NF-κB Signaling Pathway in Controlling Intervertebral Disk Cell Response to Inflammatory and Mechanical Stressors

Metformin prevents the onset and progression of intervertebral disc degeneration: New insights and potential mechanisms (Review)

Metformin has been the go‑to medical treatment for addressing type 2 diabetes mellitus (T2DM) as a frontline oral antidiabetic. Obesity, cancer and bone deterioration are linked to T2DM, which is considered a metabolic illness. Numerous diseases associated with T2DM, such as tumours, cardiovascular disease and bone deterioration, may be treated with metformin. Intervertebral disc degeneration (IVDD) is distinguished by degeneration of the spinal disc, accompanied by the gradual depletion of proteoglycans and water in the nucleus pulposus (NP) of the IVD, resulting in lower back pain. The therapeutic effect of metformin on IVDD has also attracted much attention. By stimulating AMP‑activated kinase, metformin could enhance autophagy and suppress cell senescence, apoptosis and inflammation, thus effectively delaying IVDD. The present review aimed to systematically explain the development of IVDD and mechanism of metformin in the treatment and prevention of IVDD to provide a reference for the clinical application of metformin as adjuvant therapy in the treatment of IVDD.

Melatonin-loaded self-healing hydrogel targets mitochondrial energy metabolism and promotes annulus fibrosus regeneration

Intervertebral disc (IVD) herniation is a major cause of chronic low back pain and disability. The current nucleus pulposus (NP) discectomy effectively relieves pain symptoms, but the annulus fibrosus (AF) defects are left unrepaired. Tissue engineering approaches show promise in treating AF injury and IVD degeneration; however, the presence of an inflammatory milieu at the injury site hinders the mitochondrial energy metabolism of AF cells, resulting in a lack of AF regeneration. In this study, we fabricated a dynamic self-healing hydrogel loaded with melatonin (an endocrine hormone well-known for its antioxidant and anti-inflammatory properties) and investigate whether melatonin-loaded hydrogel could promote AF defect repair by rescuing the matrix synthesis and energy metabolism of AF cells. The protective effects of melatonin on matrix components (e.g. type I and II collagen and aggrecan) in AF cells were observed in the presence of interleukin (IL)-1β. Additionally, melatonin was found to activate the nuclear factor erythroid 2-related factor signaling pathway, thereby safeguarding the mitochondrial function of AF cells from IL-1β, as evidenced by the increased level of adenosine triphosphate, mitochondrial membrane potential, and respiratory chain factor expression. The incorporation of melatonin into a self-healing hydrogel based on thiolated gelatin and β-cyclodextrin was proposed as a means of promoting AF regeneration. The successful implantation of melatonin-loaded hydrogel has been shown to facilitate in situ regeneration of AF tissue, thereby impeding IVD degeneration by preserving the hydration of nucleus pulposus in a rat box-cut IVD defect model. These findings offer compelling evidence that the development of a melatonin-loaded dynamic self-healing hydrogel can promote the mitochondrial functions of AF cells and represents a promising strategy for IVD regeneration.

The role of PIEZO ion channels in the musculoskeletal system

PIEZO1 and PIEZO2 are mechanosensitive cation channels that are highly expressed in numerous tissues throughout the body and exhibit diverse, cell-specific functions in multiple organ systems. Within the musculoskeletal system, PIEZO1 functions to maintain muscle and bone mass, sense tendon stretch, and regulate senescence and apoptosis in response to mechanical stimuli within cartilage and the intervertebral disc. PIEZO2 is essential for transducing pain and touch sensations as well as proprioception in the nervous system, which can affect musculoskeletal health. PIEZO1 and PIEZO2 have been shown to act both independently as well as synergistically in different cell types. Conditions that alter PIEZO channel mechanosensitivity, such as inflammation or genetic mutations, can have drastic effects on these functions. For this reason, therapeutic approaches for PIEZO-related disease focus on altering PIEZO1 and/or PIEZO2 activity in a controlled manner, either through inhibition with small molecules, or through dietary control and supplementation to maintain a healthy cell membrane composition. Although many opportunities to better understand PIEZO1 and PIEZO2 remain, the studies summarized in this review highlight how crucial PIEZO channels are to musculoskeletal health and point to promising possible avenues for their modulation as a therapeutic target.

