greater in females (P ≤ 0.002, correcting for body-mass and injury-model). Anterior-posterior joint mechanics were minimally altered by DMM but significantly affected by loss of the ACL (P < 0.001), with equivalent changes between ACL-injury models despite different injury mechanisms and adjacent meniscal damage. These findings suggest that despite the important role of joint injury; sex- and model-specific differences in ptOA progression and severity are not primarily driven by altered anterior-posterior knee biomechanics.

Comparative anatomy and morphology of the knee in translational models for articular cartilage disorders. Part II: Small animals

BACKGROUND

Small animal models are critical to model the complex disease mechanisms affecting a functional joint leading to articular cartilage disorders. They are advantageous for several reasons and significantly contributed to the understanding of the mechanisms of cartilage diseases among which osteoarthritis.

METHODS

Literature search in Pubmed.

RESULTS AND DISCUSSION

This narrative review summarizes the most relevant anatomical structural and functional characteristics of the knee (stifle) joints of the major small animal species, including mice, rats, guinea pigs, and rabbits compared with humans. Specific characteristics of each species, including kinematical gait parameters are provided and compared with the human situation. When placed in a proper context respecting their challenges and limitations, small animal models are important and appropriate models for articular cartilage disorders.

Blockade of IL-33 signalling attenuates osteoarthritis

Objectives

Osteoarthritis (OA) is the most common form of arthritis characterised by cartilage degradation, synovitis and pain. Disease modifying treatments for OA are not available. The critical unmet need is to find therapeutic targets to reduce both disease progression and pain. The cytokine IL‐33 and its receptor ST2 have been shown to play a role in immune and inflammatory diseases, but their role in osteoarthritis is unknown.

Methods

Non‐OA and OA human chondrocytes samples were examined for IL‐33 and ST2 expression. Novel inducible cartilage specific knockout mice (IL‐33^{Acan CreERT2}) and inducible fibroblast‐like synoviocyte knockout mice (IL‐33^{Col1a2 CreERT2}) were generated and subjected to an experimental OA model. In addition, wild‐type mice were intra‐articularly administered with either IL‐33‐ or ST2‐neutralising antibodies during experimental OA studies.

Results

IL‐33 and its receptor ST2 have increased expression in OA patients and a murine disease model. Administering recombinant IL‐33 increased OA and pain in vivo. Synovial fibroblast‐specific deletion of IL‐33 decreased synovitis but did not impact disease outcomes, whilst cartilage‐specific deletion of IL‐33 improved disease outcomes in vivo. Blocking IL‐33 signalling also reduced the release of cartilage‐degrading enzymes in human and mouse chondrocytes. Most importantly, we show the use of monoclonal antibodies against IL‐33 and ST2 attenuates both OA and pain in vivo.

Conclusion

Overall, our data reveal blockade of IL‐33 signalling as a viable therapeutic target for OA.

CCN3 (NOV) Drives Degradative Changes in Aging Articular Cartilage

Aging is a major risk factor of osteoarthritis, which is characterized by the degeneration of articular cartilage. CCN3, a member of the CCN family, is expressed in cartilage and has various physiological functions during chondrocyte development, differentiation, and regeneration. Here, we examine the role of CCN3 in cartilage maintenance. During aging, the expression of Ccn3 mRNA in mouse primary chondrocytes from knee cartilage increased and showed a positive correlation with p21 and p53 mRNA. Increased accumulation of CCN3 protein was confirmed. To analyze the effects of CCN3 in vitro, either primary cultured human articular chondrocytes or rat chondrosarcoma cell line (RCS) were used. Artificial senescence induced by H₂O₂ caused a dose-dependent increase in Ccn3 gene and CCN3 protein expression, along with enhanced expression of p21 and p53 mRNA and proteins, as well as SA-β gal activity. Overexpression of CCN3 also enhanced p21 promoter activity via p53. Accordingly, the addition of recombinant CCN3 protein to the culture increased the expression of p21 and p53 mRNAs. We have produced cartilage-specific CCN3-overexpressing transgenic mice, and found degradative changes in knee joints within two months. Inflammatory gene expression was found even in the rib chondrocytes of three-month-old transgenic mice. Similar results were observed in human knee articular chondrocytes from patients at both mRNA and protein levels. These results indicate that CCN3 is a new senescence marker of chondrocytes, and the overexpression of CCN3 in cartilage may in part promote chondrocyte senescence, leading to the degeneration of articular cartilage through the induction of p53 and p21.

A Microarray Study of Articular Cartilage in Relation to Obesity and Severity of Knee Osteoarthritis

OBJECTIVE

To query the transcript-level changes in the medial and lateral tibial plateau cartilage in tandem with obesity in patients with end-stage osteoarthritis (OA).

DESIGN

Cartilage was obtained from 23 patients (20 obese [body mass index > 30 kg/m²], 3 overweight [body mass index < 30 kg/m²]) at the time of total knee replacement. Cartilage integrity was assessed using Outerbridge scale, while radiographic changes were scored on preoperative X-rays using Kellgren-Lawrence (K-L) classification. RNA was probed for differentially expressed transcripts between medial and lateral compartments using Affymetrix Gene 2.0 ST Array and validated via real-time polymerase chain reaction. Gene ontology and pathway analyses were also queried.

RESULTS

Scoring of cartilage integrity by the Outerbridge scale indicated that the medial and lateral compartments were similar, while scoring by the K-L classification indicated that the medial compartment was more severely damaged than the lateral compartment. We observed a distinct transcript profile with >50% of transcripts unique between medial and lateral compartments. MMP13 and COL2A1 were more highly expressed in medial versus lateral compartment. Polymerase chain reaction confirmed expression of 4 differentially expressed transcripts. Numerous transcripts, biological processes, and pathways were significantly different between overweight and obese patients with a differential response of obesity on medial and lateral compartments.

CONCLUSIONS

Our findings support molecular differences between medial and lateral compartments reflective of the greater severity of OA in the medial compartment. The K-L system better reflected the molecular results than did the Outerbridge. Moreover, the molecular effect of obesity was different between the medial and lateral compartments of the same knee plausibly reflecting the molecular effects of differential biomechanical loading.

Gene Expression Profiling Studies Using Microarray in Osteoarthritis: Genes in Common and Different Conditions

Osteoarthritis (OA), which is characterized mainly by cartilage degradation, is the most prevalent joint disorder worldwide. Although OA is identified as a major cause of joint pain, disability, and socioeconomic burden, the etiology of OA is still not clearly known. Recently, gene microarray analysis has become an efficient method for the research of complex diseases and has been employed to determine what genes and pathways are involved in the pathological process of OA. In this review, OA study results over the last decade are summarized for gene expression profiling of various tissues, such as cartilage, subchondral bone, and synovium in human OA and mouse OA models. Many differentially expressed genes, which mainly involve matrix metabolism, bone turnover, and inflammation pathways, were identified in diseased compared with "normal" tissues. Nevertheless, rare common genes were reported from studies using different tissue sources, microarray chips, and research designs. Thus, future novel and carefully designed microarray studies are required to elucidate underlying genetic mechanisms in the pathogenesis of OA as well as new directions for potential OA-targeted pharmaceutical therapies.

The effect of vitamin K insufficiency on histological and structural properties of knee joints in aging mice

Objective

While a role for vitamin K in maintaining joint tissue homeostasis has been proposed based on the presence of vitamin K dependent proteins in cartilage and bone, it is not clear if low vitamin K intake is causally linked to joint tissue degeneration. To address this gap, we manipulated vitamin K status in aging mice to test its effect on age-related changes in articular cartilage and sub-chondral bone.

Methods

Eleven-month old male C57BL6 mice were randomly assigned to a low vitamin K diet containing 120 mcg phylloquinone/kg diet (n = 32) or a control diet containing 1.5 mg phylloquinone/kg diet (n = 30) for 6 months. Knees were evaluated histologically using Safranin O and H&E staining, as well as using micro-CT.

Results

Eleven mice in the low vitamin K diet group and three mice in the control group died within the first 100 days of the experiment (p = 0.024). Mice fed the low vitamin K diet had higher Safranin-O scores, indicative of more proteoglycan loss, compared to mice fed the control diet (p ≤ 0.026). The articular cartilage structure scores did not differ between the two groups (p ≥ 0.190). The sub-chondral bone parameters measured using micro CT also did not differ between the two groups (all p ≥ 0.174).

