Proinflammatory cytokines stimulate the expression of nerve growth factor by human intervertebral disc cells

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.

Characterization of pain-related behaviors in a rat model of acute-to-chronic low back pain: single vs. multi-level disc injury

Introduction

Low back pain is the most common type of chronic pain. We examined pain-related behaviors across 18 weeks in rats that received injury to one or two lumbar intervertebral discs (IVD) to determine if multi-level disc injuries enhance/prolong pain.

Methods

Twenty-three Sprague-Dawley adult female rats were used: 8 received disc puncture (DP) of one lumbar IVD (L5/6, DP-1); 8 received DP of two lumbar IVDs (L4/5 & L5/6, DP-2); 8 underwent sham surgery.

Results

DP-2 rats showed local (low back) sensitivity to pressure at 6- and 12-weeks post-injury, and remote sensitivity to pressure (upper thighs) at 12- and 18-weeks and touch (hind paws) at 6, 12 and 18-weeks. DP-1 rats showed local and remote pressure sensitivity at 12-weeks only (and no tactile sensitivity), relative to Sham DP rats. Both DP groups showed reduced distance traveled during gait testing over multiple weeks, compared to pre-injury; only DP-2 rats showed reduced distance relative to Sham DP rats at 12-weeks. DP-2 rats displayed reduced positive interactions with a novel adult female rat at 3-weeks and hesitation and freezing during gait assays from 6-weeks onwards. At study end (18-weeks), radiological and histological analyses revealed reduced disc height and degeneration of punctured IVDs. Serum BDNF and TNFα levels were higher at 18-weeks in DP-2 rats, relative to Sham DP rats, and levels correlated positively with remote sensitivity in hind paws (tactile) and thighs (pressure).

Discussion

Thus, multi-level disc injuries resulted in earlier, prolonged and greater discomfort locally and remotely, than single-level disc injury. BDNF and TNFα may have contributing roles.

Targeted screening of inflammatory mediators in spontaneous degenerative disc disease in dogs reveals an upregulation of the tumor necrosis superfamily

Background

The regulation of inflammatory mediators in the degenerating intervertebral disc (IVD) and corresponding ligamentum flavum (LF) is a topic of emerging interest. The study aimed to investigate the expression of a broad array of inflammatory mediators in the degenerated LF and IVD using a dog model of spontaneous degenerative disc disease (DDD) to determine potential treatment targets.

Methods

LF and IVD tissues were collected from 22 normal dogs (Pfirrmann grades I and II) and 18 dogs affected by DDD (Pfirrmann grades III and IV). A qPCR gene array was used to investigate the expression of 80 inflammatory genes for LF and IVD tissues, whereafter targets of interest were investigated in additional tissue samples using qPCR, western blot (WB), and immunohistochemistry.

Results

Tumor necrosis factor superfamily (TNFSF) signaling was identified as a regulated pathway in DDD, based on the significant regulation (n-fold ± SD) of various TNFSF members in the degenerated IVD, including nerve growth factor (NGF; -8 ± 10), CD40LG (464 ± 442), CD70 (341 ± 336), TNFSF Ligand 10 (9 ± 8), and RANKL/TNFSF Ligand 11 (85 ± 74). In contrast, TNFSF genes were not significantly affected in the degenerated LF compared to the control LF. Protein expression of NGF (WB) was significantly upregulated in both the degenerated LF (4.4 ± 0.5) and IVD (11.3 ± 5.6) compared to the control group. RANKL immunopositivity was significantly upregulated in advanced stages of degeneration (Thompson grades IV and V) in the nucleus pulposus and annulus fibrosus of the IVD, but not in the LF.

Conclusions

DDD involves a significant upregulation of various TNFSF members, with tissue-specific expression profiles in LF and IVD tissues. The differential involvement of TNFSF members within multiple spinal tissues from the same individual provides new insights into the inflammatory processes involved in DDD and may provide a basis to formulate hypotheses for the determination of potential treatment targets.

Updates on Pathophysiology of Discogenic Back Pain

Discogenic back pain, a subset of chronic back pain, is caused by intervertebral disc (IVD) degeneration, and imparts a notable socioeconomic health burden on the population. However, degeneration by itself does not necessarily imply discogenic pain. In this review, we highlight the existing literature on the pathophysiology of discogenic back pain, focusing on the biomechanical and biochemical steps that lead to pain in the setting of IVD degeneration. Though the pathophysiology is incompletely characterized, the current evidence favors a framework where degeneration leads to IVD inflammation, and subsequent immune milieu recruitment. Chronic inflammation serves as a basis of penetrating neovascularization and neoinnervation into the IVD. Hence, nociceptive sensitization emerges, which manifests as discogenic back pain. Recent studies also highlight the complimentary roles of low virulence infections and central nervous system (CNS) metabolic state alteration. Targeted therapies that seek to disrupt inflammation, angiogenesis, and neurogenic pathways are being investigated. Regenerative therapy in the form of gene therapy and cell-based therapy are also being explored.

The influence of intervertebral disc overloading on nociceptor calcium flickering

Introduction

Mechanical overloading can trigger a degenerative-like cascade in an organ culture of intervertebral disc (IVD). Whether the overloaded IVD can influence the activation of nociceptors (i.e., the damage sensing neurons) remains unknown. The study aims to investigate the influence of overloaded IVD conditioned medium (CM) on the activation of nociceptors.

Methods

In the static loading regime, force-controlled loading of 0.2 MPa for 20 h/day representing "long-term sitting and standing" was compared with a displacement-controlled loading maintaining original IVD height. In the dynamic loading regime, high-frequency-intensity loading representing degenerative "wear and tear" was compared with a lower-frequency-intensity loading. CM of differently loaded IVDs were collected to stimulate the primary bovine dorsal root ganglion (DRG) cultures. Calcium imaging (Fluo-4) and calcitonin gene-related peptide (CGRP) immunofluorescent labeling were jointly used to record the calcium flickering in CGRP(+) nociceptors.

Results

Force-controlled loading led to a higher IVD cell death compared to displacement-controlled loading. Both static and dynamic overloading (force-controlled and high-frequency-intensity loadings) elevated the frequency of calcium flickering in the subsurface space of CGRP(+) nociceptors compared to their mild loading counterparts.

Conclusion

In the organ culture system, IVD overloading mediated an altered IVD-nociceptor communication suggesting a biological mechanism associated with discogenic pain.

Expression of GADD45G and CAPRIN1 in Human Nucleus Pulposus: Implications for Intervertebral Disc Degeneration

Marked cellular changes occur in human intervertebral disc (IVD) degeneration during disc degeneration with biochemical changes. Genome-wide analysis of the DNA methylation profile has identified 220 differentially methylated loci associated with human IVD degeneration. Among these, two cell-cycle-associated genes, growth arrest and DNA damage 45 gamma (GADD45G) and cytoplasmic activation/proliferation-associated protein-1 (CAPRIN1), were focused on. The expression of GADD45G and CAPRIN1 in human IVDs remains unknown. We aimed to examine the expression of GADD45G and CAPRIN1 in human nucleus pulposus (NP) cells and evaluate those in human NP tissues in the early and advanced stages of degeneration according to Pfirrmann magnetic resonance imaging (MRI) and histological classifications. Human NP cells were cultured as monolayers after isolation from NP tissues by sequential enzyme digestion. Total RNA was isolated, and the mRNA expression of GADD45G and CAPRIN1 was quantified using real-time polymerase chain reaction. To examine the effects of pro-inflammatory cytokines on mRNA expression, human NP cells were cultured in the presence of IL-1β. Protein expression was evaluated using Western blotting and immunohistochemistry. GADD45G and CAPRIN1 expression was identified in human NP cells at both mRNA and protein levels. The percentage of cells immunopositive for GADD45G and CAPRIN1 significantly increased according to the Pfirrmann grade. A significant correlation between the histological degeneration score and the percentage of GADD45G-immunopositive cells was identified, but not with that of CAPRIN1-immunopositive cells. The expression of cell-cycle-associated proteins (GADD45G and CAPRIN1) was enhanced in human NP cells at an advanced stage of degeneration, suggesting that it may be regulated during the progression of IVD degeneration to maintain the integrity of human NP tissues by controlling cell proliferation and apoptosis under epigenetic alteration.

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.

Extracellular vesicle and soluble fractions of adipose tissue-derived mesenchymal stem cells secretome induce inflammatory cytokines modulation in an in vitro model of discogenic pain

BACKGROUND CONTEXT

Mesenchymal stem cells (MSCs) secretome or conditioned medium (CM) is a complex cocktail of different molecules, some of which, particularly those contained in extracellular vesicles, already have proven therapeutic applications.

PURPOSE

CM may well represent promising therapy for discogenic pain and the intention of this work is to assess its therapeutic potential using an in vitro model of this condition.

STUDY DESIGN

This is an experimental study.

METHODS

Our in vitro model comprised nucleus pulposus (NP) and annulus fibrosus (AF) cells inflamed with TNF. To assess the potential therapeutic value of CM and its components, extracellular vesicles (EVs) and soluble culture fraction (SF), cell inflammation took place under 3 different conditions: either in the presence of whole CM, isolated EVs or SF, and concentrations of pro-inflammatory cytokines, metalloproteinases (MMPs) and neurotrophic factors produced in all 3 cases were compared.

RESULTS

In the presence of whole CM, both in vitro gene expression by the NP and AF test cells and analysis of their protein content showed high modulatory effects on inflammation and MMP inhibition. The presence of EVs and SF showed similar but much smaller effects, and this was particularly marked in the case of NP cells.

CONCLUSIONS

Our results show that, compared to EVs and SF, the presence of whole CM has the greatest positive effect on the modulation of pro-inflammatory and catabolic factors. These observations suggest that CM could protect against inflammation and the resulting intervertebral disc (IVD) degeneration that leads to discogenic pain.