Investigation into the anti-inflammatory properties of metformin in intervertebral disc cells

Introduction

Intervertebral disc degeneration (IDD) is closely related to heightened inflammation in the annulus fibrosis (AF) and nucleus pulposus (NP) cells in the intervertebral disc. An imbalanced matrix homeostasis has been shown to contribute to disc degeneration and associated discogenic low back pain. Metformin, a diabetes medication, has been noted to exhibit anti-inflammatory properties through upregulation of the AMPK pathway, leading to various anti-inflammatory-related responses in hepatocytes. However, it is still unclear how metformin influences disc cellular response to inflammatory stress and the corresponding mechanism. Hence, the objective of this study is to elucidate the effects of metformin on expression of key pro-inflammatory, catabolic, and anabolic factors within rat AF cells in response to inflammatory stimulation and mechanical tensile stress.

Methods

Five Fischer 344 rats were sacrificed and their spines isolated. AF cells were cultured and plated in flexible silicone membrane-based six-well plates. Wells were split into eight groups and subjected to metformin, IL-1β, mechanical stretch, and combined treatments. Relative gene expressions of MMP-13, COX-2, iNOS, AGC, and Col1 were assessed with quantitative real-time polymerase chain reaction (qRT-PCR), and downstream prostaglandin E2 (PGE2) production was quantified with enzyme-linked immunosorbent assay (ELISA). NF-kB nuclear translocation was also quantified.

Results

Metformin in the presence of the combined stress treatments (M + IL/S) significantly increased Col1, COX-2, and MMP-13 gene expression, decreased PGE2 production compared to IL/S conditions alone. Metformin treatment of cultured rat annulus fibrosus cells significantly reduced the nuclear translocation of NF-κB after 4 h of IL-1β treatment from 43.1% in case of IL-1β treatment down to 26.2% in the case of metformin + IL-1β treatment.

Discussion

The lack of metformin-mediated suppression of inflammatory response in the nonstretch groups indicates that metformin may be enacting its effects through a stretch-dependent manner. These results suggest a foundation for pursuing further research into metformin's potential role as an anti-inflammatory agent for curtailing intervertebral disc degeneration.

An in vitro 3D annulus fibrosus cell culture model with type I collagen: An examination of cell-matrix interactions

Background

Disorders of the intervertebral disc (IVD) are widely known to result in low back pain; one of the most common debilitating conditions worldwide. As a multifaceted condition, both inflammatory environment and mechanical factors can play a crucial role in IVD damage, and in particular, in the annulus fibrosus (AF), the highly collagenous outer ring of the IVD. As a result, a better understanding of how cells from the IVD, and specifically the AF, interact and respond to their environment is imperative.

Goal

The goal of this study is to use collagen type I as an in vitro three-dimensional extracellular matrix for AF cells of IVD and briefly examine both the cellular and mechanical effect of exposure to an inflammatory stimulant.

Methods

We utilized type I collagen as a 3D in vitro model material for culturing AF cells of Sprague Dawley rat tail IVDs.

Results

We showed that the cultured cells are viable and metabolically active; these cells also induced a distinct and significant contraction on their collagen matrix. Furthermore, to demonstrate potential versatility of our model our model and its versatility, we used lipopolysaccharide (LPS), as a known inflammatory stimulant in IVDs, to manipulate the cells and their interaction. LPS treatment resulted in detectable changes to the contraction cells induced on the collagen matrix and affected the mechanical properties of these constructs.

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

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

MicroRNA‑200c‑3p suppresses intervertebral disc degeneration by targeting RAP2C/ERK signaling

