Excessive reactive oxygen species (ROS) generation in degenerative intervertebral disc (IVD) indicates the contribution of oxidative stress to IVD degeneration (IDD), giving a novel insight into the pathogenesis of IDD. ROS are crucial intermediators in the signaling network of disc cells. They regulate the matrix metabolism, proinflammatory phenotype, apoptosis, autophagy, and senescence of disc cells. Oxidative stress not only reinforces matrix degradation and inflammation, but also promotes the decrease in the number of viable and functional cells in the microenvironment of IVDs. Moreover, ROS modify matrix proteins in IVDs to cause oxidative damage of disc extracellular matrix, impairing the mechanical function of IVDs. Consequently, the progression of IDD is accelerated. Therefore, a therapeutic strategy targeting oxidative stress would provide a novel perspective for IDD treatment. Various antioxidants have been proposed as effective drugs for IDD treatment. Antioxidant supplementation suppresses ROS production in disc cells to promote the matrix synthesis of disc cells and to prevent disc cells from death and senescence in vitro. However, there is not enough in vivo evidence to support the efficiency of antioxidant supplementation to retard the process of IDD. Further investigations based on in vivo and clinical studies will be required to develop effective antioxidative therapies for IDD.

The accumulation of senescent disc cells in degenerative intervertebral disc (IVD) suggests the detrimental roles of cell senescence in the pathogenesis of intervertebral disc degeneration (IDD). Disc cell senescence decreased the number of functional cells in IVD. Moreover, the senescent disc cells were supposed to accelerate the process of IDD via their aberrant paracrine effects by which senescent cells cause the senescence of neighboring cells and enhance the matrix catabolism and inflammation in IVD. Thus, anti-senescence has been proposed as a novel therapeutic target for IDD. However, the development of anti-senescence therapy is based on our understanding of the molecular mechanism of disc cell senescence. In this review, we focused on the molecular mechanism of disc cell senescence, including the causes and various molecular pathways. We found that, during the process of IDD, age-related damages together with degenerative external stimuli activated both p53-p21-Rb and p16-Rb pathways to induce disc cell senescence. Meanwhile, disc cell senescence was regulated by multiple signaling pathways, suggesting the complex regulating network of disc cell senescence. To understand the mechanism of disc cell senescence better contributes to developing the anti-senescence-based therapies for IDD.

Intervertebral disc degeneration (IDD) is a widely recognized contributor to low back pain (LBP). The Prevention or reversal of IDD is a potential treatment for LBP. Unfortunately, current treatments for IDD are aimed at relieving symptoms rather than regenerating disc structure or function. Recently, the injection of growth factors and mesenchymal stem cell (MSC) transplantation have been shown to be promising biological therapies for IDD. Growth factors stimulate the proliferation of and matrix synthesis by intervertebral disc (IVD) cells, leading to the regeneration of degenerative discs. Growth factors, hypoxia and co-culture with nucleus pulposus (NP) cells induce MSCs to differentiate toward an NP-like phenotype, which can increase the number of functional cells in the IVD or enhance the function of endogenous disc cells to facilitate IVD regeneration. Therefore, the emerging roles of growth factors in IVD regeneration have piqued the interest of researchers. Growth factors including transforming growth factor-β (TGF-β), fibroblast growth factor (FGF), insulin-like growth factor-1 (IGF-1) and growth and differentiation factor-5 (GDF-5), among others, have been demonstrated to enhance anabolism in IVD cells and to induce NP-like differentiation of MSCs. However, the injection of TGF, IGF and FGF into human IVDs may induce unwanted blood vessel ingrowth, which accelerates the process of IDD, the injection of GDF-5 may not have the same effect. This finding suggests that GDF-5 is a preferable growth factor for use in IDD treatment compared with TGF, IGF and FGF. The GDF-5 gene is one of the few growth factor genes that have been found to be associated with IDD thus far; moreover, the GDF-5 gene defects lead to collagen and proteoglycan abnormalities in discs in mice, suggesting that GDF-5 contributes to the structural and functional maintenance of the IVD. This review is focused on the functions of GDF-5 in the IVD and on the association between GDF-5 and a genetic predisposition to IDD. The effects of GDF-5 on IVD regeneration and on MSC differentiation are also discussed. GDF-5 plays a crucial role in the pathogenesis of IDD and is a promising therapeutic agent for IDD. Additionally, stem cell transplantation has been shown to be a promising biological therapy for IDD.

