Melatonin protects vertebral endplate chondrocytes against apoptosis and calcification via the Sirt1‐autophagy pathway

Melatonin is reportedly associated with intervertebral disc degeneration (IDD). Endplate cartilage is vitally important to intervertebral discs in physiological and pathological conditions. However, the effects and mechanism of melatonin on endplate chondrocytes (EPCs) are still unclear. Herein, we studied the effects of melatonin on EPC apoptosis and calcification and elucidated the underlying mechanism. Our study revealed that melatonin treatment decreases the incidence of apoptosis and inhibits EPC calcification in a dose‐dependent manner. We also found that melatonin upregulates Sirt1 expression and activity and promotes autophagy in EPCs. Autophagy inhibition by 3‐methyladenine reversed the protective effect of melatonin on apoptosis and calcification, while the Sirt1 inhibitor EX‐527 suppressed melatonin‐induced autophagy and the protective effects of melatonin against apoptosis and calcification, indicating that the beneficial effects of melatonin in EPCs are mediated through the Sirt1‐autophagy pathway. Furthermore, melatonin may ameliorate IDD in vivo in rats. Collectively, this study revealed that melatonin reduces EPC apoptosis and calcification and that the underlying mechanism may be related to Sirt1‐autophagy pathway regulation, which may help us better understand the association between melatonin and IDD.     

SKI knockdown suppresses apoptosis and extracellular matrix degradation of nucleus pulposus cells via inhibition of the Wnt/β-catenin pathway and ameliorates disc degeneration

This study aimed to determine the effects of SKI on interleukin (IL)-1β-induced apoptosis of nucleus pulposus (NP) cells, intervertebral disc degeneration (IDD), and the Wnt signaling pathway. NP tissue specimens of different Pfirrmann grades (II–V) were collected from patients with different grades of IDD. Real-time polymerase chain reaction and western blotting were used to compare SKI mRNA and protein expression in NP tissues from patients. Using the IL-1β-induced IDD model, NP cells were infected with lentivirus-coated si-SKI to downregulate the expression of SKI and treated with LiCl to evaluate the involvement of the Wnt/β-catenin signaling pathway. Western blotting, immunofluorescence, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were used to detect NP cell apoptosis, extracellular matrix (ECM) metabolism, and related protein expression changes in the Wnt/β-catenin signaling pathway. To investigate the role of SKI in vivo, a rat IDD model was established by needle puncture of the intervertebral disc. Rats were injected with lentivirus-coated si-SKI and evaluated by magnetic resonance imaging (MRI), and hematoxylin and eosin (HE) and safranin O staining. SKI expression positively correlated with the severity of human IDD. In the IL-1β-induced NP cell degeneration model, SKI expression increased significantly and reached a peak at 24 h. SKI knockdown protected against IL-1β-induced NP cell apoptosis and ECM degradation. LiCl treatment reversed the protective effects of si-SKI on NP cells. Furthermore, lentivirus-coated si-SKI injection partially reversed the NP tissue damage in the IDD model in vivo. SKI knockdown reduced NP cell apoptosis and ECM degradation by inhibiting the Wnt/β-catenin signaling pathway, ultimately protecting against IDD. Therefore, SKI may be an effective target for IDD treatment.

     

Retracted: HO-1 overexpression alleviates senescence by inducing autophagy via the mitochondrial route in human nucleus pulposus cells

Intervertebral disc degeneration (IDD) is closely associated with aging. Our previous studies have confirmed that heme oxygenase-1 (HO-1) can inhibit nucleus pulposus (NP) cell apoptosis. However, whether or not HO-1 is involved in NP cell senescence and autophagy is unclear. Our results indicated that HO-1 expression was reduced in IDD tissues and replicative senescent NP cells. HO-1 overexpression using a lentiviral vector reduced the NP cell senescence level, protected mitochondrial function, and promoted NP cell autophagy through the mitochondrial pathway. Autophagy inhibitor 3-MA pretreatment reversed the anti-senescent and protective effects on the mitochondrial function of HO-1, which promoted the degradation of the extracellular matrix (ECM) in the intervertebral disc. In vivo, HO-1 overexpression inhibited IDD and enhanced autophagy. In summary, these results suggested that HO-1 overexpression alleviates NP cell senescence by inducing autophagy via the mitochondrial route.     

