Sucrose, But Not Glucose, Blocks IL1-β-Induced Inflammatory Response in Human Chondrocytes by Inducing Autophagy via AKT/mTOR Pathway

Immunometabolic Chaos in Septic Shock

Septic shock is associated with over 40% mortality. The immune response in septic shock is tightly regulated by cellular metabolism and transitions from early hyper-inflammation to later hypo-inflammation. Patients are susceptible to secondary infections during hypo-inflammation. The magnitude of the metabolic dysregulation and the effect of plasma metabolites on the circulating immune cells in septic shock are not reported. We hypothesized that the accumulated plasma metabolites affect the immune response in septic shock during hypo-inflammation. Our study took a unique approach. Using peripheral blood from adult septic shock patients and healthy controls, we studied: 1. Whole blood stimulation ± E. Coli lipopolysaccharide (LPS: endotoxin) to analyze plasma TNF protein, and 2. Plasma metabolomic profile by Metabolon. Inc. 3. We exposed peripheral blood mononuclear cells (PBMCs) from healthy controls to commercially available carbohydrate, amino acid, and fatty acid metabolites and studied the response to LPS. We report that: 1. The whole blood stimulation of the healthy control group showed a significantly upregulated TNF protein, while the septic shock group remained endotoxin tolerant, a biomarker for hypo-inflammation. 2. A significant accumulation of carbohydrate, amino acid, fatty acid, ceramide, sphingomyelin, and TCA cycle pathway metabolites in septic shock plasma. 3. In vitro exposure to five metabolites repressed while two metabolites upregulated the inflammatory response of PBMCs to LPS. We conclude that the endotoxin-tolerant phenotype of septic shock is associated with a simultaneous accumulation of plasma metabolites from multiple metabolic pathways, and these metabolites fundamentally influence the immune response profile of circulating cells.

Mechanisms of chondrocyte cell death in osteoarthritis: implications for disease progression and treatment

Osteoarthritis (OA) is a chronic joint disease characterized by the degeneration, destruction, and excessive ossification of articular cartilage. The prevalence of OA is rising annually, concomitant with the aging global population and increasing rates of obesity. This condition imposes a substantial and escalating burden on individual health, healthcare systems, and broader social and economic frameworks. The etiology of OA is multifaceted and not fully understood. Current research suggests that the death of chondrocytes, encompassing mechanisms such as cellular apoptosis, pyroptosis, autophagy, ferroptosis and cuproptosis, contributes to both the initiation and progression of the disease. These cell death pathways not only diminish the population of chondrocytes but also exacerbate joint damage through the induction of inflammation and other deleterious processes. This paper delineates the morphological characteristics associated with various modes of cell death and summarizes current research results on the molecular mechanisms of different cell death patterns in OA. The objective is to review the advancements in understanding chondrocyte cell death in OA, thereby offering novel insights for potential clinical interventions.

Autophagy in Osteoarthritis: A Double-Edged Sword in Cartilage Aging and Mechanical Stress Response: A Systematic Review

Background: Although osteoarthritis (OA) development is epidemiologically multifactorial, a primary underlying mechanism is still under debate. Understanding the pathophysiology of OA remains challenging. Recently, experts have focused on autophagy as a contributor to OA development. Method: To better understand the pathogenesis of OA, we survey the literature on the role of autophagy and the molecular mechanisms of OA development. To identify relevant studies, we used controlled vocabulary and free text keywords to search the MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials, Web of Science, and SCOPUS database. Thirty-one studies were included for data extraction and systematic review. Among these studies, twenty-five studies investigated the effects of autophagy in aging and OA chondrocytes, six studies examined the effects of autophagy in normal human chondrocytes, and only one study investigated the effects of mechanical stress-induced autophagy on the development of OA in normal chondrocytes. Results: The studies suggest that autophagy activation prevents OA by exerting cell-protective effects in normal human chondrocytes. However, in aging and osteoarthritis (OA) chondrocytes, the role of autophagy is intricate, as certain studies indicate that stimulating autophagy in these cells can have a cytotoxic effect, while others propose that it may have a protective (cytoprotective) effect against damage or degeneration. Conclusions: Mechanical stress-induced autophagy is also thought to be involved in the development of OA, but further research is required to identify the precise mechanism. Thus, autophagy contributions should be interpreted with caution in aging and the types of OA cartilage.

The role of autophagy in mitigating osteoarthritis progression via regulation of chondrocyte apoptosis: A review

Osteoarthritis (OA) is the most prevalent chronic joint disease with an immense socioeconomic burden; however, no treatment has achieved complete success in effectively halting or reversing cartilage degradation, which is the central pathophysiological feature of OA. Chondrocytes loss or dysfunction is a significant contributing factor to the progressive cartilage deterioration as these sole resident cells have a crucial role to produce extracellular matrix proteins, thus maintaining cartilage structure and homeostasis. It has been previously suggested that death of chondrocytes occurring through apoptosis substantially contributes to cartilage degeneration. Although the occurrence of apoptosis in osteoarthritic cartilage and its correlation with cartilage degradation is evident, the causes of chondrocyte apoptosis leading to matrix loss are still not well-understood. Autophagy, an intracellular degradative mechanism that eliminates dysfunctional cytoplasmic components to aid cell survival in unfavourable conditions, is a potential therapeutic target to inhibit chondrocyte apoptosis and reduce OA severity. Despite accumulating evidence indicating significant cytoprotective effects of autophagy against chondrocyte apoptosis, the mechanistic link between autophagy and apoptosis in chondrocytes remains to be further explored. In this review, we summarize the relevant mechanistic events that perpetuate chondrocyte apoptosis and highlight the prominent role of autophagy in modulating these events to mitigate OA progression.

Reversible assembly and disassembly of V-ATPase during the lysosome regeneration cycle

Regulation of the luminal pH of late endocytic compartments in continuously fed mammalian cells is poorly understood. Using normal rat kidney fibroblasts, we investigated the reversible assembly/disassembly of the proton pumping V-ATPase when endolysosomes are formed by kissing and fusion of late endosomes with lysosomes and during the subsequent reformation of lysosomes. We took advantage of previous work showing that sucrosomes formed by the uptake of sucrose are swollen endolysosomes from which lysosomes are reformed after uptake of invertase. Using confocal microscopy and subcellular fractionation of NRK cells stably expressing fluorescently tagged proteins, we found net recruitment of the V1 subcomplex during sucrosome formation and loss during lysosome reformation, with a similar time course to RAB7a loss. Addition of invertase did not alter mTORC1 signalling, suggesting that the regulation of reversible V-ATPase assembly/disassembly in continuously fed cells differs from that in cells subject to amino acid depletion/refeeding. Using live cell microscopy, we demonstrated recruitment of a fluorescently tagged V1 subunit during endolysosome formation and a dynamic equilibrium and rapid exchange between the cytosolic and membrane bound pools of this subunit. We conclude that reversible V-ATPase assembly/disassembly plays a key role in regulating endolysosomal/lysosomal pH in continuously fed cells.

Therapeutic targets and potential delivery systems of melatonin in osteoarthritis

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

pH-sensing G protein-coupled orphan receptor GPR68 is expressed in human cartilage and correlates with degradation of extracellular matrix during OA progression

Background

Osteoarthritis (OA) is a debilitating joints disease affecting millions of people worldwide. As OA progresses, chondrocytes experience heightened catabolic activity, often accompanied by alterations in the extracellular environment's osmolarity and acidity. Nevertheless, the precise mechanism by which chondrocytes perceive and respond to acidic stress remains unknown. Recently, there has been growing interest in pH-sensing G protein-coupled receptors (GPCRs), such as GPR68, within musculoskeletal tissues. However, function of GPR68 in cartilage during OA progression remains unknown. This study aims to identify the role of GPR68 in regulation of catabolic gene expression utilizing an in vitro model that simulates catabolic processes in OA.

Methods

We examined the expression of GPCR by analyzing high throughput RNA-Seq data in human cartilage isolated from healthy donors and OA patients. De-identified and discarded OA cartilage was obtained from joint arthroplasty and chondrocytes were prepared by enzymatic digestion. Chondrocytes were treated with GPR68 agonist, Ogerin and then stimulated IL1β and RNA isolation was performed using Trizol method. Reverse transcription was done using the cDNA synthesis kit and the expression of GPR68 and OA related catabolic genes was quantified using SYBR® green assays.

