Cholesterol accumulation caused by low density lipoprotein receptor deficiency or a cholesterol-rich diet results in ectopic bone formation during experimental osteoarthritis

[Relationship between hypercholesterolemia and osteoarthritis (preliminary results)]

AIM

To evaluate the relationship of hypercholesterolemia (HCE) with clinical, instrumental, and laboratory parameters in osteoarthritis (OA) in a multicenter, cross-sectional study.

MATERIALS AND METHODS

The study included 183 patients aged 40-75 years, with a confirmed diagnosis of stage I-III OA (ACR) of the knee joints, who signed an informed consent. The mean age was 55.6±10.7 years (40 to 75), body mass index was 29.3±6.3 kg/m2, and disease duration was 5 [1; 10] years. For each patient, a case record form was filled out, including anthropometric indicators, medical history, clinical examination data, an assessment of knee joint pain according to VAS, WOMAC, KOOS and comorbidities. All patients underwent standard radiography and ultrasound examination of the knee joints and laboratory tests.

RESULTS

HCE was detected in 59% of patients. Depending on its presence or absence, patients were divided into two groups. Patients were comparable in body mass index, waist and hip measurement, and disease duration but differed significantly in age. Individuals with elevated total cholesterol levels had higher VAS pain scores, total WOMAC and its components, an overall assessment of the patient's health, a worse KOOS index, and ultrasound findings (reduced cartilage tissue). HCE patients showed high levels of cholesterol, low-density lipoproteins, triglycerides, STX-II, and COMP (p<0.05). However, after stratification by age, many initial intergroup differences became insignificant, and differences in the WOMAC pain score persisted.

CONCLUSION

The results of the study confirmed the high prevalence of HCE in OA patients (59%). Patients with OA and increased total cholesterol have more intense pain in the knee joints.

Oxidized LDL Accelerates Cartilage Destruction and Inflammatory Chondrocyte Death in Osteoarthritis by Disrupting the TFEB-Regulated Autophagy-Lysosome Pathway

Osteoarthritis (OA) involves cartilage degeneration, thereby causing inflammation and pain. Cardiovascular diseases, such as dyslipidemia, are risk factors for OA; however, the mechanism is unclear. We investigated the effect of dyslipidemia on the development of OA. Treatment of cartilage cells with low-density lipoprotein (LDL) enhanced abnormal autophagy but suppressed normal autophagy and reduced the activity of transcription factor EB (TFEB), which is important for the function of lysosomes. Treatment of LDL-exposed chondrocytes with rapamycin, which activates TFEB, restored normal autophagy. Also, LDL enhanced the inflammatory death of chondrocytes, an effect reversed by rapamycin. In an animal model of hyperlipidemia-associated OA, dyslipidemia accelerated the development of OA, an effect reversed by treatment with a statin, an anti-dyslipidemia drug, or rapamycin, which activates TFEB. Dyslipidemia reduced the autophagic flux and induced necroptosis in the cartilage tissue of patients with OA. The levels of triglycerides, LDL, and total cholesterol were increased in patients with OA compared to those without OA. The C-reactive protein level of patients with dyslipidemia was higher than that of those without dyslipidemia after total knee replacement arthroplasty. In conclusion, oxidized LDL, an important risk factor of dyslipidemia, inhibited the activity of TFEB and reduced the autophagic flux, thereby inducing necroptosis in chondrocytes.

Efficacy and safety of pentosan polysulfate sodium in people with symptomatic knee osteoarthritis and dyslipidaemia: protocol of the MaRVeL trial

INTRODUCTION

Knee osteoarthritis (OA) is the most prevalent arthritis type and a leading cause of chronic mobility disability. While pain medications provide only symptomatic pain relief; growing evidence suggests pentosan polysulfate sodium (PPS) is chondroprotective and could have anti-inflammatory effects in knee OA. This study aims to explore the efficacy and safety of oral PPS in symptomatic knee OA with dyslipidaemia.

METHODS AND ANALYSIS

MaRVeL is a phase II, single-centre, parallel, superiority trial which will be conducted at Royal North Shore Hospital, Sydney, Australia. 92 participants (46 per arm) aged 40 and over with painful knee OA and mild to moderate structural change on X-ray (Kellgren and Lawrence grade 2 or 3) will be recruited from the community and randomly allocated to receive two cycles of either oral PPS or placebo for 5 weeks starting at baseline and week 11. Primary outcome will be the 16-week change in overall average knee pain severity measured using an 11-point Numeric Rating Scale. Main secondary outcomes include change in knee pain, patient global assessment, physical function, quality of life and other structural changes. A biostatistician blinded to allocation groups will perform the statistical analysis according to the intention-to-treat principle.

ETHICS AND DISSEMINATION

The protocol has been approved by the NSLHD Human Research Ethics Committee (HREC) (2021/ETH00315). All participants will provide written informed consent online. Study results will be disseminated through conferences, social media and academic publications.

TRIAL REGISTRATION NUMBERS

Australian New Zealand Clinical Trial Registry (ACTRN12621000654853); U1111-1265-3750.

Exploration beyond osteoarthritis: the association and mechanism of its related comorbidities

Osteoarthritis is the most prevalent age-related degenerative joint disease and a leading cause of pain and disability in aged people. Its etiology is multifaceted, involving factors such as biomechanics, pro-inflammatory mediators, genetics, and metabolism. Beyond its evident impact on joint functionality and the erosion of patients' quality of life, OA exhibits symbiotic relationships with various systemic diseases, giving rise to various complications. This review reveals OA's extensive impact, encompassing osteoporosis, sarcopenia, cardiovascular diseases, diabetes mellitus, neurological disorders, mental health, and even cancer. Shared inflammatory processes, genetic factors, and lifestyle elements link OA to these systemic conditions. Consequently, recognizing these connections and addressing them offers opportunities to enhance patient care and reduce the burden of associated diseases, emphasizing the need for a holistic approach to managing OA and its complications.

Obesity, Metabolic Syndrome, and Osteoarthritis-An Updated Review

PURPOSE OF REVIEW

Metabolic syndrome (MetS), also called the 'deadly quartet' comprising obesity, diabetes, dyslipidemia, and hypertension, has been ascertained to have a causal role in the pathogenesis of osteoarthritis (OA). This review is aimed at discussing the current knowledge on the contribution of metabolic syndrome and its various components to OA pathogenesis and progression.

RECENT FINDINGS

Lately, an increased association identified between the various components of metabolic syndrome (obesity, diabetes, dyslipidemia, and hypertension) with OA has led to the identification of the 'metabolic phenotype' of OA. These metabolic perturbations alongside low-grade systemic inflammation have been identified to inflict detrimental effects upon multiple tissues of the joint including cartilage, bone, and synovium leading to complete joint failure in OA. Recent epidemiological and clinical findings affirm that adipokines significantly contribute to inflammation, tissue degradation, and OA pathogenesis mediated through multiple signaling pathways. OA is no longer perceived as just a 'wear and tear' disease and the involvement of the metabolic components in OA pathogenesis adds up to the complexity of the disease. Given the global surge in obesity and its allied metabolic perturbations, this review aims to throw light on the current knowledge on the pathophysiology of MetS-associated OA and the need to address MetS in the context of metabolic OA management. Better regulation of the constituent factors of MetS could be profitable in preventing MetS-associated OA. The identification of key roles for several metabolic regulators in OA pathogenesis has also opened up newer avenues in the recognition and development of novel therapeutic agents.

How are Aging and Osteoarthritis Related?

