The Involvement of Protease Nexin-1 (PN1) in the Pathogenesis of Intervertebral Disc (IVD) Degeneration

A high-cholesterol diet promotes the intravasation of breast tumor cells through an LDL-LDLR axis

Most metastases in breast cancer occur via the dissemination of tumor cells through the bloodstream. How tumor cells enter the blood (intravasation) is, however, a poorly understood mechanism at the cellular and molecular levels. Particularly uncharacterized is how intravasation is affected by systemic nutrients. High levels of systemic LDL-cholesterol have been shown to contribute to breast cancer progression and metastasis in various models, but the cellular and molecular mechanisms involved are still undisclosed. Here we show that a high- cholesterol diet promotes intravasation in two mouse models of breast cancer and that this could be reverted by blocking LDL binding to LDLR in tumor cells. Moreover, we show that LDL promotes vascular invasion in vitro and the intercalation of tumor cells with endothelial cells, a phenotypic change resembling vascular mimicry (VM). At the molecular level, LDL increases the expression of SERPINE2, previously shown to be required for both VM and intravasation. Overall, our manuscript unravels novel mechanisms by which systemic hypercholesterolemia may affect the onset of metastatic breast cancer by favouring phenotypic changes in breast cancer cells and increasing intravasation.

Serpin peptidase inhibitor, clade E, member 2 in physiology and pathology: recent advancements

Serine protease inhibitors (serpins) are the most numerous and widespread multifunctional protease inhibitor superfamily and are expressed by all eukaryotes. Serpin E2 (serpin peptidase inhibitor, clade E, member 2), a member of the serine protease inhibitor superfamily is a potent endogenous thrombin inhibitor, mainly found in the extracellular matrix and platelets, and expressed in numerous organs and secreted by many cell types. The multiple functions of serpin E2 are mainly mediated through regulating urokinase-type plasminogen activator (uPA, also known as PLAU), tissue-type plasminogen activator (tPA, also known as PLAT), and matrix metalloproteinase activity, and include hemostasis, cell adhesion, and promotion of tumor metastasis. The importance serpin E2 is clear from its involvement in numerous physiological and pathological processes. In this review, we summarize the structural characteristics of the Serpin E2 gene and protein, as well as its roles physiology and disease.

TAK-715 alleviated IL-1β-induced apoptosis and ECM degradation in nucleus pulposus cells and attenuated intervertebral disc degeneration ex vivo and in vivo

BACKGROUND

Intervertebral disc degeneration (IDD) is one of the most common disorders related to the spine. Inflammation, apoptosis and extracellular matrix (ECM) degradation contribute to disc degeneration in nucleus pulposus cells (NPCs). This study focused on the role and mechanism of the p38 inhibitor TAK-715 in intervertebral disc degeneration.

METHODS

NPCs were treated with IL-1β to mimic apoptosis, followed by the addition of TAK-715. It was determined that apoptosis, inflammatory mediators (COX-2), inflammatory cytokines (HMGB1), and ECM components (collagen II, MMP9, ADAMTS5, and MMP3) existed in NPCs. In addition, the p38MAPK signaling pathways were examined. The role of TAK-715 in vivo was determined by acupuncture-induced intervertebral disc degeneration. Following an intradiscal injection of TAK-715, MRI and a histopathological analysis were conducted to assess the degree of degeneration.

RESULTS

IL-1β-induced apoptosis was alleviated by TAK-715 in vitro, and antiapoptotic proteins were upregulated. Furthermore, TAK-715 blocked IL-1β-induced inflammatory mediator production (COX-2) and inflammatory cytokine production (HMGB1) and degraded the ECM (collagen II, MMP9, ADAMTS5, and MMP3). By inhibiting the phosphorylation of p38, TAK-715 exerted its effects. In a rat tail model, TAK-715 ameliorates puncture-induced disc degeneration based on MRI and histopathology evaluations.

CONCLUSION

TAK-715 attenuated intervertebral disc degeneration in vitro and in vivo, suggesting that it might be an effective treatment for IDD.