Intervertebral disc degeneration (IDD) is a major cause of lower back pain. The high morbidity associated with this disease diminishes the quality of life of those who are affected. MicroRNAs (miRs) play crucial roles in various diseases, including IDD. However, the mechanism via which miR‑200c‑3p plays a role in the development of IDD remains unknown. The present study aimed to investigate the effect of miR‑200c‑3p on the progression of IDD and the underlying mechanism. The expression level of miR‑200c‑3p was evaluated in intervertebral disc tissues from patients with IDD. To construct the IDD cell model, the nucleus pulposus (NP) cells were treated with lipopolysaccharide (LPS) 24 h following transfection with miR‑200c‑3p mimic or inhibitor. A luciferase activity assay was performed, while reverse transcription‑quantitative PCR and western blotting were conducted to determine the RNA and protein expression levels, respectively. The expression level of miR‑200c‑3p in the intervertebral disc tissues of patients with IDD was lower than that of normal subjects. LPS treatment reduced the expression level of miR‑200c‑3p in NP cells. Moreover, miR‑200c‑3p mimic inhibited LPS‑induced NP cell apoptosis. It was found that miR‑200c‑3p attenuated inflammatory cytokine levels and extracellular matrix (ECM) degradation in NP cells. Furthermore, miR‑200c‑3p targeted Ras‑related protein 2C (RAP2C) in NP cells. RAP2C promoted apoptosis, inflammatory cytokine levels and ECM degradation by activating ERK signaling. Knockdown of RAP2C and inhibition of ERK signaling by SCH772984 partially reversed the proinflammatory effect of the miR‑200c‑3p inhibitor on LPS‑treated NP cells. Thus, miR‑200c‑3p inhibits NP cell apoptosis, inflammatory cytokine levels and ECM degradation in IDD by targeting RAP2C/ERK signaling.

TNF-α suppresses SHOX2 expression via NF-κB signaling pathway and promotes intervertebral disc degeneration and related pain in a rat model

This study was conducted to verify the relative expression patterns of SHOX2 and its regulation by tumor necrosis factor alpha (TNF-α) during the development of intervertebral disc degeneration (IVDD). A rat disc-degeneration model was subjected to disc puncture (DP) and intradiscal injections with TNF-α to determine the roles of TNF-α and SHOX2 expression in IVDD in vivo. TNF-α and SHOX2 expression patterns in different degenerative rat nucleus pulposus (NP) tissues were measured by immunohistochemistry (IHC). The effects of TNF-α on IVDD were determined by magnetic resonance imaging (MRI) and pain development of wet-dog shakes (WDS) were blinded assessment by pain-behavior testing, respectively. Changes in TNF-α on SHOX2 expression were measured by Western blot analysis and real-time reverse transcription polymerase chain reaction (RT-PCR). The roles of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) in TNF-α-mediated SHOX2 activation were studied using viral transfection, Western blot analysis, and real-time RT-PCR. In vivo, TNF-α accelerated the process of IVDD and suppressed SHOX2 expression; compared to the DP group, WDS was significantly increased in TNF-α intradiscal injection group at 2 to 6 weeks after puncture (P < .05); In NP cells, TNF-α negatively affected the IVDD-associated SHOX2 suppression. While TNF-α promotes IVDD through activation of both MAPK and NF-κB signaling, it seemed that only NF-κB signaling controlled the TNF-α-mediated SHOX2 suppression that is associated with IVDD. The results of this study indicated that TNF-α inhibits SHOX2 expression and has promoted effects on IVDD in the rat model, and these effects might be associated with through NF-κB signaling pathway and promotes IVDD and related pain in a rat model.

Moderate mechanical stimulation rescues degenerative annulus fibrosus by suppressing caveolin-1 mediated pro-inflammatory signaling pathway

Mechanical loading can induce or antagonize the extracellular matrix (ECM) synthesis, proliferation, migration, and inflammatory responses of annulus fibrosus cells (AFCs), depending on the loading mode and level. Caveolin-1 (Cav1), the core protein of caveolae, plays an important role in cellular mechanotransduction and inflammatory responses. In the present study, we presented that AFCs demonstrated different behaviors when subjected to cyclic tensile strain (CTS) for 24 h at a magnitude of 0%, 2%, 5% and 12%, respectively. It was found that 5% CTS had positive effects on cell proliferation, migration and anabolism, while 12% CTS had the opposite effects. Besides, cells exposed to interleukin-1β stimulus exhibited an increase expression in inflammatory genes, and the expression of these genes decreased after exposure to moderate mechanical loading with 5% CTS. In addition, 5% CTS decreased the level of Cav1 and integrin β1 and exhibited anti-inflammatory effects. Moreover, the expression of integrin β1 and p-p65 increased in AFCs transfected with Cav1 plasmids. In vivo results revealed that moderate mechanical stimulation could recover the water content and morphology of the discs. In conclusion, moderate mechanical stimulation restrained Cav1-mediated signaling pathway and exhibited anti-inflammatory effects on AFCs. Together with in vivo results, this study expounds the underlying molecular mechanisms on the effect of moderate mechanical stimulation on intervertebral discs (IVDs) and may provide a new therapeutic strategy for the treatment of IVD degeneration.

