Developing consistently reproducible intervertebral disc degeneration at rat caudal spine by using needle puncture

Establishment of intervertebral disc degeneration models; A review of the currently used models

One of the frequent causes of low back pain is intervertebral disc degeneration (IDD), which is followed by discogenic pain. Some significant risk factors that have been linked to the onset and progression of IDD include age, mechanical imbalance, changes in nutrition and inflammation. According to recent studies, five types of animal models are established for producing IDD: the spontaneous models, the puncture models, the biomechanical models, the chemical models and the hybrid models. These models are crucial in studying and understanding IDD's natural history and identifying potential treatment targets for IDD. In our study, we'll talk about the technical aspects of these models, the time between model establishment and the apparition of observable degradation, and their potential in various research. Each animal model should be compared to the human natural IDD pathogenesis to guide future research efforts in this area. By improving knowledge and appropriate application of various animal models, we seek to raise awareness of this illness and further translational research.

Intervertebral disc injury triggers neurogenic inflammation of adjacent healthy discs

BACKGROUND CONTEXT

Intervertebral disc degeneration is common and may play an important role in low back pain, but it is not well-understood. Previous studies have shown that the outer layer of the annulus fibrosus of a healthy disc is innervated by nociceptive nerve fibers. In the process of disc degeneration, it can grow into the inner annulus fibrosus or nucleus pulposus and release neuropeptides. Disc degeneration is associated with inflammation that produces inflammatory factors and potentiates nociceptor sensitization. Subsequently neurogenic inflammation is induced by neuropeptide release from activated primary afferent terminals. Because the innervation of a lumbar disc comes from multisegmental dorsal root ganglion neurons, does neurogenic inflammation in a degenerative disc initiate neurogenic inflammation in neighboring healthy discs by antidromic activity?

PURPOSE

This study was based on animal experiments in Sprague-Dawley rats to investigate the role of neurogenic inflammation in adjacent healthy disc degeneration induced by disc injury.

STUDY DESIGN

This was an experimental study.

METHODS

Seventy-five 12-week-old, male Sprague-Dawley rats were allocated to 3 groups (sham group, disc injury group and disc injury+TrkA antagonist group). The disc injury group was punctured in the tail disc between the eighth and ninth coccygeal vertebrae (Co8-9) to establish an animal model of tail intervertebral disc degeneration. The sham group underwent only skin puncture and the disc injury+TrkA antagonist group was intraperitoneally injected with GW441756 two days before disc puncture. The outcome measure included quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

Disc injury induced an increase in aggrecan, NGF, TrkA, CGRP, SP, IL-1β, and IL-6 mRNA levels in the injured (Co8-9) and adjacent discs (Co7-8), which reached a peak on day 1, then gradually decreased, and returned to normal on day 14. After intraperitoneal injection of GW441756 prior to puncture, the mRNA levels of the above indicators were down-regulated in Co7-8 and Co8-9 intervertebral discs on the 1st and 7th days. The protein content of the above indicators in Co7-8 and Co8-9 intervertebral discs showed roughly the same trend as mRNA levels.

CONCLUSIONS

Degeneration of one disc can induce neurogenic inflammation of adjacent healthy discs in a rat model.

CLINICAL SIGNIFICANCE

This model supports a key role of neurogenic inflammation in disc degeneration, and may play a role in the experience of low back pain.

M2 Macrophage-Derived Small Extracellular Vesicles Ameliorate Pyroptosis and Intervertebral Disc Degeneration

Intervertebral discs (IVDs) have a limited self-regenerative capacity and current strategies for IVD regeneration are unsatisfactory. Recent studies showed that small extracellular vesicles derived from M2 macrophage cells (M2-sEVs) inhibited inflammation by delivery of various bioactive molecules to recipient cells, which indicated that M2-sEVs may offer a therapeutic strategy for the repair of IVDs. Herein, we investigated the roles and mechanisms of M2-sEVs on IVD regeneration. The in vitro results demonstrated that M2-sEVs inhibited pyroptosis, preserved cellular viability, and promoted migration of nucleus pulposus cells (NPCs). Bioinformatics analysis and verification experiments of microRNA (miR) expression showed that miR-221-3p was highly expressed in M2-sEVs. The mechanism of action was explored and indicated that M2-sEVs inhibited pyroptosis of NPCs through transfer of miR-221-3p, which suppressed the expression levels of phosphatase and tensin homolog and NOD-, LRR-, and pyrin domain-containing protein 3. Moreover, we fabricated decellularized ECM-hydrogel (dECM) for sustained release of M2-sEVs, which exhibited biocompatibility and controlled release properties. The in vivo results revealed that dECM-hydrogel containing M2-sEVs (dECM/M2-sEVs) delayed the degeneration of intervertebral disc degeneration (IDD) models. In addition to demonstrating a promising therapeutic for IDD, this study provided valuable data for furthering the understanding of the roles and mechanisms of M2-sEVs in IVD regeneration.

Exosomes from umbilical cord mesenchymal stem cells ameliorate intervertebral disc degeneration via repairing mitochondrial dysfunction

Background

Reactive oxygen species (ROS), predominantly generated by mitochondria, play a crucial role in the pathogenesis of intervertebral disc degeneration (IVDD). Reduction of ROS levels may be an effective strategy to delay IVDD. In this study, we assessed whether umbilical cord mesenchymal stem cell-exosomes (UCMSC-exos) can be used to treat IVDD by suppressing ROS production caused by mitochondrial dysfunction.

Materials and methods

Human UCMSC-exos were isolated and identified. Nucleus pulposus cells (NPCs) were stimulated with H2O2 in the presence or absence of exosomes. Then, 4D label free quantitative (4D-LFQ) proteomics were used to analyze the differentially expressed (DE) proteins. Mitochondrial membrane potential (MMP), mitochondrial ROS and protein levels were determined via immunofluorescence staining, flow cytometry and western blotting respectively. Additionally, high-throughput sequencing was performed to identify the DE miRNAs in NPCs. Finally, therapeutic effects of UCMSC-exos were investigated in a puncture-induced IVDD rat model. Degenerative grades of rat IVDs were assessed using magnetic resonance imaging and histochemical staining.

Results

UCMSC-exos effectively improved the viability of NPCs and restored the expression of the extracellular matrix (ECM) proteins, collagen type II alpha-1 (COL2A1) and matrix metalloproteinase-13 induced by H2O2. Additionally, UCMSC-exos not only reduced the total intracellular ROS and mitochondrial superoxide levels, but also increased MMP in pathological NPCs. 4D-LFQ proteomics and western blotting further revealed that UCMSC-exos up-regulated the levels of the mitochondrial protein, mitochondrial transcription factor A (TFAM), in H2O2-induced NPCs. High-throughput sequencing and qRT-PCR uncovered that UCMSC-exos down-regulated the levels of miR-194-5p, a potential negative regulator of TFAM, induced by H2O2. Finally, in vivo results showed that UCMSC-exos injection improved the histopathological structure and enhanced the expression levels of COL2A1 and TFAM in the rat IVDD model.

Conclusions

Our findings suggest that UCMSC-exos promote ECM synthesis, relieve mitochondrial oxidative stress, and attenuate mitochondrial dysfunction in vitro and in vivo, thereby effectively treating IVDD.

The translational potential of this article

This study provides solid experimental data support for the therapeutic effects of UCMSC-exos on IVDD, suggesting that UCMSC-exos will be a promising nanotherapy for IVDD.

SEPHS1 attenuates intervertebral disc degeneration by delaying nucleus pulposus cell senescence through the Hippo-Yap/Taz pathway

Nucleus pulposus cell (NPC) senescence is a major cause of intervertebral disc degeneration (IVDD). Oxidative stress and reactive oxygen species (ROS) play critical roles in regulating cell senescence. Selenophosphate synthetase 1 (SEPHS1) was reported to play an important role in mitigating oxidative stress in an osteoarthritis (OA) model by reducing the production of ROS, thereby, delaying the occurrence and development of osteoarthritis. In this study, we explored the, hitherto unknown, role of SEPHS1 in IVDD in vitro and in vivo using an interleukin-1β (IL-1β)-induced NPC senescence model and a rat needle puncture IVDD model, respectively. SEPHS1 delayed NPC senescence in vitro by reducing ROS production. Age-related dysfunction was also ameliorated by the overexpression of SEPHS1 and inhibition of the Hippo-Yap/Taz signaling pathway. In vivo experiments revealed that the overexpression of SEPHS1 and inhibition of Hippo-Yap/Taz alleviated IVDD in rats. Moreover, a selenium (Se)-deficient diet and lack of SEPHS1 synergistically aggravated IVDD progression. Taken together, our results demonstrate that SEPHS1 plays a significant role in NPC senescence. Overexpression of SEPHS1 and inhibition of Hippo-Yap/Taz can delay NPC senescence, restore the balance of extracellular matrix metabolism, and attenuate IVDD. SEPHS1 could be a promising therapeutic target for IVDD.NEW & NOTEWORTHY Selenophosphate synthetase 1 (SEPHS1) deficiency leads to an increase in reactive oxygen species levels and in the subsequent activation of the Hippo-Yap/Taz signaling pathway. In the rat model of intervertebral disc degeneration (IVDD), overexpression of SEPHS1 and inhibition of Hippo-YAP/Taz mitigated the progression of disc degeneration indicating the involvement of SEPHS1 in IVDD. SEPHS1 is a promising therapeutic target for IVDD.