Results

The transcriptome analysis revealed that pH sensing GPCR were expressed in human cartilage with a notable increase in the expression of GPR68 in OA cartilage which suggest a potential role for GPR68 in the pathogenesis of OA. Immunohistochemical (IHC) and qPCR analyses in human cartilage representing various stages of OA indicated a progressive increase in GPR68 expression in cartilage associated with higher OA grades, underscoring a correlation between GPR68 expression and the severity of OA. Furthermore, IHC analysis of Gpr68 in murine cartilage subjected to surgically induced OA demonstrated elevated levels of GPR68 in knee cartilage and meniscus. Using IL1β stimulated in vitro model of OA catabolism, our qPCR analysis unveiled a time-dependent increase in GPR68 expression in response to IL1β stimulation, which correlates with the expression of matrix degrading proteases suggesting the role of GPR68 in chondrocytes catabolism and matrix degeneration. Using pharmacological activator of GPR68, our results further showed that GPR68 activation repressed the expression of MMPs in human chondrocytes.

Conclusions

Our results demonstrated that GPR68 was robustly expressed in human cartilage and mice and its expression correlates with matrix degeneration and severity of OA progression in human and surgical model. GPR68 activation in human chondrocytes further repressed the expression of MMPs under OA pathological condition. These results identify GPR68 as a possible therapeutic target in the regulation of matrix degradation during OA.

Role of autophagy in the pathogenesis and regulation of pain

Pain is a ubiquitous and highly concerned clinical symptom, usually caused by peripheral or central nervous injury, tissue damage, or other diseases. The long-term existence of pain can seriously affect daily physical function and quality of life and produce great torture on the physiological and psychological levels. However, the complex pathogenesis of pain involving molecular mechanisms and signaling pathways has not been fully elucidated, and managing pain remains highly challenging. As a result, finding new targets to pursue effective and long-term pain treatment strategies is required and urgent. Autophagy is an intracellular degradation and recycling process that maintains tissue homeostasis and energy supply, which can be cytoprotective and is vital in maintaining neural plasticity and proper nervous system function. Much evidence has shown that autophagy dysregulation is linked to the emergence of neuropathic pain, such as postherpetic neuralgia and cancer-related pain. Autophagy has also been connected to pain caused by osteoarthritis and lumbar disc degeneration. It is worth noting that in recent years, studies on traditional Chinese medicine have also proved that several traditional Chinese medicine monomers involve autophagy in the mechanism of pain relief. Therefore, autophagy can serve as a potential regulatory target to provide new ideas and inspiration for pain management.

The role of apoptosis in the pathogenesis of osteoarthritis

PURPOSE

Apoptosis is an important physiological process, making a great difference to development and tissue homeostasis. Osteoarthritis (OA) is a chronic joint disease characterized by degeneration and destruction of articular cartilage and bone hyperplasia. This purpose of this study is to provide an updated review of the role of apoptosis in the pathogenesis of osteoarthritis.

METHODS

A comprehensive review of the literature on osteoarthritis and apoptosis was performed, which mainly focused on the regulatory factors and signaling pathways associated with chondrocyte apoptosis in osteoarthritis and other pathogenic mechanisms involved in chondrocyte apoptosis.

RESULTS

Inflammatory mediators such as reactive oxygen species (ROS), nitric oxide (NO), IL-1β, tumor necrosis factor-α (TNF-α), and Fas are closely related to chondrocyte apoptosis. NF-κB signaling pathway, Wnt signaling pathway, and Notch signaling pathway activate proteins and gene targets that promote or inhibit the progression of osteoarthritis disease, including chondrocyte apoptosis and ECM degradation. Long non-coding RNAs (LncRNAs) and microRNAs (microRNAs) have gradually replaced single and localized research methods and become the main research approaches. In addition, the relationship between cellular senescence, autophagy, and apoptosis was also briefly explained.

CONCLUSION

This review offers a better molecular delineation of apoptotic processes that may help in designing new therapeutic options for OA treatment.

Oroxin B alleviates osteoarthritis through anti-inflammation and inhibition of PI3K/AKT/mTOR signaling pathway and enhancement of autophagy

BACKGROUND

Osteoarthritis (OA) is a common aging-related degenerative joint disease with chronic inflammation as its possible pathogenesis. Oroxin B (OB), a flavonoid isolated from traditional Chinese herbal medicine, possesses anti-inflammation properties which may be involved in regulating the pathogenesis of OA, but its mechanism has not been elucidated. Our study was the first to explore the potential chondroprotective effect and elucidate the underlying mechanism of OB in OA.

METHODS

In vitro, primary mice chondrocytes were stimulated with IL-1β along with or without the administration of OB or autophagy inhibitor 3-methyladenine (3-MA). Cell viability assay was measured with a cell counting kit-8 (CCK-8). The phenotypes of anabolic-related (Aggrecan and Collagen II), catabolic-related (MMP3, MMP13, and ADAMTS5), inflammation-related (iNOS, COX-2, TNF-α, IL-6, and IL-1β), and markers of related signaling pathways in chondrocytes with different treatment were detected through western blot, RT-qPCR, and immunofluorescent staining. In vivo, the destabilized medial meniscus (DMM) operation was performed to establish the OA mice model. After knee intra-articular injection with OB for 8 weeks, the mice's knee joints were obtained for subsequent histological staining and analysis.

RESULTS

OB reversed the expression level of anabolic-related proteins (Aggrecan and Collagen II) and catabolic-related (MMP3, MMP13, and ADAMTS5) in IL-1β-induced chondrocytes. Mechanistically, OB suppressed the inflammatory response stimulated by IL-1β, as the inflammation-related (iNOS, COX-2, TNF-α, IL-6, and IL-1β) markers were downregulated after the administration of OB in IL-1β-induced chondrocytes. Besides, the activation of PI3K/AKT/mTOR signaling pathway induced by IL-1β could be inhibited by OB. Additionally, the autophagy process impaired by IL-1β could be rescued by OB. What's more, the introduction of 3-MA to specifically inhibit the autophagic process impairs the protective effect of OB on cartilage. In vivo, histological staining revealed that intra-articular injection of OB attenuated the cartilage degradation, as well as reversed the expression level of anabolic and catabolic-related proteins such as Aggrecan, Collagen II, and MMP13 induced in DMM-induced OA models.

CONCLUSIONS

The study verified that OB exhibited the chondroprotective effect by anti-inflammatory, inhibiting the PI3K/AKT/mTOR signaling pathway, and enhancing the autophagy process, indicating that OB might be a promising agent for the treatment of OA.

Between Inflammation and Autophagy: The Role of Leptin-Adiponectin Axis in Cardiac Remodeling

Cardiac remodeling is the process by which the heart adapts to stressful stimuli, such as hypertension and ischemia/reperfusion; it ultimately leads to heart failure upon long-term exposure. Autophagy, a cellular catabolic process that was originally considered as a mechanism of cell death in response to detrimental stimuli, is thought to be one of the main mechanisms that controls cardiac remodeling and induces heart failure. Dysregulation of the adipokines leptin and adiponectin, which plays essential roles in lipid and glucose metabolism, and in the pathophysiology of the neuroendocrine and cardiovascular systems, has been shown to affect the autophagic response in the heart and to contribute to accelerate cardiac remodeling. The obesity-associated protein leptin is a pro-inflammatory, tumor-promoting adipocytokine whose elevated levels in obesity are associated with acute cardiovascular events, and obesity-related hypertension. Adiponectin exerts anti-inflammatory and anti-tumor effects, and its reduced levels in obesity correlate with the pathogenesis of obesity-associated cardiovascular diseases. Leptin- and adiponectin-induced changes in autophagic flux have been linked to cardiac remodeling and heart failure. In this review, we describe the different molecular mechanisms of hyperleptinemia- and hypoadiponectinemia-mediated pathogenesis of cardiac remodeling and the involvement of autophagy in this process. A better understanding of the roles of leptin, adiponectin, and autophagy in cardiac functions and remodeling, and the exact signal transduction pathways by which they contribute to cardiac diseases may well lead to discovery of new therapeutic agents for the treatment of cardiovascular remodeling.

