The expression of SIRT1 in articular cartilage of patients with knee osteoarthritis and its correlation with disease severity

Effectiveness of extracorporeal shock wave therapy on functional ability in grade IV knee osteoarthritis - a randomized controlled trial

Extracorporeal shockwave therapy (ESWT) is a non-invasive physical therapy intervention that has emerged in the recent past to address the upswing of osteoarthritis (OA). However, insufficient evidence is present to prove the efficacy of ESWT on grade IV knee osteoarthritis (KOA). The present study aimed to examine the effects of ESWT on functional ability in patients suffering from grade IV KOA. Thirty volunteers aged 45-60 years with grade IV primary KOA diagnosed by an orthopaedic surgeon based on the Kellgren-Lawrence score participated in the study. The participants were equally and randomly divided into two groups (i.e. experimental and control), with 15 participants in each group. The participants in the control group performed conventional physiotherapy (CPT) that included ultrasound therapy, isometric quadriceps, SLR and isometric hip adductor strengthening exercises. The participants in the experimental group received ESWT in addition to CPT. Lower extremity functional scale (LEFS) score was measured before and after the four weeks of intervention. In both groups, a statistically significant (p = 0.001) improvement in LEFS was observed. In the experimental groups, it improved by 81.92% and in the control groups by 48.15%. A statistically significant (p < 0.001) difference was observed in LEFS post-intervention values between both groups. As demonstrated by our trial results, the addition of ESWT to the CPT program will yield beneficial results in ameliorating the functional disability in patients with primary KOA (grade IV). Further studies are needed to confirm and apply these findings to a larger cohort.

Astaxanthin reduces inflammation and promotes a chondrogenic phenotype by upregulating SIRT1 in osteoarthritis

OBJECTIVE

To investigate the effects of astaxanthin (AST) on mouse osteoarthritis (OA) and lipopolysaccharide (LPS)-induced ATDC5 cell damage and to explore whether SIRT1 protein plays a role.

METHODS

In this study, some mouse OA models were constructed by anterior cruciate ligament transection (ACLT). Imaging, molecular biology and histopathology methods were used to study the effect of AST administration on traumatic OA in mice. In addition, LPS was used to stimulate ATDC5 cells to mimic the inflammatory response of OA. The effects of AST on the cell activity, inflammatory cytokines, matrix metalloproteinases and collagen type II levels were studied by CCK8 activity assay, reverse transcription polymerase chain reaction and protein imprinting. The role of SIRT1 protein was also detected.

RESULTS

In the mouse OA model, the articular surface collapsed, the articular cartilage thickness and cartilage matrix protein abundance were significantly decreased, while the expression of inflammatory cytokines and matrix metalloproteinases was increased; but AST treatment reversed these effects. Meanwhile, AST pretreatment could partially reverse LPS-induced ATDC5 cell damage and upregulate SIRT1 expression, but this protective effect of AST was attenuated by concurrent administration of the SIRT1 inhibitor Ex527.

CONCLUSION

AST can protect against the early stages of OA by affecting SIRT1 signalling, suggesting that AST might be a potential therapeutic agent for OA treatment.

Sirtuin 1 in osteoarthritis: Perspectives on regulating glucose metabolism

Osteoarthritis (OA) is a degenerative disease characterised by articular cartilage destruction, and its complex aetiology contributes to suboptimal clinical treatment outcomes. A close association exists between glucose metabolism dysregulation and OA pathogenesis. Owing to the unique environment of low oxygen and glucose concentrations, chondrocytes rely heavily on their glycolytic capacity, exhibiting distinct spatiotemporal differences. However, under pathological stimulation, chondrocytes undergo excessive glycolytic activity while mitochondrial respiration and other branches of glucose metabolism are compromised. This metabolic change induces cartilage degeneration by reprogramming the inflammatory responses. Sirtuins, a highly conserved family of nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases, regulate glucose metabolism in response to energy fluctuations in different cellular compartments，alleviating metabolic stress. SIRT1, the most extensively studied sirtuin, participates in maintaining glucose homeostasis in almost all key metabolic tissues. While actively contributing to the OA progression and displaying diverse biological effects in cartilage protection, SIRT1's role in regulating glucose metabolism in chondrocytes has not received sufficient attention. This review focuses on discussing the beneficial role of SIRT1 in OA progression from a metabolic regulation perspective based on elucidating the primary characteristics of chondrocyte glucose metabolism. We also summarise the potential mechanisms and therapeutic strategies targeting SIRT1 in chondrocytes to guide clinical practice and explore novel therapeutic directions.

n-3 polyunsaturated fatty acids alleviate the progression of obesity-related osteoarthritis and protect cartilage through inhibiting the HMGB1-RAGE/TLR4 signaling pathway