MSC-Derived Exosomes Ameliorate Intervertebral Disc Degeneration By Regulating the Keap1/Nrf2 Axis

Bone marrow mesenchymal stem cell derived exosomes (BMSC-exos) are a crucial means of intercellular communication and can regulate a range of biological processes by reducing inflammation, decreasing apoptosis and promoting tissue repair. The process of intervertebral disc degeneration (IVDD) is accompanied by increased reactive oxygen species (ROS) because of a decrease in the expression of Nrf2, a critical transcription factor that resists excessive ROS. Our study demonstrated that BMSC-exos decreased ROS production by inhibiting Keap1 and promoting Nrf2 expression, attenuating the apoptosis, inflammation, and degeneration of nucelus pulposus (NP) cells. BMSC-exos promoted an increase in Nrf2 and nuclear translocation, while NF-κB expression was downregulated during this process. Additionally, the expression of antioxidative proteins was elevated after treatment with BMSC-exos. In vivo, we found more NP tissue retention in the BMSC-exos-treated group, along with more expression of Nrf2 and antioxidant-related proteins. Our findings demonstrated for the first time that BMSC-exos could restore the down-regulated antioxidant response system in degenerating NP cells by modulating the Keap1/Nrf2 axis. BMSC-exos could be used as an immediate ROS modulator in the treatment of intervertebral disc degeneration. When BMSC-exos were uptaken by NPCs, the expression of Keap1 decreased and this led to increased expression of Nrf2. Nuclear translocation of Nrf2 then promoted the synthesis of antioxidants against ROS and inhibited NF-kB signalling. Cellular inflammation, apoptosis, and ECM-related indicators were further reduced. Together, the process of IVDD was alleviated.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Ginsenoside Rg1 inhibits nucleus pulposus cell apoptosis, inflammation and extracellular matrix degradation via the YAP1/TAZ pathway in rats with intervertebral disc degeneration

PURPOSE

Intervertebral disc degeneration (IDD) is one of the main causes of low back pain, which not only affects patients' life quality, but also places a great burden on the public health system. Recently, ginsenoside Rg1 has been found to act in IDD; however, the mechanism is still unclear. The purpose of this study is to explore the function of ginsenoside Rg1 and its molecular mechanism in IDD.

METHODS

The rat model of IDD and nucleus pulposus (NP) experimental groups treated with ginsenoside Rg1 was constructed for investing the role of ginsenoside Rg1 in IDD rats. In the in vitro and in vivo study, the histological morphological changes, motor threshold (MT), inflammatory factors, oxidative stress, apoptosis and expression of the YAP1/TAZ signaling pathway-related proteins of the intervertebral discs (IVD) were measured by histological staining, mechanical and thermal stimulation, ELISA, qRT-PCR, flow cytometry, and western blot, respectively.

RESULTS

Ginsenoside Rg1 significantly increased the threshold for mechanical and thermal stimulation and alleviated histological changes in IDD rats. Ginsenoside Rg1 had a significant inhibitory effect on the secretion level of inflammatory factors, redox activity, extracellular matrix (ECM) degradation in IVD tissue and NP cells, and apoptosis in NP cells. Further investigation revealed that ginsenoside Rg1 significantly inhibited the expression of YAP1/TAZ signaling pathway-related proteins. Additionally, the above inhibitory effect of ginsenoside Rg1 on IDD progression was concentration-dependent, that is, the highest concentration of ginsenoside Rg1 was most effective.

CONCLUSION

Ginsenoside Rg1 inhibits IDD progression by suppressing the activation of YAP1/TAZ signaling pathway. This means that ginsenoside Rg1 has the potential to treat IDD.

Effect of species, concentration and volume of local anesthetics on intervertebral disk degeneration in rats with discoblock

PURPOSE

Discoblock is effective in relieving discogenic low back pain, but it can also cause intervertebral disk degeneration (IDD). The effect of species, concentration and volume of local anesthetics on IDD with discoblock have not been reported. The purpose was to study the effect of species, concentration and volume of local anesthetics on IDD in rats undergoing discoblock.

METHODS

The effects of local anesthetics on nucleus pulposus cell (NPC) viability in vitro were studied. NPCs were exposed to lidocaine, bupivacaine and ropivacaine at different concentrations. NPC viability was measured. The least cytotoxic local anesthetic was used in vivo. The concentration and volume of local anesthetics on IDD in rat with discoblocks were tested in vivo. Detection indicators included X-ray, MRI, water content of the disk and histological changes.

RESULTS

The toxicity of local anesthetics to NPCs was dose and time dependent, and the cytotoxicity of different local anesthetics was different. Among the three local anesthetics, ropivacaine was the least toxic to NPCs. The effect of ropivacaine concentration on IDD was not significant, as detected by X-ray, MRI, disk water content and histology (P < 0.05). The volume of ropivacaine has a significant effect on IDD, as supported by X-ray, MRI, disk water content and histology (P < 0.05). Acupuncture itself significantly increased IDD, as detected by MRI, disk water content and histology (P < 0.05).

CONCLUSION

Ropivacaine should be selected for its low cytotoxicity. A lower volume and slow injection speed should be used to reduce IDD during discoblock.

Similarity and difference between aging and puncture-induced intervertebral disc degeneration

The purpose of our study was to investigate the changes in micromorphology and mechanical properties of intervertebral discs degeneration induced by aging and puncture. Normal group (NG), 2 weeks post-puncture degeneration group (PDG) and aging degeneration group (ADG) each included 10 rats. Plain film, magnetic resonance imaging, and histological testing were utilized to assess intervertebral disc degeneration. Atomic force microscope was utilized to analyze the microstructure and elastic modulus of the intervertebral disc, while immunohistochemistry was employed to assess alterations in the cell matrix using collagen I, collagen II, matrix metalloproteinase-3 (MMP-3), and tumour necrosis factor-α (TNF-α). The results showed that the disc height ratio between PDG and ADG decreased. In the PDG and ADG group, histological scores both increased, the gray value of the T2 signal decreased, the proportion of MMP-3 and TNF-positive cells in intervertebral disc tissues was higher (p < 0.05) and the IOD values of COL-2 lower in intervertebral disc tissues (p < 0.05). The elastic modulus of PDG and ADG annulus fibers (AF) increased compared to the NG (p < 0.05); when compared to PDG, the elastic modulus of ADG AF decreased (p < 0.05). The elastic modulus of PDG and ADG collagen increased in the nucleus pulposus (NP, p < 0.05); ADG had a greater AF diameter than NG and PDG (p < 0.05). The results indicated that ADG fiber diameter thickens, and chronic inflammation indicators rise; PDG suffers from severe extracellular matrix loss. The degeneration of the ADG and PDG intervertebral discs is different. The results provide foundation for clinical research.

Rat tail models for the assessment of injectable nucleus pulposus regeneration strategies

Back pain is a global epidemiological and socioeconomic problem often associated with intervertebral disc degeneration; a condition believed to initiate in the nucleus pulposus (NP). There is considerable interest in developing early therapeutic interventions to target the NP and halt degeneration. Rat caudal models of disc degeneration have demonstrated significant utility in the study of disease progression and its impact on tissue structure, composition, and mechanical performance. One significant advantage of the caudal model is the ease of access and high throughput nature. However, considerable variability exists across the literature in terms of experimental setup and parameters. The objective of this article is to aid researchers in the design and development of caudal puncture models by providing details and insight into the most reported experimental parameters. Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) guidelines were employed to screen the existing literature and 80 manuscripts met the inclusion criteria. Disc geometry, surgical approaches, effect of needle gauge size to induce degeneration, therapeutic volume, outcome measures, and associated limitations are considered and discussed, and a range of recommendations based on different research questions are presented.

Optineurin-mediated mitophagy as a potential therapeutic target for intervertebral disc degeneration

Low back pain is thought to be mainly caused by intervertebral disc degeneration (IVDD), and there is a lack of effective treatments. Cellular senescence and matrix degradation are important factors that cause disc degeneration. Mitochondrial dysfunction induced by oxidative stress is an important mechanism of cellular senescence and matrix degradation in the nucleus pulposus (NP), and mitophagy can effectively remove damaged mitochondria, restore mitochondrial homeostasis, and mitigate the damage caused by oxidative stress. Optineurin (OPTN) is a selective mitophagy receptor, and its role in intervertebral disc degeneration remains unclear. Here, we aimed to explore the effect of OPTN on H₂O₂-induced nucleus pulposus cell (NPCs) senescence and matrix degradation in a rat model of disc degeneration. Western blot analysis showed that OPTN expression was reduced in degenerative human and rat nucleus pulposus tissues and increased in H₂O₂-induced senescent NPCs. OPTN overexpression significantly inhibited H₂O₂-induced senescence and increased matrix-associated protein expression in NPCs, but OPTN knockdown showed the opposite effect. As previous reports have suggested that mitophagy significantly reduces mitochondrial damage and reactive oxygen species (ROS) caused by oxidative stress, and we used the mitophagy agonist CCCP, the mitophagy inhibitor cyclosporin A (CsA), and the mitochondrial ROS (mtROS) scavenger mitoTEMPO and confirmed that OPTN attenuated NPCs senescence and matrix degeneration caused by oxidative stress by promoting mitophagy to scavenge damaged mitochondria and excess reactive oxygen species, thereby slowing the progression of IVDD. In conclusion, our research suggests that OPTN is involved in IVDD and exerts beneficial effects against IVDD.

Interleukin-18 Inhibition Protects Against Intervertebral Disc Degeneration via the Inactivation of Caspase-3/9 Dependent Apoptotic Pathways

BACKGROUND

The present study was designed to identify and understand the potential effectiveness of therapeutic target in intervertebral disc degeneration (IVDD) and its regulation mechanism.