The Effects of Exercise and Restriction of Sugar-Sweetened Beverages on Muscle Function and Autophagy Regulation in High-Fat High-Sucrose-Fed Obesity Mice

BACKGROUND

Autophagy maintains muscle mass and healthy skeletal muscles. Several recent studies have associated sugar-sweetened beverage (SSB) consumption with diseases. We investigated whether muscle dysfunction due to obesity could be restored by SSB restriction (SR) alone or in combination with exercise (EX) training.

METHODS

Obese mice were subjected to SR combined with treadmill EX. Intraperitoneal glucose tolerance test, grip strength test, hanging time test, and body composition analysis were performed. Triglyceride (TG) and total cholesterol (TC) serum concentrations and TG concentrations in quadriceps muscles were analyzed. Western blot and reverse transcription-quantitative polymerase chain reaction helped analyze autophagy-related protein and mRNA expression, respectively.

RESULTS

SR alone had no significant effect on fasting blood glucose levels, glucose tolerance, and muscle function. However, it had effect on serum TC, serum TG, and BCL2 interacting protein 3 expression. SR+EX improved glucose tolerance and muscle function and increased serum TC utilization than SR alone. SR+EX reduced P62 levels, increased glucose transporter type 4 and peroxisome proliferator-activated receptor γ coactivator-1α protein expression, and improved grip strength relative to the high-fat and high-sucrose liquid (HFHS) group, and this was not observed in the HFHS+EX group.

CONCLUSION

SR induced mitophagy-related protein expression in quadriceps, without affecting muscle function. And, the combination of SR and EX activated mitophagy-related proteins and improved muscle function.

Curcumin-Alleviated Osteoarthritic Progression in Rats Fed a High-Fat Diet by Inhibiting Apoptosis and Activating Autophagy via Modulation of MicroRNA-34a

Purpose

The mechanism underlying curcumin’s protective effect on osteoarthritis (OA) has not been clarified. This study aimed to determine whether curcumin exerts a chondroprotective effect by inhibiting apoptosis via upregulation of E2F1/PITX1 and activation of autophagy via the Akt/mTOR pathway by targeting microRNA-34a (miR-34a).

Methods

Male Sprague–Dawley rats were fed a normal diet (ND) or high-fat diet (HFD) for 28 weeks. Five rats from each diet group were selected randomly for histological analysis of OA characteristics. Rats fed a HFD were given a single intra-stifle joint injection of the miR-34a mimic agomir-34a or negative control agomir (NC), followed by weekly low-dose (200 μg/kg body weight) or high-dose (400 μg/kg body weight) curcumin intra-joint injections from weeks 29 to 32. The rats’ stifle joints were submitted to histological analysis and to an apoptotic assay. Expression of miR-34a was detected using a real-time RT-PCR. E2F1 and PITX1 protein levels were determined by Western blot analysis, and the expressions of Beclin1, LC3B, p62, phosphorylated (p)-Akt, and p-mTOR were measured using immunofluorescence analysis.

Results

We found that rats fed a HFD had OA-like lesions in their articular cartilage and had increased apoptosis of chondrocytes and decreased autophagy compared to rats fed a ND. Curcumin treatment alleviated OA changes, inhibited apoptosis, and upregulated autophagy. Agomir-34a treatment reduced E2F1, PITX1, Beclin1, and LC3B expression and increased p62, p-Akt, and p-mTOR expression in HFD-fed rats given low- or high-dose curcumin. Greater numbers of apoptotic cells, lesser expression of p62, p-Akt, and p-mTOR, and greater expression of E2F1, PITX1, and LC3B were observed in the agomir-34a and high-dose curcumin-treated group than in agomir-34a and low-dose curcumin-treated group.

Conclusion

Curcumin’s chondroprotective effect was mediated by its suppression of miR-34a, apparently by reducing apoptosis, via upregulation of E2F1/PITX1, and by augmenting autophagy, likely via the Akt/mTOR pathway.

Calcyclin (S100A6) Attenuates Inflammatory Response and Mediates Apoptosis of Chondrocytes in Osteoarthritis via the PI3K/AKT Pathway

OBJECTIVE

To clarify the regulatory effect of Calcyclin (S100A6) on chondrocytes apoptosis and its relationship with progression of osteoarthritis in an effort to explore potential therapeutic targets for osteoarthritis.

METHOD

Immunofluorescence assay was produced to identify the rat chondrocyte sample and western blots assay was detected the expression changes of S100A6 between control group and osteoarthritis model which induced by interleukin-1β. Adenovirus were transfected into the chondrocytes in vitro, in order to regulate the S100A6 expression. The influence of S100A6 on inflammatory reaction of osteoarthritis was detected by RT-PCR. Also, Caspase-3 activity assay and TUNEL assay were performed to evaluate the apoptosis changes. In addition, RT-PCR and western blots were performed to verify that S100A6 mediated the PI3K/AKT signaling pathway. Through the usage of pathway regulator, we detected S100A6 produced the effect by mediating the PI3K/AKT pathway.

RESULTS

We determined the expression of S100A6 decreased in osteoarthritis model, the relative expression level in osteoarthritis model was about 0.5 fold compared with control group. Through adenovirus transfection we revealed that the inflammatory factors of osteoarthritis (interleukin-6 and matrix metalloproteinase-13) showed a negative correlation with the S100A6 expression. The relative expression level of interleukin-6 and matrix metalloproteinase-13 were 1.534 and 1.259 when S100A6 was up-regulated and the values were up to 2.445 and 2.074, respectively, when S100A6 was down-regulated. Also, the data verified the apoptosis could be reduced when the S100A6 was up-regulated and be activated when the S100A6 was down-regulated, the Caspase-3 activity was 16.512 U/μg and 24.45 U/μg respectively. Similar results were shown in TUNEL assay, the apoptosis index was 4.46% and 31.44%, respectively. Additionally, the results of polymerase chain reaction and western blots both demonstrated that the expression level of PI3K and AKT were increased when S100A6 was up-regulated, conversely the expression level of those two signal modules were reduced if the S100A6 was down-regulated. More importantly, the apoptosis triggered by S100A6 can be offset by the PI3K/AKT pathway inhibitor and activator (LY294002 and IGF-1), the values of Caspase-3 activity and apoptosis index became close to the untreated osteoarthritis group. The experimental results in this study were statistically significant.

CONCLUSION

We investigated that Calcyclin (S100A6) relieved the inflammation and mediated the chondrocyte apoptosis through PI3K/AKT pathway and we confirmed that S100A6 might be an attractive therapeutic target.

Molecular regulation of autophagy in a pro-inflammatory tumour microenvironment: New insight into the role of serum amyloid A

Chronic inflammation, systemic or local, plays a vital role in tumour progression and metastasis. Dysregulation of key physiological processes such as autophagy elicit unfavourable immune responses to induce chronic inflammation. Cytokines, growth factors and acute phase proteins present in the tumour microenvironment regulate inflammatory responses and alter crosstalk between various signalling pathways involved in the progression of cancer. Serum amyloid A (SAA) is a key acute phase protein secreted by the liver during the acute phase response (APR) following infection or injury. However, cancer and cancer-associated cells produce SAA, which when present in high levels in the tumour microenvironment contributes to cancer initiation, progression and metastasis. SAA can activate several signalling pathways such as the PI3K and MAPK pathways, which are also known modulators of the intracellular degradation process, autophagy. Autophagy can be regarded as having a double edged sword effect in cancer. Its dysregulation can induce malignant transformation through metabolic stress which manifests as oxidative stress, endoplasmic reticulum (ER) stress and DNA damage. On the other hand, autophagy can promote cancer survival during metabolic stress, hypoxia and senescence. Autophagy has been utilised to promote the efficiency of chemotherapeutic agents and can either be inhibited or induced to improve treatment outcomes. This review aims to address the known mechanisms that regulate autophagy as well as illustrating the role of SAA in modulating these pathways and its clinical implications for cancer therapy.

