Control of the Autophagy Pathway in Osteoarthritis: Key Regulators, Therapeutic Targets and Therapeutic Strategies

SNORC knockdown alleviates inflammation, autophagy defect and matrix degradation of chondrocytes in osteoarthritis development

Excessive inflammation and autophagy defect of chondrocytes play important roles in the pathological process of osteoarthritis (OA). The present study aimed to clarify the roles of small novel rich in cartilage (SNORC) in these pathological changes of chondrocytes in OA. Bioinformatics analysis of GEO dataset GSE207881 displayed that SNORC was a potential biomarker for OA. As confirmed by quantitative real-time PCR, immunohistochemical staining and western blotting, SNORC was significantly up-regulated in cartilage of OA rat model and interleukin (IL)-1β-stimulated primary rat articular chondrocytes in contrast to their corresponding normal control. Knocking down SNORC in IL-1β-induced chondrocytes obviously suppressed the production of nitric oxide (NO), IL-6, tumor necrosis factor (TNF)-α and prostaglandin E2 (PGE2) to alleviate inflammation, and reduced the protein levels of a disintegrin and metalloproteinase with thrombospondin 5 (ADAMTS5) and matrix metallopeptidase (MMP)13 and elevated collagen type 2 alpha 1 (COL2A1) level to improve matrix degradation. Down-regulation of SNORC increased Beclin1 expression and LC3II/LC3I ratio, but suppressed p62 expression to restore impaired autophagy in IL-1β-induced chondrocytes. Moreover, down-regulating SNORC mitigated mitochondrial dysfunction and apoptosis in IL-1β-stimulated chondrocytes. Mechanically, SNORC simultaneously activated the phosphatidylinositol-3-kinase/serine threonine kinase (PI3K/AKT) and c-Jun N-terminal kinase (JNK)/c-Jun signaling pathway in the IL-1β-induced chondrocyte, while re-activating the PI3K and JNK signals abolished the suppressive effect of down-regulating SNORC on IL-1β-induced chondrocyte damage. In a word, SNORC knockdown alleviates inflammation, matrix degradation, autophagy defect and excessive apoptosis of chondrocytes during OA development via suppressing the PI3K and JNK signaling pathway.

Advances in targeted therapies for age-related osteoarthritis: A comprehensive review of current research

Osteoarthritis (OA) is a common degenerative joint disease that disproportionately impacts the elderly population on a global scale. As aging is a significant risk factor for OA, there is a growing urgency to develop specific therapies that target the underlying mechanisms of aging associated with this condition. This summary seeks to offer a thorough introduction of ongoing research efforts aimed at developing therapies to combat senescence in the context of OA. Cellular senescence plays a pivotal role in both the deterioration of cartilage integrity and the perpetuation of chronic inflammation and tissue remodeling. Consequently, targeting SnCs has emerged as a promising therapeutic approach to alleviate symptoms and hinder the progression of OA. This review examines a range of approaches, including senolytic drugs targeting SnCs, senomorphics that modulate the senescence-associated secretory phenotype (SASP), and interventions that enhance immune system clearance of SnCs. Novel methodologies, such as utilizing novel materials for exosome delivery and administering anti-aging medications with precision, offer promising avenues for the precise treatment of OA. Accumulating evidence underscores the potential of targeting senescence in OA management, potentially facilitating the development of more effective and personalized therapeutic interventions.

Leptin protects chondrocytes by inhibiting autophagy via phosphoinositide 3 kinase/protein kinase B/mammalian target of rapamycin signaling pathway

Leptin has been widely studied and found to have a significant impact on the development of osteoarthritis (OA). However, there are conflicting findings regarding the impact of leptin on chondrocytes. The study aimed to examine the impact of leptin on human chondrocytes and rats with OA. In the in vitro experiment, cartilage tissue obtained from patients hospitalized for knee replacement due to OA was collected for primary culture of chondrocytes. The proliferation and apoptosis of chondrocytes were assessed using cell counting kit-8 and flow cytometry. Autophagy levels were evaluated through monodansylcadaverine staining, mRFP-GFP-LC3 fluorescence, and transmission electron microscopy. Additionally, the expression of autophagy-related genes and proteins was analyzed using qRT-PCR and western blotting. In the in vivo experiment, an OA rat model was established. Following treatment with leptin and leptin antagonists, the cartilage tissues were examined using histology analysis (hematoxylin-eosin and Safranin O/fast green staining) and immunohistochemical. Mankin's score was utilized to assess the severity of OA, while qRT-PCR and western blotting were employed to detect the expression of autophagy-related genes and proteins in the cartilage. The ability of leptin to protect chondrocytes is achieved through the inhibition of autophagy via phosphoinositide 3 kinase/protein kinase B/mammalian target of rapamycin signaling 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.