Conclusion

Our findings suggest low vitamin K status can promote joint tissue proteoglycan loss in older male mice. Future studies are needed to confirm our findings and obtain a better understanding of the molecular mechanisms underlying the role of vitamin K in joint tissue homeostasis.

Deletion of JNK Enhances Senescence in Joint Tissues and Increases the Severity of Age-Related Osteoarthritis in Mice

OBJECTIVE

To determine the role of JNK signaling in the development of osteoarthritis (OA) induced by joint injury or aging in mice.

METHODS

In the joint injury model, 12-week-old wild-type control, JNK1^-/- , JNK2^-/- , and JNK1^fl/fl JNK2^-/- aggecan-Cre^{ERT 2} double-knockout mice were subjected to destabilization of the medial meniscus (DMM) (n = 15 mice per group) or sham surgery (n = 9-10 mice per group), and OA was evaluated 8 weeks later. In the aging experiment, wild-type control, JNK1^-/- , and JNK2^-/- mice (n = 15 per group) were evaluated at 18 months of age. Mouse knee joints were evaluated by scoring articular cartilage structure, toluidine blue staining, osteophytes, and synovial hyperplasia, by histomorphometric analysis, and by immunostaining for the senescence marker p16^{INK 4a} . Production of matrix metalloproteinase 13 (MMP-13) in cartilage explants in response to fibronectin fragments was measured by enzyme-linked immunosorbent assay.

RESULTS

There were no differences after DMM surgery between the wild-type and the JNK-knockout mouse groups in articular cartilage structure, toluidine blue, or osteophyte scores or in MMP-13 production in explants. All 3 knockout mouse groups had increased subchondral bone thickness and area of cartilage necrosis compared to wild-type mice. Aged JNK-knockout mice had significantly worse articular cartilage structure scores compared to the aged wild-type control mice (mean ± SD 52 ± 24 in JNK1^-/- mice and 60 ± 25 in JNK2^-/- mice versus 32 ± 18 in controls; P = 0.02 and P = 0.004, respectively). JNK1^-/- mice also had higher osteophyte scores. Deletion of JNK resulted in increased expression of p16^{INK 4a} in the synovium and cartilage in older mice.

CONCLUSION

JNK1 and JNK2 are not required for the development of OA in the mouse DMM model. Deletion of JNK1 or JNK2 is associated with more severe age-related OA and increased cell senescence, suggesting that JNK may act as a negative regulator of senescence in the joint.

Meniscal and ligament modifications in spontaneous and post-traumatic mouse models of osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a whole joint disease that affects all joint tissues, with changes in the articular cartilage (AC), subchondral bone and synovium. Pathologies in menisci and ligaments, however, are rarely analysed, although both are known to play vital roles in the mechanical stability of the joint. The aim of our study was to describe the pathological changes in menisci and ligament during disease development in murine spontaneous and post-traumatic surgically induced OA and to quantify tissue mineralisation in the joint space using micro-computed tomography (μCT) imaging during OA progression.

METHODS

Knees of Str/ort mice (spontaneous OA model; 26-40 weeks) and C57CBA F1 mice following destabilisation of medial meniscus (DMM) surgery (post-traumatic OA model; 8 weeks after DMM), were used to assess histological meniscal and ligament pathologies. Joint space mineralised tissue volume was quantified by μCT.

RESULTS

Meniscal pathological changes in Str/ort mouse knees were associated with articular cartilage lesion severity. These meniscal changes included ossification, hyperplasia, cell hypertrophy, collagen type II deposition and Sox9 expression in the fibrous region near the attachment to the knee joint capsule. Anterior cruciate ligaments exhibited extracellular matrix changes and chondrogenesis particularly at the tibial attachment site, and ossification was seen in collateral ligaments. Similar changes were confirmed in the post-traumatic DMM model. μCT analysis showed increased joint space mineralised tissue volume with OA progression in both the post-traumatic and spontaneous OA models.

CONCLUSIONS

Modifications in meniscal and ligament mineralisation and chondrogenesis are seen with overt AC degeneration in murine OA. Although the aetiology and the consequences of such changes remain unknown, they will influence stability and load transmission of the joint and may therefore contribute to OA progression. In addition, these changes may have important roles in movement restriction and pain, which represent major human clinical symptoms of OA. Description of such soft tissue changes, in addition to AC degradation, should be an important aspect of future studies in mouse models in order to furnish a more complete understanding of OA pathogenesis.

Understanding cartilage protection in OA and injury: a spectrum of possibilities

BACKGROUND

Osteoarthritis (OA) is a prevalent musculoskeletal disease resulting in progressive degeneration of the hyaline articular cartilage within synovial joints. Current repair treatments for OA often result in poor quality tissue that is functionally ineffective compared to the hyaline cartilage and demonstrates increased failure rates post-treatment. Complicating efforts to improve clinical outcomes, animal models used in pre-clinical research show significant heterogeneity in their regenerative and degenerative responses associated with their species, age, genetic/epigenetic traits, and context of cartilage injury or disease. These can lead to variable outcomes when testing and validating novel therapeutic approaches for OA. Furthermore, it remains unclear whether protection against OA among different model systems is driven by inhibition of cartilage degeneration, enhancement of cartilage regeneration, or any combination thereof.

MAIN TEXT

Understanding the mechanistic basis underlying this context-dependent duality is essential for the rational design of targeted cartilage repair and OA therapies. Here, we discuss some of the critical variables related to the cross-species paradigm of degenerative and regenerative abilities found in pre-clinical animal models, to highlight that a gradient of regenerative competence within cartilage may exist across species and even in the greater human population, and likely influences clinical outcomes.

CONCLUSIONS

A more complete understanding of the endogenous regenerative potential of cartilage in a species specific context may facilitate the development of effective therapeutic approaches for cartilage injury and/or OA.

Periostin interaction with discoidin domain receptor-1 (DDR1) promotes cartilage degeneration

Osteoarthritis (OA) is characterized by progressive loss of articular cartilage accompanied by the new bone formation and, often, a synovial proliferation that culminates in pain, loss of joint function, and disability. However, the cellular and molecular mechanisms of OA progression and the relative contributions of cartilage, bone, and synovium remain unclear. We recently found that the extracellular matrix (ECM) protein periostin (Postn, or osteoblast-specific factor, OSF-2) is expressed at high levels in human OA cartilage. Multiple groups have also reported elevated expression of Postn in several rodent models of OA. We have previously reported that in vitro Postn promotes collagen and proteoglycan degradation in human chondrocytes through AKT/β-catenin signaling and downstream activation of MMP-13 and ADAMTS4 expression. Here we show that Postn induces collagen and proteoglycan degradation in cartilage by signaling through discoidin domain receptor-1 (DDR1), a receptor tyrosine kinase. The genetic deficiency or pharmacological inhibition of DDR1 in mouse chondrocytes blocks Postn-induced MMP-13 expression. These data show that Postn is signaling though DDR1 is mechanistically involved in OA pathophysiology. Specific inhibitors of DDR1 may provide therapeutic opportunities to treat OA.

The relationship between synovial inflammation, structural pathology, and pain in post-traumatic osteoarthritis: differential effect of stem cell and hyaluronan treatment

Background

Synovitis is implicated in the severity and progression of pain and structural pathology of osteoarthritis (OA). Increases in inflammatory or immune cell subpopulations including macrophages and lymphocytes have been reported in OA synovium, but how the particular subpopulations influence symptomatic or structural OA disease progression is unclear. Two therapies, hyaluronan (HA) and mesenchymal stem cells (MSCs), have demonstrated efficacy in some clinical settings: HA acting as device to improve joint function and provide pain relief, while MSCs may have immunomodulatory and disease-modifying effects. We used these agents to investigate whether changes in pain sensitization or structural damage were linked to modulation of the synovial inflammatory response in post-traumatic OA.

Methods

Skeletally mature C57BL6 male mice underwent medial-meniscal destabilisation (DMM) surgery followed by intra-articular injection of saline, a hyaluronan hexadecylamide derivative (Hymovis), bone marrow-derived stem cells (MSCs), or MSC + Hymovis. We quantified the progression of OA-related cartilage, subchondral bone and synovial histopathology, and associated pain sensitization (tactile allodynia). Synovial lymphocytes, monocyte/macrophages and their subpopulations were quantified by fluorescent-activated cell sorting (FACS), and the expression of key inflammatory mediators and catabolic enzyme genes quantified by real-time polymerase chain reaction (PCR).

