The Upregulation of COX2 in Human Degenerated Nucleus Pulposus: The Association of Inflammation with Intervertebral Disc Degeneration.

Intervertebral disc degeneration (IVDD) is an important risk factor of low back pain. We previously found upregulated markers of fibrosis, the late stage of chronic inflammation, in degenerated IVD with a small number of clinical specimens. Here, we aimed to study on a larger scale the association of cyclooxygenase 2 (COX2), an inflammation and/or pain marker, with IVDD. This study involved 107 LBP participants. The IVD degeneration level was graded on a 1-5 scale according to the Pfirrmann classification system. Discs at grades 1-3 were further grouped as white discs with grades 4-5 as black discs. We recorded baseline information about age, gender, body mass index (BMI), diabetes history, smoking history, and magnetic resonance imaging (MRI). Their association with IVDD was statistically analyzed. The expression level of COX2 was investigated by immunohistochemistry. The total integrated COX2 optical density (IOD), number of COX2-positive cells, and total cell number of each image were counted and analyzed by Image-Pro Plus software. The IOD and number of COX2-positive cells were divided by the total cell number to obtain COX2 expression density (IOD/cell) and COX2 positivity (cell+/cell). As a result, among the baseline information investigated, only age was found to have a significant association with IVDD. The IOD/cell was found to be significantly increased from grade 2 to grade 5, as well as in black discs compared to white discs. The cell+/cell displayed the same trend that it increased in highly degenerative discs compared to their counterparts. In conclusion, the expression of COX2 is associated with IVDD, which highlights COX2 as a biomarker for IVD degeneration and indicates the involvement of inflammation and pain signaling in IVDD.

Role of PI3K/AKT Signaling Pathway in Nucleus Pulposus Cells.

OBJECTIVE: To investigate the role of PI3K/AKT signaling pathway in nucleus pulposus (NP) cells. METHODS: Nucleus pulposus (NP) cells were isolated from SD rat, and thereafter, passage three (P3) NP cells were divided into the following experimental groups: control, PI3K/AKT agonist IGF-1 (25 ng/ml, 50 ng/ml, and 100 ng/ml), and PI3K/AKT inhibitor LY294002 (5 µM, 10 µM, and 20 µM). Flow cytometry and BrdU cell proliferation assays were performed to assess apoptosis and the proliferation rate of NP cells. Western blot analysis was performed to examine the protein expression level of Col II, Col X, Aggrecan, and MMP13. RESULTS: PI3K/AKT inhibitor LY294002 increased the rate of apoptosis in NP cells when compared to the control and decreased the proliferation rate when compared to control. Moreover, LY294002 decreased the protein expression level of Col-II and Aggrecan in NP cells. At the same time, LY294002 increased the protein expression level of MMP13 and Col-X in NP cells. Through activating PI3K/AKT, IGF-1 increased the proliferation rate when compared to control and decreased the rate of apoptosis when compared to control. Additionally, IGF-1 decreased the protein expression level of MMP13 and Col-X and increased Col-II and Aggrecan in NP cells. CONCLUSION: The inhibition of PI3K/AKT signaling pathway accelerated the apoptosis of NP cells and facilitated the extracellular matrix degradation. However, the activation of PI3K/AKT pathway partly prevented the NP cell from apoptosis and promoted their proliferation. Meanwhile, its activation also delayed the loss of extracellular matrix.

MiR-874-3p plays a protective role in intervertebral disc degeneration by suppressing MMP2 and MMP3.

Intervertebral disc degeneration (IDD) is a spinal degenerative disease and one of the most important causes of musculoskeletal disability. Matrix metalloproteinase (MMP)-mediated extracellular matrix degradation is the core process of IDD. The regulators of MMPs in the intervertebral disc are still not fully known. In this study, using quantitative reverse transcription PCR, luciferase reporter assay, Western blotting, immunofluorescence, flow cytometry, and Cell Counting Kit-8 assay, we found that the miR-874-3p expression level was significantly decreased in IDD patients. MiR-874-3p could target and repress MMP2 and MMP3 expression in nucleus pulposus cells. These results could improve the understanding of IDD and provide a possible diagnostic marker and treatment candidate for IDD. The miR-874-3p/MMP2/MMP3 axis might also provide direction for future cancer and inflammation investigations.

SIRT1 alleviates high-magnitude compression-induced senescence in nucleus pulposus cells via PINK1-dependent mitophagy.

