Toll-like receptor adaptor signaling molecule MyD88 on intervertebral disk homeostasis: in vitro, ex vivo studies

Intradiscal inflammatory stimulation induces spinal pain behavior and intervertebral disc degeneration in vivo

Degeneration of the intervertebral disc (IVD) results in a range of symptomatic (i.e., painful) and asymptomatic experiences. Components of the degenerative environment, including structural disruption and inflammatory cytokine production, often correlate with pain severity. However, the role of inflammation in the activation of pain and degenerative changes has been complex to delineate. The most common IVD injury model is puncture; however, it initiates structural damage that is not representative of the natural degenerative cascade. In this study, we utilized in vivo injection of lipopolysaccharide (LPS), a pro-inflammatory stimulus, into rat caudal IVDs using 33G needles to induce inflammatory activation without the physical tissue disruption caused by puncture using larger needles. LPS injection increased gene expression of pro-inflammatory cytokines (Tnfa, Il1b) and macrophage markers (Inos, Arg1), supported by immunostaining of macrophages (CD68, CCR7, Arg1) and systemic changes in blood cytokine and chemokine levels. Disruption of the IVD structural integrity after LPS injection was also evident through changes in histological grading, disc height, and ECM biochemistry. Ultimately, intradiscal inflammatory stimulation led to local mechanical hyperalgesia, demonstrating that pain can be initiated by inflammatory stimulation of the IVD. Gene expression of nociceptive markers (Ngf, Bdnf, Cgrp) and immunostaining for neuron ingrowth (PGP9.5) and sensitization (CGRP) in the IVD were also shown, suggesting a mechanism for the pain exhibited. To our knowledge, this rat IVD injury model is the first to demonstrate local pain behavior resulting from inflammatory stimulation of caudal IVDs. Future studies will examine the mechanistic contributions of inflammation in mediating pain.

Blocking toll-like receptor 4 mitigates static loading induced pro-inflammatory expression in intervertebral disc motion segments

While the anabolic effects of mechanical loading on the intervertebral disc (IVD) have been extensively studied, inflammatory responses to loading have not been as well characterized. Recent studies have highlighted a significant role of innate immune activation, particularly that of toll-like receptors (TLRs), in IVD degeneration. Biological responses of intervertebral disc cells to loading depend on many factors that include magnitude and frequency. The goals of this study were to characterize the inflammatory signaling changes in response to static and dynamic loading of IVD and investigate the contributions of TLR4 signaling in response to mechanical loading. Rat bone-disc-bone motion segments were loaded for 3 hr under a static load (20 % strain, 0 Hz) with or without an additional low-dynamic (4 % dynamic strain, 0.5 Hz) or high-dynamic (8 % dynamic strain, 3 Hz) strain, and results were compared to unloaded controls. Some samples were also loaded with or without TAK-242, an inhibitor of TLR4 signaling. The magnitude of NO release into the loading media (LM) was correlated with the applied frequency and strain magnitudes across different loading groups. Injurious loading profiles, such as static and high-dynamic, significantly increased Tlr4 and Hmgb1 expression while this result was not observed in the more physiologically relevant low-dynamic loading group. TAK-242 co-treatment decreased pro-inflammatory expression in static but not dynamic loaded groups, suggesting that TLR4 plays a direct role in mediating inflammatory responses of IVD to static compression. Overall, the microenvironment induced by dynamic loading diminished the protective effects of the TAK-242, suggesting that TLR4 plays a direct role in mediating inflammatory responses of IVD to static loading injury.

Downregulation of miR-760 Causes Human Intervertebral Disc Degeneration by Targeting the MyD88/Nuclear Factor-Kappa B Signaling Pathway

Dysregulation of microRNAs (miRNAs) plays a critical role in the development of intervertebral disc degeneration (IDD). In this study, we present evidence from in vitro and in vivo research to elucidate the mechanism underlying the role of miR-760 in IDD. miRNA microarray and quantitative reverse transcription-polymerase chain reaction were used to determine the miRNA profiles in patients with IDD. Functional analysis was performed to evaluate the role of miR-760 in the pathogenesis of IDD. Luciferase reporter and western blotting assays were used to confirm the miRNA targets. The expression of miR-760 was significantly decreased in degenerative nucleus pulposus (NP) cells and negatively correlated with disc degeneration grade. Functional assays demonstrated that miR-760 delivery significantly increased NP cell proliferation and promoted the expression of collagen II and aggrecan. Moreover, MyD88 was identified as a target gene of miR-760. miR-760 effectively suppressed MyD88 expression by interacting with the 3′-untranslated region, which was abolished by miR-760 binding site mutations. An in vivo experiment using an IDD mouse model showed that the upregulation of miR-760 could effectively suspend IDD. Therefore, miR-760 was found to play an important role in IDD and can be used as a promising therapeutic target for the treatment of patients with IDD.

Protective role of the alpha-1-antitrypsin in intervertebral disc degeneration

BACKGROUND

Intervertebral disc degeneration is a complex disease with high prevalence. It suggests that cell death, senescence, and extracellular matrix degradation are involved in the pathogenesis. Alpha-1 antitrypsin (AAT), a serine protease inhibitor, was previously correlated with inflammation-related diseases. However, its function on intervertebral disc degeneration remains unclear.

METHODS

A latex-enhanced immunoturbidimetric assay measured the serum level of AAT. Real-time polymerase chain reaction (RT-qPCR) and western blot were used to testify the expression of RNA and proteins related to cell apoptosis and the Wnt/β-catenin pathway. The animal model for intervertebral disc degeneration was built by disc puncture. The degeneration grades were analyzed by safranin o staining.

RESULTS

We showed that alpha-1 antitrypsin could ameliorate intervertebral disc degeneration in vitro and in vivo. We also found that the serum alpha-1 antitrypsin level in Intervertebral disc degeneration patients is negative related to the severity of intervertebral disc degeneration. Moreover, alpha-1 antitrypsin was also showed to suppress tumor necrosis factor-alpha (TNF-α) induced WNT/β-catenin signaling pathway activation in human nucleus pulposus cells.

CONCLUSIONS

Our study provides evidence for AAT to serve as a potential therapeutic reagent for the treatment of intervertebral disc degeneration.

Inhibition of toll-like receptor 4 protects against inflammation-induced mechanobiological alterations to intervertebral disc cells

Intervertebral disc (IVD) degeneration is associated with elevated levels of inflammatory cytokines implicated in disease aetiology and matrix degradation. Toll-like receptor-4 (TLR4) has been shown to participate in the inflammatory responses of the nucleus pulposus (NP) and its levels are upregulated in disc degeneration. Activation of TLR4 in NP cells leads to significant, persistent changes in cell biophysical properties, including hydraulic permeability and osmotically active water content, as well as alterations to the actin cytoskeleton. The study hypothesis was that inflammation-induced changes to cellular biomechanical properties and actin cytoskeleton of NP cells could be prevented by inhibiting TLR4 signalling. Isolated NP cells from bovine discs were treated with lipopolysaccharide (LPS), the best studied TLR4 agonist, with or without treatment with the TLR4 inhibitor TAK-242. Cellular volume regulation responses to step osmotic loading were measured and the transient volume-response was captured by time-lapse microscopy. Volume-responses were analysed using mixture theory framework to investigate hydraulic permeability and osmotically active intracellular water content. Hydraulic permeability and cell radius were significantly increased with LPS treatment and these changes were blocked in cells treated with TAK-242. LPS-induced remodelling of cortical actin and IL-6 upregulation were also mitigated by TAK-242 treatment. These findings indicated that TLR4 signalling participated in NP cell biophysical regulation and may be an important target for mitigating altered cell responses observed in IVD inflammation and degeneration.

