ROS: Crucial Intermediators in the Pathogenesis of Intervertebral Disc Degeneration. Oxid Med Cell Longev. 2017;2017:5601593. [PMID: 28392887 PMCID: PMC5368368 DOI: 10.1155/2017/5601593]

VDR promotes nucleus pulposus cell mitophagy as a protective mechanism against oxidative stress injury

Intervertebral disk degeneration (IDD) is a common aging disease. Excessive apoptosis of nucleus pulposus (NP) cells has been widely considered a main contributor to IDD. Emerging science has shown that autophagy plays a protective role against apoptosis under oxidative stress. Vitamin D receptor (VDR) is a steroid hormone receptor that can regulate autophagy. The purpose of this study was to clarify whether VDR alleviates IDD by promoting autophagy. H₂O₂ stimulation was used to establish oxidative stress conditions. Initially, the expression level of VDR in human degenerative NP tissues was measured by immunohistochemistry. In addition, the CRISPR-dCas9-VPR system and siRNA were utilized to upregulate or downregulate VDR and Parkin expression, respectively. Autophagic and apoptotic markers were determined by Western blotting and RT-qPCR. Transmission electron microscopy was used to monitor the occurrence of autophagy in rat NP cells. VDR expression was downregulated in human degenerative NP tissues and H₂O₂-stimulated rat NP cells, indicating a negative correlation between VDR expression and IDD. VDR overexpression promoted mitophagy and prevented apoptosis and mitochondrial injury under oxidative stress. Additionally, mitophagy inhibition by 3-MA abolished the protective effect of VDR activation in vitro. Furthermore, VDR activation promoted mitophagy via the PINK1/Parkin pathway in H₂O₂-treated NP cells. This study demonstrates that VDR activation ameliorates oxidative damage and decreases NP cell apoptosis by promoting PINK1/Parkin-dependent mitophagy, indicating that VDR may serve as a promising therapeutic target in the management of IDD.

Mitochondrial Dysfunction in Oxidative Stress-Mediated Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) is the most common contributor to low back pain (LBP). Recent studies have found that oxidative stress and reactive oxygen species (ROS) play an important role in IVDD. As a by‐product of aerobic respiration, ROS is mainly produced in the mitochondria by the electron transport chain and other mitochondrial located proteins. With the excessive accumulation of ROS, mitochondria are also the primary target of ROS attack in disc cells. A disrupted balance between intracellular ROS production and antioxidant capacity will lead to oxidative stress, which is the key contributor to cell apoptosis, cell senescence, excessive autophagy, and mitochondrial dysfunction. As the pivotal ingredient of oxidative stress, mitochondrial dysfunction manifests as imbalanced mitochondrial dynamics and dysregulated mitophagy. Mitochondria can alter their own dynamics through the process of fusion and fission, so that disabled mitochondria can be separated from the mitochondrial pool. Moreover, mitophagy participates by clearing these dysfunctional mitochondria. Abnormality in any of these processes either increases the production or decreases the clearance of ROS, leading to a vicious cycle that results in the death of intervertebral disc cells in large quantities, combined with degradation of the extracellular matrix and overproduction of matrix metalloproteinase. In this review, we explain the changes in mitochondrial morphology and function during oxidative stress‐mediated IVDD and highlight the important role of mitochondria in this process. Eventually, we summarize the IVDD therapeutic strategies targeting mitochondrial dysfunction based on current understanding of the role of oxidative stress in IVDD.

Mitochonic Acid-5 Inhibits Reactive Oxygen Species Production and Improves Human Chondrocyte Survival by Upregulating SIRT3-Mediated, Parkin-dependent Mitophagy

Mitochondrial dysfunction is related to the pathogenesis of osteoarthritis (OA); however, there are no effective drugs to treat OA for maintaining mitochondrial homeostasis. Studies have shown that mitochonic acid-5 (MA-5) has a protective effect against mitochondrial damage and plays a role in mitophagy. However, it is not clear whether MA-5 has a beneficial effect on inflammatory articular cartilage. Here, human OA cartilage was obtained from patients undergoing total joint replacement. Interleukin-1β (IL-1β) was used to stimulate chondrocytes and induce inflammatory injury. Cell Counting Kit-8, TUNEL, and flow cytometry assays were used to assess apoptosis. Gene expression was examined using quantitative reverse transcription-polymerase chain reaction. Mitochondrial function was evaluated using immunoblotting, mitochondrial membrane potential assay, JC-1 staining, and immunofluorescence analysis. Mitophagy was detected using immunoblotting and immunofluorescence. 3-(1H-1,2,3-triazol-4-yl) pyridine (3-TYP), a specific inhibitor of Sirtuin 3 (SIRT3), was used to block the SIRT3/Parkin pathway. Mitophagy in the cartilage sections was evaluated via immunohistochemistry. IL-1β was found to induce chondrocyte apoptosis by inhibiting SIRT3 expression and mitophagy. In addition, inflammatory damage reduced the mitochondrial membrane potential and promoted the production of intracellular reactive oxygen species (ROS), leading to increased mitochondrial division, mitochondrial fusion inhibition, and the consequent mitochondrial damage. In contrast, the MA-5 treatment inhibited excessive ROS production by upregulating mitophagy, maintaining the mitochondrial membrane potential, and reducing mitochondrial apoptosis. After chemically blocking SIRT3 with 3-TYP, Parkin-related mitophagy was also inhibited, an effect that was prevented by pretreatment of the chondrocytes with MA-5, thereby suggesting that SIRT3 is upstream of Parkin. Overall, MA-5 was found to enhance the activity of SIRT3, promote Parkin-dependent mitophagy, eliminate depolarized/damaged mitochondria in chondrocytes, and protect cartilage cells. In conclusion, MA-5 inhibits IL-1β-induced oxidative stress and protects chondrocytes by upregulating the SIRT3/Parkin-related autophagy signaling pathway.

Fucoidan-loaded nanofibrous scaffolds promote annulus fibrosus repair by ameliorating the inflammatory and oxidative microenvironments in degenerative intervertebral discs

Tissue engineering holds potential in the treatment of intervertebral disc degeneration (IDD). However, implantation of tissue engineered constructs may cause foreign body reaction and aggravate the inflammatory and oxidative microenvironment of the degenerative intervertebral disc (IVD). In order to ameliorate the adverse microenvironment of IDD, in this study, we prepared a biocompatible poly (ether carbonate urethane) urea (PECUU) nanofibrous scaffold loaded with fucoidan, a natural marine bioactive polysaccharide which has great anti-inflammatory and antioxidative functions. Compared with pure PECUU scaffold, the fucoidan-loaded PECUU nanofibrous scaffold (F-PECUU) decreased the gene and protein expression related to inflammation and the oxidative stress in the lipopolysaccharide (LPS) induced annulus fibrosus cells (AFCs) significantly (p<0.05). Especially, gene expression of Ill 6 and Ptgs2 was decreased by more than 50% in F-PECUU with 3.0 wt% fucoidan (HF-PECUU). Moreover, the gene and protein expression related to the degradation of extracellular matrix (ECM) were reduced in a fucoidan concentration-dependent manner significantly, with increased almost 3 times gene expression of Col1a2 and Acan in HF-PECUU. Further, in a 'box' defect model, HF-PECUU decreased the expression of COX-2 and deposited more ECM between scaffold layers when compared with pure PECUU. The disc height and nucleus pulposus hydration of repaired IVD reached up to 75% and 85% of those in the sham group. In addition, F-PECUU helped to maintain an integrate tissue structure with a similar compression modulus to that in sham group. Taken together, the F-PECUU nanofibrous scaffolds showed promising potential to promote AF repair in IDD treatment by ameliorating the harsh degenerative microenvironment. STATEMENT OF SIGNIFICANCE: Annulus fibrosus (AF) tissue engineering holds potential in the treatment of intervertebral disc degeneration (IDD), but is restricted by the inflammatory and oxidative microenvironment of degenerative disc. This study developed a biocompatible polyurethane scaffold (F-PECUU) loaded with fucoidan, a marine bioactive polysaccharide, for ameliorating IDD microenvironment and promoting disc regeneration. F-PECUU alleviated the inflammation and oxidative stress caused by lipopolysaccharide and prevented extracellular matrix (ECM) degradation in AF cells. In vivo, it promoted ECM deposition to maintain the height, water content and mechanical property of disc. This work has shown the potential of marine polysaccharides-containing functional scaffolds in IDD treatment by ameliorating the harsh microenvironment accompanied with disc degeneration.