Impact of NF-κB pathway on the intervertebral disc inflammation and degeneration induced by over-mechanical stretching stress

Background

Intervertebral disk degeneration (IVDD) contributes to low back pain. Increased cell apoptosis and inflammation, decreased extracellular matrix are associated with IVDD. Nuclear factor-kappa B (NF-κB) signaling pathway and inflammatory cytokines are implicated in the pathophysiology of IVDD.

Methods

In present study, we established a mechanical stretching stress-stimulated nucleus pulposus (NP) cell model. We knocked down NF-κB p65 by siRNA transfection to inhibit NF-κB and evaluated the effects of NF-κB inhibition on intervertebral disk degeneration. We applied the mechanical stretching stress on NP cells and inhibited NF-κB by siRNA, then evaluated the expression of inflammatory cytokines, matrix metalloproteinase (MMP), aggrecan, collagen II, and monitored viability and apoptosis of NP cells.

Results

Mechanical stretching stress induced the expression of TNF-α, IL-1β, NF-κB, MMP-3 and MMP-13, while inhibited the production of aggrecan and collagen II in NP cells. Mechanical stretching stress decreased the cell viability and induced apoptosis in NP cells. Inhibition of NF-κB by siRNA suppressed the production of TNF-α, IL-1β, NF-κB, MMP-3 and MMP-13, while upregulated the expression of aggrecan and collagen II in NP cells.

Conclusions

Inhibition of NF-κB by knocking down p65 suppressed over-mechanical stretching stress-induced cell apoptosis and promoted viability in NP cell. Inhibition of NF-κB suppressed inflammation and degeneration of NP cells in IVDD.

Multiscale Regulation of the Intervertebral Disc: Achievements in Experimental, In Silico, and Regenerative Research

Intervertebral disc (IVD) degeneration is a major risk factor of low back pain. It is defined by a progressive loss of the IVD structure and functionality, leading to severe impairments with restricted treatment options due to the highly demanding mechanical exposure of the IVD. Degenerative changes in the IVD usually increase with age but at an accelerated rate in some individuals. To understand the initiation and progression of this disease, it is crucial to identify key top-down and bottom-up regulations' processes, across the cell, tissue, and organ levels, in health and disease. Owing to unremitting investigation of experimental research, the comprehension of detailed cell signaling pathways and their effect on matrix turnover significantly rose. Likewise, in silico research substantially contributed to a holistic understanding of spatiotemporal effects and complex, multifactorial interactions within the IVD. Together with important achievements in the research of biomaterials, manifold promising approaches for regenerative treatment options were presented over the last years. This review provides an integrative analysis of the current knowledge about (1) the multiscale function and regulation of the IVD in health and disease, (2) the possible regenerative strategies, and (3) the in silico models that shall eventually support the development of advanced therapies.

Overexpression of LMP-1 Decreases Apoptosis in Human Nucleus Pulposus Cells via Suppressing the NF-κB Signaling Pathway

Intervertebral disc degeneration (IDD) is a prevalent disease characterized by low back pain. Increasing extracellular matrix (ECM) synthesis and decreasing nucleus pulposus cell (NPC) apoptosis are promising strategies to recover degenerated NP. LIM mineralization protein- (LMP-) 1 has anti-inflammatory potential and is a promising gene target for the treatment of NP degeneration. In this study, we measured the expression of LMP-1 in the NP of patients. Then, we constructed LMP-1-overexpressing NPCs using lentiviral vectors and investigated the effects of LMP-1 on cell proliferation, apoptosis, and ECM synthesis in NPCs. The results showed that LMP-1 was highly expressed in the NP of patients. LMP-1 overexpression significantly increased proliferation and decreased apoptosis in NPCs. The expression of collagen II and sulfated glycosaminoglycan (sGAG) in NPCs was also upregulated after LMP-1 was overexpressed. Moreover, we demonstrated that LMP-1 decreased apoptosis of NPCs by inhibiting NF-κB signaling activation. These findings suggest that LMP-1 plays an essential role in mediating apoptosis in NPCs by regulating NF-κB signaling and can be used as a gene target for the treatment of IDD.