Astragaloside IV protects ATDC5 cells from lipopolysaccharide-caused damage through regulating miR-203/MyD88

Context: Osteoarthritis (OA) is a degenerative arthrosis sickness. Astragaloside IV (AS-IV) functions by relieving inflammatory damage.Objective: We aimed to investigate the mechanism by which AS-IV protects ATD cells from lipopolysaccharide (LPS)-induced damage.Materials and methods: ATDC5 cells were transfected with miR-203 inhibitor and NC inhibitor (150 nM) or pEX-MyD88 and sh-MyD88 (50 nM) for 48 h, pre-treated by 15 μg/mL AS-IV for 24 h, then treated by 5 μg/mL LPS for 12 h. Dual-luciferase activity testing was used to determine whether miR-203 could bind to MyD88. CCK-8 and flow cytometry were used to detect cell activity and apoptosis, respectively, and qRT-PCR, western blots, and ELISA were performed to detect expression levels of miR-203 and inflammatory cytokines.Results: Based on the 50% inhibiting concentration (IC₅₀), there was no significant difference of AS-IV (0 to 15 μg/mL) on cell viability. Fifteen μg/mL was the optimal concentration of AS-IV in treating LPS-induced inflammatory damage in subsequent experiments since this was a semi-lethal concentration. AS-IV significantly reduces LPS-induced viability, apoptosis and the release of TNF-α, IL-6 and iNOS mainly through up-regulating miR-203. Further, MyD88 was a target gene of miR-203 and negatively regulated by miR-203. Knockdown of MyD88 inhibited LPS-induced inflammatory damage by inhibiting the NF-κB signal pathway.Discussion and conclusions: AS-IV protects ATDC5 cells against LPS-induced damage mainly via regulating miR-203/MyD88. Our results support a theoretical basis for in-depth study of the function of AS-IV and the clinical cure of OA.

Mesenchymal stem cells-derived exosomes ameliorate intervertebral disc degeneration through inhibiting pyroptosis

Mesenchymal stem cell (MSCs)‐based therapies have shown a promised result for intervertebral disc degeneration (IVDD) treatment. However, its molecular mechanisms remain unclear. Exosomes involve cell‐cell communication via transference of its contents among different cells, and the present potential effect on cell death regulation. This study aimed to investigate the role of MSCs‐derived exosomes on IVDD formation. Here, we first found the NLRP3‐mediated nucleus pulposus cell (NP cell) pyroptosis was activated in the IVDD mice model and lipopolysaccharide (LPS)‐induced model. However, MSCs treatment could inhibit NP cell pyroptosis in vitro. We then isolated MSCs‐derived exosomes by differential centrifugation and identified the characteristics. Secondly, we investigated the function of MSCs‐derived exosomes on LPS‐induced NP cell pyroptosis. Finally, we presented evidence that MSCs‐derived exosomal miR‐410 was a crucial regulator of pyroptosis. Results showed that MSCs‐derived exosomes play an anti‐pyroptosis role by suppressing the NLRP3 pathway. Moreover, it suggested that this effect was attributed to miR‐410, which was derived from MSCs‐exosomes and could directly bind to NLRP3mRNA. In conclusion, for the first time, we demonstrated that MSCs‐exosome treatment may inhibit pyroptosis and could be a promising therapeutic strategy for IVDD.

Cortistatin protects against intervertebral disc degeneration through targeting mitochondrial ROS-dependent NLRP3 inflammasome activation

Background: Intervertebral disc (IVD) degeneration is a common degenerative disease that can lead to collapse or herniation of the nucleus pulposus (NP) and result in radiculopathy in patients.

Methods: NP tissue and cells were isolated from patients and mice, and the expression profile of cortistatin (CST) was analysed. In addition, ageing of the NP was compared between 6-month-old WT and CST-knockout (CST^-/-) mice. Furthermore, NP tissues and cells were cultured to validate the role of CST in TNF-α-induced IVD degeneration. Moreover, in vitro and in vivo experiments were performed to identify the potential role of CST in mitochondrial dysfunction, mitochondrial ROS generation and activation of the NLRP3 inflammasome during IVD degeneration. In addition, NF-κB signalling pathway activity was tested in NP tissues and cells from CST^-/- mice.

Results: The expression of CST in NP cells was diminished in the ageing- and TNF-α-induced IVD degeneration process. In addition, compared with WT mice, aged CST^-/- mice displayed accelerated metabolic imbalance and enhanced apoptosis, and these mice showed a disorganized NP tissue structure. Moreover, TNF-α-mediated catabolism and apoptosis were alleviated by exogenous CST treatment. Furthermore, CST inhibited mitochondrial dysfunction in NP cells through IVD degeneration and suppressed activation of the NLRP3 inflammasome. In vitro and ex vivo experiments indicated that increased NF-κB pathway activity might have been associated with the IVD degeneration observed in CST^-/- mice.

Conclusion: This study suggests the role of CST in mitochondrial ROS and activation of the NLRP3 inflammasome in IVD degeneration, which might shed light on therapeutic targets for IVD degeneration.

Loss of TIMP3 expression induces inflammation, matrix degradation, and vascular ingrowth in nucleus pulposus: A new mechanism of intervertebral disc degeneration

Low back pain (LBP) is one of the most common complains in orthopedic outpatient department and intervertebral disc degeneration (IDD) is one of the most important reasons of LBP. The mechanisms of IDD contain a complex biochemical cascade which includes inflammation, vascular ingrowth, and results in degradation of matrix. In our study, we used both in vitro and in vivo models to investigate the relation between tissue inhibitor of metalloproteinase-3 (TIMP3) expression and IDD. Loss of TIMP3 expression was found in degenerative intervertebral disc (IVD), this change of expression was closely related with the dephosphorylation of smad2/3. Overexpression of TIMP3 significantly inhibited the release of TNF-α and matrix degradation induced by Lipopolysaccharide. Vascular ingrowth was also suppressed by TIMP3 in the in vitro and in vivo models. Further, animal experiments confirmed that the degeneration of IVD was reduced after overexpression of TIMP3 in nucleus pulposus. Taken together, our results indicated TIMP-3 might play an important role in the pathogenesis of IDD and therefore be a potential therapeutic target in the future.

Procyanidin B3 alleviates intervertebral disc degeneration via interaction with the TLR4/MD-2 complex

As a chronic musculoskeletal degeneration disease, intervertebral disc degeneration (IVDD) has been identified as a crucial cause for low back pain. This condition has a prevalence of 80% among adults without effective preventative therapy. Procyanidin B3 (Pro‐B3) is a procyanidin dimer, which is widely present in the human diet and has multiple functions, such as preventing inflammation. But the inhibiting effect of Pro‐B3 in IVDD development is still no known. Thus, our study aimed to demonstrate the therapeutical effect of Pro‐B3 in IVDD and explain the underlying mechanism. In vitro studies, human nucleus pulposus (NP) cells were isolated and exposed in lipopolysaccharide (LPS) to simulate IVDD development. Pro‐B3 pre‐treatment inhibited LPS‐induced production of inflammation correlated factors such as tumour necrosis factor α (TNF‐α), interleukin‐6 (IL‐6), prostaglandin E2 (PGE2) and Nitric oxide (NO). On the other hand, LPS‐medicated extracellular matrix (ECM) breakdown was blocked in Pro‐B3 treated NP cells. Additionally, Pro‐B3 treatment blocked the activation of NF‐κB/toll‐like receptor 4 pathway in LPS‐exposed NP cells. Mechanistically, Pro‐B3 could occupy MD‐2's hydrophobic pocket exhibiting high affinity for LPS to intervene LPS/TLR4/MD‐2 complex formation. In vivo, Pro‐B3 treatment prevented the loss of gelatin NP cells and structural damage of annulus fibrosus in rat IVDD model. In brief, Pro‐B3 is considered to be a treatment agent for IVDD.

Overexpression of TIMP3 inhibits discogenic pain by suppressing angiogenesis and the expression of substance P in nucleus pulposus

Approximately 50% of the cases of low back pain (LBP) are attributed to discogenic origin. The causes of discogenic pain are complicated and consist of a complex biochemical cascade. Neovascularization of intervertebral discs (IVDs) is believed to be associated with discogenic pain. The anti‑angiogenesis ability of tissue inhibitor of metalloproteinase‑3 (TIMP3) has been reported in many tumors, yet whether TIMP3 is associated with neovascularization of IVDs remains unknown. In the present study, both in vitro and in vivo models were used to investigate the association between discogenic pain and TIMP3 expression in nucleus pulposus (NP). PCR results demonstrated that inflammation induced downregulation of TIMP3 expression in NP cells. By using an adenovirus system to upregulate TIMP3 expression, the effect of TIMP3 on angiogenesis was measured by endothelial cell migration and tube formation assays. The results demonstrated that overexpression of TIMP3 suppressed angiogenesis in NP without the regulation of vascular endothelial growth factor (VEGF) expression. TNF‑α converting enzyme (TACE) expression was downregulated by TIMP3, thus inhibiting the TACE‑induced activation of TNF‑α in NP cells. Immunohistochemical staining of IVDs also confirmed that TIMP3 inhibited the expression of substance P in NP. Taken together, the present results indicated the expression of TIMP3 in NP may have a key role in the development of discogenic pain.

