Effects of interleukin-17A in nucleus pulposus cells and its small-molecule inhibitors for intervertebral disc disease

Research on the role and mechanism of IL-17 in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is one of the primary causes of low back pain (LBP), which seriously affects patients' quality of life. In recent years, interleukin (IL)-17 has been shown to be highly expressed in the intervertebral disc (IVD) tissues and serum of patients with IDD, and IL-17A has been shown to promote IDD through multiple pathways. We first searched databases such as PubMed, Cochrane, Embase, and Web of Science using the search terms "IL-17 or interleukin 17″ and "intervertebral discs". The search period ranged from the inception of the databases to December 2023. A total of 24 articles were selected after full-text screening. The main conclusion of the clinical studies was that IL-17A levels are significantly increased in the IVD tissues and serum of IDD patients. The results from the in vitro studies indicated that IL-17A can activate signaling pathways such as the NF-κB and MAPK pathways; promote inflammatory responses, extracellular matrix degradation, and angiogenesis; and inhibit autophagy in nucleus pulposus cells. The main finding of the in vivo experiments was that puncture of animal IVDs resulted in elevated levels of IL-17A within the IVD, thereby inducing IDD. Clinical studies, in vitro experiments, and in vivo experiments confirmed that IL-17A is closely related to IDD. Therefore, drugs that target IL-17A may be novel treatments for IDD, providing a new theoretical basis for IDD therapy.

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.

Cytokine Imbalance as a Biomarker of Intervertebral Disk Degeneration

The intervertebral disk degeneration (IDD) and its associated conditions are an important problem in modern medicine. The onset of IDD may be in childhood and adolescence in patients with a genetic predisposition. IDD progresses with age, leading to spondylosis, spondylarthrosis, intervertebral disk herniation, and spinal stenosis. The purpose of this review is an attempt to summarize the data characterizing the patterns of production of pro-inflammatory and anti-inflammatory cytokines in IDD and to appreciate the prognostic value of cytokine imbalance as its biomarker. This narrative review demonstrates that the problem of evaluating the contribution of pro-inflammatory and anti-inflammatory cytokines to the maintenance or alteration of cytokine balance may be a new key to unlocking the mystery of IDD development and new therapeutic strategies for the treatment of IDD in the setting of acute and chronic inflammation. The presented data support the hypothesis that cytokine imbalance is one of the most important biomarkers of IDD.

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.

Innovative immune mechanisms and antioxidative therapies of intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is the basic pathological process of many degenerative diseases of the spine, characterized by series of symptoms, among which low back pain (LBP) is the most common symptom that patients suffer a lot, which not only makes patients and individual families bear a huge pain and psychological burden, but also consumes a lot of medical resources. IDD is usually thought to be relevant with various factors such as genetic predisposition, trauma and aging, and IDD progression is tightly relevant with structural and functional alterations. IDD processes are caused by series of pathological processes, including oxidative stress, matrix decomposition, inflammatory reaction, apoptosis, abnormal proliferation, cell senescence, autophagy as well as sepsis process, among which the oxidative stress and inflammatory response are considered as key link in IDD. The production and clearance of ROS are tightly connected with oxidative stress, which would further simulate various signaling pathways. The phenotype of disc cells could change from matrix anabolism-to matrix catabolism- and proinflammatory-phenotype during IDD. Recent decades, with the relevant reports about oxidative stress and inflammatory response in IDD increasing gradually, the mechanisms researches have attracted much more attention. Consequently, this study focused on the indispensable roles of the oxidative stress and inflammatory response (especially macrophages and cytokines) to illustrate the origin, development, and deterioration of IDD, aiming to provide novel insights in the molecular mechanisms as well as significant clinical values for IDD.