Up-regulation of P21-activated kinase 1 in osteoarthritis chondrocytes is responsible for osteoarthritic cartilage destruction

Osteoarthritis is mainly caused by a degenerative joint disorder, which is characterized by the gradual degradation of articular cartilage and synovial inflammation. The chondrocyte, the unique resident cell type of articular cartilage, is crucial for the development of osteoarthritis. Previous studies revealed that P21-activated kinase-1 (PAK1) was responsible for the initiation of inflammation. The purpose of the present study was to determine the potential role of PAK1 in osteoarthritis. The level of PAK1 expression was measured by Western blot and quantitative real-time PCR in articular cartilage from osteoarthritis model rats and patients with osteoarthritis. In addition, the functional role of aberrant PAK1 expression was detected in the chondrocytes. We found that the expression of PAK1 was significantly increased in chondrocytes treated with osteoarthritis-related factors. Increased expression of PAK1 was also observed in knee articular cartilage samples from patients with osteoarthritis and osteoarthritis model rats. PAK1 was found to inhibit chondrocytes proliferation and to promote the production of inflammatory cytokines in cartilages chondrocytes. Furthermore, we found that PAK1 modulated the production of extracellular matrix and cartilage degrading enzymes in chondrocytes. Results of the present studies demonstrated that PAK1 might play an important role in the pathogenesis of osteoarthritis.

Excavating bioactivities of nanozyme to remodel microenvironment for protecting chondrocytes and delaying osteoarthritis

Osteoarthritis (OA) is the main cause of disability in the elderly. Effective intervention in the early and middle stage of osteoarthritis can greatly prevent or slow down the development of the disease, and reduce the probability of joint replacement. However, there is to date no effective intervention for early and middle-stage OA. OA microenvironment mainly destroys the balance of oxidative stress, extracellular matrix synthesis and degradation of chondrocytes under the joint action of biological and mechanical factors. Herein, hollow Prussian blue nanozymes (HPBzymes) were designed via a modified hydrothermal template-free method. The aim of this study was to investigate the effects of HPBzymes on chondrocytes and the progression of OA. The intrinsic bioactivities of HPBzymes were excavated in vitro and in vivo, remodeling microenvironment for significantly protecting chondrocytes and delaying the progression of traumatic OA by inhibiting reactive oxygen species (ROS) and Rac1/nuclear factor kappa-B (NF-κB) signaling in a rat model. HPBzyme significantly diminished interleukin (IL)-1β-stimulated inflammation, extracellular matrix degradation, and apoptosis of human chondrocytes. HPBzyme attenuated the expression of Rac1 and the ROS levels and prevented the release and nuclear translocation of NF-κB. Deeply digging the intrinsic bioactivities of nanozyme with single component to remodel microenvironment is an effective strategy for ROS-associated chronic diseases. This study reveals that excavating the bioactivities of nanomedicine deserves attention for diagnosis and treatment of severe diseases.

PLCγ1 inhibition-driven autophagy of IL-1β-treated chondrocyte confers cartilage protection against osteoarthritis, involving AMPK, Erk and Akt

Previous studies identified the involvement of phosphoinositide‐specific phospholipase C (PLC) γ1 in some events of chondrocytes. This study aims to investigate whether and how PLCγ1 modulates autophagy to execute its role in osteoarthritis (OA) progression. Rat normal or human OA chondrocytes were pretreated with IL‐1β for mimicking or sustaining OA pathological condition. Using Western blotting, immunoprecipitation, qPCR, immunofluorescence and Dimethylmethylene blue assays, and ELISA and transmission electron microscope techniques, we found that PLCγ1 inhibitor U73122 enhanced Collagen II, Aggrecan and GAG levels, accompanied with increased LC3B‐II/I ratio and decreased P62 expression level, whereas autophagy inhibitor Chloroquine partially diminished its effect. Meanwhile, U73122 dissociated Beclin1 from Beclin1‐IP3R‐Bcl‐2 complex and blocked mTOR/ULK1 axis, in which the crosstalk between PLCγ1, AMPK, Erk and Akt were involved. Additionally, by haematoxylin and eosin, Safranin O/Fast green, and immunohistochemistry staining, we observed that intra‐articular injection of Ad‐shPLCγ1‐1/2 significantly enhanced Collagen and Aggrecan levels, accompanied with increased LC3B and decreased P62 levels in a rat OA model induced by anterior cruciate ligament transection and medial meniscus resection. Consequently, PLCγ1 inhibition‐driven autophagy conferred cartilage protection against OA through promoting ECM synthesis in OA chondrocytes in vivo and in vitro, involving the crosstalk between PLCγ1, AMPK, Erk and Akt.

Pro-Inflammatory Cytokines at Ultra-Low Dose Exert Anti-Inflammatory Effect In Vitro: A Possible Mode of Action Involving Sub-Micron Particles?

Tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) are pro-inflammatory cytokines involved in acute and chronic inflammatory diseases. Indeed, immunotherapy blocking these 2 cytokines has been developed. Micro-immunotherapy (MI) also uses ultra-low doses (ULD) of pro-inflammatory cytokines, impregnated on lactose-sucrose pillules, to counteract their overexpression. The study has been conducted with 2 objectives: examine the anti-inflammatory effect in vitro and the capacity of 2 unitary medicines, TNF-α (27 CH) and IL-1β (27 CH), to reduce the secretion of TNF-α in human primary monocytes and THP-1 cells differentiated with phorbol-12-myristate-13-acetate, after lipopolysaccharide (LPS) exposure; then, investigate the presence of particles possibly containing starting materials using tunable resistive pulse sensing technique. The results show that the unitary medicines, tested at 3 pillules concentrations (5.5, 11 and 22 mM), have reduced the secretion of TNF-α in both models by about 10−20% vs. vehicle control, depending on concentration. In this exploratory study, particles (150−1000 nm) have been detected in MI ULD-impregnated pillules and a hypothesis for MI medicines mode of action has been proposed. Conscious that more evaluations are necessary, authors are cautious in the conclusions because the findings described in the study are still limited, and future investigations may lead to different hypothesis.

Oxidative stress and inflammation in osteoarthritis pathogenesis: Role of polyphenols

Osteoarthritis (OA) is the most prevalent joint degenerative disease leading to irreversible structural and functional changes in the joint and is a major cause of disability and reduced life expectancy in ageing population. Despite the high prevalence of OA, there is no disease modifying drug available for the management of OA. Oxidative stress, a result of an imbalance between the production of reactive oxygen species (ROS) and their clearance by antioxidant defense system, is high in OA cartilage and is a major cause of chronic inflammation. Inflammatory mediators, such as interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) are highly upregulated in OA joints and induce ROS production and expression of matrix degrading proteases leading to cartilage extracellular matrix degradation and joint dysfunction. ROS and inflammation are interdependent, each being the target of other and represent ideal target/s for the treatment of OA. Plant polyphenols possess potent antioxidant and anti-inflammatory properties and can inhibit ROS production and inflammation in chondrocytes, cartilage explants and in animal models of OA. The aim of this review is to discuss the chondroprotective effects of polyphenols and modulation of different molecular pathways associated with OA pathogenesis and limitations and future prospects of polyphenols in OA treatment.

The Role of Autophagy and Mitophagy in Bone Metabolic Disorders

Bone metabolic disorders include osteolysis, osteoporosis, osteoarthritis and rheumatoid arthritis. Osteoblasts and osteoclasts are two major types of cells in bone constituting homeostasis. The imbalance between bone formation by osteoblasts and bone resorption by osteoclasts has been shown to have a direct contribution to the onset of these diseases. Recent evidence indicates that autophagy and mitophagy, the selective autophagy of mitochondria, may play a vital role in regulating the proliferation, differentiation and function of osteoblasts and osteoclasts. Several signaling pathways, including PINK1/Parkin, SIRT1, MAPK8/FOXO3, Beclin-1/BECN1, p62/SQSTM1, and mTOR pathways, have been implied in the regulation of autophagy and mitophagy in these cells. Here we review the current progress about the regulation of autophagy and mitophagy in osteoblasts and osteoclasts in these bone metabolic disorders, as well as the molecular signaling activated or deactivated during this process. Together, we hope to draw attention to the role of autophagy and mitophagy in bone metabolic disorders, and their potential as a new target for the treatment of bone metabolic diseases and the requirements of further mechanism studies.

