The Role of Sirtuins in Cartilage Homeostasis and Osteoarthritis

The role of sirtuins in intervertebral disc degeneration: Mechanisms and therapeutic potential

Intervertebral disc degeneration (IDD) is one of the main causes of low back pain, which affects the patients' quality of life and health and imposes a significant socioeconomic burden. Despite great efforts made by researchers to understand the pathogenesis of IDD, effective strategies for preventing and treating this disease remain very limited. Sirtuins are a highly conserved family of (NAD+)-dependent deacetylases in mammals that are involved in a variety of metabolic processes in vivo. In recent years, sirtuins have attracted much attention owing to their regulatory roles in IDD on physiological activities such as inflammation, apoptosis, autophagy, aging, oxidative stress, and mitochondrial function. At the same time, many studies have explored the therapeutic effects of sirtuins-targeting activators or micro-RNA in IDD. This review summarizes the molecular pathways of sirtuins involved in IDD, and summarizes the therapeutic role of activators or micro-RNA targeting Sirtuins in IDD, as well as the current limitations and challenges, with a view to provide possible solutions for the treatment of IDD.

Curcumin and Resveratrol: Nutraceuticals with so Much Potential for Pseudoachondroplasia and Other ER-Stress Conditions

Natural products with health benefits, nutraceuticals, have shown considerable promise in many studies; however, this potential has yet to translate into widespread clinical use for any condition. Notably, many drugs currently on the market, including the first analgesic aspirin, are derived from plant extracts, emphasizing the historical significance of natural products in drug development. Curcumin and resveratrol, well-studied nutraceuticals, have excellent safety profiles with relatively mild side effects. Their long history of safe use and the natural origins of numerous drugs contrast with the unfavorable reputation associated with nutraceuticals. This review aims to explore the nutraceutical potential for treating pseudoachondroplasia, a rare dwarfing condition, by relating the mechanisms of action of curcumin and resveratrol to molecular pathology. Specifically, we will examine the curcumin and resveratrol mechanisms of action related to endoplasmic reticulum stress, inflammation, oxidative stress, cartilage health, and pain. Additionally, the barriers to the effective use of nutraceuticals will be discussed. These challenges include poor bioavailability, variations in content and purity that lead to inconsistent results in clinical trials, as well as prevailing perceptions among both the public and medical professionals. Addressing these hurdles is crucial to realizing the full therapeutic potential of nutraceuticals in the context of pseudoachondroplasia and other health conditions that might benefit.

G/ β- TCP composite scaffold material promotes osteogenic differentiation of bone marrow mesenchymal stem cells

To explore self-made graphene/β Graphene (G)/β- tricalcium phosphate, G/β- The effect of TCP composite scaffold material on osteogenic differentiation of BMSC. Preparation of G/β- TCP composite material was used to investigate the effect of composite material on bone marrow mesenchymal stem cell ossification/β- TCP material was used to treat primary BMSCs of rats. Cell morphology changes were observed under scanning electron microscopy, cell cycle and proliferation were detected by flow cytometry, and gene expression of chondrogenic genes Fibronectin, collagen I, collagen II, ICAM, and VCAM was detected by q-PCR. In addition, using osteogenic induction medium and G/β- TCP composite materials were co treated with BMSCs, and ALP and alizarin red staining were used to observe the effect of the materials on osteogenic differentiation. q-PCR was used to detect the gene expression of osteogenic related genes Runx2, OCN, and OPN. G/ β- After the TCP composite was co cultured with BMSC, the proportion of G0/G1 phase of BMSC cells was significantly increased, the cell proliferation ability was enhanced, and the gene expression of fibronectin, collagen I, collagen II, ICAM, and VCAM were significantly increased. The ALP staining results indicate that BMSC in G/β- After treatment with TCP composite material, significant enhancement of osteogenic ability was observed at 7,14 and 21 days. In addition, BMSC in G/β- A significant increase in calcium deposition was observed at 7,14 and 21 days after treatment with TCP composite materials. The effect of different time points on the expression of osteogenic related genes varies. At 7 and 14 days, the expression of RUNX2 was significantly reduced compared to the control, but significantly increased at 21 days; OCN significantly increased on the 21st day; OPN significantly increased at 14 days. G/β- TCP materials significantly promote the osteogenic differentiation of BMSCs.

Sirtuins, resveratrol and the intertwining cellular pathways connecting them

Sirtuins are a family of NAD+-dependent deacylases with numerous physiological and pathological implications, which lately became an attractive therapeutic target. Sirtuin-activating compounds (STACs) could be useful in disease prevention and treatment. Despite its bioavailability issues, resveratrol exerts a myriad of beneficial effects, known as the "resveratrol paradox". Modulation of sirtuins' expression and activity may, in fact, underlie many of resveratrol revered actions; however, the cellular pathways affected by modulating the activity of each sirtuin isoform, in different physio-pathological conditions, are not fully known. The purpose of this review was to summarize recent reports concerning the effects of resveratrol on the activity of sirtuins in different experimental settings, focusing on in vitro and in vivo preclinical studies. Most reports concern SIRT1, however recent studies dive into the effects initiated via other isoforms. Numerous cellular signaling pathways were reported to be modulated by resveratrol in a sirtuin-dependent manner (increased phosphorylation of MAPKs, AKT, AMPK, RhoA, BDNF, decreased activation of NLRP3 inflammasome, NF-κB, STAT3, upregulation of SIRT1/SREBP1c pathway, reduced β-amyloid via SIRT1-NF-κB-BACE1 signaling and counteracting mitochondrial damage by deacetylating PGC-1α). Thus, resveratrol may be the ideal candidate in the search for STACs as a tool for preventing and treating inflammatory and neurodegenerative diseases.