Selenium Attenuates TBHP-Induced Apoptosis of Nucleus Pulposus Cells by Suppressing Mitochondrial Fission through Activating Nuclear Factor Erythroid 2-Related Factor 2

Intervertebral disc (IVD) degeneration (IDD), the leading cause of low back pain (LBP), remains intractable due to a lack of effective therapeutic strategies. Several lines of studies have documented that nucleus pulposus cell (NPC) death induced by excessive oxidative stress is a crucial contributor to IDD. However, the concrete role and regulation mechanisms have not been fully clarified. Selenium (Se), a vital prosthetic group of antioxidant enzymes, is indispensable for maintaining redox homeostasis and promoting cell survival. However, no light was shed on the role of Se on IDD progression, especially regulation on mitochondrial dynamics and homeostasis. To fill this research gap, the current study focuses on the effects of Se, including sodium selenite (SS) and selenomethionine (Se-Met), on IDD progression and the underlying mechanisms. In vitro, we found that both SS and Se-Met alleviated tert-butyl hydroperoxide- (TBHP-) induced oxidative stress, protected mitochondrial function, and inhibited apoptosis of NPCs. Further experiments indicated that Se suppressed TBHP-induced mitochondrial fission and rescued the imbalance of mitochondrial dynamics. Promoting mitochondrial fission by carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP) partially counteracted the cytoprotective effects of Se. Moreover, blocking nuclear factor erythroid 2-related factor 2 (Nrf2) with ML385 proved that the effect of Se on regulating mitochondrial dynamics was attributed to the activation of the Nrf2 pathway. In the puncture-induced rat IDD model, a supplement of Se-Met ameliorated degenerative manifestations. Taken together, our results demonstrated that Se suppressed TBHP-induced oxidative stress and mitochondrial fission by activating the Nrf2 pathway, thereby inhibiting the apoptosis of NPCs and ameliorating IDD. Regulation of mitochondrial dynamics by Se may have a potential application value in attenuating the pathological process of IDD.

Prussian Blue Nanoparticles Stabilize SOD1 from Ubiquitination-Proteasome Degradation to Rescue Intervertebral Disc Degeneration

Discography often destroys the hypoxic environment in the intervertebral disc and accelerates intervertebral disc degeneration (IVDD). Therefore, it often fails to meet the requirements for application in clinical practice. This technology mainly increases the reactive oxygen species (ROS) in the IVD. As so, it is particularly critical to develop strategies to avoid this degeneration mechanism. Prussian blue nanoparticles (PBNPs) are found to enhance development under magnetic resonance T1 and have antioxidant enzyme activity. The key results of the present study confirm that PBNPs alleviate intracellular oxidative stress and increase the intracellular activities of antioxidant enzymes, such as superoxide dismutase 1 (SOD1). PBNPs can rescue nucleus pulposus cell degeneration by increasing oxidoreductase system-related mRNA and proteins, especially by stabilizing SOD1 from ubiquitination-proteasome degradation, thus improving the mitochondrial structure to increase antioxidation ability, and finally rescuing ROS-induced IVDD in a rat model. Therefore, it is considered that PBNPs can be a potential antioxidation-protective discography contrast agent.

CB2R Attenuates Intervertebral Disc Degeneration by Delaying Nucleus Pulposus Cell Senescence through AMPK/GSK3β Pathway

Nucleus pulposus (NP) cell (NPC) senescence is one of the main causes of intervertebral disc degeneration (IVDD). However, the underlying mechanism of NPC senescence is still unclear. The cannabinoid type 2 receptor (CB2R) is a member of the cannabinoid system and plays an important role in antioxidative stress, anti-inflammatory and antisenescence activities. In this study, we used a hydrogen peroxide (H₂O₂)-induced NPC senescence model and a rat acupuncture IVDD model to explore the role of CB2R in IVDD in vitro and in vivo. First, we confirmed that the expression of p16INK4a in the NP tissues of IVDD patients and rat acupuncture IVDD models obviously increased accompanied by a decrease in CB2R expression. Subsequently, we found that activation of CB2R significantly reduced the number of SA-β-gal positive cells and suppressed the expression of p16INK4a and senescence-related secretory phenotypes [SASP, including matrix metalloproteinase 9 and 13 (MMP9, MMP13) and high mobility group protein b1 (HMGB1)]. In addition, activation of CB2R promoted the expression of collagen type II (Col-2) and SRY-Box transcription factor 9 (SOX9), inhibit the expression of collagen type X (Col-X), and restore the balance of extracellular matrix (ECM) metabolism. In addition, the AMPK/GSK3β pathway was shown to play an important role in CB2R regulation of NPC senescence. Inhibition of AMPK expression reversed the effect of JWH015 (a CB2R agonist). Finally, we further demonstrated that in the rat IVDD model, the AMPK/GSK3β pathway was involved in the regulation of CB2R on NPC senescence. In conclusion, our experimental results prove that CB2R plays an important role in NPC senescence. Activation of CB2R can delay NPC senescence, restore the balance of ECM metabolism, and attenuate IVDD.

1,25(OH)2D3 Mitigates Oxidative Stress-Induced Damage to Nucleus Pulposus-Derived Mesenchymal Stem Cells through PI3K/Akt Pathway

Intervertebral disc degeneration (IVDD) is one of the main causes of low back pain. The local environment of the degenerated intervertebral disc (IVD) increases oxidative stress and apoptosis of endogenous nucleus pulposus-derived mesenchymal stem cells (NPMSCs) and weakens its ability of endogenous repair ability in degenerated IVDs. A suitable concentration of 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) has been certified to reduce oxidative stress and cell apoptosis. The current study investigated the protective effect and potential mechanism of 1,25(OH)₂D₃ against oxidative stress-induced damage to NPMSCs. The present results showed that 1,25(OH)₂D₃ showed a significant protective effect on NPMSCs at a concentration of 10⁻¹⁰ M for 24 h. Protective effects of 1,25(OH)₂D₃ were also exhibited against H₂O₂-induced NPMSC senescence, mitochondrial dysfunction, and reduced mitochondrial membrane potential. The Annexin V/PI apoptosis detection assay, TUNEL assay, immunofluorescence, western blot, and real-time quantitative polymerase chain reaction assay showed that pretreatment with 1,25(OH)₂D₃ could alleviate H₂O₂-induced NPMSC apoptosis, including the apoptosis rate and the expression of proapoptotic-related (Caspase-3 and Bax) and antiapoptotic-related (Bcl-2) proteins. The intracellular expression of p-Akt increased after pretreatment with 1,25(OH)₂D₃. However, these protective effects of 1,25(OH)₂D₃ were significantly decreased after the PI3K/Akt pathway was inhibited by the LY294002 treatment. In vivo, X-ray, MRI, and histological analyses showed that 1,25(OH)₂D₃ treatment relieved the degree of IVDD in Sprague–Dawley rat disc puncture models. In summary, 1,25(OH)₂D₃ efficiently attenuated oxidative stress-induced NPMSC apoptosis and mitochondrial dysfunction via PI3K/Akt pathway and is a promising candidate treatment for the repair of IVDD.

Extracellular Vesicles as an Emerging Treatment Option for Intervertebral Disc Degeneration: Therapeutic Potential, Translational Pathways, and Regulatory Considerations

Emergent approaches in regenerative medicine look toward the use of extracellular vesicles (EVs) as a next-generation treatment strategy for intervertebral disc (IVD) degeneration (IVDD) because of their ability to attenuate chronic inflammation, reduce apoptosis, and stimulate proliferation in a number of tissue systems. Yet, there are no Food and Drug Administration (FDA)-approved EV therapeutics in the market with an indication for IVDD, which motivates this article to review the current state of the field and provide an IVD-specific framework to assess its efficacy. In this systematic review, 29 preclinical studies that investigate EVs in relation to the IVD are identified, and additionally, the regulatory approval process is reviewed in an effort to accelerate emerging EV-based therapeutics toward FDA submission and timeline-to-market. The majority of studies focus on nucleus pulposus responses to EV treatment, where the main findings show that stem cell-derived EVs can decelerate the progression of IVDD on the molecular, cellular, and organ level. The findings also highlight the importance of the EV parent cell's pathophysiological and differentiation state, which affects downstream treatment responses and therapeutic outcomes. This systematic review substantiates the use of EVs as a promising cell-free strategy to treat IVDD and enhance endogenous repair.