Senescence is a crucial driver of intervertebral disc degeneration (IDD). Disc cells are exposed to high oxygen tension due to neovascularization in degenerative discs. However, the effect of oxygen tension on disc cell senescence was unknown. Herein, rat nucleus pulposus (NP) cells were cultured under 20% O₂or 1% O₂. Consequently, ROS induced by 20% O₂caused DNA damage and then activated p53‐p21‐Rb and p16‐Rb pathways via ERK signaling to induce NP cell senescence. It also induced catabolic and proinflammatory phenotype of NP cells via MAPK and NF‐κB pathways. Furthermore, 20% O₂was found to upregulate Nox4 in NP cells. Small interfering RNA against Nox4 reduced ROS production induced by 20% O₂and consequently suppressed premature senescence of NP cells. On the contrary, NP cells overexpressing Nox4 produced more ROS and rapidly developed senescent signs. In consistent with the in vitro studies, the expression of Nox4, p21, and Rb was upregulated in rat degenerative discs. This study, for the first time, demonstrates that Nox4 is an oxygen‐sensing enzyme and a main ROS source in NP cells. Nox4‐dependent ROS are genotoxic and a potent trigger of NP cell senescence. Nox4 is a potential therapeutic target for disc cell senescence and IDD.

Background: The senescence of nucleus pulposus (NP) cells plays a vital role in the pathogenesis of intervertebral disc (IVD) degeneration (IDD). NADPH oxidase 4 (NOX4)-associated oxidative stress has been shown to induce premature NP cell senescence. Enhancer of zeste homolog 2 (EZH2) is a crucial gene regulating cell senescence. The aim of this study was to investigate the roles of EZH2 in NOX4-induced NP cell senescence and a feedback loop between EZH2 and NOX4. Results: The down-regulation of EZH2 and the up-regulation of NOX4 and p16 were observed in the degenerative discs of aging rats. EZH2 regulated NP cell senescence via the H3K27me3-p16 pathway. Also, EZH2 regulated the expression of NOX4 in NP cells through the histone H3 lysine 27 trimethylation (H3K27me3) in the promoter of NOX4 gene. Furthermore, NOX4 down-regulated EZH2 expression in NP cells via the canonical Wnt/β-catenin pathway. Conclusions: A positive feedback loop between EZH2 and NOX4 is involved in regulating NP cell senescence, which provides a novel insight into the mechanism of IDD and a potential therapeutic target for IDD.

The precise diagnosis and treatment of spinal infections (SI) remains challenging for spine surgeons. Identifying the pathogens of SI through metagenomic next-generation sequencing (mNGS) may be a key approach to addressing this challenge. To evaluate the accuracy and applicability of mNGS in determining the etiology of SI. Diagnostic test study. Twenty-five patients who had a clinical suspicion of SI and underwent mNGS testing. The specificity, sensitivity, and time cost of mNGS and bacterial culture were compared. Clinical outcomes were assessed using the numeric rating scale (NRS) score, Oswestry Disability Index (ODI), and the Japanese Orthopedic Association (JOA) score. Demographic data and laboratory results (blood cell count (WBC), erythrocyte sedimentation rate (ESR), neutrophil percentage (NEUT%), and C-reactive protein level (CRP) were also evaluated. In this retrospective study, samples were obtained from 25 eligible patients via surgery or CT-guided puncture and subjected to histopathological examination, bacterial culture, and mNGS. The sensitivity and specificity of the bacterial cultures and mNGS were calculated with respect to the histopathological results as a reference. Postoperative antibiotics or antituberculosis drugs were administered on the basis of mNGS results, combined with clinical manifestations, imaging examination, and histopathology. The changes of clinical outcomes and laboratory results after treatment were observed. Of the 25 patients, 21 had a positive pathology, of which 10 showed a tuberculous pathology, and the remaining 11 showed a nontuberculous inflammatory pathology. The sensitivity of mNGS was higher than that of the bacterial culture. However, the difference in specificity between bacterial culture and mNGS was not significant. Moreover, the time needed to perform mNGS was significantly lower than that of bacterial culture and pathology. All patients were followed up for more than three months, and CRP and NEUT% significantly decreased by three months after treatment. There was no significant difference in WBC and ESR. The ODI, NRS and JOA scores were significantly improved after treatment. Metagenomic next-generation sequencing technology can play an important role in the detection of pathogens in SI and should be further investigated and applied in future studies.