Osteoarthritis (OA) is a common joint degenerative disease. There is currently no cure for OA. Dietary fatty acids have potential value in the prevention and treatment of OA. n-3 polyunsaturated fatty acids (PUFAs) have anti-inflammatory effects, but their anti-OA mechanism remains unclear. High-mobility group box 1 (HMGB1) promotes inflammation and participates the pathogenesis of OA. The purpose of this study was to investigate the protective effect of n-3 PUFAs on cartilage and whether n-3 PUFAs could exert an anti-OA effect through inhibiting HMGB1-RAGE/TLR4 signaling pathway. We established an obesity-related post-traumatic OA mice model and an in vitro study was conducted to explore the regulatory mechanism of n-3 PUFAs on HMGB1 and its signal pathway against OA. We found that diet rich in n-3 PUFAs alleviated OA-like lesions of articular cartilage with the decrease of HMGB1-RAGE/TLR4 signaling protein in mice. In SW1353 cells, DHA significantly reduced the expression of HMGB1-RAGE/TLR4 signaling protein which was up-regulated by IL-1β stimulation. HMGB1 overexpression reversed the inhibitory effect of DHA on HMGB1-RAGE/TLR4 signaling pathway. The activation of SIRT1 may participate the inhibitory effect of DHA on HMGB1-RAGE/TLR4 signaling pathway. In conclusion, n-3 PUFAs could attenuate the progression of obesity-related OA and exert protective effect on cartilage by inhibiting HMGB1-RAGE/TLR4 signaling pathway, which may be associated with the activation of SIRT1. Dietary n-3 PUFAs supplements can be considered as a potential therapeutic substance for OA.

Therapeutic targets and potential delivery systems of melatonin in osteoarthritis

Osteoarthritis (OA) is a highly prevalent age-related musculoskeletal disorder that typically results in chronic pain and disability. OA is a multifactorial disease, with increased oxidative stress, dysregulated inflammatory response, and impaired matrix metabolism contributing to its onset and progression. The neurohormone melatonin, primarily synthesized by the pineal gland, has emerged as a promising therapeutic agent for OA due to its potential to alleviate inflammation, oxidative stress, and chondrocyte death with minimal adverse effects. The present review provides a comprehensive summary of the current understanding regarding melatonin as a promising pharmaceutical agent for the treatment of OA, along with an exploration of various delivery systems that can be utilized for melatonin administration. These findings may provide novel therapeutic strategies and targets for inhibiting the advancement of OA.

Adenosine A2A receptor activation reduces chondrocyte senescence

Osteoarthritis (OA) pathogenesis is associated with reduced chondrocyte homeostasis and increased levels of cartilage cellular senescence. Chondrosenescence is the development of cartilage senescence that increases with aging joints and disrupts chondrocyte homeostasis and is associated with OA. Adenosine A2A receptor (A2AR) activation in cartilage via intra-articular injection of liposomal A2AR agonist, liposomal-CGS21680, leads to cartilage regeneration in vivo and chondrocyte homeostasis. A2AR knockout mice develop early OA isolated chondrocytes demonstrate upregulated expression of cellular senescence and aging-associated genes. Based on these observations, we hypothesized that A2AR activation would ameliorate cartilage senescence. We found that A2AR stimulation of chondrocytes reduced beta-galactosidase staining and regulated levels and cell localization of common senescence mediators p21 and p16 in vitro in the human TC28a2 chondrocyte cell line. In vivo analysis similarly showed A2AR activation reduced nuclear p21 and p16 in obesity-induced OA mice injected with liposomal-CGS21680 and increased nuclear p21 and p16 in A2AR knockout mouse chondrocytes compared to wild-type mice. A2AR agonism also increased activity of the chondrocyte Sirt1/AMPK energy-sensing pathway by enhancing nuclear Sirt1 localization and upregulating T172-phosphorylated (active) AMPK protein levels. Lastly, A2AR activation in TC28a2 and primary human chondrocytes reduced wild-type p53 and concomitantly increased p53 alternative splicing leading to increase in an anti-senescent p53 variant, Δ133p53α. The results reported here indicate that A2AR signaling promotes chondrocyte homeostasis in vitro and reduces OA cartilage development in vivo by reducing chondrocyte senescence.

DNA methylation regulates Sirtuin 1 expression in osteoarthritic chondrocytes

PURPOSE

Sirtuin 1 (SIRT1) comprises a major anti-aging longevity factor with multiple protective effects on chondrocyte homeostasis. Previous studies have reported that downregulation of SIRT1 is linked to osteoarthritis (OA) progression. In this study, we aimed to investigate the role of DNA methylation on SIRT1 expression regulation and deacetylase activity in human OA chondrocytes.

MATERIALS AND METHODS

Methylation status of SIRT1 promoter was analyzed in normal and OA chondrocytes using bisulfite sequencing analysis. CCAAT/enhancer binding protein alpha (C/EBPα) binding to SIRT1 promoter was assessed by chromatin immunoprecipitation (ChIP) assay. Subsequently, C/EBPα's interaction with SIRT1 promoter and SIRT1 expression levels were evaluated after treatment of OA chondrocytes with 5-Aza-2'-Deoxycytidine (5-AzadC). Acetylation and nuclear levels of nuclear factor kappa-B p65 subunit (NF-κΒp65) and expression levels of selected OA-related inflammatory mediators, interleukin 1β (IL-1β) and IL-6 and catabolic genes (metalloproteinase-1 (MMP-1) and MMP-9) were evaluated in 5-AzadC-treated OA chondrocytes with or without subsequent transfection with siRNA against SIRT1.

RESULTS

Hypermethylation of specific CpG dinucleotides on SIRT1 promoter was associated with downregulation of SIRT1 expression in OA chondrocytes. Moreover, we found decreased binding affinity of C/EBPα on the hypermethylated SIRT1 promoter. 5-AzadC treatment restored C/EBPα's transcriptional activity inducing SIRT1 upregulation in OA chondrocytes. Deacetylation of NF-κΒp65 in 5-AzadC-treated OA chondrocytes was prevented by siSIRT1 transfection. Similarly, 5-AzadC-treated OA chondrocytes exhibited decreased expression of IL-1β, IL-6, MMP-1 and MMP-9 which was reversed following 5-AzadC/siSIRT1 treatment.