Saikosaponin D: A potential therapeutic drug for osteoarthritis

Osteoarthritis is a degenerative joint disease. Currently, no effective therapeutic exists for osteoarthritis in the clinic setting. Inflammatory response and autophagy are key players in the occurrence and prognosis of osteoarthritis. In recent years, the regulation of inflammation and autophagy signal pathway has been touted as a potential treatment course for osteoarthritis. Saikosaponin D has anti-inflammatory and induces autophagy effects via inhibiting the nuclear transcription factor-κB, mTOR signaling pathways. Here in the report, we analyze and summarize recent evidences pertaining to the relationship between Saikosaponin and osteoarthritis. Published studies were scoured for in research databases, such as PubMed and Scopus with the keywords Saikosaponin and osteoarthritis. Phosphatidylinositol 3-kinase (PI3k)/Akt/mTOR signaling pathway is an important autophagy modulator, and can regulate chondrocytic autophagy, inflammation, and apoptosis. Saikosaponin D alleviates inflammation and regulates autophagy by inhibiting the PI3k/Akt/mTOR signaling pathway. Saikosaponin D could be a potential therapeutic drug for osteoarthritis.

Imperatorin suppresses IL-1β-induced iNOS expression via inhibiting ERK-MAPK/AP1 signaling in primary human OA chondrocytes

Joint inflammation is a key player in the pathogenesis of osteoarthritis (OA). Imperatorin, a plant-derived small molecule has been reported to have anti-inflammatory properties; however, its effect on chondrocytes is not known. Here, we investigated the effects of Imperatorin on interleukin-1β (IL-1β) induced expression of inducible nitric oxide synthase (iNOS) and nitric oxide production in primary human OA chondrocytes and cartilage explants culture under pathological conditions and explored the associated signaling pathways. We pretreated chondrocytes or explants with Imperatorin (50 μM) followed by IL-1β (1 ng/ml), and the culture supernatant was used to determine the levels of nitrite production by Griess assay and chondrocytes were harvested to prepare cell lysate or RNA for gene expression analysis of iNOS by Western blot or qPCR and in explants by immunohistochemistry (IHC). Pretreatment of primary chondrocytes and cartilage explants with Imperatorin suppressed IL-1β induced expression of iNOS and NO production. Imperatorin blocked the IL-1β-induced phosphorylation of ERK-MAPK/AP1 signaling pathway to suppress iNOS expression. The role of ERK in the regulation of iNOS expression was verified by using ERK inhibitor. Interestingly, we also found that Imperatorin binds to iNOS protein and inhibits its activity in vitro. Our data demonstrated that Imperatorin possess strong anti-inflammatory activity and may be developed as a therapeutic agent for the management of OA.

Nrf2/ARE is a key pathway for curcumin-mediated protection of TMJ chondrocytes from oxidative stress and inflammation

Temporomandibular joint osteoarthritis (TMJ OA) is a complex multifactorial disease that can be induced by inflammation and oxidative stress. Curcumin has been reported to have anti-inflammatory and antioxidant properties. Herein, the anti-inflammatory and antioxidant mechanisms of curcumin in TMJ OA were investigated. Curcumin treatment inhibited the expression of the inflammation mediators IL-6, iNOS, and COX-2 and of the matrix-degrading proteinases MMP-1, MMP-3, MMP-9, MMP-13, ADAMTS-4, and ADAMTS-5 and upregulated the mRNA levels of the cartilage anabolic factors COL2A1 and ACAN after IL-1β treatment. Curcumin treatment also decreased oxidative stress injury following IL-1β stimulation. Pathway analysis demonstrated that the ROS/Nrf2/HO-1-SOD2-NQO-1-GCLC signaling axis is a key axis through which curcumin activates the Nrf2/ARE pathway in TMJ inflammatory chondrocytes. Curcumin-induced anti-inflammatory and cartilage protective effects were significantly abrogated by specific Nrf2 siRNA. In vivo results demonstrated that curcumin treatment protected TMJ articular cartilage from progressive degradation. Our experimental results indicate that curcumin inhibits inflammation, oxidative stress, and the matrix degradation of TMJ inflammatory chondrocytes through the Nrf2/ARE signaling pathway, thereby exerting cartilage protective effects. This study provides insight into potential therapeutic approaches for TMJ OA.

COX-2 in liver fibrosis

As a vital inducible sensor, cyclooxygenase-2 (COX-2) plays an important role in the progress of hepatic fibrogenesis. Activation of hepatic stellate cells (HSCs) in the liver can significantly accelerate the onset and development of liver fibrosis. COX-2 overexpression triggers inflammation that is an important inducer in hepatic fibrosis. Increasing evidence indicates that COX-2 is involved in the main pathogenesis of liver fibrosis, such as inflammation, apoptosis, and cell senescence. Moreover, COX-2 expression is altered in patients and animal models with non-alcoholic fatty liver disease or cirrhosis. These findings suggest that COX-2 has a broad and critical role in the development of liver fibrosis. In this review, we summarize the latest advances in the regulation and signal transduction of COX-2 and its impact on liver fibrosis.

A proof of concept gene-activated titanium surface for oral implantology applications

Dental implants are very successful medical devices, yet implant failures do occur due to biological and mechanical complications. Peri-implantitis is one such biological complication that is primarily caused by bacteria and their products at the implant soft tissue interface. Bacterial infiltration can be prevented by the formation of a reliable soft tissue seal encircling dental implants. Platelet-derived growth factor-BB (PDGF-BB) has significant chemotactic and proliferative effects on various mesenchymal cell types, including fibroblasts, and therefore can be an effective molecule to enhance the peri-implant soft tissue seal. To overcome the limitations of the recombinant protein form of PDGF-BB, such as cost and the need for supraphysiological doses, we have developed and characterized a titanium surface that is rendered bioactive by coating it with polyethylenimine-plasmid DNA (pDNA) nanoplexes in the presence of sucrose. Human embryonic kidney 293T (HEK293T) cells and human primary gingival fibroblasts (GFs) were successfully transfected in culture with enhanced green fluorescent protein (EGFP)-encoding pDNA or platelet-derived growth factor subunit B (PDGFB)-encoding pDNA loaded into nanoplexes and coated onto titanium disks in a dose-dependent manner. GFs were shown to secrete PDGF-BB for at least 7 days after transfection and displayed both minimal viability loss and increased integrin-α2 expression 4 days posttransfection.

Derivation of notochordal cells from human embryonic stem cells reveals unique regulatory networks by single cell-transcriptomics

Intervertebral disc degeneration (IDD) is a public health dilemma as it is associated with low back and neck pain, a frequent reason for patients to visit the physician. During IDD, nucleus pulposus (NP), the central compartment of intervertebral disc (IVD) undergo degeneration. Stem cells have been adopted as a promising biological source to regenerate the IVD and restore its function. Here, we describe a simple, two-step differentiation strategy using a cocktail of four factors (LDN, AGN, FGF, and CHIR) for efficient derivation of notochordal cells from human embryonic stem cells (hESCs). We employed a CRISPR/Cas9 based genome-editing approach to knock-in the mCherry reporter vector upstream of the 3' untranslated region of the Noto gene in H9-hESCs and monitored notochordal cell differentiation. Our data show that treatment of H9-hESCs with the above-mentioned four factors for 6 days successfully resulted in notochordal cells. These cells were characterized by morphology, immunostaining, and gene and protein expression analyses for established notochordal cell markers including FoxA2, SHH, and Brachyury. Additionally, pan-genomic high-throughput single cell RNA-sequencing revealed an efficient and robust notochordal differentiation. We further identified a key regulatory network consisting of eight candidate genes encoding transcription factors including PAX6, GDF3, FOXD3, TDGF1, and SOX5, which are considered as potential drivers of notochordal differentiation. This is the first single cell transcriptomic analysis of notochordal cells derived from hESCs. The ability to efficiently obtain notochordal cells from pluripotent stem cells provides an additional tool to develop new cell-based therapies for the treatment of IDD.

Interaction between autophagy and the NLRP3 inflammasome

Autophagy, a metabolic pathway that plays an important role in maintaining the dynamic balance of cells, has two types, i.e. non-selective autophagy and selective autophagy. The role of non-selective autophagy is primarily to allow cells to circulate nutrients in an energy-limited environment, while selective autophagy primarily cleans up the organelles inside the cells to maintain the cell structure. The NLRP3 inflammasome is an innate immune response produced by the organism that can promote the secretion of interleukin-1β and interleukin-18 through caspase-1 activation and resist the damage of some pathogens. However, when the NLRP3 inflammasome is overactivated, it can cause various inflammatory diseases, such as inflammatory liver disease and inflammatory bowel disease. Many previous studies have shown that autophagy can inhibit the NLRP3 inflammasome, while in recent years, new studies have found that autophagy can also promote the NLRP3 inflammasome in some cases, and the NLRP3 inflammasome can, in turn, affect autophagy. In this review, the interaction between autophagy and the NLRP3 inflammasome is explored, and then the application of this interaction in disease treatment is discussed.

