SirT1 enhances survival of human osteoarthritic chondrocytes by repressing protein tyrosine phosphatase 1B and activating the insulin-like growth factor receptor pathway

Metformin prevents the onset and progression of intervertebral disc degeneration: New insights and potential mechanisms (Review)

Metformin has been the go‑to medical treatment for addressing type 2 diabetes mellitus (T2DM) as a frontline oral antidiabetic. Obesity, cancer and bone deterioration are linked to T2DM, which is considered a metabolic illness. Numerous diseases associated with T2DM, such as tumours, cardiovascular disease and bone deterioration, may be treated with metformin. Intervertebral disc degeneration (IVDD) is distinguished by degeneration of the spinal disc, accompanied by the gradual depletion of proteoglycans and water in the nucleus pulposus (NP) of the IVD, resulting in lower back pain. The therapeutic effect of metformin on IVDD has also attracted much attention. By stimulating AMP‑activated kinase, metformin could enhance autophagy and suppress cell senescence, apoptosis and inflammation, thus effectively delaying IVDD. The present review aimed to systematically explain the development of IVDD and mechanism of metformin in the treatment and prevention of IVDD to provide a reference for the clinical application of metformin as adjuvant therapy in the treatment of IVDD.

Quercetin Modulates Ferroptosis via the SIRT1/Nrf-2/HO-1 Pathway and Attenuates Cartilage Destruction in an Osteoarthritis Rat Model

Osteoarthritis (OA) is the most common joint disease, causing symptoms such as joint pain, swelling, and deformity, which severely affect patients' quality of life. Despite advances in medical treatment, OA management remains challenging, necessitating the development of safe and effective drugs. Quercetin (QUE), a natural flavonoid widely found in fruits and vegetables, shows promise due to its broad range of pharmacological effects, particularly in various degenerative diseases. However, its role in preventing OA progression and its underlying mechanisms remain unclear. In this study, we demonstrated that QUE has a protective effect against OA development both in vivo and in vitro, and we elucidated the underlying molecular mechanisms. In vitro, QUE inhibited the expression of IL-1β-induced chondrocyte matrix metalloproteinases (MMP3 and MMP13) and inflammatory mediators such as INOS and COX-2. It also promoted the expression of collagen II, thereby preventing the extracellular matrix (ECM). Mechanistically, QUE exerts its protective effect on chondrocytes by activating the SIRT1/Nrf-2/HO-1 and inhibiting chondrocyte ferroptosis. Similarly, in an OA rat model induced by anterior cruciate ligament transection (ACLT), QUE treatment improved articular cartilage damage, reduced joint pain, and normalized abnormal subchondral bone remodeling. QUE also reduced serum IL-1β, TNF-α, MMP3, CTX-II, and COMP, thereby slowing the progression of OA. QUE exerts chondroprotective effects by inhibiting chondrocyte oxidative damage and ferroptosis through the SIRT1/Nrf-2/HO-1 pathway, effectively alleviating OA progression in rats.

A Novel Role for Protein Tyrosine Phosphatase 1B in Alleviating Chondrocyte Senescence

Osteoarthritis (OA) is a kind of arthritis that impairs movement and causes joint discomfort. Recent research has demonstrated a connection between cellular senescence and the degenerative processes of OA chondrocytes. In yeast and human cells, protein tyrosine phosphatase 1B (PTP1B) knockdown prolongs longevity; however, the function of PTP1B in chondrocyte senescence has not been investigated. The goal of the current investigation was to evaluate PTP1B's contribution to human OA chondrocyte senescence. The function of PTP1B and cellular senescence in the onset of OA was investigated and confirmed by using a combination of bioinformatics techniques, clinical samples, and in vitro experimental procedures. The RNA sequencing data pertinent to the OA were obtained using the Gene Expression Omnibus database. Function enrichment analysis, protein-protein correlation analysis, the construction of the correlation regulatory network, and an investigation into possible connections between PTP1B and cellular senescence in OA were all carried out using various bioinformatic techniques. Compared with healthy cartilage, PTP1B expression was increased in OA cartilage. According to a Pearson correlation study, cellular senescence-related genes, including MAP2K1 and ABL1, were highly correlated with PTP1B expression levels in senescent chondrocytes. Furthermore, in vitro tests confirmed that PTP1B knockdown slowed cartilage degradation and prevented chondrocyte senescence in OA. In conclusion, we showed that PTP1B knockdown prevented the senescence of chondrocytes and prevented cartilage degradation in OA. These findings offer a fresh perspective on the pathophysiology of OA, opening up new avenues for OA clinical diagnosis and targeted treatment.

Two-year post-distraction cartilage-related structural improvement is accompanied by increased serum full-length SIRT1

BACKGROUND

Previously, fragments from Sirtuin 1 (SIRT1) were identified in preclinical and clinical samples to display an increase in serum levels for N-terminal (NT) SIRT1 vs. C-terminal (CT) SIRT1, indicative of early signs of OA. Here we tested NT/CT SIRT1 levels as well as a novel formulated sandwich assay to simultaneously detect both domains of SIRT1 in a manner that may inform us about the levels of full-length SIRT1 in the circulation (flSIRT1) of clinical cohorts undergoing knee joint distraction (KJD).

METHODS

We employed an indirect ELISA assay to test NT- and CT-SIRT1 levels and calculated their ratio. Further, to test flSIRT1 we utilized novel antibodies (Ab), which were validated for site specificity and used in a sandwich ELISA method, wherein the CT-reactive served as capture Ab, and its NT-reactive served as primary detection Ab. This method was employed in human serum samples derived from a two-year longitudinal study of KJD patients. Two-year clinical and structural outcomes were correlated with serum levels of flSIRT1 compared to baseline.

RESULTS

Assessing the cohort, exhibited a significant increase of NT/CT SIRT1 serum levels with increased osteophytes and PIIANP/CTX-II at baseline, while a contradictory increase in NT/CT SIRT1 was associated with less denuded bone, post-KJD. On the other hand, flSIRT1 exhibited an upward trend in serum level, accompanied by reduced denuded bone for 2-year adjusted values. Moreover, 2 year-adjusted flSIRT1 levels displayed a steeper linear regression for cartilage and bone-related structural improvement than those observed for NT/CT SIRT1.

CONCLUSIONS

Our data support that increased flSIRT1 serum levels are a potential molecular endotype for cartilage-related structural improvement post-KJD, while NT/CT SIRT1 appears to correlate with osteophyte and PIIANP/CTX-II reduction at baseline, to potentially indicate baseline OA severity.

Unraveling the path to osteoarthritis management: targeting chondrocyte apoptosis for therapeutic intervention

Osteoarthritis (OA) is a chronic disease affecting joints and further causing disabilities. This disease affects around 240 million people worldwide. It is a multifactorial disease, and its etiology is difficult to determine. Although numerous therapeutic strategies are available, the therapies are aimed at reducing pain and improving patients' quality of life. Hence, there is an urgent need to develop disease-modifying drugs (DMOAD) that can reverse or halt OA progression. Apoptosis is a cell removal process that is important in maintaining homeostatic mechanisms in the development and sustaining cell population. The apoptosis of chondrocytes is believed to play an important role in OA progression due to poor chondrocytes self-repair abilities to maintain the extracellular matrix (ECM). Hence, targeting chondrocyte apoptosis can be one of the potential therapeutic strategies in OA management. There are various mediators and targets available to inhibit apoptosis such as autophagy, endoplasmic reticulum (ER) stress, oxidative stress, and inflammation. As such, this review highlights the importance and potential targets that can be aimed to reduce chondrocyte apoptosis.

Correlation between Mitochondria-Associated Endoplasmic Reticulum Membrane-Related Genes and Cellular Senescence-Related Genes in Osteoarthritis

BACKGROUND

The role of mitochondria-associated endoplasmic reticulum membrane (MAM) formation in the development of osteoarthritis (OA) is yet unclear.