Mechanical overloading-induced nucleus pulposus (NP) cells senescence plays an important role in the pathogenesis of intervertebral disc degeneration (IVDD). The silent mating type information regulator 2 homolog-1 (SIRT1)-mediated pathway preserves the normal NP cell phenotype and mitochondrial homeostasis under multiple stresses. We aimed to investigate the role of SIRT1 in IVDD by assessing the effects of SIRT1 overexpression on high-magnitude compression-induced senescence in NP cells. High-magnitude compression induced cellular senescence and mitochondrial dysfunction in human NP cells. Moreover, SIRT1 overexpression tended to alleviate NP cell senescence and mitochondrial dysfunction under compressive stress. Given the mitophagy-inducing property of SIRT1, activity of mitophagy was evaluated in NP cells to further demonstrate the underlying mechanism. The results showed that SIRT1-overexpression attenuated senescence and mitochondrial injury in NP cells subjected to high-magnitude compression. However, depletion of PINK1, a key mitophagic regulator, impaired mitophagy and blocked the protective role of SIRT1 against compression induced senescence in NP cells. In summary, these results suggest that SIRT1 plays a protective role in alleviating NP cell senescence and mitochondrial dysfunction under high-magnitude compression, the mechanism of which is associated with the regulation of PINK1-dependent mitophagy. Our findings may provide a potential therapeutic approach for IVDD treatment.

Intradiscal injection of sesamin protects from lesion-induced degeneration.

Intervertebral disc degeneration-related diseases are common health problems in the department of orthopedics. However, there is no effective treatment protecting the intervertebral disc from degeneration. Sesamin, a kind of sesame lignans extracted from sesame seed oil, has been proved to inhibit lipopolysaccharide-induced inflammation and extracellular matrix catabolism in rat intervertebral disc in vitro and ex vivo. The present study was designed to investigate the effects of sesamin on lesion-induced intervertebral disc degeneration in vivo. Degeneration of rat tail disc was induced by puncture lesion, followed by intradiscal injection of sesamin. Magnetic resonance imaging (MRI), quantitative real-time polymerase chain reaction, histological analysis, and biochemical analysis were carried out to analyze degeneration progression 2 weeks after surgery. As shown by results, intradiscal injection of sesamin inhibited the MRI signal decrease of nucleus pulposus (NP) in T2-weighted images. The upregulated mRNA expression of MMP-3 and ADAMTS-5 induced by lesion was significantly suppressed by sesamin injection. Sesamin partly protected mRNA expression of Col2a1 and Acan from downregulation. Intradiscal injection of sesamin effectively maintained the normal morphology of disc and inhibited lesion-induced degeneration-related histological changes. Immunohistochemical assay demonstrated that the upregulation of degradative enzymes protein expression and the downregulation of type II collagen expression in NP were suppressed by sesamin. According to biochemical analysis, sesamin significantly inhibited the lesion-induced decrease of proteoglycan content in NP. The present study proved the protective effects of sesamin on lesion-induced intervertebral disc degeneration at an early stage.

AMP-Activated Protein Kinase Activation in Dorsal Root Ganglion Suppresses mTOR/p70S6K Signaling and Alleviates Painful Radiculopathies in Lumbar Disc Herniation Rat Model.

STUDY DESIGN: Animal experiment: a rat model of lumbar disc herniation (LDH) induced painful radiculopathies. OBJECTIVE: To investigate the role and mechanism of AMP-activated protein kinase (AMPK) in dorsal root ganglia (DRG) neurons in LDH-induced painful radiculopathies. SUMMARY OF BACKGROUND DATA: Overactivation of multiple pain signals in DRG neurons triggered by LDH is crucial to the development of radicular pain. AMPK is recognized as a cellular energy sensor, as well as a pain sensation modulator, but its function in LDH-induced pain hypersensitivity remains largely unknown. METHODS: The LDH rat model was established by autologous nucleus pulposus transplantation into the right lumbar 5 (L5) nerve root. At different time points after AMPK agonist metformin (250 mg/kg/d) or mammalian target of rapamycin (mTOR) inhibitor rapamycin (5 mg/kg) intraperitoneal administration, thermal and mechanical sensitivity were evaluated by measuring paw withdrawal latency (PWL) and 50% paw withdrawal thresholds (PWT). The levels of AMPK, mTOR, and p70S6K phosphorylation were determined by Western blot. We also investigated the proportion of p-AMPK positive neurons in the right L5 DRG neurons using immunofluorescence. RESULTS: LDH evoked persistent thermal hyperalgesia and mechanical allodynia on the ipsilateral paw, as indicated by the decreased PWL and 50% PWT. These pain hypersensitive behaviors were accompanied with significant inhibition of AMPK and activation of mTOR in the associated DRG neurons. Pharmacological activation of AMPK in the DRG neurons not only suppressed mTOR/p70S6K signaling, but also alleviated LDH-induced pain hypersensitive behaviors. CONCLUSION: We provide a molecular mechanism for the activation of pain signals based on AMPK-mTOR axis, as well as an intervention strategy by targeting AMPK-mTOR axis in LDH-induced painful radiculopathies. LEVEL OF EVIDENCE: N/A.

