Emerging regulators of the inflammatory process in osteoarthritis

Garlic (Allium sativum) increases SIRT1 and SIRT2 gene expressions in the kidney and liver tissues of STZ- and STZ+niacinamide-induced diabetic rats

Background

Diabetic nephropathy and liver damage are important complications of diabetes mellitus (DM). Various factors, such as sirtuins (silent information regulators or SIRTs) are associated with these complications. Sirtuins are a family of NAD+-dependent proteins, and seven types of these can be found in mammalians. In this study, we evaluated the effects of aqueous garlic extract (G) on the expressions of SIRT1 and SIRT2 genes in the kidney and liver tissues of rats with types 1 and 2 diabetes.

Methods

A total of 36 male Wistar rats (230–280 g) were randomly divided into six groups: C: normal control rats, D1M: type 1 diabetic rats (induced with streptozotocin, STZ), D1M+G: type 1 diabetic rats that treated with garlic extract, D2M: type 2 diabetic rats (induced with STZ and niacinamide), D2M+G: type 2 diabetic rats treated with garlic extract, and G: normal rats that received garlic extract. At the end of the treatment time, kidney and liver tissue samples were collected from all rats. The SIRT1 and SIRT2 gene expressions were determined by qRT-PCR.

Results

The SIRT1 and SIRT2 gene expressions in the liver and kidney tissues of diabetic rats decreased significantly compared with those in the control rats (p<0.05). After treatment with garlic extract, the gene expressions also increased significantly compared with those in the diabetic rats and are close to normal level (p<0.05).

Conclusions

Garlic extract increased the SIRT1 and SIRT2 gene expressions in the livers and kidneys of diabetic rats. The antioxidant and anti-inflammatory effects of garlic have been proven in many studies. Thus, it is possible that garlic – with its effects on this pathway of gene expression – can have antioxidant and anti-inflammatory effects, thus decreasing diabetic complications.

circRNA.33186 Contributes to the Pathogenesis of Osteoarthritis by Sponging miR-127-5p

Osteoarthritis (OA), the most prevalent age-related joint disorder, is characterized by chronic inflammation, progressive articular cartilage destruction, and subchondral bone sclerosis. Accumulating evidences indicate that circular RNAs (circRNAs) play a critical role in various diseases, but the function of circRNAs in OA remains largely unknown. Here we showed that circRNA.33186 was significantly upregulated in IL-1β)-treated chondrocytes and in cartilage tissues of a destabilized medial meniscus (DMM)-induced OA mouse model. Knockdown of circRNA.33186 increased anabolic factor (type II collagen) expression and decreased catabolic factor (MMP-13) expression. Knockdown of circRNA.33186 also promoted proliferation and inhibited apoptosis in IL-1β-treated chondrocytes. Silencing of circRNA.33186 in vivo markedly alleviated DMM-induced OA. Mechanistic study showed that circRNA.33186 directly binds to and inhibits miR-127-5p, thereby increasing MMP-13 expression, and contributes to OA pathogenesis. Taken together, our findings demonstrated a fundamental role of circRNA.33186 in OA progression and provide a potential drug target in OA therapy.

Current concepts in intraosseous Platelet-Rich Plasma injections for knee osteoarthritis

Knee osteoarthritis (OA) is a degenerative process that slowly destroys the joints producing pain and loss of function, and diminishes the quality of life. Current treatments alleviate this symptomatology but do not stop the disease, being total knee arthroplasty the only definitive solution. Among the emerging treatments, Platelet-Rich Plasma (PRP) has shown promising results in the treatment of OA. However, to improve its effectiveness, it is necessary to approach this pathology targeting the whole joint, not only the cartilage, but including other tissues such as subchondral bone. The pathological processes that occur in the subchondral bone have influence of the cartilage loss, aggravating the disease. The combination of intraarticular infiltrations with intraosseous infiltrations regulates the biological processes of the tissues, reducing the inflammatory environment and modulating the overexpression of biomolecules that generate an aberrant cellular behavior. Although the first clinical results using this technique are promising, further research and developing adequate protocols are necessary to achieve good clinical results.

Innovative regenerative medicine in the management of knee OA: The role of Autologous Protein Solution

Osteoarthritis (OA) is one of the most common causes of chronic disability in adults due to pain and altered joint function. Although most patients report pain and functional limitation, symptoms, age of onset and disease progression are extremely variable. While inflammation could play a central role in the OA pathogenesis and progression, many underpinning mechanisms are still unclear. A number of proinflammatory mediators have been found in OA joints and could play a role, such as IL-1, IL-6, IL-7, IL-8, IL-15, IL-17, IL-18, TNF-alpha, macrophage chemotactic protein (MCP)-1, interferon-induced protein (IP)-10, monokine induced by interferon (MIG), oncostatin M (OSM), growth-related oncogene (GRO)-alpha, chemokine (C-C-motif) ligand 19 (CCL19), macrophage inflammatory protein (MIP)-1beta, and TGF-alpha. Biological approaches have recently got increasing interest due to their anti-inflammatory and immunomodulatory properties, regenerative potential, and high tolerability. The primary aim of this paper is to report the current concepts on regenerative medicine for knee OA with a particular focus on Autologous Protein solution (APS). APS is a blood derived product obtained by using a proprietary device, made of APS Separator, which isolates WBCs and platelets in a small volume of plasma, and APS Concentrator, which further concentrates platelets, WBCs and plasma proteins. The result is a peculiar formulation differing from other biologic products as it contains high levels of growth factors (EGF, IGF-1, PDGF-AB, PDGF-BB, VEGF, TGF-β1) along with high concentrations of anti-inflammatory mediators (IL-1ra, sIL-1RII, sTNF-RI, sTNF-RII) and low levels of pro-inflammatory cytokines (Il-1β and TNF-α). While emerging evidence supports the use of APS, as confirmed by in vitro studies and preliminary clinical results, the real clinical potential of APS and its benefits are still under investigation.

Ageing and Osteoarthritis

The increase in global lifespan has in turn increased the prevalence of osteoarthritis which is now the most common type of arthritis. Cartilage tissue located on articular joints erodes during osteoarthritis which causes pain and may lead to a crippling loss of function in patients. The pathophysiology of osteoarthritis has been understudied and currently no disease modifying treatments exist. The only current end-point treatment remains joint replacement surgery. The primary risk factor for osteoarthritis is age. Clinical and basic research is now focused on understanding the ageing process of cartilage and its role in osteoarthritis. This chapter will outline the physiology of cartilage tissue, the clinical presentation and treatment options for the disease and the cellular ageing processes which are involved in the pathophysiology of the disease.

Baseline knee joint effusion and medial femoral bone marrow edema, in addition to MRI-based T2 relaxation time and texture measurements of knee cartilage, can help predict incident total knee arthroplasty 4-7 years later: data from the Osteoarthritis Initiative

OBJECTIVE

To evaluate if baseline pathological knee conditions as assessed via single features of the MR-based Whole-Organ Magnetic Resonance Imaging Scoring (WORMS), standard T2, and T2 gray-level co-occurrence matrix (GLCM) texture parameters of knee cartilage can serve as potential long-term radiological predictors of incident total knee arthroplasty (TKA) 4-7 years later.