Actomyosin contractility confers mechanoprotection against TNFα-induced disruption of the intervertebral disc

Inflammation triggers degradation of intervertebral disc extracellular matrix (ECM), a hallmark of disc degeneration that contributes to back pain. Mechanosensitive nucleus pulposus cells are responsible for ECM production, yet the impact of a proinflammatory microenvironment on cell mechanobiology is unknown. Using gain- and loss-of-function approaches, we show that tumor necrosis factor-α (TNFα)-induced inflammation alters cell morphology and biophysical properties (circularity, contractility, cell stiffness, and hydraulic permeability) in a mechanism dependent on actomyosin contractility in a three-dimensional (3D) culture. We found that RhoA activation rescued cells from TNFα-induced mechanobiological disruption. Using a novel explant-in-hydrogel culture system, we demonstrate that nuclear factor kappa-B nuclear translocation and transcription are mechanosensitive, and its downstream effects on ECM degradation are regulated by actomyosin contractility. Results define a scaling relationship between circularity, contractility, and hydraulic permeability that is conserved from healthy to inflammatory microenvironments and is indicative of cell mechanobiological control across scales in 3D.

TRPV4 Inhibition and CRISPR-Cas9 Knockout Reduce Inflammation Induced by Hyperphysiological Stretching in Human Annulus Fibrosus Cells

Mechanical loading and inflammation interact to cause degenerative disc disease and low back pain (LBP). However, the underlying mechanosensing and mechanotransductive pathways are poorly understood. This results in untargeted pharmacological treatments that do not take the mechanical aspect of LBP into account. We investigated the role of the mechanosensitive ion channel TRPV4 in stretch-induced inflammation in human annulus fibrosus (AF) cells. The cells were cyclically stretched to 20% hyperphysiological strain. TRPV4 was either inhibited with the selective TRPV4 antagonist GSK2193874 or knocked out (KO) via CRISPR-Cas9 gene editing. The gene expression, inflammatory mediator release and MAPK pathway activation were analyzed. Hyperphysiological cyclic stretching significantly increased the IL6, IL8, and COX2 mRNA, PGE2 release, and activated p38 MAPK. The TRPV4 pharmacological inhibition significantly attenuated these effects. TRPV4 KO further prevented the stretch-induced upregulation of IL8 mRNA and reduced IL6 and IL8 release, thus supporting the inhibition data. We provide novel evidence that TRPV4 transduces hyperphysiological mechanical signals into inflammatory responses in human AF cells, possibly via p38. Additionally, we show for the first time the successful gene editing of human AF cells via CRISPR-Cas9. The pharmacological inhibition or CRISPR-based targeting of TRPV4 may constitute a potential therapeutic strategy to tackle discogenic LBP in patients with AF injury.

Rabbit Annulus Fibrosus Cells Express Neuropeptide Y, Which Is Influenced by Mechanical and Inflammatory Stress

Objective

Rabbit annulus fibrosus (AF) cells were exposed to isolated or combined mechanical and inflammatory stress to examine the expression of neuropeptide Y (NPY). This study aims to explore the ability of AF cells to produce NPY in response to mechanical and inflammatory stress.

Methods

Lumbar AF cells of 6- to 8-month-old female New Zealand white rabbits were harvested and exposed to combinations of inflammatory (interleukin-1β) and mechanical (6% or 18%) tensile stress using the Flexcell System. NPY concentrations were measured in the media via enzyme-linked immunosorbent assay. The presence of NPY receptor-type 1 (NPY-1R) in AF cells of rabbit intervertebral discs was also analyzed via immunohistochemistry and immunofluorescence.

Results

Exposure to inflammatory stimuli showed a significant increase in the amount of NPY expression compared to control AF cells. Mechanical strain alone did not result in a significant difference in NPY expression. While combined inflammatory and mechanical stress did not demonstrate an increase in NPY expression at low (6%) levels of strain, at 18% strain, there was a large—though not statistically significant—increase in NPY expression under conditions of inflammatory stress. Lastly, immunofluorescence and immunohistochemistry of AF cells and tissue, respectively, demonstrated the presence of NPY-1R.

Conclusion

These findings demonstrate that rabbit AF cells are capable of expressing NPY, and expression is enhanced in response to inflammatory and mechanical stress. Because both inflammatory and mechanical stress contribute to intervertebral disc degeneration (IDD), this observation raises the potential of a mechanistic link between low back pain and IDD.

