Enhanced NLRP3, caspase-1, and IL- 1β levels in degenerate human intervertebral disc and their association with the grades of disc degeneration

Discogenic Low Back Pain: Anatomic and Pathophysiologic Characterization, Clinical Evaluation, Biomarkers, AI, and Treatment Options

Discogenic low back pain (LBP) is a significant clinical condition arising from degeneration of the intervertebral disc, a common yet complex cause of chronic pain, defined by fissuring in the annulus fibrosus resulting in vascularization of growing granulation tissue and growth of nociceptive nerve fibers along the laceration area. This paper delves into the anatomical and pathophysiological underpinnings of discogenic LBP, emphasizing the role of intervertebral disc degeneration in the onset of pain. The pathogenesis is multifactorial, involving processes like mitochondrial dysfunction, accumulation of advanced glycation end products, and pyroptosis, all contributing to disc degeneration and subsequent pain. Despite its prevalence, diagnosing discogenic LBP is challenging due to the overlapping symptoms with other forms of LBP and the absence of definitive diagnostic criteria. Current diagnostic approaches include clinical evaluations, imaging techniques, and the exploration of potential biomarkers. Treatment strategies range from conservative management, such as physical therapy and pharmacological interventions, to more invasive procedures such as spinal injections and surgery. Emerging therapies targeting molecular pathways involved in disc degeneration are under investigation and hold potential for future clinical application. This paper highlights the necessity of a multidisciplinary approach combining clinical, imaging, and molecular data to enhance the accuracy of diagnosis and the effectiveness of treatment for discogenic LBP, ultimately aiming to improve patient outcomes.

Exploration of the mode of death and potential death mechanisms of nucleus pulposus cells

Intervertebral disc degeneration (IVDD) is a common chronic orthopaedic disease in orthopaedics that imposes a heavy economic burden on people and society. Although it is well established that IVDD is associated with genetic susceptibility, ageing and obesity, its pathogenesis remains incompletely understood. Previously, IVDD was thought to occur because of excessive mechanical loading leading to destruction of nucleus pulposus cells (NPCs), but studies have shown that IVDD is a much more complex process associated with inflammation, metabolic factors and NPCs death and can involve all parts of the disc, characterized by causing NPCs death and extracellular matrix (ECM) degradation. The damage pattern of NPCs in IVDD is like that of some programmed cell death, suggesting that IVDD is associated with programmed cell death. Although apoptosis and pyroptosis of NPCs have been studied in IVDD, the pathogenesis of intervertebral disc degeneration can still not be fully elucidated by using only traditional cell death modalities. With increasing research, some new modes of cell death, PANoptosis, ferroptosis and senescence have been found to be closely related to intervertebral disc degeneration. Among these, PANoptosis combines essential elements of pyroptosis, apoptosis and necroptosis to form a highly coordinated and dynamically balanced programmed inflammatory cell death process. Furthermore, we believe that PANoptosis may also crosstalk with pyroptosis and senescence. Therefore, we review the progress of research on multiple deaths of NPCs in IVDD to provide guidance for clinical treatment.

Pyroptosis in Skeleton Diseases: A Potential Therapeutic Target Based on Inflammatory Cell Death

Skeletal disorders, including fractures, osteoporosis, osteoarthritis, rheumatoid arthritis, and spinal degenerative conditions, along with associated spinal cord injuries, significantly impair daily life and impose a substantial burden. Many of these conditions are notably linked to inflammation, with some classified as inflammatory diseases. Pyroptosis, a newly recognized form of inflammatory cell death, is primarily triggered by inflammasomes and executed by caspases, leading to inflammation and cell death through gasdermin proteins. Emerging research underscores the pivotal role of pyroptosis in skeletal disorders. This review explores the pyroptosis signaling pathways and their involvement in skeletal diseases, the modulation of pyroptosis by other signals in these conditions, and the current evidence supporting the therapeutic potential of targeting pyroptosis in treating skeletal disorders, aiming to offer novel insights for their management.

MINK1 deficiency stimulates nucleus pulposus cell pyroptosis and exacerbates intervertebral disc degeneration

Intervertebral disc (IVD) degeneration, induced by aging and irregular mechanical strain, is highly prevalent in the elderly population, serving as a leading cause of chronic low back pain and disability. Evolving evidence has revealed the involvement of nucleus pulposus (NP) pyroptosis in the pathogenesis of IVD degeneration, while the precise regulatory mechanisms of NP pyroptosis remain obscure. Misshapen/Nck-interacting kinase (NIK)-related kinase 1 (MINK1), a serine-threonine protein kinase, has the potential to modulate the activation of NLRP3 inflammasome, indicating its pivotal role in governing pyroptosis. In this study, to assess the significance of MINK1 in NP pyroptosis and IVD degeneration, NP tissues from patients with varying degrees of IVD degeneration, and IVD tissues from both aging-induced and lumbar spine instability (LSI) surgery-induced IVD degeneration mouse models, with or without MINK1 ablation, were meticulously evaluated. Our findings indicated a notable decline in MINK1 expression in NP tissues of patients with IVD degeneration and both mouse models as degeneration progresses, accompanied by heightened matrix degradation and increased NP pyroptosis. Moreover, MINK1 ablation led to substantial activation of NP pyroptosis in both mouse models, and accelerating ECM degradation and intensifying the degeneration phenotype in mechanically stress-induced mice. Mechanistically, MINK1 deficiency triggered NF-κB signaling in NP tissues. Overall, our data illustrate an inverse correlation between MINK1 expression and severity of IVD degeneration, and the absence of MINK1 stimulates NP pyroptosis, exacerbating IVD degeneration by activating NF-κB signaling, highlighting a potential innovative therapeutic target in treating IVD degeneration.

Pyroptosis: A spoiler of peaceful coexistence between cells in degenerative bone and joint diseases

BACKGROUND

As people age, degenerative bone and joint diseases (DBJDs) become more prevalent. When middle-aged and elderly people are diagnosed with one or more disorders such as osteoporosis (OP), osteoarthritis (OA), and intervertebral disc degeneration (IVDD), it often signals the onset of prolonged pain and reduced functionality. Chronic inflammation has been identified as the underlying cause of various degenerative diseases, including DBJDs. Recently, excessive activation of pyroptosis, a form of programed cell death (PCD) mediated by inflammasomes, has emerged as a primary driver of harmful chronic inflammation. Consequently, pyroptosis has become a potential target for preventing and treating DBJDs.

AIM OF REVIEW

This review explored the physiological and pathological roles of the pyroptosis pathway in bone and joint development and its relation to DBJDs. Meanwhile, it elaborated the molecular mechanisms of pyroptosis within individual cell types in the bone marrow and joints, as well as the interplay among different cell types in the context of DBJDs. Furthermore, this review presented the latest compelling evidence supporting the idea of regulating the pyroptosis pathway for DBJDs treatment, and discussed the potential, limitations, and challenges of various therapeutic strategies involving pyroptosis regulation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In summary, an interesting identity for the unregulated pyroptosis pathway in the context of DBJDs was proposed in this review, which was undertaken as a spoiler of peaceful coexistence between cells in a degenerative environment. Over the extended course of DBJDs, pyroptosis pathway perpetuated its activity through crosstalk among pyroptosis cascades in different cell types, thus exacerbating the inflammatory environment throughout the entire bone marrow and joint degeneration environment. Correspondingly, pyroptosis regulation therapy emerged as a promising option for clinical treatment of DBJDs.

M6A methylation-regulated autophagy may be a new therapeutic target for intervertebral disc degeneration

Degeneration of intervertebral discs is considered one of the most important causes of low back pain and disability. The intervertebral disc (IVD) is characterized by its susceptibility to various stressors that accelerate the senescence and apoptosis of nucleus pulposus cells, resulting in the loss of these cells and dysfunction of the intervertebral disc. Therefore, how to reduce the loss of nucleus pulposus cells under stress environment is the main problem in treating intervertebral disc degeneration. Autophagy is a kind of programmed cell death, which can provide energy by recycling substances in cells. It is considered to be an effective method to reduce the senescence and apoptosis of nucleus pulposus cells under stress. However, further research is needed on the mechanisms by which autophagy of nucleus pulposus cells is regulated under stress environments. M6A methylation, as the most extensive RNA modification in eukaryotic cells, participates in various cellular biological functions and is believed to be related to the regulation of autophagy under stress environments, may play a significant role in nucleus pulposus responding to stress. This article first summarizes the effects of various stressors on the death and autophagy of nucleus pulposus cells. Then, it summarizes the regulatory mechanism of m6A methylation on autophagy-related genes under stress and the role of these autophagy genes in nucleus pulposus cells. Finally, it proposes that the methylation modification of autophagy-related genes regulated by m6A may become a new treatment approach for intervertebral disc degeneration, providing new insights and ideas for the clinical treatment of intervertebral disc degeneration.