Targeting CD38 to Suppress Osteoarthritis Development and Associated Pain After Joint Injury in Mice

OBJECTIVE

This study was undertaken to determine the role of CD38, which can function as an enzyme to degrade NAD⁺ , in osteoarthritis (OA) development.

METHODS

Human knee cartilage from normal donors and OA donors were examined for CD38 expression. "Gain-of-function," through overexpression of CD38 via transient transfection, and "loss-of-function," through pharmacologic inhibition of CD38, approaches were used to assess the effects of CD38 on intracellular NAD⁺ :NADH ratio and catabolic activity in chondrocytes. We also initiated joint injury-induced OA by surgical destabilization of the medial meniscus (DMM) in CD38 knockout mice and wild-type (WT; C57BL/6) mice and in WT male mice in the presence or absence of apigenin treatment. Cartilage degradation, synovial inflammation, subchondral bone changes, and pain behavior were evaluated after DMM surgery. We also examined expression of CD38 and the neuropeptide calcitonin gene-related peptide (CGRP) in knee sections from these mice.

RESULTS

CD38 expression was up-regulated in human knee OA cartilage and in chondrocytes stimulated with the proinflammatory cytokine interleukin-1β (IL-1β). Overexpression of CD38 in chondrocytes resulted in reduced cellular NAD⁺ :NADH ratio and augmented catabolic responses to IL-1β. These effects were reversed by pharmacologic inhibition of CD38. Cartilage degradation and synovial inflammation, associated with increased CD38 expression in cartilage and synovium, osteophyte formation and subchondral bone sclerosis, and pain-like behavior linked to increased CGRP expression in the synovium were observed in WT mice after joint injury. Such effects were significantly reduced in mice deficient in CD38 through either genetic knockout or pharmacologic inhibition.

CONCLUSION

CD38 deficiency exerts OA disease-modifying effects. Inhibition of CD38 has the potential to be a novel therapeutic approach for OA treatment.

Targeting macrophage polarization as a promising therapeutic strategy for the treatment of osteoarthritis

Osteoarthritis (OA) is a chronic osteoarthropathy characterized by the progressive degeneration of articular cartilage and synovial inflammation. Early OA clinical treatments involve intra-articular injection of glucocorticoids, oral acetaminophen and non-steroidal anti-inflammatory drugs (NSAIDs), which are used for anti-inflammation and pain relief. However, long-term use of these agents will lead to inevitable side effects, even aggravate cartilage loss. At present, there are no disease-modifying OA drugs (DMOADs) yet approved by regulatory agencies. Polarization regulation of synovial macrophages is a new target for OA treatment. Inhibiting M1 polarization and promoting M2 polarization of synovial macrophages can alleviate synovial inflammation, relieve joint pain and inhibit articular cartilage degradation, which is a promising strategy for OA treatment. In this study, we describe the molecular mechanisms of macrophage polarization and its key role in the development of OA. Subsequently, we summarize the latest progress of strategies for OA treatment through macrophage reprogramming, including small molecule compounds (conventional western medicine and synthetic compounds, monomer compounds of traditional Chinese medicine), biomacromolecules, metal/metal oxides, cells, and cell derivatives, and interprets the molecular mechanisms, hoping to provide some information for DMOADs development.

SIRT6 activation rescues the age-related decline in DNA damage repair in primary human chondrocytes

While advanced age has long been recognized as the greatest risk factor for osteoarthritis (OA), the biological mechanisms behind this connection remain unclear. Previous work has demonstrated that chondrocytes from older cadaveric donors have elevated levels of DNA damage as compared to chondrocytes from younger donors. The purpose of this study was to determine whether a decline in DNA repair efficiency is one explanation for the accumulation of DNA damage with age, and to quantify the improvement in repair with activation of Sirtuin 6 (SIRT6). Using an acute irradiation model to bring the baseline level of all donors to the same starting point, this study demonstrates a decline in repair efficiency during aging when comparing chondrocytes from young (≤45 years old), middle-aged (50-65 years old), or older (>70 years old) cadaveric donors with no known history of OA or macroscopic cartilage degradation at isolation. Activation of SIRT6 in middle-aged chondrocytes with MDL-800 (20 μM) improved the repair efficiency, while inhibition with EX-527 (10 μM) inhibited the rate of repair and the increased the percentage of cells that retained high levels of damage. Treating chondrocytes from older donors with MDL-800 for 48 hours significantly reduced the amount of DNA damage, despite this damage having accumulated over decades. Lastly, chondrocytes isolated from the proximal femurs of mice between 4 months and 22 months of age revealed both an increase in DNA damage with aging, and a decrease in DNA damage following MDL-800 treatment.