Immuno-Modulatory Effects of Intervertebral Disc Cells

Low back pain is a highly prevalent, chronic, and costly medical condition predominantly triggered by intervertebral disc degeneration (IDD). IDD is often caused by structural and biochemical changes in intervertebral discs (IVD) that prompt a pathologic shift from an anabolic to catabolic state, affecting extracellular matrix (ECM) production, enzyme generation, cytokine and chemokine production, neurotrophic and angiogenic factor production. The IVD is an immune-privileged organ. However, during degeneration immune cells and inflammatory factors can infiltrate through defects in the cartilage endplate and annulus fibrosus fissures, further accelerating the catabolic environment. Remarkably, though, catabolic ECM disruption also occurs in the absence of immune cell infiltration, largely due to native disc cell production of catabolic enzymes and cytokines. An unbalanced metabolism could be induced by many different factors, including a harsh microenvironment, biomechanical cues, genetics, and infection. The complex, multifactorial nature of IDD brings the challenge of identifying key factors which initiate the degenerative cascade, eventually leading to back pain. These factors are often investigated through methods including animal models, 3D cell culture, bioreactors, and computational models. However, the crosstalk between the IVD, immune system, and shifted metabolism is frequently misconstrued, often with the assumption that the presence of cytokines and chemokines is synonymous to inflammation or an immune response, which is not true for the intact disc. Therefore, this review will tackle immunomodulatory and IVD cell roles in IDD, clarifying the differences between cellular involvements and implications for therapeutic development and assessing models used to explore inflammatory or catabolic IVD environments.

The Role of IL-17-Mediated Inflammatory Processes in the Pathogenesis of Intervertebral Disc Degeneration and Herniation: A Comprehensive Review

It has been reported that degenerated and herniated lumbar intervertebral discs show high expression of IL-17, suggesting that local immune reactions occur in patients with low back pain. While clinical sample analyses from different laboratories confirm this, it is not deeply not known on how IL-17 is induced in the pathology and their interactions with other inflammatory responses. This conscience review organizes current laboratory findings on this topic and present trajectory for full understanding on the role of IL-17 in pathology of intervertebral disc disease.

Cell sources proposed for nucleus pulposus regeneration

Lower back pain (LBP) occurs in 80% of adults in their lifetime; resulting in LBP being one of the biggest causes of disability worldwide. Chronic LBP has been linked to the degeneration of the intervertebral disc (IVD). The current treatments for chronic back pain only provide alleviation of symptoms through pain relief, tissue removal, or spinal fusion; none of which target regenerating the degenerate IVD. As nucleus pulposus (NP) degeneration is thought to represent a key initiation site of IVD degeneration, cell therapy that specifically targets the restoration of the NP has been reviewed here. A literature search to quantitatively assess all cell types used in NP regeneration was undertaken. With key cell sources: NP cells; annulus fibrosus cells; notochordal cells; chondrocytes; bone marrow mesenchymal stromal cells; adipose-derived stromal cells; and induced pluripotent stem cells extensively analyzed for their regenerative potential of the NP. This review highlights: accessibility; expansion capability in vitro; cell survival in an IVD environment; regenerative potential; and safety for these key potential cell sources. In conclusion, while several potential cell sources have been proposed, iPSC may provide the most promising regenerative potential.

Elevated lymphotoxin-α (TNFβ) is associated with intervertebral disc degeneration

Background

Intervertebral disc degeneration (IVDD) is a primary cause of degenerative disc diseases; however, the mechanisms underlying the degeneration remain unclear. The immunoinflammatory response plays an important role in IVDD progression. The inflammatory cytokine lymphotoxin-α (LTα), formerly known as TNFβ, is associated with various pathological conditions, while its role in the pathogenesis of IVDD remains elusive.

