Beta1 integrin inhibits apoptosis induced by cyclic stretch in annulus fibrosus cells via ERK1/2 MAPK pathway

Omilancor mitigates the senescence of nucleus pulposus cells induced by DDP through targeting MAP2K6

PURPOSE

This study explores the potential of Omilancor in treating Intervertebral Disc Degeneration (IDD) through MAP2K6 targeting.

METHODS

We analyzed mRNA microarray datasets to pinpoint MAP2K6 as a key regulator implicated in IDD progression. Follow-up studies demonstrated that cisplatin (DDP) could prompt cellular senescence in vitro by upregulating MAP2K6 expression. Through molecular docking and other analyses, we identified Omilancor as a compound capable of binding to MAP2K6. This interaction effectively impeded the cellular senescence induced by DDP.

RESULTS

We further showed that administration of Omilancor could significantly alleviate the degeneration of IVDs in annulus fibrosus puncture-induced rat model.

CONCLUSIONS

Omilancor shows promise as a treatment for IDD by targeting MAP2K6-mediated cellular senescence.

Calcitonin gene-related peptide attenuated discogenic low back pain in rats possibly via inhibiting microglia activation

Discogenic low back pain (DLBP) is a multifactorial disease and associated with intervertebral disc degeneration. Calcitonin gene-related protein (CGRP) plays a critical role in pain processing, while the role in DLBP remains unclear. This study aims to investigate the anti-nociceptive role and related mechanisms of CGRP in DLBP. Here we established the DLBP rat and validated the model using histology and radiography. Minocycline, a microglial inhibitor, and CGRP were intrathecally injected and the behavioral test was performed to determine hyperalgesia. Further, BV2 microglial cells and microglial activation agent lipopolysaccharide (LPS) were employed for the in vitro experiment. We observed obvious lumbar intervertebral disc degeneration and hyperalgesia at 12 weeks postoperation in DLBP group, with significantly activated microglia in the spinal cord. CGRP treatment significantly inhibited the upregulation of proinflammatory cytokines and NLRP3/caspase-1 expression induced by LPS in BV2 cells, whereas treatment with CGRP alone had little effect on BV2 cells. The intrathecal injection of CGRP into DLBP rats relieved mechanical and thermal hyperalgesia, reverted the microglial activation and decreased the expression of NLRP3/caspase-1, similar to the effects produced by minocycline. Our results provide evidence that microglial activation in the spinal cord play a key role in hyperalgesia in DLBP rats. CGRP alleviates DLBP induced hyperalgesia and inhibits microglial activation in the spinal cord. Regulation of CGRP and microglial activation may provide a new strategy for ameliorating DLBP.

Unraveling the mechanisms of intervertebral disc degeneration: an exploration of the p38 MAPK signaling pathway

Intervertebral disc (IVD) degeneration (IDD) is a worldwide spinal degenerative disease. Low back pain (LBP) is frequently caused by a variety of conditions brought on by IDD, including IVD herniation and spinal stenosis, etc. These conditions bring substantial physical and psychological pressure and economic burden to patients. IDD is closely tied with the structural or functional changes of the IVD tissue and can be caused by various complex factors like senescence, genetics, and trauma. The IVD dysfunction and structural changes can result from extracellular matrix (ECM) degradation, differentiation, inflammation, oxidative stress, mechanical stress, and senescence of IVD cells. At present, the treatment of IDD is basically to alleviate the symptoms, but not from the pathophysiological changes of IVD. Interestingly, the p38 mitogen-activated protein kinase (p38 MAPK) signaling pathway is involved in many processes of IDD, including inflammation, ECM degradation, apoptosis, senescence, proliferation, oxidative stress, and autophagy. These activities in degenerated IVD tissue are closely relevant to the development trend of IDD. Hence, the p38 MAPK signaling pathway may be a fitting curative target for IDD. In order to better understand the pathophysiological alterations of the intervertebral disc tissue during IDD and offer potential paths for targeted treatments for intervertebral disc degeneration, this article reviews the purpose of the p38 MAPK signaling pathway in IDD.

Inhibition of PP2A ameliorates intervertebral disc degeneration by reducing annulus fibrosus cells apoptosis via p38/MAPK signal pathway

BACKGROUND

Intervertebral disc degeneration (IVDD) is considered one of the main reasons for low back pain (LBP). To date, the specific pathology of IVDD remains unclear. The annulus fibrosus (AF) is an important part of the intervertebral disc, and AF cell oxidative stress, apoptosis plays a vital role in disc degeneration. Protein phosphatase 2 A (PP2A), a serine/threonine phosphatase, has regulatory functions in various processes, including apoptosis and autophagy. However, thus far, the effect of PP2A on IVDD is not clear.

METHODS

AF cells derived from caudal intervertebral discs in SD rats were used to analyze the levels of oxidative stress, apoptosis and degeneration as well as PP2A expression. A PP2A agonist (FTY720), inhibitor (microcystin-LR) and siRNA (si-PPP2CA) were employed in IVDD induced by H2O2 to investigate the levels of apoptosis and degeneration. The p38/MAPK signal pathways were evaluated, and a p38 inhibitor (SB203580) and ERK inhibitor (U0126) were added for verification. Finally, FTY720 and microcystin-LR were administered to IVDD rats to assess the effects on levels of apoptosis and degeneration and the relief of IVDD.

RESULTS

The expression of PP2A was increased in rat AF cells after H2O2 intervention. The levels of apoptosis and degeneration were higher with upregulation of PP2A but were significantly reduced after inhibition of PP2A. The PP2A inhibitor relieved cell apoptosis and degeneration by downregulating the p38/MAPK pathway. In vivo, the knockdown of PP2A resulted in a more complete morphology of discs and less apoptotic and degenerative expression.

CONCLUSIONS

This study suggests that the downregulation of PP2 A could reduce AF cell apoptosis and degeneration via the p38/MAPK pathway. It also revealed that the inhibition of PP2 A is expected to be a therapeutic target for IVDD.

Mechanism of the Mitogen-Activated Protein Kinases/Mammalian Target of Rapamycin Pathway in the Process of Cartilage Endplate Stem Cell Degeneration Induced by Tension Load

STUDY DESIGN

Basic Research.