Tanshinone IIA and Astragaloside IV Inhibit miR-223/JAK2/STAT1 Signalling Pathway to Alleviate Lipopolysaccharide-Induced Damage in Nucleus Pulposus Cells

Astragaloside IV (AS IV) and tanshinone (TS IIA) are the main natural components of Salvia miltiorrhiza and Radix Astragali, respectively. The amalgam of TS IIA and AS IV has potential therapeutic value in many inflammation-related diseases. However, the aftereffect of TS IIA and AS IV for lumbar disc herniation is not clear. Although the function of miR-223 in the inflammation-related JAK/STAT pathway is unknown, it is particularly expressed in human degenerative nucleus pulposus cells. This study has investigated the efficacy of the combined application of TS IIA and AS IV in the treatment of intervertebral disc nucleus pulposus cells (NP cells) injured by lipopolysaccharide (LPS). After miR-223 inhibitor imitated NP cells, the state of the JAK family and STAT family was recognized by Western blotting (Western blot, WB) and reverse transcriptase quantitative polymerase chain reaction (qPCR). The shRNA lentivirus interference vector targeting the STAT family was constructed, and the NP cell line stably interfering with the STAT gene was established after transfection. The expression of TNF-α, IL-6, MMP-9, MMP-3, caspase-1, and caspase-3 was detected by lipopolysaccharide (WTNP cells), control virus NP cells, STAT downregulation NP cells, enzyme-linked immunosorbent assay (ELISA), Western blot, and qPCR, respectively. The cell survival rate was detected by flow cytometry and TUNEL staining reverse transcriptase-polymerase chain reaction (qPCR). NP cells were treated with TS IIA and AS IV which had been made into different concentrations, and then, the expression of miR-223, p-STAT1, and p-JAK families was detected by WB Western blotting and qPCR. MiR-223 selectively acts on JAK2/STAT1 pathway, increases the expression of TNF-α, IL-6, MMP-9, MMP-3, caspase3-1, and caspase-3, and induces apoptosis, which can be eliminated by silencing STAT1. TS IIA combined with AS IV could inhibit the expression of miR-223, p-STAT1, and p-JAK2 in NP cells, and they showed a dose-dependent tendency to p-STAT1 and p-JAK2. This study shows that miR-223 promotes the inflammatory response and induces cell injury of NP cells by acting on the JAK2/STAT1 pathway, and the combination of TS IIA and AS IV may protect NP cells by downregulating miR-223 and inhibiting the expression of JAK2 and STAT1.

MAPK /ERK signaling pathway: A potential target for the treatment of intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a chronic skeletal muscle degenerative disease, which is considered the main cause of low back pain. It seriously affects the quality of life of patients and consequently brings a heavy economic burden to their families and the society. Although IDD is considered a natural process in degenerative lesions, it is mainly caused by aging, trauma, genetic susceptibility and other factors. It is closely related to changes in the tissue structure and function, including the progressive destruction of extracellular matrix, cell aging, cell death of the intervertebral disc (IVD), inflammation, and impairment of tissue biomechanical function. Currently, the treatment of IDD is aimed at alleviating symptoms rather than at targeting pathological changes in the IVD. Furthermore, the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling pathway is closely related to various pathological processes in IDD, and the activation of the MAPK/ERK pathway promotes the degradation of the IVD extracellular matrix, cell aging, apoptosis, and inflammatory responses. It also induces autophagy and oxidative stress that accelerate the IVD process. In our current review, we summarize the latest developments in the negative regulation of IDD after activation of the MAPK/ERK signaling pathway and emphasize on its influence on IDD. Targeting this pathway may become an attractive treatment strategy for IDD in the near future.