Naringin protects human nucleus pulposus cells against TNF-α-induced inflammation, oxidative stress, and loss of cellular homeostasis by enhancing autophagic flux via AMPK/SIRT1 activation

Activation of the proinflammatory-associated cytokine, tumor necrosis factor-α (TNF-α), in nucleus pulposus (NP) cells is essential for the pathogenesis of intervertebral disc degeneration (IDD). Restoring autophagic flux has been shown to effectively protect against IDD and is a potential target for treatment. The goal of this study was to explore particular autophagic signalings responsible for the protective effects of naringin, a known autophagy activator, on human NP cells. The results showed that significantly increased autophagic flux was observed in NP cells treated with naringin, with pronounced decreases in the inflammatory response and oxidative stress, which rescued the disturbed cellular homeostasis induced by TNF-α activation. Autophagic flux inhibition was detectable in NP cells cotreated with 3-methyladenine (3-MA, an autophagy inhibitor), partially offsetting naringin-induced beneficial effects. Naringin promoted the expressions of autophagy-associated markers via SIRT1 (silent information regulator-1) activation by AMPK (AMP-activated protein kinase) phosphorylation. Either AMPK inhibition by BML-275 or SIRT1 silencing partially counteracted naringin-induced autophagic flux enhancement. These findings indicate that naringin boosts autophagic flux through SIRT1 upregulation via AMPK activation, thus protecting NP cells against inflammatory response, oxidative stress, and impaired cellular homeostasis. Naringin can be a promising inducer of restoration autophagic flux restoration for IDD.

Ultrasound Protects Human Chondrocytes from Biochemical and Ultrastructural Changes Induced by Oxidative Stress

The aim of the study was to assess the effects of therapeutic ultrasound (US) on oxidative stress (OS)-induced changes in cultured human chondrocytes (HCH). For this, monolayer HCH were randomized in three groups: a control group (CG), a group exposed to OS (OS group), and a group exposed to US and OS (US-OS group). US exposure of the chondrocytes was performed prior to OS induction by hydrogen peroxide. Transmission electron microscopy (TEM) was used to assess the chondrocytes ultrastructure. OS and inflammatory markers were recorded. Malondialdehyde (MDA) and tumor necrosis factor (TNF)-α were significantly higher (p < 0.05) in the OS group than in CG. In the US-OS group MDA and TNF-α were significantly lower (p < 0.05) than in the OS group. Finally, in the US-OS group MDA and TNF-α were lower than in CG, but without statistical significance. TEM showed normal chondrocytes in CG. In the OS group TEM showed necrotic chondrocytes and chondrocytes with a high degree of vacuolation and cell organelles damages. In the US-OS group the chondrocytes ultrastructure was well preserved, and autophagosomes were generated. In conclusion, US could protect chondrocytes from biochemical (lipid peroxidation, inflammatory markers synthesis) and ultrastructural changes induced by OS and could stimulate autophagosomes development.

Naringin Inhibits Apoptosis Induced by Cyclic Stretch in Rat Annular Cells and Partially Attenuates Disc Degeneration by Inhibiting the ROS/NF-κB Pathway

Oxidative stress and apoptosis play important roles in the pathogenesis of various degenerative diseases. Previous studies have shown that naringin can exert therapeutic effects in multiple degenerative diseases by resisting oxidative stress and inhibiting apoptosis. Although naringin is effective in treating degenerative disc disease, the underlying mechanism remains unclear. This study is aimed at investigating the effects of naringin on oxidative stress, apoptosis, and intervertebral disc degeneration (IVDD) induced by cyclic stretch and the underlying mechanisms in vitro and in vivo. Abnormal cyclic stretch was applied to rat annulus fibrosus cells, which were then treated with naringin, to observe the effects of naringin on apoptosis, oxidative stress, mitochondrial function, and the nuclear factor- (NF-) κB signaling pathway. Subsequently, a rat model of IVDD induced by dynamic and static imbalance was established to evaluate the effects of naringin on the degree of degeneration (using imaging and histology), apoptosis, and oxidative stress in the serum and the intervertebral disc. Naringin inhibited the cyclic stretch-induced apoptosis of annulus fibrosus cells, reduced oxidative stress, improved mitochondrial function, enhanced the antioxidant capacity, and suppressed the activation of the NF-κB signaling pathway. Additionally, it reduced the degree of IVDD (evaluated using magnetic resonance imaging) and the level of oxidative stress and inhibited apoptosis and p-P65 expression in the intervertebral discs of rats. Thus, naringin can inhibit cyclic stretch-induced apoptosis and delay IVDD, and the underlying mechanism may be related to the inhibition of oxidative stress and activation of the NF-κB signaling pathway. Naringin may be an effective drug for treating degenerative disc disease.

IGF Signaling in Intervertebral Disc Health and Disease

Low back pain (LBP) is a common musculoskeletal symptom, which brings a lot of pain and economic loss to patients. One of the most common causes of LBP is intervertebral disc degeneration (IVDD). However, pathogenesis is still debated, and therapeutic options are limited. Insulin-like growth factor (IGF) signaling pathways play an important role in regulating different cell processes, including proliferation, differentiation, migration, or cell death, which are critical to the homeostasis of tissues and organs. The IGF signaling is crucial in the occurrence and progression of IVDD. The activation of IGF signaling retards IVDD by increasing cell proliferation, promoting extracellular matrix (ECM) synthesis, inhibiting ECM decomposition, and preventing apoptosis and senescence of disc cells. However, abnormal activation of IGF signaling may promote the process of IVDD. IGF signaling is currently considered to have a promising treatment prospect for IVDD. An in-depth understanding of the role of IGF signaling in IVDD may help find a novel approach for IVDD treatment.

Mesenchymal Stem Cell-Derived Extracellular Vesicles: Immunomodulatory Effects and Potential Applications in Intervertebral Disc Degeneration

Intervertebral disc (IVD) degenerative disease is a common health problem worldwide. Administration of mesenchymal stem cells (MSCs) in intervertebral disc degeneration (IVDD) has been widely explored in recent years. However, transplantation of MSCs is restricted by several factors. Currently, paracrine signaling is one of the main mechanisms by which MSCs play a therapeutic role in disc regeneration. Extracellular vehicles (EVs) are the main paracrine products of MSCs. They show great potential as an effective alternative to MSCs and play immunomodulation roles such as anti-inflammatory effects, antioxidative stress, antiapoptosis, and antiextracellular matrix (ECM) degradation during treatment of IVDD. This review focuses on the immunomodulatory effect of MSC EVs and their potential applications.

Rebalance of the Polyamine Metabolism Suppresses Oxidative Stress and Delays Senescence in Nucleus Pulposus Cells

Intervertebral disk degeneration (IDD) is a major cause of low back pain that becomes a prevalent age-related disease. However, the pathophysiological processes behind IDD are rarely known. Here, we used bioinformatics analysis based on the microarray datasets (GSE34095) to identify the differentially expressed genes (DEGs) as biomarkers and therapeutic targets in degenerated discs. From the previous studies, oxidative stress has been notified as a positive inducement of IDD, which causes DNA damage and accelerates cell senescence. Polyamine oxidase (PAOX), a member of the observed 1057 DEGs, is involved in polyamine metabolism and influences the oxidative balance in cells. However, it is uncertain if the IDD is implicated in the dysregulation of PAOX and polyamine metabolism. This study firstly verified the PAOX upregulation in human degenerated disc samples and applied an IL-1β-induced nucleus pulposus (NP) cell degeneration model to demonstrate that spermidine supplementation balanced polyamine metabolism and delayed NP cell senescence. Moreover, we confirmed that spermidine/N-acetylcysteine supplementation or Cdkn2a gene deletion stabilized the polyamine metabolism, suppressed oxidative stress, and therefore delayed the progress of IDD in older mice. Collectively, our study highlights the role of polyamine metabolism in IDD and foresees spermidine would be the advanced therapeutical drug for IDD.

Apigenin Alleviates Intervertebral Disc Degeneration via Restoring Autophagy Flux in Nucleus Pulposus Cells

Oxidative stress–induced apoptosis and senescence of nucleus pulposus (NP) cells play a crucial role in the progression of intervertebral disc degeneration (IVDD). Accumulation of studies has shown that activated autophagy and enhanced autophagic flux can alleviate IVDD. In this study, we explored the effects of apigenin on IVDD in vitro and in vivo. Apigenin was found to inhibit tert-butyl hydroperoxide (TBHP)–induced apoptosis, senescence, and ECM degradation in NP cells. In addition, apigenin treatment can restore the autophagic flux blockage caused by TBHP. Mechanistically, we found that TBHP may induce autophagosome and lysosome fusion interruption and lysosomal dysfunction, while apigenin alleviates these phenomena by promoting the nuclear translocation of TFEB via the AMPK/mTOR signaling pathway. Furthermore, apigenin also exerts a protective effect against the progression of IVDD in the puncture-induced rat model. Taken together, these findings indicate that apigenin protects NP cells against TBHP-induced apoptosis, senescence, and ECM degradation via restoration of autophagic flux in vitro, and it also ameliorates IVDD progression in rats in vivo, demonstrating its potential for serving as an effective therapeutic agent for IVDD.