The age-dependent effect of high-dose X-ray radiation on NFκB signaling, structure, and mechanical behavior of the intervertebral disc

Purpose: Ionizing radiation damages tissue and provokes inflammatory responses in multiple organ systems. We investigated the effects of high-dose X-ray radiation on the molecular inflammation and mechanical function of the intervertebral disc (IVD).Methods: Functional spine units (FSUs) containing the vertebrae-IVDs-vertebrae structure extracted from 1-month, 6-month, and 16-month-old NFκB-luciferase reporter mice and from 6-month-old myeloid differentiation factor 88 (MyD88)-null mice. After a preconditioning period in culture, the FSUs were subjected a single dose of ionizing X-ray radiation at 20 Gys, and then NFκB expression was monitored. The IVDs were then subjected to mechanical testing using dynamic compression, glycosaminoglycan (GAG) quantification, and histological analyses.Results: In the 1-month-old FSUs, the NFκB-driven luciferase activity was significantly elevated for 1 day following the exposure to radiation. The 6-month-old FSUs showed increased NFκB activity for 3 days, while the 16-month-old FSUs sustained elevated levels of NFκB activity throughout the 10-day culture period. All irradiated groups showed significant loss of disc height, GAG content, mechanical function and changes in structure. Ablation of MyD88 blunted the radiation-mediated NFκB signaling, and preserved GAG content, and the IVDs' structure and mechanical performance.Conclusions: These results suggest that high-dose radiation affects the IVDs' NFκB-dependent inflammatory processes that subsequently lead to functional deterioration. Blocking the transactivation potential of NFκB via MyD88 ablation preserved the structure and mechanical function of the FSUs. The long-term effects of radiation on IVD homeostasis should be considered in individuals susceptible to occupational and medical exposure.

ERRFI1 Inhibits Proliferation and Inflammation of Nucleus Pulposus and Is Negatively Regulated by miR-2355-5p in Intervertebral Disc Degeneration

STUDY DESIGN

In vivo and in vitro studies of the role of miR-2355-5p and its possible targets in intervertebral disc degeneration (IVDD).

OBJECTIVE

To elucidate the regulatory role of miR-2355-5p in IVDD and the underlying mechanisms.

SUMMARY OF BACKGROUND DATA

IVDD, which is caused by multiple factors, is the main cause of lower back pain with or without extremity pain. However, the underlying cellular mechanisms of IVDD pathogenesis are not well elucidated. Cell hyper-proliferation, inflammation, and epidermal growth factor receptor activation have been implicated in IVDD. Up-regulated miR-2355-5p level was identified to associate with IVDD. ERRFI1 (the product of mitogen-inducible gene 6 [MIG6]) was known to inhibit epidermal growth factor receptor activation.

METHODS

We monitored the expression of miR-2355-5p and ERRFI1 in IVDD tissues and lipopolysaccharides (LPS)-treated nucleus pulposus (NP) cells. We explored the effects of ERFFI1 on NP cells proliferation and LPS-induced pro-inflammatory cytokines production. We searched the targets of miR-2355-5p and explored the effects of miR-2355-5p on NP cells proliferation and cytokines production.

RESULTS

We identified the up-regulation of miR-2355-5p and down-regulation of ERFFI1 in IVDD samples and LPS-treated NP cells. ERFFI1 inhibited NP cells proliferation and LPS-induced pro-inflammatory cytokine production. MiR-2355-5p targeted ERFFI1 and negatively regulated ERFFI1 expression. MiR-2355-5p regulated IVDD by targeting ERFFI1.

CONCLUSION

MiR-2355-5p negatively regulated ERFFI1 and prevented the effects of ERRFI1 on inhibiting NP cells proliferation and inflammation.

LEVEL OF EVIDENCE

N/A.

MicroRNA-149 Suppresses Inflammation in Nucleus Pulposus Cells of Intervertebral Discs by Regulating MyD88

Background

Intervertebral disc degeneration (IDD) is associated with low back and neck pain, but the mechanisms underlying its pathogenesis are unclear. In this study, we explored the function of microRNA-149 (miR-149) in inflammatory response mediated by lipopolysaccharide (LPS) in nucleus pulposus (NP) cells.

Material/Methods

Quantitative real-time PCR was used to detect miRNA and mRNA levels, while Western blotting was utilized to determine protein levels. ELISA was used to examine chemokine production. The correlation between miR-149 and MyD88 was assessed by reporter assay. Apoptosis was examined by flow cytometry.

Results

miR-149 expression was significantly decreased after LPS exposure in NP cells. Overexpression of miR-149 reversed LPS-induced inhibition in aggrecan and collagen II expression and attenuated LPS-mediated promotion in the levels of MMP3, ADAMTS4, and inflammatory cytokines. Moreover, we found that miR-149 exerted its function by targeting MyD88 in NP cells.

Conclusions

miR-149 can inhibit the inflammatory response mediated by LPS in NP cells, and might be a potential target for the treatment of IDD.

Propionibacterium acnes induces discogenic low back pain via stimulating nucleus pulposus cells to secrete pro-algesic factor of IL-8/CINC-1 through TLR2-NF-κB p65 pathway

Latent infection of Propionibacterium acnes was considered as a new pathogeny for low back pain (LBP); however, there is no credible animal evidence or mechanism hypothesis. This study proved that P. acnes is a causative pathogen of bacteria-induced LBP and investigated its underlying mechanism. For this, P. acnes was firstly identified in patients' degenerated intervertebral disc (IVDs) samples. The results of patients' Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ), Japanese Orthopaedic Association (JOA), and Oswestry Disability Index (ODI) scores indicated that P. acnes-positive patients showed more severe LBP and physical disability. Then, a P. acnes-inoculated lumbar IVDs model was established in rats. The results of paw/foot withdrawal threshold and qRT-PCR indicated that P. acnes-inoculated rats had obvious LBP in behavioral evaluation and over-expression of substance P (SP) and calcitonin gene-related peptide (CGRP) in IVDs. Subsequently, enzyme-linked immunosorbent assay (ELISA) results demonstrated that increased expression of IL-8 or CINC-1 (the homolog of IL-8 in rats) in the P. acnes-positive IVDs of human and rats. The CINC-1 injected animal model proved that the cytokines were able to induce LBP. Finally, the co-culture experiments showed that nucleus pulposus cells (NPCs) were able to respond to P. acnes and secreted IL-8/CINC-1 via TLR-2/NF-κB p65 pathway. In conclusion, P. acnes had strong association with LBP by stimulating NPCs to secrete pro-algesic factor of IL-8/CINC-1 via TLR2/NF-κBp65 pathway. The finding may provide a promising alternative therapy strategy for LBP in clinical. KEY MESSAGES: Patients with P. acnes-positive IVDs tended to have more severe LBP, physical disability, and increased IL-8 expressions. P. acnes can induce LBP via IL-8/CINC-1 in IVDs. P. acnes stimulate the NPCs to secrete pro-algesic factor of IL-8/CINC-1 via TLR2/NF-κBp65 pathway.

Low back pain and disc degeneration are decreased following chronic toll-like receptor 4 inhibition in a mouse model

OBJECTIVE

Intervertebral disc degeneration is a leading cause of chronic low back pain (LBP) but current treatment is limited. Toll-like receptors (TLRs) on disc cells are activated by endogenous extracellular matrix (ECM) fragments and modulate degeneration in vitro. This study investigated whether inhibiting TLR4 slows disc degeneration and reduces behavioral signs of LBP in vivo.

DESIGN

7-9-month old wild-type and secreted protein acidic and rich in cysteine (SPARC)-null (a model of disc degeneration and LBP) male mice were treated with TAK-242 (TLR4 inhibitor) once, and following a 10-day washout, mice were treated 3 times/week for 8 weeks. Behavioral signs of axial discomfort and radiating leg pain were assessed weekly with the grip force assay and acetone test, respectively. Following treatment, pain-related spinal cord changes were evaluated and lumbar discs were excised and cultured. Cytokine secretion from discs was evaluated with protein arrays.

RESULTS

SPARC-null mice displayed elevated signs of axial and radiating pain at baseline compared to wild-type. Chronic, but not acute, TLR4 inhibition reduced behavioral signs of pain compared to vehicle. SPARC-null mice have increased calcitonin gene-related peptide (CGRP)- and glial fibrillary acidic protein (GFAP)-immunoreactivity (astrocyte marker) in the dorsal horn compared to wild-type, which is reduced by chronic TLR4 inhibition. Ex vivo degenerating discs from SPARC-null mice secrete increased levels of many pro-inflammatory cytokines, which chronic TLR4 inhibition reduced.