CLINICAL SIGNIFICANCE

Many patients' expectations are not met by current non-operative and surgical treatments for discogenic low back pain. We propose the use of the MSCs secretome for assessing its potential as cell-free therapy to treat degenerative disc disease modulating the inflammatory response.

Platelet-Rich Plasma-Releasate (PRPr) for the Treatment of Discogenic Low Back Pain Patients: Long-Term Follow-Up Survey

Background and Objectives: Clinical studies of platelet-rich plasma (PRP) for the treatment of low back pain (LBP) have been reported; however, less is known about its long-term efficiency. Materials and Methods: This study was a long-term follow-up of a previous prospective clinical feasibility study for the use of PRP releasate (PRPr) to treat discogenic LBP patients. Among 14 patients, 11 patients were evaluated for a long-term survey. The efficacy was assessed by a visual analogue scale (VAS) for LBP intensity and the Roland-Morris Disability Questionnaire (RDQ) for LBP-related disability. Radiographic disc height was evaluated for seven patients. Results: Improvements in VAS and RDQ were sustained at an average of 5.9 years after the intradiscal injection of PRPr (p < 0.01 vs. baseline, respectively). Clinically meaningful improvements (more than 30% decrease from baseline) in VAS and RDQ were identified in 91% of patients at final survey. The radiographic measurement of disc height of PRPr-injected discs showed a mild decrease (13.8% decrease compared to baseline) during the average 5.9 years. Conclusions: The results of this study with a small number of patients suggest that the intradiscal injection of PRPr has a safe and efficacious effect on LBP improvement for more than 5 years after treatment. Further large-scale studies would be needed to confirm the clinical evidence for the use of PRPr for the treatment of patients with discogenic LBP.

A High Body Mass Index and the Vacuum Phenomenon Upregulate Pain-Related Molecules in Human Degenerated Intervertebral Discs

Animal studies suggest that pain-related-molecule upregulation in degenerated intervertebral discs (IVDs) potentially leads to low back pain (LBP). We hypothesized that IVD mechanical stress and axial loading contribute to discogenic LBP’s pathomechanism. This study aimed to elucidate the relationships among the clinical findings, radiographical findings, and pain-related-molecule expression in human degenerated IVDs. We harvested degenerated-IVD samples from 35 patients during spinal interbody fusion surgery. Pain-related molecules including tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-6, calcitonin gene-related peptide (CGRP), microsomal prostaglandin E synthase-1 (mPGES1), and nerve growth factor (NGF) were determined. We also recorded preoperative clinical findings including body mass index (BMI), Oswestry Disability Index (ODI), and radiographical findings including the vacuum phenomenon (VP) and spinal instability. Furthermore, we compared pain-related-molecule expression between the VP (−) and (+) groups. BMI was significantly correlated with the ODI, CGRP, and mPGES-1 levels. In the VP (+) group, mPGES-1 levels were significantly higher than in the VP (−) group. Additionally, CGRP and mPGES-1 were significantly correlated. Axial loading and mechanical stress correlated with CGRP and mPGES-1 expression and not with inflammatory cytokine or NGF expression. Therefore, axial loading and mechanical stress upregulate CGRP and mPGES-1 in human degenerated IVDs, potentially leading to chronic discogenic LBP.

Injectable decellularized nucleus pulposus tissue exhibits neuroinhibitory properties

Background

Chronic low back pain (LBP) is a leading cause of disability, but treatments for LBP are limited. Degeneration of the intervertebral disc due to loss of neuroinhibitory sulfated glycosaminoglycans (sGAGs) allows nerves from dorsal root ganglia to grow into the core of the disc. Treatment with a decellularized tissue hydrogel that contains sGAGs may inhibit nerve growth and prevent disc-associated LBP.

Methods

A protocol to decellularize porcine nucleus pulposus (NP) was adapted from previous methods. DNA, sGAG, α-gal antigen, and collagen content were analyzed before and after decellularization. The decellularized tissue was then enzymatically modified to be injectable and form a gel at 37°C. Following this, the mechanical properties, microstructure, cytotoxicity, and neuroinhibitory properties were analyzed.

Results

The decellularization process removed 99% of DNA and maintained 74% of sGAGs and 154% of collagen compared to the controls NPs. Rheology demonstrated that regelled NP exhibited properties similar to but slightly lower than collagen-matched controls. Culture of NP cells in the regelled NP demonstrated an increase in metabolic activity and DNA content over 7 days. The collagen content of the regelled NP stayed relatively constant over 7 days. Analysis of the neuroinhibitory properties demonstrated regelled NP significantly inhibited neuronal growth compared to collagen controls.

Conclusions

The decellularization process developed here for porcine NP tissue was able to remove the antigenic material while maintaining the sGAG and collagen. This decellularized tissue was then able to be modified into a thermally forming gel that maintained the viability of cells and demonstrated robust neuroinhibitory properties in vitro. This biomaterial holds promise as an NP supplement to prevent nerve growth into the native disc and NP in vivo.

DUSP-1 Induced by PGE2 and PGE1 Attenuates IL-1β-Activated MAPK Signaling, Leading to Suppression of NGF Expression in Human Intervertebral Disc Cells

The molecular mechanism of discogenic low back pain (LBP) involves nonphysiological nerve invasion into a degenerated intervertebral disc (IVD), induced by nerve growth factor (NGF). Selective cyclooxygenase (COX)-2 inhibitors are mainly used in the treatment of LBP, and act by suppressing the inflammatory mediator prostaglandin E₂ (PGE₂), which is induced by inflammatory stimuli, such as interleukin-1β (IL-1β). However, in our previous in vitro study using cultured human IVD cells, we demonstrated that the induction of NGF by IL-1β is augmented by a selective COX-2 inhibitor, and that PGE₂ and PGE₁ suppress NGF expression. Therefore, in this study, to elucidate the mechanism of NGF suppression by PGE₂ and PGE₁, we focused on mitogen-activated protein kinases (MAPKs) and its phosphatase, dual-specificity phosphatase (DUSP)-1. IL-1β-induced NGF expression was altered in human IVD cells by MAPK pathway inhibitors. PGE₂ and PGE₁ enhanced IL-1β-induced DUSP-1 expression, and suppressed the phosphorylation of MAPKs in human IVD cells. In DUSP-1 knockdown cells established using small interfering RNA, IL-1β-induced phosphorylation of MAPKs was enhanced and prolonged, and NGF expression was significantly enhanced. These results suggest that PGE₂ and PGE₁ suppress IL-1β-induced NGF expression by suppression of the MAPK signaling pathway, accompanied by increased DUSP-1 expression.

Role of CD14-positive cells in inflammatory cytokine and pain-related molecule expression in human degenerated intervertebral discs

Multiple human and animal studies suggest that the upregulation of inflammatory cytokines and other pain-related molecules in degenerated or injured intervertebral discs (IVDs) may cause discogenic low back pain (LBP). We previously reported that macrophages in injured IVD in mice produced inflammatory cytokines, but not other pain-related molecules. CD14 is a monocyte marker expressed mainly by macrophages. The aim of the current study was to evaluate the role of CD14-positive cells in inflammatory cytokine and pain-related molecule expression in human degenerated IVD. IVD samples were harvested from 14 patients, including 10 with lumbar spinal stenosis, four with adult spinal deformity, and one with lumbar disc herniation during spinal interbody fusion surgery. Harvested IVD-derived mononuclear cells were obtained and CD14-positive (+) and CD14-negative (-) cells were separated using CD14 antibody and streptavidin-labeled magnetic beads. Inflammatory cytokines messenger RNA (mRNA) in the CD14(+) and CD14(-) cells, including tumor necrosis factor ɑ (TNFA), in, terleukin-1β (IL1B) and IL6, were determined using quantitative polymerase chain reaction (qPCR) and their expression levels were compared. To evaluate factors controlling the regulation of pain-related molecules mRNA expression, cultured CD14(-) and CD14(+) cells from IVDs were stimulated with recombinant human TNF-ɑ and IL-1β and levels of pain-related molecules, including calcitonin gene-related peptide (CGRP) and nerve growth factor (NGF) were determined using qPCR. Levels of TNFA, IL1B, IL6, and NGF in CD14(+) cells were significantly increased compared with those in CD14(-) cells (TNFA, p = 0.006; IL1B, p = .017; IL6, p = .010; NGF, p = .027). Following TNFA stimulation, NGF levels were significantly increased in CD14(-) and CD14(+) cells (CD14(-), p = .003; CD14(+), p < .001) and CGRP was significantly increased in CD14(-) IVD cells (p = .040). Following IL1B stimulation, NGF levels were significantly increased in CD14(-) cells (p = .004). CD14(+) cells had higher TNFA, IL1B, IL6, and NGF expressions than CD14(-) cells in human degenerated IVDs. Additionally, TNFA stimulation promoted the upregulation of NGF and CGRP in CD14(-) cells. These findings suggested that CD14(+) cells directly and indirectly contributed to inflammatory cytokine and pain-related molecule expression in human degenerated IVD. CD14(+) cells might be important in the pathological mechanism of chronic discogenic LBP in humans.

TGF-β regulates nerve growth factor expression in a mouse intervertebral disc injury model

Background

Intervertebral disc (IVD) degeneration is a major cause of low back pain (LBP). Following disc injury, nerve growth factor (NGF) concentrations rise in IVDs, and anti-NGF therapy has been shown to attenuate LBP in humans. Increased levels of tumor necrosis factor-α (TNF-α) and transforming growth factor-β (TGF-β) in degenerative IVDs and in in vitro studies suggest that these factors promote NGF production. However, whether these factors regulate NGF in vivo remains unclear. Thus, we studied NGF regulation in a mouse model of IVD injury.