METHODS

The role and mechanism of interleukin-18 (IL-18) in the disease were investigated. The IVDD degenerative nucleus pulposus (NP) tissues from the human and mouse models were used.A total of three groups of Male BALB/c mice were randomly made i.e control, IVDD, and IVDD+Ad-shIL-18 groups. After Ad-shIL-18 transfection, the expression of ECM synthesis related protein Aggrecan (ACAN) and Collagen II, apoptotic effector Caspases (Caspase-3, 8, 9, 12 and Cleaved-Caspase 3, 8, 9, 12), pro-apoptotic gene Bax and anti-apoptotic factors Bcl-2 in NP cells of the human were evaluated.

RESULTS

The results of our study revealed that the mRNA and protein expression levels of IL-18 were notably increased in the NP tissues of IVDD patients and mice models. In the IVDD mice model, Ad-sh-IL-18 treatment reversed the IVDD progression. The levels of Aggrecan and Collagen II, contributing to ECM degradation in NP cells, were also significantly increased. Additionally, Ad-sh-IL-18 could inhibit the NP cell's apoptosis via regulating the caspase-3/9 pathway.

CONCLUSION

The IL-18 knockdown via the caspase-3/9 pathway, might reduce the NP cell's death as well as the imbalance between catabolism and anabolism of ECM in IVDD.

Metformin inactivates the cGAS-STING pathway through autophagy and suppresses senescence in nucleus pulposus cells

Intervertebral disc degeneration (IVDD) is a complex process involving many factors, among which excessive senescence of nucleus pulposus cells (NPCs) is considered to be the main factor. Our previous study found that metformin may inhibit senescence in nucleus pulposus cells; however, its working mechanism is still largely unknown. In the current study, we found that metformin may inactivate cGAS-STING pathway during oxidative stress. Knock-down of STING may further suppress senescence, indicating metformin may exert its effect through cGAS-STING pathway. Damaged DNA is a major inducer of the activation of cGAS-STING pathway. Mechanistically, our study showed that DNA damage was reduced during metformin treatment; however, suppression of autophagy by 3-methyladenine (3MA) may compromise the effect of metformin on DNA damage. The in vivo study also showed that 3MA may recede the therapeutic effect of metformin on IVDD. Taken together, our results reveal that metformin may suppress senescence via inactivating the cGAS-STING pathway through autophagy, implying the new application of metformin in cGAS-STING pathway related diseases.

Percutaneous lumbar annular puncture: A rat model to study intervertebral disc degeneration and pain-related behavior

Background

Previous animal models of intervertebral disc degeneration (IDD) rely on open surgical approaches, which confound the degenerative response and pain behaviors due to injury to surrounding tissues during the surgical approach. To overcome these challenges, we developed a minimally invasive percutaneous puncture procedure to induce IDD in a rat model.

Methods

Ten Fischer 344 male rats underwent percutaneous annular puncture of lumbar intervertebral discs (IVDs) at L2-3, L3-4, and L4-5. Ten unpunctured rats were used as controls. Magnetic resonance imagings (MRIs), serum biomarkers, and behavioral tests were performed at baseline and 6, 12, and 18 weeks post puncture. Rats were sacrificed at 18 weeks and disc histology, immunohistochemistry, and glycosaminoglycan (GAG) assays were performed.

Results

Punctured IVDs exhibited significant reductions in MRI signal intensity and disc volume. Disc histology, immunohistochemistry, and GAG assay results were consistent with features of IDD. IVD-punctured rats demonstrated significant changes in pain-related behaviors, including total distance moved, twitching frequency, and rearing duration.

Conclusions

This is the first reported study of the successful establishment of a reproducible rodent model of a percutaneous lumbar annular puncture resulting in discogenic pain. This model will be useful to test therapeutics and elucidate the basic mechanisms of IDD and discogenic pain.

SPECT Imaging of Acute Disc Herniation by Targeting Integrin α5β1 in Rat Models

Objective

Traditional morphological imaging of intervertebral disc herniation (IVDH) is challenging in early disease diagnosis. Aiming at the early diagnosis of IVD by non-invasive molecular imaging targeting of integrin α5β1, we performed novel imaging in rats with acute IVDH for the first time.

Methods

Animal models were prepared by conducting an established needle puncture procedure through the normal intervertebral disc (IVD). The disc-injured rats underwent SPECT/CT imaging of the ^99mTc-3PisoDGR2 peptide at 1 day to 2 months postinjury. The expression change of integrin α5β1 was determined by anti-integrin α5 and anti-integrin α5β1 immunohistochemistry (IHC). Magnetic resonance imaging (MRI) was performed for comparison during disease progression. The morphological changes of the disc were determined by safranin-O staining.

Results

Rats with acute IVDH showed gradually increased disc uptake of ^99mTc-3PisoDGR2 from 1 to 7 days posttreatment, which was a significantly higher level than that of the normal disks in degenerative diseases. IHC results showed the expression of integrin α5β1 on the surface of annulus fibrosus (AF) cells and nucleus pulposus (NP) cells, which agreed with the uptake data. MRI showed a progressively decreased T2 density and MRI index throughout the investigation. Hematoxylin and eosin (HE) staining and safranin-O staining revealed a disorganized structure of the IVD as well as loss of proteoglycans after puncture.

Conclusions

The present study demonstrated a good correlation between integrin α5β1 expression and acute disc herniation. The SPECT/CT imaging of ^99mTc-3PisoDGR2 targeting integrin α5β1 may diagnose IVDH in an acute phase for early disease management.

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

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

Degenerative Nucleus Pulposus Cells Derived Exosomes Promoted Cartilage Endplate Cells Apoptosis and Aggravated Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration is a complex multifactorial disease model, which pathogenesis has not been fully defined. There are few studies on the information interaction between nucleus pulposus (NP) cells and cartilage endplate (CEP) cells. Exosomes, as a carrier of information communication between cells, have become a research hotspot recently. The purpose of this study was to explore whether degenerative NP cells-derived exosomes promoted CEP cells apoptosis and aggravated IVD degeneration. The degenerative NP cells model was induced by TNFα. NPC exosomes were isolated from the supernatant of the NP cell culture medium. The viability of NP cells and CEP cells was examined by CCK-8 assays. The exosomes were identified by TEM, NTA, and western blot. Extracellular matrix (ECM) metabolism was measured by cellular immunofluorescence and qRT-PCR. Apoptosis was detected by flow cytometry and TUNEL. X-ray and magnetic resonance imaging (MRI), as well as hematoxylin-eosin (H&E), Safranine O-Green staining was adopted to evaluate IVD degeneration grades. TNFα had a minor impact on NPC viability but inhibited ECM synthesis and promoted ECM degradation. TNFα-NPC-Exo had less effect on CEPC proliferation but promoted CEPC apoptosis and affect ECM metabolism, inhibiting aggrecan and collagen II expression and enhancing MMP-3 expression. TNFα-NPC-Exo aggravates IVD degeneration in a rat model and promoted CEPC apoptosis. In conclusion, this study demonstrated that degenerated NPC-exosome could induce apoptosis of CEPCs, inhibit ECM synthesis, and promote ECM degradation. In addition, it was proved that degenerated NPC-exosome aggravates IVD degeneration.

Rac1 regulates nucleus pulposus cells degeneration and promotes the progression of intervertebral disc degeneration

Nucleus Pulposus Cells (NPCs) dysfunction is considered as an important event related to intervertebral disc degeneration (IVDD). In the present study, tandem mass spectrometry (TMT) was used to detect total protein expression of NP in patients with IVDD and healthy controls. Bioinformatic analysis was performed to identify differentially expressed proteins that may be involved in the degeneration of NP. The results show that Rac1 may be a key protein involved in the degeneration of NP via Wnt/β-catenin pathway activation. We investigated the influence of Rac1 on IVDD degeneration and associated mechanisms. This study has the potential to advance understanding of the mechanism of occurrence of degenerative NP tissues and provide novel strategies for slowing IVDD progression.

Circ_0022382 ameliorated intervertebral disc degeneration by regulating TGF-β3 expression through sponge adsorption of miR-4726-5p

Circular RNAs (circRNAs) participate in the progression of many diseases, but knowledge on the role of circRNAs in intervertebral disc degeneration (IDD) is limited. In this study, we discovered the characteristics of a new circRNA (circ_0022382) in human endplate chondrocytes. Currently, real-time quantitative polymerase chain reaction (RT-qPCR) showed that the relative expression level of circ_0022382 was significantly lower under intermittent cyclic tension stimulation than in the control group. circ_0022382, miR-4726-5p and Transforming growth factor 3 (TGF-β3) were evaluated by RT-qPCR, Western Blot and immunofluorescence assay. Additionally, the role and mechanism of circ_0022382 in vivo were also consistent in the rat model. Furthermore, Intermittent cyclic mechanical tension can cause degeneration of endplate chondrocytes. The tension-sensitive circRNA_0022382 was decreased, and we found that circRNA_0022382 promoted morphology of endplate chondrocytes by sponge-binding miR-4726-5p down-regulation of target gene the TGF-β3 expression, thereby alleviating IDD. In a rat model of acupuncture, intervertebral disc injection of circ_0022382 relieved the progression of IDD in vivo. In conclusion, the circ_0022382/miR-4726-5p/TGF-β3 axis plays a key role in the anabolism and catabolism of the endplate chondrocyte extracellular matrix (ECM). It is suggested that circ_0022382 may provide a new approach for the prevention and treatment of IDD.