CONCLUSION

Chronic TLR4 inhibition decreased behavioral signs of LBP, pain-related neuroplasticity and disc inflammation in SPARC-null mice. TAK-242 inhibits TLR4 activation within discs, as evidenced by decreases in cytokine release. Therefore, TLRs are potential therapeutic targets to slow disc degeneration and reduce pain.

miR-148a inhibits pro-inflammatory cytokines released by intervertebral disc cells by regulating the p38/MAPK pathway

The present study aimed to verify the expression and investigate the role of microRNA (miR)-148a in intervertebral disc degeneration (IDD) and explore the associated underlying mechanisms. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to investigate levels of miR-148a in the peripheral blood mononuclear cells (PBMCs) of patients with IDD. To investigate the role of miR-148a in IDD, a stable miR-148a-overexpression/underexpression human nucleus pulposus (NP) cell line was generated by transfection with miR-148a mimic/inhibitor. Then, NP cells were treated with LPS (10 µM) to induce inflammation. The mRNA expression level of miR-148a in NP cells was determined by RT-qPCR and the expression levels of p38 and p-p38 were measured using western blotting. The mRNA expression and supernatant level of pro-inflammatory cytokines, tumor necrosis factor (TNF-α), interleukin (IL)-1β and IL-6, was evaluated by RT-qPCR and ELISA, respectively. The results indicated that miR-148a was significantly downregulated in the PBMCs of IDD patients compared with healthy controls. In vitro upregulation of miR-148a in LPS-stimulated NP cells, by transfection with miR-148a mimic, resulted in inhibition of p-p38 expression; however, inhibition of miR-148a led to overexpression of p-p38. Meanwhile, the production of pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) was significantly reduced in miR-148a-overexpressing LPS-stimulated NP cells and significantly increased in miR-148a-underexpressing NP cells. In conclusion, miR-148a inhibits pro-inflammatory cytokines released by intervertebral disc cells via regulation of the p38/mitogen-activated protein kinase pathway.

MicroRNA-194 Inhibits Lipopolysaccharide-Induced Inflammatory Response in Nucleus Pulposus Cells of the Intervertebral Disc by Targeting TNF Receptor-Associated Factor 6 (TRAF6)

Background

The dramatic increase of intervertebral disc degeneration (IDD) is considered to be a major cause of discogenic low back pain. The current study focused on the regulatory function of microRNA-194 (miR-194) on lipopolysaccharide (LPS)-induced inflammatory response in nucleus pulposus (NP) cells.

Material/Methods

LPS was used to treat NP cells to induce inflammatory responses. MiRNA and gene expression were detected by quantitative PCR. Proteins and protein expression levels were detected by Western blot and ELISA kit. Dual luciferase reporter assay was applied to identify the correlation between an miR-194- and TNF receptor-associated factor 6 (TRAF6) and to test NF-κB activity.

Results

MiR-194 expression was reduced in LPS-induced NP cells. Both miR-194 overexpression and miR-194 inhibitor could regulate extracellular matrix (ECM) genes expression (Aggrecan and collagen II), MMP3, MMP13, ADAMTS4, and ADAMTS5, as well as inflammatory cytokines-associated genes (TNF-α, IL-1, IL-6, PGE2). Through a further study of the molecular mechanism, miR-194 was proved to be involved in the regulation of TRAF6 and its downstream signal molecule, nuclear factor-kappa B (NF-κB).

Conclusions

Finding of our study suggest that miR-194 can inhibit LPS-induced inflammatory response in NP cells of the intervertebral disc (IVD) by targeting TRAF6, which may contribute development of IDD biological therapy.

MicroRNA-223 inhibits lipopolysaccharide-induced inflammatory response by directly targeting Irak1 in the nucleus pulposus cells of intervertebral disc

This study was aimed to research the effect of miR-223 on the inflammatory responses induced by lipopolysaccharide (LPS) in nucleus pulposus (NP) cells of rat intervertebral disc. Isolated rat NP cells were induced by LPS. Reverse transcriptase quantitative real-time polymerase chain reaction was used to detect gene expression. To detect protein expression, Western blot and enzyme-linked immunosorbent assay experiments were applied. The putative targeting relationship between miR-223 and Irak1 was determined using dual-luciferase reporter gene assay. We found that miR-223 was downregulated in LPS-induced NP cells. MiR-223 upregulated the expression of extracellular matrix-related genes (Aggrecan and Collagen II). Matrix degrading enzymes (ADAMTS4, ADAMTS5, MMP3 and MMP13), NO reaction-associated proteins (PGE2, COX-2 and INOS) and the expression of nuclear factor (NF)-κB signaling-related proteins were downregulated after miR-233 overexpression. In addition, luciferase reporter assays demonstrated that miR-223 directly targeted Irak1. MiR-223 overexpression could inhibit NF-κB signaling by targeting Irak1, and finally suppress the LPS-induced inflammation in NP cells. © 2018 IUBMB Life, 70(6):479-490, 2018.

Progranulin derived engineered protein Atsttrin suppresses TNF-α-mediated inflammation in intervertebral disc degenerative disease

Atsttrin, an engineered molecule composed of three fragments of progranulin(PGRN), exerts comparable anti-inflammation ability. Intervertebral disc degeneration (IDD) is involved in inflammation in which TNF-α plays a key role. This study aims to examine the effect and the mechanism of Atsttrin in the pathogenesis of intervertebral disc degeneration. For this purpose, we took advantage of murine and human intervertebral disc (IVD) and examined the expression of TNF-α in IVD tissues using immunohistochemistry and TNF-α level in peripheral sera by ELISA assay. Moreover, murine IVD was taken to undergo the Safranin O and HE staining. Furthermore, primary human nucleus pulposus cells were used for immunohistochemistry staining, fluorescent staining, Western Blot, ELISA assay and RT-PCR assay. Herein we found TNF-α expression was elevated in intervertebral disc and peripheral sera in patients with IDD. Interestingly, Atsttrin effectively inhibited TNF-α-mediated catabolism in murine disc by ex vivo study. TNF-α-induced inflammatory cytokines were strongly reduced in presence of Atsttrin in primary human disc. Mechanism study indicated Atsttrin protected against intervertebral disc degeneration by inhibiting TNF-α-induced inflammation. These findings show that Atsttrin is a potential molecular target for disc degenerative diseases.

Role of miR-589-3p in human lumbar disc degeneration and its potential mechanism

The present study aimed to investigate the role of miR-589-3p in lumbar disc degeneration (LDD) and to explore the underlying mechanisms. Nucleus pulposus (NP) cells were stimulated with lipopolysaccharide (LPS) to simulate an in vitro model of intervertebral disc degeneration. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to detect the expression level of microRNA (miR)-589-3p in the NP cells, and the results demonstrated that the increased expression of miR-589-3p in LPS stimulated NP cells compared with the control. To further investigate the role of miR-589-3p in LDD, a human NP cell line with high/low miR-589-3p expression was generated using miR-589-3p mimics/inhibitors. In addition, a human NP cell inflammation model was conducted by LPS (10 µM) treatment. Western blot analysis and RT-qPCR were performed for detection of associated genes and proteins. Protein levels of pro-inflammatory factors, including tumor necrosis factor-α (TNF-α), interleukin (IL)-1β and IL-6 were evaluated by ELISA. Flow cytometry was used for cell apoptosis determination. Furthermore, Targetscan was used to predict potential targets of miR-589-3p, and a dual luciferase reporter assay was used to verify the prediction. The findings verified that miR-589-3p was significantly upregulated in LDD. In vitro, miR-589-3p mimics/inhibitors significantly increased/reduced the production of TNF-α, IL-1β and IL-6 in LPS stimulated NP cells. Furthermore, miR-589-3p mimics/inhibitors significantly promoted/inhibited LPS stimulated NP cell apoptosis. MiR-589-3p mimics/inhibitors significantly repressed/enhanced type II collagen and aggrecan expression in LPS stimulated NP cells. In addition, it was demonstrated that mothers against decapentaplegic homolog (Smad) 4 was a direct target gene of miR-589-3p, and was negatively regulated by miR-589-3p in NP cells. In conclusion, miR-589-3p may function as a promoter in LDD development via the regulation of Smad4.