Effect of Transforming Growth Factor Beta (TGF-β) on the Degeneration of Intervertebral Discs by Regulating Nuclear Factor Kappa-Light-Chain-Enhancer of Activated B Cells/Mammalian Target of Rapamycin (NF-fcB/mTOR) Signaling Pathway

Intervertebral disc degenerative disease (IDDD) is common in orthopedics. TGF-β involves in inflammation and tissue repair. But its role in IDDD remains unclear. IDDD patients and normal intervertebral disc nucleus pulposus tissues were collected. IDDD was divided into prominent group and prolapse group. IDDD nucleus pulposus cells were isolated and divided into control group, TGF-β agonist group and TGF-β inhibitor group followed by analysis of cell proliferation by MTT, cell apoptosis by flow cytometry BALP and OC expression by Real time PCR, NF-/<B/mTOR signaling protein expression by Western blot as well as IL-1 and IL-6 secretion by ELISA. Compared with normal group, TGF-β mRNA and serum level in patients with IDDD was significantly decreased (P < 0.05), with more significant changes in prolapse group (P < 0.01). Pfirrmann grading scores were negatively correlated with TGF-β serum level (P < 0.001). TGF-β agonists can significantly promote cell proliferation, inhibit apoptosis, upregulate BALP and OC expression, inhibit NF-κB expression, increased p-mTOR level and decrease IL-1 and IL-6 secretion (P < 0.05). All these changes were significantly reversed by TGF-β inhibitors (P < 0.05). TGF-β expression in IDDD is reduced and associated with disease severity. Promoting TGF-β expression can inhibit inflammatory factors secretion, promote BALP and OC expression and cell proliferation, and inhibit the degeneration of intervertebral discs by regulating NF-/<B/mTOR signaling.

Serpins in cartilage and osteoarthritis: what do we know?

Serpins (serine proteinase inhibitors) are an ancient superfamily of structurally similar proteins, the majority of which use an elegant suicide inhibition mechanism to target serine proteinases. Despite likely evolving from a single common ancestor, the 36 human serpins have established roles regulating diverse biological processes, such as blood coagulation, embryonic development and extracellular matrix (ECM) turnover. Genetic mutations in serpin genes underpin a host of monogenic disorders — collectively termed the ‘serpinopathies’ — but serpin dysregulation has also been shown to drive pathological mechanisms in many common diseases. Osteoarthritis is a degenerative joint disorder, characterised by the progressive destruction of articular cartilage. This breakdown of the cartilage is driven by the metalloproteinases, and it has long been established that an imbalance of metalloproteinases to their inhibitors is of critical importance. More recently, a role for serine proteinases in cartilage destruction is emerging; including the activation of latent matrix metalloproteinases and cell-surface receptors, or direct proteolysis of the ECM. Serpins likely regulate these processes, as well as having roles beyond serine proteinase inhibition. Indeed, serpins are routinely observed to be highly modulated in osteoarthritic tissues and fluids by ‘omic analysis, but despite this, they are largely ignored. Confusing nomenclature and an underappreciation for the role of serine proteinases in osteoarthritis (OA) being the likely causes. In this narrative review, serpin structure, biochemistry and nomenclature are introduced, and for the first time, their putative importance in maintaining joint tissues — as well as their dysregulation in OA — are explored.

Rhizoma drynariae total flavonoids inhibit the inflammatory response and matrix degeneration via MAPK pathway in a rat degenerative cervical intervertebral disc model