lncRNA HOTAIR upregulates autophagy to promote apoptosis and senescence of nucleus pulposus cells

Intervertebral disc degeneration (IDD) is a complex and chronic disease that involves disc cell senescence, death, and extracellular matrix (ECM) degradation. HOTAIR, a long non-coding RNA (lncRNA) is reportedly associated with autophagy, whereas autophagy is shown to promote IDD. However, how it affects nucleus pulposus (NP) cells, the primary component of intervertebral discs is still unclear. We hypothesized that HOTAIR promotes NP cell apoptosis and senescence through upregulating autophagy. Thus, silencing HOTAIR should inhibit autophagy and exert a therapeutic effect on IDD. Our in vitro experiments in human NP cells revealed that HOTAIR expression positively correlated with IDD grade, and overexpression enhanced autophagy. Autophagy inhibition via 3-methyladenine reversed HOTAIR stimulatory effects on apoptosis, senescence, and ECM catabolism, while the AMP-activated protein kinase (AMPK) inhibitor Compound C suppressed HOTAIR-induced autophagy through regulating AMPK/mTOR/ULK1 pathways. Our in vivo experiment then illustrated that silencing HOTAIR ameliorates IDD in rats. Collectively, we demonstrated that HOTAIR stimulates autophagy to promote NP cell apoptosis, senescence, and ECM catabolism. Therefore, silencing HOTAIR has the potential to become a treatment option for IDD.     

PTEN promotes intervertebral disc degeneration by regulating nucleus pulposus cell behaviors

Intervertebral disc degeneration (IDD) is induced by multiple factors including increased apoptosis, decreased survival, and reduced extracellular matrix (ECM) synthesis in the nucleus pulposus (NP) cells. The tumor suppressor phosphatase and tensin homolog deleted from chromosome 10 (PTEN) is the only known lipid phosphatase counteracting the PI3K/AKT pathway. Loss of PTEN leads to activated PI3K/AKT signaling, which plays a key role in a variety of cancers. However, the role of PTEN/PI3K/AKT signaling nexus in IDD remains unknown. Here, we report that PTEN is overexpressed in degenerative NP, which correlates with inactivated AKT. Using the PTEN knockdown approach by lentivirus‐mediated short interfering RNA gene transfer technique, we report that PTEN decreases survival but induces apoptosis and senescence of NP cells. PTEN also inhibits expression and production of ECM components including collagen II, aggrecan, and proteoglycan. Furthermore, PTEN modulates the expression of ECM regulatory molecules SOX‐9 and matrix metalloproteinase‐3 (MMP‐3). Using small‐molecule AKT inhibitor GDC‐0068, we confirm that PTEN regulates NP cell behaviors through its direct targeting of PI3K/AKT. These findings demonstrate for the first time that PTEN/PI3K/AKT signaling axis plays an important role in the pathogenesis of IDD. Targeting PTEN using gene therapy may represent a promising therapeutic approach against disc degenerative diseases.     

Genistein protects intervertebral discs from degeneration via Nrf2-mediated antioxidant defense system: An in vitro and in vivo study

Oxidative stress has been reported to be closely associated with the development of intervertebral disc degeneration (IDD). IDD is one of the major causes of low back pain. Genistein (GES), one of the main isoflavones of soybean, has been shown to exert multiple biological functions on different diseases. Here, we tested the therapeutic potential of GES for IDD. In vitro experiments, we confirmed GES was nontoxic to rat nucleus pulposus cells (NPCs) within the concentration of 100 μM. Furthermore, GES was able to suppress apoptosis in tert-butyl hydroperoxide (TBHP)-treated NPCs. In the aspect of extracellular matrix (ECM), GES not only reduced metalloproteinase-13 (MMP-13) and a disintegrin-like and MMP thrombospondin type 1 motif 5 expression, but also increased aggrecan and type II collagen levels. Also, we found GES might rescue TBHP-induced NPCs degeneration by enhancing Nrf2-mediated antioxidant defense system. Silencing Nrf2 partly abolished the protective effects of GES on apoptosis and ECM disruption in TBHP-treated NPCs. Correspondingly, GES ameliorated IDD in a rat model by preserving morphology of degenerative intervertebral discs and promoting Nrf2 expression. To sum up, our study suggests that GES exerts protective effects in NPCs against degeneration and reveals the underlying mechanism of GES on Nrf2 activation in NPCs.     