Proinflammatory macrophages promote degenerative phenotypes in rat nucleus pulpous cells partly through ERK and JNK signaling.

Intervertebral disc (IVD) degeneration is the major contributor to low back pain, a highly prevalent musculoskeletal problem that represents the leading cause of disability. Proinflammatory M1 macrophages were identified in degenerated IVDs. However, their role in the pathogenesis of IVD degeneration and the underlying mechanism was largely unknown. In this study, we explored the combined effects of molecules secreted by M1 macrophages on nucleus pulposus cells, by treating rat nucleus pulposus cells (rNP) with the conditioned medium collected from M1-polarized RAW264.7 cells (MФCM). We found that MФCM caused molecular changes associated with IVD degeneration, including increased expression of key matrix catabolic genes (Adamts4, Adamts5, Mmp3, and Mmp13), reduced the expression of major matrix-associated anabolic genes ( Sox9, Acan, and Col2a1), and upregulated transcription of inflammation-related genes ( IL-1b, IL-6, Ccl2, and Ccl3), in rNP cells. Moreover, we found that MФCM activated both ERK and JNK pathways in these cells, and that inhibition of JNK pathway attenuated MФCM-induced expression of both catabolic and inflammatory genes, whereas ERK inhibition only suppressed induction of catabolic, but not inflammatory genes. Together, our data demonstrated that proinflammatory macrophages promoted the degenerative phenotypes in rNP cells in part through ERK and JNK signaling, and suggested that inhibition of these pathways may serve as a potential therapeutic approach for the treatment of IVD degeneration.

Naringin Protects Against Interleukin 1ß (IL-1ß)-Induced Human Nucleus Pulposus Cells Degeneration via Downregulation Nuclear Factor kappa B (NF-κB) Pathway and p53 Expression.

BACKGROUND Low back pain (LBP) is regarded as a frequent disease that causes disability. We aimed to explore the effect of naringin on intervertebral disc degeneration (IDD) in IL-1ß-induced human nucleus pulposus (NP) cells and its corresponding molecular mechanisms. MATERIAL AND METHODS Human NP cells were identified by toluidine blue and Safranin O staining. Cell viability was determined by MTT assay. The expression levels of matrix metalloproteinases (MMP-3, MMP-13, ADAMTS-4, ADAMTS-5, collagen II, aggrecan), inflammatory genes (tumor necrosis factor [TNF]-alpha, interleukin [IL]-6), kappa B kinase alpha (IkappaBalpha), p65 and p53 were determined by quantitative real-time polymerase chain reaction (qPCR) and western blotting. Immunofluorescence study was performed to detect the position and expression of p65 protein in IL-1ß-induced human NP cells. RESULTS Human NP cells were successfully separated from intervertebral disc tissue. We found that naringin could significantly reduce the expressions of matrix metalloproteinases (MMP-3, MMP-13, ADAMTS-4, and ADAMTS-5) and inflammatory genes in IL-1ß-stimulated human NP cells, while collagen II and aggrecan were increased at mRNA and protein level. Immunofluorescence showed that naringin pretreatment decreased the p65 protein expression in the nucleus and suppressed the phosphorylation of IkappaBalpha and p65. CONCLUSIONS These results demonstrated that naringin could attenuate matrix metalloproteinase catabolism and inflammation in IL-1ß-treated human nucleus pulposus cells via downregulating NF-kappaB pathway and p53 expression, suggesting that naringin has the potential to prevent and treat IDD.

Photobiomodulation of extracellular matrix enzymes in human nucleus pulposus cells as a potential treatment for intervertebral disk degeneration.