Mechanism of Action of Mesenchymal Stem Cell-Derived Exosomes in the Intervertebral Disc Degeneration Treatment and Bone Repair and Regeneration

Exosomes are extracellular vesicles formed by various donor cells that regulate gene expression and cellular function in recipient cells. Exosomes derived from mesenchymal stem cells (MSC-Exos) perform the regulatory function of stem cells by transporting proteins, nucleic acids, and lipids. Intervertebral disc degeneration (IDD) is one of the main causes of low back pain, and it is characterized by a decreased number of nucleus pulposus cells, extracellular matrix decomposition, aging of the annulus fibrosus, and cartilage endplate calcification. Besides, nutrient transport and structural repair of intervertebral discs depend on bone and cartilage and are closely related to the state of the bone. Trauma, disease and aging can all cause bone injury. However, there is a lack of effective drugs against IDD and bone injury. Recent MSC-Exos fine tuning has led to significant progress in the IDD treatment and bone repair and regeneration. In this review, we looked at the uniqueness of MSC-Exos, and the potential treatment mechanisms of MSC-Exos with respect to IDD, bone defects and injuries.

Extracellular Vesicles Derived From Stem Cells in Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) is the leading cause of low back pain related to degradation of cartilaginous tissues, mainly resulting from oxidative stress, cell apoptosis, and extracellular matrix degradation. Extracellular vesicles (EVs) exist in all bodily fluids and can be produced by all types of cells. Stem cell-derived EVs (SC-EVs), which are the main paracrine components of stem cells, have gained significant attention in the field of regenerative medicine. Over the past years, accumulating evidence indicates the therapeutic and diagnostic potentials of EVs in IVDD. The main mechanisms involve the induction of regenerative phenotypes, apoptosis alleviation, and immune modulation. In addition, the efficiency of SC-EVs can be enhanced by choosing appropriate donor cells and cell phenotypes, optimizing cell culture conditions, or engineering EVs to deliver drugs and targeting molecules. Given the importance and novelty of SC-EVs, we give an overview of SC-EVs and discuss the roles of SC-EVs in IVDD.

Bardoxolone Methyl Ameliorates Compression-Induced Oxidative Stress Damage of Nucleus Pulposus Cells and Intervertebral Disc Degeneration Ex Vivo

Intervertebral disc degeneration (IDD) is the main cause of low back pain, and little is known about its molecular and pathological mechanisms. According to reports, excessive compression is a high-risk factor for IDD; compressive stress can induce oxidative stress in nucleus pulposus (NP) cells during IDD progression that, in turn, promotes cell apoptosis and extracellular matrix (ECM) degradation. Currently, NP tissue engineering is considered a potential method for IDD treatment. However, after transplantation, NP cells may experience oxidative stress and induce apoptosis and ECM degradation due to compressive stress. Therefore, the development of strategies to protect NP cells under excessive compressive stress, including pretreatment of NP cells with antioxidants, has important clinical significance. Among the various antioxidants, bardoxolone methyl (BARD) is used to protect NP cells from damage caused by compressive stress. Our results showed that BARD can protect the viability of NP cells under compression. BARD inhibits compression-induced oxidative stress in NP cells by reducing compression-induced overproduction of reactive oxygen species (ROS) and malondialdehyde. Thus, BARD has a protective effect on the compression-induced apoptosis of NP cells. This is also supported by changes in the expression levels of proteins related to the mitochondrial apoptosis pathway. In addition, BARD can inhibit ECM catabolism and promote ECM anabolism in NP cells. Finally, the experimental results of the mechanism show that the activation of the Nrf2 signaling pathway participates in the protection induced by BARD in compressed NP cells. Therefore, to improve the viability and biological functions of NP cells under compression, BARD should be used during transplantation.

Mesenchymal Stem Cell-Derived Exosomes as a Novel Strategy for the Treatment of Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) has been reported to be the most prevalent contributor to low back pain, posing a significant strain on the healthcare systems on a global scale. Currently, there are no approved therapies available for the prevention of the progressive degeneration of intervertebral disc (IVD); however, emerging regenerative strategies that aim to restore the normal structure of the disc have been fundamentally promising. In the last decade, mesenchymal stem cells (MSCs) have received a significant deal of interest for the treatment of IVDD due to their differentiation potential, immunoregulatory capabilities, and capability to be cultured and regulated in a favorable environment. Recent investigations show that the pleiotropic impacts of MSCs are regulated by the production of soluble paracrine factors. Exosomes play an important role in regulating such effects. In this review, we have summarized the current treatments for disc degenerative diseases and their limitations and highlighted the therapeutic role and its underlying mechanism of MSC-derived exosomes in IVDD, as well as the possible future developments for exosomes.

G-Protein Coupled Receptor 35 Induces Intervertebral Disc Degeneration by Mediating the Influx of Calcium Ions and Upregulating Reactive Oxygen Species

Intervertebral disc degeneration (IDD) is a chronic disease affecting millions of patients; however, its specific etiology is unknown. G protein-coupled receptors (GPRs) are a superfamily of integral membrane receptors in cells, and the receptors respond to a diverse range of stimuli and participate in multiple cellular activities. Here, using RNA-sequencing (RNA-seq) methods and immunohistochemistry, we revealed that G protein-coupled receptor 35 (GPR35) may have a relationship with IDD. Then, we demonstrated that the deletion of GPR35 in nucleus pulposus cells (NPCs) with siRNA or in Gpr35^−/− mice significantly alleviated IDD caused by senescence or mechanical stress, further validating the pathological role of GPR35 in IDD. In addition, GPR35 induced the influx of Ca²⁺ and upregulation of reactive oxygen species (ROS) under mechanical stress in NPCs, which we believe to be the mechanism of GPR35-induced IDD. Finally, GPR35 caused upregulation of ROS in NPCs under mechanical stress, while excessive ROS stimulated the NPCs to express more GPR35 with a significant dose or time response. The u-regulated GPR35 could sense mechanical stress to produce more ROS and perpetuate this harmful cycle. In summary, our study shows that GPR35 plays a critical role in mediating IDD via mediating the influx of calcium ions and upregulating ROS, which implies a strong potential advantage of GPR35 as a prevention and treatment target in IDD.

The Role of Oxidative Stress in Intervertebral Disc Degeneration

Intervertebral disc degeneration is a very common type of degenerative disease causing severe socioeconomic impact, as well as a major cause of discogenic low back pain and herniated discs, placing a heavy burden on patients and the clinicians who treat them. IDD is known to be associating with a complex process involving in extracellular matrix and cellular damage, and in recent years, there is increasing evidence that oxidative stress is an important activation mechanism of IDD and that reactive oxygen and reactive nitrogen species regulate matrix metabolism, proinflammatory phenotype, autophagy and senescence in intervertebral disc cells, apoptosis, autophagy, and senescence. Despite the tremendous efforts of researchers within the field of IDD pathogenesis, the proven strategies to prevent and treat this disease are still very limited. Up to now, several antioxidants have been proved to be effective for alleviating IDD. In this article, we discussed that oxidative stress accelerates disc degeneration by influencing aging, inflammation, autophagy, and DNA methylation, and summarize some antioxidant therapeutic measures for IDD, indicating that antioxidant therapy for disc degeneration holds excellent promise.

The protective effects of dezocine on interleukin-1β-induced inflammation, oxidative stress and apoptosis of human nucleus pulposus cells and the possible mechanisms

Intervertebral disc degeneration (IDD) is a natural problem linked to the inflammation. We aimed to investigate the role of dezocine (DEZ) in the development of IDD. Human nucleus pulposus cells (HNPCs) induced by interleukin (IL)-1β was used as a cellular model of IDD. After treatment with DEZ, HNPCs viability was evaluated with a CCK-8 assay. Then, the levels of inflammatory factors, including IL-6 and tumor necrosis factor-α (TNF-α), and oxidative stress-related markers, including reactive oxygen species (ROS), malondialdehyde (MDA) and reduced glutathione (GSH), were tested by RT-qPCR or kits. TUNEL staining was employed to detect cell apoptosis and Western blot was used to determine the expression of proteins related to inflammation, oxidative stress, apoptosis, endoplasmic reticulum stress (ERS) and MAPK signaling. Afterward, PMA, a MAPK signaling pathway agonist, was adopted for exploring the regulatory effects of DEZ on MAPK pathway. Results indicated that DEZ enhanced cell viability of HNPCs after IL-1β exposure. DEZ alleviated the inflammation and oxidative stress, evidenced by decreased levels of IL-6, TNF-α, ROS, MDA, p-NF-κB p65, NF-κB p65 in nucleus, cox-2 and increased levels of NF-κB p65 in cytoplasm, GSH, SOD1 and SOD2. Moreover, DEZ notably inhibited IL-1β-induced apoptosis of HNPCs. Furthermore, DEZ suppressed the levels of ERS-related proteins. The levels of related proteins in MAPK signaling including p-P38 and p-ERK1/2 were remarkably reduced after DEZ administration. By contrast, PMA crippled the impacts of DEZ on inflammation, oxidative stress and apoptosis of HNPCs induced by IL-1β. Collectively, DEZ ameliorates IL-1β-induced HNPCs injury via inhibiting MAPK signaling.