Propionibacterium acnes Incubation in the Discs Can Result in Time-Dependent Modic Changes: A Long-Term Rabbit Model

STUDY DESIGN

A case-control study of animal model of Modic changes (MCs) on rabbits.

OBJECTIVE

To evaluate the feasibility of inducing of MCs by injection of Propionibacterium acne (P. acnes) into the lumbar intervertebral discs of rabbits.

SUMMARY OF BACKGROUND DATA

MCs have been widely observed, and assume to be closely associated with low back pain and P. acnes, but there are few animal models showing the progression of MCs.

METHODS

Ten rabbits were used for the study. The L3-4 and L4-5 discs of all rabbits were injected with 100 μL P. acnes (1.6 × 10 CFU/mL) as P. acnes group, L2-3 disc were injected with 100 μL normal saline as vehicle, and L5-6 disc was untreated (blank). MCs were investigated by magnetic resonance imaging before operation and at 2 weeks, 1, 3, 4.5, 6, and 9 months postoperatively. Following sacrifice, histological analysis, blood test and micro-computed tomography were performed. Cytokine expression in nucleus and endplate tissues was quantified using real-time polymerase chain reaction.

RESULTS

From 3 months postoperatively, the P. acnes group showed significantly decreased T1-weighted signal intensity, whereas the T2-weighted signal was significantly higher at 3 and 4.5 months, and then decreased remarkably at 6 and 9 months. Eleven of 20 inferior endplates were identified as type I MCs at 4.5 months, and 9 of 20 were identified as type II MCs at 9 months. Real-time polymerase chain reaction showed that expression of interleukin-1β, tumor necrosis factor α, interferon-γ, matrix metalloproteinase-9, and thrombospondin motifs-5 in the nucleus pulposus, and interleukin-1β, tumor necrosis factor α, and thrombospondin motifs-5 in the endplates, were significantly upregulated after injection of P. acnes. Histological slices of discs injected with P. acnes showed disc degeneration, endplate abnormalities, and inflammatory response, with micro-computed tomography confirming bone resorption.

CONCLUSION

P. acnes infection of the disc can induce degeneration of the disc and an inflammatory response in the endplate region, presenting as MCs type I and II time dependently.

LEVEL OF EVIDENCE

N/A.

Inhibition of miR-27a suppresses the inflammatory response via the p38/MAPK pathway in intervertebral disc cells

The current study aimed to investigate the role of miR-27a in intervertebral disc degeneration (IDD) and to examine the underlying mechanisms. Quantitative polymerase chain reaction (qPCR) was performed to detect the expression level of miR-27a in the nucleus pulposus (NP) tissues of patients with IDD, and the results revealed an increasing expression of miR-27a in IDD compared with the control. To further investigate the role of miR-27a in IDD, a stable human NP cell line with low miR-27a expression was generated by transfecting cells with a lentiviral antigomiR-27a inhibitor. In addition, a human NP cell inflammation model was established by lipopolysaccharide (LPS; 10 µM) stimulation. The miR-27a expression in NP cells was determined by qPCR, while the expression of its target proteins; p-p38 and nuclear factor (NF-κB) was measured by western blot analysis. Furthermore, the mRNA and protein expression levels of proinflammatory factors, including interleukin (IL)-1β, IL-6 and tumor necrosis factor-α (TNF-α), were also evaluated by qPCR and ELISA, respectively. The current results confirmed that miR-27a was significantly upregulated in IDD. In vitro, downregulation of miR-27a in LPS-stimulated NP cells by transfection with the miR-27a inhibitor resulted in suppression of p-p38 and NF-κB expression levels. Furthermore, the production of the proinflammatory factors IL-1β, IL-6 and TNF-α was significantly reduced in LPS-stimulated NP cells with downregulated miR-27a. In conclusion, miR-27a may function as a promoter in IDD development, while inhibition of miR-27a may suppress proinflammatory factors released by intervertebral disc cells by regulating the p38/mitogen-activated protein kinase (MAPK) signaling pathway.

Kaempferol slows intervertebral disc degeneration by modifying LPS-induced osteogenesis/adipogenesis imbalance and inflammation response in BMSCs

Intervertebral disc (IVD) degeneration is a common disease that represents a significant cause of socio-economic problems. Bone marrow-derived mesenchymal stem cells (BMSCs) are a potential autologous stem cell source for the nucleus pulposus regeneration. Kaempferol has been reported to exert protective effects against both osteoporosis and obesity. This study explored the effect of kaempferol on BMSCs differentiation and inflammation. The results demonstrated that kaempferol did not show any cytotoxicity at concentrations of 20, 60 and 100μM. Kaempferol enhanced cell viability by counteracting the lipopolysaccharide (LPS)-induced cell apoptosis and increasing cell proliferation. Western blot analysis of mitosis-associated nuclear antigen (Ki67) and proliferation cell nuclear antigen (PCNA) further confirmed the increased effect of kaempferol on LPS-induced decreased viability of BMSCs. Besides, kaempferol elevated LPS-induced reduced level of chondrogenic markers (SOX-9, Collagen II and Aggrecan), decreased the level of matrix-degrading enzymes, i.e., matrix metalloprotease (MMP)-3 and MMP-13, suggesting the osteogenesis of BMSC under kaempferol treatment. On the other hand, kaempferol enhanced LPS-induced decreased expression of lipid catabolism-related genes, i.e., carnitine palmitoyl transferase-1 (CPT-1). Kaempferol also suppressed the expression of lipid anabolism-related genes, i.e., peroxisome proliferators-activated receptor-γ (PPAR-γ). The Oil red O staining further convinced the inhibition effect of kaempferol on BMSCs adipogenesis. In addition, kaempferol alleviated inflammatory by reducing the level of pro-inflammatory cytokines (i.e., interleukin (IL)-6) and increasing anti-inflammatory cytokine (IL-10) via inhibiting the nucleus translocation of nuclear transcription factor (NF)-κB p65. Taken together, our research indicated that kaempferol may serve as a novel target for treatment of IVD degeneration.

The Changes in the Expression of NF-KB in a Degenerative Human Intervertebral Disc model

We aim at determining the changes in the expression of NF-kB signaling pathway in degenerative intervertebral discs. We collected normal and degenerated intervertebral discs tissues. The normal and degenerated cells were cultivated and their histopathology and immunofluoresence studies were used to observe the position of NF-kB p65 in the cell. We also treated the nucleus pulposus cells with inflammatory factors and inhibitors. Western blot was used to analyze the expression of different proteins. Real time fluorescence-based quantitative PCR was used for observation of NF-kB regulation of change in gene expression. Immunofluorescence showed that in the non-degenerative group the p65 was found in the cytoplasm of the nucleus pulposus cell while in the degenerated cell group the p65 protein was found in the nucleus of the cell. The expression of p65 increased with increase in the degree of degenerative change of the nucleus pulposus cell. RT-PCR showed that the expression of matrix metalloproteinases, aggrecanases and IL-6 was higher in the degenerative group. The amount of aggrecan and type II collagen was significantly decreased in the degenerative group. IL-1β was able to upregulate the activation of NF-kB and the expression of MMP-13 and ADAMTS-4 was also significantly increased. The effect of these proteins can be inhibited by the NF-kB inhibitor, BAY11-7082. The activation of the NK-kB signaling pathway in a degenerative intervertebral disc is gradually increased, regulating the over-expression of matrix-degrading enzymes. It plays an important role in the degradation of extracellular matrix.

Sesamin inhibits lipopolysaccharide-induced inflammation and extracellular matrix catabolism in rat intervertebral disc

Intervertebral disc (IVD) degeneration contributes to most spinal degenerative diseases, while treatment inhibiting IVD degeneration is still in the experimental stage. Sesamin, a bioactive component extracted from sesame, has been reported to exert chondroprotective and anti-inflammatory effects. Here, we analyzed the anti-inflammatory and anti-catabolic effects of sesamin on rat IVD in vitro and ex vivo. Results show that sesamin significantly inhibits the lipopolysaccharide (LPS)-induced expression of catabolic enzymes (MMP-1, MMP-3, MMP-13, ADAMTS-4, ADAMTS-5) and inflammation factors (IL-1β, TNF-α, iNOS, NO, COX-2, PGE2) in a dose-dependent manner in vitro. It is also proven that migration of macrophages induced by LPS can be inhibited by treatment with sesamin. Organ culture experiments demonstrate that sesamin protects the IVD from LPS-induced depletion of the extracellular matrix ex vivo. Moreover, sesamin suppresses LPS-induced activation of the mitogen-activated protein kinase (MAPK) pathway through inhibiting phosphorylation of JNK, the common downstream signaling pathway of LPS and IL-1β, which may be the potential mechanism of the effects of sesamin. In light of our results, sesamin protects the IVD from inflammation and extracellular matrix catabolism, presenting positive prospects in the treatment of IVD degenerative diseases.