Methods

After inducing IVD injury, we examined mRNA levels of Tnfa, Tgfb, and Ngf in IVDs from control and IVD-injured mice across 7 days. To do this, we used magnetic cell separation to isolate CD11b ( +) (macrophage-rich) and CD11b (-) (IVD cell-rich) cell fractions from injured IVDs. To study the effect of TNF-α on Ngf expression, we examined Ngf expression in injured IVDs from C57BL/6 J and Tnfa-knockout (KO) mice (C57BL/6 J background). To study the effect of TGF-β on Ngf expression, C57/BL6J mice were given an intraperitoneal injection of either the TGF-β inhibitor SB431542 or DMSO solution (vehicle) one and two days before harvesting IVDs.

Results

mRNA expression of Tnfa, Tgfb, and Ngf was significantly increased in injured IVDs. Tnfa was predominantly expressed in the CD11b ( +) fraction, and Tgfb in the CD11b (-) fraction. Ngf expression was comparable between CD11b ( +) and CD11b (-) fractions, and between wild-type and Tnfa-KO mice at post-injury day (PID) 1, 3, and 7. SB431542 suppressed TGF-β-mediated Ngf expression and NGF production in vitro. Further, administration of SB431542 significantly reduced Ngf expression in IVDs such that levels were below those observed in vehicle-treated animals at PID3 and PID7.

Conclusion

A TGF-β inhibitor reduced Ngf expression in a mouse model of IVD injury, suggesting that TGF-β may regulate NGF expression in vivo.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04509-w.

Activation of nuclear factor-kappa B by TNF promotes nucleus pulposus mineralization through inhibition of ANKH and ENPP1

Spontaneous mineralization of the nucleus pulposus (NP) has been observed in cases of intervertebral disc degeneration (IDD). Inflammatory cytokines have been implicated in mineralization of multiple tissues through their modulation of expression of factors that enable or inhibit mineralization, including TNAP, ANKH or ENPP1. This study examines the underlying factors leading to NP mineralization, focusing on the contribution of the inflammatory cytokine, TNF, to this pathologic event. We show that human and bovine primary NP cells express high levels of ANKH and ENPP1, and low or undetectable levels of TNAP. Bovine NPs transduced to express TNAP were capable of matrix mineralization, which was further enhanced by ANKH knockdown. TNF treatment or overexpression promoted a greater increase in mineralization of TNAP-expressing cells by downregulating the expression of ANKH and ENPP1 via NF-κB activation. The increased mineralization was accompanied by phenotypic changes that resemble chondrocyte hypertrophy, including increased RUNX2 and COL10A1 mRNA; mirroring the cellular alterations typical of samples from IDD patients. Disc organ explants injected with TNAP/TNF- or TNAP/shANKH-overexpressing cells showed increased mineral content inside the NP. Together, our results confirm interactions between TNF and downstream regulators of matrix mineralization in NP cells, providing evidence to suggest their participation in NP calcification during IDD.

The Effect and Possible Mechanism of Intradiscal Injection of Simvastatin in the Treatment of Discogenic Pain in Rats

To study the effect of intradiscal injection of simvastatin on discogenic pain in rats and its possible mechanism, 30 adult female rats were used in this experiment. Twenty rats were randomly divided into sham operation group (Control group), intervertebral disk degeneration group (DDD group), intervertebral disk degeneration + hydrogel group (DDD + GEL group), and intervertebral disk degeneration + simvastatin group (DDD + SIM group). The mechanical pain threshold and cold sensation in rats were measured. The contents of NF-kappa B1, RelA, GAP43, SP, CGRP, TRPM 8, IL-1β, and TNF-α in the intervertebral disk (IVD), the corresponding contents of dorsal root ganglion (DRG) and plantar skin GAP43 and TRPM 8 were quantitatively detected by PCR. The corresponding IVDs were stained to detect their degeneration. There was no significant difference in the mechanical pain threshold between the groups at each time point. From the first day to the 8th week after surgery, the cold-sensing response of the DDD group was significantly higher than that of the Control group (P < 0.05). At 7 and 8 weeks postoperatively, the cold-sensing response of the DDD + SIM group was significantly lower than that of the DDD + GEL group (P < 0.05). The levels of NF-κB1, RelA, GAP43, SP, CGRP, TRPM8, IL-1β, and TNF-α in the IVD of DDD + SIM group were significantly lower than those in DDD group (P < 0.05). The content of GAP43 and TRPM8 in rat plantar skin decreased significantly and TRPM8 in DRG decreased significantly (P < 0.05).

Pro-Inflammatory and Neurotrophic Factor Responses of Cells Derived from Degenerative Human Intervertebral Discs to the Opportunistic Pathogen Cutibacterium acnes

Previously, we proposed the hypothesis that similarities in the inflammatory response observed in acne vulgaris and degenerative disc disease (DDD), especially the central role of interleukin (IL)-1β, may be further evidence of the role of the anaerobic bacterium Cutibacterium (previously Propionibacterium) acnes in the underlying aetiology of disc degeneration. To investigate this, we examined the upregulation of IL-1β, and other known IL-1β-induced inflammatory markers and neurotrophic factors, from nucleus-pulposus-derived disc cells infected in vitro with C. acnes for up to 48 h. Upon infection, significant upregulation of IL-1β, alongside IL-6, IL-8, chemokine (C-C motif) ligand 3 (CCL3), chemokine (C-C motif) ligand 4 (CCL4), nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), was observed with cells isolated from the degenerative discs of eight patients versus non-infected controls. Expression levels did, however, depend on gene target, multiplicity and period of infection and, notably, donor response. Pre-treatment of cells with clindamycin prior to infection significantly reduced the production of pro-inflammatory mediators. This study confirms that C. acnes can stimulate the expression of IL-1β and other host molecules previously associated with pathological changes in disc tissue, including neo-innervation. While still controversial, the role of C. acnes in DDD remains biologically credible, and its ability to cause disease likely reflects a combination of factors, particularly individualised response to infection.

Painful intervertebral disc degeneration and inflammation: from laboratory evidence to clinical interventions

Low back pain (LBP), as a leading cause of disability, is a common musculoskeletal disorder that results in major social and economic burdens. Recent research has identified inflammation and related signaling pathways as important factors in the onset and progression of disc degeneration, a significant contributor to LBP. Inflammatory mediators also play an indispensable role in discogenic LBP. The suppression of LBP is a primary goal of clinical practice but has not received enough attention in disc research studies. Here, an overview of the advances in inflammation-related pain in disc degeneration is provided, with a discussion on the role of inflammation in IVD degeneration and pain induction. Puncture models, mechanical models, and spontaneous models as the main animal models to study painful disc degeneration are discussed, and the underlying signaling pathways are summarized. Furthermore, potential drug candidates, either under laboratory investigation or undergoing clinical trials, to suppress discogenic LBP by eliminating inflammation are explored. We hope to attract more research interest to address inflammation and pain in IDD and contribute to promoting more translational research.

Inflammation in the intervertebral disc herniation

Up until fairly recently, it was thought that sciatic pain in the lumbar herniated disc was caused by compression on the nerve root. However, the lumbar herniated disc shows mixed pictures which are difficult to explain by simple mechanical compromise. In recent years various immunology, immunohistochemistry and molecular biology studies have shown that the herniated tissue is not an inert material, but rather it Is biologically very active with the capability of expressing a series of inflammatory mediators: cytokines such as interleukin-1, interleukin-6, interleuquin-8 and tumor necrosis factor being the ones which stand out. The inflammation is not only induced by the chemical irritation of the bioactive substances released by the nucleus pulposus but also by an autoimmune response against itself. Thus, in addition to the mechanical factor, the biomechanical mediation plays an important role in the pathophysiology of sciatic pain and of radiculopathy. Through a review of a wide range of literature, we researched the cellular molecular mediators involved in this inflammatory process around the lumbar herniated disc and its involvement in sciatic pain.

Expression of Glial Cell Line-derived Neurotrophic Factor in the Human Intervertebral Disc

STUDY DESIGN

Biochemical and immunohistochemical analyses by the human intervertebral disc (IVD) cells and tissues.

OBJECTIVE

To examine the expression of glial cell line-derived neurotrophic factor (GDNF) and its receptors, GDNF family receptor (GFR) α1 and rearranged during transfection (RET) in the human IVD cells and the tissues with the early and advanced stages of degeneration.

SUMMARY OF BACKGROUND DATA

The neurotrophin family, including nerve growth factor, has been reported to be expressed in the IVDs and plays a role in hyperalgesia and neuronal sensitization. Despite having properties similar to the nerve growth factor, the expression of GDNF in the IVD remains unknown.

METHODS

Human IVD cells were cultured in monolayer. Immunohistochemical analyses and western blotting were performed to examine the protein levels of GDNF and its receptors. To examine the effect of proinflammatory cytokines, cells were cultured in the presence of interleukin-1β (IL-1β). The immunohistochemical expression of these proteins was also evaluated using human IVD tissues with different stages of degeneration.

RESULTS

Immunofluorescent reactivity against anti-GDNF, GFRα1, and RET antibodies was identified in human IVD cells. In protein extracts from IVD cells, those protein expressions were also identified by Western blot. IL-1β significantly stimulated the mRNA expression of GDNF compared with that of the control group. There was no significant effect of IL-1β on the mRNA expression of GFRα1 and RET. The percentage of GDNF-immunopositive cells in advanced degenerated discs was significantly higher than that in early degenerated discs, whereas those of GFRα1 and RET showed no significant differences.

CONCLUSIONS

GDNF and its receptors were constitutively expressed in the human IVD cells. GDNF expression was significantly enhanced by proinflammatory stimuli, and in the microenvironment with advanced tissue degeneration.

LEVEL OF EVIDENCE

N/A.