METHODS

A mix of bioinformatics methods and in vitro experimental methodologies was used to study and corroborate the role of MAM-related genes and cellular senescence-related genes in the development of OA. The Gene Expression Omnibus database was used to obtain the microarray information that is relevant to the OA. Several bioinformatic methods were employed to carry out function enrichment analysis and protein-protein correlation analysis, build the correlation regulatory network, and investigate potential relationships between MAM-related genes and cellular senescence-related genes in OA. These methods also served to identify the MAM-related and OA-related genes (MAM-OARGs).

RESULTS

For the additional functional enrichment analysis, a total of 13 MAM-OARGs were detected. The correlation regulatory network was also created. Hub MAM-OARGs were shown to have a strong correlation with genes relevant to cellular senescence in OA. Results of in vitro experiments further demonstrated a positive correlation between MAM-OARGs (PTPN1 and ITPR1) and cellular senescence-related and OA-related genes.

CONCLUSIONS

As a result, our findings can offer new insights into the investigations of MAM-related genes and cellular senescence-related genes, which could be linked to the OA as well as brand-new potential treatment targets.

Melatonin and bone-related diseases: an updated mechanistic overview of current evidence and future prospects

PURPOSE

Bone diseases account for an enormous cost burden on health systems. Bone disorders are considered as age-dependent diseases. The aging of world population has encouraged scientists to further explore the most effective preventive modalities and therapeutic strategies to overcome and reduce the high cost of bone disorders. Herein, we review the current evidence of melatonin's therapeutic effects on bone-related diseases.

METHODS

This review summarized evidences from in vitro, in vivo, and clinical studies regarding the effects of melatonin on bone-related diseases, with a focus on the molecular mechanisms. Electronically, Scopus and MEDLINE®/PubMed databases were searched for articles published on melatonin and bone-related diseases from inception to June 2023.

RESULTS

The findings demonstrated that melatonin has beneficial effect in bone- and cartilage-related disorders such as osteoporosis, bone fracture healing, osteoarthritis, and rheumatoid arthritis, in addition to the control of sleep and circadian rhythms.

CONCLUSION

A number of animal and clinical studies have indicated that various biological effects of melatonin may suggest this molecule as an effective therapeutic agent for controlling, diminishing, or suppressing bone-related disorders. Therefore, further clinical studies are required to clarify whether melatonin can be effective in patients with bone-related diseases.

Cisplatin triggers oxidative stress, apoptosis and pro-inflammatory responses by inhibiting the SIRT1-mediated Nrf2 pathway in chondrocytes

Although the height of the proliferating layer that was suppressed in the growth plate has been recognized as an adverse effect of cisplatin in pediatric cancer survivors, the detailed pathological mechanism has not been elucidated. Sirtuin-1 (SIRT1) has been reported as an essential modulator of cartilage homeostasis, but its role in cisplatin-induced damage of chondrocytes remains unclear. In this study, we examined how cisplatin affected the expression of SIRT1 and cell viability. Next, we showed downregulation of SIRT1 after cisplatin treatment resulted in suppression of Peroxisome proliferator-activated receptor-gamma coactivator (PGC-1α), leading to inhibition of Nrf2 nuclear translocation and subsequently decreased Heme oxygenase-1(HO-1) and NAD(P)H Quinone Dehydrogenase 1(NQO-1) expression. Blockage of the SIRT1/ PGC-1α axis not only increased oxidative stress with lower antioxidant SOD and GSH, but also contributed to mitochondrial dysfunction evidenced by the collapse of membrane potential and repression of mitochondrial DNA copy number and ATP. We also found that Cisplatin up-regulated the p38 phosphorylation, pro-inflammatory events and matrix metalloproteinases (MMPs) in chondrocytes through the SIRT1-modulated antioxidant manner. Collectively, our findings suggest that preservation of SIRT1 in chondrocytes may be a potential target to ameliorate growth plate dysfunction for cisplatin-receiving pediatric cancer survivors.

The epigenetic players and the chromatin marks involved in the articular cartilage during osteoarthritis

Epigenetics defines the modifications of the genome that do not involve a change in the nucleotide sequence of DNA. These modifications constitute a mechanism of gene regulation poorly explored in the context of cartilage physiology. They are now intensively studied by the scientific community working on articular cartilage and its related pathology such as osteoarthritis. Indeed, epigenetic regulations can control the expression of crucial gene in the chondrocytes, the only resident cells of cartilage. Some epigenetic changes are considered as a possible cause of the abnormal gene expression and the subsequent alteration of the chondrocyte phenotype (hypertrophy, proliferation, senescence…) as observed in osteoarthritic cartilage. Osteoarthritis is a joint pathology, which results in impaired extracellular matrix homeostasis and leads ultimately to the progressive destruction of cartilage. To date, there is no pharmacological treatment and the exact causes have yet to be defined. Given that the epigenetic modifying enzymes can be controlled by pharmacological inhibitors, it is thus crucial to describe the epigenetic marks that enable the normal expression of extracellular matrix encoding genes, and those associated with the abnormal gene expression such as degradative enzyme or inflammatory cytokines encoding genes. In this review, only the DNA methylation and histone modifications will be detailed with regard to normal and osteoarthritic cartilage. Although frequently referred as epigenetic mechanisms, the regulatory mechanisms involving microRNAs will not be discussed. Altogether, this review will show how this nascent field influences our understanding of the pathogenesis of OA in terms of diagnosis and how controlling the epigenetic marks can help defining epigenetic therapies.

Sirt6 attenuates chondrocyte senescence and osteoarthritis progression

Sirt6 has been implicated as a key regulator in aging-related diseases, including osteoarthritis. However, its functional role and molecular mechanism in chondrocyte senescence and osteoarthritis pathophysiology remain largely undefined. Here we show that Sirt6 deficiency exaggerates chondrocyte senescence and osteoarthritis progression, whereas intra-articular injection of adenovirus-Sirt6 markedly attenuates surgical destabilization of medial meniscus-induced osteoarthritis. Mechanistically, Sirt6 can directly interact with STAT5 and deacetylate STAT5, thus inhibiting the IL-15/JAK3-induced STAT5 translocation from cytoplasm to nucleus, which inactivates IL-15/JAK3/STAT5 signaling. Mass spectrometry revealed that Sirt6 deacetylated conserved lysine 163 on STAT5. Mutation of lysine 163 to arginine in STAT5 abolished the regulatory effect of Sirt6. In vivo, specific ablation of Sirt6 in chondrocytes exacerbated osteoarthritis. Pharmacological activation of Sirt6 substantially alleviated chondrocyte senescence. Taken together, Sirt6 attenuates chondrocyte senescence by inhibiting IL-15/JAK3/STAT5 signaling. Targeting Sirt6 represents a promising new approach for osteoarthritis.

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.

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.

Safranal Treatment Induces Sirt1 Expression and Inhibits Endoplasmic Reticulum Stress in Mouse Chondrocytes and Alleviates Osteoarthritis Progression in a Mouse Model

Osteoarthritis (OA) is an age-related degenerative disease. Oxidative stress (OS) modulates OA pathogenesis by enhancing chondrocyte apoptosis and extracellular matrix (ECM) degeneration via activation of the endoplasmic reticulum (ER) stress. Prior studies revealed that safranal plays a critical role in multiple diseases treatments, but there are no reports on its effect on OA. Therefore, investigating the effect of safranal on OA is needed. As a compound that can lead excessive reactive oxygen species (ROS) accumulation, tert-butyl hydroperoxide (TBHP) was used to induce OS and OS-mediated endoplasmic reticulum (ER) stress for imitating OA in vitro. Besides, the bilateral medial meniscus was removed to induce joint instability and excessive friction of the joint surface to establish destabilization of medial meniscus for imitating the initiation and progression of OA in vivo. We, next, conducted Western blot and RT-PCR analyses to identify biomarkers of the underlying signaling pathway. Our results demonstrated that 30 μM safranal strongly upregulated Sirt1 expression, suppressed TBHP-mediated ER stress, and, in turn, prevented chondrocyte apoptosis and ECM degeneration. Furthermore, compared with the other two classic signaling pathways of ER stress, safranal can inhibit the PERK-eIF2α-CHOP axis at the lower concentration (5 and 15 μM). In vivo, using Safranin O staining, X-ray, immunofluorescence (IF), and immunohistochemical (IHC) staining, we demonstrated that OA progression can be postponed with intraperitoneal injection of 90 and 180 mg/kg safranal in an OA mouse model. Taken together, our analyses revealed that safranal can potentially prevent OA development.