Osteoarthritis is the most prevalent degenerative joint disease and one of the leading causes of physical impairment in the world's aging population. The human lifespan has significantly increased as a result of scientific and technological advancements. According to estimates, the world's elderly population will increase by 20% by 2050. Aging and age-related changes are discussed in this review in relation to the development of OA. We specifically discussed the cellular and molecular changes that occur in the chondrocytes during aging and how these changes may make synovial joints more susceptible to OA development. These changes include chondrocyte senescence, mitochondrial dysfunction, epigenetic modifications, and decreased growth factor response. The age-associated changes occur not only in the chondrocytes but also in the matrix, subchondral bone, and synovium. This review aims to provide an overview of the interplay between chondrocytes and matrix and how age-related changes affect the normal function of cartilage and contribute to OA development. Understanding the alterations that affect the function of chondrocytes will emerge new possibilities for prospective therapeutic options for the treatment of OA.

Beyond mechanical loading: The metabolic contribution of obesity in osteoarthritis unveils novel therapeutic targets

Osteoarthritis (OA) is a prevalent progressive disease that frequently coexists with obesity. For several decades, OA was thought to be the result of ageing and mechanical stress on cartilage. Researchers' perspective has been greatly transformed when cumulative findings emphasized the role of adipose tissue in the diseases. Nowadays, the metabolic effect of obesity on cartilage tissue has become an integral part of obesity research; hoping to discover a disease-modifying drug for OA. Recently, several adipokines have been reported to be associated with OA. Particularly, metrnl (meteorin-like) and retinol-binding protein 4 (RBP4) have been recognized as emerging adipokines that can mediate OA pathogenesis. Accordingly, in this review, we will summarize the latest findings concerned with the metabolic contribution of obesity in OA pathogenesis, with particular emphasis on dyslipidemia, insulin resistance and adipokines. Additionally, we will discuss the most recent adipokines that have been reported to play a role in this context. Careful consideration of these molecular mechanisms interrelated with obesity and OA will undoubtedly unveil new avenues for OA treatment.

Intensive cholesterol-lowering treatment reduces synovial inflammation during early collagenase-induced osteoarthritis, but not pathology at end-stage disease in female dyslipidemic E3L.CETP mice

INTRODUCTION

The association between metabolic syndrome (MetS) and osteoarthritis (OA) development has become increasingly recognized. In this context, the exact role of cholesterol and cholesterol-lowering therapies in OA development has remained elusive. Recently, we did not observe beneficial effects of intensive cholesterol-lowering treatments on spontaneous OA development in E3L.CETP mice. We postulated that in the presence of local inflammation caused by a joint lesion, cholesterol-lowering therapies may ameliorate OA pathology.

MATERIALS AND METHODS

Female ApoE3∗Leiden.CETP mice were fed a cholesterol-supplemented Western type diet. After 3 weeks, half of the mice received intensive cholesterol-lowering treatment consisting of atorvastatin and the anti-PCSK9 antibody alirocumab. Three weeks after the start of the treatment, OA was induced via intra-articular injections of collagenase. Serum levels of cholesterol and triglycerides were monitored throughout the study. Knee joints were analyzed for synovial inflammation, cartilage degeneration, subchondral bone sclerosis and ectopic bone formation using histology. Inflammatory cytokines were determined in serum and synovial washouts.

RESULTS

Cholesterol-lowering treatment strongly reduced serum cholesterol and triglyceride levels. Mice receiving cholesterol-lowering treatment showed a significant reduction in synovial inflammation (P = 0.008, WTD: 95% CI: 1.4- 2.3; WTD + AA: 95% CI: 0.8- 1.5) and synovial lining thickness (WTD: 95% CI: 3.0-4.6, WTD + AA: 95% CI: 2.1-3.2) during early-stage collagenase-induced OA. Serum levels of S100A8/A9, MCP-1 and KC were significantly reduced after cholesterol-lowering treatment (P = 0.0005, 95% CI: -46.0 to -12.0; P = 2.8 × 10^-10, 95% CI: -398.3 to -152.1; P = 2.1 × 10^-9, -66.8 to -30.4, respectively). However, this reduction did not reduce OA pathology, determined by ectopic bone formation, subchondral bone sclerosis and cartilage damage at end-stage disease.

CONCLUSION

This study shows that intensive cholesterol-lowering treatment reduces joint inflammation after induction of collagenase-induced OA, but this did not reduce end stage pathology in female mice.

IL-1β inhibition combined with cholesterol-lowering therapies decreases synovial lining thickness and spontaneous cartilage degeneration in a humanized dyslipidemia mouse model

INTRODUCTION

Both systemic inflammation and dyslipidemia contribute to osteoarthritis (OA) development and have been suggested as a possible link between metabolic disease and OA development. Recently, the CANTOS trial showed a reduction in knee and hip replacements after inhibition of IL-1β in patients with a history of cardiovascular disease and high inflammatory risk. In this light, we investigated whether inhibition of IL-1β combined with cholesterol-lowering therapies can reduce OA development in dyslipidemic APOE∗3Leiden mice under pro-inflammatory dietary conditions.

MATERIALS AND METHODS

Female ApoE3∗Leiden mice were fed a cholesterol-supplemented Western-Type diet (WTD) for 38 weeks. After 14 weeks, cholesterol-lowering and anti-inflammatory treatments were started. Treatments included atorvastatin alone or with an anti-IL1β antibody, and atorvastatin combined with proprotein convertase subtilisin-kexin type 9 (PCSK9) inhibitor alirocumab without or with the anti-IL1β antibody. Knee joints were analyzed for cartilage degradation, synovial inflammation and ectopic bone formation using histology at end point.

RESULTS

Cholesterol-lowering treatment successfully decreased systemic inflammation in dyslipidemic mice, which was not further affected by inhibition of IL-1β. Synovial thickening and cartilage degeneration were significantly decreased in mice that received cholesterol-lowering treatment combined with inhibition of IL-1β (P < 0.01, P < 0.05, respectively) compared to mice fed a WTD alone. Ectopic bone formation was comparable between all groups.

CONCLUSION

These results indicate that inhibition of IL-1β combined with cholesterol-lowering therapy diminishes synovial thickening and cartilage degeneration in mice and may imply that this combination therapy could be beneficial in patients with metabolic inflammation.

Cholesterol-induced LRP3 downregulation promotes cartilage degeneration in osteoarthritis by targeting Syndecan-4

Emerging evidence suggests that osteoarthritis is associated with high cholesterol levels in some osteoarthritis patients. However, the specific mechanism under this metabolic osteoarthritis phenotype remains unclear. We find that cholesterol metabolism-related gene, LRP3 (low-density lipoprotein receptor-related protein 3) is significantly reduced in high-cholesterol diet mouse's cartilage. By using Lrp3^-/- mice in vivo and LRP3 lentiviral-transduced chondrocytes in vitro, we identify that LRP3 positively regulate chondrocyte extracellular matrix metabolism, and its deficiency aggravate the degeneration of cartilage. Regardless of diet, LRP3 overexpression in cartilage attenuate anterior cruciate ligament transection induced osteoarthritis progression in rats and Lrp3 knockout-induced osteoarthritis progression in mice. LRP3 knockdown upregulate syndecan-4 by activating the Ras signaling pathway. We identify syndecan-4 as a downstream molecular target of LRP3 in osteoarthritis pathogenesis. These findings suggest that cholesterol-LRP3- syndecan-4 axis plays critical roles in osteoarthritis development, and LRP3 gene therapy may provide a therapeutic regimen for osteoarthritis treatment.

