Role of SHOX2 in the development of intervertebral disc degeneration

TNF-α induces up-regulation of MicroRNA-27a via the P38 signalling pathway, which inhibits intervertebral disc degeneration by targeting FSTL1

The mechanism of intervertebral disc degeneration is still unclear, and there are no effective therapeutic strategies for treating this condition. miRNAs are naturally occurring macromolecules in the human body and have many biological functions. Therefore, we hope to elucidate whether miRNAs are associated with intervertebral disc degeneration and the underlying mechanisms involved. In our study, differentially expressed miRNAs were predicted by the GEO database and then confirmed by qPCR and in situ hybridization. Apoptosis of nucleus pulposus cells was detected by flow cytometry and Bcl2, Bax and caspase 3. Deposition of extracellular matrix was assessed by Alcian blue staining, and the expression of COX2 and MMP13 was detected by immunofluorescence, Western blot and qPCR. Moreover, qPCR was used to detect the expression of miR27a and its precursors. The results showed that miR27a was rarely expressed in healthy intervertebral discs but showed increased expression in degenerated intervertebral discs. Ectopic miR27a expression inhibited apoptosis, suppressed the inflammatory response and attenuated the catabolism of the extracellular matrix by targeting FSTL1. Furthermore, it seems that the expression of miR27a was up-regulated by TNF-α via the P38 signalling pathway. So we conclude that TNF-α and FSTL1 engage in a positive feedback loop to promote intervertebral disc degeneration. At the same time, miR27a is up-regulated by TNF-α via the P38 signalling pathway, which ameliorates inflammation, apoptosis and matrix degradation by targeting FSTL1. Thus, this negative feedback mechanism might contribute to the maintenance of a low degeneration load and would be beneficial to maintain a persistent chronic disc degeneration.

TNF-α suppresses SHOX2 expression via NF-κB signaling pathway and promotes intervertebral disc degeneration and related pain in a rat model

This study was conducted to verify the relative expression patterns of SHOX2 and its regulation by tumor necrosis factor alpha (TNF-α) during the development of intervertebral disc degeneration (IVDD). A rat disc-degeneration model was subjected to disc puncture (DP) and intradiscal injections with TNF-α to determine the roles of TNF-α and SHOX2 expression in IVDD in vivo. TNF-α and SHOX2 expression patterns in different degenerative rat nucleus pulposus (NP) tissues were measured by immunohistochemistry (IHC). The effects of TNF-α on IVDD were determined by magnetic resonance imaging (MRI) and pain development of wet-dog shakes (WDS) were blinded assessment by pain-behavior testing, respectively. Changes in TNF-α on SHOX2 expression were measured by Western blot analysis and real-time reverse transcription polymerase chain reaction (RT-PCR). The roles of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) in TNF-α-mediated SHOX2 activation were studied using viral transfection, Western blot analysis, and real-time RT-PCR. In vivo, TNF-α accelerated the process of IVDD and suppressed SHOX2 expression; compared to the DP group, WDS was significantly increased in TNF-α intradiscal injection group at 2 to 6 weeks after puncture (P < .05); In NP cells, TNF-α negatively affected the IVDD-associated SHOX2 suppression. While TNF-α promotes IVDD through activation of both MAPK and NF-κB signaling, it seemed that only NF-κB signaling controlled the TNF-α-mediated SHOX2 suppression that is associated with IVDD. The results of this study indicated that TNF-α inhibits SHOX2 expression and has promoted effects on IVDD in the rat model, and these effects might be associated with through NF-κB signaling pathway and promotes IVDD and related pain in a rat model.

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

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

Effects of the NF‑κB/p53 signaling pathway on intervertebral disc nucleus pulposus degeneration