Omentin-1 alleviate interleukin-1β(IL-1β)-induced nucleus pulposus cells senescence

One of the main causes of low back pain (LBP) and degenerative musculoskeletal disorders is intervertebral disc degeneration (IVDD). Inflammation-associated senescence of Human nucleus pulposus cells (HNPCs) plays an essential function in the disease progression of IVDD. Omentin-1 is an adipokine that has been recently reported to have anti-inflammatory potential. In our research, IL-1β was used to simulate the inflammatory environment in the IVDD. We investigated in vitro the effects of Omentin-1 on HNPCs, including the components of senescence, cell cycle and extracellular matrix (ECM) synthesis. The results showed that the addition of Omentin-1 improved IL-1β-induced senescence in HNPCs. G1 phase cell cycle arrest and reduced ECM synthesis in HNPCs. Furthermore, we demonstrated that the effect of Omentin-1 in reducing senescence of HNPCs is dependent on SIRT1. These findings suggest that Omentin-1 plays an important function in protecting HNPCs against senescence and has the potential for IVDD gene target therapy.

Adipokine Signaling Pathways in Osteoarthritis

Osteoarthritis (OA) is a debilitating joint disease that affects millions of individuals. The pathogenesis of OA has not been fully elucidated. Obesity is a well-recognized risk factor for OA. Multiple studies have demonstrated adipokines play a key role in obesity-induced OA. Increasing evidence show that various adipokines may significantly affect the development or clinical course of OA by regulating the pro/anti-inflammatory and anabolic/catabolic balance, matrix remodeling, chondrocyte apoptosis and autophagy, and subchondral bone sclerosis. Several signaling pathways are involved but still have not been systematically investigated. In this article, we review the cellular and molecular mechanisms of adipokines in OA, and highlight the possible signaling pathways. The review suggested adipokines play important roles in obesity-induced OA, and exert downstream function via the activation of various signaling pathways. In addition, some pharmaceuticals targeting these pathways have been applied into ongoing clinical trials and showed encouraging results. However, these signaling pathways are complex and converge into a common network with each other. In the future work, more research is warranted to further investigate how this network works. Moreover, more high quality randomised controlled trials are needed in order to investigate the therapeutic effects of pharmaceuticals against these pathways for the treatment of OA. This review may help researchers to better understand the pathogenesis of OA, so as to provide new insight for future clinical practices and translational research.

Protein tyrosine phosphatases in skeletal development and diseases

Skeletal development and homeostasis in mammals are modulated by finely coordinated processes of migration, proliferation, differentiation, and death of skeletogenic cells originating from the mesoderm and neural crest. Numerous molecular mechanisms are involved in these regulatory processes, one of which is protein posttranslational modifications, particularly protein tyrosine phosphorylation (PYP). PYP occurs mainly through the action of protein tyrosine kinases (PTKs), modifying protein enzymatic activity, changing its cellular localization, and aiding in the assembly or disassembly of protein signaling complexes. Under physiological conditions, PYP is balanced by the coordinated action of PTKs and protein tyrosine phosphatases (PTPs). Dysregulation of PYP can cause genetic, metabolic, developmental, and oncogenic skeletal diseases. Although PYP is a reversible biochemical process, in contrast to PTKs, little is known about how this equilibrium is modulated by PTPs in the skeletal system. Whole-genome sequencing has revealed a large and diverse superfamily of PTP genes (over 100 members) in humans, which can be further divided into cysteine (Cys)-, aspartic acid (Asp)-, and histidine (His)-based PTPs. Here, we review current knowledge about the functions and regulatory mechanisms of 28 PTPs involved in skeletal development and diseases; 27 of them belong to class I and II Cys-based PTPs, and the other is an Asp-based PTP. Recent progress in analyzing animal models that harbor various mutations in these PTPs and future research directions are also discussed. Our literature review indicates that PTPs are as crucial as PTKs in supporting skeletal development and homeostasis.

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.

Inhibition of Knee Osteoarthritis Progression in Mice by Administering SRT2014, an Activator of Silent Information Regulator 2 Ortholog 1

OBJECTIVE

Previous findings suggest that silent information regulator 2 ortholog 1 (SIRT1) plays essential roles in chondrocytes and prevents osteoarthritis (OA) development. The purpose of this study was to investigate the effects of intraperitoneal (i.p.) and intra-articular (i.a.) administration of the SIRT1 activator SRT2104, which has been approved for use in humans.

DESIGN

OA was induced by destabilizing the medial meniscus in the knee joint of 12-week-old CL57BL/6J mice. The mice were divided into 3 groups, that is, the control group, SRT2104 i.p.-injection group, and SRT2104 i.a.-injection group. Tissues were harvested at 4, 8, 12, and 16 weeks postsurgery. OA progression was evaluated using the Osteoarthritis Research Society International (OARSI) score. The production of OA-related proteins in cartilage and synovium was examined by immunohistochemistry.

RESULTS

OARSI scores in the control group were significantly higher at 8 and 12 weeks compared with other 2 groups. Immunohistochemical analysis showed that Sirt1 and type-2 collagen significantly increased, whereas MMP-13, ADAMTS-5, IL-1β, IL-6, cleaved caspase 3, PARP p85, acetylated NF-κB p65, and iNOS decreased significantly in cartilage tissues from the i.p. and i.a, SRT2104 groups. In the synovium, more iNOS-positive M1-like macrophages were observed in the control group than in the i.p. and i.a, SRT2104 groups, whereas more CD206-positive M2-like macrophages were detected in the i.p. and i.a. SRT2104 groups.

CONCLUSIONS

Both i.p. and i.a. SRT2104 injection reduced OA progression in the mouse OA model, suggesting that SRT2104 can serve as a new treatment for OA.

Echinacoside Upregulates Sirt1 to Suppress Endoplasmic Reticulum Stress and Inhibit Extracellular Matrix Degradation In Vitro and Ameliorates Osteoarthritis In Vivo

Background

Osteoarthritis (OA) is a progressive illness that destroys cartilage. Oxidative stress is a major contributor of OA, while endoplasmic reticulum (ER) stress is the key cellular damage under oxidative stress in chondrocytes. Echinacoside (ECH) is the main extract and active substance of Cistanche, with potent antioxidative stress (OS) properties, and currently under clinical trials in China. However, its function in OA is yet to be determined.

Purpose

We aimed to explore the specific role of ECH in the occurrence and development of OA and its underlying mechanism in vivo and in vitro.

Methods

After the mice were anesthetized, the bilateral medial knee joint meniscus resection was performed to establish the DMM model. TBHP was used to induce oxidative stress to establish the OA model in chondrocytes in vitro. Western blot and RT-PCR were used to evaluate the level of ER stress-related biomarkers such as p-PERK/PERK, GRP78, ATF4, p-eIF2α/eIF2α, and CHOP and apoptosis-related proteins such as BAX, Bcl-2, and cleaved caspase-3. Meanwhile, we used SO staining, immunofluorescence, and immunohistochemical staining to evaluate the pharmacological effects of ECH in mice in vivo.

Results

We demonstrated the effectiveness of ECH in suppressing ER stress and restoring ECM metabolism in vitro. In particular, ECH was shown to suppress tert-Butyl hydroperoxide- (TBHP-) induced OS and subsequently lower the levels of p-PERK/PERK, GRP78, ATF4, p-eIF2α/eIF2α, and CHOP in vitro. Simultaneously, ECH reduced MMP13 and ADAMTS5 levels and promoted Aggrecan and Collagen II levels, suggesting ECM degradation suppression. Moreover, we showed that ECH mediates its cellular effects via upregulation of Sirt1. Lastly, we confirmed that ECH can protect against OA in mouse OA models.

Conclusion

In summary, our findings indicate that ECH can inhibit ER stress and ECM degradation by upregulating Sirt1 in mouse chondrocytes treated with TBHP. It can also prevent OA development in vivo.