Rhizoma drynariae total flavonoids (RDTF) are extracted from Drynaria fortunei J. Sm (D. fortunei), which was a Chinese herb commonly used to treat fractures and bruises. Modern pharmacological studies indicate flavonoids have anti-inflammatory effect in clinical practice. However, its active ingredients and the mechanisms of action are far from clear. The present study aims to determine whether RDTF can protect against intervertebral disc degeneration in a rat cervical intervertebral disc model and investigate the associated molecular mechanisms. Sprague Dawley (SD) rats were randomized into five groups: control group (CG, n = 8), intervertebral disc degeneration group (NG, n = 8), low-dose RDTF-treated group (LG, n = 8), medium-dose RDTF-treated group (MG, n = 8), and high-dose RDTF-treated group (HG, n = 8). Hematoxylin and eosin (HE) staining, immunohistochemistry (IHC), immunofluorescence, ELISA, Western blot and quantitative real time PCR (qRT-PCR) assays were used to investigate inflammatory, catabolic factors and the latent regulatory mechanism of the effects of RDTF on intervertebral disc cells. HE staining showed disc degeneration in all groups except CG, and the function was restored after RDTF treatment. IHC, Western blot, qRT-PCR, immunofluorescence and ELISA results showed that RDTF prevented intervertebral disc degeneration by suppressing mitogen-activated protein kinase (MAPK) pathway, which reduced expression of intracellular matrix metalloproteinases (MMPs), such MMP3, MMP13, and inflammatory factors including interleukin-1β (IL-1β), tumour necrosis factor-α (TNF-α). Notably RDTF inhibited extracellular matrix (ECM) degeneration by increasing expression of aggrecan and collagen type II and preventing the upregulation of collagen type I and III. It suggests that RDTF has a potential therapeutic effect on cervical spondylosis.

Reactive Oxygen Species Regulate Endoplasmic Reticulum Stress and ER-Mitochondrial Ca2+ Crosstalk to Promote Programmed Necrosis of Rat Nucleus Pulposus Cells under Compression

Programmed necrosis of nucleus pulposus (NP) cells caused by excessive compression is a crucial factor in the etiopathogenesis of intervertebral disc degeneration (IVDD). The endoplasmic reticulum (ER) and mitochondria are crucial regulators of the cell death signaling pathway, and their involvement in IVDD has been reported. However, the specific role of ER stress (ERS) and ER-mitochondria interaction in compression-induced programmed necrosis of NP cells remains unknown. Our studies revealed that compression enhanced ERS and the association between ER and mitochondria in NP cells. Suppression of ERS via 4-phenylbutyrate (4-PBA) or ER-mitochondrial Ca2+ crosstalk by inhibiting the inositol 1,4,5-trisphosphate receptor, glucose-regulated protein 75, voltage-dependent anion-selective channel 1 complex (IP3R-GRP75-VDAC1 complex) protected NP cells against programmed necrosis related to the poly(ADP-ribose) polymerase (PARP) apoptosis-inducing factor (AIF) pathway. Moreover, excessive reactive oxygen species are critical activators of ERS, leading to mitochondrial Ca2+ accumulation and consequent programmed necrosis. These data indicate that ERS and ER-mitochondrial Ca2+ crosstalk may be potential therapeutic targets for the treatment of IVDD-associated disorders. These findings provide new insights into the molecular mechanisms underlying IVDD and may provide novel therapeutic targets.

The potential role and trend of HIF‑1α in intervertebral disc degeneration: Friend or foe? (Review)

Lower back pain (LBP) is one of the most common reasons for seeking medical advice in orthopedic clinics. Increasingly, research has shown that symptomatic intervertebral disc degeneration (IDD) is mostly related to LBP. This review first outlines the research and findings of studies into IDD, from the physiological structure of the intervertebral disc (IVD) to various pathological cascades. The vicious cycles of IDD are re-described in relation to the analysis of the relationship among the pathological mechanisms involved in IDD. Interestingly, a ‘chief molecule’ was found, hypoxia-inducible factor-1α (HIF-1α), that may regulate all other mechanisms involved in IDD. When the vicious cycle is established, the low oxygen tension activates the expression of HIF-1α, which subsequently enters into the hypoxia-induced HIF pathways. The HIF pathways are dichotomized as friend and foe pathways according to the oxygen tension of the IVD microenvironment. Combined with clinical outcomes and previous research, the trend of IDD development has been predicted in this paper. Lastly, an early precautionary diagnosis and treatment method is proposed whereby nucleus pulposus tissue for biopsy can be obtained through IVD puncture guided by B-ultrasound when the patient is showing symptoms but MRI imaging shows negative results. The assessment criteria for biopsy and the feasibility, superiority and challenges of this approach have been discussed. Overall, it is clear that HIF-1α is an indispensable reference indicator for the accurate diagnosis and treatment of IDD.