OBJECTIVE

Intervertebral disc degeneration (IVDD) is caused by the cartilage endplate (CEP). Cartilage endplate stem cell (CESC) is involved in the recovery of CEP degeneration. Tension load (TL) contributes a lot to the initiation and progression of IVDD. This study aims to investigate the regulatory mechanism of the Mitogen-activated protein kinases/Mammalian target of rapamycin (MAPK/mTOR) pathway during TL-induced CESC degeneration.

METHODS

CESCs were isolated from New Zealand big-eared white female rabbits (6 months old). FX-4000T cell stress loading system was applied to establish a TL-induced degeneration model of CESCs. Western blotting was used to detect the level of mTOR pathway-related proteins and autophagy markers LC3-Ⅱ, Beclin-1, and p62 in degenerative CESCs. The expression of MAPK pathway-related proteins JNK and extracellular signal-regulated kinases (ERK) in degenerated CESCs was inhibited by cell transfection to explore whether JNK and ERK play a regulatory role in TL-induced autophagy in CESCs.

RESULTS

In the CESC degeneration model, the mTOR pathway was activated. After inhibition of mTOR, the autophagy level of CESCs was increased, and the degeneration of CESCs was alleviated. The MAPK pathway was also activated in the CESC degeneration model. Inhibition of JNK expression may alleviate TL-induced CEP degeneration by inhibiting Raptor phosphorylation and activating autophagy. Inhibition of ERK expression may alleviate TL-induced CEP degeneration by inhibiting mTOR phosphorylation and activating autophagy.

CONCLUSION

Inhibition of JNK and ERK in the MAPK signaling family alleviated TL-induced CESC degeneration by inhibiting the phosphorylation of Raptor and mTOR in the mTOR pathway.

IL-1β-mediated inflammatory responses in intervertebral disc degeneration: Mechanisms, signaling pathways, and therapeutic potential

Intervertebral disc degeneration (IDD) has been widely recognized as the primary cause of low back pain and is one of the major chronic diseases imposing a severe socioeconomic burden worldwide. IDD is a degenerative process characterized by inflammatory responses, and its underlying pathological mechanisms remain complex. Genetic, developmental, biochemical, and biomechanical factors contribute to the development of IDD. There is a pressing need for an effective non-surgical treatment, mainly due to the lack of comprehensive understanding of the specific mechanisms involved and the effective therapeutic targets for IDD. Recently, interleukin (IL)-1β has been recognized as an essential inflammatory factor and a key mediator of the inflammatory process in IDD. Current studies have found that IL-1β is mainly involved in IDD by affecting the metabolism of the extracellular matrix and regulating cell death (RCD), such as apoptosis, pyroptosis, and ferroptosis (a new form of RCD). Although analysis of clinical samples from different laboratories confirmed how IL-1β is induced in IDD, its specific signal transduction pathway, and the inflammatory role mediated in IDD remains unclear. This review describes the molecules and mechanisms involved in IL-1β-mediated inflammatory responses, and their roles in resolving the inflammatory process in IDD. Understanding the signaling pathways involved in IL-1β may lead to a new class of targets that promote remission for IDD patients. This review aims to provide a framework for the treatment of IDD by analyzing the signaling mechanism and function related to IL-1β, especially in terms of inflammation, matrix metabolism, and cell death regulation.

Intervertebral disc degeneration and inflammatory microenvironment: expression, pathology, and therapeutic strategies

BACKGROUND

Intervertebral disc degeneration (IDD) is a leading cause of low back pain (LBP), posing a significant socioeconomic burden. Recent studies highlight the crucial role of inflammatory microenvironment in IDD progression.

METHOD

A keyword-based search was performed using the PubMed database for published articles.

RESULTS AND CONCLUSIONS

Dysregulated expression of inflammatory cytokines disrupts intervertebral disc (IVD) homeostasis, causing atrophy, fibrosis, and phenotypic changes in nucleus pulposus cells. Modulating the inflammatory microenvironment and restoring cytokine balance hold promise for IVD repair and regeneration. This comprehensive review systematically examines the expression regulation, pathological effects, therapeutic strategies, and future challenges associated with the inflammatory microenvironment and relevant cytokines in IDD. Key inflammatory cytokines, including interleukins (IL), tumor necrosis factor-alpha (TNF-α), and chemokines, exhibit significant pathological effects in IDD. Furthermore, major therapeutic modalities such as chemical antagonists, biologics, plant extracts, and gene transcription therapies are introduced to control and ameliorate the inflammatory microenvironment. These approaches provide valuable insights for identifying potential targets in future anti-inflammatory treatments for IDD.

Angiopoietin-2 Promotes Mechanical Stress-induced Extracellular Matrix Degradation in Annulus Fibrosus Via the HIF-1α/NF-κB Signaling Pathway

OBJECTIVE

Mechanical stress is an important risk factor for intervertebral disc degeneration (IVDD). Angiopoietin-2 (ANG-2) is regulated by mechanical stress and is widely involved in the regulation of extracellular matrix metabolism. In addition, the signaling cascade between HIF-1α and NF-κB is critical in matrix degradation. This study aims to investigate the role and molecular mechanism of ANG-2 in regulating the degeneration of annulus fibrosus (AF) through the HIF-1α/NF-κB signaling pathway.

METHODS

The bipedal standing mice IVDD model was constructed, and histological experiments were used to evaluate the degree of IVDD and the expression of ANG-2 in the AF. Mouse primary AF cells were extracted in vitro and subjected to mechanical stretching experiments. Western blot assay was used to detect the effect of mechanical stress on ANG-2, and the role of the ANG-2-mediated HIF-1α/NF-κB pathway in matrix degradation. In addition, the effect of inhibiting ANG-2 expression by siRNA or monoclonal antibody on delaying IVDD was investigated at in vitro and in vivo levels. One-way ANOVA with the least significant difference method was used for pairwise comparison of the groups with homogeneous variance, and Dunnett's method was used to compare the groups with heterogeneous variance.