CONCLUSIONS

Our results suggest the impact of DNA methylation on SIRT1 suppression in OA chondrocytes contributing to OA pathogenesis.

New insights in osteoarthritis diagnosis and treatment: Nano-strategies for an improved disease management

Osteoarthritis (OA) is a common chronic joint pathology that has become a predominant cause of disability worldwide. Even though the origin and evolution of OA rely on different factors that are not yet elucidated nor understood, the development of novel strategies to treat OA has emerged in the last years. Cartilage degradation is the main hallmark of the pathology though alterations in bone and synovial inflammation, among other comorbidities, are also involved during OA progression. From a molecular point of view, a vast amount of signaling pathways are implicated in the progression of the disease, opening up a wide plethora of targets to attenuate or even halt OA. The main purpose of this review is to shed light on the recent strategies published based on nanotechnology for the early diagnosis of the disease as well as the most promising nano-enabling therapeutic approaches validated in preclinical models. To address the clinical issue, the key pathways involved in OA initiation and progression are described as the main potential targets for OA prevention and early treatment. Furthermore, an overview of current therapeutic strategies is depicted. Finally, to solve the drawbacks of current treatments, nanobiomedicine has shown demonstrated benefits when using drug delivery systems compared with the administration of the equivalent doses of the free drugs and the potential of disease-modifying OA drugs when using nanosystems. We anticipate that the development of smart and specific bioresponsive and biocompatible nanosystems will provide a solid and promising basis for effective OA early diagnosis and treatment. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement.

1,25-Dihydroxyvitamin D Deficiency Accelerates Aging-related Osteoarthritis via Downregulation of Sirt1 in Mice

Emerging observational data suggest that vitamin D deficiency is associated with the onset and progression of knee osteoarthritis (OA). However, the relationship between vitamin D level and OA and the role of vitamin D supplementation in the prevention of knee OA are controversial. To address these issues, we analyzed the articular cartilage phenotype of 6- and 12-month-old wild-type and 1α(OH)ase^-/- mice and found that 1,25(OH)₂D deficiency accelerated the development of age-related spontaneous knee OA, including cartilage surface destruction, cartilage erosion, proteoglycan loss and cytopenia, increased OARSI score, collagen X and Mmp13 positive chondrocytes, and increased chondrocyte senescence with senescence-associated secretory phenotype (SASP). 1,25(OH)₂D₃ supplementation rescued all knee OA phenotypes of 1α(OH)ase^-/- mice in vivo, and 1,25(OH)₂D₃ rescued IL-1β-induced chondrocyte OA phenotypes in vitro, including decreased chondrocyte proliferation and cartilage matrix protein synthesis, and increased oxidative stress and cell senescence. We also demonstrated that VDR was expressed in mouse articular chondrocytes, and that VDR knockout mice exhibited knee OA phenotypes. Furthermore, we demonstrated that the down-regulation of Sirt1 in articular chondrocytes of 1α(OH)ase^-/- mice was corrected by supplementing 1,25(OH)₂D₃ or overexpression of Sirt1 in mesenchymal stem cells (MSCs) and 1,25(OH)₂D₃ up-regulated Sirt1 through VDR mediated transcription. Finally, we demonstrated that overexpression of Sirt1 in MSCs rescued knee OA phenotypes in 1α(OH)ase^-/- mice. Thus, we conclude that 1,25(OH)₂D_3, via VDR-mediated gene transcription, plays a key role in preventing the onset of aging-related knee OA in mouse models by up-regulating Sirt1, an aging-related gene that promotes articular chondrocyte proliferation and extracellular matrix protein synthesis, and inhibits senescence and SASP.

Overview of Anti-Inflammatory and Anti-Nociceptive Effects of Polyphenols to Halt Osteoarthritis: From Preclinical Studies to New Clinical Insights

Knee osteoarthritis (OA) is one of the most multifactorial joint disorders in adults. It is characterized by degenerative and inflammatory processes that are responsible for joint destruction, pain and stiffness. Despite therapeutic advances, the search for alternative strategies to target inflammation and pain is still very challenging. In this regard, there is a growing body of evidence for the role of several bioactive dietary molecules (BDMs) in targeting inflammation and pain, with promising clinical results. BDMs may be valuable non-pharmaceutical solutions to treat and prevent the evolution of early OA to more severe phenotypes, overcoming the side effects of anti-inflammatory drugs. Among BDMs, polyphenols (PPs) are widely studied due to their abundance in several plants, together with their benefits in halting inflammation and pain. Despite their biological relevance, there are still many questionable aspects (biosafety, bioavailability, etc.) that hinder their clinical application. This review highlights the mechanisms of action and biological targets modulated by PPs, summarizes the data on their anti-inflammatory and anti-nociceptive effects in different preclinical in vitro and in vivo models of OA and underlines the gaps in the knowledge. Furthermore, this work reports the preliminary promising results of clinical studies on OA patients treated with PPs and discusses new perspectives to accelerate the translation of PPs treatment into the clinics.