Senescence in osteoarthritis: from mechanism to potential treatment

Osteoarthritis (OA) is an age-related cartilage degenerative disease, and chondrocyte senescence has been extensively studied in recent years. Increased numbers of senescent chondrocytes are found in OA cartilage. Selective clearance of senescent chondrocytes in a post-traumatic osteoarthritis (PTOA) mouse model ameliorated OA development, while intraarticular injection of senescent cells induced mouse OA. However, the means and extent to which senescence affects OA remain unclear. Here, we review the latent mechanism of senescence in OA and propose potential therapeutic methods to target OA-related senescence, with an emphasis on immunotherapies. Natural killer (NK) cells participate in the elimination of senescent cells in multiple organs. A relatively comprehensive discussion is presented in that section. Risk factors for OA are ageing, obesity, metabolic disorders and mechanical overload. Determining the relationship between known risk factors and senescence will help elucidate OA pathogenesis and identify optimal treatments.

Mechanical stress-caused chondrocyte dysfunction and cartilage injury can be attenuated by dioscin via activating sirtuin1/forkhead box O1

Sirtuin1 (Sirt1)/forkhead box O1 (FoxO1) axis has been reported as a crucial regulator involved in chondral homeostasis of healthy or osteoarthritis (OA) cartilage. In our study, the aim is to investigate whether dioscin functions as an activator of Sirt1/FoxO1 to protect against mechanical stress-induced chondrocyte dysfunction in vitro and in vivo models. HERB and PubChem databases were implemented to predict dioscin-related gene targets. Cell and mouse models of OA were established to determine the pharmacological value of dioscin, a steroidal saponin. Cartilage loss in the knee joint was detected by Safranin O staining. Phosphorylation and nucleocytoplasmic shuttling of FoxO1 was observed in mechanical stress-stimulated chondrocyte and anterior cruciate ligament transection-induced cartilage injury. However, dioscin treatment repressed FoxO1 phosphorylation and cytoplasmic transfer and elevated Sirt1 protein expression. Dioscin treatment reversed mechanical stress-induced growth inhibition and apoptosis of chondrocytes and improved cartilage degradation and bone loss in the epiphysis of the distal femur. Moreover, dioscin could maintain the normal phenotype of chondrocytes via mediating multiple gene expressions. Dioscin inhibited apoptosis and metabolic disorders in OA-like chondrocytes via maintaining the transcriptional activity of FoxO1 and enhancing Sirt1 expression. Dioscin might be a potential Sirt1 activator providing a novel therapeutic schedule for the treatment of OA.

Natural medicines of targeted rheumatoid arthritis and its action mechanism

Rheumatoid arthritis (RA) is an autoimmune disease involving joints, with clinical manifestations of joint inflammation, bone damage and cartilage destruction, joint dysfunction and deformity, and extra-articular organ damage. As an important source of new drug molecules, natural medicines have many advantages, such as a wide range of biological effects and small toxic and side effects. They have become a hot spot for the vast number of researchers to study various diseases and develop therapeutic drugs. In recent years, the research of natural medicines in the treatment of RA has made remarkable achievements. These natural medicines mainly include flavonoids, polyphenols, alkaloids, glycosides and terpenes. Among them, resveratrol, icariin, epigallocatechin-3-gallate, ginsenoside, sinomenine, paeoniflorin, triptolide and paeoniflorin are star natural medicines for the treatment of RA. Its mechanism of treating RA mainly involves these aspects: anti-inflammation, anti-oxidation, immune regulation, pro-apoptosis, inhibition of angiogenesis, inhibition of osteoclastogenesis, inhibition of fibroblast-like synovial cell proliferation, migration and invasion. This review summarizes natural medicines with potential therapeutic effects on RA and briefly discusses their mechanisms of action against RA.

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.

Osteoarthritis Progression: Mitigation and Rehabilitation Strategies

Osteoarthritis is the most common form of arthritis and is a substantial burden for patients with the disease. Currently, there is no cure for osteoarthritis, but many emerging therapies have been developed to aid in the mitigation of disease progression. When osteoarthritis reaches the end-stage of disease many patients undergo total joint arthroplasty to improve quality of life, yet some experience persistent pain and mobility limitations for extended periods following surgery. This review highlights recent therapeutic advancements in osteoarthritis treatment consisting of pharmacologics, nutraceuticals, biologics, and exercise while emphasizing the current state of post-arthroplasty rehabilitation.

Primary Osteoarthritis Early Joint Degeneration Induced by Endoplasmic Reticulum Stress Is Mitigated by Resveratrol

Increasing numbers of people are living with osteoarthritis (OA) due to aging and obesity, creating an urgent need for effective treatment and preventions. Two top risk factors for OA, age and obesity, are associated with endoplasmic reticulum (ER) stress. The I-ERS mouse, an ER stress-driven model of primary OA, was developed to study the role of ER stress in primary OA susceptibility. The I-ERS mouse has the unique ability to induce ER stress in healthy adult articular chondrocytes and cartilage, driving joint degeneration that mimics early primary OA. In this study, ER stress-induced damage occurred gradually and stimulated joint degeneration with OA characteristics including increased matrix metalloproteinase activity, inflammation, senescence, chondrocyte death, decreased proteoglycans, autophagy block, and gait dysfunction. Consistent with human OA, intense exercise hastened and increased the level of ER stress-induced joint damage. Notably, loss of a critical ER stress response protein (CHOP) largely ameliorated ER stress-stimulated OA outcomes including preserving proteoglycan content, reducing inflammation, and relieving autophagy block. Resveratrol diminished ER stress-induced joint degeneration by decreasing CHOP, TNFα, IL-1β, MMP-13, pS6, number of TUNEL-positive chondrocytes, and senescence marker p16 INK4a. The finding, that a dietary supplement can prevent ER stressed-induced joint degeneration in mice, provides a preclinical foundation to potentially develop a prevention strategy for those at high risk to develop OA.