MATERIALS AND METHODS

Baseline 3-T knee MRIs of 309 subjects from the Osteoarthritis Initiative (n = 81 TKA cases, with right-knee TKA 4-7 years after enrolment, and n = 228 TKA-free matched controls) were evaluated for the presence and severity of pathological knee conditions via modified WORMS. Knee cartilage was segmented and standard T2 cartilage and T2 GLCM texture measures (contrast, variance) were computed. Statistical analysis employed conditional logistic regression.

RESULTS

We found that a one-point increase on the joint effusion scale, the bone marrow edema scale or on the cartilage lesion scale at baseline predicted incident TKA (ORs: 2.45, 1.65, and 1.37 respectively (p ≤ 0.003)). For T2 cartilage measurements, we observed that in the lateral femur, a 1-SD increase in T2 relaxation time yielded a 28% increase in the odds of TKA (1.28 [1.09-1.643], p = 0.046). When looking at cartilage texture, we similarly noted that a 1-SD increase in the cartilage texture parameter "contrast" was associated with a 33-40% increased risk of incident TKA in the lateral femur and tibia (0.003 ≤ p ≤ 0.021), as was a 1-SD increase in the texture parameter "variance" in the lateral femur (p = 0.002).

CONCLUSION

Radiological evaluation of standard knee MR images via single WORMS features and T2 standard and texture analysis at baseline can help predict the patient's individual risk for an incident TKA 4-7 years later.

Different Forms of ER Stress in Chondrocytes Result in Short Stature Disorders and Degenerative Cartilage Diseases: New Insights by Cartilage-Specific ERp57 Knockout Mice

Cartilage is essential for skeletal development by endochondral ossification. The only cell type within the tissue, the chondrocyte, is responsible for the production of macromolecules for the extracellular matrix (ECM). Before proteins and proteoglycans are secreted, they undergo posttranslational modification and folding in the endoplasmic reticulum (ER). However, the ER folding capacity in the chondrocytes has to be balanced with physiological parameters like energy and oxygen levels. Specific cellular conditions, e.g., a high protein demand, or pathologic situations disrupt ER homeostasis and lead to the accumulation of poorly folded or misfolded proteins. This state is called ER stress and induces a cellular quality control system, the unfolded protein response (UPR), to restore homeostasis. Different mouse models with ER stress in chondrocytes display comparable skeletal phenotypes representing chondrodysplasias. Therefore, ER stress itself seems to be involved in the pathogenesis of these diseases. It is remarkable that chondrodysplasias with a comparable phenotype arise independent from the sources of ER stress, which are as follows: (1) mutations in ECM proteins leading to aggregation, (2) deficiencies in ER chaperones, (3) mutations in UPR signaling factors, or (4) deficiencies in the degradation of aggregated proteins. In any case, the resulting UPR substantially impairs ECM protein synthesis, chondrocyte proliferation, and/or differentiation or regulation of autophagy and apoptosis. Notably, chondrodysplasias arise no matter if single or multiple events are affected. We analyzed cartilage-specific ERp57 knockout mice and demonstrated that the deficiency of this single protein disulfide isomerase, which is responsible for formation of disulfide bridges in ECM glycoproteins, is sufficient to induce ER stress and to cause an ER stress-related bone phenotype. These mice therefore qualify as a novel model for the analysis of ER stress in chondrocytes. They give new insights in ER stress-related short stature disorders and enable the analysis of ER stress in other cartilage diseases, such as osteoarthritis.

Chrysin protects human osteoarthritis chondrocytes by inhibiting inflammatory mediator expression via HMGB1 suppression

High‑mobility group box chromosomal protein (HMGB‑1) contributes to osteoarthritis (OA) by modulating various oxidative, inflammatory and apoptotic signaling pathways. The effect of chrysin (CH), a natural plant flavonoid, and its functional interaction with HMGB‑1, was investigated in a chondrocyte model of OA. Human chondrocytes were pre‑treated with CH, and then subsequently treated with IL‑1β to induce the formation of chondrocytes similar to those found in OA joints. Next, the expression level of HMGB‑1 was determined by immunofluorescence and western blot analysis. Additionally, inflammatory factor expression was measured by ELISA, and cell apoptosis was analyzed with flow cytometry. To further explore the effects of CH, HMGB‑1 expression was silenced following CH treatment with small interfering (si)RNA. The results demonstrated that CH inhibited cell apoptosis, dose‑dependently reduced matrix metalloproteinase (MMP) 13, collagenase and IL‑6 expression, and increased collagen α‑1 (II) chain (COL2A1) expression in human osteoarthritis chondrocytes. These effects of CH were accompanied by decreased HMGB‑1 expression. Additionally, the expression of MMP13, collagenase, IL‑6 and COL2A1, as well as apoptosis, was significantly reduced by HMGB‑1 siRNA. These results demonstrated that HMGB‑1 is critical for the protective effect of CH on human osteoarthritis chondrocytes, including cell apoptosis and inflammatory factor inhibition, which suggests that CH may have potential therapeutic effect in treating OA by protecting human osteoarthritis chondrocytes via HMGB1 suppression.

Role of Forkhead Box O Transcription Factors in Oxidative Stress-Induced Chondrocyte Dysfunction: Possible Therapeutic Target for Osteoarthritis?

Chondrocyte dysfunction occurs during the development of osteoarthritis (OA), typically resulting from a deleterious increase in oxidative stress. Accordingly, strategies for arresting oxidative stress-induced chondrocyte dysfunction may lead to new potential therapeutic targets for OA treatment. Forkhead box O (FoxO) transcription factors have recently been shown to play a protective role in chondrocyte dysfunction through the regulation of inflammation, autophagy, aging, and oxidative stress. They also regulate growth, maturation, and matrix synthesis in chondrocytes. In this review, we discuss the recent progress made in the field of oxidative stress-induced chondrocyte dysfunction. We also discuss the protective role of FoxO transcription factors as potential molecular targets for the treatment of OA. Understanding the function of FoxO transcription factors in the OA pathology may provide new insights that will facilitate the development of next-generation therapies to prevent OA development and to slow OA progression.

Role of Forkhead Box O Transcription Factors in Oxidative Stress-Induced Chondrocyte Dysfunction: Possible Therapeutic Target for Osteoarthritis?

Chondrocyte dysfunction occurs during the development of osteoarthritis (OA), typically resulting from a deleterious increase in oxidative stress. Accordingly, strategies for arresting oxidative stress-induced chondrocyte dysfunction may lead to new potential therapeutic targets for OA treatment. Forkhead box O (FoxO) transcription factors have recently been shown to play a protective role in chondrocyte dysfunction through the regulation of inflammation, autophagy, aging, and oxidative stress. They also regulate growth, maturation, and matrix synthesis in chondrocytes. In this review, we discuss the recent progress made in the field of oxidative stress-induced chondrocyte dysfunction. We also discuss the protective role of FoxO transcription factors as potential molecular targets for the treatment of OA. Understanding the function of FoxO transcription factors in the OA pathology may provide new insights that will facilitate the development of next-generation therapies to prevent OA development and to slow OA progression.