Inhibition of TNFR1 Attenuates LPS Induced Apoptosis and Inflammation in Human Nucleus Pulposus Cells by Regulating the NF-KB and MAPK Signalling Pathway

Neurochemical Research - Intervertebral disc degeneration (IDD) is accompanied by nucleus pulposus (NP) cell apoptosis, inflammation, and extracellular matrix degradation. Tumour necrosis factor...     

Therapeutic potential of melatonin in the intervertebral disc degeneration through inhibiting the ferroptosis of nucleus pulpous cells

Ferroptosis, a novel type of cell death mediated by the iron-dependent lipid peroxidation, contributes to the pathogenesis of the intervertebral disc degeneration (IDD). Increasing evidence demonstrated that melatonin (MLT) displayed the therapeutic potential to prevent the development of IDD. Current mechanistic study aims to explore whether the downregulation of ferroptosis contributes to the therapeutic capability of MLT in IDD. Current studies demonstrated that conditioned medium (CM) from the lipopolysaccharide (LPS)-stimulated macrophages caused a series of changes about IDD, including increased intracellular oxidative stress (increased reactive oxygen species and malondialdehyde levels, but decreased glutathione levels), upregulated expression of inflammation-associated factors (IL-1β, COX-2 and iNOS), increased expression of key matrix catabolic molecules (MMP-13, ADAMTS4 and ADAMTS5), reduced the expression of major matrix anabolic molecules (COL2A1 and ACAN), and increased ferroptosis (downregulated GPX4 and SLC7A11 levels, but upregulated ACSL4 and LPCAT3 levels) in nucleus pulposus (NP) cells. MLT could alleviate CM-induced NP cell injury in a dose-dependent manner. Moreover, the data substantiated that intercellular iron overload was involved in CM-induced ferroptosis in NP cells, and MLT treatment alleviated intercellular iron overload and protected NP cells against ferroptosis, and those protective effects of MLT in NP cells further attenuated with erastin and enhanced with ferrostatin-1(Fer-1). This study demonstrated that CM from the LPS-stimulated RAW264.7 macrophages promoted the NP cell injury. MLT alleviated the CM-induced NP cell injury partly through inhibiting ferroptosis. The findings support the role of ferroptosis in the pathogenesis of IDD, and suggest that MLT may serve as a potential therapeutic approach for clinical treatment of IDD.     

Spermidine promotes nucleus pulposus autophagy as a protective mechanism against apoptosis and ameliorates disc degeneration

Spermidine has therapeutic effects in many diseases including as heart diastolic function, myopathic defects and neurodegenerative disorders via autophagy activation. Autophagy has been found to mitigate cell apoptosis in intervertebral disc degeneration (IDD). Accordingly, we theorize that spermidine may have beneficial effects on IDD via autophagy stimulation. In this study, spermidine's effect on IDD was evaluated in tert‐butyl hydroperoxide (TBHP)‐treated nucleus pulposus cells of SD rats in vitro as well as in a puncture‐induced rat IDD model. We found that autophagy was actuated by spermidine in nucleus pulposus cells. In addition, spermidine treatment weakened the apoptotic effects of TBHP in nucleus pulposus cells. Spermidine increased the expression of anabolic proteins including Collagen‐II and aggrecan and decreased the expression of catabolic proteins including MMP13 and Adamts‐5. Additionally, autophagy blockade using 3‐MA reversed the beneficial impact of spermidine against nucleus pulposus cell apoptosis. Autophagy was thus important for spermidine's therapeutic effect on IDD. Spermidine‐treated rats had an accentuated T2‐weighted signal and a diminished histological degenerative grade than vehicle‐treated rats, showing that spermidine inhibited intervertebral disc degeneration in vivo. Thus, spermidine protects nucleus pulposus cells against apoptosis through autophagy activation and improves disc, which may be beneficial for the treatment of IDD.     