Involvement of regulated cell deaths in aging and age-related pathologies

Aging is a pathophysiological process that causes a gradual and permanent reduction in all biological system functions. The phenomenon is caused by the accumulation of endogenous and exogenous damage as a result of several stressors, resulting in significantly increased risks of various age-related diseases such as neurodegenerative diseases, cardiovascular diseases, metabolic diseases, musculoskeletal diseases, and immune system diseases. In addition, aging appears to be connected with mis-regulation of programmed cell death (PCD), which is required for regular cell turnover in many tissues sustained by cell division. According to the recent nomenclature, PCDs are physiological forms of regulated cell death (RCD) useful for normal tissue development and turnover. To some extent, some cell types are connected with a decrease in RCD throughout aging, whereas others are related with an increase in RCD. Perhaps the widespread decline in RCD markers with age is due to a slowdown of the normal rate of homeostatic cell turnover in various adult tissues. As a result, proper RCD regulation requires a careful balance of many pro-RCD and anti-RCD components, which may render cell death signaling pathways more sensitive to maladaptive signals during aging. Current research, on the other hand, tries to further dive into the pathophysiology of aging in order to develop therapies that improve health and longevity. In this scenario, RCD handling might be a helpful strategy for human health since it could reduce the occurrence and development of age-related disorders, promoting healthy aging and lifespan. In this review we propose a general overview of the most recent RCD mechanisms and their connection with the pathophysiology of aging in order to promote targeted therapeutic strategies.

Calcitonin gene-related peptide attenuated discogenic low back pain in rats possibly via inhibiting microglia activation

Discogenic low back pain (DLBP) is a multifactorial disease and associated with intervertebral disc degeneration. Calcitonin gene-related protein (CGRP) plays a critical role in pain processing, while the role in DLBP remains unclear. This study aims to investigate the anti-nociceptive role and related mechanisms of CGRP in DLBP. Here we established the DLBP rat and validated the model using histology and radiography. Minocycline, a microglial inhibitor, and CGRP were intrathecally injected and the behavioral test was performed to determine hyperalgesia. Further, BV2 microglial cells and microglial activation agent lipopolysaccharide (LPS) were employed for the in vitro experiment. We observed obvious lumbar intervertebral disc degeneration and hyperalgesia at 12 weeks postoperation in DLBP group, with significantly activated microglia in the spinal cord. CGRP treatment significantly inhibited the upregulation of proinflammatory cytokines and NLRP3/caspase-1 expression induced by LPS in BV2 cells, whereas treatment with CGRP alone had little effect on BV2 cells. The intrathecal injection of CGRP into DLBP rats relieved mechanical and thermal hyperalgesia, reverted the microglial activation and decreased the expression of NLRP3/caspase-1, similar to the effects produced by minocycline. Our results provide evidence that microglial activation in the spinal cord play a key role in hyperalgesia in DLBP rats. CGRP alleviates DLBP induced hyperalgesia and inhibits microglial activation in the spinal cord. Regulation of CGRP and microglial activation may provide a new strategy for ameliorating DLBP.

Mechanism exploration of Osteoking in the treatment of lumbar disc herniation based on network pharmacology and molecular docking

OBJECTIVE

Lumbar disc herniation (LDH) is a common spinal surgical disease. Low back and leg pain caused by LDH is the main factor leading to functional disability, which has caused a serious burden to patients and society. Osteoking can delay the progression of osteoporosis and osteoarthritis, and even has a significant effect on the prevention of deep vein thrombosis after fracture surgery. In recent years, it has been gradually used in the treatment of LDH and has received significant results. However, the underlying mechanism remains unclear. The aim of this study was to predict the mechanism of Osteoking in the treatment of LDH through network pharmacology and verify it by molecular docking method.

METHODS

The TCMSP database was used to collect the relevant active components and targets of Osteoking, while the GeneCards, OMIM and DisGeNET databases were utilized to collect the relevant disease targets of LDH. The Venny 2.1.0 software was employed to obtain the intersecting gene targets of Osteoking and LDH. PPI network construction and core target selection were performed using Cytoscape 3.9.0 software. The Metascape database was used for GO and KEGG enrichment analysis of the relevant targets. Finally, molecular docking was conducted using AutoDock software.

RESULTS

The study identified 116 potential targets and 26 core targets for the treatment of LDH with Osteoking. Pathways in cancer, Alzheimer's disease, microRNAs in cancer and the IL-17 signalling pathway were among the main involved signalling pathways. Molecular docking results demonstrated that the key targets AKT1, IL-6, ALB, TNF and IL-1β exhibited relatively stable binding activities with the main active components of Osteoking.

CONCLUSIONS

Osteoking can alleviate the symptoms of lumbar disc herniation through the modulation of multiple targets and signalling pathways.

Bushen Huoxue Formula Inhibits IL-1β-Induced Apoptosis and Extracellular Matrix Degradation in the Nucleus Pulposus Cells and Improves Intervertebral Disc Degeneration in Rats

Background

The method of action of Bushen Formula (BSHXF) in the treatment of intervertebral disc degeneration (IVDD) was uncovered in this work using in vivo and in vitro tests. To clarify the mechanism of action of BSHXF, we validated the rat intervertebral disc degeneration model and the nucleus pulposus cell degeneration model.

Methods

In an in vivo model of IVDD the study explores the impact of BSHXF on mitochondrial function, pro-inflammatory cytokines, pro-apoptotic factors, and matrix metalloproteinases. Additionally, it evaluates the induced degeneration of nucleus pulposus (NP) cells in an in vitro model stimulated by interleukin-1 β (IL-1β). The study measures the effects of BSHXF on both the inflammatory response and mitochondrial function.

Results

The MRI results showed that BSHXF reduced intervertebral disc volume reduction and degradation of NP tissue. HE, SO-FG and immunofluorescence further confirmed the protective effect of BSHXF on degenerative intervertebral discs. BSHXF reduced the inflammatory levels of IL-6 IL-1β and TNF-α in degenerative intervertebral disc tissue. Meanwhile, JC-1, mPTP and ROS detection revealed that BSHXF can restore mitochondrial function by regulating the expression of antioxidant proteins, playing a protective role in NP cells. Finally, the WB results showed that BSHXF can alleviate IL-1β mediate the degeneration of NP cells. BSHXF can alleviate NP cell apoptosis by inhibiting the expression of bax, cleaved caspase-3, caspase-3, and cyt-c, and increasing the expression of Bcl-2.

Conclusion

This study reveals that BSHXF inhibits the development of inflammatory factors, which may play a significant role in intervertebral disc degeneration. This implies that BSHXF is a suitable herbal medication for future research into inflammatory cytokine treatment.

Endoplasmic reticulum stress-mediated autophagy alleviates lipopolysaccharide-induced nucleus pulposus cell pyroptosis by inhibiting CHOP signaling in vitro

Pyroptosis, a newly discovered pro-inflammatory programmed necrosis of cells, serves as an initiating and promoting event that leads to intervertebral disc (IVD) degeneration (IDD). Endoplasmic reticulum stress (ERS) and autophagy are vital regulatory mechanisms of cellular homeostasis, which is also closely related to IDD. However, the role and relationship of ERS and autophagy in the pyroptosis of nucleus pulposus cell (NPC) are not well understood. In this research, we aimed to elucidate the role and mechanism of ERS-C/EBP homologous protein (CHOP) in lipopolysaccharide (LPS)-induced cell pyroptosis and determine its interaction with autophagy. ERS and autophagy inducers or inhibitors were used or not in the preconditioning of rat NPCs. Cell viability, pyroptosis-related protein expression, caspase-1 activity assay, and enzyme-linked immunosorbent assay were performed to observe rat NPC pyroptosis after the treatment of LPS. Activation of the ERS pathway and autophagy were assessed by quantitative real-time PCR, western blot analyses, and immunofluorescence staining assay to classify the molecular mechanisms. Our results showed that LPS stimulation induced NPC pyroptosis with concomitant activation of the ERS-CHOP pathway and initiated autophagy. Activation of the ERS-CHOP pathway exacerbated rat NPC pyroptosis, whereas autophagy inhibited cell pyroptosis. LPS-induced cell pyroptosis and CHOP upregulation were negatively regulated by autophagy. LPS-induced autophagy was depressed by the ERS inhibitor but aggravated by the ERS inducer. Taken together, our findings suggested that LPS induced NPC pyroptosis by activating ERS-CHOP signaling and ERS mediated LPS-induced autophagy, which in turn alleviated NPC pyroptosis by inhibiting CHOP signaling.

Pathogenesis and therapeutic implications of matrix metalloproteinases in intervertebral disc degeneration: A comprehensive review

Intervertebral disc (IVD) degeneration (IDD) is a common disorder that affects the spine and is a major cause of lower back pain (LBP). The extracellular matrix (ECM) is the structural foundation of the biomechanical properties of IVD, and its degradation is the main pathological characteristic of IDD. Matrix metalloproteinases (MMPs) are a group of endopeptidases that play an important role in the degradation and remodeling of the ECM. Several recent studies have shown that the expression and activity of many MMP subgroups are significantly upregulated in degenerated IVD tissue. This upregulation of MMPs results in an imbalance of ECM anabolism and catabolism, leading to the degradation of the ECM and the development of IDD. Therefore, the regulation of MMP expression is a potential therapeutic target for the treatment of IDD. Recent research has focused on identifying the mechanisms by which MMPs cause ECM degradation and promote IDD, as well as on developing therapies that target MMPs. In summary, MMP dysregulation is a crucial factor in the development of IDD, and a deeper understanding of the mechanisms involved is needed to develop effective biological therapies that target MMPs to treat IDD.