Metformin mitigates osteoarthritis progression by modulating the PI3K/AKT/mTOR signaling pathway and enhancing chondrocyte autophagy

Osteoarthritis (OA) is a chronic degenerative disease characterized by overall joint tissue damage. Metformin (Met) has been shown to inhibit inflammatory reactions, though its potential protective mechanism on cartilage remains unclear. This study investigated Met's potential to protect cartilage in an OA rat model. Various morphological experiments were conducted to assess changes in cartilage tissue morphology before and after Met treatment. Protein and mRNA levels of cartilage-specific genes were measured using western blot, immunohistochemical staining, and RT-qPCR. Additionally, protein levels of autophagy-related and mTOR pathway-related proteins were measured. The results indicate an imbalance in the synthesis and degradation metabolism of chondrocytes, downregulation of cellular autophagy, and activation of the PI3K/Akt/mTOR pathway after surgery. However, treatment with Met could upregulate the expression of synthetic metabolic factors, indicating its contribution to cartilage repair. Furthermore, analysis of autophagy and pathway protein levels indicated that Met effectively attenuated autophagic damage to osteoarthritic cartilage cells and abnormal activation of the PI3K/Akt/mTOR pathway. In conclusion, Met can inhibit the abnormal activation of the PI3K/AKT/mTOR signaling pathway in cartilage tissue, promote the restoration of cartilage cell autophagic function, improve the balance of cartilage cell synthesis and degradation metabolism, and thus exert a protective effect on rat joint cartilage.

Miao medicine Gu Yan Xiao tincture inhibits mTOR to stimulate chondrocyte autophagy in a rabbit model of osteoarthritis

ETHNOPHARMACOLOGICAL RELEVANCE

The Gu Yan Xiao tincture, a blend of traditional Chinese herbs, is traditionally used for osteoarthritis and related pain. This study investigated its mechanism of action in order to rationalize and validate its therapeutic use.

AIM OF THE STUDY

This study analyzed, in a rabbit model of knee osteoarthritis, whether and how Gu Yan Xiao tincture exerts therapeutic benefits by modulating chondrocyte autophagy.

MATERIALS AND METHODS

The active constituents within the GYX tincture were identified using liquid chromatography-mass spectrometry. The rabbit model was established by injecting animals with type II collagenase intra-articularly, and the effects of topically applied tincture were examined on osteoarthritis lesions of the knee using histopathology, micro-computed tomography and x-ray imaging. Effects of the tincture were also evaluated on levels of inflammatory cytokines, matrix metalloproteases, and autophagy in chondrocytes. As a positive control, animals were treated with sodium diclofenac.

RESULTS

The tincture mitigated the reduction in joint space, hyperplasia of the synovium and matrix metalloproteases in serum that occurred after injection of type II collagenase in rabbits. These therapeutic effects were associated with inhibition of mTOR and activation of autophagy in articular chondrocytes. Inhibiting mTOR with rapamycin potentiated the therapeutic effects of the tincture, while inhibiting autophagy with 3-methyladenine antagonized them.

CONCLUSIONS

Gu Yan Xiao tincture mitigates tissue injury in a rabbit model of osteoarthritis, at least in part by inhibiting mTOR and thereby promoting autophagy in chondrocytes. These results rationalize the use of the tincture not only against osteoarthritis but also potentially other diseases involving inhibition of autophagy in bones and joints.

Association between serum α-Klotho levels and osteoarthritis prevalence among middle-aged and older adults: an analysis of the NHANES 2007-2016

BACKGROUND

As individuals age, the prevalence of osteoarthritis tends to increase gradually. α-Klotho is a hormone renowned for its anti-aging properties. However, the precise role of serum α-Klotho in osteoarthritis is still not fully comprehended.

METHODS

We conducted a cross-sectional study utilizing data from the National Health and Nutrition Examination Survey (NHANES) spanning from 2007 to 2016. Serum α-Klotho levels were measured using an enzyme-linked immunosorbent assay (ELISA). Osteoarthritis was assessed through self-reported questionnaires. Through univariate and multivariate logistic regression analyses, smooth curve fitting, threshold effect analysis, and subgroup analyses, we delved into the potential association between them.