Dual Role of SIRT1 in Autophagy and Lipid Metabolism Regulation in Osteoarthritic Chondrocytes

Background and Objectives: Osteoarthritis (OA) is one of the most common and highly prevalent types of arthritis, also considered a multiphenotypic disease with a strong metabolic component. Ageing is the primary risk factor for OA, while the age-related decline in autophagic activity affects cell function and chondrocyte homeostasis. The aim of this study was to investigate the role of sirtuin 1 (SIRT1) in autophagy dysregulation and lipid metabolism in human OA chondrocytes. Materials and Methods: OA chondrocytes were treated with Resveratrol, Hydroxycloroquine (HCQ) or 3-Methyladenine (3-MA) and HCQ or 3-MA followed by siRNA against SIRT1 (siSIRT1). Then, SIRT1, AcNF-κBp65, LOX-1 and autophagy-related proteins ATG5, ATG13, PI3K class III, Beclin-1, LC3 and ULK protein levels were evaluated using Western blot. Normal articular chondrocytes were treated under serum starvation and/or siSIRT1, and the protein expression levels of the above autophagy-related proteins were evaluated. The staining patterns of LC3/p62 and LOX-1 were analyzed microscopically by immunofluorescence. SIRT1/LC3 complex formation was analyzed by immunoprecipitation. Results: SIRT1 and LOX-1 protein expression were negatively correlated in OA chondrocytes. SIRT1 regulated LOX-1 expression via NF-κΒ deacetylation, while treatment with Resveratrol enhanced SIRT1 enzymatic activity, resulting in LOX-1 downregulation and autophagy induction. In OA chondrocytes, SIRT1 was recognized as an autophagy substrate, formed a complex with LC3 and was consequently subjected to cytoplasmic autophagosome-lysosome degradation. Moreover, siSIRT1-treated normal chondrocytes showed decreased autophagic activity, while double-treated (siSIRT1 and serum starvation) cells showed no induction of autophagy. Conclusions: Our results suggest that SIRT1 regulates lipid homeostasis through LOX-1 expression regulation. Additionally, we indicate that the necessity of SIRT1 for autophagy induction in normal chondrocytes, together with its selective autophagic degradation in OA chondrocytes, could contribute to autophagy dysregulation in OA. We, therefore, suggest a novel regulatory scheme that functionally connects lipid metabolism and autophagy in late-stage OA.

Knee Osteoarthritis Progression Is Delayed in Silent Information Regulator 2 Ortholog 1 Knock-in Mice

Overexpression of silent information regulator 2 ortholog 1 (SIRT1) is associated with beneficial roles in aging-related diseases; however, the effects of SIRT1 overexpression on osteoarthritis (OA) progression have not yet been studied. The aim of this study was to investigate OA progression in SIRT1-KI mice using a mouse OA model. OA was induced via destabilization of the medial meniscus using 12-week-old SIRT1-KI and wild type (control) mice. OA progression was evaluated histologically based on the Osteoarthritis Research Society International (OARSI) score at 4, 8, 12, and 16 weeks after surgery. The production of SIRT1, type II collagen, MMP-13, ADAMTS-5, cleaved caspase 3, Poly (ADP-ribose) polymerase (PARP) p85, acetylated NF-κB p65, interleukin 1 beta (IL-1β), and IL-6 was examined via immunostaining. The OARSI scores were significantly lower in SIRT1-KI mice than those in control mice at 8, 12, and 16 weeks after surgery. The proportion of SIRT1 and type II collagen-positive-chondrocytes was significantly higher in SIRT1-KI mice than that in control mice. Moreover, the proportion of MMP-13-, ADAMTS-5-, cleaved caspase 3-, PARP p85-, acetylated NF-κB p65-, IL-1β-, and IL-6-positive chondrocytes was significantly lower in SIRT1-KI mice than that in control mice. The mechanically induced OA progression was delayed in SIRT1-KI mice compared to that in control mice. Therefore, overexpression of SIRT1 may represent a mechanism for delaying OA progression.

The potential remedy of melatonin on osteoarthritis

Osteoarthritis (OA), the most common arthritis worldwide, is a degenerative joint disease characterized by progressive cartilage breakdown, subchondral remodeling, and synovial inflammation. Although conventional pharmaceutical therapies aimed to prevent further cartilage loss and joint dysfunction, there are no ideal strategies that target the pathogenesis of OA. Melatonin exhibits a variety of regulatory properties by binding to specific receptors and downstream molecules and exerts a myriad of receptor-independent actions via intracellular targets as a chondrocyte protector, an anti-inflammation modulator, and a free radical scavenger. Melatonin also modulates cartilage regeneration and degradation by directly/indirectly regulating the expression of main circadian clock genes, such as transcriptional activators [brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein (Bmal) and circadian locomotor output cycles kaput (Clock)], transcriptional repressors [period circadian regulator (Per)1/2, cryptochrome (Cry)1/2, and Dec2], and nuclear hormone receptors [Rev-Erbs and retinoid acid-related orphan receptors (Rors)]. Owing to its effects on cartilage homeostasis, we propose a potential role for melatonin in the prevention and therapy of OA via the modulation of circadian clock genes, mitigation of chondrocyte apoptosis, anti-inflammatory activity, and scavenging of free radicals.

Long non-coding RNA MCM3AP-AS1 protects chondrocytes ATDC5 and CHON-001 from IL-1β-induced inflammation via regulating miR-138-5p/SIRT1

Osteoarthritis (OA) is a chronic inflammatory joint disease. Increased apoptosis of chondrocytes contributes to cartilage degradation in OA pathogenesis. The function of lncRNA MCM3AP-AS1 in regulating the viability of chondrocytes still awaits further elaboration. In this work, MCM3AP-AS1, miR-138-5p and SIRT1 mRNA expression levels in OA and normal cartilage tissues were detected by qRT-PCR. Besides, chondrocyte cell lines, CHON-001 and ATDC5 induced by interleukin-1β (IL-1β) were used to initiate the inflammatory response environment of OA. CCK-8 assay was used to examine the cell multiplication; meanwhile, transwell assay was utilized to detect migration. Western blot was adopted to determine SIRT1 expression in chondrocyte. Enzyme-linked immunosorbent assay (ELISA) was performed to evaluate inflammatory factor levels. In addition, the binding sites between MCM3AP-AS1 and miR-138-5p, miR-138-5p and 3'UTR of SIRT1 were validated by dual-luciferase reporter assay, RIP assay or RNA pull-down assay. It was found that MCM3AP-AS1 was declined in OA cartilage tissues, positively interrelated with SIRT1 expression while negatively correlated with miR-138-5p. MCM3AP-AS1 up-regulation enhanced the viability and migration of CHON-001 and ATDC5 cells while restraining the apoptosis and inflammatory response. Additionally, miR-138-5p overexpression counteracted the effects on chondrocytes caused by MCM3AP-AS1 overexpression. MCM3AP-AS1 could adsorb miR-138-5p, and SIRT1 was verified as a target of miR-138-5p, and SIRT1 could be up-regulated by overexpression of MCM3AP-AS1 indirectly. In conclusion, MCM3AP-AS1 has the potential to be the 'ceRNA' to regulate miR-138-5p and SIRT1 in chondrocytes, and to participate in the pathogenesis of OA.

Protective Effect of SIRT1 Activator on the Knee With Osteoarthritis

Osteoarthritis (OA), one of the most common chronic musculoskeletal disorders, is deemed to be correlated with aging. The SIRT1 activator, resveratrol, acts as a crucial regulator of aging and may have a potential therapeutic effect on OA. Rabbit OA models were established through destabilized medial meniscus surgery. A total of 40 healthy male New Zealand rabbits were divided into five groups: control group (sham operation), OA group, as well as low dose (LD), middle dose (MD), and high dose (HD) resveratrol-treated OA groups. 6 weeks after operation, 0.8 ml of normal saline was injected into the knee joints every other day in the control and OA groups, and 0.8 ml of 5, 10, and 15 μmol/L resveratrol was injected into the knee joints every other day in the LD, MD, and HD group, respectively. The rabbits were sacrificed 2 weeks after medication, and the articular cartilage of the knee joint was collected for Micro-CT, histology and Western blot analysis. Obvious articular cartilage lesion and joint space narrowing were detected in the OA group. Compared with the OA group, less osteoarthritic changes were observed in the MD and HD groups. The MD and HD groups had significantly lower bone volume fraction, trabecular number and Mankin scores than the LD and OA groups (p < 0.05). No significant difference was found between the OA and LD groups (p > 0.05). The expressions of SIRT1 and p53 detected by western blot were consistent with the aforementioned findings. Therefore, resveratrol can activate the SIRT1 gene to play a protective role in the OA process by inhibiting chondrocyte apoptosis, trabecular bone number increasing of the subchondral bone, as well as elevation of bone density. It demonstrated the importance of SIRT1 in maintaining articular cartilage health and provided a promising therapeutic intervention in the treatment of OA.