Systemic pharmacology reveal the mechanism by which the Qiangjin Zhuanggu Qufeng mixture inhibits LPS-induced pyroptosis of rat nucleus pulposus cells

OBJECTIVE

Low back pain (LBP) is a worldwide health issue primarily attributed to intervertebral disc degeneration (IVDD). Qiangjin Zhuang Qufeng mixture (QJZG), an approved hospital-based formula with years of clinical application, has demonstrated notable therapeutic effects in the treatment of LBP. Nevertheless, the underlying mechanism by which it alleviates LBP remains uncertain.

METHODS

The bioactive constituents of QJZG were initially identified using ultra-performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry (UPLC-Q-TOF-MS/MS). Subsequently, network pharmacology was employed to explore the core components and targets. In vivo and in vitro experiments were then conducted to validate the specific mechanism of action of QJZG based on the identified targets and pathways. Following that, ultra-high-performance liquid chromatography/mass spectrometry combined with 16S rRNA gene sequencing of blood and faecal samples was utilized to assess the impact of gut microbiota on faecal and serum metabolites subsequent to QJZG administration in intervertebral disc degeneration (IVDD) rats.

RESULTS

The principal constituents of QJZG were identified using UPLC-Q-TOF-MS/MS, revealing a substantial enrichment of flavonoids and triterpenes. Network pharmacology analysis indicated the potential inhibitory effects of QJZG on the NLRP3 inflammasome and downstream inflammatory factors. Furthermore, investigations demonstrated that intervertebral disc degeneration may be attributed to pyroptotic cell death within the nucleus pulposus. In vitro experiments were performed utilizing LPS to induce the inflammatory response in nucleus pulposus cells (NPC), and it was observed that QJZG-containing serum significantly suppressed key pyroptosis-related genes and downstream inflammatory factors. Additionally, in vivo experiments substantiated the capacity of QJZG to preserve disc height and ameliorate the progression of disc degeneration. Concurrently, oral pharmacotherapy in animal studies prominently involved the effects of Enterobacteriaceae and Clostridium, closely intertwined with lipid metabolism.

CONCLUSIONS

QJZG exhibited a delaying effect on IVDD by preserving the equilibrium between extracellular matrix (ECM) synthesis and degradation in NPCs. This effect was achieved through the suppression of NLRP3 inflammasome expression and the prevention of pyroptosis in NPCs.

Establishment of an animal model of adjacent segment degeneration after interbody fusion and related experimental studies

BACKGROUND

Degenerative spine conditions are common and frequent clinical diseases, and adjacent segment disease (ASD) after spinal fusion (SF) is a common complication after spinal fusion (SF). In this study, we established an animal model of ASD after interbody fusion to observe the morphologic changes of adjacent segment (AS) disks and to determine the expression and significance of tumor necrosis factor-alpha (TNF-α) and interleukin-1beta (IL-1β) in ASD tissues to provide a good experimental basis and reference for clinical prevention and treatment of ASD after interbody fusion.

METHODS

Thirty-six male and female New Zealand rabbits weighing 2.0-2.5 kg were randomly divided into control group (group A) and experimental groups (groups B, C, and D), with 9 rabbits in each group, of which groups B, C, and D were the 4-, 8-, and 12-week groups, respectively. Autologous iliac bone grafts were used as the bone graft material. In the experimental groups, a SF was performed on the C2-C3 intervertebral space. The C3-4 adjacent segments were examined. In the experimental group, the animals were subjected to gross observation, X-ray examination, hand touch inspection, and micro-computed tomography (micro-CT) 4, 8, and 12 weeks after surgery. The micromorphologic changes of the cervical disks in the segments of the control group and experimental groups were observed under light microscopy. Immunohistochemistry and Western blotting were used to detect the expression of TNF-α and IL-1β in the AS tissues after interbody fusion in the control and experimental groups.

RESULTS

The measurement data of the rabbit cervical spine bony structures indicated that the length of the vertebral body and the sagittal diameter of the lower end of the vertebral body decreased gradually from the 2nd-6th cervical vertebrae, and the difference was statistically significant (P < 0.05). The difference in the transverse diameter of the lower end of the vertebral body was not statistically significant (P > 0.05), the change in the oblique diameter of the lower end of the vertebral body fluctuated, and the difference was statistically significant (P < 0.05). The fusion rate of the cervical spine by hand touch inspection was 22.2% (2/9), 55.6% (5/9), and 88.9% (8/9) in groups B, C, and D, respectively. The differences in bone volume-to-total volume (BV/TV) and X-ray scores were statistically significant in groups B, C, and D (P < 0.05). Significant degeneration occurred in groups B, C, and D compared with group A. The expression of TNF-α and IL-1β in the intervertebral disk tissue was significantly higher in groups B, C, and D compared with group A (P < 0.05), and increased with time.

CONCLUSION

In this study, an animal model of ASD after interbody fusion fixation in rabbits was successfully established. Postoperative imaging and hand touch inspection showed a positive correlation between the amount of new intervertebral bone and the degree of fusion with time. The results of immunohistochemistry and Western blot showed that TNF-α and IL-1β were highly expressed in the AS tissues of the experimental group after interbody fusion, and the degree of disk degeneration was positively correlated with the time after interbody fusion.

IL-1β-mediated inflammatory responses in intervertebral disc degeneration: Mechanisms, signaling pathways, and therapeutic potential

Intervertebral disc degeneration (IDD) has been widely recognized as the primary cause of low back pain and is one of the major chronic diseases imposing a severe socioeconomic burden worldwide. IDD is a degenerative process characterized by inflammatory responses, and its underlying pathological mechanisms remain complex. Genetic, developmental, biochemical, and biomechanical factors contribute to the development of IDD. There is a pressing need for an effective non-surgical treatment, mainly due to the lack of comprehensive understanding of the specific mechanisms involved and the effective therapeutic targets for IDD. Recently, interleukin (IL)-1β has been recognized as an essential inflammatory factor and a key mediator of the inflammatory process in IDD. Current studies have found that IL-1β is mainly involved in IDD by affecting the metabolism of the extracellular matrix and regulating cell death (RCD), such as apoptosis, pyroptosis, and ferroptosis (a new form of RCD). Although analysis of clinical samples from different laboratories confirmed how IL-1β is induced in IDD, its specific signal transduction pathway, and the inflammatory role mediated in IDD remains unclear. This review describes the molecules and mechanisms involved in IL-1β-mediated inflammatory responses, and their roles in resolving the inflammatory process in IDD. Understanding the signaling pathways involved in IL-1β may lead to a new class of targets that promote remission for IDD patients. This review aims to provide a framework for the treatment of IDD by analyzing the signaling mechanism and function related to IL-1β, especially in terms of inflammation, matrix metabolism, and cell death regulation.

Intervertebral disc degeneration and inflammatory microenvironment: expression, pathology, and therapeutic strategies

BACKGROUND

Intervertebral disc degeneration (IDD) is a leading cause of low back pain (LBP), posing a significant socioeconomic burden. Recent studies highlight the crucial role of inflammatory microenvironment in IDD progression.

METHOD

A keyword-based search was performed using the PubMed database for published articles.

RESULTS AND CONCLUSIONS

Dysregulated expression of inflammatory cytokines disrupts intervertebral disc (IVD) homeostasis, causing atrophy, fibrosis, and phenotypic changes in nucleus pulposus cells. Modulating the inflammatory microenvironment and restoring cytokine balance hold promise for IVD repair and regeneration. This comprehensive review systematically examines the expression regulation, pathological effects, therapeutic strategies, and future challenges associated with the inflammatory microenvironment and relevant cytokines in IDD. Key inflammatory cytokines, including interleukins (IL), tumor necrosis factor-alpha (TNF-α), and chemokines, exhibit significant pathological effects in IDD. Furthermore, major therapeutic modalities such as chemical antagonists, biologics, plant extracts, and gene transcription therapies are introduced to control and ameliorate the inflammatory microenvironment. These approaches provide valuable insights for identifying potential targets in future anti-inflammatory treatments for IDD.

Development and Degeneration of the Intervertebral Disc-Insights from Across Species

Back pain caused by intervertebral disc (IVD) degeneration has a major socio-economic impact in humans, yet historically has received minimal attention in species other than humans, mice and dogs. However, a general growing interest in this unique organ prompted the expansion of IVD research in rats, rabbits, cats, horses, monkeys, and cows, further illuminating the complex nature of the organ in both healthy and degenerative states. Application of recent biotechnological advancements, including single cell RNA sequencing and complex data analysis methods has begun to explain the shifting inflammatory signaling, variation in cellular subpopulations, differential gene expression, mechanical loading, and metabolic stresses which contribute to age and stress related degeneration of the IVD. This increase in IVD research across species introduces a need for chronicling IVD advancements and tissue biomarkers both within and between species. Here we provide a comprehensive review of recent single cell RNA sequencing data alongside existing case reports and histo/morphological data to highlight the cellular complexity and metabolic challenges of this unique organ that is of structural importance for all vertebrates.