The incidence of intervertebral disc degeneration (IDD) is increasing, especially among elderly individuals. The present study aimed to investigate the effects of the NF-κB/p53 signaling pathway on IDD and its regulatory effect on associated cytokines. In the present study, human nucleus pulposus cells were isolated from patients with thoracic-lumbar fractures and patients with IDD to observe cellular morphology and detect phosphorylated (p)-p65/p53 expression levels. The locality and expression levels of p65 in interleukin (IL)-1β-stimulated nucleus pulposus cells, with or without the addition of ammonium pyrrolidinedithiocarbamate (PDTC; a NF-κB signaling pathway-specific blocker), were measured. Furthermore, the effects of IL-1β stimulation on the protein and gene expression levels of IDD-related cytokines were determined following p53 knockdown and inhibition of the NF-κB signaling pathway. The results suggested that p-p65 and p53 expression was significantly increased in IDD cells compared with normal nucleus pulposus cells. Moreover, nucleus pulposus cells isolated from patients with IDD contained less cytoplasm compared with normal nucleus pulposus cells, and p65 expression levels were higher in the cytoplasm than the nucleus of IL-1β-stimulated PDTC-treated healthy nucleus pulposus cells. Moreover, the p53 expression levels were significantly decreased following transfection with sip53. PDTC treatment and p53 knockdown significantly decreased matrix metallopeptidase (MMP)-3, MMP-13, metallopeptidases with thrombospondin type 1 motif (ADAMTS)-4 and ADAMTS-5 expression levels, and increased aggrecan and collagen type II expression levels in IL-1β-stimulated cells. The present study indicated that activation of the NF-κB/p53 signaling pathway might be related to the occurrence of IDD; therefore, the NF-κB/p53 signaling pathway may serve as a therapeutic target for IDD.

JAG2/Notch2 inhibits intervertebral disc degeneration by modulating cell proliferation, apoptosis, and extracellular matrix

Background

Intervertebral disc degeneration (IVDD)-related disorders are the major causes of low back pain. A previous study suggested that Notch activation serves as a protective mechanism and is a part of the compensatory response that maintains the necessary resident nucleus pulposus (NP) cell proliferation to replace lost or non-functional cells. However, the exact mechanism remains to be determined. In this study, we aimed to investigate the role of JAG2/Notch2 in NP cell proliferation and apoptosis.

Methods

Recombinant JAG2 or Notch2, Hes1, and Hey2 siRNAs were used to activate or inhibit Notch signaling. Cell proliferation, apoptosis, cell cycle regulatory factors, and pathways associated with Notch-mediated proliferation were examined. In vivo experiments involving an intradiscal injection of Sprague-Dawley rats were performed.

Results

Recombinant JAG2 induced Notch2 and Hes1/Hey2 expression together with NP cell proliferation. Downregulation of Notch2/Hes1/Hey2 induced G0/G1 phase cell cycle arrest in NP cells. Moreover, Notch2 mediated NP cell proliferation by regulating cyclin D1 and by activating PI3K/Akt and Wnt/β-catenin signaling. Furthermore, Notch signaling inhibited TNF-α-promoted NP cell apoptosis by suppressing the formation of the RIP1-FADD-caspase-8 complex. Finally, we found that intradiscal injection of JAG2 alleviated IVDD and that sh-Notch2 aggravated IVDD in a rat model. These results indicated that JAG2/Notch2 inhibited IVDD by modulating cell proliferation, apoptosis, and extracellular matrix. The JAG2/Notch2 axis regulated NP cell proliferation via PI3K/Akt and Wnt/β-catenin signaling and inhibited TNF-α-induced apoptosis by suppressing the formation of the RIP1-FADD-caspase-8 complex.

Conclusions

The current and previous results shed light on the therapeutic implications of targeting the JAG2/Notch2 axis to inhibit or reverse IVDD.

TNF-α enhances apoptosis by promoting chop expression in nucleus pulposus cells: role of the MAPK and NF-κB pathways