Results

MSC but not Hymovis significantly reduced late-stage (12-week post-DMM) cartilage proteoglycan loss and structural damage. Allodynia was initially reduced by both treatments but significantly better at 8 and 12 weeks by Hymovis. Chondroprotection by MSCs was not associated with specific changes in synovial inflammatory cell populations but rather regulation of post-injury synovial Adamts4, Adamts5, Mmp3, and Mmp9 expression. Reduced acute post-injury allodynia with all treatments coincided with decreased synovial macrophage and T cell numbers, while longer-term effect on pain sensitization with Hymovis was associated with increased M2c macrophages.

Conclusions

This therapeutic study in mice demonstrated a poor correlation between cartilage, bone or synovium (histo)pathology, and pain sensitization. Changes in the specific synovial inflammatory cell subpopulations may be associated with chronic OA pain sensitization, and a novel target for symptomatic treatment.

Global Gene Expression Analysis Identifies Age-Related Differences in Knee Joint Transcriptome during the Development of Post-Traumatic Osteoarthritis in Mice

Aging and injury are two major risk factors for osteoarthritis (OA). Yet, very little is known about how aging and injury interact and contribute to OA pathogenesis. In the present study, we examined age- and injury-related molecular changes in mouse knee joints that could contribute to OA. Using RNA-seq, first we profiled the knee joint transcriptome of 10-week-old, 62-week-old, and 95-week-old mice and found that the expression of several inflammatory-response related genes increased as a result of aging, whereas the expression of several genes involved in cartilage metabolism decreased with age. To determine how aging impacts post-traumatic arthritis (PTOA) development, the right knee joints of 10-week-old and 62-week-old mice were injured using a non-invasive tibial compression injury model and injury-induced structural and molecular changes were assessed. At six-week post-injury, 62-week-old mice displayed significantly more cartilage degeneration and osteophyte formation compared with young mice. Although both age groups elicited similar transcriptional responses to injury, 62-week-old mice had higher activation of inflammatory cytokines than 10-week-old mice, whereas cartilage/bone metabolism genes had higher expression in 10-week-old mice, suggesting that the differential expression of these genes might contribute to the differences in PTOA severity observed between these age groups.

FGFR3 deficiency enhances CXCL12-dependent chemotaxis of macrophages via upregulating CXCR7 and aggravates joint destruction in mice

OBJECTIVES

This study aims to investigate the role and mechanism of FGFR3 in macrophages and their biological effects on the pathology of arthritis.

METHODS

Mice with conditional knockout of FGFR3 in myeloid cells (R3cKO) were generated. Gait behaviours of the mice were monitored at different ages. Spontaneous synovial joint destruction was evaluated by digital radiographic imaging and μCT analysis; changes of articular cartilage and synovitis were determined by histological analysis. The recruitment of macrophages in the synovium was examined by immunostaining and monocyte trafficking assay. RNA-seq analysis, Western blotting and chemotaxis experiment were performed on control and FGFR3-deficient macrophages. The peripheral blood from non-osteoarthritis (OA) donors and patients with OA were analysed. Mice were treated with neutralising antibody against CXCR7 to investigate the role of CXCR7 in arthritis.

RESULTS

R3cKO mice but not control mice developed spontaneous cartilage destruction in multiple synovial joints at the age of 13 months. Moreover, the synovitis and macrophage accumulation were observed in the joints of 9-month-old R3cKO mice when the articular cartilage was not grossly destructed. FGFR3 deficiency in myeloid cells also aggravated joint destruction in DMM mouse model. Mechanically, FGFR3 deficiency promoted macrophage chemotaxis partly through activation of NF-κB/CXCR7 pathway. Inhibition of CXCR7 could significantly reverse FGFR3-deficiency-enhanced macrophage chemotaxis and the arthritic phenotype in R3cKO mice.

CONCLUSIONS

Our study identifies the role of FGFR3 in synovial macrophage recruitment and synovitis, which provides a new insight into the pathological mechanisms of inflammation-related arthritis.

Disruption of glucocorticoid signalling in osteoblasts attenuates age-related surgically induced osteoarthritis

OBJECTIVE

Aging is a major risk factor for osteoarthritis (OA). Skeletal expression and activity of the glucocorticoid-activating enzyme 11β-hydroxysteroid-dehydrogenase type 1 increases progressively with age in humans and rodents. Here we investigated the role of endogenous osteocytic and osteoblastic glucocorticoid (GC) signalling in the development of osteoarthritic bone and cartilage damage in mice.

METHODS

We utilized transgenic (tg) mice in which glucocorticoid signalling is disrupted in osteoblasts and osteocytes via overexpression of the glucocorticoid-inactivating enzyme, 11β-hydroxysteroid-dehydrogenase type 2. Osteoarthritis was induced in 10- and 22-week-old male transgenic mice (tg-OA, n = 6/group) and their wildtype littermates (WT-OA, n = 7-8/group) by surgical destabilization of the medial meniscus (DMM). Sham-operated mice served as controls (WT- & tg-Sham, n = 3-5 and 6-8/group at 10- and 22-weeks of age, respectively).

RESULTS

Sixteen weeks after DMM surgery, mice developed features of cartilage degradation, subchondral bone sclerosis and osteophyte formation. These changes did not differ between WT and tg mice when OA was induced at 10-weeks of age. However, when OA was induced at 22-weeks of age, cartilage erosion was significantly attenuated in tg-OA mice compared to WT-OA littermates. Similarly, subchondral bone volume (-5.2%, 95% confidence intervals (CI) -9.1 to -1.2%, P = 0.014) and osteophyte size (-4.0 mm², 95% CI -7.5 to -0.5 mm², P = 0.029) were significantly reduced in tg-OA compared to WT-OA mice.

CONCLUSION

Glucocorticoid signalling in cells of the osteoblast lineage promotes the development of surgically-induced osteoarthritis in older, but not younger, male mice. These data implicate osteoblasts and osteocytes in the progression of DMM-OA, via a glucocorticoid-dependent and age-related pathway.

Phenotypes of osteoarthritis: current state and future implications

In the most recent years, an extraordinary research effort has emerged to disentangle osteoarthritis heterogeneity, opening new avenues for progressing with therapeutic development and unravelling the pathogenesis of this complex condition. Several phenotypes and endotypes have been proposed albeit none has been sufficiently validated for clinical or research use as yet. This review discusses the latest advances in OA phenotyping including how new modern statistical strategies based on machine learning and big data can help advance this field of research.

Mitochondrial DNA variation and the pathogenesis of osteoarthritis phenotypes

Mitochondria and mitochondrial DNA (mtDNA) variation are now recognized as important factors in the development of osteoarthritis (OA). Mitochondria are the energy powerhouses of the cell, and also regulate different processes involved in the pathogenesis of OA including inflammation, apoptosis, calcium metabolism and the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Mitochondria contain their own genetic material, mtDNA, which evolved through the sequential accumulation of mtDNA variants to enable humans to adapt to different climates. The ROS and reactive metabolic intermediates that are by-products of mitochondrial metabolism are regulated in part by mtDNA and are among the signals that transmit information between mitochondria and the nucleus. These signals can alter nuclear gene expression and, when disrupted, affect a number of cellular processes and metabolic pathways, leading to disease. mtDNA variation influences OA-associated phenotypes, including those related to metabolism, inflammation and even ageing, as well as nuclear epigenetic regulation. This influence also enables the use of specific mtDNA haplogroups as complementary diagnostic and prognostic biomarkers of OA.

Chondroprotective Factors in Osteoarthritis: a Joint Affair

PURPOSE OF THE REVIEW

Osteoarthritis is widely regarded as a spectrum of conditions that affect all joint tissues, typified by a common entity: cartilage loss. Here, we review recent progress and challenges in chondroprotection and discuss new strategies to prevent cartilage loss in osteoarthritis.

RECENT FINDINGS

Advances in clinical, molecular, and cellular characterization are enabling improved stratification of osteoarthritis subtypes. Integration of next-generation sequencing and "omics" approaches with clinically relevant readouts shows promise in delineating both subtypes of disease and meaningful trial end points. Novel delivery strategies are enabling joint-specific delivery. Chondroprotection requires a whole joint approach, stratification of patient groups, and use of patient-relevant end points. Drug development should continue to explore new targets, while using modern technologies and recent knowledge to re-visit unsuccessful therapeutics from the past. The overarching goal for chondroprotection is to provide the right treatment(s) for the right patient at the right time.