A review of Duhuo Jisheng decoction mechanisms in intervertebral disc degeneration in vitro and animal studies

Intervertebral disc degeneration (IVDD) has become a serious public health problem, placing a heavy burden on society and the healthcare system. Its pathogenesis is not completely clear and may be closely related to mechanical damage, inflammatory factors, oxidative stress and death of nucleus pulposus cells (NPCs). The treatment of IVDD mainly includes conservative treatment and surgery. Conservative treatment is based on hormonal and anti-inflammatory drugs and massage techniques, which can relieve the pain symptoms to a certain extent, but cannot solve the problem from the root cause. Surgical treatment is mainly by removing the herniated nucleus pulposus, but it is more traumatic for IVDD patients, expensive and not suitable for all patients. Therefore, it is extremely important to clarify the pathogenesis of IVDD, to find an effective and convenient treatment and to further elaborate its mechanism of action. The effectiveness of traditional Chinese medicine in the treatment of IVDD has been well demonstrated in clinical medical research. We have been working on the Chinese herbal formula Duhuo Jisheng Decoction, which is a common formula for the treatment of degenerative disc disease. Not only does it have significant clinical effects, but it also has few adverse effects. At present, we found that its mechanism of action mainly involves regulation of inflammatory factors, reduction of apoptosis and pyroptosis of NPCs, inhibition of extracellular matrix degradation, improvement of intestinal flora, etc. However, a few relevant articles have yet comprehensively and systematically summarized the mechanisms by which they exert their effect. Therefore, this paper will comprehensively and systematically explain on it. This is of great clinical significance and social value for elucidating the pathogenesis of IVDD and improving the symptoms of patients, and will provide a theoretical basis and scientific basis for the treatment of IVDD with traditional Chinese medicine.

Ginkgetin Alleviates Intervertebral Disc Degeneration by Inhibiting Apoptosis, Inflammation, and Disturbance of Extracellular Matrix Synthesis and Catabolism via Inactivation of NLRP3 Inflammasome

BACKGROUND

Apoptosis, inflammation, and the extracellular matrix (ECM) synthesis and catabolism are compromised with intervertebral disc degeneration (IDD). Ginkgetin (GK) has been demonstrated to alleviate several diseases; however, its effect on IDD remains unknown.

METHODS

The nucleus pulposus cells (NPCs) were stimulated with interleukin (IL)-1β to construct the IDD models in vitro. Rats were used for the construction of the IDD models in vivo via the fibrous ring puncture method. The effect and mechanism of GK on IDD were determined by cell counting kit-8 (CCK-8), flow cytometry, western blot, real-time quantitative polymerase chain reaction (RT-qPCR), enzyme‑linked immunosorbent assay (ELISA), hematoxylin and eosin (HE) and safranine O staining, and immunohistochemistry (IHC) assays, respectively.

RESULTS

GK increased the cell viability and upregulated the expressions of anti-apoptosis and ECM synthesis markers in NPCs treated with IL-1β. GK also decreased apoptosis rate, and downregulated the expressions of proteins related to pro-apoptosis, ECM catabolism, and inflammation in vitro. Mechanically, GK reduced the expression of nucleotide binding oligomeric domain like receptor protein 3 (NLRP3) inflammasome-related proteins. Overexpression of NLRP3 reversed the effect of GK on the proliferation, apoptosis, inflammation, and ECM degradation in IL-1β-induced NPCs. Moreover, GK attenuated the pathological manifestations, inflammation, ECM degradation, and NLRP3 inflammasome expression in IDD rats.

CONCLUSION

GK suppressed apoptosis, inflammation, and ECM degradation to alleviate IDD via the inactivation of NLRP3 inflammasome.

Human Embryonic Stem-Cell-Derived Exosomes Repress NLRP3 Inflammasome to Alleviate Pyroptosis in Nucleus Pulposus Cells by Transmitting miR-302c

Recent studies have shown that the NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome is extensively activated in the process of intervertebral disc degeneration (IVDD), leading to the pyroptosis of nucleus pulposus cells (NPCs) and the exacerbation of the pathological development of the intervertebral disc (IVD). Exosomes derived from human embryonic stem cells (hESCs-exo) have shown great therapeutic potential in degenerative diseases. We hypothesized that hESCs-exo could alleviate IVDD by downregulating NLRP3. We measured the NLRP3 protein levels in different grades of IVDD and the effect of hESCs-exo on the H₂O₂-induced pyroptosis of NPCs. Our results indicate that the expression of NLRP3 was upregulated with the increase in IVD degeneration. hESCs-exo were able to reduce the H₂O₂-mediated pyroptosis of NPCs by downregulating the expression levels of NLRP3 inflammasome-related genes. Bioinformatics software predicted that miR-302c, an embryonic stem-cell-specific RNA, can inhibit NLRP3, thereby alleviating the pyroptosis of NPCs, and this was further verified by the overexpression of miR-302c in NPCs. In vivo experiments confirmed the above results in a rat caudal IVDD model. Our study demonstrates that hESCs-exo could inhibit excessive NPC pyroptosis by downregulating the NLRP3 inflammasome during IVDD, and miR-302c may play a key role in this process.

The mechanisms and functions of TNF-α in intervertebral disc degeneration

Low back pain (LBP) is one of the most common health problems in people's lives, which brings a massive burden to clinicians, and the leading cause of LBP is intervertebral disc degeneration (IDD). IDD is mainly caused by factors such as aging, mechanical stress, and lack of nutrition. The pathological mechanism of IDD is very complex, involving inflammatory response, cell metabolism disorder, and so on. Unfortunately, in the current treatment of IDD, only relieving symptoms as the primary means of relieving a patient's pain cannot effectively inhibit or reverse the progression of IDD. Tumor necrosis factor-α (TNF-α) is a multifunctional pro-inflammatory factor involved in many diseases' pathological processes. With the in-depth study of the pathological mechanism of IDD, more and more evidence has shown that TNF-α is an essential activator of IDD, which is related to the metabolic disorder, inflammatory responses, apoptosis, and other pathological processes of extracellular dissociation in the intervertebral disc. Therefore, anti-TNF-α therapy is an effective therapeutic target for alleviating IDD, especially in inhibiting extracellular matrix degradation and reducing inflammatory responses. This article reviews the pathological role of TNF-α in IDD and the latest research progress of TNF-α inhibitors in treating IDD.

An Injectable Engineered Cartilage Gel Improves Intervertebral Disc Repair in a Rat Nucleotomy Model

Lower back pain is a major problem caused by intervertebral disc degeneration. A common surgical procedure is lumbar partial discectomy (excision of the herniated disc causing nerve root compression), which results in further disc degeneration, severe lower back pain, and disability after discectomy. Thus, the development of disc regenerative therapies for patients who require lumbar partial discectomy is crucial. Here, we investigated the effectiveness of an engineered cartilage gel utilizing human fetal cartilage-derived progenitor cells (hFCPCs) on intervertebral disc repair in a rat tail nucleotomy model. Eight-week-old female Sprague-Dawley rats were randomized into three groups to undergo intradiscal injection of (1) cartilage gel, (2) hFCPCs, or (3) decellularized extracellular matrix (ECM) (n = 10/each group). The treatment materials were injected immediately after nucleotomy of the coccygeal discs. The coccygeal discs were removed six weeks after implantation for radiologic and histological analysis. Implantation of the cartilage gel promoted degenerative disc repair compared to hFCPCs or hFCPC-derived ECM by increasing the cellularity and matrix integrity, promoting reconstruction of nucleus pulposus, restoring disc hydration, and downregulating inflammatory cytokines and pain. Our results demonstrate that cartilage gel has higher therapeutic potential than its cellular or ECM component alone, and support further translation to large animal models and human subjects.

Macrophages and Intervertebral Disc Degeneration

The intervertebral disc (IVD) aids in motion and acts to absorb energy transmitted to the spine. With little inherent regenerative capacity, degeneration of the intervertebral disc results in intervertebral disc disease, which contributes to low back pain and significant disability in many individuals. Increasing evidence suggests that IVD degeneration is a disease of the whole joint that is associated with significant inflammation. Moreover, studies show elevated macrophage accumulation within the IVD with increasing levels of disease severity; however, we still need to understand the roles, be they causative or consequential, of macrophages during the degenerative process. In this narrative review, we discuss hallmarks of IVD degeneration, showcase evidence of macrophage involvement during disc degeneration, and explore burgeoning research aimed at understanding the molecular pathways regulating macrophage functions during intervertebral disc degeneration.

Natural products can modulate inflammation in intervertebral disc degeneration

Intervertebral discs (IVDs) play a crucial role in maintaining normal vertebral anatomy as well as mobile function. Intervertebral disc degeneration (IDD) is a common clinical symptom and is an important cause of low back pain (LBP). IDD is initially considered to be associated with aging and abnormal mechanical loads. However, over recent years, researchers have discovered that IDD is caused by a variety of mechanisms, including persistent inflammation, functional cell loss, accelerated extracellular matrix decomposition, the imbalance of functional components, and genetic metabolic disorders. Of these, inflammation is thought to interact with other mechanisms and is closely associated with the production of pain. Considering the key role of inflammation in IDD, the modulation of inflammation provides us with new options for mitigating the progression of degeneration and may even cause reversal. Many natural substances possess anti-inflammatory functions. Due to the wide availability of such substances, it is important that we screen and identify natural agents that are capable of regulating IVD inflammation. In fact, many studies have demonstrated the potential clinical application of natural substances for the regulation of inflammation in IDD; some of these have been proven to have excellent biosafety. In this review, we summarize the mechanisms and interactions that are responsible for inflammation in IDD and review the application of natural products for the modulation of degenerative disc inflammation.