Activation of Hypoxia-Inducible Factor-1α Signaling Pathway Has the Protective Effect of Intervertebral Disc Degeneration

Intervertebral discs (IVDs) have poor nutrient diffusion, because the nucleus pulposus (NP) lacks direct vascular supply and likely generates adenosine triphosphate by anaerobic glycolysis. Regulation of glycolysis is mediated by hypoxia-inducible factor-1α (HIF-1α), a transcription factor that responds to local oxygen tension. Constitutively active HIF-1α (CA HIF-1α) was created by point mutation and determined the protective role of HIF-1α in IVD degeneration. Under fluoroscopy, rat caudal IVD segments were stabbed by a needle puncture, and pcDNA3- HIF-1α wild-type (WT) or pcDNA3-CA HIF-1α was transfected into NP cell lines. The constitutive activity of CA HIF-1α was analyzed using a luciferase assay after cell lysis. Next, IVD tissue samples were retrieved from five patients with degenerative lumbar spinal stenosis at the time of surgery, and NP cells were cultured. NP cells were transfected with CA HIF-1α, and relevant gene expression was measured. HIF-1α protein levels in the nucleus were significantly higher, and transcriptional activity was 10.3-fold higher in NP cells with CA HIF-1α than in those with HIF-1α WT. Gene transfer of CA HIF-1α into NP cells enhanced the expression of Glut-1, Glut-3, aggrecan, type II collagen, and Sox9. Moreover, CA HIF-1α reduced the apoptosis of NP cells induced by the Fas ligand. The HIF-1α and collagen 2 expression levels were notably increased in the NP cells of the CA HIF-1α transfected segments in histology and immunohistochemistry study. Collectively, these results suggest that activation of HIF-1α signaling pathway may play a protective role against IVD degeneration and could be used as a future therapeutic agent.

Small Extracellular Vesicles Derived from Adipocytes Attenuate Intervertebral Disc Degeneration in Rats by Rejuvenating Senescent Nucleus Pulposus Cells and Endplate Cells by Delivering Exogenous NAMPT

Cellular senescence is a key factor in the development of intervertebral disc degeneration (IVDD). Age-associated decreases in NAD⁺ levels play a critical role in regulating cellular senescence. Previous studies have found that small extracellular vesicles (sEVs) secreted by adipocytes (Adipo-sEVs) or adipose tissue are abundant in nicotinamide phosphoribosyltransferase (NAMPT), which is the key NAD⁺ biosynthetic enzyme in mammals. Systemic injection of these sEVs significantly improves physical activity and extends the lifespan of aged mice by increasing NAD⁺ levels. However, to date, the therapeutic potential of Adipo-sEVs in other age-associated disease models, such as IVDD, has not been explored. In this study, we investigated the therapeutic effects of Adipo-sEVs on senescence of nucleus pulposus cells (NPCs) and cartilaginous endplate cells (EPCs). In vitro, Adipo-sEVs could rejuvenate the senescence of NPCs and EPCs. Age-related dysfunctions were also ameliorated by Adipo-sEVs by delivering NAMPT and activating NAD⁺ biosynthesis and the Sirt1 pathway. Further in vivo experiments revealed that Adipo-sEV-mediated delivery of NAMPT attenuated IVDD in rats by rejuvenating senescent NPCs and EPCs. Collectively, the results indicate a new cell-free tool and provide a promising sEV-mediated delivery method of NAMPT as a therapeutic approach for IVDD clinically.

Morin attenuates pyroptosis of nucleus pulposus cells and ameliorates intervertebral disc degeneration via inhibition of the TXNIP/NLRP3/Caspase-1/IL-1β signaling pathway

Intervertebral disc degeneration (IDD) is a major cause of lower back pain (LBP), a condition that causes a heavy economic burden globally. The production of cytokines, including interleukin (IL)-1β and tumor necrosis factor (TNF) α, is increased in the degenerating intervertebral disc. Thioredoxin-interacting protein (TXNIP) participates in NLRP3 inflammasome-dependent pyroptosis in liver. Therefore, we hypothesized that TXNIP maypromote pyroptosis via NLRP3/Caspase-1/IL-1β signaling pathway in nucleus pulposus (NP) cell. This study examined the effects of TXNIP on IDD, explored the underlying mechanisms of action and find Morin which is the inhibitor of TXNIP can attenuates pyroptosis of nucleus pulposus cells and ameliorates intervertebral disc degeneration. Our findings indicate that TXNIP promote pyroptosis via NLRP3/Caspase-1/IL-1β signaling pathway in NP cell. Morin considerably inhibited the TXNIP/NLRP3/Caspase-1 signaling pathway in vitro. In vivo. Our data show that TXNIP can aggravates intervertebral disc degeneration and morin may be a useful therapeutic agent for IDD.

Exosomal MATN3 of Urine-Derived Stem Cells Ameliorates Intervertebral Disc Degeneration by Antisenescence Effects and Promotes NPC Proliferation and ECM Synthesis by Activating TGF-β

Objective

Low back pain (LBP) is one of the top three causes of disability in developed countries, and intervertebral disc degeneration (IDD) is a major contributor to LBP. In the process of IDD, there is a gradual decrease in nucleus pulposus cells (NPCs) and extracellular matrix (ECM). Exosomes are important exocrine mediators of stem cells that can act directly on cells for tissue repair and regeneration. In this study, we determined the antisenescence, cell proliferation promotion, and ECM modulation effects of human urine-derived stem cell (USC) exosomes (USC-exos) on degenerated intervertebral discs and explored the underlying mechanism.

Methods and Materials

USCs were identified by multipotent differentiation and flow cytometry for mesenchymal stem cell- (MSC-) specific surface protein markers. USC-exos were isolated from the conditioned medium of USCs by ultracentrifugation and then analyzed by transmission electron microscopy (TEM), particle size analysis, and western blotting (WB) for exosome marker proteins. The effects of USC-exos on NPC proliferation and ECM synthesis were assessed by Cell Counting Kit-8 (CCK-8), WB, and immunofluorescence (IF) analyses. The protein differences between normal and degenerative intervertebral discs were mined, and the temporal and spatial variations in matrilin-3 (MATN3) content were determined by WB and IF in the intervertebral disc tissues. The candidate molecules that mediated the function of USC-exos were screened out and confirmed by multiple assays. Meanwhile, the mechanism underlying the candidate protein in USC-exos-induced cell proliferation and regulation of ECM synthesis promoting the activities of NPCs was explored. In addition, the effects of USC-exos on ameliorating intervertebral disc degeneration (IVD) in mice were examined by assessing computed tomography (CT), magnetic resonance imaging (MRI), and histological analyses.

Results

The flow cytometry results showed that USCs were positive for CD29, CD44, and CD73, which are USC surface-specific markers, but negative for CD34 and CD45. In addition, USCs showed osteogenic, adipogenic, and chondrogenic differentiation potential. USC-exos exhibited a cup-shaped morphology, with a mean diameter of 49.7 ± 7.3 nm, and were positive for CD63 and TSG101 and negative for calnexin. USC-exos could promote NPC proliferation and ECM synthesis. The protein content of the matrilin family was significantly reduced in degenerative intervertebral discs, and the decrease in MATN3 was the most significant. USC-exos were found to be rich in MATN3 protein, and exosomal MATN3 was required for USC-exos-induced promotion of NPC proliferation and ECM synthesis, as well as alleviation of intervertebral disc degeneration in IVD rats. In addition, the effects of MATN3 in USC-exos were demonstrated to be achieved by activating TGF-β, which elevated the phosphorylation level of SMAD and AKT.

Conclusions

Our study suggests that reduced MATN3 can be considered a characteristic of intervertebral disc degeneration. USC-exos may represent a potentially effective agent for alleviating intervertebral disc degeneration by promoting NPC proliferation and ECM synthesis by transferring the MATN3 protein.

Krüppel like factor 10 prevents intervertebral disc degeneration via TGF-β signaling pathway both in vitro and in vivo

Background

Krüppel like factor 10 (KLF10), which is also known as TGF-β Inducible Early Gene-1 (TIEG1), plays a crucial role in regulating cell proliferation, cell apoptosis and inflammatory reaction in human carcinoma cells. Moreover, KLF10 knockout in mice leads to severe defects associated with muscle, skeleton and heart etc. However, the function of KLF10 in intervertebral disc degeneration (IVDD) has not been reported yet.

Methods

The relationship between KLF10 and IVDD were investigated in nucleus pulposus (NP) tissues from human and rats. The role of KLF10 in NP cells was explored via loss or gain of function experiments. IVDD rat models were constructed through needle puncture and the effects of KLF10 in IVDD model of rats were investigated via intradiscal injection of KLF10.

Results

We first found that KLF10 was lowly expressed in degenerative NP tissues and the level of KLF10 showed negative correlation with the disc grades of IVDD patients. Loss or gain of function experiments demonstrated that KLF10 could inhibit apoptosis and enhance migration and proliferation of IL-1β induced NP cells. And KLF10 overexpression reduced extracellular matrix (ECM) degeneration and enhanced ECM synthesis, whereas knockdown of KLF10 resulted in adverse effects. These positive effects of KLF10 could be reversed by the inhibition of TGF-β signaling pathway. In vivo, KLF10 overexpression alleviated IVDD.

Conclusions

This is the first study to reveal that KLF10 was dysregulated in IVDD and overexpressed KLF10 could alleviate IVDD by regulating TGF-β signaling pathway both in vitro and in vivo, which were involved in prohibiting apoptosis, promoting proliferation and migration of NP cells.The translational potential of this article: Overexpression of KLF10 might be an effective therapeutic strategy in the treatment of IVDD.