Discerning the spatio-temporal disease patterns of surgically induced OA mouse models

Osteoarthritis (OA) is the most common cause of disability in ageing societies, with no effective therapies available to date. Two preclinical models are widely used to validate novel OA interventions (MCL-MM and DMM). Our aim is to discern disease dynamics in these models to provide a clear timeline in which various pathological changes occur. OA was surgically induced in mice by destabilisation of the medial meniscus. Analysis of OA progression revealed that the intensity and duration of chondrocyte loss and cartilage lesion formation were significantly different in MCL-MM vs DMM. Firstly, apoptosis was seen prior to week two and was narrowly restricted to the weight bearing area. Four weeks post injury the magnitude of apoptosis led to a 40-60% reduction of chondrocytes in the non-calcified zone. Secondly, the progression of cell loss preceded the structural changes of the cartilage spatio-temporally. Lastly, while proteoglycan loss was similar in both models, collagen type II degradation only occurred more prominently in MCL-MM. Dynamics of chondrocyte loss and lesion formation in preclinical models has important implications for validating new therapeutic strategies. Our work could be helpful in assessing the feasibility and expected response of the DMM- and the MCL-MM models to chondrocyte mediated therapies.

Epigenetic Mechanisms Underlying the Aging of Articular Cartilage and Osteoarthritis

Aging is a progressive and complicated bioprocess with overall decline in physiological function. Osteoarthritis (OA) is the most common joint disease in middle-aged and older populations. Since the prevalence of OA increases with age and breakdown of articular cartilage is its major hallmark, OA has long been thought of as "wear and tear" of joint cartilage. Nevertheless, recent studies have revealed that changes in the chondrocyte function and matrix components may reduce the material properties of articular cartilage and predispose the joint to OA. The aberrant gene expression in aging articular cartilage that is regulated by various epigenetic mechanisms plays an important role in age-related OA pathogenesis. This review begins with an introduction to the current understanding of epigenetic mechanisms, followed by mechanistic studies on the aging of joint tissues, epigenetic regulation of age-dependent gene expression in articular cartilage, and the significance of epigenetic mechanisms in OA pathogenesis. Our recent findings on age-dependent expression of 2 transcription factors, nuclear factor of activated T cell 1 (NFAT1) and SOX9, and their roles in the formation and aging of articular cartilage are summarized in the review. Chondrocyte dysfunction in aged mice, which is mediated by epigenetically regulated spontaneous reduction of NFAT1 expression in articular cartilage, is highlighted as an important advance in epigenetics and cartilage aging. Potential therapeutic strategies for age-related cartilage degeneration and OA using epigenetic molecular tools are discussed at the end.

CCL21/CCR7 axis regulating juvenile cartilage repair can enhance cartilage healing in adults

Juvenile tissue healing is capable of extensive scarless healing that is distinct from the scar-forming process of the adult healing response. Although many growth factors can be found in the juvenile healing process, the molecular mechanisms of juvenile tissue healing are poorly understood. Here we show that juvenile mice deficient in the chemokine receptor CCR7 exhibit diminished large-scale healing potential, whereas CCR7-depleted adult mice undergo normal scar-forming healing similar to wild type mice. In addition, the CCR7 ligand CCL21 was transiently expressed around damaged cartilage in juvenile mice, whereas it is rarely expressed in adults. Notably, exogenous CCL21 administration to adults decreased scar-forming healing and enhanced hyaline-cartilage repair in rabbit osteochondral defects. Our data indicate that the CCL21/CCR7 axis may play a role in the molecular control mechanism of juvenile cartilage repair, raising the possibility that agents modulating the production of CCL21 in vivo can improve the quality of cartilage repair in adults. Such a strategy may prevent post-traumatic arthritis by mimicking the self-repair in juvenile individuals.

Recent advances in understanding the regulation of metalloproteinases

Metalloproteinases remain important players in arthritic disease, in part because members of this large enzymatic family, namely matrix metalloproteinase-1 (MMP-1) and MMP-13, are responsible for the irreversible degradation of articular cartilage collagen. Although direct inhibition of MMPs fell out of vogue with the initial clinical disappointment of the first generation of compounds, interest in other mechanisms that control these important enzymes has always been maintained. Since these enzymes are critically important for tissue homeostasis, their expression and activity are tightly regulated at many levels, not just by direct inhibition by their endogenous inhibitors the tissue inhibitors of metalloproteinases (TIMPs). Focussing on MMP-13, we discuss recent work that highlights new discoveries in the transcriptional regulation of this enzyme, from defined promoter functional analysis to how more global technologies can provide insight into the enzyme’s regulation, especially by epigenetic mechanisms, including non-coding RNAs. In terms of protein regulation, we highlight recent findings into enzymatic cascades involved in MMP-13 regulation and activation. Importantly, we highlight a series of recent studies that describe how MMP-13 activity, and in fact that of other metalloproteinases, is in part controlled by receptor-mediated endocytosis. Together, these new discoveries provide a plethora of novel regulatory mechanisms, besides direct inhibition, which with renewed vigour could provide further therapeutic opportunities for regulating the activity of this class of important enzymes.

Coordinated existence of multiple gangliosides is required for cartilage metabolism

OBJECTIVE

Gangliosides, ubiquitously existing membrane components that modulate transmembrane signaling and mediate cell-to-cell and cell-to-matrix interactions, are key molecules of inflammatory and neurological disorders. However, the functions of gangliosides in the cartilage degradation process remain unclear. We investigated the functional role of gangliosides in cartilage metabolism related to osteoarthritis (OA) pathogenesis.

DESIGN

We generated knockout (KO) mice by targeting the β1, 4-N-acetylgalactosaminyltransferase (GalNAcT) gene, which encodes an enzyme of major gangliosides synthesis, and the GD3 synthase (GD3S) gene, which encodes an enzyme of partial gangliosides synthesis. In vivo OA and in vitro cartilage degradation models were used to evaluate the effect of gangliosides on the cartilage degradation process.

RESULTS

The GalNAcT and GD3S KO mice developed and grew normally; nevertheless, OA changes in these mice were enhanced with aging. The GalNAcT KO mice showed significantly enhanced OA progression compared to GD3S mice in vivo. Both GalNAcT and GD3S KO mice showed severe IL-1α-induced cartilage degradation ex vivo. Phosphorylation of MAPKs was enhanced in both GalNAcT and GD3S KOs after IL-1α stimulation. Gangliosides modulated by GalNAcT or GD3S rescued an increase of MMP-13 induced by IL-1α in mice lacking GalNAcT or GD3S after exogenous replenishment in vitro.

CONCLUSION

These data show that the deletion of gangliosides in mice enhanced OA development. Moreover, the gangliosides modulated by GalNAcT are important for cartilage metabolism, suggesting that GalNAcT is a potential target molecule for the development of novel OA treatments.

Inflammatory molecules produced by meniscus and synovium in early and end-stage osteoarthritis: a coculture study

The aim of this study was to identify the molecules and pathways involved in the cross-talk between meniscus and synovium that may play a critical role in osteoarthritis (OA) pathophysiology. Samples of synovium and meniscus were collected from patients with early and end-stage OA and cultured alone or cocultured. Cytokines, chemokines, metalloproteases, and their inhibitors were evaluated at the gene and protein levels. The extracellular matrix (ECM) changes were also investigated. In early OA cultures, higher levels of interleukin-6 (IL-6) and IL-8 messenger RNA were expressed by synovium and meniscus in coculture compared with meniscus cultured alone. RANTES release was significantly increased when the two tissues were cocultured compared with meniscus cultured alone. Increased levels of matrix metalloproteinase-3 (MMP-3) and MMP-10 proteins, as well as increased release of glycosaminoglycans and aggrecan CS846 epitope, were observed when synovium was cocultured with meniscus. In end-stage OA cultures, increased levels of IL-8 and monocyte chemoattractant protein-1 (MCP-1) proteins were released in cocultures compared with cultures of meniscus alone. Chemokine (C-C motif) ligand 21 (CCL21) protein release was higher in meniscus cultured alone and in coculture compared with synovium cultured alone. Increased levels of MMP-3 and 10 proteins were observed when tissues were cocultured compared with meniscus cultured alone. Aggrecan CS846 epitope release was increased in cocultures compared with cultures of either tissue cultured alone. Our study showed the production of inflammatory molecules by synovium and meniscus which could trigger inflammatory signals in early OA patients, and induce ECM loss in the progressive and final stages of OA pathology.