CHOP has been shown to be involved in AF cells apoptosis and disc degeneration in a rat model. The aim of this study was to investigate the regulatory effects of TNF-α on C/EBP homologous protein (CHOP) and the role of CHOP in nucleus pulposus (NP) cell apoptosis. The effects of TNF-α on chop were measured by qPCR, Western blot, and immunofluorescence. TNF receptor involvement was analyzed by small interfering RNA (siRNA), Western blotting, immunofluorescence, and qPCR. The effects of NF-κB and MAPK on TNF-α-mediated chop promoter activity were studied using siRNAs, Western blotting, immunofluorescence, and qPCR. The regulatory effects of TNF-α-induced CHOP on Bcl-2 and Bax were studied using siRNAs, Western blotting, immunofluorescence, and qPCR. Flow cytometric and TUNEL analyses were performed to investigate the effects of chop on NP cell apoptosis. Increased CHOP expression was observed in NP cells after TNF-α treatment. Treatment of cells with TNF receptor, NF-κB, and ERK/JNK-MAPK inhibitors or siRNAs abolished the effects of cytokines on CHOP expression. Pharmacological siRNA knockdown of chop promoted Bax, decreased Bcl-2, and attenuated TNF-α-mediated cell apoptosis. During intervertebral disc degeneration (IVDD), TNF-α binds to TNF receptors and controls the JNK/ERK-MAPK, and NF-κB signaling pathways in NP cells, increasing CHOP expression. This change up-regulates the pro-apoptotic protein Bax and down-regulates the anti-apoptosis protein Bcl-2, inducing cell apoptosis. This study suggests a potential therapeutic target for controlling the inflammatory-induced apoptosis associated with IVDD. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Hemoglobin stimulates the expression of ADAMTS-5 and ADAMTS-9 by synovial cells: a possible cause of articular cartilage damage after intra-articular hemorrhage

Background

ADAMTS (a disintegrin and metalloprotease with thrombospondin motifs) proteins play an important pathological role in matrix degeneration. Aggrecan degradation is a significant and critical event in early-stage osteoarthritis. To determine the effect of hemoglobin (Hb) on the ability of synovial tissues to produce ADAMTS family members, we examined the influence of Hb by synovial cells in an in vitro experimental system.

Methods

Synovial tissues were obtained from five young patients with meniscal injury under arthroscopic surgery. Primary cultures of human knee synovial cells were treated with different doses of human Hb (0, 25, 50, 100 μg/ml). The culture media were collected 24 h after Hb-treatment. In the time-course studies, cells were treated with and without 100 μg/ml Hb, and culture media were taken at 6, 12, and 24 h. To identify the proteins responsible for aggrecanase activity, Western blot analysis using antibodies against human ADAMTS-5, −8, −9, and −10; enzyme-linked immunosorbent assay (ELISA); and gene expression for ADAMTS-5 and -9 were examined. Statistical comparisons between each group were performed using paired t-tests.

Results

Western blot analysis revealed that Hb-treatment resulted in the expression of ADAMTS-5 and -9. Neither control group nor Hb-treated medium showed immunoreactivity against ADAMTS-8 or −10. In a dose-dependency study, the Hb-treated group showed significantly higher levels of ADAMTS-5 and -9 compared with the control (p < 0.05). There was no significant difference between 25, 50, and 100 μg/ml Hb-treated groups. In a time-course study, the ADAMTS-5 and -9 levels in the conditioned medium had significantly increased expression at 6, 12, and 24 h in the Hb-treated group (p < 0.05). Hb evoked significant expression of ADAMTS-9 mRNA at 12 and 24 h (p < 0.05).

Conclusions

These findings indicate that Hb induces the expression of ADAMTS-5 and -9 by synovial cells at low doses, even at an acute phase, and suggests a possible role for Hb in cartilage damage after intra-articular hemorrhage. The results also suggest a new potential therapeutic target by inhibiting the activities of ADAMTS-5 and -9 to prevent cartilage damage after intra-articular hemorrhage.

Ghrelin protects against nucleus pulposus degeneration through inhibition of NF-κB signaling pathway and activation of Akt signaling pathway

The objective of the present study was to examine the potential role of ghrelin in degeneration of nucleus pulposus (NP). Lower expression levels of ghrelin were found in human NP cells stimulated with interleukin-1β (IL-1β). Moreover, exogenous ghrelin suppressed IL-1β induced degeneration and inflammation associated biomarkers in human NP cells, including matrix metalloproteinase-13, a disintegrin and metalloproteinase with thrombospondin motifs-5, tumor necrosis factor-α and iNOS, which was possibly mediated by antagonization of NF-κB signaling. Moreover, ghrelin enhanced production of critical extracellular matrix of NP cells, including collagen 2, aggrecan, and Sox-9 in NP cells. Ghrelin also promoted NP tissue regeneration in a rabbit IVD degeneration model, which seems to be associated with growth hormone secretagogue receptor. Additionally, the protective role of ghrelin in anabolism potentially relies on activation of Akt signaling pathway. Taken together, ghrelin may represent a molecular target for prevention and treatment of intervertebral disc degeneration.