PARP-1 and SIRT-1 are Interacted in Diabetic Nephropathy by Activating AMPK/PGC-1α Signaling Pathway

INTRODUCTION

Diabetic nephropathy (DN) is a metabolic disorder characterized by the accumulation of extracellular matrix (ECM). This study aims to investigate whether exists an interplay between poly (ADP-ribose) polymerase 1 (PARP-1) and sirtuin 1 (SIRT-1) in DN via AMP-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α) signaling pathway.

METHODS

Eight-week-old male obese leptin-resistant (db/db) mice and nondiabetic control male C57BLKs/J (db/m) mice were used in this study. Body weight and blood glucose were evaluated after 6 h of fasting, which continues for 4 weeks. The kidney tissues were dissected for Western blot, immunofluorescence (IF) assay. Besides, PARP activity assay, MTT assay, NAD⁺ qualification, Western blot and IF were also performed to detect the level and relation of PARP-1 and SIRT-1 in mouse mesangial cells (MCs) with or without high glucose followed by inhibiting or elevating PARP-1 and SIRT-1, respectively.

RESULTS

Western blotting shows PARP-1 and ECM marker fibronectin (FN) are upregulated while SIRT-1 is downregulated in db/db mice (p<0.05) or in mouse MCs with high glucose (p<0.05), which are significantly restored by PARP-1 inhibitor (PJ34) (p<0.05) and SIRT-1 lentiviral transfected treatment (p<0.05), or worsened by SIRT-1 inhibitor EX527 (p<0.05). PJ34 treatment (p < 0.05) or SIRT-1 overexpression (p < 0.05) could increase PGC-1α and p-AMPK levels, concomitant with down expression of FN, however, were reversed in the presence of EX527 (p<0.05).

DISCUSSION

Our results suggest an important relationship between PARP-1 and SIRT-1 through AMPK-PGC-1α pathway, indicating a potential therapeutic method for DN.

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 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.

SIRT1 directly activates autophagy in human chondrocytes

Osteoarthritis (OA) is the most common form of arthritis worldwide with no effective treatment. Ageing is the primary risk factor for OA. We sought to investigate if there is a distinct and functional convergence of ageing-related mechanisms SIRT1 and autophagy in chondrocytes. Our results show that, levels of SIRT1 are decreased in human normal aged and OA cartilage compared with young cartilage. Moreover, silencing SIRT1 in chondrocytes lead to decreased expression of chondrogenic markers but did not alter the expression of catabolic proteases. In contrast, activation of SIRT1 increased autophagy in chondrocytes by the deacetylation of lysine residues on crucial autophagy proteins (Beclin1, ATG5, ATG7, LC3). This activation was shown to be mTOR/ULK1 independent. Our results indicate that maintenance of autophagy in chondrocytes by SIRT1 is essential for preserving cartilage integrity throughout life and therefore is a target for drug intervention to protect against OA.

The Roles of FoxO Transcription Factors in Regulation of Bone Cells Function

Forkhead box class O family member proteins (FoxOs) are evolutionarily conserved transcription factors for their highly conserved DNA-binding domain. In mammalian species, all the four FoxO members, FoxO1, FoxO3, FoxO4, and FoxO6, are expressed in different organs. In bone, the first three members are extensively expressed and more studied. Bone development, remodeling, and homeostasis are all regulated by multiple cell lineages, including osteoprogenitor cells, chondrocytes, osteoblasts, osteocytes, osteoclast progenitors, osteoclasts, and the intercellular signaling among these bone cells. The disordered FoxOs function in these bone cells contribute to osteoarthritis, osteoporosis, or other bone diseases. Here, we review the current literature of FoxOs for their roles in bone cells, focusing on helping researchers to develop new therapeutic approaches and prevent or treat the related bone diseases.

Synovium stem cell-derived matrix enhances anti-inflammatory properties of rabbit articular chondrocytes via the SIRT1 pathway

Autologous chondrocyte implantation (ACI) is a promising approach to repair cartilage defects; however, the cartilage trauma-induced inflammatory environment compromises its clinical outcomes. Cell-derived decellularized extracellular matrix (DECM) has been used as a culture substrate for mesenchymal stem cells (MSCs) to improve the cell proliferation and lineage-specific differentiation. In this study, DECM deposited by synovium-derived MSCs was used as an in vitro expansion system for rabbit articular chondrocytes and the response of DECM-expanded chondrocytes to pro-inflammatory cytokines such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) was evaluated. Compared with those grown on tissue culture polystyrene (TCPS), the proliferation rate was significantly improved in DECM-expanded chondrocytes. TCPS- and DECM-expanded chondrocytes were isolated and induced to redifferentiation in a high-density pellet culture. DECM-expanded chondrocytes exerted a stronger resistance to 1 ng/mL of IL-1β than TCPS-expanded cells, but the production of cartilage matrix in both groups was inhibited by 5 ng/mL of IL-1β. When exposed to 1 or 5 ng/mL of TNF-α, DECM-expanded chondrocytes showed higher levels of cartilage matrix synthesis than TCPS-expanded cells. In addition, the gene expression of IL-1β- or TNF-α-induced matrix degrading enzymes (MMP3, MMP9, MMP13, and ADAMTS5) was significantly lower in DECM-expanded chondrocytes than TCPS-expanded cells. Furthermore, we found that SIRT1 inhibition by nicotinamide completely counteracted the protective effect of DECM on chondrocytes in the presence of IL-1β or TNF-α, indicating that the SIRT1 signaling pathway was involved in the DECM-mediated enhancement of anti-inflammatory properties of chondrocytes. Taken together, this work suggests that stem cell-derived DECM is a superior culture substrate for in vitro chondrocyte expansion by improving proliferation and enhancing the anti-inflammatory properties of chondrocytes. DECM-expanded chondrocytes with enhanced anti-inflammatory properties hold great potential in clinically ACI-based cartilage repair.

Grape seed procyanidins suppress the apoptosis and senescence of chondrocytes and ameliorates osteoarthritis via the DPP4-Sirt1 pathway

Osteoarthritis (OA) is a complicated pathological condition affecting thousands of people around world, many with substantial unmet medical care needs and without any effective therapies.

Corneal Denervation Causes Epithelial Apoptosis Through Inhibiting NAD+ Biosynthesis

Purpose

To determine if trigeminal innervations of the corneal epithelium maintains its integrity and homeostasis through controlling the nicotinamide adenine dinucleotide (NAD) content of this tissue.

Methods

Corneal denervation of C57BL/6 mice was induced by squeezing the nerve bundles that derive from the trigeminal ganglion and was confirmed by whole-mount corneal nerve staining and the sensation test. The apoptosis of the corneal epithelium was examined by TUNEL assay and annexin V/propidium iodide staining. NAD biosynthesis-related enzymes were analyzed by quantitative PCR, immunofluorescence staining, and Western blotting. FK866, an inhibitor of nicotinamide phosphoribosyltransferase (NAMPT), exogenous nicotinamide mononucleotide (NMN), and NAD+ were used to evaluate the effect of NAD+ on the apoptosis of cultured corneal epithelial cells and epithelial detachment in denervated mice. Protein expression that related to apoptosis and phosphorylation were analyzed by Western blotting.