Increased Expression of Prolyl Endopeptidase Induced by Oxidative Stress in Nucleus Pulposus Cells Aggravates Intervertebral Disc Degeneration

A healthy microenvironment of the intervertebral disc tissue is characterized by hypoxia owing to its sparse vascular distribution. Oxidative stress plays a pivotal role in the pathological development of intervertebral disc degeneration (IVDD). We found that the expression of prolyl endopeptidase (PREP) increased in degenerative nucleus pulposus (NP) tissues. The purpose of this study was to determine whether PREP is involved in oxidative-stress-induced IVDD. Tertbutyl hydroperoxide can inhibit the expression of PREP by activating the PI3K/AKT signaling pathway at low concentrations in NP cells. Knockdown of PREP protected NP cells from apoptosis induced by oxidative stress, whereas overexpression of PREP exacerbated the apoptosis of NP cells. We also investigated the connection between the PI3K/AKT signaling pathway and PREP and found that the activation of the PI3K/AKT signaling pathway downregulated the expression of PREP by inhibiting p53. As a crucial transcription factor, p53 binds to the PREP promoter region and promotes its transcription. Overexpression of PREP also impairs protein secretion in the extracellular matrix of NP cells. Furthermore, the in vivo knockout of PREP could attenuate puncture-induced IVDD. These findings suggested that the downregulation of PREP might maintain the viability of NP cells and attenuate IVDD under oxidative stress.

The Potential Use of Mesenchymal Stem Cells and Their Derived Exosomes for Orthopedic Diseases Treatment

Musculoskeletal disorders (MSDs) are conditions that can affect muscles, bones, and joints. These disorders are very painful and severely limit patients' mobility and are more common in the elderly. MSCs are multipotent stem cells isolated from embryonic (such as the umbilical cord) and mature sources (such as adipose tissue and bone marrow). These cells can differentiate into various cells such as osteoblasts, adipocytes, chondrocytes, NP-like cells, Etc. Due to MSC characteristics such as immunomodulatory properties, ability to migrate to the site of injury, recruitment of cells involved in repair, production of growth factors, and large amount production of extracellular vesicles, these cells have been used in many regenerative-related medicine studies. Also, MSCs produce different types of EVs, such as exosomes, to the extracellular environment. Exosomes reflect MSCs' characteristics and do not have cell therapy-associated problems because they are cell-free. These vesicles carry proteins, nucleic acids, and lipids to the host cell and change their function. This review focuses on MSCs and MSCs exosomes' role in repairing dense connective tissues such as tendons, cartilage, invertebrate disc, bone fracture, and osteoporosis treatment.

Endoplasmic reticulum stress associates with the development of intervertebral disc degeneration

Endoplasmic reticulum (ER) is an important player in various intracellular signaling pathways that regulate cellular functions in many diseases. Intervertebral disc degeneration (IDD), an age-related degenerative disease, is one of the main clinical causes of low back pain. Although the pathological development of IDD is far from being fully elucidated, many studies have been shown that ER stress (ERS) is involved in IDD development and regulates various processes, such as inflammation, cellular senescence and apoptosis, excessive mechanical loading, metabolic disturbances, oxidative stress, calcium homeostasis imbalance, and extracellular matrix (ECM) dysregulation. This review summarizes the formation of ERS and the potential link between ERS and IDD development. ERS can be a promising new therapeutic target for the clinical management of IDD.

AMPK as a Potential Therapeutic Target for Intervertebral Disc Degeneration

As the principal reason for low back pain, intervertebral disc degeneration (IDD) affects the health of people around the world regardless of race or region. Degenerative discs display a series of characteristic pathological changes, including cell apoptosis, senescence, remodeling of extracellular matrix, oxidative stress and inflammatory local microenvironment. As a serine/threonine-protein kinase in eukaryocytes, AMP-activated protein kinase (AMPK) is involved in various cellular processes through the modulation of cell metabolism and energy balance. Recent studies have shown the abnormal activity of AMPK in degenerative disc cells. Besides, AMPK regulates multiple crucial biological behaviors in IDD. In this review, we summarize the pathophysiologic changes of IDD and activation process of AMPK. We also attempt to generalize the role of AMPK in the pathogenesis of IDD. Moreover, therapies targeting AMPK in alleviating IDD are analyzed, for better insight into the potential of AMPK as a therapeutic target.

LncRNA MIR155HG functions as a ceRNA of miR-223-3p to promote cell pyroptosis in human degenerative NP cells

Nucleus pulposus (NP) cell pyroptosis plays a critical role in the pathogenesis of intervertebral disk degeneration (IDD). MIR155 host gene (MIR155HG) is a long non-coding RNA with pro-inflammatory activity. However, very little is known about its role in NP cell pyroptosis. This study aimed to observe the impact of MIR155HG on cell pyroptosis and to explore the underlying mechanism in human degenerative NP cells. Our results demonstrated that MIR155HG expression was significantly increased in human degenerative NP tissue samples and showed a positive correlation with Pfirrmann score. Overexpression of MIR155HG through a lentiviral vector decreased miR-223-3p levels, up-regulated NLRP3 expression and induced cell pyroptosis in human degenerative NP cells. A ceRNA action mode was identified among MIR155HG, miR-223-3p, and NLRP3. The stimulatory effect of MIR155HG on human degenerative NP cell pyroptosis was significantly reversed by pretreatment with miR-223-3p mimic or NLRP3 siRNA. In summary, these data suggest that MIR155HG sponges miR-223-3p to promote NLRP3 expression, leading to induction of cell pyroptosis in human degenerative NP cells. Targeting MIR155HG could be a novel and promising strategy to slow down the progression of IDD.

Reducing Inflammation and Vascular Invasion in Intervertebral Disc Degeneration via Cystathionine-γ-Lyase Inhibitory Effect on E-Selectin

The incidence of degenerative spinal diseases, such as cervical spondylosis and thoracic and lumbar disc herniation, is increasing. These health problems have adversely affected human life and work. Surgical intervention is effective when intervertebral disc degeneration (IDD) causes nerve compression and/or severely limits daily activity. Early IDD patients generally do not require surgery. However, there is no effective method of impeding IDD progression. Thus, novel approaches to alleviating IDD deterioration are urgently required. Cystathionine-γ-lyase (CSE) and E-selectin (CD62E) are vital factors regulating vascular function and inflammation. However, their effects on IDD and vascular invasion in intervertebral discs (IVDs) are pending further exploration. Here, bioinformatics and human nucleus pulposus (NP) tissues analyses revealed that CSE was significantly downregulated and CD62E was upregulated in the NP tissues of IDD patients. We demonstrated that CSE overexpression, CD62E downregulation, and NF-κB (P65) inhibition mitigate inflammation and recover metabolic function in NP cells. Similarly, CSE attenuated vascular invasion induced by inflammatory irritation. Using a rat IDD model, we showed that CSE improved degeneration, inflammation, and microvascular invasion in NP tissue, whereas CD62E had the opposite effect. Taken together, our results indicated that the CSE/CD62E pathway could effectively improve the inflammatory environment and vascular invasion in IVD. Hence, the findings of this study propose a promising and valuable strategy for the treatment of patients with early IDD as well as postoperative adjuvant therapy in patients with severe IDD.

Anti-Apoptosis and Autophagy Effects of Melatonin Protect Rat Chondrocytes against Oxidative Stress via Regulation of AMPK/Foxo3 Pathways

OBJECTIVE

Emerging evidence has indicated that excessive reactive oxygen species (ROS) have detrimental effects on osteoarthritis (OA). This study aimed to elucidate the effects of melatonin (MT), an antioxidant indolamine secreted from the pineal gland, on chondrocyte senescence and cartilage degeneration, thereby clarifying the underlying mechanisms of ROS-induced OA pathogenesis.

