HMGB1 mediated autophagy and apoptosis in human nucleus pulposus cells; chloroquine amplified apoptosis by inhibiting autophagy

Intervertebral disc (IVD) degeneration (DD) is associated with low back pain, the leading cause of disability worldwide. Damage-associated molecular patterns (DAMPs) that contribute to inflammation and trigger DD have not been well characterized. Extracellular high mobility group box-1 (HMGB1) protein has been implicated as a potent DAMP and pro-inflammatory stimulus in the immune system. In this study, we show that HMGB1 and IL-6 levels increase in patients with advanced DD in comparison to early DD. This study further tested the hypothesis that HMGB1 promotes inflammatory signaling driving DD in human nucleus pulposus (NP) cells and tissue. Immunofluorescence and western blot analysis confirmed the expression of HMGB1 and its extracellular release by NP cells under cell stress. Gene expression and protein quantification indicate that HMGB1 stimulates the expression IL-6 and MMP-1 in a dose-dependent manner. The contributions of toll-like receptor (TLR) -2, -4 and receptor for advanced glycation end products (RAGE) as receptors mediating HMGB1 signaling was examined using small molecule inhibitors. Inhibition of TLR-4 signaling, with TAK-242, completely abrogated HMGB1 induced IL-6 and MMP-1 expression, whereas inhibition of TLR-2, with O-vanillin, or RAGE, with FPS-ZM1, had mild inhibitory effects. HMGB1 stimulation activated NF-ĸB signaling while TAK-242 co-treatment abrogated it. Lastly, effects of HMGB1 on matrix deposition was evaluated in a 3D culture system of human NP cells. These results implicate HMGB1 as a potent DAMP that promotes inflammation in NP cells and degradation of NP tissues. TLR4-HMGB1 axis is a potential major pathway to alleviate disc inflammation and mitigate DD. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Low back pain is a common clinical symptom of intervertebral disc degeneration (IVDD), which seriously affects the quality of life of the patients. The abnormal apoptosis and senescence of nucleus pulposus cells (NPCs) play important roles in the pathogenesis of IVDD. PHLDA2 is an imprinted gene related to cell apoptosis and tumour progression. However, its role in NPC degeneration is not yet clear. Therefore, this study was set to explore the effects of PHLDA2 on NPC senescence and apoptosis and the underlying mechanisms. The expression of PHLDA2 was examined in human nucleus pulposus (NP) tissues and NPCs. Immunohistochemical staining, magnetic resonance imaging imaging and western blot were performed to evaluate the phenotypes of intervertebral discs. Senescence and apoptosis of NPCs were assessed by SA-β-galactosidase, flow cytometry and western blot. Mitochondrial function was investigated by JC-1 staining and transmission electron microscopy. It was found that the expression level of PHLDA2 was abnormally elevated in degenerated human NP tissues and NPCs. Furthermore, knockdown of PHLDA2 can significantly inhibit senescence and apoptosis of NPCs, whereas overexpression of PHLDA2 can reverse senescence and apoptosis of NPCs in vitro. In vivo experiment further confirmed that PHLDA2 knockdown could alleviate IVDD in rats. Knockdown of PHLDA2 could also reverse senescence and apoptosis in IL-1β-treated NPCs. JC-1 staining indicated PHLDA2's knockdown impaired disruption of the mitochondrial membrane potential and also ameliorated superstructural destruction of NPCs as showed by transmission electron microscopy. Finally, we found the PHLDA2 knockdown promoted Collagen-II expression and suppressed MMP3 expression in NPCs by repressing wnt/β-catenin pathway. In conclusion, the results of the present study showed that PHLDA2 promotes IL-1β-induced apoptosis and senescence of NP cells via mitochondrial route by activating the Wnt/β-catenin pathway, and suggested that therapy targeting PHLDA2 may provide valuable insights into possible IVDD therapies.