Down‐regulation of insulin‐like growth factor binding protein 5 is involved in intervertebral disc degeneration via the ERK signalling pathway

It is obvious that epigenetic processes influence the evolution of intervertebral disc degeneration (IDD). However, its molecular mechanisms are poorly understood. Therefore, we tested the hypothesis that IGFBP5, a potential regulator of IDD, modulates IDD via the ERK signalling pathway. We showed that IGFBP5 mRNA was significantly down‐regulated in degenerative nucleus pulposus (NP) tissues. IGFBP5 was shown to significantly promote NP cell proliferation and inhibit apoptosis in vitro, which was confirmed by MTT, flow cytometry and colony formation assays. Furthermore, IGFBP5 was shown to exert its effects by inhibiting the ERK signalling pathway. The effects induced by IGFBP5 overexpression on NP cells were similar to those induced by treatment with an ERK pathway inhibitor (PD98059). Moreover, qRT‐PCR and Western blot analyses were performed to examine the levels of apoptosis‐related factors, including Bax, caspase‐3 and Bcl2. The silencing of IGFBP5 up‐regulated the levels of Bax and caspase‐3 and down‐regulated the level of Bcl2, thereby contributing to the development of human IDD. Furthermore, these results were confirmed in vivo using an IDD rat model, which showed that the induction of Igfbp5 mRNA expression abrogated the effects of IGFBP5 silencing on intervertebral discs. Overall, our findings elucidate the role of IGFBP5 in the pathogenesis of IDD and provide a potential novel therapeutic target for IDD.     

Poly (ADP‐ribose) polymerase inhibition protects against myocardial ischaemia/reperfusion injury via suppressing mitophagy

Myocardial ischaemia/reperfusion (I/R) injury attenuates the beneficial effects of reperfusion therapy. Poly(ADP‐ribose) polymerase (PARP) is overactivated during myocardial I/R injury. Mitophagy plays a critical role in the development of myocardial I/R injury. However, the effect of PARP activation on mitophagy in cardiomyocytes is unknown. In this study, we found that I/R induced PARP activation and mitophagy in mouse hearts. Poly(ADP‐ribose) polymerase inhibition reduced the infarct size and suppressed mitophagy after myocardial I/R injury. In vitro, hypoxia/reoxygenation (H/R) activated PARP, promoted mitophagy and induced cell apoptosis in cardiomyocytes. Poly(ADP‐ribose) polymerase inhibition suppressed H/R‐induced mitophagy and cell apoptosis. Parkin knockdown with lentivirus vectors inhibited mitophagy and prevented cell apoptosis in H/R‐treated cells. Poly(ADP‐ribose) polymerase inhibition prevented the loss of the mitochondrial membrane potential (ΔΨm). Cyclosporin A maintained ΔΨm and suppressed mitophagy but FCCP reduced the effect of PARP inhibition on ΔΨm and promoted mitophagy, indicating the critical role of ΔΨm in H/R‐induced mitophagy. Furthermore, reactive oxygen species (ROS) and poly(ADP‐ribosylation) of CypD and TSPO might contribute to the regulation of ΔΨm by PARP. Our findings thus suggest that PARP inhibition protects against I/R‐induced cell apoptosis by suppressing excessive mitophagy via the ΔΨm/Parkin pathway.     