Hydrostatic pressure-generated reactive oxygen species induce osteoarthritic conditions in cartilage pellet cultures

Osteoarthritis (OA) is one of the most common causes of disability and represents a major socio-economic burden. Despite intensive research, the molecular mechanisms responsible for the initiation and progression of OA remain inconclusive. In recent years experimental findings revealed elevated levels of reactive oxygen species (ROS) as a major factor contributing to the onset and progression of OA. Hence, we designed a hydrostatic pressure bioreactor system that is capable of stimulating cartilage cell cultures with elevated ROS levels. Increased ROS levels in the media did not only lead to an inhibition of glycosaminoglycans and collagen II formation but also to a reduction of already formed glycosaminoglycans and collagen II in chondrogenic mesenchymal stem cell pellet cultures. These effects were associated with the elevated activity of matrix metalloproteinases as well as the increased expression of several inflammatory cytokines. ROS activated different signaling pathways including PI3K/Akt and MAPK/ERK which are known to be involved in OA initiation and progression. Utilizing the presented bioreactor system, an OA in vitro model based on the generation of ROS was developed that enables the further investigation of ROS effects on cartilage degradation but can also be used as a versatile tool for anti-oxidative drug testing.

Evidence for Transient Receptor Potential (TRP) Channel Contribution to Arthritis Pain and Pathogenesis

Based on clinical and preclinical evidence, Transient Receptor Potential (TRP) channels have emerged as potential drug targets for the treatment of osteoarthritis, rheumatoid arthritis, and gout. This review summarizes the relevant data supporting a role for various TRP channels in arthritis pain and pathogenesis, as well as the current state of pharmacological efforts to ameliorate arthritis symptoms in patient populations.

Functional and T Cell Receptor Repertoire Analyses of Peripheral Blood and Infrapatellar Fat Pad T Cells in Knee Osteoarthritis

Objective.

Osteoarthritis (OA) is a condition that features inflammation and immune responses of innate and adaptive immunity. The role of T cells in knee OA pathogenesis is still unclear. Our aim was to characterize T cell functions and their clonality in patients with knee OA in peripheral blood (PB) and infrapatellar fat pads (IPFP).

Methods.

We isolated T cells from PB and IPFP of patients with knee OA and PB of healthy individuals and determined soluble mediators produced from these cells. In addition, we performed a clonal analysis of activated CD8+ T cells and compared the T cell receptor β-variable gene chain (TRBV) usages between T cells in PB and IPFP of patients with knee OA.

Results.

Our results suggest that in patients with knee OA, circulating T cells possess a more “cytotoxic” profile or rather impaired cytokine production, but the knee microenvironment allows for these T cells to produce proinflammatory cytokines [interleukin (IL)-1β, IL-6, tumor necrosis factor], IL-17, and interferon-γ within IPFP. Activated CD8+ IPFP T cells carry different repertoire distribution from those present in PB of patients with knee OA. Shared TRBV usage of activated CD8+ IPFP T cells among the 3 patients with knee OA was also observed.

Conclusion.

Our study describes the nature of T cells in knee OA that may be due to “unhealthy” aging or other factors that drive healthy aging T cells into a state of imbalance, thus contributing to the pathogenesis of knee OA.

Cartilage diseases

Hyaline cartilages, fibrocartilages and elastic cartilages play multiple roles in the human body including bearing loads in articular joints and intervertebral discs, providing joint lubrication, forming the external ears and nose, supporting the trachea, and forming the long bones during development and growth. The structure and organization of cartilage's extracellular matrix (ECM) are the primary determinants of normal function. Most diseases involving cartilage lead to dramatic changes in the ECM which can govern disease progression (e.g., in osteoarthritis), cause the main symptoms of the disease (e.g., dwarfism caused by genetically inherited mutations) or occur as collateral damage in pathological processes occurring in other nearby tissues (e.g., osteochondritis dissecans and inflammatory arthropathies). Challenges associated with cartilage diseases include poor understanding of the etiology and pathogenesis, delayed diagnoses due to the aneural nature of the tissue and drug delivery challenges due to the avascular nature of adult cartilages. This narrative review provides an overview of the clinical and pathological features as well as current treatment options available for various cartilage diseases. Late breaking advances are also described in the quest for development and delivery of effective disease modifying drugs for cartilage diseases including osteoarthritis, the most common form of arthritis that affects hundreds of millions of people worldwide.

Anti-inflammatory Effect of DNA Polymeric Molecules in a Cell Model of Osteoarthritis

The DNA polymeric molecules polydeoxynucleotide (PDRN) and polynucleotide (PN) can be used as new alternative treatment for osteoarthritis (OA); however, the underlying mechanisms are not fully understood. In this study, we investigated the effect of PDRN and PN on gene-expression profiles in a cell model of OA using transcriptome analysis. Under hypoxic conditions, human chondrosarcoma cells were stressed for 24 h in the presence of interleukin (IL)-1β and subsequently treated with PDRN, PN, or hyaluronic acid (HA) for another 24 h, followed by transcriptome analysis. The results of the transcriptome study comprising differentially expressed genes were analyzed using the Database of Annotation Visualization and Integrated Discovery program, which yielded Kyoto Encyclopedia of Genes and Genomes pathways. Toll-like receptor (TLR)- and nucleotide-binding oligomerization domain-like receptor (NLR)-signaling pathways were related between the IL-1β group and the group treated with DNA polymeric molecules. The genes involved in the TLR- and NLR-signaling pathways were validated using real-time quantitative polymerase chain reaction and western blot. Among these genes, IL-6, IL-1β, IL-8, and chemokine (C-C motif) ligand 3 were dramatically upregulated in the IL-1β group, but significantly downregulated in the group treated with DNA polymeric molecules. Specifically, PN treatment resulted in a greater decrease in the expression of these genes as compared with PDRN treatment. Both PDRN and PN treatments were involved in the anti-inflammatory response associated with OA progression, with PN treatment exhibiting additional anti-inflammatory properties relative to PDRN treatment. These results provide insight into potential therapeutic approaches involving PDRN and PN treatment of OA.

Inhibition of miR-449a Promotes Cartilage Regeneration and Prevents Progression of Osteoarthritis in In Vivo Rat Models

Traumatic and degenerative lesions of articular cartilage usually progress to osteoarthritis (OA), a leading cause of disability in humans. MicroRNAs (miRNAs) can regulate the differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs) and play important roles in the expression of genes related to OA. However, their functional roles in OA remain poorly understood. Here, we have examined miR-449a, which targets sirtuin 1 (SIRT1) and lymphoid enhancer-binding factor-1 (LEF-1), and observed its effects on damaged cartilage. The levels of chondrogenic markers and miR-449a target genes increased during chondrogenesis in anti-miR-449a-transfected hBMSCs. A locked nucleic acid (LNA)-anti-miR-449a increased cartilage regeneration and expression of type II collagen and aggrecan on the regenerated cartilage surface in acute defect and OA models. Furthermore, intra-articular injection of LNA-anti-miR-449a prevented disease progression in the OA model. Our study indicates that miR-449a may be a novel potential therapeutic target for age-related joint diseases like OA.