Modulation of sirtuins during monolayer chondrocyte culture influences cartilage regeneration upon transfer to a 3D culture environment

This study examined the role of sirtuins in the regenerative potential of articular chondrocytes. Sirtuins (SIRT1-7) play a key role in regulating cartilage homeostasis. By inhibiting pro-inflammatory pathways responsible for cartilage degradation and promoting the expression of key matrix components, sirtuins have the potential to drive a favourable balance between anabolic and catabolic processes critical to regenerative medicine. When subjected to osmolarity and glucose concentrations representative of the in vivo niche, freshly isolated bovine chondrocytes exhibited increases in SIRT1 but not SIRT3 gene expression. Replicating methods adopted for the in vitro monolayer expansion of chondrocytes for cartilage regenerative therapies, we found that SIRT1 gene expression declined during expansion. Manipulation of sirtuin activity during in vitro expansion by supplementation with the SIRT1-specific activator SRT1720, nicotinamide mononucleotide, or the pan-sirtuin inhibitor nicotinamide, significantly influenced cartilage regeneration in subsequent 3D culture. Tissue mass, cellularity and extracellular matrix content were reduced in response to sirtuin inhibition during expansion, whilst sirtuin activation enhanced these measures of cartilage tissue regeneration. Modulation of sirtuin activity during monolayer expansion influenced H3K27me3, a heterochromatin mark with an important role in development and differentiation. Unexpectedly, treatment of primary chondrocytes with sirtuin activators in 3D culture reduced their matrix synthesis. Thus, modulating sirtuin activity during the in vitro monolayer expansion phase may represent a distinct opportunity to enhance the outcome of cartilage regenerative medicine techniques.

Phosphoproteomics reveals the BRAF-ERK1/2 axis as an important pathogenic signaling node in cartilage degeneration

OBJECTIVE

Osteoarthritis (OA) causes gradual cellular alterations, structural anomalies and joint dysfunction. Progressive decline of chondrocyte function plays a vital role on OA pathogenesis. Although protein phosphorylation controls cartilage metabolism, its regulation mechanism in OA remains unclear. Thus, proteomic methods were used to investigate phosphorylation changes in preserved and OA articular cartilage samples, and to explore the intervention targets of phosphorylated kinase.

METHODS

Preserved (control) and lesioned (OA) cartilage samples from OA cases were assessed by phosphoproteomics. Immobilized metal affinity chromatography was performed for phosphopeptide enrichment. Quantitated phosphosites were comparatively assessed in the cartilage sample pair. Kinase-substrate enrichment analyses were carried out for identifying OA-related kinases. BRAF expression in cartilage tissues was assessed by immunohistochemical staining. The effects of BRAF inhibitor on cartilage degeneration were examined in mouse chondrocytes and OA mouse model.

RESULTS

High-sensitivity mass spectrometry-based proteomics revealed 7,471 peptides and 4,375 phosphorylated peptides differing between preserved and lesioned cartilage samples, which represented the significant alteration of kinase hubs and transduction pathways. Phosphoproteomics identified BRAF may be involved in developing OA. BRAF regulated the downstream ERK signaling pathway. In addition, BRAF was upregulated in human OA cartilage as shown by immunohistochemistry. Remarkably, BRAF inhibition alleviated cartilage degradation in a mouse model of OA through its downstream of ERK pathway activation.

CONCLUSIONS

Jointly, these findings provide an overview of phosphoproteomic alterations occurring during cartilage degeneration, identifying the BRAF-ERK1/2 Axis signaling as a potential signaling pathway involved in OA.

Metformin Prevents or Delays the Development and Progression of Osteoarthritis: New Insight and Mechanism of Action

For over 60 years, metformin has been widely prescribed by physicians to treat type 2 diabetes. Along with more in-depth research on metformin and its molecular mechanism in recent decades, metformin has also been proposed as an effective drug to prevent or delay musculoskeletal disorders, including osteoarthritis (OA). The occurrence and development of OA are deemed to be associated with the impaired mitochondrial functions of articular chondrocytes. Metformin can activate the pathways and expressions of both AMPK and SIRT1 so as to protect the mitochondrial function of chondrocytes, thereby promoting osteoblast production. Moreover, the clinical significance of the metformin combination therapy in preventing OA has also been demonstrated. This review aimed to comprehensively summarize the current research progress on metformin as a proposed drug for OA prevention or treatment.

Recharge of chondrocyte mitochondria by sustained release of melatonin protects cartilage matrix homeostasis in osteoarthritis

Recent evidence indicates that the mitochondrial functions of chondrocytes are impaired in the pathogenesis of osteoarthritis (OA). Melatonin can attenuate cartilage degradation through its antioxidant functions. This study aims to investigate whether melatonin could rescue the impaired mitochondrial functions of OA chondrocytes and protect cartilage metabolism. OA chondrocytes showed a compromised matrix synthesis capacity associated with mitochondrial dysfunction and aberrant oxidative stress. In vitro treatments with melatonin promoted the expression of cartilage extracellular matrix (ECM) components, improved adenosine triphosphate production, and attenuated mitochondrial oxidative stress. Mechanistically, either silencing of SOD2 or inhibition of SIRT1 abolished the protective effects of melatonin on mitochondrial functions and ECM synthesis. To achieve a sustained release effect, a melatonin-laden drug delivery system (DDS) was developed and intra-articular injection with DDS successfully improved cartilage matrix degeneration in a posttraumatic rat OA model. These findings demonstrate that melatonin-mediated recharge of mitochondria to rescue the mitochondrial functions of chondrocytes represents a promising therapeutic strategy to protect cartilage from OA.