RESULTS

In IVDD, the expressions of catabolic biomarkers (mmp-13, ADAMTS-4) and ANG-2 were significantly increased in AF. In addition, p65 expression was increased while HIF-1α expression was significantly decreased. The results of western blot assay showed mechanical stress significantly up-regulated the expression of ANG-2 in AF cells, and promoted matrix degradation by regulating the activity of HIF-1α/NF-κB pathway. Exogenous addition of Bay117082 and CoCl2 inhibited matrix degradation caused by mechanical stress. Moreover, injection of neutralizing antibody or treatment with siRNA to inhibit the expression of ANG-2 improved the matrix metabolism of AF and inhibited IVDD progression by regulating the HIF-1α/NF-κB signaling pathway.

CONCLUSION

In IVDD, mechanical stress could regulate the HIF-1α/NF-κB signaling pathway and matrix degradation by mediating ANG-2 expression in AF degeneration.

The Inhibitory Effect of RADKPS on Pyroptosis of Nucleus Pulposus-Derived Mesenchymal Stem Cells

Intervertebral disc (IVD) degeneration (IDD) is a primary cause of low-back pain in people, which is associated with nucleus pulposus-derived mesenchymal stem cells (NPMSCs). In this study, the involvement of lipopolysaccharide (LPS) in the pyroptosis of NPMSCs was investigated. The effect of RADKPS on the pyroptosis of NPMSCs and the underlying mechanism behind the impact of RADKPS on the proliferative capacity of NPMSCs were also studied. Pyroptosis of NPMSCs was induced with 10 μg/mL LPS and its effects on the downstream signaling pathways were explored. The protective effect of RADKPS on NPMSCs under the action of LPS and its possible mechanism were explored, using different techniques such as immunohistochemical analysis, cell proliferation assay, quantitative real-time polymerase chain reaction (qPCR), and Western blot analysis. Accordingly, caspase1/p20/p10, a protein associated with pyroptosis, was found to be overexpressed in LPS-challenged NPMSCs, Furthermore, the qPCR results demonstrated that LPS promoted the expression of pyroptosis-related gene IL-1β (p < 0.0001), while downregulating the expression of Sox-9 (p < 0.001), which was a gene associated with the extracellular matrix. The immunohistochemical results identified lowered extracellular signal-regulated kinase 1/2 (ERK1/2) expression and phosphorylated (p-)ERK1/2 in the degenerated IVD tissues. In this study, the influence of RADKPS on the proliferative ability of NPMSCs was evaluated using two-dimensional (2D) and three-dimensional (3D) cultures. It was noted that RADKPS promoted the proliferation of NPMSCs in 2D and 3D cultures. The findings of the Western blot experiments revealed that RADKPS inhibited the expression of pyroptosis-related proteins, while it upregulated the p-ERK1/2 (p < 0.001), RhoA (p < 0.01), collagen II (p < 0.01), and Sox-9 (p < 0.01), whereas ERK inhibitor PD98059 and RhoA signaling pathway inhibitor CCG-1423 inhibited their expression. These findings reveal to us that RADKPS hydrogel may protect NPMSCs from pyroptosis. It was also noted that cell proliferation-related signaling pathways may promote the proliferation of NPMSCs. The results revealed that RADKPS hydrogel could be used as a potential therapeutic approach for IDD. Impact Statement RADKPS inhibits the pyroptosis of NPMSCs and promotes the production of extracellular matrix, which has the potential of intervertebral disc biotherapy.

Aberrant mechanical loading induces annulus fibrosus cells apoptosis in intervertebral disc degeneration via mechanosensitive ion channel Piezo1

BACKGROUND

Intervertebral disc degeneration (IVDD) is closely associated with the structural damage in the annulus fibrosus (AF). Aberrant mechanical loading is an important inducement of annulus fibrosus cells (AFCs) apoptosis, which contributes to the AF structural damage and aggravates IVDD, but the underlying mechanism is still unclear. This study aims to investigate the mechanism of a mechanosensitive ion channel protein Piezo1 in aberrant mechanical loading-induced AFCs apoptosis and IVDD.

METHODS

Rats were subjected to lumbar instability surgery to induce the unbalanced dynamic and static forces to establish the lumbar instability model. MRI and histological staining were used to evaluate the IVDD degree. A cyclic mechanical stretch (CMS)-stimulated AFCs apoptosis model was established by a Flexcell system in vitro. Tunel staining, mitochondrial membrane potential (MMP) detection, and flow cytometry were used to evaluate the apoptosis level. The activation of Piezo1 was detected using western blot and calcium fluorescent probes. Chemical activator Yoda1, chemical inhibitor GSMTx4, and a lentiviral shRNA-Piezo1 system (Lv-Piezo1) were utilized to regulate the function of Piezo1. High-throughput RNA sequencing (RNA-seq) was used to explore the mechanism of Piezo1-induced AFCs apoptosis. The Calpain activity and the activation of Calpain2/Bax/Caspase3 axis were evaluated by the Calpain activity kit and western blot with the siRNA-mediated Calapin1 or Calpain2 knockdown. Intradiscal administration of Lv-Piezo1 was utilized to evaluate the therapeutic effect of Piezo1 silencing in IVDD rats.

RESULTS

Lumbar instability surgery promoted the expression of Piezo1 in AFCs and stimulated IVDD in rats 4 weeks after surgery. CMS elicited distinct apoptosis of AFCs, with enhanced Piezo1 activation. Yoda1 further promoted CMS-induced apoptosis of AFCs, while GSMTx4 and Lv-Piezo1 exhibited opposite effects. RNA-seq showed that knocking down Piezo1 inhibited the calcium signaling pathway. CMS enhanced Calpain activity and elevated the expression of BAX and cleaved-Caspase3. Calpain2, but not Calpain1 knockdown, inhibited the expression of BAX and cleaved-Caspase3 and alleviated AFCs apoptosis. Lv-Piezo1 significantly alleviated the progress of IVDD in rats after lumbar instability surgery.

CONCLUSIONS

Aberrant mechanical loading induces AFCs apoptosis to promote IVDD by activating Piezo1 and downstream Calpain2/BAX/Caspase3 pathway. Piezo1 is expected to be a potential therapeutic target in treating IVDD.