Shared KEGG pathways of icariin-targeted genes and osteoarthritis

The beneficial effects of icariin in the management of many diseases, such as chronic renal failure and heart failure, are well known. Icariin has also been shown to ameliorate osteoarthritis (OA) symptoms; however, the underlying mechanisms remain unclear. In this study, a bioinformatics analysis was performed to investigate the KEGG pathways of icariin-targeted genes involved in OA. Our study suggests that icariin plays a role in OA by regulating inflammatory cytokine production, insulin resistance, and cell survival through modulation of the NF-κB, MAPK, and Akt signaling pathways. Importantly, IKBKB, NFKBIA, MAPK8, MAPK9, and MAPK10 may be the hub genes affected by icariin when providing its beneficial effects on OA. In addition, we found that icariin decreases proinflammatory factors and inhibits chondrocyte apoptosis through suppression of the NF-κB pathway. Our study highlights a set of KEGG pathways that could explain the molecular mechanism of icariin's action on OA, suggesting that icariin could be considered as a promising therapeutic option for OA.

Redox control of chondrocyte differentiation and chondrogenesis

Chondrogenesis involves the recruitment and migration of mesenchymal cells, mesenchymal condensation, and chondrocyte differentiation and hypertrophy. Multiple factors precisely regulate chondrogenesis. Recent studies have demonstrated that the redox status of chondrocytes plays an essential role in the regulation of chondrocyte differentiation and chondrogenesis. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are important factors that change the intracellular redox status. Physiological levels of ROS/RNS act as intracellular signals in chondrocytes, and oxidative stress impairs the metabolism of chondrocytes. Under physiological conditions, the balance between ROS/RNS production and elimination ensures that redox-sensitive signalling proteins function correctly. The redox homeostasis of chondrocytes ensures that they respond appropriately to endogenous and exogenous stimuli. This review focuses on the redox regulation of key signalling pathways and transcription factors that control chondrogenesis and chondrocyte differentiation. Additionally, the mechanism by which ROS/RNS regulate signalling proteins and transcription factors in chondrocytes is also reviewed.

Chondroprotection of PPARα activation by WY14643 via autophagy involving Akt and ERK in LPS-treated mouse chondrocytes and osteoarthritis model

Autophagy maintains cellular homoeostasis. The enhancement of autophagy in chondrocytes could prevent osteoarthritis (OA) progression in articular cartilage. Peroxisome proliferator-activated receptor α (PPARα) activation may also protect articular chondrocytes against cartilage degradation in OA. However, whether the protective effect of activated PPARα is associated with autophagy induction in chondrocytes is not determined. In this study, we investigated the effect of PPARα activation by its agonist, WY14643, on the protein expression level of Aggrecan and ADAMTS5, and the protein expression level of autophagy biomarkers, including LC3B and P62, using Western blotting analysis in isolated mouse chondrocytes pre-treated with lipopolysaccharides (LPS, mimicking OA chondrocytes) with or without the autophagy inhibitor chloroquine diphosphate salt. Furthermore, Akt and ERK phosphorylation was detected in LPS-treated chondrocytes in response to WY14643. In addition, the effect of intra-articularly injected WY14643 on articular cartilage in a mouse OA model established by the destabilization of the medial meniscus was assessed using the Osteoarthritis Research Society International (OARSI) histopathology assessment system, along with the detection of Aggrecan, ADAMTS5, LC3B and P62 protein levels using immunohistochemistry assay. The results indicated that PPARα activation by WY14643 promoted proteoglycan synthesis by autophagy enhancement in OA chondrocytes in vivo and in vitro concomitant with the elevation of Akt and ERK phosphorylation. Therefore, autophagy could contribute to the chondroprotection of PPARα activation by WY14643, with the implication that PPARα activation by WY14643 may be a potential approach for OA therapy.

Inhibition of acid‑sensing ion channel 1a attenuates acid‑induced activation of autophagy via a calcium signaling pathway in articular chondrocytes

Acid-sensing ion channel 1a (ASIC1a), member of the degenerin/epithelial sodium channel protein superfamily, serves a critical role in various physiological and pathological processes. The aim of the present study was to examine the role of ASIC1a in the autophagy of rat articular chondrocytes. Autophagy was induced by acidic stimulation in rat articular chondrocytes and the extent of autophagy was evaluated via the expression levels of microtubule-associated protein 1 light chain 3II, Beclin1 and uncoordinated-51 like kinase1. Suppression of ASIC1a was achieved using small interfering RNA technology and/or inhibitor psalmotoxin-1. The expression levels of autophagy markers were measured by western blot analysis and reverse transcription-quantitative polymerase chain reaction methods. Intracellular calcium ([Ca²⁺]_i) was analyzed using a Ca²⁺-imaging method. Additionally, protein expression levels of the Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ)/5′-monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway were measured by western blot analysis. The results showed that autophagy was increased in a pH-and time-dependent manner with exposure to an acidic environment. In addition, silencing ASIC1a significantly decreased the expression levels of autophagy makers, accompanied by abrogation of the acid-induced [Ca²⁺]_i increase. Furthermore, silencing of ASIC1a downregulated the levels of CaMKKβ/β-actin and phosphorylated (p-) AMPK/AMPK, and upregulated the levels of p-mTOR/mTOR. These results indicated that ASIC1a is a potent regulator of autophagy in chondrocytes, which may be associated with decreased Ca²⁺ influx and the CaMKKβ/AMPK/mTOR pathway.

Upregulation of stanniocalcin-1 inhibits the development of osteoarthritis by inhibiting survival and inflammation of fibroblast-like synovial cells

OBJECTIVE

Osteoarthritis (OA) is a progressive and disabling disorder, characterized by synovial inflammation and joint effusion. This study aimed to explore the role of stanniocalcin-1 (STC1) in the development of OA by regulating the survival and inflammation of fibroblast-like synovial (FLS) cells.

METHODS

Microarray analyses were adopted to screen differentially expressed genes (DEGs) related to OA, and regulatory microRNA (miR) was also identified. Synovial tissue samples from patients with OA and healthy individuals were obtained to determine the expression levels of miR-454, STC1, IL-6, IL-8, and MMP3/13. The targeted relationship between miR-454 and STC1 was verified by dual-luciferase reporter gene assay. With the treatment of miR-454 mimic and STC1 overexpression vector, the effect of miR-454 and STC1 on FLS cell viability and apoptosis as well as production of inflammatory cytokines were tested.

RESULTS

STC1 with aberrant low expression was screened from GSE1919 profile in OA. STC1 was found to be downregulated in OA-FLS tissues and cells. STC1 overexpression inhibited OA-FLS cell viability but induced apoptosis of OA-FLS cells. Moreover, STC1 overexpression decreased levels of IL-6, IL-8, and MMP3/13, suggesting that STC1 overexpression suppressed inflammatory reactions. In addition, miR-454 blocked the inhibitory effects of STC1 overexpression on OA-FLS cell viability and inflammatory reaction and exerted a promotion effect of STC1 overexpression on apoptosis of OA-FLS cells.

CONCLUSIONS

Taken together, the results revealed that upregulation of STC1 could repress proliferation of OA-FLS cells and inflammatory reaction, and enhance apoptosis of OA-FLS cells, which was negatively regulated by miR-454.

Parkin clearance of dysfunctional mitochondria regulates ROS levels and increases survival of human chondrocytes

OBJECTIVE

Mitochondrial dysfunction, oxidative stress and chondrocyte death are important contributors to the development and pathogenesis of osteoarthritis (OA). In this study, we determined the expression and role of Parkin in the clearance of damaged/dysfunctional mitochondria, regulation of reactive oxygen species (ROS) levels and chondrocyte survival under pathological conditions.

METHODS

Human chondrocytes were from the unaffected area of knee OA cartilage (n = 12) and were stimulated with IL-1β to mimic pathological conditions. Mitochondrial membrane depolarization and ROS levels were determined using specific dyes and flow cytometry. Autophagy was determined by Western blotting for ATG5, Beclin1, immunofluorescence staining and confocal microscopy. Gene expression was determined by RT-qPCR. siRNA, wild-type and mutant Parkin plasmids were transfected using Amaxa system. Apoptosis was determined by PI staining of chondrocytes and TUNEL assay.

