Induction of intervertebral disc cell apoptosis and degeneration by chronic unpredictable stress

Effect of lentivirus-mediated growth and differentiation factor-5 transfection on differentiation of rabbit nucleus pulposus mesenchymal stem cells

Background

Intervertebral disc degeneration (IDD) is a natural progression of age-related processes. Associated with IDD, degenerative disc disease (DDD) is a pathologic condition implicated as a major cause of chronic lower back pain, which can have a severe impact on the quality of life of patients. As degeneration progression is associated with elevated levels of inflammatory cytokines, enhanced aggrecan and collagen degradation, and changes in the disc cell phenotype. The purpose of this study was to investigate the biological and cytological characteristics of rabbit nucleus pulposus mesenchymal stem cells (NPMSCs)—a key factor in IDD—and to determine the effect of the growth and differentiation factor-5 (GDF5) on the differentiation of rabbit NPMSCs transduced with a lentivirus vector.

Methods

An in vitro culture model of rabbit NPMSCs was established and NPMSCs were identified by flow cytometry (FCM) and quantitative real-time PCR (qRT-PCR). Subsequently, NPMSCs were randomly divided into three groups: a transfection group (the lentiviral vector carrying GDF5 gene used to transfect NPMSCs); a control virus group (the NPMSCs transfected with an ordinary lentiviral vector); and a normal group (the NPMSCs alone). FCM, qRT-PCR, and western blot (WB) were used to detect the changes in NPMSCs.

Results

The GDF5-transfected NPMSCs displayed an elongated shape, with decreased cell density, and significantly increased GDF5 positivity rate in the transfected group compared to the other two groups (P < 0.01). The mRNA levels of Krt8, Krt18, and Krt19 in the transfected group were significantly higher in comparison with the other two groups (P < 0.01), and the WB results were consistent with that of qRT-PCR.

Conclusions

GDF5 could induce the differentiation of NPMSCs. The lentiviral vector carrying the GDF5 gene could be integrated into the chromosome genome of NPMSCs and promoted differentiation of NPMSCs into nucleus pulposus cells. Our findings advance the development of feasible and effective therapies for IDD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40001-021-00624-5.

A novel circRNA-miRNA-mRNA network reveals hsa-circ-0040039 as a biomarker for intervertebral disc degeneration

Objective

Alterations in the structure and function of intervertebral discs by multifaceted chronic processes can result in intervertebral disc degeneration (IDD). The mechanisms involved in IDD are still unknown.

Methods

We investigated the possible mechanisms underlying IDD using a bioinformatics analysis of publicly available microarray expression datasets and built a circular RNA–microRNA–mRNA (circRNA–miRNA–mRNA) network based on the results. Datasets GSE67566 and GSE116726 were downloaded from the Gene Expression Omnibus (GEO) and analyzed using the limma package in R. The CircInteractome database was used to detect miRNAs related to circRNA, and TargetScan, miRDB, and miRTarBase were used to predict target mRNAs. Key target genes were annotated using Gene Ontology terms.

Results

The circRNA hsa-circ-0040039 was found to have the top log fold-change score. Analysis using Metascape showed that the associated genes were enriched mainly in the cell cycle. The Cytoscape plugin MCODE predicted that two members of the RAS oncogene family—RAB1A and RAB1B—and multiple coagulation factor deficiency (MCFD2) may play key roles in IDD.

Conclusion

Our results suggested that hsa-circ-0040039 and the related network may be potential biomarkers for IDD.

Effects of swimming on pain and inflammatory factors in rats with lumbar disc herniation