Antisense Oligonucleotide-Based Therapy on miR-181a-5p Alleviates Cartilage Degradation of Temporomandibular Joint Osteoarthritis via Promoting SIRT1

Temporomandibular joint osteoarthritis (TMJOA) condylar cartilage degeneration and abnormal subchondral bone pathological remodeling induce pain and joint dysfunction, and cartilage degeneration is considered irreversible. Very few therapeutic approaches are administrated in practice. Nucleotides have demonstrated considerable potential as a next-generation medication, and they have been applied in several models of osteoarthritis. There is a need to establish an effective protocol for TMJOA gene therapy. In the current study unilateral anterior crossbite (UAC) surgery was used to simulate mechanical stress-induced TMJOA in mice. Degeneration of condylar cartilage and destruction of subchondral bone were observed in damaged joints, and miR-181a-5p was elevated in chondrocytes. Intra-articular injection of miR-181a-5p antisense oligonucleotide (ASO) could reduce the cartilage damage and alleviate UAC-induced TMJOA progression, but it did not restore injured subchondral bone. Mechanically, miR-181a-5p evidently targeted the 3’ untranslated region of Sirt1 directly, resulting in inhibition of silent information regulator 1 expression and promoting apoptosis by elevating p53-dependent signaling, indicating that miR181a-5p ASO promoted chondrocyte survival. The present study suggests that ASO-based gene therapy may be an effective TMJOA treatment.

Melatonin: A novel candidate for the treatment of osteoarthritis

Osteoarthritis (OA), characterized by cartilage erosion, synovium inflammation, and subchondral bone remodeling, is a common joint degenerative disease worldwide. OA pathogenesis is regulated by multiple predisposing factors, including imbalanced matrix metabolism, aberrant inflammatory response, and excessive oxidative stress. Moreover, melatonin has been implicated in development of several degenerative disorders owing to its potent biological functions. With regards to OA, melatonin reportedly promotes synthesis of cartilage matrix, inhibition of chondrocyte apoptosis, attenuation of inflammatory response, and suppression of matrix degradation by regulating the TGF-β, MAPK, or NF-κB signaling pathways. Notably, melatonin has been associated with amelioration of oxidative damage by restoring the OA-impaired intracellular antioxidant defense system in articular cartilage. Findings from preliminary application of melatonin or melatonin-loaded biomaterials in animal models have affirmed its potential anti-arthritic effects. Herein, we summarize the anti-arthritic effects of melatonin on OA cartilage and demonstrate that melatonin has potential therapeutic efficacy in treating OA.

Mitochondrial quality control in cartilage damage and osteoarthritis: new insights and potential therapeutic targets

Osteoarthritis (OA) is a multifactorial arthritic disease of weight-bearing joints concomitant with chronic and intolerable pain, loss of locomotion and impaired quality of life in the elderly population. Although the prevalence of OA increases with age, its specific mechanisms have not been elucidated and effective therapeutic disease-modifying drugs have not been developed. As essential organelles in chondrocytes, mitochondria supply energy and play vital roles in cellular metabolism, proliferation and apoptosis. Mitochondrial quality control (MQC) is the key mechanism to coordinate various mitochondrial biofunctions, primarily through mitochondrial biogenesis, dynamics, autophagy and the newly discovered mitocytosis. An increasing number of studies have revealed that a loss of MQC homeostasis contributes to the cartilage damage during the occurrence and development of OA. Several master MQC-associated signaling pathways and regulators exert chondroprotective roles in OA, while cartilage damage-related molecular mechanisms have been partially identified. In this review, we summarized known mechanisms mediated by dysregulated MQC in the pathogenesis of OA and latent bioactive ingredients and drugs for the prevention and treatment of OA through the maintenance of MQC.

Ginsenoside Rg3 Attenuates TNF-α-Induced Damage in Chondrocytes through Regulating SIRT1-Mediated Anti-Apoptotic and Anti-Inflammatory Mechanisms

The upregulation of tumor necrosis factor-alpha (TNF-α) is a common event in arthritis, and the subsequent signaling cascade that leads to tissue damage has become the research focus. To explore a potential therapeutic strategy to prevent cartilage degradation, we tested the effect of ginsenoside Rg3, a bioactive component of Panax ginseng, on TNF-α-stimulated chondrocytes.TC28a2 Human Chondrocytes were treated with TNF-α to induce damage of chondrocytes. SIRT1 and PGC-1a expression levels were investigated by Western blotting assay. Mitochondrial SIRT3 and acetylated Cyclophilin D (CypD) were investigated using mitochondrial isolation. The mitochondrial mass number and mitochondrial DNA copy were studied for mitochondrial biogenesis. MitoSOX and JC-1 were used for the investigation of mitochondrial ROS and membrane potential. Apoptotic markers, pro-inflammatory events were also tested to prove the protective effects of Rg3. We showed Rg3 reversed the TNF-α-inhibited SIRT1 expression. Moreover, the activation of the SIRT1/PGC-1α/SIRT3 pathway by Rg3 suppressed the TNF-α-induced acetylation of CypD, resulting in less mitochondrial dysfunction and accumulation of reactive oxygen species (ROS). Additionally, we demonstrated that the reduction of ROS ameliorated the TNF-α-elicited apoptosis. Furthermore, the Rg3-reverted SIRT1/PGC-1α/SIRT3 activation mediated the repression of p38 MAPK, which downregulated the NF-κB translocation in the TNF-α-treated cells. Our results revealed that administration of Rg3 diminished the production of interleukin 8 (IL-8) and matrix metallopeptidase 9 (MMP-9) in chondrocytes via SIRT1/PGC-1α/SIRT3/p38 MAPK/NF-κB signaling in response to TNF-α stimulation. Taken together, we showed that Rg3 may serve as an adjunct therapy for patients with arthritis.