MicroRNA-128a represses chondrocyte autophagy and exacerbates knee osteoarthritis by disrupting Atg12

Chondrocyte loss is a prominent feature of osteoarthritis (OA). Autophagy is indispensable in maintaining the metabolic activities of cells exposed to deleterious stress. The contribution of microRNA signaling to chondrocyte autophagy in OA development remains elusive. We uncovered an association between poor autophagy and increased miR-128a expressions in articular chondrocytes of patients with end-stage knee OA and in a rat anterior cruciate ligament transection (ACLT) model for OA development. Cartilage matrix degradation and severe OA histopathology was evident upon forced miR-128a expression within the articular compartment. Intra-articular injections with miR-128a antisense oligonucleotide stabilized chondrocyte autophagy and slowed ACLT-mediated articular tissue destruction, including cartilage erosion, synovitis, osteophyte formation, and subchondral plate damage. In vitro, miR-128 signaling hindered Atg12 expression, LC3-II conversion, and autophagic puncta formation through targeting the 3′-untranslated region of Atg12. It increased apoptotic programs, diminishing cartilage formation capacity of articular chondrocytes. Inactivating histone methyltransferase EZH2 reduced methyl histone H3K27 enrichment in the miR-128a promoter and upregulated miR-128a transcription in inflamed chondrocytes. Taken together, miR-128a-induced Atg12 loss repressed chondrocyte autophagy to aggravate OA progression. EZH2 inactivation caused H3K27 hypomethylation to accelerate miR-128a actions. Interruption of miR-128a signaling attenuated chondrocyte dysfunction and delayed OA development. Our data provide new insights into how miR-128a signaling affects chondrocyte survival and articular cartilage anabolism and highlight the potential of miR-128a targeting therapy to alleviate knee OA.

Effects of Mantra Meditation versus Music Listening on Knee Pain, Function, and Related Outcomes in Older Adults with Knee Osteoarthritis: An Exploratory Randomized Clinical Trial (RCT)

OBJECTIVE

Disease-modifying treatments for OA remain elusive, and commonly used medications can have serious side effects. Although meditation and music listening (ML) have been shown to improve outcomes in certain chronic pain populations, research in OA is sparse. In this pilot RCT, we explore the effects of two mind-body practices, mantra meditation (MM) and ML, on knee pain, function, and related outcomes in adults with knee OA.

METHODS

Twenty-two older ambulatory adults diagnosed with knee OA were randomized to a MM (N=11) or ML program (N=11) and asked to practice 15-20 minutes, twice daily for 8 weeks. Core outcomes included knee pain (Knee Injury and Osteoarthritis Outcome Score [KOOS] and Numeric Rating Scale), knee function (KOOS), and perceived OA severity (Patient Global Assessment). Additional outcomes included perceived stress (Perceived Stress Scale), mood (Profile of Mood States), sleep (Pittsburgh Sleep Quality Index), and health-related quality of life (QOL, SF-36). Participants were assessed at baseline and following completion of the program.

RESULTS

Twenty participants (91%) completed the study (9 MM, 11 ML). Compliance was excellent; participants completed an average of 12.1±0.83 sessions/week. Relative to baseline, participants in both groups demonstrated improvement post-intervention in all core outcomes, including knee pain, function, and perceived OA severity, as well as improvement in mood, perceived stress, and QOL (Physical Health) (p's≤0.05). Relative to ML, the MM group showed greater improvements in overall mood and sleep (p's≤0.04), QOL-Mental Health (p<0.07), kinesiophobia (p=0.09), and two domains of the KOOS (p's<0.09).

CONCLUSIONS

Findings of this exploratory RCT suggest that a simple MM and, possibly, ML program may be effective in reducing knee pain and dysfunction, decreasing stress, and improving mood, sleep, and QOL in adults with knee OA.

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.

Alleviation of Murine Osteoarthritis by Cartilage-Specific Deletion of IκBζ

OBJECTIVE

IκBζ, an atypical IκB family member, regulates gene expression in the nucleus as a transcriptional cofactor. Although IκBζ has been extensively studied in the immune system, its specific roles in osteoarthritis (OA) are currently unknown. The objective of this study was to investigate the potential role of IκBζ in chondrocyte catabolism and OA pathogenesis. We also determined the molecular mechanism underlying its relationship to the transcription factor NF-κB.

METHODS

We determined expression levels of IκBζ in mouse chondrocytes treated with interleukin-1β (IL-1β), in human OA cartilage, and in mouse experimental OA cartilage. Adenovirus-mediated overexpression and small interfering RNA knockdown of IκBζ were performed to determine the impact of IκBζ on catabolic gene expression in vitro. Cartilage-specific IκBζ-transgenic and -knockout mice were generated and used for in vivo studies. Experimental and spontaneous OA were induced by surgical destabilization of the medial meniscus and by aging, respectively. Coimmunoprecipitation assay was used to examine the association between IκBζ and NF-κB subunits.

RESULTS

IκBζ was highly up-regulated in chondrocytes in response to IL-1β and in OA cartilage of human and mouse knee joints. Overexpression of IκBζ in chondrocytes promoted spontaneous OA development by activating chondrocyte catabolism. Genetic ablation of IκBζ in chondrocytes abolished catabolic gene induction by IL-1β and protected against the development of experimental OA. IκBζ formed complexes with NF-κB members to regulate catabolic factor expression.

CONCLUSION

These findings demonstrate a critical role for IκBζ in OA pathogenesis. Inhibition of IκBζ function might be an effective therapeutic approach for OA treatment.

Single-cell RNA-seq analysis reveals the progression of human osteoarthritis

Objectives

Understanding the molecular mechanisms underlying human cartilage degeneration and regeneration is helpful for improving therapeutic strategies for treating osteoarthritis (OA). Here, we report the molecular programmes and lineage progression patterns controlling human OA pathogenesis using single-cell RNA sequencing (scRNA-seq).

Methods

We performed unbiased transcriptome-wide scRNA-seq analysis, computational analysis and histological assays on 1464 chondrocytes from 10 patients with OA undergoing knee arthroplasty surgery. We investigated the relationship between transcriptional programmes of the OA landscape and clinical outcome using severity index and correspondence analysis.

Results

We identified seven molecularly defined populations of chondrocytes in the human OA cartilage, including three novel phenotypes with distinct functions. We presented gene expression profiles at different OA stages at single-cell resolution. We found a potential transition among proliferative chondrocytes, prehypertrophic chondrocytes and hypertrophic chondrocytes (HTCs) and defined a new subdivision within HTCs. We revealed novel markers for cartilage progenitor cells (CPCs) and demonstrated a relationship between CPCs and fibrocartilage chondrocytes using computational analysis. Notably, we derived predictive targets with respect to clinical outcomes and clarified the role of different cell types for the early diagnosis and treatment of OA.

Conclusions

Our results provide new insights into chondrocyte taxonomy and present potential clues for effective and functional manipulation of human OA cartilage regeneration that could lead to improved health.

Fetal articular cartilage regeneration versus adult fibrocartilaginous repair: secretome proteomics unravels molecular mechanisms in an ovine model

Osteoarthritis (OA), a degenerative joint disease characterized by progressive cartilage degeneration, is one of the leading causes of disability worldwide owing to the limited regenerative capacity of adult articular cartilage. Currently, there are no disease-modifying pharmacological or surgical therapies for OA. Fetal mammals, in contrast to adults, are capable of regenerating injured cartilage in the first two trimesters of gestation. A deeper understanding of the properties intrinsic to the response of fetal tissue to injury would allow us to modulate the way in which adult tissue responds to injury. In this study, we employed secretome proteomics to compare fetal and adult protein regulation in response to cartilage injury using an ovine cartilage defect model. The most relevant events comprised proteins associated with the immune response and inflammation, proteins specific for cartilage tissue and cartilage development, and proteins involved in cell growth and proliferation. Alarmins S100A8, S100A9 and S100A12 and coiled-coil domain containing 88A (CCDC88A), which are associated with inflammatory processes, were found to be significantly upregulated following injury in adult, but not in fetal animals. By contrast, cartilage-specific proteins like proteoglycan 4 were upregulated in response to injury only in fetal sheep postinjury. Our results demonstrate the power and relevance of the ovine fetal cartilage regeneration model presented here for the first time. The identification of previously unrecognized modulatory proteins that plausibly affect the healing process holds great promise for potential therapeutic interventions.