RESULTS

The study encompassed a cohort of 10,265 participants. In fully adjusted models of multivariate logistic regression analysis, we identified a negative correlation between serum ln α-Klotho and OA (OR = 0.77, 95% CI: 0.65-0.91, p = 0.003). When stratifying serum α-Klotho levels into tertiles, individuals in the highest tertile exhibited a 26% reduced risk of OA compared to those in the lowest tertile (OR = 0.84, 95% CI: 0.73-0.97, p = 0.014). Subsequent analyses indicated a linearly negative association. In subgroup analyses, we explored the relationship between serum ln α-Klotho and osteoarthritis across diverse populations, revealing the persistence of this association in the majority of subgroups.

CONCLUSION

Serum α-Klotho levels exhibit a significant negative linear correlation with the prevalence of osteoarthritis in middle-aged and elderly populations in the United States.

Chondroprotective effects of Apolipoprotein D in knee osteoarthritis mice through the PI3K/AKT/mTOR signaling pathway

BACKGROUND

Because the pathophysiology of osteoarthritis (OA) has not been fully elucidated, targeted treatments are lacking. In this study, we assessed the role and underlying mechanism apolipoprotein D (APOD) on the development of OA.

METHODS

To establish an in vitro OA model, we extracted primary chondrocytes from the cartilage of C57BL/6 mice and stimulated the chondrocytes with IL-1β. After APOD intervention or incubation with an overexpressing plasmid, we detected inflammatory-related markers using RT-qPCR, Western blotting, and ELISA. To detect apoptosis and autophagy-related markers, we used flow cytometry, immunofluorescence, and transmission electron microscopy (TEM). Finally, we measured the level of oxidative stress. We also used RNA-seq to identify the APOD-regulated downstream signaling pathways. We used an in vivo mice OA model of the anterior cruciate ligament transection (ACLT) and administered intra-articular adenovirus overexpressing APOD. To examine cartilage damage severity, we used immunohistochemical analysis (IHC), micro-CT, scanning electron microscopy (SEM), and Safranin O-fast green staining.

RESULTS

Our results showed that APOD inhibited chondrocyte inflammation, degeneration, and apoptosis induced by IL-1β. Additionally, APOD reversed autophagy inhibition and oxidative stress and also blocked activation of the PI3K/AKT/mTOR signaling pathway induced by IL-1β. Finally, overexpression of the APOD gene through adenovirus was sufficient to mitigate OA progression.

CONCLUSIONS

Our findings revealed that APOD had a chondroprotective role in OA progression by the PI3K/AKT/mTOR signaling pathway.

The dysregulated autophagy in osteoarthritis: Revisiting molecular profile

The risk factors of osteoarthritis (OA) are different and obesity, lifestyle, inflammation, cell death mechanisms and diabetes mellitus are among them. The changes in the biological mechanisms are considered as main regulators of OA pathogenesis. The dysregulation of autophagy is observed in different human diseases. During the pathogenesis of OA, the autophagy levels (induction or inhibition) change. The supportive and pro-survival function of autophagy can retard the progression of OA. The protective autophagy prevents the cartilage degeneration. Moreover, autophagy demonstrates interactions with cell death mechanisms and through inhibition of apoptosis and necroptosis, it improves OA. The non-coding RNA molecules can regulate autophagy and through direct and indirect control of autophagy, they dually delay/increase OA pathogenesis. The mitochondrial integrity can be regulated by autophagy to alleviate OA. Furthermore, therapeutic compounds, especially phytochemicals, stimulate protective autophagy in chondrocytes to prevent cell death. The protective autophagy has ability of reducing inflammation and oxidative damage, as two key players in the pathogenesis of OA.