RESULTS

IL-1β-stimulated OA chondrocytes showed high levels of ROS generation, mitochondrial membrane damage, accumulation of damaged mitochondria and higher incidence of apoptosis. IL-1β stimulation of chondrocytes with depleted Parkin expression resulted in sustained high levels of ROS, accumulation of damaged/dysfunctional mitochondria and enhanced apoptosis. Parkin translocation to depolarized/damaged mitochondria and recruitment of p62/SQSTM1 was required for the elimination of damaged/dysfunctional mitochondria in IL-1β-stimulated OA chondrocytes. Importantly we demonstrate that Parkin elimination of depolarized/damaged mitochondria required the Parkin ubiquitin ligase activity and resulted in reduced ROS levels and inhibition of apoptosis in OA chondrocytes under pathological conditions.

CONCLUSIONS

Our data demonstrates that Parkin functions to eliminate depolarized/damaged mitochondria in chondrocytes which is necessary for mitochondrial quality control, regulation of ROS levels and chondrocyte survival under pathological conditions.

Curcumin improves age-related and surgically induced osteoarthritis by promoting autophagy in mice

Reduced autophagy has been implied in chondrocyte death and osteoarthritis. Curcumin (Cur) owns therapeutic effect against osteoarthritis (OA) and enhances autophagy in various tumor cells. Whether the cartilage protection of curcumin is associated with autophagy promotion and the potential signaling pathway involved remains unclear. The present study aimed to investigate the role of autophagy in the anti-OA activity of curcumin using spontaneous and surgically induced OA mice model. Spontaneous and surgically induced OA mice model was established and treated with Cur. Articular cartilage destruction and proteoglycan loss were scored through Safranin O/Fast green staining. Apoptotic cell death was detected with TUNEL (terminal deoxynucleotidyl transferase-mediated dTUP-biotin nick end labeling assay) staining and Western blot for caspase-3, Bcl-2 associated X protein (Bax), and Bcl-2 (B-cell lymphoma-2). Light chain 3 (LC3) immunohistochemistry was used to evaluate autophagy. In vitro, primary chondrocytes were treated with interleukin 1 beta (IL-1β) and Cur. Autophagy was inhibited using 3-methyladenine. Apoptosis and autophagy were detected using flow cytometry and Western blotting assay. Curcumin treatment enhanced autophagy, reduced apoptosis, and cartilage loss in both OA models. In vitro, curcumin treatment improved IL-1β induced autophagy inhibition, cell viability decrease, and apoptosis. Mechanistically, in vivo studies suggested curcumin promoted autophagy through regulating Akt/mTOR pathway. In conclusion, our results demonstrate that curcumin-induced autophagy via Akt/mTOR signaling pathway contributes to the anti-OA effect of curcumin.

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.

Nrf2/ARE pathway attenuates oxidative and apoptotic response in human osteoarthritis chondrocytes by activating ERK1/2/ELK1-P70S6K-P90RSK signaling axis

Nrf2, a redox regulated transcription factor, has recently been shown to play a role in cartilage integrity but the mechanism remains largely unknown. Osteoarthritis (OA) is a multifactorial disease in which focal degradation of cartilage occurs. Here, we studied whether Nrf2 exerts chondroprotective effects by suppressing the oxidative stress and apoptosis in IL-1β stimulated human OA chondrocytes. Expression of Nrf2 and its target genes HO-1, NQO1 and SOD2 was significantly high in OA cartilage compared to normal cartilage and was also higher in damaged area compared to smooth area of OA cartilage of the same patient. Human chondrocytes treated with IL-1β resulted in robust Nrf2/ARE reporter activity, which was inhibited by pretreatment with antioxidants indicating that Nrf2 activity was due to IL-1β-induced ROS generation. Ectopic expression of Nrf2 significantly suppressed the IL-1β-induced generation of ROS while Nrf2 knockdown significantly increased the basal as well as IL-1β-induced ROS levels in OA chondrocytes. Further, Nrf2 activation significantly inhibited the IL-1β-induced activation of extrinsic and intrinsic apoptotic pathways as determined by inhibition of DNA fragmentation, activation of Caspase-3,-8,-9, cleavage of PARP, release of cytochrome-c, suppression of mitochondrial dysfunction and mitochondrial ROS production in OA chondrocytes. Nrf2 over-expression in OA chondrocytes increased the expression of anti-apoptotic proteins while pro-apoptotic proteins were suppressed. Importantly, Nrf2 over-expression activated ERK1/2 and its downstream targets-ELK1, P70S6K and P90RSK and suppressed the IL-1β-induced apoptosis whereas inhibition of ERK1/2 activation abrogated the protective effects of Nrf2 in OA chondrocytes. Taken together, our data demonstrate that Nrf2 is a stress response protein in OA chondrocytes with anti-oxidative and anti-apoptotic function and acts via activation of ERK1/2/ELK1-P70S6K-P90RSK signaling axis. These activities of Nrf2 make it a promising candidate for the development of novel therapies for the management of OA.

Linking Autophagy and the Dysregulated NFκB/ SNAIL/YY1/RKIP/PTEN Loop in Cancer: Therapeutic Implications

The role of autophagy in the pathogenesis of various cancers has been well documented in many reports. Autophagy in cancer cells regulates cell proliferation, viability, invasion, epithelial-to-mesenchymal transition (EMT), metastasis, and responses to chemotherapeutic and immunotherapeutic treatment strategies. These manifestations are the result of various regulatory gene products that govern autophagic, biochemical, and molecular mechanisms. In several human cancer cell models, the presence of a dysregulated circuit-namely, NFκB/SNAIL/YY1/RKIP/PTEN-that plays a major role in the regulation of tumor cell unique characteristics just listed for autophagy-regulated activities. Accordingly, the autophagic mechanism and the dysregulated circuit in cancer cells share many of the same properties and activities. Thus, it has been hypothesized that there must exist a biochemical/molecular link between the two. The present review describes the link and the association of each gene product of the dysregulated circuit with the autophagic mechanism and delineates the presence of crosstalk. Crosstalk between autophagy and the dysregulated circuit is significant and has important implications in the development of targeted therapies aimed at either autophagy or the dysregulated gene products in cancer cells.

New insights on the MMP-13 regulatory network in the pathogenesis of early osteoarthritis

Osteoarthritis (OA) is the most common joint disorder and affects approximately half of the aged population. Current treatments for OA are largely palliative until the articular cartilage has been deeply damaged and irreversible morphological changes appear. Thus, effective methods are needed for diagnosing and monitoring the progression of OA during its early stages when therapeutic drugs or biological agents are most likely to be effective. Various proteinases involved in articular cartilage degeneration in pre-OA conditions, which may represent the earliest reversible measurable changes, are considered diagnostic and therapeutic targets for early OA. Of these proteinases, matrix metalloproteinase 13 (MMP-13) has received the most attention, because it is a central node in the cartilage degradation network. In this review, we highlight the main MMP-13-related changes in OA chondrocytes, including alterations in the activity and expression level of MMP-13 by upstream regulatory factors, DNA methylation, various non-coding RNAs (ncRNAs), and autophagy. Because MMP-13 and its regulatory networks are suitable targets for the development of effective early treatment strategies for OA, we discuss the specific targets of MMP-13, including upstream regulatory proteins, DNA methylation, non-coding RNAs, and autophagy-related proteins of MMP-13, and their therapeutic potential to inhibit the development of OA. Moreover, the various entities mentioned in this review might be useful as early biomarkers and for personalized approaches to disease prevention and treatment by improving the phenotyping of early OA patients.