Results

The denervated mice showed spontaneous corneal epithelial detachment and cell apoptosis accompanied with impaired epithelial NAD+ contents due to low levels of NAMPT. Similarly, inhibition of NAMPT recapitulated epithelial detachment as in denervated mice and induced apoptosis in cultured corneal epithelial cells. The replenishment of NMN or NAD+ partially slowed down corneal nerve fiber degeneration, reduced the epithelial defect in denervated mice, and improved apoptosis induction in FK866-treated cells by restoring the activation levels of SIRT1, AKT, and CREB.

Conclusions

Corneal denervation lowered epithelial NAD+ contents through reducing the expression of NAMPT and caused cell apoptosis and epithelial defects, suggesting that corneal innervations contribute to epithelial homeostasis by regulating NAD+ biosynthesis.

Cartilage Ablation of Sirt1 Causes Inhibition of Growth Plate Chondrogenesis by Hyperactivation of mTORC1 Signaling

A growing body of evidence implies a pivotal role of sirtuin-1 (Sirt1) in chondrocyte function and homeostasis; however, its underlying mechanisms mediating chondrogenesis, which is an essential process for physiological skeletal growth, are still poorly understood. In the current study, we generated TamCartSirt1-/- [Sirt1 conditional knockout (cKO)] mice to explore the role of Sirt1 during postnatal endochondral ossification. Compared with control mice, cKO mice exhibited growth retardation associated with inhibited chondrocyte proliferation and hypertrophy, as well as activated apoptosis. These effects were regulated by hyperactivation of mammalian target of rapamycin complex 1 (mTORC1) signaling, and thereby inhibition of autophagy and induction of endoplasmic reticulum stress in growth plate chondrocytes. IP injection of the mTORC1 inhibitor rapamycin to mice with Sirt1 deletion partially neutralized such inhibitory effects of Sirt1 ablation on longitudinal bone growth, indicating the causative link between SIRT1 and mTORC1 signaling in the growth plate. Mechanistically, SIRT1 interacted with tuberous sclerosis complex 2 (TSC2), a key upstream negative regulator of mTORC1 signaling, and loss of Sirt1 inhibited TSC2 expression, resulting in hyperactivated mTORC1 signaling in chondrocytes. In conclusion, our findings suggest that loss of Sirt1 may trigger mTORC1 signaling in growth plate chondrocytes and contributes to growth retardation, thus indicating that SIRT1 is an important regulator during chondrogenesis and providing new insights into the clinical potential of SIRT1 in bone development.

The Sirt1/P53 Axis in Diabetic Intervertebral Disc Degeneration Pathogenesis and Therapeutics

Intervertebral disc degeneration (IDD) is one of the major causes of low back pain. Diabetes is a risk factor for IDD and may aggravate IDD in rats; however, the mechanism is poorly understood. Previously, we demonstrated that apoptosis and senescence were increased in diabetic nucleus pulposus (NP) tissues; in the current study, we found that hyperglycaemia may promote the incidence of apoptosis and senescence in NP cells in vitro. Meanwhile, the acetylation of P53, a master transcription factor of apoptosis and senescence, was also found increased in diabetic NP tissues in vivo as well as in hyperglycaemic NP cells in vitro. Sirt1 is an NAD⁺-dependent deacetylase, and we showed that the expression of Sirt1 was decreased in NP tissues, while hyperglycaemia could suppress the expression and activity of Sirt1 in NP cells. Furthermore, we demonstrated that butein may inhibit acetylation of P53 and protect NP cells against hyperglycaemia-induced apoptosis and senescence through Sirt1 activation, as the Sirt1 inhibitor Ex527 may counteract the protective effect of butein in hyperglycaemic NP cells. An in vivo study showed that butein could ameliorate the IDD process in diabetic rats, while Sirt1 was increased and acetyl-p53 was decreased in NP tissues in butein-treated rats. These results indicate that the Sirt1/P53 axis is involved in the pathogenesis of diabetic IDD and may serve as a therapeutic target for diabetic IDD.

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.

Sirtuins and FoxOs in osteoporosis and osteoarthritis

The sirtuin family of NAD⁺-dependent protein deacetylases promotes longevity and counteracts age-related diseases. One of the major targets of Sirtuins are the FoxO family of transcription factors. FoxOs play a major role in the adaptation of cells to a variety of stressors such as oxidative stress and growth factor deprivation. Studies with murine models of cell-specific loss- or gain-of-function of Sirtuins or FoxOs and with Sirtuin1 stimulators have provided novel insights into the function and signaling of these proteins on the skeleton. These studies have revealed that both Sirtuins and FoxOs acting directly in cartilage and bone cells are critical for normal skeletal development, homeostasis and that their dysregulation might contribute to skeletal disease. Deacetylation of FoxOs by Sirt1 in osteoblasts and osteoclasts stimulates bone formation and inhibits bone resorption, making Sirt1 ligands promising therapeutic agents for diseases of low bone mass. While a similar link has not been established in chondrocytes, Sirt1 and FoxOs both have chondroprotective actions, suggesting that Sirt1 activators may have similar efficacy in preventing cartilage degeneration due to aging or injury. In this review we summarize these advances and discuss their implications for the pathogenesis of age-related osteoporosis and osteoarthritis.

Quercetin attenuates oxidative stress-induced apoptosis via SIRT1/AMPK-mediated inhibition of ER stress in rat chondrocytes and prevents the progression of osteoarthritis in a rat model

Apoptosis of chondrocytes are the main initiator of osteoarthritis (OA) and can be explained by oxidative stress and endoplasmic reticulum (ER) stress, thus the pharmacological interventions aimed at inhibiting of these pathways may be a promising approach for the management of OA. Quercetin is a member of the flavonoid family and has antioxidant and anti-inflammatory properties in degenerative diseases. However, its effects and potential mechanisms on the pathological process of OA are not very clear. The present study aimed to investigate the protective effects of quercetin on OA and the underlying mechanisms. The tert-butyl hydroperoxide (TBHP)-stimulated rat chondrocytes and destabilization of the medial meniscus OA rat model was used to explore the protective effects of quercetin. Our results showed that quercetin treatment can attenuate oxidative stress, ER stress, and associated apoptosis. Moreover, quercetin inhibited ER stress through activating the sirtuin1/adenosine monophosphate-activated protein kinase (SIRT1/AMPK) signaling pathway. The protective effects of quercetin were also observed in OA rat model which is evidenced by abolished cartilage degeneration and decreased chondrocytes apoptosis in the knee joints. Our results suggested that quercetin is a promising treatment for OA.

Epigenetic dynamic during endochondral ossification and articular cartilage development

Within the last decade epigenetics has emerged as fundamental regulator of numerous cellular processes, including those orchestrating embryonic and fetal development. As such, epigenetic factors play especially crucial roles in endochondral ossification, the process by which bone tissue is created, as well during articular cartilage formation. In this review, we summarize the recent discoveries that characterize how DNA methylation, histone post-translational modifications and non-coding RNA (e.g., miRNA and lcnRNA) epigenetically regulate endochondral ossification and chondrogenesis.

Preclinical development of a microRNA-based therapy for intervertebral disc degeneration

Understanding the molecular mechanisms regulating the maintenance and destruction of intervertebral disc may lead to the development of new therapies for intervertebral disc degeneration (IDD). Here we present evidence from miRNA microarray analyses of clinical data sets along with in vitro and in vivo experiments that miR-141 is a key regulator of IDD. Gain- and loss-of-function studies show that miR-141 drives IDD by inducing nucleus pulposus (NP) apoptosis. Furthermore, miR-141 KO in mice attenuated spontaneous and surgically induced IDD. Mechanistically, miR-141 promotes IDD development by targeting and depleting SIRT1, a negative regulator of NF-κB pathway. Therapeutically, upregulation or downregulation of miR-141 by nanoparticle delivery in IDD model aggravated or alleviated experimental IDD, respectively. Our findings reveal a novel mechanism by which miR-141, in part, promotes IDD progression by interacting with SIRT1/NF-κB pathway. Blockade of miR-141 in vivo may serve as a potential therapeutic approach in the treatment of IDD.

Intervertebral disk degeneration (IDD) is characterized by changes in the nucleus pulposus (NP) extra cellular matrix that compromise disk structural integrity. In a miRNA screen of human IDD patient NP tissue, the authors identify deregulated miR-141 and show that direct injection of nanoparticle-coupled miR-141 into the NP alleviates IDD in mice.