Lipid Metabolism in Cartilage Development, Degeneration, and Regeneration

Lipids affect cartilage growth, injury, and regeneration in diverse ways. Diet and metabolism have become increasingly important as the prevalence of obesity has risen. Proper lipid supplementation in the diet contributes to the preservation of cartilage function, whereas excessive lipid buildup is detrimental to cartilage. Lipid metabolic pathways can generate proinflammatory substances that are crucial to the development and management of osteoarthritis (OA). Lipid metabolism is a complicated metabolic process involving several regulatory systems, and lipid metabolites influence different features of cartilage. In this review, we examine the current knowledge about cartilage growth, degeneration, and regeneration processes, as well as the most recent research on the significance of lipids and their metabolism in cartilage, including the extracellular matrix and chondrocytes. An in-depth examination of the involvement of lipid metabolism in cartilage metabolism will provide insight into cartilage metabolism and lead to the development of new treatment techniques for metabolic cartilage damage.

Activation of circulating monocytes by low-density lipoprotein-a risk factor for osteoarthritis?

Synovial macrophages are key mediators of OA pathology, and skewing of macrophage phenotype in favour of an M1-like phenotype is thought to underlie the chronicity of synovial inflammation in OA. Components of the metabolic syndrome (MetS), such as dyslipidaemia, can affect macrophage phenotype and function, which could explain the link between MetS and OA development. Recently published studies have provided novel insights into the different origins and heterogeneity of synovial macrophages. Considering these findings, we propose an important role for monocyte-derived macrophages in particular, as opposed to yolk-sac derived residential macrophages, in causing a pro-inflammatory phenotype shift. We will further explain how this can start even prior to synovial infiltration; in the circulation, monocytes can be trained by metabolic factors such as low-density lipoprotein to become extra responsive to chemokines and damage-associated molecular patterns. The concept of innate immune training has been widely studied and implicated in atherosclerosis pathology, but its involvement in OA remains uncharted territory. Finally, we evaluate the implications of these insights for targeted therapy directed to macrophages and metabolic factors.

Association of Serum Low-Density Lipoprotein, High-Density Lipoprotein, and Total Cholesterol With Development of Knee Osteoarthritis

OBJECTIVE

Studies suggest an association between elevated total serum cholesterol, particularly low-density lipoprotein (LDL), and osteoarthritis (OA). The present study was undertaken to evaluate the association between total cholesterol, LDL, and high-density lipoprotein (HDL) and risk of knee OA.

METHODS

We studied participants from the Multicenter Osteoarthritis study (MOST) cohort at risk of developing knee OA. From baseline through 7 years, repeated knee radiographs and magnetic resonance images (MRIs) were obtained, and knee symptoms were queried. From baseline fasting blood samples, lipids and lipoproteins were analyzed using standard assays. After excluding participants with baseline OA, we defined 2 sets of patients: those developing radiographic OA, and those developing symptomatic OA (knee pain and radiographic OA). Controls did not develop these outcomes. Additionally, we examined worsening of cartilage loss and synovitis on MRI and of knee pain using the Western Ontario and McMaster Universities Osteoarthritis Index scale. We carried out logistic regression adjusting for age, sex, body mass index, education, baseline pain, and depressive symptoms, testing total cholesterol and lipoproteins as continuous measures, and we performed sensitivity analyses examining whether commonly used thresholds for high cholesterol, LDL, or low HDL increased risk.

RESULTS

We studied 337 patients with incident symptomatic OA and 283 patients with incident radiographic OA. The mean age at baseline was 62 years (55% women). Neither total cholesterol, LDL, nor HDL showed a significant association with radiographic or symptomatic OA. Additionally, we found no association of these lipid measures with cartilage loss, worsening synovitis, or worsening knee pain.

CONCLUSION

Our data do not support an association between total cholesterol, LDL, or HDL with OA outcomes.

Cholesterol metabolism related genes in osteoarthritis

Cholesterol homeostasis plays a significant role in skeletal development and the dysregulation of cholesterol-related mechanism has been shown to be involved in the development of cartilage diseases including osteoarthritis (OA). Epidemiological studies have shown an association between elevated serum cholesterol levels and OA. Furthermore, abnormal lipid accumulation in chondrocytes as a result of abnormal regulation of cholesterol homeostasis has been demonstrated to be involved in the development of OA. Although, many in vivo and in vitro studies support the connection between cholesterol and cartilage degradation, the mechanisms underlying the complex interactions between lipid metabolism, especially HDL cholesterol metabolism, and OA remain unclear. The current review aims to address this problem and focuses on key molecular players of the HDL metabolism pathway and their role in ΟΑ pathogenesis. Understanding the complexity of biological processes implicated in OA pathogenesis, such as cholesterol metabolism, may lead to new targets for drug therapy of OA patients.

Nox2 Deficiency Reduces Cartilage Damage and Ectopic Bone Formation in an Experimental Model for Osteoarthritis

Osteoarthritis (OA) is a destructive disease of the joint with age and obesity being its most important risk factors. Around 50% of OA patients suffer from inflammation of the synovial joint capsule, which is characterized by increased abundance and activation of synovial macrophages that produce reactive oxygen species (ROS) via NADPH-oxidase 2 (NOX2). Both ROS and high blood levels of low-density lipoprotein (LDL) are implicated in OA pathophysiology, which may interact to form oxidized LDL (oxLDL) and thereby promote disease. Therefore, targeting NOX2 could be a viable treatment strategy for OA. Collagenase-induced OA (CiOA) was used to compare pathology between wild-type (WT) and Nox2 knockout (Nox2^−/−) C57Bl/6 mice. Mice were either fed a standard diet or Western diet (WD) to study a possible interaction between NOX2-derived ROS and LDL. Synovial inflammation, cartilage damage and ectopic bone size were assessed on histology. Extracellular ROS production by macrophages was measured in vitro using the Amplex Red assay. Nox2^−/− macrophages produced basal levels of ROS but were unable to increase ROS production in response to the alarmin S100A8 or the phorbol ester PMA. Interestingly, Nox2 deficiency reduced cartilage damage, synovial lining thickness and ectopic bone size, whereas these disease parameters were not affected by WD-feeding. These results suggest that NOX2-derived ROS are involved in CiOA development.

A single dose of anti-IL-1β antibodies prevents Western diet-induced immune activation during early stage collagenase-induced osteoarthritis, but does not ameliorate end-stage pathology

OBJECTIVE

Metabolic dysfunction can cause IL-1β mediated activation of the innate immune system, which could have important implications for the therapeutic efficacy of IL-1β neutralizing drugs as treatment for OA in the context of metabolic syndrome (MetS). In the present study, we investigated whether early treatment with a single dose of IL-1β blocking antibodies could prevent Western diet (WD) induced changes to systemic monocyte populations and their cytokine secretion profile and herewith modulate collagenase induced osteoarthritis (CiOA) pathology.

METHODS

CiOA was induced in female C57Bl/6 mice fed either a standard diet (SD) or WD and treated with a single dose of either polyclonal anti-IL-1β antibodies or control. Monocyte subsets and granulocytes in bone marrow and blood were analyzed with flow cytometry, and cytokine expression by bone marrow cells was analyzed using qPCR. Synovial cellularity, cartilage damage and osteophyte formation were assessed on histology.

RESULTS

WD feeding of C57Bl/6 mice led to increased serum levels of low-density lipoprotein (LDL) and innate immune activation in the form of an increased number of Ly6C^high cells in bone marrow and blood and increased cytokine expression of IL-6 and TNF-α by bone marrow cells. The increase in monocyte number and activity was ameliorated by anti-IL-1β treatment. However, anti-IL-1β treatment did not significantly affect synovial lining thickness, cartilage damage and ectopic bone formation during WD feeding.