Regulatory Effect of Inflammatory Mediators in Intervertebral Disc Degeneration

Intervertebral disc degeneration (IDD) is a major contributor to back, neck, and radicular pain. It is related to changes in tissue structure and function, including the breakdown of the extracellular matrix (ECM), aging, apoptosis of the nucleus pulposus, and biomechanical tissue impairment. Recently, an increasing number of studies have demonstrated that inflammatory mediators play a crucial role in IDD, and they are being explored as potential treatment targets for IDD and associated disorders. For example, interleukins (IL), tumour necrosis factor-α (TNF-α), chemokines, and inflammasomes have all been linked to the pathophysiology of IDD. These inflammatory mediators are found in high concentrations in intervertebral disc (IVD) tissues and cells and are associated with the severity of LBP and IDD. It is feasible to reduce the production of these proinflammatory mediators and develop a novel therapy for IDD, which will be a hotspot of future research. In this review, the effects of inflammatory mediators in IDD were described.

Maltol ameliorates intervertebral disc degeneration through inhibiting PI3K/AKT/NF-κB pathway and regulating NLRP3 inflammasome-mediated pyroptosis

OBJECTIVES

As one of the major causes of low back pain, intervertebral disc degeneration (IDD) has caused a huge problem for humans. Increasing evidence indicates that NLRP3 inflammasome-mediated pyroptosis of NP cells displays an important role in the progression of IDD. Maltol (MA) is a flavoring agent extracted from red ginseng. Due to its anti-inflammatory and antioxidant effects, MA has been widely considered by researchers. Therefore, we hypothesized that MA may be a potential IVD protective agent by regulating NP cells and their surrounding microenvironment.

METHODS

In vitro, qRT-PCR, and Western blot were used to explore the effect of MA on the transcription and protein expression of the anabolic protein (ADAMTS5, MMP3, MMP9) catabolic protein (Aggrecan), and pro-inflammatory factor (iNOS COX-2). Next, the effects of MA on PI3K/AKT/NF-κB pathway and pyroptosis pathway were analyzed by Western blot and immunofluorescence. Molecular docking was used to investigate the relationship between PI3K and MA. Moreover, ELISA was also used to detect the effects of MA on inflammatory factors (TNF-α, PGE2, IL-1β, and IL-18). In vivo, the effects of MA on the vertebral structure of IDD mice were studied by HE and SO staining and the effects of MA on ECM and PI3K/AKT/NF-κB and pyroptosis pathway of IDD mice were studied by immunohistochemical staining.

RESULTS

MA can ameliorate intervertebral disc degeneration in vivo and in vitro. Specifically, the molecular docking results showed that the binding degree of MA and PI3K was significant. Second, in vitro studies showed that MA inhibited the degradation of ECM and inflammatory response by inhibiting the PI3K/AKT/NF-κB pathway and the pyroptosis mediated by NLRP3 inflammasome, which increased the expression of anabolic proteins, decreased the expression of catabolic proteins, and decreased the secretion of inflammatory mediators such as IL-18 and IL-1β. In addition, according to the study results of the mouse lumbar instability model, MA also improved the tissue disorder and degradation of the intervertebral disc, reduced the loss of proteoglycan and glycosaminoglycan, and inhibited intervertebral disc inflammation, indicating that MA has a protective effect on the intervertebral disc to intervertebral disc in mice.

CONCLUSIONS

Our results suggest that MA slowed IDD development through the PI3K/AKT/NF-κB signaling pathway and NLRP3 inflammasome-mediated pyroptosis, indicating that MA appeared to be a viable medication for IDD treatment.

A20 ameliorates disc degeneration by suppressing mTOR/BNIP3 axis-mediated mitophagy

BACKGROUND

The pathological mechanism of intervertebral disc degeneration (IDD) is an unanswered question that we are committed to exploring. A20 is an anti-inflammatory protein of nucleus pulposus (NP) cells and plays a protective role in intervertebral disc degeneration.

OBJECTIVE

This study aims to investigate the molecular mechanism by which A20 attenuates disc degeneration.

METHODS

The proteins of interest were measured by immunoblotting, immunofluorescence, ELISA assay, and immunohistochemical technique to conduct related experiments. Immunofluorescence assays and mitochondrial membrane potential (JC-1) were used to assess mitophagy and mitochondrial fitness, respectively.

RESULTS

Here, we demonstrated that A20 promoted mitophagy, attenuated pyroptosis, and inhibited the degradation of the extracellular matrix, consequently significantly ameliorating disc degeneration. Mechanistically, A20 reduces pyroptosis and further suppresses cellular mTOR activity. On the one hand, A20-induced mTOR inhibition triggers BNIP3-mediated mitophagy to ensure mitochondrial fitness under LPS stimulation, as a result of mitigating mitochondrial dysfunction induced by LPS. On the other hand, A20-induced mTOR inhibition reduces the loss of mitochondrial membrane potential and the generation of Mitochondrial ROS.

CONCLUSION

The study revealed that A20 promotes BNIP3-mediated mitophagy by suppressing mTOR pathway activation against LPS-induced pyroptosis.

The regulatory role and therapeutic application of pyroptosis in musculoskeletal diseases

Pyroptosis is a controlled form of inflammatory cell death characterized by inflammasome activation, pore formation, and cell lysis. According to different caspases, pyroptosis can be divided into canonical, non-canonical, and other pathways. The role of pyroptosis in disease development has been paid more attention in recent years. The trigger factors of pyroptosis are often related to oxidative stress and proinflammatory substances, which coincide with the pathological mechanism of some diseases. Pyroptosis directly leads to cell lysis and death, and the release of cytosolic components and proinflammatory cytokines affects cell activity and amplifies the inflammatory response. All the above are involved in a series of basic pathological processes, such as matrix degradation, fibrosis, and angiogenesis. Since these pathological changes are also common in musculoskeletal diseases (MSDs), emerging studies have focused on the correlations between pyroptosis and MSDs in recent years. In this review, we first summarized the molecular mechanism of pyroptosis and extensively discussed the differences and crosstalk between pyroptosis, apoptosis, and necrosis. Next, we elaborated on the role of pyroptosis in some MSDs, including osteoarthritis, rheumatoid arthritis, osteoporosis, gout arthritis, ankylosing spondylitis, intervertebral disc degeneration, and several muscle disorders. The regulation of pyroptosis could offer potential therapeutic targets in MSDs treatment. Herein, the existing drugs and therapeutic strategies that directly or indirectly target pyroptosis pathway components have been discussed in order to shed light on the novel treatment for MSDs.

Role of Pyroptosis in Intervertebral Disc Degeneration and Its Therapeutic Implications

Intervertebral disc degeneration (IDD), a progressive and multifactorial pathological process, is predominantly associated with low back pain and permanent disability. Pyroptosis is a type of lytic programmed cell death triggered by the activation of inflammasomes and caspases. Unlike apoptosis, pyroptosis is characterized by the rupture of the plasma membrane and the release of inflammatory mediators, accelerating the destruction of the extracellular matrix (ECM). Recent studies have shown that pyrin domain-containing 3 (NLRP3) inflammasome-mediated pyroptosis in nucleus pulposus (NP) cells is activated in the progression of IDD. Furthermore, targeting pyroptosis in IDD demonstrates the excellent capacity of ECM remodeling and its anti-inflammatory properties, suggesting that pyroptosis is involved in the IDD process. In this review, we briefly summarize the molecular mechanism of pyroptosis and the pathogenesis of IDD. We also focus on the role of pyroptosis in the pathological progress of IDD and its targeted therapeutic application.

Neuropeptide Y and receptors are associated with the pyroptosis of nucleus pulposus in aging and degenerative intervertebral discs of rats

The neuropeptide Y(NPY) mediates bone metabolism and the degradation of cartilage in the peripheral nervous system. However, its role in the intervertebral disc degeneration (IDD) is less clear and warrant further study. The process of IDD has always been accompanied by inflammatory response and pyroptosis of nucleus pulposus cells (NPCs). The aim of this study was to investigate the relationship between NPY, Y1R, Y2R and pyroptosis in aging and degenerative discs and the direct effect of NPY on NPCs. First, we have assessed NPY, Y1R, Y2R and the expression of pyroptosis related protein in the immature (6 weeks), mature (16 weeks), aged (54 weeks), and degenerated discs. As part of our studies, we also have evaluated pyroptotic changes in the NPCs, induced by exposure to NPY. Our results suggested that compared with natural aging discs, the degenerative discs showed the high expression of NPY, Y1R and Y2R. Correlation analysis showed that the level of NPY and Y1R in degenerative discs were positively correlated with GSDMD, whereas there was no significant correlation between Y2R and GSDMD. In vitro, NPY treatment stimulated the activation of caspase-1-dependent pyroptosis of NPCs. However, Y1R antagonist inhibited NPY-induced pyroptosis of NPCs. Western blot confirmed that Y1R antagonist decreased the level of cleaved.GSDMD and caspase-1 in NPCs. In conclusion, our results indicated that compared with natural aging discs, the degenerated discs showed the high expression of NPY, Y1R and Y2R. NPY-Y1R involve the IDD development by the regulation of pyroptosis in the NPCs. Regulating the function of NPY may be a promising strategy for IDD treatment.