Losartan protects against osteoarthritis by repressing the TGF-β1 signaling pathway via upregulation of PPARγ

OBJECTIVE

Losartan and activation of the peroxisome proliferator-activated receptor-γ (PPARγ) have been previously reported to alleviate the progression of osteoarthritis (OA). However, the nature of the interaction between losartan and PPARγ in OA remains elusive. Therefore, we aimed to investigate the mechanism of the regulation of PPARγ by losartan in the context of OA.

METHODS

Clinical samples of OA patients were collected and the chondrocytes were further isolated, and used to construct OA chondrocyte model via induction with IL-1β. An OA mouse model was developed by the surgical destabilization of the medial meniscus (DMM). OA chondrocytes were treated with losartan, PPARγ siRNA and the PPAR-γ agonist GW1929 alone or in combination. Furthermore, the OA mice were treated with varying doses of losartan to determine the best mode of administration and treatment dose. Subsequently, the DMM mice were treated with losartan and GW9662. Expression of PPARγ, key proteins of the transforming growth factor-beta1 (TGF-β1) signaling pathway and the markers of OA degeneration were evaluated by the Western blot analysis, while effects on OA inflammatory factors were determined by ELISA.

RESULTS

The downregulation of PPARγ and the upregulation of TGF-β1 signaling pathway were detected in the OA cartilage tissues and chondrocytes. Losartan treatment or PPARγ activation contributes to reduced levels of IL-6, IL-1β, TNF-α, and COX-2, expression of TGF-β1, MMP-13, ADAMTS-4, ADAMTS-5, HtrA1, and iNOS, along with reduced Smad2 and Smad3 phosphorylation, but elevated PPARγ and Collagen II expression in vivo and in vitro. Additionally, the intraarticular injection of losartan into the knee joint proved to be the best mode of administration, and 10 ​mg/mL being the optimal treatment concentration.

CONCLUSION

Our results show that losartan could arrest the progression of OA by upregulating PPARγ expression and inactivating the TGF-β1 signaling pathway.The translational potential of this article: Our results provide a biological rationale for the use of losartan as a potential candidate for OA treatment.

Extracorporeal shockwave treatment in knee osteoarthritis: therapeutic effects and possible mechanism

Osteoarthritis (OA), the most common degenerative joint disease, is characterized by the cardinal symptoms of chronic pain and restricted joint activity. The complicated pathological changes associated with OA and unclear mechanistic etiology have rendered existing non-surgical OA management options unsatisfactory. Increasing clinical and experimental evidence suggests that extracorporeal shockwave therapy (ESWT) is beneficial in OA treatment. ESWT is found to have modifying effects on cartilage and subchondral bone alterations in OA progression, as well as the clinical complaints of patients, including chronic pain and limited joint activities. However, the specific treatment strategy regarding the dosage and frequency of ESWT is still underdetermined. This review discusses the existing evidence regarding the therapeutic indications and possible mechanism of ESWT for OA treatment.

Pharmacological Targeting of Heme Oxygenase-1 in Osteoarthritis

Osteoarthritis (OA) is a common aging-associated disease that clinically manifests as joint pain, mobility limitations, and compromised quality of life. Today, OA treatment is limited to pain management and joint arthroplasty at the later stages of disease progression. OA pathogenesis is predominantly mediated by oxidative damage to joint cartilage extracellular matrix and local cells such as chondrocytes, osteoclasts, osteoblasts, and synovial fibroblasts. Under normal conditions, cells prevent the accumulation of reactive oxygen species (ROS) under oxidatively stressful conditions through their adaptive cytoprotective mechanisms. Heme oxygenase-1 (HO-1) is an iron-dependent cytoprotective enzyme that functions as the inducible form of HO. HO-1 and its metabolites carbon monoxide and biliverdin contribute towards the maintenance of redox homeostasis. HO-1 expression is primarily regulated at the transcriptional level through transcriptional factor nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2), specificity protein 1 (Sp1), transcriptional repressor BTB-and-CNC homology 1 (Bach1), and epigenetic regulation. Several studies report that HO-1 expression can be regulated using various antioxidative factors and chemical compounds, suggesting therapeutic implications in OA pathogenesis as well as in the wider context of joint disease. Here, we review the protective role of HO-1 in OA with a focus on the regulatory mechanisms that mediate HO-1 activity.

Cartilage -specific knockout of Sirt1 significantly reduces bone quality and catch-up growth efficiency

BACKGROUND

Spontaneous catch-up (CU) growth occurs when a growth-restricting factor is resolved. However, its efficiency is sometimes inadequate and growth deficits remain permanent. The therapeutic toolbox for short stature is currently very limited, thus, finding new regulatory pathways is important for the development of novel means of treatment. Our previous studies using a nutrition-induced CU growth model showed that the level of sirtuin-1 (Sirt1) was significantly increased in food-restricted animals and decreased during CU growth.

AIM

This study sought to investigate the role of Sirt1 in modulating the response of the epiphyseal growth plate (EGP) to nutritional manipulation.

METHOD

Collagen type II-specific Sirt1 knockout (CKO) mice were tested for response to our CU growth model consisting of a period of food restriction followed by re-feeding.

RESULTS

The transgenic CKO mice weighed more than the control (CTL) mice, their EGP was higher and less organized, specifically at the resting and proliferative zones, leading to shorter bones. Ablation of Sirt1 in the chondrocytes was found to have a dramatic effect on bone mineralization on micro-CT analysis. The CKO mice were less responsive to the nutritional manipulation, and their CU growth was less efficient. They remained shorter than the CTL mice who corrected the food restriction-induced growth deficit during the re-feeding period.