Summary: Secretome proteomics identifies differential regulation of inflammation modulators during fetal and adult articular cartilage defect healing, offering novel strategies for therapy.

Specnuezhenide Decreases Interleukin-1β-Induced Inflammation in Rat Chondrocytes and Reduces Joint Destruction in Osteoarthritic Rats

As a chronic disease, osteoarthritis (OA) leads to the degradation of both cartilage and subchondral bone, its development being mediated by proinflammatory cytokines like interleukin-1β. In the present study, the anti-inflammatory effect of specnuezhenide (SPN) in OA and its underlying mechanism were studied in vitro and in vivo. The results showed that SPN decreases the expression of cartilage matrix-degrading enzymes and the activation of NF-κB and wnt/β-catenin signaling, and increases chondrocyte-specific gene expression in IL-1β-induced inflammation in chondrocytes. Furthermore, SPN treatment prevents the degeneration of both cartilage and subchondral bone in a rat model of OA. To the best of our knowledge, this study is the first to report that SPN decreases interleukin-1β-induced inflammation in rat chondrocytes by inhibiting the activation of the NF-κB and wnt/β-catenin pathways, and, thus, has therapeutic potential in the treatment of OA.

Role of the Inflammation-Autophagy-Senescence Integrative Network in Osteoarthritis

Osteoarthritis is the most common musculoskeletal disease causing chronic disability in adults. Studying cartilage aging, chondrocyte senescence, inflammation, and autophagy mechanisms have identified promising targets and pathways with clinical translatability potential. In this review, we highlight the most recent mechanistic and therapeutic preclinical models of aging with particular relevance in the context of articular cartilage and OA. Evidence supporting the role of metabolism, nuclear receptors and transcription factors, cell senescence, and circadian rhythms in the development of musculoskeletal system degeneration assure further translational efforts. This information might be useful not only to propose hypothesis and advanced models to study the molecular mechanisms underlying joint degeneration, but also to translate our knowledge into novel disease-modifying therapies for OA.

C5a aggravates dysfunction of the articular cartilage and synovial fluid in rats with knee joint immobilization

Degenerative alterations in articular cartilage are involved in the pathogenesis of osteoarthritis. The present study aimed to evaluate the role of complement component 5a (C5a) in osteoarthritic alterations in the articular cartilage and synovialis via a joint immobilization (IM) rat model. Rats were assigned to three groups: Control, IM and IM+anti‑C5a antibody (IM+anti‑C5a) groups. A terminal deoxynucleotidyl transferase dUTP nick end labeling assay and hematoxylin and eosin staining were used to evaluate the morphological alterations in the articular cartilage and synovialis. Reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) analysis, immunohistochemical analysis and western blotting were used to evaluate C5a expression in the articular cartilage and synovialis. An ELISA was used to evaluate C5a‑induced alterations in interleukin (IL)‑1β, IL‑17A and tumor necrosis factor (TNF)‑α levels in the serum and joint fluid. The results demonstrated that knee joint immobilization induced destruction of knee joint synovial fluid and cartilage in the IM and IM+anti‑C5a antibody groups. Immobilization significantly increased the expression levels of C5a in serum and joint fluid in the IM group. Immunohistochemistry, western blotting and RT‑qPCR analysis illustrated markedly increased expression of C5a in the IM group. Immobilization markedly increased the IL‑1β, IL‑17A and TNF‑α expression levels in the serum and joint fluid in the IM group. Anti‑C5a was able to decrease immobilization‑induced alterations in morphology and cytokines compared with the IM group. The expression of C5a was increased in synoviocytes and joint cartilage in the IM model. Pro‑inflammatory cytokines, including TNF‑α and IL‑1β were released in the activated synoviocytes via the induction of C5a, suggesting that C5a serves an important role in joint inflammatory processes.

Melatonin rescued interleukin 1β-impaired chondrogenesis of human mesenchymal stem cells

BACKGROUND

Osteoarthritis (OA) is a widespread arthritic disease and a primary cause of disability. Increasing evidence suggests that inflammation has a pivotal part in its pathogenesis. Interleukin-1β (IL-1β) is a primary mediator of local inflammatory processes in OA. Current therapies for OA mainly focus on the symptoms of the advanced stage of the disease. The possible utilization of bone marrow mesenchymal stem cells (BMSCs) to regenerate cartilage is an appealing method, but in the case of OA requires chondrogenesis to take place within an inflamed environment. Our previous study showed that melatonin (MLT) can promote chondrogenic differentiation of MSCs, but whether MLT can rescue IL-1β-impaired chondrogenesis in human BMSCs has not yet been established. MLT, which can have anti-inflammatory and prochondrogenic effects, has demonstrated potential in defeating IL-1β-induced inhibition of chondrogenesis and further study should be conducted.

METHODS

Human bone marrow-derived MSCs were separated and cultured based on our system that was already documented. A high-density micromass culture system was used for the chondrogenic differentiation of human BMSCs, which was also described previously. Human BMSCs were induced for chondrogenesis for 7, 14, and 21 days with the treatment of IL-1β and MLT. The cultured cartilage pellets were then evaluated by morphology, extracellular matrix accumulation, and chondrogenic, metabolic, and apoptotic marker expression. Furthermore, cell apoptosis was assessed by TUNEL assay. The phosphorylation level P65 and IκBα of the NF-κB pathway activity was explored on day 21 of chondrogenic differentiation of BMSCs.

RESULTS

The current evaluation showed that MLT can save IL-1β-impaired chondrogenesis of human BMSCs in different aspects. Firstly, MLT can restore the chondrogenic pellet size, and rescue matrix synthesis and accumulation. Secondly, MLT can upregulate chondrogenic marker COL2A1 expression at both mRNA and protein levels, and also regulate the expression levels of other chondrogenic markers like ACAN, SOX9, and COL10A1 in the presence of IL-1β. Thirdly, MLT can maintain the metabolic balance of the chondrogenic process by suppressing expression of catabolic genes, such as MMP, MMP13, and ADAMTS4. Furthermore, MLT can subdue IL-1β-induced cell apoptosis of BMSCs throughout chondrogenesis. Meanwhile, MLT suppressed the phosphorylation level of P65 and IκBα, which were elevated by IL-1β treatment, indicating that MLT can attenuate the IL-1β-induced activation of NF-κB signaling.

CONCLUSION

The current evaluation showed that MLT can save IL-1β-impaired chondrogenesis of human BMSCs by restoring the pellet size and matrix accumulation, and maintaining the metabolic balance, reducing cell apoptosis. Our study also showed that MLT can attenuate the IL-1β-induced activation of the NF-κB signaling pathway, which is the most important pathway downstream of IL-1β, and plays a crucial role in inflammation, apoptosis, and metabolism. Thus, MLT has prospects for treating OA due to its multifaceted functions, such as mitigating inflammation, maintaining metabolic balance, and mitigating apoptosis.