Oxymatrine suppresses IL-1β-induced degradation of the nucleus pulposus cell and extracellular matrix through the TLR4/NF-κB signaling pathway

Intervertebral disc degeneration is the main cause of low back pain. However, its pathomechanism has not been fully clarified yet. Previous studies have indicated that inflammation may lead to apoptosis of nucleus pulposus cells and break the balance between anabolism and catabolism of the nucleus pulposus extracellular matrix. The purpose of this study is to explore the mitigative effect of oxymatrine on extracellular matrix degradation and apoptosis of nucleus pulposus cells after interleukin-1 beta-induced inflammation, and its possible signaling pathway. We examined the gene and protein levels of collagen II, aggrecan, and MMPs (MMP2/3/9/13) and interleukin 6 in nucleus pulposus cells. The results demonstrated that oxymatrine could reduce extracellular matrix degradation and apoptosis of nucleus pulposus cells; interleukin-1 beta prompted the expression of MMPs and interleukin 6 through TLR4/NF-κB axis, while oxymatrine reduced the expression of MMPs and TNF-α induced by interleukin-1 beta. Moreover, TAK 242, as a small molecule inhibitor of TLR4 signaling, was used to detect the effect of oxymatrine on the TLR4/NF-κB signaling. The final experimental results show that oxymatrine could reduce the inflammatory response of nucleus pulposus cells and degradation of nucleus pulposus tissue. Oxymatrine may be a potential medicine to reduce disc inflammation and relieve intervertebral disc degeneration by inhibiting the TLR4/NF-κB signal pathway.

Impact statement

Currently, drug therapy is a potential treatment for patients with intervertebral disc degeneration. In the present research, oxymatrine intervenes in intervertebral disc degeneration effectively via regulating inflammation in intervertebral disc degeneration rats. Our research highlights the therapeutic potential of oxymatrine in the treatment of intervertebral disc degeneration.

Mechanobiology of annulus fibrosus and nucleus pulposus cells in intervertebral discs

Low back pain (LBP) is a chronic condition that can affect up to 80% of the global population. It is the number one cause of disability worldwide and has enormous socioeconomic consequences. One of the main causes of this condition is intervertebral disc (IVD) degeneration. IVD degenerative processes and inflammation associated with it has been the subject of many studies in both tissue and cell level. It is believed that the phenotype of the resident cells within the IVD directly affects homeostasis of the tissue. At the same time, IVDs located between vertebral bodies of spine are under various mechanical loading conditions in vivo. Therefore, investigating how mechanical loading can affect the behaviour of IVD cells has been a subject of many research articles. In this review paper, following a brief explanation of the anatomy of the IVD and its resident cells, we compiled mechanobiological studies of IVD cells (specifically, annulus fibrosus and nucleus pulposus cells) and synthesized and discussed the key findings of the field.

Pulsed Electromagnetic Fields Reduce Interleukin-6 Expression in Intervertebral Disc Cells Via Nuclear Factor-κβ and Mitogen-Activated Protein Kinase p38 Pathways

STUDY DESIGN

This is an in vitro study of bovine disc cells exposed to pulsed electromagnetic fields.

OBJECTIVE

The purpose of the present study was to investigate whether pulsed electromagnetic fields (PEMF) effects on the expression of interleukin-6 (IL-6) expression is mediated by two known inflammation regulators, nuclear factor-κB (NF-κβ) and phosphorylated mitogen-activated protein kinase p38 (p38-MAPK) signaling pathways SUMMARY OF BACKGROUND DATA.: Inflammatory cytokines play a dominant role in the pathogenesis of disc degeneration. Increasing evidence showed that PEMF, a noninvasive biophysical stimulation, can have physiologically beneficial effects on inflammation and tissue repair. Our previous research shows that PEMF treatment can reduce IL-6 expression by intervertebral disc cells. However, the underlying mechanisms of PEMF action are yet to be uncovered.

METHODS

Intervertebral disc nuclear pulposus cells were challenged with interleukin-1α (IL-1α) (for mimicking inflammatory microenvironment) and treated with PEMF simultaneously up to 4 hours. Cells were then collected for NF-κβ and phosphorylated p38-MAPK protein detection with Western blot. Additionally, the RelA (p65) subunit of NF-κβ was examined with immunostaining for assessment of NF-κβ activation.