Regulatory Effect of Inflammatory Mediators in Intervertebral Disc Degeneration

Intervertebral disc degeneration (IDD) is a major contributor to back, neck, and radicular pain. It is related to changes in tissue structure and function, including the breakdown of the extracellular matrix (ECM), aging, apoptosis of the nucleus pulposus, and biomechanical tissue impairment. Recently, an increasing number of studies have demonstrated that inflammatory mediators play a crucial role in IDD, and they are being explored as potential treatment targets for IDD and associated disorders. For example, interleukins (IL), tumour necrosis factor-α (TNF-α), chemokines, and inflammasomes have all been linked to the pathophysiology of IDD. These inflammatory mediators are found in high concentrations in intervertebral disc (IVD) tissues and cells and are associated with the severity of LBP and IDD. It is feasible to reduce the production of these proinflammatory mediators and develop a novel therapy for IDD, which will be a hotspot of future research. In this review, the effects of inflammatory mediators in IDD were described.

USP14 promotes pyroptosis of human annulus fibrosus cells derived from patients with intervertebral disc degeneration through deubiquitination of NLRP3

Intervertebral disc degeneration (IVDD) is a general disorder that results in low back pain and disability among many affected individuals. However, the current treatments for IVDD are limited to relieving the symptoms but do not solve the fundamental issue. In this study, the role of USP14 in mediating the activation of the NLRP3 inflammasome and the pyroptosis of AF cells from IVDD patients is determined in vitro, and gain- and loss-of-function assays of USP14 and the NLRP3 inflammasome are conducted. Pyroptosis of AF cells is detected by flow cytometry. The inflammatory cytokines (IL-1β and IL-18) and protein levels of NLRP3, active Caspase-1, Aggrecan, MMP3 and ADAMTS-5 are determined by ELISA and western blot analysis, respectively. The correlation between USP14 and NLRP3 is measured by coimmunoprecipitation and ubiquitination analysis. Upregulation of USP14 is accompanied by increased level of the NLRP3 inflammasome in AF cells from IVDD patients; furthermore, a positive correlation between them is observed. USP14 knockdown inhibits pyroptosis in AF cells by inducing ubiquitination of NLRP3, while overexpression of USP14 has the opposite effect, which is inhibited by the NLRP3 inflammasome inhibitor INF39. USP14 exerts its positive regulatory effect on AF cell pyroptosis by modulating the NLRP3/Caspase-1/IL-1β and IL-18 signaling axes.

Roles of focal adhesion proteins in skeleton and diseases

The skeletal system, which contains bones, joints, tendons, ligaments and other elements, plays a wide variety of roles in body shaping, support and movement, protection of internal organs, production of blood cells and regulation of calcium and phosphate metabolism. The prevalence of skeletal diseases and disorders, such as osteoporosis and bone fracture, osteoarthritis, rheumatoid arthritis, and intervertebral disc degeneration, increases with age, causing pain and loss of mobility and creating a huge social and economic burden globally. Focal adhesions (FAs) are macromolecular assemblies that are composed of the extracellular matrix (ECM), integrins, intracellular cytoskeleton and other proteins, including kindlin, talin, vinculin, paxillin, pinch, Src, focal adhesion kinase (FAK) and integrin-linked protein kinase (ILK) and other proteins. FA acts as a mechanical linkage connecting the ECM and cytoskeleton and plays a key role in mediating cell-environment communications and modulates important processes, such as cell attachment, spreading, migration, differentiation and mechanotransduction, in different cells in skeletal system by impacting distinct outside-in and inside-out signaling pathways. This review aims to integrate the up-to-date knowledge of the roles of FA proteins in the health and disease of skeletal system and focuses on the specific molecular mechanisms and underlying therapeutic targets for skeletal diseases.

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.

Increased Expression of Integrin Alpha 6 in Nucleus Pulposus Cells in Response to High Oxygen Tension Protects against Intervertebral Disc Degeneration

The destruction of the low oxygen microenvironment in nucleus pulposus (NP) cells played a critical role in the pathogenesis of intervertebral disc degeneration (IVDD). The purpose of this study was to determine the potential role of integrin alpha 6 (ITG α6) in NP cells in response to high oxygen tension (HOT) in IVDD. Immunofluorescence staining and western blot analysis showed that the levels of ITG α6 expression were increased in the NP tissue from IVDD patients and the IVDD rat model with mild degeneration, which were reduced as the degree of degeneration increases in severity. In NP cells, the treatment of HOT resulted in upregulation of ITG α6 expression, which could be alleviated by blocking the PI3K/AKT signaling pathway. Further studies found that ITG α6 could protect NP cells against HOT-induced apoptosis and oxidative stress and protect NP cells from HOT-inhibited ECM protein synthesis. Upregulation of ITG α6 expression by HOT contributed to maintaining NP tissue homeostasis through the interaction with hypoxia-inducible factor-1α (HIF-1α). Furthermore, silencing of ITG α6 in vivo could obviously accelerate puncture-induced IVDD. Taken together, these results revealed that the increase of ITG α6 expression by HOT in NP cells might be a protective factor in IVD degeneration as well as restore NP cell function.

Delayed notochordal cell disappearance through integrin α5β1 mechanotransduction during ex-vivo dynamic loading-induced intervertebral disc degeneration

The loss of nucleus pulposus (NP) notochordal cells is one of the key initial hallmarks of age-related intervertebral disc degeneration. Although the transmembrane mechanoreceptor integrin α5β1 is important in the process of disc degeneration, the relationship between integrin α5β1 and notochordal cell disappearance remains unclear. The purpose of this study was to elucidate the role of integrin α5β1 in the homeostasis of notochordal cells using an ex-vivo dynamic loading culture system that we developed. Rat tail functional spinal units (n = 80 from 40 rats) were cultured under unloading or 1.3-MPa, 1.0-Hz dynamic compressive loading for 48 or 144 h with or without an integrin α5β1 inhibitor. Disc histomorphology, cell viability, apoptosis, senescence, and phenotypic expression were investigated. Consequently, histological degenerative disc changes with decreased cell viability and increased cell apoptosis and senescence were observed with an extended loading duration. Immunofluorescence revealed that the expression of notochordal cell markers, CD24 and brachyury, and chondrocyte markers, collagen type II and SRY-box 9, declined with loading. In particular, reduction in notochordal cell marker expression was more dramatic than that in chondrocyte marker expression. Apoptotic terminal deoxynucleotidyl transferase dUTP nick-end labeling positivity was also higher in brachyury-positive notochordal cells. Furthermore, all these changes were delayed by inhibiting integrin α5β1. Findings of our dynamic loading regimen with a relatively high pressure suggest reproducibility of the cellularity and phenotypic disappearance of NP notochordal cells during adolescence, the susceptibility of notochordal cells to mechanical stimuli partially through the integrin α5β1 pathway, and future potential treatment of integrin regulation for intervertebral disc disease.