Ethanolic Extract of Propolis Modulates Autophagy-Related microRNAs in Osteoarthritic Chondrocytes

Osteoarthritis is a multifactorial joint disease characterized by degeneration, and aging stands as a significant risk factor. Autophagy, a crucial cellular homeostasis mechanism, is influenced by aging and closely linked to cartilage health. This correlation between autophagy, cell death, and OA underscores its relevance in disease progression. MicroRNAs have emerged as autophagy regulators, with miRNA-based interventions showing promise in preclinical models. Remarkably, the ethanolic extract of propolis exhibits positive effects on autophagy-related proteins and healthy cartilage markers in an in vitro osteoarthritis model. The aim of this brief report was to evaluate through in silico analysis and postulate five microRNAs that could regulate autophagy proteins (AKT1, ATG5, and LC3) and assess whether the ethanolic extract of propolis could regulate the expression of these microRNAs. Among the examined miRNAs (miR-19a, miR-125b, miR-181a, miR-185, and miR-335), the ethanolic extract of propolis induced significant changes in four of them. Specifically, miR-125b responded to EEP by counteracting IL-1β-induced effects, while miR-181a, miR-185, and miR-335 exhibited distinct patterns of expression under EEP treatment. These findings unveil a potential link between miRNAs, EEP, and autophagy modulation in OA, offering promising therapeutic insights. Nevertheless, further validation and clinical translation are warranted to substantiate these promising observations.

Il-1β Promotes Superficial Zone Cells Senescence in Articular Cartilage by Inhibiting Autophagy

OBJECTIVE

The superficial zone cells in articular cartilage (SFZCs) have been identified as stem/progenitor chondrocytes and promoted cell self-renewal in the osteoarthritis (OA). Several studies emphasized the involvement of senescence and autophagy in OA. Interleukin-1β (IL-1β) is one of the main inflammatory mediators of OA, and whether it induces senescence and autophagy in SFZCs remains unclear. The present study aimed to investigate autophagy flux, mitochondrial function, and intracellular reactive oxygen species (ROS) that resulted in senescence in SFZCs induced by IL-1β.

METHODS

Using western blotting, reverse transcription-quantitative PCR, immunofluorescence, intracellular ROS detection, mitochondrial staining, and determination of mitochondrial membrane potential, we tested senescence and autophagy markers in SFZCs induced by IL-1β in vitro. The consequences of mitochondrial function and ROS were also studied with IL-1β-induced senescence.

RESULTS

IL-1β treatment decreased SFZC proliferation, induced SFZC senescence, and reduced SFZCs' chondrogenic differentiation capacity. Moreover, IL-1β impaired autophagy flux, and the autophagy activator, rapamycin, attenuated the senescence of SFZCs. IL-1β-induced autophagy defect resulted in mitochondrial dysfunction and overproduction of ROS, and autophagy activation notably protected against mitochondrial dysfunction and reduced the levels of ROS. Moreover, antioxidant N-acetylcysteine reversed the senescence of IL-1β in SFZCs.

CONCLUSION

IL-1β promotes autophagy impairment and subsequently results in dysfunctional mitochondria and overproduction of ROS, which finally causes SFZC senescence.

Failure of cartilage regeneration: emerging hypotheses and related therapeutic strategies

Osteoarthritis (OA) is a disabling condition that affects billions of people worldwide and places a considerable burden on patients and on society owing to its prevalence and economic cost. As cartilage injuries are generally associated with the progressive onset of OA, robustly effective approaches for cartilage regeneration are necessary. Despite extensive research, technical development and clinical experimentation, no current surgery-based, material-based, cell-based or drug-based treatment can reliably restore the structure and function of hyaline cartilage. This paucity of effective treatment is partly caused by a lack of fundamental understanding of why articular cartilage fails to spontaneously regenerate. Thus, research studies that investigate the mechanisms behind the cartilage regeneration processes and the failure of these processes are critical to instruct decisions about patient treatment or to support the development of next-generation therapies for cartilage repair and OA prevention. This Review provides a synoptic and structured analysis of the current hypotheses about failure in cartilage regeneration, and the accompanying therapeutic strategies to overcome these hurdles, including some current or potential approaches to OA therapy.

CircRNAs in osteoarthritis: research status and prospect

Osteoarthritis (OA) is the most common joint disease globally, and its progression is irreversible. The mechanism of osteoarthritis is not fully understood. Research on the molecular biological mechanism of OA is deepening, among which epigenetics, especially noncoding RNA, is an emerging hotspot. CircRNA is a unique circular noncoding RNA not degraded by RNase R, so it is a possible clinical target and biomarker. Many studies have found that circRNAs play an essential role in the progression of OA, including extracellular matrix metabolism, autophagy, apoptosis, the proliferation of chondrocytes, inflammation, oxidative stress, cartilage development, and chondrogenic differentiation. Differential expression of circRNAs was also observed in the synovium and subchondral bone in the OA joint. In terms of mechanism, existing studies have mainly found that circRNA adsorbs miRNA through the ceRNA mechanism, and a few studies have found that circRNA can serve as a scaffold for protein reactions. In terms of clinical transformation, circRNAs are considered promising biomarkers, but no large cohort has tested their diagnostic value. Meanwhile, some studies have used circRNAs loaded in extracellular vesicles for OA precision medicine. However, there are still many problems to be solved in the research, such as the role of circRNA in different OA stages or OA subtypes, the construction of animal models of circRNA knockout, and more research on the mechanism of circRNA. In general, circRNAs have a regulatory role in OA and have particular clinical potential, but further studies are needed in the future.