RESULTS

As expected, Western blot results showed that both NF-κβ and phosphorylated p38 expression were significantly increased by IL-1α treatment. This induction was significantly inhibited to control condition levels by PEMF treatment. Immunostaining demonstrated similar trends, that PEMF treatment reduced the NF-κβ activation induced by IL-1α exposure.

CONCLUSION

Our data indicate that the previously-reported inhibitory effect of PEMF treatment on disc inflammation is mediated by NF-κβ and phosphorylated p38-MAPK signaling pathways. These results further establish PEMFs anti-inflammatory activity, and may inform potential future clinical uses for management of inflammation associated with disc degeneration.

LEVEL OF EVIDENCE

N/A.

Aberrant mechanosensing in injured intervertebral discs as a result of boundary-constraint disruption and residual-strain loss

In fibrous tissues, pre-stressed boundary constraints at bone interfaces instil residual strain throughout the tissue, even when unloaded. For example, internal swelling pressures in the central nucleus pulposus of the intervertebral disc generate pre-strain in the outer annulus fibrosus. With injury and depressurization, these residual strains are lost. Here, we show that the loss of residual strains in the intervertebral disc alters the microenvironment and instigates aberrant tissue remodelling and the adoption of atypical cellular phenotypes. By using puncture surgery of the annulus fibrosus in rabbits, ex vivo puncture experiments, and electrospun nanofibrous scaffolds recapitulating evolving boundary constraints, we show that the loss of residual strain promotes short-term apoptosis and the emergence of a fibrotic phenotype, that local fibre organization and cellular contractility mediate this process, and that the aberrant cellular changes could be abrogated by targeting the cell-mechanosensing machinery with small molecules. Our findings indicate that injury to dense connective tissues under pre-strain alters boundary constraints and residual strain, leading to aberrant mechanosensing, which in turn promotes disease progression.

MicroRNA-143-5p targeting eEF2 gene mediates intervertebral disc degeneration through the AMPK signaling pathway

Background

Intervertebral disc degeneration (IDD) is a major contributor to back, neck, and radicular pain, and the treatment of IDD is costly and relatively ineffective. Dysregulation of microRNAs (miRNAs) has been reported to be involved in IDD. The purpose of our study is to illustrate the potential that miR-143-5p targeting eEF2 gene mediates IDD.

Methods

Following the establishment of the IDD rat models, expression of miR-143-5p, eEF2, Bcl-2, Bax, AMPK, mTOR, cyclinD, COL2, ACAN, and DCN was detected. The NP cells isolated from degenerative intervertebral disc (IVD) were introduced with a series of mimic, inhibitor, or AICAR to explore the functional role of miR-143-5p in IDD and to characterize the relationship between miR-143-5p and eEF2. Cell viability, cell cycle, apoptosis, and senescence were also evaluated.

Results

A reduction in eEF2, an increase in miR-143-5p, and activation of the AMPK signaling pathway were observed in degenerative IVD. Moreover, increased senescent NP cells were observed in degenerative IVD. eEF2 was confirmed as a target gene of miR-143-5p. miR-143-5p was found to activate the AMPK signaling pathway. The restoration of miR-143-5p or the activation of AMPK signaling pathway decreased COL2, ACAN, and DCN expression, coupled with the inhibition of NP cell proliferation and differentiation, and promotion of NP apoptosis and senescence. On the contrary, the inhibition of miR-143-5p led to the reversed results.

Conclusion

The results demonstrated that the inhibition of miR-143-5p may act as a suppressor for the progression of IDD.

Mechanotransduction and cell biomechanics of the intervertebral disc

Mechanical loading of the intervertebral disc (IVD) initiates cell-mediated remodeling events that contribute to disc degeneration. Cells of the IVD, nucleus pulposus (NP) and anulus fibrosus (AF), will exhibit various responses to different mechanical stimuli which appear to be highly dependent on loading type, magnitude, duration, and anatomic zone of cell origin. Cells of the NP, the innermost region of the disc, exhibit an anabolic response to low-moderate magnitudes of static compression, osmotic pressure, or hydrostatic pressure, while higher magnitudes promote a catabolic response marked by increased protease expression and activity. Cells of the outer AF are responsive to physical forces in a manner that depends on frequency and magnitude, as are cells of the NP, though they experience different forces, deformations, pressure, and osmotic pressure in vivo. Much remains to be understood of the mechanotransduction pathways that regulate IVD cell responses to loading, including responses to specific stimuli and also differences among cell types. There is evidence that cytoskeletal remodeling and receptor-mediated signaling are important mechanotransduction events that can regulate downstream effects like gene expression and posttranslational biosynthesis, all of which may influence phenotype and bioactivity. These and other mechanotransduction events will be regulated by known and to-be-discovered cell-matrix and cell-cell interactions, and depend on composition of extracellular matrix ligands for cell interaction, matrix stiffness, and the phenotype of the cells themselves. Here, we present a review of the current knowledge of the role of mechanical stimuli and the impact upon the cellular response to loading and changes that occur with aging and degeneration of the IVD.