Duhuo jisheng decoction suppresses matrix degradation and apoptosis in human nucleus pulposus cells and ameliorates disc degeneration in a rat model.

IntroductionNucleus pulposus (NP) cells have a phenotype similar to articular cartilage (AC) cells. However, the matrix of the NP is clearly different to that of AC suggesting that specific cell phenotypes exist. The aim of this study was to identify novel genes that could be used to distinguish bovine NP cells from AC and annulus fibrosus (AF) cells, and to further determine their expression in normal and degenerate human intervertebral disc (IVD) cells.MethodsMicroarrays were conducted on bovine AC, AF and NP cells, using Affymetrix Genechip® Bovine Genome Arrays. Differential expression levels for a number of genes were confirmed by quantitative real time polymerase chain reaction (qRT-PCR) on bovine, AC, AF and NP cells, as well as separated bovine NP and notochordal (NC) cells. Expression of these novel markers were further tested on normal human AC, AF and NP cells, and degenerate AF and NP cells.ResultsMicroarray comparisons between NP/AC&AF and NP/AC identified 34 NP-specific and 49 IVD-specific genes respectively that were differentially expressed ≥100 fold. A subset of these were verified by qRT-PCR and shown to be expressed in bovine NC cells. Eleven genes (SNAP25, KRT8, KRT18, KRT19, CDH2, IBSP, VCAN, TNMD, BASP1, FOXF1 & FBLN1) were also differentially expressed in normal human NP cells, although to a lesser degree. Four genes (SNAP25, KRT8, KRT18 and CDH2) were significantly decreased in degenerate human NP cells, while three genes (VCAN, TNMD and BASP1) were significantly increased in degenerate human AF cells. The IVD negative marker FBLN1 was significantly increased in both degenerate human NP and AF cells.ConclusionsThis study has identified a number of novel genes that characterise the bovine and human NP and IVD transcriptional profiles, and allows for discrimination between AC, AF and NP cells. Furthermore, the similarity in expression profiles of the separated NP and NC cell populations suggests that these two cell types may be derived from a common lineage. Although interspecies variation, together with changes with IVD degeneration were noted, use of this gene expression signature will benefit tissue engineering studies where defining the NP phenotype is paramount.

Intervertebral disc degeneration (IDD) is a common disease with a high morbidity rate, which results in a significant deterioration in the quality of life of patients. MicroRNAs (miRNAs/miRs) are a class of endogenous small non-coding RNAs that influence target genes and serve critical roles in numerous biological processes. However, the role of miR-489-3p in lumbar disc degeneration is yet to be elucidated. In the present study, human NP cells were treated with 10 ng/ml lipopolysaccharide (LPS) for 24 h to investigate the role of miR-489-3p in IDD in an in vitro model. Reverse transcription-quantitative (RT-q)PCR was performed to determine the expression levels of miR-489-3p. Then, the TargetScan database was used to predict the potential binding sites between miR-489-3p and Toll-like receptor (TLR)4, and a dual-luciferase reporter assay was performed to verify the findings. Subsequently, RT-qPCR and western blotting were used to analyze the expression levels of TLR4. In addition, human nucleus pulposus (NP) cells were transfected with a miR-489-3p mimic and TLR4 overexpression plasmid to study the effects of miR-489-3p on LPS-induced human NP cells. Cell apoptosis and cell viability were also determined using flow cytometry and MTT assays, respectively. Finally, ELISAs were performed to analyze the levels of inflammatory factors. The expression levels of miR-489-3p were discovered to be downregulated in LPS-treated human NP cells. In addition, TLR4 was revealed to be a direct target gene of miR-489-3p, and its expression levels were upregulated in LPS-treated human NP cells. miR-489-3p was found to inhibit the LPS-induced decreases in cell viability and increases in apoptosis, and the concentration of inflammatory cytokines. Furthermore, miR-489-3p suppressed the LPS-induced decreases in extracellular matrix deposition via decreasing the expression levels of aggrecan and collagen type II in human NP cells. Finally, the results revealed that miR-489-3p inhibited the LPS-induced activation of the NF-κB signaling pathway in human NP cells. Conversely, all of the effects of miR-489-3p on LPS-induced human NP cells were reversed by the TLR4 overexpression plasmid. These findings suggested that miR-489-3p may represent a novel therapeutic target for the treatment of IDD.

