The role and mechanism of autophagy-regulated Keap1/Nrf2 pathway in oxidative stress-induced cartilage endplate cell apoptosis.

Macrophage infiltration and polarization have been increasingly observed in intervertebral disc (IVD) degeneration (IDD). However, their biological roles in IDD are still unrevealed. We harvested conditioned media (CM) derived from a spectrum of macrophages induced from THP-1 cells, and examined how they affect nucleus pulposus cells (NPCs) in vitro, by studying cell proliferation, extracellular matrix (ECM) synthesis, and pro-inflammation expression; and in vivo by injection CM in a rat IDD model. Then, high-throughput sequencing was used to detect differentially expressed genes (DEGs). Gene Ontology (GO), the Kyoto Encyclopedia of Genes and Genomes (KEGG), and protein-protein interaction (PPI) networks were used to further analysis. Higher CCR7+ (M1 marker) and CD206+ (M2 marker) cell counts were found in the degenerated human IVD tissues as compared with the control. Furthermore, the cell co-culture model showed M1CM attenuated NPC proliferation, downregulated the expression of ECM anabolic genes encoding aggrecan and collagen IIα1, upregulated the expression of ECM catabolic genes encoding MMP-13, and inflammation-related genes encoding IL-1β, IL-6, and IL-12, while M2CM showed contrasting trends. In IDD model, higher histological scores and lower disc height index were found following M1CM treatment, while M2CM exhibited opposite results. M1CM injection decreased ECM anabolic and increased ECM catabolic, as well as the upregulation of inflammation-related genes after 8 weeks treatment, while M2CM slowed down these trends. Finally, a total of 637 upregulated and 655 downregulated genes were detected in M1CM treated NPCs, and 975 upregulated genes and 930 downregulated genes in the M2CM groups. The top 30 GO terms were shown and the most significant KEGG pathway was cell cycle in both groups. Based on the PPI analysis, the five most significant hub genes were PLK1, KIF20A, RRM2, CDC20, and UBE2C in the M1CM groups and RRM2, CCNB1, CDC20, PLK1, and UBE2C in the M2CM groups. In conclusion, macrophage polarization exhibited diverse roles in IDD progression, with M1CM exacerbating cell proliferation suppression and IVD degeneration, while M2CM attenuated IDD development. These findings may facilitate the further elucidation of the role of macrophage polarization in IDD, and provide novel insights into the therapeutic potential of macrophages.

Ferristatin II protects nucleus pulposus against degeneration through inhibiting ferroptosis and activating HIF-1α pathway mediated mitophagy.

Modulating a favorable inflammatory microenvironment that facilitates the recovery of degenerated discs is a key strategy in the treatment of intervertebral disc (IVD) degeneration (IDD). More interestingly, well-mechanized tissue-engineered scaffolds have been proven in recent years to be capable of sensing mechanical transduction to enhance the proliferation and activation of nucleus pulposus cells (NPC) and have demonstrated an increased potential in the treatment and recovery of degenerative discs. Additionally, existing surgical procedures may not be suitable for IDD treatment, warranting the requirement of new regenerative therapies for the restoration of disc structure and function. In this study, a light-sensitive injectable polysaccharide composite hydrogel with excellent mechanical properties was prepared using dextrose methacrylate (DexMA) and fucoidan with inflammation-modulating properties. Through numerous in vivo experiments, it was shown that the co-culture of this composite hydrogel with interleukin-1β-stimulated NPCs was able to promote cell proliferation whilst preventing inflammation. Additionally, activation of the caveolin1-yes-associated protein (CAV1-YAP) mechanotransduction axis promoted extracellular matrix (ECM) metabolism and thus jointly promoted IVD regeneration. After injection into an IDD rat model, the composite hydrogel inhibited the local inflammatory response by inducing macrophage M2 polarization and gradually reducing the ECM degradation. In this study, we propose a fucoidan-DexMA composite hydrogel, which provides an attractive approach for IVD regeneration.

Transplantation of dedifferentiation fat cells promotes intervertebral disc regeneration in a rat intervertebral disc degeneration model