Ferulic acid suppresses interleukin-1β-induced degeneration of chondrocytes isolated from patients with osteoarthritis through the SIRT1/AMPK/PGC-1α signaling pathway

Background

Interleukin‐1β (IL‐1β) is involved in osteoarthritis pathogenesis and mediates a series of toxic processes including the production of matrix metalloproteinase and inflammatory regulators which are suppressed by activation of silent information regulator 1 (SIRT1). We aimed to determine the effects of ferulic acid (FA) on IL‐1β‐induced osteoarthritis chondrocyte degeneration.

Methods

We examined the effects of FA on osteoarthritis chondrocyte viability and SIRT1 activation. The impact of FA on IL‐1β‐induced osteoarthritis chondrocyte toxicity was determined by prostaglandin E2 (PGE₂), nitrite, IL‐6, components of the extracellular matrix, and markers of oxidative stress. Finally, we determined whether these effects were mediated through SIRT1 by inhibiting SIRT1 activity using SIRT1 inhibitor Sirtinol.

Results

We found that FA activated SIRT1/AMPK/PGC‐1α signaling pathway and attenuated IL‐1β‐induced osteoarthritis chondrocyte degeneration by suppressing the production of IL‐6, PGE₂, nitrite, Collagen I, Runx‐2, MMP‐1, MMP‐3, and MMP‐13, enhancing Collagen II and Aggrecan expression and inhibiting oxidative stress. Inhibition of SIRT1 by Sirtinol attenuated the protective effects of FA.

Conclusion

Our findings reveal that FA prevents IL‐1β‐induced osteoarthritis chondrocyte toxicity, which suggests that FA may be a potential therapy for osteoarthritis and warrants further investigation for its clinical application.

In Vitro Evaluation of the Anti-Inflammatory Effect of KMUP-1 and In Vivo Analysis of Its Therapeutic Potential in Osteoarthritis

Osteoarthritis is a degenerative arthropathy that is mainly characterized by dysregulation of inflammatory responses. KMUP-1, a derived chemical synthetic of xanthine, has been shown to have anti-inflammatory and antioxidant properties. Here, we aimed to investigate the in vitro anti-inflammatory and in vivo anti-osteoarthritis effects of KMUP-1. Protein and gene expressions of inflammation markers were determined by ELISA, Western blotting and microarray, respectively. RAW264.7 mouse macrophages were cultured and pretreated with KMUP-1 (1, 5, 10 μM). The productions of TNF-α, IL-6, MMP-2 and MMP- 9 were reduced by KMUP-1 pretreatment in LPS-induced inflammation of RAW264.7 cells. The expressions of iNOS, TNF-α, COX-2, MMP-2 and MMP-9 were also inhibited by KMUP-1 pretreatment. The gene expression levels of TNF and COX families were also downregulated. In addition, KMUP-1 suppressed the activations of ERK, JNK and p38 as well as phosphorylation of IκBα/NF-κB signaling pathways. Furthermore, SIRT1 inhibitor attenuated the inhibitory effect of KMUP-1 in LPS-induced NF-κB activation. In vivo study showed that KMUP-1 reduced mechanical hyperalgesia in monoiodoacetic acid (MIA)-induced rats OA. Additionally, KMUP-1 pretreatment reduced the serum levels of TNF-α and IL-6 in MIA-injected rats. Moreover, macroscopic and histological observation showed that KMUP-1 reduced articular cartilage erosion in rats. Our results demonstrated that KMUP-1 inhibited the inflammatory responses and restored SIRT1 in vitro, alleviated joint-related pain and cartilage destruction in vivo. Taken together, KMUP-1 has the potential to improve MIA-induced articular cartilage degradation by inhibiting the levels and expression of inflammatory mediators suggesting that KMUP-1 might be a potential therapeutic agent for OA.

Sirtuin 6 (SIRT6) regulates redox homeostasis and signaling events in human articular chondrocytes

The nuclear localized protein deacetylase, SIRT6, has been identified as a crucial regulator of biological processes that drive aging. Among these processes, SIRT6 can promote resistance to oxidative stress conditions, but the precise mechanisms remain unclear. The objectives of this study were to examine the regulation of SIRT6 activity by age and oxidative stress and define the role of SIRT6 in maintaining redox homeostasis in articular chondrocytes. Although SIRT6 levels did not change with age, SIRT6 activity was significantly reduced in chondrocytes isolated from older adults. Using dimedone-based chemical probes that detect oxidized cysteines, we identified that SIRT6 is oxidized in response to oxidative stress conditions, an effect that was associated with reduced SIRT6 activity. Enhancement of SIRT6 activity through adenoviral SIRT6 overexpression specifically increased the basal levels of two antioxidant proteins, peroxiredoxin 1 (Prx1) and sulfiredoxin (Srx) and decreased the levels of an inhibitor of antioxidant activity, thioredoxin interacting protein (TXNIP). Conversely, in chondrocytes derived from mice with cartilage specific Sirt6 knockout, Sirt6 loss decreased Prx1 levels and increased TXNIP levels. SIRT6 overexpression decreased nuclear-generated H2O2 levels and oxidative stress-induced accumulation of nuclear phosphorylated p65. Our data demonstrate that SIRT6 activity is altered with age and oxidative stress conditions associated with aging. SIRT6 contributes to chondrocyte redox homeostasis by regulating specific members of the Prx catalytic cycle. Targeted therapies aimed at preventing the age-related decline in SIRT6 activity may represent a novel strategy to maintain redox balance in joint tissues and decrease catabolic signaling events implicated in osteoarthritis (OA).