Activation of β1 integrins and caveolin-1 by TF/FVIIa promotes IGF-1R signaling and cell survival

The tissue factor/coagulation factor VIIa (TF/FVIIa) complex induces transactivation of the IGF-1 receptor (IGF-1R) in a number of different cell types. The mechanism is largely unknown. The transactivation leads to protection from apoptosis and nuclear translocation of the IGF-1R. The aim of this study was to clarify the signaling pathway between TF and IGF-1R after FVIIa treatment with PC3 and DU145 prostate or MDA-MB-231 breast cancer cells as model systems. Protein interactions, levels, and phosphorylations were assessed by proximity ligation assay or flow cytometry in intact cells and by western blot on cell lysates. The transactivation of the IGF-1R was found dependent on TF/FVIIa-induced activation of β1-integrins. A series of experiments led to the conclusion that the caveolae protein caveolin-1 prevented IGF-1R activation in resting cells via its scaffolding domain. TF/FVIIa/β1-integrins terminated this inhibition by activation of Src family kinases and subsequent phosphorylation of caveolin-1 on tyrosine 14. This phosphorylation was not seen after treatment with PAR1 or PAR2 agonists. Consequently, the protective effect of FVIIa against apoptosis induced by the death receptor agonist TRAIL and the de novo synthesis of cyclin D1 induced by nuclear IGF-1R accumulation were both significantly reduced by down-regulation of β1-integrins or overexpression of the caveolin-1 scaffolding domain. In conclusion, we present a plausible mechanism for the interplay between TF and IGF-1R involving FVIIa, β1-integrins, Src family proteins, and caveolin-1. Our results increase the knowledge of diseases associated with TF and IGF-1R overexpression in general but specifically of TF-mediated signaling with focus on cell survival.

Phyllanthin inhibits MOLT-4 leukemic cancer cell growth and induces apoptosis through the inhibition of AKT and JNK signaling pathway

Among cancers, leukemia is a multistep progression that involves genetic modifications of normal hematopoietic progenitor cells to cancerous cells. In recent times, leukemia cases and their mortality rate have increased rapidly. Therefore, the immense need for a therapeutic approach is crucial that can control this type of cancer. Phyllanthin is a lignan compound constituent from the Phyllanthus species and has numerous beneficial effects as a dietary component. The present study aims to determine the impact of phyllanthin on the MOLT-4 cytotoxic effect. MOLT-4 cells and MS-5 cells were cultured at different concentrations of phyllanthin (5, 10, 25, 50, 75, and 100 μM/ml), and the viability was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method. The level of reactive oxygen species, the membrane potential of mitochondria, apoptosis by 2',7'-dichlorofluorescin-diacetate (DCF-DA), rhodamine, acridine orange (AO)/ethidium bromide (EB), 4',6-diamidino-2-phenylindole (DAPI)/propidium iodide (PI) staining, gene expression of signaling molecules, and protein levels were assessed by reverse-transcription polymerase chain reaction and western blot analysis. Phyllanthin did not show toxicity toward MS-5 cells and significantly decreased the cell viability of MOLT-4 cells with an IC₅₀ value of 25 µM/ml. Also, phyllanthin induced the production of reactive oxygen species and led to the loss of mitochondrial membrane potential. AO/EB and DAPI/PI staining fluorescent image confirmed the induction of apoptosis by phyllanthin treatment. The messenger RNA (mRNA) expression of cell cycle regulator cyclin D1, antiapoptotic gene Bcl-2, NF-κB, and TNF-α decreased, but the proapoptotic Bax mRNA expression was increased. The phosphorylated protein levels of p-PI3K1/2, p-ERK1/2, and p-AKT were decreased, whereas the levels of p-p38 and p-JNKT1/2 increased. Our results confirmed that phyllanthin inhibits the MOLT-4 cells, increases apoptosis, and inhibits MOLT-4 migration and cell invasion. Therefore, phyllanthin can be used as a potential target for leukemia treatment.

Multiscale Regulation of the Intervertebral Disc: Achievements in Experimental, In Silico, and Regenerative Research

Intervertebral disc (IVD) degeneration is a major risk factor of low back pain. It is defined by a progressive loss of the IVD structure and functionality, leading to severe impairments with restricted treatment options due to the highly demanding mechanical exposure of the IVD. Degenerative changes in the IVD usually increase with age but at an accelerated rate in some individuals. To understand the initiation and progression of this disease, it is crucial to identify key top-down and bottom-up regulations' processes, across the cell, tissue, and organ levels, in health and disease. Owing to unremitting investigation of experimental research, the comprehension of detailed cell signaling pathways and their effect on matrix turnover significantly rose. Likewise, in silico research substantially contributed to a holistic understanding of spatiotemporal effects and complex, multifactorial interactions within the IVD. Together with important achievements in the research of biomaterials, manifold promising approaches for regenerative treatment options were presented over the last years. This review provides an integrative analysis of the current knowledge about (1) the multiscale function and regulation of the IVD in health and disease, (2) the possible regenerative strategies, and (3) the in silico models that shall eventually support the development of advanced therapies.