The aim of the present study was to identify the effect of swimming on nerve root pain in rats with lumbar disc herniation (LDH). A total of 72 male Sprague Dawley rats (215±15 g) were randomly divided into three groups (n=24/group): The sham operation, model and exercise intervention groups, with the latter undergoing 4 weeks of swimming training. On days 0, 7, 14 and 28 following surgery, the changes in the post-limb mechanical claw threshold, the phospholipase A2 (PLA2), interleukin (IL)-6 and tumor necrosis factor (TNF)-α mRNA expression levels, the secretory PLA2 (sPLA2) expression, the IL-6 and TNF-α content, the nuclear factor (NF)-κBp65 protein expression level in the nucleus pulposus, and the apoptotic rate of the nucleus pulposus cells were detected. The results demonstrated that, in the model group, the threshold of hind paw withdrawal was decreased, and that the sPLA2 expression, IL-6 and TNF-α content, PLA2, IL-6 and TNF-α mRNA and NF-κBp65 protein expression levels in the nucleus pulposus were increased. The apoptotic rate of the nucleus pulposus cells was increased from day 7 following surgery, as compared with the sham operation group. In the exercise intervention group, the hind paw withdrawal threshold increased and the TNF-α and IL-6 content, sPLA2 expression and PLA2, IL-6 and TNF-α mRNA and NF-κBp65 protein expression levels were decreased from day 14 following surgery, and the apoptotic nucleus pulposus cells were decreased from day 7 following surgery, as compared with the model group. Collectively, the present data suggest that swimming can significantly reduce nerve root pain and inhibit inflammatory reaction in LDH, which can have positive effects on the treatment of LDH.

BMP7-Based Functionalized Self-Assembling Peptides Protect Nucleus Pulposus-Derived Stem Cells From Apoptosis In Vitro

Tissue engineering has shown great success in the treatment of intervertebral disk degeneration (IVDD) in the past decade. However, the adverse and harsh microenvironment associated in the intervertebral disks remains a great obstacle for the survival of transplanted cells. Although increasing numbers of new materials have been created or modified to overcome this hurdle, a new effective strategy of biological therapy is still required. In this study, bone morphogenic protein 7 (BMP7)-based functionalized self-assembling peptides were developed by conjugating a bioactive motif from BMP-7 (RKPS) onto the C-terminal of the peptide RADARADARADARADA (RADA16-I) at a ratio of 1:1 to form a new RADARKPS peptide. Human nucleus pulposus-derived stem cells (NPDCs) were cultured in the presence of RADA-RKPS or RADA16-I in an apoptosis-promoting environment that was induced by tumor necrosis factor-alpha, and cells were cultured with RADA16-I in normal medium that served as the control group. After 48 h of apoptosis induction, the viability, proliferation, apoptosis rate, and expression of apoptosis-related genes of NPDCs in the different groups were evaluated, and the differentiation of NPDCs toward nucleus pulposus-like cells was tested. The results showed that the RADA-RKPS peptide could significantly protect the survival and proliferation of NPDCs. In addition, the application of RADA-RKPS decreased the rate of cell apoptosis, as detected by TUNEL-positive staining. Furthermore, our in vitro study confirmed the apoptosis-protecting effects of RADA-RKPS peptides, which significantly reduced the BAX/BCL-2 ratio of NPDCs and upregulated the gene expression of collagen II a1, aggrecan, and Sox-9 after 48 h of apoptosis induction. Collectively, these lines of evidence suggest that RADA-RKPS peptides confer a protective effect to NPDCs in an apoptosis environment, suggesting their potential application in the development of new biological treatment strategies for IVDD.

Protective effect of cannabidiol on hydrogen peroxide‑induced apoptosis, inflammation and oxidative stress in nucleus pulposus cells

Cannabidiol, a major component of marijuana, protects nerves, and exerts antispasmodic, anti-inflammatory and anti‑anxiety effects. In the current study, the protective effect of cannabidiol was observed to prevent hydrogen peroxide (H2O2)‑induced apoptosis, inflammation and oxidative stress in nucleus pulposus cells. Nucleus pulposus cells were isolated from rats and cultured in vitro, and H2O2 was used to construct the nucleus pulposus cell model. Cell viability of the nucleus pulposus cells was assessed using a 3‑(4,5-dimethylthiazol-2-yl)-2,5‑diphenyltetrazolium bromide assay. The ratio of apoptotic cells, and caspase‑3 or cyclooxygenase‑2 (COX‑2) mRNA expression was analyzed by annexin V‑fluorescein isothiocyanate/propidium‑iodide staining and reverse transcription‑quantitative polymerase chain reaction, respectively. The quantities of interleukin (IL)‑1β and interleukin‑6 were measured using a series of assay kits. B-cell lymphoma 2 (Bcl‑2) and inducible nitric oxide synthase (iNOS) protein expression levels were analyzed using western blotting. The present study identified that cannabidiol enhanced cell viability and reduced apoptosis in H2O2‑treated nucleus pulposus cells in vitro using a lumbar disc herniation (LDH) model. In addition, cannabidiol reduced caspase‑3 gene expression and augmented the Bcl‑2 protein expression levels in the nucleus pulposus cells following H2O2 exposure. Pre‑treatment with cannabidiol suppressed the promotion of COX‑2, iNOS, IL‑1β and IL‑6 expression in the nucleus pulposus cells following H2O2 exposure. Taken together, these results suggest that cannabidiol potentially exerts its protective effect on LDH via the suppression of anti‑apoptosis, anti‑inflammation and anti‑oxidative activities in nucleus pulposus cells.