Propionibacterium acnes infected intervertebral discs cause vertebral bone marrow lesions consistent with Modic changes

Modic type I change (MC1) are vertebral bone marrow lesions adjacent to degenerated discs that are specific for discogenic low back pain. The etiopathogenesis is unknown, but occult discitis, in particular with Propionibacteria acnes (P. acnes), has been suggested as a possible etiology. If true, antibiotic therapy should be considered for patients with MC1. However, this hypothesis is controversial. While some studies report up to 40% infection rate in herniated discs, others fail to detect infected discs and attribute reports of positive cultures to contamination during sampling procedure. Irrespective of the clinical controversy, whether it is biologically plausible for P. acnes to cause MC1 has never been investigated. Therefore, the objective of this study was to test if P. acnes can proliferate within discs and cause reactive changes in the adjacent bone marrow. P. acnes was aseptically isolated from a symptomatic human L4/5 disc with MC1 and injected into rat tail discs. We demonstrate proliferation of P. acnes and up-regulation of IL-1 and IL-6 within three days of inoculation. At day-7, disc degeneration was apparent along with fibrotic endplate erosion. TNF-α immunoreactivity was enhanced within the effected endplates along with cellular infiltrates. The bone marrow appeared normal. At day-14, endplates and trabecular bone close to the disc were almost completely resorbed and fibrotic tissue extended into the bone marrow. T-cells and TNF-α immunoreactivity were identified at the disc/marrow junction. On MRI, bone marrow showed MC1-like changes. In conclusion, P. acnes proliferate within the disc, induce degeneration, and cause MC1-like changes in the adjacent bone marrow. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1447-1455, 2016.

MyD88-dependent Toll-like receptor 4 signal pathway in intervertebral disc degeneration

Lower back pain (LBP) is a common and remitting problem. One of the primary causes of LBP is thought to be degeneration of the intervertebral disc (IVD). The aim of the present study was to investigate the role of the myeloid differentiation primary-response protein 88 (MyD88)-dependent Toll-like receptor 4 (TLR4) signal pathway in the mechanism of IVD degeneration. IVD nucleus pulposus cells isolated and cultured from the lumbar vertebrae of Wistar rats were stimulated by various doses of lipopolysaccharide (LPS; 0.1, 1, 10 and 100 µg/ml) to simulate IVD degeneration. Cells were rinsed and cultured in serum-free Dulbecco's modified Eagle's medium/F12. Reverse transcription-quantitative polymerase chain reaction was used to determine the levels of TLR4, MyD88, tumor necrosis factor α (TNFα), and interleukin-1β (IL-1β) mRNA expression after 1, 3, 6, 9 and 12 h of incubation. Additionally, western blot and enzyme-linked immunosorbent assay analyses were used to determine the levels of TLR4, MyD88, TNFα, and IL-1β protein expression after 24, 48 and 72 h of incubation. The levels of TLR4, MyD88, TNFα and IL-1β mRNA all increased in the cells stimulated by 10 µg/ml LPS at 3, 6 and 9 h (all P<0.001). Furthermore, the levels of TLR4, MyD88, TNFα and IL-1β protein all increased at 24, 48 and 72 h (all P<0.001). Additionally, the mRNA and protein levels of TLR4, MyD88, TNFα and IL-1β increased significantly in the cells stimulated by 1, 10 and 100 µg/ml LPS compared with the control group, and reached a peak in the 10 µg/ml LPS group (all P<0.001). These results suggest that the MyD88-dependent TLR4 signal pathway is a target pathway in IVD degeneration. This pathway is time phase- and dose-dependent, and when activated can lead to the release of inflammatory factors that participate in IVD degeneration.

Cordycepin inhibits LPS-induced inflammatory and matrix degradation in the intervertebral disc

Cordycepin is a component of the extract obtained from Cordyceps militaris and has many biological activities, including anti-cancer, anti-metastatic and anti-inflammatory effects. Intervertebral disc degeneration (IDD) is a degenerative disease that is closely related to the inflammation of nucleus pulposus (NP) cells. The effect of cordycepin on NP cells in relation to inflammation and degeneration has not yet been studied. In our study, we used a rat NP cell culture and an intervertebral disc (IVD) organ culture model to examine the inhibitory effects of cordycepin on lipopolysaccharide (LPS)-induced gene expression and the production of matrix degradation enzymes (MMP-3, MMP-13, ADAMTS-4, and ADAMTS-5) and oxidative stress-associated factors (nitric oxide and PGE2). We found a protective effect of cordycepin on NP cells and IVDs against LPS-induced matrix degradation and macrophage infiltration. In addition, western blot and luciferase assay results demonstrated that pretreatment with cordycepin significantly suppressed the LPS-induced activation of the NF-κB pathway. Taken together, the results of our research suggest that cordycepin could exert anti-inflammatory and anti-degenerative effects on NP cells and IVDs by inhibiting the activation of the NF-κB pathway. Therefore, cordycepin may be a potential treatment for IDD in the future.

Thalidomide represses inflammatory response and reduces radiculopathic pain by inhibiting IRAK-1 and NF-κB/p38/JNK signaling

Intervertebral disc (IVD) disease, the most common cause of disc failure and low back pain, is characterized by age-related changes in the adult disc. In this study we aimed to analyze the potential of thalidomide for the treatment of IVD disease, through identifying and explaining its anti-inflammatory and anti-catabolic activity in both in vitro IVD cell culture and in vivo animal model. Inflammatory response was induced by IL-1β, then the activity and expression of inflammatory mediators and pathways were assessed in the presence or absence of thalidomide. The p38 inhibitor SB203580 was also used to investigate the involvement of the MAPK pathway in the observed effects. Moreover the analgesic properties of thalidomide were analyzed by the von Frey filament test in Sprague-Dawley rats. Our results indicated that thalidomide significantly inhibited the expression of pro-inflammatory mediators and matrix metalloproteinases in vitro, as well as radiculopathic pain in vivo, most probably by modulation of the activity of IRAK-1 and its downstream effectors p38, JNK and NF-κB. Our current study strongly supports the potential of thalidomide for the treatment of pain and inflammation in degenerative disc disease.

Discovery of the drivers of inflammation induced chronic low back pain: from bacteria to diabetes

The intervertebral disc is a unique avascular organ that supports axial skeleton flexion and rotation. The high proteoglycan content of the nucleus pulposus tissue, present at the center of the disc, is pivotal for its mechanical function, distribution of compressive loads. Chronic low back pain, a prevalent and costly condition, is strongly associated with disc degeneration. Degenerated discs exhibit high levels of inflammatory cytokines, matrix catabolizing enzymes, and an overall reduction in proteoglycan content. Although the cytokine profile of diseased discs has been widely studied, little is known of what initiates and drives inflammation and subsequent low back pain. Recent studies have shown that anaerobic bacteria are present in a high percentage of painful, herniated discs and long-term treatment with antibiotics resolves symptoms associated with chronic low back pain. It is thought that these anaerobic bacteria in the disc may stimulate inflammation through toll-like receptors to further exacerbate disc degeneration. Despite the promise and novelty of this theory, there are other possible inflammatory mediators that need careful consideration. The metabolic environment associated with diabetes and atypical matrix degradation products also have the ability to activate many of the same inflammatory pathways as seen during microbial infection. It is therefore imperative that the research community must investigate the contribution of all possible drivers of inflammation to address the wide spread problem of discogenic chronic low back pain.