Intervertebral disc degeneration (IDD) is considered to be the leading cause of low back pain (LBP). The progression of IDD is closely related to the inflammatory microenvironment, which results in extracellular matrix degradation and cell death. One of the proteins, which have been shown to participate in the inflammatory response, is the bromodomain-containing protein 9 (BRD9). This study aimed to investigate the role and mechanism of BRD9 in regulating IDD. The tumor necrosis factor-α (TNF-α) was used to mimic the inflammatory microenvironment in vitro. Western blot, RT-PCR, immunohistochemistry, immunofluorescence, and flow cytometry were used to demonstrate the effect of BRD9 inhibition or knockdown on matrix metabolism and pyroptosis. We found that the expression of BRD9 was upregulated as IDD progressed. BRD9 inhibition or knockdown alleviated TNF-α-induced matrix degradation, reactive oxygen species (ROS) production, and pyroptosis in rat nucleus pulposus cells. Mechanistically, RNA-seq was used to investigate the mechanism of BRD9 in promoting IDD. Further investigation revealed that BRD9 regulated NOX1 expression. Inhibition of NOX1 could abrogate matrix degradation, ROS production, and pyroptosis caused by BRD9 overexpression. In vivo, the radiological and histological evaluation showed that the pharmacological inhibition of BRD9 alleviated IDD development in rat IDD model. Our results indicated that BRD9 could promote IDD via the NOX1/ROS/ NF-κB axis by inducing matrix degradation and pyroptosis. Targeting BRD9 may be a potential therapeutic strategy in treating IDD.

Intervertebral Disc degeneration (IDD) is one of the leading causes of disability, and current therapies are ineffective. Phosphodiesterase 4B (PDE4B) plays an essential role in regulating the activation of nuclear factor E2-related factor 2 (Nrf2), while Nrf2 regulates ferroptosis. However, it is still unknown whether PDE4B is involved in the development of IDD. In this study, we explored the role of PDE4B on ferroptosis and Nrf2 in IDD pathogenesis by in vivo and in vitro experiments. The findings suggested that the expressions of PDE4B, ASCL4, and TRFC were significantly upregulated, and the expression of Nrf2 was significantly downregulated in nucleus pulposus (NP) tissues from human IDD patients dependent on IDD degeneration. Overexpression of PDE4B (PDE4B-OE) in NP cells upregulated the expression of ASCL4 and TRFC, and downregulated the expression of Nrf2. Meanwhile, the level of cytokine and oxidative stress were upregulated. Ferroptosis inhibitor Fer-1 or Nrf2 activator dimethyl fumarate (DMF) suppressed the effect of PDE4B-OE, while ferroptosis inducer elastin enhanced the effect of PDE4B-OE. In the IDD rat model, PDE4 inhibitor roflumilast, ferroptosis inhibitor Fer-1, or Nrf2 activator dimethyl fumarate (DMF) delayed IDD pathogenesis. While administration of ferroptosis inducer elastin enhanced IDD pathogenesis. Combination with PDE4B inhibitor and ferroptosis inhibitor Fer-1 significantly synergistic reversed IDD pathogenesis. While combination with PDE4B inhibitor or Nrf2 activator and elastin also decreased the degree of the IDD. The IHC suggested PDE4 inhibitor downregulated the expression of ASCL4 and TRFC. However, the combination effect of the Nrf2 activator was not obvious. Our study suggested that aberrant PDE4B activation in NP tissues induces pathological changes in IDD mediated by ferroptosis, and PDE4 inhibitor reveres the process of IDD by suppressing ferroptosis, and has a synergic effect with ferroptosis inhibitor. So PDE4B inhibition may be a potential therapeutic strategy for IDD.

Intervertebral disc degeneration (IDD) is a primary health problem worldwide that involves oxidative stress, ferroptosis, and lipid metabolism. However, the underlying mechanism remains unclear. We investigated whether the transcription factor BTB and CNC homology 1 (BACH1) affected IDD progression by regulating HMOX1/GPX4-mediated ferroptosis and lipid metabolism in nucleus pulposus cells (NPCs). A rat IDD model was created to detect BACH1 expression in intervertebral disc tissues. Next, rat NPCs were isolated and treated with tert-butyl hydroperoxide (TBHP). BACH1, HMOX1, and GPX4 were knocked down, and oxidative stress and ferroptosis-related marker levels were examined. The binding of BACH1 to HMOX1 and of BACH1 to GPX4 was verified using chromatin immunoprecipitation (ChIP). Finally, untargeted lipid metabolism analysis was performed. An IDD model was successfully created, and BACH1 activity was found to be enhanced in the rat IDD tissues. BACH1 inhibited TBHP-induced oxidative stress and oxidative stress-induced ferroptosis in NPCs. Simultaneously, ChIP verified that BACH1 protein bound to HMOX1 and targeted the HMOX1 transcription inhibition to affect oxidative stress in NPCs. ChIP also verified that BACH1 bound to GPX4 and targeted the GPX4 inhibition to affect ferroptosis in NPCs. Finally, BACH1 inhibition in vivo improved IDD and affected lipid metabolism. The transcription factor BACH1 promoted IDD by regulating HMOX1/GPX4 to mediate oxidative stress, ferroptosis, and lipid metabolism in NPCs.