Evaluation of the neutrophil-lymphocyte ratio as a measure of distress in rats

The ability to evaluate distress in laboratory animals is needed in order to ensure that husbandry and experimental procedures do not negatively impact animal welfare. Accurate measurement of acute stress and chronic stress, and distinguishing between stress that is harmful (distress) and stress that does no harm (eustress), can be challenging. Whereas corticosterone concentrations are commonly used to measure stress in laboratory animals, the neutrophil-lymphocyte ratio has been proposed as a potentially better indicator of chronic stress. Furthermore, an association between such measures of stress and concurrent behavioral indicators of negative welfare is required to determine their accuracy in evaluating distress. The authors compared serum corticosterone concentrations and neutrophil-lymphocyte ratios to assess acute or chronic stress in male Sprague Dawley rats. Elevated serum corticosterone concentrations, but not neutrophil-lymphocyte ratios, were associated with acute stress exposure, whereas elevated neutrophil-lymphocyte ratios, but not serum corticosterone concentrations, were associated with chronic stress exposure. Because the neutrophil-lymphocyte ratio differences corresponded with a behavioral indicator of distress in chronically stressed rats, it may serve as a valuable tool for the physiological assessment of distress in rats.

Adipose-derived stromal cells protect intervertebral disc cells in compression: implications for stem cell regenerative disc therapy

Introduction: Abnormal biomechanics plays a role in intervertebral disc degeneration. Adipose-derived stromal cells (ADSCs) have been implicated in disc integrity; however, their role in the setting of mechanical stimuli upon the disc's nucleus pulposus (NP) remains unknown. As such, the present study aimed to evaluate the influence of ADSCs upon NP cells in compressive load culture.

Methods: Human NP cells were cultured in compressive load at 3.0MPa for 48 hours with or without ADSCs co-culture (the ratio was 50:50). We used flow cytometry, live/dead staining and scanning electron microscopy (SEM) to evaluate cell death, and determined the expression of specific apoptotic pathways by characterizing the expression of activated caspases-3, -8 and -9. We further used real-time (RT-) PCR and immunostaining to determine the expression of the extracellular matrix (ECM), mediators of matrix degradation (e.g. MMPs, TIMPs and ADAMTSs), pro-inflammatory factors and NP cell phenotype markers.

Results: ADSCs inhibited human NP cell apoptosis via suppression of activated caspase-9 and caspase-3. Furthermore, ADSCs protected NP cells from the degradative effects of compressive load by significantly up-regulating the expression of ECM genes (SOX9, COL2A1 and ACAN), tissue inhibitors of metalloproteinases (TIMPs) genes (TIMP-1 and TIMP-2) and cytokeratin 8 (CK8) protein expression. Alternatively, ADSCs showed protective effect by inhibiting compressive load mediated increase of matrix metalloproteinases (MMPs; MMP-3 and MMP-13), disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs; ADAMTS-1 and 5), and pro-inflammatory factors (IL-1beta, IL-6, TGF-beta1 and TNF-alpha).

Conclusions: Our study is the first in vitro study assessing the impact of ADSCs on NP cells in an un-physiological mechanical stimulation culture environment. Our study noted that ADSCs protect compressive load induced NP cell death and degradation by inhibition of activated caspase-9 and -3 activity; regulating ECM and modulator genes, suppressing pro-inflammatory factors and preserving CK8. Consequently, the protective impact of ADSCs found in this study provides an essential understanding and expands our knowledge as to the utility of ADSCs therapy for intervertebral disc regeneration.