Induced pluripotent stem cell-derived mesenchymal stem cells deliver exogenous miR-105-5p via small extracellular vesicles to rejuvenate senescent nucleus pulposus cells and attenuate intervertebral disc degeneration

Background

Mesenchymal stem cell-derived small extracellular vesicles (MSC-sEVs) have emerged as a promising new therapeutic strategy for intervertebral disc degeneration (IVDD). However, the drawbacks of MSCs, including their invasive access, the donor age, and their limited proliferative capacity, hinder the quantity and quality of MSC-sEVs. Induced pluripotent stem cell-derived MSCs (iMSCs) provide an indefinite source of MSCs with well-defined phenotype and function. This study aimed to investigate the therapeutic effect of sEVs derived from iMSC (iMSC-sEVs) on IVDD and explore the underlying molecular mechanisms.

Methods

IVDD models were established by puncturing discs from the tails of rats. Then, iMSC-sEVs were injected into the punctured discs. The degeneration of punctured discs was assessed using MRI and HE and immunofluorescence staining. The age-related phenotypes were used to determine the effects of iMSC-sEVs on senescent nucleus pulposus cells (NPCs) in vitro. Western blotting was used to detect the expression of Sirt6. miRNA sequencing analysis was used to find miRNAs that potentially mediate the activation of Sirt6.

Results

After intradiscally injecting iMSC-sEVs, NPC senescence and IVDD were significantly improved. iMSC-sEVs could rejuvenate senescent NPCs and restore the age-related function by activating the Sirt6 pathway in vitro. Further, microRNA sequence analysis showed that iMSC-sEVs were highly enriched in miR-105-5p, which played a pivotal role in the iMSC-sEV-mediated therapeutic effect by downregulating the level of the cAMP-specific hydrolase PDE4D and could lead to Sirt6 activation.

Conclusion

iMSC-sEVs could rejuvenate the senescence of NPCs and attenuate the development of IVDD. iMSC-sEVs exerted their anti-ageing effects by delivering miR-105-5p to senescent NPCs and activating the Sirt6 pathway. Our findings indicate that iMSCs are a promising MSC candidate for obtaining sEVs on a large scale, while avoiding several defects related to the present applications of MSCs, and that iMSC-sEVs could be a novel cell-free therapeutic tool for the treatment of IVDD.

ACTG1 regulates intervertebral disc degeneration via the NF-κB-p65 and Akt pathways

ACTG1 is a member of the actin family but is not a muscle actin gene. The ACTG1 mutation leads to hearing loss in humans, and the knockdown of ACTG1 suppresses the proliferation and migration of tumor cells; however, its role in intervertebral disc degeneration (IDD) is yet unclear. Bioinformatics methods revealed that ACTG1 might be a hub gene in IDD. Furthermore, the expression ACTG1 in severely degenerated nucleus pulposus (NP) tissues (Pfirrmann grade IV and V) was low as compared to that in mildly degenerated samples (Pfirrmann grade II and III). Moreover, the ACTG1 level was negatively correlated with human disc degeneration grades. The low expression of ACTG1 is also found in degenerated NP tissues in the rat. To further explore the function of ACTG1 in IDD, the gene expression was depleted in human NP cells via siRNA transfection. The ablation of ACTG1 increased MMP3 expression but decreased the level of collagen II. Excessive apoptosis was observed in ACTG1 knockdown groups, indicating that the absence of ACTG1 exacerbated IDD. GO function and pathway enrichment analysis for differentially expressed genes (DEGs) of two microarray datasets (GSE56081 and GSE42611) indicated that inflammatory response plays a crucial role in IDD. Interestingly, in the protein-protein interaction (PPI) network, ACTG1 is connected to the proteins of inflammation-related pathways. Furthermore, ACTG1 knockdown upregulated P-P65 level but suppressed P-Akt expression. These data collectively demonstrated that ACTG1 regulated the development of IDD through the NF-κB-p65 and Akt pathways, and ACTG1 may be a novel marker and therapeutic target of IDD in the future.

Danshen Attenuates Intervertebral Disc Degeneration via Antioxidation in SD Rats

Objective

To investigate the effects of Danshen on the imaging and histological parameters, expression levels of ECM-associated proteins and inflammatory factors, and antioxidative activity in the degenerated intervertebral disc (IVD) of SD rats.

Methods

Sixty male rats were randomly divided into three groups (control, IDD, and Danshen IDD). Percutaneous needle puncture in Co8-9 intervertebral disc was conducted in all rats of the IDD and Danshen IDD groups to induce intervertebral disc degeneration (IDD). After operation, animals of the Danshen IDD group were administrated with Danshen granules (3 g/kg body weight ) by gavage once a day. Four weeks later, the coccygeal vertebrae were harvested and used for imaging (disc height and MR signal), histological, immunohistochemical, and biochemical [water content, glycosaminoglycans (GAG), superoxide dismutase (SOD2), glutathione (GSH), and malondialdehyde (MDA)] analyses.

Results

The puncture induced significant decreased IVD space and MR T2 signal at both 2 and 4 weeks, which were attenuated by Danshen treatment. The disc degeneration in the IDD group (HE and Safranin O-Fast Green histological staining was markedly more serious compared with that in the control group. Four weeks of Danshen treatment significantly alleviated this degeneration compared with the IDD group. Needle puncture resulted in the upregulation of IL-1β and TNF-α, MMP-3, and downregulation of COL2 and aggrecan in the IDD group. However, this change was significantly weakened by Danshen treatment. Significantly lower water and GAG content, as well as the SOD2 and GSH levels, in the IDD group were found compared with those in the control group. However, the above parameters of the Danshen IDD group were significantly higher than those of the IDD group. Danshen treatment significantly decreased the content of MDA which was increased by needle puncture in the IDD group.

Conclusion

Danshen can attenuate intervertebral disc degeneration in SD rats by suppressing the oxidation reaction.

Advanced Glycation End Product Inhibitor Pyridoxamine Attenuates IVD Degeneration in Type 2 Diabetic Rats

Type 2 diabetes mellitus (T2DM) is associated with advanced glycation end product (AGE) enrichment and considered a risk factor for intervertebral disc (IVD) degeneration. We hypothesized that systemic AGE inhibition, achieved using pyridoxamine (PM), attenuates IVD degeneration in T2DM rats. To induce IVD degeneration, lumbar disc injury or sham surgery was performed on Zucker Diabetic Sprague Dawley (ZDSD) or control Sprague Dawley (SD) rats. Post-surgery, IVD-injured ZDSD rats received daily PM dissolved in drinking water or water only. The resulting groups were SD uninjured, SD injured, ZDSD uninjured, ZDSD injured, and ZDSD injured + PM. Levels of blood glycation and disc degeneration were investigated. At week 8 post-surgery, glycated serum protein (GSP) levels were increased in ZDSDs compared to SDs. PM treatment attenuated this increase. Micro-MRI analysis demonstrated IVD dehydration in injured versus uninjured SDs and ZDSDs. In the ZDSD injured + PM group, IVD dehydration was diminished compared to ZDSD injured. AGE levels were decreased and aggrecan levels increased in ZDSD injured + PM versus ZDSD injured rats. Histological and immunohistochemical analyses further supported the beneficial effect of PM. In summary, PM attenuated GSP levels and IVD degeneration processes in ZDSD rats, demonstrating its potential to attenuate IVD degeneration in addition to managing glycemia in T2DM.

NF-κB inhibitor, NEMO-binding domain peptide attenuates intervertebral disc degeneration

BACKGROUND CONTEXT

Nonphysiological mechanical loading and inflammation are both critically involved in intervertebral disc (IVD) degeneration, which is characterized by an increase in cytokines and matrix metalloproteases (MMPs) in the nucleus pulposus (NP). This process is known to be mediated by the NF-κB pathway.

CLINICAL SIGNIFICANCE

Current clinical treatments for IVD degeneration focus on the alleviation of symptoms rather than targeting the underlying mechanism. Injection of an NF-κB inhibitor may attenuate the progression of IVD degeneration.

PURPOSE

To investigate the ability of the NF-κB inhibitor, NEMO binding domain peptide (NBD), to alter IVD degeneration processes by reducing IL-1β- and mechanically-induced cytokine and MMP levels in human nucleus pulposus cells in vitro, and by attenuating IVD degeneration in an in vivo rat model for disc degeneration.

STUDY DESIGN

Experimental in vitro and animal model.

PATIENT SAMPLE

Discarded specimens of lumbar disc from 21 patients, and 12 Sprague Dawley rats.

OUTCOME MEASURES

Gene and protein expression, cell viability, µMRI and histology.

METHODS

IL-1β-prestimulated human nucleus pulposus cells embedded into fibrin constructs were loaded in the Flexcell FX-5000 compression system at 5 kPa and 1 Hz for 48 hours in the presence and absence of NBD. Unloaded hNPC/fibrin constructs served as controls. Cell viability in loaded and unloaded constructs was quantified, and gene and protein expression levels determined. For in vivo testing, a rat needle disc puncture model was employed. Experimental groups included injured discs with and without NBD injection and uninjured controls. Levels of disc degeneration were determined via µMRI, qPCR and histology. Funding sources include $48,874 NASS Young Investigator Research Grant and $119,174 NIH 5K01AR071512-02. There were no applicable financial relationships or conflicts of interest.