Oxidative stress-induced autophagy dysfunction is involved in the pathogenesis of intervertebral disc degeneration (IVDD). MicroRNAs (miRNAs) not only have been regarded as important regulators of IVDD but also reported to be related to autophagy. This research was aimed to explore the role of miR-130b-3p in IVDD and its regulation on autophagy mechanism. The miR-130b-3p expression in the patient's degenerative nucleus pulposus (NP) samples and rat NP tissues was detected by qRT-PCR and FISH assay. The miR-130b-3p was knocked down or overexpressed in the human NP cells by lentivirus transfection. TBHP was used to induce oxidative stress in the human NP cells. Apoptosis, senescence, and autophagy were evaluated by flow cytometry, β-gal staining, immunofluorescence, electron microscopy, and Western blot in the miR-130b-3p knocked down human NP cells under TBHP treatment. The relationship between the miR-130b-3p and ATG14 or PRKAA1 was confirmed by luciferase assay. The siRNA transfection was used to knock down the ATG14 and PRKAA1 expression, and then the human NP cells functions were further determined. In the in vivo experiment, the IVDD rat model was constructed and an adeno-associated virus (AAV)-miR-130b-3p inhibitor was intradiscally injected. After that, MRI and histological staining were conducted to evaluate the role of miR-130b-3p inhibition in the IVDD rat model. We found that the miR-130b-3p was upregulated in the degenerative NP samples from humans and rats. Interestingly, the inhibition of miR-130b-3p rescued oxidative stress-induced dysfunction of the human NP cells, and miR-130b-3p inhibition upregulated autophagy. Mechanistically, we confirmed that the miR-130b-3p regulated the ATG14 and PRKAA1 directly and the knockdown of the ATG14 or PRKAA1 as well as the treatment of autophagy inhibitor blockaded the autophagic flux and reversed the protective effects of miR-130b-3p inhibition in the TBHP-induced human NP cells. Furthermore, the inhibition of the miR-130b-3p via AAV- miR-130b-3p injection ameliorated the IVDD in a rat model. These data demonstrated that the miR-130b-3p inhibition could upregulate the autophagic flux and alleviate the IVDD via targeting ATG14 and PRKAA1.The translational potential of this article: The suppression of miR-130b-3p may become an effective therapeutic strategy for IVDD.

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

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.

Intervertebral disc degeneration (IVDD) is a progressive degenerative disorder of the spine characterized by oxidative stress and cellular dysfunction. Current clinical treatments for IVDD include surgical procedures, such as discectomy and spinal fusion, as well as pharmacological therapies using analgesics and anti‐inflammatory agents. However, these strategies primarily offer symptomatic relief and do not address the underlying causes of IVDD. Targeting oxidative stress has emerged as a promising therapeutic approach, yet its effectiveness remains limited. To overcome this limitation, an antioxidant carbon dot of selenomethionine (Se‐Met‐CD) is developed for efficient IVDD therapy. Se‐Met‐CD effectively scavenges excess reactive oxygen species (ROS), alleviates oxidative stress, and restores intracellular redox homeostasis in nucleus pulposus cells. Se‐Met‐CD exhibits an antioxidant capacity 3.1 times that of its precursor, Se‐Met, when compared at the same concentration. In hydrogen peroxide (H2O2)‐treated nucleus pulposus cells, Se‐Met‐CD significantly reduces intracellular ROS levels to 17.7% of those in untreated control cells. In a puncture‐induced IVDD rat model, Se‐Met‐CD demonstrates remarkable therapeutic efficacy by significantly attenuating disc degeneration, reflected in lower Pfirrmann and histological scores. These results underscore the potential of Se‐Met‐CD to treat IVDD by scavenging ROS, restoring antioxidant balance, and modulating the local microenvironments.

Chronic low back pain due to intervertebral disc (IVD) degeneration (IVDD) is a major global health burden. Interactions between IVD tissues and surrounding structures are important for spinal health and pathology, yet many studies focus on structures within the IVD and neglect a deeper investigation of adjacent tissues. This study describes a newly identified intervertebral fat pad (IVFP) in rat lumbar spines, its changes following IVD injury, and similar structures in mice and humans. IVFPs were analyzed histologically using naive and injured IVDs from a rat model of IVDD, in which 5-month-old rats underwent a triple-puncture annulus fibrosus (AF) injury of L3-4, L4-5, and L5-6 IVDs. Sagittal and coronal histologic samples were stained with safranin O/fast green and analyzed at 3, 7, 14, and 56 days post-injury. Naive and sham IVDs demonstrated the consistent presence of an IVFP between the anterior AF and anterior longitudinal ligament (ALL) in anterior and anterolateral regions of the IVD, without presence at posterior or postero-lateral IVD regions. The IVFP gradually disappeared in injured IVDs, and became largely absent by 56 days post-injury. Post-injury changes to the IVFP also included adipocyte shrinkage, fibrous tissue infiltration, and gradual IVFP disappearance, together suggesting progressive degeneration. IVFP-like structures were identified histologically in mouse and human IVDs, providing evidence of its presence across species. Fat pads studied in other musculoskeletal joints play roles in health and disease, suggesting a need for further study investigating the potential role of the IVFP in IVDD pathomechanisms and therapeutics.