CONCLUSIONS

Single-dose systemic anti-IL-1β treatment prevented WD-induced innate immune activation during early stage CiOA in C57Bl/6 mice, but did not ameliorate joint pathology.

The role of oxidation of low-density lipids in pathogenesis of osteoarthritis: A narrative review

Osteoarthritis (OA) is a chronic joint disorder that causes degeneration of cartilage, synovial inflammation, and formation of osteophytes. Aging, obesity, and sex are considered the main risk factors of OA. Recent studies have suggested that metabolic syndrome (MetS) disorders, such as hypertension, hyperlipidemia, diabetes mellitus, and obesity, may be involved in the pathogenesis and progression of OA. MetS disorders are common diseases that also result in atherosclerosis. Researchers believe that OA and atherosclerosis have underlying similar molecular mechanisms because the prevalence of both diseases increases with age. Oxidation of low-density lipoprotein (ox-LDL) is believed to play a role in the pathogenesis of atherosclerosis. Recent reports have shown that ox-LDL and low-density lipoprotein receptor 1 (LOX-1) are involved in the pathogenesis of OA. The purpose of this narrative review is to summarize the current understanding of the role of the LOX-1/ox-LDL system in the pathogenesis of OA and to reveal common underlying molecular pathways that are shared by MetS in OA and the LOX-1/ox-LDL system.

The role of metabolism in chondrocyte dysfunction and the progression of osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease characterized by low-grade inflammation and high levels of clinical heterogeneity. Aberrant chondrocyte metabolism is a response to changes in the inflammatory microenvironment and may play a key role in cartilage degeneration and OA progression. Under conditions of environmental stress, chondrocytes tend to adapt their metabolism to microenvironmental changes by shifting from one metabolic pathway to another, for example from oxidative phosphorylation to glycolysis. Similar changes occur in other joint cells, including synoviocytes. Switching between these pathways is implicated in metabolic alterations that involve mitochondrial dysfunction, enhanced anaerobic glycolysis, and altered lipid and amino acid metabolism. The shift between oxidative phosphorylation and glycolysis is mainly regulated by the AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) pathways. Chondrocyte metabolic changes are likely to be a feature of different OA phenotypes. Determining the role of chondrocyte metabolism in OA has revealed key features of disease pathogenesis. Future research should place greater emphasis on immunometabolism and altered metabolic pathways as a means to understand the pathophysiology of age-related OA. This knowledge will advance the development of new drugs against therapeutic targets of metabolic significance.

Modulation of the Inflammatory Process by Hypercholesterolemia in Osteoarthritis

Objective: Several studies have linked metabolic syndrome to the development of osteoarthritis (OA) through hypercholesterolemia, one of its components. However, epidemiological studies showed contradictory results, and it is not clear how hypercholesterolemia itself, or oxidized LDL (oxLDL)-a pathological molecule potentially involved in this relationship-could be affecting OA. The objectives of this study were to investigate the effect of hypercholesterolemia induced by high-fat diet (HFD) in cartilage from OA rabbits, and how oxLDL affect human chondrocyte inflammatory and catabolic responses. Design: New Zealand rabbits were fed with HFD for 18 weeks. On week 6, OA was surgically induced. At the end of the study, cartilage damage and IL-1β, IL-6, MCP-1, MMP-13, and COX-2 expression in articular cartilage were evaluated. In addition, cultured human OA articular chondrocytes were treated with oxLDL at concentrations equivalent to those expected in synovial fluid from HFD rabbits, in the presence of IL-1β and TNFα. The effect of oxLDL on cell viability, nitric oxide production and catabolic and pro-inflammatory gene expression was evaluated. Results: HFD intake did not modify cartilage structure or pro-inflammatory and catabolic gene expression and protein presence, both in healthy and OA animals. OxLDL did not affect human chondrocyte viability, ADAMTS5 and liver X receptor (LXR) α gene expression, but decreased the induction of IL-1β, IL-6, MCP-1, MMP-13, iNOS, and COX-2 gene expression and MMP-13 and COX-2 protein presence, evoked by cytokines. Conclusions: Our data suggest that cholesterol intake per se may not be deleterious for articular cartilage. Instead, cholesterol de novo synthesis and altered cholesterol metabolism could be involved in the associations observed in human disease.

Electroacupuncture Prevents Osteoarthritis of High-Fat Diet-Induced Obese Rats

The effects of acupuncture on osteoarthritis (OA) pathogenesis have been demonstrated in vitro and in animal models. However, the potential for acupuncture to mediate protective effects on obese-induced OA has not been examined. Here, we investigated the effects of different acupuncture patterns on OA pathogenesis in high-fat diet- (HFD-) induced obese rats. After 12-week diet-induced obesity, obese rats were treated with three acupuncture protocols for 2 weeks, including ST36, GB34, and ST36+GB34. The results showed that the three acupuncture protocols both prevented obesity-induced cartilage matrix degradation and MMP expression and mitigated obesity-induced systemic and local inflammation but had different regulatory effects on lipid metabolism and gut microbiota disorder of obese-induced OA rats. Furthermore, the three acupuncture protocols increased the microbial diversity and altered the structure of community of feces in obese rats. We found that ST36 and GB34 could inhibit proinflammatory shift in the gut microbiome with an increase in the ratio of Bacteroidetes/Firmicutes and promote the recovery of relative abundance of Clostridium, Akkermansia, Butyricimonas, and Lactococcus. Although both ST36 and GB34 had an anti-inflammatory effect on serum inflammatory mediators, only the acupuncture protocol with both ST36 and GB34 could effectively inhibit LPS-mediated joint inflammation in obesity rats. Therefore, relieving obesity-related chronic inflammation, lipid metabolism disorder, and gut microbiota disorder may be an important mechanism for acupuncture with ST36 and GB34 to promote OA recovery.

Identifying effector molecules, cells, and cytokines of innate immunity in OA

Inflammatory changes are observed in affected joints of osteoarthritis (OA) patients and are thought to be involved in the pathology that develops along OA progression. This narrative review provides an overview of the various cell types that are present in the joint during OA and which alarmins, cytokines, chemokines, growth factors, and other mediators they produce. Moreover, the involvement of more systemic processes like inflammaging and its associated cellular senescence in the context of OA are discussed.

Osteoarthritis and type 2 diabetes: From pathogenetic factors to therapeutic intervention

Over the last decades, osteoarthritis (OA) and type 2 diabetes (T2D) prevalence increased due to the global ageing population and the pandemic obesity. They currently affect a substantial part of the Western world population and are characterized by enhancing the risk of disability and reduction of quality of life. OA is a multifactorial condition whose development derives from the interaction between individual and environmental factors: The best known primarily include age, female gender, genetic determinants, articular biomechanics, and obesity (OB). Given the high prevalence of OA and T2D and their association with OB and inflammation, several studies have been conducted to investigate the causative role of biological characteristics proper to T2D on the development of OA. This review aims to analyse the relationship between of OA and T2D, in order to explain the pathophysiological drivers of the degenerative process and to delineate possible targets to which appropriate treatments may be addressed in the near future.

Lipidomic identification of plasma lipids associated with pain behaviour and pathology in a mouse model of osteoarthritis

INTRODUCTION

Osteoarthritis (OA) is the most common form of joint disease, causing pain and disability. Previous studies have demonstrated the role of lipid mediators in OA pathogenesis.