Preclinical ex-vivo Testing of Anti-inflammatory Drugs in a Bovine Intervertebral Degenerative Disc Model

Discogenic low back pain (LBP) is a main cause of disability and inflammation is presumed to be a major driver of symptomatic intervertebral disc degeneration (IDD). Anti-inflammatory agents are currently under investigation as they demonstrated to alleviate symptoms in patients having IDD. However, their underlying anti-inflammatory and regenerative activity is poorly explored. The present study sought to investigate the potential of Etanercept and Tofacitinib for maintaining disc homeostasis in a preclinical intervertebral disc (IVD) organ culture model within IVD bioreactors allowing for dynamic loading and nutrient exchange. Bovine caudal IVDs were cultured in a bioreactor system for 4 days to simulate physiological or degenerative conditions: (1) Phy—physiological loading (0.02–0.2 MPa; 0.2 Hz; 2 h/day) and high glucose DMEM medium (4.5 g/L); (2) Deg+Tumor necrosis factor α (TNF-α)—degenerative loading (0.32–0.5 MPa; 5 Hz; 2 h/day) and low glucose DMEM medium (2 g/L), with TNF-α injection. Etanercept was injected intradiscally while Tofacitinib was supplemented into the culture medium. Gene expression in the IVD tissue was measured by RT-qPCR. Release of nitric oxide (NO), interleukin 8 (IL-8) and glycosaminoglycan (GAG) into the IVD conditioned medium were analyzed. Cell viability in the IVD was assessed using lactate dehydrogenase and ethidium homodimer-1 staining. Immunohistochemistry was performed to assess protein expression of IL-1β, IL-6, IL-8, and collagen type II in the IVD tissue. Etanercept and Tofacitinib downregulated the expression of IL-1β, IL-6, IL-8, Matrix metalloproteinase 1 (MMP1), and MMP3 in the nucleus pulposus (NP) tissue and IL-1β, MMP3, Cyclooxygenase-2 (COX2), and Nerve growth factor (NGF) in the annulus fibrosus (AF) tissue. Furthermore, Etanercept significantly reduced the IL-1β positively stained cells in the outer AF and NP regions. Tofacitinib significantly reduced IL-1β and IL-8 positively stained cells in the inner AF region. Both, Etanercept and Tofacitinib reduced the GAG loss to the level under physiological culture condition. Etanercept and Tofacitinib are able to neutralize the proinflammatory and catabolic environment in the IDD organ culture model. However, combined anti-inflammatory and anabolic treatment may be required to constrain accelerated IDD and relieving inflammation-induced back pain.

Histomorphology and immunohistochemical patterns in degenerative disc disease and clinical-radiological correlations: a prospective study

PURPOSE

Degenerative disc disease (DDD) is a common condition causing low-back pain, disability and, eventually, neurological symptoms. This investigation aimed to investigate intervertebral disc DDD-related changes, evaluating histomorphology and cytokines secretion, and their clinical-radiological correlations.

METHODS

This is a monocentric prospective observational study. A cohort of patients who underwent microdiscectomy for DDD, from June 2018 to January 2019, were enrolled. Discs samples were examined for histomorphology, chondrons count, immunohistochemistry for Hif-1α, Nf200 and Egr-1. Demographical and clinical data were also collected.

RESULTS

Twenty patients were finally included. MRI evaluation showed a Modic I alteration in nine patients and a Modic II in 11. The disability grade was low-moderate (ODI score was ≤ 40%) in eight patients and high (ODI score > 40%) in 12. The Modic I was associated with a low-moderate disability in two (22%) patients and to a high disability in seven (88%) (p < 0.01). In Modic I group and in ODI > 40% groups, there were a significative higher mean disability grade 48.4 (± 8.3)%, number of chondrons per section, cells per chondron, Nf200+ nerve fibers and Hif-1α expression, compared with Modic II and ODI ≤ 40% groups, respectively. There were no differences in terms of Egr-1 expression.

CONCLUSIONS

The discs with Modic I MRI signal could represent potential targets for medical treatments, whereas Modic II seems to be a more likely point of no return in a degenerative process. Therefore, further investigations are to better investigate inflammatory pathways and degenerative mechanisms in DDD.

CoQ10 ameliorates monosodium glutamate-induced alteration in detrusor activity and responsiveness in rats via anti-inflammatory, anti-oxidant and channel inhibiting mechanisms

Background

Competent detrusor muscles with coordinated contraction and relaxation are crucial for normal urinary bladder storage and emptying functions. Hence, detrusor instability, and subsequently bladder overactivity, may lead to undesirable outcomes including incontinence. Multiple mechanisms may underlie the pathogenesis of detrusor overactivity including inflammation and oxidative stress. Herein, we tested the possibility that CoQ10 may have a potential therapeutic role in detrusor overactivity.

Methods

Forty adult male Wistar albino rats weighing 100-150 g were used in the present study. Rats were divided (10/group) into control (receiving vehicles), monosodium glutamate (MSG)-treated (receiving 5 mg/kg MSG daily for 15 consecutive days), MSG + OO-treated (receiving concomitantly 5 mg/kg MSG and olive oil for 15 consecutive days), MSG + CoQ10-treated (receiving concomitantly 5 mg/kg MSG and 100 mg/kg CoQ10 daily for 15 consecutive days) groups.

Results

MSG resulted in significant increase in bladder weight and sensitised the bladder smooth muscles to acetylcholine. MSG has also resulted in significant increase in bladder TNF-α, IL-6, malondialdehyde, nerve growth factor and connexion 43, with significant decrease in the antioxidant enzymes superoxide dismutase and catalase. Olive oil had no effect on MSG induced alterations of different parameters. Treatment with CoQ10 has resulted in a significant restoration of all the altered parameters.

Conclusion

Taken together, our results suggest that CoQ10 antagonizes the deleterious effects of MSG on detrusor activity. We propose that CoQ10 could be a therapeutic strategy targeting urinary bladder dysfunction.

A percutaneous, minimally invasive annulus fibrosus needle puncture model of intervertebral disc degeneration in rabbits

PURPOSE

Various animal models have been proposed to mimic the pathophysiologic process of intervertebral disc degeneration, a leading cause of back pain. The purpose of this study is to describe a minimally invasive technique via percutaneous needle puncture of the annulus fibrosus in New Zealand white rabbits.

METHODS

Under fluoroscopic guidance, an 18-gauge spinal needle was inserted 2 cm lateral to the midline spinous process. The needle was slowly advanced at approximately 45° angle until it was adjacent to the L5/L6 disc space. Lateral and anteroposterior views were used to verify correct needle position before advancing into the nucleus pulposus. The rabbits underwent weekly X-rays for 4 weeks to assess disc height index. MRI T2 relaxation was evaluated at week four to assess morphological changes. Discs were histologically graded on a 12-point scale to assess degeneration and compared to discs obtained from uninjured rabbits.

RESULTS

There were no complications associated with the percutaneous needle puncture procedure. All animals survived the duration of the experiment. Four weeks after injury, the disc height had progressively narrowed to approximately 50% of baseline. MRI assessment at the 4-week time point demonstrated a mean T2 relaxation time at the L5/L6 level that was 20.9% of the T2 relaxation time at the uninjured L4/L5 disc level ( p < 0.001). Histological analysis demonstrated lamellar disorganization of the annulus and decreased cellularity and proteoglycan content within the injured nucleus compared to uninjured control discs.

CONCLUSION

The present study demonstrated a reliable technique of inducing an annular tear via a percutaneous needle puncture. Compared to open surgical approaches, the percutaneous model produces similar progressive disc degeneration while minimizing harm to the animal subjects.

CLINICAL RELEVANCE

The present study establishes a technique for the introduction of novel therapeutic agents to treat disc degeneration that may translate to future clinical trials.

Changes in Nerve Growth Factor Expression and Macrophage Phenotype Following Intervertebral Disc Injury in Mice

Nerve growth factor (NGF) is increased in intervertebral discs (IVDs) after disc injury and anti-NGF therapy improves low back pain in humans. Furthermore, M1 and M2 macrophage subtypes play a role in degenerative IVD injury. We examined M1 and M2 macrophage markers and NGF and cytokine expression in IVD-derived cells from control and IVD-injured mice for 28 days following injury. Ngf messenger RNA (mRNA) expression was increased 1 day after injury in injured compared with control mice, and persisted for up to 28 days. Flow cytometric analysis demonstrated that the proportion of F4/80+ CD11b+ cells was significantly increased from 1 day after injury for up to 28 days in injured compared to control mice. mRNA expression of M1 macrophage markers Tnfa, Il1b, and Nos2 was significantly increased 1 day after injury in injured compared to control mice, before gradually decreasing. At 28 days, no significant difference was observed in M1 markers. The M2a marker, Ym1, was significantly increased 1 day after injury in injured compared with control mice, while M2a and M2c markers Tgfb and Cd206 were significantly increased 7, 14, and 28 days after injury. Tumor necrosis factor α (TNF-α) and transforming growth factor β (TGF-β) stimulated Ngf mRNA and NGF protein expression in IVD cells. Our results suggest that TNF-α and TGF-β may stimulate NGF production under inflammatory and non-inflammatory conditions following IVD injury. As TNF-α and TGF-β are produced by M1 and M2 macrophages, further investigations are needed to reveal the role of macrophages in NGF expression following IVD injury. Our results may aid in developing treatments for IVD-related LBP pathology. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1798-1804, 2019.

Safety of intradiscal delivery of triamcinolone acetonide by a poly(esteramide) microsphere platform in a large animal model of intervertebral disc degeneration

BACKGROUND CONTEXT

Local corticosteroids have been used to relieve symptoms of chronic low back pain, although treatment effects have been shown to wear off relatively fast. Prolonging corticosteroid presence by controlled release from biomaterials may allow for longer pain relief while circumventing adverse effects such as high bolus dosages.