Identification of TGFβ-related genes regulated in murine osteoarthritis and chondrocyte hypertrophy by comparison of multiple microarray datasets

OBJECTIVE

Osteoarthritis (OA) is a joint disease characterized by progressive degeneration of articular cartilage. Some features of OA, including chondrocyte hypertrophy and focal calcification of articular cartilage, resemble the endochondral ossification processes. Alterations in transforming growth factor β (TGFβ) signaling have been associated with OA as well as with chondrocyte hypertrophy. Our aim was to identify novel candidate genes implicated in chondrocyte hypertrophy during OA pathogenesis by determining which TGFβ-related genes are regulated during murine OA and endochondral ossification.

METHODS

A list of 580 TGFβ-related genes, including TGFβ signaling pathway components and TGFβ-target genes, was generated. Regulation of these TGFβ-related genes was assessed in a microarray of murine OA cartilage: 1, 2 and 6 weeks after destabilization of the medial meniscus (DMM). Subsequently, genes regulated in the DMM model were studied in two independent murine microarray datasets on endochondral ossification: the growth plate and transient embryonic cartilage (joint development).

RESULTS

A total of 106 TGFβ-related genes were differentially expressed in articular cartilage of DMM-operated mice compared to sham-control. From these genes, 43 were similarly regulated during chondrocyte hypertrophy in the growth plate or embryonic joint development. Among these 43 genes, 18 genes have already been associated with OA. The remaining 25 genes were considered as novel candidate genes involved in OA pathogenesis and endochondral ossification. In supplementary data of published human OA microarrays we found indications that 15 of the 25 novel genes are indeed regulated in articular cartilage of human OA patients.

CONCLUSION

By focusing on TGFβ-related genes during OA and chondrocyte hypertrophy in mice, we identified 18 known and 25 new candidate genes potentially implicated in phenotypical changes in chondrocytes leading to OA. We propose that 15 of these candidates warrant further investigation as therapeutic target for OA as they are also regulated in articular cartilage of OA patients.

Identification of transcription factors responsible for dysregulated networks in human osteoarthritis cartilage by global gene expression analysis

OBJECTIVE

Osteoarthritis (OA) is the most prevalent joint disease. As disease-modifying therapies are not available, novel therapeutic targets need to be discovered and prioritized for their importance in mediating the abnormal phenotype of cells in OA-affected joints. Here, we generated a genome-wide molecular profile of OA to elucidate regulatory mechanisms of OA pathogenesis and to identify possible therapeutic targets using integrative analysis of mRNA-sequencing data obtained from human knee cartilage.

DESIGN

RNA-sequencing (RNA-seq) was performed on 18 normal and 20 OA human knee cartilage tissues. RNA-seq datasets were analysed to identify genes, pathways and regulatory networks that were dysregulated in OA.

RESULTS

RNA-seq data analysis revealed 1332 differentially expressed (DE) genes between OA and non-OA samples, including known and novel transcription factors (TFs). Pathway analysis identified 15 significantly perturbed pathways in OA with ECM-related, PI3K-Akt, HIF-1, FoxO and circadian rhythm pathways being the most significantly dysregulated. We selected DE TFs that are enriched for regulating DE genes in OA and prioritized these TFs by creating a cartilage-specific interaction subnetwork. This analysis revealed eight TFs, including JUN, Early growth response (EGR)1, JUND, FOSL2, MYC, KLF4, RELA, and FOS that both target large numbers of dysregulated genes in OA and are themselves suppressed in OA.

CONCLUSIONS

We identified a novel subnetwork of dysregulated TFs that represent new mediators of abnormal gene expression and promising therapeutic targets in OA.

Expression of p16INK 4a is a biomarker of chondrocyte aging but does not cause osteoarthritis

Cellular senescence drives a functional decline of numerous tissues with aging by limiting regenerative proliferation and/or by producing pro‐inflammatory molecules known as the senescence‐associated secretory phenotype (SASP). The senescence biomarker p16^INK4a is a potent inhibitor of the cell cycle but is not essential for SASP production. Thus, it is unclear whether p16^INK4a identifies senescence in hyporeplicative cells such as articular chondrocytes and whether p16^INK4a contributes to pathologic characteristics of cartilage aging. To address these questions, we examined the role of p16^INK4a in murine and human models of chondrocyte aging. We observed that p16^INK4amRNA expression was significantly upregulated with chronological aging in murine cartilage (~50‐fold from 4 to 18 months of age) and in primary human chondrocytes from 57 cadaveric donors (r² = .27, p < .0001). Human chondrocytes exhibited substantial replicative potential in vitro that depended on the activity of cyclin‐dependent kinases 4 or 6 (CDK4/6), and proliferation was reduced in cells from older donors with increased p16^INK4a expression. Moreover, increased chondrocyte p16^INK4a expression correlated with several SASP transcripts. Despite the relationship between p16^INK4a expression and these features of senescence, somatic inactivation of p16^INK4a in chondrocytes of adult mice did not mitigate SASP expression and did not alter the rate of osteoarthritis (OA) with physiological aging or after destabilization of the medial meniscus. These results establish that p16^INK4a expression is a biomarker of dysfunctional chondrocytes, but that the effects of chondrocyte senescence on OA are more likely driven by production of SASP molecules than by loss of chondrocyte replicative function.

Osteoarthritis induced by destabilization of the medial meniscus is reduced in germ-free mice

OBJECTIVE

To determine the contribution of the gut microbiota to the development of injury-induced osteoarthritis (OA).

DESIGN

OA was induced using the destabilized medial meniscus (DMM) model in 20 germ-free (GF) C57BL/6J male mice housed in a gnotobiotic facility and 23 strain-matched specific pathogen free (SPF) mice in 2 age groups -13.5 weeks avg age at DMM (17 SPF and 15 GF) and 43 weeks avg age at DMM (6 SPF and 5 GF). OA severity was measured using scores for articular cartilage structure (ACS), loss of safranin O (SafO) staining, osteophyte size, and synovial hyperplasia. Microbiome analysis by 16S rRNA amplicon sequencing was performed on stool samples and LPS and LPS binding protein (LBP) were measured in plasma.

RESULTS

Compared to the SPF DMM mice, the maximum (MAX) ACS score per joint was 28% lower (p = 0.036) in GF DMM mice while the SafO sum score of all sections evaluated per joint was decreased by 31% (p = 0.009). The differences between SPF and GF mice in these scores were greater when only the younger mice were included in the analysis. The younger GF DMM mice also had significant reductions in osteophyte size (36%, P = 0.0119) and LBP (27%, P = 0.007) but not synovial scores or LPS. Differences in relative abundance of a number of Operational Taxonomic Units (OTUs) were noted between SPF mice with high vs low maximum ACS scores.

CONCLUSIONS

These results suggest factors related to the gut microbiota promote the development of OA after joint injury.

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.

Impairment of chondrocyte proliferation after exposure of young murine cartilage to an aged systemic environment in a heterochronic parabiosis model

AIM:

The aim of this study was to investigate whether an aged systemic environment could impair young cartilage tissue in mice.

METHODS:

Mice differing in age were randomly divided into three groups. Group 1 was the experimental group (Y/O group) consisting of the heterochronic parabiosis model (2-month-old/12-month-old, young/old). Group 2 was the surgical control group (Y/Y group) with the isochronic parabiosis model (2-month-old/2-month-old, young/young). Group 3 consisted of the ageing control mice (2-month-old alone, Y group). Young knee cartilages collected from all three groups at 4 months after surgery were compared. Fluorescence molecular tomography (FMT) was used to confirm whether the two mice in parabiosis shared a common blood circulation at 2 weeks after surgery. The knee joints of young mice were examined radiologically at 4 months after surgery. Histological scoring was assigned to grade the severity of osteoarthritis (OA). Immunohistochemistry and quantitative reverse transcription polymerase chain reaction were used to evaluate OA-related protein expression and gene expression, and chondrocyte proliferation was determined with EdU staining.