OBJECTIVES

To explore potential alterations in the plasma lipidomic profile in an established mouse model of OA, with a view to identification of potential biomarkers of pain and/or pathology.

METHODS

Pain behaviour was assessed following destabilisation of the medial meniscus (DMM) model of OA (n = 8 mice) and compared to sham controls (n = 7). Plasma and knee joints were collected at 16 weeks post-surgery. Plasma samples were analysed using ultra-high performance liquid chromatography accurate mass high resolution mass spectrometry (UHPLC-HR-MS) to identify potential differences in the lipidome, using multivariate and univariate statistical analyses. Correlations between pain behaviour, joint pathology and levels of lipids were investigated.

RESULTS

24 lipids, predominantly from the lipid classes of cholesterol esters (CE), fatty acids (FA), phosphatidylcholines (PC), N-acylethanolamines (NAE) and sphingomyelins (SM), were differentially expressed in DMM plasma compared to sham plasma. Six of these lipids which were increased in the DMM model were identified as CE(18:2), CE(20:4), CE(22:6), PC(18:0/18:2), PC(38:7) and SM(d34:1). CEs were positively correlated with pain behaviour and all six lipid species were positively correlated with cartilage damage. Pathways shown to be involved in altered lipid homeostasis in OA were steroid biosynthesis and sphingolipid metabolism.

CONCLUSION

We identify plasma lipid species associated with pain and/or pathology in a DMM model of OA.

Understanding the Molecular Mechanisms Underlying the Pathogenesis of Arthritis Pain Using Animal Models

Arthritis, including osteoarthritis (OA) and rheumatoid arthritis (RA), is the leading cause of years lived with disability (YLD) worldwide. Although pain is the cardinal symptom of arthritis, which is directly related to function and quality of life, the elucidation of the mechanism underlying the pathogenesis of pain in arthritis has lagged behind other areas, such as inflammation control and regulation of autoimmunity. The lack of therapeutics for optimal pain management is partially responsible for the current epidemic of opioid and narcotic abuse. Recent advances in animal experimentation and molecular biology have led to significant progress in our understanding of arthritis pain. Despite the inherent problems in the extrapolation of data gained from animal pain studies to arthritis in human patients, the critical assessment of molecular mediators and translational studies would help to define the relevance of novel therapeutic targets for the treatment of arthritis pain. This review discusses biological and molecular mechanisms underlying the pathogenesis of arthritis pain determined in animal models of OA and RA, along with the methodologies used.

S100 family proteins in inflammation and beyond

The S100 family proteins possess a variety of intracellular and extracellular functions. They interact with multiple receptors and signal transducers to regulate pathways that govern inflammation, cell differentiation, proliferation, energy metabolism, apoptosis, calcium homeostasis, cell cytoskeleton and microbial resistance. S100 proteins are also emerging as novel diagnostic markers for identifying and monitoring various diseases. Strategies aimed at targeting S100-mediated signaling pathways hold a great potential in developing novel therapeutics for multiple diseases. In this chapter, we aim to summarize the current knowledge about the role of S100 family proteins in health and disease with a major focus on their role in inflammatory conditions.

High LDL levels lessen bone destruction during antigen-induced arthritis by inhibiting osteoclast formation and function

Rheumatoid arthritis (RA) is a chronic inflammatory disease, characterized by severe joint inflammation and bone destruction as the result of increased numbers and activity of osteoclasts. RA is often associated with metabolic syndrome, whereby elevated levels of LDL are oxidized into oxLDL, which might affect osteoclastogenesis. In this study, we induced antigen-induced arthritis (AIA) in Apoe^-/- mice, which spontaneously develop high LDL levels, to investigate the effects of high LDL/oxLDL levels on osteoclast differentiation and bone destruction. Whereas basal levels of bone resorption were comparable between naive WT and Apoe^-/- mice, induction of AIA resulted in a significant reduction of bone destruction in Apoe^-/- mice as compared to WT controls. In line with that, the TRAP⁺ area on the cortical bone was significantly decreased. The absence of Apoe did affect neither the numbers of CD11b⁺Ly6C^high and CD11b^-/Ly6C^high osteoclast precursors (OCPs) in the BM of naïve mice nor their in vitro osteoclastogenic potential as indicated by comparable mRNA expression of osteoclast markers. Addition of oxLDL, but not LDL, to pre-osteoclasts from day 3 and mature osteoclasts from day 6 of osteoclastogenesis strongly reduced the number of TRAP⁺ osteoclasts and their resorptive capacity. This coincided with a decreased expression of various osteoclast markers. Interestingly, oxLDL significantly lowered the expression of osteoclast-associated receptor (Oscar) and the DNAX adaptor protein-12 encoding gene Tyrobp, which regulate the immunoreceptor tyrosine-based activation motif (ITAM) co-stimulation pathway that is strongly involved in osteoclastogenesis. Collectively, our findings suggest that under inflammatory conditions in the joint, high LDL levels lessen bone destruction during AIA, probably by formation of oxLDL that inhibits osteoclast formation and activity through modulation of the ITAM-signaling.

Cardiometabolic Polygenic Risk Scores and Osteoarthritis Outcomes: A Mendelian Randomization Study Using Data From the Malmö Diet and Cancer Study and the UK Biobank

Objective

To investigate the causal role of cardiometabolic risk factors in osteoarthritis (OA) using associated genetic variants.

Methods

We studied 27,691 adults from the Malmö Diet and Cancer Study (MDCS) and replicated novel findings among 376,435 adults from the UK Biobank. Trait‐specific polygenic risk scores for low‐density lipoprotein (LDL) and high‐density lipoprotein (HDL) cholesterol levels, triglyceride levels, body mass index (BMI), fasting plasma glucose (FPG) levels, and systolic blood pressure (BP) were used to test the associations of genetically predicted elevations in each trait with incident OA diagnosis (n = 3,559), OA joint replacement (n = 2,780), or both (total OA; n = 4,226) in Mendelian randomization (MR) analyses in the MDCS, and with self‐reported and/or hospital‐diagnosed OA (n = 65,213) in the UK Biobank. Multivariable MR, MR‐Egger, and weighted median MR were used to adjust for potential pleiotropic biases.

Results

In the MDCS, genetically predicted elevation in LDL cholesterol level was associated with a lower risk of OA diagnosis (odds ratio [OR] 0.83 [95% confidence interval (95% CI) 0.73–0.95] per 1SD increase) and total OA (OR 0.87 [95% CI 0.78–0.98]), which was supported by multivariable MR for OA diagnosis (OR 0.84 [95% CI 0.75–0.95]) and total OA (0.87 [95% CI 0.78–0.97]), and by conventional 2‐sample MR for OA diagnosis (OR 0.86 [95% CI 0.75–0.98]). MR‐Egger indicated no pleiotropic bias. Genetically predicted elevation in BMI was associated with an increased risk of OA diagnosis (OR 1.65 [95% CI 1.14–2.41]), while MR‐Egger indicated pleiotropic bias and a larger association with OA diagnosis (OR 3.25 [1.26–8.39]), OA joint replacement (OR 3.81 [95% CI 1.39–10.4]), and total OA (OR 3.41 [95% CI 1.43–8.15]). No associations were observed between genetically predicted HDL cholesterol level, triglyceride level, FPG level, or systolic BP and OA outcomes. The associations with LDL cholesterol levels were replicated in the UK Biobank (OR 0.95 [95% CI 0.93–0.98]).