Background/Aims: Nucleus pulposus cell (NPC) apoptosis is the main factor in intervertebral disc degeneration (IDD); thus, inhibiting the excessive apoptosis of nucleus pulposus cells may be a potential way to alleviate IDD. The effect of Hemeoxygenase-1 (HO-1) on human NPC apoptosis has never been reported. Our study aimed to investigate the effect and mechanism of HO-1 on apoptosis in human degenerative NPCs. Methods: Nucleus pulposus tissues were collected from patients with lumbar vertebral fracture (LVF) and IDD. The expression of HO-1 and P65 in intervertebral discs was determined using immunohistochemistry and western blot analysis. Apoptosis of human nucleus pulposus cells was quantified by flow cytometric analysis. A recombinant lentiviral vector overexpressing HO-1 and HO-1-siRNA was used to promote or silence the expression of HO-1 in nucleus pulposus cells. The NF-κB inhibitor PDTC was used to inhibit the NF-κB pathway. Results: Our study demonstrated that compared with normal samples, IDD samples showed down-regulation of HO-1 expression and up-regulation of P65 expression. Overexpression of HO-1 inhibited the increase in nucleus pulposus cell apoptosis after IL-1β treatment and simultaneously inhibited the expression of p-P65. Furthermore, after treatment with PDTC, the number of apoptotic cells was significantly decreased with or without overexpression of HO-1. Conclusion: HO-1 might play a significant role in IDD, and HO-1 protected degenerative human NPCs against apoptosis induced by IL-1β through the NF-κB pathway. These findings would aid in the development of novel therapeutic approaches for IDD treatment.

Intervertebral disc degeneration (IDD) is characterized by excessive apoptosis of nucleus pulposus (NP) cells and hyperactive extracellular matrix (ECM) catabolism. Our previous studies revealed the relationship between human islet amyloid polypeptide (hIAPP) and NP cell apoptosis. However, the role of hIAPP aggregates in IDD has not yet been investigated. This study aimed to determine whether the accumulation of hIAPP aggregates promotes IDD progression. The aggregation of hIAPP increased in human NP tissues during IDD. The deposition of hIAPP aggravated the compression-induced IDD that promoted NP cell apoptosis and ECM degradation via IL-1β/IL-1Ra signaling in an ex vivo rat disc model. Moreover, neutralizing IL-1β augmented the protective effects of hIAPP overexpression by decreasing hIAPP aggregation in human NP cells. These results suggest that the aggregation of hIAPP promotes NP cell apoptosis and ECM degradation ex vivo and in vitro by disrupting the balance of IL-1β/IL-1Ra signaling.

Human degenerative disc disease (DDD) is characterized by progressive loss of human nucleus pulposus (HNP) cells and extracellular matrix, in which the massive deposition are secreted by HNP cells. Cell therapy to supplement HNP cells to degenerated discs has been thought to be a promising strategy to treat DDD. However, obtaining a large quality of fully functional HNP cells has been severely hampered by limited proliferation capacity of HNP cells in vitro. Previous studies have used lipofectamine or recombinant adeno-associated viral (rAAV) vectors to deliver human telomerase reverse transcriptase (hTERT) into ovine or HNP cells to prolong the activity of nucleus pulposus cells with limited success. Here we developed a lentiviral vector bearing both hTERT and a gene encoding green fluorescence protein (L-hTERT/EGFP). This vector efficiently mediated both hTERT and EGFP into freshly isolated HNP cells. The expressions of both transgenes in L-hTERT/EGFP transduced HNP cells were detected up to day 210 post viral infection, which was twice as long as rAAV vector did. Furthermore, we observed restored telomerase activity, maintained telomere length, delayed cell senescence, and increased cell proliferation rate in those L-hTERT/EGFP transduced HNP cells. Our study suggests that lentiviral vector might be a useful gene delivery vehicle for HNP cell therapy to treat DDD.