Icariin Activates Autophagy via Down-Regulation of the NF-κB Signaling-Mediated Apoptosis in Chondrocytes

Osteoarthritis (OA) is a common chronic and degenerative joint condition that is mainly characterized by cartilage degradation, osteophyte formation, and joint stiffness. The NF-κB signaling pathway in inflammation, autophagy, and apoptosis plays a prominent role in the progression of OA. Icariin, a prenylated flavonol glycoside extracted from Epimedium, have been proven to exert anti-osteoporotic and anti-inflammatory effects in OA. However, the action mechanisms of its effect on chondrocytes have yet to be elucidated. In the present study, we demonstrated that the in vitro therapeutic effects of icariin on rat chondrocytes in a dose-dependent manner. We found that TNF-α induced the production of IL-1, IL-6, IL-12, reactive oxygen species (ROS), nitric oxide (NO), Caspase-3, and Caspase-9 in chondrocytes. We also provided evidence that TNF-α inhibited autophagy markers (Atg 5, Atg 7) and prevented LC3 I translate to LC3 II. Furthermore, TNF-α induced matrix metalloproteinase (MMP)3 and MMP9 expression. The negative effects of TNF-α on chondrocytes can be partially blocked by treating with icariin or ammonium pyrrolidinedithiocarbamate (PDTC, an NF-κB inhibitor). The present study data also suggested that icariin suppressed both TNF-α-stimulated p65 nuclear translocation and IκBα protein degradation. These results indicated that icariin protected against OA by suppressing inflammatory cytokines and apoptosis, through activation of autophagy via NF-κB inhibition. In conclusion, icariin appears to favorably modulate autophagy and apoptosis in chondrocytes making it a promising compound for cartilage tissue engineering in the treatment of OA.

Schisandrin B ameliorated chondrocytes inflammation and osteoarthritis via suppression of NF-κB and MAPK signal pathways

Introduction

Osteoarthritis (OA) is the most prevalent joint disorder in the elderly population, and inflammatory mediators like IL-1β were thought to play central roles in its development. Schisandrin B, the main active component derived from Schisandra chinensis, exhibited anti-oxidative and antiinflammatory properties.

Methods

In the present study, the protective effect and the underlying mechanism of Schisan-drin B on OA was investigated in vivo and in vitro.

Results

The results showed that Schisandrin B decreased IL-1β-induced upregulation of matrix metalloproteinase 3 (MMP3), MMP13, IL-6, and inducible nitric oxide synthase (iNOS) and increased IL-1β-induced downregulation of collagen II, aggrecan, and sox9 as well. Schisandrin B significantly decreased IL-1β-induced p65 phosphorylation and nuclear translocation of p65 in rat chondrocytes. Mitogen-activated protein kinase (MAPK) activation was also inhibited by Schisandrin B, as evidenced by the reduction of p38, extracellular signal-regulated kinase (Erk), and c-Jun amino-terminal kinase (Jnk) phosphorylation. In addition, Schisandrin B prevented cartilage degeneration in rat OA model with significantly lower Mankin’s score than the control group.

Conclusion

Our study demonstrated that Schisandrin B ameliorated chondrocytes inflammation and OA via suppression of nuclear factor-κB (NF-κB) and MAPK signal pathways, indicating a therapeutic potential in OA treatment.

CCL17 blockade as a therapy for osteoarthritis pain and disease

Background

Granulocyte macrophage-colony stimulating factor (GM-CSF) has been implicated in the pathogenesis of a number of inflammatory diseases and in osteoarthritis (OA). We identified previously a new GM-CSF→Jmjd3→interferon regulatory factor 4 (IRF4)→chemokine (c-c motif) ligand 17 (CCL17) pathway, which is important for the development of inflammatory arthritis pain and disease. Tumour necrosis factor (TNF) can also be linked with this pathway. Here we investigated the involvement of the pathway in OA pain and disease development using the GM-CSF-dependent collagenase-induced OA (CiOA) model.

Methods

CiOA was induced in C57BL/6 wild-type (WT), Irf4^−/−, Ccl17^E/E, Ccr4^−/−, Tnf^−/− and GM-CSF^−/− mice. Additionally, therapeutic targeting of CCL17, Jmjd3 and cyclooxygenase 2 (COX-2) was evaluated. Development of pain (assessment of weight distribution) and OA disease (histologic scoring of synovitis, cartilage destruction and osteophyte size) were assessed. Synovial joint cells, including neutrophils, macrophages, fibroblasts and endothelial cells, were isolated (cell sorting) and gene expression analyzed (quantitative PCR).

Results

Studies in the gene-deficient mice indicated that IRF4, CCL17 and the CCL17 receptor, CCR4, but not TNF, were required for CiOA pain and optimal cartilage destruction and osteophyte size. Therapeutic neutralization of CCL17 and Jmjd3 ameliorated both pain and disease, whereas the COX-2 inhibitor only ameliorated pain. In the synovium Ccl17 mRNA was expressed only in the macrophages in a GM-CSF-dependent and IRF4-dependent manner.

Conclusions

The GM-CSF→Jmjd3→IRF4→CCL17 pathway is important for the development of CiOA, with CCL17 thus being a potential therapeutic target for the treatment of both OA pain and disease.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1560-9) contains supplementary material, which is available to authorized users.

Senescent cells and osteoarthritis: a painful connection

Senescent cells (SnCs) are associated with age-related pathologies. Osteoarthritis is a chronic disease characterized by pain, loss of cartilage, and joint inflammation, and its incidence increases with age. For years, the presence of SnCs in cartilage isolated from patients undergoing total knee artificial implants has been noted, but these cells' relevance to disease was unclear. In this Review, we summarize current knowledge of SnCs in the multiple tissues that constitute the articular joint. New evidence for the causative role of SnCs in the development of posttraumatic and age-related arthritis is reviewed along with the therapeutic benefit of SnC clearance. As part of their senescence-associated secretory phenotype, SnCs secrete cytokines that impact the immune system and its response to joint tissue trauma. We present concepts of the immune response to tissue trauma as well as the interactions with SnCs and the local tissue environment. Finally, we discuss therapeutic implications of targeting SnCs in treating osteoarthritis.

Intra-articular injection of methylprednisolone for reducing pain in knee osteoarthritis: A systematic review and meta-analysis

BACKGROUND

To evaluate the efficacy and safety of intra-articular methylprednisolone for reducing pain in patients with knee osteoarthritis.

METHODS

We conduct electronic searches of Medline (1966-2017.11), PubMed (1966-2017.11), Embase (1980-2017.11), ScienceDirect (1985-2017.11), and the Cochrane Library (1900-2017.11) for randomized clinical trials comparing the use of methylprednisolone to treat knee osteoarthritis. The primary outcomes are Western Ontario and McMaster Universities Arthritis Index (WOMAC) pain scores and WOMAC function scores. Each outcome was combined and calculated using the statistical software STATA 12.0. Fixed/random effect model was adopted based on the heterogeneity tested by I statistic.

RESULTS

A total of 739 patients were analyzed across 4 randomized controlled trials (RCTs). The present meta-analysis revealed that there were significant differences between groups regarding the WOMAC pain scores at 4 weeks (WMD = -1.384, 95% CI: -1.975 to -0.793, P = .000), 12 weeks (WMD = -1.587, 95% CI: -2.489 to -0.685, P = .001), and 24 weeks (WMD = -1.563, 95% CI: -2.245 to -0.881, P = .000). Significant differences were identified in terms of physical function at 4 weeks (WMD = -7.925, 95% CI: -13.359 to -2.491, P = .004), 12 weeks (WMD = -7.314, 95% CI: -13.308 to -1.320, P = .117), and 24 weeks (WMD = -6.484, 95% CI: -11.256 to -1.711, P = .008).