Crocin exerts anti-inflammatory and anti-catabolic effects on rat intervertebral discs by suppressing the activation of JNK

As intervertebral disc (IVD) degeneration has been proven to contribute to low back pain (LBP), drug treatment aiming at attenuating IVD degeneration may prove to be benefiical. Crocin, a bioactive component of saffron, has been found to exert anti-inflammatory effects on cartilage. In the present study, the anti-inflammatory and anti-catabolic effects of crocin on rat IVDs were analyzed in vitro and ex vivo. Nucleus pulposus (NP) cells were isolated from the lumbar IVDs of Sprague-Dawley rats. The NP cells were first treated with various concentrations of crocin, and then stimulated with lipopolysaccharide (LPS) to induce inflammation. Subsequently, RT-qPCR and enzyme-linked immunosorbent assay were carried out to measure the expression levels of catabolic enzymes, pro-inflammatory factors and the components of the extracellular matrix (ECM). In addition, western blot analysis was also used to investigate the related signaling pathways. The whole spinal motion segment (vertebra-IVD-vertebra section) of the rats was isolated and cultured in the presence or absence of LPS and crocin for 7 days. The ex vivo effects of crocin on the ECM of the IVD structures were determined by histological and biochemical analysis. In vitro, crocin significantly inhibited the LPS-induced overexpression of catabolic enzymes [matrix metalloproteinase (MMP)-1, MMP-3, MMP-13, a disintegrin-like and metalloprotease (reprolysin type) with thrombospondin type 1 motif (ADAMTS)-4 and ADAMTS‑5], pro-inflammatory factors [interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6 and inducible nitric oxide synthase (iNOS)] and Toll-like receptor (TLR)‑2 in a concentration-dependent manner. Notably, crocin partly prevented the downregulation of aggrecan and type II collagen (collagen‑II). Moreover, crocin suppressed the LPS-induced activation of the mitogen-activated protein kinase (MAPK) pathway by inhibiting the phosphorylation of c-Jun N-terminal kinase (JNK). Ex vivo experiments demonstrated that crocin protected the rat IVDs from the LPS-induced depletion of the ECM components, including proteoglycan and collagen-II. In conclusion, crocin effectively suppressed the degeneration-related inflammation and catabolism in rat IVDs in vitro and ex vivo, suggesting that crocin has potential for use as a therapuetic strategy in the treatment of LBP.

Disc in flames: Roles of TNF-α and IL-1β in intervertebral disc degeneration

The intervertebral disc is an important mechanical structure that allows range of motion of the spinal column. Degeneration of the intervertebral disc--incited by aging, traumatic insult, genetic predisposition, or other factors--is often defined by functional and structural changes in the tissue, including excessive breakdown of the extracellular matrix, increased disc cell senescence and death, as well as compromised biomechanical function of the tissue. Intervertebral disc degeneration is strongly correlated with low back pain, which is a highly prevalent and costly condition, significantly contributing to loss in productivity and health care costs. Disc degeneration is a chronic, progressive condition, and current therapies are limited and often focused on symptomatic pain relief rather than curtailing the progression of the disease. Inflammatory processes exacerbated by cytokines tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) are believed to be key mediators of disc degeneration and low back pain. In this review, we describe the contributions of TNF-α and IL-1β to changes seen during disc degeneration at both cellular and tissue level, as well as new evidence suggesting a link between infection of the spine and low back pain, and the emerging therapeutic modalities aimed at combating these processes.

What is the preclinical evidence on platelet rich plasma and intervertebral disc degeneration?

PURPOSE

Intervertebral disc degeneration is a common disease that usually starts from the third decade of life and it represents a significant cause of socio-economic problems. The accepted surgical treatment for disc degeneration is disc removal and vertebral fusion or, in selected cases, intervertebral disc arthroplasty. Several studies have demonstrated the ability of platelet rich plasma (PRP) to stimulate cell proliferation and extracellular matrix regeneration. However, literature results are still limited and more studies are required to clarify the role of PRP in the prevention or in the treatment of degenerative disc disease. The aim of this review is to summarize and critically analyze the current preclinical evidence about the use of PRP in intervertebral disc degeneration.

METHODS

Literature search was performed through various combinations of the following keywords: Intervertebral Disc Degeneration, Platelet Rich Plasma, PRP, Intervertebral disc regeneration. Papers included in our review cover the period between 2006 and 2014. The PRISMA 2009 checklist was followed.

RESULTS

At the end of the review process, 12 articles were included in our final manuscript, including 6 "in vitro" and 6 "in vivo" studies. All the included studies lead to positive preclinical results. No standardization of methodological analysis was observed.

CONCLUSION

It is not possible to draw definitive evidence about the use of PRP in IVD regeneration. We advise a proper standardization of the methodological analysis in order to compare the available data and achieve definitive results. This should be the cornerstone for future clinical applications.

MMPs and ADAMTSs in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is the most common diagnosis in patients with low back pain, a leading cause of musculoskeletal disability worldwide. The major components of extracellular matrix (ECM) within the discs are type II collagen (Col II) and aggrecan. Excessive destruction of ECM, especially loss of Col II and aggrecan, plays a critical role in promoting the occurrence and development of IDD. Matrix metalloproteinases (MMPs) and a disintegrin and metalloprotease with thrombospondin motifs (ADAMTSs) are primary enzymes that degrade collagens and aggrecan. There is a large and growing body of evidence that many members of MMPs and ADAMTSs are highly expressed in degenerative IVD tissue and cells, and are closely involved in ECM breakdown and the process of disc degeneration. In contrast, targeting these enzymes has shown promise for promoting ECM repair and mitigating disc regeneration. In the current review, after a brief description regarding the biology of MMPs and ADAMTSs, we mainly focus on their expression profiles, roles and therapeutic potential in IDD. A greater understanding of the catabolic pathways involved in IDD will help to develop potential prophylactic or regenerative biological treatment for degenerative disc disease in the future.

Tanshinone IIA represses inflammatory response and reduces radiculopathic pain by inhibiting IRAK-1 and NF-κB/p38/JNK signaling

Intervertebral disc (IVD) disease, a most common cause of disc failure and low back pain, is characterized by age-related changes in the adult disc. In this study we aimed to investigate the potential of Tanshinone IIA (TSA) for the treatment of IVD disease, through exploring its anti-inflammatory and anti-catabolic activities in both in vitro IVD cell culture and in vivo animal models. After the inflammatory response was induced in IVD cells by IL-1β, the activity and expression of inflammatory mediators, and potentially involved pathways were investigated in the presence or absence of TSA. The p38-MAPK inhibitor, SB239063, was also used to investigate the involvement of the MAPK signaling pathway in the observed effects. Meanwhile, the analgesic properties of TSA were analyzed by the von Frey filament test in Sprague-Dawley rats. Our results indicated that TSA significantly inhibited the expression of pro-inflammatory mediators and matrix metalloproteinases in vitro, as well as radiculopathic pain in vivo, probably by modulation of the activity of interleukin-1 receptor-associated kinase 1 (IRAK-1) and its downstream effectors p38, JNK and NF-κB. Our current study strongly demonstrates the potential of TSA for the treatment of inflammation and followed pain in degenerative disc disease.

Progranulin knockout accelerates intervertebral disc degeneration in aging mice

Intervertebral disc (IVD) degeneration is a common degenerative disease, yet much is unknown about the mechanisms during its pathogenesis. Herein we investigated whether progranulin (PGRN), a chondroprotective growth factor, is associated with IVD degeneration. PGRN was detectable in both human and murine IVD. The levels of PGRN were upregulated in murine IVD tissue during aging process. Loss of PGRN resulted in an early onset of degenerative changes in the IVD tissue and altered expressions of the degeneration-associated molecules in the mouse IVD tissue. Moreover, PGRN knockout mice exhibited accelerated IVD matrix degeneration, abnormal bone formation and exaggerated bone resorption in vertebra with aging. The acceleration of IVD degeneration observed in PGRN null mice was probably due to the enhanced activation of NF-κB signaling and β-catenin signaling. Taken together, PGRN may play a critical role in homeostasis of IVD, and may serve as a potential molecular target for prevention and treatment of disc degenerative diseases.