Notochordal cell-derived conditioned medium protects human nucleus pulposus cells from stress-induced apoptosis

ObjectiveTo investigate the protective effect and mechanism of shikonin on human intervertebral disk degeneration.MethodsHuman primary nucleus pulposus (NP) cells cultured in vitro were used for the experiments. The effects of different concentrations of shikonin (1, 2, 4, 8, and 16 µM) on the activity of lipopolysaccharide (LPS)‐induced NP cells were determined using the CCK‐8 assay, and the appropriate drug concentration was determined. The experiment was divided into the control, LPS, and LPS + shikonin groups. ELISA and Western blot were used to detect the expression of the inflammatory factors tumor necrosis factor (TNF)‐α and interleukin (IL)‐1β. NP cell apoptosis was measured using Western blot and caspase 3 activity. Western blot and immunofluorescence assays were used to detect the protein expression of p‐P65 and P65 and the nuclear translocation of P65.ResultsThe CCK‐8 assay showed that shikonin had no cytotoxic effect on NP cells and increased the activity of LPS‐induced NP cells, especially at a concentration of 4 μM. Shikonin reversed the expression of the inflammatory cytokines TNF‐α and IL‐1β and apoptosis‐related molecules Bax, Bcl‐2, and cleaved caspase 3 in LPS‐induced NP cells. In addition, shikonin significantly decreased apoptosis and caspase‐3 activity in LPS‐induced NP cells. Furthermore, shikonin treatment significantly inhibited the expression of p‐P65 and nuclear translocation of P65, and nuclear factor‐kappa B (NF‐κB) pathway inhibitor Pyrrolidinedithiocarbamate ammonium (PDTC) significantly enhanced the anti‐inflammatory and antiapoptotic effects of shikonin in LPS‐induced NP cells.ConclusionShikonin significantly inhibited the inflammatory response and apoptosis of human primary NP cells, possibly through the NF‐κB pathway.

BackgroundLow 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-1β-induced human nucleus pulposus (NP) cells and its corresponding molecular mechanisms.Material/MethodsHuman 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]-α, interleukin [IL]-6), kappa B kinase α (IκBα), 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-1β-induced human NP cells.ResultsHuman 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-1β-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 IκBα and p65.ConclusionsThese results demonstrated that naringin could attenuate matrix metalloproteinase catabolism and inflammation in IL-1β-treated human nucleus pulposus cells via downregulating NF-κB pathway and p53 expression, suggesting that naringin has the potential to prevent and treat IDD.

Intervertebral disc degeneration (IDD) is a degenerative condition associated with impaired mitophagy. MANF has been shown to promote mitophagy in murine kidneys; however, its role in IDD remains unexplored. This study aimed to elucidate the mechanism by which MANF influences IDD development through the regulation of mitophagy. Human nucleus pulposus (NP) cells were exposed to tert-butyl hydroperoxide (TBHP) to establish an oxidative stress-induced cellular model. The expression levels of MANF in NP cells were quantified using quantitative real-time PCR (qPCR) and Western blotting. The impact of MANF on TBHP-induced NP cells was evaluated by assessing cell viability, apoptosis, and the levels of mitophagy-related proteins. The underlying mechanisms were further investigated using RNA-binding protein immunoprecipitation (RIP), dual-luciferase reporter assays, qPCR, and Western blotting. Results indicated that MANF expression was significantly downregulated in both IDD patients and TBHP-induced NP cells. Overexpression of MANF inhibited apoptosis, enhanced cell viability, and promoted mitophagy in TBHP-treated NP cells. MFN2 was identified as a downstream target of MANF, and MANF overexpression upregulated MFN2 expression in NP cells, whereas TBHP markedly suppressed MFN2 expression. Furthermore, knockdown of MFN2 partially reversed the effects of MANF overexpression on apoptosis, cell viability, and mitophagy in TBHP-treated NP cells. Collectively, these findings demonstrate that MANF overexpression enhances mitophagy by upregulating MFN2 expression, thereby mitigating oxidative stress-induced apoptosis in NP cells. These results provide novel insights into the pathogenesis of IDD.