USP14 promotes pyroptosis of human annulus fibrosus cells derived from patients with intervertebral disc degeneration through deubiquitination of NLRP3

Intervertebral disc degeneration (IVDD) is a general disorder that results in low back pain and disability among many affected individuals. However, the current treatments for IVDD are limited to relieving the symptoms but do not solve the fundamental issue. In this study, the role of USP14 in mediating the activation of the NLRP3 inflammasome and the pyroptosis of AF cells from IVDD patients is determined in vitro, and gain- and loss-of-function assays of USP14 and the NLRP3 inflammasome are conducted. Pyroptosis of AF cells is detected by flow cytometry. The inflammatory cytokines (IL-1β and IL-18) and protein levels of NLRP3, active Caspase-1, Aggrecan, MMP3 and ADAMTS-5 are determined by ELISA and western blot analysis, respectively. The correlation between USP14 and NLRP3 is measured by coimmunoprecipitation and ubiquitination analysis. Upregulation of USP14 is accompanied by increased level of the NLRP3 inflammasome in AF cells from IVDD patients; furthermore, a positive correlation between them is observed. USP14 knockdown inhibits pyroptosis in AF cells by inducing ubiquitination of NLRP3, while overexpression of USP14 has the opposite effect, which is inhibited by the NLRP3 inflammasome inhibitor INF39. USP14 exerts its positive regulatory effect on AF cell pyroptosis by modulating the NLRP3/Caspase-1/IL-1β and IL-18 signaling axes.

Pyroptosis and Intervertebral Disc Degeneration: Mechanistic Insights and Therapeutic Implications

Low back pain (LBP) is a common problem worldwide, resulting in great patient suffering and great challenges for the social health system. Intervertebral disc (IVD) degeneration (IVDD) is widely acknowledged as one of the key causes of LBP. Accumulating evidence suggests that aberrant pyroptosis of IVD cells is involved in the pathogenesis of IVDD progression, however, the comprehensive roles of pyroptosis in IVDD have not been fully established, leaving attempts to treat IVDD with anti-pyroptosis approaches questionable. In this review, we summarize the characteristics of pyroptosis and emphasize the effects of IVD cell pyroptosis on the pathological progression of IVDD, including secretion of cytokines, nucleus pulposus cell apoptosis and autophagy, accelerated extracellular matrix degradation, annulus fibrosus rupture, cartilage endplate calcification, vascularization, sensory and sympathetic fiber neoinnervation, and infiltrating lymphatic vessels. Finally, we discuss several interventions used to treat IVDD by targeting pyroptosis. This review provides novel insights into the crucial role of IVD cell pyroptosis in IVDD pathogenesis, and could be informative for developing novel therapeutic approaches for IVDD and LBP.

Hydrogel-Embedded Poly(Lactic-co-Glycolic Acid) Microspheres for the Delivery of hMSC-Derived Exosomes to Promote Bioactive Annulus Fibrosus Repair

OBJECTIVE

Intervertebral disk degeneration is a prevalent postoperative complication after discectomy, underscoring the need to develop preventative and bioactive treatment strategies that decelerate degeneration and seal annulus fibrosus (AF) defects. Human mesenchymal stem cell-derived exosomes (MSC-Exos) hold promise for cell-free bioactive repair; however, their ability to promote AF repair is poorly understood. The objective of this study was to evaluate the ability of MSC-Exos to promote endogenous AF repair processes and integrate MSC-Exos within a biomaterial delivery system.

DESIGN

We characterize biophysical and biochemical properties of normoxic (Nx) and hypoxic (Hx) preconditioned MSC-Exos from young, healthy donors and examine their effects on AF cell proliferation, migration, and gene expression. We then integrate a poly(lactic-co-glycolic acid) microsphere (PLGA µSphere) delivery platform within an interpenetrating network hydrogel to facilitate sustained MSC-Exo delivery.

RESULTS

Hx MSC-Exos led to a more robust response in AF cell proliferation and migration than Nx MSC-Exos and was selected for a downstream protection experiment. Hx MSC-Exos maintained a healthy AF cell phenotype under a TNFα challenge in vitro and attenuated catabolic responses. In all functional assays, AF cell responses were more sensitive to Hx MSC-Exos than Nx MSC-Exos. PLGA µSpheres released MSC-Exos over a clinically relevant timescale without affecting hydrogel modulus or pH upon initial embedment and µSphere degradation.

CONCLUSIONS

This MSC-Exo treatment strategy may offer benefits of stem cell therapy without the need for exogenous stem cell transplantation by stimulating cell proliferation, promoting cell migration, and protecting cells from the degenerative proinflammatory microenvironment.

Role of Caspase Family in Intervertebral Disc Degeneration and Its Therapeutic Prospects

Intervertebral disc degeneration (IVDD) is a common musculoskeletal degenerative disease worldwide, of which the main clinical manifestation is low back pain (LBP); approximately, 80% of people suffer from it in their lifetime. Currently, the pathogenesis of IVDD is unclear, and modern treatments can only alleviate its symptoms but cannot inhibit or reverse its progression. However, in recent years, targeted therapy has led to new therapeutic strategies. Cysteine-containing aspartate proteolytic enzymes (caspases) are a family of proteases present in the cytoplasm. They are evolutionarily conserved and are involved in cell growth, differentiation, and apoptotic death of eukaryotic cells. In recent years, it has been confirmed to be involved in the pathogenesis of various diseases, mainly by regulating cell apoptosis and inflammatory response. With continuous research on the pathogenesis and pathological process of IVDD, an increasing number of studies have shown that caspases are closely related to the IVDD process, especially in the intervertebral disc (IVD) cell apoptosis and inflammatory response. Therefore, herein we study the role of caspases in IVDD with respect to the structure of caspases and the related signaling pathways involved. This would help explore the strategy of regulating the activity of the caspases involved and develop caspase inhibitors to prevent and treat IVDD. The aim of this review was to identify the caspases involved in IVDD which could be potential targets for the treatment of IVDD.

Intervertebral disc cell chondroptosis elicits neutrophil response in Staphylococcus aureus spondylodiscitis

To understand the pathophysiology of spondylodiscitis due to Staphylococcus aureus, an emerging infectious disease of the intervertebral disc (IVD) and vertebral body with a high complication rate, we combined clinical insights and experimental approaches. Clinical data and histological material of nine patients suffering from S. aureus spondylodiscitis were retrospectively collected at a single center. To mirror the clinical findings experimentally, we developed a novel porcine ex vivo model mimicking acute S. aureus spondylodiscitis and assessed the interaction between S. aureus and IVD cells within their native environment. In addition, the inflammatory features underlying this interaction were assessed in primary human IVD cells. Finally, mirroring the clinical findings, we assessed primary human neutrophils for their ability to respond to secreted inflammatory modulators of IVD cells upon the S. aureus challenge. Acute S. aureus spondylodiscitis in patients was characterized by tissue necrosis and neutrophil infiltration. Additionally, the presence of empty IVD cells’ lacunae was observed. This was mirrored in the ex vivo porcine model, where S. aureus induced extensive IVD cell death, leading to empty lacunae. Concomitant engagement of the apoptotic and pyroptotic cell death pathways was observed in primary human IVD cells, resulting in cytokine release. Among the released cytokines, functionally intact neutrophil-priming as well as broad pro- and anti-inflammatory cytokines which are known for their involvement in IVD degeneration were found. In patients as well as ex vivo in a novel porcine model, S. aureus IVD infection caused IVD cell death, resulting in empty lacunae, which was accompanied by the release of inflammatory markers and recruitment of neutrophils. These findings offer valuable insights into the important role of inflammatory IVD cell death during spondylodiscitis and potential future therapeutic approaches.

Mechanical Stretch-Induced NLRP3 Inflammasome Expression on Human Annulus Fibrosus Cells Modulated by Endoplasmic Reticulum Stress

Excessive mechanical loading is a major cause of spinal degeneration, typically originating from a tear in the annulus fibrosus (AF). Endoplasmic reticulum (ER) stress and NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome have been implicated in the pathogenesis of intervertebral disc (IVD) degeneration. However, the causal relationship between the mechanical stretching of AF cells and the NLRP3 inflammasome response associated with ER stress remains scarce. To elucidate the pathogenesis and regulatory mechanisms of mechanical stretch-induced IVD degeneration, human AF cell lines were subjected to different degrees of cyclic stretching to simulate daily spinal movements. Our results indicated that 15% high cyclic stretch (HCS) induced the expression of NLRP3 and interleukin-1 beta (IL-1β) and was also responsible for the increased expression of NADPH (nicotinamide adenine dinucleotide phosphate) oxidase 2 (NOX2) and reactive oxygen species (ROS) in human AF cells. In addition, HCS increased the expression of glucose-regulated protein 78 (GRP78), an ER stress chaperone, which was neutralized with tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor. In addition, HCS was found to induce thioredoxin-interacting protein (TXNIP) expression and NLRP3 inflammasome activation, which can be suppressed by si-NOX2 or the NOX2 inhibitor GSK2795039. Consequently, HCS upregulated ER stress and ROS production, leading to increased NLRP3 and IL-1β expression in human AF cells, and may further accelerate IVD degeneration.