MicroRNA-146a reduces IL-1 dependent inflammatory responses in the intervertebral disc

Because miR-146a expression in articular chondrocytes is associated with osteoarthritis (OA), we assessed whether miR-146a is linked to cartilage degeneration in the spine. Monolayer cultures of nucleus pulposus (NP) cells from the intervertebral discs (IVD) of bovine tails were transfected with a miR-146a mimic. To provoke inflammatory responses and catabolic extracellular matrix (ECM) degradation, cells were co-treated with interleukin-1 (IL-1). Transfection of miR-146a decreases IL-1 induced mRNA levels of inflammatory genes and catabolic proteases in NP cells based on quantitative real-time reverse transcriptase PCR (qRT-PCR) analysis. Similarly, miR146a suppresses IL-1 induced protein levels of matrix metalloproteinases and aggrecanases as revealed by immunoblotting. Disc segments from wild type (WT) and miR-146a knockout (KO) mice were cultured ex vivo in the presence or absence of IL-1 for 3days. Histological and immuno-histochemical (IHC) analyses of disc organ cultures revealed that IL-1 mediates changes in proteoglycan (PG) content and in-situ levels of catabolic proteins (MMP-13 and ADAMTS-5) in the nucleus pulposus of the disc. However, these IL-1 effects are more pronounced in miR-146a KO discs compared to WT discs. For example, absence of miR-146a increases the percentage of MMP-13 and ADAMTS-5 positive cells after treatment with IL-1. Thus, miR-146a appears to protect against IL-1 induced IVD degeneration and inflammation. Stimulation of endogenous miR-146a expression or exogenous delivery of miRNA-146a are viable therapeutic strategies that may decelerate disc degeneration and regain a normal homeostatic balance in extracellular matrix production and turn-over.

Expression and regulation of toll-like receptors (TLRs) in human intervertebral disc cells

PURPOSE

Although inflammatory processes play an essential role in painful intervertebral disc (IVD) degeneration, the underlying regulatory mechanisms are not well understood. This study was designed to investigate the expression, regulation and importance of specific toll-like receptors (TLRs)--which have been shown to play an essential role e.g. in osteoarthritis--during degenerative disc disease.

METHODS

The expression of TLRs in human IVDs was measured in isolated cells as well as in normal or degenerated IVD tissue. The role of IL-1β or TNF-α in regulating TLRs (expression/activation) as well as in regulating activity of down-stream pathways (NF-κB) and expression of inflammation-related genes (IL-6, IL-8, HSP60, HSP70, HMGB1) was analyzed.

RESULTS

Expression of TLR1/2/3/4/5/6/9/10 was detected in isolated human IVD cells, with TLR1/2/4/6 being dependent on the degree of IVD degeneration. Stimulation with IL-1β or TNF-α moderately increased TLR1/TLR4 mRNA expression (TNF-α only), and strongly increased TLR2 mRNA expression (IL-1β/TNF-α), with the latter being confirmed on the protein level. Stimulation with IL-1β, TNF-α or Pam3CSK4 (a TLR2-ligand) stimulated IL-6 and IL-8, which was inhibited by a TLR2 neutralizing antibody for Pam3CSK4; IL-1β and TNF-α caused NF-κB activation. HSP60, HSP70 and HMGB1 did not increase IL-6 or IL-8 and were not regulated by IL-1β/TNF-α.

CONCLUSION

We provide evidence that several TLRs are expressed in human IVD cells, with TLR2 possibly playing the most crucial role. As TLRs mediate catabolic and inflammatory processes, increased levels of TLRs may lead to aggravated disc degeneration, chronic inflammation and pain development. Especially with the identification of more endogenous TLR ligands, targeting these receptors may hold therapeutic promise.

Role of cytokines in intervertebral disc degeneration: pain and disc content

Degeneration of the intervertebral discs (IVDs) is a major contributor to back, neck and radicular pain. IVD degeneration is characterized by increases in levels of the proinflammatory cytokines TNF, IL-1α, IL-1β, IL-6 and IL-17 secreted by the IVD cells; these cytokines promote extracellular matrix degradation, chemokine production and changes in IVD cell phenotype. The resulting imbalance in catabolic and anabolic responses leads to the degeneration of IVD tissues, as well as disc herniation and radicular pain. The release of chemokines from degenerating discs promotes the infiltration and activation of immune cells, further amplifying the inflammatory cascade. Leukocyte migration into the IVD is accompanied by the appearance of microvasculature tissue and nerve fibres. Furthermore, neurogenic factors, generated by both disc and immune cells, induce expression of pain-associated cation channels in the dorsal root ganglion. Depolarization of these ion channels is likely to promote discogenic and radicular pain, and reinforce the cytokine-mediated degenerative cascade. Taken together, an enhanced understanding of the contribution of cytokines and immune cells to these catabolic, angiogenic and nociceptive processes could provide new targets for the treatment of symptomatic disc disease. In this Review, the role of key inflammatory cytokines during each of the individual phases of degenerative disc disease, as well as the outcomes of major clinical studies aimed at blocking cytokine function, are discussed.

Extracellular signal-regulated kinase inhibition modulates rat annulus fibrosus cell response to interleukin-1

STUDY DESIGN

Rat annulus fibrosus (AF) cells were activated with interleukin-1 (IL-1) with or without extracellular signal-regulated kinase (ERK) inhibition. Factors associated with the anabolic/catabolic balance of the disc were determined.

OBJECTIVE

To clarify the role of ERK pathway in AF cells response to IL-1.

SUMMARY OF BACKGROUND DATA

IL-1 plays an important role in intervertebral disc degeneration. ERK is an important inflammatory pathway that plays a crucial role in the expression of inflammatory and catabolic genes induced by IL-1 in chondrocytes. However, the role of the ERK pathway in AF cells response to IL-1 has not been fully investigated.

METHODS

Rat AF cells in monolayer culture were exposed to IL-1, with or without ERK inhibition; ribonucleic acid was isolated for real time polymerase chain reaction analysis of gene expression, conditioned media analyzed for nitrite, prostaglandin E-2, and IL-6, Western blot was performed to detect the changes of protein expression.

RESULTS

ERK specific inhibitor U0126 significantly inhibited IL-1-induced ERK activation. IL-1-dependent upregulation of iNOS, IL-6, Cox-2, (MMP)-3, and MMP-13 was significantly reduced by ERK inhibition. The decreased gene expression of collagen I, collagen II, collagen IX, and IGF-1 induced by IL-1 was also reversed by U0126. Gene expression of ADAMTS-4, ADAMTS-5, and TGF-b were not affected by IL-1 or ERK inhibition. IL-1 moderately upregulated aggrecan and TIMP-1 expression, ERK inhibition had no significant effect on aggrecan expression but decreased TIMP-1 expression in the presence of IL-1. ERK inhibition reversed the changes of protein expression of MMP-3, MMP-13, TIMP-1, aggrecan and collagen II induced by IL-1. IL-1-induced nitric oxide, prostaglandin E-2, and IL-6 accumulation were also reduced by ERK inhibition.

CONCLUSION

These results suggest that IL-1 induces an imbalance between anabolic and catabolic events in AF cells, ERK inhibition could provide some protection against the adverse effects of IL-1.

LEVEL OF EVIDENCE

N/A.

Do changing toll-like receptor profiles in different layers and grades of osteoarthritis cartilage reflect disease severity?

OBJECTIVE

Cartilage degeneration in osteoarthritis (OA) leads to release of potential danger signals. The aim of our study was to profile OA cartilage for the Toll-like receptor (TLR) danger signal receptors.

METHODS

Osteochondral cylinders from total knee replacements were graded using OA Research Society International score and stained for proteoglycans, collagenase-cleaved type II collagen, and TLR 1-10, which were analyzed histomorphometrically.

RESULTS

Grade 1 OA lesions contained 22%-55% TLR 1-9-positive cells in the surface zone, depending on the TLR type. In Grade 2 TLR, immunoreactivity was 60%-100% (p < 0.01) and it was even higher in Grades 3 and 4 (p < 0.01 vs Grade 1). TLR-positive cells in Grade 1 middle zone were low, 0-19.9%, but were 5.1%-32.7% in Grade 2 (p < 0.01) and 34%-83% in Grades 3-4 samples (p < 0.001). TLR values in Grade 5 were low (14.3%-28.7%; p < 0.001). In Grades 3-4 OA, cartilage matrix stained strongly for TLR. In Grade 1, COL2-3/4M was restricted to chondrocytes, but was increasingly seen in matrix upon progress of OA to Grade 4, and then declined.

CONCLUSION

Cells in the gliding surface zone are fully equipped with TLR in mild OA. Their proportion increases and extends to the middle or even the deep zone, reflecting OA progression. COL2A-3/4M staining suggests Endo180-mediated intake for intralysosomal degradation by cathepsins in Grade 1, but in higher grades this chondrocyte-mediated clearance fails and the matrix demonstrates extensive collagenase-induced damage. Detached and/or partially degraded matrix components can then act as endogenous danger signals (damage-associated molecular patterns or DAMP) and stimulate increasingly TLR-equipped chondrocytes to inflammation. At the peak inflammatory response, soluble TLR may exert negative feedback, explaining in part the low TLR levels in Grade 5 OA.