Comprehensive RNA expression profile of therapeutic adipose‑derived mesenchymal stem cells co‑cultured with degenerative nucleus pulposus cells

Stem cell-based therapy is a promising alternative to conventional approaches to treating intervertebral disc degeneration (IDD). However, comprehensive understanding of stem cell-based therapy at the gene level is still lacking. In the present study, we identified the expression profiles of messenger RNAs (mRNAs) and long non-coding RNAs (lncRNAs) expressed within a co-culture system of adipose-derived mesenchymal stem cells (ASCs) and degenerative nucleus pulposus cells (NPCs) and explored the signaling pathways involved and their regulatory networks. Microarray analysis was used to compare ASCs co-cultured with degenerative NPCs to ASCs cultured alone, and the underlying regulatory pattern, including the signaling pathways and competing endogenous RNA (ceRNA) network, was analyzed with robust bioinformatics methods. The results showed that 360 lncRNAs and 1757 mRNAs were differentially expressed by ASCs, and the microarray results were confirmed by quantitative PCR. Moreover, 589 Gene Ontology terms were upregulated, whereas 661 terms were downregulated. A total of 299 signaling pathways were significantly altered. A Path-net and a Signal-net were built to show interactions among differentially expressed genes. An mRNA-lncRNA co-expression network was constructed to reveal the interplay among differentially expressed mRNAs and lncRNAs, whereas a ceRNA network was built to investigate their connections with microRNAs involved in IDD. To the best of our knowledge, this original and comprehensive exploration reveals differentially expressed lncRNAs and mRNAs of ASCs stimulated by degenerative NPCs, underscoring the regulation pattern within the co-culture system at the gene level. These data may further understanding of NPC-directed differentiation of ASCs and facilitate the application of ASCs in future treatments for IDD.

The mechano-response of murine annulus fibrosus cells to cyclic tensile strain is frequency dependent

The intervertebral disk (IVD) is a composite structure essential for spine stabilization, load bearing, and movement. Biomechanical factors are important contributors to the IVD microenvironment regulating joint homeostasis; however, the cell type-specific effectors of mechanotransduction in the IVD are not fully understood. The current study aimed to determine the effects of cyclic tensile strain (CTS) on annulus fibrosus (AF) cells and identify mechano-sensitive pathways. Using a cell-type specific reporter mouse to differentiation NP and AF cells from the murine IVD, we characterized AF cells in dynamic culture exposed to CTS (6% strain) at specific frequencies (0.1 Hz, 1.0 Hz, or 2.0 Hz). We demonstrate that our culture model maintains the phenotype of primary AF cells and that the bioreactor system delivers uniform biaxial strain across the cell culture surface. We show that exposure of AF cells to CTS induces cytoskeleton reorganization resulting in stress fiber formation, with acute exposure to CTS at 2.0 Hz inducing a significant yet transient increase ERK1/2 pathway activation. Using SYBPR-based qPCR to assess the expression of extracellular matrix (ECM) genes, ECM-remodeling genes, candidate mechano-sensitive genes, inflammatory cytokines and cell surface receptors, we demonstrated that exposure of AF cells to CTS at 0.1 Hz increased Acan, Prg4, Col1a1 and Mmp3 expression. AF cells exposed to CTS at 1.0 Hz showed a significant increase in the expression of Acan, Myc, and Tnfα. Exposure of AF cells to CTS at 2.0 Hz induced a significant increase in Acan, Prg4, Cox2, Myc, Fos, and Tnfα expression. Among the cell surface receptors assessed, AF cells exposed to CTS at 2.0 Hz showed a significant increase in Itgβ1, Itgα5, and Trpv4 expression. Our findings demonstrate that the response of AF cells to CTS is frequency dependent and suggest that mechanical loading may directly contribute to matrix remodeling and the onset of local tissue inflammation in the murine IVD.

Silencing arginine kinase/integrin β1 subunit by transgenic plant expressing dsRNA inhibits the development and survival of Plutella xylostella

BACKGROUND

Plutella xylostella is a devastating agricultural insect pest of cruciferous plants, including crops. Plant-mediated RNA interference (RNAi) is currently being developed for plant protection. In this study, we investigated the response of P. xylostella exposed to transgenic Arabidopsis thaliana plants that expressed double-stranded RNA (dsRNA) targeting P. xylostella genes of arginine kinase (PxAK) and integrin β₁ subunit (Pxβ).

RESULTS

Transgenic plants producing dsRNAs of the 384-bp fragment of PxAK (dsAK plants), the 497-bp fragment of Pxβ (dsβ plants), and the 881 bp of the combination of both genes (dsAK-β plants) were generated and verified. Insect bioassay with these transgenic plants showed that the development of P. xylostella was affected, causing longer developmental time, and lower pupal weight and pupation rate. P. xylostella mortality rates were 25.0% when exposed to dsAK plants, 22.5% with dsβ plants, and 30.0% with dsAK-β plants, which were all higher than 7.5% for the wild-type plant. PxAK and Pxβ in P. xylostella were suppressed by 26.6-79.7% at the transcription level by the transgenic plants.

CONCLUSION

These results suggest that plant-mediated RNAi targeting single gene or both PxAK and Pxβ may have the potential to control P. xylostella. © 2019 Society of Chemical Industry.

Inactivation of FAM20B causes cell fate changes in annulus fibrosus of mouse intervertebral disc and disc defects via the alterations of TGF-β and MAPK signaling pathways

Intervertebral disc (IVD) disorder is often caused by the defect of annulus fibrosus (AF), especially that of the outer AF. Studies about the mechanisms governing the development of the outer AF are needed for a better understanding of pathogenesis of IVD defects. Glycosaminoglycans (GAGs) are essential components of extracellular matrix (ECM) in AF. FAM20B is a newly identified xylose kinase that catalyzes the biosynthesis of GAGs. In this study, we created Fam20B conditional knockout (cKO) mice in which FAM20B was inactivated in type I collagen-expressing cells, the main type of cells in the outer AF of IVD. The cKO mice showed severe spine deformity and remarkable IVD defects associated with AF malformation. The AF of cKO mice had a lower level of chondroitin sulfate and heparan sulfate, and the outer AF cells lost their normal fibroblast-like morphology and acquired chondrocyte phenotypes, expressing a higher level of Sox 9 and type II collagen along with a reduced level of type I collagen. The level of phospho-Smad 2 and phospho-Smad 3, and that of scleraxis, a downstream target molecule of canonical TGF-β signaling pathway were significantly lower in the AF of cKO mice. The AF in cKO mice also manifested altered levels in the molecules associated with the activations of MAPK pathway; the changes included the increase of phospho-P38 and phospho-ERK and a decrease of phospho-JNK. These results indicate that FAM20B plays an essential role in the development of AF by regulating the TGF-β signaling and MAPK signaling pathways.