Adipokine human Resistin promotes obesity-associated inflammatory intervertebral disc degeneration via pro-inflammatory cytokine cascade activation

Adipokine human Resistin (hResistin), is known to be associated with insulin resistance and secrete low-grade pro-inflammatory cytokines in obesity. Although studies on low-grade inflammation of adipokine hResistin are known, studies on the effects and mechanisms of intervertebral disc degeneration (IVDD) are still lacking. Thus, we investigated the adipokine hResistin with or without pro-inflammatory cytokine IL-1β in intervertebral disc (IVD) cells such as human annulus fibrosus (hAF) and nucleus pulposus (hNP). The protein expression changes in IL-1β, IL-6, IL-8, MMP-1, MMP-3, and MMP-13, induced by the combined-hResistin and IL-1β stimulation on hAF cells, was significantly greater than that of the same induced by mono-IL-1β stimulation. Similarly, in the case of the protein expression change of inflammatory mediators induced by the combined-hResistin and IL-1β stimulation on hNP cells was also significantly greater than that of the same induced by mono-IL-1β stimulation. These results improve understanding of hResistin on inflammatory IVDD but also with other obesity-related inflammatory diseases.

Treatment of Intervertebral Disc Degeneration

Intervertebral disc degeneration (IDD) causes a variety of signs and symptoms, such as low back pain (LBP), intervertebral disc herniation, and spinal stenosis, which contribute to high social and economic costs. IDD results from many factors, including genetic factors, aging, mechanical injury, malnutrition, and so on. The pathological changes of IDD are mainly composed of the senescence and apoptosis of nucleus pulposus cells (NPCs), the progressive degeneration of extracellular matrix (ECM), the fibrosis of annulus fibrosus (AF), and the inflammatory response. At present, IDD can be treated by conservative treatment and surgical treatment based on patients' symptoms. However, all of these can only release the pain but cannot reverse IDD and reconstruct the mechanical function of the spine. The latest research is moving towards the field of biotherapy. Mesenchymal stem cells (MSCs) are regard as the potential therapy of IDD because of their ability to self-renew and differentiate into a variety of tissues. Moreover, the non-coding RNAs (ncRNAs) are found to regulate many vital processes in IDD. There have been many successes in the in vitro and animal studies of using biotherapy to treat IDD, but how to transform the experimental data to real therapy which can apply to humans is still a challenge. This article mainly reviews the treatment strategies and research progress of IDD and indicates that there are many problems that need to be solved if the new biotherapy is to be applied to clinical treatment of IDD. This will provide reference and guidance for clinical treatment and research direction of IDD.

MFG-E8 alleviates intervertebral disc degeneration by suppressing pyroptosis and extracellular matrix degradation in nucleus pulposus cells via Nrf2/TXNIP/NLRP3 axis

Intervertebral disc degeneration (IVDD) is a chronic age-related degenerative disease accompanied by complex pathophysiological mechanisms. Increasing evidence indicates that NLRP3 inflammasome mediated pyroptosis of nucleus pulposus (NP) cells displays an important role in the pathological progression of IVDD. Milk fat globule-EGF factor-8 (MFG-E8) is an endogenously secreted glycoprotein with beneficial effects of anti-inflammatory, antioxidant, and modulation of NLRP3 inflammasome. However, the effect of MFG-E8 on IVDD remains unclear. In this study, our purpose is to clarify the expression changes of MFG-E8 in the IVDD process and explore the role and mechanism of MFG-E8. We found that MFG-E8's expression was reduced in degraded nucleus pulposus tissues of humans and rats as well as hydrogen peroxide (H2O2)-treated NP cells. Exogenous supplementation of MFG-E8 could rescue H2O2-induced oxidative stress, mitochondrial dysfunction, and NLRP3 inflammasome activation and protect NP cells from pyroptosis and extracellular matrix (ECM) degradation. Mechanistically, Nrf2/TXNIP/NLRP3 axis plays a crucial role in MFG-E8-mediated suppression of the above-pathological events. In vivo, we established a rat intervertebral disc acupuncture model and found that MFG-E8 administration effectively alleviated IVDD development by imageological and histomorphological evaluation. Overall, our findings revealed the internal mechanisms underlying MFG-E8 regulation in NP cells and its intrinsic value for IVDD therapy.

Pyroptosis and Sarcopenia: Frontier Perspective of Disease Mechanism

With global ageing, sarcopenia, as an age-related disease, has brought a heavy burden to individuals and society. Increasing attention has been given to further exploring the morbidity mechanism and intervention measures for sarcopenia. Pyroptosis, also known as cellular inflammatory necrosis, is a kind of regulated cell death that plays a role in the ageing progress at the cellular level. It is closely related to age-related diseases such as cardiovascular diseases, Alzheimer’s disease, osteoarthritis, and sarcopenia. In the process of ageing, aggravated oxidative stress and poor skeletal muscle perfusion in ageing muscle tissues can activate the nod-like receptor (NLRP) family to trigger pyroptosis. Chronic inflammation is a representative characteristic of ageing. The levels of inflammatory factors such as TNF-α may activate the signaling pathways of pyroptosis by the NF-κB-GSDMD axis, which remains to be further studied. Autophagy is a protective mechanism in maintaining the integrity of intracellular organelles and the survival of cells in adverse conditions. The autophagy of skeletal muscle cells can inhibit the activation of the pyroptosis pathway to some extent. A profound understanding of the mechanism of pyroptosis in sarcopenia may help to identify new therapeutic targets in the future. This review article focuses on the role of pyroptosis in the development and progression of sarcopenia.

VEGF mitigates bisphosphonate-induced apoptosis and differentiation inhibition of MC3T3-E1 cells

The present study aimed to investigate whether VEGF was involved in bisphosphonate (BP)-induced apoptosis and differentiation of osteoblasts. Murine MC3T3-E1 osteoblasts were stimulated with zoledronic acid (ZA) for 7 days. VEGF mRNA and protein expression levels were determined via reverse transcription-quantitative PCR and western blot analysis, respectively. Cell viability was evaluated using Cell Counting Kit-8 assay. In addition, the cell apoptotic rate and the expression levels of apoptosis-related proteins were measured using a TUNEL staining kit and western blot analysis, respectively. To evaluate mineralization, cells were stained with alizarin red, while the secretion levels of alkaline phosphatase (ALP) were measured using the corresponding assay kit. Finally, the expression levels of differentiation-related proteins and proteins of the Nod-like receptor family pyrin domain-containing 3 (NLRP3)/caspase 1/gasdermin D (GSDMD) pyroptosis pathway were measured by western blot analysis. VEGF expression level was notably decreased in ZA-stimulated MC3T3-E1 cells. However, the viability of these cells was enhanced following VEGF addition. Furthermore, VEGF attenuated apoptosis, promoted mineralization and increased ALP activity in ZA-stimulated MC3T3-E1 cells. The ZA-mediated decrease in the protein expression of the osteogenic genes osteopontin, osteocalcin and runt-related transcription factor 2 was restored after MC3T3-E1 cell treatment with 10 ng/ml VEGF. The present study demonstrated that VEGF could attenuate BP-induced apoptosis and differentiation of MC3T3 cells by regulating the NLRP3/caspase 1/GSDMD pathway.

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.

The mitochondrial antioxidant SS-31 attenuated lipopolysaccharide-induced apoptosis and pyroptosis of nucleus pulposus cells via scavenging mitochondrial ROS and maintaining the stability of mitochondrial dynamics

Evidence has shown that effects from inflammation and mitochondrial dysfunction lead to pyroptosis and apoptosis of nucleus pulposus (NP) cells. Damaged mitochondria release dangerous molecules such as reactive oxygen species (ROS), activating the NLRP3 inflammasome. SS-31 is a mitochondria-targeting peptide that has been used in the treatment of many diseases by scavenging ROS and ameliorating mitochondrial function. This study found that SS-31 ameliorated lipopolysaccharide (LPS)-induced loss of cell viability, ROS production, and apoptosis in NP cells. Moreover, mitochondrial dynamics and ATP synthesis were restored on pretreatment with SS-31 compared with the LPS group. For the molecular mechanism research, SS-31 stabilized mitochondrial morphology and inhibited the activation of the NF-κB pathway and the activation of the NLRP3 inflammasome. To evaluate whether the inhibition of NLRP3 inflammasome activation by SS-31 is dependent on the clearance of mitochondrial ROS, we comparatively analyzed the activation of NLRP3 inflammasome in NP cells pretreated with SS-31 and the ROS scavenger N-acetyl-L-cysteine (NAC). The results indicate that SS-31 could inhibit NLRP3 inflammasome activation by limiting the production of mitochondrial ROS. To sum up, our results revealed that SS-31 inhibits LPS-induced apoptosis, pyroptosis, and inflammation in NP cells via scavenging ROS and maintaining the stability of mitochondrial dynamics, which could be considered a promising therapeutic intervention for disk degeneration.