RESULTS

Mechanical compression of hNPC/fibrin constructs resulted in upregulation of MMP-3 and IL-8. Supplementation of media with 10 μM NBD during loading increased cell viability, and decreased MMP-3 gene and protein levels. IVD injury in rat resulted in an increase in MMP-3, IL-1β and IL-6 gene expression. Injections of 250 µg of NBD during disc injury resulted in decreased IL-6 gene expression. µMRI analysis demonstrated a reduction of disc hydration in response to disc needle injury, which was attenuated in NBD-treated IVDs. Histological evaluation showed NP and AF lesion in injured discs, which was attenuated by NBD injection.

CONCLUSIONS

The results of this study show NBD peptide's capacity to reduce IL-1β- and loading-induced MMP-3 levels in hNPC/fibrin constructs while increasing the cells' viability, and to attenuate IVD degeneration in rat, involving downregulation of IL-6. Therefore, NBD may be a potential therapeutic agent to treat IVD degeneration.

The circular RNA circ-GRB10 participates in the molecular circuitry inhibiting human intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is the most common degenerative disease all over the word. Our previous study confirmed that the downregulated circ-GRB10 directly interacts with miR-328-5p, which modulate ERBB2 and leads to the degeneration of intervertebral disc; however, the underpinning mechanism of circ-GRB10 dysregulation remains unclear. We identified that FUS and demonstrated that circ-GBR10 biosynthesis in nucleus pulposus (NP) cells was promoted by FUS, whose expression was controlled by miR-141-3p. In addition, ERBB2 downregulation led to decreased Erk1/2 phosphorylation which enhanced miR-141-3p production in NP cells. In vivo data indicated that circ-GRB10 inhibited IDD in rat model. The present study revealed that miR-141-3p and FUS are key factors that regulate circ-GRB10 synthesis in NP cells. In addition, circ-GBR10 participates in the molecular circuitry that controls human IDD development. These findings provide a basis for further functional, diagnostic and therapeutic studies of circ-GRB10 in IDD.

Optimization of a rat lumbar IVD degeneration model for low back pain

INTRODUCTION

Intervertebral disc (IVD) degeneration is often associated with low back pain and radiating leg pain. The purpose of this study is to develop a reproducible and standardized preclinical model of painful lumbar IVD degeneration by evaluation of structural and behavioral changes in response to IVD injury with increasing needle sizes. This model can be used to develop new therapies for IVD degeneration.

METHODS

Forty-five female Sprague Dawley rats underwent anterior lumbar disc needle puncture at levels L4-5 and L5-6 under fluoroscopic guidance. Animals were randomly assigned to four different experimental groups: needle sizes of 18 Gauge (G), 21G, 23G, and sham control. To monitor the progression of IVD degeneration and pain, the following methods were employed: μMRI, qRT-PCR, histology, and biobehavioral analysis.

RESULTS

T1- and T2-weighted μMRI analysis showed a correlation between the degree of IVD degeneration and needle diameter, with the most severe degeneration in the 18G group. mRNA expression of markers for IVD degeneration markers were dysregulated in the 18G and 21G groups, while pro-nociceptive markers were increased in the 18G group only. Hematoxylin and Eosin (H&E) and Alcian Blue/Picrosirius Red staining confirmed the most pronounced IVD degeneration in the 18G group. Randall-Selitto and von Frey tests showed increased hindpaw sensitivity in the 18G group.

CONCLUSION

Our findings demonstrate that anterior disc injury with an 18G needle creates severe IVD degeneration and mechanical hypersensitivity, while the 21G needle results in moderate degeneration with no increased pain sensitivity. Therefore, needle sizes should be selected depending on the desired phenotype for the pre-clinical model.

The circular RNA FAM169A functions as a competitive endogenous RNA and regulates intervertebral disc degeneration by targeting miR-583 and BTRC

Intervertebral disc degeneration (IDD) is an important factor leading to low back pain, although the underlying mechanisms remain poorly understood. In this study we examined the role of circular RNA FAM169A (circ-FAM169A) in degenerative nucleus pulposus (NP) tissues, and validated its function in cultured human NP cells. Overexpression of circ-FAM169A in NP cells markedly enhanced extracellular matrix (ECM) catabolism and suppressed ECM anabolism in NP cells. Furthermore, circ-FAM169A sequestered miR-583, which could potentially upregulate BTRC, an inducer of the NF-κB signaling pathway. In conclusion, the present study revealed that circ-FAM169A promotes IDD development via miR-583/BTRC signaling. These findings provide a potential therapeutic option for the treatment of IDD.

Omega-3 Fatty Acid Supplementation Reduces Intervertebral Disc Degeneration

Background

Intervertebral disc (IVD) degeneration is a common cause of lower back pain, which carries substantial morbidity and economic cost. Omega-3 fatty acids (n-3 FA) are known to reduce inflammatory processes with a relatively benign side effect profile. This study aimed to investigate the effect of n-3 FA supplementation on IVD degeneration.

Material/Methods

Two non-contiguous lumbar discs of 12 Sprague Dawley rats were needle-punctured to induce disc degeneration. Post-surgery, rats were randomly assigned to either a daily n-3 FA diet (530 mg/kg/day of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in a 2: 1 ratio, administered in sucrose solution) or control diet (sucrose solution only), which was given for the duration of the study. After 1 month, blood serum arachidonic acid/eicosapentaenoic acid (AA/EPA) ratios were analyzed. After 2 months, micro-MRI (magnetic resonance imaging) analysis and histological staining of disc explants were performed to analyze the IVD.

Results

A reduction of blood AA/EPA ratios from 40 to 20 was demonstrated after 1 month of daily supplementation with n-3 FA. Micro-MRI analysis showed an injury-induced reduction of IVD hydration, which was attenuated in rats receiving n-3 FA. Histological evaluation demonstrated the destruction of nucleus pulposus tissue in response to needle puncture injury, which was less severe in the n-3 FA diet group.

Conclusions

The results of this study suggest that n-3 FA dietary supplementation reduces systemic inflammation by lowering AA/EPA ratios in blood serum and has potential protective effects on the progression of spinal disc degeneration, as demonstrated by reduced needle injury-induced dehydration of intervertebral discs and reduced histological signs of IVD degeneration.

Pulsed electromagnetic fields reduce acute inflammation in the injured rat-tail intervertebral disc

Pro-inflammatory cytokines are recognized contributors to intervertebral disc (IVD) degeneration and discogenic pain. We have recently reported the anti-inflammatory effect of pulsed electromagnetic fields (PEMF) on IVD cells in vitro. Whether these potentially therapeutic effects are sufficiently potent to influence disc health in vivo has not been demonstrated. We report here the effect of PEMF on acute inflammation arising from a rat-tail IVD injury model. Disc degeneration was induced by percutaneously stabbing the Co6-7, Co7-8, and Co8-9 levels using a 20-gauge needle. Seventy-two (72) rats were divided into three groups: sham control, needle stab, needle stab+PEMF. Treated rats were exposed to PEMF immediately following surgery and for either 4 or 7 days (4 hr/d). Stab and PEMF effects were evaluated by measuring inflammatory cytokine gene expression (RT-PCR) and protein levels (ELISA assay), anabolic and catabolic gene expression (RT-PCR), and histologic changes. We observed in untreated animals that at day 7 after injury, inflammatory cytokines (interleukin [IL]-6, tumor necrosis factor α, and IL-1β) were significantly increased at both gene and protein levels (P < .05). Similarly, catabolic factors (MMP [metalloproteinases]-2, MMP-13 and the transcriptional factor NF-kβ gene expression) were significantly increased (P < .05). At day 7, PEMF treatment significantly inhibited inflammatory cytokine gene and protein expression induced by needle stab injury (P < .05). At day 4, PEMF downregulated FGF-1 and upregulated MMP-2 compared to the stab-only group. These data demonstrate that previously reported anti-inflammatory effects of PEMF on disc cells carry over to the in vivo situation, suggesting potential therapeutic benefits. Though we observed an inhibitory effect of PEMF on acute inflammatory cytokine expression, a consistent effect was not observed for acute changes in disc histology and anabolic and catabolic factor expression. Therefore, these findings should be further investigated in studies of longer duration following needle-stab injury.

CircERCC2 ameliorated intervertebral disc degeneration by regulating mitophagy and apoptosis through miR-182-5p/SIRT1 axis

The molecular mechanism of intervertebral disc degeneration (IVDD) remains unclear. This study aimed to investigate the role of circular RNAs (circRNAs) in the pathogenesis of IVDD. We sued nucleus pulposus (NP) tissues of patients, tert-butyl hydroperoxide (TBHP) stimulated NP cells (NPCs), and IVDD rat model to explore the interaction between circERCC2 and miR-182-5p/SIRT1 axis. The results showed that downregulation of circERCC2 increased the level of miR-182-5p and decreased the level of SIRT1 in degenerative NP tissues in vivo as well as in TBHP-stimulated NPCs in vitro. Treatment of SIRT1-si activated apoptosis and inhibited mitophagy. Moreover, miR-182-5p-si could regulate the mitophagy and the apoptosis of NPCs by targeting SIRT1. The effects of circERCC2 on NPCs and IVDD rat model were mediated by miR-182-5p/SIRT1 axis. In conclusion, this study provides the first evidence that circERCC2 could ameliorate IVDD through miR-182-5p/SIRT1 axis by activating mitophagy and inhibiting apoptosis, and suggests that circERCC2 is a potentially effective therapeutic target for IVDD.