Dynamic imaging demonstrates that pulsed electromagnetic fields (PEMF) suppress IL-6 transcription in bovine nucleus pulposus cells

Inflammatory cytokines play a dominant role in the pathogenesis of disc degeneration. Pulsed electromagnetic fields (PEMF) are noninvasive biophysical stimulus that has been used extensively in the orthopaedic field for many years. However, the specific cellular responses and mechanisms involved are still unclear. The objective of this study was to assess the time-dependent PEMF effects on pro-inflammatory factor IL-6 expression in disc nucleus pulposus cells using a novel green fluorescence protein (GFP) reporter system. An MS2-tagged GFP reporter system driven by IL-6 promoter was constructed to visualize PEMF treatment effect on IL-6 transcription in single living cells. IL-6-MS2 reporter-labeled cells were treated with IL-1α to mimic the in situ inflammatory environment of degenerative disc while simultaneously exposed to PEMF continuously for 4 h. Time-lapse imaging was recorded using a confocal microscope to track dynamic IL-6 transcription activity that was demonstrated by GFP. Finally, real-time RT-PCR was performed to confirm the imaging data. Live cell imaging demonstrated that pro-inflammatory factor IL-1α significantly promoted IL-6 transcription over time as compared with DMEM basal medium condition. Imaging and PCR data demonstrated that the inductive effect of IL-1α on IL-6 expression could be significantly inhibited by PEMF treatment in a time-dependent manner (early as 2 h of stimulus initiation). Our data suggest that PEMF may have a role in the clinical management of patients with chronic low back pain. Furthermore, this study shows that the MS2-tagged GFP reporter system is a useful tool for visualizing the dynamic events of mechanobiology in musculoskeletal research. © 2017 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:778-787, 2018.

BMSC paracrine activity attenuates interleukin-1β-induced inflammation and apoptosis in rat AF cells via inhibiting relative NF-κB signaling and the mitochondrial pathway

We previously showed that bone mesenchymal stem cells (BMSCs) inhibit interleukin-1 beta (IL-1β) induced degenerative effects in NP cells by their paracrine activity, but the anti-inflammatory and anti-apoptotic effect of BMSC paracrine activity and the relative signaling pathway were not further investigated in annulus fibrosus (AF) cells. In this study, AF cells were exposed to IL-1β, which was applied to mimic intervertebral disc degeneration (IDD) in vitro. Indirect co-culture with BMSCs in a transwell co-culture system reduced the activity of nuclear factor-κB-p65 (NF-κB-p65) through the restoration of its inhibitor IκBa. Real time polymerase chain reaction (PT-PCR) and Western blotting revealed that the up-regulation of MMP-3 and MMP-13 induced by IL-1β were impeded by BMSC co-culture, and the decrease in aggrecan, collagen I and TIMP-1 were reversed. An ELISA showed that the increased inflammatory factors, such as nitrite, prostaglandin E-2 (PGE-2), IL-6 and cyclooxygenase-2 (COX-2), were decreased by the BMSC co-culture. Furthermore, the apoptosis rate of AF cells were detected by flow cytometry, and the apoptosis-related proteins, such as Bax, Bcl-2 and caspase-3, were analyzed by Western blotting and ELISA. The changes in mitochondrial membrane potentials were also detected by confocal microscopy. The results showed that IL-1β induced apoptosis of AF cells was attenuated by co-culturing, which suppressed the functions of the mitochondria function. We suggest that BMSC paracrine activity has an anti-inflammation effect and anti-apoptotic effect on IDD, and it is mediated, at least in part, via the relative NF-κF and mitochondrial apoptotic pathways in AF cells.