Atorvastatin inhibited TNF-α induced matrix degradation in rat nucleus pulposus cells by suppressing NLRP3 inflammasome activity and inducing autophagy through NF-κB signaling

Intervertebral disc degeneration (IDD) is one of the main causes of lower back pain (LBP). It results from an imbalance between the degradation and synthesis of extracellular matrix (ECM) components in nucleus pulposus (NP) cells. Atorvastatin, an HMG-CoA reductase inhibitor, plays a vital role in many diseases, such as cardiovascular disease and osteoarthritis. However, the effect of atorvastatin on IDD is unclear. Herein, we demonstrated that atorvastatin affects matrix degradation induced by TNF-α and demonstrated the mechanism by which TNF-α modulates matrix metabolism in rat NP cells. Real-time PCR, western blotting and immunofluorescence staining were performed to detect the mRNA and protein expression of related genes. mRFP-GFP-LC3 adenovirus plasmid transfection and transmission electron microscopy (TEM) were used to detect cell autophagy. NLRP3 inhibitor and lentiviral vectors containing shRNA-NLRP3 were used to show the effect of NLRP3 on autophagic flux and the NF-κB signaling pathway. The results revealed that atorvastatin might suppress matrix degradation induced by TNF-α by suppressing NLRP3 inflammasome activity and inducing autophagic flux. Moreover, atorvastatin suppressed NF-κB signaling induced by TNF-α. NF-κB signaling inhibition suppressed NLRP3 inflammasome activity, and NLRP3 inhibition suppressed NF-κB signaling activation induced by TNF-α. NLRP3 inhibition or NLRP3 knockdown induced autophagic flux in the presence of TNF-α. Overall, the present study demonstrated that atorvastatin might suppress matrix degradation induced by TNF-α and further revealed the crosstalk among NLRP3 inflammasome activity, autophagy and NF-κB signaling.

Tissue Renin-Angiotensin System (tRAS) Induce Intervertebral Disc Degeneration by Activating Oxidative Stress and Inflammatory Reaction

Lumbar intervertebral disc degeneration (IDD) has been the major contributor to low back pain (LBP). IDD is an chronic inflammation process, with the activation of plentiful inflammation-related cytokines and ECM degradation-related enzymes. In the past few years, hypertension has been reported to correlate with LBP. In addition, the local tissue renin-angiotensin system (tRAS) has been identified in multiple tissues, including the spinal cord, skin, kidney, heart, and bone. Recently, tRAS has also been established in both bovine and human intervertebral disc tissues, especially in the degenerated disc tissue. However, the exact of tRAS and IDD remains unknown. In this present study, proteomic analysis, molecular biology analysis, and animal model were all used. Firstly, we revealed that tRAS was excessively activated in the human degenerated intervertebral disc tissue via proteomic analysis and molecular biology analysis. Then, in vitro experiment suggested that Ang II could decrease the cell viability of human NP cells and promote NP cell apoptosis, senescence, oxidative stress, and NLRP3 activation in human NP cells. In addition, Ang II could also trigger degeneration and fibrosis phenotype in human NP cells. Finally, the animal model demonstrated that the local activated ACE/Ang II axis in the NP tissue could accelerate IDD in aging spontaneously hypertensive rats (SHR). Collectively, the degenerated intervertebral disc tissue showed excessively activated tRAS, and local activated tRAS could induce NP cell senescence, apoptosis, oxidative stress, and inflammatory reaction to promote IDD. These biological effects of Ang II on human NP cells may provide novel insight into further treatment of IDD.

Roles of NLRP3 inflammasome in intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) is one of the leading causes of low back pain and one of the most common health problems in the world. The nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing-3 (NLRP3) inflammasome, as a pattern recognition receptor, has been shown to be associated with the pathological processes of many diseases in recent years. With the exploration of the mechanism of IVDD, recent studies have shown that activation of the NLRP3 inflammasome is associated with intervertebral disc (IVD) inflammation, pyroptosis, extracellular matrix degradation and apoptosis of IVD cells. In this review, we summarize the structural characteristics of NLRP3 inflammasome and the activation signalling mechanisms. We also describe the role of the NLRP3 inflammasome in the pathological process of IVDD and the application of the targeting the NLRP3 inflammasome in IVDD treatment.

Polymorphism of IL-1β rs16944(T/C) Associated with Serum Levels of IL-1β and Subsequent Stimulation of Extracellular Matrix Degradation Affects Intervertebral Disk Degeneration Susceptibility

Purpose

To investigate the association of polymorphism of IL-1β rs16944(T/C) with intervertebral disk degeneration (IDD), explore the possible mechanism and evaluate the predictive value of IL-1β for IDD.

Patients and Methods

A total of 196 consecutive patients with IDD were recruited, and 196 healthy controls were matched to these patients based on sex and age (±3 years). The polymorphisms of IL-1β rs16944(T/C), rs1143623(G/C), rs10490571(T/C) and rs2853550(A/G) were determined, and serum IL-1β, MMP-1, MMP-3, MMP-9 and a disintegrin-like and metalloproteinase with thrombospondin motif-4 (ADAMTS-4) levels were measured. Univariate analysis was performed with Student t-test or one-way ANOVA followed by post hoc and Chi-square test. Variables with two-sided P<0.10 were included in multivariate analysis, which employed a backward stepwise logistic regression model. Receiver operating characteristic (ROC) curve was used to evaluate the predictive value.

Results

Multivariate analysis showed that the polymorphism of IL-1β rs16944(T/C) was independently associated with IDD. The risk for IDD was significantly increased in TT and TC genotype compared with CC genotype, and the OR of TT genotype was higher than that of TC genotype. ANOVA analysis showed that serum concentration of IL-1β was highest in IL-1β rs16944 TT genotype, intermediate in TC genotype, and lowest in CC genotype. Similarly, serum concentrations of MMP-3 and ADAMTS-4 demonstrated the same tendency of TT > TC > CC genotype. Serum concentrations of MMP-1 and MMP-9 were higher in TT genotype than in TC and CC genotype. The area under curve (AUC) of IL-1β levels in predicting IDD was 0.788 (SE: 0.023, P=0.001, 95% CI: 0.742–0.834), and the predictive value was modest with a sensitivity of 77.0% and a specificity of 75%.

Conclusion

Polymorphism of IL-1β rs16944(T/C) affected IDD susceptibility through upregulation of serum levels of IL-1β and subsequent stimulation of ECM degradation. IL-1β levels could be applied in predicting IDD.

Nicotinamide Phosphoribosyl Transferase Controls NLRP3 Inflammasome Activity Through MAPK and NF-κB Signaling in Nucleus Pulposus Cells, as Suppressed by Melatonin

Intervertebral disc degeneration (IDD) is characterized by an imbalance between matrix synthesis and degradation in intervertebral discs. However, the causes of this imbalance remain elusive. Previous studies revealed that NLRP3 inflammasome plays a vital role in IDD and nicotinamide phosphoribosyl transferase (NAMPT) is involved in matrix degradation induced by IL-1β. In the current study, real-time PCR, western blot and NAMPT knockdown, or overexpression experiments were used to detect the regulatory effects of NAMPT on NLRP3 inflammasome activity in nucleus pulposus (NP) cells. The results revealed that NAMPT downregulation or overexpression controlled the matrix degradation induced by TNF-α by modulating NLRP3 inflammasome activity. Moreover, the NAMPT inhibition study demonstrated MAPK and NF-κB signaling play a key role in above process. In addition, melatonin was reported to play a protective role in matrix metabolism of NP cells. Herein, real-time PCR, western blot analysis, and immunofluorescence staining experiments revealed that melatonin showed protective effects against TNF-α-induced matrix degradation by downregulating NAMPT and reducing NLRP3 inflammasome activity in NP cells. The current investigation verified that melatonin could alleviate matrix degradation induced by TNF-α by suppressing NAMPT and NLRP3 inflammasome activity. Moreover, NAMPT downregulation controlled the matrix degradation induced by TNF-α by suppressing NLRP3 inflammasome activity through MAPK and NF-κB signaling in NP cells.

A New Hope in Spinal Degenerative Diseases: Piezo1

As a newly discovered mechanosensitive ion channel protein, the piezo1 protein participates in the transmission of mechanical signals on the cell membrane and plays a vital role in mammalian biomechanics. Piezo1 has attracted widespread attention since it was discovered in 2010. In recent years, studies on piezo1 have gradually increased and deepened. In addition to the discovery that piezo1 is expressed in the respiratory, cardiovascular, gastrointestinal, and urinary systems, it is also stably expressed in cells such as mesenchymal stem cells (MSCs), osteoblasts, osteoclasts, chondrocytes, and nucleus pulposus cells that constitute vertebral bodies and intervertebral discs. They can all receive external mechanical stimulation through the piezo1 protein channel to affect cell proliferation, differentiation, migration, and apoptosis to promote the occurrence and development of lumbar degenerative diseases. Through reviewing the relevant literature of piezo1 in the abovementioned cells, this paper discusses the effect of piezo1 protein expression under mechanical stress stimuli on spinal degenerative disease, providing the molecular basis for the pathological mechanism of spinal degenerative disease and also a new basis, ideas, and methods for the prevention and treatment of this degenerative disease.