Methods

Real-time quantitative polymerase chain reaction (RT-qPCR), Western blotting (WB), and enzyme-linked immunosorbent assays were used to assess the levels of LTα in human nucleus pulposus (NP) tissues between degeneration and control groups. The plasma concentrations of LTα and C-reactive protein (CRP) were compared between healthy and IVDD patients. Rat primary NP cells were cultured and identified via immunofluorescence. Methyl-thiazolyl-tetrazolium assays and flow cytometry were used to evaluate the effects of LTα on rat NP cell viability. After NP cells were treated with LTα, degeneration-related molecules (Caspase-3, Caspase-1, matrix metalloproteinase (MMP) -3, aggrecan and type II collagen) were measured via RT-qPCR and WB.

Results

The levels of both the mRNA and protein of LTα in human degenerated NP tissue significantly increased. Plasma LTα and CRP did not differ between healthy controls and IVDD patients. Rat primary NP cells were cultured, and the purity of primary NP cells was > 90%. Cell experiments showed inversely proportional relationships among the LTα dose, treatment time, and cell viability. The optimal conditions (dose and time) for LTα treatment to induce rat NP cell degeneration were 5 μg/ml and 48 ~ 72 h. The apoptosis rate and the levels of Caspase-3, Caspase-1, and MMP-3 significantly increased after LTα treatment, while the levels of type II collagen and aggrecan were decreased, and the protein expression levels were consistent with their mRNA expression levels.

Conclusions

This study demonstrated that elevated LTα is closely associated with IVDD and that LTα may induce NP cell apoptosis and reduce important extracellular matrix (ECM) proteins, which cause adverse effects on IVDD progress. Moreover, the optimal conditions for LTα treatment to induce NP cell degeneration were determined.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-020-03934-7.

Differential proteomic analysis of fetal and geriatric lumbar nucleus pulposus: immunoinflammation and age-related intervertebral disc degeneration

BACKGROUND

Intervertebral disc degeneration (IVDD) is a major cause of low back pain. Although the mechanism of degeneration remains unclear, aging has been recognized as a key risk factor for IVDD. Most studies seeking to identify IVDD-associated molecular alterations in the context of human age-related IVDD have focused only on a limited number of proteins. Differential proteomic analysis is an ideal method for comprehensively screening altered protein profiles and identifying the potential pathways related to pathological processes such as disc degeneration.

METHODS

In this study, tandem mass tag (TMT) labeling was combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) for differential proteomic analysis of human fetal and geriatric lumbar disc nucleus pulposus (NP) tissue. Parallel reaction monitoring (PRM) and Western blotting (WB) techniques were used to identify target proteins. Bioinformatic analyses, including Gene Ontology (GO) annotation, domain annotation, pathway annotation, subcellular localization and functional enrichment analyses, were used to interpret the potential significance of the protein alterations in the mechanism of IVDD. Student's t-tests and two-tailed Fisher's exact tests were used for statistical analysis.

RESULTS

Six hundred forty five proteins were significantly upregulated and 748 proteins were downregulated in the geriatric group compared with the fetal group. Twelve proteins were verified to have significant differences in abundance between geriatric and fetal NP tissue; most of these have not been previously identified as being associated with human IVDD. The potential significance of the differentially expressed proteins in age-related IVDD was analyzed from multiple perspectives, especially with regard to the association of the immunoinflammatory response with IVDD.

CONCLUSIONS

Differential proteomic analysis was used as a comprehensive strategy for elucidating the protein alterations associated with age-related IVDD. The findings of this study will aid in the screening of new biomarkers and molecular targets for the diagnosis and therapy of IVDD. The results may also significantly enhance our understanding of the pathophysiological process and mechanism of age-related IVDD.