CONCLUSIONS

Sirt1 appears to be important for normal regulation of the EGP. In its absence, the EGP is less organized and CU growth is less efficient. These results suggest that SIRT1 may serve as a novel therapeutic target for short stature.

Epigenetic Therapies for Osteoarthritis

Osteoarthritis (OA) is an age-associated disease characterized by chronic joint pain resulting from degradation of articular cartilage, inflammation of the synovial lining, and changes to the subchondral bone. Despite the wide prevalence, no FDA-approved disease-modifying drugs exist. Recent evidence has demonstrated that epigenetic dysregulation of multiple molecular pathways underlies OA pathogenesis, providing a new mechanistic and therapeutic axis with the advantage of targeting multiple deregulated pathways simultaneously. In this review, we focus on the epigenetic regulators that have been implicated in OA, their individual roles, and potential crosstalk. Finally, we discuss the pharmacological molecules that can modulate their activities and discuss the potential advantages and challenges associated with epigenome-based therapeutics for OA.

Epigenetic regulation of chondrocyte hypertrophy and apoptosis through Sirt1/P53/P21 pathway in surgery-induced osteoarthritis

Sirt1 involved in cellular aging and aging-related diseases, including osteoarthritis (OA). Our previous study showed Sirt1 played a role in the pathogenesis of OA, however, the underlying mechanisms are still poorly elicited. In this study, we investigated the role of Sirt1 in epigenetically regulating P53/P21 pathway in a Sirt1 loss model. Sirt1 deletion male mice (n = 10) with destabilization of the medial meniscus (DMM) were used to observe its role on OA development. Then, the relationships between SIRT1 and P53 were detected by Coimmunoprecipitation (CoIP), and the gain-off function of P53 gene was indicated by P53 activators and inhibitors in vitro. Finally, human cartilage samples from patients with OA were collected. Sirt1 deletion mice displayed a spontaneous OA development, manifesting severe chondrocytes hypertrophy markers MMP13 and ADAMTS5, highly expressed P53 and P21. Strikingly, surgery-induced meniscus injury promoted the OA pathogenesis and apoptosis in Sirt1 deficient mice. Ultimately, our CoIP data demonstrated that Sirt1 directly interacted with P53 in vitro. However inhibition of P53 alleviated OA progression. We also observed that chondrocyte apoptosis and P53 increased in osteoarthritis (OA) progression with a declining expression of Sirt1 in human cartilage. Loss of Sirt1 in cartilage led to accelerated OA pathogenesis via aberrant activation of p53/p21 mediated senescence associated secretory phenotype, hypertrophy and apoptosis.

A study on the mechanism of Wnt inhibitory factor 1 in osteoarthritis

INTRODUCTION

In our study we aimed to investigate the mechanism of Wnt inhibitory factor 1 (WIF1) on regulating chondrocyte proliferation and apoptosis via reactive oxygen species (ROS) and the Wnt/βcatenin signaling pathway in osteoarthritis (OA).

MATERIAL AND METHODS

Osteoarthritis chondrocytes were treated with interleukin 1β (IL-1β) to simulate an inflammatory condition. Quantitative real-time polymerase chain reaction (qRT-PCR) and western blot were applied for detecting WIF1 expression in OA chondrocytes. MTT assay and flow cytometry were carried out to analyze the cell proliferation and apoptosis. Content of ROS was detected using flow cytometry, and activity of the Wnt/βcatenin signaling pathway was detected using immunofluorescence, western blot and luciferase reporter assay. Western blot and enzyme-linked immunosorbent assay (ELISA) were performed to detect the expression of apoptosis-related proteins and secretion of matrix metalloproteinases (MMPs).

RESULTS

WIF1 expression in OA chondrocytes was significantly lower than in normal chondrocytes. After WIF1 cDNA transfection, the aberrantly high ROS level in OA chondrocytes was down-regulated, which led to the increase of proliferation and reduction of apoptosis. The Wnt/βcatenin signaling pathway was suppressed by WIF1 overexpression and the secretion of MMPs was therefore reduced.

CONCLUSIONS

Up-regulation of WIF1 would promote proliferation and suppress apoptosis of OA chondrocytes through eliminating ROS production and reduce secretion of MMPs via blocking the Wnt/βcatenin signaling pathway.

The role of sirtuin 1 and its activator, resveratrol in osteoarthritis

Osteoarthitis (OA) is the most common aging-related joint pathology; the aging process results in changes to joint tissues that ultimately contribute to the development of OA. Articular chondrocytes exhibit an aging-related decline in their proliferative and synthetic capacity. Sirtuin 1 (SIRT 1), a longevity gene related to many diseases associated with aging, is a nicotinamide adenine dinucleotide (NAD⁺)-dependent protein deacetylase and master metabolic regulator. Along with its natural activator resveratrol, SIRT 1 actively participates in the OA pathological progress. SIRT 1 expression in osteoarthritic cartilage decreases in the disease progression of OA; it appears to play a predominantly regulatory role in OA. SIRT 1 can regulate the expression of extracellular matrix (ECM)-related proteins; promote mesenchymal stem cell differentiation; play anti-catabolic, anti-inflammatory, anti-oxidative stress, and anti-apoptosis roles; participate in the autophagic process; and regulate bone homeostasis in OA. Resveratrol can activate SIRT 1 in order to inhibit OA disease progression. In the future, activating SIRT 1 via resveratrol with improved bioavailability may be an appropriate therapeutic approach for OA.