SIRT1 induces resistance to apoptosis in human granulosa cells by activating the ERK pathway and inhibiting NF-κB signaling with anti-inflammatory functions

SIRT1, a member of the sirtuin family, has recently emerged as a vital molecule in controlling ovarian function. The aims of the present study were to investigate SIRT1 expression and analyze SIRT1-mediated apoptosis in human granulosa cells (GCs). Human ovarian tissues were subjected to immunohistochemistry for localization of SIRT1 expression. SIRT1 knockdown in a human ovarian GC tumor line (COV434) was achieved by small interfering RNA, and the relationship between apoptosis and SIRT1 was assessed by quantitative reverse transcription polymerase chain reaction and western blotting. We further detected SIRT1 expression in human luteinized GCs. Associations among SIRT1 knockdown, SIRT1 stimulation (resveratrol) and expression of ERK1/2 and apoptotic regulatory proteins were analyzed in cell lines and luteinized GCs. Resveratrol downregulated the levels of nuclear factor (NF)-κB/p65, but this inhibitory effect was attenuated by suppressing SIRT1 activity. The NF-κB/p65 inhibitor pyrrolidine dithiocarbamate achieved similar anti-apoptosis effects. These results suggest that SIRT1 might play an anti-apoptotic role in apoptosis processes in GCs, possibly by sensing and regulating the ERK1/2 pathway, which has important clinical implications. Thus, our study provides a mechanistic link, whereby activation of SIRT1 function might help to sustain human reproduction by maintaining GCs as well as oocytes, offering a novel approach for developing a new class of therapeutic anti-inflammatory agents.

Intraperitoneal injection of the SIRT1 activator SRT1720 attenuates the progression of experimental osteoarthritis in mice

Objectives

This study aimed to examine the effects of SRT1720, a potent SIRT1 activator, on osteoarthritis (OA) progression using an experimental OA model.

Methods

Osteoarthritis was surgically induced by destabilization of the medial meniscus in eight-week-old C57BL/6 male mice. SRT1720 was administered intraperitoneally twice a week after surgery. Osteoarthritis progression was evaluated histologically using the Osteoarthritis Research Society International (OARSI) score at four, eight, 12 and 16 weeks. The expression of SIRT1, matrix metalloproteinase 13 (MMP-13), a disintegrin and metalloproteinase with thrombospondin motifs-5 (ADAMTS-5), cleaved caspase-3, PARP p85, and acetylated nuclear factor (NF)-κB p65 in cartilage was examined by immunohistochemistry. Synovitis was also evaluated histologically. Primary mouse epiphyseal chondrocytes were treated with SRT1720 in the presence or absence of interleukin 1 beta (IL-1β), and gene expression changes were examined by real-time polymerase chain reaction (PCR).

Results

The OARSI score was significantly lower in mice treated with SRT1720 than in control mice at eight and 12 weeks associated with the decreased size of osteophytes at four and eight weeks. The delayed OA progression in the mice treated with SRT1720 was also associated with increased SIRT1-positive chondrocytes and decreased MMP-13-, ADAMTS-5-, cleaved caspase-3-, PARP p85-, and acetylated NF-κB p65-positive chondrocytes and decreased synovitis at four and eight weeks. SRT1720 treatment partially rescued the decreases in collagen type II alpha 1 (COL2A1) and aggrecan caused by IL-1β, while also reducing the induction of MMP-13 by IL-1β in vitro.

Conclusion

The intraperitoneal injection of SRT1720 attenuated experimental OA progression in mice, indicating that SRT1720 could be a new therapeutic approach for OA.Cite this article: K. Nishida, T. Matsushita, K. Takayama, T. Tanaka, N. Miyaji, K. Ibaraki, D. Araki, N. Kanzaki, T. Matsumoto, R. Kuroda. Intraperitoneal injection of the SIRT1 activator SRT1720 attenuates the progression of experimental osteoarthritis in mice. Bone Joint Res 2018;7:252-262. DOI: 10.1302/2046-3758.73.BJR-2017-0227.R1.

Sirtuin-1 (SIRT1) stimulates growth-plate chondrogenesis by attenuating the PERK-eIF-2α-CHOP pathway in the unfolded protein response

The NAD⁺-dependent deacetylase sirtuin-1 (SIRT1) has emerged as an important regulator of chondrogenesis and cartilage homeostasis, processes that are important for physiological skeletal growth and that are dysregulated in osteoarthritis. However, the functional role and underlying mechanism by which SIRT1 regulates chondrogenesis remain unclear. Using cultured rat metatarsal bones and chondrocytes isolated from rat metatarsal rudiments, here we studied the effects of the SIRT1 inhibitor EX527 or of SIRT1 siRNA on chondrocyte proliferation, hypertrophy, and apoptosis. We show that EX527 or SIRT1 siRNA inhibits chondrocyte proliferation and hypertrophy and induces apoptosis. We also observed that SIRT1 inhibition mainly induces the PERK-eIF-2α-CHOP axis of the endoplasmic reticulum (ER) stress response in growth-plate chondrocytes. Of note, EX527- or SIRT1 siRNA-mediated inhibition of metatarsal growth and growth-plate chondrogenesis were partly neutralized by phenylbutyric acid, a chemical chaperone that attenuates ER stress. Moreover, EX527-mediated impairment of chondrocyte function (i.e. of chondrocyte proliferation, hypertrophy, and apoptosis) was partly reversed in CHOP^-/- cells. We also present evidence that SIRT1 physically interacts with and deacetylates PERK. Collectively, our findings indicate that SIRT1 deacetylates PERK and attenuates the PERK-eIF-2α-CHOP axis of the unfolded protein response pathway and thereby promotes growth-plate chondrogenesis and longitudinal bone growth.

Homocysteine causes dysfunction of chondrocytes and oxidative stress through repression of SIRT1/AMPK pathway: A possible link between hyperhomocysteinemia and osteoarthritis

Emerging evidence has indicated that the perturbed expression of homocysteine (Hcy) may induce mitochondrial dysfunction and disturb bone metabolism. Sirtuin 1 (SIRT1) and AMP-activated protein kinase (AMPK) are two critical sensors that regulate mitochondrial biogenesis and have been recognized as therapeutic targets in osteoarthritis (OA). This study was designed to test whether Hcy caused pro-osteoarthritic changes through modulation of SIRT1 and AMPK. Our results showed that administration of Hcy reduced the SIRT1/AMPK/PGC-1α signaling in chondrocytes, leading to mitochondrial dysfunction as a result of increased oxidative stress and apoptosis. Moreover, we demonstrated that the expression of NF-κB, COX-2, IL-8, and MMP-13 were elevated subsequent to inhibition of SIRT1/AMPK/PGC-1α/PPAR-γ pathway by homocysteine, thereby causing detrimental effects on chondrocytes. In the animal model of diet-induced hyperhomocysteinemia (HHcy), we observed the similar findings that SIRT1/PGC-1α/PPAR-γ cascades were downregulated with elevated MMP-13 and COX-2. Taken together, data from the current study revealed that the reduced SIRT1 by Hcy may contribute to degradative cartilage process, which provided insight into the etiology of OA.