TNF-α Regulates ITGβ1 and SYND4 Expression in Nucleus Pulposus Cells: Activation of FAK/PI3K Signaling

Integrins can function synergistically with syndecan-4 (SYND4) and bind to the fibronectin (FN) matrix, resulting in the regulation of tissue regeneration. This study aimed to explore the effects of TNF-α on the formation of FN/ITGβ1/SYND4 complex and the relative mechanism in NP cells. The expression of FN-ITG-SYND4 at the cellular level under TNF-α stimulation was detected by immunofluorescent staining, western blotting, and RT-PCR. ITGβ1 is a crucial component of ITG FN-induced FAK signaling, which was detected using dual mode. And, the involved signaling down stream pathways were also detected. FN is a preferred adhesion substrate for NP cells and that integrin β1 (ITGβ1) and SYND4 work synergistically during ECM engagement in a focal adhesion kinase (FAK)-dependent fashion. The PI3k/Akt pathway is obviously down-regulated, resulting in decreased adherence capacity and increased anoikis. TNF-α induction could weaken FAK activity and downstream levels of phospho-PI3K and Akt, resulting in decreased adherence capacity and increased apoptosis. Thus, TNF-α is essential for the formation of FN/ITGβ1/SYND4 complex in NP cells and further elucidates the inflammatory mechanism of NP cells degeneration.

Protease Nexin I is a feedback regulator of EGF/PKC/MAPK/EGR1 signaling in breast cancer cells metastasis and stemness

Breast cancer is the most prevalent cancer in women worldwide, which remains incurable once metastatic. Breast cancer stem cells (BCSCs) are a small subset of breast cancer cells, which are the radical cause of drug resistance, tumor relapse, and metastasis in breast cancer. The extracellular serine protease inhibitor serpinE2, also named protease nexin-1 (PN-1), contributes to enhanced metastasis of cancer cells mainly by remodeling the tumor matrix. In this study, we found that PN-1 was up-regulated in breast cancer, which promoted cell invasion, migration and stemness. Furthermore, by using specific inhibitors, we discovered that epidermal growth factor (EGF) up-regulated PN-1 in breast cancer cells through cascade activation of epidermal growth factor receptor (EGFR) to the activation of protein kinase Cδ (PKCδ), mitogen-activated protein kinase (MEK) and extracellular signal-related kinase (ERK), which finally led to the up-regulation of early growth response protein 1 (EGR1). Moreover, EGF signaling was further activated as a feedback of PN-1 up-regulation through PN-1 blocking HtrA1. Taken together, our findings revealed a novel signaling axis that up-regulated PN-1 expression in breast cancer cells, and the new mechanism of PN-1-promoted breast cancer metastasis, which may provide new insights into identifying novel therapeutic targets for breast cancer.

Fibronectin induced ITGβ1/FAK-dependent apoptotic pathways determines the fate of degenerative NP cells

Intervertebral disc (IVD) degeneration is caused by a decrease in nucleus pulposus (NP) cells, due mainly to apoptosis. Focal adhesion kinase (FAK) is involved in the integrin (ITG)-mediated control of cell adhesion and anoikis (apoptosis). To explore the involvement of ITGβ1/FAK-dependent apoptotic pathways in disc degeneration, histological, and molecular biological studies on the protein expression of fibronectin (FN), ITGβ1, and syndecan 4 (SYND4) in non-degenerative and degenerative NP tissues were conducted. Degenerative NP cells were isolated and cultured in the presence of SYND4 and/or ITGβ1, with or without an FAK inhibitor. The effects of upregulation or knockdown of ITGβ1 gene expression were also examined. The TUNEL assay was used to determine the percentage of apoptotic cells. Western blotting was used to detect the expression of SYND4, ITGβ1, FAK, and downstream pathway proteins. The results showed that extracellular FN was degraded during the IVD degeneration process, detrimentally affecting the function, and survival of NP cells. The apoptotic rate was increased by ITGβ1 activation, but partially reduced by FN. After ITGβ1 knockdown, the FAK/PI3 K/AKT axis was activated in the ITGβ1/FAK-dependent pathways, resulting in increased cell adherence capacity and decreased anoikis. FN rescued the degenerative NP cells from anoikis through the FAK-dependent signaling pathways. In conclusion, the extracellular matrix protein FN is essential for maintaining the function and survival of NP cells through ITGβ1/FAK-dependent apoptotic pathways during disc degeneration. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:439-448, 2019.