Are Nutraceuticals Beneficial in Chronic Kidney Disease?

Chronic kidney disease (CKD) is a worldwide health problem in which prevalence is constantly rising. The pathophysiology of CKD is complicated and has not been fully resolved. However, elevated oxidative stress is considered to play a vital role in the development of this disease. CKD is also thought to be an inflammatory disorder in which uremic toxins participate in the development of the inflammatory milieu. A healthy, balanced diet supports the maintenance of a good health status as it helps to reduce the risk of the development of chronic diseases, including chronic kidney disease, diabetes mellitus, and hypertension. Numerous studies have demonstrated that functional molecules and nutrients, including fatty acids and fiber as well as nutraceuticals such as curcumin, steviol glycosides, and resveratrol not only exert beneficial effects on pro-inflammatory and anti-inflammatory pathways but also on gut mucosa. Nutraceuticals have attracted great interest recently due to their potential favorable physiological effects on the human body and their safety. This review presents some nutraceuticals in which consumption could exert a beneficial impact on the development and progression of renal disease as well cardiovascular disease.

The Role of HDACs and HDACi in Cartilage and Osteoarthritis

Epigenetics plays an important role in the pathogenesis and treatment of osteoarthritis (OA). In recent decades, HDAC family members have been associated with OA. This paper aims to describe the different role of HDACs in the pathogenesis of OA through interaction with microRNAs and the regulation of relevant signaling pathways. We found that HDACs are involved in cartilage and chondrocyte development but also play a crucial role in OA. However, the distinct HDAC mechanism in the pathogenesis and treatment of OA require further investigation. Furthermore, HDAC inhibitors (HDACi) can protect cartilage from disease, which may represent a potential therapeutic approach against OA.

The role of SIRT1 in BMP2-induced chondrogenic differentiation and cartilage maintenance under oxidative stress

Articular cartilage defects are common in the clinic but difficult to treat. Exploring the chondrogenic molecular mechanisms of mesenchymal stem cells (MSCs) is of great theoretical interest and industrial significance. Bone morphogenetic protein 2 (BMP2) is a key factor that induces cartilage differentiation and can induce stem cell chondrogenic differentiation. However, the oxidative stress in the microenvironment during cartilage injury and degeneration inhibits cartilage regeneration and homeostasis. Silent mating type information regulator 2 homolog-1 (SIRT1) is an important histone deacetylase that regulates proliferation, differentiation, aging, and inflammation processes; moreover, it is an essential factor for chondrogenesis. The specific mechanism of SIRT1 in cartilage differentiation and homeostasis is still unclear. First, we investigated whether SIRT1 could coordinate BMP2-induced chondrogenic differentiation. Second, we investigated the protective effect of SIRT1 on BMP2-induced MSCs under oxidative stress. The results showed that SIRT1 could promote BMP2-induced chondrogenic differentiation of MSCs, and reduce the apoptosis and decomposition of extracellular matrix under oxidative stress. In summary, these results suggested that SIRT1 plays an important coordination role in BMP2-induced chondrogenic differentiation of stem cells and cartilage maintenance under oxidative stress, establishing the experimental basis for exploring the use of SIRT1 in cartilage defect repair.

SOX9 in cartilage development and disease

SOX9 is a pivotal transcription factor in chondrocytes, a lineage essential in skeletogenesis. Its mandatory role in transactivating many cartilage-specific genes is well established, whereas its pioneer role in lineage specification, which along with transactivation defines master transcription factors, remains to be better defined. Abundant, but yet incomplete evidence exists that intricate molecular networks control SOX9 activity during the multi-step chondrogenesis pathway. They include a highly modular genetic regulation, post-transcriptional and post-translational modifications, and varying sets of functional partners. Fully uncovering SOX9 actions and regulation is fundamental to explain mechanisms underlying many diseases that directly or indirectly affect SOX9 activities and to design effective disease treatments. We here review current knowledge, highlight recent discoveries, and propose new research directions to answer remaining questions.

Role of NGF-TrkA signaling in calcification of articular chondrocytes

Nerve growth factor (NGF) is a key regulator of chronic osteoarthritic pain, but the exact targets of NGF action on human articular cartilage is unknown. This study aimed to test the hypothesis that the NGF-tropomyosin receptor kinase A (TrkA) (high-affinity NGF receptor) pathway plays a role in the calcification process of human articular chondrocytes (hACs). A 14-aa small peptide of NGF (Nsp) previously shown to activate NGF signaling in rat PC12 cells was used as an NGF signaling agonist, and recombinant NGF and the pan-Trk inhibitor GNF-5837 were employed as signaling modulating agents. The functional consequences of NGF-TrkA signaling were examined in human healthy articular chondrocytes maintained under conditions supportive of osteogenesis in vitro. The NGF-mimetic bioactivity of Nsp was first confirmed on the basis of maintenance of neurite outgrowth in PC12 cells. Primary human chondrocytes responded to Nsp in vitro. Perturbation of NGF signaling with NGF, Nsp, and GNF-5837 resulted in a strong induction of chondrocyte calcification, and gene expression data suggested that the Indian Hedgehog-parathyroid hormone-related protein signaling axis was involved. These findings suggest functional involvement of NGF signaling in calcification of hACs and the importance of NGF signaling in articular cartilage homeostasis.-Jiang, Y., Tuan, R. S. Role of NGF-TrkA signaling in calcification of articular chondrocytes.