DESIGN

Hydrogen peroxide (H₂O₂) was used to induce oxidative stress in rat chondrocytes. ROS levels were evaluated using cytometry and immunofluorescence. Cell viability was detected using the Cell Counting Kit-8 (CCK-8) assay. Western blotting and qPCR (Quantiative Real-Time Polymerase Chain Reaction) were used to examine apoptosis and autophagy. For in vivo experiments, male Sprague-Dawley rats were randomly divided into a sham-operated group, DMM (destabilization of the medial meniscus) surgery group, and surgery groups that received melatonin. Knee joints were collected and stained for histological analysis.

RESULTS

The data demonstrated that melatonin treatment significantly suppressed H₂O₂-induced matrix degradation and apoptosis, and maintained mitochondrial redox homeostasis. In addition, an enhancement of autophagic flux was observed through western blotting. These findings corresponded with activation of the AMPK/Foxo3 signaling pathways upon melatonin treatment. Histological staining and transmission electron microscopy (TEM) micrographs also demonstrated that melatonin alleviated cartilage ossification and chondrocyte hypertrophy in vivo.

CONCLUSIONS

Our results indicated that melatonin protected chondrocytes via mitochondrial redox homeostasis and autophagy. The effects of melatonin on senescence may apply to other age-related diseases. Thus, melatonin may have multiple potential therapeutic applications.

Injectable self-healing hydrogel with siRNA delivery property for sustained STING silencing and enhanced therapy of intervertebral disc degeneration

Inflammatory responses of nucleus pulposus (NP) can induce imbalanced anabolism and catabolism of extracellular matrix, and the cytosolic dsDNA accumulation and STING–NF–κB pathway activation found in NP inflammation are considered as fairly important cause of intervertebral disc (IVD) degeneration. Herein, we constructed a siSTING delivery hydrogel of aldehyde hyaluronic acid (HA-CHO) and poly(amidoamine) PAMAM/siRNA complex to intervene the abnormal STING signal for IVD degeneration treatment, where the formation of dynamic Schiff base bonds in the system (siSTING@HP^gel) was able to overcome the shortcomings such as low cellular uptake, short half-life, and rapid degradation of siRNA-based strategy. PAMAM not only formed complexes with siRNA to promote siRNA transfection, but also served as dynamic crosslinker to construct hydrogel, and the injectable and self-healing hydrogel efficiently and steadily silenced STING expression in NP cells. Finally, the siSTING@HP^gel significantly eased IVD inflammation and slowed IVD degeneration by prolonging STING knockdown in puncture-induced IVD degeneration rat model, revealing that STING pathway was a therapeutic target for IVD degeneration and such novel hydrogel had great potential for being applied to many other diseases for gene delivery.

•

STING-NF-κB pathway activation was identified an important cause of intervertebral disc degeneration.

•

PAMAM was employed as both linker and gene vector for siRNA delivery.

•

The injectable self-healing hydrogel could significantly ease the IVD inflammation and degeneration by prolonging STING knockdown.

•

This novel hydrogel system opened new ways of thinking and had great potential for gene delivery.

Dimethyl Fumarate Ameliorates Nucleus Pulposus Cell Dysfunction through Activating the Nrf2/HO-1 Pathway in Intervertebral Disc Degeneration

Background

Oxidative stress, inflammation, and nucleus pulposus cells (NPCs) apoptosis are involved in pathogenesis of intervertebral disc (IVD) degeneration (IVDD). Dimethyl fumarate (DMF) has been found to effectively depress oxidative stress and inflammation via the Nrf2 pathway. Hence, this project was designed to explore the underlying mechanisms of how DMF protects NPCs from damage by LPS challenge.

Methods and Results

CCK8 assay and flow cytometry of apoptosis indicated that DMF treatment attenuated LPS-induced NPC damage. Western blot analysis demonstrated that DMF enhanced the expressions of nuclear factor-erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) in LPS-challenged NPCs. DMF treatment significantly decreased the accumulation of ROS, downregulated inflammatory cytokines (p-NF-κB, IL-1β, and TNF-α), and ER stress-associated apoptosis proteins (Bip, calpain-1, caspase-12, caspase-3, and Bax) in LPS-challenged NPCs. The level of antiapoptotic protein Bcl-2 was promoted by DMF treatment in LPS-challenged NPCs. Glutathione (GSH) assay showed that DMF treatment improved reduced to oxidized glutathione ratio in LPS-challenged NPCs. Furthermore, the results of western blot analysis indicated that in LPS-challenged NPCs, DMF treatment ameliorated the elevated levels of matrix degradation enzymes (MMP-13, aggrecanase 1) and type I collagen and the reduced levels of matrix composition (type II collagen and ACAN). However, Nrf2 knockdown abolished these protective effects of DMF.

Conclusion

Our data suggested that treatment with DMF mitigated LPS-induced oxidative stress, inflammation, and ER stress-associated apoptosis in NPCs via the Nrf2/HO-1 signaling pathway, thus reliving LPS-induced dysfunction of NPCs, which offered a novel potential pharmacological treatment strategy for IVDD.

Exosomes Derived from Bone Mesenchymal Stem Cells Alleviate Compression-Induced Nucleus Pulposus Cell Apoptosis by Inhibiting Oxidative Stress

Oxidative stress is relevant in compression-induced nucleus pulposus (NP) cell apoptosis and intervertebral disc (IVD) degeneration. Exosomes derived from bone mesenchymal stem cells (BMSCs-Exos) are key secretory products of MSCs, with important roles in tissue regeneration. This research is aimed at studying the protective impact of BMSCs-Exos on NP cell apoptosis caused by compression and investigating the underlying mechanisms. Our results indicated that we isolated BMSCs successfully. Exosomes were isolated from the BMSCs and found to alleviate the inhibitory effect that compression has on proliferation and viability in NP cells, decreasing the toxic effects of compression-induced NP cells. AnnexinV/PI double staining and TUNEL assays indicated that the BMSCs-Exos reduced compression-induced apoptosis. In addition, our research found that BMSCs-Exos suppressed compression-mediated NP oxidative stress by detecting the ROS and malondialdehyde level. Furthermore, BMSCs-Exos increased the mitochondrial membrane potential and alleviated compression-induced mitochondrial damage. These results indicate that BMSCs-Exos alleviate compression-mediated NP apoptosis by suppressing oxidative stress, which may provide a promising cell-free therapy for treating IVD degeneration.

Antioxidant Effects of Resveratrol in Intervertebral Disk

Intervertebral disk (IVD) degeneration (IVDD) can cause various spinal degenerative diseases. Cumulative evidence has indicated that IVDD can result from inflammation, apoptosis, autophagy, biomechanical changes and other factors. Currently, lack of conservative treatment for degenerative spinal diseases leads to an urgent demand for clinically applicable medication to ameliorate the progression of IVDD. Resveratrol (3,5,4'-trihydroxy-trans-stilbene), a polyphenol compound extracted from red wine or grapes, has shown protective effects on IVD, alleviating the progression of IVDD. Resveratrol has been demonstrated as a scavenger of free radicals both in vivo and in vitro. The antioxidant effects of resveratrol are likely attributed to its regulation on mitochondrial dysfunction or the elimination of reactive oxygen species. This review will summarize the mechanisms of the reactive oxygen species production and elaborate the mechanisms of resveratrol in retarding IVDD progression, providing a comprehensive understanding of the antioxidant effects of resveratrol in IVD.

The Dual Effect of Abnormal Serum Uric Acid on Intervertebral Disc Degeneration

An abnormal serum uric acid (SUA) level is associated with many diseases. To our knowledge, there is no research on the association between SUA and intervertebral disc degeneration (IDD). The purpose of this study was to determine the relationship between SUA and IDD. From June 2011 to July 2020, 691 patients undergoing surgery for lumbar disc herniation (LDH) were included in the LDH group, and 684 patients who underwent endoscopic surgery for knee trauma were included in the non-LDH group. We examined the baseline characteristics of all these patients and divided the SUA level into 10 groups according to the percentiles in males, females, and the total population. Subsequently, the relationship between the SUA level and IDD was further analyzed. There was no statistically significant difference in the baseline characteristics of the two groups (p > 0.05). Among the 10 groups, the LDH rate was higher at both lower and higher SUA levels. In multiple logistic regression analysis, after adjustment for age, sex, body mass index, smoking, and drinking, when the SUA level was <20% or >80%, compared with 60-80%, the odds ratio (OR) and 95% confidence interval (CI) of LDH of the total population were 1.821 (1.125-2.946) and 1.701 (1.186-2.438), respectively, and in the males, they were 1.922 (1.169-3.161) and 2.800 (1.766, 4.439), respectively. In females, when the SUA was <20%, there was a higher LDH rate (OR = 1.951, 95% CI 1.091-3.486). The present study suggests that there is a U-shaped relationship between SUA and IDD, being particularly prominent among male. Lower and higher SUA level may be risk factors for IDD.