Angiopoietin-2 promotes extracellular matrix degradation in human degenerative nucleus pulposus cells

In contrast to healthy intervertebral discs (IVDs), degenerate IVDs become vascularized. Here, we determined the role of an angiogenesis promoter, angiopoietin (Ang)-2, in the pathology of IVD degeneration (IDD). We evaluated degree of IDD using the Pfirrmann grading system. We used quantitative real-time polymerase chain reaction and western blotting to analyze ANG2 gene expression and Ang-2 protein levels, respectively. The involvement of Ang-2 in IVD degradation and regulation of nuclear factor-κB (NF-κB) signaling was examined by immunohistochemistry, western blotting and immunofluorescence. As a result, 10 samples with grades II and III IDD were categorized as the mild IDD group; for comparison, another 10 specimens with grades IV and V constituted the severe IDD group. Ang-2 expression was significantly higher in severe IDD than in mild IDD. Exogenous Ang-2 administration led to increased production of catabolic proteinases and loss of aggrecan and collagen II in degenerative NP cell cultures, which was mediated by the NF-κB signaling pathway. Elevated Ang-2 levels also increased interleukin-1β expression in degenerative NP cells. We conclude that the release of Ang-2 aggravates NP cell degradation and plays an important role in IDD. Ang-2 may thus constitute a novel therapeutic target for the treatment of IVD.

Simvastatin Inhibits IL-1β-Induced Apoptosis and Extracellular Matrix Degradation by Suppressing the NF-kB and MAPK Pathways in Nucleus Pulposus Cells

Statins are widely used hypocholesterolemic drugs that block the mevalonate pathway. Some studies have shown that statins may have the potential to inhibit intervertebral disk (IVD) degeneration (IDD). Interleukin (IL)-1β, a catabolic cytokine, is a key regulator of IDD. This study aimed to investigate the mechanism underlying the effect of simvastatin on IDD. The viability of nucleus pulposus (NP) cells was determined by the methyl-thiazolyl-tetrazolium (MTT) assay. The apoptosis of NP cells was measured by flow cytometric analysis, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and western blotting of relevant apoptotic proteins. The protein levels of catabolic factors and anabolic factors were determined by western blotting. The cells were stimulated with IL-1β in the absence or presence of simvastatin to investigate the effects on matrix metalloproteinase (MMP)-3, MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4, ADAMTS-5, type II collagen, and aggrecan expression. Our findings indicate that simvastatin considerably inhibited IL-1β-induced apoptosis in NP cells. We also found that simvastatin attenuated IL-1β-induced expression and MMP-3, MMP-13, ADAMTS-4, and ADAMTS-5 activities and also reduced the decrease in type II collagen and aggrecan expression. In addition, simvastatin considerably suppressed the nuclear translocation and activation of nuclear factor-kappa B (NF-KB) by inhibiting p65 phosphorylation and translocation and blocking inhibitor kB-α degradation. It also inhibited MAPK pathway activation by blocking c-Jun N-terminal kinase (JNK), p38, and ERK phosphorylation. The results of our study revealed that simvastatin is a potential agent for IDD prevention and treatment.