Exosomal miR-532-5p from bone marrow mesenchymal stem cells reduce intervertebral disc degeneration by targeting RASSF5

The transplantation of bone marrow mesenchymal stem cells (BMSCs) has been found to be used as an effective therapy of intervertebral disc degeneration (IDD). However, the underlying mechanisms of BMSCs in the progress of IDD are not fully explained. In this study, we found that exosomes derived from BMSCs (BMSCs-Exos) inhibited the apoptotic rate, extracellular matrix (ECM) degradation, and fibrosis deposition in TNF-α-induced nucleus pulposus cells (NPCs). Importantly, the level of miR-532-5p was observed to be decreased in apoptotic NPCs, but abundant in BMSCs-Exos with TNF-α treatment. The results showed that BMSCs-Exos under TNF-α stimuli exerted better effects on NPCs than BMSCs-Exos, which might be mitigated by the inhibition of miR-532-5p in BMSCs-Exos. The gain-of-function results suggested that the direct overexpression of miR-532-5p in NPCs could inhibit TNF-α-induced increase of apoptotic process, activation of apoptotic proteins, imbalance of anabolism/catabolism levels, and accumulation of collagen I. In addition, RASSF5 was demonstrated to be a target of miR-532-5p. Knockdown of RASSF5 could decrease the apoptotic cells and reduce the activated apoptotic protein levels in TNF-α-induced NPCs. Overall, these data indicate that exosomes from BMSCs may suppress TNF-α-induced apoptosis, ECM degradation, and fibrosis deposition in NPCs through the delivery of miR-532-5p via targeting RASSF5. This work provides a promising therapeutic strategy for the progress of IDD.

The Immune Privilege of the Intervertebral Disc: Implications for Intervertebral Disc Degeneration Treatment

The intervertebral disc (IVD) is the largest avascular organ of the body. It is composed of three parts: the nucleus pulposus (NP), the annulus fibrosus (AF) and the cartilaginous endplate (CEP). The central NP is surrounded by the AF and sandwiched by the two CEPs ever since its formation. This unique structure isolates the NP from the immune system of the host. Additionally, molecular factors expressed in IVD have been shown inhibitive effect on immune cells and cytokines infiltration. Therefore, the IVD has been identified as an immune privilege organ. The steady state of immune privilege is fundamental to the homeostasis of the IVD. The AF and the CEP, along with the immunosuppressive molecular factors are defined as the blood-NP barrier (BNB), which establishes a strong barrier to isolate the NP from the host immune system. When the BNB is damaged, the auto-immune response of the NP occurs with various downstream cascade reactions. This effect plays an important role in the whole process of IVD degeneration and related complications, such as herniation, sciatica and spontaneous herniated NP regression. Taken together, an enhanced understanding of the immune privilege of the IVD could provide new targets for the treatment of symptomatic IVD disease. However, the underlying mechanism above is still not fully clarified. Accordingly, the current study will extensively review and discuss studies regarding the immune privilege of the IVD.

Effects of interleukin-17A in nucleus pulposus cells and its small-molecule inhibitors for intervertebral disc disease

Intervertebral discs (IVD) degeneration, which is caused by ageing or mechanical stress, leads to IVD disease, including back pain and sciatica. The cytokine interleukin (IL)-17A is elevated in NP cells during IVD disease. Here we explored the pharmacotherapeutic potential of IL-17A for the treatment of IVD disease using small-molecule inhibitors that block binding of IL-17A to the IL-17A receptor (IL-17RA). Treatment of NP cells with IL-17A increased expression of cyclooxygenase-2 (COX-2), IL-6, matrix metalloproteinase (MMP)-3 and MMP-13. These increases were suppressed by an IL-17A-neutralizing antibody, and small molecules that were identified as inhibitors by binding to the IL-17A-binding region of IL-17RA. IL-17A signalling also altered sulphated glycosaminoglycan deposition and spheroid colony formation, while treatment with small-molecule inhibitors of IL-17A attenuated this response. Furthermore, mitogen-activated protein kinase pathways were activated by IL-17A stimulation and induced IL-6 and COX-2 expression, while small-molecule inhibitors of IL-17A suppressed their expression. Taken together, these results show that IL-17A is a valid target for IVD disease therapy and that small-molecule inhibitors that inhibit the IL-17A-IL-17RA interaction may be useful for pharmacotherapy of IVD disease.