A novel signature of autophagy-related immunophenotyping biomarkers in osteoarthritis

AIMS

We aimed to provide an autophagy-related signature to seek immunophenotyping biomarkers in osteoarthritis (OA).

MATERIALS AND METHODS

Microarray expression profiling of OA subchondral bone samples and screening of an autophagy database for autophagy-related differentially expressed genes (au-DEGs) between OA and normal samples were performed. A weighted gene co-expression network analysis (WGCNA) was constructed using au-DEGs to identify key modules significantly associated with clinical information of OA samples. OA-related autophagy hub genes were identified based on the connectivity with the phenotypes of genes in key modules and the protein-protein interaction (PPI) network in which the genes in the modules are involved, followed by feasibility verification of autophagy hub genes by bioinformatics analysis and biological experiments.

KEY FINDINGS

We screened 754 au-DEGs between OA and control samples, and co-expression networks were constructed using au-DEGs. Three OA-related autophagy hub genes (HSPA5, HSP90AA1, and ITPKB) were identified. Based on the hub gene expression profiles, OA samples were divided into two clusters with significantly different expression profiles and distinct immunological features, and the three hub genes were significantly differentially expressed between the clusters. Differences in hub genes between OA and control samples regarding sex, age, and grades of OA were examined using external datasets and experimental validation.

SIGNIFICANCE

Three autophagy-related markers of OA were identified using bioinformatics methods, and these markers may be useful for the autophagy-related immunophenotyping of OA. The present data may facilitate the diagnosis of OA, as well as the design of immunotherapies and individualized medical treatments.

The Role of Regulated Programmed Cell Death in Osteoarthritis: From Pathogenesis to Therapy

Osteoarthritis (OA) is a worldwide chronic disease that can cause severe inflammation to damage the surrounding tissue and cartilage. There are many different factors that can lead to osteoarthritis, but abnormally progressed programmed cell death is one of the most important risk factors that can induce osteoarthritis. Prior studies have demonstrated that programmed cell death, including apoptosis, pyroptosis, necroptosis, ferroptosis, autophagy, and cuproptosis, has a great connection with osteoarthritis. In this paper, we review the role of different types of programmed cell death in the generation and development of OA and how the different signal pathways modulate the different cell death to regulate the development of OA. Additionally, this review provides new insights into the radical treatment of osteoarthritis rather than conservative treatment, such as anti-inflammation drugs or surgical operation.

Mulberroside A alleviates osteoarthritis via restoring impaired autophagy and suppressing MAPK/NF-κB/PI3K-AKT-mTOR signaling pathways

Osteoarthritis (OA) is a trauma-/age-related degenerative disease characterized by chronic inflammation as one of its pathogenic mechanisms. Mulberroside A (MA), a natural bioactive withanolide, demonstrates anti-inflammatory properties in various diseases; however, little is known about the effect of MA on OA. We aim to examine the role of MA on OA and to identify the potential mechanisms through which it protects articular cartilage. In vitro, MA improved inflammatory response, anabolism, and catabolism in IL-1β-induced OA chondrocytes. The chondroprotective effects of MA were attributed to suppressing the MAPK, NF-κB, and PI3K-AKT-mTOR signaling pathways, as well as promoting the autophagy process. In vivo, intra-articular injection of MA reduced the cartilage destruction and reversed the change of anabolic and catabolic-related proteins in destabilized medial meniscus (DMM)-induced OA models. Thus, the study indicates that MA exhibits a chondroprotective effect and might be a promising agent for OA treatment.