Intervertebral disc (IVD) degeneration is associated with imbalances between catabolic and anabolic responses, regulated by extracellular matrix (ECM)-modifying enzymes such as matrix metalloproteinases (MMPs) and their endogenous tissue inhibitors of metalloproteinases (TIMPs). Potential contributing factors, such as interleukin (IL)-1ß and tumor necrosis factor (TNF)-α, derived from infiltrated, activated macrophages within IVD tissues, can trigger abnormal production of ECM-modifying enzymes and progression of IVD degeneration. Novel therapies for regulating ECM-modifying enzymes can prevent or ameliorate IVD degeneration. Photobiomodulation (PBM), known to regulate wound repair, exhibits regenerative potential by modulating biological molecules. This study examined the effects of PBM, administered at various wavelengths (630, 525, and 465 nm) and energy densities (16, 32, and 64 J/cm2), on the production of ECM-modifying enzymes in replicated degenerative IVD. Our results showed that PBM selectively inhibited the production of ECM-modifying enzymes in a dose- and wavelength-dependent manner, suggesting that it could be a novel tool for treating symptomatic IVD degeneration.

Protective role of 17ß-estradiol on tumor necrosis factor-α-induced apoptosis in human nucleus pulposus cells.

The molecular mechanisms underlying protection and pathogenesis in spinal degenerative diseases remain unclear. Tumor necrosis factor-α (TNF-α) has been demonstrated to induce apoptosis of inte rvertebral disc (IVD) cells during IVD degeneration, and 17ß­estradiol (17ß­E2) has a protective effect against IVD cell apoptosis. However, the underlying molecular mechanism by which 17ß­E2 protects nucleus pulposus (NP) cells remains to be investigated. The aim of the present study was to evaluate whether 17ß­E2 modulates apoptosis of human NP cells induced by TNF­α. In addition, the concentration­response effect of 17ß­E2 on human NP cells was investigated. Human NP cells were cultured in complete medium, which was replaced every three days until the culture was ~80% confluent. Cells were treated with 100 ng/ml TNF­α for 48 h, with or without pretreatment with various concentrations of 17ß­E2, and ICI 182,780, for 30 min. Morphologic alterations characteristic of apoptosis were observed by inverted phase­contrast microscopy and Hoechst 33258 staining; the apoptosis rate was analyzed by flow cytometry. A Cell Counting kit­8 assay was used to assess cell proliferation. Furthermore, caspase­3 activity was determined and proteins associated with apoptosis were analyzed by western blotting. The level of apoptosis and caspase­3 activity in human NP cells increased, whereas proliferation and the expression of poly ADP­ribose polymerase decreased following TNF­α treatment. These effects of TNF­α were abolished by pretreatment with 17ß­E2 in a concentration­dependent manner. The results of the present study indicated that 17ß­E2 serves a critical role in the survival of degenerative human NP cells.

An ultrastructural study of chondroptosis: programmed cell death in degenerative intervertebral discs in vivo.

Apoptosis has been regarded to mediate intervertebral disc degeneration (IDD); however, the basic question of how the apoptotic bodies are cleared in the avascular intervertebral disc without phagocytes, which are essential to apoptosis, remains to be elucidated. Our goals were to investigate the ultrastructure of nucleus pulposus (NP) cells undergoing chondroptosis, a variant of apoptotic cell death, in a rabbit annular needle-puncture model of IDD. Experimental IDD was induced by puncturing discs with a 16-G needle in New Zealand rabbits. At 4 and 12 weeks after puncture, progressive degeneration was demonstrated by X-ray, magnetic resonance imaging and histological staining. TUNEL staining suggested a significant increase in the apoptosis index in the degenerated NP. However, the percentage of apoptotic cells with the classic ultrastructure morphology was much less than that with chondroptotic ultrastructure morphology under transmission electron microscopy (TEM). The chondroptotic cells from the early to late stage were visualized under TEM. In addition, the percentage of chondroptotic cells was significantly enhanced in the degenerated NP. Furthermore, 'paralyzed' cells were found in the herniated tissue. Western blotting revealed an increase in caspase3 expression in the degenerated NP. The expression of the Golgi protein (58K) was increased by the fourth week after puncture but decreased later. These findings indicate that chondroptosis is a major type of programmed cell death in the degenerated rabbit NP that may be related to the progressive development of IDD.