Resveratrol Suppresses Annulus Fibrosus Cell Apoptosis through Regulating Oxidative Stress Reaction in an Inflammatory Environment

During disc degeneration, the increase of inflammatory cytokines and decrease of disc cell density are two prominent features. Enhanced inflammatory reaction contributes to disc annulus fibrosus (AF) cell apoptosis. In this study, we investigated whether resveratrol can suppress AF cell apoptosis in an inflammatory environment. Rat disc AF cells were cultured in medium with or without tumor necrosis factor-α (TNF-α). Resveratrol was added along with the culture medium supplemented with TNF-α. Caspase-3 activity, cell apoptosis ratio, expression of apoptosis-associated molecules (Bcl-2, Bax, caspase-3, cleaved PARP, and cleaved caspase-3), reactive oxygen species (ROS) content, and the total superoxide dismutase (SOD) activity were measured. Our results showed that TNF-α significantly increased caspase-3 activity and AF cell apoptosis ratio and upregulated gene/protein expression of Bax, caspase-3, cleaved caspase-3, and cleaved PARP, whereas it downregulated the expression of Bcl-2. Moreover, TNF-α significantly increased ROS content but decreased the total SOD activity. Further analysis demonstrated that resveratrol partly attenuated the effects of TNF-α on AF cell apoptosis-associated parameters, decreased ROS content, and increased the total SOD activity in the AF cells treated with TNF-α. In conclusion, resveratrol attenuates inflammatory cytokine TNF-α-induced AF cell apoptosis through regulating oxidative stress reaction in vitro. This study sheds a new light on the protective role of resveratrol in alleviating disc degeneration.

The REDD1/TXNIP Complex Accelerates Oxidative Stress-Induced Apoptosis of Nucleus Pulposus Cells through the Mitochondrial Pathway

The death of nucleus pulposus (NP) cells is an important cause of intervertebral disc (IVD) degeneration. Redox disturbance caused by dysfunctional mitochondria has been considered as a vital risk for NP cell survival. It is valuable to identify key proteins maintaining mitochondrial function in NP cells. A previous study found that regulated in development and DNA damage response 1 (REDD1) are upregulated during intervertebral disc degeneration and that REDD1 can cause NP cell apoptosis. Thus, the present study further explores the effect of REDD1 on IVD degeneration. Our results showed that REDD1 promotes NP cell apoptosis via the mitochondrial pathway. Importantly, REDD1 formed a complex with TXNIP to strengthen its own action, and the combination was consolidated under H₂O₂-induced oxidative stress. The combined inhibition of the REDD1/TXNIP complex was better than that of REDD1 or TXNIP alone in restoring cell proliferation and accelerating apoptosis. Moreover, p53 acts as the transcription factor of REDD1 to regulate the REDD1/TXNIP complex under oxidative stress. Altogether, our results demonstrated that the REDD1/TXNIP complex mediated H₂O₂-induced human NP cell apoptosis and IVD degeneration through the mitochondrial pathway. Interferences on these sites to achieve mitochondrial redox homeostasis may be a novel therapeutic strategy for oxidative stress-associated IVD degeneration.

Peptide Location Fingerprinting Reveals Tissue Region-Specific Differences in Protein Structures in an Ageing Human Organ

In ageing tissues, long-lived extracellular matrix (ECM) proteins are susceptible to the accumulation of structural damage due to diverse mechanisms including glycation, oxidation and protease cleavage. Peptide location fingerprinting (PLF) is a new mass spectrometry (MS) analysis technique capable of identifying proteins exhibiting structural differences in complex proteomes. PLF applied to published young and aged intervertebral disc (IVD) MS datasets (posterior, lateral and anterior regions of the annulus fibrosus) identified 268 proteins with age-associated structural differences. For several ECM assemblies (collagens I, II and V and aggrecan), these differences were markedly conserved between degeneration-prone (posterior and lateral) and -resistant (anterior) regions. Significant differences in peptide yields, observed within collagen I α2, collagen II α1 and collagen V α1, were located within their triple-helical regions and/or cleaved C-terminal propeptides, indicating potential accumulation of damage and impaired maintenance. Several proteins (collagen V α1, collagen II α1 and aggrecan) also exhibited tissue region (lateral)-specific differences in structure between aged and young samples, suggesting that some ageing mechanisms may act locally within tissues. This study not only reveals possible age-associated differences in ECM protein structures which are tissue-region specific, but also highlights the ability of PLF as a proteomic tool to aid in biomarker discovery.

The potential role of melatonin in retarding intervertebral disc ageing and degeneration: A systematic review

Intervertebral disc degeneration (IDD) is a common degenerative disease of the musculoskeletal system that develops with age. It is regarded as the main cause of chronic low back pain in the elderly. IDD has various causes, including ageing, mechanical overloading, and nutritional deficiency. Melatonin is a pleiotropic indole hormone secreted by the pineal gland and plays an important role in resisting various degenerative diseases. The serum levels of melatonin decline with age and are reported to be negatively correlated with the symptomatic and histopathological scores of IDD. In vivo studies have shown that exogenous administration of melatonin could maintain the structural integrity of the intervertebral disc and inhibit the development of IDD. Mechanistically, by interacting with its membrane or intracellular receptors, melatonin can promote autophagic flux, scavenge free radicals, inhibit the release of pro-inflammatory factors, and block apoptotic pathways, thereby enhancing anti-stress abilities and matrix anabolism in different types of disc cells. Therefore, melatonin supplementation may be a promising therapeutic strategy for IDD. This review aimed to summarize the latest findings regarding the therapeutic potential of melatonin in IDD.

SIRT3 mitigates intervertebral disc degeneration by delaying oxidative stress-induced senescence of nucleus pulposus cells

Senescence of nucleus pulposus (NP) cells (NPC) is a major cause of intervertebral disc degeneration (IVDD), so delay NPC senescence may be beneficial for mitigating IVDD. We studied the effect and mechanism of silent information regulator 2 homolog 3 (SIRT3) on NPC senescence in vivo and in vitro. First, we observed SIRT3 expression in normal and degenerated NPC with immunohistochemical and immunofluorescence staining. Second, using SIRT3 lentivirus transfection, reactive oxygen species probe, senescence-associated β-galactosidase staining, polymerase chain reaction, and western blot to observe the oxidative stress, senescence, and degeneration degree among groups. Subsequently, pretreatment with adenosine monophosphate-activated protein kinase (AMPK) agonists and inhibitors, observing oxidative stress, senescence, and degeneration degree among groups. Finally, the IVDD model was constructed and divided into Ctrl, Vehicle, LV-shSIRT3, and LV-SIRT3 groups. X-ray and magnetic resonance imaging scans were performed on rat's tails after 1 week; hematoxylin and eosin and safranin-O staining were used to evaluate the degree of IVDD; immunofluorescence staining was used to observe SIRT3 expression; immunohistochemical staining was used to observe oxidative stress, senescence, and degeneration degree of NP. We found that SIRT3 expression is reduced in degenerated NP tissues but increased in H2 O2 -induced NPC. Moreover, SIRT3 upregulation decreased oxidative stress, delayed senescence, and degeneration of NPC. In addition, activation of the AMPK/PGC-1α pathway can partially mitigate the NPC oxidative stress, senescence, and degeneration caused by SIRT3 knockdown. The study in vivo revealed that local SIRT3 overexpression can significantly reduce oxidative stress and ECM degradation of NPC, delay NPC senescence, thereby mitigating IVDD. In summary, SIRT3 mediated by the AMPK/PGC-1α pathway mitigates IVDD by delaying oxidative stress-induced NPC senescence.

Melatonin Inhibits Annulus Fibrosus Cell Senescence through Regulating the ROS/NF-κB Pathway in an Inflammatory Environment

Inflammation response is an important reason for disc cell senescence during disc degeneration. Recently, melatonin is suggested to protect against disc degeneration. However, the effects of melatonin on annulus fibrosus (AF) cell senescence are not fully studied. The main purpose of this study was to investigate the effects of melatonin on AF cell senescence in an inflammatory environment and the underlying mechanism. Rat disc AF cells were cultured in a medium with tumor necrosis factor-α (TNF-α). Melatonin was added along with the medium to observe its protective effects. Compared with the control AF cells, TNF-α significantly declined cell proliferation potency and telomerase activity, elevated senescence-associated β-galactosidase (SA-β-Gal) activity, upregulated protein expression of senescence markers (p16 and p53), and increased reactive oxygen species (ROS) content and activity of the NF-κB pathway. However, when the TNF-α-treated AF cells were incubated with melatonin, ROS content and activity of the NF-κB pathway were decreased, and those parameters reflecting cell senescence indicated that AF cell senescence was also partly alleviated. Together, melatonin suppresses AF cell senescence through regulating the ROS/NF-κB pathway in an inflammatory environment. This study sheds a new light that melatonin may be promising to retard inflammation-caused disc degeneration.