BackgroundLow-intensity pulsed ultrasound (LIPUS) is a safe and noninvasive rehabilitative physical therapy with anti-inflammatory effects. The current study investigated the effect of LIPUS on the inflammation of nucleus pulposus (NP) cells and its underlying mechanism.MethodsHuman NP cells were acquired from lumbar disc herniation tissue samples and cultured for experiments. Human NP cells were treated with LPS and then exposed to LIPUS (15 mW/cm2, 30 mW/cm2 and 60 mW/cm2) for 20 min daily for 3 days to determine the appropriate intensity to inhibit the expression of the inflammatory factors TNF-α and IL-1β. The gene and protein expression of aggrecan, collagen II, MMP-3 and MMP-9 was measured by real‐time PCR and western blotting, respectively. The activity of the nuclear factor‐kappa B (NF‐κB) pathway was examined by western blotting and immunofluorescence. After pretreatment with the NF-κB inhibitor PDTC, the expression of TNF-α, IL-1β, MMP-3 and MMP-9 was measured by real‐time PCR.ResultsLIPUS at intensities of 15 mW/cm2, 30 mW/cm2 and 60 mW/cm2 inhibited LPS-induced NP cell expression of the inflammatory factors TNF-α and IL-1β, especially at 30 mW/cm2. LIPUS significantly upregulated the gene and protein expression of aggrecan and collagen II and downregulated the gene and protein expression of MMP-3 and MMP-9 in LPS-induced NP cells. The NF‐κB signaling pathway was inhibited by LIPUS through inhibiting the protein expression of p-P65 and the translocation of P65 into the nucleus in LPS-induced NP cells. In addition, LIPUS had similar effects as the NF-κB inhibitor PDTC by inhibiting the NF-κB signaling pathway, inflammation and catabolism in LPS-induced human degenerative nucleus pulposus cells.ConclusionLIPUS inhibited inflammation and catabolism through the NF‐κB pathway in human degenerative nucleus pulposus cells.

Panax notoginseng saponins inhibits oxidative stress- induced human nucleus pulposus cell apoptosis and delays disc degeneration in vivo and in vitro

Resveratrol (RSV) is known to play a role of anti-TNF-α in a number of cell types. However, whether RSV modulates the effects of TNF-α on human nucleus pulposus (NP) cells is unknown. The purpose of this study is to investigate whether RSV regulates TNF-α-induced matrix metalloproteinase-3 (MMP-3) expression. Via quantitative real-time polymerase chain reaction (qRT-PCR) analysis, we found that MMP-3 expression induced by TNF-α was inhibited by RSV treatment. Depending on Western blot and qRT-PCR assay, we found that RSV induced autophagy in human NP cells, whereas inhibition of autophagy remarkably abolished the restraining role of RSV in the TNF-α-mediated up-regulation of MMP-3. Furthermore, RSV increased SIRT1 expression and SIRT1 knockdown significantly suppressed RSV-induced autophagy in NP cells. RSV also activated AMP-activated protein kinase (AMPK), while inhibition of AMPK notably abolished RSV-induced SIRT1 expression. Our data showed that RSV attenuated TNF-α-induced MMP-3 expression in human NP cells by activating autophagy via AMPK/SIRT1 signaling pathway. This new finding suggested that RSV might act as a novel preventive and therapeutic role in intervertebral disc degeneration.