Microparticles for controlled growth differentiation factor 6 delivery to direct adipose stem cell-based nucleus pulposus regeneration

Currently, there is no effective long‐term treatment for intervertebral disc (IVD) degeneration, making it an attractive candidate for regenerative therapies. Hydrogel delivery of adipose stem cells (ASCs) in combination with controlled release of bioactive molecules is a promising approach to halt IVD degeneration and promote regeneration. Growth differentiation factor 6 (GDF6) can induce ASC differentiation into anabolic nucleus pulposus (NP) cells and hence holds promise for IVD regeneration. Here, we optimised design of novel poly(DL‐lactic acid‐co‐glycolic acid) (PLGA)–polyethylene glycol–PLGA microparticles to control GDF6 delivery and investigated effect of released GDF6 on human ASCs differentiation to NP cells. Recombinant human (rh)GDF6 was loaded into microparticles and total protein and rhGDF6 release assessed. The effect of microparticle loading density on distribution and gel formation was investigated through scanning electron microscopy. ASC differentiation to NP cells was examined after 14 days in hydrogel culture by quantitative polymerase chain reaction, histological, and immunohistochemical staining in normoxic and IVD‐like hypoxic conditions. RhGDF6 microparticles were distributed throughout gels without disrupting gelation and controlled rhGDF6 release over 14 days. Released GDF6 significantly induced NP differentiation of ASCs, with expression comparable with or exceeding media supplemented rhGDF6. Microparticle‐delivered rhGDF6 also up‐regulated sulphated glycosaminoglycan and aggrecan secretion in comparison with controls. In hypoxia, microparticle‐delivered rhGDF6 continued to effectively induce NP gene expression and aggrecan production. This study demonstrates the effective encapsulation and controlled delivery of rhGDF6, which maintained its activity and induced ASC differentiation to NP cells and synthesis of an NP‐like matrix suggesting suitability of microparticles for controlled growth factor release in regenerative strategies for treatment of IVD degeneration.

TFEB protects nucleus pulposus cells against apoptosis and senescence via restoring autophagic flux

OBJECTIVE

Excessive apoptosis and senescence of nucleus pulposus (NP) cells are major pathological changes in intervertebral disc degeneration (IVDD) development; previous studies demonstrated pharmacologically or genetically stimulation of autophagy may inhibit apoptosis and senescence in NP cells. Transcription factor EB (TFEB) is a master regulator of autophagic flux via initiating autophagy-related genes and lysosomal biogenesis. This study was performed to confirm whether TFEB was involved in IVDD development and its mechanism.

METHODS

TFEB activity was detected in NP tissues in puncture-induced rat IVDD model by immunofluorescence as well as in tert-Butyl hydroperoxide (TBHP), the reactive oxygen species (ROS) donor to induce oxidative stress, treated NP cells by western blot. After TFEB overexpression in NP cells with lentivirus transfection, autophagic flux, apoptosis and senescence percentage were assessed. In in vivo study, the lentivirus-normal control (LV-NC) or lentivirus-TFEB (LV-TFEB) were injected into the center space of the NP tissue, after 4 or 8 weeks, Magnetic resonance imaging (MRI), X ray, Hematoxylin-Eosin (HE) and Safranin O staining were used to evaluate IVDD grades.

RESULTS

The nuclear localization of TFEB declined in degenerated rat NP tissue as well as in TBHP treated NP cells. Applying lentivirus to transfect NP cells, TFEB overexpression restored the TBHP-induced autophagic flux blockage and protected NP cells against apoptosis and senescence; these protections of TFEB are diminished by chloroquine-medicated autophagy inhibition. Furthermore, TFEB overexpression ameliorates the puncture-induced IVDD development in rats.

CONCLUSIONS

Experimental IVDD inhibited the TFEB activity. TFEB overexpression suppressed TBHP-induced apoptosis and senescence via autophagic flux stimulation in NP cell and alleviates puncture-induced IVDD development in vivo.

Effect of hyperlipidaemia to accelerate intervertebral disc degeneration in the injured rat caudal disc model

BACKGROUND

Dyslipidaemia is a well-known risk factor for the development of atherosclerosis, however, little is known about the effect of dyslipidaemia on intervertebral disc degeneration (IVDD). Thus, the purpose of this study is to investigate the relationship between dyslipidaemia and IVDD, and to identify the possible mechanism by which dyslipidaemia aggravates the degeneration of intervertebral discs.

METHODS

Hyperlipidaemia rats were induced, thirty male Wistar rats were randomly divided into two groups: normal chow diet control group (CON) and high-fat diet group (HFD) for 8 weeks. And then, a rat disc degeneration model was established, rats were divided into three experimental groups: the normal chow diet + sham surgery group (CON-Sham); the normal chow diet + needle puncture group (CON-NP); and the high-fat diet + needle puncture group (HFD-NP), all rats were continually fed with normal chow diet or HFD 8 weeks. At the end of the experiment, the discs were harvested and histomorphological analysis, immunohistochemistry staining, real-time PCR and western blot were performed for all groups.

RESULTS

The degenerative histological score of disc in the HFD-NP group was significantly higher than the CON-NP group. Immunohistochemical analysis revealed remarkable reductions in aggrecan and collagen type II expressions, and significant increases in IL-1β, TNF-α, MMP-13, HIF-1α and P65 expression in the HFD-NP group. RT-PCR and western blot analysis showed that the mRNA levels and protein expressions of MMP-13 and TIMP-1 were higher in the HFD-NP group.

CONCLUSIONS

Hyperlipidaemia resulted in an exaggerated degenerative changes and altered expression and transcription of the degeneration-associated molecules in the rat disc tissue. These results raise the possibility that hyperlipidaemia may accelerate the progression of disc degeneration.

Disc degeneration promotes regional inhomogeneity in the trabecular morphology of loaded rat tail vertebrae

Background

There is a close relationship between the vertebral trabecular morphology and the condition of the associated disc.

Objective

The relationship between disc degeneration and vertebral trabecular inhomogeneity is unclear. This study aimed to analyse the regional changes of vertebral trabecular morphology after disc degeneration.

Methods

Thirty male Sprague–Dawley rats were randomly assigned to five groups. Group 1 served as an experimental group for the assessment of disc degeneration induced by needle puncture. Group 2 served as a sham group for trabecular morphology analysis. In Group 3, rats had their tail bent between the eighth and tenth coccygeal vertebrae. In Group 4, the tail of rats was bent with a compression load of 4.5 N. In Group 5, rats first underwent disc degeneration induced by a needle puncture before their tail was bent with a compressive load of 4.5 N. Magnetic resonance imaging was performed on all groups, and histological examination was performed on rodents from Group 1. The ninth coccygeal vertebrae of rats from Groups 2–5 were scanned by Micro-computed tomography. Trabecular morphologic changes were assessed in the concave and convex regions by bone volume fraction, trabecular number, trabecular thickness and trabecular separation.

Results

Vertebral trabecular morphology in the concave region improved significantly, whereas the convex region was of significantly lower trabecular morphologic parameters with disc degeneration. The difference in trabecular morphologic parameters between the convex and concave regions increased significantly after disc degeneration.

Conclusion

Disc degeneration promotes regional inhomogeneity in the vertebral trabecular morphology, with the convex region of the vertebrae having the worse trabecular bone morphology than the concave region.

The translational potential of this article

Our study indicates that disc degeneration promotes regional inhomogeneity in the vertebral trabecular morphology. Regional variations in trabecular microarchitecture are helpful to predict vertebral fragility. This may help to elucidate the mechanisms by which disc degeneration contributes to vertebral fracture.

Quantitative MRI correlates with histological grade in a percutaneous needle injury mouse model of disc degeneration

Low back pain due to disc degeneration is a major cause of morbidity and health care expenditures worldwide. While stem cell-based therapies hold promise for disc regeneration, there is an urgent need to develop improved in vivo animal models to further develop and validate these potential treatments. The objectives of this study were to characterize a percutaneous needle injury model of intervertebral disc degeneration in the mouse caudal spine, and compare two non-invasive quantitative imaging techniques, microcomputed tomography and magnetic resonance imaging (MRI), as effective measures of disc degeneration in this model. Percutaneous needle injury of mouse caudal discs was undertaken using different needle sizes and injury types (unilateral or bilateral annulus fibrosus (AF) puncture). Mice were euthanized 4 weeks post-injury, and MRI and microcomputed tomography were used to determine T2 relaxation time of the NP and disc height index, respectively. Disc condition was then further assessed using semi-quantitative histological grading. Bilateral AF puncture with either 27 or 29G needles resulted in significantly lower T2 relaxation times compared to uninjured controls, while disc height index was not significantly affected by any injury type. There was a strong, inverse linear relationship between histological grade and NP T2 relaxation time. In this study, we demonstrated that quantitative MRI can detect disc degeneration in the mouse caudal spine 4 weeks following percutaneous needle injury, and may therefore serve as a surrogate for histology in longitudinal studies of both disc degeneration and cell-based therapies for disc regeneration using this model. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2771-2779, 2018.

Time-Course Investigation of Intervertebral Disc Degeneration Induced by Different Sizes of Needle Punctures in Rat Tail Disc

Background

This study aimed to determine the best size needle to use in inducing IVDD and to find the proper time point of disc degeneration suitable for further biologic treatment study.

Material/Methods

First, rat tail level 5/6, 7/8, and 9/10 discs were punctured by 18G, 21G, or 25G needles. Then, degeneration was assessed by radiography, MRI, and histological evaluation at 2, 4, and 6 weeks after puncture. Later, real-time reverse transcriptase (RT-PCR) was used to examine mRNA expressions of aggrecan, collagen type II, hypoxia-inducible factor-1α (HIF-1α), glucose transporter1 (GLUT-1), and vascular endothelial growth factor (VEGF).