CONCLUSION

Intra-articular methylprednisolone injection was associated with an improved pain relief and physical function in patients with knee osteoarthritis. Additionally, no severe adverse effects were observed. Due to the limited quality of the evidence currently available, higher quality RCTs were required.

Treatment of Osteoarthritis With Low-level Laser Therapy, Acupuncture, and Herbal Therapy: A Case Report

Osteoarthritis is a challenging diagnosis to navigate and treat. Management options range from nonpharmacological agents to surgical repair. No specific combination of therapies has yet been identified for optimal management although a variety of therapeutic options have been studied. This case report details the use of low-level laser therapy, acupuncture, and herbal medicine in a 64-y-old female with radiographically confirmed osteoarthritis. Near-complete resolution of her symptoms was associated with the multiple therapies outlined in this case report.

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

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

CLINICAL SIGNIFICANCE

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

Rescue of Learning and Memory Deficits in the Human Nonsyndromic Intellectual Disability Cereblon Knock-Out Mouse Model by Targeting the AMP-Activated Protein Kinase-mTORC1 Translational Pathway

A homozygous nonsense mutation in the cereblon (CRBN) gene results in autosomal recessive, nonsyndromic intellectual disability that is devoid of other phenotypic features, suggesting a critical role of CRBN in mediating learning and memory. In this study, we demonstrate that adult male Crbn knock-out (Crbn^KO) mice exhibit deficits in hippocampal-dependent learning and memory tasks that are recapitulated by focal knock-out of Crbn in the adult dorsal hippocampus, with no changes in social or repetitive behavior. Cellular studies identify deficits in long-term potentiation at Schaffer collateral CA1 synapses. We further show that Crbn is robustly expressed in the mouse hippocampus and Crbn^KO mice exhibit hyperphosphorylated levels of AMPKα (Thr172). Examination of processes downstream of AMP-activated protein kinase (AMPK) finds that Crbn^KO mice have a selective impairment in mediators of the mTORC1 translation initiation pathway in parallel with lower protein levels of postsynaptic density glutamatergic proteins and higher levels of excitatory presynaptic markers in the hippocampus with no change in markers of the unfolded protein response or autophagy pathways. Acute pharmacological inhibition of AMPK activity in adult Crbn^KO mice rescues learning and memory deficits and normalizes hippocampal mTORC1 activity and postsynaptic glutamatergic proteins without altering excitatory presynaptic markers. Thus, this study identifies that loss of Crbn results in learning, memory, and synaptic defects as a consequence of exaggerated AMPK activity, inhibition of mTORC1 signaling, and decreased glutamatergic synaptic proteins. Thus, Crbn^KO mice serve as an ideal model of intellectual disability to further explore molecular mechanisms of learning and memory.SIGNIFICANCE STATEMENT Intellectual disability (ID) is one of the most common neurodevelopmental disorders. The cereblon (CRBN) gene has been linked to autosomal recessive, nonsyndromic ID, characterized by an intelligence quotient between 50 and 70 but devoid of other phenotypic features, making cereblon an ideal protein for the study of the fundamental aspects of learning and memory. Here, using the cereblon knock-out mouse model, we show that cereblon deficiency disrupts learning, memory, and synaptic function via AMP-activated protein kinase hyperactivity, downregulation of mTORC1, and dysregulation of excitatory synapses, with no changes in social or repetitive behaviors, consistent with findings in the human population. This establishes the cereblon knock-out mouse as a model of pure ID without the confounding behavioral phenotypes associated with other current models of ID.

Glucagon-like peptide-1 receptor regulates endoplasmic reticulum stress-induced apoptosis and the associated inflammatory response in chondrocytes and the progression of osteoarthritis in rat

Treatments for osteoarthritis (OA) are designed to restore chondrocyte function and inhibit cell apoptosis. Previous studies have shown that activation of the glucagon-like peptide-1 receptor (GLP-1R) leads to anti-inflammatory and anti-apoptotic effects. However, the role of GLP-1R in the pathological process of OA is unclear. In present work, we aimed to demonstrate the potential effect of GLP-1R on chondrocytes and elucidate its underlying mechanisms. We found that activation of GLP-1R with liraglutide could protect chondrocytes against endoplasmic reticulum stress and apoptosis induced by interleukin (IL)-1β or triglycerides (TGs). These effects were partially attenuated by GLP-1R small interfering RNA treatment. Moreover, inhibiting PI3K/Akt signaling abolished the protective effects of GLP-1R by increase the apoptosis activity and ER stress. Activating GLP-1R suppressed the nuclear factor kappa-B pathway, decreased the release of inflammatory mediators (IL-6, tumor necrosis factor α), and reduced matrix catabolism in TG-treated chondrocytes; these effects were abolished by GLP-1R knockdown. In the end, liraglutide attenuated rat cartilage degeneration in an OA model of knee joints in vivo. Our results indicate that GLP-1R is a therapeutic target for the treatment of OA, and that liraglutide could be a therapeutic candidate for this clinical application.

Emerging Players at the Intersection of Chondrocyte Loss of Maturational Arrest, Oxidative Stress, Senescence and Low-Grade Inflammation in Osteoarthritis

The prevalence of Osteoarthritis (OA) is increasing because of the progressive aging and unhealthy lifestyle. These risk factors trigger OA by removing constraints that keep the tightly regulated low turnover of the extracellular matrix (ECM) of articular cartilage, the correct chondrocyte phenotype, and the functionality of major homeostatic mechanisms, such as mitophagy, that allows for the clearance of dysfunctional mitochondria, preventing increased production of reactive oxygen species, oxidative stress, and senescence. After OA onset, the presence of ECM degradation products is perceived as a “danger” signal by the chondrocytes and the synovial macrophages that release alarmins with autocrine/paracrine effects on the same cells. Alarmins trigger innate immunity in the joint, with important systemic crosstalks that explain the beneficial effects of dietary interventions and improved lifestyle. Alarmins also boost low-grade inflammation: the release of inflammatory molecules and chemokines sustained by continuous triggering of NF-κB within an altered cellular setting that allows its higher transcriptional activity. Chemokines exert pleiotropic functions in OA, including the recruitment of inflammatory cells and the induction of ECM remodeling. Some chemokines have been successfully targeted to attenuate structural damage or pain in OA animal models. This represents a promising strategy for the future management of human OA.

The pericellular hyaluronan of articular chondrocytes

The story of hyaluronan in articular cartilage, pericellular hyaluronan in particular, essentially is also the story of aggrecan. Without properly tethered aggrecan, the load bearing function of cartilage is compromised. The anchorage of aggrecan to the cell surface only occurs due to the binding of aggrecan to hyaluronan-with hyaluronan tethered either to a hyaluronan synthase or by multivalent binding to CD44. In this review, details of hyaluronan synthesis are discussed including how HAS2 production of hyaluronan is necessary for normal chondrocyte development and matrix assembly, how an abundance or deficit of pericellular hyaluronan alters chondrocyte metabolism, and whether hyaluronan size matters or changes with aging or disease. The biomechanical role and matrix assembly function of hyaluronan in addition to the functions of hyaluronidases are discussed. The turnover of hyaluronan is considered including mechanisms by which its turnover, at least in part, is mediated by endocytosis by chondrocytes and regulated by aggrecan degradation. Differences between turnover and clearance of newly synthesized hyaluronan and aggrecan versus the half-life of hyaluronan remaining within the inter-territorial matrix of cartilage are discussed. The release of neutral pH-acting hyaluronidase activity remains one unanswered question concerning the loss of cartilage hyaluronan in osteoarthritis. Signaling events driven by changes in hyaluronan-chondrocyte interactions may involve a chaperone function of CD44 with other receptors/cofactors as well as the changes in hyaluronan production functioning as a metabolic rheostat.