Melatonin activates Parkin translocation and rescues the impaired mitophagy activity of diabetic cardiomyopathy through Mst1 inhibition

Mitophagy eliminates dysfunctional mitochondria and thus plays a cardinal role in diabetic cardiomyopathy (DCM). We observed the favourable effects of melatonin on cardiomyocyte mitophagy in mice with DCM and elucidated their underlying mechanisms. Electron microscopy and flow cytometric analysis revealed that melatonin reduced the number of impaired mitochondria in the diabetic heart. Other than decreasing mitochondrial biogenesis, melatonin increased the clearance of dysfunctional mitochondria in mice with DCM. Melatonin increased LC3 II expression as well as the colocalization of mitochondria and lysosomes in HG‐treated cardiomyocytes and the number of typical autophagosomes engulfing mitochondria in the DCM heart. These results indicated that melatonin promoted mitophagy. When probing the mechanism, increased Parkin translocation to the mitochondria may be responsible for the up‐regulated mitophagy exerted by melatonin. Parkin knockout counteracted the beneficial effects of melatonin on the cardiac mitochondrial morphology and bioenergetic disorders, thus abolishing the substantial effects of melatonin on cardiac remodelling with DCM. Furthermore, melatonin inhibited Mammalian sterile 20‐like kinase 1 (Mst1) phosphorylation, thus enhancing Parkin‐mediated mitophagy, which contributed to mitochondrial quality control. In summary, this study confirms that melatonin rescues the impaired mitophagy activity of DCM. The underlying mechanism may be attributed to activation of Parkin translocation via inhibition of Mst1.     

Melatonin reverses tumor necrosis factor-alpha-induced metabolic disturbance of human nucleus pulposus cells via MTNR1B/Gαi2/YAP signaling

Background: Intervertebral disc degeneration (IDD), the main cause of low back pain, is closely related to the inflammatory microenvironment in the nucleus pulposus (NP). Tumor necrosis factor-α (TNF-α) plays an important role in inflammation-related metabolic disturbance of NP cells. Melatonin has been proven to regulate the metabolism of NP cells, but whether it can protect NP cells from TNF-α-induced damage is still unclear. Therefore, this study aims to investigate the role and specific mechanism of melatonin on regulating the metabolism of NP cells in the inflammatory microenvironment.Methods: Western blotting, RT-qPCR and immunohistochemistry were used to detect the expression of melatonin membrane receptors (MTNR1A/B) and TNF-α in human NP tissues. In vitro, human primary NP cells were treated with or without vehicle, TNF-α and melatonin. And the metabolic markers were also detected by western blotting and RT-qPCR. The activity of NF-κB signaling and Hippo/YAP signaling were assessed by western blotting and immunofluorescence. Membrane receptors inhibitors, pathway inhibitors, lentiviral infection, plasmids transfection and immunoprecipitation were used to explore the specific mechanism of melatonin. In vivo, the rat IDD model was constructed and melatonin was injected intraperitoneally to evaluate its therapeutical effect on IDD.Results: The upregulation of TNF-α and downregulation of melatonin membrane receptors (MTNR1A/B) were observed in degenerative NP tissues. Then we demonstrated that melatonin could alleviate the development of IDD in a rat model and reverse TNF-α-impaired metabolism of NP cells in vitro. Further investigation revealed that the protective effects of melatonin on NP cells mainly rely on MTNR1B, which subsequently activates Gαi2 protein. The activation of Gαi2 could upregulate the yes-associated protein (YAP) level, resulting in anabolic enhancement of NP cells. In addition, melatonin-mediated YAP upregulation increased the expression of IκBα and suppressed the TNF-α-induced activation of the NF-κB pathway, thereby inhibiting the catabolism of NP cells.Conclusions: Our results revealed that melatonin can reverse TNF-α-impaired metabolism of NP cells via the MTNR1B/Gαi2/YAP axis and suggested that melatonin can be used as a potential therapeutic drug in the treatment of IDD.     

Andrographolide prevents human nucleus pulposus cells against degeneration by inhibiting the NF-κB pathway