RESULTS:

FMT imaging confirmed cross-circulation in the parabiotic pairs. The percentage of EdU-positive chondrocytes in young mice from the Y/O group was significantly lower compared with those of the Y/Y and Y groups (p <0.05 for both). There was no statistically significant difference in the mRNA expression of collagen type II (Col2), collagen type X (Col10), and matrix metalloproteinase 13 (MMP13) among the three groups (P>0.05), but expression of sex-determining region Y box 9 (Sox9) mRNA in young cartilage from the Y/O group was markedly attenuated compared to those in the Y/Y and Y groups (p <0.05 for both). In the Y/O group, mRNA expression of runt-related transcription factor 2 (Runx2) in young cartilage was significantly increased compared to the Y/Y and Y groups (p <0.05 for both). The changes in Col2, Col10, MMP13, Runx2 and Sox9 at the protein level mimicked the alterations found at the mRNA level. Loss of cartilage proteoglycan in young mice from the Y/O group was significantly greater compared to the Y/Y and Y groups (p <0.05 for both), despite the lack of significant difference among the three groups in OARIS and osteophytosis scores.

CONCLUSION:

Heterochronic parabiosis exerts a negative effect on chondrocyte proliferation in the knee cartilage of young mice.

Combined bioinformatics analysis reveals gene expression and DNA methylation patterns in osteoarthritis

Osteoarthritis (OA) is a common type of arthritis, which may cause pain and disability. Alterations in gene expression and DNA methylation have been proven to be associated with the development of OA. The aim of the present study was to identify potential therapeutic targets and associated processes for OA via the combined analysis of gene expression and DNA methylation datasets. The gene expression and DNA methylation profiles were obtained from the Gene Expression Omnibus, and differentially expressed genes (DEGs) and differentially methylated sites (DMSs) were identified in the present study, using R programming software. The enriched functions of DEGs and DMSs were obtained via the Database for Annotation, Visualization and Integrated Discovery. Finally, cross analysis of DEGs and DMSs was performed to identify genes that exhibited differential expression and methylation simultaneously. The protein‑protein interaction (PPI) network of overlaps between DEGs and DMSs was obtained using the Human Protein Reference Database; the topological properties of PPI network overlaps were additionally obtained. Hub genes in the PPI network were further confirmed via reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). The results of the present study revealed that the majority of DEGs and DMSs were upregulated and hypomethylated in patients with OA, respectively. DEGs and DMSs were primarily involved in inflammatory, immune and gene expression regulation‑associated processes and pathways. Cross analysis revealed 30 genes that exhibited differential expression and methylation in OA simultaneously. Topological analysis of the PPI network revealed that numerous genes, including G protein subunit α1 (GNAI1), runt related transcription factor 2 (RUNX2) and integrin subunit β2 (ITGB2), may be involved in the development of OA. Additionally, RT‑qPCR analysis of GNAI1, RUNX2 and ITGB2 provided further confirmation. Numerous known and novel therapeutic targets were obtained via network analysis. The results of the present study may be beneficial for the diagnosis and treatment of OA.

A six-gene-based prognostic signature for hepatocellular carcinoma overall survival prediction

AIMS

The purpose of this study was to propose a pipeline to identify prognostic signature for HCC overall survival (OS) prediction based on HCC gene expression datasets from The Cancer Genome Atlas (TCGA).

RESULTS

Differential expression analysis identified 3573 genes aberrantly expressed (DEGs) in HCC samples. Univariate cox regression analysis obtained 1605 and 1067 HCC OS and relapse free survival (RFS) related genes, which are abbreviated as OS-Gene and RFS-Gene respectively. Besides, there are 55 overlaps among DEGs, OS-Genes and RFS-Genes. Further prioritization of the 55 overlapping genes through Sure Independence Screening (SIS) resulted in 6 genes, including SRL, TTC26, CPSF2, TAF3, C16orf46 and CSN1S1, and the prognostic signature is the weighted combination of their expression values. Kaplan-Meier analysis based on the prognostic score (PS) of every sample indicates higher PS is associated with better HCC OS. Robustness of the prognostic signature was evaluated through another HCC gene expression datasets from the Gene Expression Omnibus (GEO). What's more, univariate and multivariate cox regression analysis indicate significant associations between stage/PS and HCC OS.

CONCLUSIONS

Our study provides a pipeline for the identification of prognostic signature for HCC OS prediction, which should also be suit for other types of cancers.

Molecular influence of anterior cruciate ligament tear remnants on chondrocytes: a biologic connection between injury and osteoarthritis

OBJECTIVE

Anterior cruciate ligament (ACL) injury initiates a cascade of events often leading to osteoarthritis (OA). ACL reconstruction does not alter the course of OA, suggesting that heightened OA risk is likely due to factors in addition to the joint instability. We showed that torn ACL remnants express periostin (POSTN) in the acute phase of injury. Considering that ACL injury predisposes to OA and that POSTN is associated with cartilage metabolism, we hypothesize that ACL injury affects chondrocytes via POSTN.

DESIGN

Cartilage was obtained from osteoarthritic patients and ACL remnants were collected from patients undergoing ACL reconstruction. Crosstalk between ACL remnants and chondrocytes was studied in a transwell co-culture system. Expression of POSTN and other anabolic and catabolic genes was assessed via real-time polymerase chain reaction (PCR). Immunostaining for periostin was performed in human and mouse cartilage. The impact of exogenous periostin and siRNA-mediated ablation of periostin on matrix metabolism and cell migration was examined. Furthermore, the effect of anabolic (transforming growth factor beta 1 [TGF-β1]) and catabolic (interleukin 1 beta [IL-1β]) factors on POSTN expression was investigated.

RESULTS

ACL remnants induced expression of POSTN, MMP13 and ADAMTS4. Periostin levels were significantly higher in osteoarthritic compared to normal cartilage. Exogenous periostin induced MMP13 expression and cell migration, and repressed COL1A1 expression while POSTN knockdown inhibited expression of both anabolic and catabolic genes and impeded cell migration. TGF-β1 and IL-1β treatment did not alter POSTN expression but influenced chondrocyte metabolism as determined by quantification of anabolic and catabolic genes via real-time PCR.

CONCLUSIONS

ACL remnants can exert paracrine effects on cartilage, altering cellular homeostasis. Over time, this metabolic imbalance could contribute to OA development.

Chemokine receptor-7 (CCR7) deficiency leads to delayed development of joint damage and functional deficits in a murine model of osteoarthritis

Elevated chemokine receptor Ccr7 is observed in knee osteoarthritis (OA) and associated with severity of symptoms. In this study, we confirmed that CCR7 protein expression is elevated in synovial tissue from OA patients by immunohistochemical staining. We then investigated whether Ccr7 deficiency impacted structural and functional joint degeneration utilizing a murine model of OA. OA-like disease was induced in male C57BL/6 and Ccr7-deficient (Ccr7^-/- ) mice by destabilization of the medial meniscus (DMM). Functional deficits were measured by computer integrated monitoring of spontaneous activity every 4 weeks after DMM surgery up 16 weeks. Joint degeneration was evaluated at 6 and 19 weeks post-surgery by histopathology, and subchondral bone changes analyzed by microCT. Results showed reduction in locomotor activities in DMM-operated C57BL/6 mice by 8 weeks, while activity decreases in Ccr7^-/- mice were delayed until 16 weeks. Histopathologic evaluation showed minimal protection from early cartilage degeneration (p = 0.06) and osteophytosis (p = 0.04) in Ccr7^-/- mice 6 weeks post-DMM compared to C57BL/6 controls, but not at 19 weeks. However, subchondral bone mineral density (p = 0.03) and histologic sclerosis (p = 0.02) increased in response to surgery in C57BL/6 mice at 6 weeks, while Ccr7^-/- mice were protected from these changes. Our results are the first to demonstrate a role for Ccr7 in early development of functional deficits and subchondral bone changes in the DMM model. Understanding the mechanism of Ccr7 receptor signaling in the initiation of joint pathology and disability will inform the development of innovative therapies to slow symptomatic OA development after injury. Published 2017. This article is a U.S. Government work and is in the public domain in the USA. J Orthop Res 36:864-875, 2018.