TGF-β1 reduces the oxidative stress-induced autophagy and apoptosis in rat annulus fibrosus cells through the ERK signaling pathway

Background

The aim of this study is to explore the effects of TGF-β1 on autophagy and apoptosis induced by exogenous hydrogen peroxide (H₂O₂) in annulus fibrosus (AF) cells and possible signal pathways involved in this process.

Methods

AF cells were isolated from rat lumbar discs and subjected to different concentrations of exogenous H₂O₂ (50, 100, 200 μmol/L) for different time periods (0.5, 1, 2, and 4 h). Cell viability was determined by CCK-8 assay, and the levels of autophagy and apoptosis were evaluated by Western blotting and caspase 3, 8, 9 activity assay. By administration with different concentrations of TGF-β1 (5, 10, 20 ng/mL), the effects of TGF-β1 on autophagy and apoptosis induced by H₂O₂ were observed, and the possible signaling pathways were also investigated by using various apoptosis inhibitors or an autophagy inhibitor Bafilomycin A (Baf A) in AF cells.

Results

H₂O₂ significantly impaired cell viability in a dose- and time-dependent manner. H₂O₂ also induced a sudden and the highest level of autophagy at 1 h, and gradually increased apoptosis through ERK pathway. The mitochondrial pathway was involved in H₂O₂-induced apoptosis in AF cells. TGF-β1 reduced the expression of p-ERK and downregulated the expressions of Beclin-1, LC3 II/I, and mitochondrial-related apoptotic proteins (Bax/Bcl-2, caspase-9). Meanwhile, TGF-β1 downregulated the level of intracellular H₂O₂ through upregulating the expression level of glutathione peroxidase-1 (GPx-1).

Conclusions

TGF-β1 reduced autophagy and apoptosis induced by exogenous H₂O₂ through downregulating the expression of ERK in AF cells. TGF-β1 could downregulate the level of ERK and intracellular H₂O₂ by upregulating GPx-1.

Interleukin-1β induces apoptosis in annulus fibrosus cells through the extracellular signal-regulated kinase pathway

PURPOSE

The loss of intervertebral disc (IVD) cells due to excessive apoptosis induced by inflammatory cytokines is a major cause of IVD degeneration. This study aims to explore the mechanism of interleukin-1β (IL-1β)-induced apoptosis of annulus fibrosus cells (AFCs). It's hypothesized that IL-1β induces apoptosis through the extracellular signal-regulated kinase (ERK) pathway in AFCs.

METHODS

The mRNA and protein expression levels of apoptosis-associated genes were analyzed by quantitative real-time PCR and Western blotting. The apoptotic rate was measured by flow cytometry. Three experimental groups were established, including Control, IL-1β, and IL-1β+U0126 groups, respectively.

RESULTS

Increase in the expression of apoptosis-associated genes including B-cell lymphoma-2 associated X (Bax), caspase-3, and caspase-9, and meanwhile, decrease in the expression of B-cell lymphoma-2 (Bcl-2) gene were found in patients with degenerative IVDs. In in vitro tests, both apoptosis and phosphorylated ERK expression in rat AFCs decreased in the IL-1β+U0126 group compared with the IL-1β group. The expression levels of Bax, caspase-3, and caspase-9 in AFCs decreased significantly in the IL-1β+U0126 group compared with those in the IL-1β group. The expression level of Bcl-2, on the other hand, significantly increased.

CONCLUSIONS

Findings from this study suggest that IL-1β induces apoptosis in AFCs through the ERK pathway, and therefore, ERK inhibition may provide certain protection against the adverse effects of IL-1β.

Mechanotransduction and cell biomechanics of the intervertebral disc

Mechanical loading of the intervertebral disc (IVD) initiates cell-mediated remodeling events that contribute to disc degeneration. Cells of the IVD, nucleus pulposus (NP) and anulus fibrosus (AF), will exhibit various responses to different mechanical stimuli which appear to be highly dependent on loading type, magnitude, duration, and anatomic zone of cell origin. Cells of the NP, the innermost region of the disc, exhibit an anabolic response to low-moderate magnitudes of static compression, osmotic pressure, or hydrostatic pressure, while higher magnitudes promote a catabolic response marked by increased protease expression and activity. Cells of the outer AF are responsive to physical forces in a manner that depends on frequency and magnitude, as are cells of the NP, though they experience different forces, deformations, pressure, and osmotic pressure in vivo. Much remains to be understood of the mechanotransduction pathways that regulate IVD cell responses to loading, including responses to specific stimuli and also differences among cell types. There is evidence that cytoskeletal remodeling and receptor-mediated signaling are important mechanotransduction events that can regulate downstream effects like gene expression and posttranslational biosynthesis, all of which may influence phenotype and bioactivity. These and other mechanotransduction events will be regulated by known and to-be-discovered cell-matrix and cell-cell interactions, and depend on composition of extracellular matrix ligands for cell interaction, matrix stiffness, and the phenotype of the cells themselves. Here, we present a review of the current knowledge of the role of mechanical stimuli and the impact upon the cellular response to loading and changes that occur with aging and degeneration of the IVD.

The long non-coding RNA NEAT1 contributes to extracellular matrix degradation in degenerative human nucleus pulposus cells

Intervertebral disc degeneration is a complex disease involving genetic and environmental factors and multiple cellular processes. The role and expression of the lncRNA NEAT1 were assessed in intervertebral disc degeneration. NEAT1 expression was assessed in degenerative and control nucleus pulposus using RT-PCR. Western blotting and RT-PCR were also used to investigate p53 and p21 levels in nucleus pulposus tissues. NEAT1 function in degenerative nucleus pulposus cells was assessed with gain- and loss-of-function experiments. ERK/MAPK signaling was also examined. NEAT1, p53, and p21 were dramatically upregulated in intervertebral disc degeneration. Furthermore, catabolic MMP13 and ADAMTS5 were dysregulated and collagen II and aggrecan were downregulated after NEAT1 overexpression. This effect was reversed by transfection with si-NEAT1 in degenerative nucleus pulposus cells. In addition, NEAT1 was found to affect the activation of the ERK/MAPK pathway. The NEAT1-induced ECM degradation may involve ERK1/2/MAPK signaling. LncRNA NEAT1 may represent a novel molecular target for intervertebral disc degeneration treatment by preventing nucleus pulposus ECM degradation. Impact statement For the first time, our study demonstrates that lncRNA NEAT1 plays a role in the occurrence and development of IDD by participating in extracellular matrix remodeling. This lncRNA regulates catabolic MMP13 and ADAMTS5 and anabolic collagen II and aggrecan by affecting the ERK/MAPK signaling pathway in degenerative human nucleus pulposus (NP) cells. Our research provides a scientific basis for targeting of NEAT1 for the 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.