Bevacizumab tested for treatment of knee osteoarthritis via inhibition of synovial vascular hyperplasia in rabbits

Background/objective

Osteoarthritis (OA) is the most common joint disorder. Angiogenesis and synovial hyperplasia are important factors in the development of OA. Previous studies demonstrated that bevacizumab, an antibody against vascular endothelial growth factor in angiogenesis for cancer treatment, might be a potential candidate for the treatment of OA. However, experimental studies were lacking in whether bevacizumab would be able to attenuate the severity of OA. In this study, we used normal New Zealand rabbits and a rabbit knee immobilization model of OA, to investigate the toxicity and efficacy of bevacizumab.

Methods

In the safety test of bevacizumab, sixteen rabbits were randomly divided into 2 groups: control group and bevacizumab group (n = 8 per group). We evaluated the blood chemistry and histology of normal rabbit joints after bevacizumab treatment. In the efficacy test of bevacizumab, thirty-two rabbits were used for establishing OA model and then randomly divided into 4 groups: bevacizumab group, sodium hyaluronate (SH) group, triamcinolone acetonide (TA) group and control group (n = 8 per group). We used histological evaluations and immunohistochemistry to examine the responses to bevacizumab treatment in a rabbit model of knee immobilization-induced OA.

Results

Bevacizumab treatment did not show any adverse effects histologically on normal joints. Blood tests and Mankin's score of cartilage revealed no significant difference between the bevacizumab and control groups (p > 0.05). The bevacizumab, SH, and TA groups attenuated articular cartilage degeneration and showed less synovial hyperplasia compared to the control group macroscopically and histologically, while the effect of the bevacizumab group was most obvious (p < 0.05). Immunohistochemistry revealed significantly lower vascular endothelial growth factor (VEGF) expression in the synovium and matrix metalloproteinase-1 (MMP-1) in the cartilage in the bevacizumab, SH, and TA groups compared to the control group (p < 0.05), while the expression of VEGF and MMP-1 in the bevacizumab group was the lowest among the four groups (p < 0.05).

Conclusions

Intra-articular injection of 4-mg bevacizumab in rabbit knees did not show adverse effects. The bevacizumab treatment prevented joint inflammation in terms of inhibition of reduced angiogenesis, inhibited synovial proliferation, and reduced VEGF and MMP-1 expression. Compared with SH and TA, bevacizumab protected the cartilage and produced a better therapeutic effect on primary knee OA in rabbits, which imply that bevacizumab, an anticancer drug, may become a potentially effective drug for the treatment of OA.

The translational potential of this article

Our study confirmed the therapeutic effect of bevacizumab on rabbit primary knee OA. This study demonstrated that bevacizumab may have clinical implications and contribute to the development of new OA treatments.

The effect of lentivirus-mediated SIRT1 gene knockdown in the ATDC5 cell line via inhibition of the Wnt signaling pathway

SIRT1 is a highly conserved type III acetyltransferase gene located on chromosome 10 in mammals that belong to the Sirtuins family. In order to explore the effects of the SIRT1 gene in the ATDC5 cell line, an RNAi SIRT1 target sequence was designed and synthesized, aimed to knockdown the expression of SIRT1 in ATDC5 by a lentivirus. Gene chip, qrt-PCR, and WES analyses were used to detect the expression of SIRT1 and changes to the Wnt signaling pathway, while detecting any changes in proliferation and differentiation factors. The results showed that the expressions of the SIRT1 gene, mRNA, and protein were lower after transfection of the RNAi SIRT1sequence into ATDC5 cells. The Wnt signaling pathway, especially the classical pathway, was inhibited by the knockdown of SIRT1. The cartilaginous proliferation and differentiation of ATDC5 cells were simultaneously inhibited, and apoptosis was accelerated. In summary, knocking down SIRT1 gene increased the degeneration of ATDC5 cells via inhibiting the Wnt signaling pathway. We also found some novel factors related to the Wnt signaling pathway after SIRT1 gene knockdown (BIRC3, IL1RAP, PPP3CA, PPP2R2A, PPP2R5E, GSN, PPP2R1B, etc), which might provide new clues in disease research related to chondrocyte degeneration.

Osteoarthritis year in review 2017: biology

This Year in Review was derived from a personal selection of articles investigating biological mechanisms of osteoarthritis (OA) and presented at the OARSI World Congress on April 30, 2017. Selected articles were published between the March, 2016 and April, 2017 OARSI meetings. PubMed/MEDLINE searches were performed using the terms "osteoarthritis", "cartilage", "subchondral bone", "synovium", "synovitis", and "ageing". Biomechanical, genetic, genomic, epigenomic, biomarker, clinical, imaging, and tissue engineering studies were excluded since they are covered by other articles in this series. Several new and emerging themes were identified. Incorporating new technologies such as designer genetic engineering, nanotechnology, and bio-selective nuclear medicine tracers into study designs helps to gain important insights into OA pathophysiology. Potentially critical differences exist between biological mechanisms of post-traumatic, age-associated, and metabolic phenotypes of OA. The concept of OA stages is highlighted, demonstrating how this may influence which biological mechanisms are at play and the need for strategic timing of treatment interventions. Not all inflammation is bad and fine-tuning a balance within inflammatory signaling mechanisms may be a path to regain joint homeostasis. Not only is the joint an organ system, sub-regions within each joint tissue, especially the joint lining, may play distinct roles in damage and repair. To accompany the review, the interaction among studies spanning multiple areas is summarized schematically.

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.

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.