Sirtuin 1-Chromatin-Binding Dynamics Points to a Common Mechanism Regulating Inflammatory Targets in SIV Infection and in the Aging Brain

Microglia and macrophages are the main non-neuronal subsets of myeloid origin in the brain, and are critical regulators in neurodegenerative disorders, where inflammation is a key factor. Since HIV infection results in neurological perturbations that are similar to those in aging, we examined microglial and infiltrating myeloid subsets in the search for changes that might resemble the ones in aging. For that, we used the SIV infection in rhesus macaques to model neuroAIDS. We found that Sirt-1, a molecule that impacts survival and health in many models, was decreased in cell preparations containing a majority of microglia and myeloid cells from the brain of infected macaques. The role of Sirt-1 in neuroAIDS is unknown. We hypothesized that Sirt-1 silencing functions are affected by SIV. Mapping of Sirt-1 binding patterns to chromatin revealed that the number of Sirt-1-bound genes was 29.6% increased in myeloid cells from infected animals with mild or no detectable neuropathology, but 51% was decreased in severe neuropathology, compared to controls. Importantly, Sirt-1-bound genes in controls largely participate in neuroinflammation. Promoters of type I IFN pathway genes IRF7, IRF1, IFIT1, and AIF1, showed Sirt-1 binding in controls, which was consistently lost after infection, together with higher transcription. Loss of Sirt-1 binding was also found in brains from old uninfected animals, suggesting a common regulation. The role of Sirt-1 in regulating these inflammatory markers was confirmed in two different in vitro models, where Sirt-1 blockage modulated IRF7, IRF1 and AIF1 levels both in human macrophage cell lines and in human blood-derived monocytes from various normal donors, stimulated with a TLR9 agonist. Our data suggests that Sirt-1-inflammatory gene silencing is disturbed by SIV infection, resembling aging in brains. These findings may impact our knowledge on the contribution of myeloid subsets to the neurological consequences of HIV infection, aggravated and overlapping with the aging process.

Paracrine effects of human adipose-derived mesenchymal stem cells in inflammatory stress-induced senescence features of osteoarthritic chondrocytes

Aging and exposure to stress would determine the chondrocyte phenotype in osteoarthritis (OA). In particular, chronic inflammation may contribute to stress-induced senescence of chondrocytes and cartilage degeneration during OA progression. Recent studies have shown that adipose-derived mesenchymal stem cells exert paracrine effects protecting against degenerative changes in chondrocytes. We have investigated whether the conditioned medium (CM) from adipose-derived mesenchymal stem cells may regulate senescence features induced by inflammatory stress in OA chondrocytes. Our results indicate that CM down-regulated senescence markers induced by interleukin-1β including senescence-associated β-galactosidase activity, accumulation of γH2AX foci and morphological changes with enhanced formation of actin stress fibers. Treatment of chondrocytes with CM also decreased the production of oxidative stress, the activation of mitogen-activated protein kinases, and the expression of caveolin-1 and p21. The effects of CM were related to the reduction in p53 acetylation which would be dependent on the enhancement of Sirtuin 1 expression. Therefore, CM may exert protective effects in degenerative joint conditions by countering the premature senescence of OA chondrocytes induced by inflammatory stress.

miR-4262 regulates chondrocyte viability, apoptosis, autophagy by targeting SIRT1 and activating PI3K/AKT/mTOR signaling pathway in rats with osteoarthritis

The present study aimed to investigate the effect and underlying mechanism of microRNA (miR)-4262 in the development of osteoarthritis (OA) in rats. Primary chondrocytes were separated from Sprague-Dawley rats and then treated with tumor necrosis factor-α (TNF-α). The level of miR-4262 was detected in TNF-α-treated chondrocytes, and then the miR-4262 or its target gene sirtuin type 1 (SIRT1) level was overexpressed, or knocked down. Furthermore, cell viability, cell apoptosis, cell autophagy and matrix synthesis, as well as the expressions of proteins associated with the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway were detected. miR-4262 was significantly overexpressed in TNF-α-treated chondrocytes compared with untreated cells (P<0.05). TNF-α treatment or miR-4262 overexpression significantly decreased cell viability, autophagy-related proteins levels and matrix synthesis-related proteins levels, as well as increased the apoptotic rate in chondrocytes (P<0.05). Overexpression of SIRT1 significantly increased cell viability, autophagy-related proteins levels and matrix synthesis-related proteins levels, as well as decreased the apoptotic rate in TNF-α-treated chondrocytes (P<0.05). In addition, the effects of miR-4262 on cell viability, cell apoptosis, cell autophagy and matrix synthesis were inhibited by SIRT1 (P<0.05). Furthermore, upregulated miR-4262 remarkably increased the expressions of phosphorylated (p)-PI3K, p-AKT and p-mTOR (P<0.05) in TNF-α treated chondrocytes. The present study revealed that the upregulation of miR-4262 may promote the occurrence and development of OA in rats by regulating cell viability, cell apoptosis, cell autophagy, and matrix synthesis. Furthermore, these roles of miR-4262 may be associated with PI3K/AKT/mTOR signaling pathway.

The Role of Sirtuins in Cartilage Homeostasis and Osteoarthritis

The past decade has witnessed many advances in the understanding of sirtuin biology and related regulatory circuits supporting the capacity of these proteins to serve as energy-sensing molecules that contribute to healthspan in various tissues, including articular cartilage. Hence, there has been a significant increase in new investigations that aim to elucidate the mechanisms of sirtuin function and their roles in cartilage biology, skeletal development, and pathologies such as osteoarthritis (OA), rheumatoid arthritis (RA), and intervertebral disc degeneration (IVD). The majority of the work carried out to date has focused on SIRT1, although SIRT6 has more recently become a focus of some investigations. In vivo work with transgenic mice has shown that Sirt1 and Sirt6 are essential for maintaining cartilage homeostasis and that the use of sirtuin-activating molecules such as resveratrol may have beneficial effects on cartilage anabolism. Current thinking is that SIRT1 exerts positive effects on cartilage by encouraging chondrocyte survival, especially under stress conditions, which may provide a mechanism supporting the use of sirtuin small-molecule activators (STACS) for future therapeutic interventions in OA and other degenerative pathologies of joints, especially those that involve articular cartilage.

Epigenetics in osteoarthritis: Potential of HDAC inhibitors as therapeutics

Osteoarthritis (OA) is the most common joint disease and the leading cause of chronic disability in middle-aged and older populations worldwide. The development of disease modifying therapy for OA is in its infancy largely because the regulatory mechanisms for the molecular effectors of OA pathogenesis are poorly understood. Recent studies identified epigenetic events as a critical regulator of molecular players involved in the induction and development of OA. Epigenetic mechanisms include DNA methylation, non-coding RNA and histone modifications. The aim of this review is to briefly highlight the recent advances in the epigenetics of cartilage and potential of HDACs (Histone deacetylases) inhibitors in the therapeutic management of OA. We summarize the recent studies utilizing HDAC inhibitors as potential therapeutics for inhibiting disease progression and preventing the cartilage destruction in OA. HDACs control normal cartilage development and homeostasis and understanding the impact of HDACs inhibitors on the disease pathogenesis is of interest because of its importance in affecting overall cartilage health and homeostasis. These findings also shed new light on cartilage disease pathophysiology and provide substantial evidence that HDACs may be potential novel therapeutic targets in OA.

Beclin 1 overexpression inhibits chondrocyte apoptosis and downregulates extracellular matrix metabolism in osteoarthritis

In the present study, the expression of Beclin 1 in osteoarthritis (OA) cartilage tissue was investigated, and also its role in proliferation, apoptosis and expression of matrix metalloproteinases (MMPs) in chondrocytes obtained from patients with OA. Beclin 1 expression in cartilage tissue from OA patients, and in the age- and sex-matched controls, was detected by immunohistochemistry, semi-quantitative polymerase chain reaction and western blotting. Chondrocytes were divided into control and Beclin 1-overexpressed groups. After transfection for 48, 72 and 96 h, cell viability, apoptosis, the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway and MMPs were examined. The mRNA and protein expression levels of Beclin 1 were significantly decreased in cartilage tissue from OA patients compared with the sex- and age-matched controls (P<0.05). In chondrocytes from OA patients, Beclin 1 overexpression significantly increased cell viability (P<0.05). Beclin 1 overexpression additionally decreased the degree of apoptosis, as demonstrated by Hoechst staining and flow cytometric analysis. B-cell lymphoma-2 (Bcl-2) was upregulated, and Bcl-2 associated X was downregulated, following Beclin 1 overexpression (P<0.05). The PI3K/Akt/mTOR signaling pathway was mitigated following Beclin 1 overexpression (P<0.05). In addition, MMP1, MMP3 and MMP13 were downregulated after Beclin 1 overexpression (P<0.05). Taken together, low expression levels of Beclin 1 may contribute towards the degeneration of chondrocytes. Beclin 1 overexpression increased cell viability, inhibited apoptosis and MMPs, likely via the PI3K/Akt/mTOR signaling pathway.