The role of lncRNA MALAT1 in intervertebral degenerative disc disease

Intervertebral degenerative disc disease (IDDD) is a common disease in clinic that causes pain and heavy financial burden on patients with poor prognosis. However, the pathogenesis of IDDD is not clear. Long non-coding RNA (LncRNA) is involved in regulating various body growth and pathological processes by affecting cell proliferation, differentiation, and apoptosis. However, the role of lncRNAs in IDDD is rarely reported. This study aims to investigate the role and mechanism of lncRNA MALAT1 in the development of IDDD. The nucleus pulposus of the intervertebral disc were collected and the primary nucleus pulposus cells were isolated and cultured. The cells were divided into three groups, including IDDD group, empty plasmid group transfected by pcDNA3.1, or MALAT1 group transfected by pcDNA3.1-MALAT1. MALAT1 expression was detected by real-time PCR. Cell proliferation was assessed by MTT assay. Caspase 3 activity was tested by the activity detection kit. IL-1 and IL-6 levels were analyzed by ELISA. The expression of MALAT1 in IDDD nucleus pulposus cells was significantly lower than that in control group (P < 0.05). The expression of MALAT1 was significantly increased after transfection with pcDNA3.1-MALAT1 plasmid in IDDD nucleus pulposus cells, which obviously inhibited cell proliferation, enhanced Caspase 3 activity, and promoted the secretion of IL-1 and IL-6 compared with IDDD group (P < 0.05). MALAT1 level decreased in IDDD nucleus pulposus cells. Upregulation of MALAT1 expression restrained IDDD through suppressing inflammation; inhibiting nucleus pulposus cell apoptosis, and promoting cell proliferation.

The role of angiopoietin-2 in nucleus pulposus cells during human intervertebral disc degeneration

Although evidence shows that intervertebral disc degeneration is generally characterized by angiogenesis, the role of angiopoietin has not been investigated. This study examined the presence of angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) within the native intervertebral disc (IVD) and elucidated their functions in the regulation of nucleus pulposus (NP) cells. Initial investigation of uncultured NP tissue revealed that Ang-1 and Ang-2 were expressed by native NP cells. Ang-2 expression was significantly increased in infiltrated and degenerate samples relative to normal samples. The ratio of Ang-2/Ang-1 in tissues from patients increased markedly with increasing age and level of degeneration of the IVD. The ratio of both Ang-2/Ang-1 mRNA and protein increased over time when cells were subjected to constant pressure at 1 Mpa in vitro. Our findings indicate that Ang-2 plays a role in suppressing cell adhesion and viability, and promotes the apoptosis of NP cells and that Ang-2 can inhibit the pathways stimulated by Ang-1 and fibronectin. Ang-2 release during IVD degeneration causes higher ratio of Ang-2 to Ang-1, further inhibits NP cell viability and adhesion, promoting apoptosis by blocking PI3K/Akt signaling. The present study therefore provides new insights into the role of the angiopoietin-Tie system in the pathogenesis of IVD degeneration.

Dysregulated miR-127-5p contributes to type II collagen degradation by targeting matrix metalloproteinase-13 in human intervertebral disc degeneration

BACKGROUND

Intervertebral disc degeneration (IDD) is a chronic disease associated with the degradation of extracellular matrix (ECM). Matrix metalloproteinase (MMP)-13 is a major enzyme that mediates the degradation of ECM components. MMP-13 has been predicted to be a potential target of miR-127-5p. However, the exact function of miR-127-5p in IDD is still unclear.

OBJECTIVE

We designed this study to evaluate the correlation between miR-127-5p level and the degeneration of human intervertebral discs and explore the potential mechanisms.

METHODS

miR-127-5p levels and MMP-13 mRNA levels were detected by quantitative real-time polymerase chain reaction (qPCR). To determine whether MMP-13 is a target of miR-127-5p, dual luciferase reporter assays were performed. miR-127-5p mimic and miR-127-5p inhibitor were used to overexpress or downregulate miR-127-5p expression in human NP cells, respectively. Small interfering RNA (siRNA) was used to knock down MMP-13 expression in human NP cells. Type II collagen expression in human NP cells was detected by qPCR, western blotting, and immunofluorescence staining.