Resveratrol inhibits IL-1β-mediated nucleus pulposus cell apoptosis through regulating the PI3K/Akt pathway

Nucleus pulposus (NP) cell apoptosis is a classical cellular character during intervertebral disc degeneration (IDD). Previous studies have shown that inflammatory cytokine-induced NP cell apoptosis plays an important role in disc degeneration. The present study was aimed to investigate whether resveratrol can suppress IL-1β-mediated NP cell apoptosis and the potential signal transduction pathway. Experimental rat NP cells were treated with culture medium containing IL-1β (20 ng/ml) for 7 days. Control NP cells were cultured in the baseline medium. Resveratrol was added along with culture medium to investigate its effects. The inhibitor LY294002 was used to study the role of the PI3K/Akt pathway. NP cell apoptosis was reflected by the caspase-3 activity, cell apoptosis ratio, and expression of apoptosis-related molecules (Bcl-2, Bax, caspase-3, cleaved caspase-3, and cleaved PARP). Compared with the control NP cells, IL-1β significantly increased caspase-3 activity, NP cell apoptosis ratio and mRNA/protein expression of Bax, caspase-3, cleaved caspase-3 and cleaved PARP, but decreased mRNA expression of Bcl-2. However, resveratrol partly suppressed the effects of IL-1β on those cell apoptosis-related parameters. Further analysis showed that IL-1β significantly decreased activity of the PI3K/Akt pathway whereas resveratrol partly increased activity of the PI3K/Akt pathway in NP cells treated with IL-1β. Additionally, when the inhibitor LY294002 was added along with the resveratrol, its protective effects against IL-1β-induced NP cell apoptosis were attenuated. In conclusion, resveratrol suppresses IL-1β-mediated NP cell apoptosis through activating the PI3K/Akt pathway. Resveratrol may be an effective drug to attenuate inflammatory cytokine-induced disc degenerative changes.

Involvement of epigenetics in osteoarthritis

Osteoarthritis (OA) is the most prevalent chronic age-related arthritic disease that mainly affects the diarthrodial joints. Nevertheless, there is no treatment currently available that can effectively reduce symptoms or slow down or stop disease progression. The lack of disease-modifying therapies could be explained by the complex pathogenesis of OA, which is still not completely understood. Intertwined epigenetic mechanisms such as DNA methylation, histone modifications, and noncoding RNAs (ncRNAs) have been indicated as important cellular tools to maintain tissue homeostasis upon environmental challenges. The current review illustrates that dysfunctional epigenetic control mechanisms in the articular cartilage likely play an important role in driving OA pathophysiology.

Activation of AMPK-SIRT3 signaling is chondroprotective by preserving mitochondrial DNA integrity and function

OBJECTIVE

In osteoarthritis (OA), articular chondrocytes manifest mitochondrial damage, including mitochondrial DNA 4977-bp (mtDNA⁴⁹⁷⁷) deletion that impairs mitochondrial function. OA chondrocytes have decreased activity of AMPK, an energy biosensor that promotes mitochondrial biogenesis. Here, we tested if pharmacologic AMPK activation, via downstream activation of predominately mitochondrially localized sirtuin 3 (SIRT3), reverses existing decreases in mitochondrial DNA (mtDNA) integrity and function in human OA chondrocytes and limits mouse knee OA development.

DESIGN

We assessed mtDNA integrity and function including the common mtDNA⁴⁹⁷⁷ deletion and mtDNA content, mitochondrial reactive oxygen species (mtROS) generation, oxygen consumption and intracellular ATP levels. Phosphorylation of AMPKα, expression and activity of SIRT3, acetylation and expression of the mitochondrial antioxidant enzyme SOD2 and DNA repair enzyme 8-oxoguanine glycosylase (OGG1), and expression of subunits of mitochondrial respiratory complexes were examined. We assessed effect of pharmacologic activation of AMPK on age-related spontaneous mouse knee OA.

RESULTS

The mtDNA⁴⁹⁷⁷ deletion was detected in both OA chondrocytes and menadione-treated normal chondrocytes, associated with increased mtROS, decreased SIRT3, and increased acetylation of SOD2 and OGG1. AMPKα1 deficient chondrocytes exhibited significantly reduced SIRT3 activity. AMPK pharmacologic activation attenuated existing mtDNA⁴⁹⁷⁷ deletion and improved mitochondrial functions in OA chondrocytes via SIRT3 by reducing acetylation and increasing expression of SOD2 and OGG1, and limited aging-associated mouse knee OA development and progression.

CONCLUSIONS

AMPK activation, via SIRT3, limits oxidative stress and improves mtDNA integrity and function in OA chondrocytes. These effects likely contribute to chondroprotective effects of AMPK activity.

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.