PURPOSE

The purpose of this study was to evaluate the safety and efficacy of intradiscal controlled release of triamcinolone acetonide (TAA) by poly(esteramide) microspheres in a canine degenerated intervertebral disc (IVD) model.

STUDY DESIGN

In a preclinical experimental large animal model, the effect of prolonged glucocorticoid exposure on disc degeneration was evaluated.

METHODS

Degeneration was accelerated by nucleotomy of lumbar IVDs of Beagle dogs. After 4 weeks, microspheres loaded with 8.4 µg TAA, and 0.84mg TAA were administered to the degenerated IVDs by intradiscal injection (n=6 per group). Empty microspheres (n=6) and all adjacent non-nucleotomized noninjected IVDs were included as controls (n=24). Immediately prior to TAA administration and after 12 weeks, magnetic resonance imaging was performed. Degenerative changes were evaluated by disc height index, Pfirrmann grading, T1ρ and T2 mapping values, postmortem CT scans, macroscopic and microscopic grading, and biochemical/immunohistochemical analysis of inflammation and extracellular matrix content. In addition, nerve growth factor (NGF) protein expression, a biomarker for pain, was scored in nucleus pulposus (NP) tissues. The study was funded by a research grant from Health Holland (1.3million euros = 1.5million US dollars).

RESULTS

Macroscopic evaluation and CT images postmortem were consistent with mild disc degeneration. Other abnormalities were not observed. Nucleotomy-induced degeneration and inflammation was mild, reflected by moderate Pfirrmann grades and PGE₂ levels. Regardless of TAA dosage, local sustained delivery did not affect disc height index nor Pfirrmann grading, T1ρ and T2 mapping values, PGE₂ tissue levels, collagen, GAG, and DNA content. However, the low dosage of TAA microspheres significantly reduced NGF immunopositivity in degenerated NP tissue.

CONCLUSIONS

This is the first in vivo application in a preclinical large animal model of a controlled release formulation of corticosteroids in mild IVD degeneration. Sustained release of TAA locally in the IVD appeared safe and reduced NGF expression, suggesting its potential applicability for pain relief, although beneficial effects were absent on tissue degeneration.

CLINICAL SIGNIFICANCE

The present platform seems to be promising in extending the local controlled delivery of TAA with the potency to provide long-standing analgesia in the subset of LBP patients suffering from discogenic pain.

Electrical impulse effects on degenerative human annulus fibrosus model to reduce disc pain using micro-electrical impulse-on-a-chip

Electrical stimulation of cells and tissues for therapeutic benefit is a well-established method. Although animal studies can emulate the complexity of an organism’s physiology, lab-on-a-chip platforms provide a suitable primary model for follow-up animal studies. Thus, inexpensive and easy-to-use platforms for in vitro human cell studies are required. In the present study, we designed a micro-electrical impulse (micro-EI)-on-a-chip (micro-EI-chip), which can precisely control electron density and adjust the frequency based on a micro-EI. The micro-EI-chip can stimulate cells at various micro-EI densities (0–500 mV/mm) and frequencies (0–300 Hz), which enables multiple co-culture of different cell types with or without electrical stimulation. As a proof-of-concept study, a model involving degenerative inflamed human annulus fibrosus (hAF) cells was established in vitro and the effects of micro-EI on inflamed hAF cells were evaluated using the micro-EI-chip. Stimulation of the cells (150 mV/mm at 200 Hz) inhibited the secretion of inflammatory cytokines and downregulated the activities of extracellular matrix-modifying enzymes and matrix metalloproteinase-1. These results show that micro-EI stimulation could affect degenerative diseases based on inflammation, implicating the micro-EI-chip as being useful for basic research of electroceuticals.

Behavioral Compensations and Neuronal Remodeling in a Rodent Model of Chronic Intervertebral Disc Degeneration

Low back pain is associated with degeneration of the intervertebral disc, but specific mechanisms of pain generation in this pathology remain unknown. Sensory afferent nerve fiber growth into the intervertebral disc after injury-induced inflammation may contribute to discogenic pain. We describe a clinically relevant behavioral phenotype in a rodent model of chronic intervertebral disc degeneration which provides a means to map sensory neuron changes to a single affected lumbar intervertebral disc. Unilateral disc puncture of one lumbar intervertebral disc revealed a bilateral behavioral phenotype characterized by gait changes and decreased activity. Moreover, neurons extracted from the dorsal root ganglia in animals with intervertebral disc injury demonstrated altered TRPV1 activation in vitro independent of exogenous NGF administration. Finally, neuronal nuclear hypertrophy and elevated expression of p75NTR provide evidence of active adaptation of innervating sensory neurons in chronic intervertebral disc degeneration. Therefore, this model and findings provide the template for future studies to establish specific mechanisms of nociceptive pain in chronic intervertebral disc degeneration.

Platelet-rich plasma in the management of chronic low back pain: a critical review

Low back pain (LBP) is now regarded as the first cause of disability worldwide and should be a priority for future research on prevention and therapy. Intervertebral disc (IVD) degeneration is an important pathogenesis of LBP. Platelet-rich plasma (PRP) is an autologous blood concentrate that contains a natural concentration of autologous growth factors and cytokines and is currently widely used in the clinical setting for tissue regeneration and repair. PRP has great potential to stimulate cell proliferation and metabolic activity of IVD cells in vitro. Several animal studies have shown that the injection of PRP into degenerated IVDs is effective in restoring structural changes (IVD height) and improving the matrix integrity of degenerated IVDs as evaluated by magnetic resonance imaging (MRI) and histology. The results of this basic research have shown the great possibility that PRP has significant biological effects for tissue repair to counteract IVD degeneration. Clinical studies for evaluating the effects of the injection of PRP into degenerated IVDs for patients with discogenic LBP have been reviewed. Although there was only one double-blind randomized controlled trial, all the studies reported that PRP was safe and effective in reducing back pain. While the clinical evidence of tissue repair of IVDs by PRP treatment is currently lacking, there is a great possibility that the application of PRP has the potential to lead to a feasible intradiscal therapy for the treatment of degenerative disc diseases. Further large-scale studies may be required to confirm the clinical evidence of PRP for the treatment of discogenic LBP.

Notochordal cell matrix: An inhibitor of neurite and blood vessel growth?

Blood vessel and neurite ingrowth into the degenerating intervertebral disc (IVD) are related to pain. In reported studies, notochordal cell (NC)-conditioned medium (NCCM) induced a regenerative response of nucleus pulposus (NP) cells, but also inhibition of neurite and vessel formation. NC matrix (NCM) derived from NC-rich NP tissue, induced even stronger anabolic effects than NCCM. Thus, the aim was to investigate whether NCM has similar anti-neurogenic and -angiogenic properties as NCCM. NCM and NCCM where produced from porcine NC-rich NP tissue. Human umbilical vein endothelial cells (HUVECs) were cultured in base medium (BM, 300 mOsm), NCCM (produced at 300 and 400 mOsm), NCM, or with chondroitin sulfate (CS, positive control) in angiogenesis-inducing medium, after which vessel length was measured. Although CS alone inhibited vessel growth, NCCM (both osmolarities) stimulated vessel formation by HUVECs. NCM did not affect vessel growth relative to BM. SH-SY5Y cells were cultured in BM, NCCM, and NCM on poly-D-lysine coated and polystyrene surfaces, and analyzed for neurite length and percentage of neurite expressing cells. On coated surfaces, neither NCCM nor NCM affected neurite growth. On a polystyrene surface, NCCM and NCM induced a higher number of neurite-expressing cells. NCCM's previously reported anti-angiogenic and -neurogenic effects were not observed in this study. Although addition of CS inhibited HUVEC vessel formation, other factors may be present in NCCM and NCM that affect neurite and vessel growth. Therefore, future studies testing an NC-based regenerative strategy should carefully assess the risk of such adverse effects in an in vivo setting. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. J Orthop Res 36:3188-3195, 2018.

Mechanical loading of intervertebral disc modulates microglia proliferation, activation, and chemotaxis

OBJECTIVE

The aim of the study is to assess the effects of the neuroinflammatory microenvironment of a mechanically-induced degenerating intervertebral disc (IVD) on neuroinflammatory like cells such as microglia, in order to comprehend the role of microglial cells in degenerative disc disease.

METHODS

Bovine caudal IVDs were kept in culture in an ex vivo bioreactor under high frequency loading and limited nutrition or in free swelling conditions as control samples. Conditioned media (CM) were collected, analysed for cytokine and neurotrophin content and applied to microglial cells for neuroinflammatory activation assessment.

RESULTS

Degenerative conditioned medium (D-CM) induced a higher production of interleukin (IL)-8, nerve growth factor (NGF), interferon (IFN)-γ, IL-17 from IVD cells than unloaded control conditioned medium (U-CM). Upon 48 h of co-incubation with microglia, D-CM stimulated microglia proliferation, activation, with increased expression of ionized calcium binding adaptor molecule 1 (IBA1) and CD68, and chemotaxis. Moreover, an increment of nitrite production was observed. Interestingly, D-CM caused an upregulation of IL-1β, IL-6, tumour necrosis factor α (TNFα), inducible NO synthase (iNOS), IBA1, and vascular endothelial growth factor (VEGF) genes in microglia. Similar results were obtained when microglia were treated with the combination of the measured cytokines.

CONCLUSIONS

Our findings show that in IVD degenerative microenvironment, IL-8, NGF, IFN-γ, IL-17 drive activation of microglia in the spinal cord and increase upregulation of neuroinflammatory markers. This, in turn, enhances the inflammatory milieu within IVD tissues and in the peridiscal space, aggravating the cascade of degenerative events. This study provides evidence for an important role of microglia in maintaining IVD neuroinflammatory microenvironment and probably inducing low back pain.