Advantages of RNA-seq compared to RNA microarrays for transcriptome profiling of anterior cruciate ligament tears

Microarrays and RNA-seq are at the forefront of high throughput transcriptome analyses. Since these methodologies are based on different principles, there are concerns about the concordance of data between the two techniques. The concordance of RNA-seq and microarrays for genome-wide analysis of differential gene expression has not been rigorously assessed in clinically derived ligament tissues. To demonstrate the concordance between RNA-seq and microarrays and to assess potential benefits of RNA-seq over microarrays, we assessed differences in transcript expression in anterior cruciate ligament (ACL) tissues based on time-from-injury. ACL remnants were collected from patients with an ACL tear at the time of ACL reconstruction. RNA prepared from torn ACL remnants was subjected to Agilent microarrays (N = 24) and RNA-seq (N = 8). The correlation of biological replicates in RNA-seq and microarrays data was similar (0.98 vs. 0.97), demonstrating that each platform has high internal reproducibility. Correlations between the RNA-seq data and the individual microarrays were low, but correlations between the RNA-seq values and the geometric mean of the microarrays values were moderate. The cross-platform concordance for differentially expressed transcripts or enriched pathways was linearly correlated (r = 0.64). RNA-Seq was superior in detecting low abundance transcripts and differentiating biologically critical isoforms. Additional independent validation of transcript expression was undertaken using microfluidic PCR for selected genes. PCR data showed 100% concordance (in expression pattern) with RNA-seq and microarrays data. These findings demonstrate that RNA-seq has advantages over microarrays for transcriptome profiling of ligament tissues when available and affordable. Furthermore, these findings are likely transferable to other musculoskeletal tissues where tissue collection is challenging and cells are in low abundance. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:484-497, 2018.

A mouse model for chronic pain-induced increase in ethanol consumption

Chronic pain conditions are often comorbid with alcohol abuse. "Self-medication" with alcohol introduces a host of problems associated with the abuse of alcohol which over time has the potential of exacerbating the painful condition. Despite the prevalence of chronic pain being associated with alcohol abuse, rodent models which mimic the comorbid conditions are lacking. In this study, we model osteoarthritis (OA) in C57BL/6J mice by surgically destabilizing the medial meniscus (DMM). Sham-operated mice served as controls. Thirteen weeks after surgery, DMM but not sham-operated mice exhibited pronounced incapacitance of the surgically manipulated hind limb compared with the nonsurgically manipulated hind limb. At this time, the mice were exposed to the 2-bottle ethanol choice, beginning with 2.5% with a gradual increasing to 20%. Compared with sham controls, DMM mice consumed more EtOH and preferred EtOH over water at the 20% EtOH concentration. Histological analysis verified that the DMM mice exhibited significant damage to the articular cartilage and osteophyte growth compared with sham controls and these measures of the severity of OA correlated with the amount of ethanol intake. Thus, the combination of the DMM model of OA with the enhanced two-bottle ethanol choice is a potential preclinical approach in mice by which the basis of the comorbid association of alcohol abuse and chronic pain conditions can be explored.

Cell-type-specific gene expression patterns in the knee cartilage in an osteoarthritis rat model

Osteoarthritis (OA) is a chronic degenerative disease that leads to joint failure, pain, and disability. Gene regulation is implicated as a driver of the imbalance between the expression of catabolic and anabolic factors that eventually leads to the degeneration of osteoarthritic cartilage. In our model, knee-joint OA was induced in male Wistar rats by intra-articular sodium monoiodoacetate (MIA) injections. Whole-genome microarrays were used to analyse the alterations in gene expression during the time-course of OA development (at 2, 14, and 28 days post-injection) in rat knee joints. The identified co-expressed groups of genes were analysed for enriched regulatory mechanisms, functional classes, and cell-type-specific expression. This analysis revealed 272 regulated transcripts (ANOVA FDR < 0.1% and fold > 2). Functionally, the five major gene expression patterns (A–E) were connected to PPAR signalling and adipogenesis (in cluster A), WNT signalling (in cluster B), endochondral ossification (in cluster C), matrix metalloproteinases and the ACE/RAGE pathway (in cluster D), and the Toll-like receptor, and IL-1 signalling pathways (in cluster E). Moreover, the dynamic profiles of these transcriptional changes were assigned to cellular compartments of the knee joint. Classifying the molecular processes associated with the development of cartilage degeneration provides novel insight into the OA disease process. Our study identified groups of co-regulated genes that share functional relationships and that may play an important role in the early and intermediate stages of OA.

High hydrostatic pressure induces pro-osteoarthritic changes in cartilage precursor cells: A transcriptome analysis

Due to the high water content of cartilage, hydrostatic pressure is likely one of the main physical stimuli sensed by chondrocytes. Whereas, in the physiological range (0 to around 10 MPa), hydrostatic pressure exerts mostly pro-chondrogenic effects in chondrocyte models, excessive pressures have been reported to induce detrimental effects on cartilage, such as increased apoptosis and inflammation, and decreased cartilage marker expression. Though some genes modulated by high pressure have been identified, the effects of high pressure on the global gene expression pattern have still not been investigated. In this study, using microarray technology and real-time PCR validation, we analyzed the transcriptome of ATDC5 chondrocyte progenitors submitted to a continuous pressure of 25 MPa for up to 24 h. Several hundreds of genes were found to be modulated by pressure, including some not previously known to be mechano-sensitive. High pressure markedly increased the expression of stress-related genes, apoptosis-related genes and decreased that of cartilage matrix genes. Furthermore, a large set of genes involved in the progression of osteoarthritis were also induced by high pressure, suggesting that hydrostatic pressure could partly mimic in vitro some of the genetic alterations occurring in osteoarthritis.

Systems approaches in osteoarthritis: Identifying routes to novel diagnostic and therapeutic strategies

Systems orientated research offers the possibility of identifying novel therapeutic targets and relevant diagnostic markers for complex diseases such as osteoarthritis. This review demonstrates that the osteoarthritis research community has been slow to incorporate systems orientated approaches into research studies, although a number of key studies reveal novel insights into the regulatory mechanisms that contribute both to joint tissue homeostasis and its dysfunction. The review introduces both top-down and bottom-up approaches employed in the study of osteoarthritis. A holistic and multiscale approach, where clinical measurements may predict dysregulation and progression of joint degeneration, should be a key objective in future research. The review concludes with suggestions for further research and emerging trends not least of which is the coupled development of diagnostic tests and therapeutics as part of a concerted effort by the osteoarthritis research community to meet clinical needs. © 2017 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:1573-1588, 2017.

Joint loads resulting in ACL rupture: Effects of age, sex, and body mass on injury load and mode of failure in a mouse model

Anterior cruciate ligament (ACL) tears are a common knee injury with a known but poorly understood association with secondary joint injuries and post-traumatic osteoarthritis (OA). Female sex and age are known risk factors for ACL injury but these variables are rarely explored in mouse models of injury. This study aimed to further characterize a non-surgical ACL injury model to determine its clinical relevance across a wider range of mouse specifications. Cadaveric and anesthetized C57BL/6 mice (9-52 weeks of age) underwent joint loading to investigate the effects of age, sex, and body mass on ACL injury mechanisms. The ACL injury load (whole joint load required to rupture the ACL) was measured from force-displacement data, and mode of failure was assessed using micro-dissection and histology. ACL injury load was found to increase with body mass and age (p < 0.001) but age was not significant when controlling for mass. Sex had no effect. In contrast, the mode of ACL failure varied with both age and sex groups. Avulsion fractures (complete or mixed with mid-substance tears) were common in all age groups but the proportion of mixed and mid-substance failures increased with age. Females were more likely than males to have a major avulsion relative to a mid-substance tear (p < 0.01). This data compliments studies in human cadaveric knees, and provides a basis for determining the severity of joint injury relative to a major ACL tear in mice, and for selecting joint loading conditions in future experiments using this model. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1754-1763, 2017.

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.

Increased Activity of the Chondrocyte Translational Apparatus Accompanies Osteoarthritic Changes in Human and Rodent Knee Cartilage

OBJECTIVE

Degeneration of articular cartilage is central to the pathology of osteoarthritis (OA). However, the molecular mechanisms leading to these irreversible changes are still poorly understood. This study was undertaken to investigate how changes in the chondrocyte translational apparatus may contribute to the development and progression of knee OA.

METHODS

Articular cartilage from the knees of normal healthy subjects and patients with OA was used to analyze the activity of different components of the translational machinery. Chondrocytes isolated from lesional and nonlesional areas of the human OA cartilage were used to estimate the relative rate of protein synthesis by metabolic labeling. Experimental OA was induced by transection of the anterior cruciate ligament of rats to investigate changes in the translational apparatus associated with OA. The role of interleukin-1β (IL-1β) signaling was assessed in vitro using rat articular chondrocytes. In human or rodent knee cartilage, messenger RNA expression was analyzed by quantitative polymerase chain reaction, and protein levels were determined by immunohistochemistry and Western blotting.