Resveratrol delivery by ultrasound-mediated nanobubbles targeting nucleus pulposus cells

Aim: To improve nucleus pulposus cell-targeted therapy for intervertebral disc degeneration (IDD) by fabricating a novel kind of ultrasound (US)-mediated poly(lactic-co-glycolic acid) nanobubbles (NBs) as a means of targeted drug delivery. Materials & methods: The resveratrol (RES)-embedded NBs were synthesized using a double-emulsion method. The active NP cell-targeting biomarker CDH2 antibody (AbCDH2) was further conjugated to the NBs using a carbodiimide method. Then, this RES/AbCDH2 NBs were examined by physical properties, specifc cell-targeting ability, anticatabolism effect in vitro and in vivo. Results: RES/AbCDH2 NBs exhibited high RES-loading efficiency, and US triggered accelerated RES release. Furthermore, RES/AbCDH2 NB treatment exhibited excellent anticatabolic ability in vitro; and in an IDD rabbit model, US-mediated RES/AbCDH2 NB injection effectively retarded the degenerative process of the intervertebral disc in vivo. Conclusion: The combination of US irradiation and drug delivery through RES/AbCDH2 NBs can be considered as a novel treatment option for IDD.

[Resveratrol regulate the extracellular matrix expression via Wnt/β-catenin pathway in nucleus pulposus cells]

Objective

To investigate the regulatory effect of resveratrol (RES) on the extracellular matrix (ECM) expression of nucleus pulposus cells (NPC), and its relative molecular mechanism.

Methods

Ten patients receiving discectomy were collected, of which 5 patients were young with spinal burst fracture, classified as control group; the rest 5 patients were senile with lumbar disc herniation, classified as degenerative group. The nucleus pulposus tissue of 2 groups were collected, the in situexpression of β-catenin was detected by immunohistochemistry, and the protein expressions of collagen type Ⅱ and Aggrecan were detected by Western blot. The NPC were isolated and cultured from degenerative nucleus pulposus tissues. RES treated the third-passage NPC with (group B) or without IL-1β (group C), to further determine the protein expressions of collagen type Ⅱ and Aggrecan by Western blot, the unstimulated cells were set up as blank control group (group A). Moreover, NPC treated with small interfering RNA (siRNA) targeted silent SIRT1 or β-catenin were used to determine the protein and gene expressions of β-catenin and SIRT1 by Western blot and real-time fluorescence quantitative PCR. In addition, the third-passage NPC treated with complete medium (group 1), IL-1β (group 2), RES+IL-1β (group 3), and SIRT1-siRNA+RES+IL-1β (group 4) for 24 hours were used to detect the nuclear translocation of β-catenin by cell immunofluorescence staining. Finally, the third-passage NPC treated with complete medium (group Ⅰ), IL-1β (group Ⅱ), IL-1β+β-catenin-siRNA (group Ⅲ), IL-1β+RES (group Ⅳ), and IL-1β+RES+SIRT1-siRNA (group Ⅴ) for 24 hours were used to detect the protein expressions of collagen type Ⅱ and Aggrecan by Western blot.

Results

Immunohistochemical staining and Western blot detection showed that when compared with control group, the cell proportion of expression of β-catenin were significantly increased in degenerative group ( t=4.616, P=0.010); the protein expression of β-catenin was also significantly increased and the protein expressions of collagen type Ⅱ and Aggrecan were significantly decreased ( P<0.05). In cytology experiments, the protein expression of β-catenin in group B was significantly higher than that in groups A and C, and the protein expressions of collagen type Ⅱ and Aggrecan in group B were significantly lower than those in groups A and C ( P<0.05). After transfection of siRNA, the protein expressions of SIRT1 and β-catenin significantly decreased ( P<0.05). The results of cell immunofluorescence staining further confirmed that when compared with group 3, after the SIRT1 was silenced by siRNA in group 4, the attenuated nuclear translocation of β-catenin by RES treatment was aggravated. Western blot results showed that the protein expressions of collagen type Ⅱ and Aggrecan in group Ⅱ were significantly lower than those in group Ⅰ( P<0.05); after transfection of β-catenin-siRNA in group Ⅲ, the degradation of ECM by IL-1β was obviously inhibited, the protein expressions of collagen type Ⅱ and Aggrecan were significantly increased when compared with group Ⅱ ( P<0.05); after transfection of SIRT1-siRNA in group Ⅴ, the protective effect of RES on the degradation of ECM was inhibited, the protein expressions of collagen type Ⅱ and Aggrecan were significantly decreased when compared with group Ⅳ ( P<0.05).

Conclusion

RES regulates the ECM expression of NPC via Wnt/β-catenin signaling pathway, which provide a new idea for intervertebral disc degeneration disease treatment.

SIRT7 is an important regulator of cartilage homeostasis and osteoarthritis development

Sirtuins (SIRT1-7) are NAD+-dependent deacetylase/deacylases that regulate a wide variety of biological functions. Although the roles of sirtuins in cartilage homeostasis and cartilage diseases have been well studied, there is no information on the contribution of SIRT7 to cartilage homeostasis and osteoarthritis (OA) pathologies. Here, we demonstrate that Sirt7 knockout mice are resistant to the development of aging-associated OA and forced exercise-induced OA. Attenuation of Sirt7 in the murine chondrogenic cell line ATDC5 increased the deposition of a glycosaminoglycan-rich extracellular matrix and the mRNA expression of extracellular matrix components such as Col2a1 and Acan. Mechanistically, we found that SIRT7 suppressed the transcriptional activity of SOX9, which is an important transcription factor in chondrocytes, and that the enzymatic activity of SIRT7 was required for its function. Our results indicate that SIRT7 is a novel important regulator of cartilage homeostasis and OA development.