Intervertebral disc degeneration (IDD) is among the most common spinal disorders, pathologically characterized by excessive cell apoptosis and production of proinflammatory factors. Pharmacological targeting of nucleus pulposus (NP) degeneration may hold promise in IDD therapy, but it is limited by adverse side effects and nonspecificity of drugs. In this study, we used a natural compound, andrographolide (ANDRO), which has been widely used to intervene inflammatory and apoptotic diseases in the investigation of NP degeneration based on IDD-patients-derived NP cells by lipopolysaccharide (LPS) treatment for the preservation of degeneration. The results showed that LPS maintained the degeneration status of NP cells as evidenced by a high apoptosis rate and the expression of degenerative and inflammatory mediators after LPS treatment. ANDRO reversed the effects of LPS-caused degeneration of NP cells and maintained the phenotype of NP cells, as demonstrated by flow cytometry, degenerative mediators (ADAMTS4 and ADAMTS5), inflammatory factors (COX2, PGE2, MMP-13, and MMP-3), biomarkers of NP cells (SOX9, ACAN, and COL2A1) expressions, and glycosaminoglycan secretion. We also found the involvement of the nuclear factor kappa-light-chain-enhancer of the activated B cells (NF-κB) pathway in ANDRO treatment, indicating that ANDRO prevented the LPS-preserved degeneration of NP cells by inhibiting the NF-κB pathway. This study may provide a reference for clinic medication of IDD therapy.     

Circular RNAs in nucleus pulposus cell function and intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common cause of low back pain, which inflicts more global disability than any other condition. Although IDD was deemed to be a natural process that comes with ageing, a growing body of evidence suggested that both genetic and environmental factors could modify the development of IDD. In this connection, aberrant function of nucleus pulposus cells has been implicated in IDD pathogenesis. Circular RNAs are a novel class of endogenous non‐coding RNAs that play crucial regulatory roles in diverse cellular processes. Recently, deregulation of circRNAs in nucleus pulposus cells was found to functionally participate in IDD development. In this review, we summarize the current knowledge regarding the deregulation of circRNAs in IDD in relation to their actions on nucleus pulposus cell functions, including cell proliferation, apoptosis and extracellular matrix synthesis/degradation. The potential clinical utilities of circRNAs as therapeutic targets for the management of IDD are also discussed.     

Emerging role and therapeutic implication of mTOR signalling in intervertebral disc degeneration

Intervertebral disc degeneration (IDD), an important cause of chronic low back pain (LBP), is considered the pathological basis for various spinal degenerative diseases. A series of factors, including inflammatory response, oxidative stress, autophagy, abnormal mechanical stress, nutritional deficiency, and genetics, lead to reduced extracellular matrix (ECM) synthesis by intervertebral disc (IVD) cells and accelerate IDD progression. Mammalian target of rapamycin (mTOR) is an evolutionarily conserved serine/threonine kinase that plays a vital role in diverse degenerative diseases. Recent studies have shown that mTOR signalling is involved in the regulation of autophagy, oxidative stress, inflammatory responses, ECM homeostasis, cellular senescence, and apoptosis in IVD cells. Accordingly, we reviewed the mechanism of mTOR signalling in the pathogenesis of IDD to provide innovative ideas for future research and IDD treatment.     

Melatonin suppresses senescence‐derived mitochondrial dysfunction in mesenchymal stem cells via the HSPA1L–mitophagy pathway

Mesenchymal stem cells (MSCs) are a popular cell source for stem cell‐based therapy. However, continuous ex vivo expansion to acquire large amounts of MSCs for clinical study induces replicative senescence, causing decreased therapeutic efficacy in MSCs. To address this issue, we investigated the effect of melatonin on replicative senescence in MSCs. In senescent MSCs (late passage), replicative senescence decreased mitophagy by inhibiting mitofission, resulting in the augmentation of mitochondrial dysfunction. Treatment with melatonin rescued replicative senescence by enhancing mitophagy and mitochondrial function through upregulation of heat shock 70 kDa protein 1L (HSPA1L). More specifically, we found that melatonin‐induced HSPA1L binds to cellular prion protein (PrP^C), resulting in the recruitment of PrP^C into the mitochondria. The HSPA1L‐PrP^C complex then binds to COX4IA, which is a mitochondrial complex IV protein, leading to an increase in mitochondrial membrane potential and anti‐oxidant enzyme activity. These protective effects were blocked by knockdown of HSPA1L. In a murine hindlimb ischemia model, melatonin‐treated senescent MSCs enhanced functional recovery by increasing blood flow perfusion, limb salvage, and neovascularization. This study, for the first time, suggests that melatonin protects MSCs against replicative senescence during ex vivo expansion for clinical application via mitochondrial quality control.