Inhibiting tumor necrosis factor-alpha at time of induced intervertebral disc injury limits long-term pain and degeneration in a rat model

Background

Painful intervertebral disc (IVD) degeneration has tremendous societal costs and few effective therapies. Intradiscal tumor necrosis factor‐alpha (TNFα) is commonly associated with low back pain, but the direct relationship remains unclear.

Purpose

Treatment strategies for low back pain require improved understanding of the complex relationships between pain, intradiscal pro‐inflammatory cytokines, and structural IVD degeneration. A rat in vivo lumbar IVD puncture model was used to 1) determine the role of TNFα in initiating painful IVD degeneration, and 2) identify statistical relationships between painful behavior, IVD degeneration, and intradiscal pro‐inflammatory cytokine expression.

Methods

Lumbar IVDs were punctured anteriorly and injected with TNFα, anti‐TNFα, or saline and compared with sham and naive controls. Hindpaw mechanical hyperalgesia was assayed weekly to determine pain over time. 6‐weeks post‐surgery, animals were sacrificed, and IVD degeneration, IVD height, and intradiscal TNFα and interleukin‐1 beta (IL‐1β) expressions were assayed.

Results

Intradiscal TNFα injection increased pain and IVD degeneration whereas anti‐TNFα alleviated pain to sham level. Multivariate step‐wise linear regression identified pain threshold was predicted by IVD degeneration and intradiscal TNFα expression. Pain threshold was also linearly associated with IVD height loss and IL‐1β.

Discussion

The significant associations between IVD degeneration, height loss, inflammation, and painful behavior highlight the multifactorial nature of painful IVD degeneration and the challenges to diagnose and treat a specific underlying factor. We concluded that TNFα is an initiator of painful IVD degeneration and its early inhibition can mitigate pain and degeneration. Intradiscal TNFα inhibition following IVD injury may warrant investigation for its potential to alter downstream painful IVD degeneration processes.

Macrophage-derived inflammatory cytokines regulate growth factors and pain-related molecules in mice with intervertebral disc injury

Upregulation of inflammatory cytokines and various growth factors is a significant contributor to discogenic low back pain. The aim of this study was to investigate possible regulation of pain-related molecules by macrophages and the role of macrophage-derived molecules in injured intervertebral disc (IVD)s. C57BL/6J mice were used in this study. We characterized the expression profiles of genes for tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, nerve growth factor (NGF), and vascular endothelial growth factor (VEGF) in both intact and injured IVDs. We examined whether macrophage depletion, induced by systemic injection of clodronate-laden liposomes, affected the expression of these molecules in injured IVDs. The effect of TNF-alpha on cultured F4/80-CD11b-cells in injured IVDs was investigated. Expression of TNF-alpha and IL-1beta was significantly increased in injured IVDs, but decreased by macrophage depletion. Expression of NGF and VEGF was also significantly increased, but by contrast was not decreased by macrophage depletion. TNF-alpha treatment of F4/80-cells from injured IVDs upregulated NGF, VEGF, cyclooxygenase (COX)-2, and microsomal prostaglandin E synthase-1 (mPGES1). IVD injury upregulated inflammatory cytokines and various growth factors. Macrophages in the injured IVDs produced inflammatory cytokines, but not growth factors. Macrophage-derived inflammatory cytokines regulate growth factors and pain-related molecules. These findings demonstrate further complexity in the pathogenesis of discogenic pain. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Link N as a therapeutic agent for discogenic pain

Neurotrophins (NTs) are the major contributors of sensory axonal sprouting, neural survival, regulation of nociceptive sensory neurons, inflammatory hyperalgesia, and neuropathic pain. Intervertebral disc (IVD) cells constitutively express NTs. Their expression is upregulated by proinflammatory cytokines present in the IVD during degeneration, which can promote peripheral nerve ingrowth and hyperinnervation, leading to discogenic pain. Currently, there are no targeted therapies that decrease hyperinnervation in degenerative disc disease. Link N is a naturally occurring peptide with a high regenerative potential in the IVD. Therefore, the suitability of Link N as a therapeutic peptide for suppressing NTs, which are known modulators and mediators of pain, was investigated. The aim of the present study is to determine the effect of Link N on NTs expression, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and their cognate receptors TrkA and TrkB as they are directly correlated with symptomatic back pain. Furthermore, the neurotransmitter (substance P) was also evaluated in human annulus fibrosus (AF) cells stimulated with cytokines. Human AF cells isolated from normal IVDs were stimulated with interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in the presence or absence of Link N. NGF release in the media was evaluated by Western blotting. Total RNA was isolated and gene expression was measured using real-time PCR. Gene expression of NGF, BDNF, TrkA, and TrkB significantly decreased in human disc cells stimulated with either IL-1β or TNF-α supplemented with Link N when compared to the cells stimulated only with IL-1β or TNF-α. NGF protein expression was also suppressed in AF cells coincubated with Link N and IL-1β when compared to the cells stimulated only with IL-1β. Link N can suppress the stimulation of NGF, BDNF, and their receptors TrkA and TrkB in AF cells in an inflammatory milieu. Thus, coupled with previous observations, this suggests that administration of Link N has the potential to not only repair the discs in early stages of the disease but also suppress pain.

ISSLS PRIZE IN BASIC SCIENCE 2018: Growth differentiation factor-6 attenuated pro-inflammatory molecular changes in the rabbit anular-puncture model and degenerated disc-induced pain generation in the rat xenograft radiculopathy model

PURPOSE

To elucidate the effects of growth differentiation factor-6 (GDF6) on: (i) gene expression of inflammatory/pain-related molecules and structural integrity in the rabbit intervertebral disc (IVD) degeneration model, and (ii) sensory dysfunction and changes in pain-marker expression in dorsal nerve ganglia (DRGs) in the rat xenograft radiculopathy model.

METHODS

Forty-six adolescent rabbits received anular-puncture in two non-consecutive lumbar IVDs. Four weeks later, phosphate-buffered saline (PBS) or GDF6 (1, 10 or 100 µg) was injected into the nucleus pulposus (NP) of punctured discs and followed for 4 weeks for gene expression analysis and 12 weeks for structural analyses. For pain assessment, eight rabbits were sacrificed at 4 weeks post-injection and NP tissues of injected discs were transplanted onto L5 DRGs of 16 nude rats to examine mechanical allodynia. The rat DRGs were analyzed immunohistochemically.

RESULTS

In GDF6-treated rabbit NPs, gene expressions of interleukin-6, tumor necrosis factor-α, vascular endothelial growth factor, prostaglandin-endoperoxide synthase 2, and nerve growth factor were significantly lower than those in the PBS group. GDF6 injections resulted in partial restoration of disc height and improvement of MRI disc degeneration grades with statistical significance in rabbit structural analyses. Allodynia induced by xenograft transplantation of rabbit degenerated NPs onto rat DRGs was significantly reduced by GDF6 injection. Staining intensities for ionized calcium-binding adaptor molecule-1 and calcitonin gene-related peptide in rat DRGs of the GDF6 group were significantly lower than those of the PBS group.

CONCLUSION

GDF6 injection may change the pathological status of degenerative discs and attenuate degenerated IVD-induced pain.

Inflammatory Processes Associated with Canine Intervertebral Disc Herniation

Intervertebral disc herniation (IVDH) is an important pathology in humans and also in dogs. While the molecular disease mechanisms are well investigated in humans, little is known about the inflammatory mediators in naturally occurring canine IVDH. The objective of this study was to investigate whether the involved proinflammatory cytokines in human IVDH are also key cytokines in canine IVDH and thus to elucidate the suitability of the dog as a model for human trials. 59 samples from 25 dogs with surgically confirmed thoracolumbar IVDH were collected and classified in three subgroups: herniated (H), affected non-herniated (NH) disc, and adjacent non-affected (NA) disc. Discs from 11 healthy dogs acted as controls (C). Samples were analyzed for IL-1, IL-6, IL-8, and TNF-α expression (qPCR/ELISA) as well as cell infiltration and activation of the MAP kinase pathways (immunohistochemistry). Gene and protein expression of all key cytokines could be detected in IVDH affected dogs. Canine IVDH was significantly associated with a higher gene expression of IL-6 (H > C, NH > C) and TNF-α (H > C, NH > C, NA > C) and a significant down-regulation of IL-1β (H < C). Dogs with spontaneous pain had significantly higher IL-6 mRNA compared to those with pain arising only upon palpation. An inter-donor comparison (H and HN relative to NA) revealed a significant increase of IL-6 gene expression (H > NA, NH > NA). IL-8 (H > C, NA > C) and TNF-α (NH > C) protein levels were significantly increased in diseased dogs while inversely, IL-6 protein levels were significantly higher in patients with better clinical outcome. Aside from resident IVD cells, mostly monocytes and macrophages were found in extruded material, with concomitant activation of extracellular signal-regulated kinase p38 in the majority of samples. Dogs with spontaneous IVDH might provide a useful model for human disc diseases. Although the expression of key cytokines found in human IVDH was also demonstrated in canine tissue, the inflammatory mechanisms accompanying canine IVDH diverges partially from humans, which will require further investigations in the future. In dogs, IL-6 seems to play an important pathological role and may represent a new potential therapeutic target for canine patients.