Palmatine activation of TFEB enhances autophagy and alleviates endoplasmic reticulum stress in intervertebral disc degeneration.

Intervertebral disc degeneration (IDD) is a chronic degenerative disease and one of the main causes of low back pain (LBP). Currently, there is no effective treatment. Ferroptosis is a cell-regulated process that depends on iron deposition and lipid peroxidation. Inhibiting ferroptosis in nucleus pulposus cells is considered a potential strategy for the treatment of IDD. Gallic acid (GA) is naturally present in a variety of plants and has anti-inflammatory, antioxidant and analgesic effects. It has been shown to alleviate ferroptosis. However, the role of GA in IDD ferroptosis remains unclear. This study explored the pathological mechanism of GA in IDD in relation to ferroptosis: (1) to identify ferroptosis-related targets for GA treatment of IDD using network pharmacology and molecular docking technology, (2) to evaluate the therapeutic effect of GA in an IDD rat model and changes in ferroptosis-related targets, (3) to investigate the changes of oxidative stress and lipid peroxidation products in NP cells after GA intervention, and (4) to study the changes of ferroptosis-related proteins and iron ions in cells and mitochondria after GA intervention. Experimental results confirmed that GA can treat IDD by reducing the degradation of extracellular matrix (ECM) and pathological changes in IDD. GA can also mitigate ferroptosis by reducing oxidative stress and lipid peroxidation in rat nucleus pulposus (NP) cells. The alleviation of disc degeneration ferroptosis by GA may be closely associated with the key ferroptosis proteins P53 and NRF2.

Intervertebral disc degeneration (IVDD) is one of the main causes of low back pain. Existing literature has confirmed the occurrence of ferroptosis in IVDD. With the widespread application of artificial intelligence (AI), an increasing number of compounds have been screened for their potential to alleviate IVDD. BRD-K20733377 is one such compound with anti-aging properties. Preliminary experiments have shown that BRD-K20733377 can significantly inhibit cellular ferroptosis. However, research on the potential therapeutic targets and mechanisms of BRD-K20733377 in IVDD remains limited. This study aims to explore the main targets and potential mechanisms of BRD-K20733377 in the treatment of IVDD. Network pharmacology, bioinformatics, machine learning algorithms, molecular docking, molecular dynamics, and Mendelian randomization were used to comprehensively analyze the effects, potential targets, and mechanisms of BRD-K20733377 in IVDD. Rat nucleus pulposus-derived mesenchymal stem cells (NPMSCs) were selected for in vitro experiments. Cell viability was measured by CCK-8 and flow cytometry, while antioxidant defense, lipid peroxidation, and iron metabolism were explored using JC-1, Reactive Oxygen Species (ROS), FerroOrange dye, Lipid peroxides, Malondialdehyde (MDA), and Mitochondrial transmission electron microscopy. The expression levels of ferroptosis-related proteins were detected by Western blot and immunofluorescence. In the rat IVDD model, the effects of BRD-K20733377 on pain threshold, pain behavior, and its therapeutic efficacy were evaluated. Predictive results identified 30 genes related to ferroptosis in BRD-K20733377 and IVDD, revealing that the potential mechanism of BRD-K20733377 in treating IVDD is closely associated with ferroptosis. In addition, functional enrichment analysis indicated that these genes are involved in multiple signaling pathways. Machine learning algorithms further identified the core targets STAT3 and NFKB1, and Mendelian randomization validated their direct causal relationship with IVDD. In vitro experiments confirmed that BRD-K20733377 inhibited IVDD by reducing intracellular Fe²⁺ levels and lipid peroxidation, thus regulating ferroptosis. Theoretically, BRD-K20733377 may inhibit NPMSCs ferroptosis via STAT3/NFKB1 axis. Ferroptosis-related proteins and immunofluorescence results further supported this mechanism. In vivo experiments showed that BRD-K20733377 significantly improved the behavior of SD rats, reduced pain scores, and alleviated IVDD. BRD-K20733377 inhibits ferroptosis through the STAT3/NFKB1 axis, thereby alleviating IVDD. This provides a new perspective for the study of IVDD and could serve as a potential therapeutictarget for IVDD.