Psychosocial factors partially mediate the relationship between mechanical hyperalgesia and self-reported pain

Background and aims:

Amplification of sensory signalling within the nervous system along with psychosocial factors contributes to the variation and severity of knee pain. Quantitative sensory testing (QST) is a non-invasive test battery that assesses sensory perception of thermal, pressure, mechanical and vibration stimuli used in the assessment of pain. Psychosocial factors also have an important role in explaining the occurrence of pain. The aim was to determine whether QST measures were associated with self-reported pain, and whether those associations were mediated by psychosocial factors.

Methods:

Participants with knee pain identified from a population-based cohort completed a tender point count and a reduced QST battery of thermal, mechanical and pressure pain thresholds, temporal summation, mechanical pain sensitivity (MPS), dynamic mechanical allodynia (DMA) and vibration detection threshold performed following the protocol by the German Research Network on Neuropathic Pain. QST assessments were performed at the most painful knee and opposite forearm (if pain-free). Participants were asked to score for their global and knee pain intensities within the past month (range 0–10), and complete questionnaire items investigating anxiety, depression, illness perceptions, pain catastrophising, and physical functioning. QST measures (independent variable) significantly correlated (Spearman’s rho) with self-reported pain intensity (dependent variable) were included in structural equation models with psychosocial factors (latent mediators).

Results:

Seventy-two participants were recruited with 61 participants (36 women; median age 64 years) with complete data included in subsequent analyses. Tender point count was significantly correlated with global pain intensity. DMA at the knee and MPS at the most painful knee and opposite pain-free forearm were significantly correlated with both global pain and knee pain intensities. Psychosocial factors including pain catastrophising sub-scales (rumination and helplessness) and illness perceptions (consequences and concern) were significant partial mediators of the association with global pain intensity when loaded on to a latent mediator for: tender point count [75% total effect; 95% confidence interval (CI) 22%, 100%]; MPS at the knee (49%; 12%, 86%); and DMA at the knee (63%; 5%, 100%). Latent psychosocial factors were also significant partial mediators of the association between pain intensity at the tested knee with MPS at the knee (30%; 2%, 58%), but not for DMA at the knee.

Conclusions:

Measures of mechanical hyperalgesia at the most painful knee and pain-free opposite forearm were associated with increased knee and global pain indicative of altered central processing. Psychosocial factors were significant partial mediators, highlighting the importance of the central integration of emotional processing in pain perception.

Implications:

Associations between mechanical hyperalgesia at the forearm and knee, psychosocial factors and increased levels of clinical global and knee pain intensity provide evidence of altered central processing as a key mechanism in knee pain, with psychological factors playing a key role in the expression of clinical pain.

Osteoarthritis and the Complement Cascade

Accumulating evidence demonstrates that complement activation is involved in the pathogenesis of osteoarthritis (OA). However, the intimate complement regulation and cross talk with other signaling pathways in joint-associated tissues remain incompletely understood. Recent insights are summarized and discussed here, to put together a more comprehensive picture of complement involvement in OA pathogenesis. Complement is regulated by several catabolic and inflammatory mediators playing a key role in OA. It seems to be involved in many processes observed during OA development and progression, such as extracellular cartilage matrix (ECM) degradation, chondrocyte and synoviocyte inflammatory responses, cell lysis, synovitis, disbalanced bone remodeling, osteophyte formation, and stem cell recruitment, as well as cartilage angiogenesis. In reverse, complement can be activated by various ECM components and their cleavage products, which are released during OA-associated cartilage degradation. There are, however, some other cartilage ECM components that can inhibit complement, underlining the diverse effects of ECM on the complement activation. It is hypothesized that complement might also be directly activated by mechanical stress, thereby contributing to OA. The question arises whether keeping the complement activation in balance could represent a future therapeutic strategy in OA treatment and in the prevention of its progression.

Rosmarinic acid down-regulates NO and PGE2 expression via MAPK pathway in rat chondrocytes

Rosmarinic acid (RosA) is a water-soluble polyphenol, which can be isolated from many herbs such as orthosiphon diffuses and rosmarinus officinalis. Previous studies have shown that RosA possesses various biological properties. In this study, we investigate the anti-osteoarthritic effects of RosA in rat articular chondrocytes. Chondrocytes were pre-treated with RosA, followed by the stimulation of IL-1β. Real-time PCR and Western blot were performed to detect the expression of matrix metalloproteinase (MMP)-1, MMP-3 and MMP-13. Nitric oxide and PGE2 production were measured by Griess reagent and enzyme-linked immunosorbent assay (ELISA). The expression of mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) was also investigated by Western blot analysis. We found that RosA down-regulated the MMPs expression as well as nitric oxide and PGE2 production in IL-1β-induced chondrocytes. In addition, RosA inhibited p38 and JNK phosphorylation as well as p65 translocation. The results suggest that RosA may be considered a possible agent in the treatment of OA.

Vitexin alleviates ER-stress-activated apoptosis and the related inflammation in chondrocytes and inhibits the degeneration of cartilage in rats

Excessive extracellular matrix degradation and chondrocyte apoptosis are the pathological features of osteoarthritis (OA).

Mesenchymal Stromal/stem Cell-derived Extracellular Vesicles Promote Human Cartilage Regeneration In Vitro

Osteoarthritis (OA) is a rheumatic disease leading to chronic pain and disability with no effective treatment available. Recently, allogeneic human mesenchymal stromal/stem cells (MSC) entered clinical trials as a novel therapy for OA. Increasing evidence suggests that therapeutic efficacy of MSC depends on paracrine signalling. Here we investigated the role of extracellular vesicles (EVs) secreted by human bone marrow derived MSC (BMMSC) in human OA cartilage repair.

Methods: To test the effect of BMMSC-EVs on OA cartilage inflammation, TNF-alpha-stimulated OA chondrocyte monolayer cultures were treated with BMMSC-EVs and pro-inflammatory gene expression was measured by qRT-PCR after 48 h. To assess the impact of BMMSC-EVs on cartilage regeneration, BMMSC-EVs were added to the regeneration cultures of human OA chondrocytes, which were analyzed after 4 weeks for glycosaminoglycan content by 1,9-dimethylmethylene blue (DMMB) assay. Furthermore, paraffin sections of the regenerated tissue were stained for proteoglycans (safranin-O) and type II collagen (immunostaining).

Results: We show that BMMSC-EVs inhibit the adverse effects of inflammatory mediators on cartilage homeostasis. When co-cultured with OA chondrocytes, BMMSC-EVs abrogated the TNF-alpha-mediated upregulation of COX2 and pro-inflammatory interleukins and inhibited TNF-alpha-induced collagenase activity. BMMSC-EVs also promoted cartilage regeneration in vitro. Addition of BMMSC-EVs to cultures of chondrocytes isolated from OA patients stimulated production of proteoglycans and type II collagen by these cells.

Conclusion: Our data demonstrate that BMMSC-EVs can be important mediators of cartilage repair and hold great promise as a novel therapeutic for cartilage regeneration and osteoarthritis.