Immunohistochemical localization of nerve growth factor, tropomyosin receptor kinase A, and p75 in the bone and articular cartilage of the mouse femur

Sequestration of nerve growth factor (NGF) significantly attenuates skeletal pain in both animals and humans. However, relatively little is known about the specific cell types that express NGF or its cognate receptors tropomyosin receptor kinase A (TrkA) and p75 in the intact bone and articular cartilage. In the present study, antibodies raised against NGF, TrkA, and p75 (also known as CD271) were used to explore the expression of these antigens in the non-decalcified young mouse femur. In general, all three antigens displayed a remarkably restricted expression in bone and cartilage with less than 2% of all DAPI+ cells in the femur displaying expression of any one of the three antigens. Robust NGF immunoreactivity was found in mostly CD-31− blood vessel-associated cells, a small subset of CD-31+ endothelial cells, an unidentified group of cells located at the subchondral bone/articular cartilage interface, and a few isolated, single cells in the bone marrow. In contrast, p75 and TrkA were almost exclusively expressed by nerve fibers located nearby NGF+ blood vessels. The only non-neuronal expression of either p75 or TrkA in the femur was the expression of p75 by a subset of cells located in the deep and middle zone of the articular cartilage. Understanding the factors that tightly regulate the basal level of expression in normal bone and how the expression of NGF, TrkA, and p75 change in injury, disease, and aging may provide insights into novel therapies that can reduce skeletal pain and improve skeletal health.

Proinflammatory Cytokines IL-1β and TNF-α Influence Human Annulus Cell Signaling Cues for Neurite Growth: In Vitro Coculture Studies

STUDY DESIGN

Institutional review board-approved research using human annulus cells cocultured with F11 nerve cells.

OBJECTIVE

To perform functional, kinetic assays of neurite dynamics and media neurotrophin measurements to test whether proinflammatory cytokines influence annulus cells' signaling cues for neurite growth/repulsion.

SUMMARY OF BACKGROUND DATA

Nerves grow in response to signaling molecules called neurotrophins, which disc cells produce (e.g., brain-derived neurotrophic factor [BDNF], glial cell line-derived neurotrophic factor [GDNF], and neurotrophin 3 [NT3]) and which influence neuron survival, differentiation, and migration. How proinflammatory cytokines influence disc signaling cues for neurite growth/repulsion is poorly understood.

METHODS

Studies used our previous model of 4-day human annulus cell-F11 nerve cell coculture to assess effects of added proinflammatory cytokines interleukin 1 beta (IL-1β; 10 pmol/L) or tumor necrosis factor alpha (TNF-α) (10 pmol/L). Annulus cells were cultured from 6 Thompson grade I, 9 grade II, 8 grade III, 11 grade IV, and 7 grade V discs. Neurite lengths were measured following control conditions or with added IL-1β or TNF-α, and conditioned media assayed with RayBiotech Growth Factor Arrays. Standard statistical methods used analysis of variance and Spearman correlation coefficient testing associations of neurite length with neurotrophin levels.

RESULTS

IL-1-β or TNF-α significantly increased neurite lengths (P < 0.001) and BDNF, NT3, and GDNF media levels (P ≤ 0.01) versus controls. Significant positive correlations were present between media neurotrophin levels for BDNF, NT3, and GDNF and neurite lengths under control conditions, following addition of IL-1β, and following addition of TNF-α. Novel data showed production of the neurotrophin amphiregulin.

CONCLUSION

In vitro data supported the hypothesis that nerve-disc cell interactions may be influenced by the heightened proinflammatory milieu present in degenerating discs, leading to increased nerve migration. Data may have direct clinical relevance/implications for nerve ingrowth and pain in the outer annulus (where disc cell numbers are high), and in regions where nerves penetrate into the disc via annular tears.

LEVEL OF EVIDENCE

N/A.

Looking beyond the intervertebral disc: the need for behavioral assays in models of discogenic pain

Orthopedic research into chronic discogenic back pain has commonly focused on aging- and degeneration-related changes in intervertebral disc structure, biomechanics, and biology. However, the primary spine-related reason for physician office visits is pain. The ambiguous nature of the human condition of discogenic low back pain motivates the use of animal models to better understand the pathophysiology. Discogenic back pain models must consider both emergent behavioral changes following pain induction and changes in the nervous system that mediate such behavior. Looking beyond the intervertebral disc, we describe the different ways to classify pain in human patients and animal models. We describe several behavioral assays that can be used in rodent models to augment disc degeneration measurements and characterize different types of pain. We review rodent models of discogenic pain that employed behavioral pain assays and highlight a need to better integrate neuroscience and orthopedic science methods to extend current understanding of the complex and multifactorial pathophysiology of discogenic back pain.

Periprosthetic UHMWPE Wear Debris Induces Inflammation, Vascularization, and Innervation After Total Disc Replacement in the Lumbar Spine

BACKGROUND

The pathophysiology and mechanisms driving the generation of unintended pain after total disc replacement (TDR) remain unexplored. Ultrahigh-molecular-weight polyethylene (UHMWPE) wear debris from TDRs is known to induce inflammation, which may result in pain.

QUESTIONS/PURPOSES

The purpose of this study was to determine whether (1) periprosthetic UHMWPE wear debris induces immune responses that lead to the production of tumor necrosis factor-α (TNFα) and interleukin (IL)-1ß, the vascularization factors, vascular endothelial growth factor (VEGF) and platelet-derived growth factor-bb (PDGFbb), and the innervation/pain factors, nerve growth factor (NGF) and substance P; (2) the number of macrophages is associated with the production of the aforementioned factors; (3) the wear debris-induced inflammatory pathogenesis involves an increase in vascularization and associated innervation.

METHODS

Periprosthetic tissues from our collection of 11 patients with contemporary TDRs were evaluated using polarized light microscopy to quantify UHMWPE wear particles. The major reason for revision (mean implantation time of 3 years [range, 1-6 years]) was pain. For control subjects, biopsy samples from four patients with degenerative disc disease with severe pain and autopsy samples from three normal patients with no history of back pain were also investigated. Immunohistochemistry and histology were used to identify secretory factors, macrophages, and blood vessels. Immunostained serial sections were imaged at ×200 magnification and using MATLAB and NIH ImageJ, a threshold was determined for each factor and used to quantify positive staining normalized to tissue sectional area. The Mann-Whitney U test was used to compare results from different patient groups, whereas the Spearman Rho test was used to determine correlations. Significance was based on p < 0.05.

RESULTS

The mean percent area of all six inflammatory, vascularization, and innervation factors was higher in TDR tissues when compared with normal disc tissues. Based on nonparametric data analysis, those factors showing the most significant increase included TNFα (5.17 ± 1.76 versus 0.05 ± 0.03, p = 0.02), VEGF (3.02 ± 1.01 versus 0.02 ± 0.002, p = 0.02), and substance P (4.15 ± 1.01 versus 0.08 ± 0.04, p = 0.02). The mean percent area for IL-1ß (2.41 ± 0.66 versus 0.13 ± 0.13, p = 0.01), VEGF (3.02 ± 1.01 versus 0.34 ± 0.29, p = 0.04), and substance P (4.15 ± 1.01 versus 1.05 ± 0.46, p = 0.01) was also higher in TDR tissues when compared with disc tissues from patients with painful degenerative disc disease. Five of the factors, TNFα, IL-1ß, VEGF, NGF, and substance P, strongly correlated with the number of wear particles, macrophages, and blood vessels. The most notable correlations included TNFα with wear particles (p < 0.001, ρ = 0.63), VEGF with macrophages (p = 0.001, ρ = 0.71), and NGF with blood vessels (p < 0.001, ρ = 0.70). Of particular significance, the expression of PDGFbb, NGF, and substance P was predominantly localized to blood vessels/nerve fibers.

CONCLUSIONS

These findings indicate wear debris-induced inflammatory reactions can be linked to enhanced vascularization and associated innervation/pain factor production at periprosthetic sites around TDRs. Elucidating the pathogenesis of inflammatory particle disease will provide information needed to identify potential therapeutic targets and treatment strategies to mitigate pain and potentially avoid revision surgery.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Magnetic Resonance Imaging Signal Characteristics of Medishield: Early Postoperative Profile in a Rabbit Interlaminotomy Model

OBJECTIVE

Application of Medishield to the nerve root is common during spinal surgery to create a mechanical barrier from pain mediators and reduce scar formation. However, Medishield's signal characteristics on magnetic resonance imaging (MRI) have not yet been examined.

METHODS

Microsurgical interlaminotomy was performed on 2 lower lumbar segments in 17 adult New Zealand white rabbits. After dural exposure, applications of 1 mL (autologous blood clot or Medishield) were randomized for each level. On postoperative days 1 through 3, various MRI sequences in 1.5T were performed including T1-weighted, T2-w, T1-gadolinium-weighted, susceptibility-weighted and turbo inversion recovery magnitude (TIRM) sequence. Signaling characteristics were analyzed by 3 blinded observers. Inter-rater agreement was calculated using Fleiss's kappa coefficient (κ). Positive and negative likelihood ratios in detecting Medishield by MRI were determined.

RESULTS

Of 24 MRIs performed, TIRM sequence identified Medishield with the highest likelihood ratio. Medishield's positive likelihood ratio was highest (5.8) on postoperative day 1 with interobserver agreement of 93% (κ = 0.75); these rates declined to 2.5 and 1.4 on postoperative days 2 and 3 with interobserver agreements of 71% (κ = 0.43) and 83% (κ = 0.67), respectively. Medishield adherence was confirmed in each rabbit by histologic examinations.

CONCLUSION

Understanding that radiologic detection of Medishield diminished over time as its signal characteristics became less distinguishable from a blood clot is essential in clinical practice. Medishield was detected on postoperative day 1 but not 2 days later after hemodynamic changes had occurred. These results may provide a guide for postoperative findings, such as differential diagnosis of hematoma.