Autophagy Is a Crucial Path in Chondrogenesis of Adipose-Derived Mesenchymal Stromal Cells Laden in Hydrogel

Autophagy is a cellular process that contributes to the maintenance of cell homeostasis through the activation of a specific path, by providing the necessary factors in stressful and physiological situations. Autophagy plays a specific role in chondrocyte differentiation; therefore, we aimed to analyze this process in adipose-derived mesenchymal stromal cells (ASCs) laden in three-dimensional (3D) hydrogel. We analyzed chondrogenic and autophagic markers using molecular biology, immunohistochemistry, and electron microscopy. We demonstrated that ASCs embedded in 3D hydrogel showed an increase expression of typical autophagic markers Beclin 1, LC3, and p62, associated with clear evidence of autophagic vacuoles in the cytoplasm. During ASCs chondrogenic differentiation, we showed that autophagic markers declined their expression and autophagic vesicles were rare, while typical chondrogenic markers collagen type 2, and aggrecan were significantly increased. In line with developmental animal models of cartilage, our data showed that in a 3D hydrogel, ASCs increased their autophagic features. This path is the fundamental prerequisite for the initial phase of differentiation that contributes to fueling the cells with energy and factors necessary for chondrogenic differentiation.

Pulsed Electromagnetic Field Alleviates Intervertebral Disc Degeneration by Activating Sirt1-Autophagy Signaling Network

Intervertebral disc (IVD) degeneration is regarded as a major contributor to low back pain (LBP), causing serious economic burden on individuals and society. Unfortunately, there are limited effective treatment for IVD degeneration. Pulsed electromagnetic field (PEMF) is an economical and effective physical therapy method, with reduced side-effects. It offers certain protection to a number of degenerative diseases. Therefore, understanding the underlying mechanism of PEMF on IVD is important for improving the PEMF therapeutic efficiency. In this study, PEMF up-regulated extracellular matrix (ECM) related genes in degenerated nucleus pulposus (NP) cells. It also increased SIRT1 expression and promoted autophagy in degenerated NP cells. In contrast, the autophagy suppressor 3-methyladenine (3-MA) reversed the beneficial effect of PEMF on ECM production. Similarly, the SIRT1 enzyme activity suppressor EX 527 also inhibited the effect of PEMF on autophagy and ECM production in NP cells, thereby suggesting that PEMF regulated ECM related genes expression through SIRT1-autophagy signaling pathway. Lastly, PEMF significantly reduced IVD degeneration in a rat model of IVD degeneration in vivo. In summary, our study uncovers a critical role of SIRT1-dependent autophagy signaling pathway in ECM protection and thus in the establishment of therapeutic effect of PEMF on IVD degeneration.

Cyclic mechanical strain with high-tensile triggers autophagy in growth plate chondrocytes

Background

Mechanical loading has been widely considered to be essential for growth plate to maintain metabolism and development. Cyclic mechanical strain has been demonstrated to induce autophagy, whereas the relationship between cyclic tensile strain (CTS) and autophagy in growth plate chondrocytes (GPCs) is not clear. The objective of this study was to investigate whether CTS can regulate autophagy in GPCs in vitro and explore the potential mechanisms of this regulation.

Methods

The 2-week-old Sprague–Dawley rat GPCs were subjected to CTS of varying magnitude and duration at a frequency of 2.0 Hz. The mRNA levels of autophagy-related genes were measured by RT-qPCR. The autophagy in GPCs was verified by transmission electron microscopy (TME), immunofluorescence and Western blotting. The fluorescence-activated cell sorting (FACS) was employed to detect the percentage of apoptotic and necrotic cells.

Results

In GPCs, CTS significantly increased the mRNA and protein levels of autophagy-related genes, such as LC3, ULK1, ATG5 and BECN1 in a magnitude- and time-dependent manner. There was no significant difference in the proportion of apoptotic and necrotic cells between control group and CTS group. The autophagy inhibitors, 3-methyladenine (3MA) and chloroquine (CQ) reversed the CTS-induced autophagy via promoting the formation of autophagosomes. Cytochalasin D (cytoD), an inhibitor of G-actin polymerization into F-actin, could effectively block the CTS-induced autophagy in GPCs.

Conclusion

Cyclic mechanical strain with high-tensile triggers autophagy in GPCs, which can be suppressed by 3MA and CQ, and cytoskeletal F-actin microfilaments organization plays a key role in chondrocytes’ response to mechanical loading.