Lumbar spine abnormalities in patients with obstructive sleep apnoea

Previous studies suggested cervical spondylosis as a risk factor for development of obstructive sleep apnoea (OSA). We aimed to assess lumbar disc degeneration in patients with OSA and correlate the findings with symptoms and disease severity. Twenty-seven patients with OSA and 29 non-OSA controls underwent sleep studies and lumbar magnetic resonance imaging (MRI), and completed the Epworth Sleepiness Scale and the 24-item Roland-Morris Disability Questionnaire (RMDQ) questionnaires. Plasma klotho was determined with enzyme-linked immunosorbent assay. Patients with OSA had higher number of disc bulges (4.6 ± 3.7 vs. 1.7 ± 2.5, p < 0.01) and anterior spondylophytes (2.7 ± 4.2 vs. 0.8 ± 2.1, p < 0.01), increased disc degeneration (total Pfirrmann score 16.7 ± 4.7 vs. 13.2 ± 4.1, p < 0.01) and vertebral fatty degeneration (7.8 ± 4.7 vs. 3.8 ± 3.7, p < 0.01). There was no difference in the RMDQ score (0/0-3.5/ vs. 0/0-1/, p > 0.05). Markers of OSA severity, including the oxygen desaturation index and percentage of total sleep time spent with saturation < 90% as well as plasma levels of klotho were correlated with the number of disc bulges and anterior spondylophytes (all p < 0.05). OSA is associated with lumbar spondylosis. Our study highlights the importance of lumbar imaging in patients with OSA reporting lower back pain.

HIF-1α-Mediated miR-623 Regulates Apoptosis and Inflammatory Responses of Nucleus Pulposus Induced by Oxidative Stress via Targeting TXNIP

Excessive apoptosis and inflammatory responses of nucleus pulposus (NP) cells induced by oxidative stress contribute to intervertebral disc degeneration (IVDD). Though some microRNAs are associated with IVDD, the specific microRNA that can mediate apoptotic and inflammatory responses of NP cells induced by oxidative stress synchronously still needs further identification. Here, we find that microRNA-623 (miR-623) is downregulated in IVDD and its expression is regulated by hypoxia-inducible factor-1α (HIF-1α) under oxidative stress conditions. Mechanistically, HIF-1α is observed to promote miR-623 expression by directly binding to its promoter region (-1,994/-1,987 bp). Functionally, miR-623 is found to work as an intermediator in alleviating apoptosis and inflammatory responses of NP cells induced by oxidative stress via regulating thioredoxin-interacting protein (TXNIP) expression by directly targeting its 3'-untranslated region (3'-UTR). Thus, on elucidating the expression and functional mechanisms of miR-623, our study suggests that miR-623 can be a valuable therapeutic target for treating oxidative stress-induced IVDD.

Natural Products of Pharmacology and Mechanisms in Nucleus Pulposus Cells and Intervertebral Disc Degeneration

Intervertebral disc degeneration (IDD) is one of the main causes of low back pain (LBP), which severely reduces the quality of life and imposes a heavy financial burden on the families of affected individuals. Current research suggests that IDD is a complex cell-mediated process. Inflammation, oxidative stress, mitochondrial dysfunction, abnormal mechanical load, telomere shortening, DNA damage, and nutrient deprivation contribute to intervertebral disc cell senescence and changes in matrix metabolism, ultimately causing IDD. Natural products are widespread, structurally diverse, afford unique advantages, and exhibit great potential in terms of IDD treatment. In recent years, increasing numbers of natural ingredients have been shown to inhibit the degeneration of nucleus pulposus cells through various modes of action. Here, we review the pharmacological effects of natural products on nucleus pulposus cells and the mechanisms involved. An improved understanding of how natural products target signalling pathways will aid the development of anti-IDD drugs. This review focuses on potential IDD drugs.

Mitochondrial quality control in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common and early-onset pathogenesis in the human lifespan that can increase the risk of low back pain. More clarification of the molecular mechanisms associated with the onset and progression of IDD is likely to help establish novel preventive and therapeutic strategies. Recently, mitochondria have been increasingly recognized as participants in regulating glycolytic metabolism, which has historically been regarded as the main metabolic pathway in intervertebral discs due to their avascular properties. Indeed, mitochondrial structural and functional disruption has been observed in degenerated nucleus pulposus (NP) cells and intervertebral discs. Multilevel and well-orchestrated strategies, namely, mitochondrial quality control (MQC), are involved in the maintenance of mitochondrial integrity, mitochondrial proteostasis, the mitochondrial antioxidant system, mitochondrial dynamics, mitophagy, and mitochondrial biogenesis. Here, we address the key evidence and current knowledge of the role of mitochondrial function in the IDD process and consider how MQC strategies contribute to the protective and detrimental properties of mitochondria in NP cell function. The relevant potential therapeutic treatments targeting MQC for IDD intervention are also summarized. Further clarification of the functional and synergistic mechanisms among MQC mechanisms may provide useful clues for use in developing novel IDD treatments.

Deficiency of MIF Accentuates Overloaded Compression-Induced Nucleus Pulposus Cell Oxidative Damage via Depressing Mitophagy

Established studies proved that mechanical compression loading had multiple effects on the biological behavior of the intervertebral disc (IVD). However, the regulating mechanism involved in this process remains unclear. The current study is aimed at exploring the potential bioregulators and signaling pathways involved in the compression-associated biological changes of nucleus pulposus (NP) cells. Tandem mass tag- (TMT-) based quantitative proteomics was exerted to analyze the differentially expressed proteins (DEPs) and signal pathways among the different groups of NP cells cultured under noncompression, low-compression (LC), and high-compression (HC) loading. Eight potential protective bioregulators for the NP cell survival under different compression loading were predicted by the proteomics, among which macrophage migration inhibitory factor (MIF) and oxidative stress-related pathways were selected for further evaluation, due to its similar function in regulating the fate of the cartilage endplate- (CEP-) derived cells. We found that deficiency of MIF accentuates the accumulation of ROS, mitochondrial dysfunction, and senescence of NP cells under overloaded mechanical compression. The potential molecular mechanism involved in this process is related to the mitophagy regulating role of MIF. Our findings provide a better understanding of the regulatory role of mechanical compression on the cellular fate commitment and matrix metabolism of NP, and the potential strategies for treating disc degenerative diseases via using MIF-regulating agents.

PBN protects NP cells from AAPH-induced degenerative changes by inhibiting the ERK1/2 pathway

Aim: Intervertebral disc (IVD) degeneration (IDD) is one of the main causes for spinal degenerative diseases, such as disk herniation, spinal canal stenosis, and spinal deformities. Growing evidence has highlighted the contribution of oxidative stress in pathogenesis of IDD, and antioxidant treatment is thus considered to be a promising therapeutic strategy for IDD. The aim of this study was to investigate whether N-tert-butyl-α-phenylnitrone (PBN), a free radical scavenger, could attenuate the pathological changes of IDD by alleviating oxidative stress.Materials and Methods: Nucleus pulposus (NP) cells were isolated from rabbit lumbar disks. MTT assay, real-time PCR and western blotting were employed to evaluate the effects of PBN on oxidative damages induced by 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) in NP cells.Results: AAPH induced oxidative stress and the subsequent degenerative changes in NP cells via the ERK/MAPK pathway. On the contrary, the oxidative stress induced by AAPH was significantly ameliorated by PBN. Moreover, PBN also attenuated AAPH-induced expression of matrix degradation proteases and apoptosis. PBN suppresses AAPH-induced activation of ERK/MAPK pathway, which may be the underlying mechanism for the protective effects of PBN.Conclusions: Our study for the first time identified a novel role and mechanism for PBN in protecting the IVD against oxidative stress, matrix catabolism and apoptosis, which may have implications for its further application in combating IVD degenerative diseases.Abbreviations: AAPH: 2,2'-azobis(2-methylpropanimidamidine) dihydrochloride; ADAMTS: a disintegrin and metalloproteinase with thrombospondin motifs; AF: annulus fibrosus; CEP: cartilage endplate; DCF: 2'7'-dichlorofluorescein; IDD: intervertebral disc degeneration; IVD: intervertebral disc; LPS: lipopolysaccharide; MMP: matrix metalloproteinase; MTT: methyl-thiazolyl-tetrazolium; NP: nucleus pulposus; PBN: N-tert-butyl-alfa-phenylnitrone; PGs: proteoglycans; ROS: reactive oxygen species; SDS: sodium dodecyl sulfate.