Conclusion

Our MR study provides evidence of a causal role of lower LDL cholesterol level and higher BMI in OA.

Physiologic and pathologic effects of dietary free fatty acids on cells of the joint

Fatty acids (FAs) are potent organic compounds that not only can be used as an energy source during nutrient deprivation but are also involved in several essential signaling cascades in cells. Therefore, a balanced intake of different dietary FAs is critical for the maintenance of cellular functions and tissue homeostasis. A diet with an imbalanced fat composition creates a risk for developing metabolic syndrome and various musculoskeletal diseases, including osteoarthritis (OA). In this review, we summarize the current state of knowledge and mechanistic insights regarding the role of dietary FAs, such as saturated FAs, omega-6 polyunsaturated FAs (PUFAs), and omega-3 PUFAs on joint inflammation and OA pathogeneses. In particular, we review how different types of dietary FAs and their derivatives distinctly affect a variety of cells within the joint, including chondrocytes, osteoblasts, osteoclasts, and synoviocytes. Understanding the molecular mechanisms underlying the effects of FAs on metabolic behavior, anabolic, and catabolic processes, as well as the inflammatory response of joint cells, may help identify therapeutic targets for the prevention of metabolic joint diseases.

Independent effects of dietary fat and sucrose content on chondrocyte metabolism and osteoarthritis pathology in mice

Obesity is one of the most significant risk factors for knee osteoarthritis. However, therapeutic strategies to prevent or treat obesity-associated osteoarthritis are limited because of uncertainty about the etiology of disease, particularly with regard to metabolic factors. High-fat-diet-induced obese mice have become a widely used model for testing hypotheses about how obesity increases the risk of osteoarthritis, but progress has been limited by variation in disease severity, with some reports concluding that dietary treatment alone is insufficient to induce osteoarthritis in mice. We hypothesized that increased sucrose content of typical low-fat control diets contributes to osteoarthritis pathology and thus alters outcomes when evaluating the effects of a high-fat diet. We tested this hypothesis in male C57BL/6J mice by comparing the effects of purified diets that independently varied sucrose or fat content from 6 to 26 weeks of age. Outcomes included osteoarthritis pathology, serum metabolites, and cartilage gene and protein changes associated with cellular metabolism and stress-response pathways. We found that the relative content of sucrose versus cornstarch in low-fat iso-caloric purified diets caused substantial differences in serum metabolites, joint pathology, and cartilage metabolic and stress-response pathways, despite no differences in body mass or body fat. We also found that higher dietary fat increased fatty acid metabolic enzymes in cartilage. The findings indicate that the choice of control diets should be carefully considered in mouse osteoarthritis studies. Our study also indicates that altered cartilage metabolism might be a contributing factor to how diet and obesity increase the risk of osteoarthritis.

Summary: The contribution of metabolic factors to obesity-associated knee osteoarthritis is uncertain. Here, we show how dietary fat and sucrose independently alter cartilage metabolic enzymes and osteoarthritis pathophysiology in mice.

Treatment of collagenase-induced osteoarthritis with a viral vector encoding TSG-6 results in ectopic bone formation

Objective

Tumor necrosis factor-inducible gene 6 (TSG-6) has anti-inflammatory and chondroprotective effects in mouse models of inflammatory arthritis. Because cartilage damage and inflammation are also observed in osteoarthritis (OA), we determined the effect of viral overexpression of TSG-6 in experimental osteoarthritis.

Methods

Bone marrow-derived cells were differentiated to multinucleated osteoclasts in the presence of recombinant TSG-6 or after transduction with a lentiviral TSG-6 expression vector. Multi-nucleated osteoclasts were analyzed after tartrate resistant acid phosphatase staining and resorption activity was determined on dentin slices. Collagenase-induced osteoarthritis (CIOA) was induced in C57BL/6 mice after intra-articular injection of an adenoviral TSG-6 or control luciferase expression vector. Inflammation-related protease activity was measured using bioluminescent Prosense probes. After a second adenovirus injection, cartilage damage was assessed in histological sections stained with Safranin-O. Ectopic bone formation was scored in X-ray images of the affected knees.

Results

TSG-6 did not inhibit the formation of multi-nucleated osteoclasts, but caused a significant reduction in the resorption activity on dentin slices. Adenoviral TSG-6 gene therapy in CIOA could not reduce the cartilage damage compared to the luciferase control virus and no significant difference in inflammation-related protease activity was noted between the TSG-6 and control treated group. Instead, X-ray analysis and histological analysis revealed the presence of ectopic bone formation in the TSG-6 treated group.

Conclusion

Gene therapy based on the expression of TSG-6 could not provide cartilage protection in experimental osteoarthritis, but instead resulted in increased ectopic bone formation.

What is the evidence for a role for diet and nutrition in osteoarthritis?

As current treatment options in OA are very limited, OA patients would benefit greatly from some ability to self-manage their condition. Since diet may potentially affect OA, we reviewed the literature on the relationship between nutrition and OA risk or progression, aiming to provide guidance for clinicians. For overweight/obese patients, weight reduction, ideally incorporating exercise, is paramount. The association between metabolic syndrome, type-2 diabetes and OA risk or progression may partly explain the apparent benefit of dietary-lipid modification resulting from increased consumption of long-chain omega-3 fatty-acids from oily fish/fish oil supplements. A strong association between OA and raised serum cholesterol together with clinical effects in statin users suggests a potential benefit of reduction of cholesterol by dietary means. Patients should ensure that they meet the recommended intakes for micronutrients such as vitamin K, which has a role in bone/cartilage mineralization. Evidence for a role of vitamin D supplementation in OA is unconvincing.

Metabolic dysregulation accelerates injury-induced joint degeneration, driven by local inflammation; an in vivo rat study

Evidence is growing for the existence of an obesity-related phenotype of osteoarthritis in which low-grade inflammation and a disturbed metabolic profile play a role. The contribution of an obesity-induced metabolic dysbalance to the progression of the features of osteoarthritis upon mechanically induced cartilage damage was studied in a rat in vivo model. Forty Wistar rats were randomly allocated 1:1 to a standard diet or a high-fat diet. After 12 weeks, in 14 out of 20 rats in each group, cartilage was mechanically damaged in the right knee joint. The remaining six animals in each group served as controls. After a subsequent 12 weeks, serum was collected for metabolic state, subchondral bone changes assessed by μCT imaging, osteoarthritis severity determined by histology, and macrophage presence assessed by CD68 staining. The high-fat diet increased statistically all relevant metabolic parameters, resulting in a dysmetabolic state and subsequent synovial inflammation, whereas cartilage degeneration was hardly influenced. The high-fat condition in combination with mechanical cartilage damage resulted in a clear statistically significant progression of the osteoarthritic features, with increased synovitis and multiple large osteophytes. Both the synovium and osteophytes contained numerous CD68 positive cells. It is concluded that a metabolic dysbalance due to a high-fat diet increases joint inflammation without cartilage degeneration. The dysmetabolic state clearly accelerates progression of osteoarthritis upon surgically induced cartilage damage supported by inflammatory responses as demonstrated by histology and increased CD68 expressing cells localized on the synovial membrane and osteophytes. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:881-890, 2018.