Results

Significant differences were identified in almost all parameters compared with the control group in the 18G and 21G group at almost all time points. To assess the effect of different needle sizes on DHI, we used magnetic resonance imaging (MRI), grade, and mRNA expression. We found significant differences between different groups, except for DHI between the 21G group and 25G group and MRI grade between the 18G and 21G group at the 2-week time point. In assessing the effect of different needle sizes on HE staining score and toluidine blue staining grade, statistical differences were observed at some time points. The effects of time on all parameters were significant at almost all time points in all groups.

Conclusions

The middle-size needle (21G) performed better in inducing disc degeneration. The 2-week time point may be better for use in further experimental studies.

Leaping the hurdles in developing regenerative treatments for the intervertebral disc from preclinical to clinical

Chronic back and neck pain is a prevalent disability, often caused by degeneration of the intervertebral disc. Because current treatments for this condition are less than satisfactory, a great deal of effort is being applied to develop new solutions, including regenerative strategies. However, the path from initial promising idea to clinical use is fraught with many hurdles to overcome. Many of the keys to success are not necessarily linked to science or innovation. Successful translation to clinic will also rely on planning and awareness of the hurdles. It will be essential to plan your entire path to clinic from the outset and to do this with a multidisciplinary team. Take advice early on regulatory aspects and focus on generating the proof required to satisfy regulatory approval. Scientific demonstration and societal benefits are important, but translation cannot occur without involving commercial parties, which are instrumental to support expensive clinical trials. This will only be possible when intellectual property can be protected sufficiently to support a business model. In this manner, commercial, societal, medical, and scientific partners can work together to ultimately improve patient health. Based on literature surveys and experiences of the co-authors, this opinion paper presents this pathway, highlights the most prominent issues and hopefully will aid in your own translational endeavors.

Neonatal mouse intervertebral discs heal with restored function following herniation injury

Adult intervertebral discs (IVDs) have poor endogenous healing capacity, because of their challenging microenvironment and complex mechanical demands, which can result in painful IVD herniation. There are no regenerative strategies available to improve IVD healing and restore its function. Neonatal mice are excellent models of mammalian regeneration, but there are no studies of the regenerative capacity of neonatal IVDs. In this study, we developed a neonatal model of improved IVD healing to inform repair strategies after herniation. In vivo puncture injuries were performed to simulate herniation with complete annulus fibrosus (AF) tears in caudal IVDs of neonatal (postnatal d 5) and adult (4-6 mo) Scleraxis green fluorescent protein ( ScxGFP) mice. Acute and long-term healing responses were assessed with histologic, radiologic, and biomechanical measurements. Neonates underwent accelerated IVD healing compared to adults with functional restoration and enhanced structural repair after herniation. A population of ScxGFP^- cells identified in the neonatal repair site may be associated with this improved healing and warrants future investigation. In summary, function of neonatal IVDs was restored after herniation injury, whereas that of adult discs was not. This improved healing response is likely driven by multiple mechanisms that may include differences in mechanical loading and available repair cells during growth.-Torre, O. M., Das, R., Berenblum, R. E., Huang, A. H., Iatridis, J. C. Neonatal mouse intervertebral discs heal with restored function following herniation injury.

Optimization of puncture injury to rat caudal disc for mimicking early degeneration of intervertebral disc

The caudal discs of rats have been proposed as a puncture model in which intervertebral disc (IVD) degeneration can be induced and novel therapies can be tested. For biological repair, treatments for ongoing IVD degeneration are ideally administered during the earlier stages. The purpose of this study was to elucidate the optimal puncture needle size for creating a model that mimicked the earlier stages of IVD degeneration. According to the disc height index, histologic score, and MRI grading, a puncture needle sized 21G or larger induced rapid degenerative processes in rat caudal discs during the initial 2-4 weeks. The degenerative changes were severe and continued deteriorating after 4 weeks. Conversely, puncture injury induced by needles sized 25G or smaller also produced degenerative changes in rat caudal discs during initial 2-4 weeks; however, the changes were less severe. Furthermore, the degenerative process became stabilized and showed no further deterioration or spontaneous recovery after 4 weeks. In the discs punctured by 25G needles, the expression of collagen I was increased at 2-4 weeks with a gradually fibrotic transformation thereafter. The expressions of collagen II and SOX9 were enhanced initially but returned to pre-injury levels at 4-8 weeks. The above-mentioned findings were more compatible with earlier degeneration in discs punctured by needles sized 25G or smaller than by needles sized 21G or larger, and the appropriate timing for intradiscal administration of proposed therapeutic agents would be 4 weeks or longer after puncture. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:202-211, 2018.

Dysregulation of YAP by the Hippo pathway is involved in intervertebral disc degeneration, cell contact inhibition, and cell senescence

The Hippo pathway plays important roles in wound healing, tissue repair and regeneration, and in the treatment of degenerative diseases, by regulating cell proliferation and apoptosis in mammals. Intervertebral disc degeneration (IDD) is one of the major causes of low back pain, a widespread issue associated with a heavy economic burden. However, the mechanism underlying how the Hippo pathway regulates IDD is not well understood. Here, we demonstrate that the Hippo pathway is involved in natural IDD. Activation and dephosphorylation of yes-associated protein (YAP) were observed in younger rat discs, and decreased gradually with age. Surprisingly, Hippo pathway suppression was accompanied by overexpression of YAP, caused by acute disc injury, suggesting a limited ability for self-repair in IDD. We also demonstrated that YAP is inhibited by cell-to-cell contact via the Hippo pathway in vitro. Phosphorylation by large tumor suppressor kinases 1/2 (LATS1/2) led to cytoplasmic translocation and inactivation of YAP. YAP dephosphorylation was mainly localized in the nucleus and regulated by the Hippo pathway, whereas YAP dephosphorylation occurred in the cytoplasm and was associated with nucleus pulposus cell (NPC) senescence. Moreover, NPCs were transfected with shYAP and it accelerates the premature senescence of cells by interfered Hippo pathway through YAP. Therefore, our results indicate that the Hippo pathway plays an important role in maintaining the homeostasis of intervertebral discs and controlling NPC proliferation.

Novel rat tail discitis model using bioluminescent Staphylococcus aureus

Management of spondylodiscitis is a challenging clinical problem requiring medical and surgical treatment strategies. The purpose of this study was to establish a rat model of spondylodiscitis that utilizes bioluminescent Staphylococcus aureus (S. aureus), thus permitting in vivo surveillance of infection intensity. Inocula of the bioluminescent S. aureus strain XEN36 were created in concentrations of 10² CFU/0.1 ml, 10⁴  CFU/0.1 ml, and 10⁶  CFU/0.1 ml. Three groups of rats were injected with the bacteria in the most proximal intervertebral tail segment. The third most proximal tail segment was injected with saline as a control. Bioluminescence was measured at baseline, 3 days, and weekly for a total of 6 weeks. Detected bioluminescence for each group peaked at day 3 and returned to baseline in 21 days. The average intensity was highest for the experimental group injected with the most concentrated bacterial solution (10⁶  CFU/0.1 ml). Radiographic analysis revealed loss of intervertebral disc space and evidence of osseous bridging. Saline-injected spaces exhibited no decrease in intervertebral spacing as compared to distal sites. Histologic analysis revealed neutrophilic infiltrates, destruction of the annulus fibrosus and nucleus pulposus, destruction of vertebral endplates, and osseous bridging. Saline-injected discs exhibited preserved annulus fibrosus and nucleus pulposus on histology. This study demonstrates that injection of bioluminescent S. aureus into the intervertebral disc of a rat tail is a viable animal model for spondylodiscitis research. This model allows for real-time, in vivo quantification of infection intensity, which may decrease the number of animals required for infection studies of the intervertebral disc. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2075-2081, 2017.

Effect of Propionibacterium acnes (PA) injection on intervertebral disc degeneration in a rat model: Does it mimic modic changes?

INTRODUCTION

Multiple reports of bacterial isolates in human disc tissue have suggested a role of low-grade infection on intervertebral disc degeneration and modic changes (MC) generation. Animal models have been extensively used to study IDD; however, until recently, no consideration had been given to eventual infectious processes. To reproduce the phenomena by inoculating an infecting agent would support the infectious hypothesis. Therefore, we studied the effect of Propionibacterium acnes (PA) inoculation on rat-tails and determined whether it would produce MCs on the adjacent endplates.

HYPOTHESIS

Disc infection with PA would accelerate IDD compared with the standard model and would also lead to MCs on the adjacent endplates.

METHODS

Twelve Sprague-Dawley rats were randomized to receive a needle puncture in a caudal tail disc with either saline (control) or an inoculum of 5×10⁷ CFU of strain 1a PA. Twelve weeks later, the rats were euthanized and the tails were analyzed. The main assessment criteria were obtained from the post-mortem MRI: T2 values of punctured discs and adjacent endplates, as well as disc volumes. A histological grading score for IDD was also used, measuring the morphology and cellularity of the nucleus and annulus, as well as endplate disruption.

RESULTS

The median T2 value and disc volume were smaller in PA-punctured discs [T2 value: 30ms (23-44) vs. 61ms (38-132), respectively, P=0.01; 0.01mm³ (0.01-0.05) vs. 0.5mm³ (0.01-5.35), respectively; P=0.049]. There was no change in the adjacent endplates. There was no significant difference in histological grading between the test and control [13 (10-14) vs. 10.5 (6-13); P=0.05].

DISCUSSION

Inoculation of caudal discs with PA generated increased degeneration; however, no MCs were observed on the adjacent endplates. A better understanding of low-grade disc infections is still needed.

LEVEL OF EVIDENCE

V (animal study).