Acidic pH promotes intervertebral disc degeneration: Acid-sensing ion channel -3 as a potential therapeutic target

The aetiology of intervertebral disc (IVD) degeneration remains poorly understood. Painful IVD degeneration is associated with an acidic intradiscal pH but the response of NP cells to this aberrant microenvironmental factor remains to be fully characterised. The aim here was to address the hypothesis that acidic pH, similar to that found in degenerate IVDs, leads to the altered cell/functional phenotype observed during IVD degeneration, and to investigate the involvement of acid-sensing ion channel (ASIC) -3 in the response. Human NP cells were treated with a range of pH, from that of a non-degenerate (pH 7.4 and 7.1) through to mildly degenerate (pH 6.8) and severely degenerate IVD (pH 6.5 and 6.2). Increasing acidity of pH caused a decrease in cell proliferation and viability, a shift towards matrix catabolism and increased expression of proinflammatory cytokines and pain-related factors. Acidic pH resulted in an increase in ASIC-3 expression. Importantly, inhibition of ASIC-3 prevented the acidic pH induced proinflammatory and pain-related phenotype in NP cells. Acidic pH causes a catabolic and degenerate phenotype in NP cells which is inhibited by blocking ASIC-3 activity, suggesting that this may be a useful therapeutic target for treatment of IVD degeneration.

The Contribution of Biomechanical-Biological Interactions of the Spine to Low Back Pain

OBJECTIVE

The objective of this mini-review is to examine a subset of literature that demonstrates multiple interactions between mechanics and biology within the spine and propose how incorporation of these mechano-biologic interactions can be applied to improve the conceptual understanding of tissue tolerances.

BACKGROUND

Low back pain represents a major musculoskeletal problem in the workplace. Traditional biomechanical assessments have employed tissue tolerances as an approach for reducing workplace injuries; however, development of more universal biologically sensitive tolerances requires incorporation of mechano-biologic interactions.

METHODS

A focused literature review addressing the interactions between mechanical loading and biology in the spine.

RESULTS

Mechanical loads applied to the body are distributed across all spatial scales from the body to the tissues to the cells. These mechanical loads regulate cellular metabolism and over time can lead to tissue strengthening or weakening. Mechanical loading also interacts with the biologic environment (e.g., tissue inflammation, nerve sensitization) to influence the perception of pain, thereby changing the risk of experiencing pain. Biologic tissues also exhibit time-dependent changes in mechanical behaviors that occur throughout the day and with disease, suggesting tissue tolerances are time dependent.

CONCLUSION

Incorporating mechano-biologic interactions into the traditional tissue tolerance paradigm through describing tissue tolerances as a function of multiple factors (e.g., preexisting risk factors, underlying pathology, and time) may lead to the development of tissue tolerances that are more representative of the in vivo situation.

APPLICATION

Efforts must work toward incorporating biological concepts into tissue tolerances in order to improve risk assessment tools.

Human annulus signaling cues for nerve outgrowth: In vitro studies

The relationship between neurotrophins produced by human annulus cells, such as neurotrophin-4 (NT4) and brain-derived neurotrophic factor (BDNF) which function in neurite survival and outgrowth, and nerve ingrowth into the disc remains poorly understood. In this work, we tested F11 neurite growth during exposure to control media, media with added nerve growth factor (NGF), conditioned media (CM) harvested from previous human annulus culture, or co-culture with annulus cells. Co-culture of F11 cells with annulus cells significantly increased media levels of amphiregulin, BDNF, glial-derived neurotrophic factor, and vascular endothelial growth factor compared to levels from in culture of F11 cells alone (p ≤ 0.04). Cell-based assays of neurite growth revealed that BDNF levels present in CM bore a significant (p = 0.01) positive relationship to neurite length and accounted for 38.5% of the change in neurite length. NT4 levels produced during co-culture with annulus cells bore a significant (p = 0.04) positive relationship to neurite length and accounted for 40.9% of the change in length. Statement of clinical significance: In vitro findings point to a potential role of annulus cells related to nerve ingrowth in vivo, and may have relevance in the outer annulus (where cell numbers are high) or in regions where nerves penetrate into annular tears or fissures. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1456-1465, 2016.

PGE1 Attenuates IL-1β-induced NGF Expression in Human Intervertebral Disc Cells

STUDY DESIGN

In vitro study using isolated human intervertebral disc (IVD) cells.

OBJECTIVE

To investigate the effects of prostaglandin (PG)E1 and its orally available derivative limaprost on the regulation of nerve growth factor (NGF) expression and to compare their actions with other prostanoids using interleukin (IL)-1-stimulated human IVD cells.

SUMMARY OF BACKGROUND DATA

We previously reported that a selective COX-2 inhibitor enhanced, whereas PGE2 suppressed the induction of NGF by IL-1 in human IVD cells, and proposed that PGE2 can suppress NGF expression by a negative feedback mechanism.

METHODS

Isolated human IVD cells were stimulated with IL-1 in the presence or absence of increasing concentrations of PGE2, PGE1, limaprost, PGI2, PGD2, or PGF2α (10-10,000 nM). For some experiments, an E-series prostanoid receptor (EP)4 antagonist (L-161,982) was added prior to the stimulation. NGF expression was determined by real-time polymerase chain reaction and its protein level was quantified by enzyme-linked immunosorbent assay.

RESULTS

PGE2, PGE1, and limaprost inhibited the IL-1-mediated induction of NGF in a concentration-dependent manner, with IC50 values of 9.9, 10.6, and 70.9 nM, respectively. PGI2 also suppressed NGF expression but to a much less extent. PGD2, on the other hand, significantly enhanced NGF expression, whereas PGF2α had no effect. Protein expression levels of NGF mirrored its mRNA levels. The suppression of NGF expression by PGE2 and PGE1 was partly reversed by L-161,982.

CONCLUSION

PGE1 and limaprost exhibited a novel pharmacological action that suppresses NGF expression in human IVD cells, and other prostanoids differentially regulated NGF expression. Limaprost has been used to treat patients with lumbar spinal stenosis in Japan and was proved to be effective in relieving symptoms. Our in vitro results may explain, in part, the mechanism of action of limaprost for low back pain.

LEVEL OF EVIDENCE

N/A.

Dysregulated miR-98 Contributes to Extracellular Matrix Degradation by Targeting IL-6/STAT3 Signaling Pathway in Human Intervertebral Disc Degeneration

Intervertebral disc degeneration (IDD) is associated with dysregulated expression of microRNAs (miRNAs). However, the precise molecular mechanisms underlying this disorder remain unclear. Therefore, we tested the hypothesis that miRNAs modulate IDD through effects on the IL-6/STAT3 signaling pathway, a potential regulator of IDD. The miRNA expression profile was determined in nucleus pulposus (NP) tissues from patients with IDD and controls, employing miRNA microarray and quantitative real-time PCR (RT-qPCR). Biological functions of differential expression miRNAs were further investigated using immunofluorescent staining. Luciferase reporter assays and Western blotting were performed to determine miRNA targets. We identified 41 miRNAs that were differentially expressed in patients compared with controls. Following RT-qPCR confirmation, miR-98 was significantly downregulated in degenerative NP tissues. Moreover, its level was inversely correlated with grade of disc degeneration. Through gain-of-function and loss-of-function studies, miR-98 was shown to significantly promote type II collagen expression in NP cells. Interleukin-6 (IL-6) was identified as a target of miR-98. Knockdown of IL-6 induced effects on NP cells similar to those induced by miR-98. In contrast, IL-6 treatment abrogated the effects induced by miR-98 upregulation. Moreover, miR-98 dramatically suppressed expression of STAT3 target gene, MMP2. IL-6 treatment antagonized this effect, whereas knockdown of IL-6 by IL-6 short hairpin RNA (shIL-6) induced inhibitory effects on the expression of p-STAT3 and its main target genes, similar to miR-98. The mRNA level of IL-6 was inversely correlated with that of miR-98 in degenerative NP tissues. These results suggest the downregulation of miR-98 could promote IDD through the IL-6/STAT3 signaling pathway. Our findings also highlight miR-98 as a novel hopeful therapeutic target for IDD.

Rho-Associated Kinase Inhibitor Immortalizes Rat Nucleus Pulposus and Annulus Fibrosus Cells: Establishment of Intervertebral Disc Cell Lines With Novel Approaches

STUDY DESIGN

Establishment of immortalized cell lines derived from rat intervertebral disc cells by Rho-associated kinase (ROCK) inhibitor, Y-27632.

OBJECTIVE

To determine whether rat nucleus pulposus (NP) and annulus fibrosus (AF) cells could be immortalized, retain their phenotype, and used as cell lines for in vitro cell biology.

SUMMARY OF BACKGROUND DATA

Intervertebral disc degeneration is a major factor for most low-back pain. However, the mechanism of the disease is not well understood by the limitation to obtain sufficient amounts of primary disc cells. Therefore, the establishment of disc cell lines will help in vitro molecular signaling studies to understand the mechanism of degenerative disc disease.

METHODS

Cells were isolated from the NP and AF tissues of lumbar discs of adult Sprague Dawley rat. Tissues were digested and cultured with DMEM/Ham's F-12 (1:1) and 20% FBS and antibiotics. From day 3, cells were grown in the presence of 10  μM Y-27632, a well-characterized inhibitor of the ROCK, and subcultured by trypsinization, passaging them 1:3 onto 100  mm culture dishes. Morphologic and genetic analyses were performed on the different passaged cells.

RESULTS

ROCK inhibitor successfully immortalized rat NP and AF cells. They passaged for over 50 generations with sustained expression levels of several NP and AF cell markers. In addition, they retained phenotypic features similar to the primary parental NP and AF cells when the cells were challenged with different cytokines and growth factors.

CONCLUSION

We established immortalized rat NP and AF cell lines using a method of treating cells with ROCK inhibitor Y-27632 and demonstrated that these immortalized cells retain the properties of primary cells and could serve as useful tools for in vitro signaling studies or drug screening studies to develop novel therapeutic strategies.

LEVEL OF EVIDENCE

N/A.