RESULTS

Several novel traits of OA chondrocytes were identified, including up-regulation of the serine/threonine kinases Akt-2 and Akt-3 at the posttranscriptional level and an increased rate of total protein synthesis, likely attributable to inactivation of eukaryotic initiation factor 4E binding protein 1 (4E-BP1), a known repressor of cap-dependent translation. Inactivation of 4E-BP1 was dependent on the activity of mechanistic target of rapamycin and was crucial for the up-regulation of protein synthesis in general and expression of matrix metalloproteinase 13 and ADAMTS-5 in particular. In addition, treatment of articular chondrocytes with IL-1β led to inactivation of 4E-BP1 and up-regulation of protein synthesis.

CONCLUSION

Precise control of protein synthesis is vital for cartilage homeostasis, and its dysregulation contributes to the molecular pathology of OA. The results of this study therefore identify a novel set of potential therapeutic targets to ameliorate the effects of knee OA.

Immediate Administration of Intraarticular Triamcinolone Acetonide After Joint Injury Modulates Molecular Outcomes Associated With Early Synovitis

OBJECTIVE

To test whether intraarticular corticosteroid injection mitigates injury-induced synovitis and collagen degradation after anterior cruciate ligament transection (ACLT) and to characterize the synovial response using a functional genomics approach in a preclinical model of posttraumatic osteoarthritis.

METHODS

Yorkshire pigs underwent unilateral ACLT without subsequent corticosteroid injection (the ACLT group; n = 6) or ACLT with immediate injection of 20 mg triamcinolone acetonide (the steroid group; n = 6). A control group of pigs (the intact group; n = 6) did not undergo surgery. Total synovial membrane cellularity and synovial fluid concentration of C1,2C neoepitope-bearing collagen fragments 14 days after injury were primary end points and were compared between the ACLT, steroid, and intact groups. Cells were differentiated by histologic phenotype and counted, while RNA sequencing was used to quantify transcriptome-wide gene expression and monocyte, macrophage, and lymphocyte markers.

RESULTS

In the intact group, total cellularity was 13% (95% confidence interval [95% CI] 9-16) and the C1,2C concentration was 0.24 μg/ml (95% CI 0.08-0.39). In the ACLT group, significant increases were observed in total cellularity (to 21% [95% CI 16-27]) and C1,2C concentration (to 0.49 μg/ml [95% CI 0.39-0.59]). Compared to values in the ACLT group, total cellularity in the steroid group was nonsignificantly decreased to 17% (95% CI 15-18) (P = 0.26) and C1,2C concentration in the steroid group was significantly decreased to 0.29 μg/ml (95% CI 0.23-0.35) (P = 0.04). A total of 255 protein-coding transcripts were differentially expressed between the ACLT group and the intact group. These genes mainly enriched pathways related to cellular immune response, proteolysis, and angiogenesis. Mononuclear leukocytes were the dominant cell type in cell-dense areas. MARCO, SOCS3, CCR1, IL4R, and MMP2 expression was significantly associated with C1,2C levels.

CONCLUSION

Early intraarticular immunosuppression mitigated injury-induced increases in collagen fragments, an outcome better predicted by specific marker expression than by histologic measures of synovitis.

Aging Promotes Sirtuin 3-Dependent Cartilage Superoxide Dismutase 2 Acetylation and Osteoarthritis

OBJECTIVE

To quantify functional age-related changes in the cartilage antioxidant network in order to discover novel mediators of cartilage oxidative stress and osteoarthritis (OA) pathophysiology.

METHODS

We evaluated histopathologic changes of knee OA in 10-, 20-, and 30-month-old male F344BN rats and analyzed cartilage oxidation according to the ratio of reduced to oxidized glutathione. Antioxidant gene expression and protein abundance were analyzed by quantitative reverse transcription-polymerase chain reaction and selected reaction-monitoring mass spectrometry, respectively. Superoxide dismutase 2 (SOD2) activity and acetylation were analyzed by colorimetric enzyme assays and Western blotting, respectively. We examined human OA cartilage to evaluate the clinical relevance of SOD2 acetylation, and we tested age-related changes in the mitochondrial deacetylase sirtuin 3 (SIRT-3) in rats and mice.

RESULTS

Cartilage oxidation and OA severity in F344BN rats increased with age and were associated with an increase in SOD2 expression and protein abundance. However, SOD2-specific activity decreased with age due to elevated posttranslational lysine acetylation. Consistent with these findings, SIRT-3 levels decreased substantially with age, and treatment with SIRT-3 increased SOD2 activity in an age-dependent manner. SOD2 was also acetylated in human OA cartilage, and activity was increased with SIRT-3 treatment. Moreover, in C57BL/6J mice, cartilage SIRT-3 expression decreased with age, and whole-body deletion of SIRT-3 accelerated the development of knee OA.

CONCLUSION

Our results show that SIRT-3 mediates age-related changes in cartilage redox regulation and protects against early-stage OA. These findings suggest that mitochondrial acetylation promotes OA and that restoration of SIRT-3 in aging cartilage may improve cartilage resistance to oxidative stress by rescuing acetylation-dependent inhibition of SOD2 activity.

A genome-wide transcriptomic analysis of articular cartilage during normal maturation in pigs

OBJECTIVE

The articular cartilage undergoes dramatic changes in structure and composition during post-natal maturation, but the associated transcriptional changes are not well characterized. Compared to a mature stage, the immature articular cartilage shows developmental features such as increased thickness, presence of blood vessels, and the presence of a deep layer of growth cartilage which undergoes endochondral ossification. These features decrease during normal development. Following maturation, the articular cartilage is known to undergo few minor modifications. Since mature articular cartilage has poor regenerative and repair capacity compared to the immature articular cartilage, a better understanding of the molecular changes during the normal postnatal articular cartilage development might reveal insights on the molecular adaptation. It may also provide new therapeutic strategies. The purpose of this study was to determine the differential expression of genes in the femoral head articular cartilage of 6-weeks old and 6-months old pigs using a genome-wide transcriptomic analysis.

METHODS

The articular cartilage of the femoral head of 6-weeks and 6-months old normal pigs was assessed for thickness and vascularity (number of vascular canals) using Safranin O/Fast Green staining of paraffin sections (n=4 pigs/age group). The measurements were determined using Image J software. RNA was isolated from the femoral head articular cartilage from 6-weeks and 6-months old pigs (n=8 pigs/age group). A microarray analysis was performed using an Affymetrix Porcine GeneChip Array. A gene enrichment analysis and a functional clustering analysis were performed by DAVID and STRING software, respectively. The differential expression of selected genes was confirmed by a quantitative RTPCR analysis.

RESULTS

The femoral head articular cartilage showed a significant decrease in thickness and number of vascular canals in 6-months old compared to 6-weeks old pigs. A microarray analysis revealed a differential gene expression of 576 genes, with 206 genes that were significantly upregulated and 370 genes that were significantly downregulated (>2-fold change, p<0.05) at 6-months compared to 6-weeks of age. Among the upregulated genes, DAVID analysis revealed that a significant number of genes represented the biological processes of responses to external stimuli, and wounding and inflammation at 6-months of age. These processes involved genes representing secretory and signaling proteins such as MMP-1, MMP-3, IL-8 and STAT3 suggesting increased inflammatory activity. In addition, an assessment of the downregulated genes indicated a decrease in the expression of genes representing the biological processes of developmental processes (e.g. BMPR1A, BMPR2, ACVR2, periostin, SFRP2, COL5A3) and regulation of blood vessel size (e.g. alpha adrenergic receptor 1B, alpha-SMA) at 6-months of age. A real-time qRTPCR analysis of selected upregulated genes, fibronectin, MMP-3, IL-8 and downregulated genes, BMPR2, PECAM, CCL2, TLR4 confirmed the differential gene expression in the microarray analysis.

CONCLUSION

During the process of articular cartilage maturation from 6-weeks to 6-months of age in normal pigs, genes associated with inflammatory responses to injury were upregulated and genes involved in the development and vascular responses were downregulated. These findings suggest that during articular cartilage maturation, the transcriptional changes might increase the susceptibility of cartilage to inflammatory damage and decrease the regenerative capacity.