Wogonin, a natural flavonoid, intercalates with genomic DNA and exhibits protective effects in IL-1β stimulated osteoarthritis chondrocytes

Wogonin has recently been shown to possess anti-inflammatory and chondroprotective properties and is of considerable interest due to its broad pharmacological activities. The present study highlights that Wogonin binds DNA and exerts chondroprotective effects in vitro. Wogonin showed strong binding with chondrocytes genomic DNA in vitro. The mode of binding of Wogonin to genomic-DNA was assessed by competing Wogonin with EtBr or DAPI, known DNA intercalator and a minor groove binder, respectively. EtBr fluorescence reduced significantly with increase in Wogonin concentration suggesting possible DNA intercalation of Wogonin. Further, in silico molecular docking of Wogonin on mammalian DNA also indicated possible intercalation of Wogonin with DNA. The denaturation and FRET studies revealed that Wogonin prevents denaturation of DNA strands and provide stability to genomic DNA against a variety of chemical denaturants. The cellular uptake study showed that Wogonin enters osteoarthritis chondrocytes and was mainly localized in the nucleus. Wogonin treatment to OA chondrocytes protects the fragmentation of genomic DNA in response to IL-1β as evaluated by DNA ladder and TUNEL assay. Treatment of chondrocytes with Wogonin resulted in significant suppression of IL-1β-mediated induction of ROS. Further, Wogonin exhibited protective potential through potent suppression of extrinsic and intrinsic apoptotic pathways and induction of anti-apoptotic proteins in IL-1β-stimulated osteoarthritis chondrocytes. Our data thus suggest that DNA intercalation by Wogonin may result in the stabilization of genomic DNA leading to protective activity.

Autophagy and inflammation

Autophagy is a homeostatic mechanism involved in the disposal of damaged organelles, denatured proteins as well as invaded pathogens through a lysosomal degradation pathway. Recently, increasing evidences have demonstrated its role in both innate and adaptive immunity, and thereby influence the pathogenesis of inflammatory diseases. The detection of autophagy machinery facilitated the measurement of autophagy during physiological and pathophysiological processes. Autophagy plays critical roles in inflammation through influencing the development, homeostasis and survival of inflammatory cells, including macrophages, neutrophils and lymphocytes; effecting the transcription, processing and secretion of a number of cytokines, as well as being regulated by cytokines. Recently, autophagy-dependent mechanisms have been studied in the pathogenesis of several inflammatory diseases, including infectious diseases, Crohn’s disease, cystic fibrosis, pulmonary hypertension, chronic obstructive pulmonary diseases and so on. These studies suggested that modulation of autophagy might lead to therapeutic interventions for diseases associated with inflammation. Here we highlight recent advances in investigating the roles of autophagy in inflammation as well as inflammatory diseases.

NPM1 Mutant Mediated PML Delocalization and Stabilization Enhances Autophagy and Cell Survival in Leukemic Cells

Accumulating evidence has defined nucleophosmin 1 (NPM1) mutation as a driver genetic event in acute myeloid leukemia (AML), whereas the pathogenesis of NPM1-mutated AML remains to be fully elucidated. In this study, we showed that mutant NPM1 elevated autophagic activity and autophagic activation contributed to leukemic cell survival in vitro. Meanwhile, we also found high expression of promyelocytic leukemia gene (PML) and its cytoplasmic dislocation in primary NPM1-mutated AML blasts and NPM1-mA positive OCI-AML3 cells. Mechanically, mutant NPM1 interacted with PML and mediated it delocalization as well as stabilization. Notably, NPM1-mA knockdown impaired autophagic activity, while induced expression of PML reversed this effect. Finally, we confirmed that PML modulated autophagic activity via AKT signal. These findings suggest that aberrant PML expression and autophagy are beneficial to the leukemic transformation driven by NPM1 mutations. This indicates an attractive therapeutic avenue for PML targeting and/or autophagy inhibition in the treatment of NPM1-mutated AML.

Wogonin, a plant derived small molecule, exerts potent anti-inflammatory and chondroprotective effects through the activation of ROS/ERK/Nrf2 signaling pathways in human Osteoarthritis chondrocytes

Osteoarthritis (OA), characterized by progressive destruction of articular cartilage, is the most common form of human arthritis. Here, we evaluated the potential chondroprotective and anti-inflammatory effects of Wogonin, a naturally occurring flavonoid, in IL-1β-stimulated human OA chondrocytes and cartilage explants. Wogonin completely suppressed the expression and production of inflammatory mediators including IL-6, COX-2, PGE₂, iNOS and NO in IL-1β-stimulated OA chondrocytes. Further, Wogonin exhibits potent chondroprotective potential by switching the signaling axis of matrix degradation from catabolic towards anabolic ends and inhibited the expression, production and activities of matrix degrading proteases including MMP-13, MMP-3, MMP-9, and ADAMTS-4 in OA chondrocytes, and blocked the release of s-GAG and COL2A1 in IL-1β-stimulated OA cartilage explants. Wogonin also elevated the expression of cartilage anabolic factors COL2A1 and ACAN in chondrocytes and inhibited the IL-1β-mediated depletion of COL2A1 and proteoglycan content in the matrix of cartilage explants. The suppressive effect of Wogonin was not mediated through the inhibition of MAPKs or NF-κB activation. Instead, Wogonin induced mild oxidative stress through the generation of ROS and depletion of cellular GSH, thereby modulating the cellular redox leading to the induction of Nrf2/ARE pathways through activation of ROS/ERK/Nrf2/HO-1-SOD2-NQO1-GCLC signaling axis in OA chondrocytes. Molecular docking studies revealed that Wogonin can disrupt KEAP-1/Nrf-2 interaction by directly blocking the binding site of Nrf-2 in the KEAP-1 protein. Genetic ablation of Nrf2 using specific siRNA, significantly abrogated the anti-inflammatory and chondroprotective potential of Wogonin in IL-1β-stimulated OA chondrocytes. Our data indicates that Wogonin exerts chondroprotective effects through the suppression of molecular events involved in oxidative stress, inflammation and matrix degradation in OA chondrocytes and cartilage explants. The study provides novel insights into the development of Nrf2 as a promising candidate and Wogonin as a therapeutic agent for the management of OA.

A Polyphenol-rich Pomegranate Fruit Extract Suppresses NF-κB and IL-6 Expression by Blocking the Activation of IKKβ and NIK in Primary Human Chondrocytes

Pomegranate fruit extract (PE) rich in polyphenols has been shown to exert chondroprotective effects, but the mechanism is not established. Here, we used an in vitro model of inflammation in osteoarthritis (OA) to investigate the potential of PE to suppress interleukin 1 beta (IL-1β)-stimulated expression of inflammatory cytokine IL-6, generation of reactive oxygen species (ROS) levels, and investigated the mechanism of NF-κB inhibition by analyzing the activation of the kinases upstream of IκBα in primary human chondrocytes. Total and phosphorylated forms of kinases and expression of IL-6 were determined at protein and mRNA levels by western immunoblotting and Taqman assay, respectively. Dihydrorhodamine 123 staining estimated ROS generation. Pomegranate fruit extract inhibited the mRNA and protein expression of IL-6, generation of ROS, and inhibited the IL-1β-mediated phosphorylation of inhibitor of nuclear factor kappa-B kinase subunit beta (IKKβ), expression of IKKβ mRNA, degradation of IκBα, and activation and nuclear translocation of NF-κB/p65 in human chondrocytes. Importantly, phosphorylation of NF-κB-inducing kinase was blocked by PE in IL-1β-treated human OA chondrocytes. Taken together, these data suggest that PE exerts the chondroprotective effect(s) by suppressing the production of IL-6 and ROS levels. Inhibition of NF-κB activation by PE was blocked via modulation of activation of upstream kinases in human OA chondrocytes. Copyright © 2017 John Wiley & Sons, Ltd.

Dataset of effect of Wogonin, a natural flavonoid, on the viability and activation of NF-κB and MAPKs in IL-1β-stimulated human OA chondrocytes

This article contains data related to the article "Wogonin, a plant derived small molecule exerts potent anti-inflammatory and chondroprotective effects through activation of ROS/ERK/Nrf2 signaling pathways in human Osteoarthritis chondrocytes" (Khan et al. 2017) [1]. The data are related to effects of Wogonin on the viability and IL-1β-stimulated activation of NF-κB and ERK1/2, JNK1/2 and p38 MAPKs in human OA chondrocytes. Gene expression data representing the chondrogenic phenotype and the efficiency of Nrf2 knockdown in monolayer culture of human OA chondrocytes were shown. Moreover, mass spectrometric calibration curve of Wogonin used to quantify the intracellular uptake were also presented. The data are presented in the form of figures and significance of these has been given in the research article (Khan et al. 2017) [1].