Bilobalide Exerts Anti-Inflammatory Effects on Chondrocytes Through the AMPK/SIRT1/mTOR Pathway to Attenuate ACLT-Induced Post-Traumatic Osteoarthritis in Rats

Although osteoarthritis (OA) significantly affects the quality of life of the elderly, there is still no effective treatment strategy. The standardized Ginkgo biloba L. extract preparation has been shown to have a wide range of therapeutic effects. Bilobalide, a unique ingredient of Ginkgo biloba, has anti-inflammatory and antioxidant pharmacological properties, but its mechanism of action on OA remains unknown. In this study, we investigated the effects of bilobalide on the development of OA through in vivo and in vitro experiments, as well as its potential anti-inflammatory mechanisms. The in vitro experiments demonstrated that bilobalide significantly inhibited the production of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and matrix metalloproteinase 13 (MMP13) in ATDC5 chondrocytes induced by Interleukin-1β (IL-1β). At the molecular level, bilobalide induced chondrocyte autophagy by activating the AMPK/SIRT1/mTOR signaling pathway, which increased the expression of autophagy-related Atg genes, up-regulated the expression of LC3 protein, and reduced the expression of the p62 protein. In vivo, bilobalide exerted significant anti-inflammatory and anti-extracellular matrix (ECM) degradation effects in a rat model of post-traumatic OA (PTOA) induced by anterior cruciate ligament transection (ACLT). Bilobalide could relieve joint pain in PTOA rats, inhibit the expression of iNOS and COX-2 protein in cartilage via the AMPK/SIRT1/mTOR pathway, and reduce the level of ECM degradation biomarkers in serum. In conclusion, bilobalide exhibits vigorous anti-inflammatory activity, presenting it as an interesting potential therapeutic agent for OA.

Modulation of miR-204 Expression during Chondrogenesis

RUNX2 and SOX9 are two pivotal transcriptional regulators of chondrogenesis. It has been demonstrated that RUNX2 and SOX9 physically interact; RUNX2 transactivation may be inhibited by SOX9. In addition, RUNX2 exerts reciprocal inhibition on SOX9 transactivity. Epigenetic control of gene expression plays a major role in the alternative differentiation fates of stem cells; in particular, it has been reported that SOX9 can promote the expression of miRNA (miR)-204. Our aim was therefore to investigate the miR-204-5p role during chondrogenesis and to identify the relationship between this miR and the transcription factors plus downstream genes involved in chondrogenic commitment and differentiation. To evaluate the role of miR-204 in chondrogenesis, we performed in vitro transfection experiments by using Mesenchymal Stem Cells (MSCs). We also evaluated miR-204-5p expression in zebrafish models (adults and larvae). By silencing miR-204 during the early differentiation phase, we observed the upregulation of SOX9 and chondrogenic related genes compared to controls. In addition, we observed the upregulation of COL1A1 (a RUNX2 downstream gene), whereas RUNX2 expression of RUNX2 was slightly affected compared to controls. However, RUNX2 protein levels increased in miR-204-silenced cells. The positive effects of miR204 silencing on osteogenic differentiation were also observed in the intermediate phase of osteogenic differentiation. On the contrary, chondrocytes’ maturation was considerably affected by miR-204 downregulation. In conclusion, our results suggest that miR-204 negatively regulates the osteochondrogenic commitment of MSCs, while it positively regulates chondrocytes’ maturation.

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.

Pharmaceutical therapeutics for articular regeneration and restoration: state-of-the-art technology for screening small molecular drugs

Articular cartilage damage caused by sports injury or osteoarthritis (OA) has gained increased attention as a worldwide health burden. Pharmaceutical treatments are considered cost-effective means of promoting cartilage regeneration, but are limited by their inability to generate sufficient functional chondrocytes and modify disease progression. Small molecular chemical compounds are an abundant source of new pharmaceutical therapeutics for cartilage regeneration, as they have advantages in design, fabrication, and application, and, when used in combination, act as powerful tools for manipulating cellular fate. In this review, we present current achievements in the development of small molecular drugs for cartilage regeneration, particularly in the fields of chondrocyte generation and reversion of chondrocyte degenerative phenotypes. Several clinically or preclinically available small molecules, which have been shown to facilitate chondrogenesis, chondrocyte dedifferentiation, and cellular reprogramming, and subsequently ameliorate cartilage degeneration by targeting inflammation, matrix degradation, metabolism, and epigenetics, are summarized. Notably, this review introduces essential parameters for high-throughput screening strategies, including models of different chondrogenic cell sources, phenotype readout methodologies, and transferable advanced systems from other fields. Overall, this review provides new insights into future pharmaceutical therapies for cartilage regeneration.

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.