Cyclic Compressive Stress Regulates Apoptosis in Rat Osteoblasts: Involvement of PI3K/Akt and JNK MAPK Signaling Pathways

It is widely accepted that physiological mechanical stimulation suppresses apoptosis and induces synthesis of extracellular matrix by osteoblasts; however, the effect of stress overloading on osteoblasts has not been fully illustrated. In the present study, we investigated the effect of cyclic compressive stress on rat osteoblasts apoptosis, using a novel liquid drop method to generate mechanical stress on osteoblast monolayers. After treatment with different levels of mechanical stress, apoptosis of osteoblasts and activations of mitogen-activated protein kinases (MAPKs) and PI3-kinase (PI3K)/Akt signaling pathways were investigated. Osteoblasts apoptosis was observed after treated with specific inhibitors prior to mechanical stimulation. Protein levels of Bax/Bcl-2/caspase-3 signaling were determined using western blot with or without inhibitors of PI3K/Akt and phosphorylation of c-jun N-terminal kinase (JNK) MAPK. Results showed that mechanical stimulation led to osteoblasts apoptosis in a dose-dependent manner and a remarkable activation of MAPKs and PI3K/Akt signaling pathways. Activation of PI3K/Akt protected against apoptosis, whereas JNK MAPK increased apoptosis via regulation of Bax/Bcl-2/caspase-3 activation. In summary, the PI3K/Akt and JNK MAPK signaling pathways played opposing roles in osteoblasts apoptosis, resulting in inhibition of apoptosis upon small-magnitude stress and increased apoptosis upon large-magnitude stress.

Toxicogenomic analysis identifies the apoptotic pathway as the main cause of hepatotoxicity induced by tributyltin

Tributyltin (TBT) is one of the most widely used organotin biocides, which has severe endocrine-disrupting effects on marine species and mammals. Given that TBT accumulates at higher levels in the liver than in any other organ, and it acts mainly as a hepatotoxic agent, it is important to clearly delineate the hepatotoxicity of TBT. However, most of the available studies on TBT have focused on observations at the cellular level, while studies at the level of genes and proteins are limited; therefore, the molecular mechanisms of TBT-induced hepatotoxicity remains largely unclear. In the present study, we applied a toxicogenomic approach to investigate the effects of TBT on gene expression in the human normal liver cell line HL7702. Gene expression profiling identified the apoptotic pathway as the major cause of hepatotoxicity induced by TBT. Flow cytometry assays confirmed that medium- and high-dose TBT treatments significantly increased the number of apoptotic cells, and more cells underwent late apoptosis in the high-dose TBT group. The genes encoding heat shock proteins (HSPs), kinases and tumor necrosis factor receptors mediated TBT-induced apoptosis. These findings revealed novel molecular mechanisms of TBT-induced hepatotoxicity, and the current microarray data may also provide clues for future studies.

Molecular mechanisms of cell death in intervertebral disc degeneration (Review)

Intervertebral discs (IVDs) are complex structures that consist of three parts, namely, nucleus pulposus, annulus fibrosus and cartilage endplates. With aging, IVDs gradually degenerate as a consequence of many factors, such as microenvironment changes and cell death. Human clinical trial and animal model studies have documented that cell death, particularly apoptosis and autophagy, significantly contribute to IVD degeneration. The mechanisms underlying this phenomenon include the activation of apoptotic pathways and the regulation of autophagy in response to nutrient deprivation and multiple stresses. In this review, we briefly summarize recent progress in understanding the function and regulation of apoptosis and autophagy signaling pathways. In particular, we focus on studies that reveal the functional mechanisms of these pathways in IVD degeneration.

Bacitracin Inhibits the Migration of U87-MG Glioma Cells via Interferences of the Integrin Outside-in Signaling Pathway

Objective

Protein disulfide isomerase (PDI) acts as a chaperone on the cell surface, and it has been reported that PDI is associated with the tumor cell migration and invasion. The aims of this study are to investigate the anti-migration effect of bacitracin, which is an inhibitor of PDI, and the associated factor in this process.

Methods

U87-MG glioma cells were treated with bacitracin in 1.25, 2.5, 3.75, and 5.0 mM concentrations. Western blot with caspase-3 was applied to evaluate the cytotoxicity of bacitracin. Adhesion, morphology, migration assays, and organotypic brain-slice culture were performed to evaluate the effect of bacitracin to the tumor cell. Western blot, PCR, and gelatin zymography were performed to investigate the associated factors. Thirty glioma tissues were collected following immunohistochemistry and Western blot.

Results

Bacitracin showed a cytotoxicity in 3rd (p<0.05) and 4th (p<0.001) days, in 5.0 Mm concentration. The cell adhesion significantly decreased and the cells became a round shape after treated with bacitracin. The migration ability, the expression of phosphorylated focal adhesion kinase (p-FAK) and matrix metalloproteinase-2 (MMP-2) decreased in a bacitracin dose- and time-dependent manner. The U87-MG cells exhibited low-invasiveness in the 2.5 mM, compared with the untreated in organotypic brain-slice culture. PDI was expressed in the tumor margin, and significantly increased with histological glioma grades (p<0.001).

Conclusion

Bacitracin, as a functional inhibitor of PDI, decreased the phosphorylated FAK and the secreted MMP-2, which are the downstream of integrin and play a major role in cell migration and invasion, might become one of the feasible therapeutic strategies for glioblastoma.