LOX-1 deficient mice show resistance to zymosan-induced arthritis

Recent data suggest that the lectin-like oxidized low-density lipoprotein (ox-LDL) receptor-1 (LOX-1)/ox-LDL system may be involved in the pathogenesis of arthritis. We aimed to demonstrate the roles of the LOX- 1/ox-LDL system in arthritis development by using LOX-1 knockout (KO) mice. Arthritis was induced in the right knees of C57Bl/6 wild-type (WT) and LOX-1 KO mice via zymosan injection. Saline was injected in the left knees. Arthritis development was evaluated using inflammatory cell infiltration, synovial hyperplasia, and cartilage degeneration scores at 1, 3, and 7 days after administration. LOX-1, ox-LDL, and matrix metalloproteinase-3 (MMP-3) expression in the synovial cells and chondrocytes was evaluated by immunohistochemistry. The LOX-1, ox-LDL, and MMP-3 expression levels in synovial cells were scored on a grading scale. The positive cell rate of LOX-1, ox-LDL, and MMP-3 in chondrocytes was measured. The correlation between the positive cell rate of LOX-1 or ox-LDL and the cartilage degeneration score was also examined. Inflammatory cell infiltration, synovial hyperplasia, and cartilage degeneration were significantly reduced in the LOX-1 KOmice with zymosan-induced arthritis (ZIA) compared to WT mice with ZIA. In the saline-injected knees, no apparent arthritic changes were observed. LOX-1 and ox-LDL expression in synovial cells and chondrocytes were detected in the knees of WT mice with ZIA. No LOX-1 and ox-LDL expression was detected in the knees of LOX-1 KO mice with ZIA or the salineinjected knees of both mice. MMP-3 expression in the synovial cells and chondrocytes was also detected in knees of both mice with ZIA, and was significantly less in the LOX-1 KO mice than in WT mice. The positive cell rate of LOX-1 or ox-LDL and the cartilage degeneration score showed a positive correlation. Our data show the involvement of the LOX-1/ox-LDL system in murine ZIA development. LOX-1-positive synovial cells and chondrocytes are potential therapeutic targets for arthritis prevention.

Low-density lipoprotein receptor deficiency impaired mice osteoblastogenesis in vitro

Postmenopausal osteoporosis affected most elderly women with co-existence of lipid and bone metabolism disorders. However, the cellular and molecular mechanisms underlying the parallel progression and cross-talk of these systems remained unclear. In the present study, low-density lipoprotein receptor knockout (LDLR^-/-) mice were chosen to elucidate the effect of LDLR in regulating the differentiation of osteoblasts, which were responsible for bone formation and modulation of osteoclastogenesis. Primary osteoblasts were isolated from the calvarium of newborn LDLR^-/- or wild-type mice followed by osteoblastic differentiation culture in vitro. Alkaline phosphatase activity was significantly decreased in LDLR^-/- osteoblasts compared to wild-type controls, combined with calcium deposit formation delay, implying impaired osteoblastogenesis in vitro. Consistent with these findings, the expression of runt-related transcription factor 2 (Runx2) was decreased 3 days after differentiation in LDLR^-/- osteoblasts compared to wild-type controls. Moreover, the expression of Osterix was decreased 7 days after differentiation in LDLR^-/- osteoblasts compared to wild-type controls, later than Runx2.However, the osteoclastogenesis modulation role of osteoblasts was unaffected by the LDLR deficiency, evidenced by the same level of osteoprotegerin (OPG)/receptor activator of nuclear factor-κ B ligand (RANKL) axis between LDLR^-/- and wild-type control osteoblasts. Our results provide a novel insight into the role of LDLR during osteoblastic differentiation and improve understanding of cross-talk between bone and lipid metabolisms.

Association between metabolic syndrome and knee osteoarthritis: a cross-sectional study

Background

Osteoarthritis (OA) is the most prevalent chronic joint disease in China. The aim of this study was to examine the association between metabolic syndrome (MetS) and knee OA in a population-based Chinese study.

Methods

Data included in this analysis is from a cross-sectional study, i.e., the Xiangya Hospital Health Management Center Study. MetS was diagnosed according to the criteria defined by the Chinese Diabetes Society. Radiographic knee OA was defined as changes equivalent to Kellgren-Lawrence (K-L) grade 2 or above at least one side. Associations between MetS and its components with OA were evaluated by conducting multivariable adjusted logistic regression.

Results

A total of 5764 participants were included in the present study. The unadjusted OR (1.27, 95%CI: 1.10–1.47, P = 0.001), age-sex adjusted OR (1.17, 95%CI: 1.01–1.36, P = 0.041) and multivariable adjusted OR (1.17, 95%CI: 1.01–1.36, P = 0.043) all suggested a positive association between MetS and knee OA. Besides, its components (e.g., overweight, hypertension and dyslipidemia) were also associated with the prevalence of radiographic knee OA respectively, after adjusting for some confounding factors. In addition, with the accumulation of MetS components, the prevalence of knee OA increased. Furthermore, MetS as a whole was associated with the prevalence of knee osteophyte (OSP) (OR = 1.72, 95%CI: 1.42–2.09, P < 0.001), but not joint space narrowing (JSN) (OR = 1.06, 95%CI: 0.91–1.23, P = 0.449).

Conclusions

The findings of the present study indicated that there was a positive association between the prevalence of MetS and knee OA. However, MetS as a whole was associated with the higher prevalence of knee OSP, but not JSN, which should shed light on our understanding the association between MetS and OA.

Increased synovial lipodystrophy induced by high fat diet aggravates synovitis in experimental osteoarthritis

BACKGROUND

Metabolic syndrome (MetS) may be associated with knee osteoarthritis (OA), but the association between the individual components and OA are not well-understood. We aimed to study the effect of hypercholesterolemia on synovial inflammation in knee OA.

METHODS

OA was surgically induced in rabbits fed with standard diet (OA group, n = 10) or in rabbits fed with high fat diet (OA-HFD, n = 10). Healthy rabbits receiving standard diet (Control, n = 10) or fed with HFD (HFD, n = 6) were also monitored. Twelve weeks after OA induction, synovial membranes were isolated and processed for studies.

RESULTS

Animals fed HFD showed higher levels of total serum cholesterol, triglycerides and C-reactive protein than control rabbits. Twelve weeks after OA induction, synovial membrane inflammation and macrophage infiltration were increased in rabbits with OA, particularly in the OA-HFD group. Extensive decrease of synovial adipose tissue area, adipocyte size and perilipin-1A synthesis were observed in the OA-HFD group in comparison to the OA and control groups. The HFD further increased the proinflammatory mediators IL-1β, IL-6 and TNF in the OA synovium. However, the synovial gene expression of adipokines, such as leptin and adiponectin, were markedly decreased in the rabbits with OA, especially in the OA-HFD group, in correlation with adipose tissue loss. However, circulating leptin was upregulated in the HFD and OA-HFD groups.

CONCLUSION

Our results indicate that a HFD is an aggravating factor worsening synovial membrane inflammation during OA, guided by increased infiltration of macrophages and removal of the adipose tissue, together with a remarkable presence of proinflammatory factors. Synovial adipocytes and dyslipemia could probably play pivotal roles in OA joint deterioration in patients with MetS, supporting that the link between obesity and OA transcends mechanical loading.

Aging and osteoarthritis: Central role of the extracellular matrix

Osteoarthritis (OA), is a major cause of severe joint pain, physical disability and quality of life impairment in the aging population across the developed and developing world. Increased catabolism in the extracellular matrix (ECM) of the articular cartilage is a key factor in the development and progression of OA. The molecular mechanisms leading to an impaired matrix turnover have not been fully clarified, however cellular senescence, increased expression of inflammatory mediators as well as oxidative stress in association with an inherently limited regenerative potential of the tissue, are all important contributors to OA development. All these factors are linked to and tend to be maximized by aging. Nonetheless the role of aging in compromising joint stability and function in OA has not been completely clarified yet. This review will systematically analyze cellular and structural changes taking place in the articular cartilage and bone in the pathogenesis of OA which are linked to aging. A particular emphasis will be placed on age-related changes in the phenotype of the articular chondrocytes.