RESULTS

We confirmed that miR-127-5p was significantly downregulated in nucleus pulposus (NP) tissue of degenerative discs and its expression was inversely correlated with MMP-13 mRNA levels. We reveal that MMP-13 may act as a target of miR-127-5p. Expression of miR-127-5p was inversely correlated with type II collagen expression in human NP cells. Moreover, suppression of MMP-13 expression by siRNA blocked downstream signaling and increased type II collagen expression.

CONCLUSION

Dysregulated miR-127-5p contributed to the degradation of type II collagen by targeting MMP-13 in human IDD. Our findings highlight that miR-127-5p may serve as a new therapeutic target in IDD.

Down-regulation of islet amyloid polypeptide expression induces death of human annulus fibrosus cells via mitochondrial and death receptor pathways

Islet amyloid polypeptide (IAPP) exerts its biological effects by participating in the regulation of glucose metabolism and cell apoptosis. The main goal of the present study was to investigate the expression of IAPP in degenerated intervertebral disc tissue and IAPP's modulation of extracellular matrix (ECM) catabolic and anabolic genes in human AF cells. We found that the expression of IAPP, the calcitonin receptor, and receptor activity modifying protein decreased considerably in AF cells during the progression of intervertebral disc degeneration (IDD). Meanwhile, transfection with pLV-siIAPP decreased the expression of IAPP and its receptors and reduced glucose uptake and the expression of aggrecan, Col2A1, and BG. Down-regulation of IAPP also induced a significant increase in reactive oxygen species generation in AF cells, along with a decrease in matrix metalloproteinases and an increase in the concentration of cellular Ca²⁺_, ultimately leading to death. Further analysis revealed that siIAPP intervention promoted the release of cytochrome c from mitochondria, resulting in the activation of Caspase-3 and Caspase-9. In contrast, significantly decreased expression of Caspase-3 and Caspase-9 was observed in AF cells transfected with pLV-IAPP. The concentrations of Fas and FasL proteins were significantly decreased in AF cells transfected with PLV-IAPP, while activation of the Fas/FasL system and cell death were induced by siIAPP intervention. Mechanistically, AMPK/Akt-mTOR signaling pathways were involved. In conclusion, down-regulation of IAPP expression induces the death of human AF cells via mitochondrial and death receptor pathways, potentially offering a novel therapeutic target for the treatment of IDD.

The noncoding RNA linc-ADAMTS5 cooperates with RREB1 to protect from intervertebral disc degeneration through inhibiting ADAMTS5 expression

Previous studies have indicated the important roles of ADAMTS5 in intervertebral disc degeneration (IDD). However, the mechanisms that regulate ADAMTS5 expression in nuclear pulposus (NP) cells remain largely unknown. Evidence suggests that intergenic transcription may be associated with genes that encode transcriptional regulators. Here, we identified a long intergenic noncoding RNA, linc-ADAMTS5, which was transcribed in the opposite direction to ADAMTS5. In the present study, through mining computational algorithm programs, and publicly available data sets, we identified Ras-responsive element-binding protein 1 (RREB1) as a crucial transcription factor regulating the expression of ADAMTS5 in NP cells. RNA pull-down, RNA immunoprecipitation (RIP), in vitro binding assays, and gain- and loss-of-function studies indicated that a physical interaction between linc-ADAMTS5 and splicing factor proline/glutamine-rich (SFPQ) facilitated the recruitment of RREB1 to binding sites within the ADAMTS5 promoter to induce chromatin remodeling. This resulted in subdued ADAMTS5 levels in cultured NP cells involving histone deacetylases (HDACs). In clinical NP tissues, linc-ADAMTS5 and RREB1 were correlated negatively with ADAMTS5 expression. Taken together, these results demonstrate that RREB1 cooperates with noncoding RNA linc-ADAMTS5 to inhibit ADAMTS5 expression, thereby affecting degeneration of the extracellular matrix (ECM) of the intervertebral disc (IVD).