Resveratrol downregulates inflammatory pathway activated by lymphotoxin α (TNF-β) in articular chondrocytes: Comparison with TNF-α

While Lymphotoxin α (TNF-β), a product of lymphocytes, is known to play a pivotal role in inflammatory joint environment, resveratrol has been shown to possess anti-inflammatory and chondroprotective effects via activation of the histondeacetylase Sirt1. Whether TNF-β induction of inflammatory pathways in primary human chondrocytes (PCH) can be modulated by resveratrol, was investigated. Monolayer and alginate cultures of PCH were treated with TNF-β, anti-TNF-β, nicotinamide (NAM), antisense oligonucleotides against Sirt1 (Sirt1-ASO) and/or resveratrol and co-cultured with T-lymphocytes. We found that resveratrol suppressed, similar to anti-TNF-β, TNF-β-induced increased adhesiveness in an inflammatory microenvironment of T-lymphocytes and PCH. In contrast, knockdown of Sirt1 by mRNA abolished the inhibitory effects of resveratrol on the TNF-β-induced adhesiveness, suggesting the essential role of this enzyme for resveratrol-mediated anti-inflammatory signaling. Similar results were obtained in PCH stimulated with TNF-α. Sirt1-ASO, NAM or TNF-β, similar to T-lymphocytes induced inflammatory microenvironment by down-regulation of cartilage-specific proteins, Sox9, Ki67 and enhanced NF-κB-regulated gene products involved in inflammatory and degradative processes in cartilage (MMP-9/-13, COX-2, caspase-3), NF-κB activation and its translocation to the nucleus. Moreover, resveratrol reversed the TNF-β-, NAM-, T-lymphocytes-induced up-regulation of various NF-κB-regulated gene products. Down-regulation of Sirt1 by mRNA interference abrogated the effect of resveratrol on TNF-β-induced effects. Ultrastructural and cell viability assay investigations revealed that resveratrol revoked TNF-β-induced dose-dependent degradative/apoptotic morphological changes, cell viability and proliferation in PCH. Taken together, suppression of TNF-β-induced inflammatory microenvironment in PCH by resveratrol/Sirt1 might be a novel therapeutic approach for targeting inflammation during rheumatoid arthritis.

SIRT1 promotes tumor-like invasion of fibroblast-like synoviocytes in rheumatoid arthritis via targeting TIMP1

Suppression of tissue inhibitor of matrix metalloproteinase (TIMP) is associated with the tumor-like invasion of fibroblast-like synoviocytes (FLSs) that occurs during rheumatoid arthritis-related cartilage destruction. Silent information regulator 2 homolog1 (SIRT1), a histone deacetylase, is widely involved in transcriptional regulation, genomic stability, metabolism and DNA repair. Recent studies suggest that SIRT1 may also impact inflammatory response and the proliferation of FLSs in rheumatoid arthritis (RA). However, it is unknown whether SIRT1 has a role in the tumor-like invasion of FLSs in rheumatoid arthritis. Herein we report that SIRT1 contributes to FLS invasion and cartilage destruction via a TIMP1-dependent mechanism. Elevated SIRT1 in RA synovia suppresses TIMP1 expression via deacetylation of TIMP1-associated histones, thereby disrupting the binding of the transcription factor specificity protein 1 (Sp1) to the TIMP1 promoter. In rats with collagen-induced arthritis, depletion of SIRT1 remarkably promoted TIMP1 expression in synovial tissues and ameliorated cartilage destruction. These results describe a new role for SIRT1 and demonstrate its potential value as a therapeutic target for rheumatoid arthritis.

DOT1L safeguards cartilage homeostasis and protects against osteoarthritis

Osteoarthritis is the most prevalent and crippling joint disease, and lacks curative treatment, as the underlying molecular basis is unclear. Here, we show that DOT1L, an enzyme involved in histone methylation, is a master protector of cartilage health. Loss of DOT1L disrupts the molecular signature of healthy chondrocytes in vitro and causes osteoarthritis in mice. Mechanistically, the protective function of DOT1L is attributable to inhibition of Wnt signalling, a pathway that when hyper-activated can lead to joint disease. Unexpectedly, DOT1L suppresses Wnt signalling by inhibiting the activity of sirtuin-1 (SIRT1), an important regulator of gene transcription. Inhibition of SIRT1 protects against osteoarthritis triggered by loss of DOT1L activity. Modulating the DOT1L network might therefore be a therapeutic approach to protect the cartilage against osteoarthritis.

The acetyl code in rheumatoid arthritis and other rheumatic diseases

Growing evidence supports the idea that aberrancies in epigenetic processes contribute to the onset and progression of human immune-mediated inflammatory diseases, such as rheumatoid arthritis (RA). Epigenetic regulators of histone tail modifications play a role in chromatin accessibility and transcriptional responses to inflammatory stimuli. Among these, histone deacetylases (HDACs) regulate the acetylation status of histones and nonhistone proteins, essential for immune responses. Broad-spectrum HDAC inhibitors are well-known anti-inflammatory agents and reduce disease severity in animal models of arthritis; however, selective HDAC inhibitors remain poorly studied. In this review, we describe emerging findings regarding the aberrant acetyl code in RA and other rheumatic disorders which may help identify not only novel diagnostic and prognostic clinical biomarkers for RA, but also new targets for epigenetic pharmacological applications.