Metabolic syndrome-associated osteoarthritis

PURPOSE OF REVIEW

Interest in the metabolic syndrome-associated osteoarthritis phenotype is increasing. Here, we summarize recently published significant findings.

RECENT FINDINGS

Meta-analyses confirmed an association between type 2 diabetes and osteoarthritis and between cardiovascular diseases and osteoarthritis. Recent advances in the study of metabolic syndrome-associated osteoarthritis have focused on a better understanding of the role of metabolic diseases in inducing or aggravating joint damage. In-vivo models of obesity, diabetes, or dyslipidemia have helped to better decipher this association. They give emerging evidence that, beyond the role of common pathogenic mechanisms for metabolic diseases and osteoarthritis (i.e., low-grade inflammation and oxidative stress), metabolic diseases have a direct systemic effect on joints. In addition to the impact of weight, obesity-associated inflammation is associated with osteoarthritis severity and may modulate osteoarthritis progression in mouse models. As well, osteoarthritis synovium from type 2 diabetic patients shows insulin-resistant features, which may participate in joint catabolism. Finally, exciting data are emerging on the association of gut microbiota and circadian rhythm and metabolic syndrome-associated osteoarthritis.

SUMMARY

The systemic role of metabolic syndrome in osteoarthritis pathophysiology is now better understood, but new avenues of research are being pursued to better decipher the metabolic syndrome-associated osteoarthritis phenotype.

Serum Lipid Levels and Risk Of Hand Osteoarthritis: The Chingford Prospective Cohort Study

The development of hand osteoarthritis (HOA) could be linked to hyperlipidaemia. No longitudinal studies have addressed the relationship between serum lipid profile and HOA. The study aim was to determine the association between serum lipid profile and the incidence of radiographic hand osteoarthritis (RHOA). All women in a prospective population-based cohort from the Chingford study with available baseline lipid measurements and without RHOA on a baseline were included. Study outcome was the incidence of RHOA in year 11 of follow-up. Serum lipid profile variables were analysed as continuous variables and categorised into quartiles. The association between serum lipid profile and RHOA was modeled using multivariable logistic regression. Overall RHOA incidence was 51.6% (45.7–57.4%). An inverse association between HDL cholesterol levels and the incidence of RHOA was observed by quartile: OR of 0.36 [95%CI 0.17–0.75], 0.52 [95%CI 0.26–1.06], and 0.48 [95%CI 0.22–1.03]. Triglycerides levels showed a significant trend. No relationship was found with total or LDL cholesterol. Higher levels of HDL cholesterol appear to protect against RHOA after 11 years of follow-up. More research is needed to elucidate HOA risk factors, the mechanisms related to the lipid pathway, and the effects of lipid-lowering agents on reducing the incidence of OA.

Systemic and Local Adipose Tissue in Knee Osteoarthritis

Osteoarthritis is a common chronic joint disorder affecting older people. The knee is the major joint affected. The symptoms of osteoarthritis include limited range of motion, joint swelling, and pain causing disability. There are no disease modifying drugs available, and treatments are mainly focused on pain management. Total knee replacement performed at the end stage of the disease is considered the only cure available. It has been found that obese people have an increased risk to develop not only knee but also hand osteoarthritis. This supports the concept that adipose tissue might be related to osteoarthritis not only through overloading. As matter of fact, obesity induces a low grade systemic inflammatory state characterized by the production and secretion of several adipocytokines that may have a role in osteoarthritis development. Furthermore, hypertension, impaired glucose, and lipid metabolism, which are comorbidities associated with obesity, have been shown to alter the joint tissue homeostasis. Moreover, infrapatellar fat pad in the knee has been demonstrated to be a local source of adipocytokines and potentially contribute to osteoarthritis pathogenesis. Here, we discuss the role of systemic and local adipose tissue in knee osteoarthritis. J. Cell. Physiol. 232: 1971-1978, 2017. © 2016 Wiley Periodicals, Inc.

Arterial Calcification in Diabetes Mellitus: Preclinical Models and Translational Implications

Diabetes mellitus increasingly afflicts our aging and dysmetabolic population. Type 2 diabetes mellitus and the antecedent metabolic syndrome represent the vast majority of the disease burden-increasingly prevalent in children and older adults. However, type 1 diabetes mellitus is also advancing in preadolescent children. As such, a crushing wave of cardiometabolic disease burden now faces our society. Arteriosclerotic calcification is increased in metabolic syndrome, type 2 diabetes mellitus, and type 1 diabetes mellitus-impairing conduit vessel compliance and function, thereby increasing the risk for dementia, stroke, heart attack, limb ischemia, renal insufficiency, and lower extremity amputation. Preclinical models of these dysmetabolic settings have provided insights into the pathobiology of arterial calcification. Osteochondrogenic morphogens in the BMP-Wnt signaling relay and transcriptional regulatory programs driven by Msx and Runx gene families are entrained to innate immune responses-responses activated by the dysmetabolic state-to direct arterial matrix deposition and mineralization. Recent studies implicate the endothelial-mesenchymal transition in contributing to the phenotypic drift of mineralizing vascular progenitors. In this brief overview, we discuss preclinical disease models that provide mechanistic insights-and point to challenges and opportunities to translate these insights into new therapeutic strategies for our patients afflicted with diabetes mellitus and its arteriosclerotic complications.

Synovial macrophages promote TGF-β signaling and protect against influx of S100A8/S100A9-producing cells after intra-articular injections of oxidized low-density lipoproteins

OBJECTIVE

Low-density lipoproteins (LDL) in inflamed synovium is oxidized and taken-up by synoviocytes. In this study, we investigate whether direct injection of oxidized LDL (oxLDL) into a normal murine knee joint induces joint pathology and whether synovial macrophages are involved in that process.

DESIGN

Synovium was obtained from end-stage osteoarthritis (OA) patients in order to analyze LDL-uptake. Murine knee joints were injected five consecutive days with oxLDL, LDL, or vehicle (phosphate buffered saline (PBS)). This procedure was repeated in mice depleted of synovial macrophages by intra-articular injection of clodronate liposomes 7 days prior to the consecutive injections. Joint pathology was investigated by immunohistochemistry, flow cytometry (FCM) and synovial RNA expression and protein production.

RESULTS

Synovial tissue of OA patients showed extensive accumulation of apolipoprotein B. Multiple injections of oxLDL in murine knee joints significantly increased TGF-β activity in synovial wash-outs, but did not induce catabolic or inflammatory processes. In contrast, repeated injections of oxLDL in macrophage-depleted knee joints led to increased synovial thickening in combination with significantly upregulated protein and RNA levels of CCL2 and CCL3. FCM-analyses revealed increased presence of monocytes and neutrophils in the synovium, which was confirmed by immunohistochemistry. Also protein levels of S100A8/A9 were significantly increased in synovial wash-outs of oxLDL-injected joints, as was expression of aggrecanase-induced neo-epitopes. Interestingly, no raise in TGF-β concentrations was measured in macrophage-depleted joints.

CONCLUSIONS

OxLDL can affect joint pathology, since synovial macrophages promote anabolic processes after oxLDL injections. In absence of synovial macrophages, however, oxLDL induces production of pro-inflammatory mediators and aggrecanase activity combined with increased influx of monocytes and neutrophils.